WorldWideScience

Sample records for sandy rippled beds

  1. A study on the stability of laminar open-channel flow over a sandy rippled bed

    Institute of Scientific and Technical Information of China (English)

    BAI; Yuchuan; XU; Haijue

    2005-01-01

    The bed of a river often features some kinds of bedform, such as sand ripples, dunes, and so on. Even if the bed is smooth initially, disturbances arising from the bed or other external sources will cause the laminar flow in an open channel to become unstable as soon as the flow develops, thereby leading to the formation of sand ripples on the bed. In return, the formation of the sand ripples will modify the instability path of the laminar flow passing over them. The wavy character of the bed will induce further instability of the flow, which is essentially different from that on a smooth bed: the neutral curve will move forward and the critical Reynolds number will decrease. The flow is unstable in response to a wider range of the disturbance wave number, or the laminar flow instability can happen more easily. The propagation speed of the sand ripples also affects the flow instability, since the stability of open channel flow over a movable bed is fundamentally different from that on a rigid bed. These instability effects are discussed in detail in this paper.

  2. Hurricane Sandy's Fingerprint: Ripple Bedforms at an Inner Continental Shelf Sorted Bedform Field Site

    Science.gov (United States)

    DuVal, C.; Trembanis, A. C.; Beaudoin, J. D.; Schmidt, V. E.; Mayer, L. A.

    2013-12-01

    The hydrodynamics and seabed morphodynamics on the inner continental shelf and near shore environments have increasing relevance with continued development of near shore structures, offshore energy technologies and artificial reef construction. Characterizing the stresses on and response of the seabed near and around seabed objects will inform best practices for structural design, seabed mine and unexploded ordnance detection, and archaeological and benthic habitat studies. As part of an ONR funded project, Delaware's Redbird Reef is being studied for object scour and sorted bedform morphodynamics (Trembanis et al., in press). Central to this study are the effects of large storm events, such as Hurricane Sandy, which have had significant impact on the seafloor. Previous studies of inner shelf bedform dynamics have typically focused on near bed currents and bed stressors (e.g. Trembanis et al., 2004), sorted bedforms (e.g. Green et al., 2004) and object scour (e.g. Quinn, 2006; Trembanis et al., 2007; Mayer et al., 2007), but our understanding of the direct effects of objects and object scour on bedform morphodynamics is still incomplete. With prominent sorted bedform ripple fields, the Delaware Redbird artificial reef site, composed of 997 former New York City subway cars, as well as various military vehicles, tugboats, barges and ballasted tires, has made an ideal study location (Raineault et al., 2013 and 2011). Acoustic mapping of the Redbird reef three days prior to Sandy and two days after the following nor'easter, captured the extensive effects of the storms to the site, while acoustic Doppler current profilers characterized both the waves and bottom currents generated by the storm events. Results of the post-Sandy survey support the theory of sorted bedform evolution proposed by Murray and Thieler (2004). Acoustic imagery analysis indicates a highly energized and mobile bed during the storms, leading to self-organization of bedforms and creation of large

  3. Wave plus current over a ripple-covered bed

    DEFF Research Database (Denmark)

    Fredsøe, Jørgen; Andersen, Ken Haste; Sumer, B. Mutlu

    1999-01-01

    -visualization study in the laboratory with ripples, 22 cm in length, and 3.5 cm in height. One wave-alone, three current-alone, and three combined waves and current tests were conducted. The wave-velocity-to-current-velocity ratio ranges from 1 to 2.4. The orbiral-amplitude-ro-ripple-length ratio (at the bed) is 0...... of the now around fixed ripples by use of a k - w model to calculate the roughness, and friction of a rippled bed. (C) 1999 Elsevier Science B.V. All rights reserved....

  4. Geometry and dynamics of wave ripples in the nearshore zone of a coarse sandy beach

    Science.gov (United States)

    Masselink, G.; Austin, M. J.; O'Hare, T. J.; Russell, P. E.

    2007-10-01

    Extensive measurements of ripple characteristics and dynamics along with associated suspended sediment fluxes and hydrodynamic conditions were made in the shoaling and surf zones of a macrotidal coarse grained beach at Sennen Cove, Cornwall, England (median grain diameter 0.69 mm). Suborbital vortex ripples were observed during the majority of the study period with height ˜5 cm and length ˜35 cm. The scale and shape of the ripples did not vary significantly as the bed shear stress increased during wave shoaling and breaking. However, ripple migration rates (onshore directed) were strongly dependent on their location relative to the breakpoint, increasing from ˜0.1 cm min-1 under shoaling waves to 2 cm min-1 in the outer surf zone during low-energy conditions. Farther inside the surf zone, ripples persisted but migration rates slowed, probably owing to the presence of the offshore-directed mean flow which impedes landward migration of the ripples. Under low-wave conditions (during which measured sediment fluxes peaked around the outer surf zone and decreased through the saturated surf zone), bed form transport rates under shoaling waves were of the same magnitude as net suspended sediment fluxes but at least an order of magnitude smaller in the outer surf zone. Under high-energy conditions (during which suspended sediment fluxes in the surf zone were offshore directed owing to the presence of the seaward directed mean flow), bed form transport rates were several orders of magnitude smaller than suspended fluxes.

  5. Dependence of ripple dimensions on cohesive and non-cohesive bed properties in the intertidal Dee Estuary

    Science.gov (United States)

    Lichtman, Ian; Thorne, Peter; Baas, Jacobus; O'Boyle, Louise; Cooke, Richard; Amoudry, Laurent; Bell, Paul; Aspden, Rebecca; Bass, Sarah; Davies, Alan; Hope, Julie; Malarkey, Jonathan; Manning, Andrew; Parsons, Daniel; Paterson, David; Peakall, Jeffrey; Schindler, Robert; Ye, Leiping

    2014-05-01

    located above a sandy bed, and the two others were above mixed beds of different mud content. The tide covered a full cycle from neaps to neaps and the weather provided onshore and offshore winds of varying strength. Bedform measurements were taken every half an hour using an Acoustic Ripple Profiler (ARP) that covered an area of about two square metres. Dynamic measurements of tides and waves were made using an Acoustic Doppler Velocimeter (ADV) at 8 Hz. Bed samples were taken when the tidal flats dried out at low tide and a sediment trap collected suspended load near the bed. In the presentation, comparisons of the sites will be made from measurements of the proportion of mud and biological sediment binders at each site and the ripple dimensions for different hydrodynamic conditions. Key words: bed morphology, current ripple, mixed sediment, cohesion, hydrodynamics, observations, tidal flat, estuary, Dee

  6. Cross Ripples and Wave Directional Spectra

    Science.gov (United States)

    Cheel, R. A.; Hay, A. E.

    2006-12-01

    Cross ripples are a 3-dimensional bed state composed of two sets of ripples with different orientations: one set of smaller wavelength (4-10 cm) ripples residing within the troughs of a larger wavelength (30-50 cm) set. Cross ripples occur at intermediate wave energies. In contrast, at slightly higher energies the bed undergoes a transition to a highly 2-dimensional linear transition rippled state. In this study, the characteristics of the wave directional spectra during the occurrences of these 2- and 3-dimensional bed states are compared. The rotary fanbeam sonar record from SandyDuck97 shows that cross ripples and linear transition ripples occurred in approximately 11% and 42% of the sonar images respectively. Wave directional spectra are calculated with the Iterative Maximum Likelihood Method from collocated measurements of pressure and horizontal velocity. Using the sonar record and wave directional spectra the correlation between bimodal wave directional spectra and the occurrence of the two distinct ripple types is examined and compared. Since ripple crest alignment is typically orthogonal to the direction of wave propagation, one possible creation mechanism for cross ripples is a bidirectional wave field. We find that bimodality of the wave spectrum, neither in direction nor in frequency, is unique to the occurrence of cross ripples.

  7. Linear and nonlinear instabilities of a granular bed: determination of the scales of ripples and dunes in rivers

    CERN Document Server

    Franklin, Erick de Moraes

    2016-01-01

    Granular media are frequently found in nature and in industry and their transport by a fluid flow is of great importance to human activities. One case of particular interest is the transport of sand in open-channel and river flows. In many instances, the shear stresses exerted by the fluid flow are bounded to certain limits and some grains are entrained as bed-load: a mobile layer which stays in contact with the fixed part of the granular bed. Under these conditions, an initially flat granular bed may be unstable, generating ripples and dunes such as those observed on the bed of rivers. In free-surface water flows, dunes are bedforms that scale with the flow depth, while ripples do not scale with it. This article presents a model for the formation of ripples and dunes based on the proposition that ripples are primary linear instabilities and that dunes are secondary instabilities formed from the competition between the coalescence of ripples and free surface effects. Although simple, the model is able to expl...

  8. Stability characteristics of the open channel flow above the asymmetrical irregular sand ripples

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Sandy bed cannot keep its original smoothness as the flows pass. With the increase of the flow intensity, the bed forms will appear as sand ripples and dune in turn. Among these morphologies, the sand ripple scale is the smallest, which is generally symmetrical when it just appears, but as time goes on, the asymmetrical form gradually develops. Just because of this sand ripples asymmetry, it manifests the influence of the flow on the bed morphology and also the impact on the laminar flow dynamical process, especially the stability characteristics. The stability features of laminar flow on open channels with the asymmetrical sand ripples are discussed, and also the results on the symmetrical sand ripples are compared in detail.

  9. Comparison of wastewater-associated contaminants in the bed sediment of Hempstead Bay, New York, before and after Hurricane Sandy

    Science.gov (United States)

    Fisher, Shawn C.; Phillips, Patrick; Brownawell, Bruce J.; Browne, James

    2016-01-01

    Changes in bed sediment chemistry of Hempstead Bay (HB) have been evaluated in the wake of Hurricane Sandy, which resulted in the release of billions of liters of poorly-treated sewage into tributaries and channels throughout the bay. Surficial grab samples (top 5 cm) collected before and (or) after Hurricane Sandy from sixteen sites in HB were analyzed for 74 wastewater tracers and steroid hormones, and total organic carbon. Data from pre- and post-storm comparisons of the most frequently detected wastewater tracers and ratios of steroid hormone and of polycyclic aromatic hydrocarbon concentrations indicate an increased sewage signal near outfalls and downstream of where raw sewage was discharged. Median concentration of wastewater tracers decreased after the storm at sites further from outfalls. Overall, changes in sediment quality probably resulted from a combination of additional sewage inputs, sediment redistribution, and stormwater runoff in the days to weeks following Hurricane Sandy.

  10. Shape and Dimensions of Ripples

    DEFF Research Database (Denmark)

    Jacobsen, Niels Gjøl

    In this work, the flow and bed load transport over ripple profiles under the influence of oscillatory will be investigated. The investigation is made through a parametric study, where the bed shape and the ripple steepness are varied. For the sediment transport, the Shields parameter relative to ...

  11. Estuarine bed-sediment-quality data collected in New Jersey and New York after Hurricane Sandy, 2013

    Science.gov (United States)

    Fischer, Jeffrey M.; Phillips, Patrick J.; Reilly, Timothy J.; Focazio, Michael J.; Loftin, Keith A.; Benzel, William M.; Jones, Daniel K.; Smalling, Kelly L.; Fisher, Shawn C.; Fisher, Irene J.; Iwanowicz, Luke R.; Romanok, Kristin M.; Jenkins, Darkus E.; Bowers, Luke; Boehlke, Adam; Foreman, William T.; Deetz, Anna C.; Carper, Lisa G.; Imbrigiotta, Thomas E.; Birdwell, Justin E.

    2015-01-01

    This report describes a reconnaissance study of estuarine bed-sediment quality conducted June–October 2013 in New Jersey and New York after Hurricane Sandy in October 2012 to assess the extent of contamination and the potential long-term human and ecological impacts of the storm. The study, funded through the Disaster Relief Appropriations Act of 2013 (PL 113-2), was conducted by the U.S. Geological Survey in cooperation with the U.S. Environmental Protection Agency and the National Oceanographic and Atmospheric Administration. In addition to presenting the bed-sediment-quality data, the report describes the study design, documents the methods of sample collection and analysis, and discusses the steps taken to assure the quality of the data.

  12. Regional variability in bed-sediment concentrations of wastewater compounds, hormones and PAHs for portions of coastal New York and New Jersey impacted by hurricane Sandy

    Science.gov (United States)

    Phillips, Patrick; Gibson, Cathy A; Fisher, Shawn C.; Fisher, Irene; Reilly, Timothy J.; Smalling, Kelly L.; Romanok, Kristin M.; Foreman, William T.; ReVello, Rhiannon C.; Focazio, Michael J.; Jones, Daniel K.

    2016-01-01

    Bed sediment samples from 79 coastal New York and New Jersey, USA sites were analyzed for 75 compounds including wastewater associated contaminants, PAHs, and other organic compounds to assess the post-Hurricane Sandy distribution of organic contaminants among six regions. These results provide the first assessment of wastewater compounds, hormones, and PAHs in bed sediment for this region. Concentrations of most wastewater contaminants and PAHs were highest in the most developed region (Upper Harbor/Newark Bay, UHNB) and reflected the wastewater inputs to this area. Although the lack of pre-Hurricane Sandy data for most of these compounds make it impossible to assess the effect of the storm on wastewater contaminant concentrations, PAH concentrations in the UHNB region reflect pre-Hurricane Sandy conditions in this region. Lower hormone concentrations than predicted by the total organic carbon relation occurred in UHNB samples, suggesting that hormones are being degraded in the UHNB region.

  13. Wave-formed sediment ripples: Transient analysis of ripple spectral development

    Science.gov (United States)

    Davis, Joseph P.; Walker, David J.; Townsend, Murray; Young, Ian R.

    2004-07-01

    A new method has been developed that models the changes a wave-formed rippled sediment bed undergoes as it is actively evolving between two given equilibrium states due to a change in surface wave conditions. The transient analysis of rippled beds has received very little attention within the literature. Dynamic changes within ripple parameters have implications for the estimation of flow dissipation and sediment transport by changing the bottom roughness height. The method uses the spectral density function of the rippled bed and is based on a series of ripple growth and ripple transition experimental tests. The ripple evolution model was developed from the well-known Logistic Growth Law. Fitting the general solution of the logistic nonlinear differential equation to the experimental data enabled the evolution rate of the bed to be determined for each experimental test. It was concluded that there was no difference between the evolution rate determined from the ripple growth tests and the ripple transition tests. This indicated that the two types of growth are special cases of the same evolution processes, which is adequately modeled by the logistic growth equation. A functional dependence was established between the ripple evolution rate and the Shields parameter. This allows the evolution rate to be estimated from flow and sediment properties. The estimation of the rate at which rippled sediment beds evolve under a variable sea state has the potential to lead to significant improvements to the way ripple transition and hence bottom roughness is approximated in coastal wave models.

  14. A Granular Model of Rolling Grain Ripples

    CERN Document Server

    Andersen, K H

    1999-01-01

    A simple model is presented for the formation of rolling grain ripples on a flat sand bed by the oscillatory flow from a surface wave. The model is related to physical parameters of the problem, and is solved for the equilibrium spacing and height of the ripples. Good agreement between the model and measurements of rolling grain ripples is demonstrated. It is found that the length of the ripples scale with the square-root of the non-dimensional shear stress on a flat bed.

  15. Gravelly to sandy braidplain deposition in the czerwona góra beds and stryczowice beds (middle buntsandstein) of the northeastern holy cross mountains (poland)

    Science.gov (United States)

    Mader, Detlef; Barczuk, Andrezej

    The Czerwona Góra Beds and Stryczowice Beds in the northeastern part of the Holy Cross Mountains in Poland represent the installation of an extensive open high-energy braidplain following the precursory buildout of a chain of restricted alluvial fans in the preceding Zwola Beds which initiate the Buntsandstein deposition. The conglomerates and sandstones originate in channels of braided rivers as gravelly longitudinal bars, sandy transverse bars and sand sheets on the floor of the watercourses and on moderately-elevated platforms within the streams. Topstratum deposition particularly including suspension settling is very restricted due to effective primary suppression of origin as a consequence of persistence of vigorous floods. Resulting from short periodicity and large extension of high-water surges, the conglomerates and sandstones which successively accumulate on the bottom of the streams coalesce by vertical stacking and lateral amalgamation to thick and extensive complexes of multistorey substratum deposits. Indications of minor aeolian influence are only present in the basal Zwola Beds, with some reworked ventifacts testifying to almost complete subsequent destruction of rarely formed aeolian features in very limited spots of the river complex. The petrographical composition and textural maturity of the gravel is largely independent from the depositional processes. The laterally changing composition of the pebbles and cobbles in the Czerwona Góra Beds with almost exclusive presence of siliceous clasts around Czerwona Góra and occurrence of considerable amounts of carbonate clasts around Stryczowice testifies to a diversified regional geology in the provenance area and to delivery of the detritus in several discrete flows which are directed to different areas and which are laterally overlapping. Preferential downcutting of the carbonate source rocks below the base level of erosion and absence of significant rejuvenation of the relief results in upwards

  16. Pattern formation - Instabilities in sand ripples

    DEFF Research Database (Denmark)

    Hansen, J. L.; v. Hecke, M.; Haaning, A.

    2001-01-01

    Sand ripples are seen below shallow wavy water and are formed whenever water oscillates over a bed of sand. Here we analyse the instabilities that can upset this perfect patterning when the ripples are subjected to large changes in driving amplitude or frequency, causing them to deform both...

  17. Origin of the Two Scales of Wind Ripples on Mars

    Science.gov (United States)

    Lapotre, Mathieu G. A.; Ewing, Ryan C.; Lamb, Michael P.; Fischer, Woodward W.; Grotzinger, John P.; Rubin, David M.; Lewis, Kevin W.; Day, Mackenzie; Gupta, Sanjeev; Banham, Steeve G.; Bridges, Nathan T.; DesMarais, David J.; Fraeman, Abigail A.; Grant, John A.; Herkenhoff, Kenneth E.; Ming, Douglas W.; Mischna, Michael A.; Rice, Melissa S.; Sumner, Dawn A.; Vasavada, Ashwin R.; Yingst, R. Aileen

    2016-01-01

    Earth's sandy deserts host two main types of bedforms - decimeter-scale ripples and larger dunes. Years of orbital observations on Mars also confirmed the existence of two modes of active eolian bedforms - meter-scale ripples, and dunes. By analogy to terrestrial ripples, which are thought to form from a grain mechanism, it was hypothesized that large martian ripples also formed from grain impacts, but spaced further apart due to elongated saltation trajectories from the lower martian gravity and different atmospheric properties. However, the Curiosity rover recently documented the coexistence of three scales of bedforms in Gale crater. Because a grain impact mechanism cannot readily explain two distinct and coeval ripple modes in similar sand sizes, a new mechanism seems to be required to explain one of the scales of ripples. Small ripples are most similar to Earth's impact ripples, with straight crests and subdued profiles. In contrast, large martian ripples are sinuous and asymmetric, with lee slopes dominated by grain flows and grainfall deposits. Thus, large martian ripples resemble current ripples formed underwater on Earth, suggesting that they may form from a fluid-drag mechanism. To test this hypothesis, we develop a scaling relation to predict the spacing of fluid-drag ripples from an extensive flume data compilation. The size of large martian ripples is predicted by our scaling relation when adjusted for martian atmospheric properties. Specifically, we propose that the wavelength of martian wind-drag ripples arises from the high kinematic viscosity of the low-density atmosphere. Because fluid density controls drag-ripple size, our scaling relation can help constrain paleoatmospheric density from wind-drag ripple stratification.

  18. Development of Flaser and Lenticular Bedding in Response to Tropical Cyclones

    Science.gov (United States)

    Richardson, M. D.; Briggs, K. B.

    2005-05-01

    Flaser and lenticular deposits (sensu Reineck and Wunderlich) are common in the sedimentary record and generally found associated with rippled seafloors in tidally influenced coastal waters. These features are thought to be created by deposition of suspended fine-grained mud onto a rippled sandy seafloor during quiescent periods, followed by migration of sand ripples during periods of strong tidal currents. The size of these mud deposits range from small lenses the size of ripple wavelengths (flasers) to large interconnected mud beds containing sand deposits (lenticular deposits). The development of flaser and lenticular bedding was observed on a mostly sandy shelf (5-20 m water depths) in the northeastern Gulf of Mexico after the passage of Hurricane Ivan and subsequent tropical storms. The mud was probably derived from backwash from lagoonal areas behind barrier islands after the passage of Hurricane Ivan (16 September 2004) and the mobilization of sand ripples was a result of storms. Suspended mud was deposited over the rippled seafloor during a period of relative calm. Subsequent storms Hurricane Jeanne (26 September) and, later, Tropical Storm Matthew (8-10 October) mobilized sediments creating 50-100 cm wavelength sand ripples that migrated over the freshly deposited mud layers creating buried features ranging from small, isolated flaser deposits to lenticular deposits within mud to mud deposits covering 100's of square meters. Mud deposit thicknesses ranged from 2 cm to as much as 15-20 cm. The temporal persistence of these features is unknown but similar flaser and lenticular bedding has been observed in chirp sonar records and sediment vibra-core samples from sediment depths below that conceivably mobilized by Hurricanes.

  19. A particle model of rolling grain ripples under waves

    DEFF Research Database (Denmark)

    Andersen, Ken Haste

    2001-01-01

    A simple model for the formation of rolling grain ripples on a flat sand bed by the oscillatory flow generated by a surface wave is presented. An equation of motion is derived for the individual ripples, seen as "particles," on the otherwise flat bed. The model accounts for the initial appearance...... of the ripples, the subsequent coarsening of the ripples, and the final equilibrium state. The model is related to the physical parameters of the problem, and an analytical approximation for the equilibrium spacing of the ripples is developed. It is found that the spacing between the ripples scales...... with the square-root of the nondimensional shear stress (the Shields parameter) on a flat bed. The results of the model are compared with measurements, and reasonable agreement between the model and the measurements is demonstrated. ©2001 American Institute of Physics....

  20. A comparison of fish communities of subtidal seagrass beds and sandy seabeds in 13 marine embayments of a Caribbean island, based on species, families, size distribution and functional groups

    Science.gov (United States)

    Nagelkerken, I.; van der Velde, G.

    2004-08-01

    Differences in fish community structure between different estuaries, lagoons and bays can be very large, and generalisations are complicated by the use of a wide variety of sampling methods. In the present study, fish communities of subtidal seagrass beds and sandy seabeds in 13 marine embayments of a single Caribbean island were therefore sampled using a uniform method. The objective of the study was to determine whether the seagrass and sandy seabed habitats of various embayments are characterised by typical fish assemblages which differ in terms of taxa (species, families), size classes (life stages) and functional groups (ecological species groups, feeding time and diet). This was linked to the hypothesis that differences in fish assemblages between habitats in different embayments are larger at taxonomic levels than at the level of functional groups. A second objective was to determine the most useful discriminating features between the two habitat types. The above hypothesis was rejected, since differences in fish assemblages from different seagrass and sandy seabed sites did not increase from functional to taxonomic level, but from size class to diet/species to family/feeding time to ecological species group. However, the seagrass and sandy seabed habitats could each be characterised by typical fish assemblages which differed in taxonomical and functional group composition, irrespective of differences in environmental and biotic variables between the embayments in which these habitats were situated. The two habitat types could be best characterised on the basis of fish family, ecological species group, feeding time and size distribution. Seagrass beds mainly harboured nocturnally active nursery species (Haemulidae, Lutjanidae, etc.), whose relative abundance was related to vegetation (mainly seagrass) cover. Sandy seabeds mainly harboured diurnally active bay species (Gerreidae, etc.) whose relative abundance was related to cover of bare sand. Similarities

  1. DPTM simulation of aeolian sand ripple

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Aeolian sand ripple and its time evolution are simulated by the discrete particle tracing method (DPTM) presented in this paper. The difference between this method and the current methods is that the former can consider the three main factors relevant to the formation of natural aeolian sand ripples,which are the wind-blown sand flux above the sand bed formed by lots of sand particles with different di-ameters,the particle-bed collision and after it the rebound and ejection of sand particles in the sand bed,the saltation of high-speed sand particles and the creep of low-speed sand particles,respectively. The simulated aeolian sand ripple is close to the natural sand ripple not only in basic shape and characteristic,particle size segregation and stratigraphy,but also in formation stages. In addition,three important speeds can be obtained by this method,which are the propagation speed of the saturated aeolian sand ripple and the critical frictional wind speeds of emergence and disappearance of sand ripple.

  2. DPTM simulation of aeolian sand ripple

    Institute of Scientific and Technical Information of China (English)

    ZHENG XiaoJing; BO TianLi; XIE Li

    2008-01-01

    Aeolian sand ripple and its time evolution are simulated by the discrete particle tracing method (DPTM) presented in this paper.The difference between this method and the current methods is that the former can consider the three main factors relevant to the formation of natural aeolian sand ripples, which are the wind-blown sand flux above the sand bed formed by lots of sand particles with different di-ameters, the particle-bed collision and after it the rebound and ejection of sand particles in the sand bed, the saltation of high-speed sand particles and the creep of low-speed sand particles, respectively.The simulated aeolian sand ripple is close to the natural sand ripple not only in basic shape and characteristic, particle size segregation and stratigraphy, but also in formation stages.In addition, three important speeds can be obtained by this method, which are the propagation speed of the saturated aeolian sand ripple and the critical frictional wind speeds of emergence and disappearance of sand ripple.

  3. Dune-like dynamic of Martian Aeolian large ripples

    Science.gov (United States)

    Silvestro, S.; Vaz, D. A.; Yizhaq, H.; Esposito, F.

    2016-08-01

    Martian dunes are sculpted by meter-scale bed forms, which have been interpreted as wind ripples based on orbital data. Because aeolian ripples tend to orient and migrate transversely to the last sand-moving wind, they have been widely used as wind vanes on Earth and Mars. In this report we show that Martian large ripples are dynamically different from Earth's ripples. By remotely monitoring their evolution within the Mars Science Laboratory landing site, we show that these bed forms evolve longitudinally with minimal lateral migration in a time-span of ~ six terrestrial years. Our observations suggest that the large Martian ripples can record more than one wind direction and that in certain cases they are more similar to linear dunes from a dynamic point of view. Consequently, the assumption of the transverse nature of the large Martian ripples must be used with caution when using these features to derive wind directions.

  4. Relaxation time effects of wave ripples on tidal beaches

    Science.gov (United States)

    Austin, M. J.; Masselink, G.; O'Hare, T. J.; Russell, P. E.

    2007-08-01

    Seabed roughness due to wave ripples is a key factor in controlling sediment transport processes in the nearshore zone. Roughness is commonly considered a function of the ripple geometry, which in turn, can be predicted from sediment and hydrodynamic parameters. Existing ripple predictors consider the bed morphology to be in equilibrium with the hydrodynamics, whereas recent laboratory measurements show that the time scale for ripple development is of the order of tens of minutes to hours. Here we show that wave ripples on tidal beaches are significantly affected by relaxation time effects, with ripple height and length progressively increasing during the rising tide and remaining constant during the falling tide. Moreover, we examine the ripples in the context of existing empirical models and suggest how the temporal evolution over a tidal cycle may be predicted.

  5. Combined Effects of Dam Removal and Past Sediment Mining on a Relatively Large Lowland Sandy Gravelly Bed River (Vienne River, France).

    Science.gov (United States)

    Rodrigues, S.; Ursache, O.; Bouchard, J. P.; Juge, P.

    2014-12-01

    Dam removal is of growing interest for the management of sediment fluxes, morphological evolution and ecological restoration of rivers. If dam removal experiments are well documented for small streams, examples of lowland and large rivers are scarce. We present the morphological response of a relatively large lowland river (Vienne River, France) to a dam removal. The objective is to understand and quantify the morphological adaptation on a reach of 50 km and over 15 years associated with the dam removal and the presence of ancient sand pits located along the riverbed. This study is based on field data collected during 7 surveys performed between 1998 and 2013. This dataset focuses on bed geometry, sediment grain size, and bedload fluxes. It was combined with a 1D numerical model to assess flow dynamics and sediment transport before and after dam removal. Results show that dam removal triggered both regressive and progressive erosions and that discharges higher than 100 m3.s-1 were sufficient to erode the sandy sediments trapped by the dam whereas gravels were mobilised for discharges higher than 300 m3.s-1. Since 1999, large bedload sediment waves coming from upstream migrated downstream at an average celerity of 2.2 km.year-1 and were trapped by three ancient sand pits located downstream. Some of these pits constitute efficient sediment traps even 15 years after dam removal. As a result, between 2002 and 2013, the slope of the river bed adjusted gently and observed morphological processes were minors compared with the time period between 1998 and 2002.

  6. Permeation through graphene ripples

    Science.gov (United States)

    Liang, Tao; He, Guangyu; Wu, Xu; Ren, Jindong; Guo, Hongxuan; Kong, Yuhan; Iwai, Hideo; Fujita, Daisuke; Gao, Hongjun; Guo, Haiming; Liu, Yingchun; Xu, Mingsheng

    2017-06-01

    Real graphene sheets show limited anti-permeation performance deviating from the ideally flat honeycomb carbon lattice that is impermeable to gases. Ripples in graphene are prevalent and they could significantly influence carrier transport. However, little attention has been paid to the role of ripples in the permeation properties of graphene. Here, we report that gases can permeate through graphene ripples at room temperature. The feasibility of gas permeation through graphene ripples is determined by detecting the initial oxidation sites of Cu surface covered with isolated graphene domain. Nudged elastic band (NEB) calculations demonstrate that the oxygen atom permeation occurs via the formation of C-O-C bond, in which process the energy barrier through the rippled graphene lattice is much smaller than that through a flat graphene lattice, rendering permeation through ripples more favorable. Combining with the recent advances in atoms intercalation between graphene and metal substrate for transfer-free and electrically insulated graphene, this discovery provides new perspectives regarding graphene’s limited anti-permeation performance and evokes for rational design of graphene-based encapsulation for barrier and selective gas separation applications through ripple engineering.

  7. Rippling of Graphene

    Science.gov (United States)

    Moura, Maria; Thompson-Flagg, Rebecca; Marder, Michael

    2010-03-01

    Experiments found that free standing, single-layer graphene sheets display ripples [1]. Here we show that graphene can develop ripples as a consequence of adsorbed molecules sitting on random sites. The adsorbates cause the bonds between the carbon atoms to lengthen slightly. Static buckles then result from a mechanism like the one that leads to buckling of leaves. Ripples caused by roughly 20% coverage of adsorbates are consistent with experimental observation. We show why this mechanism is more likely to explain ripples than are thermal fluctuations or the Mermin-Wagner theorem (previously invoked [2]). This work was recently published [3]. [4pt] [1] J. C. Meyer, A. K. Geim, M. I. Katsnelson, K. S. Novoselov, T. J. Booth, and S. Roth, Nature, 446, 60 (2007). [0pt] [2] A. Fasolino, J. H. Los, and M. I. Katsnelson, Nature Materials, 6, 858, (2007). [0pt] [3] R. Thompson-Flagg, M. J. B. Moura, and M. Marder, EPL, 85, 46002 (2009).

  8. Wave-induced ripple development in mixed clay-sand substrates

    Science.gov (United States)

    Wu, Xuxu; Parsons, Daniel; Baas, Jaco H.; Mouazé, Dominique; McLelland, Stuart; Amoudry, Laurent; Eggenhuisen, Jorris; Cartigny, Matthieu; Ruessink, Gerben

    2016-04-01

    This paper reports on a series of experiments that aim to provide a fuller understanding of ripple development within clay-sand mixture substrates under oscillatory flow conditions. The work was conducted in the Total Environment Simulator at the University of Hull and constituted 6 separate runs, in which 5 runs were conducted under identical sets of regular waves (an additional run was conducted under irregular waves, but is not discussed in present paper). The bed content was systematically varied in its composition ranging from a pure sand bed through to a bed comprising 7.4% clay. A series of state-of-the-art measurements were employed to quantify interactions of near-bed hydrodynamics, sediment transport, and turbulence over rippled beds formed by wave action, during and after, each run. The experimental results demonstrate the significant influence of the amount of cohesive clay materials in the substrate on ripple evolution under waves. Most importantly, addition of clay in the bed dramatically slowed down the rate of ripple development and evolution. The equilibrium time of each run increased exponentially from 30 minutes under the control conditions of a pure sand bed, rising to ~350 minutes for the bed with the highest fraction of clay. The paper discusses the slower ripple growth rates with higher cohesive fractions, via an influence on critical shear, but highlights that the end equilibrium size of ripples is found to be independent of increasing substrate clay fraction. The suspended particles mass (SPM) concentration indicates that clay particles were suspended and winnowed by wave action. Additionally, laser granulometry of the final substrates verified that ripple crests were composed of pure sand layers that were absent at ripple troughs, reflecting a relatively higher winnowing efficiency at wave ripples crest. The winnowing process and its efficiency is inexorably linked to wave ripple development and evolution. The implications of the results

  9. Comparison of surface emissions and subsurface distribution of cis- and trans-1,3-dichloropropene and chloropicrin in sandy field beds covered with four different plastic films.

    Science.gov (United States)

    Ou, Li-Tse; Thomas, John E; Allen, L Hartwell; Vu, Joseph C; Dickson, Donald W

    2008-06-01

    The purpose of this study was to conduct a field study at a Florida field site on surface emissions and subsurface distribution of cis-and trans-1,3-dichloropropene (1,3-D) and chloropicrin (CP) in raised beds injected with Telone C35 with four replications. A total of 16 beds were applied with Telone C35 by chisel injection and covered with four different plastic films, 4 beds for each film. Each bed was installed with five 20-cm long soil pore air probes and a surface air collection pan at arbitrarily locations along the length of each bed for sampling soil pore air and surface air, respectively, for analysis of the three biologically active compounds, cis- and trans-1,3-D and CP. We found that average concentrations of the three compounds at 20-cm depth among the beds covered with four different plastic films generally were not statistically different. Among the four beds covered with the same plastic film, average concentrations of the three compounds were statistically different only in the four metallic PE covered beds at 5 and 24 hours after injection. Volatilization rates of the three compounds among the beds covered with four different plastic films, with the exception of CP at 48 hours after injection, were not statistically different. It appeared that initial upward diffusion and volatilization flux were influenced by solar radiation. Initial subsurface concentrations of the three compounds and volatilization flux, especially cis-1,3-D, were greater in the beds on the east side of the field than that in the beds on the west side of the field. Whether or not difference in initial subsurface concentrations of the compounds between east side beds and west side beds may influence fumigant efficacy remains to be determined.

  10. Colonization dynamics of ciliate morphotypes modified by shifting sandy sediments.

    Science.gov (United States)

    Risse-Buhl, Ute; Felsmann, Katja; Mutz, Michael

    2014-08-01

    Sandy stream-bed sediments colonized by a diverse ciliate community are subject to various disturbance regimes. In microcosms, we investigated the effect of sediment shifting on the colonization dynamics of 3 ciliate morphotypes differing in morphology, behavior and feeding strategy. The dynamics of the ciliate morphotypes inhabiting sediment pore water and overlying water were observed at 3 sediment shifting frequencies: (1) stable sediments, (2) periodically shifting sediments such as migrating ripples, and (3) continuously shifting sediments as occurring during scour events of the uppermost sediment. Sediment shifting significantly affected the abundance and growth rate of the ciliate morphotypes. The free-swimming filter feeder Dexiostoma campylum was vulnerable to washout by sediment shifting since significantly higher numbers occurred in the overlying water than in pore water. Abundance of D. campylum only increased in pore water of stable sediments. On the contrary, the vagile grasper feeder Chilodonella uncinata and the sessile filter feeder Vorticella convallaria had positive growth rates and successfully colonized sediments that shifted periodically and continuously. Thus, the spatio-temporal pattern of sediment dynamics acts as an essential factor of impact on the structure, distribution and function of ciliate communities in sand-bed streams.

  11. Ripple marks as indicators of Late Ordovician sedimentary environments in Northwest Estonia

    Directory of Open Access Journals (Sweden)

    Hints, Linda

    2008-03-01

    Full Text Available Late Ordovician sedimentary environments promoting the development of ripple marks in shallow shelf carbonate deposits of northern Estonia are analysed. Ripple marks are described using different parameters (wavelength, height, and wave and asymmetry indexes. Rippled bedding is exposed in a large area in the uppermost Keila Stage, on the upper boundary of micritic-peloidal limestones (Pääsküla Member of the Kahula Formation. Beds with ripples are overlain by organodetrital lime­stones (Saue Member of the Kahula Formation transitional to grainstones or mud mounds of the Vasalemma Formation. The content of peloids in the Pääsküla Member is relatively high and their size (0.04–0.06 mm corresponds to the grain size of sediments capable of forming ripple marks. Weakly asymmetrical sinusoidal ripple marks are oriented in a north–south direction and have likely been formed in the shallow-water zone of the shoal at some distance from the shore. The wave-current origin of the studied ripples can be inferred from ripple indexes. Ripples were subjected to some erosion and in the shallowing-upwards conditions a rocky bottom with the Trypanites ichnofacies evolved. The rippled surface terminates a small-scale cycle (parasequence of the depositional sequence.

  12. Formation of sand ripples under a turbulent liquid flow

    CERN Document Server

    Franklin, Erick de Moraes

    2016-01-01

    Sand ripples are commonly observed in both nature and industry. For example, they are found on riverbeds and in oil pipelines that transport sand. In both natural and industrial cases, ripples increase friction between the bed and fluid and are related to flooding, high pressure drops, and transients. Ripples appear when sediments are entrained as bed load (a mobile granular layer) and are usually considered to be the result of initial bedforms that eventually saturate. Given the small aspect ratio of the initial bedforms, linear analyses can be used to understand the formation of ripples. This paper presents a linear stability analysis of a granular bed under a turbulent flow of a liquid. This analysis takes into consideration all the main mechanisms and parameters involved in the turbulent liquid case, including some important parameters that have not yet been considered together such as the bed compactness and the bed-load threshold shear stress. The results of this analysis are compared with published exp...

  13. Wavelength selection and symmetry breaking in orbital wave ripples

    Science.gov (United States)

    Nienhuis, Jaap H.; Perron, J. Taylor; Kao, Justin C. T.; Myrow, Paul M.

    2014-10-01

    Sand ripples formed by waves have a uniform wavelength while at equilibrium and develop defects while adjusting to changes in the flow. These patterns arise from the interaction of the flow with the bed topography, but the specific mechanisms have not been fully explained. We use numerical flow models and laboratory wave tank experiments to explore the origins of these patterns. The wavelength of "orbital" wave ripples (λ) is directly proportional to the oscillating flow's orbital diameter (d), with many experimental and field studies finding λ/d ≈ 0.65. We demonstrate a coupling that selects this ratio: the maximum length of the flow separation zone downstream of a ripple crest equals λ when λ/d ≈ 0.65. We show that this condition maximizes the growth rate of ripples. Ripples adjusting to changed flow conditions develop defects that break the bed's symmetry. When d is shortened sufficiently, two new incipient crests appear in every trough, but only one grows into a full-sized crest. Experiments have shown that the same side (right or left) wins in every trough. We find that this occurs because incipient secondary crests slow the flow and encourage the growth of crests on the next flank. Experiments have also shown that when d is lengthened, ripple crests become increasingly sinuous and eventually break up. We find that this occurs because crests migrate preferentially toward the nearest adjacent crest, amplifying any initial sinuosity. Our results reveal the mechanisms that form common wave ripple patterns and highlight interactions among unsteady flows, sediment transport, and bed topography.

  14. Wandering gravel-bed rivers and high-constructive stable channel sandy fluvial systems in the Ross River area, Yukon Territory, Canada

    Directory of Open Access Journals (Sweden)

    Darrel G.F. Long

    2011-07-01

    Gravel-dominated strata, inter-bedded with, and overlying coal-bearing units, are interpreted as deposits of wandering gravel-bed rivers, with sinuosity approaching 1.4. In most exposures they appear to be dominated by massive and thin planar-bedded granule to small pebble conglomerates, which would traditionally be interpreted as sheet-flood or longitudinal bar deposits of a high-gradient braided stream or alluvial fan. Architectural analysis of exposures in an open-pit shows that the predominance of flat bedding is an artefact of the geometry of the roadside exposures. In the pit the conglomerates are dominated by large scale cross stratification on a scale of 1–5.5 m. These appear to have developed as downstream and lateral accretion elements on side-bars and on in-channel bars in water depths of 2–12 m. Stacking of strata on domed 3rd order surfaces suggests development of longitudinal in-channel bar complexes similar to those observed in parts of the modern Rhône River system. Mudstone preserved in some of the channels reflects intervals of channel abandonment or avulsion. Minimum channel width is from 70 to 450 m.

  15. Study of frequency pattern of coherent turbulent flow over ripples using image processing with implication in river restoration

    Directory of Open Access Journals (Sweden)

    A. Keshavarzi

    2011-08-01

    Full Text Available River channel change and bed scourings are source of major environmental problem for fish and aquatic habitat. The bed form such as ripples and dunes is the result of an interaction between turbulent flow structure and sediment particles at the bed. The structure of turbulent flow over ripples is important to understand initiation of sediment entrainment and its transport. The focus of this study is the measurement and analysis of the dominant bursting events and the flow structure over ripples in the bed of a channel. Two types of ripples with sinusoidal and triangular forms were tested in this study. The velocities of flow over the ripples were measured in three dimensions using an Acoustic Doppler Velocimeter with a sampling rate of 50 Hz. These velocities were measured at different points within the flow depth from the bed and at different longitudinal positions along the flume. A CCD camera was used to capture 1500 sequential images from the bed and to monitor sediment movement at different positions along the bed. Application of image processing technique enabled us to compute the number of entrained and deposited particles over the ripples. From a quadrant decomposition of instantaneous velocity fluctuations close to the bed, it was found that bursting events downstream of the second ripple, in Quadrants 1 and 3, were dominant whereas upstream of the ripple, Quadrants 2 and 4 were dominant. More importantly consideration of these results indicates that the normalized occurrence probabilities of sweep events are in phase with the bed forms whereas those of ejection event are out of phase with the bed form. Therefore entrainment would be expected to occur upstream and deposition occurs downstream of the ripple. These expectations were confirmed by measurement of entrained and deposited sediment particles from the bed. These above information can be used in practical application for rivers where restoration is required.

  16. Three-dimensional sand ripples as the product of vortex instability

    CERN Document Server

    Franklin, Erick de Moraes

    2016-01-01

    Three-dimensional sand ripples can be observed under steady liquid flows in both nature and industry. Some examples are the ripples observed on the bed of rivers and in petroleum pipelines conveying sand. Although of importance, the formation of these patterns is not completely understood. There are theoretical and experimental evidence that aquatic ripples grow from two-dimensional bed instabilities, so that a straight vortex is formed just downstream of their crests. The proposition of Raudkivi (2006), that three-dimensionality has its origin in a vortex instability, is employed here. This paper presents a linear stability analysis of the downstream vortex in order to obtain the transverse scales of three-dimensional ripples. The obtained wavelength is compared with experimentally observed ripples.

  17. Decifering mega-ripple variability in an anthropogenically steered environment: implications for mine burial studies

    OpenAIRE

    Papili, S.; Baeye, M.; Van Lancker, V.

    2013-01-01

    In 2007 the Ministery of Defence, in collaboration with Ghent University, developed a project on the understanding of mega-ripple variability in view of improving mine burial prediction models in sandbank areas. Results will assist in the monitoring of sea-mines, heritage of two World Wars, nowadays partially or totally buried by sandy bedforms.

  18. Hurricane Sandy and earthquakes

    OpenAIRE

    MAVASHEV BORIS; MAVASHEV IGOR

    2013-01-01

    Submit for consideration the connection between formation of a hurricane Sandy and earthquakes. As a rule, weather anomalies precede and accompany earthquakes. The hurricane Sandy emerged 2 days prior to strong earthquakes that occurred in the area. And the trajectory of the hurricane Sandy matched the epicenter of the earthquakes. Possibility of early prediction of natural disasters will minimize the moral and material damage.

  19. A Stellar Ripple

    Science.gov (United States)

    2006-01-01

    This false-color composite image shows the Cartwheel galaxy as seen by the Galaxy Evolution Explorer's far ultraviolet detector (blue); the Hubble Space Telescope's wide field and planetary camera 2 in B-band visible light (green); the Spitzer Space Telescope's infrared array camera at 8 microns (red); and the Chandra X-ray Observatory's advanced CCD imaging spectrometer-S array instrument (purple). Approximately 100 million years ago, a smaller galaxy plunged through the heart of Cartwheel galaxy, creating ripples of brief star formation. In this image, the first ripple appears as an ultraviolet-bright blue outer ring. The blue outer ring is so powerful in the Galaxy Evolution Explorer observations that it indicates the Cartwheel is one of the most powerful UV-emitting galaxies in the nearby universe. The blue color reveals to astronomers that associations of stars 5 to 20 times as massive as our sun are forming in this region. The clumps of pink along the outer blue ring are regions where both X-rays and ultraviolet radiation are superimposed in the image. These X-ray point sources are very likely collections of binary star systems containing a blackhole (called massive X-ray binary systems). The X-ray sources seem to cluster around optical/ultraviolet-bright supermassive star clusters. The yellow-orange inner ring and nucleus at the center of the galaxy result from the combination of visible and infrared light, which is stronger towards the center. This region of the galaxy represents the second ripple, or ring wave, created in the collision, but has much less star formation activity than the first (outer) ring wave. The wisps of red spread throughout the interior of the galaxy are organic molecules that have been illuminated by nearby low-level star formation. Meanwhile, the tints of green are less massive, older visible-light stars. Although astronomers have not identified exactly which galaxy collided with the Cartwheel, two of three candidate galaxies can be

  20. Dissolved and Bubble Gas Concentrations in Sandy Surficial Sediments of the West Florida Sand Sheet

    Science.gov (United States)

    2016-06-21

    Dissolved and Bubble Gas Concentrations in Sandy Surficial Sediments of the West Florida Sand Sheet Christopher Martens Dept. of Marine Sciences CB...TITLE AND SUBTITLE Dissolved and Bubble Gas Concentrations in Sandy Surficial Sediments of the West Florida Sand Sheet 5a. CONTRACT NUMBER 5b. GRANT...was noted that there was substantially higher organic material in the shallow troughs of the sand ripples than on the crests. Most of this appears

  1. Validating Experimental Bedform Dynamics on Cohesive Sand-Mud Beds in the Dee Estuary

    Science.gov (United States)

    Baas, Jaco H.; Baker, Megan; Hope, Julie; Malarkey, Jonathan; Rocha, Renata

    2014-05-01

    Recent laboratory experiments and field measurements have shown that small quantities of cohesive clay, and in particular 'sticky' biological polymers, within a sandy substrate dramatically reduce the development rate of sedimentary bedforms, with major implications for sediment transport rate calculations and process interpretations from the sedimentary record. FURTHER INFORMATION Flow and sediment transport predictions from sedimentary structures found in modern estuaries and within estuarine geological systems are impeded by an almost complete lack of process-based knowledge of the behaviour of natural sediments that consist of mixtures of cohesionless sand and biologically-active cohesive mud. Indeed, existing predictive models are largely based on non-organic cohesionless sands, despite the fact that mud, in pure form or mixed with sand, is the most common sediment on Earth and also the most biologically active interface across a range of Earth-surface environments, including rivers and shallow seas. The multidisciplinary COHBED project uses state-of-the-art laboratory and field technologies to measure the erosional properties of mixed cohesive sediment beds and the formation and stability of sedimentary bedforms on these beds, integrating the key physical and biological processes that govern bed evolution. The development of current ripples on cohesive mixed sediment beds was investigated as a function of physical control on bed cohesion versus biological control on bed cohesion. These investigations included laboratory flume experiments in the Hydrodynamics Laboratory (Bangor University) and field experiments in the Dee estuary (at West Kirby near Liverpool). The flume experiments showed that winnowing of fine-grained cohesive sediment, including biological stabilisers, is an important process affecting the development rate, size and shape of the cohesive bedforms. The ripples developed progressively slower as the kaolin clay fraction in the sandy substrate

  2. Fluid Dynamical Control of Spacing and Symmetry Breaking in Orbital Wave Ripples

    Science.gov (United States)

    Nienhuis, J.; Perron, J.; Kao, J. C.; Myrow, P.

    2013-12-01

    Sand ripples in coastal environments and the rock record are a ubiquitous signature of the interaction of flows, bed topography and sediment transport. A common class of ripples, orbital wave ripples, exhibits a well-known linear relationship between the wavelength of the ripple pattern and the amplitude of wave-generated oscillatory flow. Based on this relationship, the ripple wavelength is often used as a paleoenvironmental indicator; and the height and spacing of modern ripples are major controls on bed roughness. However, the mechanism that selects the observed ratio of ripple wavelength to flow amplitude has not been explained. Orbital wave ripples are sustained by zones of reversed flow on the lee side of the crest that moves sand upslope toward the crest. Using a lattice Boltzmann numerical flow model to simulate two-dimensional flow over a rippled bed, we demonstrate a coupling of flow and ripples that leads to the observed equilibrium: if the ratio between the orbital diameter (double the flow amplitude) and ripple wavelength is 0.65 - the equilibrium ratio observed in laboratory experiments and in the field - the maximum length of the separation zone downstream of a ripple crest is exactly equal to the ripple wavelength. Longer separation zones, with vortices advected further, will erode the neighboring crest. Shorter separation zones will not be able to erode the adjacent troughs. In addition to this equilibrium morphology, orbital wave ripples display characteristic patterns as they evolve in response to changes in wave conditions. Multiple experiments have shown that large-scale symmetry is lost during adjustment to a new equilibrium. When the wave orbital diameter is shortened sufficiently, two new crests appear in every trough. Of these two, one decays, while the other keeps growing. Interestingly, the same side (right or left) is observed to 'win' in every trough. When the orbital diameter is lengthened, a 'bulging' instability occurs, in which

  3. The wave plus current flow over vortex ripples at an arbitrary angle

    DEFF Research Database (Denmark)

    Andersen, Ken Haste; Faraci, C

    2003-01-01

    to a regular ripple pattern formation. Numerical simulations were conducted changing the direction between the waves and the current from 0degrees to 90degrees and the ratio between the current strength and the wave orbital velocity from 0.2 to 1.5. Close to the bed, the current aligns parallel to the ripple....... (C) 2002 Elsevier Science B.V. All rights reserved....

  4. Windblown Dunes and Ripples

    Science.gov (United States)

    2003-01-01

    MGS MOC Release No. MOC2-411, 4 July 2003July 4, 2003, is the 6th anniversary of the Mars Pathfinder landing. One of the elements carried to the red planet by Pathfinder was the Wind Sock Experiment. This project was designed to measure wind activity by taking pictures of three aluminum 'wind socks.' While the winds at the Mars Pathfinder site did not blow particularly strong during the course of that mission, dust storms seen from orbit and Earth-based telescopes attest to the fact that wind is a major force of change on the dry, desert surface of Mars today. This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) narrow angle image shows dark sand dunes and lighter-toned ripples trapped among the mountainous central peak of an old impact crater in Terra Tyrrhena near 13.9oS, 246.7oW. The dune slip faces--the steepest slope on the larger dunes--indicate sand transport is from the top/upper left toward the bottom/lower right. North is toward the top/upper right; the picture is 3 km (1.9 mi) across. Sunlight illuminates the scene from the upper left. This picture was obtained in April 2003.

  5. The formation and migration of sand ripples in closed conduits: experiments with turbulent water flows

    CERN Document Server

    Florez, Jorge Eduar Cardona

    2016-01-01

    The transport of solid particles by a fluid flow is frequently found in nature and industry. Some examples are the transport of sand in rivers and hydrocarbon pipelines. When the shear stresses exerted by a fluid flow on a granular bed remain moderate, some grains are set in motion without fluidizing the bed; the moving grains form a layer, known as bed load, that moves while maintaining contact with the fixed part of the bed. Under bed load conditions, the granular bed may become unstable, generating ripples and dunes. Sand ripples are commonly observed in closed conduits and pipes such as in petroleum pipelines, sewer systems, and dredging lines. Although of importance for many scientific domains and industrial applications, the formation of ripples in closed conduits is not well understood, and the problem is still open. This paper presents an experimental study on the formation and migration of sand ripples under a turbulent closed-conduit flow and bed-load conditions. In our experiments, fully-developed ...

  6. Mathematical Relationship Between Particle Reynolds Number and Ripple Factor using Tapi River Data, India.

    Directory of Open Access Journals (Sweden)

    S. M. Yadav

    2011-02-01

    Full Text Available The computation of bed load allows for the fact that only part of the shear stress is used for transport of sediments and some of the shear stress is wasted in overcoming the resistance due to bed forms therefore the total shear stress developed in the open channel requires correction in the form of correction factor called ripple factor. Different methods have been followed for correcting the actual shear stress in order to compute the sediment load. Correction factors are based on particular characteristics grain size of particle. In the present paper the ripple factor has been obtained for non uniform bed material considering the various variables like discharge, hydraulic mean depth, flow velocity, bed slope, average diameter of particle etc. by collecting the field data of Tapi river for 15 years for a particular gauging station. The ripple factor is obtained using Meyer Peter and Muller formula, Einstein Formula, Kalinske’s formula, Du Boy’s formula, Shield’s formula, Bagnold’s formula, average of six formulae and multiple regression analysis. The variation of ripple factor with particle Reynolds Number is studied. The ripple factor obtained by different approaches are further analyzed using Origin software and carrying out multiple regression on the 15 years of data with more than 10 parameters, ripple factor by multiple regression has been obtained. These values are further analysed and giving statistical mean to the parameters a relationship of power form has been developed. The ripple factor increases with the increase in the value of Particle Reynolds number. The large deviation is observed in case of Kalinske’s approach when compare with other approaches

  7. Characterizing and hindcasting ripple bedform dynamics: Field test of non-equilibrium models utilizing a fingerprint algorithm

    Science.gov (United States)

    DuVal, Carter B.; Trembanis, Arthur C.; Skarke, Adam

    2016-03-01

    Ripple bedform response to near bed forcing has been found to be asynchronous with rapidly changing hydrodynamic conditions. Recent models have attempted to account for this time variance through the introduction of a time offset between hydrodynamic forcing and seabed response with varying success. While focusing on temporal ripple evolution, spatial ripple variation has been partly neglected. With the fingerprint algorithm ripple bedform parameterization technique, spatial variation can be quickly and precisely characterized, and as such, this method is particularly useful for evaluation of ripple model spatio-temporal validity. Using time-series hydrodynamic data and synoptic acoustic imagery collected at an inner continental shelf site, this study compares an adapted time-varying ripple geometric model to observed field observations in light of the fingerprint algorithm results. Multiple equilibrium ripple predictors are tested within the time-varying model, with the algorithm results serving as the baseline geometric values. Results indicate that ripple bedforms, in the presence of rapidly changing high-energy conditions, reorganize at a slower rate than predicted by the models. Relict ripples were found to be near peak-forcing wavelengths after rapidly decaying storm events, and still present after months of sub-critical flow conditions.

  8. Transition from wavelets to ripples in a laboratory flume with a diverging channel

    Institute of Scientific and Technical Information of China (English)

    William B.RAUEN; Binliang LIN; Roger A.FALCONER

    2008-01-01

    An experimental investigation on the initiation and development of bed forms on a bed of fine silica sand was conducted under alluvial flow conditions in a laboratory flume with a diverging channel.The main aims of the study were to assess:I)the steepness of bed forms in the transition stage of development;and ii)the threshold height of wavelets(nt)that triggered the start of ripple development.Detailed bed profile measurements were carried out using an acoustic Doppler probe,traversed longitudinally over the sediment bed at various experimentation times.The bed form dimensions were extracted from such bed profile records and analysed for the wavelet,transition and equilibrium stages.It was found that the steepness of ripples in the transition and equilibrium stages were similar,confirming predictions of previous mathematical model simulations.A lognormal distribution fitted the wavelet length data.The wavelet threshold height was estimated as ηt≈7 mm,or y+≈80 in wall units.Such a height magnitude suggested that ripple development could be triggered by the wavelets reaching the outer flow zone of a turbulent boundary layer.The ηt value obtained corresponded generally to the intersection point between two predictive equations for bed form dimensions.A formulation was developed to predict ηt as a function of the sediment grain size,which was confirmed for the fine sand used in this study.

  9. Analyzing Hurricane Sandy

    Science.gov (United States)

    Convertino, Angelyn; Meyer, Stephan; Edwards, Becca

    2015-03-01

    Post-tropical Storm Sandy underwent extratropical transition shortly before making landfall in southern New Jersey October 29 2012. Data from this system was compared with data from Hurricane Ike (2008) which represents a classic hurricane with a clear eye wall and symmetry after landfall. Storm Sandy collided with a low pressure system coming in from the north as the hurricane made landfall on the US East coast. This contributed to Storm Sandy acting as a non-typical hurricane when it made landfall. Time histories of wind speed and wind direction were generated from data provided by Texas Tech's StickNet probes for both storms. The NOAA Weather and Climate program were used to generate radar loops of reflectivity during the landfall for both storms; these loops were compared with time histories for both Ike and Sandy to identify a relationship between time series data and storm-scale features identified on radar.

  10. Climbing ripple structure and associated storm-lamination from a Proterozoic carbonate platform succession: Their environmental and petrogenetic significance

    Indian Academy of Sciences (India)

    Asru K Chaudhuri

    2005-06-01

    The Mesoproterozoic Pandikunta Limestone, a shallow water carbonate platform succession in the Pranhita–Godavari Valley, south India, displays well developed climbing ripple lamination and storm deposited structures, such as HCS, wave ripple-lamination, combined-flow ripple-lamination and low angle trough cross-stratification. Different types of stratification developed in calcisiltite with minor amounts of very fine quartz sand and silt. The climbing ripple structures exhibit a complex pattern of superposition of different types (type A, B and S) within cosets pointing to a fluctuating rate of suspension deposition versus bedform migration, and an unsteady character of the flow. Close association of climbing ripple structures, HCS with anisotropic geometry, wavy lamination and combined-flow ripple-lamination suggest that the structures were formed by storm generated combined-flow in a mid-shelf area above the storm wave base. The combined-flow that deposited the climbing ripple structures had a strong unidirectional flow component of variable magnitude. The climbing ripple structure occurs as a constituent of graded stratified beds with an ordered vertical sequence of different types of lamination, reflecting flow deceleration and increased rate of suspension deposition. It is inferred that the beds were deposited from high-density waning flows in the relatively deeper part of the ancient shelf. The structures indicate that the Pandikunta platform was subjected to open marine circulation and intense storm activities. The storm deposited beds, intercalated with beds of lime-mudstone, consist primarily of fine sand and silt size carbonate particles that were hydrodynamically similar to quartz silt. Detrital carbonate particles are structureless and are of variable roundness. The particles were generated as primary carbonate clasts in coastal areas by mechanical disintegration of rapidly lithified beds, stromatolites or laminites, and the finest grade was

  11. Mars Rover Curiosity Traverses of Sand Ripples

    Science.gov (United States)

    Stein, N.; Arvidson, R. E.; Zhou, F.; Heverly, M.; Maimone, M.; Hartman, F.; Bellutta, P.; Iagnemma, K.; Senatore, C.

    2014-12-01

    Martian sand ripples present a challenge for rover mobility, with drives over ripples often characterized by high wheel sinkage and slippage that can lead to incipient embedding. Since landing in Gale Crater, Curiosity has traversed multiple sand ripples, including the transverse aeolian ridge (TAR) straddling Dingo Gap on sols 533 and 535. On sol 672, Curiosity crossed backward over a series of sand ripples before ending its drive after high motor currents initiated visual odometry (VO) processing, which detected 77% slip, well in excess of the imposed 60% slip limit. At the end of the drive, the right front wheel was deeply embedded at the base of a ripple flank with >20 cm sinkage and the rear wheels were near a ripple crest. As Curiosity continues its approach to Mount Sharp it will have to cross multiple ripples, and thus it is important to understand Curiosity's performance on sol 672 and over similar ripples. To this end the sol 672 drive was simulated in ARTEMIS (Adams-Based Rover Terramechanics Interaction Simulator), a software tool consisting of realistic rover mechanical models, a wheel-terrain interaction module for deformable and non-deformable surfaces, and realistic terrain models. ARTEMIS results, Dumont Dunes tests performed in the Mojave Desert using the Scarecrow test rover, and single wheel tests performed at MIT indicate that the high slip encountered on sol 672 likely occurred due to a combination of rover attack angle, ripple geometry, and soil properties. When ripple wavelength approaches vehicle length, the rover can reach orientations in which the leading wheels carry minimal normal loads and the trailing wheels sink deeply, resulting in high slippage and insufficient thrust to propel the rover over ripples. Even on relatively benign (i.e. low tilt) terrains, local morphology can impose high sinkage, thus impeding rover motion. Work is underway to quantify Curiosity's drive performance over various ripple geometries to retrieve soil

  12. Modelling and measurement of sand transport processes over full-scale ripples in oscillatory flow

    NARCIS (Netherlands)

    Werf, van der Jebbe J.; Ribberink, Jan S.; O'Donoghue, Tom; Doucette, Jeffrey C.

    2006-01-01

    A new series of laboratory experiments was performed in the Aberdeen Oscillatory Flow Tunnel (AOFT) and the Large Oscillating Water Tunnel (LOWT) to investigate time-averaged suspended sand concentrations and transport rates over rippled beds in regular and irregular oscillatory flow. The wave-induc

  13. On the formation of current ripples

    DEFF Research Database (Denmark)

    Bartholdy, Jesper; Ernstsen, Verner Brandbyge; Flemming, Burg W.

    2015-01-01

    For grain sizes finer than coarse sand, the first flow-transverse bedforms to develop are current ripples. Although numerous studies have analysed different aspects of bedform morphodynamics, to date no comprehensive physical explanation for the formation of ripples has been given. We offer...... such an explanation based on a virtual boundary layer concept, and present a model predicting ripple height on the basis of grain size, current velocity and water depth. The model contradicts the conventional view of current ripples as bedforms not scaling with flow depth. Furthermore, it confirms the dependence...

  14. Laboratory Experiments of Sand Ripples with Bimodal Size Distributions Under Asymmetric Oscillatory Flows

    Science.gov (United States)

    Calantoni, J.; Landry, B. J.

    2010-12-01

    The dynamics of sand ripples are vital to understanding numerous coastal processes such as sediment transport, wave attenuation, boundary layer development, and seafloor acoustic properties. Though significant laboratory research has been conducted to elucidate oscillatory flow morphodynamics under various constant and transient forcing conditions, the majority of the previous experiments were conducted only for beds with unimodal size distributions of sediment. Recent oscillatory flow experiments as well as past laboratory observations in uniform flows suggest that the presence of heterogeneous size sand compositions may significantly impact ripple morphology, resulting in a variety of observable effects (e.g., sediment sorting, bed armoring, and altered transport rates). Experimental work was conducted in a small oscillatory flow tunnel at the Sediment Dynamics Laboratory at the Naval Research Laboratory, Stennis Space Center. Three different monochromatic oscillatory forcings having velocity asymmetry were used to study sand ripple dynamics over five bimodal and two unimodal sediment beds. The seven different mixtures were composed using two unimodal sands of different colors (blue/white) and median grain diameters (d=0.31 mm / d=0.65 mm) combined into various mixtures by mass (i.e., 0/100; 10/90; 25/75; 50/50; 75/25; 90/10; and 100/0 which denotes mass percentage of blue/white sand, respectively, within each mixture). High-definition video of the sediment bed profile was acquired in conjunction with sediment trap measurements to resolve differences in ripple geometries, migration and evolution rates due to the different sediment mixtures and flow conditions. Observational findings clearly illustrate sediment stratification within ripple crests and the depth of the active mixing layer in addition to supporting sediment sorting in previous research on symmetric oscillatory flows in which the larger grains collect on top of ripple crests and smaller grains in the

  15. Molecular structure of the lecithin ripple phase

    NARCIS (Netherlands)

    de Vries, AH; Yefimov, S; Mark, AE; Marrink, SJ

    2005-01-01

    Molecular dynamics simulations of lecithin lipid bilayers in water as they are cooled from the liquid crystalline phase show the spontaneous formation of rippled bilayers. The ripple consists of two domains of different length and orientation, connected by a kink. The organization of the lipids in

  16. Parallelization of Reversible Ripple-carry Adders

    DEFF Research Database (Denmark)

    Thomsen, Michael Kirkedal; Axelsen, Holger Bock

    2009-01-01

    The design of fast arithmetic logic circuits is an important research topic for reversible and quantum computing. A special challenge in this setting is the computation of standard arithmetical functions without the generation of \\emph{garbage}. Here, we present a novel parallelization scheme...... wherein $m$ parallel $k$-bit reversible ripple-carry adders are combined to form a reversible $mk$-bit \\emph{ripple-block carry adder} with logic depth $\\mathcal{O}(m+k)$ for a \\emph{minimal} logic depth $\\mathcal{O}(\\sqrt{mk})$, thus improving on the $mk$-bit ripple-carry adder logic depth $\\mathcal......{O}(m\\cdot k)$. The underlying mechanisms of the parallelization scheme are formally proven correct. We also show designs for garbage-less reversible comparison circuits. We compare the circuit costs of the resulting ripple-block carry adder with known optimized reversible ripple-carry adders in measures...

  17. Sandy inland braidplain deposition with local aeolian sedimentation in the lower and middle parts of the buntsandstein and sandy coastal braidplain deposition in the topmost zechstein in the sudetes (Lower Silesia, Poland)

    Science.gov (United States)

    Mroczkowski, Jerzy; Mader, Detlef

    The lower and middle parts of the Buntsandstein between Röt and Zechstein in the Sudetes (Lower Silesia, Poland) crop out in the marginal seams of the North Sudetic Trough and the Intra Sudetic Trough. The continental red beds originate in predominantly sandy braided river systems of an extensive inland alluvial plain in almost arid climate. The sediments are laid down in channels and floodplains of a moderately- to highly-braided, sandy to pebbly stream complex consisting of narrowly- to moderately-spaced low-sinuosity watercourses and narrow to wide overbank plains between the channels. Rapid aggradation and abandonment, quick lateral migration or high avulsion rates of the considerably mobile streams result in effective combing of the interchannel areas. Persistent high-energy overspilling of watercourse banks and invasion of bed-load-saturated flood surges into the overbank areas often lead to primary restriction or even suppression of formation of topstratum suspension fines. Secondarily, the silty-clayey and fine sandy overbank sediments which could occasionally originate in remote or sheltered lakes and ponds are frequently completely reworked by considerable lateral and vertical erosion during sidewards displacement of the rivers. As a result of both primary-depositional restriction and secondary-erosional removal of floodplain fines, the channel sediments are commonly stacked upon each other to multistorey stream sand complexes. Emergence and desiccation of parts of the alluvial plain sometimes give rise to aeolian deflation and accumulation of the winnowed sand to small dunelets and wind ripple trains. The aeolian depositional environment representing a more peripheral erg facies with sheet sand interdune milieu could not be fully ascertained due to poor outcrop conditions, but is likely to occur locally in view of comparative interpretation with other mixed dune and river sand sequences in the Mid-European Buntsandstein. Variations of fluvial style are

  18. THE LOSS OF STABILITY OF LAMINAR FLOW IN OPEN CHANNEL AND THE MECHANISM OF SAND RIPPLE FORMATION

    Institute of Scientific and Technical Information of China (English)

    白玉川; 罗纪生

    2002-01-01

    In the flow on a mobile bed in an open channel, sand ripple often appears after the sediment begins to move. Different scholars have different views on the formation of sand ripples. This paper holds that as the ripple in general is very small, its formation is due to the instability of the laminar flow or the evolution of the small-scale coherent structures in the sublayer adjacent to the wall of the open channel. When the shear stresses caused by the disturbing waves or the coherent structure near the bed surface boundary and the water flow itself are greater than the shields stresses, responses on the bed surface appear and the sand ripple forms. If the frequency of the shear stress caused by the disturbance is close to the natural frequency of the sand grains that produced resonance,such a phenomenon is called the "detection property" of the sediment. It is at this point that the maximum resonance appears and the sand ripple develops rapidly.

  19. Graphene cardboard: From ripples to tunable metamaterial

    Science.gov (United States)

    Koskinen, Pekka

    2014-03-01

    Recently, graphene was introduced with tunable ripple texturing, a nanofabric enabled by graphene's remarkable elastic properties. However, one can further envision sandwiching the ripples, thus constructing composite nanomaterial, graphene cardboard. Here, the basic mechanical properties of such structures are investigated computationally. It turns out that graphene cardboard is highly tunable material, for its elastic figures of merit vary orders of magnitude, with Poisson ratio tunable from 10 to -0.5 as one example. These trends set a foundation to guide the design and usage of metamaterials made of rippled van der Waals solids.

  20. Hummocky cross-stratification-like structures and combined-flow ripples in the Punta Negra Formation (Lower-Middle Devonian, Argentine Precordillera): A turbiditic deep-water or storm-dominated prodelta inner-shelf system?

    Science.gov (United States)

    Basilici, Giorgio; de Luca, Pedro Henrique Vieira; Poiré, Daniel G.

    2012-08-01

    Turbidity-current and storm-induced deposits may exhibit similarities, in particularly when the latter is laid down by a combination of oscillatory and unidirectional flows. Recent progress in facies analysis helps to discriminate the sedimentary effects of oscillatory from unidirectional components of the flow. On the basis of detailed analysis of sedimentary facies, strata geometry, and palaeocurrent data, the present study reinterprets the Punta Negra Formation (PNF) (Lower-Middle Devonian, Argentine Precordillera), previously considered as a depositional system of deep-water, as a storm-dominated prodeltaic shelf depositional system. In the sandstone beds of the PNF, planar, low-angle and undulating laminations with weakly asymmetric hummocky and swaley bedforms, combined-flow ripples, accretionary hummocky cross-stratification-like (HCS-like), and anisotropic HCS-like suggest the action of oscillatory currents combined with unidirectional currents in forming the deposits. Different hypotheses on the origin of the oscillatory currents have been examined. The most convincing interpretation is that the oscillatory component of the velocity is attributed to storm-induced waves. The palaeocurrent data indicate offshore current directions, suggesting that the unidirectional flow was a gravity-induced bottom current. Inverse grading at the base and overlying normally graded divisions of the sandstone beds testify to waxing-waning behaviour of the depositional flows; interbedding of sedimentary structures (undulating laminations, low-angle and parallel laminations, and combined-flow ripples) in the lower and intermediate divisions of the beds indicate fluctuations of flow velocity. This organisation of the sedimentary structures permits association of the unidirectional component with hyperpycnal bottom currents. The terrestrial origin of the hyperpycnal flows is suggested by the abundance of terrestrial plant remains, the mineralogical and textural immaturity of the

  1. Rippled disc electrostatic generator/motor configurations utilizing magnetic insulation

    Energy Technology Data Exchange (ETDEWEB)

    Post, Richard F

    2017-04-04

    Electrostatic generators/motors designs are provided that generally may include a first rippled stator centered about a longitudinal axis; a second rippled stator centered about the axis, a first rippled rotor centered about the axis and located between the first rippled stator and the second rippled stator. A magnetic field having field lines about parallel with the average plane of at least one of the first rippled stator or the second rippled stator is provided with either a Halbach array configuration or a conductor array configuration.

  2. Sand ripples under sea waves. Part 4. Tile ripple formation

    NARCIS (Netherlands)

    Roos, Pieter C.; Blondeaux, P.

    2001-01-01

    We investigate the formation of small-scale three-dimensional bedforms due to interactions of an erodible bed with a sea wave that obliquely approaches the coast, being partially reflected at the beach. In this case the trajectories of fluid particles at the top of the bottom boundary layer are

  3. Hippocampal CA1 Ripples as Inhibitory Transients.

    Directory of Open Access Journals (Sweden)

    Paola Malerba

    2016-04-01

    Full Text Available Memories are stored and consolidated as a result of a dialogue between the hippocampus and cortex during sleep. Neurons active during behavior reactivate in both structures during sleep, in conjunction with characteristic brain oscillations that may form the neural substrate of memory consolidation. In the hippocampus, replay occurs within sharp wave-ripples: short bouts of high-frequency activity in area CA1 caused by excitatory activation from area CA3. In this work, we develop a computational model of ripple generation, motivated by in vivo rat data showing that ripples have a broad frequency distribution, exponential inter-arrival times and yet highly non-variable durations. Our study predicts that ripples are not persistent oscillations but result from a transient network behavior, induced by input from CA3, in which the high frequency synchronous firing of perisomatic interneurons does not depend on the time scale of synaptic inhibition. We found that noise-induced loss of synchrony among CA1 interneurons dynamically constrains individual ripple duration. Our study proposes a novel mechanism of hippocampal ripple generation consistent with a broad range of experimental data, and highlights the role of noise in regulating the duration of input-driven oscillatory spiking in an inhibitory network.

  4. Hippocampal CA1 Ripples as Inhibitory Transients.

    Science.gov (United States)

    Malerba, Paola; Krishnan, Giri P; Fellous, Jean-Marc; Bazhenov, Maxim

    2016-04-01

    Memories are stored and consolidated as a result of a dialogue between the hippocampus and cortex during sleep. Neurons active during behavior reactivate in both structures during sleep, in conjunction with characteristic brain oscillations that may form the neural substrate of memory consolidation. In the hippocampus, replay occurs within sharp wave-ripples: short bouts of high-frequency activity in area CA1 caused by excitatory activation from area CA3. In this work, we develop a computational model of ripple generation, motivated by in vivo rat data showing that ripples have a broad frequency distribution, exponential inter-arrival times and yet highly non-variable durations. Our study predicts that ripples are not persistent oscillations but result from a transient network behavior, induced by input from CA3, in which the high frequency synchronous firing of perisomatic interneurons does not depend on the time scale of synaptic inhibition. We found that noise-induced loss of synchrony among CA1 interneurons dynamically constrains individual ripple duration. Our study proposes a novel mechanism of hippocampal ripple generation consistent with a broad range of experimental data, and highlights the role of noise in regulating the duration of input-driven oscillatory spiking in an inhibitory network.

  5. WAVE BOTTOM LAYERS DYNAMIC WITH SUSPENDED SEDIMENT OVER VORTEX RIPPLES

    Institute of Scientific and Technical Information of China (English)

    JIANG Chang-bo; BAI Yu-chuan; ZHAO Zi-dan; ZHANG Hong-wu

    2004-01-01

    Vortex ripple is widely formed in the coastal region, and the dynamic of vortex is quite important because it is responsible for sediment transport. The flow structure around the vortex ripples can be modeled as 2D flow due to the geometry of the flow boundaries. In this paper, 2D Large-Ed dy-Simulation (LES) method was used to predict the flow structure and the dynamic of vortex in the bottom layers under the action of the wave, the numerical simulation results show a completely process of vortex formation, evolvement and disappearance. Based on the study of flow structure, the suspended sediment transport was modeled in present paper. The simulated sediment concentrations were compared to measurements from the literature. The agreement between the time averaged simulated concentration profiles and measurements is satisfactory. For a high setting velocity, the suspended sediment is confined to the vicinity of the bed, and it is dominated by the local bottom shear stress. For a small setting velocity,the suspension is more dominated by the characteristic of vor tex. There are two suspended sediment transport peaks observed in the cross-section at the trough and crest in the half period, the second peak is due to the separation bubble taking the sediment.

  6. Prediction of Ripple Properties in Shelf Seas. Mark 2 Predictor for Time Evolution

    Science.gov (United States)

    2005-12-01

    coefficient that governs the rate of change (small for small waves, large for large waves). Eq (4.4) applies for a step change from one steady wave...during one tide. He also reported geological evidence of current ripples in turbidite beds found in the Pyrenees Mountains (Spain), many of which showed... Government in 1947, the Company became a private entity in 1982, and has since operated as an independent, non profit distributing firm committed to

  7. Listening to Whispers of Ripple: Linking Wallets and Deanonymizing Transactions in the Ripple Network

    Directory of Open Access Journals (Sweden)

    Moreno-Sanchez Pedro

    2016-10-01

    Full Text Available The decentralized I owe you (IOU transaction network Ripple is gaining prominence as a fast, low-cost and efficient method for performing same and cross-currency payments. Ripple keeps track of IOU credit its users have granted to their business partners or friends, and settles transactions between two connected Ripple wallets by appropriately changing credit values on the connecting paths. Similar to cryptocurrencies such as Bitcoin, while the ownership of the wallets is implicitly pseudonymous in Ripple, IOU credit links and transaction flows between wallets are publicly available in an online ledger. In this paper, we present the first thorough study that analyzes this globally visible log and characterizes the privacy issues with the current Ripple network. In particular, we define two novel heuristics and perform heuristic clustering to group wallets based on observations on the Ripple network graph. We then propose reidentification mechanisms to deanonymize the operators of those clusters and show how to reconstruct the financial activities of deanonymized Ripple wallets. Our analysis motivates the need for better privacy-preserving payment mechanisms for Ripple and characterizes the privacy challenges faced by the emerging credit networks.

  8. Molecular structure of the lecithin ripple phase

    Science.gov (United States)

    de Vries, Alex H.; Yefimov, Serge; Mark, Alan E.; Marrink, Siewert J.

    2005-04-01

    Molecular dynamics simulations of lecithin lipid bilayers in water as they are cooled from the liquid crystalline phase show the spontaneous formation of rippled bilayers. The ripple consists of two domains of different length and orientation, connected by a kink. The organization of the lipids in one domain of the ripple is found to be that of a splayed gel; in the other domain the lipids are gel-like and fully interdigitated. In the concave part of the kink region between the domains the lipids are disordered. The results are consistent with the experimental information available and provide an atomic-level model that may be tested by further experiments. molecular dynamics simulation | structural model

  9. Ripples and Dunes in Directionally Varying Flows--Three Decades of Experiments, Theory, and Modeling (Invited)

    Science.gov (United States)

    Rubin, D. M.

    2013-12-01

    The morphology and dynamics of ripples and dunes have received considerable study for the past half-century, but most studies have focused on only the small subset of flows that are convenient to study in a lab: using flumes with flows that are constant in direction or wave tanks with flows that reverse by 180°. Many natural flows are free to change in direction by other angles (seasonal or daily cycles in wind direction; reversing wave-generated flows combined with alongshore currents; reversing tidal currents in curved channels; unsteady separated flows). A handful of studies have addressed a broader set of such flows using specialized lab setups (rotating beds in unidirectional flows; oscillating or pulsed beds in static or flowing water; unsteady flows that arise in channel expansions or topographic depressions). Other studies have applied theory or modeling (usually incorporating simplified relations between topography, flow, and sediment transport) to bedform morphology and orientation. The studies that have addressed this broader variety of natural flows have found that compared to the relatively sinuous barchanoid morphology of ripples and dunes in unidirectional flows, bedforms in bi-directional flows can have relatively long straight crests (wave ripples or linear dunes); and multi-directional flows have been shown to produce brick- or tile-pattern ripples under interfering waves, star dunes in deserts, and polygonal dunes within craters on Mars. The topic receiving most study in directionally varying flows is bedform orientation in bi-directional flows. A number of lab, field, theoretical, and modeling studies have found that bedforms arise with the orientation subject to maximum gross-normal transport, but some recent results suggest other orientations are possible where a bed is only partially covered in sand.

  10. Collisions, Cannibals, and the Memory of Long-lost Bed Forms: The Hyster(et)ical Story Revealed

    Science.gov (United States)

    Jerolmack, D. J.; Martin, R. L.

    2015-12-01

    Sandy river-bed morphology often lags changes in water discharge, producing hysteresis in the relation between discharge and bed-form geometry. While this effect is well known, its origins are not. In this talk we present experimental and field results that reveal these origins. We show that the primary mechanism of bed form growth in a rising flood is merger induced by collisions, which occur due to a dispersion in migration rates. At the start of a flood the bed forms are small and transport rate is high, so growth is rapid. Conversely, on the falling limb of a flood the bed forms are large while the transport rate is small. If the flood recedes rapidly enough, the large bed forms cease migrating and small, secondary bed forms emerge on their backs. These smaller features cannibalize the original, relict structures which slowly diffuse away. (We do not distinguish between ripples and dunes, the data do not indicate any reason to do so, and we therefore recuse ourselves from discussing that tiring topic.). The timescale of decay is much larger than growth, leaving a memory of peak-flood conditions that may persist until the next flood. Thus, the timescales of both growth (Tg) and decay (Td) are related to a simple bed form turnover time - the time to displace a bed form's volume by transport - however, the turnover time is different for growth vs. decay. This reveals three different regimes for the response of bed forms to a flood: (1) a slow flood with a timescale Tf > Td > Tg is quasi-steady, i.e., bed forms grow and shrink with no lag between morphology and flow; (2) an intermediate flood with Td > Tf > Tg exhibits quasi-steady growth, but decay lags the flow; and (3) a fast flood with Td > Tg > Tf produces a lag between morphology and flow over the entire hydrograph. Regimes 2 and 3 produce hysteretical behavior, with 3 being the most extreme. We discuss the implications of these results for: predicting stage-discharge relations, anticipating and understanding

  11. Extraction of sandy bedforms features through geodesic morphometry

    Science.gov (United States)

    Debese, Nathalie; Jacq, Jean-José; Garlan, Thierry

    2016-09-01

    State-of-art echosounders reveal fine-scale details of mobile sandy bedforms, which are commonly found on continental shelfs. At present, their dynamics are still far from being completely understood. These bedforms are a serious threat to navigation security, anthropic structures and activities, placing emphasis on research breakthroughs. Bedform geometries and their dynamics are closely linked; therefore, one approach is to develop semi-automatic tools aiming at extracting their structural features from bathymetric datasets. Current approaches mimic manual processes or rely on morphological simplification of bedforms. The 1D and 2D approaches cannot address the wide ranges of both types and complexities of bedforms. In contrast, this work attempts to follow a 3D global semi-automatic approach based on a bathymetric TIN. The currently extracted primitives are the salient ridge and valley lines of the sand structures, i.e., waves and mega-ripples. The main difficulty is eliminating the ripples that are found to heavily overprint any observations. To this end, an anisotropic filter that is able to discard these structures while still enhancing the wave ridges is proposed. The second part of the work addresses the semi-automatic interactive extraction and 3D augmented display of the main lines structures. The proposed protocol also allows geoscientists to interactively insert topological constraints.

  12. Measuring Social Capital Change Using Ripple Mapping

    Science.gov (United States)

    Baker, Barbara; Johannes, Elaine M.

    2013-01-01

    This article provides a detailed description of how to implement a ripple mapping activity to assess youth program effects on community capital and concludes with examples from Maine and Kansas. The maps lead to group reflection on project outcomes and further research and evaluation questions for group members. The results from five Maine…

  13. Caveolin-3 Mutations in Rippling Muscle Disease

    Directory of Open Access Journals (Sweden)

    J Gordon Millichap

    2003-05-01

    Full Text Available Two unrelated patients with novel homozygous missense mutations (L86P and A92T in caveolin-3 gene (CAV3, presenting with a severe form of rippling muscle disease (RMD, are reported from the University of Bonn, and other centers in Germany.

  14. A Simple Ripple Filter for FLUKA

    DEFF Research Database (Denmark)

    Bassler, Niels; Herrmann, Rochus

    In heavy ion radiotherapy, pristine C-12 beams are usually widened a few mm (FWHM) along the beam axis, before the actual spread out Bragg peak (SOBP) is build. The pristine beam widening is commonly performed with a ripple filter, known from the facility at GSI (Darmstadt) and at HIT (Heidelberg...

  15. Sandy PMO Disaster Relief Appropriations Act of 2013 Financial Data

    Data.gov (United States)

    Department of Homeland Security — Sandy PMO: Disaster Relief Appropriations Act of 2013 (Sandy Supplemental Bill) Financial Data. This is the Sandy Supplemental Quarterly Financial Datasets that are...

  16. Hurricane Sandy Poster (October 29, 2012)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Hurricane Sandy poster. Multi-spectral image from Suomi-NPP shows Hurricane Sandy approaching the New Jersey Coast on October 29, 2012. Poster size is approximately...

  17. Sand Ripple Dynamics on the Inner Shelf

    Science.gov (United States)

    2006-01-01

    Sand Ripple Dynamics on the Inner Shelf Donald N. Slinn Department of Civil and Coastal Engineering, University of Florida Gainesville, FL 32611...Florida,Department of Civil and Coastal Engineering,Gainesville,FL,32611-6590 8. PERFORMING ORGANIZATION REPORT NUMBER 9. SPONSORING/MONITORING AGENCY...2002. 452: p. 1-24. Acrivos, A., Shear-Induced Particle Diffusion in Concentrated Suspensions of Noncolloidal Particles. Journal of Rheology , 1995

  18. Bed Bugs

    Science.gov (United States)

    Prevent, identify, and treat bed bug infestations using EPA’s step-by-step guides, based on IPM principles. Find pesticides approved for bed bug control, check out the information clearinghouse, and dispel bed bug myths.

  19. On Sandy Shores. Teacher's Guide.

    Science.gov (United States)

    Strang, Craig; And Others

    The activities in this guide (for grades 2-4) transport students to the sandy shore, one of the most fascinating ecosystems on the planet. At this ecological juncture a multiplicity of life forms find ways to survive, thrive, and interact with each other. Using a wide variety of learning formats, students explore and deepen their understanding of…

  20. A 10 MHz ripple-based on-time controlled buck converter with dual ripple compensation

    Institute of Scientific and Technical Information of China (English)

    Lü Danzhu; Yu Jiale; Hong Zhiliang

    2013-01-01

    A 10 MHz ripple-based on-time controlled buck converter is presented.A novel low-cost dual ripple compensation,which consists of coupling capacitor compensation and passive equivalent series resistance compensation,is proposed to achieve a fast load transient response and robust stability simultaneously.Implemented in a 2P4M 0.35 μm CMOS process,the converter achieves fix-frequency output with a ripple of below 10 mV and an overshoot of 10 mV at 400 mA step load transient response.With width optimization of the power transistors in an ultra-heavy load and PFM control in a light load,the efficiency stays at over 83% for a load range from 20 mA to 1.5 A and the peak efficiency reaches 90.16%.

  1. Variability of Bed Drag on Cohesive Beds under Wave Action

    Directory of Open Access Journals (Sweden)

    Ilgar Safak

    2016-04-01

    Full Text Available Drag force at the bed acting on water flow is a major control on water circulation and sediment transport. Bed drag has been thoroughly studied in sandy waters, but less so in muddy coastal waters. The variation of bed drag on a muddy shelf is investigated here using field observations of currents, waves, and sediment concentration collected during moderate wind and wave events. To estimate bottom shear stress and the bed drag coefficient, an indirect empirical method of logarithmic fitting to current velocity profiles (log-law, a bottom boundary layer model for combined wave-current flow, and a direct method that uses turbulent fluctuations of velocity are used. The overestimation by the log-law is significantly reduced by taking turbulence suppression due to sediment-induced stratification into account. The best agreement between the model and the direct estimates is obtained by using a hydraulic roughness of 10 - 4 m in the model. Direct estimate of bed drag on the muddy bed is found to have a decreasing trend with increasing current speed, and is estimated to be around 0.0025 in conditions where wave-induced flow is relatively weak. Bed drag shows an increase (up to fourfold with increasing wave energy. These findings can be used to test the bed drag parameterizations in hydrodynamic and sediment transport models and the skills of these models in predicting flows in muddy environments.

  2. Variability of bed drag on cohesive beds under wave action

    Science.gov (United States)

    Safak, Ilgar

    2016-01-01

    Drag force at the bed acting on water flow is a major control on water circulation and sediment transport. Bed drag has been thoroughly studied in sandy waters, but less so in muddy coastal waters. The variation of bed drag on a muddy shelf is investigated here using field observations of currents, waves, and sediment concentration collected during moderate wind and wave events. To estimate bottom shear stress and the bed drag coefficient, an indirect empirical method of logarithmic fitting to current velocity profiles (log-law), a bottom boundary layer model for combined wave-current flow, and a direct method that uses turbulent fluctuations of velocity are used. The overestimation by the log-law is significantly reduced by taking turbulence suppression due to sediment-induced stratification into account. The best agreement between the model and the direct estimates is obtained by using a hydraulic roughness of 10  m in the model. Direct estimate of bed drag on the muddy bed is found to have a decreasing trend with increasing current speed, and is estimated to be around 0.0025 in conditions where wave-induced flow is relatively weak. Bed drag shows an increase (up to fourfold) with increasing wave energy. These findings can be used to test the bed drag parameterizations in hydrodynamic and sediment transport models and the skills of these models in predicting flows in muddy environments.

  3. Enhanced water droplet mobility on superhydrophobic rippled nanoshell array

    Science.gov (United States)

    Im, Hwon; Ji, Seungmuk; Moon, Dong-Il; Lim, Hyuneui; Choi, Yang-Kyu

    2016-10-01

    A 3-dimensional rippled nanoshell structure (a hollow pillar with wriggly sidewall morphology) is demonstrated for superhydrophobicity. As a control group, a straight nanoshell structure without a rippled shape was also prepared. The rippled structure showed improved superhydrophobicity with a large contact angle and a small sliding angle compared to the straight nanoshell structure. These enhancements originate from the minimum of interfacial energy at the triple-phase contact line, which is located at the most protruded circular line along the rippled structure. Using a drop impingement test, the stabilization of a Cassie Baxter state on the rippled structure was also verified. The experimental observation of wetting transition from a Cassie-Baxter to a Wenzel state is well explained by a revamped capillary pressure model, which was customized for the rippled structure.

  4. Robot Vibrations Caused by Torque Ripples in Power Transmission Mechanisms

    OpenAIRE

    小島, 宏行; 田口, 和哉; 辻, 浩明

    1989-01-01

    When an industrial robot with a power transmission mechanism such as a harmonic drive gear is operated, vibrations resulting from the torque ripple of the power transmission mechanism are frequently generated. However, few studies on robot vibration characteristics owing to torque ripples have been reported. In this paper, the vibrations of a horizontal two-link robot are investigated with consideration given to the torque ripple and the nonlinearity of the power transmission mechanism. In th...

  5. Automatic detection and visualisation of MEG ripple oscillations in epilepsy

    Directory of Open Access Journals (Sweden)

    Nicole van Klink

    2017-01-01

    Full Text Available High frequency oscillations (HFOs, 80–500 Hz in invasive EEG are a biomarker for the epileptic focus. Ripples (80–250 Hz have also been identified in non-invasive MEG, yet detection is impeded by noise, their low occurrence rates, and the workload of visual analysis. We propose a method that identifies ripples in MEG through noise reduction, beamforming and automatic detection with minimal user effort. We analysed 15 min of presurgical resting-state interictal MEG data of 25 patients with epilepsy. The MEG signal-to-noise was improved by using a cross-validation signal space separation method, and by calculating ~2400 beamformer-based virtual sensors in the grey matter. Ripples in these sensors were automatically detected by an algorithm optimized for MEG. A small subset of the identified ripples was visually checked. Ripple locations were compared with MEG spike dipole locations and the resection area if available. Running the automatic detection algorithm resulted in on average 905 ripples per patient, of which on average 148 ripples were visually reviewed. Reviewing took approximately 5 min per patient, and identified ripples in 16 out of 25 patients. In 14 patients the ripple locations showed good or moderate concordance with the MEG spikes. For six out of eight patients who had surgery, the ripple locations showed concordance with the resection area: 4/5 with good outcome and 2/3 with poor outcome. Automatic ripple detection in beamformer-based virtual sensors is a feasible non-invasive tool for the identification of ripples in MEG. Our method requires minimal user effort and is easily applicable in a clinical setting.

  6. Dynamical models for sand ripples beneath surface waves

    DEFF Research Database (Denmark)

    Andersen, Ken Haste; Chabanol, M.-L.; v. Hecke, M.

    2001-01-01

    We introduce order parameter models for describing the dynamics of sand ripple patterns under oscillatory flow. A crucial ingredient of these models is the mass transport between adjacent ripples, which we obtain from detailed numerical simulations for a range of ripple sizes. Using this mass...... transport function, our models predict the existence of a stable band of wave numbers limited by secondary instabilities. Small ripples coarsen in our models and this process leads to a sharply selected final wave number, in agreement with experimental observations....

  7. Effect of Intrinsic Ripples on Elasticity of the Graphene Monolayer.

    Science.gov (United States)

    Lee, Seungjun

    2015-12-01

    The effect of intrinsic ripples on the mechanical response of the graphene monolayer is investigated under uniaxial loading using molecular dynamics (MD) simulations with a focus on nonlinear behavior at a small strain. The calculated stress-strain response shows a nonlinear relation through the entire range without constant slopes as a result of the competition between ripple softening and bond stretching hardening. For a small strain, entropic contribution is dominant due to intrinsic ripples, leading to elasticity softening. As the ripples flatten at increasing strain, the energetic term due to C-C bonds stretching competes with the entropic contribution, followed by energetic dominant deformation. Elasticity softening is enhanced at increased temperature as the ripple amplitude increases. The study shows that the intrinsic ripple of graphene affects elasticity. This result suggests that a change of ripple amplitudes due to various environmental conditions such as temperature, and substrate interactions can lead to a change of the mechanical properties of graphene. The understanding of the rippling effect on the mechanical behavior of 2D materials is useful for strain-based ripple manipulation for their engineering applications.

  8. Passband ripple observed in MSFVW delay lines

    Science.gov (United States)

    Talisa, S. H.; Emtage, P. R.; Daniel, M. R.; Adam, J. D.

    1986-09-01

    It is suggested that the long-period (100-200 MHz) ripple noted in magnetostatic forward volume wave (MSFVW) delay lines comprising YIG samples a few millimeters wide by a few centimeters long is due to the nonuniformity in the DC demagnetizing field across the YIG sample width. The results indicate that even very small variations in the internal field near the center of the sample can cause the MSFVWs to focus at distances close to the input transducers, and that ray bending is stronger outside the central half of the sample. Experimental studies confirm the strong effects of sample width on the breadth and smoothness of the passband.

  9. Bed forms created by simulated waves and currents in a large flume

    Science.gov (United States)

    Lacy, Jessica R.; Rubin, David M.; Ikeda, Hiroshi; Mokudai, Kuniyasu; Hanes, Daniel M.

    2007-01-01

    The morphology and evolution of bed forms created by combinations of waves and currents were investigated using an oscillating plate in a 4-m-wide flume. Current speed ranged from 0 to 30 cm/s, maximum oscillatory velocity ranged from 20 to 48 cm/s, oscillation period was 8 s (except for one run with 12 s period), and the median grain size was 0.27 mm. The angle between oscillations and current was 90°, 60°, or 45°. At the end of each run the sand bed was photographed and ripple dimensions were measured. Ripple wavelength was also determined from sonar images collected throughout the runs. Increasing the ratio of current to wave (i.e., oscillatory) velocity decreased ripple height and wavelength, in part because of the increased fluid excursion during the wave period. Increasing the ratio of current to waves, or decreasing the angle between current and waves, increased the three-dimensionality of bed forms. During the runs, ripple wavelength increased by a factor of about 2. The average number of wave periods for evolution of ripple wavelength to 90% of its final value was 184 for two-dimensional ripples starting from a flat bed. Bed form orientations at the end of each run were compared to four potential controlling factors: the directions of waves, current, maximum instantaneous bed shear stress, and maximum gross bed form normal transport (MGBNT). The directions of waves and of MGBNT were equally good predictors of bed form orientations, and were significantly better than the other two factors.

  10. Wavelength selection of rippling patterns in myxobacteria

    Science.gov (United States)

    Bonilla, L. L.; Glavan, A.; Marquina, A.

    2016-01-01

    Rippling patterns of myxobacteria appear in starving colonies before they aggregate to form fruiting bodies. These periodic traveling cell density waves arise from the coordination of individual cell reversals, resulting from an internal clock regulating them and from contact signaling during bacterial collisions. Here we revisit a mathematical model of rippling in myxobacteria due to Igoshin et al. [Proc. Natl. Acad. Sci. USA 98, 14913 (2001), 10.1073/pnas.221579598 and Phys. Rev. E 70, 041911 (2004), 10.1103/PhysRevE.70.041911]. Bacteria in this model are phase oscillators with an extra internal phase through which they are coupled to a mean field of oppositely moving bacteria. Previously, patterns for this model were obtained only by numerical methods, and it was not possible to find their wave number analytically. We derive an evolution equation for the reversal point density that selects the pattern wave number in the weak signaling limit, shows the validity of the selection rule by solving numerically the model equations, and describes other stable patterns in the strong signaling limit. The nonlocal mean-field coupling tends to decohere and confine patterns. Under appropriate circumstances, it can annihilate the patterns leaving a constant density state via a nonequilibrium phase transition reminiscent of destruction of synchronization in the Kuramoto model.

  11. Large wind ripples on Mars: A record of atmospheric evolution.

    Science.gov (United States)

    Lapotre, M G A; Ewing, R C; Lamb, M P; Fischer, W W; Grotzinger, J P; Rubin, D M; Lewis, K W; Ballard, M J; Day, M; Gupta, S; Banham, S G; Bridges, N T; Des Marais, D J; Fraeman, A A; Grant, J A; Herkenhoff, K E; Ming, D W; Mischna, M A; Rice, M S; Sumner, D A; Vasavada, A R; Yingst, R A

    2016-07-01

    Wind blowing over sand on Earth produces decimeter-wavelength ripples and hundred-meter- to kilometer-wavelength dunes: bedforms of two distinct size modes. Observations from the Mars Science Laboratory Curiosity rover and the Mars Reconnaissance Orbiter reveal that Mars hosts a third stable wind-driven bedform, with meter-scale wavelengths. These bedforms are spatially uniform in size and typically have asymmetric profiles with angle-of-repose lee slopes and sinuous crest lines, making them unlike terrestrial wind ripples. Rather, these structures resemble fluid-drag ripples, which on Earth include water-worked current ripples, but on Mars instead form by wind because of the higher kinematic viscosity of the low-density atmosphere. A reevaluation of the wind-deposited strata in the Burns formation (about 3.7 billion years old or younger) identifies potential wind-drag ripple stratification formed under a thin atmosphere.

  12. Angular tuning of the magnetic birefringence in rippled cobalt films

    Energy Technology Data Exchange (ETDEWEB)

    Arranz, Miguel A., E-mail: MiguelAngel.Arranz@uclm.es [Facultad de Ciencias y Tecnologías Químicas, Universidad de Castilla-La Mancha, Avda. Camilo J. Cela 10, 13071 Ciudad Real (Spain); Colino, José M. [Instituto de Nanociencia, Nanotecnología y Materiales Moleculares, Universidad de Castilla-La Mancha, Campus de la Fábrica de Armas, 45071 Toledo (Spain)

    2015-06-22

    We report the measurement of magnetically induced birefringence in rippled Co films. For this purpose, the magneto-optical properties of ion beam eroded ferromagnetic films were studied using Kerr magnetometry and magnetic birefringence in the transmitted light intensity. Upon sufficient ion sculpting, these ripple surface nanostructures developed a defined uniaxial anisotropy in the in-plane magnetization, finely tuning the magnetic birefringence effect. We have studied its dependence on the relative orientation between the ripple direction and the magnetic field, and found this effect to be dramatically correlated with the capability to neatly distinguish the mechanisms for the in-plane magnetization reversal, i.e., rotation and nucleation. This double refraction corresponds univocally to the two magnetization axes, parallel and perpendicular to the ripples direction. We have also observed that tuned birefringence in stack assemblies of rippled Co films, which enables us to technically manipulate the number and direction of refraction axes.

  13. Large wind ripples on Mars: A record of atmospheric evolution

    Science.gov (United States)

    Lapotre, M. G. A.; Ewing, R. C.; Lamb, M. P.; Fischer, W. W.; Grotzinger, J. P.; Rubin, D. M.; Lewis, K. W.; Ballard, M. J.; Day, M.; Gupta, S.; Banham, S. G.; Bridges, N. T.; Des Marais, D. J.; Fraeman, A. A.; Grant, J. A.; Herkenhoff, K. E.; Ming, D. W.; Mischna, M. A.; Rice, M. S.; Sumner, D. A.; Vasavada, A. R.; Yingst, R. A.

    2016-07-01

    Wind blowing over sand on Earth produces decimeter-wavelength ripples and hundred-meter- to kilometer-wavelength dunes: bedforms of two distinct size modes. Observations from the Mars Science Laboratory Curiosity rover and the Mars Reconnaissance Orbiter reveal that Mars hosts a third stable wind-driven bedform, with meter-scale wavelengths. These bedforms are spatially uniform in size and typically have asymmetric profiles with angle-of-repose lee slopes and sinuous crest lines, making them unlike terrestrial wind ripples. Rather, these structures resemble fluid-drag ripples, which on Earth include water-worked current ripples, but on Mars instead form by wind because of the higher kinematic viscosity of the low-density atmosphere. A reevaluation of the wind-deposited strata in the Burns formation (about 3.7 billion years old or younger) identifies potential wind-drag ripple stratification formed under a thin atmosphere.

  14. Pyramidal cell-interneuron interactions underlie hippocampal ripple oscillations.

    Science.gov (United States)

    Stark, Eran; Roux, Lisa; Eichler, Ronny; Senzai, Yuta; Royer, Sebastien; Buzsáki, György

    2014-07-16

    High-frequency ripple oscillations, observed most prominently in the hippocampal CA1 pyramidal layer, are associated with memory consolidation. The cellular and network mechanisms underlying the generation, frequency control, and spatial coherence of the rhythm are poorly understood. Using multisite optogenetic manipulations in freely behaving rodents, we found that depolarization of a small group of nearby pyramidal cells was sufficient to induce high-frequency oscillations, whereas closed-loop silencing of pyramidal cells or activation of parvalbumin- (PV) or somatostatin-immunoreactive interneurons aborted spontaneously occurring ripples. Focal pharmacological blockade of GABAA receptors abolished ripples. Localized PV interneuron activation paced ensemble spiking, and simultaneous induction of high-frequency oscillations at multiple locations resulted in a temporally coherent pattern mediated by phase-locked interneuron spiking. These results constrain competing models of ripple generation and indicate that temporally precise local interactions between excitatory and inhibitory neurons support ripple generation in the intact hippocampus.

  15. PathShuffle: Credit Mixing and Anonymous Payments for Ripple

    Directory of Open Access Journals (Sweden)

    Moreno-Sanchez Pedro

    2017-07-01

    Full Text Available The I owe you (IOU credit network Ripple is one of the most prominent alternatives in the burgeoning field of decentralized payment systems. Ripple’s path-based transactions set it apart from cryptocurrencies such as Bitcoin. Its pseudonymous nature, while still maintaining some regulatory capabilities, has motivated several financial institutions across the world to use Ripple for processing their daily transactions. Nevertheless, with its public ledger, a credit network such as Ripple is no different from a cryptocurrency in terms of weak privacy; recent demonstrative deanonymization attacks raise important concerns regarding the privacy of the Ripple users and their transactions. However, unlike for cryptocurrencies, there is no known privacy solution compatible with the existing credit networks such as Ripple.

  16. Real-Time Simulation of Aeolian Sand Movement and Sand Ripple Evolution: A Method Based on the Physics of Blown Sand

    Institute of Scientific and Technical Information of China (English)

    Ning Wang; Bao-Gang Hu

    2012-01-01

    Simulation and visualization of aeolian sand movement and sand ripple evolution are a challenging subject.In this paper,we propose a physically based modeling and simulating method that can be used to synthesize sandy terrain in various patterns.Our method is based on the mechanical behavior of individual sand grains,which are widely studied in the physics of blown sand.We accounted significant mechanisms of sand transportation into the sand model,such as saltation,successive saltation and collapsing,while simplified the vegetation model and wind field model to make the simulation feasible and affordable.We implemented the proposed method on the programming graphics processing unit (GPU) to get real-time simulation and rendering.Finally,we proved that our method can reflect many characteristics of sand ripple evolution through several demonstrations.We also gave several synthesized desert scenes made from the simulated height field to display its significance on application.

  17. Characteristics of ripple structures revealed in OH airglow images

    Science.gov (United States)

    Li, Jing; Li, Tao; Dou, Xiankang; Fang, Xin; Cao, Bing; She, Chiao-Yao; Nakamura, Takuji; Manson, Alan; Meek, Chris; Thorsen, Denise

    2017-03-01

    Small-scale ripple structures observed in OH airglow images are most likely induced by either dynamic instability due to large wind shear or convective instability due to superadiabatic lapse rate. Using the data set taken in the mesopause region with an OH all-sky imager at Yucca Ridge Field Station, Colorado (40.7°N, 104.9°W), from September 2003 to December 2005, we study the characteristics and seasonal variations of ripple structures. By analyzing the simultaneous background wind and temperature observed by the nearby sodium temperature/wind lidar at Fort Collins, Colorado (40.6°N, 105°W), and a nearby medium-frequency radar at Platteville, Colorado (40.2°N, 105.8°W), we are able to statistically study the possible relation between ripples and the background atmosphere conditions. Characteristics and seasonal variations of ripples are presented in detail in this study. The occurrence frequency of ripples exhibits clear seasonal variability, with peak in autumn. The occurrence of ripples shows a local time dependence, which is most likely associated with the solar tides. The lifetime and spatial scale of these ripples are typically 5-20 min and 5-10 km, respectively, and most of the ripples move preferentially either southward or northward. However, more than half of the observed ripples do not advect with background flow; they have higher Richardson numbers than those ripples that advect with background flow. It is possible that they are not instability features but wave structures that are hard to be distinguished from the real instability features.

  18. Thermal ripples in model molybdenum disulfide monolayers

    Energy Technology Data Exchange (ETDEWEB)

    Remsing, Richard C.; Klein, Michael L. [Institute for Computational Molecular Science, Center for the Computational, Design of Functional Layered Materials, and Department of Chemistry, Temple University, 1925 N. 12th St., 19122, Philadelphia, PA (United States); Waghmare, Umesh V. [Theoretical Sciences Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, 560 064, Jakkur, Bangalore (India)

    2017-01-15

    Molybdenum disulfide (MoS{sub 2}) monolayers have the potential to revolutionize nanotechnology. To reach this potential, it will be necessary to understand the behavior of this two-dimensional (2D) material on large length scales and under thermal conditions. Herein, we use molecular dynamics (MD) simulations to investigate the nature of the rippling induced by thermal fluctuations in monolayers of the 2H and 1T phases of MoS{sub 2}. The 1T phase is found to be more rigid than the 2H phase. Both monolayer phases are predicted to follow long wavelength scaling behavior typical of systems with anharmonic coupling between vibrational modes as predicted by classic theories of membrane-like systems. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  19. Chirped mirrors with low dispersion ripple.

    Science.gov (United States)

    Pervak, V; Naumov, S; Krausz, F; Apolonski, A

    2007-10-17

    We demonstrate a chirped dielectric multilayer mirror (CM) with controlled reflectivity and dispersion in the wavelength range 760-840 nm. It exhibits a reflectivity of >99.9% and a mean group delay dispersion (GDD) of about -30 fs(2) with a theoretical GDD ripple of less than 0.5 fs(2) in the working spectral range. Deviations of the measured GDD from the calculated one are restricted to less than +/- 3 fs(2), limited by our measurement system. Simulations reveal that a dispersive delay line composed of 120 bounces off these mirrors introduces negligible distortion to a femtosecond pulse and largely preserves its contrast. The mirrors constitute an ideal tool for precision intracavity or extracavity dispersion control in the range of several thousand fs(2), particularly if pulses with high contrast are to be generated.

  20. Ripple reduction control of the undulation pump total artificial heart.

    Science.gov (United States)

    Saito, Itsuro; Chinzei, Tsuneo; Mochizuki, Shuichi; Abe, Yusuke; Isoyama, Takashi; Iwasaki, Kiyotaka; Suzuki, Takafumi; Karita, Tatsuro; Ono, Toshiya; Kouno, Akimasa; Ishimaru, Mitsuhiko; Baba, Atsushi; Ozeki, Toshinaga; Tohyama, Takahiro; Kobayashi Si, Shin-ichi; Imachi, Kou

    2002-01-01

    An undulation pump total artificial heart (UPTAH) in which the revolutions of the motor are converted to undulation motion of a disk has been developed. In an experiment, a goat using the UPTAH survived for 54 days. However, a large ripple was observed in the device's output pressure and flow waveform. In calculating the spectrum of the ripple, we found that the ripple mainly comprised 2 frequency sine waves: 1 having the same frequency as and 1 having double the frequency of the motor revolutions. To reduce the ripple, 2 sine waves, 1 having the same frequency as and 1 having double the frequency of the motor revolutions, were provided to the motor current to modulate the pulse width of the pulse width modulation controlling the motor revolutions. This ripple control method reduced the pressure ripple by 90% in a mock circulation and by 70% in animal experiments. These results revealed that the ripple generated in the UPTAH could be controlled through the use of motor control software.

  1. Geometric control of rippling in supported polymer nanolines.

    Science.gov (United States)

    Tirumala, Vijay R; Stafford, Christopher M; Ocola, Leonidas E; Douglas, Jack F; Mahadevan, L

    2012-03-14

    We study the swelling behavior of finlike polymer line gratings supported on a rigid substrate and show that the edge-supported polymer laminae undergo a rippling instability with a well-defined ripple wavelength λ transverse to the plane of the solid supporting substrate and a ripple amplitude that monotonically decreases from its maximum at the free-edge. These ripple patterns develop due to inhomogeneous compressive strains that arise from the geometric constraints that progressively suppress swelling near the supporting substrate where the laminae are clamped. By experimentally examining the influence of swelling strain and pattern geometry on the observed rippling instability, we find that the ripple wavelength λ scales with line width w for sufficiently long gratings, which is consistent with a simple theory. These trends were validated for polymer nanoline test patterns having w between (50 to 250) nm and a height-to-width aspect-ratio in the range 0.5 to 5. Our results suggest that line geometry, rather than material properties, governs the onset of rippling and suggest simple rules for their control.

  2. Design and Analysis of LT Codes with Decreasing Ripple Size

    DEFF Research Database (Denmark)

    Sørensen, Jesper Hemming; Popovski, Petar; Østergaard, Jan

    2012-01-01

    In this paper we propose a new design of LT codes, which decreases the amount of necessary overhead in comparison to existing designs. The design focuses on a parameter of the LT decoding process called the ripple size. This parameter was also a key element in the design proposed in the original...... work by Luby. Specifically, Luby argued that an LT code should provide a constant ripple size during decoding. In this work we show that the ripple size should decrease during decoding, in order to reduce the necessary overhead. Initially we motivate this claim by analytical results related...

  3. Analysis of Input and Output Ripples of PWM AC Choppers

    Directory of Open Access Journals (Sweden)

    Pekik Argo Dahono

    2008-11-01

    Full Text Available This paper presents an analysis of input and output ripples of PWM AC choppers. Expressions of input and output current and voltage ripples of single-phase PWM AC choppers are first derived. The derived expressions are then extended to three-phase PWM AC choppers. As input current and output voltage ripples specification alone cannot be used to determine the unique values of inductance and capacitance of the LC filters, an additional criterion based on the minimum reactive power is proposed. Experimental results are included in this paper to show the validity of the proposed analysis method.

  4. Simulations of Neutral Beam Ion Ripple Loss on EAST

    Institute of Scientific and Technical Information of China (English)

    李吉波; 丁斯晔; 吴斌; 胡纯栋

    2012-01-01

    Predictions on the ripple loss of neutral beam fast ions on EAST are investigated with a guiding center code, including both ripple and collisional effects. A 6% to 16% loss of neutral beam ions is predicted for typical EAST experiments, and a synergistic enhancement of fast ion loss is found for toroidal field (TF) ripples with collisions. The lost ions are strongly localized and will cause a maximum heat load of - 0.05 MW/m^2 on the first wall.

  5. Methods of torque ripple reduction for flux reversal motor

    Science.gov (United States)

    Vakil, Gaurang; Sheth, N. K.; Miller, David

    2009-04-01

    This paper presents two-dimensional finite element based results for various methods of torque ripple reduction in flux-reversal motors. The effects of variation in magnet and rotor pole heights, rotor pole skewing, and multiple teeth per rotor pole on the cogging torque, developed torque, torque ripple, and phase inductance and also an optimum value of the magnet and rotor pole heights, skew angle, and choice of teeth per rotor pole with the teeth depth resulting in torque ripple reduction are presented.

  6. FPGA Implementation of ADPLL with Ripple Reduction Techniques

    Directory of Open Access Journals (Sweden)

    Manoj kumar

    2012-05-01

    Full Text Available In this paper FPGA implementation of ADPLL using Verilog is presented. ADPLL with ripple reduction techniques is also simulated and implemented on FPGA. For simulation ISE Xilinx 10.1 CAD is used.Vertex5 FPGA (Field Programmable Gate Array is used for implementation. ADPLL performance improvement, while using ripple reduction techniques is also discussed. The ADPLL is designed at the central frequency of 100 kHz. The frequency range of ADPLL is 0 kHz to 199 kHz. But when it is implemented with ripple reduction techniques, the frequency range observed is from 11 kHz to 216 kHz.

  7. FPGA Implementation of ADPLL with Ripple Reduction Techniques

    Directory of Open Access Journals (Sweden)

    Manoj Kumar

    2012-04-01

    Full Text Available In this paper FPGA implementation of ADPLL using Verilog is presented. ADPLL with ripple reduction techniques is also simulated and implemented on FPGA. For simulation ISE Xilinx 10.1 CAD is used.Vertex5 FPGA (Field Programmable Gate Array is used for implementation. ADPLL performance improvement, while using ripple reduction techniques is also discussed. The ADPLL is designed at the central frequency of 100 kHz. The frequency range of ADPLL is 0 kHz to 199 kHz. But when it is implemented with ripple reduction techniques, the frequency range observed is from 11 kHz to 216 kHz.

  8. Laser Plasmas : Effect of rippled laser beam on excitation of ion acoustic wave

    Indian Academy of Sciences (India)

    Nareshpal Singh Saini; Tarsem Singh Gill

    2000-11-01

    Growth of a radially symmetrical ripple, superimposed on a Gaussian laser beam in collisional unmagnetised plasma is investigated. From numerical computation, it is observed that self-focusing of main beam as well as ripple determine the growth dynamics of ripple with the distance of propagation. The effect of growing ripple on excitation of ion acoustic wave (IAW) has also been studied

  9. Effect of a TBM on the Toroidal Magnetic Field Ripple in the ITER and Measures to Reduce the Ripple

    Energy Technology Data Exchange (ETDEWEB)

    Bae, Young Dug; Lee, Dong Won; Kim, Suk Kwon; Hong, Bong Guen

    2008-11-15

    The ITER (International Thermonuclear Experimental Reactor) tokamak has 18 toroidal magnetic field (TF) coils, and the discreteness of these TF coils causes toroidally non-axisymmetric perturbations of the magnetic field. It is called a TF ripple and could lead to losses of high-energy particles, and an unfavorable heat load on the plasma facing components. In the ITER design, a ferromagnetic insert (FI) is employed to reduce the TF ripple, and an optimization of the FI design is ongoing. Also, since test blanket modules (TBMs) will be installed in the ITER, which are made of a ferromagnetic material, they also affect the TF ripple. We assessed the effects of the thickness of the FIs on the TF ripple in order to optimize the FI. And we analyzed how the TBMs distort the TF, and calculated the TF ripple for various amounts of a ferromagnetic material and the positions of the TBMs. A simple correction coil was adopted in order to reduce the TBM induced TF ripple to the required value of 0.3 %. We proposed technically available measures to reduce the TF ripple to the required value.

  10. Membrane Potential Dynamics of CA1 Pyramidal Neurons during Hippocampal Ripples in Awake Mice.

    Science.gov (United States)

    Hulse, Brad K; Moreaux, Laurent C; Lubenov, Evgueniy V; Siapas, Athanassios G

    2016-02-17

    Ripples are high-frequency oscillations associated with population bursts in area CA1 of the hippocampus that play a prominent role in theories of memory consolidation. While spiking during ripples has been extensively studied, our understanding of the subthreshold behavior of hippocampal neurons during these events remains incomplete. Here, we combine in vivo whole-cell and multisite extracellular recordings to characterize the membrane potential dynamics of identified CA1 pyramidal neurons during ripples. We find that the subthreshold depolarization during ripples is uncorrelated with the net excitatory input to CA1, while the post-ripple hyperpolarization varies proportionately. This clarifies the circuit mechanism keeping most neurons silent during ripples. On a finer timescale, the phase delay between intracellular and extracellular ripple oscillations varies systematically with membrane potential. Such smoothly varying delays are inconsistent with models of intracellular ripple generation involving perisomatic inhibition alone. Instead, they suggest that ripple-frequency excitation leading inhibition shapes intracellular ripple oscillations.

  11. Influences of microbial activity and sediment disturbance on hyporheic exchange in sandy sediments

    Science.gov (United States)

    Mendoza-Lera, C.; Mutz, M.

    2012-04-01

    Besides the vertical hydraulic gradient, sediment permeability is the main controlling factor of water exchange across the stream bed. Reduction of permeability by microbial activity is reported from unidirectional percolated sediment columns. We investigated effects of algal and bacterial activity on hyporheic exchange (vertical water flux, VWF) under semi-natural stream conditions in 16 outdoor sand-bed flumes during 30 day. Variability of bedform was considered by 8 flumes having plane-bed and 8 flumes ripple-bed. To gain information on the relative significance of algae and heterotrophic microorganisms, half of the flumes were operated under constant dark conditions (no-light flumes), while the others were exposed to daylight. After 21 days, the upper 2 cm of the sediments was manually disturbed simulating moderate sediment dynamics which frequently occurs in natural sand-bed streams. VWF was measured by tracing loss of uranine from the water column while flumes were operating in re-circulating mode. Algae and bacterial abundance, organic matter, and CaCO3 content in sediments were determined. Sediment potential respiration (SPR) was measured in flow through respiration chambers and oxygen bubbles from primary production were sampled. As expected, initial VWF was higher in ripple-bed. After 13 days, VWF was completely inhibited in both plane and ripple-bed flumes under daylight conditions. In no-light flumes reduction of VWF was moderate. Microbial precipitation of calcium carbonate and production of oxygen bubbles in the uppermost sediments blocked the pore space. After 3 weeks, abundance and biomass of algae and SPR in the upper 2 cm of sediment were higher in daylight flumes than in no-light flumes, while bacterial abundance was higher in no-light flumes. The sediment disturbance at day 21 released the oxygen bubbles increased bed permeability and therefore restored VWF to initial rates in day-light flumes. SPR was unaffected by the sediment disturbance. In

  12. Development of an ultra low field-ripple electromagnet

    Energy Technology Data Exchange (ETDEWEB)

    Kawamura, Naritoshi, E-mail: nari.kawamura@kek.jp [Muon Science Laboratory, High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801 (Japan); Irie, Yoshiro [Muon Science Laboratory, High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801 (Japan); Accelerator Laboratory, High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801 (Japan); Fujimori, Hiroshi; Miyake, Yasuhiro [Muon Science Laboratory, High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801 (Japan)

    2014-03-21

    We developed an ultra low field-ripple magnet by adopting a mineral insulation cable (MIC) which is used under high radiation field, and of which conductor is surrounded by MgO insulation layer and copper sheath. Magnetic field due to an alternating current in conductor is canceled by the induced current in the sheath. We made a solenoid magnet by MIC, and observed this cancelation effect in alternating currents from 50 Hz to 2.4 kHz. This effect has a tendency which is inversely proportion to the AC frequency, and the field ripple is suppressed by 10{sup −2} in 50 Hz and 3×10{sup −4} in 2.4 kHz. Namely, a power supply with the current ripple of 10{sup −4} is expected to generate a magnetic field with the ripple of 10{sup −6} or lower.

  13. Exploring rippled scour depressions offshore Huntington Beach, CA

    Science.gov (United States)

    Phillips, Eleyne L.; Storlazzi, Curt D.; Dartnell, Peter; Edwards, Brian D.

    2007-01-01

    U.S. Geological Survey (USGS) scientists used 1999 multibeam data, and 2002 lidar data collected on the inner shelf off southern California to investigate a field of (<1 m) features, termed "Rippled Scour Depressions" (RSDs). RSDs are elongate, shore-normal, and bathymetrically depressed features; their morphology was determined from multibeam and lidar bathymetry. Wavelengths of ripples seen within RSDs and on the surrounding seafloor were calculated from photography and video collected in 2004 and related to sediment samples collected in the same year. The RSDs were divided into two areas: Region I RSDs contained large (∼80 cm wavelength), straight-crested ripples with coarse-grained lag, and decreased in area between 1999 and 2002; Region II RSDs were smaller, in shallower water, closer to shore, and contained shorter (∼30 cm wavelength) ripples, and increased in area from 1999–2002. The RSDs did not display marked alongshore asymmetry.

  14. Analysis of ripple formation in single crystal spot welds

    Science.gov (United States)

    Rappaz, M.; Corrigan, D.; Boatner, L. A.

    1997-01-01

    Stationary spot welds have been made at the (001) surface of Fe-l5%Ni-15%Cr single crystals using a Gas Tungsten Arc (GTA). On the top surface of the spot welds, very regular and concentric ripples were observed after solidification by differential interference color microscopy. Their height (typically 1--5 micrometers and spacing, typically approximately 60 micrometers) decreased with the radius of the pool. These ripples were successfully accounted for in terms of capillary-wave theory using the fundamental mode frequency f(sub 0) given by the first zero of the zero-order Bessel function. The spacing d between the ripples was then equated to v(sub s)/f(sub 0), where v(sub s) is the solidification rate. From the measured ripple spacing, the velocity of the pool was deduced as a function of the radius, and this velocity was in good agreement with the results of a heat-flow simulation.

  15. Dynamic Rippling, Middle-Out Reasoning and Lemma Discovery

    Science.gov (United States)

    Johansson, Moa; Dixon, Lucas; Bundy, Alan

    We present a succinct account of dynamic rippling, a technique used to guide the automation of inductive proofs. This simplifies termination proofs for rippling and hence facilitates extending the technique in ways that preserve termination. We illustrate this by extending rippling with a terminating version of middle-out reasoning for lemma speculation. This supports automatic speculation of schematic lemmas which are incrementally instantiated by unification as the rippling proof progresses. Middle-out reasoning and lemma speculation have been implemented in higher-order logic and evaluated on typical libraries of formalised mathematics. This reveals that, when applied, the technique often finds the needed lemmas to complete the proof, but it is not as frequently applicable as initially expected. In comparison, we show that theory formation methods, combined with simpler proof methods, offer an effective alternative.

  16. MD 1691: Active halo control using tune ripple at injection

    CERN Document Server

    Garcia Morales, Hector; Bruce, Roderik; Redaelli, Stefano; Fitterer, Miriam; Fiascaris, Maria; Nisbet, David; Thiesen, Hugues; Valentino, Gianluca; Xu, Chen; CERN. Geneva. ATS Department

    2017-01-01

    In this MD we performed halo excitation through tune ripple. This consists in an excitation that introduces new resonance sidebands around the existing resonance lines. In presence of sufficient detuning with amplitude, these sidebands can in principle affect only the dynamics of the halo particles at large amplitudes. Tune ripple was induced through a current modulation of the warm trim quadrupoles in IR7. This is the first time this method is experimentally tested at the LHC.

  17. Electromagnetic effects on rippling instability and tokamak edge fluctuations

    Energy Technology Data Exchange (ETDEWEB)

    Murakami, Sadayoshi; Saleem, Hamid [National Inst. for Fusion Science, Toki, Gifu (Japan)

    1998-07-01

    Electromagnetic effects on rippling mode are investigated as a cause of low frequency electromagnetic fluctuations in tokamak edge region. It is shown that, in a current-carrying resistive plasma, the purely growing electrostatic rippling mode can turn out to be an electromagnetic oscillatory instability. The resistivity fluctuation and temperature gradient are the main sources of this instability, which requires both parallel and perpendicular wave vectors. The Alfven waves in a coupled dispersion relation are found heavily damped in such dissipative plasmas. (author)

  18. Maintaining Stability During a Conducted-Ripple EMC Test

    Science.gov (United States)

    Vorperian, Vatche

    2007-01-01

    An improved technique, and electronic circuitry to implement the technique, have been developed for a military-standard electromagnetic-compatibility (EMC) test in which one analyzes susceptibility to low-frequency ripple conducted into the equipment under test via a DC power line. In the traditional technique for performing the particular test, the ripple is coupled onto the DC power line via a transformer. Depending upon some design details of the equipment under test, the inductance of the transformer can contribute a degree of instability that results in an oscillation of amplitude large enough to destroy the equipment. It is usually possible to suppress the oscillation by connecting a damping resistor to the primary terminals of the ripple-injection transformer. However, it is important to emphasize the usually in the preceding sentence: sometimes, the resistive damping becomes insufficient to suppress destructive oscillation. In addition, undesirably, the resistor contributes to power dissipation and power demand, and thereby also necessitates the use of a larger ripple voltage amplifier. Yet another disadvantage of the transformer-coupling technique is that the transformer introduces low-frequency distortion of the injected ripple voltage. The improved technique makes it possible to inject ripple with very low distortion at low frequency, without inducing oscillation. In this technique, a transformer is not used: Instead, power is fed to the equipment under test via series power field-effect transistors (FETs) controlled by a summing operational amplifier. One of the inputs to the amplifier controls the DC component of the power-line voltage; the other input, generated by an external oscillator, controls the ripple component. The circuitry for implementing this technique includes panel displays, an internal power supply for the operational amplifier and panel displays, and amplitude controls for the DC and ripple powerline voltage components.

  19. Suppressing rippling with minimized corner rounding through OPC fragmentation optimization

    Science.gov (United States)

    Wang, Jingyu; Wei, Alexander; Wilkinson, William; Chen, Norman

    2016-10-01

    As technology shrinks, the requirements placed on the post-OPC solution become so exacting that even small residual optical effects are significant. Simultaneously minimizing rippling and corner rounding cannot be accom- plished in parallel in wafer patterning especially when complex asymmetric pixelated sources are used. While either effect can be moderated by accurate application of optical proximity correction, they are both charac- teristic of unfiltered diffraction due to asymmetric illumination or design geometry and will remain inherent. Corrections that over emphasize reduced corner-rounding necessarily sacrifice edge convergence, resulting in a standing wave or unacceptable rippling along an entire edge. OPC can be used to reduce the magnitude of this rippling, but fragment placing is extremely critical. In this paper, we discuss optimized OPC fragmentation that offers balanced consideration to suppressing rippling and minimizing corner rounding. Specifically, we correlate design shapes with simulated post-OPC contours to account for design geometry-dependent rippling signature given existing illumination conditions. In contrast to adaptive fragmentation that relies on multiple iterations of simulation of intensity extrema redistribution, our method predicts the optimum contour as allowed by process and fragments the mask accordingly. The maximum imaging curvature resolvable by process coupled with the rippling signature, gives rise to the exact locations of the inflection points of the wafer contour. From there we achieve the best correction results by segmenting edges at the inflection points.

  20. Controlled ripple texturing of suspended graphene and ultrathin graphite membranes.

    Science.gov (United States)

    Bao, Wenzhong; Miao, Feng; Chen, Zhen; Zhang, Hang; Jang, Wanyoung; Dames, Chris; Lau, Chun Ning

    2009-09-01

    Graphene is nature's thinnest elastic material and displays exceptional mechanical and electronic properties. Ripples are an intrinsic feature of graphene sheets and are expected to strongly influence electronic properties by inducing effective magnetic fields and changing local potentials. The ability to control ripple structure in graphene could allow device design based on local strain and selective bandgap engineering. Here, we report the first direct observation and controlled creation of one- and two-dimensional periodic ripples in suspended graphene sheets, using both spontaneously and thermally generated strains. We are able to control ripple orientation, wavelength and amplitude by controlling boundary conditions and making use of graphene's negative thermal expansion coefficient (TEC), which we measure to be much larger than that of graphite. These results elucidate the ripple formation process, which can be understood in terms of classical thin-film elasticity theory. This should lead to an improved understanding of suspended graphene devices, a controlled engineering of thermal stress in large-scale graphene electronics, and a systematic investigation of the effect of ripples on the electronic properties of graphene.

  1. IMPLEMENTASI SANDI HILL UNTUK PENYANDIAN CITRA

    Directory of Open Access Journals (Sweden)

    JJ Siang

    2002-01-01

    Full Text Available Hill's code is one of text encoding technique. In this research, Hill's code is extended to image encoding. The image used is BMP 24 bit format. 2x2 and 3x3 matrices is used as a key. The results show that Hill's code is suitable for image whose RGB values vary highly. On the contrary, it is not suitable for less varied RGB images since its original pattern is still persisted in encrypted image. Hill's code for image encoding has also disadvantage in the case that the key matrix is not unique. However, for daily application, with good key matrix, Hill's code can be applied to encode image since it's process only deals with simple matrix operation so it become fast. Abstract in Bahasa Indonesia : Sandi Hill merupakan salah satu teknik penyandian teks. Dalam penelitian ini, pemakaian sandi Hill diperluas dari teks ke citra bertipe BMP 24 bit. Matriks yang dipakai berordo 2x2 dan 3x3. Hasil percobaan menunjukkan bahwa sandi Hill cocok untuk enkripsi citra dengan variasi nilai RGB antar piksel berdekatan yang tinggi (seperti foto, tapi tidak cocok untuk citra dengan variasi nilai RGB yang rendah (seperti gambar kartun karena pola citra asli masih tampak dalam citra sandi. Sandi Hill juga memiliki kelemahan dalam hal tidak tunggalnya matriks kunci yang dapat dipakai. Akan tetapi untuk pemakaian biasa, dengan pemilihan matriks kunci yang baik, sandi Hill dapat dipakai untuk penyandian karena hanya melibatkan operasi matriks biasa sehingga prosesnya relatif cepat. Kata kunci: Sandi Hill, Citra, Relatif Prima.

  2. Morphodynamics of a granular bed in a water-filled cylinder subjected to perturbed oscillations

    Science.gov (United States)

    Duran-Matute, Matias; van Gorp, Thijs; van Heijst, Gertjan

    2015-11-01

    We study experimentally the morphodynamics of a granular bed at the bottom of an oscillating water-filled cylinder. The granules are translucent PMMA particles with a typical size of 2mm. The bed thickness is measured in real time using a light attenuation technique. As shown already by previous work, the bed remains flat close to the center of the cylinder, and radial ripples form at outer radii. The size of the inner flat region and the number or ripples depend on the frequency and amplitude of the cylinder's oscillation. In the present work, we are interested in the dynamics and control of the bed forms when the primary sinusoidal signal of the oscillation is perturbed by adding a second sinusoidal signal with a relatively small amplitude, a different frequency, and a phase lag. Varying the parameters of the secondary signal results in a signal that can be asymmetric or modulated, for example. These properties translate into the bed producing simple behavior like the propagation of the ripples at a constant speed or more complex behavior like the time dependent coarsening and thinning of the ripples. This research is funded by NWO (the Netherlands) through the VENI grant 863.13.022.

  3. EAARL Coastal Topography-Sandy Hook 2007

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — A first surface/bare earth elevation map (also known as a Digital Elevation Model, or DEM) of the Gateway National Recreation Area's Sandy Hook Unit in New Jersey...

  4. Heterotrophic bacterial populations in tropical sandy beaches

    Digital Repository Service at National Institute of Oceanography (India)

    Nair, S.; LokaBharathi, P.A.

    Distribution pattern of heterotrophic bacterial flora of three sandy beaches of the west coast of India was studied. The population in these beaches was microbiologically different. Population peaks of halotolerant and limnotolerant forms were...

  5. Modelling TF ripple loss of alpha particles in TFTR DT experiments

    Energy Technology Data Exchange (ETDEWEB)

    Redi, M.H.; Budny, R.V.; Darrow, D.S. [and others

    1995-07-01

    Modelling of TF ripple loss of alphas in DT experiments on TFTR now includes neoclassical calculations of first orbit loss, stochastic ripple diffusion, ripple trapping and collisional effects. A rapid way to simulate experiment has been developed which uses a simple stochastic domain model for TF ripple loss within the TRANSP analysis code, with the ripple diffusion threshold evaluated by comparison with more accurate but computationally expensive Hamiltonian coordinate guiding center code simulations. Typical TF collisional ripple loss predictions are 6-10% loss of alphas for TFTR D-T experiments at I{sub p} = 1.0-2.0 MA and R = 2.52 m.

  6. VHTR Construction Ripple Effect using Inter-Industry Analysis

    Energy Technology Data Exchange (ETDEWEB)

    Lee, T. H.; Lee, K. Y.; Shin, Y. J. [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2015-10-15

    As a part of a VHTR economic analysis, we have studied the VHTR construction cost and operation and maintenance cost. However, it is somewhat difficult to expect the exact cost due to insufficient reference data and experience. As a result, we propose quantitative analysis techniques for ripple effects such as the production inducement effect, added value inducement effect, and employment inducement effect for VHTR 600MWt x 4 module construction and operation ripple effect based on NOAK. This paper presents a new method for the ripple effect and preliminary ripple effect consequence. We proposed a ripple effect analysis method using a time series and inter-industry table. As a result, we can predict that a 600MWth x 4 module VHTR reactor construction will bring about a 43771 employment effect, 24160 billion KRW production effect, and 4472 billion added value effect for 22 years. It is necessary to use the sub-account values of an inter-industry table to obtain a more precise effect result. However, the methodology can be applied with minor modification to another reactor type.

  7. Thermal dynamics of silver clusters grown on rippled silica surfaces

    Science.gov (United States)

    Bhatnagar, Mukul; Ranjan, Mukesh; Jolley, Kenny; Lloyd, Adam; Smith, Roger; Mukherjee, Subroto

    2017-02-01

    Silver nanoparticles have been deposited on silicon rippled patterned templates at an angle of incidence of 70° to the surface normal. The templates are produced by oblique incidence argon ion bombardment and as the fluence increases, the periods and heights of the structures increase. Structures with periods of 20 nm, 35 nm and 45 nm have been produced. Moderate temperature vacuum annealing shows the phenomenon of cluster coalescence following the contour of the more exposed faces of the ripple for the case of 35 nm and 45 nm but not at 20 nm where the silver aggregates into larger randomly distributed clusters. In order to understand this effect, the morphological changes of silver nanoparticles deposited on an asymmetric rippled silica surface are investigated through the use of molecular dynamics simulations for different deposition angles of incidence between 0° and 70° and annealing temperatures between 500 K and 900 K. Near to normal incidence, clusters are observed to migrate over the entire surface but for deposition at 70°, a similar patterning is observed as in the experiment. The random distribution of clusters for the periodicity ≈ of 20 nm is linked to the geometry of the silica surface which has a lower ripple height than the longer wavelength structures. Calculations carried out on a surface with such a lower ripple height also demonstrate a similar effect.

  8. Nonlinear dynamical characteristics of bed load motion

    Institute of Scientific and Technical Information of China (English)

    BAI; Yuchuan; XU; Haijue; XU; Dong

    2006-01-01

    Bed forms of various kinds that evolve naturally on the bottom of sandy coasts and rivers are a result of the kinematics of bed load transport. Based on the group motion of particles in the bed load within the bottom layer, a study on the nonlinear dynamics of bed load transport is presented in this paper. It is found that some development stages, such as the initiation, the equilibrium sediment transport, and the transition from a smooth bed to sand dunes, can be accounted for by different states in the nonlinear system of the bed load transport. It is verified by comparison with experimental data reported by Laboratoire Nationae D'Hydraulique, Chatou, France, that the evolution from a smooth bed to sand dunes is determined by mutation in the bed load transport. This paper presents results that may offer theoretical explanations to the experimental observations. It is also an attempt to apply the state-of-the-art nonlinear science to the classical sediment transport mechanics.

  9. Channeling motion of gold nanospheres on a rippled glassed surface

    Science.gov (United States)

    Gnecco, Enrico; Nita, Pawel; Casado, Santiago; Pimentel, Carlos; Mougin, Karine; Caterina Giordano, Maria; Repetto, Diego; Buatier de Mongeot, Francesco

    2014-12-01

    Gold nanospheres have been manipulated by atomic force microscopy on a rippled glass surface produced by ion beam sputtering and coated with an ultrathin (10 nm thick) graphitic layer. This substrate is characterized by irregular wavy grooves running parallel to a preferential direction. Measurements in ambient conditions show that the motion of the nanoparticles is confined to single grooves (‘channels’), along which the particles move till they are trapped by local bottlenecks. At this point, the particles cross the ripple pattern in a series of consecutive jumps and continue their longitudinal motion along a different channel. Moreover, due to the asymmetric shape of the ripple profiles, the jumps occur in the direction of minimum slope, resembling a ratchet mechanism. Our results are discussed, extending a collisional model, which was recently developed for the manipulation of nanospheres on flat surfaces, to the specific geometry of this problem.

  10. A Wave Modulation Model of Ripples over Long Surface Waves

    Institute of Scientific and Technical Information of China (English)

    CONG Peixiu; ZHENG Guizhen

    2011-01-01

    A study is presented on the modulation of ripples induced by a long surface wave (LW) and a new theoretical modulation model is proposed. In this model, the wind surface stress modulation is related to the modulation of tipple spectrum. The model results show that in the case of LW propagating in the wind direction with the wave age parameter of LW increasing, the area with enhanced shear stress shifts from the region near the LW crest on the upwind slope to the LW trough. With a smaller wave age parameter of LW, the tipple modulation has the maximum on the upwind slope in the vicinity of LW crest, while with a larger parameter the enhancement of ripple spectrum does not occur in that region. At low winds the amplitude of ripple modulation transfer function (MTF) is larger in the gravity wave range, while at moderate or high winds it changes little in the range from short gravity waves to capillary waves.

  11. Nonlinear vibration and rippling instability for embedded carbon nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Soltani, Payam; Mehdipour, I. [Islamic Azad University, Semnan (Iran, Islamic Republic of); Farshidianfar, A. [Ferdowsi University of Mashhad, Mashhad (Iran, Islamic Republic of); Ganji, D. D. [Babol University of Technology, Babol (Iran, Islamic Republic of)

    2012-04-15

    Based on the rippling deformations, a nonlinear continuum elastic model is developed to analyze the transverse vibration of single walled carbon nanotubes (SWCNTs) embedded on a Winkler elastic foundation. The nonlinear natural frequency has been derived analytically for typical boundary conditions using the perturbation method of multi-scales. The results indicate that the nonlinear resonant frequency due to the rippling is related to the stiffness of the foundation, the boundary conditions, the excitation load-to-damping ratio, and the diameter-to-length ratio. Moreover, the rippling instability of carbon nanotubes, as a structural instability, is introduced and the influences of several effective parameters on this kind of instability are widely discussed.

  12. Output Current Ripple Reduction Algorithms for Home Energy Storage Systems

    Directory of Open Access Journals (Sweden)

    Jin-Hyuk Park

    2013-10-01

    Full Text Available This paper proposes an output current ripple reduction algorithm using a proportional-integral (PI controller for an energy storage system (ESS. In single-phase systems, the DC/AC inverter has a second-order harmonic at twice the grid frequency of a DC-link voltage caused by pulsation of the DC-link voltage. The output current of a DC/DC converter has a ripple component because of the ripple of the DC-link voltage. The second-order harmonic adversely affects the battery lifetime. The proposed algorithm has an advantage of reducing the second-order harmonic of the output current in the variable frequency system. The proposed algorithm is verified from the PSIM simulation and experiment with the 3 kW ESS model.

  13. Mechanisms of sharp wave initiation and ripple generation.

    Science.gov (United States)

    Schlingloff, Dániel; Káli, Szabolcs; Freund, Tamás F; Hájos, Norbert; Gulyás, Attila I

    2014-08-20

    Replay of neuronal activity during hippocampal sharp wave-ripples (SWRs) is essential in memory formation. To understand the mechanisms underlying the initiation of irregularly occurring SWRs and the generation of periodic ripples, we selectively manipulated different components of the CA3 network in mouse hippocampal slices. We recorded EPSCs and IPSCs to examine the buildup of neuronal activity preceding SWRs and analyzed the distribution of time intervals between subsequent SWR events. Our results suggest that SWRs are initiated through a combined refractory and stochastic mechanism. SWRs initiate when firing in a set of spontaneously active pyramidal cells triggers a gradual, exponential buildup of activity in the recurrent CA3 network. We showed that this tonic excitatory envelope drives reciprocally connected parvalbumin-positive basket cells, which start ripple-frequency spiking that is phase-locked through reciprocal inhibition. The synchronized GABA(A) receptor-mediated currents give rise to a major component of the ripple-frequency oscillation in the local field potential and organize the phase-locked spiking of pyramidal cells. Optogenetic stimulation of parvalbumin-positive cells evoked full SWRs and EPSC sequences in pyramidal cells. Even with excitation blocked, tonic driving of parvalbumin-positive cells evoked ripple oscillations. Conversely, optogenetic silencing of parvalbumin-positive cells interrupted the SWRs or inhibited their occurrence. Local drug applications and modeling experiments confirmed that the activity of parvalbumin-positive perisomatic inhibitory neurons is both necessary and sufficient for ripple-frequency current and rhythm generation. These interneurons are thus essential in organizing pyramidal cell activity not only during gamma oscillation, but, in a different configuration, during SWRs.

  14. Comparative study between the measured ripple in a x-ray equipment and calculated ripple; Estudo comparativo entre o ripple medido em um equipamento de raios X e o ripple calculado

    Energy Technology Data Exchange (ETDEWEB)

    Tiecher, Maria Ester S.; Pereira, Leslie; Dias, Simone K. [Instituto de Radioprotecao e Dosimetria (IRD), Rio de Janeiro, RJ (Brazil)]. E-mail: mester@ird.gov.br; leslie@ird.gov.br; simone@ird.gov.br

    2005-07-01

    This work was developed to evaluate the percentage of difference between the measured and calculated ripple in order to show up the necessity of calibration of kVp measuring instruments. To reduce this difference is very important since this can lead to a bad image quality and a high dose. The objective of the work is to demonstrate the necessity of calibration of non-invasive kV measuring instruments since the image quality is directly related to the dose and to the voltage potential applied to the x ray tube. X ray equipment can have the following systems for producing high voltage: tri-phase, constant potential (high frequency) and single-phase. In all of those systems there is a factor called ripple, which is the difference between the highest and lowest value of the kV during the exposure time. This factor is very important mainly for calibration purposes. A comparison between the ripple measured with an invasive meter and the calculated one. The data for calculating the ripple were obtained with a non-invasive instrument. The tests were done in a high frequency x-ray system model Pulsar Plus manufactured by VMI. For the data acquisition a program developed using the LabView software was applied. Lately the data were processed using an Excel spreadsheet. The equipment applied in this work were a Dynalyser III from Radcal Corporation and a 4000M+ from Victoreen. Some National standards like the 453 Health Minister regulation [1] and international recommendations like IEC 61627 [2] define the checking tests for kVp [3]. The same recommendation indicates a ripple percentage lower than 10% for a tri-phase or high frequency x ray machines. If the instrument present a value higher it need to be repaired and cannot be applied for calibration purposes. Meanwhile the ripples measured in this work were higher than this value. (au0010th.

  15. Large variations in the onset of rippling in concentric nanotubes

    Science.gov (United States)

    Jackman, H.; Krakhmalev, P.; Svensson, K.

    2014-01-01

    We present a detailed experimental study of the onset of rippling in highly crystalline carbon nanotubes. Modeling has shown that there should be a material constant, called the critical length, describing the dependence of the critical strain on the nanotube outer radius. Surprisingly, we have found very large variations, by a factor of three, in the critical length. We attribute this to a supporting effect from the inner walls in multiwalled concentric nanotubes. We provide an analytical expression for the maximum deflection prior to rippling, which is an important design consideration in nanoelectromechanical systems utilizing nanotubes.

  16. Buck supplies output voltage ripple reduction using fuzzy control

    Directory of Open Access Journals (Sweden)

    Nicu BIZON

    2007-12-01

    Full Text Available Using the PWM control for switching power supplies the peaks EMI noise appear at the switching frequency and its harmonics. Using randomize or chaotic PWM control techniques in these systems the power spectrum is spread out in all frequencies band spectral emissions, but with a bigger ripple in the output voltage. The proposed nonlinear feedback control method, which induces chaos, is based by fuzzy rules that minimize the output voltage ripple. The feasibility and effectiveness of this relative simple method is shown by simulation. A comparison with the previous control method is included, too.

  17. PWM Switching Strategy for Torque Ripple Minimization in BLDC Motor

    Science.gov (United States)

    Salah, Wael A.; Ishak, Dahaman; Hammadi, Khaleel J.

    2011-05-01

    This paper describes a new PWM switching strategy to minimize the torque ripples in BLDC motor which is based on sensored rotor position control. The scheme has been implemented using a PIC microcontroller to generate a modified Pulse Width Modulation (PWM) signals for driving power inverter bridge. The modified PWM signals are successfully applied to the next up-coming phase current such that its current rise is slightly delayed during the commutation instant. Experimental results show that the current waveforms of the modified PWM are smoother than that in conventional PWM technique. Hence, the output torque exhibits lower ripple contents.

  18. Laser absorption and electron propagation in rippled plasma targets

    Science.gov (United States)

    Shukla, Chandrasekhar; Das, Amita; Patel, Kartik

    2016-10-01

    Efficient absorption of laser energy and the collimated propagation of relativistic electron beams (generated by the laser target interaction) in plasma are two issues which are of significant importance for applications such as fast ignition scheme of inertial confinement fusion (ICF). It is shown with the help of 2-D Particle- In- Cell simulations that introducing density ripples transverse to the laser propagation direction enhances the efficiency of laser power absorption. Furthermore, the density ripples are also instrumental in suppressing the Weibel instability of the propagating electron beam (which is responsible for the divergence of the beam). A physical understanding of the two effects is also provided.

  19. Modelling ac ripple currents in HTS coated conductors

    Science.gov (United States)

    Xu, Zhihan; Grilli, Francesco

    2015-10-01

    Dc transmission using high temperature superconducting (HTS) coated conductors (CCs) offers a promising solution to the globally growing demand for effective, reliable and economic transmission of green energy up to the gigawatt level over very long distances. The credible estimation of the losses and thereby the heat dissipation involved, where ac ripples (introduced in rectification/ac-dc conversion) are viewed as a potential source of notable contribution, is highly essential for the rational design of practical HTS dc transmission cables and corresponding cryogenic systems to fulfil this demand. Here we report a targeted modelling study into the ac losses in a HTS CC subject to dc and ac ripple currents simultaneously, by solving Maxwell’s equations using the finite element method (FEM) in the commercial software package COMSOL. It is observed that the instantaneous loss exhibits only one peak per cycle in the HTS CC subject to sinusoidal ripples, given that the amplitude of the ac ripples is smaller than approximately 20% of that of the dc current. This is a distinct contrast to the usual observation of two peaks per cycle in a HTS CC subject to ac currents only. The unique mechanism is also revealed, which is directly associated with the finding that, around any local minima of the applied ac ripples, the critical state of -J c is never reached at the edges of the HTS CC, as it should be according to the Bean model. When running further into the longer term, it is discovered that the ac ripple loss of the HTS CC in full-wave rectification decays monotonically, at a speed which is found to be insensitive to the frequency of the applied ripples within our targeted situations, to a relatively low level of approximately 1.38 × 10-4 W m-1 in around 1.7 s. Comparison between this level and other typical loss contributions in a HTS dc cable implies that ac ripple currents in HTS CCs should only be considered as a minor source of dissipation in superconducting dc

  20. Variable wind ripple migration at Great Sand Dunes National Park and Preserve, observed by timelapse imaging

    Science.gov (United States)

    Lorenz, Ralph D.; Valdez, Andrew

    2011-10-01

    Granule ripples at Great Sand Dunes National Park and Preserve (GSDNPP) were observed using inexpensive digital timelapse cameras over a 70-day period in winter 2010-2011. The ripples migrated during a handful of discrete events — visible ripple movement occurred on only 11 days during the observation period. The movement conditions are documented with hourly and 15-minute records from two nearby weather stations, and by a cup anemometer at the site itself. During the most prominent movement episode, when local winds averaged ~ 10 m/s, ripples of several sizes were observed simultaneously and a reciprocal relationship of ripple size and propagation speed was seen, with small (~ 10 cm) ripples moving at ~ 1.4 cm/min, and larger (~ 80 cm) ripples at ~ 0.15 cm/min. Ripple sizes and morphologies evolve throughout the observation period.

  1. Penetration grouting reinforcement of sandy gravel

    Institute of Scientific and Technical Information of China (English)

    YANG Ping; PENG Zhen-bin; TANG Yi-qun; PENG Wen-xiang; HE Zhong-ming

    2008-01-01

    To study the relationship between grouting effect and grouting factors, three factors (seven parameters) directionless pressure and small cycle grouting model experiment on sandy gravel was done, which was designed according to uniform design method. And regressing was applied to analysis of the test data. The two models test results indicate that when the diffusing radius of grout changes from 26 to 51 era, the grouted sandy gravel compressing strength changes fTom 2.13 to 12.30 MPa; the relationship between diffusing radius(R) and water cement ratio(m), permeability coefficient(k), grouting pressure(p), grouting time(t) is R=19.953m0.121k0.429p0.412t0.437, the relationship between compressing strength(P) and porosity(n), water cement ratio, grouting pressure, grouting time is P=0.984n0.517m-1.488p0.118t0.031.So the porosity of sandy gravel, the permeability coefficient of sandy gravel, grouting pressure, grouting time, water cement ratio are main factors to influence the grouting effect. The grouting pressure is the main factor to influence grouting diffusing radius, and the water cement ratio is the main factor to influence grouted sandy gravel compressing strength.

  2. Microscopy study of ripples created on steel surface by use of ultra short laser pulses

    NARCIS (Netherlands)

    Vincenc Obona, J.; Ocelik, V.; Visser, B.; Visser, B.; de Hosson, J.Th.M.; Skolski, J.Z.P.; Mitko, S.; Mitko, V.S.; Römer, Gerardus Richardus, Bernardus, Engelina; Huis in 't Veld, Bert

    2010-01-01

    This paper concentrates on ripples on the surface of steel that arise from lasermaterial interaction. In particular we have observed two different sets of ripples on steel samples that were machined by 210 fs laser pulses with 800 nm wavelength at normal incidence. Small ripples were found with

  3. [Simulation alfalfa growth in Wulanbuhe sandy region].

    Science.gov (United States)

    Bai, Wenming; Bao, Xuemei

    2002-12-01

    Based on the theories of accumulated temperature and on the physio-ecological characteristics of Medicago sativa, a simulation model for its growth under soil water stress in arid sandy region was developed. The model was mainly composed of four modules: the stage module of growth, the dynamic module of leaf area index, the accumulated module of dry matter, and the distributive module of dry matter. After simulating and calculating, the model could be used to predict the growing progress and dynamic changes of leaf area and yield for herbage in sandy region. The result shows that the application of the model to production is usually effective.

  4. Ripple design of LT codes for AWGN channel

    DEFF Research Database (Denmark)

    Sørensen, Jesper Hemming; Koike-Akino, Toshiaki; Orlik, Philip;

    2012-01-01

    In this paper, we present an analytical framework for designing LT codes in additive white Gaussian noise (AWGN) channels. We show that some of analytical results from binary erasure channels (BEC) also hold in AWGN channels with slight modifications. This enables us to apply a ripple-based design...

  5. Ripple Design of LT Codes for BIAWGN Channels

    DEFF Research Database (Denmark)

    Sørensen, Jesper Hemming; Koike-Akino, Toshiaki; Orlik, Philip;

    2014-01-01

    This paper presents a novel framework, which enables a design of rateless codes for binary input additive white Gaussian noise (BIAWGN) channels, using the ripple-based approach known from the works for the binary erasure channel (BEC). We reveal that several aspects of the analytical results from...

  6. Epidemic Modelling by Ripple-Spreading Network and Genetic Algorithm

    Directory of Open Access Journals (Sweden)

    Jian-Qin Liao

    2013-01-01

    Full Text Available Mathematical analysis and modelling is central to infectious disease epidemiology. This paper, inspired by the natural ripple-spreading phenomenon, proposes a novel ripple-spreading network model for the study of infectious disease transmission. The new epidemic model naturally has good potential for capturing many spatial and temporal features observed in the outbreak of plagues. In particular, using a stochastic ripple-spreading process simulates the effect of random contacts and movements of individuals on the probability of infection well, which is usually a challenging issue in epidemic modeling. Some ripple-spreading related parameters such as threshold and amplifying factor of nodes are ideal to describe the importance of individuals’ physical fitness and immunity. The new model is rich in parameters to incorporate many real factors such as public health service and policies, and it is highly flexible to modifications. A genetic algorithm is used to tune the parameters of the model by referring to historic data of an epidemic. The well-tuned model can then be used for analyzing and forecasting purposes. The effectiveness of the proposed method is illustrated by simulation results.

  7. Uncovering Transdisciplinary Team Project Outcomes through Ripple Effect Mapping

    Science.gov (United States)

    Daniels, Catherine H.; Chalker-Scott, Linda; Martini, Nicole

    2016-01-01

    The Garden Team at Washington State University is a transdisciplinary, geographically dispersed group of faculty and staff. As with many such teams, member retention requires effort, as busy individuals may not see the overall benefits of active team membership. Ripple effect mapping is a strategy that can illustrate the tangible and often…

  8. Thermomechanics of monolayer graphene: Rippling, thermal expansion and elasticity

    Science.gov (United States)

    Gao, Wei; Huang, Rui

    2014-05-01

    Thermomechanical properties of monolayer graphene with thermal fluctuation are studied by both statistical mechanics analysis and molecular dynamics (MD) simulations. While the statistical mechanics analysis in the present study is limited by a harmonic approximation, significant anharmonic effects are revealed by MD simulations. The amplitude of out-of-plane thermal fluctuation is calculated for graphene membranes under both zero stress and zero strain conditions. It is found that the fluctuation amplitude follows a power-law scaling with respect to the linear dimension of the membrane, but the roughness exponents are different for the two conditions due to anharmonic interactions between bending and stretching modes. Such thermal fluctuation or rippling is found to be responsible for the effectively negative in-plane thermal expansion of graphene at relatively low temperatures, while a transition to positive thermal expansion is predicted as the anharmonic interactions suppress the rippling effect at high temperatures. Subject to equi-biaxial tension, the amplitude of thermal rippling decreases nonlinearly, and the in-plane stress-strain relation of graphene becomes nonlinear even at infinitesimal strain, in contrast with classical theory of linear elasticity. It is found that the tangent biaxial modulus of graphene depends on strain non-monotonically, decreases with increasing temperature, and depends on membrane size. Both statistical mechanics and MD simulations suggest considerable entropic contribution to the thermomechanical properties of graphene, and as a result thermal rippling is intricately coupled with thermal expansion and thermoelasticity for monolayer graphene membranes.

  9. Ripple Effect Mapping: A "Radiant" Way to Capture Program Impacts

    Science.gov (United States)

    Kollock, Debra Hansen; Flage, Lynette; Chazdon, Scott; Paine, Nathan; Higgins, Lorie

    2012-01-01

    Learn more about a promising follow-up, participatory group process designed to document the results of Extension educational efforts within complex, real-life settings. The method, known as Ripple Effect Mapping, uses elements of Appreciative Inquiry, mind mapping, and qualitative data analysis to engage program participants and other community…

  10. Nonlinear Mechanism of Bed Load Transport

    Institute of Scientific and Technical Information of China (English)

    XU Haijue; BAI Yuchuan; NG Chiu-On

    2009-01-01

    From the group movement of the bed load within the bottom layer, details of the nonlinear dynamic characteristics of bed load movement are discussed in this paper. Whether the sediment is initiated into motion cor-responds to whether the constant term in the equation is equal to zero. If constant term is zero and no dispersive force is considered, the equation represents the traditional Shields initiation curve, and if constant term is zero with-out the dispersive force being considered, then a new Shields curve which is much lower than the traditional one is got, The fixed point of the equation corresponds to the equilibrium sediment transport of bed load. In the mutation analysis, we have found that the inflection point is the demarcation point of breaking. In theory, the breaking point corresponds to the dividing boundary line, across which the bed form changes from flat bed to sand ripple or sand dune. Compared with the experimental data of Chatou Hydraulic Lab in France, the conclusions are verified.

  11. Ripple due to asymmetry in symmetrical Cockcroft-Walton cascade rectifier circuit

    Science.gov (United States)

    Zhang, Haibo; Takaoka, Akio

    1994-12-01

    We experimentally examine the ripple and its spectra in the dc output of a symmetrical Cockcroft-Walton (CW) cascade rectifier circuit. Results show that the ripple due to the load consists of even harmonics and the ripple due to the circuit asymmetry consists of odd harmonics. In the latter, the ripple caused by the asymmetry of circuit elements cannot be compensated for completely through the asymmetry of the input voltage because of nonlinearity of a CW circuit. Approximately, the residual ripple is inversely proportional to the load resistance.

  12. Prediction of the bed-load transport by gas-liquid stratified flows in horizontal ducts

    CERN Document Server

    Franklin, Erick de Moraes

    2016-01-01

    Solid particles can be transported as a mobile granular bed, known as bed-load, by pressure-driven flows. A common case in industry is the presence of bed-load in stratified gas-liquid flows in horizontal ducts. In this case, an initially flat granular bed may be unstable, generating ripples and dunes. This three-phase flow, although complex, can be modeled under some simplifying assumptions. This paper presents a model for the estimation of some bed-load characteristics. Based on parameters easily measurable in industry, the model can predict the local bed-load flow rates and the celerity and the wavelength of instabilities appearing on the granular bed.

  13. Interstitial meiofauna of Namib sandy beaches

    African Journals Online (AJOL)

    1988-03-16

    Mar 16, 1988 ... sandy beaches on the Namibian coast, Langstrand and Cape Cross. A transverse ... prominent in the mid-shore at Cape Cross but occurred in low numbers at Langstrand , where archiannelids ... Koop (1983) recorded the faunal composition of local .... four replicate sediment cores were taken at 15 cm.

  14. Bibliography of sandy beaches and sandy beach organisms on the African continent

    CSIR Research Space (South Africa)

    Bally, R

    1986-01-01

    Full Text Available This bibliography covers the literature relating to sandy beaches on the African continent and outlying islands. The bibliography lists biological, chemical, geographical and geological references and covers shallow marine sediments, surf zones off...

  15. 77 FR 74341 - Establishing the Hurricane Sandy Rebuilding Task Force

    Science.gov (United States)

    2012-12-14

    ... the Hurricane Sandy Rebuilding Task Force By the authority vested in me as President by the.... Hurricane Sandy made landfall on October 29, 2012, resulting in major flooding, extensive structural damage... assist the affected region. A disaster of Hurricane Sandy's magnitude merits a comprehensive...

  16. Field investigation of surface sand and dust movement over different sandy grasslands in the Otindag Sandy Land, China

    Science.gov (United States)

    Liu, Shulin; Wang, Tao; Chen, Guangting; Guo, Jian; Xue, Xian; Ma, Shaoxiu

    2008-01-01

    The characteristics of sand and dust movement over different sandy grasslands in China’s Otindag Sandy Land were explored based on field observations and laboratory analyses. Threshold wind speeds (the speed required to initiate sand movement) at a height of 2 m above the ground were estimated in the field for different surface types. Threshold wind speed above shifting dunes in the study area is about 4.6 m s-1 at this height. This value was smaller than values observed above other surfaces, resulting in a greater risk of blowing sand above these dunes. Differences in sand transport rates (STR) as a function of the severity of desertification resulted primarily from differences in surface vegetation cover and secondarily from the soil’s grain-size distribution. STR increased exponentially with increasing near-bed wind velocity. Under the same wind conditions, STR increased with increasing severity of desertification: from 0.08 g cm-2 min-1 above semi-fixed dunes to 8 g cm-2 min-1 above semi-shifting dunes and 25 g cm-2 min-1 above shifting dunes. Vegetation’s affect on STR was clearly large. Different components of sand and dust were trapped over different lands: mostly sand grains but little dust were trapped above shifting dunes, but much dust was collected over semi-shifting and semi-fixed dunes. Human disturbance is likely to produce dust even from fixed dunes as a result of trampling by animals and vehicle travel. In addition, spring rainfall decreased the risk of sand and dust movement by accelerating germination of plants and the formation of a soil crust.

  17. Depositional models of sandy debrites and turbidites of Palaeogene reservoir sands in deep-lacustrine environments, South China

    Science.gov (United States)

    Li, Y.; Chen, G.

    2013-12-01

    Two depositional models are proposed for deep-lacustrine petroleum reservior sands (Palaeogene) in the Fushan Sag, Beibuwan Basin, South China. This facies trend is used as a template for predicting the distribution of reservoir facies of the Fushan oilfield. Based on examination of 150m of conventional cores from 13 drilled wells, four depositional facies have been interpreted: (1) fine-grained massive sandstone with floating mudstone clasts and planar clast fabric (sandy debrite); (2) fine-grained sandstone and siltstone showing contorted bedding, sand injection, and ptygmatic folding (sandy slump), (3) fine-grained sandstone with thin layers of normal grading and flute casts (turbidite), and (4) mudstone with faint laminae (suspension fallout). Combined with multiple seismic attributes, two depositional models are characterized by (1) sublacustrine fan: thick turbidite units occur at the bottom of the western sag beneath a series of normal faults slope. (2) Thinner deposition of sandy debrites mainly distribute at the bottom of eastern sag far from sandy slump at the lake margin slope, which interpreted to be controlled by "two-step" flexure slope break. The transfer zone located in the centre area is confirmed to be the primary origin for such differential depositions. In our study area, sandy debrites constitute the producing petroleum reservoirs, but turbidites are non reservoirs. This dramatic understanding will well account for "eastern much more than western" distribution of proven petroleum reserves and be applicable to predicting reservoir distribution.

  18. Concentration profiles for fine and coarse sediments suspended by waves over ripples: An analytical study with the 1-DV gradient diffusion model

    CERN Document Server

    Absi, Rafik

    2010-01-01

    Field and laboratory measurements of suspended sediments over wave ripples show, for time-averaged concentration profiles in semi-log plots, a contrast between upward convex profiles for fine sand and upward concave profiles for coarse sand. Careful examination of experimental data for coarse sand shows a near-bed upward convex profile beneath the main upward concave profile. Available models fail to predict these two profiles for coarse sediments. The 1-DV gradient diffusion model predicts the main upward concave profile for coarse sediments thanks to a suitable $\\beta$(y)-function (where $\\beta$ is the inverse of the turbulent Schmidt number and y is the distance from the bed). In order to predict the near-bed upward convex profile, an additional parameter {\\alpha} is needed. This parameter could be related to settling velocity ($\\alpha$ equal to inverse of dimensionless settling velocity) or to convective sediment entrainment process. The profiles are interpreted by a relation between second derivative of ...

  19. High Speed Boosted Cmos Differential Logic for Ripple Carry Adders

    Directory of Open Access Journals (Sweden)

    Meenu Roy,

    2014-01-01

    Full Text Available This paper describes a high speed boosted CMOS differential logic which is applicable in Ripple Carry Adders. The proposed logic operating with supply voltage approaching the MOS threshold voltage. The logic style improves switching speed by boosting the gate-source voltage of transistors along timing critical signal path. It allows a single boosting circuit to be shared by complementary outputs as a result the area overhead also minimizes. As compared to the conventional logic gates the EDP (energy delay product is improved. The test sets of logic gates and adders where designed in tsmc0.18μm of Mentor Graphics EDA tool. The experimental result for Ripple Carry Adders using the proposed logic style revealed that the addition time is reduced as compared with the conventional CMOS circuits.

  20. Ripple formation on nickel irradiated with radially polarized femtosecond beams.

    Science.gov (United States)

    Tsibidis, George D; Skoulas, Evangelos; Stratakis, Emmanuel

    2015-11-15

    We report on the morphological effects induced by the inhomogeneous absorption of radially polarized femtosecond laser irradiation of nickel (Ni) in sub-ablation conditions. A theoretical prediction of the morphology profile is performed, and the role of surface plasmon excitation in the production of self-formed periodic ripple structures is evaluated. Results indicate a smaller periodicity of the ripples profile compared to that attained under linearly polarized irradiation conditions. A combined hydrodynamical and thermoelastic model is presented in laser beam conditions that lead to material melting. The simulation results are presented to be in good agreement with the experimental findings. The ability to control the size of the morphological changes via modulating the beam polarization may provide an additional route for controlling and optimizing the outcome of laser micro-processing.

  1. Stabilization of beam-weibel instability by equilibrium density ripples

    Energy Technology Data Exchange (ETDEWEB)

    Mishra, S. K., E-mail: nishfeb@gmail.com; Kaw, Predhiman; Das, A.; Sengupta, S. [Institute for Plasma Research (IPR), Gandhinagar 382428 (India); Ravindra Kumar, G. [Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005 (India)

    2014-01-15

    In this paper, we present an approach to achieve suppression/complete stabilization of the transverse electromagnetic beam Weibel instability in counter streaming electron beams by modifying the background plasma with an equilibrium density ripple, shorter than the skin depth; this weakening is more pronounced when thermal effects are included. On the basis of a linear two stream fluid model, it is shown that the growth rate of transverse electromagnetic instabilities can be reduced to zero value provided certain threshold values for ripple parameters are exceeded. We point out the relevance of the work to recent experimental investigations on sustained (long length) collimation of fast electron beams and integral beam transport for laser induced fast ignition schemes, where beam divergence is suppressed with the assistance of carbon nano-tubes.

  2. Benthic solute exchange and carbon mineralization in two shallow subtidal sandy sediments: Effect of advective pore-water exchange

    DEFF Research Database (Denmark)

    Cook, Perran L. M.; Wenzhofer, Frank; Glud, Ronnie N.;

    2007-01-01

    of O-2 distribution across ripples, and also deep subsurface O-2 pools, being observed. Mineralization pathways were predominantly aerobic when benthic mineralization rates were low and advective pore-water flow high as a result of well-developed sediment topography. By contrast, mineralization...... proceeded predominantly through sulfate reduction when benthic mineralization rates were high and advective pore-water flow low as a result of poorly developed topography. Previous studies of benthic mineralization in shallow sandy sediments have generally ignored these dynamics and, hence, have overlooked......We conducted four field campaigns to evaluate benthic O-2 consumption and the effect of advective pore-water flow in nearshore permeable sediments in the North Sea and Baltic Sea. Advective pore-water transport had a marked effect on the benthic exchange of O-2 and TCO2 in benthic chamber...

  3. Coherent transition radiation from REB in plasma ripple

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The coherent transition-radiation emission from an underdense relativistic beam of electrons, travelling through a dense plasma ripple, was studied. The evolution of this radiation field is described by a set of self-consistent pendulum-wave equations. Analytic calculations of the small-signal gain and numerical computations of the nonlinear saturation of this emission are presented. It is shown that such a device may provide a source of tunable coherent radiation ranging from the microwave to the infrared region.

  4. A phenomenological model for self-rippling energy of free graphene monolayers

    Science.gov (United States)

    Wu, Bingjie; Ru, C. Q.

    2016-07-01

    Several candidate phenomenological expressions are studied for self-rippling energy that drives ripple formation of free single-layer graphene sheets. One phenomenological expression is admitted, while all others are rejected because they cannot admit stable periodic ripple mode. The admitted phenomenological expression contains two terms: one quadratic term which acts like a compressive force and has a destabilizing effect, and another fourth-order term which acts like a nonlinear elastic foundation and has a stabilizing effect. The two associated coefficients depend on specific mechanism of self-rippling and can be determined based on observed wavelength and amplitude of ripple mode. Based on the admitted expression, the effect of an applied force on ripple formation is studied. The present model predicts that the rippling can be controlled or even suppressed with an applied tensile force or collapsed into narrow wrinkles (of deformed wavelengths down to around 2 nm) under an applied compressive force, and the estimated minimum tensile strain to suppress rippling is in remarkable agreement with some known data. Our results show that self-rippling energy dominates ripple formation of sufficiently long free graphene ribbons, although it cannot drive self-rippling of sufficiently short free graphene ribbons. Consequently, a critical length is estimated so that self-rippling occurs only when the length of free single-layer graphene ribbons is much longer than the critical length. The estimated critical length is reasonably consistent with the known fact that self-rippling cannot occur in shorter free graphene sheets (say, of length below 20 nm).

  5. Conceptual study of electron ripple injection for tokamak transport control

    Energy Technology Data Exchange (ETDEWEB)

    Choe, W.; Ono, M. [Princeton Univ., NJ (United States). Plasma Physics Lab.; Chang, C.S. [New York Univ., NY (United States). Courant Inst. of Mathematical Sciences

    1995-08-01

    A non-intrusive method for inducing radial electric field based on electron ripple injection is under development by the Princeton CDX-U group. The radial electric field is known to play an important role in the L-H and H-VH mode transition according to the recent theoretical and experimental research. It is therefore important to develop a non-intrusive tool to control the radial electric field profile in tokamak plasmas. The present technique utilizes externally-applied local magnetic ripple fields to trap electrons at the edge, allowing them to penetrate towards the plasma center via {gradient}B and curvature drifts, causing the flux surfaces to charge up negatively. Electron cyclotron resonance heating is utilized to increase the trapped population and the electron drift velocity by raising the perpendicular energy of trapped electrons. In order to quantify the effects of cyclotron resonance heating on electrons, the temperature anisotropy of resonant electrons in a tokamak plasma is calculated. For the calculation of anisotropic temperatures, energy moments of the bounce-averaged Fokker-Planck equation with a bi-Maxwellian distribution function for heated electrons are solved, assuming a moderate wave power and a constant quasilinear diffusion coefficient. Simulation using a guiding-center orbit model have been performed to understand the behavior of suprathermal electrons in the presence of ripple fields. Examples for CDX-U and ITER parameters are given.

  6. Ripple-Spreading Network Model Optimization by Genetic Algorithm

    Directory of Open Access Journals (Sweden)

    Xiao-Bing Hu

    2013-01-01

    Full Text Available Small-world and scale-free properties are widely acknowledged in many real-world complex network systems, and many network models have been developed to capture these network properties. The ripple-spreading network model (RSNM is a newly reported complex network model, which is inspired by the natural ripple-spreading phenomenon on clam water surface. The RSNM exhibits good potential for describing both spatial and temporal features in the development of many real-world networks where the influence of a few local events spreads out through nodes and then largely determines the final network topology. However, the relationships between ripple-spreading related parameters (RSRPs of RSNM and small-world and scale-free topologies are not as obvious or straightforward as in many other network models. This paper attempts to apply genetic algorithm (GA to tune the values of RSRPs, so that the RSNM may generate these two most important network topologies. The study demonstrates that, once RSRPs are properly tuned by GA, the RSNM is capable of generating both network topologies and therefore has a great flexibility to study many real-world complex network systems.

  7. Electron ripple injection concept for tokamak transport control

    Science.gov (United States)

    Choe, W.; Ono, M.; Chang, C. S.

    1996-02-01

    A non-intrusive method for inducing a radial electric field (Er) based on electron ripple injection (ERI) is under development by the Princeton CDX-U group. Since Er is known to play an important role in the L-H and H-VH mode transition, it is therefore important to develop a non-intrusive tool to control the Er profile in tokamak plasmas. The present technique utilizes externally-applied local magnetic ripple fields to trap electrons at the edge, allowing them to penetrate towards the plasma center via ∇B and curvature drifts, causing the flux surfaces to charge up negatively. Electron cyclotron resonance heating (ECRH) is utilized to increase the trapped population and the electron drift velocity by raising the perpendicular energy of trapped electrons. The temperature anisotropy of resonant electrons in a tokamak plasma is calculated in order to investigate effects of ECRH on electrons. Simulations using a guiding-center orbit model have been performed to understand the behavior of suprathermal electrons in the presence of ripple fields. Examples for CDX-U and ITER are given.

  8. Nanoscale rippling on polymer surfaces induced by AFM manipulation.

    Science.gov (United States)

    D'Acunto, Mario; Dinelli, Franco; Pingue, Pasqualantonio

    2015-01-01

    Nanoscale rippling induced by an atomic force microscope (AFM) tip can be observed after performing one or many scans over the same area on a range of materials, namely ionic salts, metals, and semiconductors. However, it is for the case of polymer films that this phenomenon has been widely explored and studied. Due to the possibility of varying and controlling various parameters, this phenomenon has recently gained a great interest for some technological applications. The advent of AFM cantilevers with integrated heaters has promoted further advances in the field. An alternative method to heating up the tip is based on solvent-assisted viscoplastic deformations, where the ripples develop upon the application of a relatively low force to a solvent-rich film. An ensemble of AFM-based procedures can thus produce nanoripples on polymeric surfaces quickly, efficiently, and with an unprecedented order and control. However, even if nanorippling has been observed in various distinct modes and many theoretical models have been since proposed, a full understanding of this phenomenon is still far from being achieved. This review aims at summarizing the current state of the art in the perspective of achieving control over the rippling process on polymers at a nanoscale level.

  9. Reactivity of periodically rippled graphene grown on Ru(0001)

    Energy Technology Data Exchange (ETDEWEB)

    Borca, B; Calleja, F; Hinarejos, J J; Vazquez de Parga, A L; Miranda, R [Departamento de Fisica de la Materia Condensada, Universidad Autonoma de Madrid, Cantoblanco, E-28049 Madrid (Spain)

    2009-04-01

    We report here the reactivity of epitaxial graphene islands and complete monolayers on Ru(0001) towards molecular oxygen and air. The graphene is prepared by thermal decomposition of ethylene molecules pre-adsorbed on an Ru(0001) surface in an ultra-high vacuum chamber. The graphene layer presents a periodically rippled structure that is dictated by the misfit between graphene and Ru(0001) lattice parameters. The periodic ripples produce spatial charge redistribution in the graphene and modifies its electronic structure around the Fermi level. In order to investigate the reactivity of graphene we expose graphene islands to a partial pressure of oxygen and following the evolution of the surface by STM during the exposure. For the exposure to air we removed the sample from the UHV chamber and we re-introduce it after several hours, taking STM images before and after. The surface areas not covered by the graphene islands present a dramatic change but the graphene structure, even the borders of the islands, remain intact. In the case of a complete graphene monolayer the exposure to oxygen or to air does not affect or destroy the rippled structure of the graphene monolayer.

  10. Morphodynamic Impacts of Hurricane Sandy on the Inner-shelf (Invited)

    Science.gov (United States)

    Trembanis, A. C.; Beaudoin, J. D.; DuVal, C.; Schmidt, V. E.; Mayer, L. A.

    2013-12-01

    Through the careful execution of precision high-resolution acoustic sonar surveys over the period of October 2012 through July 2013, we have obtained a unique set of high-resolution before and after storm measurements of seabed morphology and in situ hydrodynamic conditions (waves and currents) capturing the impact of the storm at an inner continental shelf field site known as the 'Redbird reef' (Raineault et al., 2013). Understanding the signature of this storm event is important for identifying the impacts of such events and for understanding the role that such events have in the transport of sediment and marine debris on the inner continental shelf. In order to understand and characterize the ripple dynamics and scour processes in an energetic, heterogeneous inner-shelf setting, a series of high-resolution geoacoustic surveys were conducted before and after Hurricane Sandy. Our overall goal is to improve our understanding of bedform dynamics and spatio-temporal length scales and defect densities through the application of a recently developed fingerprint algorithm technique (Skarke and Trembanis, 2011). Utilizing high-resolution swath sonar collected by an AUV and from surface vessel multibeam sonar, our study focuses both on bedforms in the vicinity of manmade seabed objects (e.g. shipwrecks and subway cars) and dynamic natural ripples on the inner-shelf in energetic coastal settings with application to critical military operations such as mine countermeasures. Seafloor mapping surveys were conducted both with a ship-mounted multibeam echosounder (200 kHz and 400 kHz) and an Autonomous Underwater Vehicle (AUV) configured with high-resolution side-scan sonar (900 and 1800 kHz) and a phase measuring bathymetric sonar (500 kHz). These geoacoustic surveys were further augmented with data collected by in situ instruments placed on the seabed that recorded measurements of waves and currents at the site before, during, and after the storm. Multibeam echosounder map of

  11. Screening of cellulose decomposing fungi in sandy dune soil of Horqin Sandy Land

    Institute of Scientific and Technical Information of China (English)

    ShaoKun Wang; XueYong Zhao; XiaoAn Zuo; XinPing Liu; Hao Qu; Wei Mao; JianYing Yun

    2015-01-01

    Cellulose decomposing fungi play an important role in litter decomposition and are decisive in nutrient cycling in sandy land ecosystems. Thirty-one strains were isolated to select efficient cellulose decomposers, and four efficient cellulose decomposing fungi (NM3-1, NM3-2, NM3-3, and NM3-4) were screened using a CMC (carboxymethyl cellulose) carbon source in dune soil of Horqin Sandy Land. They were identified as Asperigillus calidoustus, Fusarium oxysporum, Fusarium solani, and Hypocrea lixii by rDNA-ITS molecular biological methods. Cloth decomposition rates were 15.71%, 15.89%, 17.29%, and 17.89%by the four efficient decomposers incubated for 30 days, respectively. Screening of efficient cellulose decomposers can not only increase the dune soil functional microbe bank, but can also accelerate litter decom-position and available nutrient input in the Horqin Sandy Land.

  12. Controlled nanodot fabrication by rippling polycarbonate surface using an AFM diamond tip

    OpenAIRE

    2014-01-01

    The single scratching test of polymer polycarbonate (PC) sample surface using an atomic force microscope (AFM) diamond tip for fabricating ripple patterns has been studied with the focus on the evaluation of the effect of the tip scratching angle on the pattern formation. The experimental results indicated that the different oriented ripples can be easily machined by controlling the scratching angles of the AFM. And, the effects of the normal load and the feed on the ripples formation and the...

  13. Simulation analyzing of torque-ripple minimization for switched reluctance motor

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Discusses the inevitability of torque-ripple of switchedreluctance motor (SRM) for its double saliency construction and switch power supply, and the minimization of torque-ripple, under traditional current chopping control mode, and presents a varying current amplitude chopping control method with a linear control model of varying current amplitude chopping shown, and the simulation of torque profiles under two kinds of current chopping control modes to demonstrate the validity of decreasing torque-ripple.

  14. Simulation and control of morphological changes due to dam removal in the Sandy River, Oregon, USA

    Science.gov (United States)

    Ding, Y.; Altinakar, M. S.

    2015-03-01

    A one-dimensional channel evolution simulation model (CCHE1D) is applied to assess morphological changes in a reach of the Sandy River, Oregon, USA, due to the Marmot Dam removal in 2007. Sediment transport model parameters (e.g. sediment transport capacity, bed roughness coefficient) were calibrated using observed bed changes after the dam removal. The validated model is then applied to assess long-term morphological changes in response to a 10-year hydrograph selected from historical storm water records. The long-term assessment of sedimentation gives a reasonable prediction of morphological changes, expanding erosion in reservoir and growing deposition immediately downstream of the dam site. This prediction result can be used for managing and planning river sedimentation after dam removal. A simulation-based optimization model is also applied to determine the optimal sediment release rates during dam-removal that will minimize the morphological changes in the downstream reaches.

  15. Influence of turbulence on bed load sediment transport

    DEFF Research Database (Denmark)

    Sumer, B. Mutlu; Chua, L.; Cheng, N. S.;

    2003-01-01

    This paper summarizes the results of an experimental study on the influence of an external turbulence field on the bedload sediment transport in an open channel. The external turbulence was generated by: (1) with a horizontal pipe placed halfway through the depth, h; (2) with a series of grids...... correlated with the sediment transport rate. The sediment transport increases markedly with increasing turbulence level.......-bed experiments and the ripple-covered-bed experiments. In the former case, the flow in the presence of the turbulence generator was adjusted so that the mean bed shear stress was the same as in the case without the turbulence generator in order to single out the effect of the external turbulence on the sediment...

  16. Scattering of oblique surface waves by the edge of small deformation on a porous ocean bed

    Science.gov (United States)

    Mohapatra, Smrutiranjan

    2015-06-01

    The scattering of oblique incident surface waves by the edge of a small cylindrical deformation on a porous bed in an ocean of finite depth, is investigated here within the framework of linearized water wave theory. Using perturbation analysis, the corresponding problem governed by modified Helmholtz equation is reduced to a boundary value problem for the first-order correction of the potential function. The first-order potential and, hence, the reflection and transmission coefficients are obtained by a method based on Green's integral theorem with the introduction of appropriate Green's function. Consideration of a patch of sinusoidal ripples shows that when the quotient of twice the component of the incident field wave number along x-direction and the ripple wave number approaches one, the theory predicts a resonant interaction between the bed and the free-surface, and the reflection coefficient becomes a multiple of the number of ripples. Again, for small angles of incidence, the reflected energy is more as compared to the other angles of incidence. It is also observed that the reflected energy is somewhat sensitive to the changes in the porosity of the ocean bed. From the derived results, the solutions for problems with impermeable ocean bed can be obtained as particular cases.

  17. Neocortical very fast oscillations (ripples, 80-200 Hz) during seizures: intracellular correlates.

    Science.gov (United States)

    Grenier, François; Timofeev, Igor; Steriade, Mircea

    2003-02-01

    Multi-site field potential and intracellular recordings from various neocortical areas were used to study very fast oscillations or ripples (80-200 Hz) during electrographic seizures in cats under ketamine-xylazine anesthesia. The animals displayed spontaneously occurring and electrically induced seizures comprising spike-wave complexes (2-3 Hz) and fast runs (10-20 Hz). Neocortical ripples had much higher amplitudes during seizures than during the slow oscillation preceding the onset of seizures. A series of experimental data from the present study supports the hypothesis that ripples are implicated in seizure initiation. Ripples were particularly strong at the onset of seizures and halothane, which antagonizes the occurrence of ripples, also blocked seizures. The firing of electrophysiologically defined cellular types was phase-locked with ripples in simultaneously recorded field potentials. This indicates that ripples during paroxysmal events are associated with a coordination of firing in a majority of neocortical neurons. This was confirmed with dual intracellular recordings. Based on the amplitude that neocortical ripples reach during paroxysmal events, we propose a mechanism by which neocortical ripples during normal network activity could actively participate in the initiation of seizures on reaching a certain threshold amplitude. This mechanism involves a vicious feedback loop in which very fast oscillations in field potentials are a reflection of synchronous action potentials, and in turn these oscillations help generate and synchronize action potentials in adjacent neurons through electrical interactions.

  18. Mechanical behavior of carbon nanotubes in the rippled and buckled phase

    Science.gov (United States)

    Jackman, H.; Krakhmalev, P.; Svensson, K.

    2015-02-01

    We have studied the mechanical behavior of multi-walled carbon nanotubes for bending strains beyond the onset for rippling and buckling. We found a characteristic drop in the bending stiffness at the rippling and buckling onset and the relative retained stiffness was dependent on the nanotube dimensions and crystallinity. Thin tubes are more prone to buckle, where some lose all of their bending stiffness, while thicker tubes are more prone to ripple and on average retain about 20% of their bending stiffness. In defect rich tubes, the bending stiffness is very low prior to rippling, but these tubes retain up to 70% of their initial bending stiffness.

  19. Selective display of multiple patterns encoded with different oriented ripples using femtosecond laser

    Science.gov (United States)

    Li, Jiawen; Li, Guoqiang; Hu, Yanlei; Zhang, Chenchu; Li, Xiaohong; Chu, Jiaru; Huang, Wenhao

    2015-08-01

    Uniform oriented ripples were induced on stainless steel surface by polarized femtosecond laser. Multiple patterns were successfully encoded with the different oriented ripples on the surface without spatial overlap. Each pattern can be selectively displayed with structural color while the others cannot be in the meantime when white light is irradiated on the surface from different directions. The influence of ripples with different periods for selecting pattern is also investigated. The ripple period is crucial to the color effects. This approach can be used in the fields of color display, identifying codes and anti-counterfeiting patterns.

  20. Unclassical ripple patterns in single-crystal silicon produced by femtosecond laser irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Zhang Wei [State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083 (China); State Key Laboratory of Transient Optics and Photonics, Xi' an Institute of Optics and Precision Mechanics of Chinese Academy of Sciences, Xi' an, Shaanxi 710119 (China); Cheng Guanghua [State Key Laboratory of Transient Optics and Photonics, Xi' an Institute of Optics and Precision Mechanics of Chinese Academy of Sciences, Xi' an, Shaanxi 710119 (China); Feng Qiang, E-mail: qfeng@skl.ustb.edu.cn [State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083 (China); National Center for Materials Service Safety, University of Science and Technology Beijing, Beijing 100083 (China)

    2012-12-15

    Highlights: Black-Right-Pointing-Pointer Transition from classical ripples to unclassical ripples. Black-Right-Pointing-Pointer Laser fluence has a significant effect on the unclassical ripple period. Black-Right-Pointing-Pointer Relationship between structures and their parametric dependence is established. Black-Right-Pointing-Pointer Capillary wave is responsible for the formation of unclassical ripples. - Abstract: Laser-induced periodic surface structures (LIPSS) in single-crystal silicon upon irradiation with multiple linearly polarized femtosecond (fs) laser pulses (120 fs, 800 nm, 1 kHz) were investigated under different laser fluence and pulse number. Unclassical ripples (U-ripples), which were nearly parallel to the polarization of the laser beam, were observed to form gradually on the top of classical ripples with the effective pulse number. Their periods were significantly longer than the laser wavelength, and increased with increasing both the laser fluence and pulse number in the current study. The relationship between the types of ripple patterns and their parametric dependence was established. The mechanism of U-ripple formation was attributed to the capillary wave, arising from the inhomogeneous temperature gradient combined with the electric field of the pulses in the molten surface layer.

  1. Excitation and inhibition compete to control spiking during hippocampal ripples: intracellular study in behaving mice.

    Science.gov (United States)

    English, Daniel F; Peyrache, Adrien; Stark, Eran; Roux, Lisa; Vallentin, Daniela; Long, Michael A; Buzsáki, György

    2014-12-01

    High-frequency ripple oscillations, observed most prominently in the hippocampal CA1 pyramidal layer, are associated with memory consolidation. The cellular and network mechanisms underlying the generation of the rhythm and the recruitment of spikes from pyramidal neurons are still poorly understood. Using intracellular, sharp electrode recordings in freely moving, drug-free mice, we observed consistent large depolarizations in CA1 pyramidal cells during sharp wave ripples, which are associated with ripple frequency fluctuation of the membrane potential ("intracellular ripple"). Despite consistent depolarization, often exceeding pre-ripple spike threshold values, current pulse-induced spikes were strongly suppressed, indicating that spiking was under the control of concurrent shunting inhibition. Ripple events were followed by a prominent afterhyperpolarization and spike suppression. Action potentials during and outside ripples were orthodromic, arguing against ectopic spike generation, which has been postulated by computational models of ripple generation. These findings indicate that dendritic excitation of pyramidal neurons during ripples is countered by shunting of the membrane and postripple silence is mediated by hyperpolarizing inhibition.

  2. Control of periodic ripples growth on metals by femtosecond laser ellipticity.

    Science.gov (United States)

    Tang, Yanfu; Yang, Jianjun; Zhao, Bo; Wang, Mingwei; Zhu, Xiaonong

    2012-11-01

    Formation of the periodic ripples on metallic surfaces is investigated comprehensively using variable ellipticities of femtosecond lasers. Compared with the linearly polarized incidence, the well defined grating-like ripple structures rather than the uniform arrays of nanoparticle can always be obtained for the elliptical polarization lasers. The ripple orientation is slanted clockwise or anticlockwise depending on the laser helicity but always display a maximum angle of 45°. Theoretical analyses indicate that no circular polarization is achieved for femtosecond lasers passing through quarter waveplate, and the induced ripple orientation is determined by the major axis of the polarization ellipse. The simulation results agree well with the experimental observations.

  3. A non-unity torque sharing function for torque ripple minimization of switched reluctance generators

    DEFF Research Database (Denmark)

    Park, Kiwoo; Liu, Xiao; Chen, Zhe

    2013-01-01

    This paper presents a new torque ripple minimization technique for a Switched Reluctance Generator (SRG). Although the SRG has many advantageous characteristics as a generator, it has not been widely employed in the industry. One of the most notorious disadvantages of the SRG is its high torque r...... ripple. In this paper, a non-unity Torque Sharing Function (TSF) is proposed to minimize the torque ripple over a wide speed range of operation. Simulation results are presented to verify the effectiveness of the proposed torque ripple minimization technique....

  4. Bed rest during pregnancy

    Science.gov (United States)

    ... page: //medlineplus.gov/ency/patientinstructions/000581.htm Bed rest during pregnancy To use the sharing features on ... few days or weeks. This is called bed rest. Bed rest used to be recommended routinely for ...

  5. Multispectral Kerr frequency comb initiated by Faraday ripples

    CERN Document Server

    Huang, Shu-Wei

    2016-01-01

    In a uniform microresonator, the generation of a broadband Kerr frequency comb is triggered by Turing patterns. Here, we study a distinctly different route to initiate the Kerr frequency comb by Faraday ripples. Momentum conservation is ensured by azimuthal modulation of the cavity dispersion. With a good agreement with the theoretical analysis, we demonstrate a multispectral Kerr frequency comb covering telecommunication O, C, L, and 2 {\\mu}m bands. Comb coherence and absence of a subcomb offset are confirmed by cw heterodyne beat note and amplitude noise spectra measurements. The device can be used for achieving broadband optical frequency synthesizer and high-capacity coherent telecommunication.

  6. Threats to sandy beach ecosystems: A review

    Science.gov (United States)

    Defeo, Omar; McLachlan, Anton; Schoeman, David S.; Schlacher, Thomas A.; Dugan, Jenifer; Jones, Alan; Lastra, Mariano; Scapini, Felicita

    2009-01-01

    We provide a brief synopsis of the unique physical and ecological attributes of sandy beach ecosystems and review the main anthropogenic pressures acting on the world's single largest type of open shoreline. Threats to beaches arise from a range of stressors which span a spectrum of impact scales from localised effects (e.g. trampling) to a truly global reach (e.g. sea-level rise). These pressures act at multiple temporal and spatial scales, translating into ecological impacts that are manifested across several dimensions in time and space so that today almost every beach on every coastline is threatened by human activities. Press disturbances (whatever the impact source involved) are becoming increasingly common, operating on time scales of years to decades. However, long-term data sets that describe either the natural dynamics of beach systems or the human impacts on beaches are scarce and fragmentary. A top priority is to implement long-term field experiments and monitoring programmes that quantify the dynamics of key ecological attributes on sandy beaches. Because of the inertia associated with global climate change and human population growth, no realistic management scenario will alleviate these threats in the short term. The immediate priority is to avoid further development of coastal areas likely to be directly impacted by retreating shorelines. There is also scope for improvement in experimental design to better distinguish natural variability from anthropogenic impacts. Sea-level rise and other effects of global warming are expected to intensify other anthropogenic pressures, and could cause unprecedented ecological impacts. The definition of the relevant scales of analysis, which will vary according to the magnitude of the impact and the organisational level under analysis, and the recognition of a physical-biological coupling at different scales, should be included in approaches to quantify impacts. Zoning strategies and marine reserves, which have not

  7. Formational Mechanisms and Morphology of Windblown Coarse-Grained Sand Ripples at White Sands, New Mexico

    Science.gov (United States)

    Glade, R.; Jerolmack, D. J.; Pelletier, J. D.

    2014-12-01

    Coarse-grained ripples, also known as "megaripples," are large sand ripples found in both aeolian and aquatic environments on Earth, and are common on Mars. The formation and morphology of coarse-grained ripples are not as well understood as more common splash ripples. Current understanding suggests that formative wind speeds are above the saltation threshold for the fine grains, but below this threshold for coarse grains found on the crests, such that they creep. Based on this idea, we hypothesize that wind speeds above this coarse-grain saltation threshold will destroy the ripples. We further hypothesize that these ripples do not have an equilibrium size; rather, their size is related to the persistence of formative winds in a given direction. To test this model, we studied windblown coarse-grained ripples in White Sands, New Mexico. Terrestrial LiDAR was used to obtain high resolution ripple morphology and migration over a three month period. Wind velocity profiles and concurrent saltating grain size data were collected during a wind storm to directly relate modes of transport to particle size and wind stress. These local data were used to calibrate wind records from a nearby meteorological station to estimate local fluid stress using a long-term record. LiDAR data indicate that these ripples were destroyed and reoriented between March and June 2013, while the wind record shows that the coarse-grain saltation threshold was indeed exceeded during this time. Morphological analysis indicates that the lee slope of these ripples is set by saltation impact - similar to splash ripples - but that height, wavelength and stoss slope are not related to instantaneous transport conditions. The historical wind record also shows that the range of wind directions decreases rapidly with increasing speed, restricting strong winds to a narrow range of direction. From these results we explore the idea that coarse-grained ripples are typically larger and less frequently destroyed

  8. Hurricane Sandy science plan: coastal impact assessments

    Science.gov (United States)

    Stronko, Jakob M.

    2013-01-01

    Hurricane Sandy devastated some of the most heavily populated eastern coastal areas of the Nation. With a storm surge peaking at more than 19 feet, the powerful landscape-altering destruction of Hurricane Sandy is a stark reminder of why the Nation must become more resilient to coastal hazards. In response to this natural disaster, the U.S. Geological Survey (USGS) received a total of $41.2 million in supplemental appropriations from the Department of the Interior (DOI) to support response, recovery, and rebuilding efforts. These funds support a science plan that will provide critical scientific information necessary to inform management decisions for recovery of coastal communities, and aid in preparation for future natural hazards. This science plan is designed to coordinate continuing USGS activities with stakeholders and other agencies to improve data collection and analysis that will guide recovery and restoration efforts. The science plan is split into five distinct themes: coastal topography and bathymetry, impacts to coastal beaches and barriers, impacts of storm surge, including disturbed estuarine and bay hydrology, impacts on environmental quality and persisting contaminant exposures, impacts to coastal ecosystems, habitats, and fish and wildlife. This fact sheet focuses assessing impacts to coastal beaches and barriers.

  9. Elevated Serum Aminotransferases Secondary to Rippling Muscle Disease

    Directory of Open Access Journals (Sweden)

    Kumanan Nalankilli

    2013-05-01

    Full Text Available A 43-year-old man was referred by his general practitioner to the hepatology clinic with deranged serum aminotransferases, discovered as part of routine blood tests. The objective was to identify the cause of elevated serum aminotransferases in this patient in a systematic manner. Thorough history and physical examination revealed a background history of rippling muscle disease secondary to caveolin-3 protein deficiency, with typical clinical signs. There was a positive family history of musculoskeletal disease in the patient's father and brother. Previous diagnostic tests performed to investigate the patient's musculoskeletal symptoms, including muscle biopsies, were revisited. Subsequent systematic investigations such as blood tests, liver ultrasound scan and Fibroscan® were performed to exclude potential causes of the deranged serum aminotransferases. Liver biopsy was not performed. A consistent pattern of chronic low-grade elevations of serum aminotransferases, less than three times the upper limit of the normal range, was found. This was associated with a consistently elevated serum creatine kinase and normal renal function tests. Previous muscle biopsies had revealed chronic degenerative and regenerative changes suggestive of a focal necrotizing myopathy. Liver ultrasound scan and Fibroscan® were normal. With exclusion of other liver diseases and identification of profoundly elevated serum creatine kinase concentration, the deranged aminotransferases were attributed to rippling muscle disease.

  10. High speed non-latching squid binary ripple counter

    Energy Technology Data Exchange (ETDEWEB)

    Silver, A.H.; Phillips, R.R.; Sandell, R.D.

    1985-03-01

    High speed, single flux quantum (SFQ) binary scalers are important components in superconducting analog-to-digital converters (ADC). This paper reviews the concept for a SQUID ADC and the design of an SFQ binary ripple counter, and reports the simulation of key components, and fabrication and performance of non-latching SQUID scalers and SFQ binary ripple counters. The SQUIDs were fabricated with Nb/Nb/sub 2/O/sub 5//PbIn junctions and interconnected by monolithic superconducting transmission lines and isolation resistors. Each SQUID functioned as a bistable flip-flop with the input connected to the center of the device and the output across one junction. All junctions were critically damped to optimize the pulse response. Operation was verified by observing the dc I-V curves of successive SQUIDs driven by a cw pulse train generated on the same chip. Each SQUID exhibited constant-voltage current steps at 1/2 the voltage of the preceding device as expected from the Josephson voltage-to-frequency relation. Steps were observed only for the same voltage polarity of successive devices and for proper phase bias of the SQUID. Binary frequency division was recorded up to 40GHz for devices designed to operate to 28GHz.

  11. Missing lynx and trophic cascades in food webs: A reply to Ripple et al.

    Science.gov (United States)

    John R. Squires; Nicholas J. DeCesare; Mark Hebblewhite; Joel Berger

    2012-01-01

    Ripple et al. (2011) proposed a hypothesis that the recovery of gray wolves (Canis lupus) may positively affect the viability of threatened Canada lynx (Lynx canadensis) populations in the contiguous United States through indirect species interactions. Ripple et al. (2011) proposed 2 key trophic linkages connecting wolf restoration with lynx recovery. First, recovering...

  12. The dimensions of sand ripples in full-scale oscillatory flows

    NARCIS (Netherlands)

    O'Donoghue, T.; Doucette, J.C.; Werf, van der J.J.; Ribberink, J.S.

    2006-01-01

    New large-scale experiments have been carried out in two oscillatory flow tunnels to study ripple regime sand suspension and net sand transport processes in full-scale oscillatory flows. The paper focuses on ripple dimensions and the new data are combined with existing data to make a large dataset o

  13. Mode-selective terahertz emission from rippled air irradiated by femtosecond laser pulses

    Science.gov (United States)

    Shin, Junghun; Zhidkov, Alexei; Jin, Zhan; Hosokai, Tomonao; Kodama, Ryosuke

    2014-04-01

    Terahertz (THz) emission from rippled air is studied in multidimensional particle-in-cell simulations that include optical field ionization. The ionization modulation in a plasma channel produced by a laser pulse propagating along a ripple and the pulse self-focusing result in THz mode selection with the generation of intense signals having quasi-monochromatic spectral distributions.

  14. Asynchronous ripple oscillations between left and right hippocampi during slow-wave sleep.

    Science.gov (United States)

    Villalobos, Claudio; Maldonado, Pedro E; Valdés, José L

    2017-01-01

    Spatial memory, among many other brain processes, shows hemispheric lateralization. Most of the published evidence suggests that the right hippocampus plays a leading role in the manipulation of spatial information. Concurrently in the hippocampus, memory consolidation during sleep periods is one of the key steps in the formation of newly acquired spatial memory traces. One of the most characteristic oscillatory patterns in the hippocampus are sharp-wave ripple (SWR) complexes. Within this complex, fast-field oscillations or ripples have been demonstrated to be instrumental in the memory consolidation process. Since these ripples are relevant for the consolidation of memory traces associated with spatial navigation, and this process appears to be lateralized, we hypothesize that ripple events between both hippocampi would exhibit different temporal dynamics. We tested this idea by using a modified "split-hyperdrive" that allows us to record simultaneous LFPs from both right and left hippocampi of Sprague-Dawley rats during sleep. We detected individual events and found that during sleep periods these ripples exhibited a different occurrence patterns between hemispheres. Most ripple events were synchronous between intra- rather than inter-hemispherical recordings, suggesting that ripples in the hippocampus are independently generated and locally propagated within a specific hemisphere. In this study, we propose the ripples' lack of synchrony between left and right hippocampi as the putative physiological mechanism underlying lateralization of spatial memory.

  15. Evolution of a Rippled Membrane during Phospholipase A2 Hydrolysis Studied by Time-Resolved AFM

    DEFF Research Database (Denmark)

    Leidy, Chad; Mouritsen, Ole G.; Jørgensen, Kent;

    2004-01-01

    The sensitivity of phospholipase A2 (PLA2) for lipid membrane curvature is explored by monitoring, through time-resolved atomic force microscopy, the hydrolysis of supported double bilayers in the ripple phase. The ripple phase presents a corrugated morphology. PLA2 is shown to have higher activi...

  16. Stochastic Ripple Diffusion of Energetic Particles in Reversed Magnetic Shear Tokamak

    Institute of Scientific and Technical Information of China (English)

    GAO Qing-Di; LONG Yong-Xing

    2004-01-01

    @@ The stochastic ripple diffusion is investigated in a realistic reversed magnetic shear discharge. Rippled field produces variations in the velocity of trapped particles leading to excursion of the tip position for successive banana bounces. When the excursion is large enough, the trapped energetic particles are lost rapidly via stochastic banana diffusion.

  17. Influence of PWM Modes on Commutation Torque Ripples in Sensorless Brushless DC Motor Control System

    Institute of Scientific and Technical Information of China (English)

    ZHANGXiang-jun; CHENBo-shi; 等

    2001-01-01

    This paper introduces four PWM modes used in the sensorless brushless DC motor control system,analyzes their different influences on the commutation torque ripple in detail,and selects the best PWM mode in four given types to reduce commutation torque ripple of Brushless OC( BLDC) motors,Simulation and experimental results show that the selection is correct and practical.

  18. Temperature-controlled structure and kinetics of ripple phases in one- and two-component supported lipid bilayers

    DEFF Research Database (Denmark)

    Kaasgaard, Thomas; Leidy, Chad; Crowe, J.H.

    2003-01-01

    ripples was seen. From height profiles of the AFM images, estimates of the amplitudes of the different ripple phases are reported. To elucidate the processes of ripple formation and disappearance, a ripple-phase DPPC lipid bilayer was taken through the pretransition in the cooling and the heating......Temperature-controlled atomic force microscopy (AFM) has been used to visualize and study the structure and kinetics of ripple phases in one-component dipalmitoylphosphaticlylcholine (DPPC) and two-component dimyristoylphosphatidylcholine-distearoylphosphatidylcholine (DMPC-DSPC) lipid bilayers....... The lipid bilayers are mica-supported double bilayers in which ripple-phase formation occurs in the top bilayer. In one-component DPPC lipid bilayers, the stable and metastable ripple phases were observed. In addition, a third ripple structure with approximately twice the wavelength of the metastable...

  19. Temperature-controlled structure and kinetics of ripple phases in one- and two-component supported lipid bilayers

    DEFF Research Database (Denmark)

    Kaasgaard, Thomas; Leidy, Chad; Crowe, J.H.

    2003-01-01

    ripples was seen. From height profiles of the AFM images, estimates of the amplitudes of the different ripple phases are reported. To elucidate the processes of ripple formation and disappearance, a ripple-phase DPPC lipid bilayer was taken through the pretransition in the cooling and the heating...... was heated from the ripple phase and into the ripple-phase/fluid-phase coexistence temperature region, the AFM images revealed that several dynamic properties of the ripple phase are important for the melting behavior of the lipid mixture. Onset of melting is observed at grain boundaries between different......Temperature-controlled atomic force microscopy (AFM) has been used to visualize and study the structure and kinetics of ripple phases in one-component dipalmitoylphosphaticlylcholine (DPPC) and two-component dimyristoylphosphatidylcholine-distearoylphosphatidylcholine (DMPC-DSPC) lipid bilayers...

  20. 78 FR 32296 - Second Allocation of Public Transportation Emergency Relief Funds in Response to Hurricane Sandy...

    Science.gov (United States)

    2013-05-29

    ... Response to Hurricane Sandy: Response, Recovery & Resiliency AGENCY: Federal Transit Administration (FTA... recipients most severely affected by Hurricane Sandy: the Metropolitan Transportation Authority, New Jersey... Federal Register notice, bringing the total amount of Hurricane Sandy Emergency Relief funds allocated...

  1. Sand Bed Morphodynamics under Standing Waves and Vegetated Conditions

    Science.gov (United States)

    Landry, B. J.; Garcia, M. H.

    2010-12-01

    Littoral processes such as sediment transport, wave attenuation, and boundary layer development are governed by the presence of bathymetric features, which include large-scale sand bars upon which smaller-scale sand ripples are superimposed, as well as the presence of submarine vegetation. Numerous studies on sand ripples and bars have aided to elucidate the dynamics in oscillatory flows; however, the effect of vegetation on the system is less understood. Recent laboratory studies have focused on quantifying wave attenuation by emergent vegetation as a natural method to mitigate storm surges. The emergent vegetation, while promising for coastal protection, alters sediment transport rates directly by the physical presence of the plants near the bed and indirectly from reduction in near-bed shear stresses due to attenuated wave energy. The experimental work herein focuses on the area near the deeply submerged vegetated canopy limit (current work has a ratio of mean still water depth to plant height, H/h, = 7.9) to minimize the effect on the surface waves and discern the direct impact vegetation has on sand bed morphodynamics. Experiments were conducted in the large wave tank (49-m long by 1.83-m wide by 1.22-m deep) in the Ven Te Chow Hydrosystems Laboratory at the University of Illinois in which a high reflection wave forcing was used over a uniform sand bed with a 0.25-mm median sediment diameter in which staggered and uniform arrangements of idealized vegetation (i.e., 6.35-mm diameter rigid wooden cylinders) were positioned along the bed (e.g., at predetermined sand bar troughs and over an entire sand bar). The resulting bathymetric evolution from the vegetated case experiments were compared to the base case of no vegetation using two optical methods: a high-resolution laser displacement sensor for three-dimensional surveys and digitized profiles via high-definition panoramic images of the entire test section. The experimental findings illustrate the profound

  2. Penetration of a resonant magnetic perturbation in an adiabatically rippled plasma slab

    CERN Document Server

    Dewar, Robert L; Bhattacharjee, Amitava; Yoshida, Zensho

    2016-01-01

    The adiabatic limit of a recently proposed dynamical extension of Taylor relaxation, \\emph{multi-region relaxed magnetohydrodynamics} (MRxMHD) is summarized, with special attention to the appropriate definition of relative magnetic helicity. The formalism is illustrated using a simple two-region, sheared-magnetic-field model similar to the Hahm--Kulsrud--Taylor (HKT) rippled-boundary slab model. In MRxMHD a linear Grad--Shafranov equation applies, even at finite ripple amplitude. The adiabatic switching on of boundary ripple excites a shielding current sheet opposing reconnection at a resonant surface. The perturbed magnetic field as a function of ripple amplitude is calculated by invoking conservation of magnetic helicity in the two regions separated by the current sheet. At low ripple amplitude "half islands" appear on each side of the current sheet, locking the rotational transform at the resonant value. Beyond a critical amplitude these islands disappear and the rotational transform develops a discontinui...

  3. The properties and causes of rippling in quasi-perpendicular collisionless shock fronts

    Directory of Open Access Journals (Sweden)

    R. E. Lowe

    Full Text Available The overall structure of quasi-perpendicular, high Mach number collisionless shocks is controlled to a large extent by ion reflection at the shock ramp. Departure from a strictly one-dimensional structure is indicated by simulation results showing that the surface of such shocks is rippled, with variations in the density and all field components. We present a detailed analysis of these shock ripples, using results from a two-dimensional hybrid (particle ions, electron fluid simulation. The process that generates the ripples is poorly understood, because the large gradients at the shock ramp make it difficult to identify instabilities. Our analysis reveals new features of the shock ripples, which suggest the presence of a surface wave mode dominating the shock normal magnetic field component of the ripples, as well as whistler waves excited by reflected ions.

    Key words. Space plasma physics (numerical simulation studies; shock waves; waves and instabilities

  4. Femtosecond laser fabrication of large-area periodic surface ripple structure on Si substrate

    Energy Technology Data Exchange (ETDEWEB)

    Hong, L. [School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore); Singapore Institute of Manufacturing Technology, 71 Nanyang Drive, Singapore 638075 (Singapore); Rusli [School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore); Wang, X.C., E-mail: xcwang@SIMTech.a-star.edu.sg [Singapore Institute of Manufacturing Technology, 71 Nanyang Drive, Singapore 638075 (Singapore); Zheng, H.Y. [Singapore Institute of Manufacturing Technology, 71 Nanyang Drive, Singapore 638075 (Singapore); Wang, H. [School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 (Singapore); Yu, H.Y. [South University of Science and Technology of China, Shenzhen (China)

    2014-04-01

    In this paper, we report the fabrication of a large area uniformly distributed periodic nano-ripple structure on silicon substrate through the proper scanning of a line-shaped femtosecond laser beam. The fabricated nano-ripple structure has a periodicity of ∼600 nm and a ripple depth of ∼300 nm. The modulation depth is much deeper than the one previously reported. The developed structure is demonstrated to be able to substantially reduce light reflection due to the effective optical coupling between the incident sunlight with the nano-ripple structure and exhibit an absorption enhancement of ∼41% compared with planar silicon wafer. The physics underlying the formation of the nano-ripple structure is also discussed.

  5. Collisional stochastic ripple diffusion of alpha particles and beam ions on TFTR

    Energy Technology Data Exchange (ETDEWEB)

    Redi, M.H.; Zarnstorff, M.C.; White, R.B.; Budny, R.V.; Janos, A.C.; Owens, D.K.; Schivell, J.F.; Scott, S.D.; Zweben, S.J.

    1995-07-01

    Predictions for ripple loss of fast ions from TFTR are investigated with a guiding center code including both collisional and ripple effects. A synergistic enhancement of fast ion diffusion is found for toroidal field ripple with collisions. The total loss is calculated to be roughly twice the sum of ripple and collisional losses calculated separately. Discrepancies between measurements and calculations of plasma beta at low current and large major radius are resolved when both effects are included for neutral beam ions. A 20--30% reduction in alpha particle heating is predicted for q{sub a} = 6--14, R = 2.6 m DT plasmas on TFTR due to first orbit and collisional stochastic ripple diffusion.

  6. Thrust ripple optimization and experiment for a permanent magnet linear synchronous motor

    Institute of Scientific and Technical Information of China (English)

    XU Yue-tong; FU Jian-zhong; CHEN Zi-chen

    2006-01-01

    Thrust ripple such as end force,slot force and normal force are key factors that affect the properties of permanent magnet linear synchronous motors (PMLSM).According to different mechanics and analytical models,end force resulting from open magnetic circuit of PMLSM was greatly decreased by optimizing the length of the PMLSM mover.Slot force caused by slot effect was greatly reduced by using fraction slot structure,and normal force was calculated through the finite element method (FEM).After thrust ripple was calculated,its uniform formula was obtained through Fourier series nonlinear regression.An experimental system was set up to measure thrust ripple,and experiment results demonstrated that experimental force ripple was quite in line with that calculated by the fitting formula.The optimal theory and analysis method is effective,and the obtained formula can be utilized to compensate thrust ripple in practical applications and improve the motion performance of PMLSM.

  7. FORCE RIPPLE SUPPRESSION TECHNOLOGY FOR LINEAR MOTORS BASED ON BACK PROPAGATION NEURAL NETWORK

    Institute of Scientific and Technical Information of China (English)

    ZHANG Dailin; CHEN Youping; AI Wu; ZHOU Zude; KONG Ching Tom

    2008-01-01

    Various force disturbances influence the thrust force of linear motors when a linear motor (LM) is running. Among all of force disturbances, the force ripple is the dominant while a linear motor runs in low speed. In order to suppress the force ripple, back propagation(BP) neural network is proposed to learn the function of the force ripple of linear motors, and the acquisition method of training samples is proposed based on a disturbance observer. An off-line BP neural network is used mainly because of its high running efficiency and the real-time requirement of the servo control system of a linear motor. By using the function, the force ripple is on-line compensated according to the position of the LM. The experimental results show that the force ripple is effectively suppressed by the compensation of the BP neural network.

  8. Organic matter dynamics in coarse sandy calcareous soils

    NARCIS (Netherlands)

    Pronk, A.A.; Reuler, van H.

    2011-01-01

    The decomposition of organic matter in coarse sandy calcareous soils (beach sand) is thought to be much higher than in acid fine sandy soils but relatively little research is performed on these soils. Laboratory incubation experiments in which the release of soil carbon (C) is determined may overest

  9. Comparing auditory filter bandwidths, spectral ripple modulation detection, spectral ripple discrimination, and speech recognition: Normal and impaired hearinga)

    Science.gov (United States)

    Davies-Venn, Evelyn; Nelson, Peggy; Souza, Pamela

    2015-01-01

    Some listeners with hearing loss show poor speech recognition scores in spite of using amplification that optimizes audibility. Beyond audibility, studies have suggested that suprathreshold abilities such as spectral and temporal processing may explain differences in amplified speech recognition scores. A variety of different methods has been used to measure spectral processing. However, the relationship between spectral processing and speech recognition is still inconclusive. This study evaluated the relationship between spectral processing and speech recognition in listeners with normal hearing and with hearing loss. Narrowband spectral resolution was assessed using auditory filter bandwidths estimated from simultaneous notched-noise masking. Broadband spectral processing was measured using the spectral ripple discrimination (SRD) task and the spectral ripple depth detection (SMD) task. Three different measures were used to assess unamplified and amplified speech recognition in quiet and noise. Stepwise multiple linear regression revealed that SMD at 2.0 cycles per octave (cpo) significantly predicted speech scores for amplified and unamplified speech in quiet and noise. Commonality analyses revealed that SMD at 2.0 cpo combined with SRD and equivalent rectangular bandwidth measures to explain most of the variance captured by the regression model. Results suggest that SMD and SRD may be promising clinical tools for diagnostic evaluation and predicting amplification outcomes. PMID:26233047

  10. Comparing auditory filter bandwidths, spectral ripple modulation detection, spectral ripple discrimination, and speech recognition: Normal and impaired hearing.

    Science.gov (United States)

    Davies-Venn, Evelyn; Nelson, Peggy; Souza, Pamela

    2015-07-01

    Some listeners with hearing loss show poor speech recognition scores in spite of using amplification that optimizes audibility. Beyond audibility, studies have suggested that suprathreshold abilities such as spectral and temporal processing may explain differences in amplified speech recognition scores. A variety of different methods has been used to measure spectral processing. However, the relationship between spectral processing and speech recognition is still inconclusive. This study evaluated the relationship between spectral processing and speech recognition in listeners with normal hearing and with hearing loss. Narrowband spectral resolution was assessed using auditory filter bandwidths estimated from simultaneous notched-noise masking. Broadband spectral processing was measured using the spectral ripple discrimination (SRD) task and the spectral ripple depth detection (SMD) task. Three different measures were used to assess unamplified and amplified speech recognition in quiet and noise. Stepwise multiple linear regression revealed that SMD at 2.0 cycles per octave (cpo) significantly predicted speech scores for amplified and unamplified speech in quiet and noise. Commonality analyses revealed that SMD at 2.0 cpo combined with SRD and equivalent rectangular bandwidth measures to explain most of the variance captured by the regression model. Results suggest that SMD and SRD may be promising clinical tools for diagnostic evaluation and predicting amplification outcomes.

  11. The nature of the bed load transport in the mouth of the river to the non-tidal sea (the Vistula River, Poland)

    Science.gov (United States)

    Lisimenka, Aliaksandr; Zwoliński, Zbigniew; Rudowski, Stanisław

    2015-04-01

    The Vistula, Poland's primary river, is the second largest river of the Baltic Sea Basin considering the average river flow and drainage area and one of the least regulated amongst large rivers in Europe. The main Vistula river mouth is a cross-cut artificial channel of about 3000 m length, 400 m width and up to 10 m depth. Results of three measurements campaigns which were carried out in the main Vistula river mouth in October 2013, March and June 2014 are presented. The area of interest was mapped using boat mounted high-resolution Reson Seabat 7101 multibeam echosounder system (MBES). River flow field information was obtained with Rio Grande 1200 kHz Acoustic Doppler Current Profiler (ADCP) along the designated 14 cross-section profiles at an interval of 250 m. Seismoacoustic measurements were carried out using Innomar SES-2000 parametric sub-bottom profiler along the longitudinal profiles at an interval of 30 m. At the end of each measurement campaign, 20-30 grab samples were collected in places chosen on the basis of current bathymetric map and were analyzed by sieving method. The obtained results have revealed comprehensive riverbed morphology of the river channel which is characterized by presence of multiple generations of small to large sandy dunes of various orientations, whose asymmetries indicate a general seaward migration. On the basis of newly developed method for quantitative analysis of subaqueous straight-crested rippled bottom roughness with using of the 2D Discrete Fourier Transform (2D DFT) algorithm which involved a calculation of low-order spectral moments, primary parameters of the observed bedforms such as crest-line spatial alignment, wavelength and height are determined. Depth-averaged flow velocities indicate spatial variability with increased flow velocities achieve up to 0.75 m/s in the mainstream. Analysis of the seismoacoustic data confirms seaward migration of the observed sand dunes and shows that, in general, dynamic sediment

  12. Rediscovering community--reflections after Hurricane Sandy.

    Science.gov (United States)

    See, Sharon

    2013-01-01

    Hoboken, New Jersey, is a town of 50,000 residents located across the Hudson River from New York City. Most of Hoboken's infrastructure was compromised during Hurricane Sandy as a result of flooding and power outages that rendered many businesses inoperable, including all of the pharmacies in town. Despite a focus on emergency preparedness since Hurricane Katrina and 9/11, there were no contingencies in place to facilitate and assess the medication needs of the community in the event of a natural disaster. This essay describes how the author rediscovered the meaning of community, and through working with colleagues in other health care disciplines and non-health care volunteers, provided care to patients in suboptimal circumstances.

  13. Hurricane Sandy science plan: New York

    Science.gov (United States)

    Ransom, Clarice N.

    2013-01-01

    Hurricane Sandy is a stark reminder of why the Nation must become more resilient to coastal hazards. More than one-half of the U.S. population lives within 50 miles of a coast, and this number is increasing. The U.S. Geological Survey (USGS) is one of the largest providers of geologic and hydrologic information in the world. Federal, State, and local partners depend on the USGS science to know how to prepare for hurricane hazards and reduce losses from future hurricanes. The USGS works closely with other bureaus within the Department of the Interior, the Federal Emergency Management Agency, the National Oceanic Atmospheric Administration, the U.S. Army Corps of Engineers, the Environmental Protection Agency, and many State and local agencies to identify their information needs before, during, and after hurricanes.

  14. Nitrate reduction in an unconfined sandy aquifer

    DEFF Research Database (Denmark)

    Postma, Diederik Jan; Boesen, Carsten; Kristiansen, Henning;

    1991-01-01

    Nitrate distribution and reduction processes were investigated in an unconfined sandy aquifer of Quaternary age. Groundwater chemistry was studied in a series of eight multilevel samplers along a flow line, deriving water from both arable and forested land. Results show that plumes of nitrate...... processes of O2 and NO3- occur at rates that are fast compared to the rate of downward water transport. Nitrate-contaminated groundwater contains total contents of dissolved ions that are two to four times higher than in groundwater derived from the forested area. The persistence of the high content...... of total dissolved ions in the NO3- free anoxic zone indicates the downward migration of contaminants and that active nitrate reduction is taking place. Nitrate is apparently reduced to N2 because both nitrite and ammonia are absent or found at very low concentrations. Possible electron donors...

  15. Ripples and Shear Bands in Plowed Granular Media

    CERN Document Server

    Gravish, Nick; Goldman, Daniel I

    2009-01-01

    Monodisperse packings of dry, air-fluidized granular media typically exist between volume fractions from $\\Phi$= 0.585 to 0.64. We demonstrate that the dynamics of granular drag are sensitive to volume fraction $\\Phi$ and their exists a transition in the drag force and material deformation from smooth to oscillatory at a critical volume fraction $\\Phi_{c}=0.605$. By dragging a submerged steel plate (3.81 cm width, 6.98 cm depth) through $300 \\mu m$ glass beads prepared at volume fractions between 0.585 to 0.635 we find that below $\\Phi_{c}$ the media deformation is smooth and non-localized while above $\\Phi_{c}$ media fails along distinct shear bands. At high $\\Phi$ the generation of these shear bands is periodic resulting in the ripples on the surface. Work funded by The Burroughs Wellcome Fund and the Army Research Lab MAST CTA

  16. The Ripple Pond: Enabling Spiking Networks to See

    Directory of Open Access Journals (Sweden)

    Saeed eAfshar

    2013-11-01

    Full Text Available We present the biologically inspired Ripple Pond Network (RPN, a simply connected spiking neural network which performs a transformation converting two dimensional images to one dimensional temporal patterns suitable for recognition by temporal coding learning and memory networks. The RPN has been developed as a hardware solution linking previously implemented neuromorphic vision and memory structures such as frameless vision sensors and neuromorphic temporal coding spiking neural networks. Working together such systems are potentially capable of delivering end-to-end high-speed, low-power and low-resolution recognition for mobile and autonomous applications where slow, highly sophisticated and power hungry signal processing solutions are ineffective. Key aspects in the proposed approach include utilising the spatial properties of physically embedded neural networks and propagating waves of activity therein for information processing, using dimensional collapse of imagery information into amenable temporal patterns and the use of asynchronous frames for information binding.

  17. Self-focusing dynamics of patches of ripples

    Science.gov (United States)

    Milewski, P. A.; Wang, Z.

    2016-10-01

    The dynamics of focussing of extended patches of nonlinear capillary-gravity waves within the primitive fluid dynamic equations is presented. It is found that, when the envelope has certain properties, the patch focusses initially in accordance to predictions from nonlinear Schrödinger equation, and focussing can concentrate energy to the vicinity of a point or a curve on the fluid surface. After initial focussing, other effects dominate and the patch breaks up into a complex set of localised structures-lumps and breathers-plus dispersive radiation. We perform simulations both in the inviscid regime and for small viscosities. Lastly we discuss throughout the similarities and differences between the dynamics of ripple patches and self-focussing light beams.

  18. Effects of magnetic ripple on 3D equilibrium and alpha particle confinement in the European DEMO

    Science.gov (United States)

    Pfefferlé, D.; Cooper, W. A.; Fasoli, A.; Graves, J. P.

    2016-11-01

    An assessment of alpha particle confinement is performed in the European DEMO reference design. 3D MHD equilibria with nested flux-surfaces and single magnetic axis are obtained with the VMEC free-boundary code, thereby including the plasma response to the magnetic ripple created by the finite number of TF coils. Populations of fusion alphas that are consistent with the equilibrium profiles are evolved until slowing-down with the VENUS-LEVIS orbit code in the guiding-centre approximation. Fast ion losses through the last-closed flux-surface are numerically evaluated with two ripple models: (1) using the 3D equilibrium and (2) algebraically adding the non-axisymmetric ripple perturbation to the 2D equilibrium. By virtue of the small ripple field and its non-resonant nature, both models quantitatively agree. Differences are however noted in the toroidal location of particles losses on the last-closed flux-surface, which in the first case is 3D and in the second not. Superbanana transport, i.e. ripple-well trapping and separatrix crossing, is expected to be the dominant loss mechanism, the strongest effect on alphas being between 100-200 KeV. Above this, stochastic ripple diffusion is responsible for a rather weak loss rate, as the stochastisation threshold is observed numerically to be higher than analytic estimates. The level of ripple in the current 18 TF coil design of the European DEMO is not found to be detrimental to fusion alpha confinement.

  19. Asynchronous ripple oscillations between left and right hippocampi during slow-wave sleep

    Science.gov (United States)

    Villalobos, Claudio

    2017-01-01

    Spatial memory, among many other brain processes, shows hemispheric lateralization. Most of the published evidence suggests that the right hippocampus plays a leading role in the manipulation of spatial information. Concurrently in the hippocampus, memory consolidation during sleep periods is one of the key steps in the formation of newly acquired spatial memory traces. One of the most characteristic oscillatory patterns in the hippocampus are sharp-wave ripple (SWR) complexes. Within this complex, fast-field oscillations or ripples have been demonstrated to be instrumental in the memory consolidation process. Since these ripples are relevant for the consolidation of memory traces associated with spatial navigation, and this process appears to be lateralized, we hypothesize that ripple events between both hippocampi would exhibit different temporal dynamics. We tested this idea by using a modified "split-hyperdrive" that allows us to record simultaneous LFPs from both right and left hippocampi of Sprague-Dawley rats during sleep. We detected individual events and found that during sleep periods these ripples exhibited a different occurrence patterns between hemispheres. Most ripple events were synchronous between intra- rather than inter-hemispherical recordings, suggesting that ripples in the hippocampus are independently generated and locally propagated within a specific hemisphere. In this study, we propose the ripples’ lack of synchrony between left and right hippocampi as the putative physiological mechanism underlying lateralization of spatial memory. PMID:28158285

  20. Torque Ripple Reduction of Reluctance Torque Assisted Motors Using Asymmetric Flux Barriers

    Science.gov (United States)

    Hiramoto, Kenji; Takeda, Yoji; Sanada, Masayuki; Morimoto, Shigeo

    Interior permanent magnet synchronous motor (IPMSM) is efficient and can be operated in wide speed region; therefore it is used widely. However, torque ripple of reluctance torque assisted motors, for example IPMSM and synchronous reluctance motor (SynRM), is very large. The skew is known in the prior art as a torque ripple reduction method of AC motors. Although the skew is effective for torque ripple reduction, structure is complicated and it has the disadvantage that average torque will decrease. The discontinuous variation of magnetic resistance between flux barriers and teeth cause the torque ripple. In this paper, in order to ease the discontinuous variation of magnetic resistance, flux barriers are asymmetrically designed so that the relative position relation between flux barriers and teeth may not be in agreement as much as possible. As a result, the torque ripple can be reduced dramatically without the average torque decrease. The experimental motor has been fabricated and the results of measuring torque ripple prove the validity of the torque ripple reduction using asymmetric flux barriers.

  1. Landscape Visual Quality and Meiofauna Biodiversity on Sandy Beaches

    Science.gov (United States)

    Felix, Gabriela; Marenzi, Rosemeri C.; Polette, Marcos; Netto, Sérgio A.

    2016-10-01

    Sandy beaches are central economic assets, attracting more recreational users than other coastal ecosystems. However, urbanization and landscape modification can compromise both the functional integrity and the attractiveness of beach ecosystems. Our study aimed at investigating the relationship between sandy beach artificialization and the landscape perception by the users, and between sandy beach visual attractiveness and biodiversity. We conducted visual and biodiversity assessments of urbanized and semiurbanized sandy beaches in Brazil and Uruguay. We specifically examined meiofauna as an indicator of biodiversity. We hypothesized that urbanization of sandy beaches results in a higher number of landscape detractors that negatively affect user evaluation, and that lower-rated beach units support lower levels of biodiversity. We found that urbanized beach units were rated lower than semiurbanized units, indicating that visual quality was sensitive to human interventions. Our expectations regarding the relationship between landscape perception and biodiversity were only partially met; only few structural and functional descriptors of meiofauna assemblages differed among classes of visual quality. However, lower-rated beach units exhibited signs of lower environmental quality, indicated by higher oligochaete densities and significant differences in meiofauna structure. We conclude that managing sandy beaches needs to advance beyond assessment of aesthetic parameters to also include the structure and function of beach ecosystems. Use of such supporting tools for managing sandy beaches is particularly important in view of sea level rise and increasing coastal development.

  2. Adaptive feedforward of estimated ripple improves the closed loop system performance significantly

    Energy Technology Data Exchange (ETDEWEB)

    Kwon, S.; Regan, A.; Wang, Y.M.; Rohlev, T.

    1998-12-31

    The Low Energy Demonstration Accelerator (LEDA) being constructed at Los Alamos National Laboratory will serve as the prototype for the low energy section of Acceleration Production of Tritium (APT) accelerator. This paper addresses the problem of LLRF control system for LEDA. The authors propose an estimator of the ripple and its time derivative and a control law which is based on PID control and adaptive feedforward of estimated ripple. The control law reduces the effect of the deterministic cathode ripple that is due to high voltage power supply and achieves tracking of desired set points.

  3. Online high voltage power supply ripple estimation and feedforward in LEDA

    Energy Technology Data Exchange (ETDEWEB)

    Kwon, S.; Regan, A.; Wang, Y.M.; Rohlev, T.

    1999-06-01

    The Low Energy Demonstration Accelerator (LEDA) being constructed at Los Alamos National Laboratory will serve as the prototype for the low energy section of Acceleration Production of Tritium (APT) accelerator. This paper addresses the problem of LLRF control system for LEDA. They propose an estimator of the ripple and its time derivative and a control law which is based on PID control and adaptive feedforward of estimated ripple. The control law reduces the effect of the deterministic cathode ripple that is due to high voltage power supply and achieves tracking of desired set points.

  4. Final Report: Mechanisms of sputter ripple formation: coupling among energetic ions, surface kinetics, stress and composition

    Energy Technology Data Exchange (ETDEWEB)

    Chason, Eric; Shenoy, Vivek

    2013-01-22

    Self-organized pattern formation enables the creation of nanoscale surface structures over large areas based on fundamental physical processes rather than an applied template. Low energy ion bombardment is one such method that induces the spontaneous formation of a wide variety of interesting morphological features (e.g., sputter ripples and/or quantum dots). This program focused on the processes controlling sputter ripple formation and the kinetics controlling the evolution of surfaces and nanostructures in high flux environments. This was done by using systematic, quantitative experiments to measure ripple formation under a variety of processing conditions coupled with modeling to interpret the results.

  5. Magnetic ripple and the modeling of lower-hybrid current drive in tokamaks

    Energy Technology Data Exchange (ETDEWEB)

    Peysson, Y.; Arslanbekov, R.; Basiuk, V.; Carrasco, J.; Litaudon, X.; Moreau, D. [Association Euratom-CEA, Centre d`Etudes de Cadarache, 13 - Saint-Paul-lez-Durance (France). Dept. de Recherches sur la Fusion Controlee; Bizarro, J.P. [Instituto Superior Tecnico, Lisbon (Portugal). Lab. de Quimica Organica

    1996-01-01

    Using ray-tracing, a detailed investigation of the lower hybrid (LH) wave propagation in presence of toroidal magnetic field ripple is presented. By coupling ray tracing with a one-dimensional relativistic Fokker-Planck code, simulations of LH experiments have been performed for the Tore Supra tokamak. Taking into account magnetic ripple in LH simulations, a better agreement is found between numerical predictions and experimental observations, such as non-thermal Bremsstrahlung emission, current profile, ripple-induced power losses in local magnetic mirrors, when plasma conditions correspond to the ` `few passes` regime. (author). 47 refs.

  6. Effects of the poloidal variation of the magnetic field ripple on enhanced heat transport in tokamaks

    Energy Technology Data Exchange (ETDEWEB)

    Uckan, N.A.; Tsang, K.T.; Callen, J.D.

    1976-06-01

    The use of a finite number of coils to generate the toroidal field of a tokamak introduces a magnetic field asymmetry and is responsible for an additional particle trapping that can affect the plasma confinement. The enhanced transport coefficients associated with the ripple-induced drifts have been calculated. The calculations include both the radial and poloidal variation in the magnitude of the field ripple. It is found that the consideration of poloidal variation significantly reduces the ripple-trapped transport but does not affect the banana-drift diffusion. Results relevant to the ORNL Experimental Power Reactor (EPR) reference design are discussed.

  7. Advanced RF-KO slow-extraction method for the reduction of spill ripple

    CERN Document Server

    Noda, K; Shibuya, S; Uesugi, T; Muramatsu, M; Kanazawa, M; Takada, E; Yamada, S

    2002-01-01

    Two advanced RF-knockout (RF-KO) slow-extraction methods have been developed at HIMAC in order to reduce the spill ripple for accurate heavy-ion cancer therapy: the dual frequency modulation (FM) method and the separated function method. As a result of simulations and experiments, it was verified that the spill ripple could be considerably reduced using these advanced methods, compared with the ordinary RF-KO method. The dual FM method and the separated function method bring about a low spill ripple within standard deviations of around 25% and of 15% during beam extraction within around 2 s, respectively, which are in good agreement with the simulation results.

  8. Advanced RF-KO slow-extraction method for the reduction of spill ripple

    Science.gov (United States)

    Noda, K.; Furukawa, T.; Shibuya, S.; Uesugi, T.; Muramatsu, M.; Kanazawa, M.; Takada, E.; Yamada, S.

    2002-10-01

    Two advanced RF-knockout (RF-KO) slow-extraction methods have been developed at HIMAC in order to reduce the spill ripple for accurate heavy-ion cancer therapy: the dual frequency modulation (FM) method and the separated function method. As a result of simulations and experiments, it was verified that the spill ripple could be considerably reduced using these advanced methods, compared with the ordinary RF-KO method. The dual FM method and the separated function method bring about a low spill ripple within standard deviations of around 25% and of 15% during beam extraction within around 2 s, respectively, which are in good agreement with the simulation results.

  9. Rippling Patterns in Aggregates of Myxobacteria Arise from Cell-Cell Collisions

    Science.gov (United States)

    Börner, Uwe; Deutsch, Andreas; Reichenbach, Hans; Bär, Markus

    2002-07-01

    Experiments with myxobacterial aggregates reveal standing waves called rippling patterns. Here these structures are modeled with a simple discrete model based on the interplay between migration and collisions of cells. Head-to-head collisions of cells result in cell reversals. To correctly reproduce the rippling patterns, a refractory phase after each cell reversal has to be assumed, during which further reversal is prohibited. The duration of this phase determines the wavelength and period of the ripple patterns as well as the reversal frequency of single cells.

  10. Evaluation of wet tantalum capacitors after exposure to extended periods of ripple current, volume 2

    Science.gov (United States)

    Ward, C. M.

    1975-01-01

    The application of tantalum capacitors in the Viking Lander includes dc voltage and ripple current electrical stress, high temperature during nonoperating times (sterilization), and high vibration and shock loads. The capacitors must survive these severe environments without any degradation if reliable performance is to be achieved. A test program was established to evaluate both wet-slug tantalum and wet-foil capacitors under conditions accurately duplicating actual Viking applications. Test results of the electrical performance characteristics during extended periods of ripple current, the characteristics of the internal silver migration as a function of extended periods of ripple current, and the existence of any memory characteristics are presented.

  11. Evaluation of wet tantalum capacitors after exposure to extended periods of ripple current, volume 1

    Science.gov (United States)

    Watson, G. W.; Lasharr, J. C.; Shumaker, M. J.

    1974-01-01

    The application of tantalum capacitors in the Viking Lander includes both dc voltage and ripple current electrical stress, high temperature during nonoperating times (sterilization), and high vibration and shock loads. The capacitors must survive these severe environments without any degradation if reliable performance is to be achieved. A test program was established to evaluate both wet-slug tantalum and wet-foil capacitors under conditions accurately duplicating actual Viking applications. Test results of the electrical performance characteristics during extended periods of ripple current, the characteristics of the internal silver migration as a function for extended periods of ripple current, and the existence of any memory characteristics are presented.

  12. ADAPTIVE CONTROL APPROACH FOR PERIODIC RATE RIPPLES IN INERTIAL GUIDANCE TEST EQUIPMENT

    Institute of Scientific and Technical Information of China (English)

    XUGuo-zhu; LIUYue; ZHANGYuan-sheng

    2005-01-01

    The rate performance of inertial guidance test equipment (IGTE) affects the performance testing of inertia devices and navigation systems. Periodic rate ripples caused by periodic disturbances have a great effect on the rate performance of rotation test tables. The mechanism caused by the rate ripple in IGTE is analyzed. Based on the nonlinear self-adaptive control system approach, a control system scheme is proposed to eliminate the period disturbances for its uncertainty. Experimental results show that the periodic rate ripple can efficiently be controlled.

  13. Acidification of sandy grasslands - consequences for plant diversity

    DEFF Research Database (Denmark)

    Olsson, Pål Axel; Mårtensson, Linda-Maria; Bruun, Hans Henrik

    2009-01-01

    Questions: (1) Does soil acidification in calcareous sandy grasslands lead to loss of plant diversity? (2) What is the relationship between the soil content of lime and the plant availability of mineral nitrogen (N) and phosphorus (P) in sandy grasslands? Location: Sandy glaciofluvial deposits...... in south-eastern Sweden covered by xeric sand calcareous grasslands (EU habitat directive 6120). Methods: Soil and vegetation were investigated in most of the xeric sand calcareous grasslands in the Scania region (136 sample plots distributed over four or five major areas and about 25 different sites...

  14. Fit-for-purpose phosphorus management: do riparian buffers qualify in catchments with sandy soils?

    Science.gov (United States)

    Weaver, David; Summers, Robert

    2014-05-01

    Hillslope runoff and leaching studies, catchment-scale water quality measurements and P retention and release characteristics of stream bank and catchment soils were used to better understand reasons behind the reported ineffectiveness of riparian buffers for phosphorus (P) management in catchments with sandy soils from south-west Western Australia (WA). Catchment-scale water quality measurements of 60 % particulate P (PP) suggest that riparian buffers should improve water quality; however, runoff and leaching studies show 20 times more water and 2 to 3 orders of magnitude more P are transported through leaching than runoff processes. The ratio of filterable reactive P (FRP) to total P (TP) in surface runoff from the plots was 60 %, and when combined with leachate, 96 to 99 % of P lost from hillslopes was FRP, in contrast with 40 % measured as FRP at the large catchment scale. Measurements of the P retention and release characteristics of catchment soils (bank soil (bank soils suggest that catchment soils contain more P, are more P saturated and are significantly more likely to deliver FRP and TP in excess of water quality targets than stream bank soils. Stream bank soils are much more likely to retain P than contribute P to streams, and the in-stream mixing of FRP from the landscape with particulates from stream banks or stream beds is a potential mechanism to explain the change in P form from hillslopes (96 to 99 % FRP) to large catchments (40 % FRP). When considered in the context of previous work reporting that riparian buffers were ineffective for P management in this environment, these studies reinforce the notion that (1) riparian buffers are unlikely to provide fit-for-purpose P management in catchments with sandy soils, (2) most P delivered to streams in sandy soil catchments is FRP and travels via subsurface and leaching pathways and (3) large catchment-scale water quality measurements are not good indicators of hillslope P mobilisation and transport

  15. Bed Bugs - Multiple Languages

    Science.gov (United States)

    ... Are Here: Home → Multiple Languages → All Health Topics → Bed Bugs URL of this page: https://medlineplus.gov/languages/ ... V W XYZ List of All Topics All Bed Bugs - Multiple Languages To use the sharing features on ...

  16. Bed Bugs and Schools

    Science.gov (United States)

    Bed bugs have long been a pest – feeding on blood, causing itchy bites and generally irritating their human hosts. They are successful hitchhikers, and can move from an infested site to furniture, bedding, baggage, boxes, and clothing.

  17. A new hypothesis and exploratory model for the formation of large-scale inner-shelf sediment sorting and ``rippled scour depressions''

    Science.gov (United States)

    Murray, A. Brad; Thieler, E. Robert

    2004-02-01

    Recent observations of inner continental shelves in many regions show numerous collections of relatively coarse sediment, which extend kilometers in the cross-shore direction and are on the order of 100 m wide. These "rippled scour depressions" have been interpreted to indicate concentrated cross-shelf currents. However, recent observations strongly suggest that they are associated with sediment transport along-shore rather than cross-shore. A new hypothesis for the origin of these features involves the large wave-generated ripples that form in the coarse material. Wave motions interacting with these large roughness elements generate near-bed turbulence that is greatly enhanced relative to that in other areas. This enhances entrainment and inhibits settling of fine material in an area dominated by coarse sediment. The fine sediment is then carried by mean currents past the coarse accumulations, and deposited where the bed is finer. We hypothesize that these interactions constitute a feedback tending to produce accumulations of fine material separated by self-perpetuating patches of coarse sediments. As with many types of self-organized bedforms, small features would interact as they migrate, leading to a better-organized, larger-scale pattern. As an initial test of this hypothesis, we use a numerical model treating the transport of coarse and fine sediment fractions, treated as functions of the local bed composition—a proxy for the presence of large roughness elements in coarse areas. Large-scale sorted patterns exhibiting the main characteristics of the natural features result robustly in the model, indicating that this new hypothesis offers a plausible explanation for the phenomena.

  18. ON THE PHYSICS OF FLOW-DRIVEN SEDIMENTS (BED-LOAD)

    Institute of Scientific and Technical Information of China (English)

    Ulrich C. E. ZANKE

    2001-01-01

    More than three dozen significant formulae for bed-load transport have been developed over a period of more than 100 years with varying degrees of success. Major problems have been the use of completely or partly empirical approaches and too few data for fitting. This paper presents an analytical formulation for bed-load transport. It is based on a balance of forces for the determination of the thickness of the moving bed-load layer and on the determination of the velocity of this layer. The formula derived is compared to a set of approx. 2000 data published by 32 authors. It is demonstrated that the basic form of the MPM-formula is a special case of the analytical solution. The derivation also includes the effect of bed features such as ripples and dunes on quantitative transport.

  19. Introduction to Bed Bugs

    Science.gov (United States)

    ... that there are ways to control bed bugs. Getting good, solid information is the first step in both prevention and control. While there is no chemical quick fix, there are effective strategies to control bed bugs involving both non-chemical and chemical methods. Bed bugs can be hard to find and ...

  20. The protection of sandy shores - Can we afford to ignore the contribution of seagrass?

    Science.gov (United States)

    Paul, Maike

    2017-08-15

    Shore nourishment is considered an effective soft coastal protection measure for sandy shorelines. However, sand demand and costs are high, especially as nourishment has to be repeated regularly due to ongoing erosion. Seagrass meadows are able to trap and stabilise sediment by reducing bed shear stress. Moreover, they reduce flow velocity and wave energy in regions beyond their boundaries. Especially small species may not provide these ecosystem services sufficiently to protect shorelines from erosion, but they may stabilise beach profiles enough to increase nourishment intervals. This review discusses the potential benefits of integrating ecosystem services provided by seagrass meadows, both existing and newly planted, in nourishment plans, and also addresses potential limitations such as unsuitable hydrodynamic conditions and seasonality. Finally, it highlights knowledge gaps that should be addressed by interdisciplinary research to improve nourishment plans and use seagrass ecosystem services to their full potential. Copyright © 2017 Elsevier Ltd. All rights reserved.

  1. On the Impact Angle of Hurricane Sandy's New Jersey Landfall

    Science.gov (United States)

    Hall, Timothy M.; Sobel, Adam H.

    2013-01-01

    Hurricane Sandy's track crossed the New Jersey coastline at an angle closer to perpendicular than any previous hurricane in the historic record, one of the factors contributing to recordsetting peak-water levels in parts of New Jersey and New York. To estimate the occurrence rate of Sandy-like tracks, we use a stochastic model built on historical hurricane data from the entire North Atlantic to generate a large sample of synthetic hurricanes. From this synthetic set we calculate that under long-term average climate conditions, a hurricane of Sandy's intensity or greater (category 1+) makes NJ landfall at an angle at least as close to perpendicular as Sandy's at an average annual rate of 0.0014 yr-1 (95% confidence range 0.0007 to 0.0023); i.e., a return period of 714 years (95% confidence range 435 to 1429).

  2. 2014 USGS CMGP Lidar: Post Sandy (Long Island, NY)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — TASK NAME: Long Island New York Sandy LIDAR lidar Data Acquisition and Processing Production Task USGS Contract No. G10PC00057 Task Order No. G14PD00296 Woolpert...

  3. Hurricane Sandy: Rapid Response Imagery of the Surrounding Regions

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The imagery posted on this site is of Hurricane Sandy. The aerial photography missions were conducted by the NOAA Remote Sensing Division. The images were acquired...

  4. 2008 USDA Forest Service Lidar: Sandy River Study Area

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Watershed Sciences, Inc. collected Light Detection and Ranging (LiDAR) data for the Sandy River study area in collaboration with the USDA Forest Service. The areas...

  5. James J. Howard Marine Sciences Laboratory @ Sandy Hook

    Data.gov (United States)

    Federal Laboratory Consortium — The James J. Howard Marine Sciences Laboratory, located on the New Jersey shore at Sandy Hook, is a state-of-the-art marine research facility shared by the National...

  6. Studies on Thiobacilli spp. isolated from sandy beaches of Kerala

    Digital Repository Service at National Institute of Oceanography (India)

    Gore, P.S.; Raveendran, O.; Unnithan, R.V.

    Occurrence, isolation and oxidative activity of Thiobacilli spp. from some sandy beaches of Kerala are reported. These organisms were encountered in polluted beaches and were dominant during monsoon in all the beaches...

  7. James J. Howard Marine Sciences Laboratory @ Sandy Hook

    Data.gov (United States)

    Federal Laboratory Consortium — The James J. Howard Marine Sciences Laboratory, located on the New Jersey shore at Sandy Hook, is a state-of-the-art marine research facility shared by the National...

  8. 2014 USGS CMGP Lidar: Sandy Restoration (Delaware and Maryland)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Geographic Extent: SANDY_Restoration_DE_MD_QL2 Area of Interest covers approximately 3.096 square miles. Lot #5 contains the full project area Dataset Description:...

  9. Short Communication Energy and ash contents of sandy beach ...

    African Journals Online (AJOL)

    macrofauna found on three exposed sandy beaches on the west coast ... that they often form the predominant shore type (Bally,. McQuaid ... their sediments are given in Table I. Animals ..... The biochemical composition of the tropical intertida1 ...

  10. A New Method for Reducing Commutation Torque Ripples in BLDC Motors

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    A new compensation method and an algorithm for compensating for the commutation torque ripples of the trapezoidal EMF brushless DC motor are put forward. Simulation and experimental results show that this method is correct and practical.

  11. Contribution of synchrotron oscillation to spill ripple in RF-knockout slow-extraction

    Science.gov (United States)

    Furukawa, T.; Noda, K.

    2005-02-01

    We have studied the effect of synchrotron oscillations on the spill ripple in RF-knockout extraction, in order to investigate the ripple component of the synchrotron-oscillation frequency and to suppress this component. By using a simplified model of RF-knockout extraction and the simulation, it was found that the following conditions are essential for suppressing the spill ripple including the component of the synchrotron-oscillation frequency: (1) sufficient amplitude of the synchrotron oscillation and (2) uniform distribution in longitudinal phase-space. In the experiment at the Heavy Ion Medical Accelerator in Chiba (HIMAC) synchrotron, the debunch-recapture was carried out before the extraction to obtain the larger oscillation amplitude and the uniform distribution in the longitudinal phase-space. In this article, the contribution of the synchrotron oscillation to the spill ripple is described in detail.

  12. A high voltage ratio and low ripple interleaved DC-DC converter for fuel cell applications.

    Science.gov (United States)

    Chang, Long-Yi; Chao, Kuei-Hsiang; Chang, Tsang-Chih

    2012-01-01

    This paper proposes a high voltage ratio and low ripple interleaved boost DC-DC converter, which can be used to reduce the output voltage ripple. This converter transfers the low DC voltage of fuel cell to high DC voltage in DC link. The structure of the converter is parallel with two voltage-doubler boost converters by interleaving their output voltages to reduce the voltage ripple ratio. Besides, it can lower the current stress for the switches and inductors in the system. First, the PSIM software was used to establish a proton exchange membrane fuel cell and a converter circuit model. The simulated and measured results of the fuel cell output characteristic curve are made to verify the correctness of the established simulation model. In addition, some experimental results are made to validate the effectiveness in improving output voltage ripple of the proposed high voltage ratio interleaved boost DC-DC converters.

  13. Ultrafast thermal dynamics of nano-ripples formation via laser double pulses excitation

    Science.gov (United States)

    Du, Guangqing; Wu, Yanmin; Uddin, Noor; Yang, Qing; Chen, Feng; Lu, Yu; Bian, Hao; Hou, Xun

    2016-09-01

    The ultrafast thermal dynamics of nano-ripples formation on gold film via ultrafast laser double pulses excitation is theoretically investigated by numerical simulations. The non-equilibrium thermal modulations with respect to the electron and phonon energy transfers within gold film is proposed for predicting the nano-ripples formation. It is revealed that the nano-ripples contrast on gold film surface can be well controlled via tuning the pulse energy ratio, pulse separation and pulse exchange of ultrafast laser double-pulse. It is attributed to the tunable energy transfer routes between the electron thermal diffusion and the electron-phonon coupling via tuning double pulses parameters. The study provides theoretical basis for producing high-contrast ripples for a wide range application in the fields such as high-absorptive solar cells, surface friction devices and super-hydrophobic surface.

  14. Subwavelength ripples adjustment based on electron dynamics control by using shaped ultrafast laser pulse trains.

    Science.gov (United States)

    Jiang, Lan; Shi, Xuesong; Li, Xin; Yuan, Yanping; Wang, Cong; Lu, Yongfeng

    2012-09-10

    This study reveals that the periods, ablation areas and orientations of periodic surface structures (ripples) in fused silica can be adjusted by using designed femtosecond (fs) laser pulse trains to control transient localized electron dynamics and corresponding material properties. By increasing the pulse delays from 0 to 100 fs, the ripple periods are changed from ~550 nm to ~255 nm and the orientation is rotated by 90°. The nearwavelength/subwavelength ripple periods are close to the fundamental/second-harmonic wavelengths in fused silica respectively. The subsequent subpulse of the train significantly impacts free electron distributions generated by the previous subpulse(s), which might influence the formation mechanism of ripples and the surface morphology.

  15. Analysis of Torque Ripple Reduction in Induction Motor DTC Drive with Multiple Voltage Vectors

    Directory of Open Access Journals (Sweden)

    ROSIC, M. M.

    2015-02-01

    Full Text Available This paper shows an analysis of torque ripple reduction in modified DTC algorithm by using multiple voltage vectors with the appropriate multilevel hysteresis controller. A short theoretical background of classical and proposed DTC algorithm was given at the beginning. Experimental results of the proposed DTC algorithm, implemented on digital signal processor F2812, were analysed in comparison with classical DTC. It is shown that the torque ripple can be reduced by selecting voltage vectors with an appropriate intensity. Motor current oversampling was used to analyse the estimated torque behaviour during one DSP sampling period. Furthermore, the analysis of torque ripple reduction with oversampled torque values was conducted in relation to the number of available voltage vectors. The analysis shows that the proposed DTC algorithm allows significant torque ripple reduction while retaining the simplicity, small computational burden and good dynamic characteristics of the classical DTC.

  16. New Torque Estimation Method Considering Spatial Harmonics and Torque Ripple Reduction in Permanent Magnet Synchronous Motors

    Science.gov (United States)

    Hida, Hajime; Tomigashi, Yoshio; Ueyama, Kenji; Inoue, Yukinori; Morimoto, Shigeo

    This paper proposes a new torque estimation method that takes into account the spatial harmonics of permanent magnet synchronous motors and that is capable of real-time estimation. First, the torque estimation equation of the proposed method is derived. In the method, the torque ripple of a motor can be estimated from the average of the torque calculated by the conventional method (cross product of the fluxlinkage and motor current) and the torque calculated from the electric input power to the motor. Next, the effectiveness of the proposed method is verified by simulations in which two kinds of motors with different components of torque ripple are considered. The simulation results show that the proposed method estimates the torque ripple more accurately than the conventional method. Further, the effectiveness of the proposed method is verified by performing on experiment. It is shown that the torque ripple is decreased by using the proposed method to the torque control.

  17. Nanoscale ripple formation in Co/Si(100) thin films with Ar{sup +} beam etching

    Energy Technology Data Exchange (ETDEWEB)

    Arranz, M A [Fac. Ciencias Quimicas, Universidad de Castilla-La Mancha, Camilo Jose Cela 10, 13071, Ciudad Real (Spain); Colino, Jose M, E-mail: HiguelAngel.Arranz@uclm.e [Instituto de Nanociencia, NanotecnologIa y Materiales Moleculares, UCLM, Campus de la Fabrica de Armas, 45071 Toledo (Spain)

    2010-01-01

    We have investigated the formation of nanoscale ripples on etched Co/Si(100) films with Ar{sup +} beam in grazing incidence. Topography and dimensions of those nanoscale patterns were characterized by means of atomic force microscopy. Polycrystalline cobalt thin films were deposited by d.c. magnetron sputtering onto Si(100) wafers and, later transferred in situ to a process chamber for the production of ripples. Their average width, W{sub d}, and separation between them, i.e. their periodicity {Lambda}, were found to monotonously increase first with the etching time and, finally, reach saturation values for long irradation times (around 30 min). The same Ar{sup +} beam etching applied on thicker Co films resulted in much wider and higher ripples, providing a more defined nanostructure for ulterior uniaxial magnetic anisotropy measurements. These changes in the ripple dimensions on increasing the Co film thickness are discussed in terms of the surface roughness in the as-deposited film.

  18. Control of surface ripple amplitude in ion beam sputtered polycrystalline cobalt films

    Energy Technology Data Exchange (ETDEWEB)

    Colino, Jose M., E-mail: josemiguel.colino@uclm.es [Institute of Nanoscience, Nanotechnology and Molecular Materials, University of Castilla-La Mancha, Campus de la Fabrica de Armas, Toledo 45071 (Spain); Arranz, Miguel A. [Facultad de Ciencias Quimicas, University of Castilla-La Mancha, Ciudad Real 13071 (Spain)

    2011-02-15

    We have grown both polycrystalline and partially textured cobalt films by magnetron sputter deposition in the range of thickness (50-200 nm). Kinetic roughening of the growing film leads to a controlled rms surface roughness values (1-6 nm) increasing with the as-grown film thickness. Ion erosion of a low energy 1 keV Ar+ beam at glancing incidence (80{sup o}) on the cobalt film changes the surface morphology to a ripple pattern of nanometric wavelength. The wavelength evolution at relatively low fluency is strongly dependent on the initial surface topography (a wavelength selection mechanism hereby confirmed in polycrystalline rough surfaces and based on the shadowing instability). At sufficiently large fluency, the ripple wavelength steadily increases on a coarsening regime and does not recall the virgin surface morphology. Remarkably, the use of a rough virgin surface makes the ripple amplitude in the final pattern can be controllably increased without affecting the ripple wavelength.

  19. Relativistic nonlinearity and wave-guide propagation of rippled laser beam in plasma

    Indian Academy of Sciences (India)

    R K Khanna; K Baheti

    2001-06-01

    In the present paper we have investigated the self-focusing behaviour of radially symmetrical rippled Gaussian laser beam propagating in a plasma. Considering the nonlinearity to arise from relativistic phenomena and following the approach of Akhmanov et al, which is based on the WKB and paraxial-ray approximation, the self-focusing behaviour has been investigated in some detail. The effect of the position and width of the ripple on the self-focusing of laser beam has been studied for arbitrary large magnitude of nonlinearity. Results indicate that the medium behaves as an oscillatory wave-guide. The self-focusing is found to depend on the position parameter of ripple as well as on the beam width. Values of critical power has been calculated for different values of the position parameter of ripple. Effects of axially and radially inhomogeneous plasma on self-focusing behaviour have been investigated and presented here.

  20. Versatile CAMAC power supply controller-monitor with built-in ramping and ripple monitor

    Energy Technology Data Exchange (ETDEWEB)

    Kang, H.; Horelick, D.

    1984-10-01

    An integrated power supply controller-monitor has been designed and is in use to control large power supplies for SLC dc magnets. This single-width CAMAC module contains a 14-bit DAC, a 14-bit ADC, and several channels of optically coupled digital status and control signals. Additional features include built-in selectable ramping rates, self-test capabilities, and a ripple monitor circuit to measure ac ripple in the power supply current.

  1. Design of Low-Torque-Ripple Synchronous Reluctance Motor with External Rotor

    Directory of Open Access Journals (Sweden)

    Lavrinovicha L.

    2017-02-01

    Full Text Available The paper presents new designs for synchronous reluctance motors that have external rotor (segment-shaped rotor, rotor with additional non-magnetic space to the quadrature axis of the rotor, and rotor with several flux barriers. Impact of the external rotor configuration on the electromagnetic torque and torque ripple is analysed. Electromagnetic torque ripple factor is calculated for each studied motor using the results of magnetic field numerical calculations.

  2. Calculation of prompt loss and toroidal field ripple loss under neutral beam injection on EAST

    Science.gov (United States)

    Wu, Bin; Hao, Baolong; White, Roscoe; Wang, Jinfang; Zang, Qing; Han, Xiaofeng; Hu, Chundong

    2017-02-01

    Neutral beam injection is a major auxiliary heating method in the EAST experimental campaign. This paper gives detailed calculations of beam loss with different plasma equilibria using the guiding center code ORBIT and NUBEAM/TRANSP. Increasing plasma current can dramatically lower the beam ion prompt loss and ripple loss. Countercurrent beam injection gives a much larger prompt loss fraction than co-injection, and ripple-induced collisionless stochastic diffusion is the dominant loss channel.

  3. Studies of suprathermal electron loss in the magnetic ripple of Tore Supra

    Energy Technology Data Exchange (ETDEWEB)

    Basiuk, V.; Lipa, M.; Martin, G.; Chantant, M.; Guilhem, D.; Imbeaux, F.; Mitteau, R.; Peysson, Y.; Surle, F. [Association Euratom-CEA sur la fusion, CEA Cadarache, 13108 St. Paul-Lez-Durance (France)

    2000-03-01

    A new prototype of protection against fast electron trapped in the magnetic ripple was installed on Tore-Supra in 1998. It was designed to support the high flux of fast electron generated by lower hybrid in the CIEL project (up to 6 MW/m{sup 2}) during steady state experiments. So it is actively cooled and allows a direct measurement of the energy lost in the ripple. (author)

  4. Removal of Direct Current Link Harmonic Ripple in Single Phase Voltage Source Inverter Systems Using Supercapacitors

    Science.gov (United States)

    2016-09-01

    current. In practice , SC bank voltage dropped as low as approximately 5.0 V before the BBC entered DCM and data became invalid. 44 B. LABORATORY...distribution is unlimited 12b. DISTRIBUTION CODE 13. ABSTRACT (maximum 200 words) For an Energy Management System (EMS)-controlled microgrid that... bank as the only DC energy storage device, the DC link voltage ripple causes a second-order harmonic ripple in battery current that leads to a

  5. Collaborative Strategy on Bed Bugs

    Science.gov (United States)

    The Collaborative Strategy on Bed Bugs was developed by the Federal Bed Bug Workgroup to clarify the federal role in bed bug control and highlight ways that government, community, academia and private industry can work together on bed bug issues.

  6. EAARL-B Coastal Topography--Eastern New Jersey, Hurricane Sandy, 2012: First Surface, Pre-Sandy

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — ASCII xyz and binary point-cloud data, as well as a digital elevation model (DEM) of a portion of the New Jersey coastline, pre- and post-Hurricane Sandy (October...

  7. Study on rate ripple and its adaptive suppression method in inertia guidance test equipment

    Institute of Scientific and Technical Information of China (English)

    ZHANG Yuan-sheng; XU Guo-zhu; LIU Yue

    2007-01-01

    This paper discusses causes of the rate ripple in inertia guidance test equipment IGET, systematically analyses their effects on the rate ripple in IGTE. The analysis result shows: The rate ripple caused by the periodic errors of inductosyn and angular encoder is higher at high speed than that caused by nagnetic ripple torque and friction torque, and it cannot be eliminated by adjusting control parameters of the system. And based on the nonlinear adaptive control system theory, the paper puts forward a new control system scheme to eliminate the rate ripple caused by the periodic errors of inductosyn and angular encoder, develops the adaptive control rules and makes simulation and test. Experimental result shows a significant improvement on those tables for the period disturbs under the system scheme designed. By this plan,with the input of rate 200°/s, the rate ripple falls from 5°/s to 0. 4°/s within about 6s adaptive adjustment time, being a twelfth of before adaptation,which can not be reached by common classical controls. The experimental results conform with the simulation,which proves the validity and practicability of the plan.

  8. Ripple-associated high-firing interneurons in the hippocampal CA1 region

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    By simultaneously recording the activity of individual neurons and field potentials in freely behaving mice, we found two types of interneurons firing at high frequency in the hippocampal CA1 region, which had high correlations with characteristic sharp wave-associated ripple oscillations (100―250 Hz) during slow-wave sleep. The firing of these two types of interneurons highly synchronized with ripple oscillations during slow-wave sleep, with strongly increased firing rates corresponding to individual ripple episodes. Interneuron type I had at most one spike in each sub-ripple cycle of ripple episodes and the peak firing rate was 310±33.17 Hz. Interneuron type II had one or two spikes in each sub-ripple cycle and the peak firing rate was 410±47.61 Hz. During active exploration, their firing was phase locked to theta oscillations with the highest probability at the trough of theta wave. Both two types of interneurons increased transiently their firing rates responding to the startling shake stimuli. The results showed that these two types of high-frequency interneurons in the hippocampal CA1 region were involved in the modulation of the hippocampal neural network during different states.

  9. Ripple-associated high-firing interneurons in the hippocampal CA1 region

    Institute of Scientific and Technical Information of China (English)

    WANG Ying; ZHANG Lu; PAN JingWei; XIE Kun; LI ShiQi; WANG ZhiRu; LIN LongNian

    2008-01-01

    By simultaneously recording the activity of individual neurons and field potentials in freely behaving mice, we found two types of interneurons firing at high frequency in the hippocampal CA1 region,which had high correlations with characteristic sharp wave-associated ripple oscillations (100-250 Hz)during slow-wave sleep. The firing of these two types of interneurons highly synchronized with ripple oscillations during slow-wave sleep, with strongly increased firing rates corresponding to individual ripple episodes. Interneuron type Ⅰ had at most one spike in each sub-ripple cycle of ripple episodes and the peak firing rate was 310±33.17 Hz. Interneuron type Ⅱ had one or two spikes in each sub-ripple cycle and the peak firing rate was 410±47.61 Hz. During active exploration, their firing was phase locked to theta oscillations with the highest probability at the trough of theta wave. Both two types of interneurons increased transiently their firing rates responding to the startling shake stimuli. The results showed that these two types of high-frequency interneurone in the hippocsmpal CA1 region were involved in the modulation of the hippocampal neural network during different states.

  10. A High Power Density Integrated Charger for Electric Vehicles with Active Ripple Compensation

    Directory of Open Access Journals (Sweden)

    Liwen Pan

    2015-01-01

    Full Text Available This paper suggests a high power density on-board integrated charger with active ripple compensation circuit for electric vehicles. To obtain a high power density and high efficiency, silicon carbide devices are reported to meet the requirement of high-switching-frequency operation. An integrated bidirectional converter is proposed to function as AC/DC battery charger and to transfer energy between battery pack and motor drive of the traction system. In addition, the conventional H-bridge circuit suffers from ripple power pulsating at second-order line frequency, and a scheme of active ripple compensation circuit has been explored to solve this second-order ripple problem, in which a pair of power switches shared traction mode, a ripple energy storage capacitor, and an energy transfer inductor. Simulation results in MATLAB/Simulink validated the eligibility of the proposed topology. The integrated charger can work as a 70 kW motor drive circuit or a converter with an active ripple compensation circuit for 3 kW charging the battery. The impact of the proposed topology and control strategy on the integrated charger power losses, efficiency, power density, and thermal performance has also been analysed and simulated.

  11. Jianshangou Bed of the Yixian Formation in West Liaoning, China

    Institute of Scientific and Technical Information of China (English)

    CHEN; Peiji; WANG; Qifei; ZHANG; Haichun; GAO; Meizhen; LI

    2005-01-01

    The Jianshangou Bed is a set of fossil-bearing sedimentary interlayers of the basal volcano-sedimentary deposits of Yixian Formation in western Liaoning. It is rich in volcanic composition and consists of upper and lower grey-black shale, basal sandy conglomerate, top tuffaceous sandstone, middle massive silty mudstone and siltstone, as well as andesite, with a thickness of 28-95 m. The Jianshangou Bed is famous all over the world for its bearing early birds, angiosperms and feathered dinosaurs, and it also yields bivalves, gastropods, conchostracans, ostracods, shrimps, insects, fish, amphibians, primitive mammals and other reptiles.These fossils are typical representatives of the Late Mesozoic Jehol Biota from eastern Asia. The Chaomidianzi and Sihetun formations, proposed in recent years, are regarded as the junior synonyms of the Jianshangou Bed. The Jehol Biota is endemic to eastern Asia, however, it has a large geographic distribution, more than half of the European territory. Many species of the biota have close relationships with the late Jurassic European counterparts, e.g. both Confuciusornis and Archaeopteryx are primitive birds, Sinosauropteryx has a similar skeleton construction with Compsognathus, the ostracode assemblage from the Jianshangou Bed is close to that from the Purbeck Bed in England, and Aeschnidium occurs in both the Jianshangou Bed and Solnhofen of Germany. Based on the biostratigraphic correlation, the Jianshangou Bed is more probably late Tithonian in age. The latest zircon U-Pb dating of the Jianshangou Bed gives 125.2 Ma, and is close to the feldspar Ar/Ar dating of 124.6 Ma. A glauconite dating of 125 Ma was once got from England near the J/K boundary within the Purbeck Bed, so it is still problematic to place the J/K boundary at 130, 135, 137, 142 or 145.5 Ma in the International Stratigraphic Charts.

  12. Self-organized surface ripple pattern formation by ion implantation

    Science.gov (United States)

    Hofsäss, Hans; Zhang, Kun; Bobes, Omar

    2016-10-01

    Ion induced ripple pattern formation on solid surfaces has been extensively studied in the past and the theories describing curvature dependent ion erosion as well as redistribution of recoil atoms have been very successful in explaining many features of the pattern formation. Since most experimental studies use noble gas ion irradiation, the incorporation of the ions into the films is usually neglected. In this work we show that the incorporation or implantation of non-volatile ions also leads to a curvature dependent term in the equation of motion of a surface height profile. The implantation of ions can be interpreted as a negative sputter yield; and therefore, the effect of ion implantation is opposite to the one of ion erosion. For angles up to about 50°, implantation of ions stabilizes the surface, whereas above 50°, ion implantation contributes to the destabilization of the surface. We present simulations of the curvature coefficients using the crater function formalism and we compare the simulation results to the experimental data on the ion induced pattern formation using non-volatile ions. We present several model cases, where the incorporation of ions is a crucial requirement for the pattern formation.

  13. Brazilian sandy beach macrofauna production: a review

    Directory of Open Access Journals (Sweden)

    Marcelo Petracco

    2012-12-01

    Full Text Available The state of the art of the studies on the production of Brazilian sandy beach macrofauna was analyzed on the basis of the data available in the literature. For this purpose, the representativeness of the production dataset was examined by latitudinal distribution, degree of exposure and morphodynamic state of beaches, taxonomic groups, and methods employed. A descriptive analysis was, further, made to investigate the trends in production of the more representative taxonomic groups and species of sandy beach macrofauna. A total of 69 macrofauna annual production estimates were obtained for 38 populations from 25 studies carried out between 22º56'S and 32º20'S. Production estimates were restricted to populations on beaches located on the southern and southeastern Brazilian coast. Most of the populations in the dataset inhabit exposed dissipative sandy beaches and are mainly represented by mollusks and crustaceans, with a smaller number of polychaetes. The trends in production among taxonomic groups follow a similar pattern to that observed on beaches throughout the world, with high values for bivalves and decapods. The high turnover rate (P/B ratio of the latter was due to the presence of several populations of the mole crab Emerita brasiliensis, which can attain high values of productivity, in the dataset. Most of the studies focus on the comparison of production and, especially, of P/B ratio according to life history traits in populations of the same species/taxonomic group. Despite the importance of life history-production studies, other approaches, such as the effect of man-induce disturbances on the macrofauna, should be undertaken in these threatened environments.O estado da arte dos estudos de produção da macrofauna de praias arenosas brasileiras foi analisado a partir de informações disponíveis na literatura. Para essa finalidade, a representatividade dos dados de produção foi examinada de acordo com a distribuição latitudinal

  14. A note on the solution of water wave scattering problem involving small deformation on a porous channel-bed

    Science.gov (United States)

    Mohapatra, S.; Sarangi, M. R.

    2017-03-01

    The solution of water wave scattering problem involving small deformation on a porous bed in a channel, where the upper surface is bounded above by an infinitely extent rigid horizontal surface, is studied here within the framework of linearized water wave theory. In such a situation, there exists only one mode of waves propagating on the porous surface. A simplified perturbation analysis, involving a small parameter ɛ ( ≪ 1), which measures the smallness of the deformation, is employed to reduce the governing Boundary Value Problem (BVP) to a simpler BVP for the first-order correction of the potential function. The first-order potential function and, hence, the first-order reflection and transmission coefficients are obtained by the method based on Fourier transform technique as well as Green's integral theorem with the introduction of appropriate Green's function. Two special examples of bottom deformation: the exponentially damped deformation and the sinusoidal ripple bed, are considered to validate the results. For the particular example of a patch of sinusoidal ripples, the resonant interaction between the bed and the upper surface of the fluid is attained in the neighborhood of a singularity, when the ripples wavenumbers of the bottom deformation become approximately twice the components of the incident field wavenumber along the positive x-direction. Also, the main advantage of the present study is that the results for the values of reflection and transmission coefficients are found to satisfy the energy-balance relation almost accurately.

  15. Sandy River Delta Habitat Restoration Project, Annual Report 2001.

    Energy Technology Data Exchange (ETDEWEB)

    Kelly, Virginia; Dobson, Robin L.

    2002-11-01

    The Sandy River Delta is located at the confluence of the Sandy and Columbia Rivers, just east of Troutdale, Oregon. It comprises about 1,400 land acres north of Interstate 84, managed by the USDA Forest Service, and associated river banks managed by the Oregon Division of State Lands. Three islands, Gary, Flag and Catham, managed by Metro Greenspaces and the State of Oregon lie to the east, the Columbia River lies to the north and east, and the urbanized Portland metropolitan area lies to the west across the Sandy River. Sandy River Delta was historically a wooded, riparian wetland with components of ponds, sloughs, bottomland woodland, oak woodland, prairie, and low and high elevation floodplain. It has been greatly altered by past agricultural practices and the Columbia River hydropower system. Restoration of historic landscape components is a primary goal for this land. The Forest Service is currently focusing on restoration of riparian forest and wetlands. Restoration of open upland areas (meadow/prairie) would follow substantial completion of the riparian and wetland restoration. The Sandy River Delta is a former pasture infested with reed canary grass, blackberry and thistle. The limited over story is native riparian species such as cottonwood and ash. The shrub and herbaceous layers are almost entirely non-native, invasive species. Native species have a difficult time naturally regenerating in the thick, competing reed canary grass, Himalayan blackberry and thistle. A system of drainage ditches installed by past owners drains water from historic wetlands. The original channel of the Sandy River was diked in the 1930's, and the river diverted into the ''Little Sandy River''. The original Sandy River channel has subsequently filled in and largely become a slough. The FS acquired approximately 1,400 acres Sandy River Delta (SRD) in 1991 from Reynolds Aluminum (via the Trust for Public Lands). The Delta had been grazed for many years

  16. Hurricane Sandy Washover Deposits on Southern Long Beach Island, NJ

    Science.gov (United States)

    Bishop, J. M.; Richmond, B. M.; Kane, H. H.; Lunghino, B.

    2015-12-01

    Hurricane Sandy washover deposits were investigated at Forsyth National Wildlife Refuge (FNWR) on Southern Long Beach Island, New Jersey in order to map deposit thickness and characterize the sedimentary deposits. FNWR was chosen as a field area because there has been relatively little anthropogenic shoreline modification since washover deposition from Hurricane Sandy. Sediment, elevation, and geophysical data were collected during the April 2015 field campaign, approximately two and a half years after the storm. Sediment deposit data included trenches, stratigraphic descriptions, bulk sediment samples, push cores, Russian cores, and photos. Computed tomography (CT) scanning was conducted on push cores in order to acquire high resolution imaging of density, grain size, and sedimentary structure. Profiles of washover elevation were measured using Differential GPS with Real Time Kinematic processing. Ground Penetrating Radar data was collected to image the depth of the deposit and identify sedimentary structures. These data sets are compared to pre- and post -Sandy lidar surveys in order to determine post-Sandy modification in the two and a half years following the hurricane. We compare sediment thickness and sedimentary characteristics to hurricane Sandy deposits elsewhere along the U.S. eastern seaboard and to tsunami deposits.

  17. EAARL Coastal Topography - Sandy Hook 2007

    Science.gov (United States)

    Nayegandhi, Amar; Brock, John C.; Wright, C. Wayne; Stevens, Sara; Yates, Xan; Bonisteel, Jamie M.

    2008-01-01

    These remotely sensed, geographically referenced elevation measurements of Lidar-derived topography were produced as a collaborative effort between the U.S. Geological Survey (USGS), Florida Integrated Science Center (FISC), St. Petersburg, FL; the National Park Service (NPS), Northeast Coastal and Barrier Network, Kingston, RI; and the National Aeronautics and Space Administration (NASA), Wallops Flight Facility, VA. This project provides highly detailed and accurate datasets of Gateway National Recreation Area's Sandy Hook Unit in New Jersey, acquired on May 16, 2007. The datasets are made available for use as a management tool to research scientists and natural resource managers. An innovative airborne Lidar instrument originally developed at the NASA Wallops Flight Facility, and known as the Experimental Advanced Airborne Research Lidar (EAARL) was used during data acquisition. The EAARL system is a raster-scanning, waveform-resolving, green-wavelength (532-nanometer) Lidar designed to map near-shore bathymetry, topography, and vegetation structure simultaneously. The EAARL sensor suite includes the raster-scanning, water-penetrating full-waveform adaptive Lidar, a down-looking red-green-blue (RGB) digital camera, a high-resolution multi-spectral color infrared (CIR) camera, two precision dual-frequency kinematic carrier-phase GPS receivers and an integrated miniature digital inertial measurement unit, which provide for submeter georeferencing of each laser sample. The nominal EAARL platform is a twin-engine Cessna 310 aircraft, but the instrument may be deployed on a range of light aircraft. A single pilot, a Lidar operator, and a data analyst constitute the crew for most survey operations. This sensor has the potential to make significant contributions in measuring sub-aerial and submarine coastal topography within cross-environmental surveys. Elevation measurements were collected over the survey area using the EAARL system, and the resulting data were then

  18. A Non-Unity Torque Sharing Function for Torque Ripple Minimization of Switched Reluctance Generators in Wind Power Systems

    Directory of Open Access Journals (Sweden)

    Hye-Ung Shin

    2015-10-01

    Full Text Available This paper deals with a new torque ripple minimization method for a Switched Reluctance Generator (SRG. Although, the SRG has many advantages including simple and robust construction, and high power density as a generator, it has not been widely employed in the industry. One of the major drawbacks of the SRG is its high torque ripple that results in high noise operation of the generator. In this paper, a non-unity Torque Sharing Function (TSF is proposed to minimize the torque ripple over a wide speed range of operation. Simulations as well as experimental results are presented to verify the effectiveness of the proposed torque ripple minimization technique.

  19. Plasmonic and Mie scattering control of far-field interference for regular ripple formation on various material substrates.

    Science.gov (United States)

    Obara, Go; Maeda, Naoki; Miyanishi, Tomoya; Terakawa, Mitsuhiro; Nedyalkov, Nikolay N; Obara, Minoru

    2011-09-26

    We present experimental and theoretical results on plasmonic control of far-field interference for regular ripple formation on semiconductor and metal. Experimental observation of interference ripple pattern on Si substrate originating from the gold nanosphere irradiated by femtosecond laser is presented. Gold nanosphere is found to be an origin for ripple formation. Arbitrary intensity ripple patterns are theoretically controllable by depositing desired plasmonic and Mie scattering far-field pattern generators. The plasmonic far-field generation is demonstrated not only by metallic nanostructures but also by the controlled surface structures such as ridge and trench structures on various material substrates.

  20. Serotonin dependent masking of hippocampal sharp wave ripples.

    Science.gov (United States)

    ul Haq, Rizwan; Anderson, Marlene L; Hollnagel, Jan-Oliver; Worschech, Franziska; Sherkheli, Muhammad Azahr; Behrens, Christoph J; Heinemann, Uwe

    2016-02-01

    Sharp wave ripples (SPW-Rs) are thought to play an important role in memory consolidation. By rapid replay of previously stored information during slow wave sleep and consummatory behavior, they result from the formation of neural ensembles during a learning period. Serotonin (5-HT), suggested to be able to modify SPW-Rs, can affect many neurons simultaneously by volume transmission and alter network functions in an orchestrated fashion. In acute slices from dorsal hippocampus, SPW-Rs can be induced by repeated high frequency stimulation that induces long-lasting LTP. We used this model to study SPW-R appearance and modulation by 5-HT. Although stimulation in presence of 5-HT permitted LTP induction, SPW-Rs were "masked"--but appeared after 5-HT wash-out. This SPW-R masking was dose dependent with 100 nM 5-HT being sufficient--if the 5-HT re-uptake inhibitor citalopram was present. Fenfluramine, a serotonin releaser, could also mask SPW-Rs. Masking was due to 5-HT1A and 5-HT2A/C receptor activation. Neither membrane potential nor membrane conductance changes in pyramidal cells caused SPW-R blockade since both remained unaffected by combining 5-HT and citalopram. Moreover, 10 and 30 μM 5-HT mediated SPW-R masking preceded neuronal hyperpolarization and involved reduced presynaptic transmitter release. 5-HT, as well as a 5-HT1A agonist, augmented paired pulse facilitation and affected the coefficient of variance. Spontaneous SPW-Rs in mice hippocampal slices were also masked by 5-HT and fenfluramine. While neuronal ensembles can acquire long lasting LTP during higher 5-HT levels, lower 5-HT levels enable neural ensembles to replay previously stored information and thereby permit memory consolidation memory.

  1. Did Hurricane Sandy influence the 2012 US presidential election?

    Science.gov (United States)

    Hart, Joshua

    2014-07-01

    Despite drawing on a common pool of data, observers of the 2012 presidential campaign came to different conclusions about whether, how, and to what extent "October surprise" Hurricane Sandy influenced the election. The present study used a mixed correlational and experimental design to assess the relation between, and effect of, the salience of Hurricane Sandy on attitudes and voting intentions regarding President Barack Obama and Mitt Romney in a large sample of voting-aged adults. Results suggest that immediately following positive news coverage of Obama's handling of the storm's aftermath, Sandy's salience positively influenced attitudes toward Obama, but that by election day, reminders of the hurricane became a drag instead of a boon for the President. In addition to theoretical implications, this study provides an example of how to combine methodological approaches to help answer questions about the impact of unpredictable, large-scale events as they unfold.

  2. Hurricane Sandy, Disaster Preparedness, and the Recovery Model.

    Science.gov (United States)

    Pizzi, Michael A

    2015-01-01

    Hurricane Sandy was the second largest and costliest hurricane in U.S. history to affect multiple states and communities. This article describes the lived experiences of 24 occupational therapy students who lived through Hurricane Sandy using the Recovery Model to frame the research. Occupational therapy student narratives were collected and analyzed using qualitative methods and framed by the Recovery Model. Directed content and thematic analysis was performed using the 10 components of the Recovery Model. The 10 components of the Recovery Model were experienced by or had an impact on the occupational therapy students as they coped and recovered in the aftermath of the natural disaster. This study provides insight into the lived experiences and recovery perspectives of occupational therapy students who experienced Hurricane Sandy. Further research is indicated in applying the Recovery Model to people who survive disasters. Copyright © 2015 by the American Occupational Therapy Association, Inc.

  3. Convective-absolute nature of ripple instabilities on ice and icicles

    Science.gov (United States)

    Camporeale, Carlo; Vesipa, Riccardo; Ridolfi, Luca

    2017-05-01

    Film hydrodynamics is crucial in water-driven morphological pattern formation. A prominent example is given by icicle ripples and ice ripples, which are regular patterns developing on freezing-melting inclined surfaces bounding open-channel flows. By a suitable mathematical model based on conservation principles and the use of the cusp map method, in this paper we address the convective-absolute nature of these two kinds of instabilities. The obtained results show that icicle ripples, which develop at inverted (overhang) conditions, have subcentimetric wavelengths which are unstable when the Reynolds number of the liquid flow (Re ) is small and the supercooling is intensive. With the increase in Re , the instability switches from absolute to convective. Ice ripples instead exhibit the opposite dependance on Re and are highly affected by the surface slope. In addition, the evaluation of the so-called absolute wave number, which is responsible for the asymptotic impulse response, suggests a different interpretation of some recent experiments about ice ripples.

  4. Pitch strength and pitch dominance of iterated rippled noises in hearing-impaired listeners.

    Science.gov (United States)

    Leek, M R; Summers, V

    2001-06-01

    Reports using a variety of psychophysical tasks indicate that pitch perception by hearing-impaired listeners may be abnormal, contributing to difficulties in understanding speech and enjoying music. Pitches of complex sounds may be weaker and more indistinct in the presence of cochlear damage, especially when frequency regions are affected that form the strongest basis for pitch perception in normal-hearing listeners. In this study, the strength of the complex pitch generated by iterated rippled noise was assessed in normal-hearing and hearing-impaired listeners. Pitch strength was measured for broadband noises with spectral ripples generated by iteratively delaying a copy of a given noise and adding it back into the original. Octave-band-pass versions of these noises also were evaluated to assess frequency dominance regions for rippled-noise pitch. Hearing-impaired listeners demonstrated consistently weaker pitches in response to the rippled noises relative to pitch strength in normal-hearing listeners. However, in most cases, the frequency regions of pitch dominance, i.e., strongest pitch, were similar to those observed in normal-hearing listeners. Except where there exists a substantial sensitivity loss, contributions from normal pitch dominance regions associated with the strongest pitches may not be directly related to impaired spectral processing. It is suggested that the reduced strength of rippled-noise pitch in listeners with hearing loss results from impaired frequency resolution and possibly an associated deficit in temporal processing.

  5. Adhesion modification of neural stem cells induced by nanoscale ripple patterns

    Science.gov (United States)

    Pedraz, P.; Casado, S.; Rodriguez, V.; Giordano, M. C.; Buatier de Mongeot, F.; Ayuso-Sacido, A.; Gnecco, E.

    2016-03-01

    We have studied the influence of anisotropic nanopatterns (ripples) on the adhesion and morphology of mouse neural stem cells (C17.2) on glass substrates using cell viability assay, optical microscopy and atomic force microscopy. The ripples were produced by defocused ion beam sputtering with inert Ar ions, which physically remove atoms from the surface at the energy of 800 eV. The ripple periodicity (∼200 nm) is comparable to the thickness of the cytoplasmatic microspikes (filopodia) which link the stem cells to the substrate. All methods show that the cell adhesion is significantly lowered compared to the same type of cells on flat glass surfaces. Furthermore, the AFM analysis reveals that the filopodia tend to be trapped parallel or perpendicular to the ripples, which limits the spreading of the stem cell on the rippled substrate. This opens the perspective of controlling the micro-adhesion of stem cells and the orientation of their filopodia by tuning the anisotropic substrate morphology without chemical reactions occurring at the surface.

  6. Learning-induced plasticity regulates hippocampal sharp wave-ripple drive.

    Science.gov (United States)

    Girardeau, Gabrielle; Cei, Anne; Zugaro, Michaël

    2014-04-01

    Hippocampal sharp wave-ripples (SPW-Rs) and associated place-cell reactivations are crucial for spatial memory consolidation during sleep and rest. However, it remains unclear how learning and consolidation requirements influence and regulate subsequent SPW-R activity. Indeed, SPW-R activity has been observed not only following complex behavioral tasks, but also after random foraging in familiar environments, despite markedly different learning requirements. Because transient increases in SPW-R rates have been reported following training on memory tasks, we hypothesized that SPW-R activity following learning (but not routine behavior) could involve specific regulatory processes related to ongoing consolidation. Interfering with ripples would then result in a dynamic compensatory response only when initial memory traces required consolidation. Here we trained rats on a spatial memory task, and showed that subsequent sleep periods where ripple activity was perturbed by timed electrical stimulation were indeed characterized by increased SPW-R occurrence rates compared with control sleep periods where stimulations were slightly delayed in time and did not interfere with ripples. Importantly, this did not occur following random foraging in a familiar environment. We next showed that this dynamic response was abolished following injection of an NMDA receptor blocker (MK-801) before, but not after training. Our results indicate that NMDA receptor-dependent processes occurring during learning, such as network "tagging" and plastic changes, regulate subsequent ripple-mediated consolidation of spatial memory during sleep.

  7. Synaptic gating at axonal branches, and sharp-wave ripples with replay: a simulation study.

    Science.gov (United States)

    Vladimirov, Nikita; Tu, Yuhai; Traub, Roger D

    2013-11-01

    Mechanisms of place cell replay occurring during sharp-wave ripples (SPW-Rs) remain obscure due to the fact that ripples in vitro depend on non-synaptic mechanisms, presumably via axo-axonal gap junctions between pyramidal cells. We suggest a model of in vivo SPW-Rs in which synaptic excitatory post-synaptic potentials (EPSPs) control the axonal spiking of cells in SPW-Rs: ripple activity remains hidden in the network of axonal collaterals (connected by gap junctions) due to conduction failures, unless there is a sufficient dendritic EPSP. The EPSP brings the axonal branching point to threshold, and action potentials from the collateral start to propagate to the soma and to the distal axon. The model coherently explains multiple experimental data on SPW-Rs, both in vitro and in vivo. The mechanism of synaptic gating leads to the following implication: a sequence of pyramidal cells can be replayed at ripple frequency by the superposition of subthreshold dendritic EPSPs and ripple activity in the axonal plexus. Replay is demonstrated in both forward and reverse directions. We discuss several testable predictions. In general, the mechanism of synaptic gating suggests that pyramidal cells under certain conditions can act like a transistor.

  8. Hippocampal ripple-contingent training accelerates trace eyeblink conditioning and retards extinction in rabbits.

    Science.gov (United States)

    Nokia, Miriam S; Penttonen, Markku; Wikgren, Jan

    2010-08-25

    There are at least two distinct oscillatory states of the hippocampus that are related to distinct behavioral patterns. Theta (4-12 Hz) oscillation has been suggested to indicate selective attention during which the animal concentrates on some features of the environment while suppressing reactivity to others. In contrast, sharp-wave ripples ( approximately 200 Hz) can be seen in a state in which the hippocampus is at its most responsive to any kind of afferent stimulation. In addition, external stimulation tends to evoke and reset theta oscillation, the phase of which has been shown to modulate synaptic plasticity in the hippocampus. Theoretically, training on a hippocampus-dependent learning task contingent upon ripples could enhance learning rate due to elevated responsiveness and enhanced phase locking of the theta oscillation. We used a brain-computer interface to detect hippocampal ripples in rabbits to deliver trace eyeblink conditioning and extinction trials selectively contingent upon them. A yoked control group was trained regardless of their ongoing neural state. Ripple-contingent training expedited acquisition of the conditioned response early in training and evoked stronger theta-band phase locking to the conditioned stimulus. Surprisingly, ripple-contingent training also resulted in slower extinction in well trained animals. We suggest that the ongoing oscillatory activity in the hippocampus determines the extent to which a stimulus can induce a phase reset of the theta oscillation, which in turn is the determining factor of learning rate in trace eyeblink conditioning.

  9. Diversity of sharp-wave-ripple LFP signatures reveals differentiated brain-wide dynamical events.

    Science.gov (United States)

    Ramirez-Villegas, Juan F; Logothetis, Nikos K; Besserve, Michel

    2015-11-17

    Sharp-wave-ripple (SPW-R) complexes are believed to mediate memory reactivation, transfer, and consolidation. However, their underlying neuronal dynamics at multiple scales remains poorly understood. Using concurrent hippocampal local field potential (LFP) recordings and functional MRI (fMRI), we study local changes in neuronal activity during SPW-R episodes and their brain-wide correlates. Analysis of the temporal alignment between SPW and ripple components reveals well-differentiated SPW-R subtypes in the CA1 LFP. SPW-R-triggered fMRI maps show that ripples aligned to the positive peak of their SPWs have enhanced neocortical metabolic up-regulation. In contrast, ripples occurring at the trough of their SPWs relate to weaker neocortical up-regulation and absent subcortical down-regulation, indicating differentiated involvement of neuromodulatory pathways in the ripple phenomenon mediated by long-range interactions. To our knowledge, this study provides the first evidence for the existence of SPW-R subtypes with differentiated CA1 activity and metabolic correlates in related brain areas, possibly serving different memory functions.

  10. Diversity of sharp-wave–ripple LFP signatures reveals differentiated brain-wide dynamical events

    Science.gov (United States)

    Ramirez-Villegas, Juan F.; Logothetis, Nikos K.; Besserve, Michel

    2015-01-01

    Sharp-wave–ripple (SPW-R) complexes are believed to mediate memory reactivation, transfer, and consolidation. However, their underlying neuronal dynamics at multiple scales remains poorly understood. Using concurrent hippocampal local field potential (LFP) recordings and functional MRI (fMRI), we study local changes in neuronal activity during SPW-R episodes and their brain-wide correlates. Analysis of the temporal alignment between SPW and ripple components reveals well-differentiated SPW-R subtypes in the CA1 LFP. SPW-R–triggered fMRI maps show that ripples aligned to the positive peak of their SPWs have enhanced neocortical metabolic up-regulation. In contrast, ripples occurring at the trough of their SPWs relate to weaker neocortical up-regulation and absent subcortical down-regulation, indicating differentiated involvement of neuromodulatory pathways in the ripple phenomenon mediated by long-range interactions. To our knowledge, this study provides the first evidence for the existence of SPW-R subtypes with differentiated CA1 activity and metabolic correlates in related brain areas, possibly serving different memory functions. PMID:26540729

  11. Hippocampal sharp wave/ripples during sleep for consolidation of associative memory.

    Directory of Open Access Journals (Sweden)

    Wiâm Ramadan

    Full Text Available The beneficial effect of sleep on memory has been well-established by extensive research on humans, but the neurophysiological mechanisms remain a matter of speculation. This study addresses the hypothesis that the fast oscillations known as ripples recorded in the CA1 region of the hippocampus during slow wave sleep (SWS may provide a physiological substrate for long term memory consolidation. We trained rats in a spatial discrimination task to retrieve palatable reward in three fixed locations. Hippocampal local field potentials and cortical EEG were recorded for 2 h after each daily training session. There was an increase in ripple density during SWS after early training sessions, in both trained rats and in rats randomly rewarded for exploring the maze. In rats learning the place -reward association, there was a striking further significant increase in ripple density correlated with subsequent improvements in behavioral performance as the rat learned the spatial discrimination aspect of the task. The results corroborate others showing an experience-dependent increase in ripple activity and associated ensemble replay after exploratory activity, but in addition, for the first time, reveal a clear further increase in ripple activity related to associative learning based on spatial discrimination.

  12. A ripple-spreading genetic algorithm for the aircraft sequencing problem.

    Science.gov (United States)

    Hu, Xiao-Bing; Di Paolo, Ezequiel A

    2011-01-01

    When genetic algorithms (GAs) are applied to combinatorial problems, permutation representations are usually adopted. As a result, such GAs are often confronted with feasibility and memory-efficiency problems. With the aircraft sequencing problem (ASP) as a study case, this paper reports on a novel binary-representation-based GA scheme for combinatorial problems. Unlike existing GAs for the ASP, which typically use permutation representations based on aircraft landing order, the new GA introduces a novel ripple-spreading model which transforms the original landing-order-based ASP solutions into value-based ones. In the new scheme, arriving aircraft are projected as points into an artificial space. A deterministic method inspired by the natural phenomenon of ripple-spreading on liquid surfaces is developed, which uses a few parameters as input to connect points on this space to form a landing sequence. A traditional GA, free of feasibility and memory-efficiency problems, can then be used to evolve the ripple-spreading related parameters in order to find an optimal sequence. Since the ripple-spreading model is the centerpiece of the new algorithm, it is called the ripple-spreading GA (RSGA). The advantages of the proposed RSGA are illustrated by extensive comparative studies for the case of the ASP.

  13. Family Structures, Relationships, and Housing Recovery Decisions after Hurricane Sandy

    Directory of Open Access Journals (Sweden)

    Ali Nejat

    2016-04-01

    Full Text Available Understanding of the recovery phase of a disaster cycle is still in its infancy. Recent major disasters such as Hurricane Sandy have revealed the inability of existing policies and planning to promptly restore infrastructure, residential properties, and commercial activities in affected communities. In this setting, a thorough grasp of housing recovery decisions can lead to effective post-disaster planning by policyholders and public officials. The objective of this research is to integrate vignette and survey design to study how family bonds affected rebuilding/relocating decisions after Hurricane Sandy. Multinomial logistic regression was used to investigate respondents’ family structures before Sandy and explore whether their relationships with family members changed after Sandy. The study also explores the effect of the aforementioned relationship and its changes on households’ plans to either rebuild/repair their homes or relocate. These results were compared to another multinomial logistic regression which was applied to examine the impact of familial bonds on respondents’ suggestions to a vignette family concerning rebuilding and relocating after a hurricane similar to Sandy. Results indicate that respondents who lived with family members before Sandy were less likely to plan for relocating than those who lived alone. A more detailed examination shows that this effect was driven by those who improved their relationships with family members; those who did not improve their family relationships were not significantly different from those who lived alone, when it came to rebuilding/relocation planning. Those who improved their relationships with family members were also less likely to suggest that the vignette family relocate. This study supports the general hypothesis that family bonds reduce the desire to relocate, and provides empirical evidence that family mechanisms are important for the rebuilding/relocating decision

  14. Fluidized bed calciner apparatus

    Science.gov (United States)

    Owen, Thomas J.; Klem, Jr., Michael J.; Cash, Robert J.

    1988-01-01

    An apparatus for remotely calcining a slurry or solution feed stream of toxic or hazardous material, such as ammonium diurante slurry or uranyl nitrate solution, is disclosed. The calcining apparatus includes a vertical substantially cylindrical inner shell disposed in a vertical substantially cylindrical outer shell, in which inner shell is disposed a fluidized bed comprising the feed stream material to be calcined and spherical beads to aid in heat transfer. Extending through the outer and inner shells is a feed nozzle for delivering feed material or a cleaning chemical to the beads. Disposed in and extending across the lower portion of the inner shell and upstream of the fluidized bed is a support member for supporting the fluidized bed, the support member having uniform slots for directing uniform gas flow to the fluidized bed from a fluidizing gas orifice disposed upstream of the support member. Disposed in the lower portion of the inner shell are a plurality of internal electric resistance heaters for heating the fluidized bed. Disposed circumferentially about the outside length of the inner shell are a plurality of external heaters for heating the inner shell thereby heating the fluidized bed. Further, connected to the internal and external heaters is a means for maintaining the fluidized bed temperature to within plus or minus approximately 25.degree. C. of a predetermined bed temperature. Disposed about the external heaters is the outer shell for providing radiative heat reflection back to the inner shell.

  15. Three perspectives on bedload transport at a sandy gravel beach (Advocate Harbour, Nova Scotia) with focus on sediment properties

    Science.gov (United States)

    Stark, N.; Hay, A. E.; Guest, T.; Hatcher, M. G.; Cheel, R. A.; Barclay, D. J.; Zedel, L. J.; Lake, C. B.

    2012-12-01

    Bedload transport is the major transport mode for coarse sediment in coastal zones. Understanding its mechanisms requires knowledge of the driving force (hydrodynamics), the stabilizing force (sediment properties), and the bed characteristics (bed roughness, bed slope, bedforms). During a 3-week-long field experiment at Advocate Beach, Nova Scotia, bedload transport was targeted from three perspectives: (i) The water column: using a new acoustic Doppler profiler (MFDop), 3D flow velocities were monitored to assess bed shear stress over a range of conditions. Additionally, sediment concentrations close to the bed (~10 cm) were determined by water sampling under calm conditions (0.15-0.6 g/l) and within the shorebreak (1-50 g/l). (ii) The bed: rotary sonars were used to observe the development of ripples and bed elevation change as a measure of ongoing sediment transport. Also, the net displacement of 20 marked cobbles on the seabed surface was measured, revealing significant changes in transport direction and distance (ranging from 0 to 50 m). (iii) The sediment properties: grain size ranged from medium sand to small cobbles. The finer-grained particles were rounded, but showed an elliptic to plate-like shape. Grain size distributions varied significantly across the shoreface as well as under different hydrodynamic conditions. Observed beach cusps were strongly sorted (coarse pebbles at the horns, coarse sand in the bays). Direct shear tests were carried out to determine peak shear strengths of the sediment and friction angles. Peak shear strengths under low normal stress (0.47 kPa) can be compared best to surficial sediment conditions, and did not exceed 9 kPa in the case of the sands. The sediment showed a surprisingly strong dilative behavior during shearing and high friction angles considering the grain size, the low load and low density conditions during the tests. Thus, grain shape and the particle re-organization under shearing played important roles. Finally

  16. Sandy Deposits of the 2006 Java Tsunami

    Science.gov (United States)

    Setja Atmadja, C. M.; Yulianto, E.

    2007-05-01

    A field reconnaissance was performed out a week after Java tsunami on July, last year. It focused on documentation of sedimentary deposit as the first step to study delineate tsunami history in extend to tsunami hazard assessments. In a region with tremendous tsunami thread, the 2006 Java tsunami still gave a shock with at least 650 death tolls at 300 km affected coast line. The slight felt shaking onshore and unobvious leading recession of sea water were probably the reason as these were the reverse indications of tsunami to the lessons learned from the great Sumatra 2004 event. In addition, although tsunami of similar size have struck the southern coast of Java at least twice in the last century, in 1921 and 1994, tsunami history and the potential threat is still unknown to local population. Three shore normal transects across coastal plain were made in the two affected sites to exhibit the recent tsunami deposit thickness, internal layering, and landward extent. During the documentation, we also discovered two additional sand beds at the end of 2006 deposit landward extent in greater depth. All this information may provides preliminary information to better identify the geologic traces of earlier Javanese tsunami which in turn may help constructing Java's tsunami history.

  17. Magnetic anisotropies in ferromagnetic and exchange-coupled systems on rippled surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Liedke, Maciej Oskar; Liedke, Bartosz; Marko, Daniel; Keller, Adrian; Muecklich, Arndt; Facsko, Stefan; Fassbender, Juergen [FZ Dresden-Rossendorf, FWI, Dresden (Germany); Cizmar, Erik; Zvyagin, Sergei; Wosnitza, Joachim [FZ Dresden-Rossendorf, HLD, Dresden (Germany)

    2008-07-01

    The influence of a surface and interface modulation on the magnetic properties of ferromagnetic materials (Py, Fe and Co) and an exchange bias system (Py/FeMn) is studied. A periodic surface modulation (the so-called ripples) is achieved by low energy ion erosion. Subsequently the magnetic stack is deposited. Due to the film morphology a strong uniaxial anisotropy is induced in the ferromagnetic layers, which is fixed in its orientation along ripples elongation. In the case of the exchange bias system the direction of the induced unidirectional anisotropy can be varied by means of different field annealing cycles. For all mutual orientations both anisotropy contributions are superimposed independently. The angular dependence of the magnetization reversal behavior can be described perfectly by a coherent rotation model. In addition, the magnitude of the uniaxial and the unidirectional anisotropy scales with the step density or wave length of the rippled substrate, which is in full agreement with theoretical predictions.

  18. Analysis of Commutation Torque Ripple Minimization for Brushless DC Motor Based on SEPIC Converter

    Directory of Open Access Journals (Sweden)

    R.Jogarao

    2016-11-01

    Full Text Available Brushless DC Motors (BLDCM are widely used in automated industrial applications like Computer Numerical Control (CNC machinery, aerospace applications and in the field of robotics.But it still suffers from commutation torque which mainly depends on speed and transient line commutation interval. BLDC MOTOR torque ripple causes increased acoustic noise and undesirable speed fluctuation. This paper presents a new circuit topology and dc link voltage current in the control strategy to keep incoming and outgoing phase currents changing at the same rate during commutation. In this paper dc-dc single ended primary inductor converter (SEPIC a switch selection circuit are employed in front of inverter. In order to obtain the desired commutation voltage resulting in reduced commutation torque ripple. Compared with simulation result conventional system and proposed method can obtain desired voltage much faster and minimize commutation torque ripple more efficiently.

  19. Efficient and ripple-mitigating dc-dc converter for residential fuel cell system

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Yong [Danfoss Solar Inverters, Hardware, Jyllandsgade 28, 6400 Soenderborg (Denmark); Choi, Seeyoung [Digital Appliance Division, Samsung Electronics Co. Ltd., Maetan-3Dong, Suwon, Gyeonggi (Korea); Lee, Eunchul [Willings Co. Ltd., SK Ventium, 522 Dangjung-Dong, Gunpo-Si, Gyeonggi-Do (Korea)

    2009-01-15

    Proton exchange membrane fuel cell (PEMFC) systems for residential application require efficient and ripple-mitigating power conditioning system (PCS). The key point to reach it, is the design and control of the dc-dc converter. Based on the theoretical and experimental analysis of the traditional converter, this paper proposes a novel parallel-series full bridge (P-SFB) dc-dc converter, and improves its phase shifting scheme. This paper also proposes a novel controller for low frequency ripple current suppressing applied on the converter. The experimental results verify that, the dc-dc converter achieves a peak efficiency of 95.5%. Therefore PCS's maximum efficiency reaches 92.9%. And the input current ripple is reduced significantly with the new controller. (author)

  20. A Zero Input Current Ripple ZVS/ZCS Boost Converter with Boundary-Mode Control

    Directory of Open Access Journals (Sweden)

    Ching-Ming Lai

    2014-10-01

    Full Text Available In this paper, in order to achieve zero ripple conditions, the use of a ripple mirror (RM circuit for the boost converter is proposed. The operation modes are studied and steady-state analyses performed to show the merits of the proposed converter. It is found that the proposed RM circuit technique can provide much better flexibility than the two-phase interleaved boost converter for locating the zero ripple operating point in the design stage. In addition, the choice of using a boundary-mode control is mainly based on the consideration of achieving both ZVS (zero voltage switching/ZCS (zero current switching soft-switching and constant on-time control for the converter. To verify the performance of the proposed converter, a 48 V input and 200 W/200 V output prototype is constructed. Experimental results verify the effectiveness of the proposed converter.

  1. Dithering Digital Ripple Correlation Control for Photovoltaic Maximum Power Point Tracking

    Energy Technology Data Exchange (ETDEWEB)

    Barth, C; Pilawa-Podgurski, RCN

    2015-08-01

    This study demonstrates a new method for rapid and precise maximum power point tracking in photovoltaic (PV) applications using dithered PWM control. Constraints imposed by efficiency, cost, and component size limit the available PWM resolution of a power converter, and may in turn limit the MPP tracking efficiency of the PV system. In these scenarios, PWM dithering can be used to improve average PWM resolution. In this study, we present a control technique that uses ripple correlation control (RCC) on the dithering ripple, thereby achieving simultaneous fast tracking speed and high tracking accuracy. Moreover, the proposed method solves some of the practical challenges that have to date limited the effectiveness of RCC in solar PV applications. We present a theoretical derivation of the principles behind dithering digital ripple correlation control, as well as experimental results that show excellent tracking speed and accuracy with basic hardware requirements.

  2. High Ripples Reduction in DTC of Induction Motor by Using a New Reduced Switching Table

    Science.gov (United States)

    Mokhtari, Bachir; Benkhoris, Mohamed F.

    2016-05-01

    The direct torque and flux control (DTC) of electrical motors is characterized by ripples of torque and flux. Among the many solutions proposed to reduce them is to use modified switching tables which is very advantageous; because its implementation is easy and requires no additional cost compared to other solutions. This paper proposes a new reduced switching table (RST) to improve the DTC by reducing harmful ripples of torque and flux. This new switching table is smaller than the conventional one (CST) and depends principally at the flux error. This solution is studied by simulation under Matlab/Simulink and experimentally validated on a testbed with DSPACE1103. The results obtained of a DTC with RST applied to a three-phase induction motor (IM) show a good improvement and an effectiveness of proposed solution, the torque ripple decreases about 47% and 3% for the stator flux compared with a basic DTC.

  3. Amplitude equation for under water sand-ripples in one dimension

    DEFF Research Database (Denmark)

    Sand-ripples under oscillatory water flow form periodic patterns with wave lengths primarily controlled by the amplitude d of the water motion. We present an amplitude equation for sand-ripples in one spatial dimension which captures the formation of the ripples as well as secondary bifurcations...... observed when the amplitude $d$ is suddenly varied. The equation has the form h_t=- ε(h-mean(h))+((h_x)^2-1)h_(xx)- h_(xxxx)+ δ((h_x)^2)_(xx) which, due to the first term, is neither completely local (it has long-range coupling through the average height mean(h)) nor has local sand conservation. We argue...

  4. Small interfering ribonucleic acid induces liquid-to-ripple phase transformation in a phospholipid membrane

    Science.gov (United States)

    Choubey, Amit; Nomura, Ken-ichi; Kalia, Rajiv K.; Nakano, Aiichiro; Vashishta, Priya

    2014-09-01

    Small interfering ribonucleic acid (siRNA) molecules play a pivotal role in silencing gene expression via the RNA interference mechanism. A key limitation to the widespread implementation of siRNA therapeutics is the difficulty of delivering siRNA-based drugs to cells. Here, we examine changes in the structure and dynamics of a dipalmitoylphosphatidylcholine bilayer in the presence of a siRNA molecule and mechanical barriers to siRNA transfection in the bilayer. Our all-atom molecular dynamics simulation shows that siRNA induces a liquid crystalline-to-ripple phase transformation in the bilayer. The ripple phase consists of a major region of non-interdigitated and a minor region of interdigitated lipid molecules with an intervening kink. In the ripple phase, hydrocarbon chains of lipid molecules have large compressive stresses, which present a considerable barrier to siRNA transfection.

  5. An Analysis of Ripple and Error Fields Induced by a Blanket in the CFETR

    Science.gov (United States)

    Yu, Guanying; Liu, Xufeng; Liu, Songlin

    2016-10-01

    The Chinese Fusion Engineering Tokamak Reactor (CFETR) is an important intermediate device between ITER and DEMO. The Water Cooled Ceramic Breeder (WCCB) blanket whose structural material is mainly made of Reduced Activation Ferritic/Martensitic (RAFM) steel, is one of the candidate conceptual blanket design. An analysis of ripple and error field induced by RAFM steel in WCCB is evaluated with the method of static magnetic analysis in the ANSYS code. Significant additional magnetic field is produced by blanket and it leads to an increased ripple field. Maximum ripple along the separatrix line reaches 0.53% which is higher than 0.5% of the acceptable design value. Simultaneously, one blanket module is taken out for heating purpose and the resulting error field is calculated to be seriously against the requirement. supported by National Natural Science Foundation of China (No. 11175207) and the National Magnetic Confinement Fusion Program of China (No. 2013GB108004)

  6. Femtosecond laser-induced subwavelength ripples formed by asymmetrical grating splitting

    Science.gov (United States)

    Feng, Pin; Jiang, Lan; Li, Xin; Zhang, Kaihu; Shi, Xuesong; Li, Bo; Lu, Yongfeng

    2016-05-01

    The formation process and mechanism of subwavelength ripples were studied upon irradiation of ZnO by a femtosecond laser (800 nm, 50 fs, 1 kHz). An abnormally asymmetrical grating-splitting phenomenon was discovered. At relatively high laser fluences (F = 0.51-0.63 J/cm2), near-wavelength ripples were split asymmetrically to create subwavelength laser-induced periodic surface structures (LIPSS) with dual gaps (˜230 nm and ˜430 nm) on the primary grooves. At relatively low laser fluences (F = 0.4-0.45 J/cm2), near-wavelength ripples were split symmetrically, leading to the formation of uniform subwavelength structures with a period of ˜340 nm. The splitting phenomena are related to the varying laser beam dose induced by the overlapping during line scanning. The two grating-splitting types further imply that the dominated mechanism for LIPSS formation may be changed under different processing conditions.

  7. DTC Based Induction Motor Speed Control Using 10-Sector Methodology for Torque Ripple Reduction

    Science.gov (United States)

    Pavithra, S.; Dinesh Krishna, A. S.; Shridharan, S.

    2014-09-01

    A direct torque control (DTC) drive allows direct and independent control of flux linkage and electromagnetic torque by the selection of optimum inverter switching modes. It is a simple method of signal processing which gives excellent dynamic performance. Also transformation of coordinates and voltage decoupling are not required. However, the possible discrete inverter switching vectors cannot always generate exact stator voltage required, to obtain the demanded electromagnetic torque and flux linkages. This results in the production of ripples in the torque as well as flux waveforms. In the present paper a torque ripple reduction methodology is proposed. In this method the circular locus of flux phasor is divided into 10 sector as compared to six sector divisions in conventional DTC method. The basic DTC scheme and the 10-sector method are simulated and compared for their performance. An analysis is done with sector increment so that finally the torque ripple varies slightly as the sector is increased.

  8. Energy-separated sequential irradiation for ripple pattern tailoring on silicon surfaces

    Science.gov (United States)

    Kumar, Tanuj; Kumar, Manish; Panchal, Vandana; Sahoo, P. K.; Kanjilal, D.

    2015-12-01

    Nanoscale ripples on semiconductor surfaces have potential application in biosensing and optoelectronics, but suffer from uncontrolled surface-amorphization when prepared by conventional ion-irradiation methods. A two-step, energy-separated sequential-irradiation enables simultaneous control of surface-amorphization and ripple-dimensions on Si(1 0 0). The evolution of ripples using 100 keV Ar+ bombardment and further tuning of the patterns using a sequential-irradiation by 60 keV Ar+ at different fluences are demonstrated. The advantage of this approach as opposed to increased fluence at the same energy is clarified by atomic force microscopy and Rutherford backscattering spectroscopy investigations. The explanation of our findings is presented through DAMAGE simulation.

  9. Disruption of ripple-associated hippocampal activity during rest impairs spatial learning in the rat.

    Science.gov (United States)

    Ego-Stengel, Valérie; Wilson, Matthew A

    2010-01-01

    The hippocampus plays a key role in the acquisition of new memories for places and events. Evidence suggests that the consolidation of these memories is enhanced during sleep. At the neuronal level, reactivation of awake experience in the hippocampus during sharp-wave ripple events, characteristic of slow-wave sleep, has been proposed as a neural mechanism for sleep-dependent memory consolidation. However, a causal relation between sleep reactivation and memory consolidation has not been established. Here we show that disrupting neuronal activity during ripple events impairs spatial learning. We trained rats daily in two identical spatial navigation tasks followed each by a 1-hour rest period. After one of the tasks, stimulation of hippocampal afferents selectively disrupted neuronal activity associated with ripple events without changing the sleep-wake structure. Rats learned the control task significantly faster than the task followed by rest stimulation, indicating that interfering with hippocampal processing during sleep led to decreased learning.

  10. Small interfering ribonucleic acid induces liquid-to-ripple phase transformation in a phospholipid membrane

    Energy Technology Data Exchange (ETDEWEB)

    Choubey, Amit; Nomura, Ken-ichi; Kalia, Rajiv K.; Nakano, Aiichiro; Vashishta, Priya [Collaboratory for Advanced Computing and Simulations, Department of Physics and Astronomy, Department of Computer Science, Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-0242 (United States)

    2014-09-15

    Small interfering ribonucleic acid (siRNA) molecules play a pivotal role in silencing gene expression via the RNA interference mechanism. A key limitation to the widespread implementation of siRNA therapeutics is the difficulty of delivering siRNA-based drugs to cells. Here, we examine changes in the structure and dynamics of a dipalmitoylphosphatidylcholine bilayer in the presence of a siRNA molecule and mechanical barriers to siRNA transfection in the bilayer. Our all-atom molecular dynamics simulation shows that siRNA induces a liquid crystalline-to-ripple phase transformation in the bilayer. The ripple phase consists of a major region of non-interdigitated and a minor region of interdigitated lipid molecules with an intervening kink. In the ripple phase, hydrocarbon chains of lipid molecules have large compressive stresses, which present a considerable barrier to siRNA transfection.

  11. Amplitude equation and long-range interactions in underwater sand ripples in one dimension

    DEFF Research Database (Denmark)

    Schnipper, Teis; Mertens, Keith; Ellegaard, Clive;

    2008-01-01

    We present an amplitude equation for sand ripples under oscillatory flow in a situation where the sand is moving in a narrow channel and the height profile is practically one dimensional. The equation has the form h(t)=epsilon-(h-(h) over bar) + ((h(x))(2)-1)h(xx)-h(xxxx) + delta((h(x))(2))(xx) w...... finally present surprising experimental results showing that long-range coupling is indeed seen in the initial details of the doubling transition, where in fact two small ripples are initially formed, followed by global symmetry breaking removing one of them....... in particular on the so-called doubling transition, a secondary instability caused by the sudden decrease in the amplitude of the water motion, leading to the appearance of a new ripple in each trough. This transition is well reproduced for sufficiently large delta (asymmetry between trough and crest). We...

  12. Stress vs sputtering effects in the propagation of surface ripples produced by ion-beam sputtering

    Energy Technology Data Exchange (ETDEWEB)

    Moreno-Barrado, A. [Instituto de Investigación Tecnológica (IIT) and Grupo Interdisciplinar de Sistemas Complejos (GISC), Universidad Pontificia Comillas, E-28015 Madrid (Spain); Castro, M. [GISC and Grupo de Dinámica No Lineal (DNL), Escuela Técnica Superior de Ingeniería (ICAI), Universidad Pontificia Comillas, E-28015 Madrid (Spain); Muñoz-García, J. [Departamento de Matemáticas and GISC, Universidad Carlos III de Madrid, Avenida de la Universidad 30, E-28911 Leganés (Spain); Cuerno, R., E-mail: cuerno@math.uc3m.es [Departamento de Matemáticas and GISC, Universidad Carlos III de Madrid, Avenida de la Universidad 30, E-28911 Leganés (Spain)

    2015-12-15

    Under low energy ion irradiation, periodic features (ripples) can develop on the surfaces of semiconductor materials, with typical sizes in the nanometric range. Recently, a theory of pattern formation has been able to account for the variability with the ion/target combination of the critical angle value separating conditions on ion incidence that induce the presence or the absence of ripples. Such a theory is based in the accumulation of stress in the damaged irradiated layer and its relaxation via surface-confined viscous flow. Here we explore the role of stress, and its competition with purely erosive mechanisms, to determine the sign of the velocity with which the ripple pattern moves across the target plane. Based on this theory, we discuss different situations and make specific testable predictions for the change of sign in that velocity.

  13. Hierarchical nesting of slow oscillations, spindles and ripples in the human hippocampus during sleep.

    Science.gov (United States)

    Staresina, Bernhard P; Bergmann, Til Ole; Bonnefond, Mathilde; van der Meij, Roemer; Jensen, Ole; Deuker, Lorena; Elger, Christian E; Axmacher, Nikolai; Fell, Juergen

    2015-11-01

    During systems-level consolidation, mnemonic representations initially reliant on the hippocampus are thought to migrate to neocortical sites for more permanent storage, with an eminent role of sleep for facilitating this information transfer. Mechanistically, consolidation processes have been hypothesized to rely on systematic interactions between the three cardinal neuronal oscillations characterizing non-rapid eye movement (NREM) sleep. Under global control of de- and hyperpolarizing slow oscillations (SOs), sleep spindles may cluster hippocampal ripples for a precisely timed transfer of local information to the neocortex. We used direct intracranial electroencephalogram recordings from human epilepsy patients during natural sleep to test the assumption that SOs, spindles and ripples are functionally coupled in the hippocampus. Employing cross-frequency phase-amplitude coupling analyses, we found that spindles were modulated by the up-state of SOs. Notably, spindles were found to in turn cluster ripples in their troughs, providing fine-tuned temporal frames for the hypothesized transfer of hippocampal memory traces.

  14. Effects of Super Strom Sandy on Depositional Environments Offshore Long Island, New York

    Science.gov (United States)

    Hosseini, P.; McHugh, C. M.; Christensen, B. A.; Dutton, J.; Brownawell, B.; Gurung, D.

    2013-12-01

    Hurricane Sandy's landfall affected the coastlines over a broad swath of mid-Atlantic including New York, New Jersey, Delaware, Maryland, Virginia, and North Carolina. The effects included breaching, overwash and erosion of barrier islands, some of which are heavily populated and sustained extensive damage. The peak storm-tide elevation produced by Hurricane Sandy measured by USGS stations in Jamaica Bay was about 3.5 m, 1.4 m more than the historical peak-water level elevations in the same area. As part of a National Science Foundation RAPID response we sampled the sediment in West Bay, Middle Bay, East Bay, Jones Inlet and Reynolds Channel of Long Island, New York from the R/V Pritchard. The sediment sampling took place 4 months after the storm and prior to any similar large storms. The sampling strategy was designed to characterize the post-storm sedimentation in distinct depositional environments. In this survey 156 grab samples were recovered from areas, many of which had been sampled prior to the storm. The samples were analyzed for grain size variability, short-lived radioisotopes and x-ray fluorescence elemental analyses. Google Earth images from before and after the storm reveal moderate to severe erosion and overwash of the dunes in Jones inlet, and Middle and East Bays. The Long Beach barrier island tidal marshes were submerged for several days post Sandy and underwent severe erosion. The storm surge brought from offshore a layer of coarse sand that was deposited over mussel beds. Most of the mussels were dead indicative of the strength of the waves. Be-7 concentrations allowed tracking the path of the storm from the bays and inlets, to the offshore. Some of the highest Be-7 concentrations ever detected in the local estuaries: 5,329, 4,955 and 4,553 pCi/kg were measured in West Bay and Middle Bay Channels. Additionally, unusually high Be-7 concentrations of 2,130 pCi/kg were recorded ~5.24 km offshore from Long Beach barrier island four months after the

  15. Coastal Topography--Northeast Atlantic Coast, Post-Hurricane Sandy, 2012

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Derived products of a portion of the New York, Delaware, Maryland, Virginia, and North Carolina coastlines, post-Hurricane Sandy (Sandy was an October 2012...

  16. Coastal Topography--Northeast Atlantic Coast, Post-Hurricane Sandy, 2012: Lidar-extracted dune features

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Dune crest and toe positions along a portion of the New York, Delaware, Maryland, Virginia, and North Carolina coastlines, post-Hurricane Sandy (Sandy was an October...

  17. Coastal Topography--Northeast Atlantic Coast, Post-Hurricane Sandy, 2012

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Derived products of a portion of the New York, Delaware, Maryland, Virginia, and North Carolina coastlines, post-Hurricane Sandy (Sandy was an October 2012 hurricane...

  18. 2012 U.S. Geological Survey Topographic Lidar: Northeast Atlantic Coast Post-Hurricane Sandy

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Binary point-cloud data were produced for a portion of the New York, Delaware, Maryland, Virginia, and North Carolina coastlines, post-Hurricane Sandy (Sandy was an...

  19. Coastal Topography--Northeast Atlantic Coast, Post-Hurricane Sandy, 2012: Digital elevation model (DEM)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — A DEM was produced for a portion of the New York, Delaware, Maryland, Virginia, and North Carolina coastlines, post-Hurricane Sandy (Sandy was an October 2012...

  20. 2012 U.S. Geological Survey Topographic Lidar: Northeast Atlantic Coast Post-Hurricane Sandy

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Binary point-cloud data were produced for a portion of the New York, Delaware, Maryland, Virginia, and North Carolina coastlines, post-Hurricane Sandy (Sandy was an...

  1. STATUS, CAUSES AND COMBATING SUGGESTIONS OF SANDY DESERTIFICATION IN QINGHAI-TIBET PLATEAU

    Institute of Scientific and Technical Information of China (English)

    LIU Yi-hua; DONG Guang-rong; LI Sen; DONG Yu-xiang

    2005-01-01

    The Qinghai-Tibet Plateau is one of the major sandy desertification regions of China. Based on the recent investigation on sandy desertification, this paper analyses the status such as the type, area, distribution and damage of sandy land desertification in the plateau. Through the analysis on the factors affecting sandy desertification in the region's natural and socio-economic systems as well as the processes and their interrelations, it can be concluded that sandy desertification in the Qinghai-Tibet Plateau resulted from the combined actions of normal natural sand drift processes, natural sandy desertification processes caused by climatic changes and man-made sandy desertification caused by improper human activities. In addition, it also predicts the possible developmental trend including the increase in desertification area and the enhancement in desertification developmental degree with the exacerbation of the complex processes, and finally puts forward some strategic suggestions to combat sandy desertification in the coming years.

  2. Simple Design Approach for Low Torque Ripple and High Output Torque Synchronous Reluctance Motors

    Directory of Open Access Journals (Sweden)

    Mohamed Nabil Fathy Ibrahim

    2016-11-01

    Full Text Available The rotor design of Synchronous Reluctance Motors (SynRMs has a large effect on their efficiency, torque density and torque ripple. In order to achieve a good compromise between these three goals, an optimized rotor geometry is necessary. A finite element method (FEM is a good tool for the optimization. However, the computation time is an obstacle as there are many geometrical parameters to be optimized. The flux-barrier widths and angles are the two most crucial parameters for the SynRM output torque and torque ripple. This paper proposes an easy-to-use set of parametrized equations to select appropriate values for these two rotor parameters. With these equations, the reader can design a SynRM of distributed windings with a low torque ripple and with a better average torque. The methodology is valid for a wide range of SynRMs. To check the validity of the proposed equations, the sensitivity analysis for the variation of these two parameters on the SynRM torque and torque ripple is carried out. In addition, the analysis in this paper gives insight into the behavior of the machine as a function of these two parameters. Furthermore, the torque and torque ripple of SynRMs having a rotor with three, four and five flux-barriers are compared with three literature approaches. The comparison shows that the proposed equations are effective in choosing the flux-barrier angles and widths for low torque ripple and better average torque. Experimental results have been obtained to confirm the FEM results and to validate the methodology for choosing the rotor parameters.

  3. A unifying model for planform straightness of ripples and dunes in air and water

    Science.gov (United States)

    Rubin, David M.

    2012-01-01

    Geologists, physicists, and mathematicians have studied ripples and dunes for more than a century, but despite considerable effort, no general model has been proposed to explain perhaps the most fundamental property of their morphology: why are some bedforms straight, continuous, parallel, and uniform in planform geometry (i.e. two-dimensional) whereas others are irregular (three-dimensional)? Here we argue that physical coupling along the crest of a bedform is required to produce straight crests and that along-crest flow and sand transport provide effective physical mechanisms for that coupling. Ripples and dunes with the straightest and most continuous crests include longitudinal and oblique dunes in unidirectional flows, wave ripples, dunes in reversing flows, wind ripples, and ripples migrating along a slope. At first glance, these bedforms appear quite different (ripples and dunes; air and water; transverse, oblique, and longitudinal orientations relative to the net sand-transport direction), but they all have one property in common: a process that increases the amount of along-crest sand transport (that lengthens and straightens their crests) relative to the across-crest transport (that makes them migrate and take the more typical and more three-dimensional planform geometry). In unidirectional flows that produce straight bedforms, along-crest transport of sand is caused by along-crest flow (non-transverse bedform orientation), gravitational transport along an inclined crest, or ballistic splash in air. Bedforms in reversing flows tend to be straighter than their unidirectional counterparts, because reverse transport across the bedform crest reduces the net across-crest transport (that causes the more typical irregular geometry) relative to the along-crest transport (that smoothes and straightens planform geometry).

  4. A Preliminary Study on the Red Beds in the Northern Heyuan Basin, Guangdong Province, China

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    The red beds of the northern Heyuan Basin (Guangdong Province, China) are more than 4,000 m thick.Based on the lithological characters, in ascending order these beds are divided into the Dafeng Formation, Zhutian Formation, and Zhenshui Formation of the Nanxiong Group, Shanghu Formation and Danxia Formation. The Nanxiong Group with relatively mature coarse clastic rocks attains about 2 940 m in thickness. The Dafeng Formation is 837 m thick,consisting of conglomerates and sandy conglomerates; the Zhutian Formation, which is 1,200 m thick, consists of purplish red sandstone with gravels, poorly sorted sandstone, feldspathic quartzose sandstone banded granular conglomerate,siltstone, and sandy mudstone. The Zhutian Formation is rich in calcareous concretions. Heyuannia (Oviraptoridae) and turtle fossils were found in this formation. The Zhenshui Formation deposited to a thickness of 900 m consists of coarse sediments, including granular conglomerate, and gravelly sandstone with well developed cross-beddings; the Shanghu Formation, which is 820 m thick, consists of purplish red granular conglomerate coarse sandstone intercalated with fine siltstone; the Danxia Formation characterized by the Danxia landform is composed of coarse clastic gravels and sandy gravels. The lower part of the Nanxiong Group whence dinosaur eggs and derived oviraptorosaurs come, belongs to the Late Cretaceous. No fossils are found in the Shanghu Formation or the Danxia Formation, but their stratigraphic order of superposition on the Nanxiong Group clearly shows their younger age.

  5. Complex burrows of the mud shrimp Callianassa truncata and their geochemical impact in the sea bed

    DEFF Research Database (Denmark)

    Ziebis, W.; Forster, S.; Huettel, M.

    1996-01-01

    the overlying water and rapid consumption within the sea bed, Macrofauna organisms living within the sea bed affect the physical structure of the sea floor, its chemical zonations and the exchange processes across the sediment-water interface(3,4). Thalassinidean mud-shrimps are often abundant in tropical......). Here we report the use of a diver observatory within the seabed, along with in situ measurements, to assess the geochemical impact of the mud-shrimp Callianassa truncata Giard and Bonnier (Decapoda, Thalassinidea), a species that commonly inhabits sandy sediments in the Mediterranean sea....

  6. Complex burrows of the mud shrimp Callianassa truncata and their geochemical impact in the sea bed

    DEFF Research Database (Denmark)

    Ziebis, W.; Forster, S.; Huettel, M.;

    1996-01-01

    the overlying water and rapid consumption within the sea bed, Macrofauna organisms living within the sea bed affect the physical structure of the sea floor, its chemical zonations and the exchange processes across the sediment-water interface(3,4). Thalassinidean mud-shrimps are often abundant in tropical......). Here we report the use of a diver observatory within the seabed, along with in situ measurements, to assess the geochemical impact of the mud-shrimp Callianassa truncata Giard and Bonnier (Decapoda, Thalassinidea), a species that commonly inhabits sandy sediments in the Mediterranean sea....

  7. On ripples and rafts: Curvature induced nanoscale structures in lipid membranes

    Science.gov (United States)

    Schmid, Friederike; Dolezel, Stefan; Lenz, Olaf; Meinhardt, Sebastian

    2014-03-01

    We develop an elastic theory that predicts the spontaneous formation of nanoscale structures in lipid bilayers which locally phase separate between two phases with different spontaneous monolayer curvature. The theory rationalizes in a unified manner the observation of a variety of nanoscale structures in lipid membranes: Rippled states in one-component membranes, lipid rafts in multicomponent membranes. Furthermore, we report on recent observations of rippled states and rafts in simulations of a simple coarse-grained model for lipid bilayers, which are compatible with experimental observations and with our elastic model.

  8. Reduction of torque ripple in DTC induction motor drive with discrete voltage vectors

    Directory of Open Access Journals (Sweden)

    Rosić Marko

    2014-01-01

    Full Text Available This paper presents а practical implementation of direct torque control (DTC of an induction machine on MSK2812 DSP platform, and the analysis of possibilities for reduction of torque ripple. Basic theoretical background relating the DTC was primarily set and the obtained experimental results have been given. It is shown that the torque ripple can be reduced by adjusting the intensity of voltage vectors and by modification of hysteresis comparator, while the simplicity of the basic DTC algorithm has been maintained. [Projekat Ministarstva nauke Republike Srbije, br. TR33016

  9. Phase-matched relativistic second harmonic generation in clusters with density ripple

    Science.gov (United States)

    Vij, Shivani; Aggarwal, Munish; Kant, Niti

    2017-01-01

    An intense short-pulse laser obliquely incident on a clustered gas quickly converts the atomic clusters into hot plasma balls. The laser beam produces a second harmonic due to nonlinear response of cluster and plasma electrons. For enhancement of efficiency of second harmonic generation, there should be appropriate phase-matching between the incident laser beam and the generated harmonic. To achieve the required phase-matching, the ripple in cluster density and plasma electron density outside the cluster is introduced. The efficiency of second harmonic generation is sensitive to the angle between ripple wave vector k→o and the direction of the incident laser beam.

  10. Bandgap engineering of rippled MoS2 monolayer under external electric field

    Science.gov (United States)

    Qi, Jingshan; Li, Xiao; Qian, Xiaofeng; Feng, Ji

    2013-04-01

    In this letter we propose a universal strategy combining external electric field with the ripple of membrane to tune the bandgap of semiconducting atomic monolayer. By first-principles calculations we show that the bandgap of rippled MoS2 monolayer can be tuned in a large range by vertical external electric field, which is expected to have little effect on MoS2 monolayer. This phenomenon can be explained from charge redistribution under external electric field by a simple model. This may open an avenue of optimizing monolayer MoS2 for electronic and optoelectronic applications by surface patterning.

  11. Torque Ripple Suppression Integrated Starter/Generator Control Strategy for Brushless Wound-Field Synchronous Motor

    Institute of Scientific and Technical Information of China (English)

    骆光照; 张围围; 杨南方; 马鹏; 刘卫国

    2012-01-01

    A flux linkage compensation field oriented control (FOC) method was proposed to suppress the speed and torque ripples of a hrusbless wound-fleld synchronous motor in its starting process. The starting process was analyzed and the model of wound-field synchronous electric machine was established. The change of field current of the electric machine was described mathematically for simplified exciter and rotate rectifier. Based on the traditional field control, the flux linkage compensation was introduced in d-axis current to counteract the flux ripple. Some simulation and preliminary experiments were implemented. The results show that the proposed method is feasible and effective.

  12. A measurement of ripple current in the by-pass resistor of synchrotron magnets: new method for mode separation measurement

    Energy Technology Data Exchange (ETDEWEB)

    Aoki, Takashi; Nishikigouri, Kazuto; Gushiken, Tsutomu; Sano, Yoshinobu; Togashi, Tomohito [Accelerator Engineering Corp. Konakadai, Chiba (Japan); Kumada, Masayuki; Takada, Eiichi; Noda, Koji; Kanazawa, Mitsutaka

    1997-12-31

    We report a result of the ripple measurement in the by-pass resistor circuit of HIMAC synchrotron main magnet coils. The result shows clear separation of common- and normal- mode components in the frequency domain. An interpretation of the data and relevant characteristic of the method such as ripple sensitivity are discussed. (author)

  13. Higher-order paraxial theory of the propagation of ring rippled laser beam in plasma: Relativistic ponderomotive regime

    Energy Technology Data Exchange (ETDEWEB)

    Purohit, Gunjan, E-mail: gunjan75@gmail.com; Rawat, Priyanka [Department of Physics, Laser-Plasma Computational Laboratory, DAV PG College, Dehradun, Uttarakhand (India); Chauhan, Prashant [Department of Physics and Material Science and Engineering, Jaypee Institute of Information Technology, Uttar Pradesh (India); Mahmoud, Saleh T. [Department of Physics, College of Science, UAE University, PO Box 17551 Al-Ain (United Arab Emirates)

    2015-05-15

    This article presents higher-order paraxial theory (non-paraxial theory) for the ring ripple formation on an intense Gaussian laser beam and its propagation in plasma, taking into account the relativistic-ponderomotive nonlinearity. The intensity dependent dielectric constant of the plasma has been determined for the main laser beam and ring ripple superimposed on the main laser beam. The dielectric constant of the plasma is modified due to the contribution of the electric field vector of ring ripple. Nonlinear differential equations have been formulated to examine the growth of ring ripple in plasma, self focusing of main laser beam, and ring rippled laser beam in plasma using higher-order paraxial theory. These equations have been solved numerically for different laser intensities and plasma frequencies. The well established experimental laser and plasma parameters are used in numerical calculation. It is observed that the focusing of the laser beams (main and ring rippled) becomes fast in the nonparaxial region by expanding the eikonal and other relevant quantities up to the fourth power of r. The splitted profile of laser beam in the plasma is observed due to uneven focusing/defocusing of the axial and off-axial rays. The growths of ring ripple increase when the laser beam intensity increases. Furthermore, the intensity profile of ring rippled laser beam gets modified due to the contribution of growth rate.

  14. Effects of soil amendment on soil characteristics and maize yield in Horqin Sandy Land

    Science.gov (United States)

    Zhou, L.; Liu, J. H.; Zhao, B. P.; Xue, A.; Hao, G. C.

    2016-08-01

    A 4-year experiment was conducted to investigate the inter-annual effects of sandy soil amendment on maize yield, soil water storage and soil enzymatic activities in sandy soil in Northeast China in 2010 to 2014. We applied the sandy soil amendment in different year, and investigated the different effects of sandy soil amendment in 2014. There were six treatments including: (1) no sandy soil amendment application (CK); (2) one year after applying sandy soil amendment (T1); (3) two years after applying sandy soil amendment(T2); (4) three years after applying sandy soil amendment(T3); (5)four years after applying sandy soil amendment(T4); (6) five years after applying sandy soil amendment (T5). T refers to treatment, and the number refers to the year after application of the sandy soil amendment. Comparing with CK, sandy soil amendments improved the soil water storage, soil urease, invertase, and catalase activity in different growth stages and soil layers, the order of soil water storage in all treatments roughly performed: T3 > T5 > T4 > T2 > T1 > CK. the order of soil urease, invertase, and catalase activity in all treatments roughly performed: T5 > T3 > T4 > T2 > T1 > CK. Soil application of sandy soil amendment significantly (p≤⃒0.05) increased the grain yield and biomass yield by 22.75%-41.42% and 29.92%-45.45% respectively, and maize yield gradually increased with the years go by in the following five years. Sandy soil amendment used in poor sandy soil had a positive effect on soil water storage, soil enzymatic activities and maize yield, after five years applied sandy soil amendment (T5) showed the best effects among all the treatments, and deserves further research.

  15. Deaths associated with Hurricane Sandy - October-November 2012.

    Science.gov (United States)

    2013-05-24

    On October 29, 2012, Hurricane Sandy hit the northeastern U.S. coastline. Sandy's tropical storm winds stretched over 900 miles (1,440 km), causing storm surges and destruction over a larger area than that affected by hurricanes with more intensity but narrower paths. Based on storm surge predictions, mandatory evacuations were ordered on October 28, including for New York City's Evacuation Zone A, the coastal zone at risk for flooding from any hurricane. By October 31, the region had 6-12 inches (15-30 cm) of precipitation, 7-8 million customers without power, approximately 20,000 persons in shelters, and news reports of numerous fatalities (Robert Neurath, CDC, personal communication, 2013). To characterize deaths related to Sandy, CDC analyzed data on 117 hurricane-related deaths captured by American Red Cross (Red Cross) mortality tracking during October 28-November 30, 2012. This report describes the results of that analysis, which found drowning was the most common cause of death related to Sandy, and 45% of drowning deaths occurred in flooded homes in Evacuation Zone A. Drowning is a leading cause of hurricane death but is preventable with advance warning systems and evacuation plans. Emergency plans should ensure that persons receive and comprehend evacuation messages and have the necessary resources to comply with them.

  16. Hurricane Sandy: An Educational Bibliography of Key Research Studies

    Science.gov (United States)

    Piotrowski, Chris

    2013-01-01

    There, undoubtedly, will be a flurry of research activity in the "Superstorm" Sandy impact area on a myriad of disaster-related topics, across academic disciplines. The purpose of this study was to review the disaster research related specifically to hurricanes in the educational and social sciences that would best serve as a compendium…

  17. Patterns of species richness in sandy beaches of South America

    African Journals Online (AJOL)

    Species richness of the intertidal macroinfauna of exposed sandy beaches around South America is reviewed in relation ... The middle shore is prim

  18. Microfungi diversity isolation from sandy soil of Acapulco touristic beaches

    Science.gov (United States)

    Microscopic fungi diversity in marine sandy soil habitats is associated with key functions of beach ecosystems. There are few reports on their presence in Mexican beaches. Although standard methods to obtain the fungi from soil samples are established, the aim of this pilot study was to test the pla...

  19. 78 FR 46999 - Additional Waivers and Alternative Requirements for Hurricane Sandy Grantees in Receipt of...

    Science.gov (United States)

    2013-08-02

    ... URBAN DEVELOPMENT Additional Waivers and Alternative Requirements for Hurricane Sandy Grantees in... impacted and distressed areas declared a major disaster due to Hurricane Sandy (see 78 FR 14329, published....) (Stafford Act), due to Hurricane Sandy and other eligible events in calendar years 2011, 2012, and 2013....

  20. 77 FR 74891 - Order Granting Exemptions From Certain Rules of Regulation SHO Related to Hurricane Sandy

    Science.gov (United States)

    2012-12-18

    ... COMMISSION Order Granting Exemptions From Certain Rules of Regulation SHO Related to Hurricane Sandy December 12, 2012. I. Introduction Hurricane Sandy made landfall along the mid-Atlantic Coast on October 29... in the Vault at the time Hurricane Sandy made landfall, facilitating DTCC's ability to...

  1. 78 FR 33467 - Second Allocation of Public Transportation Emergency Relief Funds in Response to Hurricane Sandy...

    Science.gov (United States)

    2013-06-04

    ... Response to Hurricane Sandy: Response, Recovery & Resiliency; Correction AGENCY: Federal Transit... by Hurricane Sandy. This amount was in addition to the initial $2 billion allocation announced in the... allocation restoration FTA Section 5324 Emergency Relief Program Allocations for Hurricane Sandy, by...

  2. 33 CFR 165.507 - Security Zone; Chesapeake Bay, between Sandy Point and Kent Island, MD.

    Science.gov (United States)

    2010-07-01

    ... south (eastbound) span of the William P. Lane Jr. Memorial Bridge, from the western shore at Sandy Point..., between Sandy Point and Kent Island, MD. 165.507 Section 165.507 Navigation and Navigable Waters COAST... Guard District § 165.507 Security Zone; Chesapeake Bay, between Sandy Point and Kent Island, MD. (a...

  3. Tapered bed bioreactor

    Science.gov (United States)

    Scott, Charles D.; Hancher, Charles W.

    1977-01-01

    A vertically oriented conically shaped column is used as a fluidized bed bioreactor wherein biologically catalyzed reactions are conducted in a continuous manner. The column utilizes a packing material a support having attached thereto a biologically active catalytic material.

  4. Bed Bugs FAQs

    Science.gov (United States)

    ... Bed bugs have been found in five-star hotels and resorts and their presence is not determined ... sleep. These areas include apartments, shelters, rooming houses, hotels, cruise ships, buses, trains, and dorm rooms. They ...

  5. Moving-bed sorbents

    Energy Technology Data Exchange (ETDEWEB)

    Ayala, R.E.; Gupta, R.P.; Chuck, T.

    1995-12-01

    The objective of this program is to develop mixed-metal oxide sorbent formulations that are suitable for moving-bed, high-temperature, desulfurization of coal gas. Work continues on zinc titanates formulations and Z-sorb III sorbent.

  6. Bed Bug Information Clearinghouse

    Science.gov (United States)

    Its purpose is to help states, communities, and consumers in efforts to prevent and control bed bug infestations. Currently includes only reviewed material from federal/state/local government agencies, extension services, and universities.

  7. Bed Bug Tips

    Science.gov (United States)

    How to deal with bed bugs in one printable page. Ten tips include ensuring correct insect identification, reducing clutter, understand integrated pest management, using mattress and box spring encasements, and heat treatment.

  8. Diffraction of Oblique Water Waves by Small Uneven Channel-bed in a Two-layer Fluid

    Institute of Scientific and Technical Information of China (English)

    Smrutiranjan Mohapatra

    2014-01-01

    Obliquely incident water wave scattering by an uneven channel-bed in the form of a small bottom undulation in a two-layer fluid is investigated within the frame work of three-dimensional linear water wave theory. The upper fluid is assumed to be bounded above by a rigid lid, while the lower one is bounded below by a bottom surface having a small deformation and the channel is unbounded in the horizontal directions. Assuming irrotational motion, perturbation technique is employed to calculate the first-order corrections to the velocity potentials in the two fluids by using Fourier transform approximately, and also to calculate the reflection and transmission coefficients in terms of integrals involving the shape function representing the bottom deformation. Consideration of a patch of sinusoidal ripples shows that the reflection coefficient is an oscillatory function of the ratio of twice the component of the wave number along x-axis and the ripple wave number. When this ratio approaches one, the theory predicts a resonant interaction between the bed and interface, and the reflection coefficient becomes a multiple of the number of ripples. High reflection of incident wave energy occurs if this number is large.

  9. Diffraction of oblique water waves by small uneven channel-bed in a two-layer fluid

    Science.gov (United States)

    Mohapatra, Smrutiranjan

    2014-09-01

    Obliquely incident water wave scattering by an uneven channel-bed in the form of a small bottom undulation in a two-layer fluid is investigated within the frame work of three-dimensional linear water wave theory. The upper fluid is assumed to be bounded above by a rigid lid, while the lower one is bounded below by a bottom surface having a small deformation and the channel is unbounded in the horizontal directions. Assuming irrotational motion, perturbation technique is employed to calculate the first-order corrections to the velocity potentials in the two fluids by using Fourier transform approximately, and also to calculate the reflection and transmission coefficients in terms of integrals involving the shape function representing the bottom deformation. Consideration of a patch of sinusoidal ripples shows that the reflection coefficient is an oscillatory function of the ratio of twice the component of the wave number along x-axis and the ripple wave number. When this ratio approaches one, the theory predicts a resonant interaction between the bed and interface, and the reflection coefficient becomes a multiple of the number of ripples. High reflection of incident wave energy occurs if this number is large.

  10. Analysis of Ripple Effects on Frequency Response Characteristics of Switching Regulators

    Science.gov (United States)

    Sakai, Eiji; Nakahara, Masatoshi

    In this paper we clarify for the boost and the buck-boost converter that the ripple effect is not ignorable for the frequency response, and reveal that it causes the unexpected characteristics where either the phase lag or the phase lead appears depending on the shape of waveform of the ramp generator in the PWM circuit. Eventually the phase margin for the stability drastically changes depending on the slope direction (normal or reverse) of the sawtooth waveform of the ramp generator even in the same circuit configuration. For the ripple effects we propose the general analysis model and analyze them of the boost and the buck-boost converters. As the result we identify that the ripple effects are caused mainly by the variation of the slope and the average of the ripple, and reveal that the both converters have the asymmetric characteristics for the slope direction of the sawtooth waveform of the ramp generator and there is more advantage for the stability in case of the reverse slope direction than in case of the normal one. It also clarified that the effect of ESR of the output capacitor of the converter on the frequency response is different according to the shape of the sawtooth waveforms. The proposed analysis method is validated by the experiments and simulations.

  11. Disrupting neural activity related to awake-state sharp wave-ripple complexes prevents hippocampal learning

    Directory of Open Access Journals (Sweden)

    Miriam Shirin Nokia

    2012-12-01

    Full Text Available Oscillations in hippocampal local-field potentials reflect the crucial involvement of the hippocampus in memory trace formation: theta (4-8 Hz oscillations and ripples (~200 Hz occurring during sharp waves are thought to mediate encoding and consolidation, respectively. During sharp wave-ripple complexes (SPW-Rs, hippocampal cell firing closely follows the pattern that took place during the initial experience, most likely reflecting replay of that event. Disrupting hippocampal ripples using electrical stimulation either during training in awake animals or during sleep after training retards spatial learning. Here, adult rabbits were trained in trace eyeblink conditioning, a hippocampus-dependent associative learning task. A bright light was presented to the animals during the inter-trial interval, when awake, either during SPW-Rs or irrespective of their neural state. Learning was particularly poor when the light was presented following SPW-Rs. While the light did not disrupt the ripple itself, it elicited a theta-band oscillation, a state that does not usually coincide with SPW-Rs. Thus, it seems that consolidation depends on neuronal activity within and beyond the hippocampus taking place immediately after, but by no means limited to, hippocampal SPW-Rs.

  12. Deterministic Agent-Based Path Optimization by Mimicking the Spreading of Ripples.

    Science.gov (United States)

    Hu, Xiao-Bing; Wang, Ming; Leeson, Mark S; Di Paolo, Ezequiel A; Liu, Hao

    2016-01-01

    Inspirations from nature have contributed fundamentally to the development of evolutionary computation. Learning from the natural ripple-spreading phenomenon, this article proposes a novel ripple-spreading algorithm (RSA) for the path optimization problem (POP). In nature, a ripple spreads at a constant speed in all directions, and the node closest to the source is the first to be reached. This very simple principle forms the foundation of the proposed RSA. In contrast to most deterministic top-down centralized path optimization methods, such as Dijkstra's algorithm, the RSA is a bottom-up decentralized agent-based simulation model. Moreover, it is distinguished from other agent-based algorithms, such as genetic algorithms and ant colony optimization, by being a deterministic method that can always guarantee the global optimal solution with very good scalability. Here, the RSA is specifically applied to four different POPs. The comparative simulation results illustrate the advantages of the RSA in terms of effectiveness and efficiency. Thanks to the agent-based and deterministic features, the RSA opens new opportunities to attack some problems, such as calculating the exact complete Pareto front in multiobjective optimization and determining the kth shortest project time in project management, which are very difficult, if not impossible, for existing methods to resolve. The ripple-spreading optimization principle and the new distinguishing features and capacities of the RSA enrich the theoretical foundations of evolutionary computation.

  13. Observing trans-Planckian ripples in the primordial power spectrum with future large scale structure probes

    DEFF Research Database (Denmark)

    Hamann, Jan; Hannestad, Steen; Sloth, Martin Snoager;

    2008-01-01

    -Planckian ripples can be made even if the amplitude is as low as 10^-4. Data from the Large Synoptic Survey Telescope (LSST) and the proposed future 21 cm survey with the Fast Fourier Transform Telescope (FFTT) will be particularly useful in this regard. If the scale of inflation is close to its present upper bound...

  14. The "Ripple Effect" of a University Sponsored Death and Dying Symposium.

    Science.gov (United States)

    Cook, Alicia S.; And Others

    1985-01-01

    Conducted a follow-up study of a three-week, university sponsored death and dying symposium to measure attitudes of nonattendees. The findings showed a declining taboo regarding death education and a "ripple effect" in which individuals are affected by a death education program even though they do not attend it. (JAC)

  15. Pattern dynamics of vortex ripples in sand: Nonlinear modeling and experimental validation

    DEFF Research Database (Denmark)

    Andersen, Ken Haste; Abel, M.; Krug, J.;

    2002-01-01

    Vortex ripples in sand are studied experimentally in a one-dimensional setup with periodic boundary conditions. The nonlinear evolution, far from the onset of instability, is analyzed in the framework of a simple model developed for homogeneous patterns. The interaction function describing the mass...

  16. Restrictions on TWT Helix Voltage Ripple for Acceptable Notch Filter Performance

    Energy Technology Data Exchange (ETDEWEB)

    Hyslop, B.

    1984-12-01

    An ac ripple on the helix voltage of the 1-2 GHz TWT's creates FM sidebands that cause amplitude and phase modulation of the microwave TWT output signal. A limit of 16 volts peak-to-peak is required for acceptable superconducting notch filter performance.

  17. Lattice gas cellular automation model for rippling and aggregation in myxobacteria

    Science.gov (United States)

    Alber, Mark S.; Jiang, Yi; Kiskowski, Maria A.

    2004-05-01

    A lattice gas cellular automation (LGCA) model is used to simulate rippling and aggregation in myxobacteria. An efficient way of representing cells of different cell size, shape and orientation is presented that may be easily extended to model later stages of fruiting body formation. This LGCA model is designed to investigate whether a refractory period, a minimum response time, a maximum oscillation period and non-linear dependence of reversals of cells on C-factor are necessary assumptions for rippling. It is shown that a refractory period of 2-3 min, a minimum response time of up to 1 min and no maximum oscillation period best reproduce rippling in the experiments of Myxococcus xanthus. Non-linear dependence of reversals on C-factor is critical at high cell density. Quantitative simulations demonstrate that the increase in wavelength of ripples when a culture is diluted with non-signaling cells can be explained entirely by the decreased density of C-signaling cells. This result further supports the hypothesis that levels of C-signaling quantitatively depend on and modulate cell density. Analysis of the interpenetrating high density waves shows the presence of a phase shift analogous to the phase shift of interpenetrating solitons. Finally, a model for swarming, aggregation and early fruiting body formation is presented.

  18. Torque ripple minimization in a doubly salient permanent magnet motors by skewing the rotor teeth

    Science.gov (United States)

    Sheth, N. K.; Sekharbabu, A. R. C.; Rajagopal, K. R.

    2006-09-01

    This paper presents the effects of skewing the rotor teeth on the performance of an 8/6 doubly salient permanent magnet motor using a simple method, which utilizes the results obtained from the 2-D FE analysis. The optimum skewing angle is obtained as 12-15° for the least ripple torque without much reduction in the back-emf.

  19. Influence of pulsed laser heating on morphological relaxation of surface ripples.

    Science.gov (United States)

    Khenner, M

    2005-07-01

    A continuum (Mullins-type) model is proposed for the nonisothermal, isotropic evolution of a crystal surface on which mass transport occurs by surface diffusion. The departure from constant temperature is assumed induced by incident pulsed radiation. It has been shown experimentally and theoretically [see, e.g., Yakunkin, High Temp. 26, 585 (1988); Yilbas and Kalyon, J. Phys. D. 34, 222 (2001)] that such a heating mode gives rise to the quasistationary regime, in which the surface temperature of a thick solid film oscillates about the mean value with the pulse repetition frequency. The implications of oscillatory driving with high frequency values on relaxation of surface ripples are examined; in particular, the traveling wave solutions with decreasing amplitude are detected numerically. Pulsed heating also results in faster smoothing of the ripple, compared to the case when the surface is at constant temperature which is same as the mean temperature in the pulsed heating mode. Impact on ripple shape is minor for ripple amplitudes considered.

  20. Dendritic spikes induce ripples in parvalbumin interneurons during hippocampal sharp waves.

    Science.gov (United States)

    Chiovini, Balázs; Turi, Gergely F; Katona, Gergely; Kaszás, Attila; Pálfi, Dénes; Maák, Pál; Szalay, Gergely; Szabó, Mátyás Forián; Szabó, Gábor; Szadai, Zoltán; Káli, Szabolcs; Rózsa, Balázs

    2014-05-21

    Sharp-wave ripples are transient oscillatory events in the hippocampus that are associated with the reactivation of neuronal ensembles within specific circuits during memory formation. Fast-spiking, parvalbumin-expressing interneurons (FS-PV INs) are thought to provide fast integration in these oscillatory circuits by suppressing regenerative activity in their dendrites. Here, using fast 3D two-photon imaging and a caged glutamate, we challenge this classical view by demonstrating that FS-PV IN dendrites can generate propagating Ca(2+) spikes during sharp-wave ripples. The spikes originate from dendritic hot spots and are mediated dominantly by L-type Ca(2+) channels. Notably, Ca(2+) spikes were associated with intrinsically generated membrane potential oscillations. These oscillations required the activation of voltage-gated Na(+) channels, had the same frequency as the field potential oscillations associated with sharp-wave ripples, and controlled the phase of action potentials. Furthermore, our results demonstrate that the smallest functional unit that can generate ripple-frequency oscillations is a segment of a dendrite.

  1. The fluence threshold of femtosecond laser blackening of metals: The effect of laser-induced ripples

    Science.gov (United States)

    Ou, Zhigui; Huang, Min; Zhao, Fuli

    2016-05-01

    With the primary controlling factor of the laser fluence, we have investigated femtosecond laser blackening of stainless steel, brass, and aluminum in visible light range. In general, low reflectance about 5% can be achieved in appropriate ranges of laser fluences for all the treated metal surfaces. Significantly, towards stainless steel and brass a fluence threshold of blackening emerges unusually: a dramatic reflectance decline occurs in a specific, narrow fluence range. In contrast, towards aluminum the reflectance declines steadily over a wide fluence range instead of the threshold-like behavior from steel and brass. The morphological characteristics and corresponding reflectance spectra of the treated surfaces indicates that the blackening threshold of stainless steel and brass corresponds to the fluence threshold of laser-induced subwavelength ripples. Such periodic ripples growing rapidly near ablation threshold absorb visible light efficiently through grating coupling and cavity trapping promoted by surface plasmon polaritons. Whereas, for aluminum, with fluence increasing the looming ripples are greatly suppressed by re-deposited nanoparticle aggregates that present intrinsic colors other than black, and until the formation of large scale "ravines" provided with strong light-trapping, sufficient blackening is achieved. In short, there are different fluence dependencies for femtosecond laser blackening of metals, and the specific blackening fluence threshold for certain metals in the visible range originates in the definite fluence threshold of femtosecond laser-induced ripples.

  2. Relationship between channel interaction and spectral-ripple discrimination in cochlear implant users.

    Science.gov (United States)

    Jones, Gary L; Won, Jong Ho; Drennan, Ward R; Rubinstein, Jay T

    2013-01-01

    Cochlear implant (CI) users can achieve remarkable speech understanding, but there is great variability in outcomes that is only partially accounted for by age, residual hearing, and duration of deafness. Results might be improved with the use of psychophysical tests to predict which sound processing strategies offer the best potential outcomes. In particular, the spectral-ripple discrimination test offers a time-efficient, nonlinguistic measure that is correlated with perception of both speech and music by CI users. Features that make this "one-point" test time-efficient, and thus potentially clinically useful, are also connected to controversy within the CI field about what the test measures. The current work examined the relationship between thresholds in the one-point spectral-ripple test, in which stimuli are presented acoustically, and interaction indices measured under the controlled conditions afforded by direct stimulation with a research processor. Results of these studies include the following: (1) within individual subjects there were large variations in the interaction index along the electrode array, (2) interaction indices generally decreased with increasing electrode separation, and (3) spectral-ripple discrimination improved with decreasing mean interaction index at electrode separations of one, three, and five electrodes. These results indicate that spectral-ripple discrimination thresholds can provide a useful metric of the spectral resolution of CI users.

  3. Density ripples in expanding low-dimensional gases as a probe of correlations

    DEFF Research Database (Denmark)

    Imambekov, A.; Mazets, I. E.; Petrov, D. S.

    2009-01-01

    fluctuations. For the case of free ballistic expansion relevant to current experiments, we present simple analytical relations between the spectrum of "density ripples" and the correlation functions of the original confined systems. We analyze several physical regimes, including weakly and strongly interacting...

  4. On the limits of uniaxial magnetic anisotropy tuning by a ripple surface pattern

    Energy Technology Data Exchange (ETDEWEB)

    Arranz, Miguel A. [Facultad de Ciencias Químicas, Universidad de Castilla-La Mancha, Avda. Camilo J. Cela 10, 13071 Ciudad Real (Spain); Colino, Jose M., E-mail: josemiguel.colino@uclm.es [Instituto de Nanociencia, Nanotecnología y Materiales Moleculares, Universidad de Castilla-La Mancha, Campus de la Fábrica de Armas, 45071 Toledo (Spain); Palomares, Francisco J. [Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Científicas, c/ Sor Juana Inés de la Cruz 3, 28049 Madrid (Spain)

    2014-05-14

    Ion beam patterning of a nanoscale ripple surface has emerged as a versatile method of imprinting uniaxial magnetic anisotropy (UMA) on a desired in-plane direction in magnetic films. In the case of ripple patterned thick films, dipolar interactions around the top and/or bottom interfaces are generally assumed to drive this effect following Schlömann's calculations for demagnetizing fields of an ideally sinusoidal surface [E. Schlömann, J. Appl. Phys. 41, 1617 (1970)]. We have explored the validity of his predictions and the limits of ion beam sputtering to induce UMA in a ferromagnetic system where other relevant sources of magnetic anisotropy are neglected: ripple films not displaying any evidence of volume uniaxial anisotropy and where magnetocrystalline contributions average out in a fine grain polycrystal structure. To this purpose, the surface of 100 nm cobalt films grown on flat substrates has been irradiated at fixed ion energy, fixed ion fluency but different ion densities to make the ripple pattern at the top surface with wavelength Λ and selected, large amplitudes (ω) up to 20 nm so that stray dipolar fields are enhanced, while the residual film thickness t = 35–50 nm is sufficiently large to preserve the continuous morphology in most cases. The film-substrate interface has been studied with X-ray photoemission spectroscopy depth profiles and is found that there is a graded silicon-rich cobalt silicide, presumably formed during the film growth. This graded interface is of uncertain small thickness but the range of compositions clearly makes it a magnetically dead layer. On the other hand, the ripple surface rules both the magnetic coercivity and the uniaxial anisotropy as these are found to correlate with the pattern dimensions. Remarkably, the saturation fields in the hard axis of uniaxial continuous films are measured up to values as high as 0.80 kG and obey a linear dependence on the parameter ω{sup 2}/Λ/t in quantitative

  5. The biogenic emission potential of nitric oxide from sandy soils

    Science.gov (United States)

    Yu, J. B.; Meixner, F. X.; Sun, Z. G.; Chen, X. B.; Mamtimin, B.

    2009-04-01

    There are about 160.9 Mha of sandy land in China, about 17.6% of total Chinese area, which mainly distributed in 35°-50° N. The western Songnen Plain, which located in the semi-arid region of Northeastern China, is one of the main sandy soil distribution regions. The changes of land use in sandy soil are accompanied by changes in biogeochemical cycles of nutrients, particularly of the air-surface exchange of trace gases like nitric oxide. Our study, based on results obtained by a laboratory incubation technique, focuses on (a) NO production and consumption in sandy soils from two types of land use as function of soil temperature and soil moisture, and (b) The biogenic emission potential of nitric oxide from sandy soils in semi-arid region. At 25˚C, average NO production (in terms of mass of N) was 0.016,and 0.013 ng kg-1s-1 in sandy soils from soybean land (SL) and man-made forest (MF), re¬spectively. NO consumption rate constant ranged from 0.26×10-6 to 7.28×10-6 m3 kg-1s-1. At 25˚C and under optimum soil moisture conditions for NO production, the NO compensation point mixing ratio was about 266 and 161 ug m-3 (465,and 281 ppb) for soils of SL and MF, respectively. Statistically sound relationships have been observed between NO fluxes and soil moisture (optimum curves). NO fluxes also increased exponentially with soil temperature at any given soil moisture. The optimum soil moisture for which maximum NO flux was observed was independent of soil temperature. The maximum of NO flux potentials for SL and MF soils (at 25°C) were 59.6 and 36.5 ng m-2s-1 at water-filled pore space (%WFPS) of 26 and 24, respectively. The NO flux potential was about 2 times larger for cropland soil than for man-made forest soils, most likely due to fertilizer application to the cropland soils.

  6. Landscape Change and Sandy Desertification Monitoring and Assessment

    Directory of Open Access Journals (Sweden)

    Eltahir M. Elhadi

    2009-01-01

    Full Text Available Problem statement: The objective of this study is to develop techniques for assessing and analyzing sand desertification in the northern part of Shaanxi Province, China. Approach: In order to reveal the process of land degradation, especially the latest situation of sandy desertification, a method integrating remote sensing, Geographic Information System (GIS and field survey was employed to build a sandy desertification dataset for analysis. Remote Sensing images included the Landsat Thematic Mapper (TM images in 1987 and Landsat Enhanced Thematic Mapper Plus (ETM+ images in 1999. Eight land-cover classes, including active sand dunes, fixed sand dunes, semi-fixed sand dunes, grass land, farm land, wet land, built up area and unused land and Normalized Difference Vegetation Index (NDVI, were identified. Results: The results showed that the active sand dunes and semi-fixed sand dunes have increased with a change rate of 128.70 and 55.65 km2 year-1, respectively, in the meantime the fixed sand dunes has decreased with a decreasing rate of 182.14 km2 year-1. During the 1987s, the area of sandy desertified land reached 12,006.11 km2 (57.17% of the total sandy area, of which severely desertified, medium desertified and slightly desertified land areas were 4,442.23, 4,253.45 and 3,310.43 km2, respectively. By the year 1999, the area of desertified land was increased to 13,782.30 km2 (65.63% of the total sandy area, of which severely desertified, medium desertified and slightly desertified land areas were 5,169.89, 4,918.15 and 3,694.26 km2, respectively increasing by 1,776.19 km2. Conclusion: Spatial change detection based on active sand dunes showed that the expansion area was much larger than the reversion in the past two decades and that several active sand belts has been formed, suggesting that sandy desertification of northern part of Shaanxi Province, China, will be a long-term task.

  7. Sandy Desertification Status and its Driving Mechanism in North Tibet Plateau

    Institute of Scientific and Technical Information of China (English)

    DONG Yuxiang

    2004-01-01

    As the main body of Qinghai-Tibetan Plateau, North Tibet Plateau is one of three major sandy desertification regions in China and also a representative sandy desertification zone of Qinghai-Tibet Plateau. Accordingly, it is an important region for the study of recent sandy desertification processes and formation mechanism. From such aspects as desertified land types, areas and distributions etc., this paper analyses in detail the sandy desertification status on North Tibet Plateau,and qualitatively and quantitatively deals with the main factors that affect recent sandy desertification processes and the driving mechanism. Research results show that North Tibet Plateau is an important sandy desertification region in China characterized with large desertified land areas, diversified types,high severity, extensive distributions and serious damages. Sandy desertification occurrence and development resulted from combined effects of natural factors, anthropogenic factors, natural processes and man-made processes, of which climatic change is the main driving force.

  8. High frequency vibration characteristics of electric wheel system under in-wheel motor torque ripple

    Science.gov (United States)

    Mao, Yu; Zuo, Shuguang; Wu, Xudong; Duan, Xianglei

    2017-07-01

    With the introduction of in-wheel motor, the electric wheel system encounters new vibration problems brought by motor torque ripple excitation. In order to analyze new vibration characteristics of electric wheel system, torque ripple of in-wheel motor based on motor module and vector control system is primarily analyzed, and frequency/order features of the torque ripple are discussed. Then quarter vehicle-electric wheel system (QV-EWS) dynamics model based on the rigid ring tire assumption is established and the main parameters of the model are identified according to tire free modal test. Modal characteristics of the model are further analyzed. The analysis indicates that torque excitation of in-wheel motor is prone to arouse horizontal vibration, in which in-phase rotational, anti-phase rotational and horizontal translational modes of electric wheel system mainly participate. Based on the model, vibration responses of the QV-EWS under torque ripple are simulated. The results show that unlike vertical low frequency (lower than 20 Hz) vibration excited by road roughness, broadband torque ripple will arouse horizontal high frequency (50-100 Hz) vibration of electric wheel system due to participation of the three aforementioned modes. To verify the theoretical analysis, the bench experiment of electric wheel system is conducted and vibration responses are acquired. The experiment demonstrates the high frequency vibration phenomenon of electric wheel system and the measured order features as well as main resonant frequencies agree with simulation results. Through theoretical modeling, analysis and experiments this paper reveals and explains the high frequency vibration characteristics of electric wheel system, providing references for the dynamic analysis, optimal design of QV-EWS.

  9. Automated detection of epileptic ripples in MEG using beamformer-based virtual sensors

    Science.gov (United States)

    Migliorelli, Carolina; Alonso, Joan F.; Romero, Sergio; Nowak, Rafał; Russi, Antonio; Mañanas, Miguel A.

    2017-08-01

    Objective. In epilepsy, high-frequency oscillations (HFOs) are expressively linked to the seizure onset zone (SOZ). The detection of HFOs in the noninvasive signals from scalp electroencephalography (EEG) and magnetoencephalography (MEG) is still a challenging task. The aim of this study was to automate the detection of ripples in MEG signals by reducing the high-frequency noise using beamformer-based virtual sensors (VSs) and applying an automatic procedure for exploring the time-frequency content of the detected events. Approach. Two-hundred seconds of MEG signal and simultaneous iEEG were selected from nine patients with refractory epilepsy. A two-stage algorithm was implemented. Firstly, beamforming was applied to the whole head to delimitate the region of interest (ROI) within a coarse grid of MEG-VS. Secondly, a beamformer using a finer grid in the ROI was computed. The automatic detection of ripples was performed using the time-frequency response provided by the Stockwell transform. Performance was evaluated through comparisons with simultaneous iEEG signals. Main results. ROIs were located within the seizure-generating lobes in the nine subjects. Precision and sensitivity values were 79.18% and 68.88%, respectively, by considering iEEG-detected events as benchmarks. A higher number of ripples were detected inside the ROI compared to the same region in the contralateral lobe. Significance. The evaluation of interictal ripples using non-invasive techniques can help in the delimitation of the epileptogenic zone and guide placement of intracranial electrodes. This is the first study that automatically detects ripples in MEG in the time domain located within the clinically expected epileptic area taking into account the time-frequency characteristics of the events through the whole signal spectrum. The algorithm was tested against intracranial recordings, the current gold standard. Further studies should explore this approach to enable the localization of

  10. Analysis and Minimization of Output Current Ripple for Discontinuous Pulse-Width Modulation Techniques in Three-Phase Inverters

    Directory of Open Access Journals (Sweden)

    Gabriele Grandi

    2016-05-01

    Full Text Available This paper gives the complete analysis of the output current ripple in three-phase voltage source inverters considering the different discontinuous pulse-width modulation (DPWM strategies. In particular, peak-to-peak current ripple amplitude is analytically evaluated over the fundamental period and compared among the most used DPWMs, including positive and negative clamped (DPWM+ and DPWM−, and the four possible combinations between them, usually named as DPWM0, DPWM1, DPWM2, and DPWM3. The maximum and the average values of peak-to-peak current ripple are estimated, and a simple method to correlate the ripple envelope with the ripple rms is proposed and verified. Furthermore, all the results obtained by DPWMs are compared to the centered pulse-width modulation (CPWM, equivalent to the space vector modulation to identify the optimal pulse-width modulation (PWM strategy as a function of the modulation index, taking into account the different average switching frequency. In this way, the PWM technique providing for the minimum output current ripple is identified over the whole modulation range. The analytical developments and the main results are experimentally verified by current ripple measurements with a three-phase PWM inverter prototype supplying an induction motor load.

  11. Large-eddy simulation of formation of three-dimensional aeolian sand ripples in a turbulent field

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    With the method of large-eddy simulation,the equation of spherule motion and the method of immersed boundary condition,numerical simulations of three-dimen-sional turbulent aeolian motion and the formation of sand ripples under three-di-mensional turbulent wind and the mutual actions of saltation and creeping motion were carried out. The resulting sand ripples have the form that is flat on the upwind side and steep on the leeward,which is identical to the sand ripples in nature. We also realized the self-restoration process of three-dimensional sand ripples,which shows the correctness of the method of numerical simulation and the models of saltation and creeping. Finally,We analyzed the influence of sand ripples on the three-dimensional turbulent wind field,and found that due to the appearance and development of sand ripples,in the normal direction of ground there exists stronger energy exchange,and moreover,there is close correspondence between the forms of sand ripples and the vorticity close to the ground surface.

  12. Quantifying the digital traces of Hurricane Sandy on Flickr.

    Science.gov (United States)

    Preis, Tobias; Moat, Helen Susannah; Bishop, Steven R; Treleaven, Philip; Stanley, H Eugene

    2013-11-05

    Society's increasing interactions with technology are creating extensive "digital traces" of our collective human behavior. These new data sources are fuelling the rapid development of the new field of computational social science. To investigate user attention to the Hurricane Sandy disaster in 2012, we analyze data from Flickr, a popular website for sharing personal photographs. In this case study, we find that the number of photos taken and subsequently uploaded to Flickr with titles, descriptions or tags related to Hurricane Sandy bears a striking correlation to the atmospheric pressure in the US state New Jersey during this period. Appropriate leverage of such information could be useful to policy makers and others charged with emergency crisis management.

  13. Quantifying the Digital Traces of Hurricane Sandy on Flickr

    OpenAIRE

    Preis, Tobias; Moat, Helen Susannah; Bishop, Steven R.; Treleaven, Philip; Stanley, H. Eugene

    2013-01-01

    Society’s increasing interactions with technology are creating extensive “digital traces” of our collective human behavior. These new data sources are fuelling the rapid development of the new field of computational social science. To investigate user attention to the Hurricane Sandy disaster in 2012, we analyze data from Flickr, a popular website for sharing personal photographs. In this case study, we find that the number of photos taken and subsequently uploaded to Flickr with titles, desc...

  14. Kinetic Monte Carlo simulation of ripple formation by sputtering: Effects of multiple defects and Ehrlich-Schwoebel barriers

    Science.gov (United States)

    Ishii, Yohei; Chan, Wai Lun; Chason, Eric

    2012-02-01

    Periodic structures known as sputter ripples have been produced on many surfaces but many aspects of their formation are not understood. We have developed Kinetic Monte Carlo (KMC) simulations to model ripple formation based on the same sputtering and diffusion processes found in a widely-used continuum model. In the current work, we extend the simulations to include the effects of multiple defect production and barriers to interlayer diffusion to determine if these can account for experimental measurements which find more rapid ripple growth than predicted theoretically.

  15. Ripple-Free Graphene Sheets on Alkanethiol Self-Assembled Monolayers Provided from Unzipped Multi-Walled Carbon Nanotubes.

    Science.gov (United States)

    Koo, Hyunmo; Lee, Nam-Suk; Shin, Hoon-Kyu; Noh, Jaegeun; Majima, Yutaka; Cho, Gyoujin

    2015-02-01

    Octanethiol (C8S, CH3(CH2)7SH) self-assembled monolayers/Au(111) were utilized as an inert surface to provide ripple-free graphene oxide layers provided from chemically unzipped multi-walled carbon nanotubes (MWCNTs). The resulting graphene oxide monolayers were characterized with atomic resolution by UHV-STM. The honeycomb structure for the graphene monolayer and "three-for-six" triangular pattern for the multi-layer graphene sheets on C8S SAMs were clearly observed without ripples by the high-resolution UHV-STM. These results provide new insight into the preparation of ripple-free graphene monolayers.

  16. Numerical and experimental verification of a theoretical model of ripple formation in ice growth under supercooled water film flow

    Energy Technology Data Exchange (ETDEWEB)

    Ueno, K; Farzaneh, M [NSERC/Hydro-Quebec/UQAC Industrial Chair on Atmospheric Icing of Power Network Equipment (CIGELE) and Canada Research Chair on Engineering of Power Network Atmospheric Icing (INGIVRE), Universite du Quebec a Chicoutimi, 555 Boulevard de l' Universite, Chicoutimi, Quebec, G7H 2B1 (Canada); Yamaguchi, S [Snow and Ice Research Center, National Research Institute for Earth Science and Disaster Prevention, Nagaoka, 940-0821 (Japan); Tsuji, H [Research Institute for Applied Mechanics, Kyushu University, Kasuga, Fukuoka, 816-8580 (Japan)], E-mail: kazuto.ueno@uqac.ca

    2010-04-15

    Little is known about morphological instability of a solidification front during the crystal growth of a thin film of flowing supercooled liquid with a free surface: for example, the ring-like ripples on the surface of icicles. The length scale of the ripples is nearly 1 cm. Two theoretical models for the ripple formation mechanism have been proposed. However, these models lead to quite different results because of differences in the boundary conditions at the solid-liquid interface and liquid-air surface. The validity of the assumption used in the two models is numerically investigated and some of the theoretical predictions are compared with experiments.

  17. Brazilian sandy beaches: characteristics, ecosystem services, impacts, knowledge and priorities

    Directory of Open Access Journals (Sweden)

    Antonia Cecília Zacagnini Amaral

    Full Text Available ABSTRACT Sandy beaches constitute a key ecosystem and provide socioeconomic goods and services, thereby playing an important role in the maintenance of human populations and in biodiversity conservation. Despite the ecological and social importance of these ecosytems, Brazilian sandy beaches are significantly impacted by human interference, chemical and organic pollution and tourism, as well as global climate change. These factors drive the need to better understand the environmental change and its consequences for biota. To promote the implementation of integrated studies to detect the effects of regional and global environmental change on beaches and on other benthic habitats of the Brazilian coast, Brazilian marine researchers have established The Coastal Benthic Habitats Monitoring Network (ReBentos. In order to provide input for sample planning by ReBentos, we have conducted an intensive review of the studies conducted on Brazilian beaches and summarized the current knowledge about this environment. In this paper, we present the results of this review and describe the physical, biological and socioeconomics features of Brazilian beaches. We have used these results, our personal experience and worldwide literature to identify research projects that should be prioritized in the assessment of regional and global change on Brazilian sandy beaches. We trust that this paper will provide insights for future studies and represent a significant step towards the conservation of Brazilian beaches and their biodiversity.

  18. Hurricane Sandy washover deposits on Fire Island, New York

    Science.gov (United States)

    La Selle, SeanPaul M.; Lunghino, Brent D.; Jaffe, Bruce E.; Gelfenbaum, Guy; Costa, Pedro J.M.

    2017-02-16

    Washover deposits on Fire Island, New York, from Hurricane Sandy in 2012 were investigated a year after the storm to document the sedimentary characteristics of hurricane washover features. Sediment data collected in the field includes stratigraphic descriptions and photos from trenches, bulk sediment samples, U-channels, and gouge and push cores. Samples and push cores were further analyzed in the laboratory for grain size, density variations using x-ray computed tomography (CT), and surface microtexture using a scanning electron microscope (SEM). Elevation profiles of washover features were measured using Differential Global Positioning System (DGPS) with Real Time Kinematic processing. The DGPS elevations were compared to lidar (light detection and ranging) data from pre- and post-Sandy surveys to assess the degree to which washover deposit thicknesses changed within the year following deposition. Hurricane Sandy washover deposits as much as 1 meter thick were observed in trenches. Initial results show that the upper parts of the deposits have been reworked significantly in some places by wind, but there are still areas where the deposits are almost entirely intact. Where mostly intact, the washover deposits consist of massive or weakly laminated sand near the base, overlain by more strongly laminated sands.

  19. Bed bug deterrence

    Directory of Open Access Journals (Sweden)

    Haynes Kenneth F

    2010-09-01

    Full Text Available Abstract A recent study in BMC Biology has determined that the immature stage of the bed bug (the nymph signals its reproductive status to adult males using pheromones and thus avoids the trauma associated with copulation in this species. The success of this nymphal strategy of deterrence is instructive. Against the background of increasing problems with bed bugs, this research raises the question whether pheromones might be used to control them. See research article http://www.biomedcentral.com/1741-7007/8/121

  20. in Spouted Bed

    Directory of Open Access Journals (Sweden)

    Bronislaw Buczek

    2013-01-01

    Full Text Available Samples of active coke, fresh and spent after cleaning flue gases from communal waste incinerators, were investigated. The outer layers of both coke particles were separately removed by comminution in a spouted bed. The samples of both active cokes were analysed by means of densities, mercury porosimetry, and adsorption technique. Remaining cores were examined to determine the degree of consumption of coke by the sorption of hazardous emissions (SO2, HCl, and heavy metals through its bed. Differences in contamination levels within the porous structure of the particles were estimated. The study demonstrated the effectiveness of commercial active coke in the cleaning of flue gases.

  1. Inverse magnetic fabric in unconsolidated sandy event deposits in Kiritappu Marsh, Hokkaido, Japan

    Science.gov (United States)

    Kon, Shusaku; Nakamura, Norihiro; Nishimura, Yuichi; Goto, Kazuhisa; Sugawara, Daisuke

    2017-03-01

    Anisotropy of magnetic susceptibility (AMS) and anisotropy of anhysteretic remanence magnetization (AARM) were evaluated for samples collected from units of two unconsolidated sandy event layers, presumed to be paleo-tsunami deposits, from Kiritappu Marsh, northeastern Japan. The AARM technique isolates the fabric of fine-grained (titano)magnetite from AMS fabric of all minerals in deposits. Bulk susceptibilities of the older event layer were weaker than those of the younger event layer. Our AMS results show that the principal minimum AMS axes (Kmin) were distributed along the horizontal bedding plane, suggesting the presence of an AMS ;inverse fabric; where magnetic axes are interchanged. Our AARM results indicated the principal maximum AARM axes (kmax) are parallel to the AMS Kmin, whereas the AARM intermediate and minimum axes (kint and kmin) are related to the AMS Kmax and Kint. Moreover, the shape of anisotropy parameters revealed that the AMS is oblate (Kmax ≈ Kint), whereas the AARM is prolate (kint ≈ kmin). We found the presence of single-domain sized titanomagnetites in the mud matrix based on electron microscopy observations. AARM is regarded as a complementary tool to estimate paleocurrent directions using grain fabrics of unconsolidated sediments. However, these lines of evidence confirm that our AMS fabrics showed ;inverse fabric;, providing no information about flow directions at this locality. Although this effect is uncommon in soft sediments, it requires caution to estimate paleocurrent directions using AMS.

  2. Physical criteria for distinguishing sandy tsunami and storm deposits using modern examples

    Science.gov (United States)

    Morton, Robert A.; Gelfenbaum, Guy; Jaffe, Bruce E.

    2007-01-01

    Modern subaerial sand beds deposited by major tsunamis and hurricanes were compared at trench, transect, and sub-regional spatial scales to evaluate which attributes are most useful for distinguishing the two types of deposits. Physical criteria that may be diagnostic include: sediment composition, textures and grading, types and organization of stratification, thickness, geometry, and landscape conformity. Published reports of Pacific Ocean tsunami impacts and our field observations suggest that sandy tsunami deposits are generally 30 cm thick, generally extend The distinctions between tsunami and storm deposits are related to differences in the hydrodynamics and sediment-sorting processes during transport. Tsunami deposition results from a few high-velocity, long-period waves that entrain sediment from the shoreface, beach, and landward erosion zone. Tsunamis can have flow depths greater than 10 m, transport sediment primarily in suspension, and distribute the load over a broad region where sediment falls out of suspension when flow decelerates. In contrast, storm inundation generally is gradual and prolonged, consisting of many waves that erode beaches and dunes with no significant overland return flow until after the main flooding. Storm flow depths are commonly

  3. The Safety of Hospital Beds

    Science.gov (United States)

    Gervais, Pierre; Pooler, Charlotte; Merryweather, Andrew; Doig, Alexa K.; Bloswick, Donald

    2015-01-01

    To explore the safety of the standard and the low hospital bed, we report on a microanalysis of 15 patients’ ability to ingress, move about the bed, and egress. The 15 participants were purposefully selected with various disabilities. Bed conditions were randomized with side rails up or down and one low bed with side rails down. We explored the patients’ use of the side rails, bed height, ability to lift their legs onto the mattress, and ability to turn, egress, and walk back to the chair. The standard bed was too high for some participants, both for ingress and egress. Side rails were used by most participants when entering, turning in bed, and exiting. We recommend that side rails be reconsidered as a means to facilitate in-bed movement, ingress, and egress. Furthermore, single deck height settings for all patients are not optimal. Low beds as a safety measure must be re-evaluated. PMID:28462302

  4. Spatial distribution of sandy desertificationchange in the west of Jilin Province

    Institute of Scientific and Technical Information of China (English)

    LIUHuiqing; XUJiawei; LVXinmiao

    2003-01-01

    The sandy land of the western part of Jilin Province is located in the ecotone of semi-humid and semi-arid area in the temperate zone of China. The sandy desertification has widely spread in the region because of the vulnerable natural conditions and the unreasonable human activity; as a result of this, the precious land resources and the economic development in the area have been seriously impacted. In this paper, the sandy land ecologic environment geographic information system is established based on the multi-spectral, multi-temporal Landsat TM images and field investigation. The comprehensive indexes of sandy desertification extent assessment which include vegetation degradation, wind erosion extent and soil depth are presented to classify the sandy land in western Jilin into three levels--slight, moderate and severe sandy desertification with the support of GIS platform. The results demonstrate that the sandy desertification has been partly controlled in the past twenty years, except some small sites. However, this doesn't necessarily mean that there is nothing for more concern. The two main causes of sandy desertification have not been eliminated yet, one is its natural factor, especially the physical and chemical characters of sandy soil and dry climate; another is the immoderate economic activity of human being that has highly accelerated the sandy desertification process.

  5. Active toroidal field ripple compensation and MHD feedback control coils in FAST

    Energy Technology Data Exchange (ETDEWEB)

    Ramogida, G., E-mail: giuseppe.ramogida@enea.it [Associazione Euratom-ENEA sulla Fusione, ENEA – C.R. Frascati, Via E. Fermi 45, I-00044 Frascati, RM (Italy); Calabrò, G.; Cocilovo, V.; Crescenzi, F.; Crisanti, F.; Cucchiaro, A. [Associazione Euratom-ENEA sulla Fusione, ENEA – C.R. Frascati, Via E. Fermi 45, I-00044 Frascati, RM (Italy); Di Gironimo, G. [Associazione Euratom-ENEA, CREATE – Università di Napoli Federico II, Via Claudio 21, I-80125 Napoli (Italy); Fresa, R. [Università della Basilicata, Via Nazario Sauro 85, I-85100 Potenza (Italy); Fusco, V. [Associazione Euratom-ENEA sulla Fusione, ENEA – C.R. Frascati, Via E. Fermi 45, I-00044 Frascati, RM (Italy); Martin, P. [Associazione Euratom-ENEA, Consorzio RFX, Corso Stati Uniti 4, I-35127, Padova (Italy); Mastrostefano, S. [Associazione Euratom-ENEA, CREATE – DIEI Università di Cassino, Via Di Biasio 43, I-03043 Cassino, FR (Italy); Mozzillo, R. [Associazione Euratom-ENEA, CREATE – Università di Napoli Federico II, Via Claudio 21, I-80125 Napoli (Italy); Nuzzolese, F. [Università della Basilicata, Via Nazario Sauro 85, I-85100 Potenza (Italy); Renno, F. [Associazione Euratom-ENEA, CREATE – Università di Napoli Federico II, Via Claudio 21, I-80125 Napoli (Italy); Rita, C. [Associazione Euratom-ENEA sulla Fusione, ENEA – C.R. Frascati, Via E. Fermi 45, I-00044 Frascati, RM (Italy); Villone, F. [Associazione Euratom-ENEA, CREATE – DIEI Università di Cassino, Via Di Biasio 43, I-03043 Cassino, FR (Italy); Vlad, G. [Associazione Euratom-ENEA sulla Fusione, ENEA – C.R. Frascati, Via E. Fermi 45, I-00044 Frascati, RM (Italy)

    2013-10-15

    Highlights: ► Active Ripple Compensating System (ARCS) consists of 18 off-centre poloidal coils between plasma and Toroidal Field Coils. ► The current in ARCS, adjustable and opposite to that in TFC, reduces the toroidal ripple below 0.2% at any toroidal fields. ► Feedback Active Control System (FACS) consists of two arrays of 9 in-vessel saddle coils fed by an MHD feedback controller. ► FACS allows robust feedback stabilization of low toroidal number MHD modes enabling plasma operations at low safety factor. ► ARCS and FACS are included in the whole FAST model and first engineering assessments show their feasibility and capability. -- Abstract: The Fusion Advanced Study Torus (FAST) has been proposed as a high magnetic field, compact size tokamak providing a flexible integrated environment to study physics and technology issues in ITER and DEMO relevant conditions. FAST has a quite large natural toroidal field ripple (around 1.5%) due to its compactness and to the number of access ports: this ripple must be lowered to an acceptable level to allow safe operations and a good confinement quality. An Active Ripple Compensating System (ARCS) has been designed, based on a set of poloidal coils placed between the plasma chamber and the Toroidal Field Coils (TFCs). These ARCS coils will be fed with adjustable currents, opposite in direction respect to the TFC currents, and will allow lowering the ripple up to zero and beyond. The CAD model of FAST including the ARCS coils has been completed and preliminary electromagnetic and thermal analyses have been carried out. Moreover, a Feedback Active Control System (FACS) composed of two arrays of in-vessel saddle coils has been designed to allow safe high plasma current, low safety factor operation and to mitigate possibly large ELMs effects in FAST. These FACS coils will be fed by a feedback system to control MHD modes: a first engineering assessment of the current requirements has been carried out.

  6. MULTISTAGE FLUIDIZED BED REACTOR

    Science.gov (United States)

    Jonke, A.A.; Graae, J.E.A.; Levitz, N.M.

    1959-11-01

    A multistage fluidized bed reactor is described in which each of a number of stages is arranged with respect to an associated baffle so that a fluidizing gas flows upward and a granular solid downward through the stages and baffles, whereas the granular solid stopsflowing downward when the flow of fluidizing gas is shut off.

  7. Fluidized bed combustion chamber

    Energy Technology Data Exchange (ETDEWEB)

    Kullendorff, A.; Wikner, J.

    1985-03-25

    The chamber is confined in a pressure vessel. The lower part of the chamber has tilted parallel gutters up to the height of the fluidized bed. The slope of the gutter walls is 5 degrees-15 degrees and the top area of the gutters is 1.3 to 3 times larger than their bottom.

  8. Bed Bug Myths

    Science.gov (United States)

    Learn the truth about bed bugs, such as how easy they are to see with the naked eye, their preferred habitat, whether they transmit diseases, their public health effects, and whether pesticides are the best way to deal with an infestation.

  9. Surviving Bed Rest

    Science.gov (United States)

    ... your pregnancy — and your bed rest start a family tree that you can share with your child someday firm up your baby-name choices; use books and websites for ideas organize photo albums read anything — ... people (friends and family) whom you know will probably give gifts build ...

  10. Effects of Fucus vesiculosus covering intertidal mussel beds in the Wadden Sea

    Science.gov (United States)

    Albrecht, A.; Reise, K.

    1994-06-01

    The brown alga Fucus vesiculosus forma mytili (Nienburg) Nienhuis covered about 70% of mussel bed ( Mytilus edulis) surface area in the lower intertidal zone of Königshafen, a sheltered sandy bay near the island of Sylt in the North Sea. Mean biomass in dense patches was 584 g ash-free dry weight m-2 in summer. On experimental mussel beds, fucoid cover enhanced mud accumulation and decreased mussel density. The position of mussels underneath algal canopy was mainly endobenthic (87% of mussels with >1/3 of shell sunk into mud). In the absence of fucoids, mussels generated epibenthic garlands (81% of mussels with Fucus vesiculosus on mussel beds in the intertidal Wadden Sea affects mussels and their epibionts negatively, but supports various herbivores and increases overall benthic diversity.

  11. Fourier Series Learning Control for Torque Ripple Minimization in Permanent Magnet Synchronous Motors

    Directory of Open Access Journals (Sweden)

    Eduardo Espíndola-López

    2016-09-01

    Full Text Available A new Fourier Series Learning Controller (FSLC for velocity control on a Permanent Magnet Synchronous Motor (PMSM is proposed and implemented. An analysis of the error convergence for the FSLC is presented, and the update law for the Fourier series coefficients is specified. The field-oriented control method is used as a basic element to implement three different controllers for a PMSM. The performance of the FSLC is compared with two control methods, a classical PI (Proportional Integral controller and an artificial neural network controller. The periodic nature of torque ripple in PMSMs is considered as a periodic disturbance, which must be compensated by the controller. With the FSLC implementation, a substantial reduction of the velocity ripple is obtained. Furthermore, a higher speed of learning is achieved with the FSLC in comparison with the artificial neural network.

  12. Monte Carlo Simulations of New 2D Ripple Filters for Particle Therapy Facilities

    DEFF Research Database (Denmark)

    Ringbæk, Toke Printz; Weber, Uli; Petersen, Jørgen B.B.

    2014-01-01

    for various ion types, initial particle energies and distances from the RiFi to the phantom surface as well as in the depth of the phantom. The beam delivery and monitor system (BAMS) used at Marburg, the Heidelberg Ionentherapiezentrum (HIT), Universit ̈tsklinikum Heidelberg, Germany and the GSI...... expressions for dmax and d0.01 ; both are inversely related to the angular distribution. Increasing scatter from the beam delivery and monitoring system results in reduced dmax and d0.01 . Furthermore, dmax and d0.01 are found to be proportional to the ripple filter period λ. Conclusion: Our findings clearly......Introduction: At particle therapy facilities with pencil beam scanning, the implementation of a Ripple Filter (RiFi) broadens the Bragg peak (BP), which leads to fewer energy steps from the accelerator required to obtain a homogeneous dose coverage of the planned target volume (PTV...

  13. Emergent spontaneous symmetry breaking and emergent symmetry restoration in rippling gravitational background

    Energy Technology Data Exchange (ETDEWEB)

    Kurkov, Maxim A. [Universidade Federal do ABC, CMCC, Santo Andre, SP (Brazil)

    2016-06-15

    We study effects of a rippling gravitational background on a scalar field with a double well potential, focusing on the analogy with the well known dynamics of the Kapitza's pendulum. The ripples are rendered as infinitesimal but rapidly oscillating perturbations of the scale factor. We find that the resulting dynamics crucially depends on a value of the parameter ξ in the ξRφ{sup 2} vertex. For the time-dependent perturbations of a proper form the resulting effective action is generally covariant, and at a high enough frequency at ξ < 0 and at ξ > 1/6 the effective potential has a single minimum at zero, thereby restoring spontaneously broken symmetry of the ground state. On the other side, at 0 < ξ < 1/6 spontaneous symmetry breaking emerges even when it is absent in the unperturbed case. (orig.)

  14. Targets, ripples and spirals in a precipitation system with anomalous dispersion.

    Science.gov (United States)

    Ayass, Mahmoud M; Lagzi, Istvan; Al-Ghoul, Mazen

    2015-08-14

    We present a novel reaction-diffusion system that exhibits three-dimensional superdiffusive traveling waves without utilizing any external forces. These waves include single circular targets, spirals, and ripples as well as phase-like waves. The system is based on the interplay of the precipitation reaction of mercuric iodide in a gel medium, its polymorphic transformation to a different crystalline form, and its redissolution in excess iodide. A phase diagram is constructed as a function of the initial concentrations of the reagents. The spatiotemporal evolution of these waves is thoroughly analyzed and seems to be a consequence of an anomalous dispersion relationship. Pattern selection and wavelengths of propagating waves are found to depend on initial concentrations of the reactants. The breakup of the waves is also investigated. While the breakdown of ripples and spirals is shown to be a consequence of a Doppler-like instability in conjunction with anomalous dispersion, the targets undergo a boundary defect-mediated breakup.

  15. Prediction of subharmonic oscillation in switching regulators: from a slope to a ripple standpoint

    Science.gov (United States)

    El Aroudi, A.; Al-Numay, M.; Calvente, J.; Giral, R.; Rodriguez, E.; Alarcón, E.

    2016-12-01

    New exact critical conditions for predicting subharmonic instability in switching regulators are approximated by simple design-oriented expressions valid under practical conditions. These simplified expressions contain the ripple and slope information of the feedback control signal. Depending on the converter topology, the controller used and values of parasitic parameters, either the slope or the ripple can be dominant in predicting instability. A discussion on the validity of this interpretation is illustrated through six different examples of switching regulators using the concept of the spectral radius and the relative degree of the system loop. Using this approach, the boundary between the desired stable region and the subharmonic instability can be easily obtained. The theoretical results are validated by means of numerical simulations.

  16. Toward Improving Prediction of Sediment Transport over Wave-Induced Ripples

    CERN Document Server

    Absi, Rafik

    2011-01-01

    Sediment transport over wave-induced ripples is a very complex phenomenon where available models fail to provide accurate predictions. For coastal engineering applications, the 1-DV advection-diffusion equation could be used with an additional parameter {\\alpha} related to the process of vortex shedding above ripples (Absi, 2010). The aim of this study is to provide simple practical analytical tools. An analytical eddy viscosity profile was validated by DNS data of turbulent channel flows (Absi et al., 2011). In this study, we will show that: (1) the period-averaged eddy viscosity in oscillatory boundary layers could be described by this simple analytical formulation; (2) The shape of the vertical profile is validated by period-averaged eddy viscosity of baseline (BSL) k-{\\omega} model (Suntoyo and Tanaka, 2009) for sinusoidal and asymmetric waves; (3) The vertical eddy viscosity profile depends on the wave non-linearity parameter and requires therefore a specific calibration.

  17. Observing trans-Planckian ripples in the primordial power spectrum with future large scale structure probes

    Energy Technology Data Exchange (ETDEWEB)

    Hamann, Jan [LAPTH (Laboratoire d' Annecy-le-Vieux de Physique Theorique, CNRS UMR5108 and Universite de Savoie), BP 110, F-74941 Annecy-le-Vieux Cedex (France); Hannestad, Steen; Sloth, Martin S [Department of Physics and Astronomy, University of Aarhus, Ny Munkegade, DK-8000 Aarhus C (Denmark); Wong, Yvonne Y Y, E-mail: hamann@lapp.in2p3.fr, E-mail: sth@phys.au.dk, E-mail: sloth@phys.au.dk, E-mail: ywong@mppmu.mpg.de [Max-Planck-Institut fuer Physik (Werner-Heisenberg-Institut), Foehringer Ring 6, D-80805 Muenchen (Germany)

    2008-09-15

    We revisit the issue of ripples in the primordial power spectra caused by trans-Planckian physics, and the potential for their detection by future cosmological probes. We find that for reasonably large values of the first slow-roll parameter {epsilon} ({approx}>0.001), a positive detection of trans-Planckian ripples can be made even if the amplitude is as low as 10{sup -4}. Data from the Large Synoptic Survey Telescope (LSST) and the proposed future 21 cm survey with the Fast Fourier Transform Telescope (FFTT) will be particularly useful in this regard. If the scale of inflation is close to its present upper bound, a scale of new physics as high as {approx}0.2 M{sub P} could lead to observable signatures.

  18. Observing trans-Planckian ripples in the primordial power spectrum with future large scale structure probes

    CERN Document Server

    Hamann, Jan; Sloth, Martin S; Wong, Yvonne Y Y

    2008-01-01

    We revisit the issue of ripples in the primordial power spectra caused by trans-Planckian physics, and the potential for their detection by future cosmological probes. We find that for reasonably large values of the first slow-roll parameter epsilon (> 0.001), a positive detection of trans-Planckian ripples can be made even if the amplitude is as low as 10^-4. Data from the Large Synoptic Survey Telescope (LSST) and the proposed future 21 cm survey with the Fast Fourier Transform Telescope (FFTT) will be particularly useful in this regard. If the scale of inflation is close to its present upper bound, a scale of new physics as high as 0.2 M_Planck could lead to observable signatures.

  19. Water level response in back-barrier bays unchanged following Hurricane Sandy

    Science.gov (United States)

    Aretxabaleta, Alfredo L.; Butman, Bradford; Ganju, Neil K.

    2014-01-01

    On 28–30 October 2012, Hurricane Sandy caused severe flooding along portions of the northeast coast of the United States and cut new inlets across barrier islands in New Jersey and New York. About 30% of the 20 highest daily maximum water levels observed between 2007 and 2013 in Barnegat and Great South Bay occurred in 5 months following Hurricane Sandy. Hurricane Sandy provided a rare opportunity to determine whether extreme events alter systems protected by barrier islands, leaving the mainland more vulnerable to flooding. Comparisons between water levels before and after Hurricane Sandy at bay stations and an offshore station show no significant differences in the transfer of sea level fluctuations from offshore to either bay following Sandy. The post-Hurricane Sandy bay high water levels reflected offshore sea levels caused by winter storms, not by barrier island breaching or geomorphic changes within the bays.

  20. Bathing a patient in bed

    Science.gov (United States)

    ... medlineplus.gov/ency/patientinstructions/000427.htm Bathing a patient in bed To use the sharing features on this page, please enable JavaScript. Some patients cannot safely leave their beds to bathe. For ...

  1. VA National Bed Control System

    Data.gov (United States)

    Department of Veterans Affairs — The VA National Bed Control System records the levels of operating, unavailable and authorized beds at each VAMC, and it tracks requests for changes in these levels....

  2. Analysis of Commutation Torque Ripple Minimization for Brushless DC Motor Based on SEPIC Converter

    OpenAIRE

    R.Jogarao; Mouliswararao.Reddy; G. Ashok

    2016-01-01

    Brushless DC Motors (BLDCM) are widely used in automated industrial applications like Computer Numerical Control (CNC) machinery, aerospace applications and in the field of robotics.But it still suffers from commutation torque which mainly depends on speed and transient line commutation interval. BLDC MOTOR torque ripple causes increased acoustic noise and undesirable speed fluctuation. This paper presents a new circuit topology and dc link voltage current in the control strategy to keep inco...

  3. Study of the Power Supply Ripple Effect on teh Dynamics at SPEAR

    Energy Technology Data Exchange (ETDEWEB)

    Terebilo, A.; Pellegrini, C.; /UCLA; Cornacchia, M.; Corbett, J.; Martin, D.; /SLAC

    2011-09-14

    For long term stability analysis time variation of tunes is important. We have proposed and tested a technique for measuring the magnitude of this variation. This was made possible by using tune extraction algorithms that require small number of turns thus giving an instantaneous tune of the machine. In this paper we demonstrate the measured effect of the tune modulation with 60 Hz power supplies ripple, power line interference from SLAC linac operating at 30 Hz repetition rate, and nonperiodic variation.

  4. Modeling AC ripple currents in HTS coated conductors by integral equations

    Science.gov (United States)

    Grilli, Francesco; Xu, Zhihan

    2016-12-01

    In several HTS applications, the superconducting tapes experience the simultaneous presence of DC and AC excitations. For example in high-current DC cables, where the transport current is not perfectly constant, but it exhibits some ripples at different frequencies introduced by the rectification process (AC-DC conversion). These ripples give rise to dissipation, whose magnitude and possible influence on the device's cooling requirements need to be evaluated. Here we report a study of the AC losses in a HTS coated conductor subjected to DC currents and AC ripples simultaneously. The modeling approach is based on an integral equation method for thin superconductors: the superconducting tape is modeled as a 1-D object with a non-linear resistivity, which includes the dependence of the critical current density Jc on the magnetic field. The model, implemented in a commercial finite-element program, runs very fast (the simulation of one AC cycle typically takes a few seconds on standard desktop workstation): this allows simulating a large number of cycles and estimating when the AC ripple losses stabilize to a constant value. The model is used to study the influence of the flux creep power index n on the stabilization speed and on the AC loss values, as well as the effect of using a field-dependent Jc instead of a constant one. The simulations confirm that the dissipation level should not be a practical concern in HTS DC cables. At the same time, however, they reveal a strong dependence of the results upon the power index n and the form of Jc , which spurs the question whether the power-law is the most suitable description of the superconductor's electrical behavior for this kind of analysis.

  5. Assessment of waveform control method for mitigation of low-frequency current ripple

    OpenAIRE

    Zhu, GR; Wang, HR; Xiao, CY; Kang, Y.; Tan, SC

    2013-01-01

    Waveform control method can mitigate such a low-frequency ripple current being drawn from the DC distribution while the DC distribution system delivers AC power to the load through a differential inverter. Assessment on the waveform control method and comparative study between with and without waveform control method are proposed in this paper1. Experimental results are provided to explain the operation and showcase the performance between with and without the waveform control method. Results...

  6. A generalized discrete model linking rippling pattern formation and individual cell reversal statistics in colonies of myxobacteria

    Science.gov (United States)

    Börner, Uwe; Deutsch, Andreas; Bär, Markus

    2006-06-01

    Self-organization processes in multicellular aggregates of bacteria and amoebae offer fascinating insights into the evolution of cooperation and differentiation of cells. During myxobacterial development a variety of spatio-temporal patterns emerges such as counterpropagating waves of cell density that are known as rippling. Recently, several models have been introduced that qualitatively reproduce these patterns. All models include active motion and a collision-triggered reversal of individual bacteria. Here, we present a systematic study of a generalized discrete model that is based on similar assumptions as the continuous model by Igoshin et al (2001 Proc. Natl Acad. Sci. USA 98 14913). We find counterpropagating as well as unidirectional rippling waves in extended regions of the parameter space. If the interaction strength and the degree of cooperativity are large enough, rippling patterns appear even in the absence of a refractory period. We show for the first time that the experimentally observed double peak in the reversal statistics of bacteria in rippling colonies (Welch and Kaiser 2001 Proc. Natl Acad. Sci. USA 98 14907) can be reproduced in simulations of counterpropagating rippling waves which are dominant in experiments. In addition, the reversal statistics in the pre-rippling phase is correctly reproduced.

  7. Comparison of Output Current Ripple in Single and Dual Three-Phase Inverters for Electric Vehicle Motor Drives

    Directory of Open Access Journals (Sweden)

    Jelena Loncarski

    2015-04-01

    Full Text Available The standard solution for the traction system in battery powered electric vehicles (EVs is a two-level (2L inverter feeding a three-phase motor. A simple and effective way to achieve a three-level (3L inverter in battery-supplied electric vehicles consists of using two standard three-phase 2L inverters with the open-end winding connection of standard three-phase ac motors. The 3L inverter solution can be usefully adopted in EVs since it combines several benefits such as current ripple reduction, increment of phase motor voltage with limited voltage ratings of the two battery banks, improvement in system reliability, etc. The reduction in current ripple amplitude is particularly relevant since it is a source of electromagnetic interference and audio noise from the inverter-motor power connection cables and from the motor itself. By increasing the inverter switching frequency the ripple amplitude is reduced, but the drive efficiency decreases due to the proportionally increased switching losses. In this paper the peak-to-peak ripple amplitude of the dual-2L inverter is evaluated and compared with the corresponding ripple of the single-2L inverter, considering the same voltage and power motor ratings. The ripple analysis is carried out as a function of the modulation index to cover the whole modulation range of the inverter, and the theoretical results are verified with experimental tests carried out by an inverter-motor drive prototype.

  8. Hippocampal sharp wave‐ripple: A cognitive biomarker for episodic memory and planning

    Science.gov (United States)

    2015-01-01

    ABSTRACT Sharp wave ripples (SPW‐Rs) represent the most synchronous population pattern in the mammalian brain. Their excitatory output affects a wide area of the cortex and several subcortical nuclei. SPW‐Rs occur during “off‐line” states of the brain, associated with consummatory behaviors and non‐REM sleep, and are influenced by numerous neurotransmitters and neuromodulators. They arise from the excitatory recurrent system of the CA3 region and the SPW‐induced excitation brings about a fast network oscillation (ripple) in CA1. The spike content of SPW‐Rs is temporally and spatially coordinated by a consortium of interneurons to replay fragments of waking neuronal sequences in a compressed format. SPW‐Rs assist in transferring this compressed hippocampal representation to distributed circuits to support memory consolidation; selective disruption of SPW‐Rs interferes with memory. Recently acquired and pre‐existing information are combined during SPW‐R replay to influence decisions, plan actions and, potentially, allow for creative thoughts. In addition to the widely studied contribution to memory, SPW‐Rs may also affect endocrine function via activation of hypothalamic circuits. Alteration of the physiological mechanisms supporting SPW‐Rs leads to their pathological conversion, “p‐ripples,” which are a marker of epileptogenic tissue and can be observed in rodent models of schizophrenia and Alzheimer's Disease. Mechanisms for SPW‐R genesis and function are discussed in this review. © 2015 The Authors Hippocampus Published by Wiley Periodicals, Inc. PMID:26135716

  9. Sterile Acellular Dermal Collagen as a Treatment for Rippling Deformity of Breast

    Directory of Open Access Journals (Sweden)

    Brittany Busse

    2014-01-01

    Full Text Available Prosthetic implants are frequently used for breast augmentation and breast reconstruction following mastectomy. Unfortunately, long-term aesthetic results of prosthetic breast restoration may be hindered by complications such as rippling, capsular contracture, and implant malposition. The advent of use of acellular dermal matrices has greatly improved the outcomes of prosthetic breast reconstruction. We describe a case of rippling deformity of breast that was treated using an acellular dermal matrix product, AlloMax. The patient presented with visible rippling of bilateral prosthetic breast implants as well as significant asymmetry of the breasts after multiple excisional biopsies for right breast ductal carcinoma in situ. A 6×10 cm piece of AlloMax was placed on the medial aspect of each breast between the implant and the skin flap. Follow-up was performed at 1 week, 3 months, and 1 year following the procedure. The patient recovered well from the surgery and there were no complications. At her first postoperative follow-up the patient was extremely satisfied with the result. At her 3-month and 1-year follow-up she had no recurrence of her previous deformity and no new deformity.

  10. Evolution of ripple morphology on Si(1 0 0) by 60-keV argon ions

    Energy Technology Data Exchange (ETDEWEB)

    Garg, Sandeep Kumar, E-mail: sandeep@iopb.res.in [Institute of Physics, Sachivalaya Marg, Bhubaneswar 751005 (India); Venugopal, V.; Basu, T. [Institute of Physics, Sachivalaya Marg, Bhubaneswar 751005 (India); Sinha, O.P. [Amity Institute of Nano Technology, Amity University, Noida 201303 (India); Rath, S. [Department of Physics and Astrophysics, University of Delhi, Delhi 110007 (India); Kanjilal, D. [Inter-Univeristy Accelerator Centre, Aruna Asaf Ali Marg, New Delhi 110067 (India); Som, T. [Institute of Physics, Sachivalaya Marg, Bhubaneswar 751005 (India)

    2012-02-15

    In this paper, we report on evolution of ripple morphology on Si(1 0 0) surface due to 60 keV Ar{sup +}-ion implantation to the fluence of 2 Multiplication-Sign 10{sup 18} ions cm{sup -2} and over a large incident angular window of 075 Degree-Sign . Room temperature implantations were carried out by using a uniform current density of 20 {mu}A cm{sup -2}. Atomic force microscopic (AFM) studies indicate that ripple morphology starts to appear at an incident angle 45 Degree-Sign and becomes more prominent at higher incident angles. AFM studies also reveal that while the ripple wavelength decreases with increasing angle of incidence, the amplitude increases with the same. We also observe a systematic variation in the surface roughness with incident angle. Micro-Raman studies show that the sub-surface silicon layer becomes amorphous whose depth keeps reducing at higher incident angles. The results are attributed to viscous flow mechanism.

  11. Torque Ripple Minimization and Performance Investigation of an In-Wheel Permanent Magnet Motor

    Directory of Open Access Journals (Sweden)

    A. Mansouri

    2016-06-01

    Full Text Available Recently, electric vehicle motoring has become a topic of interest, due to the several problems caused by thermal engines such as pollution and high oil prices. Thus, electric motors are increasingly applied in vehicle’ applications and relevant research about these motors and their applications has been performed. Of particular interest are the improvements regarding torque production capability, the minimization of torque ripple and iron losses. The present work deals with the optimum design and the performance investigation of an outer rotor permanent magnet motor for in-wheel electric vehicle application. At first, and in order to find the optimum motor design, a new based particle-swarm multi-objective optimization procedure is applied. Three objective functions are used: efficiency maximization, weight and ripple torque minimization. Secondly, the effects of the permanent magnets segmentation, the stator slots opening, and the separation of adjacent magnets by air are outlined. The aim of the paper is the design of a topology with smooth output torque, low ripple torque, low iron losses and mechanical robustness.

  12. Novel torque ripple minimization algorithm for direct torque control of induction motor drive

    Institute of Scientific and Technical Information of China (English)

    LONG Bo; GUO Gui-fang; HAO Xiao-hong; LI Xiao-ning

    2009-01-01

    To elucidate the principles of notable torque and flux ripple during the steady state of the conventional direct torque control (DTC) of induction machines, the factors of influence torque variation are examined. A new torque ripple minimization algorithm is proposed. The novel method eradicated the torque ripple by imposing the required stator voltage vector in each control cycle. The M and T axial components of the stator voltage are accomplished by measuring the stator flux error and the expected incremental value of the torque at every sampling time. The maximum angle rotation allowed is obtained. Experimental results showed that the proposed method combined with the space vector pulse width modulation(SVPWM) could be implemented in most existing digital drive controllers, offering high performance in both steady and transient states of the induction drives at full speed range. The result of the present work imphes that torque fluctuation could be eliminated by imposing proper stator voltage, and the proposed scheme could not only maintain constant switching frequency for the inverter, but also solve the heating problem and current harmonics in traditional induction motor drives.

  13. Wrinkled, rippled and crumpled graphene: an overview of formation mechanism, electronic properties, and applications

    Directory of Open Access Journals (Sweden)

    Shikai Deng

    2016-05-01

    Full Text Available Distinctive from their 1D and 0D counterparts, 2D nanomaterials (2DNs exhibit surface corrugations (wrinkles and ripples and crumples. Thermal vibrations, edge instabilities, thermodynamically unstable (interatomic interactions, strain in 2D crystals, thermal contraction, dislocations, solvent trapping, pre-strained substrate-relaxation, surface anchorage and high solvent surface tension during transfer cause wrinkles or ripples to form on graphene. These corrugations on graphene can modify its electronic structure, create polarized carrier puddles, induce pseudomagnetic field in bilayers and alter surface properties. This review outlines the different mechanisms of wrinkle, ripple and crumple formation, and the interplay between wrinkles’ and ripples’ attributes (wavelength/width, amplitude/height, length/size, and bending radius and graphene's electronic properties and other mechanical, optical, surface, and chemical properties. Also included are brief discussions on corrugation-induced reversible wettability and transmittance in graphene, modulation of its chemical potential, enhanced energy storage and strain sensing via relaxation of corrugations. Finally, the review summarizes the future areas of research for 2D corrugations and crumples.

  14. Hippocampal sharp wave-ripple: A cognitive biomarker for episodic memory and planning.

    Science.gov (United States)

    Buzsáki, György

    2015-10-01

    Sharp wave ripples (SPW-Rs) represent the most synchronous population pattern in the mammalian brain. Their excitatory output affects a wide area of the cortex and several subcortical nuclei. SPW-Rs occur during "off-line" states of the brain, associated with consummatory behaviors and non-REM sleep, and are influenced by numerous neurotransmitters and neuromodulators. They arise from the excitatory recurrent system of the CA3 region and the SPW-induced excitation brings about a fast network oscillation (ripple) in CA1. The spike content of SPW-Rs is temporally and spatially coordinated by a consortium of interneurons to replay fragments of waking neuronal sequences in a compressed format. SPW-Rs assist in transferring this compressed hippocampal representation to distributed circuits to support memory consolidation; selective disruption of SPW-Rs interferes with memory. Recently acquired and pre-existing information are combined during SPW-R replay to influence decisions, plan actions and, potentially, allow for creative thoughts. In addition to the widely studied contribution to memory, SPW-Rs may also affect endocrine function via activation of hypothalamic circuits. Alteration of the physiological mechanisms supporting SPW-Rs leads to their pathological conversion, "p-ripples," which are a marker of epileptogenic tissue and can be observed in rodent models of schizophrenia and Alzheimer's Disease. Mechanisms for SPW-R genesis and function are discussed in this review.

  15. Sub-wavelength Ripple Formation on Silicon Induced by Femtosecond Laser Radiation

    Institute of Scientific and Technical Information of China (English)

    ZHOU Ming; YUAN Dong-Qing; ZHANG Wei; SHEN Jian; LI Bao-Jia; SONG Juan; CAI Lan

    2009-01-01

    Periodic microstructures on silicon bulk are formed by the irradiation of the femtosecond laser with the laser wavelength of 8OO nm and the pulse length of 130 fs.We investigate the surface periodic ripple structures produced by femtosecond laser treatment.The effects of feedrate of sample,v,on laser-induced surface topography are studied.We find that the femtosecond laser produce periodic ripples of the sub-micron level on silicon surface.At the same time,we realize the optimal conditions to produce these surface structures.When choosing N A=0.3,and v = 2000 μm/s or 3000 μm/s,we find a series of periodic-structure ripples where the spacing is about 120 nm and the width is about 450 nm.The experimental results indicate that femtosecond laser treatment can produce line arrays on the sub-micron level,which is a positive factor for fabricating grating and other optical applications in nanoscales.

  16. Three-dimensional surface maps link local atrophy and fast ripples in human epileptic hippocampus.

    Science.gov (United States)

    Ogren, Jennifer A; Wilson, Charles L; Bragin, Anatol; Lin, Jack J; Salamon, Noriko; Dutton, Rebecca A; Luders, Eileen; Fields, Tony A; Fried, Itzhak; Toga, Arthur W; Thompson, Paul M; Engel, Jerome; Staba, Richard J

    2009-12-01

    There is compelling evidence that pathological high-frequency oscillations (HFOs), called fast ripples (FR, 150-500Hz), reflect abnormal synchronous neuronal discharges in areas responsible for seizure genesis in patients with mesial temporal lobe epilepsy (MTLE). It is hypothesized that morphological changes associated with hippocampal atrophy (HA) contribute to the generation of FR, yet there is limited evidence that hippocampal FR-generating sites correspond with local areas of atrophy. Interictal HFOs were recorded from hippocampal microelectrodes in 10 patients with MTLE. Rates of FR and ripple discharge from each microelectrode were evaluated in relation to local measures of HA obtained using 3-dimensional magnetic resonance imaging (MRI) hippocampal modeling. Rates of FR discharge were 3 times higher in areas of significant local HA compared with rates in nonatrophic areas. Furthermore, FR occurrence correlated directly with the severity of damage in these local atrophic regions. In contrast, we found no difference in rates of ripple discharge between local atrophic and nonatrophic areas. The proximity between local HA and microelectrode-recorded FR suggests that morphological changes such as neuron loss and synaptic reorganization may contribute to the generation of FR. Pathological HFOs, such as FR, may provide a reliable surrogate marker of abnormal neuronal excitability in hippocampal areas responsible for the generation of spontaneous seizures in patients with MTLE. Based on these data, it is possible that MRI-based measures of local HA could identify FR-generating regions, and thus provide a noninvasive means to localize epileptogenic regions in hippocampus.

  17. The INES System; 2, Ripple Correction and Absolute Calibration for IUE High Resolution Spectra

    CERN Document Server

    Cassatella, A; González-Riestra, R; Ponz, J D; Barbero, J F G; Talavera, A; Wamsteker, W

    1999-01-01

    In this paper we document the results of the study which led to the ripple correction and absolute calibration algorithms applied to the high resolution spectra processed with the NEWSIPS software for the Final Archive of the IUE Project. In this analysis, based on a very large number of spectra, we find that both K and the alpha parameters (not only the former as previously believed) vary with order number. This fact, together with the finding that the central peaks of the blaze function vary also as a function of the THDA temperature (for the SWP camera) and of the date of observations (for the LWP and LWR cameras), makes the ripple correction algorithm more complex than previously considered but, at the same time, considerably more reliable. As for the high resolution absolute calibration, the method followed is similar to the one implemented in IUESIPS. The internal accuracy of the high resolution calibration is about 4%. We note that the ripple correction and absolute calibration algorithms here describe...

  18. Oriented gold ripple-like structures on poly-L-lactic acid

    Energy Technology Data Exchange (ETDEWEB)

    Juřík, Petr, E-mail: petr.jurik@gmail.com [Department of Solid State Engineering, Institute of Chemical Technology, Prague (Czech Republic); Slepička, Petr [Department of Solid State Engineering, Institute of Chemical Technology, Prague (Czech Republic); Mistrík, Jan; Janíček, Petr [Department of Applied Physics and Mathematics, University of Pardubice (Czech Republic); Rimpelová, Silvie [Department of Biochemistry and Microbiology, Institute of Chemical Technology, Prague (Czech Republic); Kolská, Zdeňka [Faculty of Science, University of J. E. Purkyně, Ústí nad Labem (Czech Republic); Švorčík, Václav [Department of Solid State Engineering, Institute of Chemical Technology, Prague (Czech Republic)

    2014-12-01

    Highlights: • We prepared oriented ripple-like structures on polymer surface with thin gold layer. • These structures show preferential orientation over large areas which is unusual for heat induced wrinkling. • Significant electrical and optical anisotropy was observed. • Zeta-potential, XPS, goniometry and ellipsometry suggest formation of gold lines separated by polymer gaps. • Increase in cell growth in comparison with poly-styrene mock was observed. - Abstract: In this paper chemical, morphological, electrical and biological properties of poly-L-lactic acid thin films with gold nanolayers were studied. These samples were examined as-sputtered and annealed at glass transition temperature. Morphological changes of poly-L-lactic films introduced by annealing were studied by means of atomic force microscopy. This method showed formation of oriented ripple-like structures on the surface of the film. X-ray photoelectron spectroscopy, goniometry, ellipsometry, sheet resistance measurement and electrokinetic analysis were used to determine distribution of gold on the surface. Combined data suggests that these ripple-like structures were formed by gold lines with insulating polymer gaps in between. These lines show preferential orientation over large areas and under proper conditions offer simple way to form electrically anisotropic material on large scale. Also cytocompatibility was studied showing increased cell adhesion and proliferation of mouse embryonic fibroblasts offering another use for these easily formed structures.

  19. Torque Ripple Suppression in an External-Meshed Magnetic Gear Train

    Directory of Open Access Journals (Sweden)

    Yi-Chang Wu

    2013-01-01

    Full Text Available Magnetic gear trains transmit torque through noncontact magnetic couplings rather than conjugate gear teeth; they have the unique advantages of reduced maintenance and improved reliability, inherent overload protection, high efficiency, precise peak torque transmission, and tolerance for misalignment. Smooth and steadily transmitted torque is an important characteristic for a magnetic gear train. It is necessary for the reduction of possible mechanical vibration, position inaccuracy, and acoustic noise. This paper investigates the transmitted torque characteristics, especially torque ripple reduction, of an external-meshed magnetic gear train using finite-element analysis (FEA. The topological structure and working principles of a simple magnetic gear train with parallel axes are introduced. With the aid of a commercial FEA package, the transmitted torque waveform of a magnetic gear train is numerically calculated. The effects of geometrical parameters on the maximum transmitted torque and torque ripple are further discussed in terms of obtaining a magnetic gear train with high transmitted torque or low torque ripple. This examination offers insights beneficial to future magnetic gear mechanism design.

  20. Study on weld pool behaviors and ripple formation in dissimilar welding under pulsed laser

    Science.gov (United States)

    Liang, Rong; Luo, Yu

    2017-08-01

    A three-transient numerical model is developed to study the dissimilar metal welding under pulsed laser. The melting, resolidification and vaporization inducing recoil pressure are considered in this model. Their effects on molten pool dynamic and the weld bead formation are studied. The similar metal welding and dissimilar metal welding under pulsed laser are respectively simulated by using this model. It is found that surface ripples are caused mainly by the periodical laser and molten pool solidification. In the first, this model is validated by the weld bead geometry comparison between the simulated and experimental results in similar metal welding. Then, this model is applied to simulate the dissimilar metal welding under pulsed laser. The results show that the distributions of the temperature, melt-flow velocity and surface ripples are asymmetric due to the differences in physical properties of the materials. The higher pulse overlapping factor decreases the solidification rate, leading to the more uniform penetration depths and the finer ripples. Good agreements between the experimental observations and simulation results are obtained by the proposed model.

  1. Ripple-modulated electronic structure of a 3D topological insulator.

    Science.gov (United States)

    Okada, Yoshinori; Zhou, Wenwen; Walkup, D; Dhital, Chetan; Wilson, Stephen D; Madhavan, V

    2012-01-01

    Three-dimensional topological insulators host linearly dispersing states with unique properties and a strong potential for applications. An important ingredient in realizing some of the more exotic states in topological insulators is the ability to manipulate local electronic properties. Direct analogy to the Dirac material graphene suggests that a possible avenue for controlling local properties is via a controlled structural deformation such as the formation of ripples. However, the influence of such ripples on topological insulators is yet to be explored. Here we use scanning tunnelling microscopy to determine the effects of one-dimensional buckling on the electronic properties of Bi(2)Te(3.) By tracking spatial variations of the interference patterns generated by the Dirac electrons we show that buckling imposes a periodic potential, which locally modulates the surface-state dispersion. This suggests that forming one- and two-dimensional ripples is a viable method for creating nanoscale potential landscapes that can be used to control the properties of Dirac electrons in topological insulators.

  2. Minimization of Torque Ripple in DTC of Induction Motor Using Fuzzy Mode Duty Cycle Controller

    Directory of Open Access Journals (Sweden)

    Turki Y. Abdalla

    2011-06-01

    Full Text Available Among all control methods for induction motor drives, Direct Torque Control (DTC seems to be particularly interesting being independent of machine rotor parameters and requiring no speed or position sensors. The DTC scheme is characterized by the absence of PI regulators, coordinate transformations, current regulators and PWM signals generators. In spite of its simplicity, DTC allows a good torque control in steady state and transient operating conditions to be obtained. However, the presence of hysterics controllers for flux and torque could determine torque and current ripple and variable switching frequency operation for the voltage source inverter. This paper is aimed to analyze DTC principles, and the problems related to its implementation, especially the torque ripple and the possible improvements to reduce this torque ripple by using a proposed fuzzy based duty cycle controller. The effectiveness of the duty ratio method was verified by simulation using Matlab/Simulink software package. The results are compared with that of the traditional DTC models.

  3. Performances improvements and torque ripple minimization for VSI fed induction machine with direct control torque.

    Science.gov (United States)

    Abdelli, R; Rekioua, D; Rekioua, T

    2011-04-01

    This paper describes a torque ripple reduction technique with constant switching frequency for direct torque control (DTC) of an induction motor (IM). This method enables a minimum torque ripple control. In order to obtain a constant switching frequency and hence a torque ripple reduction, we propose a control technique for IM. It consists of controlling directly the electromagnetic torque by using a modulated hysteresis controller. The design methodology is based on space vector modulation (SVM) of electrical machines with digital vector control. MATLAB simulations supported with experimental study are used. The simulation and experimental results of this proposed algorithm show an adequate dynamic to IM; however, the research can be extended to include synchronous motors as well. The implementation of the proposed algorithm is described. It doesn't require any PI controller in the torque control loop. The hardware inverter is controlled digitally using a Texas Instruments TMS320F240 digital signal processor (DSP) with composed C codes for generating the required references. The results obtained from simulation and experiments confirmed the feasibility of the proposed strategy compared to the conventional one.

  4. AC Loss of Ripple Current in Superconducting DC Power Transmission Cable

    Science.gov (United States)

    Yoshitomi, K.; Otabe, E. S.; Vyatkin, V. S.; Kiuchi, M.; Matsushita, T.; Hamabe, M.; Yamaguchi, S.; Inada, R.

    As a method of largely reducing the transmission loss in the electric power grid, superconducting direct current (DC) power transmission cable has been investigated. Using superconducting DC power transmission cables, large amounts of current and energy can be transferred compared to conventional copper cables. In this case, an alternating current (AC) is converted to DC and superposed AC which is known as ripple current, and the energy loss by the ripple current is generated. Therefore it is desired to estimate the energy loss density for the case of DC current and superposed AC current for a design of DC transmission cable system. In this study, the hysteresis loss for DC current of 2 kA rectified from 60 Hz alternating current is calculated using the Bean model, and coupling loss was also estimated. The diameter of the cable was 40 mm. The ripple currents generated by multi-pulse rectifiers, 6-pulse, 12-pulse, and 24-pulse were considered. It is found that the total AC loss including the hysteresis loss and the coupling loss is considerably smaller than the supposed heat loss of 0.5 W/m which is obtained with a newly developed cable.

  5. Caesium-137 in sandy sediments of the River Loire (FR): Assessment of an alluvial island evolving over the last 50 years

    Energy Technology Data Exchange (ETDEWEB)

    Detriche, Sebastien; Rodrigues, Stephane; Macaire, Jean-Jacques; Breheret, Jean-Gabriel; Bakyono, Jean-Paul [Universite Francois-Rabelais de Tours, CNRS/INSU UMR 6113 ISTO, Universite d' Orleans Faculte des Sciences et Techniques, Laboratoire de Geologie des Environnements Aquatiques Continentaux, Parc de Grandmont, 37200 Tours (France); Bonte, Philippe [UMR CNRS-CEA 1572, Laboratoire des Sciences du Climat et de l' Environnement - LSCE, CNRS, Domaine du CNRS, Bat. 12, 91198 Gif-sur-Yvette (France); Juge, Philippe [CETU-Elmis ingenieries, Antenne Universitaire en Val de Vienne, 11 quai Danton, 37500 Chinon (France)

    2010-07-01

    Recent sedimentological and morphological evolution of an island in the River Loire (FR) was investigated using the {sup 137}Cs method. This study describes the morphological adjustment of the island in the last 50 years, which corresponds to the increased bed incision of this sandy, multiple-channel environment because of, among other things, the increase in sediment extraction up to 1995. The results show that some {sup 137}Cs can be retained by sandy particles, potentially in clay minerals forming weathering features included in detrital sand grains. From a morphological perspective, significant lateral erosion can be observed in the upstream part of the island, while a weak lateral accretion occurs in its downstream section. Data about {sup 137}Cs and aerial photographs show that the morphology of the island margins has undergone significant changes leading to a lateral migration, while the centre of the island has remained relatively stable or is slowly eroding. The migration of the island depends on: (1) the withdrawal of inherited pre-incision morphological units, such as levees, or the development of new units, such as a channel shelf; (2) water and sediment supply from surrounding channels during flood events; (3) preferential sediment trapping (20 mm year{sup -1}) from the presence of riparian vegetation on the bank of the secondary channel that is subject to narrowing. The sedimentological and morphological response of the island in the context of incision of the Loire river bed is expressed mainly by lateral migration and secondarily by a low vertical adjustment. (authors)

  6. Online Media Use and Adoption by Hurricane Sandy Affected Fire and Police Departments

    OpenAIRE

    Chauhan, Apoorva

    2014-01-01

    In this thesis work, I examine the use and adoption of online communication media by 840 fire and police departments that were affected by the 2012 Hurricane Sandy. I began by exploring how and why these fire and police departments used (or did not use) online media to communicate with the public during Hurricane Sandy. Results show that fire and police departments used online media during Hurricane Sandy to give timely and relevant information to the public about things such as evacuations, ...

  7. Morphology of rain water channelization in systematically varied model sandy soils

    OpenAIRE

    Wei, Y.; Cejas, C. M.; Barrois, R.; Dreyfus, R.; Durian, D. J.

    2014-01-01

    We visualize the formation of fingered flow in dry model sandy soils under different raining conditions using a quasi-2d experimental set-up, and systematically determine the impact of soil grain diameter and surface wetting property on water channelization phenomenon. The model sandy soils we use are random closely-packed glass beads with varied diameters and surface treatments. For hydrophilic sandy soils, our experiments show that rain water infiltrates into a shallow top layer of soil and...

  8. Longitudinal Impact of Hurricane Sandy Exposure on Mental Health Symptoms

    Directory of Open Access Journals (Sweden)

    Rebecca M. Schwartz

    2017-08-01

    Full Text Available Hurricane Sandy hit the eastern coast of the United States in October 2012, causing billions of dollars in damage and acute physical and mental health problems. The long-term mental health consequences of the storm and their predictors have not been studied. New York City and Long Island residents completed questionnaires regarding their initial Hurricane Sandy exposure and mental health symptoms at baseline and 1 year later (N = 130. There were statistically significant decreases in anxiety scores (mean difference = −0.33, p < 0.01 and post-traumatic stress disorder (PTSD scores (mean difference = −1.98, p = 0.001 between baseline and follow-up. Experiencing a combination of personal and property damage was positively associated with long-term PTSD symptoms (ORadj 1.2, 95% CI [1.1–1.4] but not with anxiety or depression. Having anxiety, depression, or PTSD at baseline was a significant predictor of persistent anxiety (ORadj 2.8 95% CI [1.1–6.8], depression (ORadj 7.4 95% CI [2.3–24.1 and PTSD (ORadj 4.1 95% CI [1.1–14.6] at follow-up. Exposure to Hurricane Sandy has an impact on PTSD symptoms that persists over time. Given the likelihood of more frequent and intense hurricanes due to climate change, future hurricane recovery efforts must consider the long-term effects of hurricane exposure on mental health, especially on PTSD, when providing appropriate assistance and treatment.

  9. Geomechanics of bedded salt

    Energy Technology Data Exchange (ETDEWEB)

    Serata, S.; Milnor, S.W.

    1979-06-08

    Creep data from the literature search is reinterpreted by SGI, resulting in a better understanding of the temperature and stress state dependence of the octahedral creep rate and the octahedral shear strength. The concept of a transition strength between the elastic and the plastic states is in agreement with the data. The elastic and rheological properties of salt are described, and a set of constitutive equations is presented. The dependence of material properties on parameters such as temperature is considered. Findings on the permeability of salt are summarized, and the in-situ behavior of openings in bedded salt is described based on extensive engineering experience. A stress measuring system utilizing a finite element computer code is discussed. Geological factors affecting the stability of salt openings are considered, and the Stress Control Technique for designing stable openings in bedded salt formations is explained.

  10. Emergency evacuation orders: considerations and lessons from Hurricane Sandy.

    Science.gov (United States)

    O'Neil, Patrick D

    2014-01-01

    This article analyzes the problems surrounding the execution of emergency evacuation orders by evaluating Hurricane Sandy and the emergency actions taken by the State of New Jersey and the City of Atlantic City New Jersey. The analysis provides an overview of the legal authority granting emergency powers to governors and mayors to issue evacuation proclamations in addition to an evaluation of the New Jersey's emergency evacuation mandate and subsequent compliance. The article concludes with provision of planning and preparedness recommendations for public managers facing similar hazards, including a recommendation for provision of emergency shelter contingencies within the threat zone in anticipation of citizen noncompliance evacuation orders.

  11. Measured and Estimated Volatilisation of Naphthalene from a Sandy Soil

    DEFF Research Database (Denmark)

    Lindhardt, Bo; Christensen, Thomas Højlund

    1994-01-01

    The non-steady-state fluxes of naphthalene from an artificially contaminated sandy soil at different water contents were measured in the laboratory, at 10°C. The soil contained 1.1% of organic carbon and the water content varied between 2.8 and 14% w/w. The diffusive flux of naphthalene from the ...... the fluxes by a factor of 1.5 to 6.4. The largest deviation between predicted and observed dynamic fluxes was found at high water contents. For the cover soil, half-life times of 1 to 2 days were estimated by the model for naphthalene degradation....

  12. Uncertainties in sandy shorelines evolution under the Bruun rule assumption

    Directory of Open Access Journals (Sweden)

    Gonéri eLe Cozannet

    2016-04-01

    Full Text Available In the current practice of sandy shoreline change assessments, the local sedimentary budget is evaluated using the sediment balance equation, that is, by summing the contributions of longshore and cross-shore processes. The contribution of future sea-level-rise induced by climate change is usually obtained using the Bruun rule, which assumes that the shoreline retreat is equal to the change of sea-level divided by the slope of the upper shoreface. However, it remains unsure that this approach is appropriate to account for the impacts of future sea-level rise. This is due to the lack of relevant observations to validate the Bruun rule under the expected sea-level rise rates. To address this issue, this article estimates the coastal settings and period of time under which the use of the Bruun rule could be (invalidated, in the case of wave-exposed gently-sloping sandy beaches. Using the sedimentary budgets of Stive (2004 and probabilistic sea-level rise scenarios based on IPCC, we provide shoreline change projections that account for all uncertain hydrosedimentary processes affecting idealized coasts (impacts of sea-level rise, storms and other cross-shore and longshore processes. We evaluate the relative importance of each source of uncertainties in the sediment balance equation using a global sensitivity analysis. For scenario RCP 6.0 and 8.5 and in the absence of coastal defences, the model predicts a perceivable shift toward generalized beach erosion by the middle of the 21st century. In contrast, the model predictions are unlikely to differ from the current situation in case of scenario RCP 2.6. Finally, the contribution of sea-level rise and climate change scenarios to sandy shoreline change projections uncertainties increases with time during the 21st century. Our results have three primary implications for coastal settings similar to those provided described in Stive (2004 : first, the validation of the Bruun rule will not necessarily be

  13. Remediation of Diesel Fuel Contaminated Sandy Soil using Ultrasonic Waves

    Directory of Open Access Journals (Sweden)

    Wulandari P.S.

    2010-01-01

    Full Text Available Ultrasonic cleaning has been used in industry for some time, but the application of ultrasonic cleaning in contaminated soil is just recently received considerable attention, it is a very new technique, especially in Indonesia. An ultrasonic cleaner works mostly by energy released from the collapse of millions of microscopic cavitations near the dirty surface. This paper investigates the use of ultrasonic wave to enhance remediation of diesel fuel contaminated sandy soil considering the ultrasonic power, soil particle size, soil density, water flow rate, and duration of ultrasonic waves application.

  14. Virtual Test Bed

    Science.gov (United States)

    2016-06-07

    project is to develop a benchmark system for evaluating models for predicting the characteristics of ocean wind waves. SCIENTIFIC OBJECTIVES A...transformation-scale models (i.e. models which treat the physics of waves propagating from offshore areas into the coastline). Each phase is further divided...to be assembled within the virtual test bed. Wind fields for running these tests will be obtained from Oceanweather, Inc. from a separate ONR

  15. First-Year Downstream Sediment Budget Following the Marmot Dam Removal from the Sandy River, Oregon

    Science.gov (United States)

    Podolak, C. J.; Wilcock, P. R.; Pittman, A.

    2008-12-01

    The October 2007 removal of the Marmot Dam, from the Sandy River, OR, provides an opportunity to assess the impact of increased sediment flux on a river channel. The Sandy River drains the west flank of Mt Hood and typically carries a large load of sand and gravel. The 14-meter-tall dam impounded over 750,000 m3 of sediment, only a small amount of which was removed during the decommissioning. Using a one- dimensional modeling approach, it was assessed that the river could transport the accumulated sediment without large adverse impacts downstream of the dam (Cui et al, 2008 - abstract submitted). In order to observe the actual changes to the river due to the dam removal and to test the modeled predictions, a significant monitoring effort has be in place on the Sandy River including bedload and suspended load measurements, discharge measurements, high-fidelity topographic surveys, repeat photography, multiple airborne LIDAR flights, long profile surveys, as well as mapping and characterizing the grain sizes throughout several reaches downstream of the dam. A key step in the quest to describe and predict the spatial distribution of the sediment throughout the downstream reach is to first account for all the sediment (both stored in the reservoir and supplied from upstream). Here, we examine the transport and deposition downstream of the dam through a 2-fraction sediment budget approach using the former dam as the upstream limit of the reach and choosing a the mouth of a bedrock gorge 7 km below the dam site as the downstream limit. Suspended sediment and bedload measurements taken by the USGS just below the dam site (Major et al, 2008 - abstract submitted) are combined with suspended sediment and bedload measurements collected just below the mouth of the gorge and the annual hydrograph to define the sediment fluxes into and out of the reach. Repeat surveys in the reach below the dam (Wallick et al, 2008 - abstract submitted) provide the measure of change in storage

  16. Mental health outcomes at the Jersey Shore after Hurricane Sandy.

    Science.gov (United States)

    Boscarino, Joseph A; Hoffman, Stuart N; Kirchner, H Lester; Erlich, Porat M; Adams, Richard E; Figley, Charles R; Solhkhah, Ramon

    2013-01-01

    On October 29, 2012, Hurricane Sandy made landfall in the most densely populated region in the US. In New Jersey, thousands of families were made homeless and entire communities were destroyed in the worst disaster in the history of the state. The economic impact of Sandy was huge, comparable to Hurricane Katrina. The areas that sustained the most damage were the small- to medium-sized beach communities along New Jersey's Atlantic coastline. Six months following the hurricane, we conducted a random telephone survey of 200 adults residing in 18 beach communities located in Monmouth County. We found that 14.5% (95% CI = 9.9-20.2) of these residents screened positive for PTSD and 6.0% (95% CI = 3.1-10.2) met criteria for major depression. Altogether 13.5% (95% CI = 9.1-19.0) received mental health counseling and 20.5% (95% CI = 15.1-26.8) sought some type of mental health support in person or online, rates similar to those reported in New York after the World Trade Center disaster In multivariate analyses, the best predictors of mental health status and service use were having high hurricane exposure levels, having physical health limitations, and having environmental health concerns. Research is needed to assess the mental health status and service use of Jersey Shore residents over time, to evaluate environmental health concerns, and to better understand the storm's impact among those with physical health limitations.

  17. The bioremediation potential of marine sandy sediment microbiota

    Directory of Open Access Journals (Sweden)

    Dan Răzvan POPOVICIU

    2012-11-01

    Full Text Available The natural microbiota from marine sandy sediments on the Romanian sea coast was tested for resilience in case of hydrocarbon contamination, for estimating the number of (culturable hydrocarbon and lipid oil-degrading microorganisms and for determining the influence of inorganic nitrate and phosphate nutrients on hydrocarbon spill bioremediation process, by microcosm experiments.Results show that hydrocarbon contamination affects the bacteriobenthos both in terms of cell numbers and composition. Bacterial numbers showed a rapid decrease (28% in four days, followed by a relatively fast recovery (two weeks. The pollution favoured the increase of Gram-positive bacterial proportion (from around 25% to 33%Sandy sediment microbiota in both sites studied contained microorganisms able to use mineral or lipid oils as sole carbon sources, usually around 103-104/cm3, with variations according to the sediment grain size and substrate used.The biostimulation experiments showed that, in absence of water dynamism (and, implicitly, an efficient oxygenation, the addition of nitrogen and phosphorus can be ineffective and even inhibit the remediation process, probably due to eutrophication.

  18. Trophic niche shifts driven by phytoplankton in sandy beach ecosystems

    Science.gov (United States)

    Bergamino, Leandro; Martínez, Ana; Han, Eunah; Lercari, Diego; Defeo, Omar

    2016-10-01

    Stable isotopes (δ13C and δ15N) together with chlorophyll a and densities of surf diatoms were used to analyze changes in trophic niches of species in two sandy beaches of Uruguay with contrasting morphodynamics (i.e. dissipative vs. reflective). Consumers and food sources were collected over four seasons, including sediment organic matter (SOM), suspended particulate organic matter (POM) and the surf zone diatom Asterionellopsis guyunusae. Circular statistics and a Bayesian isotope mixing model were used to quantify food web differences between beaches. Consumers changed their trophic niche between beaches in the same direction of the food web space towards higher reliance on surf diatoms in the dissipative beach. Mixing models indicated that A. guyunusae was the primary nutrition source for suspension feeders in the dissipative beach, explaining their change in dietary niche compared to the reflective beach where the proportional contribution of surf diatoms was low. The high C/N ratios in A. guyunusae indicated its high nutritional value and N content, and may help to explain the high assimilation by suspension feeders at the dissipative beach. Furthermore, density of A. guyunusae was higher in the dissipative than in the reflective beach, and cell density was positively correlated with chlorophyll a only in the dissipative beach. Therefore, surf diatoms are important drivers in the dynamics of sandy beach food webs, determining the trophic niche space and productivity. Our study provides valuable insights on shifting foraging behavior by beach fauna in response to changes in resource availability.

  19. A Coordinated USGS Science Response to Hurricane Sandy

    Science.gov (United States)

    Jones, S.; Buxton, H. T.; Andersen, M.; Dean, T.; Focazio, M. J.; Haines, J.; Hainly, R. A.

    2013-12-01

    In late October 2012, Hurricane Sandy came ashore during a spring high tide on the New Jersey coastline, delivering hurricane-force winds, storm tides exceeding 19 feet, driving rain, and plummeting temperatures. Hurricane Sandy resulted in 72 direct fatalities in the mid-Atlantic and northeastern United States, and widespread and substantial physical, environmental, ecological, social, and economic impacts estimated at near $50 billion. Before the landfall of Hurricane Sandy, the USGS provided forecasts of potential coastal change; collected oblique aerial photography of pre-storm coastal morphology; deployed storm-surge sensors, rapid-deployment streamgages, wave sensors, and barometric pressure sensors; conducted Light Detection and Ranging (lidar) aerial topographic surveys of coastal areas; and issued a landslide alert for landslide prone areas. During the storm, Tidal Telemetry Networks provided real-time water-level information along the coast. Long-term networks and rapid-deployment real-time streamgages and water-quality monitors tracked river levels and changes in water quality. Immediately after the storm, the USGS serviced real-time instrumentation, retrieved data from over 140 storm-surge sensors, and collected other essential environmental data, including more than 830 high-water marks mapping the extent and elevation of the storm surge. Post-storm lidar surveys documented storm impacts to coastal barriers informing response and recovery and providing a new baseline to assess vulnerability of the reconfigured coast. The USGS Hazard Data Distribution System served storm-related information from many agencies on the Internet on a daily basis. Immediately following Hurricane Sandy the USGS developed a science plan, 'Meeting the Science Needs of the Nation in the Wake of Hurricane Sandy-A U.S. Geological Survey Science Plan for Support of Restoration and Recovery'. The plan will ensure continuing coordination of internal USGS activities as well as

  20. Space Vector Modulation for DC-Link Current Ripple Reduction in Back-To-Back Current Source Converters for Microgrid Applications

    DEFF Research Database (Denmark)

    Guo, Xiaoqiang; Xu, David; Guerrero, Josep M.

    2015-01-01

    instability. Conventionally, with a given switching frequency and rated voltage, the current ripple can be reduced by increasing the dc-link inductor, but it leads to bulky size, high cost and slow dynamic response. In order to solve this problem, this paper reveals that the current ripple can......Back-to-back converters have been typically used to interconnect the microgrids. For a back-to-back current source converter, the dc-link current ripple is one of the important parameters. A large ripple will cause the electromagnetic interference, undesirable high-frequency losses, and system...

  1. Understanding and predicting bed humidity in fluidized bed granulation.

    Science.gov (United States)

    Hu, Xinhui; Cunningham, John; Winstead, Denita

    2008-04-01

    Bed humidity is a critical parameter that needs to be controlled in a fluidized bed granulation to ensure reliability. To predict and control the bed humidity during the fluidized bed granulation process, a simple model based on the mass conservation of moisture was developed. The moisture mass balance model quantitatively simulates the effects of spray rate, binder solution concentration, airflow rate, inlet air temperature, and dew point on the bed humidity. The model was validated by a series of granulations performed in different scale granulators including Glatt GPCG-1, GPCG-15, and GPCG-60. Good agreement was observed between the theoretical prediction and the measured loss on drying (LOD). The model developed in the current work enables us to choose the appropriate parameters for the fluidized bed granulation and can be used as a valuable tool in process scaling-up.

  2. Coal Bed Methane Primer

    Energy Technology Data Exchange (ETDEWEB)

    Dan Arthur; Bruce Langhus; Jon Seekins

    2005-05-25

    During the second half of the 1990's Coal Bed Methane (CBM) production increased dramatically nationwide to represent a significant new source of income and natural gas for many independent and established producers. Matching these soaring production rates during this period was a heightened public awareness of environmental concerns. These concerns left unexplained and under-addressed have created a significant growth in public involvement generating literally thousands of unfocused project comments for various regional NEPA efforts resulting in the delayed development of public and fee lands. The accelerating interest in CBM development coupled to the growth in public involvement has prompted the conceptualization of this project for the development of a CBM Primer. The Primer is designed to serve as a summary document, which introduces and encapsulates information pertinent to the development of Coal Bed Methane (CBM), including focused discussions of coal deposits, methane as a natural formed gas, split mineral estates, development techniques, operational issues, producing methods, applicable regulatory frameworks, land and resource management, mitigation measures, preparation of project plans, data availability, Indian Trust issues and relevant environmental technologies. An important aspect of gaining access to federal, state, tribal, or fee lands involves education of a broad array of stakeholders, including land and mineral owners, regulators, conservationists, tribal governments, special interest groups, and numerous others that could be impacted by the development of coal bed methane. Perhaps the most crucial aspect of successfully developing CBM resources is stakeholder education. Currently, an inconsistent picture of CBM exists. There is a significant lack of understanding on the parts of nearly all stakeholders, including industry, government, special interest groups, and land owners. It is envisioned the Primer would being used by a variety of

  3. Bed Rest Muscular Atrophy

    Science.gov (United States)

    Greenleaf, John E.

    2000-01-01

    A major debilitating response from prolonged bed rest (BR) is muscle atrophy, defined as a "decrease in size of a part of tissue after full development has been attained: a wasting away of tissue as from disuse, old age, injury or disease". Part of the complicated mechanism for the dizziness, increased body instability, and exaggerated gait in patients who arise immediately after BR may be a result of not only foot pain, but also of muscular atrophy and associated reduction in lower limb strength. Also, there seems to be a close association between muscle atrophy and bone atrophy. A discussion of many facets of the total BR homeostatic syndrome has been published. The old adage that use determines form which promotes function of bone (Wolff's law) also applies to those people exposed to prolonged BR (without exercise training) in whom muscle atrophy is a consistent finding. An extreme case involved a 16-year-old boy who was ordered to bed by his mother in 1932: after 50 years in bed he had "a lily-white frame with limbs as thin as the legs of a ladder-back chair". These findings emphasize the close relationship between muscle atrophy and bone atrophy. In addition to loss of muscle mass during deconditioning, there is a significant loss of muscle strength and a decrease in protein synthesis. Because the decreases in force (strength) are proportionately greater than those in fiber size or muscle cross-sectional area, other contributory factors must be involved; muscle fiber dehydration may be important.

  4. Bed Rest Muscular Atrophy

    Science.gov (United States)

    Greenleaf, John E.

    2000-01-01

    A major debilitating response from prolonged bed rest (BR) is muscle atrophy, defined as a "decrease in size of a part of tissue after full development has been attained: a wasting away of tissue as from disuse, old age, injury or disease". Part of the complicated mechanism for the dizziness, increased body instability, and exaggerated gait in patients who arise immediately after BR may be a result of not only foot pain, but also of muscular atrophy and associated reduction in lower limb strength. Also, there seems to be a close association between muscle atrophy and bone atrophy. A discussion of many facets of the total BR homeostatic syndrome has been published. The old adage that use determines form which promotes function of bone (Wolff's law) also applies to those people exposed to prolonged BR (without exercise training) in whom muscle atrophy is a consistent finding. An extreme case involved a 16-year-old boy who was ordered to bed by his mother in 1932: after 50 years in bed he had "a lily-white frame with limbs as thin as the legs of a ladder-back chair". These findings emphasize the close relationship between muscle atrophy and bone atrophy. In addition to loss of muscle mass during deconditioning, there is a significant loss of muscle strength and a decrease in protein synthesis. Because the decreases in force (strength) are proportionately greater than those in fiber size or muscle cross-sectional area, other contributory factors must be involved; muscle fiber dehydration may be important.

  5. Coastal topography–Northeast Atlantic coast, post-hurricane Sandy, 2012

    Science.gov (United States)

    Stockdon, Hilary F.; Doran, Kara S.; Sopkin, Kristin L.; Smith, Kathryn E.L.; Fredericks, Xan

    2013-01-01

    This Data Series contains lidar-derived bare-earth (BE) topography, dune elevations, and mean-high-water shoreline position datasets for most sandy beaches for Fire Island, New York, and from Cape Henlopen, Delaware to Cape Lookout, North Carolina. The data were acquired post-Hurricane Sandy, which made landfall as an extratropical cyclone on October 29, 2012.

  6. Abrasive wear based predictive maintenance for systems operating in sandy conditions

    NARCIS (Netherlands)

    Woldman, M.; Tinga, T.; Heide, E. van der; Masen, M.A.

    2015-01-01

    Machines operating in sandy environments are damaged by the abrasive action of sand particles that enter the machine and become entrapped between components and contacting surfaces. In the case of the military services the combination of a sandy environment and the wide range of tasks to be fulfille

  7. Heterogeneous water flow and pesticide transport in cultivated sandy soils : description of model concepts

    NARCIS (Netherlands)

    Leistra, M.; Boesten, J.J.T.I.

    2011-01-01

    There is ample experimental evidence that complications in water flow and pesticide transport can occur in cultivated humic-sandy and loamy-sandy soils. As a result, pesticide leaching to groundwater and water courses can be higher than expected. We made an inventory of mechanistic/deterministic mod

  8. Measuring Sandy Bottom Dynamics by Exploiting Depth from Stereo Video Sequences

    DEFF Research Database (Denmark)

    Musumeci, Rosaria E.; Farinella, Giovanni M.; Foti, Enrico;

    2013-01-01

    In this paper an imaging system for measuring sandy bottom dynamics is proposed. The system exploits stereo sequences and projected laser beams to build the 3D shape of the sandy bottom during time. The reconstruction is used by experts of the field to perform accurate measurements and analysis i...

  9. Marine meiofauna, carbon and nitrogen mineralization in sandy and soft sediments of Disko Bay, West Greenland

    DEFF Research Database (Denmark)

    Rysgaard, S.; Christensen, P.B.; Sørensen, Martin Vinther

    2000-01-01

    belonging to Platyhelminthes, Rotifera, Gastrotricha, and Protodriloidae (Polychaeta) occurred only at the sandy locality, whereas Kinorhyncha, Foraminifera, and Cumacea (Crustacea) occurred only at the muddy stations. The larger number of meiofauna individuals at the sandy locality may in part be explained...

  10. Fine-scale spatial distribution of plants and resources on a sandy soil in the Sahel

    NARCIS (Netherlands)

    Rietkerk, M; Ouedraogo, T; Kumar, L; Sanou, S; van Langevelde, F; Kiema, A; van de Koppel, J; van Andel, J; Hearne, J; Skidmore, AK; de Ridder, N; Stroosnijder, L; Prins, HHT

    We studied fine-scale spatial plant distribution in relation to the spatial distribution of erodible soil particles, organic matter, nutrients and soil water on a sandy to sandy loam soil in the Sahel. We hypothesized that the distribution of annual plants would be highly spatially autocorrelated

  11. Fine-scale spatial distribution of plants and resources on a sandy soil in the Sahel

    NARCIS (Netherlands)

    Rietkerk, M.G.; Ouedraogo, T.; Kumar, L.; Sanou, S.; Langevelde, F. van; Kiema, A.; Koppel, J. van de; Andel, J. van; Hearne, J.; Skidmore, A.K.; Ridder, N. de; Stroosnijder, L.; Prins, H.H.T.

    2002-01-01

    We studied fine-scale spatial plant distribution in relation to the spatial distribution of erodible soil particles, organic matter, nutrients and soil water on a sandy to sandy loam soil in the Sahel. We hypothesized that the distribution of annual plants would be highly spatially autocorrelated

  12. Nitrate leaching to groundwater at experimental farm "De Marke" and other Dutch sandy soils

    NARCIS (Netherlands)

    Hack-ten Broeke, M.J.D.

    2001-01-01

    This study focuses on nitrate leaching to the groundwater as a result of the land use system of experimental farm 'De Marke', translated to other sandy soils in the Netherlands. The land use was extrapolated to five major sandy soil map units, selected from the 1: 50 000 Soil Map of the Netherlands,

  13. 33 CFR 80.170 - Sandy Hook, NJ to Tom's River, NJ.

    Science.gov (United States)

    2010-07-01

    ... 33 Navigation and Navigable Waters 1 2010-07-01 2010-07-01 false Sandy Hook, NJ to Tom's River, NJ. 80.170 Section 80.170 Navigation and Navigable Waters COAST GUARD, DEPARTMENT OF HOMELAND SECURITY INTERNATIONAL NAVIGATION RULES COLREGS DEMARCATION LINES Atlantic Coast § 80.170 Sandy Hook, NJ to Tom's River...

  14. Racing for the Bed

    Institute of Scientific and Technical Information of China (English)

    1999-01-01

    No one knows when the people ofMacheng City began to employthe marriage custom of racingfor the bed, once a custom unique to theTujia ethnic minority. It is said that at the end of awedding, bride and bridegroom enter thebridal chamber together and race for thebed. The one who is the first to sit on thebed will be the master of the new familyIt sounds unreasonable, but quite anumber of people believe in it.Therefore, on the wedding night, manybrides and bridegrooms try their best to

  15. Biparticle fluidized bed reactor

    Science.gov (United States)

    Scott, C.D.

    1993-12-14

    A fluidized bed reactor system which utilizes a fluid phase, a retained fluidized primary particulate phase, and a migratory second particulate phase is described. The primary particulate phase is a particle such as a gel bead containing an immobilized biocatalyst. The secondary particulate phase, continuously introduced and removed in either cocurrent or countercurrent mode, acts in a secondary role such as a sorbent to continuously remove a product or by-product constituent from the fluid phase. Introduction and removal of the sorbent phase is accomplished through the use of feed screw mechanisms and multivane slurry valves. 3 figures.

  16. The fate of fresh and stored 15N-labelled sheep urine and urea applied to a sandy and a sandy loam soil using different application strategies

    DEFF Research Database (Denmark)

    Sørensen, P.; Jensen, E.S.

    1996-01-01

    .), or it was applied to ryegrass one month after sowing. In a sandy loam soil, 62% of the incorporated urine N and 78% of the incorporated urea N was recovered in three cuts of herbage after 5 months. In a sandy soil, 51-53% of the labelled N was recovered in the herbage and the distribution of labelled N in plant...... and soil was not significantly different for incorporated urine and urea. Almost all the supplied labelled N was accounted for in soil and herbage in the sandy loam soil, whereas 33-34% of the labelled N was unaccounted for in the sandy soil. When the stored urine was applied to the soil surface, 20...... unaccounted for was probably mainly lost by ammonia volatilization. Significantly more urine- than urea-derived N (36 and 19%, respectively) was immobilized in the sandy loam soil, whereas the immobilization of N from urea and urine was similar in the sandy soil (13-16%). The distribution of urine N, whether...

  17. Seasonal variation of bivalve larvae on an exposed sandy beach on Kashima-nada: Tips for the sandy beach recruitment process

    Science.gov (United States)

    Sawada, Hideki; Saito, Hajime; Adachi, Kumiko; Toyohara, Haruhiko

    2011-02-01

    Bivalves are often the dominant macrobenthos species in exposed sandy beach environments. However, our understanding of their recruitment processes before post-settlement stages on sandy beaches with highly energetic environments is incomplete. To clarify the characteristics of the free-swimming planktonic stage that affects recruitment efficiency in sandy shore ecosystems, we investigated the temporal (weekly-biweekly) variation of bivalve planktonic larval concentration coupled with oceanographic conditions on an exposed sandy shore on the sea of Kashima-nada, Japan, from summer 2003 to autumn 2005. Larvae were observed throughout the year, but the surge of larval concentration composed of sandy beach and sessile bivalves occurred most prominently in summer, from August to September. The peak concentration of larvae during this season was more than 1000 times higher than in other seasons. The larval concentration was positively correlated with water temperature and northward wind velocity and negatively correlated with each of the nutrient concentrations. On the other hand, chlorophyll a concentration and salinity seemed to have little effect on the larval concentration. Based on this fundamental knowledge, further investigations about planktonic larvae in sandy beaches are needed.

  18. Coastal Topography--Northeast Atlantic Coast, Post-Hurricane Sandy, 2012: Lidar point-cloud data (LAS)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Binary point-cloud data were produced for a portion of the New York, Delaware, Maryland, Virginia, and North Carolina coastlines, post-Hurricane Sandy (Sandy was an...

  19. Progress in sandy desertification research of China%中国沙漠化研究进展

    Institute of Scientific and Technical Information of China (English)

    王涛

    2004-01-01

    Sandy desertification is land degradation characterized by wind erosion mainly resulted from the excessive human activities in arid, semiarid and part of sub-humid regions in northern China. The research on sandy desertification has experienced more than 5 decades of arduous course of the struggle along with the establishment and development of China′s desert science. Researches in this field have made a great contribution to the national economic construction, and environmental protection. This paper focuses on presenting the major progress and achievements in the sandy desertification research during the last 50 years, including the stages of study on sandy desertification,background environment of sandy desertification and its changes, the conception, causes, process,monitoring and assessment of sandy desertification, the vegetation succession, landscape ecology, plant physiology, impacts on ecosystem, high-effective use of water and land resources and sustainable development in sandy desertified regions, sandy desertification control models and techniques etc.

  20. Coastal Topography--Northeast Atlantic Coast, Post-Hurricane Sandy, 2012: Lidar point-cloud data (LAS)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Binary point-cloud data were produced for a portion of the New York, Delaware, Maryland, Virginia, and North Carolina coastlines, post-Hurricane Sandy (Sandy was an...

  1. A New Adaptive Self-Tuning Fourier Coefficients Algorithm for Periodic Torque Ripple Minimization in Permanent Magnet Synchronous Motors (PMSM

    Directory of Open Access Journals (Sweden)

    Gilberto Herrera-Ruíz

    2013-03-01

    Full Text Available A New Adaptive Self-Tuning Fourier Coefficients Algorithm for Periodic Torque Ripple Minimization in Permanent Magnet Synchronous Motors (PMSM Torque ripple occurs in Permanent Magnet Synchronous Motors (PMSMs due to the non-sinusoidal flux density distribution around the air-gap and variable magnetic reluctance of the air-gap due to the stator slots distribution. These torque ripples change periodically with rotor position and are apparent as speed variations, which degrade the PMSM drive performance, particularly at low speeds, because of low inertial filtering. In this paper, a new self-tuning algorithm is developed for determining the Fourier Series Controller coefficients with the aim of reducing the torque ripple in a PMSM, thus allowing for a smoother operation. This algorithm adjusts the controller parameters based on the component’s harmonic distortion in time domain of the compensation signal. Experimental evaluation is performed on a DSP-controlled PMSM evaluation platform. Test results obtained validate the effectiveness of the proposed self-tuning algorithm, with the Fourier series expansion scheme, in reducing the torque ripple.

  2. A new adaptive self-tuning Fourier coefficients algorithm for periodic torque ripple minimization in permanent magnet synchronous motors (PMSM).

    Science.gov (United States)

    Gómez-Espinosa, Alfonso; Hernández-Guzmán, Víctor M; Bandala-Sánchez, Manuel; Jiménez-Hernández, Hugo; Rivas-Araiza, Edgar A; Rodríguez-Reséndiz, Juvenal; Herrera-Ruíz, Gilberto

    2013-03-19

    A New Adaptive Self-Tuning Fourier Coefficients Algorithm for Periodic Torque Ripple Minimization in Permanent Magnet Synchronous Motors (PMSM) Torque ripple occurs in Permanent Magnet Synchronous Motors (PMSMs) due to the non-sinusoidal flux density distribution around the air-gap and variable magnetic reluctance of the air-gap due to the stator slots distribution. These torque ripples change periodically with rotor position and are apparent as speed variations, which degrade the PMSM drive performance, particularly at low speeds, because of low inertial filtering. In this paper, a new self-tuning algorithm is developed for determining the Fourier Series Controller coefficients with the aim of reducing the torque ripple in a PMSM, thus allowing for a smoother operation. This algorithm adjusts the controller parameters based on the component's harmonic distortion in time domain of the compensation signal. Experimental evaluation is performed on a DSP-controlled PMSM evaluation platform. Test results obtained validate the effectiveness of the proposed self-tuning algorithm, with the Fourier series expansion scheme, in reducing the torque ripple.

  3. Analysis of Peak-to-Peak Current Ripple Amplitude in Seven-Phase PWM Voltage Source Inverters

    Directory of Open Access Journals (Sweden)

    Gabriele Grandi

    2013-08-01

    Full Text Available Multiphase systems are nowadays considered for various industrial applications. Numerous pulse width modulation (PWM schemes for multiphase voltage source inverters with sinusoidal outputs have been developed, but no detailed analysis of the impact of these modulation schemes on the output peak-to-peak current ripple amplitude has been reported. Determination of current ripple in multiphase PWM voltage source inverters is important for both design and control purposes. This paper gives the complete analysis of the peak-to-peak current ripple distribution over a fundamental period for multiphase inverters, with particular reference to seven-phase VSIs. In particular, peak-to-peak current ripple amplitude is analytically determined as a function of the modulation index, and a simplified expression to get its maximum value is carried out. Although reference is made to the centered symmetrical PWM, being the most simple and effective solution to maximize the DC bus utilization, leading to a nearly-optimal modulation to minimize the RMS of the current ripple, the analysis can be readily extended to either discontinuous or asymmetrical modulations, both carrier-based and space vector PWM. A similar approach can be usefully applied to any phase number. The analytical developments for all different sub-cases are verified by numerical simulations.

  4. Modulation power of porous materials and usage as ripple filter in particle therapy.

    Science.gov (United States)

    Printz Ringbæk, Toke; Simeonov, Yuri; Witt, Matthias; Engenhart-Cabillic, Rita; Kraft, Gerhard; Zink, Klemens; Weber, Uli

    2017-04-07

    Porous materials with microscopic structures like foam, sponges, lung tissues and lung substitute materials have particular characteristics, which differ from those of solid materials. Ion beams passing through porous materials show much stronger energy straggling than expected for non-porous solid materials of the same thickness. This effect depends on the microscopic fine structure, the density and the thickness of the porous material. The beam-modulating effect from a porous plate enlarges the Bragg peak, yielding similar benefits in irradiation time reduction as a ripple filter. A porous plate can additionally function as a range shifter, which since a higher energy can be selected for the same penetration depth in the body reduces the scattering at the beam line and therefore improves the lateral fall-off. Bragg curve measurements of ion beams passing through different porous materials have been performed in order to determine the beam modulation effect of each. A mathematical model describing the correlation between the mean material density, the porous pore structure size and the strength of the modulation has been developed and a new material parameter called 'modulation power' is defined as the square of the Gaussian sigma divided by the mean water-equivalent thickness of the porous absorber. Monte Carlo simulations have been performed in order to validate the model and to investigate the Bragg peak enlargement, the scattering effects of porosity and the lateral beam width at the end of the beam range. The porosity is found to only influence the lateral scattering in a negligible way. As an example of a practical application, it is found that a 20 mm and 50 mm plate of Gammex LN300 performs similar to a 3 mm and 6 mm ripple filter, respectively, and at the same time can improve the sharpness of the lateral beam due to its multifunctionality as a ripple filter and a range shifter.

  5. Surface morphology evolution during plasma etching of silicon: roughening, smoothing and ripple formation

    Science.gov (United States)

    Ono, Kouichi; Nakazaki, Nobuya; Tsuda, Hirotaka; Takao, Yoshinori; Eriguchi, Koji

    2017-10-01

    Atomic- or nanometer-scale roughness on feature surfaces has become an important issue to be resolved in the fabrication of nanoscale devices in industry. Moreover, in some cases, smoothing of initially rough surfaces is required for planarization of film surfaces, and controlled surface roughening is required for maskless fabrication of organized nanostructures on surfaces. An understanding, under what conditions plasma etching results in surface roughening and/or smoothing and what are the mechanisms concerned, is of great technological as well as fundamental interest. In this article, we review recent developments in the experimental and numerical study of the formation and evolution of surface roughness (or surface morphology evolution such as roughening, smoothing, and ripple formation) during plasma etching of Si, with emphasis being placed on a deeper understanding of the mechanisms or plasma–surface interactions that are responsible for. Starting with an overview of the experimental and theoretical/numerical aspects concerned, selected relevant mechanisms are illustrated and discussed primarily on the basis of systematic/mechanistic studies of Si etching in Cl-based plasmas, including noise (or stochastic roughening), geometrical shadowing, surface reemission of etchants, micromasking by etch inhibitors, and ion scattering/chanelling. A comparison of experiments (etching and plasma diagnostics) and numerical simulations (Monte Carlo and classical molecular dynamics) indicates a crucial role of the ion scattering or reflection from microscopically roughened feature surfaces on incidence in the evolution of surface roughness (and ripples) during plasma etching; in effect, the smoothing/non-roughening condition is characterized by reduced effects of the ion reflection, and the roughening-smoothing transition results from reduced ion reflections caused by a change in the predominant ion flux due to that in plasma conditions. Smoothing of initially rough

  6. Ripples on graphene and their effect on lattice and electronic properties

    Science.gov (United States)

    Katsnelson, Mikhail

    2009-03-01

    A discovery of graphene, a new allotrope of carbon [1], representing the simplest, one-atom thick, membrane, opens exciting perspectives in statistical physics of two-dimensional systems in general. As expected from theory of flexible membranes [2], free suspended graphene is corrugated (rippled) due to thermal bending fluctuations, which was confirmed by experiment [3] and atomistic simulations [4]. This makes graphene strongly anharmonic crystal leading to anomalous temperature dependences of its thermal expansion, elastic moduli and other thermodynamic and mechanical properties. The ripples are also a source of pseudomagnetic gauge field [5] acting on Dirac fermions which leads to important consequences for the electronic structure such as a formation of midgap states [6,7]. Quenched ripples can be also important sources of electron scattering limiting charge-carrier mobility in graphene [8]. Possible mechanisms of this quenching are discussed. [3pt] [1] K.S. Novoselov et al, Science 306, 666 (2004). [0pt] [2] Statistical Mechanics of Membranes and Surfaces, ed. by D. R. Nelson, T. Piran, and S. Weinberg (World Sci, Singapore 2004). [0pt] [3] J.C. Meyer et al, Nature 446, 60 (2007). [0pt] [4] A. Fasolino, J.H. Los, and M.I. Katsnelson, Nature Mater. 6, 858 (2007). [0pt] [5] S.V. Morozov et al, Phys. Rev. Lett. 97, 016801 (2006). [0pt] [6] F. Guinea, M.I. Katsnelson, and M.A.H. Vozmediano, Phys. Rev. B 77, 075422 (2008). [0pt] [7] T.O. Wehling et al, Europhys. Lett. 84, 17003 (2008). [0pt] [8] M.I. Katsnelson and A.K. Geim, Phil. Trans. Royal Soc. A 366, 195 (2008).

  7. Modulation power of porous materials and usage as ripple filter in particle therapy

    Science.gov (United States)

    Printz Ringbæk, Toke; Simeonov, Yuri; Witt, Matthias; Engenhart-Cabillic, Rita; Kraft, Gerhard; Zink, Klemens; Weber, Uli

    2017-04-01

    Porous materials with microscopic structures like foam, sponges, lung tissues and lung substitute materials have particular characteristics, which differ from those of solid materials. Ion beams passing through porous materials show much stronger energy straggling than expected for non-porous solid materials of the same thickness. This effect depends on the microscopic fine structure, the density and the thickness of the porous material. The beam-modulating effect from a porous plate enlarges the Bragg peak, yielding similar benefits in irradiation time reduction as a ripple filter. A porous plate can additionally function as a range shifter, which since a higher energy can be selected for the same penetration depth in the body reduces the scattering at the beam line and therefore improves the lateral fall-off. Bragg curve measurements of ion beams passing through different porous materials have been performed in order to determine the beam modulation effect of each. A mathematical model describing the correlation between the mean material density, the porous pore structure size and the strength of the modulation has been developed and a new material parameter called ‘modulation power’ is defined as the square of the Gaussian sigma divided by the mean water-equivalent thickness of the porous absorber. Monte Carlo simulations have been performed in order to validate the model and to investigate the Bragg peak enlargement, the scattering effects of porosity and the lateral beam width at the end of the beam range. The porosity is found to only influence the lateral scattering in a negligible way. As an example of a practical application, it is found that a 20 mm and 50 mm plate of Gammex LN300 performs similar to a 3 mm and 6 mm ripple filter, respectively, and at the same time can improve the sharpness of the lateral beam due to its multifunctionality as a ripple filter and a range shifter.

  8. Sharp wave/ripple network oscillations and learning-associated hippocampal maps.

    Science.gov (United States)

    Csicsvari, Jozsef; Dupret, David

    2014-02-01

    Sharp wave/ripple (SWR, 150-250 Hz) hippocampal events have long been postulated to be involved in memory consolidation. However, more recent work has investigated SWRs that occur during active waking behaviour: findings that suggest that SWRs may also play a role in cell assembly strengthening or spatial working memory. Do such theories of SWR function apply to animal learning? This review discusses how general theories linking SWRs to memory-related function may explain circuit mechanisms related to rodent spatial learning and to the associated stabilization of new cognitive maps.

  9. Ripple formation on silver after irradiation with radially polarized ultrashort-pulsed lasers

    CERN Document Server

    Tsibidis, George D

    2016-01-01

    We report on the morphological effects induced by the inhomogeneous absorption of cylindrically polarized femtosecond laser irradiation of silver (Ag) in sub-ablation conditions. A theoretical prediction of the role of surface plasmon excitation in the production of self-formed periodic ripples structures is evaluated. Furthermore, a combined hydrodynamical and thermoelastic model is presented to account for the influence of temperature-related lattice movements in laser beam conditions that are sufficient to produce material melting. The ability to control the size of the morphological changes via modulating the beam polarization aims to provide a systematic methodology for controlling and optimizing the outcome of laser micro-processing.

  10. Engineering Modeling of Wave-Related Suspended Sediment Transport Over Ripples

    CERN Document Server

    Absi, Rafik

    2011-01-01

    The aim of our study is to improve the description of suspended sediment transport over wave ripples. We will first show the importance of sediment diffusivity with convective transfer (hereafter called) which is different from the sediment diffusivity associated to turbulent flux . It is possible to interpret concentration profiles, in semi-log plots, thanks to a relation between second derivative of the logarithm of concentration and derivative of (Absi, 2010). An analytical profile for will be presented and validated by experimental data obtained by Thorne et al. (2009) for medium sand. The proposed profile allows a good description of suspended sediment concentrations for fine and coarse sediments.

  11. Current ripple in the coils of the TJ-II Spanish stellarator

    Energy Technology Data Exchange (ETDEWEB)

    Perez, A.; Acero, J.; Alberdi, B.; Del Rio, J.M. [JEMA SA, Lasarte-Oria (Spain); Almoguera, L.; Blaumoser, M.; Kirpitchev, I.; Mendez, P. [Asociacion EURATOM-CIEMAT para Fusion, Madrid (Spain)

    1995-12-31

    High precision coil current control, stability and ripple content are very important aspects for a stellarator design. The TJ-II coils will be supplied by network commutated current converters and therefore the coil currents will contain harmonics which have to be kept to a very low level. An analytical investigation as well as numerous simulations with EMTP, SABER{reg_sign} and other softwares, have been done in order to predict the harmonic currents and to verify the completion with the specified maximum levels. The calculations and the results are presented.

  12. MPPT control of Photovoltaic using SEPIC converter to reduce the input current ripples

    Directory of Open Access Journals (Sweden)

    M. R. Banaei

    2014-01-01

    Full Text Available This paper presents P&O control method for maximum power point tracking(MPPT of PV system under varying irradiation and temperature conditions. This algorithm will identify the suitable duty ratio in which the DC/DC SEPIC converter should be operated to maximize the power output. In this paper, the SEPIC converter has been compared with conventional boost converter about reducing the input current ripple. Also, both converters and their control strategies have been analyzed and simulated using Simulink/Matlab software. Simulation results show that the SEPIC converter reduces input current better than conventional boost converter.

  13. Design and Implement of Low Ripple and Quasi-digital Power Supply

    Science.gov (United States)

    Xiangli, Li; Yanjun, Wei; Hanhong, Qi; Yan, Ma

    A switch linearity hybrid power supply based on single chip microcomputer is designed which merged the merits of the switching and linear power supply. Main circuit includes pre-regulator which works in switching mode and series regulator which works in linear mode. Two-stage regulation mode was adopted in the main circuit of the power. A single chip computer (SCM) and high resolution of series D/A and A/D converters are applied to control and measurement which achieved continuous adjustable and low ripple constant current or voltage power supply

  14. Mega-ripples in Iran: A new analog for transverse aeolian ridges on Mars

    Science.gov (United States)

    Foroutan, M.; Zimbelman, J. R.

    2016-08-01

    A new terrestrial analog site for transverse aeolian ridges (TARs) is described in this study. The Lut desert of Iran hosts large ripple-like aeolian bedforms, with the same horizontal length scales and patterns of TARs on Mars. Different classes of TARs and different types of other aeolian features such as sand dunes, zibars, dust devil tracks and yardangs can be found in this area, which signify an active aeolian region. This area represents a unique site to study the formation and evolution of these enigmatic features, with potential relevance toward a better understanding of TARs on Mars.

  15. Aspects Concerning the Torque Ripple Control of the Brushless DC Motor

    Directory of Open Access Journals (Sweden)

    BALUTA, G.

    2013-05-01

    Full Text Available This paper deals with two advanced numerical structures to control the electromagnetic torque ripple of Brushless Direct Current Motors (BLDCM, indirectly achieved by phase currents control and directly by the Direct Torque Control (DTC technique. In DTC there was implemented an observer to increase the rudimentary transducer resolution, containing three Hall Effect sensors. The experimental results describe the evolution of torque in both situations of control and are obtained by applying a control strategy for an electric drive system with BLDCM with trapezoidal Back-EMF in Two-Phase Mode.

  16. The three-level ripples induced by femtosecond laser on a 6H-SiC single crystal and the formation mechanism

    Science.gov (United States)

    Song, Juan; Tao, Wenjun; Gong, Min; Ye, Junyi; Dai, Ye; Ma, Guohong; Qiu, Jianrong

    2016-04-01

    In this paper, a line-scanning irradiation of 6H-SiC single crystal by a femtosecond laser focus was implemented for laser fluence of 2.2 J/cm2 at different scanning velocities from 1000 down to 100 μm/s. The morphology of the obtained ablation lines characterized by a scanning electron microscope shows that there progressively appear three-level ripples with average period of about 222, 600 nm and that between them. Possible formation mechanisms for these three-level ripples were analyzed by numerical simulation employing finite-difference time-domain method (FDTD). Analysis shows that as Obara proposed, the interference of incident wave with the wave scattered by scratches possibly left by fine polishing is the most possible reason for inducing 222 nm-period and 600 nm-period ripples. Main discussions were focused on the orientation characteristics of ripples. Both isolated scratches and crossed scratches with different orientation angles were considered for evaluating their role in field redistribution. The detailed simulations indicate that for scratches oriented 90° with respect to laser polarization generate a pair of strongest ripple-like optical field enhancement compared to scratches with other orientation angles. It is these advantages of 90°-oriented scratch in field enhancement that make the final ripple perpendicular to laser polarization most competitive and finally left on the surface. This complements the physical picture of Obara et al. in terms of their negligence in addressing the orientation characteristics of ripples. Further FDTD simulation of the interaction of incident wave with as-formed 600 nm-period ripples shows that the optical field enhancement located between any two adjacent 600 nm-period ripples is the driving force for splitting 600 nm-period ripples into the third ripples with period between 222 and 600 nm.

  17. Hurricane Sandy: Shared Trauma and Therapist Self-Disclosure.

    Science.gov (United States)

    Rao, Nyapati; Mehra, Ashwin

    2015-01-01

    Hurricane Sandy was one of the most devastating storms to hit the United States in history. The impact of the hurricane included power outages, flooding in the New York City subway system and East River tunnels, disrupted communications, acute shortages of gasoline and food, and a death toll of 113 people. In addition, thousands of residences and businesses in New Jersey and New York were destroyed. This article chronicles the first author's personal and professional experiences as a survivor of the hurricane, more specifically in the dual roles of provider and trauma victim, involving informed self-disclosure with a patient who was also a victim of the hurricane. The general analytic framework of therapy is evaluated in the context of the shared trauma faced by patient and provider alike in the face of the hurricane, leading to important implications for future work on resilience and recovery for both the therapist and patient.

  18. Performance of social network sensors during Hurricane Sandy.

    Directory of Open Access Journals (Sweden)

    Yury Kryvasheyeu

    Full Text Available Information flow during catastrophic events is a critical aspect of disaster management. Modern communication platforms, in particular online social networks, provide an opportunity to study such flow and derive early-warning sensors, thus improving emergency preparedness and response. Performance of the social networks sensor method, based on topological and behavioral properties derived from the "friendship paradox", is studied here for over 50 million Twitter messages posted before, during, and after Hurricane Sandy. We find that differences in users' network centrality effectively translate into moderate awareness advantage (up to 26 hours; and that geo-location of users within or outside of the hurricane-affected area plays a significant role in determining the scale of such an advantage. Emotional response appears to be universal regardless of the position in the network topology, and displays characteristic, easily detectable patterns, opening a possibility to implement a simple "sentiment sensing" technique that can detect and locate disasters.

  19. Performance of social network sensors during Hurricane Sandy.

    Science.gov (United States)

    Kryvasheyeu, Yury; Chen, Haohui; Moro, Esteban; Van Hentenryck, Pascal; Cebrian, Manuel

    2015-01-01

    Information flow during catastrophic events is a critical aspect of disaster management. Modern communication platforms, in particular online social networks, provide an opportunity to study such flow and derive early-warning sensors, thus improving emergency preparedness and response. Performance of the social networks sensor method, based on topological and behavioral properties derived from the "friendship paradox", is studied here for over 50 million Twitter messages posted before, during, and after Hurricane Sandy. We find that differences in users' network centrality effectively translate into moderate awareness advantage (up to 26 hours); and that geo-location of users within or outside of the hurricane-affected area plays a significant role in determining the scale of such an advantage. Emotional response appears to be universal regardless of the position in the network topology, and displays characteristic, easily detectable patterns, opening a possibility to implement a simple "sentiment sensing" technique that can detect and locate disasters.

  20. Public support for policies to reduce risk after Hurricane Sandy.

    Science.gov (United States)

    Greenberg, Michael R; Weiner, Marc D; Noland, Robert; Herb, Jeanne; Kaplan, Marjorie; Broccoli, Anthony J

    2014-06-01

    A phone survey was conducted in New Jersey in 2013 four months after the second of two major devastating tropical storms (Sandy in 2012 and Irene in 2011). The objective was to estimate public support for restricting land uses in flood zones, requiring housing to be built to resist storm waters, and otherwise increasing mitigation and resilience. Respondents who supported these mitigation and resilience policies disproportionately were concerned about global climate change, trusted climate scientists and the federal government, and were willing to contribute to a redevelopment program through taxes, bonds, and fees. They also tended to have collectivist and egalitarian worldviews. Half of the respondents supported at least four of the seven risk-reducing policies. How their support translates into public policy remains to be seen. Lack of willingness to personally fund these policies is an obstacle.

  1. Copper and zinc distribution coefficients for sandy aquifer materials

    DEFF Research Database (Denmark)

    Christensen, Thomas Højlund; Astrup, Thomas; Boddum, J. K.

    2000-01-01

    ; Zn: 6±22,800 l/kg) and correlating them to the characteristics of the aquifer material (particle size distribution, organic C content, surface area, pH) revealed good correlation with pH in the range 5.3± 8.9 (Cu: r 2=0.72; Zn: r 2=0.94). Including any other of the measured aquifer characteristics...... improved the correlation only a few percent. The results indicate that the mobility of Cu and Zn in sandy aquifers, as re¯ected in the measured Kd values, is very restricted at pH values above 6, since the relative migration velocity is less than 1%. However, at lower pH values, Zn seems to become mobile...

  2. Remediation of sandy soils using surfactant solutions and foams.

    Science.gov (United States)

    Couto, Hudson J B; Massarani, Guilio; Biscaia, Evaristo C; Sant'Anna, Geraldo L

    2009-05-30

    Remediation of sandy soils contaminated with diesel oil was investigated in bench-scale experiments. Surfactant solution, regular foams and colloidal gas aphrons were used as remediation fluids. An experimental design technique was used to investigate the effect of relevant process variables on remediation efficiency. Soils prepared with different average particle sizes (0.04-0.12 cm) and contaminated with different diesel oil contents (40-80 g/kg) were used in experiments conducted with remediation fluids. A mathematical model was proposed allowing for the determination of oil removal rate-constant (k(v)) and oil content remaining in the soil after remediation (C(of)) as well as estimation of the percentage of oil removed. Oil removal efficiencies obtained under the central experimental design conditions were 96%, 88% and 35% for aphrons, regular foams and surfactant solutions, respectively. High removal efficiencies were obtained using regular foams and aphrons, demanding small amounts of surfactant.

  3. Visual Odometry for Planetary Exploration Rovers in Sandy Terrains

    Directory of Open Access Journals (Sweden)

    Linhui Li

    2013-05-01

    Full Text Available Visual odometry provides planetary exploration rovers with accurate knowledge of their position and orientation, which needs effective feature tracking results, especially in barren sandy terrains. In this paper, a stereovision based odometry algorithm is proposed for a lunar rover, which is composed of corner extraction, feature tracking and motion estimation. First, a morphology based image enhancement method is studied to guarantee enough corners are extracted. Second, a Random Sample Consensus (RANSAC algorithm is proposed to make a robust estimation of the fundamental matrix, which is the basic and critical part of feature matching and tracking. Then, the 6 degrees of freedom rover position and orientation is estimated by the RANSAC algorithm. Finally, experiments are performed in a simulated lunar surface environment using a prototype rover, which have confirmed the feasibility and effectiveness of the proposed method.

  4. Performance of Social Network Sensors during Hurricane Sandy

    Science.gov (United States)

    Kryvasheyeu, Yury; Chen, Haohui; Moro, Esteban; Van Hentenryck, Pascal; Cebrian, Manuel

    2015-01-01

    Information flow during catastrophic events is a critical aspect of disaster management. Modern communication platforms, in particular online social networks, provide an opportunity to study such flow and derive early-warning sensors, thus improving emergency preparedness and response. Performance of the social networks sensor method, based on topological and behavioral properties derived from the “friendship paradox”, is studied here for over 50 million Twitter messages posted before, during, and after Hurricane Sandy. We find that differences in users’ network centrality effectively translate into moderate awareness advantage (up to 26 hours); and that geo-location of users within or outside of the hurricane-affected area plays a significant role in determining the scale of such an advantage. Emotional response appears to be universal regardless of the position in the network topology, and displays characteristic, easily detectable patterns, opening a possibility to implement a simple “sentiment sensing” technique that can detect and locate disasters. PMID:25692690

  5. Nematode Faunal Response to Grassland Degradation in Horqin Sandy Land

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The responses of soil nematode communities to grassland degradation were studied under undegraded grassland (UG),degraded grassland (DG), and improved grassland (IG), in Horqin Sandy Land, Inner Mongolia, Northeast China. Soil samples were collected at depths of 0-10, 10-20, and 20-30 cm. Total organic carbon (TOC) and total nitrogen (TN)exhibited positive effects on the total number of nematodes and trophic groups. Significant treatment effects were found in the total number of nematodes, plant parasites, and omnivores-predators. Measures taken in the improved grassland could improve the number of omnivore-predators, especially in the deeper soil layers. Nematode richness was lower in the DG treatment than in the IG and UG treatments. The food web structure index (SI) was significantly higher in the UG and IG treatments than in the DG treatment. A higher SI suggested a food web with more trophic linkages and relatively healthy ecosystems.

  6. Extraction Efficiency of Belonolaimus longicaudatus from Sandy Soil.

    Science.gov (United States)

    McSorley, R; Frederick, J J

    1991-10-01

    Numbers of Belonolaimus longicaudatus extracted from sandy soils (91-92% sand) by sieving and centrifugation were only 40-55% of those extracted by sieving and incubation on a Baermann tray. Residues normally discarded at each step of the sieving plus Baermann tray extraction procedure were examined for nematodes to obtain estimates of extraction efficiencies. For third-stage and fourth-stage juveniles, males, and females, estimates of extraction efficiency ranged from 60 to 65% in one experiment and 73 to 82% in another. Estimated extraction efficiencies for second-stage juveniles were lower (33% in one experiment, 67% in another) due to losses during sieving. When sterilized soil was seeded with known numbers of B. longicaudatus, 60% of second-stage juveniles and 68-76% of other stages were recovered. Most stages of B. longicaudatus could be extracted from these soils by sieving plus Baermann incubation with an efficiency of 60-70%.

  7. 78 FR 52560 - Hurricane Sandy Rebuilding Task Force-Rebuild-by-Design; Announcement of Selection of Design Teams

    Science.gov (United States)

    2013-08-23

    ... URBAN DEVELOPMENT Hurricane Sandy Rebuilding Task Force--Rebuild-by-Design; Announcement of Selection of Design Teams AGENCY: Hurricane Sandy Task Force, HUD. ACTION: Notice. SUMMARY: In June 2013, the Hurricane Sandy Task Force launched Rebuild by Design, a multi-stage regional design competition to...

  8. Quantifying human mobility perturbation and resilience in Hurricane Sandy.

    Science.gov (United States)

    Wang, Qi; Taylor, John E

    2014-01-01

    Human mobility is influenced by environmental change and natural disasters. Researchers have used trip distance distribution, radius of gyration of movements, and individuals' visited locations to understand and capture human mobility patterns and trajectories. However, our knowledge of human movements during natural disasters is limited owing to both a lack of empirical data and the low precision of available data. Here, we studied human mobility using high-resolution movement data from individuals in New York City during and for several days after Hurricane Sandy in 2012. We found the human movements followed truncated power-law distributions during and after Hurricane Sandy, although the β value was noticeably larger during the first 24 hours after the storm struck. Also, we examined two parameters: the center of mass and the radius of gyration of each individual's movements. We found that their values during perturbation states and steady states are highly correlated, suggesting human mobility data obtained in steady states can possibly predict the perturbation state. Our results demonstrate that human movement trajectories experienced significant perturbations during hurricanes, but also exhibited high resilience. We expect the study will stimulate future research on the perturbation and inherent resilience of human mobility under the influence of hurricanes. For example, mobility patterns in coastal urban areas could be examined as hurricanes approach, gain or dissipate in strength, and as the path of the storm changes. Understanding nuances of human mobility under the influence of such disasters will enable more effective evacuation, emergency response planning and development of strategies and policies to reduce fatality, injury, and economic loss.

  9. Glider observations and modeling of sediment transport in Hurricane Sandy

    Science.gov (United States)

    Miles, Travis; Seroka, Greg; Kohut, Josh; Schofield, Oscar; Glenn, Scott

    2015-03-01

    Regional sediment resuspension and transport are examined as Hurricane Sandy made landfall on the Mid-Atlantic Bight (MAB) in October 2012. A Teledyne-Webb Slocum glider, equipped with a Nortek Aquadopp current profiler, was deployed on the continental shelf ahead of the storm, and is used to validate sediment transport routines coupled to the Regional Ocean Modeling System (ROMS). The glider was deployed on 25 October, 5 days before Sandy made landfall in southern New Jersey (NJ) and flew along the 40 m isobath south of the Hudson Shelf Valley. We used optical and acoustic backscatter to compare with two modeled size classes along the glider track, 0.1 and 0.4 mm sand, respectively. Observations and modeling revealed full water column resuspension for both size classes for over 24 h during peak waves and currents, with transport oriented along-shelf toward the southwest. Regional model predictions showed over 3 cm of sediment eroded on the northern portion of the NJ shelf where waves and currents were the highest. As the storm passed and winds reversed from onshore to offshore on the southern portion of the domain waves and subsequently orbital velocities necessary for resuspension were reduced leading to over 3 cm of deposition across the entire shelf, just north of Delaware Bay. This study highlights the utility of gliders as a new asset in support of the development and verification of regional sediment resuspension and transport models, particularly during large tropical and extratropical cyclones when in situ data sets are not readily available.

  10. Revealing accumulation zones of plastic pellets in sandy beaches.

    Science.gov (United States)

    Moreira, Fabiana T; Balthazar-Silva, Danilo; Barbosa, Lucas; Turra, Alexander

    2016-11-01

    Microplastics such as pellets are reported worldwide on sandy beaches, and have possible direct and indirect impacts on the biota and physical characteristics of the habitats where they accumulate. Evaluations of their standing stock at different spatial scales generate data on levels of contamination. This information is needed to identify accumulation zones and the specific beach habitats and communities that are likely to be most affected. Standing stocks of plastic pellets were evaluated in 13 sandy beaches in São Paulo state, Brazil. The sampling strategy incorporated across-shore transects from coastal dunes and backshores, and vertical profiles of the accumulated pellets down to 1 m depth below the sediment surface. Accumulation zones were identified at regional (among beaches) and local (between compartments) scales. At the regional scale pellet density tended to increase at beaches on the central and southwestern coast, near ports and factories that produce and transport the largest amounts of pellets in the country. At the local scale coastal dunes showed larger accumulations of pellets than backshores. For both compartments pellets tended to occur deeper in areas where standing stocks were larger. Most of the pellets were concentrated from the surface down to 0.4 m depth, suggesting that organisms inhabiting this part of the sediment column are more exposed to the risks associated with the presence of pellets. Our findings shed light on the local and regional scales of spatial variability of microplastics and their consequences for assessment and monitoring schemes in coastal compartments. Copyright © 2016. Published by Elsevier Ltd.

  11. High-density turbidity currents: Are they sandy debris flows?

    Energy Technology Data Exchange (ETDEWEB)

    Shanmugam, G. [Mobil Exploration and Producing Technical Center, Dallas, TX (United States)

    1996-01-01

    Conventionally, turbidity currents are considered as fluidal flows in which sediment is supported by fluid turbulence, whereas debris flows are plastic flows in which sediment is supported by matrix strength, dispersive pressure, and buoyant lift. The concept of high-density turbidity current refers to high-concentration, commonly non-turbulent, flows of fluids in which sediment is supported mainly by matrix strength, dispersive pressure, and buoyant lift. The conventional wisdom that traction carpets with entrained turbulent clouds on top represent high-density turbidity currents is a misnomer because traction carpets are neither fluidal nor turbulent. Debris flows may also have entrained turbulent clouds on top. The traction carpet/debris flow and the overriding turbulent clouds are two separate entities in terms of flow rheology and sediment-support mechanism. In experimental and theoretical studies, which has linked massive sands and floating clasts to high-density turbidity currents, the term high-density turbidity current has actually been used for laminar flows. In alleviating this conceptual problem, sandy debris flow is suggested as a substitute for high-density turbidity current. Sandy debris flows represent a continuous spectrum of processes between cohesive and cohesionless debris flows. Commonly they are rheologically plastic. They may occur with or without entrained turbulent clouds on top. Their sediment-support mechanisms include matrix strength, dispersive pressure, and buoyant lift. They are characterized by laminar flow conditions, a moderate to high grain concentration, and a low to moderate mud content. Although flows evolve and transform during the course of transport in density-stratified flows, the preserved features in a deposit are useful to decipher only the final stages of deposition. At present, there are no established criteria to decipher transport mechanism from the depositional record.

  12. Mitigation of Liquefaction in Sandy Soils Using Stone Columns

    Science.gov (United States)

    Selcuk, Levent; Kayabalı, Kamil

    2010-05-01

    Soil liquefaction is one of the leading causes of earthquake-induced damage to structures. Soil improvement methods provide effective solutions to reduce the risk of soil liquefaction. Thus, soil ground treatments are applied using various techniques. However, except for a few ground treatment methods, they generally require a high cost and a lot of time. Especially in order to prevent the risk of soil liquefaction, stone columns conctructed by vibro-systems (vibro-compaction, vibro-replacement) are one of the traditional geotechnical methods. The construction of stone columns not only enhances the ability of clean sand to drain excess pore water during an earthquake, but also increases the relative density of the soil. Thus, this application prevents the development of the excess pore water pressure in sand during earthquakes and keeps the pore pressure ratio below a certain value. This paper presents the stone column methods used against soil liquefaction in detail. At this stage, (a) the performances of the stone columns were investigated in different spacing and diameters of columns during past earthquakes, (b) recent studies about design and field applications of stone columns were presented, and (c) a new design method considering the relative density of soil and the capacity of drenage of columns were explained in sandy soil. Furthermore, with this new method, earthquake performances of the stone columns constructed at different areas were investigated before the 1989 Loma Prieta and the 1994 Northbridge earthquakes, as case histories of field applications, and design charts were compiled for suitable spacing and diameters of stone columns with consideration to the different sandy soil parameters and earhquake conditions. Key Words: Soil improvement, stone column, excess pore water pressure

  13. Quantifying human mobility perturbation and resilience in Hurricane Sandy.

    Directory of Open Access Journals (Sweden)

    Qi Wang

    Full Text Available Human mobility is influenced by environmental change and natural disasters. Researchers have used trip distance distribution, radius of gyration of movements, and individuals' visited locations to understand and capture human mobility patterns and trajectories. However, our knowledge of human movements during natural disasters is limited owing to both a lack of empirical data and the low precision of available data. Here, we studied human mobility using high-resolution movement data from individuals in New York City during and for several days after Hurricane Sandy in 2012. We found the human movements followed truncated power-law distributions during and after Hurricane Sandy, although the β value was noticeably larger during the first 24 hours after the storm struck. Also, we examined two parameters: the center of mass and the radius of gyration of each individual's movements. We found that their values during perturbation states and steady states are highly correlated, suggesting human mobility data obtained in steady states can possibly predict the perturbation state. Our results demonstrate that human movement trajectories experienced significant perturbations during hurricanes, but also exhibited high resilience. We expect the study will stimulate future research on the perturbation and inherent resilience of human mobility under the influence of hurricanes. For example, mobility patterns in coastal urban areas could be examined as hurricanes approach, gain or dissipate in strength, and as the path of the storm changes. Understanding nuances of human mobility under the influence of such disasters will enable more effective evacuation, emergency response planning and development of strategies and policies to reduce fatality, injury, and economic loss.

  14. Controlling the ripple density and heights: a new way to improve the electrical performance of CVD-grown graphene

    Science.gov (United States)

    Park, Won-Hwa; Jo, Insu; Hong, Byung Hee; Cheong, Hyeonsik

    2016-05-01

    We report a new way to enhance the electrical performances of large area CVD-grown graphene through controlling the ripple density and heights after transfer onto SiO2/Si substrates by employing different cooling rates during fabrication. We find that graphene films prepared with a high cooling rate have reduced ripple density and heights and improved electrical characteristics such as higher electron/hole mobilities as well as reduced sheet resistance. The corresponding Raman analysis also shows a significant decrease of the defects when a higher cooling rate is employed. We suggest a model that explains the improved morphology of the graphene film obtained with higher cooling rates. From these points of view, we can suggest a new pathway toward a relatively lower density and heights of ripples in order to reduce the flexural phonon-electron scattering effect, leading to higher lateral carrier mobilities.We report a new way to enhance the electrical performances of large area CVD-grown graphene through controlling the ripple density and heights after transfer onto SiO2/Si substrates by employing different cooling rates during fabrication. We find that graphene films prepared with a high cooling rate have reduced ripple density and heights and improved electrical characteristics such as higher electron/hole mobilities as well as reduced sheet resistance. The corresponding Raman analysis also shows a significant decrease of the defects when a higher cooling rate is employed. We suggest a model that explains the improved morphology of the graphene film obtained with higher cooling rates. From these points of view, we can suggest a new pathway toward a relatively lower density and heights of ripples in order to reduce the flexural phonon-electron scattering effect, leading to higher lateral carrier mobilities. Electronic supplementary information (ESI) available: Reproducible data set. See DOI: 10.1039/c6nr00706f

  15. Richtmyer-Meshkov instability of a flat interface subjected to a rippled shock wave

    Science.gov (United States)

    Zou, Liyong; Liu, Jinhong; Liao, Shenfei; Zheng, Xianxu; Zhai, Zhigang; Luo, Xisheng

    2017-01-01

    The Richtmyer-Meshkov (RM) instability of a nominally flat interface (N2/SF6 ) subjected to a rippled shock, as the counterpart of a corrugated interface interacting with a planar shock, is studied experimentally in a vertical shock tube using both schlieren photography and fog visualization diagnostics. The nonplanar incident shock wave is produced by a planar shock diffracting around a rigid cylinder, and the flat interface is created by a membraneless technique. Three different distances η (the ratio of spacing from cylinder to interface over cylinder diameter) are considered. Schlieren images indicate that the nonplanar incident shock can be divided into three different segments separated by two triple points. Fog visualization pictures show the formation of overall "Λ " shaped interface structures and a N2 cavity at the center and two interface steps at both sides. With the increase of the dimensionless time, the dimensionless interface amplitude increases as well as the penetration depth of the cavity, and both curves exhibit reasonable collapse for different η numbers. Through equating the preinterface perturbation of the rippled shock with a preshock perturbation of a corrugated interface, the growth rate of this instability is found to be noticeably smaller than that of the standard RM instability.

  16. Analytical evaluation of DC capacitor RMS current and voltage ripple in neutral-point clamped inverters

    Indian Academy of Sciences (India)

    K S GOPALAKRISHNAN; SANTOSH JANAKIRAMAN; SOUMITRA DAS; G NARAYANAN

    2017-06-01

    The sizing of the DC-link capacitor in a three-level inverter is based on the RMS current flowing through it. This paper analyses the DC-link capacitor RMS current in a neutral-point clamped (NPC) inverter and expresses the same as a function of modulation index, line-side current amplitude and power factor. Analytical closed-form expressions are derived for the capacitor RMS current for single-phase half-bridge,single-phase full-bridge and three-phase three-leg topologies of a three-level inverter. The worst-case capacitor current stress is determined for each topology based on the analytical expressions. Further, analytical expressions are derived for the RMS values of low-frequency and high-frequency capacitor currents. These expressions are then used to estimate voltage ripple across the DC capacitor for sinusoidally modulated three-phase NPC inverter. The analytical expressions for the RMS current and voltage ripple are validated experimentally over a wide range of operating points.

  17. Integrating turbulent flow, biogeochemical, and poromechanical processes in rippled coastal sediment (Invited)

    Science.gov (United States)

    Cardenas, M. B.; Cook, P. L.; Jiang, H.; Traykovski, P.

    2010-12-01

    Coastal sediments are the locus of multiple coupled processes. Turbulent flow associated with waves and currents induces porewater flow through sediment leading to fluid exchange with the water column. This porewater flow is determined by the hydraulic and elastic properties of the sediment. Porewater flow also ultimately controls biogeochemical reactions in the sediment whose rates depend on delivery of reactants and export of products. We present results from numerical modeling studies directed at integrating these processes with the goal of shedding light on these complex environments. We show how denitrification rates inside ripples are largest at intermediate permeability which represents the optimal balance of reactant delivery and anoxic conditions. It is clear that nutrient cycling and distribution within the sediment is strongly dependent on the character of the multidimensional flow field inside of sediment. More recent studies illustrate the importance of the elastic properties of the saturated sediment on modulating fluid exchange between the water column and the sediment when pressure fluctuations along the sediment-water interface occur at the millisecond scale. Pressure fluctuations occur at this temporal scale due to turbulence and associated shedding of vortices due to the ripple geometry. This suggests that biogeochemical cycling may also be affected by these high-frequency elastic effects. Future studies should be directed towards this and should take advantage of modeling tools such as those we present.

  18. Inactivation of Stigmatella aurantiaca CsgA gene impares rippling formation

    Directory of Open Access Journals (Sweden)

    Milosevic-Đeric Ana

    2015-01-01

    Full Text Available Stigmatella aurantiaca fruiting body development depends on cell-cell interactions. One type of the signaling molecule stigmolone isolated from S. aurantiaca cells acts to help cells to stay together in the aggregation phase. Another gene product involved in intercellular signaling in S. aurantiaca is the csgA homolog of Myxococcus xanthus. In close relative M. xanthus C signal the product of the csgA gene is required for rippling, aggregation and sporulation. Isolation of homologous gene in S. aurantiaca implicates a probable role of CsgA in intercellular communication. Inactivation of the gene by insertion mutagenesis caused alterations in S. aurantiaca fruiting. The motility behavior of the cells during development was changed as well as their ability to stay more closely together in the early stages of development. Inactivation of the csgA gene completely abolished rippling of the cells. This indicates the crucial role of the CsgA protein in regulating this rhythmic behavior.

  19. Momentum transport studies in JET H-mode discharges with an enhanced toroidal field ripple

    Energy Technology Data Exchange (ETDEWEB)

    De Vries, P C; Howell, D H; Giroud, C; Parail, V [EURATOM/CCFE Association, Culham Science Centre, Abingdon, OX14 3DB (United Kingdom); Versloot, T W [FOM institute for Plasma Physics Rijnhuizen, Association EURATOM-FOM, PO Box 1207, Nieuwegein (Netherlands); Salmi, A [Association Euratom-Tekes, Helsinki University of Technology, PO Box 4100, 02015 TKK (Finland); Hua, M-D [Imperial College, SW7 2BY, London (United Kingdom); Saibene, G [Fusion for Energy Joint Undertaking, 0819 Barcelona (Spain); Tala, T, E-mail: Peter.de.Vries@jet.efda.or [Association Euratom-Tekes, VTT, PO Box 1000, 02044 VTT (Finland)

    2010-06-15

    In this study, enhancement of the toroidal field (TF) ripple has been used as a tool in order to reveal the impact of the momentum pinch on the rotation profiles in H-mode JET discharges. The analysis showed that flatter rotation profiles were obtained in discharges with a high TF ripple, attributed to a smaller inward momentum convection. An average inward momentum pinch of approximately V{sub p} {approx} 3.4 m s{sup -1} and a normalized pinch value of RV{sub p}/{chi} {approx} 6.6 could explain the observation. The data show that the momentum at the edge affects the peaking of the rotation and momentum density profiles. Under the assumption that the heat and momentum diffusivities are equal, an estimate of the levels of the momentum pinch in all discharges in the JET rotation database was made. For H-mode discharge these ranged from 0.3 m s{sup -1} < V{sub p} < 17 m s{sup -1}, with 2 < RV{sub p}/{chi} < 10. A larger momentum pinch was found in discharges with a smaller density profile gradient length, i.e. a more peaked density profile.

  20. A Modified Bridgeless Converter for SRM Drive with Reduced Ripple Current

    Directory of Open Access Journals (Sweden)

    Maheswari C krishnakumar

    2015-06-01

    Full Text Available Single Phase Switched Reluctance Motor is more popular in many industrial purposes for high speed applications because of its robust and rugged construction. For low cost and variable speed drive applications SRM are widely used.Due to doubly salient structure of motor, the torque pulsations are high when compared to other sinusoidal machines. The major drawback in using SRM drive is torque pulsations and increased number of switching components. In order to overcome these drawbacks, a bridgeless Single Ended Primary Inductor Converter (SEPIC is proposed. The major advantages of this converter are continuous output current,smaller voltage ripple and reduced semiconductor current stress when compared to the conventional SEPIC converter. The ripple free input current is obtained by using additional winding of input inductor and auxiliary capacitors. To achieve high efficiency, active power factor correction circuits (PFC are employed to precise the power factor. Further, the unity power factor can be obtained by making the input current during switching period proportional to the input voltage is proposed. The proposed system consists of reduced components and it is also capable of reducing the conduction losses. The working principles and the waveforms of proposed converter are analyzed. To analyze the circuit operation, theoretical analysis and simulation results are provided. Finally, the  comparison between the waveforms of conventional SEPIC and proposed system is presented by using MATLAB/Simulink tools.