Laser Shock Wave-Assisted Patterning on NiTi Shape Memory Alloy Surfaces

NASA Astrophysics Data System (ADS)

Ilhom, Saidjafarzoda; Seyitliyev, Dovletgeldi; Kholikov, Khomidkohodza; Thomas, Zachary; Er, Ali O.; Li, Peizhen; Karaca, Haluk E.; San, Omer

2018-01-01

Shape memory alloys (SMAs) are a unique class of smart materials and they were employed in various applications in engineering, biomedical, and aerospace technologies. Here, we report an advanced, efficient, and low-cost direct imprinting method with low environmental impact to create thermally controllable surface patterns. Patterned microindents were generated on Ni50Ti50 (at. %) SMAs using an Nd:YAG laser with 1064 nm wavelength at 10 Hz. Laser pulses at selected fluences were focused on the NiTi surface and generated pressure pulses of up to a few GPa. Optical microscope images showed that surface patterns with tailorable sizes can be obtained. The depth of the patterns increases with laser power and irradiation time. Upon heating, the depth profile of SMA surfaces changed where the maximum depth recovery ratio of 30% was observed. Recovery ratio decreased and stabilized when the number of pulses and thus the well depth were further increased. A numerical simulation of pressure evolution in shape memory alloys showed a good agreement with the experimental results. The stress wave closely followed the rise time of the laser pulse to its peak value and initial decay. Rapid attenuation and dispersion of the stress wave were found in our simulation.

Laser Shock Wave-Assisted Patterning on NiTi Shape Memory Alloy Surfaces

NASA Astrophysics Data System (ADS)

Ilhom, Saidjafarzoda; Seyitliyev, Dovletgeldi; Kholikov, Khomidkohodza; Thomas, Zachary; Er, Ali O.; Li, Peizhen; Karaca, Haluk E.; San, Omer

2018-03-01

Shape memory alloys (SMAs) are a unique class of smart materials and they were employed in various applications in engineering, biomedical, and aerospace technologies. Here, we report an advanced, efficient, and low-cost direct imprinting method with low environmental impact to create thermally controllable surface patterns. Patterned microindents were generated on Ni50Ti50 (at. %) SMAs using an Nd:YAG laser with 1064 nm wavelength at 10 Hz. Laser pulses at selected fluences were focused on the NiTi surface and generated pressure pulses of up to a few GPa. Optical microscope images showed that surface patterns with tailorable sizes can be obtained. The depth of the patterns increases with laser power and irradiation time. Upon heating, the depth profile of SMA surfaces changed where the maximum depth recovery ratio of 30% was observed. Recovery ratio decreased and stabilized when the number of pulses and thus the well depth were further increased. A numerical simulation of pressure evolution in shape memory alloys showed a good agreement with the experimental results. The stress wave closely followed the rise time of the laser pulse to its peak value and initial decay. Rapid attenuation and dispersion of the stress wave were found in our simulation.

Coherent scattering of a spherical wave from an irregular surface. [antenna pattern effects

NASA Technical Reports Server (NTRS)

Fung, A. K.

1983-01-01

The scattering of a spherical wave from a rough surface using the Kirchhoff approximation is considered. An expression representing the measured coherent scattering coefficient is derived. It is shown that the sphericity of the wavefront and the antenna pattern can become an important factor in the interpretation of ground-based measurements. The condition under which the coherent scattering-coefficient expression reduces to that corresponding to a plane wave incidence is given. The condition under which the result reduces to the standard image solution is also derived. In general, the consideration of antenna pattern and sphericity is unimportant unless the surface-height standard deviation is small, i.e., unless the coherent scattering component is significant. An application of the derived coherent backscattering coefficient together with the existing incoherent scattering coefficient to interpret measurements from concrete and asphalt surfaces is shown.

The Effect of the South Asia Monsoon on the Wind Sea and Swell Patterns in the Arabian Sea

NASA Astrophysics Data System (ADS)

Semedo, Alvaro

2015-04-01

Ocean surface gravity waves have a considerable impact on coastal and offshore infrastructures, and are determinant on ship design and routing. But waves also play an important role on the coastal dynamics and beach erosion, and modulate the exchanges of momentum, and mass and other scalars between the atmosphere and the ocean. A constant quantitative and qualitative knowledge of the wave patterns is therefore needed. There are two types of waves at the ocean surface: wind-sea and swell. Wind-sea waves are growing waves under the direct influence of local winds; as these waves propagate away from their generation area, or when their phase speed overcomes the local wind speed, they are called swell. Swell waves can propagate thousands of kilometers across entire ocean basins. The qualitative analysis of ocean surface waves has been the focus of several recent studies, from the wave climate to the air-sea interaction community. The reason for this interest lies mostly in the fact that waves have an impact on the lower atmosphere, and that the air-sea coupling is different depending on the wave regime. Waves modulate the exchange of momentum, heat, and mass across the air-sea interface, and this modulation is different and dependent on the prevalence of one type of waves: wind sea or swell. For fully developed seas the coupling between the ocean-surface and the overlaying atmosphere can be seen as quasi-perfect, in a sense that the momentum transfer and energy dissipation at the ocean surface are in equilibrium. This can only occur in special areas of the Ocean, either in marginal seas, with limited fetch, or in Open Ocean, in areas with strong and persistent wind speed with little or no variation in direction. One of these areas is the Arabian Sea, along the coasts of Somalia, Yemen and Oman. The wind climate in the Arabian sea is under the direct influence of the South Asia monsoon, where the wind blows steady from the northeast during the boreal winter, and reverses direction to blow also steady but stronger from the southwest during the boreal summer months. During the summer monsoon the wind pattern in the north Arabian Sea is rather intricate, with a large scale synoptic forcing with a high pressure cell over the ocean and a thermal low pressure system in-land, but also with at least two low-level wind jets, the Finlater (or Somali) jet, and the Oman coastal jet. This wind pattern leads to a particular wave pattern and seasonal variability. The monsoon wind pattern has a direct influence in the wave climate in that area, The particular wind-sea and swell climates of the Arabian Sea are presented. The study is based on the ERA-Interim wave reanalysis from the European Centre for Medium-Range Weather Forecasts.

Spaceborne imaging radar - Geologic and oceanographic applications

NASA Technical Reports Server (NTRS)

Elachi, C.

1980-01-01

Synoptic, large-area radar images of the earth's land and ocean surface, obtained from the Seasat orbiting spacecraft, show the potential for geologic mapping and for monitoring of ocean surface patterns. Structural and topographic features such as lineaments, anticlines, folds and domes, drainage patterns, stratification, and roughness units can be mapped. Ocean surface waves, internal waves, current boundaries, and large-scale eddies have been observed in numerous images taken by the Seasat imaging radar. This article gives an illustrated overview of these applications.

Excitation of Love waves in a thin film layer by a line source.

NASA Technical Reports Server (NTRS)

Tuan, H.-S.; Ponamgi, S. R.

1972-01-01

The excitation of a Love surface wave guided by a thin film layer deposited on a semiinfinite substrate is studied in this paper. Both the thin film and the substrate are considered to be elastically isotropic. Amplitudes of the surface wave in the thin film region and the substrate are found in terms of the strength of a line source vibrating in a direction transverse to the propagating wave. In addition to the surface wave, the bulk shear wave excited by the source is also studied. Analytical expressions for the bulk wave amplitude as a function of the direction of propagation, the acoustic powers transported by the surface and bulk waves, and the efficiency of surface wave excitation are obtained. A numerical example is given to show how the bulk wave radiation pattern depends upon the source frequency, the film thickness and other important parameters of the problem. The efficiency of surface wave excitation is also calculated for various parameter values.

Waves and Crops

ERIC Educational Resources Information Center

Bennett, J.

1973-01-01

Discusses wave patterns on the surfaces of ripening wheat and barley crops when the wind is moderately strong. Examines the structure of the turbulence over such natural surfaces and conditions under which the crop may be damaged by the wind. (JR)

Acoustic tweezers: patterning cells and microparticles using standing surface acoustic waves (SSAW).

PubMed

Shi, Jinjie; Ahmed, Daniel; Mao, Xiaole; Lin, Sz-Chin Steven; Lawit, Aitan; Huang, Tony Jun

2009-10-21

Here we present an active patterning technique named "acoustic tweezers" that utilizes standing surface acoustic wave (SSAW) to manipulate and pattern cells and microparticles. This technique is capable of patterning cells and microparticles regardless of shape, size, charge or polarity. Its power intensity, approximately 5x10(5) times lower than that of optical tweezers, compares favorably with those of other active patterning methods. Flow cytometry studies have revealed it to be non-invasive. The aforementioned advantages, along with this technique's simple design and ability to be miniaturized, render the "acoustic tweezers" technique a promising tool for various applications in biology, chemistry, engineering, and materials science.

Hyperthermia apparatus

DOEpatents

Larsen, Lawrence E.

2000-01-01

A hyperthermia apparatus, suitable for transurethral application, has an energy radiating element comprising a leaky-wave antenna. The leaky wave antenna radiation pattern is characterized by a surface wave which propagates along an aperture formed by openings (small in comparison to a wavelength) in the outer conductor of a transmission line. Appropriate design of the leaky wave antenna produces a uniform, broadside pattern of temperature elevation that uniformly heats all or part of the periurethral tissues.

Strait of Gibraltar as seen from STS-60

NASA Image and Video Library

1994-02-09

STS060-88-070 (3-11 Feb 1994) --- This view shows sunglint in the Strait of Gibralter. In this photograph a high pressure atmospheric system over the Iberian Peninsula has set the conditions for seeing a plankton bloom along the Moroccan coast in the Alboran Sea (Western Mediterranean) coastal counter current as well as illumining the influence of winds in the sunglint pattern near the Strait of Gibraltar. Where the water is ruffled from a wind gust, such as off Cadiz, Spain, the surface is less reflective and thus appears dark. A combination of the effects of the tide and the surface winds through the Strait of Gibraltar have created a unique sunglint pattern at the entrance of the Mediterranean. The Atlantic Ocean waters are flowing with the tide through the Strait of Gibraltar into the Mediterranean Sea and are probably smoothing out some of the smaller waves at the surface. The incoming tide generates internal waves as can be faintly seen in this photograph. The incoming relatively cooler, less dense Atlantic water flows over the warm, more saline Mediterranean water. As the tide moves into the Strait of Gibraltar it encounters the Camarinal Sill, which is like a cliff under the water, south of Camarinal Point, Spain. Internal waves are generated at this sill and they travel along the density boundary between the Atlantic water and the Mediterranean water masses. There is little evidence of the internal waves at the surface of the ocean. We can see them in spacecraft photography because of the sunglint which reflects off the different water layers in differential patterns. The internal waves also smooth out some of the bands of capillary waves at the surface. That is, the sun reflects more brightly from these smooth areas, showing the pattern of the underwater waves more prominently than do the surface waves. The Bay of Cadiz on the southwest coast of Spain, the Rock of Gibraltar, and the Moroccan coast are also beautifully illustrated in this photography. The focus for scientists, however, remains the high clarity and spatial resolution given by sunglint studies to physical phenomena in the ocean.

The roles of mid-myocardial and epicardial cells in T-wave alternans development: a simulation study.

PubMed

Janusek, D; Svehlikova, J; Zelinka, J; Weigl, W; Zaczek, R; Opolski, G; Tysler, M; Maniewski, R

2018-05-08

The occurrence of T-wave alternans in electrocardiographic signals was recently linked to susceptibility to ventricular arrhythmias and sudden cardiac death. Thus, by detecting and comprehending the origins of T-wave alternans, it might be possible to prevent such events. Here, we simulated T-wave alternans in a computer-generated human heart model by modulating the action potential duration and amplitude during the first part of the repolarization phase. We hypothesized that changes in the intracardiac alternans patterns of action potential properties would differentially influence T-wave alternans measurements at the body surface. Specifically, changes were simulated globally in the whole left and right ventricles to simulate concordant T-wave alternans, and locally in selected regions to simulate discordant and regional discordant, hereinafter referred to as "regional", T-wave alternans. Body surface potential maps and 12-lead electrocardiographic signals were then computed. In depth discrimination, the influence of epicardial layers on T-wave alternans development was significantly higher than that of mid-myocardial cells. Meanwhile, spatial discrimination revealed that discordant and regional action potential property changes had a higher influence on T-wave alternans amplitude than concordant changes. Notably, varying T-wave alternans sources yielded distinct body surface potential map patterns for T-wave alternans amplitude, which can be used for location of regions within hearts exhibiting impaired repolarization. The highest ability for T-wave alternans detection was achieved in lead V1. Ultimately, we proposed new parameters Vector Magnitude Alternans and Vector Angle Alternans, with higher ability for T-wave alternans detection when using multi-lead electrocardiographic signals processing than for single leads. Finally, QT alternans was found to be associated with the process of T-wave alternans generation. The distributions of the body surface T-wave alternans amplitude have been shown to have unique patterns depending on the type of alternans (concordant, discordant or regional) and the location of the disturbance in the heart. The influence of epicardial cells on T-wave alternans development is significantly higher than that of mid-myocardial cells, among which the sub-endocardial layer exerted the highest influence. QT interval alternans is identified as a phenomenon that correlate with T-wave alternans.

Patterns of Alloy Deformation by Pulsed Pressure

NASA Astrophysics Data System (ADS)

Chebotnyagin, L. M.; Potapov, V. V.; Lopatin, V. V.

2015-06-01

Patterns of alloy deformation for optimization of a welding regime are studied by the method of modeling and deformation profiles providing high deformation quality are determined. A model of stepwise kinetics of the alloy deformation by pulsed pressure from the expanding plasma channel inside of a deformable cylinder is suggested. The model is based on the analogy between the acoustic and electromagnetic wave processes in long lines. The shock wave pattern of alloy deformation in the presence of multiple reflections of pulsed pressure waves in the gap plasma channel - cylinder wall and the influence of unloading waves from free surfaces are confirmed.

Faraday wave lattice as an elastic metamaterial.

PubMed

Domino, L; Tarpin, M; Patinet, S; Eddi, A

2016-05-01

Metamaterials enable the emergence of novel physical properties due to the existence of an underlying subwavelength structure. Here, we use the Faraday instability to shape the fluid-air interface with a regular pattern. This pattern undergoes an oscillating secondary instability and exhibits spontaneous vibrations that are analogous to transverse elastic waves. By locally forcing these waves, we fully characterize their dispersion relation and show that a Faraday pattern presents an effective shear elasticity. We propose a physical mechanism combining surface tension with the Faraday structured interface that quantitatively predicts the elastic wave phase speed, revealing that the liquid interface behaves as an elastic metamaterial.

Interannual variability of the Submonthly Wave Patterns over the Western North Pacific

NASA Astrophysics Data System (ADS)

Ko, K. C.

2017-12-01

This study examines the interannual variability of the 5-16 day wave patterns by separating them into active (A4mV) and inactive (I4mV) years on the basis of the 4-month (July-October) variance of a Japan-South China Sea (JSCS) circulation index from 1979 to 2013. The sea surface temperature for the A4mV years exhibited an ENSO pattern but a reversed anomaly pattern was observed in the I4mV years. Composite results indicate that tropical cyclone (TC) tracks are closely linked to the activity of the wave patterns. When the wave patterns were strong with a solid wave structure in the A4mV years, TCs would follow the propagation routes of the cyclonic anomalies of the wave patterns and separated into two types of tracks: straight-moving and recurving. However, in the I4mV years when the wave patterns were weak and poorly organized, the shapes of the cyclonic anomalies became irregular and sporadic. The weakening structure of the wave patterns in the I4mV years would induce the TCs to undergo more scattered routes near Taiwan and east coast of China. Therefore, Taiwan experienced more rainfall in the I4mV years.

Flow of a falling liquid curtain onto a moving substrate

NASA Astrophysics Data System (ADS)

Liu, Yekun; Itoh, Masahiro; Kyotoh, Harumichi

2017-10-01

In this study, we investigate a low-Weber-number flow of a liquid curtain bridged between two vertical edge guides and the upper surface of a moving substrate. Surface waves are observed on the liquid curtain, which are generated due to a large pressure difference between the inner and outer region of the meniscus on the substrate, and propagate upstream. They are categorized as varicose waves that propagate upstream on the curtain and become stationary because of the downstream flow. The Kistler’s equation, which governs the flow in thin liquid curtains, is solved under the downstream boundary conditions, and the numerical solutions are studied carefully. The solutions are categorized into three cases depending on the boundary conditions. The stability of the varicose waves is also discussed as wavelets were observed on these waves. The two types of modes staggered and peak-valley patterns are considered in the present study, and they depend on the Reynolds number, the Weber number, and the amplitude of the surface waves. The former is observed in our experiment, while the latter is predicted by our calculation. Both the types of modes can be derived using the equations with periodic coefficients that originated from the periodic base flow due to the varicose waves. The stability analysis of the waves shows that the appearance of the peak-valley pattern requires a significantly greater amplitude of the waves, and a significantly higher Weber number and Reynolds number compared to the condition in which the staggered pattern is observed.

Surface Acoustic Waves Grant Superior Spatial Control of Cells Embedded in Hydrogel Fibers.

PubMed

Lata, James P; Guo, Feng; Guo, Jinshan; Huang, Po-Hsun; Yang, Jian; Huang, Tony Jun

2016-10-01

By exploiting surface acoustic waves and a coupling layer technique, cells are patterned within a photosensitive hydrogel fiber to mimic physiological cell arrangement in tissues. The aligned cell-polymer matrix is polymerized with short exposure to UV light and the fiber is extracted. These patterned cell fibers are manipulated into simple and complex architectures, demonstrating feasibility for tissue-engineering applications. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Viscous and Turbulent Stress Measurements over Wind-driven Surface Waves

NASA Astrophysics Data System (ADS)

Yousefi, K.; Veron, F.; Buckley, M. P.; Hara, T.; Husain, N.

2017-12-01

In recent years, the exchange of momentum and scalars between the atmosphere and the ocean has been the subject of several investigations. Although the role of surface waves on the air-sea momentum flux is now well established, detailed quantitative measurements of the turbulence in the airflow over surface waves remain scarce. The current incomplete physical understanding of the airflow dynamics impedes further progress in developing physically based parameterizations for improved weather and sea state predictions, particularly in high winds and extreme conditions. Using combined Particle Image Velocimetry (PIV) and Laser Induced Fluorescence (LIF) in the laboratory, we have acquired detailed quantitative measurements of the airflow over wind-driven waves and down to within the viscous sub-layer. Various wind-wave conditions are examined with mean wind speeds ranging from 0.86 to 16.63 m s-1. The mean, turbulent, and wave-induced velocity fields are then extracted from instantaneous two-dimensional velocity measurements. Individual airflow separation events precipitate abrupt and dramatic along-wave variations in the surface viscous stress. In the bulk flow above the waves, these separation events are a source of intense vorticity. Phase averages of the viscous stress present a pattern of along-wave asymmetry near the surface; it is highest on the upwind of wave crest with its peak value about the crest and its minimum occurs at the middle of the leeward side of waves. The contribution of the viscous stress to the total momentum flux is not negligible particularly for low to moderate wind speeds and this contribution decreases with increasing wind speed. Away from the surface, the distribution of turbulent Reynolds stress forms a negative-positive pattern along the wave crest with a separation-induced maximum above the downwind side of the wave. Our measurements will be discussed in the context of available previous results.

Terahertz-wave near-field imaging with subwavelength resolution using surface-wave-assisted bow-tie aperture

NASA Astrophysics Data System (ADS)

Ishihara, Kunihiko; Ohashi, Keishi; Ikari, Tomofumi; Minamide, Hiroaki; Yokoyama, Hiroyuki; Shikata, Jun-ichi; Ito, Hiromasa

2006-11-01

We demonstrate the terahertz-wave near-field imaging with subwavelength resolution using a bow-tie shaped aperture surrounded by concentric periodic structures in a metal film. A subwavelength aperture with concentric periodic grooves, which are known as a bull's eye structure, shows extremely large enhanced transmission beyond the diffraction limit caused by the resonant excitation of surface waves. Additionally, a bow-tie aperture exhibits extraordinary field enhancement at the sharp tips of the metal, which enhances the transmission and the subwavelength spatial resolution. We introduced a bow-tie aperture to the bull's eye structure and achieved high spatial resolution (˜λ/17) in the near-field region. The terahertz-wave near-field image of the subwavelength metal pattern (pattern width=20μm) was obtained for the wavelength of 207μm.

Recoverable stress induced two-way shape memory effect on NiTi surface using laser-produced shock wave

NASA Astrophysics Data System (ADS)

Seyitliyev, Dovletgeldi; Li, Peizhen; Kholikov, Khomidkhodza; Grant, Byron; Thomas, Zachary; Alal, Orhan; Karaca, Haluk E.; Er, Ali O.

2017-02-01

The surfaces of Ni50Ti50 shape memory alloys (SMAs) were patterned by laser scribing. This method is more simplistic and efficient than traditional indentation techniques, and has also shown to be an effective method in patterning these materials. Different laser energy densities ranging from 5 mJ/pulse to 56 mJ/pulse were used to observe recovery on SMA surface. The temperature dependent heat profiles of the NiTi surfaces after laser scribing at 56 mJ/pulse show the partially-recovered indents, which indicate a "shape memory effect (SME)" Experimental data is in good agreement with theoretical simulation of laser induced shock wave propagation inside NiTi SMAs. Stress wave closely followed the rise time of the laser pulse to its peak values and initial decay. Further investigations are underway to improve the SME such that the indents are recovered to a greater extent.

Ultrafast optical measurements of surface waves on a patterned layered nanostructure

NASA Astrophysics Data System (ADS)

Daly, Brian; Bjornsson, Matteo; Connolly, Aine; Mahat, Sushant; Rachmilowitz, Bryan; Antonelli, George; Myers, Alan; Yoo, Hui-Jae; Singh, Kanwal; King, Sean

2015-03-01

We report ultrafast optical pump-probe measurements of 12 - 54 GHz surface acoustic waves (SAWs) on patterned layered nanostructures. These very high frequency SAWs were generated and detected on the following patterned film stack: 25 nm physically vapor deposited TiN / 180 nm porous PECVD-grown a-SiOC:H dielectric / 12 nm non-porous PECVD-grown a-SiOC:H etch-stop / 100 nm CVD-grown a-SiO2 / Si (100) substrate. The TiN layer was dry plasma etched to form lines of rectangular cross section with pitches of 420 nm, 250 nm, 180 nm, and 168 nm and the lines were oriented parallel to the [110] direction on the wafer surface. The absorption of ultrafast pulses from a Ti:sapphire oscillator operating at 800 nm generated SAWs that were detected by time-delayed probe pulses from the same oscillator via a reflectivity change (ΔR) . In each of the four cases the SAW frequency increased with decreasing pitch, but not in a linear way as had been seen in previous experiments of this sort. By comparing the results with mechanical simulations, we present evidence for the detection of different types of SAWs in each case, including Rayleigh-like waves, Sezawa waves, and leaky or radiative waves. This work was supported by NSF Award DMR1206681.

Preliminary Examination of Pulse Shapes From GLAS Ocean Returns

NASA Astrophysics Data System (ADS)

Swift, T. P.; Minster, B.

2003-12-01

We have examined GLAS data collected over the Pacific ocean during the commission phase of the ICESat mission, in an area where sea state is well documented. The data used for this preliminary analysis were acquired during two passes along track 95, on March 18 and 26 of 2003, along the stretch offshore southern California. These dates were chosen for their lack of cloud cover; large (4.0 m) and small (0.7 m) significant wave heights, respectively; and the presence of waves emanating from single distant Pacific storms. Cloud cover may be investigated using MODIS images (http://acdisx.gsfc.nasa.gov/data/dataset/MODIS/), while models of significant wave heights and wave vectors for offshore California are archived by the Coastal Data Information Program (http://cdip.ucsd.edu/cdip_htmls/models.shtml). We find that the shape of deep-ocean GLAS pulse returns is diagnostic of the state of the ocean surface. A calm surface produces near-Gaussian, single-peaked shot returns. In contrast, a rough surface produces blurred shot returns which often feature multiple peaks; these peaks are typically separated by total path lengths on the order of one meter. Gaussian curves fit to rough-water returns are therefore less reliable and lead to greater measurement error; outliers in the ocean surface elevation product are mostly the result of poorly fit low-energy shot returns. Additionally, beat patterns and aliasing artifacts may arise from the sampling of deep-ocean wave trains by GLAS footprints separated by 140m. The apparent wavelength of such patterns depends not only on the wave frequency, but also on the angle between the ICESat ground track and the azimuth of the wave crests. We present a preliminary analysis of such patterns which appears to be consistent with a simple geometrical model.

Frequency dependent steering with backward leaky waves via photonic crystal interface layer.

PubMed

Colak, Evrim; Caglayan, Humeyra; Cakmak, Atilla O; Villa, Alessandro D; Capolino, Filippo; Ozbay, Ekmel

2009-06-08

A Photonic Crystal (PC) with a surface defect layer (made of dimers) is studied in the microwave regime. The dispersion diagram is obtained with the Plane Wave Expansion Method. The dispersion diagram reveals that the dimer-layer supports a surface mode with negative slope. Two facts are noted: First, a guided (bounded) wave is present, propagating along the surface of the dimer-layer. Second, above the light line, the fast traveling mode couple to the propagating spectra and as a result a directive (narrow beam) radiation with backward characteristics is observed and measured. In this leaky mode regime, symmetrical radiation patterns with respect to the normal to the PC surface are attained. Beam steering is observed and measured in a 70 degrees angular range when frequency ranges in the 11.88-13.69 GHz interval. Thus, a PC based surface wave structure that acts as a frequency dependent leaky wave antenna is presented. Angular radiation pattern measurements are in agreement with those obtained via numerical simulations that employ the Finite Difference Time Domain Method (FDTD). Finally, the backward radiation characteristics that in turn suggest the existence of a backward leaky mode in the dimer-layer are experimentally verified using a halved dimer-layer structure.

Connections Between the Spring Breakup of the Southern Hemisphere Polar Vortex, Stationary Waves, and Air-sea Roughness

NASA Technical Reports Server (NTRS)

Garfinkel, Chaim I.; Oman, Luke David; Barnes, Elizabeth A.; Waugh, Darryn W.; Hurwitz, Margaret H.; Molod, Andrea M.

2013-01-01

A robust connection between the drag on surface-layer winds and the stratospheric circulation is demonstrated in NASA's Goddard Earth Observing System Chemistry-Climate Model (GEOSCCM). Specifically, an updated parameterization of roughness at the air-sea interface, in which surface roughness is increased for moderate wind speeds (4ms to 20ms), leads to a decrease in model biases in Southern Hemispheric ozone, polar cap temperature, stationary wave heat flux, and springtime vortex breakup. A dynamical mechanism is proposed whereby increased surface roughness leads to improved stationary waves. Increased surface roughness leads to anomalous eddy momentum flux convergence primarily in the Indian Ocean sector (where eddies are strongest climatologically) in September and October. The localization of the eddy momentum flux convergence anomaly in the Indian Ocean sector leads to a zonally asymmetric reduction in zonal wind and, by geostrophy, to a wavenumber-1 stationary wave pattern. This tropospheric stationary wave pattern leads to enhanced upwards wave activity entering the stratosphere. The net effect is an improved Southern Hemisphere vortex: the vortex breaks up earlier in spring (i.e., the spring late-breakup bias is partially ameliorated) yet is no weaker in mid-winter. More than half of the stratospheric biases appear to be related to the surface wind speed biases. As many other chemistry climate models use a similar scheme for their surface layer momentum exchange and have similar biases in the stratosphere, we expect that results from GEOSCCM may be relevant for other climate models.

Faraday instability on patterned surfaces

NASA Astrophysics Data System (ADS)

Feng, Jie; Rubinstein, Gregory; Jacobi, Ian; Stone, Howard

2013-11-01

We show how micro-scale surface patterning can be used to control the onset of the Faraday instability in thin liquid films. It is well known that when a liquid film on a planar substrate is subject to sufficient vibrational accelerations, the free surface destabilizes, exhibiting a family of non-linear standing waves. This instability remains a canonical problem in the study of spontaneous pattern formation, but also has practical uses. For example, the surface waves induced by the Faraday instability have been studied as a means of enhanced damping for mechanical vibrations (Genevaux et al. 2009). Also the streaming within the unstable layer has been used as a method for distributing heterogeneous cell cultures on growth medium (Takagi et al. 2002). In each of these applications, the roughness of the substrate significantly affects the unstable flow field. We consider the effect of patterned substrates on the onset and behavior of the Faraday instability over a range of pattern geometries and feature heights where the liquid layer is thicker than the pattern height. Also, we describe a physical model for the influence of patterned roughness on the destabilization of a liquid layer in order to improve the design of practical systems which exploit the Faraday instability.

Acoustic tweezers via sub-time-of-flight regime surface acoustic waves.

PubMed

Collins, David J; Devendran, Citsabehsan; Ma, Zhichao; Ng, Jia Wei; Neild, Adrian; Ai, Ye

2016-07-01

Micrometer-scale acoustic waves are highly useful for refined optomechanical and acoustofluidic manipulation, where these fields are spatially localized along the transducer aperture but not along the acoustic propagation direction. In the case of acoustic tweezers, such a conventional acoustic standing wave results in particle and cell patterning across the entire width of a microfluidic channel, preventing selective trapping. We demonstrate the use of nanosecond-scale pulsed surface acoustic waves (SAWs) with a pulse period that is less than the time of flight between opposing transducers to generate localized time-averaged patterning regions while using conventional electrode structures. These nodal positions can be readily and arbitrarily positioned in two dimensions and within the patterning region itself through the imposition of pulse delays, frequency modulation, and phase shifts. This straightforward concept adds new spatial dimensions to which acoustic fields can be localized in SAW applications in a manner analogous to optical tweezers, including spatially selective acoustic tweezers and optical waveguides.

Faraday wave patterns on a square cell network

NASA Astrophysics Data System (ADS)

Peña-Polo, Franklin; Vargas, Carlos A.; Vásquez-González, Benjamín; Medina, Abraham; Trujillo, Leonardo; Klapp, Jaime; Sigalotti, Leonardo Di G.

2017-05-01

We present the experimental observations of the Faraday instability when the vibrated liquid is contained in a network of small square cells for exciting frequencies in the range 10≤ F≤ 24 Hz. A sweep of the parameter space has been performed to investigate the amplitudes and frequencies of the driving force for which different patterns form over the network. Regular patterns in the form of square lattices are observed for driving frequencies in the range 10≤ F<14 Hz, while ordered matrices of oscillons are formed for 1423 Hz, disordered periodic patterns appear within individual cells for a small range of amplitudes. In this case, the wave field is dominated by oscillating blobs that interact on the capillary-gravity scale. A Pearson correlation analysis of the recorded videos shows that for all ordered patterns, the surface waves are periodic and correspond to Faraday waves of dominant frequency equal to half the excitation frequency (i.e., f=F/2). In contrast, the oscillons formed for 1423 Hz are not subharmonic and correspond to periodic harmonic waves with f=nF/2 (for n=2,4,\\ldots ). We find that the experimentally determined minimum forcing necessary to destabilize the rest state and generate surface waves is consistent with a recent stability analysis of stationary solutions as derived from a new dispersion relation for time-periodic waves with nonzero forcing and dissipation.

Deep Ocean Tsunami Waves off the Sri Lankan Coast

NASA Technical Reports Server (NTRS)

2004-01-01

The initial tsunami waves resulting from the undersea earthquake that occurred at 00:58:53 UTC (Coordinated Universal Time) on December 26, 2004, off the island of Sumatra, Indonesia, took a little over 2 hours to reach the teardrop-shaped island of Sri Lanka. Additional waves continued to arrive for many hours afterward. At approximately 05:15 UTC, as NASA's Terra satellite passed overhead, the Multi-angle Imaging SpectroRadiometer (MISR) captured this image of deep ocean tsunami waves about 30-40 kilometers from Sri Lanka's southwestern coast. The waves are made visible due to the effects of changes in sea-surface slope on the reflected sunglint pattern, shown here in MISR's 46-degree-forward-pointing camera. Sunglint occurs when sunlight reflects off a water surface in much the same way light reflects off a mirror, and the position of the Sun, angle of observation, and orientation of the sea surface determines how bright each part of the ocean appears in the image. These large wave features were invisible to MISR's nadir (vertical-viewing) camera. The image covers an area of 208 kilometers by 207 kilometers. The greatest impact of the tsunami was generally in an east-west direction, so the havoc caused by the tsunami along the southwestern shores of Sri Lanka was not as severe as along the eastern coast. However, substantial damage did occur in this region' as evidenced by the brownish debris in the water' because tsunami waves can diffract around land masses. The ripple-like wave pattern evident in this MISR image roughly correlates with the undersea boundary of the continental shelf. The surface wave pattern is likely to have been caused by interaction of deep waves with the ocean floor, rather than by the more usually observed surface waves, which are driven by winds. It is possible that this semi-concentric pattern represents wave reflection from the continental land mass; however, a combination of wave modeling and detailed bathymetric data is required to fully understand the dynamics. Examination of other MISR images of this area, taken under similar illumination conditions, has not uncovered any surface patterns resembling those seen here. This image is an example of how MISR's multi-angular capability provides unique information for understanding how tsunamis propagate. Another application of MISR data enabled scientists to measure the motion of breaking tsunami waves along the eastern shores of Andhra Pradesh, India. The Multi-angle Imaging SpectroRadiometer observes the daylit Earth continuously and every 9 days views the entire globe between 82 degrees North and 82 degrees South latitude. These data products were generated from a portion of the imagery acquired during Terra orbit 26720 and utilize data from within blocks 85 to 86 within World Reference System-2 path 142. MISR was built and is managed by NASA's Jet Propulsion Laboratory, Pasadena, CA, for NASA's Office of Earth Science, Washington, DC. The Terra satellite is managed by NASA's Goddard Space Flight Center, Greenbelt, MD. Image courtesy NASA/GSFC/LaRC/JPL, MISR Team. Text by Clare Averill (Raytheon ITSS/JPL); Michael Garay and David J. Diner (JPL, California Institute of Technology); and Vasily Titov (NOAA/Pacific Marine Environmental Laboratory and University of Washington/Joint Institute for the Study of the Atmosphere and Oceans).

Structure of the airflow above surface waves

NASA Astrophysics Data System (ADS)

Buckley, Marc; Veron, Fabrice

2016-04-01

Weather, climate and upper ocean patterns are controlled by the exchanges of momentum, heat, mass, and energy across the ocean surface. These fluxes are, in turn, influenced by the small-scale physics at the wavy air-sea interface. We present laboratory measurements of the fine-scale airflow structure above waves, achieved in over 15 different wind-wave conditions, with wave ages Cp/u* ranging from 1.4 to 66.7 (where Cp is the peak phase speed of the waves, and u* the air friction velocity). The experiments were performed in the large (42-m long) wind-wave-current tank at University of Delaware's Air-Sea Interaction laboratory (USA). A combined Particle Image Velocimetry and Laser Induced Fluorescence system was specifically developed for this study, and provided two-dimensional airflow velocity measurement as low as 100 um above the air-water interface. Starting at very low wind speeds (U10~2m/s), we directly observe coherent turbulent structures within the buffer and logarithmic layers of the airflow above the air-water interface, whereby low horizontal velocity air is ejected away from the surface, and higher velocity fluid is swept downward. Wave phase coherent quadrant analysis shows that such turbulent momentum flux events are wave-phase dependent. Airflow separation events are directly observed over young wind waves (Cp/u*<3.7) and counted using measured vorticity and surface viscous stress criteria. Detached high spanwise vorticity layers cause intense wave-coherent turbulence downwind of wave crests, as shown by wave-phase averaging of turbulent momentum fluxes. Mean wave-coherent airflow motions and fluxes also show strong phase-locked patterns, including a sheltering effect, upwind of wave crests over old mechanically generated swells (Cp/u*=31.7), and downwind of crests over young wind waves (Cp/u*=3.7). Over slightly older wind waves (Cp/u* = 6.5), the measured wave-induced airflow perturbations are qualitatively consistent with linear critical layer theory.

Differentiation of red wines using an electronic nose based on surface acoustic wave devices.

PubMed

García, M; Fernández, M J; Fontecha, J L; Lozano, J; Santos, J P; Aleixandre, M; Sayago, I; Gutiérrez, J; Horrillo, M C

2006-02-15

An electronic nose, utilizing the principle of surface acoustic waves (SAW), was used to differentiate among different wines of the same variety of grapes which come from the same cellar. The electronic nose is based on eight surface acoustic wave sensors, one is a reference sensor and the others are coated by different polymers by spray coating technique. Data analysis was performed by two pattern recognition methods; principal component analysis (PCA) and probabilistic neuronal network (PNN). The results showed that electronic nose was able to identify the tested wines.

Characterization of rotary-percussion drilling as a seismic-while-drilling source

NASA Astrophysics Data System (ADS)

Xiao, Yingjian; Hurich, Charles; Butt, Stephen D.

2018-04-01

This paper focuses on an evaluation of rotary-percussion drilling (RPD) as a seismic source. Two field experiments were conducted to characterize seismic sources from different rocks with different strengths, i.e. weak shale and hard arkose. Characterization of RPD sources consist of spectral analysis and mean power measurements, along with field measurements of the source radiation patterns. Spectral analysis shows that increase of rock strength increases peak frequency and widens bandwidth, which makes harder rock more viable for seismic-while-drilling purposes. Mean power analysis infers higher magnitude of body waves in RPD than in conventional drillings. Within the horizontal plane, the observed P-wave energy radiation pattern partially confirms the theoretical radiation pattern under a single vertical bit vibration. However a horizontal lobe of energy is observed close to orthogonal to the axial bit vibration. From analysis, this lobe is attributed to lateral bit vibration, which is not documented elsewhere during RPD. Within the horizontal plane, the observed radiation pattern of P-waves is generally consistent with a spherically-symmetric distribution of energy. In addition, polarization analysis is conducted on P-waves recorded at surface geophones for understanding the particle motions. P-wave particle motions are predominantly in the vertical direction showing the interference of the free-surface.

Interannual coherent variability of SSTA and SSHA in the Tropical Indian Ocean

NASA Astrophysics Data System (ADS)

Feng, J. Q.

2012-01-01

Sea surface height derived from the multiple ocean satellite altimeter missions (TOPEX/Poseidon, Jason-1, ERS, Envisat et al.) and sea surface temperature from National Centers for Environmental Prediction (NCEP) over 1993-2008 are analyzed to investigate the coherent patterns between the interannual variability of the sea surface and subsurface in the Tropical Indian Ocean, by jointly adopting Singular Value Decomposition (SVD) and Extended Associate Pattern Analysis (EAPA) methods. Results show that there are two dominant coherent modes with the nearly same main period of about 3-5 yr, accounting for 86 % of the total covariance in all, but 90° phase difference between them. The primary pattern is characterized by a east-west dipole mode associated with the mature phase of ENSO, and the second presents a sandwich mode having one sign anomalies along Sumatra-Java coast and northeast of Madagascar, whilst an opposite sign between the two regions. The robust correlations of the sea surface height anomaly (SSHA) with sea surface temperature anomaly (SSTA) in the leading modes indicate a strong interaction between them, though the highest correlation coefficient appears with a time lag. And there may be some physical significance with respect to ocean dynamics implied in SSHA variability. Analyzing results show that the features of oceanic waves with basin scale, of which the Rossby wave is prominent, are apparent in the dominant modes. It is further demonstrated from the EAPA that the equatorial eastward Kelvin wave and off-equatorial westward Rossby wave as well as their reflection in the east and west boundary, respectively, are important dynamic mechanisms in the evolution of the two leading coherent patterns. Results of the present study suggest that the upper ocean thermal variations on the timescale of interannual coherent with the ocean dynamics in spatial structure and temporal evolution are mainly attributed to the ocean waves.

Dynamic patterns in a supported lipid bilayer driven by standing surface acoustic waves.

PubMed

Hennig, Martin; Neumann, Jürgen; Wixforth, Achim; Rädler, Joachim O; Schneider, Matthias F

2009-11-07

In the past decades supported lipid bilayers (SLBs) have been an important tool in order to study the physical properties of biological membranes and cells. So far, controlled manipulation of SLBs is very limited. Here we present a new technology to create lateral patterns in lipid membranes controllable in both space and time. Surface acoustic waves (SAWs) are used to generate lateral standing waves on a piezoelectric substrate which create local "traps" in the lipid bilayer and lead to a lateral modulation in lipid concentration. We demonstrate that pattern formation is reversible and does not affect the integrity of the lipid bilayer as shown by extracting the diffusion constant of fluid membranes. The described method could possibly be used to design switchable interfaces for the lateral transport and organization of membrane bound macromolecules to create dynamic bioarrays and control biofilm formation.

Flow Visualization and Pattern Formation in Vertically Falling Liquid Films

NASA Astrophysics Data System (ADS)

Balakotaiah, Vemuri; Malamataris, Nikolaos

2008-11-01

Analytical results of a low-dimensional two equation h-q model and results of a direct numerical simulation of the transient two-dimensional Navier Stokes equations are presented for vertically falling liquid films along a solid wall. The numerical study aims at the elucidation of the hydrodynamics of the falling film. The analytical study aims at the calculation of the parameter space where pattern formation occurs for this flow. It has been found that when the wave amplitude exceeds a certain magnitude, flow reversal occurs in the film underneath the minimum of the waves [1]. The instantaneous vortical structures possess two hyperbolic points on the vertical wall and an elliptic point in the film. As the wave amplitude increases further, the elliptic point reaches the free surface of the film and two more hyperbolic points are formed in the free surface that replace the elliptic point. Between the two hyperbolic points on the free surface, the streamwise component of velocity is negative and the film is divided into asymmetric patterns of up and down flows. Depending on the value of the Kapitza number, these patterns are either stationary or oscillatory. Physical reasons for the influence of the Kapitza number on pattern formation are given. Movies are shown where the pattern formation is demonstrated. [1] N.A.Malamataris and V.Balakotaiah (2008), AIChE J., 54(7), p. 1725-1740

Non-leaky modes and bandgaps of surface acoustic waves in wrinkled stiff-film/compliant-substrate bilayers

NASA Astrophysics Data System (ADS)

Li, Guo-Yang; Xu, Guoqiang; Zheng, Yang; Cao, Yanping

2018-03-01

Surface acoustic wave (SAW) devices have found a wide variety of technical applications, including SAW filters, SAW resonators, microfluidic actuators, biosensors, flow measurement devices, and seismic wave shields. Stretchable/flexible electronic devices, such as sensory skins for robotics, structural health monitors, and wearable communication devices, have received considerable attention across different disciplines. Flexible SAW devices are essential building blocks for these applications, wherein piezoelectric films may need to be integrated with the compliant substrates. When piezoelectric films are much stiffer than soft substrates, SAWs are usually leaky and the devices incorporating them suffer from acoustic losses. In this study, the propagation of SAWs in a wrinkled bilayer system is investigated, and our analysis shows that non-leaky modes can be achieved by engineering stress patterns through surface wrinkles in the system. Our analysis also uncovers intriguing bandgaps (BGs) related to the SAWs in a wrinkled bilayer system; these are caused by periodic deformation patterns, which indicate that diverse wrinkling patterns could be used as metasurfaces for controlling the propagation of SAWs.

Interference phenomena in the refraction of a surface polariton by vertical dielectric barriers

NASA Technical Reports Server (NTRS)

Shen, T. P.; Wallis, R. F.; Maradudin, A. A.; Stegeman, G. I.

1984-01-01

A normal mode analysis is used to calculate the transmission and reflection coefficients for a surface polariton propagating along the interface between a surface active medium and a dielectric and incident normally on a vertical dielectric barrier of finite thickness or a thin dielectric film of finite length. The efficiencies of conversion of the surface polariton into transmitted and reflected bulk waves are also determined. The radiation patterns associated with the latter waves are presented.

Backscattered EM-wave manipulation using low cost 1-bit reflective surface at W-band

NASA Astrophysics Data System (ADS)

Taher Al-Nuaimi, Mustafa K.; Hong, Wei; He, Yejun

2018-04-01

The design of low cost 1-bit reflective (non-absorptive) surfaces for manipulation of backscattered EM-waves and radar cross section (RCS) reduction at W-band is presented in this article. The presented surface is designed based on the reflection phase cancellation principle. The unit cell used to compose the proposed surface has an obelus (division symbol of short wire and two disks above and below) like shape printed on a grounded dielectric material. Using this unit cell, surfaces that can efficiently manipulate the backscattered RCS pattern by using the proposed obelus-shaped unit cell (as ‘0’ element) and its mirrored unit cell (as ‘1’ element) in one surface with a 180°  ±  35° reflection phase difference between their reflection phases are designed. The proposed surfaces can generate various kinds of backscattered RCS patterns, such as single, three, or four lobes or even a low-level (reduced RCS) diffused reflection pattern when those two unit cells are distributed randomly across the surface aperture. For experimental characterization purposes, a 50  ×  50 mm2 surface is fabricated and measured.

Locomotion of Paramecium in patterned environments

NASA Astrophysics Data System (ADS)

Park, Eun-Jik; Eddins, Aja; Kim, Junil; Yang, Sung; Jana, Saikat; Jung, Sunghwan

2011-10-01

Ciliary organisms like Paramecium Multimicronucleatum locomote by synchronized beating of cilia that produce metachronal waves over their body. In their natural environments they navigate through a variety of environments especially surfaces with different topology. We study the effects of wavy surfaces patterned on the PDMS channels on the locomotive abilities of Paramecium by characterizing different quantities like velocity amplitude and wavelength of the trajectories traced. We compare this result with the swimming characteristics in straight channels and draw conclusions about the effects of various patterned surfaces.

Wave-current interaction study in the Gulf of Alaska for detection of eddies by synthetic aperture radar

NASA Technical Reports Server (NTRS)

Liu, Antony K.; Peng, Chich Y.; Schumacher, James D.

1994-01-01

High resolution Esa Remote Sensing Satellite-1 (ERS-1) Synthetic Aperture Radar (SAR) images are used to detect a mesoscale eddy. Such features limit dispersal of pollock larvae and therefore likely influence recruitment of fish in the Gulf of Alaska. During high sea states and high winds, the direct surface signature of the eddy was not clearly visible, but the wave refraction in the eddy area was observed. The rays of the wave field are traced out directly from the SAR image. The ray pattern gives information on the refraction pattern and on the relative variation of the wave energy along a ray through wave current interaction. These observations are simulated by a ray-tracing model which incorporates a surface current field associated with the eddy. The numerical results of the model show that the waves are refracted and diverge in the eddy field with energy density decreasing. The model-data comparison for each ray shows the model predictions are in good agreement with the SAR data.

Acoustic tweezing of particles using decaying opposing travelling surface acoustic waves (DOTSAW).

PubMed

Ng, Jia Wei; Devendran, Citsabehsan; Neild, Adrian

2017-10-11

Surface acoustic waves offer a versatile and biocompatible method of manipulating the location of suspended particles or cells within microfluidic systems. The most common approach uses the interference of identical frequency, counter propagating travelling waves to generate a standing surface acoustic wave, in which particles migrate a distance less than half the acoustic wavelength to their nearest pressure node. The result is the formation of a periodic pattern of particles. Subsequent displacement of this pattern, the prerequisite for tweezing, can be achieved by translation of the standing wave, and with it the pressure nodes; this requires changing either the frequency of the pair of waves, or their relative phase. Here, in contrast, we examine the use of two counterpropagating traveling waves of different frequency. The non-linearity of the acoustic forces used to manipulate particles, means that a small frequency difference between the two waves creates a substantially different force field, which offers significant advantages. Firstly, this approach creates a much longer range force field, in which migration takes place across multiple wavelengths, and causes particles to be gathered together in a single trapping site. Secondly, the location of this single trapping site can be controlled by the relative amplitude of the two waves, requiring simply an attenuation of one of the electrical drive signals. Using this approach, we show that by controlling the powers of the opposing incoherent waves, 5 μm particles can be migrated laterally across a fluid flow to defined locations with an accuracy of ±10 μm.

On the unsteady gravity-capillary wave pattern found behind a slow moving localized pressure distribution

NASA Astrophysics Data System (ADS)

Masnadi, N.; Duncan, J. H.

2013-11-01

The non-linear response of a water surface to a slow-moving pressure distribution is studied experimentally using a vertically oriented carriage-mounted air-jet tube that is set to translate over the water surface in a long tank. The free surface deformation pattern is measured with a full-field refraction-based method that utilizes a vertically oriented digital movie camera (under the tank) and a random dot pattern (above the water surface). At towing speeds just below the minimum phase speed of gravity-capillary waves (cmin ~ 23 cm/s), an unsteady V-shaped pattern is formed behind the pressure source. Localized depressions are generated near the source and propagate in pairs along the two arms of the V-shaped pattern. These depressions are eventually shed from the tips of the pattern at a frequency of about 1 Hz. It is found that the shape and phase speeds of the first depressions shed in each run are quantitatively similar to the freely-propagating gravity-capillary lumps from potential flow calculations. In the experiments, the amplitudes of the depressions decrease by approximately 60 percent while travelling 12 wavelengths. The depressions shed later in each run behave in a less consistent manner, probably due to their interaction with neighboring depressions.

Atmospheric Circulation Patterns over East Asia and Their Connection with Summer Precipitation and Surface Air Temperature in Eastern China during 1961-2013

NASA Astrophysics Data System (ADS)

Li, Shuping; Hou, Wei; Feng, Guolin

2018-04-01

Based on the NCEP/NCAR reanalysis data and Chinese observational data during 1961-2013, atmospheric circulation patterns over East Asia in summer and their connection with precipitation and surface air temperature in eastern China as well as associated external forcing are investigated. Three patterns of the atmospheric circulation are identified, all with quasi-barotropic structures: (1) the East Asia/Pacific (EAP) pattern, (2) the Baikal Lake/Okhotsk Sea (BLOS) pattern, and (3) the eastern China/northern Okhotsk Sea (ECNOS) pattern. The positive EAP pattern significantly increases precipitation over the Yangtze River valley and favors cooling north of the Yangtze River and warming south of the Yangtze River in summer. The warm sea surface temperature anomalies over the tropical Indian Ocean suppress convection over the northwestern subtropical Pacific through the Ekman divergence induced by a Kelvin wave and excite the EAP pattern. The positive BLOS pattern is associated with below-average precipitation south of the Yangtze River and robust cooling over northeastern China. This pattern is triggered by anomalous spring sea ice concentration in the northern Barents Sea. The anomalous sea ice concentration contributes to a Rossby wave activity flux originating from the Greenland Sea, which propagates eastward to North Pacific. The positive ECNOS pattern leads to below-average precipitation and significant warming over northeastern China in summer. The reduced soil moisture associated with the earlier spring snowmelt enhances surface warming over Mongolia and northeastern China and the later spring snowmelt leads to surface cooling over Far East in summer, both of which are responsible for the formation of the ECNOS pattern.

Laser-speckle-visibility acoustic spectroscopy in soft turbid media.

PubMed

Wintzenrieth, Frédéric; Cohen-Addad, Sylvie; Le Merrer, Marie; Höhler, Reinhard

2014-01-01

We image the evolution in space and time of an acoustic wave propagating along the surface of turbid soft matter by shining coherent light on the sample. The wave locally modulates the speckle interference pattern of the backscattered light, which is recorded using a camera. We show both experimentally and theoretically how the temporal and spatial correlations in this pattern can be analyzed to obtain the acoustic wavelength and attenuation length. The technique is validated using shear waves propagating in aqueous foam. It may be applied to other kinds of acoustic waves in different forms of turbid soft matter such as biological tissues, pastes, or concentrated emulsions.

Laser-speckle-visibility acoustic spectroscopy in soft turbid media

NASA Astrophysics Data System (ADS)

Wintzenrieth, Frédéric; Cohen-Addad, Sylvie; Le Merrer, Marie; Höhler, Reinhard

2014-01-01

We image the evolution in space and time of an acoustic wave propagating along the surface of turbid soft matter by shining coherent light on the sample. The wave locally modulates the speckle interference pattern of the backscattered light, which is recorded using a camera. We show both experimentally and theoretically how the temporal and spatial correlations in this pattern can be analyzed to obtain the acoustic wavelength and attenuation length. The technique is validated using shear waves propagating in aqueous foam. It may be applied to other kinds of acoustic waves in different forms of turbid soft matter such as biological tissues, pastes, or concentrated emulsions.

Probing Thermomechanics at the Nanoscale: Impulsively Excited Pseudosurface Acoustic Waves in Hypersonic Phononic Crystals

PubMed Central

2011-01-01

High-frequency surface acoustic waves can be generated by ultrafast laser excitation of nanoscale patterned surfaces. Here we study this phenomenon in the hypersonic frequency limit. By modeling the thermomechanics from first-principles, we calculate the system’s initial heat-driven impulsive response and follow its time evolution. A scheme is introduced to quantitatively access frequencies and lifetimes of the composite system’s excited eigenmodes. A spectral decomposition of the calculated response on the eigemodes of the system reveals asymmetric resonances that result from the coupling between surface and bulk acoustic modes. This finding allows evaluation of impulsively excited pseudosurface acoustic wave frequencies and lifetimes and expands our understanding of the scattering of surface waves in mesoscale metamaterials. The model is successfully benchmarked against time-resolved optical diffraction measurements performed on one-dimensional and two-dimensional surface phononic crystals, probed using light at extreme ultraviolet and near-infrared wavelengths. PMID:21910426

High-Resolution Structural and Electronic Properties of Epitaxial Topological Crystalline Insulator Films

NASA Astrophysics Data System (ADS)

Dagdeviren, Omur; Zhou, Chao; Zou, Ke; Simon, Georg; Albright, Stephen; Mandal, Subhasish; Morales-Acosta, Mayra; Zhu, Xiaodong; Ismail-Beigi, Sohrab; Walker, Frederick; Ahn, Charles; Schwarz, Udo; Altman, Eric

Revealing the local electronic properties of surfaces and their link to structural properties is an important problem for topological crystalline insulators (TCI) in which metallic surface states are protected by crystal symmetry. The microstructure and electronic properties of TCI SnTe film surfaces grown by molecular beam epitaxy were characterized using scanning probe microscopy. These results reveal the influence of various defects on the electronic properties: tilt boundaries leading to dislocation arrays that serve as periodic nucleation sites for pit growth; screw dislocations, and point defects. These features have varying length scale and display variations in the electronic structure of the surface, which are mapped with scanning tunneling microscopy images as standing waves superimposed on atomic scale images of the surface topography that consequently shape the wave patterns. Since the growth process results in symmetry breaking defects that patterns the topological states, we propose that the scanning probe tip can pattern the surface and electronic structure and enable the fabrication of topological devices on the SnTe surface. Financial support from the National Science Foundation through the Yale Materials Research Science and Engineering Center (Grant No. MRSEC DMR-1119826) and FAME.

Generation of intermittent gravitocapillary waves via parametric forcing

NASA Astrophysics Data System (ADS)

Castillo, Gustavo; Falcón, Claudio

2018-04-01

We report on the generation of an intermittent wave field driven by a horizontally moving wave maker interacting with Faraday waves. The spectrum of the local gravitocapillary surface wave fluctuations displays a power law in frequency for a wide range of forcing parameters. We compute the probability density function of the local surface height increments, which show that they change strongly across time scales. The structure functions of these increments are shown to display power laws as a function of the time lag, with exponents that are nonlinear functions of the order of the structure function. We argue that the origin of this scale-invariant intermittent spectrum is the Faraday wave pattern breakup due to its advection by the propagating gravity waves. Finally, some interpretations are proposed to explain the appearance of this intermittent spectrum.

Grating-patterned FeCo coated surface acoustic wave device for sensing magnetic field

NASA Astrophysics Data System (ADS)

Wang, Wen; Jia, Yana; Xue, Xufeng; Liang, Yong; Du, Zhaofu

2018-01-01

This study addresses the theoretical and experimental investigations of grating-patterned magnetostrictive FeCo coated surface acoustic wave (SAW) device for sensing magnetic field. The proposed sensor is composed of a configuration of differential dual-delay-line oscillators, and a magnetostrictive FeCo grating array deposited along the SAW propagation path of the sensing device, which suppresses effectively the hysteresis effect by releasing the internal binding force in FeCo. The magnetostrictive strain and ΔE effect from the FeCo coating modulates the SAW propagation characteristic, and the corresponding shift in differential oscillation frequency was utilized to evaluate the measurant. A theoretical model is performed to investigate the wave propagation in layered structure of FeCo/LiNbO3 in the effect of magnetostrictive, and allowing determining the optimal structure. The experimental results indicate that higher sensitivity, excellent linearity, and lower hysteresis error over the typical FeCo thin-film coated sensor were achieved from the grating-patterned FeCo coated sensor successfully.

Tutorial review of seismic surface waves' phenomenology

NASA Astrophysics Data System (ADS)

Levshin, A. L.; Barmin, M. P.; Ritzwoller, M. H.

2018-03-01

In recent years, surface wave seismology has become one of the leading directions in seismological investigations of the Earth's structure and seismic sources. Various applications cover a wide spectrum of goals, dealing with differences in sources of seismic excitation, penetration depths, frequency ranges, and interpretation techniques. Observed seismic data demonstrates the great variability of phenomenology which can produce difficulties in interpretation for beginners. This tutorial review is based on the many years' experience of authors in processing and interpretation of seismic surface wave observations and the lectures of one of the authors (ALL) at Workshops on Seismic Wave Excitation, Propagation and Interpretation held at the Abdus Salam International Center for Theoretical Physics (Trieste, Italy) in 1990-2012. We present some typical examples of wave patterns which could be encountered in different applications and which can serve as a guide to analysis of observed seismograms.

Free Surface Wave Interaction with a Horizontal Cylinder

NASA Astrophysics Data System (ADS)

Oshkai, P.; Rockwell, D.

1999-10-01

Classes of vortex formation from a horizontal cylinder adjacent to an undulating free-surface wave are characterized using high-image-density particle image velocimetry. Instantaneous representations of the velocity field, streamline topology and vorticity patterns yield insight into the origin of unsteady loading of the cylinder. For sufficiently deep submergence of the cylinder, the orbital nature of the wave motion results in multiple sites of vortex development, i.e., onset of vorticity concentrations, along the surface of the cylinder, followed by distinctive types of shedding from the cylinder. All of these concentrations of vorticity then exhibit orbital motion about the cylinder. Their contributions to the instantaneous values of the force coefficients are assessed by calculating moments of vorticity. It is shown that large contributions to the moments and their rate of change with time can occur for those vorticity concentrations having relatively small amplitude orbital trajectories. In a limiting case, collision with the surface of the cylinder can occur. Such vortex-cylinder interactions exhibit abrupt changes in the streamline topology during the wave cycle, including abrupt switching of the location of saddle points in the wave. The effect of nominal depth of submergence of the cylinder is characterized in terms of the time history of patterns of vorticity generated from the cylinder and the free surface. Generally speaking, generic types of vorticity concentrations are formed from the cylinder during the cycle of the wave motion for all values of submergence. The proximity of the free surface, however, can exert a remarkable influence on the initial formation, the eventual strength, and the subsequent motion of concentrations of vorticity. For sufficiently shallow submergence, large-scale vortex formation from the upper surface of the cylinder is inhibited and, in contrast, that from the lower surface of the cylinder is intensified. Moreover, decreasing the depth of submergence retards the orbital migration of previously shed concentrations of vorticity about the cylinder.

Analysis of moving surface structures at a laser-induced boiling front

NASA Astrophysics Data System (ADS)

Matti, R. S.; Kaplan, A. F. H.

2014-10-01

Recently ultra-high speed imaging enabled to observe moving wave patterns on metal melts that experience laser-induced boiling. In laser materials processing a vertical laser-induced boiling front governs processes like keyhole laser welding, laser remote fusion cutting, laser drilling or laser ablation. The observed waves originate from temperature variations that are closely related to the melt topology. For improved understanding of the essential front mechanisms and of the front topology, for the first time a deeper systematic analysis of the wave patterns was carried out. Seven geometrical shapes of bright or dark domains were distinguished and categorized, in particular bright peaks of three kinds and dark valleys, often inclined. Two categories describe special flow patterns at the top and bottom of the front. Dynamic and statistical analysis has revealed that the shapes often combine or separate from one category to another when streaming down the front. The brightness of wave peaks typically fluctuates during 20-50 μs. This variety of thermal wave observations is interpreted with respect to the accompanying surface topology of the melt and in turn for governing local mechanisms like absorption, shadowing, boiling, ablation pressure and melt acceleration. The findings can be of importance for understanding the key process mechanisms and for optimizing laser materials processing.

Complex seismic anisotropy beneath Germany from shear wave splitting and surface wave models

NASA Astrophysics Data System (ADS)

Campbell, L.; Long, M. D.; Becker, T. W.; Lebedev, S.

2013-12-01

Seismic anisotropy beneath stable continental interiors likely reflects a host of processes, including deformation in the lower crust, frozen anisotropy from past deformation processes in the lithospheric mantle, and present-day mantle flow in the asthenosphere. Because the anisotropic structure beneath continental interiors is generally complicated and often exhibits heterogeneity both laterally and with depth, a complete characterization of anisotropy and its interpretation in terms of deformational processes is challenging. In this study, we aim to expand our understanding of continental anisotropy by characterizing in detail the geometry and strength of azimuthal anisotropy beneath Germany and the surrounding region, using a combination of shear wave splitting and surface wave constraints. We utilize data from long-running broadband stations in and around Germany, collected from a variety of national and temporary European networks. We measure the splitting of SKS, SKKS, and PKS phases, with the aim of obtaining the best possible backazimuthal coverage. Preliminary results indicate that anisotropy beneath Germany is generally complex; we observe shear wave splitting patterns that are complicated and are inconsistent with a single horizontal layer of anisotropy beneath the station. Observed delay times are generally small (<1 sec), and there is a preponderance of null *KS arrivals in the dataset, with null measurements detected over a fairly large range of backazimuths. We also observe dramatic differences in splitting patterns over relatively short horizontal distances. Although we note backazimuthal variations in splitting at several stations, we do not observe a clear 90-degree periodicity that one would expect for the case of multiple anisotropic layers. We are currently carrying out comparisons between our observed splitting patterns and those predicted from tomographic models of azimuthal anisotropy derived from surface wave observations. The ultimate goal of this work is to combine different types of observations (shear wave splitting, surface wave models, and eventually anisotropic receiver function analysis) to place precise constraints on the anisotropic structure beneath Germany, and to interpret this structure in terms of on-going and past deformational processes in the crust and mantle.

Clustering of Synoptic Pattern over the Korean Peninsula from Meteorological Models

NASA Astrophysics Data System (ADS)

Kim, Jinah; Heo, Kiyoung; Choi, Jungwoon; Jung, Sanghoon

2017-04-01

Numerical modeling data on meteorological and ocean science is one of example of big geographic data sources. The properties of the data including the volume, variety, and dynamic aspects pose new challenges for geographic visualization, and visual geoanalytics using big data analysis using machine learning method. A combination of algorithmic and visual approaches that make sense of large volumes of various types of spatiotemporal data are required to gain knowledge about complex phenomena. In the East coast of Korea, it is suffering from property damages and human causalities due to abnormal high waves (swell-like high-height waves). It is known to be caused by local meteorological conditions on the East Sea of Korean Peninsula in previous research and they proposed three kinds of pressure patterns that generate abnormal high waves. However, they cannot describe all kinds of pressure patterns that generate abnormal high waves. In our study, we propose unsupervised machine learning method for pattern clustering and applied it to classify a pattern which has occurred abnormal high waves using numerical meteorological model's reanalysis data from 2000 to 2015 and past historical records of accidents by abnormal high waves. About 25,000 patterns of total spatial distribution of sea surface pressure are clustered into 30 patterns and they are classified into seasonal sea level pressure patterns based on meteorological characteristics of Korean peninsula. Moreover, in order to determine the representative patterns which occurs abnormal high waves, we classified it again using historical accidents cases among the winter season pressure patterns. In this work, we clustered synoptic pattern over the Korean Peninsula in meteorological modeling reanalysis data and we could understand a seasonal variation through identifying the occurrence of clustered synoptic pattern. For the future work, we have to identify the relationship of wave modeling data for better understanding of abnormal high waves and we will develop pattern decision system to predict abnormal high waves in advances. This research was a part of the project titled "Development of Korea Operational Oceanographic System (KOOS), Phase 2" and "Investigation of Large Swell Waves and Rip currents and Development of The Disaster Response System," funded by the Ministry of Oceans & Fisheries Korea (Grant PM59691 and PM59240).

Tidal-Induced Ocean Dynamics as Cause of Enceladus' Tiger Stripe Pattern

NASA Astrophysics Data System (ADS)

Vermeersen, B. L.; Maas, L. R.; van Oers, S.; Rabitti, A.; Jara-Orue, H.

2013-12-01

One of the most peculiar features on Saturn moon Enceladus is its so-called tiger stripe pattern at the geologically active South Polar Terrain (SPT), as first observed in detail by the Cassini spacecraft early 2005. It is generally assumed that the four almost parallel surface lines that constitute this pattern are faults in the icy surface overlying a confined salty water reservoir. Indeed, later Cassini observations have shown that salty water jets originate from the tiger stripes [e.g., Hansen et al., Science, 311, 1422-1425, 2006; Postberg et al., Nature, 474, 620-622, 2011]. The periodic activity of the tiger stripe faults shows a strong correlation with tidal forcing. Jets emanating from specific fault lines seem to be triggered at those places of the faults where tidal-induced stresses are largest immediately following closest orbital approach with Saturn [e.g., Hurford et al., Nature, 447, 292-294, 2007]. Thus jet activity seems to be directly induced by tidal forcing. However, this does not explain the characteristic regular pattern of the stripes themselves. Here we explore the possibility that this pattern is formed and maintained by induced, tidally and rotationally driven, fluid motions in the ocean underneath the icy surface of the tiger-stripe region. The remarkable spatial regularity of Enceladus' SPT fault lines is reminiscent of that observed at the surface of confined density-stratified fluids by the action of induced internal gravity waves. Theoretical analysis, numerical simulations and laboratory water tank experiments all indicate that wave attractors - particular limit orbits to which waves are focused in a fluid basin - naturally emerge in gravitationally (radial salt concentration or temperature differences) or rotationally stratified confined fluids as a function of forcing periodicity and fluid basin geometry [Maas et al., Nature, 338, 557-561, 1997]. We have found that ocean dynamical wave attractors induced by tidal-effective forcing of Enceladus' SPT salty water basin can reproduce the general characteristics of the observed tiger stripe pattern and even offer the possibility of constraining the 3D-form of the salty water basin underlying Enceladus' SPT. Vertical cross section of one of the water tank experiments. The tank is uniformly stratified with salty water and harmonically shaken. Wave attractors impinge at the surface of the tank at A, B and C, which are places where an overlying plate experiences enhanced stress levels. Distances A-B and B-C are not the same due to a sloping floor of the fluid tank. The length of the tank is about 1.5 m. Numbers at the bottom indicate mm.

Patterning and manipulating microparticles into a three-dimensional matrix using standing surface acoustic waves

NASA Astrophysics Data System (ADS)

Nguyen, T. D.; Tran, V. T.; Fu, Y. Q.; Du, H.

2018-05-01

A method based on standing surface acoustic waves (SSAWs) is proposed to pattern and manipulate microparticles into a three-dimensional (3D) matrix inside a microchamber. An optical prism is used to observe the 3D alignment and patterning of the microparticles in the vertical and horizontal planes simultaneously. The acoustic radiation force effectively patterns the microparticles into lines of 3D space or crystal-lattice-like matrix patterns. A microparticle can be positioned precisely at a specified vertical location by balancing the forces of acoustic radiation, drag, buoyancy, and gravity acting on the microparticle. Experiments and finite-element numerical simulations both show that the acoustic radiation force increases gradually from the bottom of the chamber to the top, and microparticles can be moved up or down simply by adjusting the applied SSAW power. Our method has great potential for acoustofluidic applications, building the large-scale structures associated with biological objects and artificial neuron networks.

Links of the significant wave height distribution in the Mediterranean sea with the Northern Hemisphere teleconnection patterns

NASA Astrophysics Data System (ADS)

Lionello, P.; Galati, M. B.

2008-06-01

This study analyzes the link between the SWH (Significant Wave Height) distribution in the Mediterranean Sea during the second half of the 20th century and the Northern Hemisphere SLP (Sea Level Pressure) teleconnection patterns. The SWH distribution is computed using the WAM (WAve Model) forced by the surface wind fields provided by the ERA-40 reanalysis for the period 1958-2001. The time series of mid-latitude teleconnection patterns are downloaded from the NOAA web site. This study shows that several mid-latitude patterns are linked to the SWH field in the Mediterranean, especially in its western part during the cold season: East Atlantic Pattern (EA), Scandinavian Pattern (SCA), North Atlantic Oscillation (NAO), East Atlantic/West Russia Pattern (EA/WR) and East Pacific/ North Pacific Pattern (EP/NP). Though the East Atlantic pattern exerts the largest influence, it is not sufficient to characterize the dominant variability. NAO, though relevant, has an effect smaller than EA and comparable to other patterns. Some link results from possibly spurious structures. Patterns which have a very different global structure are associated to similar spatial features of the wave variability in the Mediterranean Sea. These two problems are, admittedly, shortcomings of this analysis, which shows the complexity of the response of the Mediterranean SWH to global scale SLP teleconnection patterns.

Frequency power analyses of seismic sources on firn

NASA Astrophysics Data System (ADS)

Sanz, Christopher; Diez, Anja; Coen, Hofstede; Kristoffersen, Yngve; Mayer, Christoph; Lambrecht, Astrid; Miller, Heinz; Eisen, Olaf

2013-04-01

A great obstacle for seismic surveys on firn-covered ice masses is the ability of firn to strongly attenuate seismic energy and divert downward ray paths away from the vertical because of the velocity gradient. The standard way to overcome these limitations is the drilling of shotholes about 10-30 m deep. However, drilling of shotholes is a time and energy consuming task. Another possibility is to use vibroseismic sources at the surface and increase the signal-to-noise ratio by repeated stacking. However, compared to explosive charges, vibroseismic signals are bandlimited per se. As a third variant, we investigate the usage of ordered patterns of surface charges consisting of detonation cord. Previous applications of detonation cord only explored their general comparison to bulk explosives when deployed in a linear fashion, i.e. a single line. Our approach extends these results to other geometries, like fan- or comb-shaped patterns. These have two advantages: first, over the pattern area a locally plane wave is generated, limiting the spherical and velocity-gradient induced spreading of energy during propagation; second, the ratio between seismic wave speed of the firn and the detonation cord of typically about 1:5 causes the wave to propagate in an angle downward. When using large offsets like a snow streamer, it is possible to direct the refected energy towards the streamer, depending on offset range and reflector depth. We compare the different source types for several surveys conducted in Antarctica in terms of frequency spectra. Our results show that ordered patterns of detonation cord serve as suitable seismic surface charges, avoiding the need to drill shotholes. Moreover, an example of a short profile with patterned surface charges is presented. The technique can be of advantage for surveys in remote areas, which can only be accessed by aircrafts.

Data-based diffraction kernels for surface waves from convolution and correlation processes through active seismic interferometry

NASA Astrophysics Data System (ADS)

Chmiel, Malgorzata; Roux, Philippe; Herrmann, Philippe; Rondeleux, Baptiste; Wathelet, Marc

2018-05-01

We investigated the construction of diffraction kernels for surface waves using two-point convolution and/or correlation from land active seismic data recorded in the context of exploration geophysics. The high density of controlled sources and receivers, combined with the application of the reciprocity principle, allows us to retrieve two-dimensional phase-oscillation diffraction kernels (DKs) of surface waves between any two source or receiver points in the medium at each frequency (up to 15 Hz, at least). These DKs are purely data-based as no model calculations and no synthetic data are needed. They naturally emerge from the interference patterns of the recorded wavefields projected on the dense array of sources and/or receivers. The DKs are used to obtain multi-mode dispersion relations of Rayleigh waves, from which near-surface shear velocity can be extracted. Using convolution versus correlation with a grid of active sources is an important step in understanding the physics of the retrieval of surface wave Green's functions. This provides the foundation for future studies based on noise sources or active sources with a sparse spatial distribution.

Light Meets Water in Nonlocal Media: Surface Tension Analogue in Optics

NASA Astrophysics Data System (ADS)

Horikis, Theodoros P.; Frantzeskakis, Dimitrios J.

2017-06-01

Shallow water wave phenomena find their analogue in optics through a nonlocal nonlinear Schrödinger (NLS) model in 2 +1 dimensions. We identify an analogue of surface tension in optics, namely, a single parameter depending on the degree of nonlocality, which changes the sign of dispersion, much like surface tension does in the shallow water wave problem. Using multiscale expansions, we reduce the NLS model to a Kadomtsev-Petviashvili (KP) equation, which is of the KPII (KPI) type, for strong (weak) nonlocality. We demonstrate the emergence of robust optical antidark solitons forming Y -, X -, and H -shaped wave patterns, which are approximated by colliding KPII line solitons, similar to those observed in shallow waters.

Light Meets Water in Nonlocal Media: Surface Tension Analogue in Optics.

PubMed

Horikis, Theodoros P; Frantzeskakis, Dimitrios J

2017-06-16

Shallow water wave phenomena find their analogue in optics through a nonlocal nonlinear Schrödinger (NLS) model in 2+1 dimensions. We identify an analogue of surface tension in optics, namely, a single parameter depending on the degree of nonlocality, which changes the sign of dispersion, much like surface tension does in the shallow water wave problem. Using multiscale expansions, we reduce the NLS model to a Kadomtsev-Petviashvili (KP) equation, which is of the KPII (KPI) type, for strong (weak) nonlocality. We demonstrate the emergence of robust optical antidark solitons forming Y-, X-, and H-shaped wave patterns, which are approximated by colliding KPII line solitons, similar to those observed in shallow waters.

Flow profiling of a surface-acoustic-wave nanopump.

PubMed

Guttenberg, Z; Rathgeber, A; Keller, S; Rädler, J O; Wixforth, A; Kostur, M; Schindler, M; Talkner, P

2004-11-01

The flow profile in a capillary gap and the pumping efficiency of an acoustic micropump employing surface acoustic waves is investigated both experimentally and theoretically. Ultrasonic surface waves on a piezoelectric substrate strongly couple to a thin liquid layer and generate a quadrupolar streaming pattern within the fluid. We use fluorescence correlation spectroscopy and fluorescence microscopy as complementary tools to investigate the resulting flow profile. The velocity was found to depend on the applied power approximately linearly and to decrease with the inverse third power of the distance from the ultrasound generator on the chip. The found properties reveal acoustic streaming as a promising tool for the controlled agitation during microarray hybridization.

Flow profiling of a surface-acoustic-wave nanopump

NASA Astrophysics Data System (ADS)

Guttenberg, Z.; Rathgeber, A.; Keller, S.; Rädler, J. O.; Wixforth, A.; Kostur, M.; Schindler, M.; Talkner, P.

2004-11-01

The flow profile in a capillary gap and the pumping efficiency of an acoustic micropump employing surface acoustic waves is investigated both experimentally and theoretically. Ultrasonic surface waves on a piezoelectric substrate strongly couple to a thin liquid layer and generate a quadrupolar streaming pattern within the fluid. We use fluorescence correlation spectroscopy and fluorescence microscopy as complementary tools to investigate the resulting flow profile. The velocity was found to depend on the applied power approximately linearly and to decrease with the inverse third power of the distance from the ultrasound generator on the chip. The found properties reveal acoustic streaming as a promising tool for the controlled agitation during microarray hybridization.

The interannual variation in monthly temperature over Northeast China during summer

NASA Astrophysics Data System (ADS)

Chen, Wei; Lu, Riyu

2014-05-01

The interannual variations of summer surface air temperature over Northeast China (NEC) were investigated through a month-to-month analysis from May to August. The results suggested that the warmer temperature over NEC is related to a local positive 500-hPa geopotential height anomaly for all four months. However, the teleconnection patterns of atmospheric circulation anomalies associated with the monthly surface air temperature over NEC behave as a distinguished subseasonal variation, although the local positive height anomaly is common from month to month. In May and June, the teleconnection pattern is characterized by a wave train in the upper and middle troposphere from the Indian Peninsula to NEC. This wave train is stronger in June than in May, possibly due to the positive feedback between the wave train and the South Asian rainfall anomaly in June, when the South Asian summer monsoon has been established. In July and August, however, the teleconnection pattern associated with the NEC temperature anomalies is characterized by an East Asia/Pacific (EAP) or Pacific/Japan (PJ) pattern, with the existence of precipitation anomalies over the Philippine Sea and the South China Sea. This pattern is much clearer in July corresponding to the stronger convection over the Philippine Sea compared to that in August.

Sedimentation Waves on the Martian North Polar Cap: Analogy with Megadunes in Antarctica

NASA Astrophysics Data System (ADS)

Herny, C.; Masse, M.; Bourgeois, O.; Carpy, S.; Le Mouelic, S.; Appéré, T.; Smith, I. B.; Spiga, A.; Perret, L.; Rodriguez, S.; Piquet, T.; Gaudin, D.; Le Menn, E.

2014-12-01

Complex feedbacks between katabatic winds and the cryosphere may lead to the development of sedimentation waves at the surface of ice sheets. These have been first described and named megadunes in Antarctica. Here we use topographic data, optical images, spectroscopic data and radar soundings, acquired by Mars orbiters, to show that the surface of the Martian North Polar Cap displays two superimposed sets of sedimentation waves with differing wavelengths. These sedimentation waves grow and migrate upwind in response to the development of periodic accumulation/ablation patterns controlled by katabatic winds. They have similarities with Antarctic megadunes regarding their surface morphology, texture, grain size, and internal stratigraphic architecture. Based on this analogy, we are currently developing a model of ice/wind interaction at the surface of ice sheets. In Antarctica the accumulation processes on megadunes fields is generally attributed to the wind-blown snow transport while on sedimentation waves of the North Polar Cap of Mars the accumulation seems to be dominated by sublimation/condensation processes at the surface. The model is designed to explore the implication of the water vapor mass transfer and heat transfer on the development of sedimentation waves both on Mars and Earth.

The Effect of the Leeuwin Current on Offshore Surface Gravity Waves in Southwest Western Australia

NASA Astrophysics Data System (ADS)

Wandres, Moritz; Wijeratne, E. M. S.; Cosoli, Simone; Pattiaratchi, Charitha

2017-11-01

The knowledge of regional wave regimes is critical for coastal zone planning, protection, and management. In this study, the influence of the offshore current regime on surface gravity waves on the southwest Western Australian (SWWA) continental shelf was examined. This was achieved by coupling the three dimensional, free surface, terrain-following hydrodynamic Regional Ocean Modelling System (ROMS) and the third generation wave model Simulating WAves Nearshore (SWAN) using the Coupled Ocean-Atmosphere-WaveSediment Transport (COAWST) model. Different representative states of the Leeuwin Current (LC), a strong pole-ward flowing boundary current with a persistent eddy field along the SWWA shelf edge were simulated and used to investigate their influence on different large wave events. The coupled wave-current simulations were compared to wave only simulations, which represented scenarios in the absence of a background current field. Results showed that the LC and the eddy field significantly impact SWWA waves. Significant wave heights increased (decreased) when currents were opposing (aligning with) the incoming wave directions. During a fully developed LC system significant wave heights were altered by up to ±25% and wave directions by up to ±20°. The change in wave direction indicates that the LC may modify nearshore wave dynamics and consequently alter sediment patterns. Operational regional wave forecasts and hindcasts may give flawed predictions if wave-current interaction is not properly accounted for.

Picosecond ultrasonic study of surface acoustic waves on periodically patterned layered nanostructures.

PubMed

Colletta, Michael; Gachuhi, Wanjiru; Gartenstein, Samuel A; James, Molly M; Szwed, Erik A; Daly, Brian C; Cui, Weili; Antonelli, George A

2018-07-01

We have used the ultrafast pump-probe technique known as picosecond ultrasonics to generate and detect surface acoustic waves on a structure consisting of nanoscale Al lines on SiO 2 on Si. We report results from ten samples with varying pitch (1000-140 nm) and SiO 2 film thickness (112 nm or 60 nm), and compare our results to an isotropic elastic calculation and a coarse-grained molecular dynamics simulation. In all cases we are able to detect and identify a Rayleigh-like surface acoustic wave with wavelength equal to the pitch of the lines and frequency in the range of 5-24 GHz. In some samples, we are able to detect additional, higher frequency surface acoustic waves or independent modes of the Al lines with frequencies close to 50 GHz. We also describe the effects of probe beam polarization on the measurement's sensitivity to the different surface modes. Copyright © 2018 Elsevier B.V. All rights reserved.

Fourier analysis of surface plasmon waves launched from single nanohole and nanohole arrays: unraveling tip-induced effects.

PubMed

Chang, Y C; Chu, J Y; Wang, T J; Lin, M W; Yeh, J T; Wang, J K

2008-01-21

The authors report the investigation of surface plasmon waves (SPW) generated by single nanohole and nanohole arrays. Scattering-type scanning near-field microscopy is used to directly observe near-field distribution. The images after Fourier transformation display characteristic patterns that match with the derived analytic formula. The correspondence helps to identify the role of the scanning tip in generating SPW, making possible of the removal of this tip-induced effect. This study provides a means to perform in-depth investigation on surface plasmon polaritons.

Shape measurement and vibration analysis of moving speaker cone

NASA Astrophysics Data System (ADS)

Zhang, Qican; Liu, Yuankun; Lehtonen, Petri

2014-06-01

Surface three-dimensional (3-D) shape information is needed for many fast processes such as structural testing of material, standing waves on loudspeaker cone, etc. Usually measurement is done from limited number of points using electrical sensors or laser distance meters. Fourier Transform Profilometry (FTP) enables fast shape measurement of the whole surface. Method is based on angled sinusoidal fringe pattern projection and image capturing. FTP requires only one image of the deformed fringe pattern to restore the 3-D shape of the measured object, which makes real-time or dynamic data processing possible. In our experiment the method was used for loudspeaker cone distortion measurement in dynamic conditions. For sound quality issues it is important that the whole cone moves in same phase and there are no partial waves. Our imaging resolution was 1280x1024 pixels and frame rate was 200 fps. Using our setup we found unwanted spatial waves in our sample cone.

Computer program to solve two-dimensional shock-wave interference problems with an equilibrium chemically reacting air model

NASA Technical Reports Server (NTRS)

Glass, Christopher E.

1990-01-01

The computer program EASI, an acronym for Equilibrium Air Shock Interference, was developed to calculate the inviscid flowfield, the maximum surface pressure, and the maximum heat flux produced by six shock wave interference patterns on a 2-D, cylindrical configuration. Thermodynamic properties of the inviscid flowfield are determined using either an 11-specie, 7-reaction equilibrium chemically reacting air model or a calorically perfect air model. The inviscid flowfield is solved using the integral form of the conservation equations. Surface heating calculations at the impingement point for the equilibrium chemically reacting air model use variable transport properties and specific heat. However, for the calorically perfect air model, heating rate calculations use a constant Prandtl number. Sample calculations of the six shock wave interference patterns, a listing of the computer program, and flowcharts of the programming logic are included.

Computer program to solve two-dimensional shock-wave interference problems with an equilibrium chemically reacting air model

NASA Astrophysics Data System (ADS)

Glass, Christopher E.

1990-08-01

The computer program EASI, an acronym for Equilibrium Air Shock Interference, was developed to calculate the inviscid flowfield, the maximum surface pressure, and the maximum heat flux produced by six shock wave interference patterns on a 2-D, cylindrical configuration. Thermodynamic properties of the inviscid flowfield are determined using either an 11-specie, 7-reaction equilibrium chemically reacting air model or a calorically perfect air model. The inviscid flowfield is solved using the integral form of the conservation equations. Surface heating calculations at the impingement point for the equilibrium chemically reacting air model use variable transport properties and specific heat. However, for the calorically perfect air model, heating rate calculations use a constant Prandtl number. Sample calculations of the six shock wave interference patterns, a listing of the computer program, and flowcharts of the programming logic are included.

Internal and surface waves in vibrofluidized granular materials: Role of cohesion

NASA Astrophysics Data System (ADS)

Huang, Kai

2018-05-01

Wave phenomena in vibrofluidized dry and partially wet granular materials confined in a quasi-two-dimensional geometry are investigated with numerical simulations considering individual particles as hard spheres. Short-ranged cohesive interactions arising from the formation of liquid bridges between adjacent particles are modeled by changing the velocity-dependent coefficient of restitution. Such a change effectively suppresses the formation of surface waves, in agreement with previous experimental observations. The difference in pattern creation arises from the suppressed momentum transfer due to wetting and it can be quantitatively understood from an analysis of binary impacts.

Impedance of strip-traveling waves on an elastic half space - Asymptotic solution

NASA Technical Reports Server (NTRS)

Crandall, S. H.; Nigam, A. K.

1973-01-01

The dynamic normal-load distribution across a strip that is required to maintain a plane progressive wave along its length is studied for the case where the strip is of infinite length and lies on the surface of a homogeneous isotropic elastic half space. This configuration is proposed as a preliminary idealized model for analyzing the dynamic interaction between soils and flexible foundations. The surface load distribution across the strip and the motion of the strip are related by a pair of dual integral equations. An asymptotic solution is obtained for the limiting case of small wavelength. The nature of this solution depends importantly on the propagation velocity of the strip-traveling wave in comparison with the Rayleigh wave speed, the shear wave speed and the dilatational wave speed. When the strip-traveling wave propagates faster than the Rayleigh wave speed, a pattern of trailing Rayleigh waves is shed from the strip. The limiting amplitude of the trailing waves is provided by the asymptotic solution.

Chladni Patterns on Drumheads: A "Physics of Music" Experiment

ERIC Educational Resources Information Center

Worland, Randy

2011-01-01

In our "Physics of Music" class for non-science majors, we have developed a laboratory exercise in which students experiment with Chladni sand patterns on drumheads. Chladni patterns provide a kinesthetic, visual, and entertaining way to illustrate standing waves on flat surfaces and are very helpful when making the transition from one-dimensional…

ASTER Waves

NASA Image and Video Library

2000-10-06

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

Spatial structures arising along a surface wave produced plasma column: an experimental study

NASA Astrophysics Data System (ADS)

Atanassov, V.; Mateev, E.

2007-04-01

The formation of spatial structures in high-frequency and microwave discharges has been known for several decades. Nevertheless it still raises increased interest, probably due to the variety of the observed phenomena and the lack of adequate and systematic theoretical interpretation. In this paper we present preliminary results on observation of spatial structures appearing along a surface wave sustained plasma column. The experiments have been performed in noble gases (xenon and neon) at low to intermediate pressure and the surface wave has been launched by a surfatron. Under these conditions we have observed and documented: i) appearance of stationary plasma rings; ii) formation of standing-wave striationlike patterns; iii) contraction of the plasma column; iv) plasma column transition into moving plasma balls and filaments. Some of the existing theoretical considerations of these phenomena are reviewed and discussed.

Lunar ionosphere exploration method using auroral kilometric radiation

NASA Astrophysics Data System (ADS)

Goto, Yoshitaka; Fujimoto, Takamasa; Kasahara, Yoshiya; Kumamoto, Atsushi; Ono, Takayuki

2011-01-01

The evidence of a lunar ionosphere provided by radio occultation experiments performed by the Soviet spacecraft Luna 19 and 22 has been controversial for the past three decades because the observed large density is difficult to explain theoretically without magnetic shielding from the solar wind. The KAGUYA mission provided an opportunity to investigate the lunar ionosphere with another method. The natural plasma wave receiver (NPW) and waveform capture (WFC) instruments, which are subsystems of the lunar radar sounder (LRS) on board the lunar orbiter KAGUYA, frequently observe auroral kilometric radiation (AKR) propagating from the Earth. The dynamic spectra of the AKR sometimes exhibit a clear interference pattern that is caused by phase differences between direct waves and waves reflected on a lunar surface or a lunar ionosphere if it exists. It was hypothesized that the electron density profiles above the lunar surface could be evaluated by comparing the observed interference pattern with the theoretical interference patterns constructed from the profiles with ray tracing. This method provides a new approach to examining the lunar ionosphere that does not involve the conventional radio occultation technique.

An Analysis of Characteristics of Magnetostatic Waves Propagating in Nonhomogeneous Fields Across the Ferrospinel Film Thickness

NASA Astrophysics Data System (ADS)

Velikanova, Yu. V.; Vinogradova, M. R.; Mitlina, L. A.

2018-06-01

The amplitude-frequency characteristics (AFCs) of magnetostatic waves in the films of magnesium-manganese ferrospinels with nanostructured inhomogeneities are discussed. A common effect, observed in the film AFCs under different process conditions, is the `oscillations of propagation' of magnetostatic waves as a function of the frequency. The oscillation pattern is thought to depend on the inhomogeneous exchange parameters and the surface anisotropy constants. The wave instability is characterized by the resonant interaction of the dipole magnetostatic waves with the surface spin waves. It is shown that the ferrospinel films with periodic nanostructured inhomogeneities of 30-40 nm could be treated as magnon crystals. An inclusion of the inhomogeneity into consideration allows one to provide reasoning for the formation of the rejection bands within the range 9-12 GHz, whose frequencies correspond to Bragg frequencies.

Multi-year predictability in a coupled general circulation model

NASA Astrophysics Data System (ADS)

Power, Scott; Colman, Rob

2006-02-01

Multi-year to decadal variability in a 100-year integration of a BMRC coupled atmosphere-ocean general circulation model (CGCM) is examined. The fractional contribution made by the decadal component generally increases with depth and latitude away from surface waters in the equatorial Indo-Pacific Ocean. The relative importance of decadal variability is enhanced in off-equatorial “ wings” in the subtropical eastern Pacific. The model and observations exhibit “ENSO-like” decadal patterns. Analytic results are derived, which show that the patterns can, in theory, occur in the absence of any predictability beyond ENSO time-scales. In practice, however, modification to this stochastic view is needed to account for robust differences between ENSO-like decadal patterns and their interannual counterparts. An analysis of variability in the CGCM, a wind-forced shallow water model, and a simple mixed layer model together with existing and new theoretical results are used to improve upon this stochastic paradigm and to provide a new theory for the origin of decadal ENSO-like patterns like the Interdecadal Pacific Oscillation and Pacific Decadal Oscillation. In this theory, ENSO-driven wind-stress variability forces internal equatorially-trapped Kelvin waves that propagate towards the eastern boundary. Kelvin waves can excite reflected internal westward propagating equatorially-trapped Rossby waves (RWs) and coastally-trapped waves (CTWs). CTWs have no impact on the off-equatorial sub-surface ocean outside the coastal wave guide, whereas the RWs do. If the frequency of the incident wave is too high, then only CTWs are excited. At lower frequencies, both CTWs and RWs can be excited. The lower the frequency, the greater the fraction of energy transmitted to RWs. This lowers the characteristic frequency (reddens the spectrum) of variability off the equator relative to its equatorial counterpart. At low frequencies, dissipation acts as an additional low pass filter that becomes more effective, as latitude increases. At the same time, ENSO-driven off-equatorial surface heating anomalies drive mixed layer temperature responses in both hemispheres. Both the eastern boundary interactions and the accumulation of surface heat fluxes by the surface mixed layer act to low pass filter the ENSO-forcing. The resulting off-equatorial variability is therefore more coherent with low pass filtered (decadal) ENSO indices [e.g. NINO3 sea-surface temperature (SST)] than with unfiltered ENSO indices. Consequently large correlations between variability and NINO3 extend further poleward on decadal time-scales than they do on interannual time-scales. This explains why decadal ENSO-like patterns have a broader meridional structure than their interannual counterparts. This difference in appearance can occur even if ENSO indices do not have any predictability beyond interannual time-scales. The wings around 15-20°S, and sub-surface variability at many other locations are predictable on interannual and multi-year time-scales. This includes westward propagating internal RWs within about 25° of the equator. The slowest of these take up to 4 years to reach the western boundary. This sub-surface predictability has significant oceanographic interest. However, it is linked to only low levels of SST variability. Consequently, extrapolation of delayed action oscillator theory to decadal time-scales might not be justified.

Laser speckle visibility acoustic spectroscopy in soft turbid media

NASA Astrophysics Data System (ADS)

Wintzenrieth, Frédéric; Cohen-Addad, Sylvie; Le Merrer, Marie; Höhler, Reinhard

2014-03-01

We image the evolution in space and time of an acoustic wave propagating along the surface of turbid soft matter by shining coherent light on the sample. The wave locally modulates the speckle interference pattern of the backscattered light and the speckle visibility[2] is recorded using a camera. We show both experimentally and theoretically how the temporal and spatial correlations in this pattern can be analyzed to obtain the acoustic wavelength and attenuation length. The technique is validated using shear waves propagating in aqueous foam.[3] It may be applied to other kinds of acoustic wave in different forms of turbid soft matter, such as biological tissues, pastes or concentrated emulsions. Now at Université Lyon 1 (ILM).

Site response, shallow shear-wave velocity, and wave propagation at the San Jose, California, dense seismic array

USGS Publications Warehouse

Hartzell, S.; Carver, D.; Williams, R.A.; Harmsen, S.; Zerva, A.

2003-01-01

Ground-motion records from a 52-element dense seismic array near San Jose, California, are analyzed to obtain site response, shallow shear-wave velocity, and plane-wave propagation characteristics. The array, located on the eastern side of the Santa Clara Valley south of the San Francisco Bay, is sited over the Evergreen basin, a 7-km-deep depression with Miocene and younger deposits. Site response values below 4 Hz are up to a factor of 2 greater when larger, regional records are included in the analysis, due to strong surface-wave development within the Santa Clara Valley. The pattern of site amplification is the same, however, with local or regional events. Site amplification increases away from the eastern edge of the Santa Clara Valley, reaching a maximum over the western edge of the Evergreen basin, where the pre-Cenozoic basement shallows rapidly. Amplification then decreases further to the west. This pattern may be caused by lower shallow shear-wave velocities and thicker Quaternary deposits further from the edge of the Santa Clara Valley and generation/trapping of surface waves above the shallowing basement of the western Evergreen basin. Shear-wave velocities from the inversion of site response spectra based on smaller, local earthquakes compare well with those obtained independently from our seismic reflection/refraction measurements. Velocities from the inversion of site spectra that include larger, regional records do not compare well with these measurements. A mix of local and regional events, however, is appropriate for determination of site response to be used in seismic hazard evaluation, since large damaging events would excite both body and surface waves with a wide range in ray parameters. Frequency-wavenumber, plane-wave analysis is used to determine the backazimuth and apparent velocity of coherent phases at the array. Conventional, high-resolution, and multiple signal characterization f-k power spectra and stacked slowness power spectra are compared. These spectra show surface waves generated/ scattered at the edges of the Santa Clara Valley and possibly within the valley at the western edge of the Evergreen basin.

Interannual tropical Pacific sea surface temperature anomalies teleconnection to Northern Hemisphere atmosphere in November

NASA Astrophysics Data System (ADS)

King, Martin P.; Herceg-Bulić, Ivana; Kucharski, Fred; Keenlyside, Noel

2018-03-01

We investigate the Northern Hemisphere atmospheric circulation anomalies associated to the sea surface temperature (SST) anomalies that are related to the eastern-Pacific and central-Pacific El Nino-Southern Oscillations in the late autumn (November). This research is motivated by the need for improving understanding of the autumn climate conditions which can impact on winter climate, as well as the relative lack of study on the boreal autumn climate processes compared to winter. Using reanalysis and SST datasets available from the late nineteenth century through the recent years, we found that there are two major atmospheric responses; one is a hemispheric-wide wave number-4 pattern, another has a more annular pattern. Both of these project on the East Atlantic pattern (southward-shifted North Atlantic Oscillation) in the Atlantic sector. Which of the patterns is active is suggested to depend on the background mean flow, with the annular anomaly active in the most recent decades, while the wave-4 pattern in the decades before. This switch is associated with a change of correlation sign in the North Pacific. We discuss the robustness of this finding. The ability of two atmospheric general circulation models (ICTP-AGCM and ECHAM-AGCM) to reproduce the teleconnections is also examined. Evidence provided shows that the wave-4 pattern and the East Atlantic pattern signals can be reproduced by the models, while the shift from this to an annular response for the recent years is not found conclusively.

Folded Coplanar Waveguide Slot Antenna on Silicon Substrates With a Polyimide Interface Layer

NASA Technical Reports Server (NTRS)

Bacon, Andrew; Ponchak, George E.; Papapolymerou, John; Bushyager, Nathan; Tentzeris, Manos; Williams, W. D. (Technical Monitor)

2002-01-01

A novel mm-wave Coplanar Waveguide (CPW) folded slot antenna is characterized on low-resistivity Si substrate (1 omega-cm) and a high resistivity Si substrate with a polyimide interface layer for the first time. The antenna resonates around 30 GHz with a return loss greater than 14.6 dB. Measured radiation patterns indicate the existence of a main lobe, but the radiation pattern is affected by a strong surface wave mode, which is greater in the high resistivity Si wafer.

Process For Patterning Dispenser-Cathode Surfaces

NASA Technical Reports Server (NTRS)

Garner, Charles E.; Deininger, William D.

1989-01-01

Several microfabrication techniques combined into process cutting slots 100 micrometer long and 1 to 5 micrometer wide into tungsten dispenser cathodes for traveling-wave tubes. Patterned photoresist serves as mask for etching underlying aluminum. Chemically-assisted ion-beam etching with chlorine removes exposed parts of aluminum layer. Etching with fluorine or chlorine trifluoride removes tungsten not masked by aluminum layer. Slots enable more-uniform low-work function coating dispensed to electron-emitting surface. Emission of electrons therefore becomes more uniform over cathode surface.

The variability of temperature and precipitation over Korean Peninsula induced by off-equatorial western Pacific precipitation during boreal summer

NASA Astrophysics Data System (ADS)

Jeong, Yerim; Ham, Yoo-Geun

2016-04-01

The convection activity and variability are active in Tropic-subtropic area because of equatorial warm pool. The variability's impacts on not only subtropic also mid-latitude. The impact effects on through teleconnection between equatorial and mid-latitude like Pacific-Japan(PJ) pattern. In this paper, two groups are divided based on PJ pattern and JJA Korean precipitation for the analysis that Korean precipitation is affected by PJ pattern. 'PJ+NegKorpr' is indicated when PJ pattern occur that JJA(Jun-July_August) Korean precipitation has negative value. In this case, positive precipitation in subtropic is expanded to central Pacific. And the positive precipitation's pattern is increasing toward north. Because, the subtropical south-eastly wind is forming subtropical precipitation's pattern through cold Kelvin wave is expanding eastward. Cold Kelvin wave is because of Indian negative SST. Also, Korea has negative moisture advection and north-eastly is the role that is moving high-latitude's cold and dry air to Korea. So strong high pressure is formed in Korea. The strong high pressure involves that short wave energy is increasing on surface. As a result, The surface temperature is increased on Korea. But the other case, that 'PJ_Only' case, is indicated when PJ pattern occur and JJA Korean precipitation doesn't have negative value over significant level. The subtropic precipitation's pattern in 'PJ_Only' shows precipitation is confined in western Pacific and expended northward to 25°N near 130°E. And tail of precipitation is toward equatorial(south-eastward). Also, Korean a little positive moisture advection and south-westly is the role that is moving low-latitude's warm and wet air to Korea. So weak high pressure is formed in Korea. The weak high pressure influence amount of short wave energy, so Korean surface temperature is lower. In addition, the case of 'PJ_Only' and Pacific Decal Oscillation(PDO) are occur at the same time has negative impact in Korea temperature through subtropical cyclone and positive PDO. The positive PDO is the role that negative temperature in Korea. So, Korean temperature confined lower by subtropical cyclone and positive PDO. In summary, the relation between PJ pattern and JJA Korean temperature and precipitation depends on subtropical precipitation's pattern. And The subtropical precipitation is effected by Indian SST and PDO's teleconnection.

Insights into the diurnal cycle of global Earth outgoing radiation using a numerical weather prediction model

NASA Astrophysics Data System (ADS)

Gristey, Jake J.; Chiu, J. Christine; Gurney, Robert J.; Morcrette, Cyril J.; Hill, Peter G.; Russell, Jacqueline E.; Brindley, Helen E.

2018-04-01

A globally complete, high temporal resolution and multiple-variable approach is employed to analyse the diurnal cycle of Earth's outgoing energy flows. This is made possible via the use of Met Office model output for September 2010 that is assessed alongside regional satellite observations throughout. Principal component analysis applied to the long-wave component of modelled outgoing radiation reveals dominant diurnal patterns related to land surface heating and convective cloud development, respectively explaining 68.5 and 16.0 % of the variance at the global scale. The total variance explained by these first two patterns is markedly less than previous regional estimates from observations, and this analysis suggests that around half of the difference relates to the lack of global coverage in the observations. The first pattern is strongly and simultaneously coupled to the land surface temperature diurnal variations. The second pattern is strongly coupled to the cloud water content and height diurnal variations, but lags the cloud variations by several hours. We suggest that the mechanism controlling the delay is a moistening of the upper troposphere due to the evaporation of anvil cloud. The short-wave component of modelled outgoing radiation, analysed in terms of albedo, exhibits a very dominant pattern explaining 88.4 % of the variance that is related to the angle of incoming solar radiation, and a second pattern explaining 6.7 % of the variance that is related to compensating effects from convective cloud development and marine stratocumulus cloud dissipation. Similar patterns are found in regional satellite observations, but with slightly different timings due to known model biases. The first pattern is controlled by changes in surface and cloud albedo, and Rayleigh and aerosol scattering. The second pattern is strongly coupled to the diurnal variations in both cloud water content and height in convective regions but only cloud water content in marine stratocumulus regions, with substantially shorter lag times compared with the long-wave counterpart. This indicates that the short-wave radiation response to diurnal cloud development and dissipation is more rapid, which is found to be robust in the regional satellite observations. These global, diurnal radiation patterns and their coupling with other geophysical variables demonstrate the process-level understanding that can be gained using this approach and highlight a need for global, diurnal observing systems for Earth outgoing radiation in the future.

Measurement of hurricane winds and waves with a synthetic aperture radar

NASA Technical Reports Server (NTRS)

Shemdin, O. H.; King, D. B.

1979-01-01

An analysis of data collected in a hurricane research program is presented. The data were collected with a Synthetic Aperture Radar (SAR) during five aircraft flights in the Atlantic in August and September, 1976. Work was conducted in two areas. The first is an analysis of the L-band SAR data in a scatterometer mode to determine the surface windspeeds in hurricanes, in a similar manner to that done by an X-band scatterometer. The second area was to use the SAR to examine the wave patterns in hurricanes. The wave patterns in all of the storms are similar and show a marked radial asymmetry.

Long-Term Stability of Polymer-Coated Surface Transverse Wave Sensors for the Detection of Organic Solvent Vapors.

PubMed

Stahl, Ullrich; Voigt, Achim; Dirschka, Marian; Barié, Nicole; Richter, Christiane; Waldbaur, Ansgar; Gruhl, Friederike J; Rapp, Bastian E; Rapp, Michael; Länge, Kerstin

2017-11-03

Arrays with polymer-coated acoustic sensors, such as surface acoustic wave (SAW) and surface transverse wave (STW) sensors, have successfully been applied for a variety of gas sensing applications. However, the stability of the sensors' polymer coatings over a longer period of use has hardly been investigated. We used an array of eight STW resonator sensors coated with different polymers. This sensor array was used at semi-annual intervals for a three-year period to detect organic solvent vapors of three different chemical classes: a halogenated hydrocarbon (chloroform), an aliphatic hydrocarbon (octane), and an aromatic hydrocarbon (xylene). The sensor signals were evaluated with regard to absolute signal shifts and normalized signal shifts leading to signal patterns characteristic of the respective solvent vapors. No significant time-related changes of sensor signals or signal patterns were observed, i.e., the polymer coatings kept their performance during the course of the study. Therefore, the polymer-coated STW sensors proved to be robust devices which can be used for detecting organic solvent vapors both qualitatively and quantitatively for several years.

Precise Manipulation and Patterning of Protein Crystals for Macromolecular Crystallography Using Surface Acoustic Waves.

PubMed

Guo, Feng; Zhou, Weijie; Li, Peng; Mao, Zhangming; Yennawar, Neela H; French, Jarrod B; Huang, Tony Jun

2015-06-01

Advances in modern X-ray sources and detector technology have made it possible for crystallographers to collect usable data on crystals of only a few micrometers or less in size. Despite these developments, sample handling techniques have significantly lagged behind and often prevent the full realization of current beamline capabilities. In order to address this shortcoming, a surface acoustic wave-based method for manipulating and patterning crystals is developed. This method, which does not damage the fragile protein crystals, can precisely manipulate and pattern micrometer and submicrometer-sized crystals for data collection and screening. The technique is robust, inexpensive, and easy to implement. This method not only promises to significantly increase efficiency and throughput of both conventional and serial crystallography experiments, but will also make it possible to collect data on samples that were previously intractable. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nonlinear periodic wavetrains in thin liquid films falling on a uniformly heated horizontal plate

NASA Astrophysics Data System (ADS)

Issokolo, Remi J. Noumana; Dikandé, Alain M.

2018-05-01

A thin liquid film falling on a uniformly heated horizontal plate spreads into fingering ripples that can display a complex dynamics ranging from continuous waves, nonlinear spatially localized periodic wave patterns (i.e., rivulet structures) to modulated nonlinear wavetrain structures. Some of these structures have been observed experimentally; however, conditions under which they form are still not well understood. In this work, we examine profiles of nonlinear wave patterns formed by a thin liquid film falling on a uniformly heated horizontal plate. For this purpose, the Benney model is considered assuming a uniform temperature distribution along the film propagation on the horizontal surface. It is shown that for strong surface tension but a relatively small Biot number, spatially localized periodic-wave structures can be analytically obtained by solving the governing equation under appropriate conditions. In the regime of weak nonlinearity, a multiple-scale expansion combined with the reductive perturbation method leads to a complex Ginzburg-Landau equation: the solutions of which are modulated periodic pulse trains which amplitude and width and period are expressed in terms of characteristic parameters of the model.

Visualizing light with electrons

NASA Astrophysics Data System (ADS)

Fitzgerald, J. P. S.; Word, R. C.; Koenenkamp, R.

2014-03-01

In multiphoton photoemission electron microscopy (nP-PEEM) electrons are emitted from surfaces at a rate proportional to the surface electromagnetic field amplitude. We use 2P-PEEM to give nanometer scale visualizations of light of diffracted and waveguide fields around various microstructures. We use Fourier analysis to determine the phase and amplitude of surface fields in relation to incident light from the interference patterns. To provide quick and intuitive simulations of surface fields, we employ two dimensional Fresnel-Kirchhoff integration, a technique based on freely propagating waves and Huygens' principle. We find generally good agreement between simulations and experiment. Additionally diffracted wave simulations exhibit greater phase accuracy, indicating that these waves are well represented by a two dimensional approximation. The authors gratefully acknowledge funding of this research by the US-DOE Basic Science Office under Contract DE-FG02-10ER46406.

A finite element model of a MEMS-based surface acoustic wave hydrogen sensor.

PubMed

El Gowini, Mohamed M; Moussa, Walied A

2010-01-01

Hydrogen plays a significant role in various industrial applications, but careful handling and continuous monitoring are crucial since it is explosive when mixed with air. Surface Acoustic Wave (SAW) sensors provide desirable characteristics for hydrogen detection due to their small size, low fabrication cost, ease of integration and high sensitivity. In this paper a finite element model of a Surface Acoustic Wave sensor is developed using ANSYS12© and tested for hydrogen detection. The sensor consists of a YZ-lithium niobate substrate with interdigital electrodes (IDT) patterned on the surface. A thin palladium (Pd) film is added on the surface of the sensor due to its high affinity for hydrogen. With increased hydrogen absorption the palladium hydride structure undergoes a phase change due to the formation of the β-phase, which deteriorates the crystal structure. Therefore with increasing hydrogen concentration the stiffness and the density are significantly reduced. The values of the modulus of elasticity and the density at different hydrogen concentrations in palladium are utilized in the finite element model to determine the corresponding SAW sensor response. Results indicate that with increasing the hydrogen concentration the wave velocity decreases and the attenuation of the wave is reduced.

An experimental study of the Rayleigh-Taylor instability critical wave length

NASA Astrophysics Data System (ADS)

Kong, Xujing; Wang, Youchun; Zhang, Shufei; Xu, Hongkun

1992-06-01

A physical model has been constructed to represent the condensate film pattern on a horizontal downward-facing surface with fins, which is based on visual observation in experiment. The results of analysis using this model confirms the validity of the critical wave length formula obtained from Rayleigh-Taylor stability analysis. This formula may be used as a criterion to design horizontal downward-facing surfaces with fins that can best destabilize the condensate film, thus enhancing condensation heat transfer.

Free-surface tracking of submerged features to infer hydrodynamic flow characteristics

NASA Astrophysics Data System (ADS)

Mandel, Tracy; Rosenzweig, Itay; Koseff, Jeffrey

2016-11-01

As sea level rise and stronger storm events threaten our coastlines, increased attention has been focused on coastal vegetation as a potentially resilient, financially viable tool to mitigate flooding and erosion. However, the actual effect of this "green infrastructure" on near-shore wave fields and flow patterns is not fully understood. For example, how do wave setup, wave nonlinearity, and canopy-generated instabilities change due to complex bottom roughness? Answering this question requires detailed knowledge of the free surface. We develop easy-to-use laboratory techniques to remotely measure physical processes by imaging the apparent distortion of the fixed features of a submerged cylinder array. Measurements of surface turbulence from a canopy-generated Kelvin-Helmholtz instability are possible with a single camera. A stereoscopic approach similar to Morris (2004) and Gomit et al. (2013) allows for measurement of waveform evolution and the effect of vegetation on wave steepness and nonlinearity.

Simulation of pattern and defect detection in periodic amplitude and phase structures using photorefractive four-wave mixing

NASA Astrophysics Data System (ADS)

Nehmetallah, Georges; Banerjee, Partha; Khoury, Jed

2015-03-01

The nonlinearity inherent in four-wave mixing in photorefractive (PR) materials is used for adaptive filtering. Examples include script enhancement on a periodic pattern, scratch and defect cluster enhancement, periodic pattern dislocation enhancement, etc. through intensity filtering image manipulation. Organic PR materials have large space-bandwidth product, which makes them useful in adaptive filtering techniques in quality control systems. For instance, in the case of edge enhancement, phase conjugation via four-wave mixing suppresses the low spatial frequencies of the Fourier spectrum of an aperiodic image and consequently leads to image edge enhancement. In this work, we model, numerically verify, and simulate the performance of a four wave mixing setup used for edge, defect and pattern detection in periodic amplitude and phase structures. The results show that this technique successfully detects the slightest defects clearly even with no enhancement. This technique should facilitate improvements in applications such as image display sharpness utilizing edge enhancement, production line defect inspection of fabrics, textiles, e-beam lithography masks, surface inspection, and materials characterization.

Measurements of radiated elastic wave energy from dynamic tensile cracks

NASA Technical Reports Server (NTRS)

Boler, Frances M.

1990-01-01

The role of fracture-velocity, microstructure, and fracture-energy barriers in elastic wave radiation during a dynamic fracture was investigated in experiments in which dynamic tensile cracks of two fracture cofigurations of double cantilever beam geometry were propagating in glass samples. The first, referred to as primary fracture, consisted of fractures of intact glass specimens; the second configuration, referred to as secondary fracture, consisted of a refracture of primary fracture specimens which were rebonded with an intermittent pattern of adhesive to produce variations in fracture surface energy along the crack path. For primary fracture cases, measurable elastic waves were generated in 31 percent of the 16 fracture events observed; the condition for radiation of measurable waves appears to be a local abrupt change in the fracture path direction, such as occurs when the fracture intersects a surface flaw. For secondary fractures, 100 percent of events showed measurable elastic waves; in these fractures, the ratio of radiated elastic wave energy in the measured component to fracture surface energy was 10 times greater than for primary fracture.

Trench formation in <110> silicon for millimeter-wave switching device

NASA Astrophysics Data System (ADS)

Datta, P.; Kumar, Praveen; Nag, Manoj; Bhattacharya, D. K.; Khosla, Y. P.; Dahiya, K. K.; Singh, D. V.; Venkateswaran, R.; Kumar, Devender; Kesavan, R.

1999-11-01

Anisotropic etching using alkaline solution has been adopted to form trenches in silicon while fabricating surface oriented bulk window SPST switches. An array pattern has been etched on silicon with good control on depth of trenches. KOH-water solution is seen to yield a poor surface finish. Use of too much of additive like isopropyl alcohol improves the surface condition but distorts the array pattern due to loss of anisotropy. However, controlled use of this additive during the last phase of trench etching is found to produce trenched arrays with desired depth, improved surface finish and minimum distortion of lateral dimensions.

Serial number coding and decoding by laser interference direct patterning on the original product surface for anti-counterfeiting.

PubMed

Park, In-Yong; Ahn, Sanghoon; Kim, Youngduk; Bae, Han-Sung; Kang, Hee-Shin; Yoo, Jason; Noh, Jiwhan

2017-06-26

Here, we investigate a method to distinguish the counterfeits by patterning multiple reflective type grating directly on the surface of the original product and analyze the serial number from its rotation angles of diffracted fringes. The micro-sized gratings were fabricated on the surface of the material at high speeds by illuminating the interference fringe generated by passing a high-energy pulse laser through the Fresnel biprism. In addition, analysis of the grating's diffraction fringes was performed using a continuous wave laser.

Deep Roots of Cratons From Surface-wave Tomography

NASA Astrophysics Data System (ADS)

Cara, M.; Debayle, E.; Lévêque, J. J.

Thanks to the application of multimode waveform inversion techniques to various sets of surface wave seismograms recorded on global networks of broad-band seismome- ters, either permanent (IRIS, Geoscope) or temporary (PASSCAL, INSU), unprece- dented lateral- and depth-resolution can be achieved in upper-mantle surface-wave tomography. With a depth-resolution around 50 km and a lateral resolution around 250 km in the upper mantle, Sv velocity models beneath Australia, South-America, Eurasia and East-Africa show fast velocity anomalies associated with shield generally confined to the uppermost 200 km of the mantle. We show on cross-sections taken across different continents that there is no evidence so far for "thermal and/or com- positional" lithospheric roots extending deeper than 300 km in the continental regions we have investigated. In addition, surface wave azimuthal anisotropy can be used as an indicator of the me- chanical thickness of the lithosphere when a clear change in the pattern of anisotropic directions is observed with depth. The fast moving Australian plate shows the clear- est example of such a change occuring at relatively shallow depths (150 km) within the high seismic velocity lid. This suggests that seismic anisotropy defines a "me- chanical" lithosphere that does not coincide with the "thermal and/or compositional" lithosphere probably imaged by velocity anomalies. However, beneath other slowly moving plates, such a change in pattern is less clear and there is a tendency of seismic anisotropy to disappear at the bottom of the lid.

DNA concentration modulation on supported lipid bilayers switched by surface acoustic waves.

PubMed

Hennig, Martin; Wolff, Manuel; Neumann, Jürgen; Wixforth, Achim; Schneider, Matthias F; Rädler, Joachim O

2011-12-20

Spatially addressable arrays of molecules embedded in or anchored to supported lipid bilayers are important for on-chip screening and binding assays; however, methods to sort or accumulate components in a fluid membrane on demand are still limited. Here we apply in-plane surface acoustic shear waves (SAWs) to laterally accumulate double-stranded DNA segments electrostatically bound to a cationic supported lipid bilayer. The fluorescently labeled DNA segments are found to segregate into stripe patterns with a spatial frequency corresponding to the periodicity of the standing SAW wave (~10 μm). The DNA molecules are accumulated 10-fold in the regions of SAW antinodes. The superposition of two orthogonal sets of SAW sources creates checkerboard like arrays of DNA demonstrating the potential to generate arrayed fields dynamically. The pattern relaxation time of 0.58 s, which is independent of the segment length, indicates a sorting and relaxation mechanism dominated by lipid diffusion rather than DNA self-diffusion. © 2011 American Chemical Society

Improved acoustic levitation apparatus

NASA Technical Reports Server (NTRS)

Berge, L. H.; Johnson, J. L.; Oran, W. A.; Reiss, D. A.

1980-01-01

Concave driver and reflector enhance and shape levitation forces in acoustic resonance system. Single-mode standing-wave pattern is focused by ring element situated between driver and reflector. Concave surfaces increase levitating forces up to factor of 6 as opposed to conventional flat surfaces, making it possible to suspend heavier objects.

Slot-grating flat lens for telecom wavelengths.

PubMed

Pugh, Jonathan R; Stokes, Jamie L; Lopez-Garcia, Martin; Gan, Choon-How; Nash, Geoff R; Rarity, John G; Cryan, Martin J

2014-07-01

We present a stand-alone beam-focusing flat lens for use in the telecommunications wavelength range. Light incident on the back surface of the lens propagates through a subwavelength aperture and is heavily diffracted on exit and partially couples into a surface plasmon polariton and a surface wave propagating along the surface of the lens. Interference between the diffracted wave and re-emission from a grating patterned on the surface produces a highly collimated beam. We show for the first time a geometry at which a lens of this type can be used at telecommunication wavelengths (λ=1.55 μm) and identify the light coupling and re-emission mechanisms involved. Measured beam profile results at varying incident wavelengths show excellent agreement with Lumerical FDTD simulation results.

Stickney-forming impact on PHOBOS - Crater shape and induced stress distribution

NASA Astrophysics Data System (ADS)

Fujiwara, A.

1991-02-01

The results of the present simplified modeling of the size and rim shape of the Phobos crater Stickney, together with the impact-generated stress patterns on the surface of the crater, account for the general features observed and suggest, on the basis of some of the P-waves' surface stress pattern, that a region of higher tensile stress may have occurred in the vicinity of 0 deg latitude and 270 deg W. The correlation of this pattern with the focusing of groove patterns that occurs on the trailing side of Phobos is suggested to demonstrate a connection between these grooves and the Stickney crater-forming impact.

Scalable patterning using laser-induced shock waves

NASA Astrophysics Data System (ADS)

Ilhom, Saidjafarzoda; Kholikov, Khomidkhodza; Li, Peizhen; Ottman, Claire; Sanford, Dylan; Thomas, Zachary; San, Omer; Karaca, Haluk E.; Er, Ali O.

2018-04-01

An advanced direct imprinting method with low cost, quick, and minimal environmental impact to create a thermally controllable surface pattern using the laser pulses is reported. Patterned microindents were generated on Ni50Ti50 shape memory alloys and aluminum using an Nd: YAG laser operating at 1064 nm combined with a suitable transparent overlay, a sacrificial layer of graphite, and copper grid. Laser pulses at different energy densities, which generate pressure pulses up to a few GPa on the surface, were focused through the confinement medium, ablating the copper grid to create plasma and transferring the grid pattern onto the surface. Scanning electron microscope and optical microscope images show that various patterns were obtained on the surface with high fidelity. One-dimensional profile analysis indicates that the depth of the patterned sample initially increases with the laser energy and later levels off. Our simulations of laser irradiation process also confirm that high temperature and high pressure could be generated when the laser energy density of 2 J/cm2 is used.

Nonlinear hydrodynamic stability and transition; Proceedings of the IUTAM Symposium, Nice, France, Sept. 3-7, 1990

NASA Astrophysics Data System (ADS)

Theoretical and experimental research on nonlinear hydrodynamic stability and transition is presented. Bifurcations, amplitude equations, pattern in experiments, and shear flows are considered. Particular attention is given to bifurcations of plane viscous fluid flow and transition to turbulence, chaotic traveling wave covection, chaotic behavior of parametrically excited surface waves in square geometry, amplitude analysis of the Swift-Hohenberg equation, traveling wave convection in finite containers, focus instability in axisymmetric Rayleigh-Benard convection, scaling and pattern formation in flowing sand, dynamical behavior of instabilities in spherical gap flows, and nonlinear short-wavelength Taylor vortices. Also discussed are stability of a flow past a two-dimensional grid, inertia wave breakdown in a precessing fluid, flow-induced instabilities in directional solidification, structure and dynamical properties of convection in binary fluid mixtures, and instability competition for convecting superfluid mixtures.

High quality factor surface Fabry-Perot cavity of acoustic waves

NASA Astrophysics Data System (ADS)

Xu, Yuntao; Fu, Wei; Zou, Chang-ling; Shen, Zhen; Tang, Hong X.

2018-02-01

Surface acoustic wave (SAW) resonators are critical components in wireless communications and many sensing applications. They have also recently emerged as a subject of study in quantum acoustics at the single phonon level. Acoustic loss reduction and mode confinement are key performance factors in SAW resonators. Here, we report the design and experimental realization of high quality factor Fabry-Perot SAW resonators formed in between the tapered phononic crystal mirrors patterned on a GaN-on-sapphire material platform. The fabricated SAW resonators are characterized by both an electrical network analyzer and an optical heterodyne vibrometer. We observed standing Rayleigh waves inside the cavity, with an intrinsic quality factor exceeding 1.3 × 104 at ambient conditions.

Observations and interpretation of fundamental mode Rayleigh wavefields recorded by the Transportable Array (USArray)

USGS Publications Warehouse

Pollitz, F.F.

2008-01-01

Broadband recordings of the dense Transportable Array (TA) in the western United States provide unparalleled detailed images of long-period seismic surface wavefields. With 400 stations spanning most of the western United States, wavefronts of fundamental mode Rayleigh waves may be visualized coherently across the array at periods ???40 s. In order to constrain the Rayleigh wave phase velocity structure in the western United States, I assemble a data set of vertical component seismograms from 53 teleseismic events recorded by the TA from April 2006 to October 2007. Complex amplitude spectra from these recordings at peni ods 27-100 s are interpreted using the multiplane wave tomographic method of Friederich and Wielandt (1995) and Pollitz (1999). This analysis yields detailed surface wave phase velocity and three-dimensional shear wave velocity patterns across the North American plate boundary zone, elucidating the active processes in the highly heterogeneous western U.S. upper mantle.

Detailed Anatomical and Electrophysiological Models of Human Atria and Torso for the Simulation of Atrial Activation

PubMed Central

Ferrer, Ana; Sebastián, Rafael; Sánchez-Quintana, Damián; Rodríguez, José F.; Godoy, Eduardo J.; Martínez, Laura; Saiz, Javier

2015-01-01

Atrial arrhythmias, and specifically atrial fibrillation (AF), induce rapid and irregular activation patterns that appear on the torso surface as abnormal P-waves in electrocardiograms and body surface potential maps (BSPM). In recent years both P-waves and the BSPM have been used to identify the mechanisms underlying AF, such as localizing ectopic foci or high-frequency rotors. However, the relationship between the activation of the different areas of the atria and the characteristics of the BSPM and P-wave signals are still far from being completely understood. In this work we developed a multi-scale framework, which combines a highly-detailed 3D atrial model and a torso model to study the relationship between atrial activation and surface signals in sinus rhythm. Using this multi scale model, it was revealed that the best places for recording P-waves are the frontal upper right and the frontal and rear left quadrants of the torso. Our results also suggest that only nine regions (of the twenty-one structures in which the atrial surface was divided) make a significant contribution to the BSPM and determine the main P-wave characteristics. PMID:26523732

Time-resolved coherent X-ray diffraction imaging of surface acoustic waves

PubMed Central

Nicolas, Jan-David; Reusch, Tobias; Osterhoff, Markus; Sprung, Michael; Schülein, Florian J. R.; Krenner, Hubert J.; Wixforth, Achim; Salditt, Tim

2014-01-01

Time-resolved coherent X-ray diffraction experiments of standing surface acoustic waves, illuminated under grazing incidence by a nanofocused synchrotron beam, are reported. The data have been recorded in stroboscopic mode at controlled and varied phase between the acoustic frequency generator and the synchrotron bunch train. At each time delay (phase angle), the coherent far-field diffraction pattern in the small-angle regime is inverted by an iterative algorithm to yield the local instantaneous surface height profile along the optical axis. The results show that periodic nanoscale dynamics can be imaged at high temporal resolution in the range of 50 ps (pulse length). PMID:25294979

Time-resolved coherent X-ray diffraction imaging of surface acoustic waves.

PubMed

Nicolas, Jan-David; Reusch, Tobias; Osterhoff, Markus; Sprung, Michael; Schülein, Florian J R; Krenner, Hubert J; Wixforth, Achim; Salditt, Tim

2014-10-01

Time-resolved coherent X-ray diffraction experiments of standing surface acoustic waves, illuminated under grazing incidence by a nanofocused synchrotron beam, are reported. The data have been recorded in stroboscopic mode at controlled and varied phase between the acoustic frequency generator and the synchrotron bunch train. At each time delay (phase angle), the coherent far-field diffraction pattern in the small-angle regime is inverted by an iterative algorithm to yield the local instantaneous surface height profile along the optical axis. The results show that periodic nanoscale dynamics can be imaged at high temporal resolution in the range of 50 ps (pulse length).

Reduction and coding of synthetic aperture radar data with Fourier transforms

NASA Technical Reports Server (NTRS)

Tilley, David G.

1995-01-01

Recently, aboard the Space Radar Laboratory (SRL), the two roles of Fourier Transforms for ocean image synthesis and surface wave analysis have been implemented with a dedicated radar processor to significantly reduce Synthetic Aperture Radar (SAR) ocean data before transmission to the ground. The object was to archive the SAR image spectrum, rather than the SAR image itself, to reduce data volume and capture the essential descriptors of the surface wave field. SAR signal data are usually sampled and coded in the time domain for transmission to the ground where Fourier Transforms are applied both to individual radar pulses and to long sequences of radar pulses to form two-dimensional images. High resolution images of the ocean often contain no striking features and subtle image modulations by wind generated surface waves are only apparent when large ocean regions are studied, with Fourier transforms, to reveal periodic patterns created by wind stress over the surface wave field. Major ocean currents and atmospheric instability in coastal environments are apparent as large scale modulations of SAR imagery. This paper explores the possibility of computing complex Fourier spectrum codes representing SAR images, transmitting the coded spectra to Earth for data archives and creating scenes of surface wave signatures and air-sea interactions via inverse Fourier transformations with ground station processors.

Laser shock wave assisted patterning on NiTi shape memory alloy surfaces

NASA Astrophysics Data System (ADS)

Seyitliyev, Dovletgeldi; Li, Peizhen; Kholikov, Khomidkhodza; Grant, Byron; Karaca, Haluk E.; Er, Ali O.

2017-02-01

An advanced direct imprinting method with low cost, quick, and less environmental impact to create thermally controllable surface pattern using the laser pulses is reported. Patterned micro indents were generated on Ni50Ti50 shape memory alloys (SMA) using an Nd:YAG laser operating at 1064 nm combined with suitable transparent overlay, a sacrificial layer of graphite, and copper grid. Laser pulses at different energy densities which generates pressure pulses up to 10 GPa on the surface was focused through the confinement medium, ablating the copper grid to create plasma and transferring the grid pattern onto the NiTi surface. Scanning electron microscope (SEM) and optical microscope images of square pattern with different sizes were studied. One dimensional profile analysis shows that the depth of the patterned sample initially increase linearly with the laser energy until 125 mJ/pulse where the plasma further absorbs and reflects the laser beam. In addition, light the microscope image show that the surface of NiTi alloy was damaged due to the high power laser energy which removes the graphite layer.

Free Motion Scanning System

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

Sword, Charles K.

The present invention relates to an ultrasonic scanner and method for the imaging of a part surface, the scanner comprising: a probe assembly spaced apart from the surface including at least two tracking signals for emitting electromagnetic radiation and a transmitter for emitting ultrasonic waves onto a surface in order to induce at least a portion of said waves to be reflected from the surface, at least one detector for receiving the electromagnetic radiation wherein the detector is positioned to receive said radiation from the tracking signals, an analyzing means for recognizing a three-dimensional location of the tracking signals basedmore » on said emitted electromagnetic radiation, a differential conversion means for generating an output signal representative of the waveform of the reflected waves, and a means for relating said tracking signal location with the output signal and projecting an image of the resulting data. The scanner and method are particularly useful to acquire ultrasonic inspection data by scanning the probe-over a complex part surface in an arbitrary scanning pattern.« less

Interference patterns of a horizontal electric dipole over layered dielectric media.

NASA Technical Reports Server (NTRS)

Tsang, L.; Kong, J. A.; Simmons, G.

1973-01-01

Interference patterns for electromagnetic fields due to a subsurface reflector below a layered lossy dielectric are calculated with the geometrical optics approximation for use in interpreting data to be collected on the moon by Apollo 17 as well as data currently being obtained on terrestrial glaciers. The radiating antenna lies on the surface. All six field components are calculated and studied. For the endfire solutions, the peak of the first reflected wave is found to be different from that of the broadside ones. To facilitate a physical discussion, we plotted the radiation patterns due to the antenna on the surface.

Triboelectrification-Enabled Self-Powered Data Storage.

PubMed

Kuang, Shuang Yang; Zhu, Guang; Wang, Zhong Lin

2018-02-01

Data storage by any means usually requires an electric driving power for writing or reading. A novel approach for self-powered, triboelectrification-enabled data storage (TEDS) is presented. Data are incorporated into a set of metal-based surface patterns. As a probe slides across the patterned surface, triboelectrification between the scanning probe and the patterns produces alternatively varying voltage signal in quasi-square wave. The trough and crest of the quasi-square wave signal are coded as binary bits of "0" and "1," respectively, while the time span of the trough and the crest is associated with the number of bits. The storage of letters and sentences is demonstrated through either square-shaped or disc-shaped surface patterns. Based on experimental data and numerical calculation, the theoretically predicted maximum data storage density could reach as high as 38.2 Gbit in -2 . Demonstration of real-time data retrieval is realized with the assistance of software interface. For the TEDS reported in this work, the measured voltage signal is self-generated as a result of triboelectrification without the reliance on an external power source. This feature brings about not only low power consumption but also a much more simplified structure. Therefore, this work paves a new path to a unique approach of high-density data storage that may have widespread applications.

Formation and characterization of perpendicular mode Si ripples by glancing angle O{sub 2}{sup +} sputtering at room temperature

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

Mollick, S. A.; Ghose, D.

Off-normal low energy ion beam sputtering of solid surfaces often leads to morphological instabilities resulting in the spontaneous formation of ripple structures in nanometer length scales. In the case of Si surfaces at ambient temperature, ripple formation is found to take place normally at lower incident angles with the wave vector parallel to the ion beam direction. The absence of ripple pattern on Si surface at larger angles is due to the dominance of ion beam polishing effect. We have shown that a gentle chemical roughening of the starting surface morphology can initiate ripple pattern under grazing incidence ion beammore » sputtering (theta>64 deg. with respect to the surface normal), where the ripple wave vector is perpendicular to the ion beam direction. The characteristics of the perpendicular mode ripples are studied as a function of pristine surface roughness (2-30 nm) and projectile fluence (5x10{sup 16}-1.5x10{sup 18} O atoms cm{sup -2}). The quality of the morphological structure is assessed from the analysis of ion induced topological defects.« less

The oceanic boundary layer driven by wave breaking with stochastic variability. Part 1. Direct numerical simulations

NASA Astrophysics Data System (ADS)

Sullivan, Peter P.; McWilliams, James C.; Melville, W. Kendall

2004-05-01

We devise a stochastic model for the effects of breaking waves and fit its distribution functions to laboratory and field data. This is used to represent the space time structure of momentum and energy forcing of the oceanic boundary layer in turbulence-resolving simulations. The aptness of this breaker model is evaluated in a direct numerical simulation (DNS) of an otherwise quiescent fluid driven by an isolated breaking wave, and the results are in good agreement with laboratory measurements. The breaker model faithfully reproduces the bulk features of a breaking event: the mean kinetic energy decays at a rate approaching t(-1) , and a long-lived vortex (eddy) is generated close to the water surface. The long lifetime of this vortex (more than 50 wave periods) makes it effective in energizing the surface region of oceanic boundary layers. Next, a comparison of several different DNS of idealized oceanic boundary layers driven by different surface forcing (i.e. constant current (as in Couette flow), constant stress, or a mixture of constant stress plus stochastic breakers) elucidates the importance of intermittent stress transmission to the underlying currents. A small amount of active breaking, about 1.6% of the total water surface area at any instant in time, significantly alters the instantaneous flow patterns as well as the ensemble statistics. Near the water surface a vigorous downwelling upwelling pattern develops at the head and tail of each three-dimensional breaker. This enhances the vertical velocity variance and generates both negative- and positive-signed vertical momentum flux. Analysis of the mean velocity and scalar profiles shows that breaking effectively increases the surface roughness z_o by more than a factor of 30; for our simulations z_o/lambda {≈} 0.04 to 0.06, where lambda is the wavelength of the breaking wave. Compared to a flow driven by a constant current, the extra mixing from breakers increases the mean eddy viscosity by more than a factor of 10 near the water surface. Breaking waves alter the usual balance of production and dissipation in the turbulent kinetic energy (TKE) budget; turbulent and pressure transports and breaker work are important sources and sinks in the budget. We also show that turbulent boundary layers driven by constant current and constant stress (i.e. with no breaking) differ in fundamental ways. The additional freedom provided by a constant-stress boundary condition permits finite velocity variances at the water surface, so that flows driven by constant stress mimic flows with weakly and statistically homogeneous breaking waves.

Excito-oscillatory dynamics as a mechanism of ventricular fibrillation.

PubMed

Gray, Richard A; Huelsing, Delilah J

2008-04-01

The instabilities associated with reentrant spiral waves are of paramount importance to the initiation and maintenance of tachyarrhythmias, especially ventricular fibrillation (VF). In addition to tissue heterogeneities, there are only a few basic purported mechanisms of spiral wave breakup, most notably restitution. We test the hypothesis that oscillatory membrane properties act to destabilize spiral waves. We recorded transmembrane potential (V(m)) from isolated rabbit myocytes using a constant current stimulation protocol. We developed a mathematical model that included both the stable excitable equilibrium point at resting V(m) (-80 mV) and the unstable oscillatory equilibrium point at elevated V(m) (-10 mV). Spiral wave dynamics were studied in 2-dimensional grids using variants of the model. All models showed restitution and reproduced the experimental values of transmembrane resistance at rest and during the action potential plateau. Stable spiral waves were observed when the model showed only 1 equilibrium point. However, spatio-temporal complexity was observed if the model showed both excitable and oscillatory equilibrium points (i.e., excito-oscillatory models). The initial wave breaks resulted from oscillatory waves expanding in all directions; after a few beats, the patterns were characterized by a combination of unstable spiral waves and target patterns consistent with the patterns observed on the heart surface during VF. In our model, this VF-like activity only occurred when the single cell period of V(m) oscillations was within a specific range. The VF-like patterns observed in our excito-oscillatory models could not be explained by the existing proposed instability mechanisms. Our results introduce the important suggestion that membrane dynamics responsible for V(m) oscillations at elevated V(m) levels can destabilize spiral waves and thus may be a novel therapeutic target for preventing VF.

Dual band sensitivity enhancements of a VO(x) microbolometer array using a patterned gold black absorber.

PubMed

Smith, Evan M; Panjwani, Deep; Ginn, James; Warren, Andrew P; Long, Christopher; Figuieredo, Pedro; Smith, Christian; Nath, Janardan; Perlstein, Joshua; Walter, Nick; Hirschmugl, Carol; Peale, Robert E; Shelton, David

2016-03-10

Infrared-absorbing gold black has been selectively patterned onto the active surfaces of a vanadium-oxide-based infrared bolometer array. Patterning by metal lift-off relies on protection of the fragile gold black with an evaporated oxide, which preserves much of gold black's high absorptance. This patterned gold black also survives the dry-etch removal of the sacrificial polyimide used to fabricate the air-bridge bolometers. For our fabricated devices, infrared responsivity is improved 22% in the long-wave IR and 70% in the mid-wave IR by the gold black coating, with no significant change in detector noise, using a 300°C blackbody and 80 Hz chopping rate. The increase in the time constant caused by the additional mass of gold black is ∼15%.

Predictive Sea State Estimation for Automated Ride Control and Handling - PSSEARCH

NASA Technical Reports Server (NTRS)

Huntsberger, Terrance L.; Howard, Andrew B.; Aghazarian, Hrand; Rankin, Arturo L.

2012-01-01

PSSEARCH provides predictive sea state estimation, coupled with closed-loop feedback control for automated ride control. It enables a manned or unmanned watercraft to determine the 3D map and sea state conditions in its vicinity in real time. Adaptive path-planning/ replanning software and a control surface management system will then use this information to choose the best settings and heading relative to the seas for the watercraft. PSSEARCH looks ahead and anticipates potential impact of waves on the boat and is used in a tight control loop to adjust trim tabs, course, and throttle settings. The software uses sensory inputs including IMU (Inertial Measurement Unit), stereo, radar, etc. to determine the sea state and wave conditions (wave height, frequency, wave direction) in the vicinity of a rapidly moving boat. This information can then be used to plot a safe path through the oncoming waves. The main issues in determining a safe path for sea surface navigation are: (1) deriving a 3D map of the surrounding environment, (2) extracting hazards and sea state surface state from the imaging sensors/map, and (3) planning a path and control surface settings that avoid the hazards, accomplish the mission navigation goals, and mitigate crew injuries from excessive heave, pitch, and roll accelerations while taking into account the dynamics of the sea surface state. The first part is solved using a wide baseline stereo system, where 3D structure is determined from two calibrated pairs of visual imagers. Once the 3D map is derived, anything above the sea surface is classified as a potential hazard and a surface analysis gives a static snapshot of the waves. Dynamics of the wave features are obtained from a frequency analysis of motion vectors derived from the orientation of the waves during a sequence of inputs. Fusion of the dynamic wave patterns with the 3D maps and the IMU outputs is used for efficient safe path planning.

Impact of northern Eurasian snow cover in autumn on the warm Arctic-cold Eurasia pattern during the following January and its linkage to stationary planetary waves

NASA Astrophysics Data System (ADS)

Xu, Xinping; He, Shengping; Li, Fei; Wang, Huijun

2018-03-01

The connection between Eurasian snow cover (SC) in autumn and Eurasian winter mean surface air temperature (SAT) has been identified by many studies. However, some recent observations indicate that early and late winter climate sometimes shows an out-of-phase relationship, suggesting that the winter mean situation might obscure the important relationships that are relevant for scientific research and applications. This study investigates the relationship between October northern Eurasian SC (NESC; 58°-68°N, 30°-90°E) and Eurasian SAT during the winter months and finds a significant relationship only exists in January. Generally, following reduced October NESC, the East Asian trough and Ural high are intensified in January, and anomalous northeasterly winds prevail in mid-latitudes, causing cold anomalies over Eurasia. Meanwhile, anomalous southwesterly winds along the northern fringe of the Ural high favor warm anomalies in the Arctic. The dynamical mechanism for the connection between NESC in October and the warm Arctic-cold Eurasia (WACE) anomaly in January is further investigated from the perspective of quasi-stationary planetary wave activity. It is found that planetary waves with zonal wavenumber-1 (ZWN1) play a dominant role in this process. Specifically, the ZWN1 pattern of planetary-scale waves concurrent with October NESC anomaly extends from the surface to the upper-stratosphere. It persists in the stratosphere through November-December and propagates downward to the surface by the following January, making the connection between October NESC and January climate possible. Additionally, the influence of October NESC on the January WACE pattern has intensified since the early-2000s.

Tidal-Induced Internal Ocean Waves as an Explanation for Enceladus' Tiger Stripe Pattern and Hotspot Activity

NASA Astrophysics Data System (ADS)

Vermeersen, B. L. A.; Maas, L. R.; van Oers, S.; Rabitti, A.; Jara-Orue, H.

2014-12-01

One of the most peculiar features on Saturn moon Enceladus is its so-called tiger stripe pattern at the geologically active South Polar Terrain (SPT), as first observed in detail by the Cassini spacecraft early 2005. It is generally assumed that the four almost parallel surface lines that constitute this pattern are faults in the icy surface overlying a confined salty water reservoir. Indeed, later Cassini observations have shown that salty water jets originate from the tiger stripes [e.g., Hansen et al., Science, 311, 1422-1425, 2006; Postberg et al., Nature, 474, 620-622, 2011]. More recently, Porco et al. [Astron. J., 148:45, Sep. 2014] and Nimmo et al. [Astron. J., 148:46, Sep. 2014] have reported strong evidence that the geysers are not caused by frictional heating at the surface, but that geysers must originate deeper in Enceladus' interior. Tidal flexing models, like those of Hurford et al., Nature, 447, 292-294, 2007, give a good match for the brightness variations Cassini observes, but they seem to fail to reproduce the exact timing of plume brightening. Although jet activity is thus strongly connected to tidal forcing, another mechanism must be involved as well. Last year, we formulated the original idea [Vermeersen et al., AGU Fall Meeting 2013, abstract #P53B-1848] that the tiger stripe pattern is formed and maintained by induced, tidally and rotationally driven, wave-attractor motions in the ocean underneath the icy surface of the tiger-stripe region. Such wave-attractor motions are observed in water tank experiments in laboratories on Earth and in numerical experiments [Maas et al., Nature, 338, 557-561, 1997; Drijfhout and Maas, J. Phys. Oceanogr., 37, 2740-2763, 2007; Hazewinkel et al., Phys. Fluids, 22, 107102, 2010]. The latest observations by Porco et al. and Nimmo et al. seem to be in agreement with this tidal-induced wave attractor phenomenon, both with respect to tiger stripe pattern and with respect to timing of hotspot activity. However, in contrast to the thin ocean/thick ice sheet model as anticipated in Fig. 12 of Porco et al. (2014), our lab experiments suggest that attractors are generated most efficiently at aspect ratio O(1), implying that distance between stripes might actually approximately directly represent local ocean depth in a thin ice sheet/thick ocean setting.

Low frequency events on Montserrat

NASA Astrophysics Data System (ADS)

Visser, K.; Neuberg, J.

2003-04-01

Earthquake swarms observed on volcanoes consist generally of low frequency events. The low frequency content of these events indicates the presence of interface waves at the boundary of the magma filled conduit and the surrounding country rock. The observed seismic signal at the surface shows therefore a complicated interference pattern of waves originating at various parts of the magma filled conduit, interacting with the free surface and interfaces in the volcanic edifice. This research investigates the applicability of conventional seismic tools on these low frequency events, focusing on hypocenter location analysis using arrival times and particle motion analysis for the Soufrière Hills Volcano on Montserrat. Both single low frequency events and swarms are observed on this volcano. Synthetic low frequency events are used for comparison. Results show that reliable hypocenter locations and particle motions can only be obtained if the low frequency events are single events with an identifiable P wave onset, for example the single events preceding swarms on Montserrat or the first low frequency event of a swarm. Consecutive events of the same swarm are dominated by interface waves which are converted at the top of the conduit into weak secondary P waves and surface waves. Conventional seismic tools fail to correctly analyse these events.

High-order modes of spoof surface plasmonic wave transmission on thin metal film structure.

PubMed

Liu, Xiaoyong; Feng, Yijun; Zhu, Bo; Zhao, Junming; Jiang, Tian

2013-12-16

Recently, conformal surface plasmon (CSP) structure has been successfully proposed that could support spoof surface plasmon polaritons (SPPs) on corrugated metallic strip with ultrathin thickness [Proc. Natl. Acad. Sci. U.S.A. 110, 40-45 (2013)]. Such concept provides a flexible, conformal, and ultrathin wave-guiding element, very promising for application of plasmonic devices, and circuits in the frequency ranging from microwave to mid-infrared. In this work, we investigated the dispersions and field patterns of high-order modes of spoof SPPs along CSP structure of thin metal film with corrugated edge of periodic array of grooves, and carried out direct measurement on the transmission spectrum of multi-band of surface wave propagation at microwave frequency. It is found that the mode number and mode bands are mainly determined by the depth of the grooves, providing a way to control the multi-band transmission spectrum. We have also experimentally verified the high-order mode spoof SPPs propagation on curved CSP structure with acceptable bending loss. The multi-band propagation of spoof surface wave is believed to be applicable for further design of novel planar devices such as filters, resonators, and couplers, and the concept can be extended to terahertz frequency range.

Short wind waves on the ocean: Wavenumber-frequency spectra

NASA Astrophysics Data System (ADS)

Plant, William J.

2015-03-01

Dominant surface waves on the ocean exhibit a dispersion relation that confines their energy to a curve in a wavenumber-frequency spectrum. Short wind waves on the ocean, on the other hand, are advected by these dominant waves so that they do not exhibit a well-defined dispersion relation over many realizations of the surface. Here we show that the short-wave analog to the dispersion relation is a distributed spectrum in the wavenumber-frequency plane that collapses to the standard dispersion relation in the absence of long waves. We compute probability distributions of short-wave wavenumber given a (frequency, direction) pair and of short-wave frequency given a (wavenumber, direction) pair. These two probability distributions must yield a single spectrum of surface displacements as a function of wavenumber and frequency, F(k,f). We show that the folded, azimuthally averaged version of this spectrum has a "butterfly" pattern in the wavenumber-frequency plane if significant long waves are present. Integration of this spectrum over frequency yields the well-known k-3 wavenumber spectrum. When integrated over wavenumber, the spectrum yields an f-4 form that agrees with measurement. We also show that a cut through the unfolded F(k,f) at constant k produces the well-known form of moderate-incidence-angle Doppler spectra for electromagnetic scattering from the sea. This development points out the dependence of the short-wave spectrum on the amplitude of the long waves.

Lateral engineering of surface states - towards surface-state nanoelectronics.

PubMed

García de Abajo, F J; Cordón, J; Corso, M; Schiller, F; Ortega, J E

2010-05-01

Patterned metal surfaces can host electron quantum waves that display interference phenomena over distances of a few nanometres, thus providing excellent information carriers for future atomic-scale devices. Here we demonstrate that collimation and waveguiding of surface electrons can be realized in silver-induced strain dislocation networks on Cu(111) surfaces, as a conceptual proof-of-principle of surface-state nanoelectronics (SSNE). The Ag/Cu(111) system exhibits featured surface bands with gaps at the Fermi energy, which are basic requirements for a potential SSNE material. We establish a solid analogy between the behavior of surface-state electrons and surface plasmons in patterned metal surfaces, thus facilitating the transfer of existing knowledge on plasmonic structures to the new scenario presented by engineered electronic surface-state nanostructures, with the advantage of a 1000-fold reduction in wavelength and geometrical parameters.

Observations of Quasi-Love Waves in Tibet Indicates Coherent Deformation of the Crust and Upper Mantle

NASA Astrophysics Data System (ADS)

Chen, X.; Park, J. J.

2012-12-01

The high uplift of the Tibet area is caused by the continental collision between the Indian plate and the Eurasian plate. The style of deformation along with the collision is still being debated, particularly whether the deformation is vertically coherent or not, i.e., whether the upper mantle deforms coherently with the crust. In this work, we have used quasi-Love (QL) waves to constrain the anisotropy pattern around the Tibet region. The existence of anisotropy gradients has been identified with the observations of QL waves, which is a converted Rayleigh-wave motion that follows the arrival of the Love wave. Further, the locations of the anisotropy gradients have been pinned with the delay time between the Love wave and the QL wave, which is determined from cross-correlation. Our results show that the frequency content of Tibetan QL wave is centered around 10 mHz, indicating the depth range of anisotropy should be in the asthenosphere. Most of the scatterers of QL wave that we can detect lie outside the Tibet Plateau. Their distribution correlates well with the boundary of the Persia-Tibet- Burma orogeny, which has been identified from surface geologic data. This correlation, between surface geology and upper mantle anisotropy inferred from QL observations at the orogenic boundary, suggests that the crust and upper mantle of the orogeny are deforming coherently. Other scatterers that are off the Persia-Tibet-Burma orogenic boundary mostly cluster in two locations, the Tarim Basin, and the Bangong-Nujiang Suture, where there could exist contrasting anisotropy patterns in the upper mantle. The deformation in the Tibet region is complicated, yet our research suggests a vertically coherent deformation style of the upper mantle in Tibet.

Measurement of tidal and residual currents in the Strait of Hormuz

NASA Astrophysics Data System (ADS)

Azizpour, Jafar; Siadatmousavi, Seyed Mostafa; Chegini, Vahid

2016-09-01

Quantifying the current in the Strait of Hormuz (SH) is vital for understanding the circulation in the Persian Gulf. To measure the current in the strait, four subsurface moorings were deployed at four different stations close to SH from early November 2012 to the end of January 2013. Tidal current were dominant in the SH. The tides in the SH were complex partially standing waves and the dominant pattern varied from being primarily semi-diurnal to diurnal. The phase difference between tidal constituents of current and sea level elevation time series was used as an index to show the partially progressive wave pattern inside the study area. At mooring positions 3 and 4, located to the left of SH, the phase differences were close to 160° and 100°, respectively. It indicates partially progressive waves in opposite direction at these stations. K1 and M2 were the two main constituents at all stations inside the study area. At surface, the magnitude of semi-major axis of ellipses for M2 constituent was larger than corresponding value for K1 whereas at the bottom layer, the opposite pattern was observed. The M2 rotary coefficients at mooring 1 illustrated that current vector at the bottom layer rotated in opposite direction compared to current vectors at the middle and surface layers. The rotation was counterclockwise in the bottom layer, while it was clockwise in the surface and middle layers.

Method and apparatus for atomic imaging

DOEpatents

Saldin, Dilano K.; de Andres Rodriquez, Pedro L.

1993-01-01

A method and apparatus for three dimensional imaging of the atomic environment of disordered adsorbate atoms are disclosed. The method includes detecting and measuring the intensity of a diffuse low energy electron diffraction pattern formed by directing a beam of low energy electrons against the surface of a crystal. Data corresponding to reconstructed amplitudes of a wave form is generated by operating on the intensity data. The data corresponding to the reconstructed amplitudes is capable of being displayed as a three dimensional image of an adsorbate atom. The apparatus includes a source of a beam of low energy electrons and a detector for detecting the intensity distribution of a DLEED pattern formed at the detector when the beam of low energy electrons is directed onto the surface of a crystal. A device responsive to the intensity distribution generates a signal corresponding to the distribution which represents a reconstructed amplitude of a wave form and is capable of being converted into a three dimensional image of the atomic environment of an adsorbate atom on the crystal surface.

The Network Spinal Wave as a Central Pattern Generator.

PubMed

Senzon, Simon A; Epstein, Donald M; Lemberger, Daniel

2016-07-01

This article explains the research on a unique spinal wave visibly observed in association with network spinal analysis care. Since 1997, the network wave has been studied using surface electromyography (sEMG), characterized mathematically, and determined to be a unique and repeatable phenomenon. The authors provide a narrative review of the research and a context for the network wave's development. The sEMG research demonstrates that the movement of the musculature of the spine during the wave phenomenon is electromagnetic and mechanical. The changes running along the spine were characterized mathematically at three distinct levels of care. Additionally, the wave has the mathematical properties of a central pattern generator (CPG). The network wave may be the first CPG discovered in the spine unrelated to locomotion. The mathematical characterization of the signal also demonstrates coherence at a distance between the sacral to cervical spine. According to mathematical engineers, based on studies conducted a decade apart, the wave itself is a robust phenomenon and the detection methods for this coherence may represent a new measure for central nervous system health. This phenomenon has implications for recovery from spinal cord injury and for reorganizational healing development.

The Network Spinal Wave as a Central Pattern Generator

PubMed Central

Epstein, Donald M.; Lemberger, Daniel

2016-01-01

Abstract Objectives: This article explains the research on a unique spinal wave visibly observed in association with network spinal analysis care. Since 1997, the network wave has been studied using surface electromyography (sEMG), characterized mathematically, and determined to be a unique and repeatable phenomenon. Methods: The authors provide a narrative review of the research and a context for the network wave's development. Results: The sEMG research demonstrates that the movement of the musculature of the spine during the wave phenomenon is electromagnetic and mechanical. The changes running along the spine were characterized mathematically at three distinct levels of care. Additionally, the wave has the mathematical properties of a central pattern generator (CPG). Conclusions: The network wave may be the first CPG discovered in the spine unrelated to locomotion. The mathematical characterization of the signal also demonstrates coherence at a distance between the sacral to cervical spine. According to mathematical engineers, based on studies conducted a decade apart, the wave itself is a robust phenomenon and the detection methods for this coherence may represent a new measure for central nervous system health. This phenomenon has implications for recovery from spinal cord injury and for reorganizational healing development. PMID:27243963

DIVERSITY SURFACES AND SPECIES WAVE FRONTS IN A SOIL MICROARTHROPOD ASSEMBLAGE: ADDING THE DIMENSION OF TIME

EPA Science Inventory

As a general rule, animal species of intermediate size within a given taxonomic group are most abundant in nature. It is not known if these patterns occur in small-bodied taxa, such as soil microarthropods, or how these patterns change through time. Here I show that Oribatida (Ac...

The use of remote sensing and linear wave theory to model local wave energy around Alphonse Atoll, Seychelles

NASA Astrophysics Data System (ADS)

Hamylton, S.

2011-12-01

This paper demonstrates a practical step-wise method for modelling wave energy at the landscape scale using GIS and remote sensing techniques at Alphonse Atoll, Seychelles. Inputs are a map of the benthic surface (seabed) cover, a detailed bathymetric model derived from remotely sensed Compact Airborne Spectrographic Imager (CASI) data and information on regional wave heights. Incident energy at the reef crest around the atoll perimeter is calculated as a function of its deepwater value with wave parameters (significant wave height and period) hindcast in the offshore zone using the WaveWatch III application developed by the National Oceanographic and Atmospheric Administration. Energy modifications are calculated at constant intervals as waves transform over the forereef platform along a series of reef profile transects running into the atoll centre. Factors for shoaling, refraction and frictional attenuation are calculated at each interval for given changes in bathymetry and benthic coverage type and a nominal reduction in absolute energy is incorporated at the reef crest to account for wave breaking. Overall energy estimates are derived for a period of 5 years and related to spatial patterning of reef flat surface cover (sand and seagrass patches).

Babinet's principle and the band structure of surface waves on patterned metal arrays

NASA Astrophysics Data System (ADS)

Edmunds, J. D.; Taylor, M. C.; Hibbins, A. P.; Sambles, J. R.; Youngs, I. J.

2010-05-01

The microwave response of an array of square metal patches and its complementary structure, an array of square holes, has been experimentally studied. The resonant phenomena, which yield either enhanced transmission or reflection, are attributed to the excitation of diffractively coupled surface waves. The band structure of these surface modes has been quantified for both p-(transverse magnetic) and s-(transverse electric) polarized radiation and is found to be dependent on the periodicity of the electric and magnetic fields on resonance. The results are in excellent accord with predictions from finite element method modeling and the electromagnetic form of Babinet's principle [Babinet, C. R. Acad. Sci. 4, 638 (1837)].

Fast interaction of atoms with crystal surfaces: coherent lighting

NASA Astrophysics Data System (ADS)

Gravielle, M. S.

2017-11-01

Quantum coherence of incident waves results essential for the observation of interference patterns in grazing incidence fast atom diffraction (FAD). In this work we investigate the influence of the impact energy and projectile mass on the transversal length of the surface area that is coherently illuminated by the atomic beam, after passing through a collimating aperture. Such a transversal coherence length controls the general features of the interference structures, being here derived by means of the Van Cittert-Zernike theorem. The coherence length is then used to build the initial coherent wave packet within the Surface Initial Value Representation (SIVR) approximation. The SIVR approach is applied to fast He and Ne atoms impinging grazingly on a LiF(001) surface along a low-indexed crystallographic direction. We found that with the same collimating setup, by varying the impact energy we would be able to control the interference mechanism that prevails in FAD patterns, switching between inter-cell and unit-cell interferences. These findings are relevant to use FAD spectra adequately as a surface analysis tool, as well as to choose the appropriate collimating scheme for the observation of interference effects in a given collision system.

Laboratory modeling of edge wave generation over a plane beach by breaking waves

NASA Astrophysics Data System (ADS)

Abcha, Nizar; Ezersky, Alexander; Pelinovsky, Efim

2015-04-01

Edge waves play an important role in coastal hydrodynamics: in sediment transport, in formation of coastline structure and coastal bottom topography. Investigation of physical mechanisms leading to the edge waves generation allows us to determine their effect on the characteristics of spatially periodic patterns like crescent submarine bars and cusps observed in the coastal zone. In the present paper we investigate parametric excitation of edge wave with frequency two times less than the frequency of surface wave propagating perpendicular to the beach. Such mechanism of edge wave generation has been studied previously in a large number of papers using the assumption of non-breaking waves. This assumption was used in theoretical calculations and such conditions were created in laboratory experiments. In the natural conditions, the wave breaking is typical when edge waves are generated at sea beach. We study features of such processes in laboratory experiments. Experiments were performed in the wave flume of the Laboratory of Continental and Coast Morphodynamics (M2C), Caen. The flume is equipment with a wave maker controlled by computer. To model a plane beach, a PVC plate is placed at small angle to the horizontal bottom. Several resistive probes were used to measure characteristics of waves: one of them was used to measure free surface displacement near the wave maker and two probes were glued on the inclined plate. These probes allowed us to measure run-up due to parametrically excited edge waves. Run-up height is determined by processing a movie shot by high-speed camera. Sub-harmonic generation of standing edge waves is observed for definite control parameters: edge waves represent themselves a spatial mode with wavelength equal to double width of the flume; the frequency of edge wave is equal to half of surface wave frequency. Appearance of sub-harmonic mode instability is studied using probes and movie processing. The dependence of edge wave exponential growth rate index on the amplitude of surface wave is found. On the plane of parameters (amplitude - frequency) of surface wave we have found a region corresponding parametric instability leading to excitation of edge waves. It is shown that for small super criticalities, the amplitude of edge wave grows with amplitude of surface wave. For large amplitude of surface wave, wave breaking appears and parametric instability is suppressed. Such suppression of instability is caused by increasing of turbulent viscosity in near shore zone. It was shown that parametric excitation of edge wave can increase significantly (up to two times) the maximal run-up. Theoretical model is developed to explain suppression of instability due to turbulent viscosity. This theoretical model is based on nonlinear mode amplitude equation including terms responsible for parametric forcing, frequency detuning, nonlinear detuning, linear and nonlinear edge wave damping. Dependence of coefficients on turbulent viscosity is discussed.

Unified Application of Vapor Screen Flow Visualization and Pressure Sensitive Paint Measurement Techniques to Vortex- and Shock Wave-Dominated Flow Fields

NASA Technical Reports Server (NTRS)

Erickson, Gary E.

2010-01-01

Laser vapor screen (LVS) flow visualization and pressure sensitive paint (PSP) techniques were applied in a unified approach to wind tunnel testing of slender wing and missile configurations dominated by vortex flows and shock waves at subsonic, transonic, and supersonic speeds. The off-surface cross-flow patterns using the LVS technique were combined with global PSP surface static pressure mappings to characterize the leading-edge vortices and shock waves that coexist and interact at high angles of attack. The synthesis of LVS and PSP techniques was also effective in identifying the significant effects of passive surface porosity and the presence of vertical tail surfaces on the flow topologies. An overview is given of LVS and PSP applications in selected experiments on small-scale models of generic slender wing and missile configurations in the NASA Langley Research Center (NASA LaRC) Unitary Plan Wind Tunnel (UPWT) and 8-Foot Transonic Pressure Tunnel (8-Foot TPT).

Unified Application Vapor Screen Flow Visualization and Pressure Sensitive Paint Measurement Techniques to Vortex- and Shock Wave-Dominated Flow Fields

NASA Technical Reports Server (NTRS)

Erickson, Gary E.

2008-01-01

Laser vapor screen (LVS) flow visualization and pressure sensitive paint (PSP) techniques were applied in a unified approach to wind tunnel testing of slender wing and missile configurations dominated by vortex flows and shock waves at subsonic, transonic, and supersonic speeds. The off-surface cross-flow patterns using the LVS technique were combined with global PSP surface static pressure mappings to characterize the leading-edge vortices and shock waves that coexist and interact at high angles of attack (alpha). The synthesis of LVS and PSP techniques was also effective in identifying the significant effects of passive surface porosity and the presence of vertical tail surfaces on the flow topologies. An overview is given of LVS and PSP applications in selected experiments on small-scale models of generic slender wing and missile configurations in the NASA Langley Research Center (NASA LaRC) Unitary Plan Wind Tunnel (UPWT) and 8-Foot Transonic Pressure Tunnel (8-Foot TPT).

Ultrafast Imaging of Chiral Surface Plasmon by Photoemission Electron Microscopy

NASA Astrophysics Data System (ADS)

Dai, Yanan; Dabrowski, Maciej; Petek, Hrvoje

We employ Time-Resolved Photoemission Electron Microscopy (TR-PEEM) to study surface plasmon polariton (SPP) wave packet dynamics launched by tunable (VIS-UV) femtosecond pulses of various linear and circular polarizations. The plasmonic structures are micron size single-crystalline Ag islands grown in situ on Si surfaces and characterized by Low Energy Electron Microscopy (LEEM). The local fields of plasmonic modes enhance two and three photon photoemission (2PP and 3PP) at the regions of strong field enhancement. Imaging of the photoemission signal with PEEM electron optics thus images the plasmonic fields excited in the samples. The observed PEEM images with left and right circularly polarized light show chiral images, which is a consequence of the transverse spin momentum of surface plasmon. By changing incident light polarization, the plasmon interference pattern shifts with light ellipticity indicating a polarization dependent excitation phase of SPP. In addition, interferometric-time resolved measurements record the asymmetric SPP wave packet motion in order to characterize the dynamical properties of chiral SPP wave packets.

Shock wave-free interface interaction

NASA Astrophysics Data System (ADS)

Frolov, Roman; Minev, Peter; Krechetnikov, Rouslan

2016-11-01

The problem of shock wave-free interface interaction has been widely studied in the context of compressible two-fluid flows using analytical, experimental, and numerical techniques. While various physical effects and possible interaction patterns for various geometries have been identified in the literature, the effects of viscosity and surface tension are usually neglected in such models. In our study, we apply a novel numerical algorithm for simulation of viscous compressible two-fluid flows with surface tension to investigate the influence of these effects on the shock-interface interaction. The method combines together the ideas from Finite Volume adaptation of invariant domains preserving algorithm for systems of hyperbolic conservation laws by Guermond and Popov and ADI parallel solver for viscous incompressible NSEs by Guermond and Minev. This combination has been further extended to a two-fluid flow case, including surface tension effects. Here we report on a quantitative study of how surface tension and viscosity affect the structure of the shock wave-free interface interaction region.

Role of entrapped vapor bubbles during microdroplet evaporation

NASA Astrophysics Data System (ADS)

Putnam, Shawn A.; Byrd, Larry W.; Briones, Alejandro M.; Hanchak, Michael S.; Ervin, Jamie S.; Jones, John G.

2012-08-01

On superheated surfaces, the air bubble trapped during impingement grows into a larger vapor bubble and oscillates at the frequency predicted for thermally induced capillary waves. In some cases, the entrapped vapor bubble penetrates the droplet interface, leaving a micron-sized coffee-ring pattern of pure fluid. Vapor bubble entrapment, however, does not influence the evaporation rate. This is also true on laser heated surfaces, where a laser can thermally excite capillary waves and induce bubble oscillations over a broad range of frequencies, suggesting that exciting perturbations in a pinned droplets interface is not an effective avenue for enhancing evaporative heat transfer.

Band gaps and Brekhovskikh attenuation of laser-generated surface acoustic waves in a patterned thin film structure on silicon

NASA Astrophysics Data System (ADS)

Maznev, A. A.

2008-10-01

Surface acoustic modes of a periodic array of copper and SiO2 lines on a silicon substrate are studied using a laser-induced transient grating technique. It is found that the band gap formed inside the Brillouin zone due to “avoided crossing” of Rayleigh and Sezawa modes is much greater than the band gap in the Rayleigh wave dispersion formed at the zone boundary. Another unexpected finding is that a very strong periodicity-induced attenuation is observed above the longitudinal threshold rather than above the transverse threshold.

Spatial patterns of cyanobacterial mat growth on sand ripples

NASA Astrophysics Data System (ADS)

Mariotti, G.; Klepac-Ceraj, V.; Perron, J. T.; Bosak, T.

2016-02-01

Photosynthetic microbial mats produce organic matter, cycle nutrients, bind pollutants and stabilize sediment in sandy marine environments. Here, we investigate the influence of bedforms and wave motion on the growth rate, composition and spatial variability of microbial mats by growing cyanobacterial mats on a rippled bed of carbonate sand in a wave tank. The tank was forced with an oscillatory flow with velocities below the threshold for sediment motion yet able to induce a porewater flow within the sediment. Different spatial patterns developed in mats depending on the initial biochemistry of the water medium. When growing in a medium rich in nitrogen, phosphorous and micronutrients, mats grew faster on ripple troughs than on ripple crests. After two months, mats covered the bed surface uniformly, and the microbial communities on the crests and in the troughs had similar compositions. Differences in bed shear stress and nutrient availability between crests and troughs were not able to explain the faster growth in the troughs. We hypothesize that this growth pattern is due to a "strainer" effect, i.e. the suspended bacteria from the inoculum were preferentially delivered to troughs by the wave-induced porewater flow. In the experiments initiated in a medium previously used up by a microbial mat and thus depleted in nutrients, mats grew preferentially on the ripple crests. This spatial pattern persisted for nearly two years, and the microbial composition on troughs and crests was different. We attribute this pattern to the upwelling of porewater in the crests, which increased the delivery of nutrients from sediment to the cyanobacteria on the bed surface. Thus, the macroscopic patterns formed by photosynthetic microbial mats on sand ripples may be used to infer whether mats are nutrient-limited and whether they are recently colonized or older than a month.

Doubly-excited pulse-waves on flowing liquid films: experiments and numerical simulations

NASA Astrophysics Data System (ADS)

Adebayo, Idris; Xie, Zhihua; Che, Zhizhao; Wray, Alex; Matar, Omar

2016-11-01

The interaction patterns between doubly-excited pulse waves on a flowing liquid film are studied both experimentally and numerically. The flowing film is constituted on an inclined glass substrate while pulse-waves are excited on the film surface by means of a solenoid valve connected to a relay which receives signals from customised Matlab routines. The effect of varying the system parameters i.e. film flow rate, inter-pulse interval and substrate inclination angle on the pulse interaction patterns are then studied. Results show that different interaction patterns exist for these binary pulses; which include a singular behaviour, complete merger, partial merger and total non-coalescence. A regime map of these patterns is then plotted for each inclination angles examined, based on the film Re and the inter-pulse interval. Finally, the individual effect of the system parameters on the merging distance of these binary pulses in the merger mode is then studied and the results validated using both numerical simulations and mathematical modelling. Funding from the Nigerian Government (for Idris Adebayo), and the EPSRC through a programme Grant MEMPHIS (EP/K003976/1) gratefully acknowledged.

Acousto-optical assessment of skin viscoelasticity

NASA Astrophysics Data System (ADS)

Kirkpatrick, Sean J.; Duncan, Donald D.

2003-07-01

A multiphysics approach, combining acoustics, optics, and mechanics can be used to detect regions of skin with distinct mechanical behavior that may indicate a pathology, such as a cancerous skin lesion. Herein, an acousto-optical approach to evaluating the viscoelastic behavior of superficial skin layers will be presented. The method relies upon inducing low frequency guided surface waves in the skin and detecting these waves by monitoring the shift in the backscattered laser speckle pattern created by illuminating a small region of the skin with coherent light. Artificial lesions in the form of chemical cross-linking and chemical softening were induced in superficial porcine skin layers and detected based upon variations in local mechanical behavior. The lesions affect not only the time-of-flight of the guided surface waves, but also change the relative phase of the acoustic waves as determined optically. The method may be applicable in the study and diagnosis of superficial skin lesions.

Optical assessment of tissue mechanics: acousto-optical elastography of skin

NASA Astrophysics Data System (ADS)

Kirkpatrick, Sean J.

2003-10-01

A multiphysics approach, combining acoustics, optics, and mechanics can be used to detect regions of skin with distinct mechanical behavior that may indicate a pathology, such as a cancerous skin lesion. Herein, an acousto - optical approach to evaluating the viscoelastic behavior of superficial skin layers will be presented. The method relies upon inducing low frequency guided surface waves in the skin and detecting these waves by monitoring the shift in the backscattered laser speckle pattern created by illuminating a small region of the skin with coherent light. Artificial lesions in the form of chemical cross-linking and chemical softening were induced in superficial porcine skin layers and detected based upon variations in local mechanical behavior. The lesions affect not only the time-of-flight of the guided surface waves, but also change the relative phase of the acoustic waves as determined optically. The method may be applicable in the study and diagnosis of superficial skin lesions.

Cold season Africa-Asia multidecadal teleconnection pattern and its relation to the Atlantic multidecadal variability

NASA Astrophysics Data System (ADS)

Sun, Cheng; Li, Jianping; Ding, Ruiqiang; Jin, Ze

2017-06-01

A prominent teleconnection pattern of multidecadal variability of cold season (November to April) upper-level atmospheric circulation over North Africa and Eurasia (NA-EA) is revealed by empirical orthogonal function analysis of the Twentieth Century Reanalysis data. This teleconnection pattern is characterized by an eastward propagating wave train with a zonal wavenumber of 5-6 between 20° and 40°N, extending from the northwest coast of Africa to East Asia, and thus is referred to as the Africa-Asia multidecadal teleconnection pattern (AAMT). One-point correlation maps show that the teleconnectivity of AAMT is strong and further demonstrate the existence of the AAMT. The AAMT shapes the spatial structure of multidecadal change in atmospheric circulation over the NA-EA region, and in particular the AAMT pattern and associated fields show similar structures to the change occurring around the early 1960s. A strong in-phase relationship is observed between the AAMT and Atlantic multidecadal variability (AMV) and this connection is mainly due to Rossby wave dynamics. Barotropic modeling results suggest that the upper-level Rossby wave source generated by the AMV can excite the AAMT wave train, and Rossby wave ray tracing analysis further highlights the role of the Asian jet stream in guiding the wave train to East Asia. The AAMT acts as an atmospheric bridge conveying the influence of AMV onto the downstream multidecadal climate variability. The AMV is closely related to the coordinated change in surface and tropospheric air temperatures over Northwest Africa, the Arabian Peninsula and Central China, which may result from the adiabatic expansion/compression of air associated with the AAMT.

Pressure-gradient-driven nearshore circulation on a beach influenced by a large inlet-tidal shoal system

USGS Publications Warehouse

Shi, F.; Hanes, D.M.; Kirby, J.T.; Erikson, L.; Barnard, P.; Eshleman, J.

2011-01-01

The nearshore circulation induced by a focused pattern of surface gravity waves is studied at a beach adjacent to a major inlet with a large ebb tidal shoal. Using a coupled wave and wave-averaged nearshore circulation model, it is found that the nearshore circulation is significantly affected by the heterogeneous wave patterns caused by wave refraction over the ebb tidal shoal. The model is used to predict waves and currents during field experiments conducted near the mouth of San Francisco Bay and nearby Ocean Beach. The field measurements indicate strong spatial variations in current magnitude and direction and in wave height and direction along Ocean Beach and across the ebb tidal shoal. Numerical simulations suggest that wave refraction over the ebb tidal shoal causes wave focusing toward a narrow region at Ocean Beach. Due to the resulting spatial variation in nearshore wave height, wave-induced setup exhibits a strong alongshore nonuniformity, resulting in a dramatic change in the pressure field compared to a simulation with only tidal forcing. The analysis of momentum balances inside the surf zone shows that, under wave conditions with intensive wave focusing, the alongshore pressure gradient associated with alongshore nonuniform wave setup can be a dominant force driving circulation, inducing heterogeneous alongshore currents. Pressure-gradient- forced alongshore currents can exhibit flow reversals and flow convergence or divergence, in contrast to the uniform alongshore currents typically caused by tides or homogeneous waves.

Deep-water bedforms induced by refracting Internal Solitary Waves

NASA Astrophysics Data System (ADS)

Falcini, Federico; Droghei, Riccardo; Casalbore, Daniele; Martorelli, Eleonora; Mosetti, Renzo; Sannino, Gianmaria; Santoleri, Rosalia; Latino Chiocci, Francesco

2017-04-01

Subaqueous bedforms (or sand waves) are typically observed in those environments that are exposed to strong currents, characterized by a dominant unidirectional flow. However, sand-wave fields may be also observed in marine environments where no such current exists; the physical processes driving their formation are enigmatic or not well understood. We propose that internal solitary waves (ISWs), induced by tides, can produce an effective, unidirectional boundary flow filed that forms asymmetric sand waves. We test this idea by examining a sand-wave field off the Messina Strait, where we hypothesize that ISWs formed at the interface between intermediate and surface waters are refracted by topography. Hence, we argue that the deflected pattern (i.e., the depth-dependent orientation) of the sand-wave field is due to refraction of such ISWs. Combining field observations and numerical modelling, we show that ISWs can account for three key features: ISWs produce fluid velocities capable of mobilizing bottom sediments; the predicted refraction pattern resulting from the interaction of ISWs with bottom topography matches the observed deflection of the sand waves; and predicted migration rates of sand waves match empirical estimates. This work shows how ISWs may contribute to sculpting the structure of continental margins and it represents a promising link between the geological and oceanographic communities.

Numerical studies of the KP line-solitons

NASA Astrophysics Data System (ADS)

Chakravarty, S.; McDowell, T.; Osborne, M.

2017-03-01

The Kadomtsev-Petviashvili (KP) equation admits a class of solitary wave solutions localized along distinct rays in the xy-plane, called the line-solitons, which describe the interaction of shallow water waves on a flat surface. These wave interactions have been observed on long, flat beaches, as well as have been recreated in laboratory experiments. In this paper, the line-solitons are investigated via direct numerical simulations of the KP equation, and the interactions of the evolved solitary wave patterns are studied. The objective is to obtain greater insight into solitary wave interactions in shallow water and to determine the extent the KP equation is a good model in describing these nonlinear interactions.

Dependence of Arctic climate on the latitudinal position of stationary waves and to high-latitudes surface warming

NASA Astrophysics Data System (ADS)

Shin, Yechul; Kang, Sarah M.; Watanabe, Masahiro

2017-12-01

Previous studies suggest large uncertainties in the stationary wave response under global warming. Here, we investigate how the Arctic climate responds to changes in the latitudinal position of stationary waves, and to high-latitudes surface warming that mimics the effect of Arctic sea ice loss under global warming. To generate stationary waves in an atmospheric model coupled to slab ocean, a series of experiments is performed where the thermal forcing with a zonal wavenumber-2 (with zero zonal-mean) is prescribed at the surface at different latitude bands in the Northern Hemisphere. When the stationary waves are generated in the subtropics, the cooling response dominates over the warming response in the lower troposphere due to cloud radiative effects. Then, the low-level baroclinicity is reduced in the subtropics, which gives rise to a poleward shift of the eddy driven jet, thereby inducing substantial cooling in the northern high latitudes. As the stationary waves are progressively generated at higher latitudes, the zonal-mean climate state gradually becomes more similar to the integration with no stationary waves. These differences in the mean climate affect the Arctic climate response to high-latitudes surface warming. Additional surface heating over the Arctic is imposed to the reference climates in which the stationary waves are located at different latitude bands. When the stationary waves are positioned at lower latitudes, the eddy driven jet is located at higher latitude, closer to the prescribed Arctic heating. As baroclinicity is more effectively perturbed, the jet shifts more equatorward that accompanies a larger reduction in the poleward eddy transport of heat and momentum. A stronger eddy-induced descending motion creates greater warming over the Arctic. Our study calls for a more accurate simulation of the present-day stationary wave pattern to enhance the predictability of the Arctic warming response in a changing climate.

Source characteristics of the Nicaraguan tsunami earthquake of September 2, 1992

NASA Astrophysics Data System (ADS)

Ide, Satoshi; Imamura, Fumihiko; Yoshida, Yasuhiro; Abe, Katsuyuki

1993-05-01

The source mechanisms of the Nicaraguan tsunami earthquake of September 2, 1992 is studied via waveforms of body waves and surface waves recorded on global broadband seismographs. The possibility of a single force is ruled out from radiation patterns and the amplitude ratio of Rayleigh and Love waves. The main shock is interpreted as low-angle thrust fault with strike of 302 deg, dip of 16 deg, and slip of 87 deg, the Cocos plate underthrusting beneath the Caribbean plate. The seismic moment from surface wave analysis is 3.0 x 10 exp 20 Nm. The source dimension is estimated to be 200 x 100 km from the aftershock area. The inversion results of body waves suggest bilateral rupture with rupture velocity as low as 1.5 km/s and duration time of about 100 s. The source process time is unusually long, from which it is inferred that the associated crustal deformation has a long time constant.

Stokes waves revisited: Exact solutions in the asymptotic limit

NASA Astrophysics Data System (ADS)

Davies, Megan; Chattopadhyay, Amit K.

2016-03-01

The Stokes perturbative solution of the nonlinear (boundary value dependent) surface gravity wave problem is known to provide results of reasonable accuracy to engineers in estimating the phase speed and amplitudes of such nonlinear waves. The weakling in this structure though is the presence of aperiodic "secular variation" in the solution that does not agree with the known periodic propagation of surface waves. This has historically necessitated increasingly higher-ordered (perturbative) approximations in the representation of the velocity profile. The present article ameliorates this long-standing theoretical insufficiency by invoking a compact exact n -ordered solution in the asymptotic infinite depth limit, primarily based on a representation structured around the third-ordered perturbative solution, that leads to a seamless extension to higher-order (e.g., fifth-order) forms existing in the literature. The result from this study is expected to improve phenomenological engineering estimates, now that any desired higher-ordered expansion may be compacted within the same representation, but without any aperiodicity in the spectral pattern of the wave guides.

The radiation from slots in truncated dielectric-covered surfaces

NASA Technical Reports Server (NTRS)

Hwang, Y. M.; Kouyoumjian, R. G.; Pathak, P. H.

1974-01-01

A theoretical approach based on the geometrical theory of diffraction is used to study the electromagnetic radiation from a narrow slot in a dielectric-covered perfectly-conducting surface terminated at an edge. The total far-zone field is composed of a geometrical optics field and a diffracted field. The geometrical optics field is the direct radiation from the slot to the field point. The slot also generates surface waves which are incident at the termination of the dielectric cover, where singly-diffracted rays and reflected surface waves are excited. The diffraction and reflection coefficients are obtained from the canonical problem of the diffraction of a surface wave by a right-angle wedge where the dielectric-covered surface is approximated by an impedance surface. This approximation is satisfactory for a very thin cover; however, the radiation from its vertical and faces cannot be neglected in treating the thicker dielectric cover. This is taken into account by using a Kirchhoff-type approximation, which contributes a second term to the diffraction coefficient previously obtained. The contributions from the geometrical optics field, the singly-diffracted rays and all significant multiply-diffracted rays are summed to give the total radiation. Calculated and measured patterns are found to be in good agreement.

Unifying models of dialect spread and extinction using surface tension dynamics

PubMed Central

2018-01-01

We provide a unified mathematical explanation of two classical forms of spatial linguistic spread. The wave model describes the radiation of linguistic change outwards from a central focus. Changes can also jump between population centres in a process known as hierarchical diffusion. It has recently been proposed that the spatial evolution of dialects can be understood using surface tension at linguistic boundaries. Here we show that the inclusion of long-range interactions in the surface tension model generates both wave-like spread, and hierarchical diffusion, and that it is surface tension that is the dominant effect in deciding the stable distribution of dialect patterns. We generalize the model to allow population mixing which can induce shrinkage of linguistic domains, or destroy dialect regions from within. PMID:29410847

Simulating three dimensional wave run-up over breakwaters covered by antifer units

NASA Astrophysics Data System (ADS)

Najafi-Jilani, A.; Niri, M. Zakiri; Naderi, Nader

2014-06-01

The paper presents the numerical analysis of wave run-up over rubble-mound breakwaters covered by antifer units using a technique integrating Computer-Aided Design (CAD) and Computational Fluid Dynamics (CFD) software. Direct application of Navier-Stokes equations within armour blocks, is used to provide a more reliable approach to simulate wave run-up over breakwaters. A well-tested Reynolds-averaged Navier-Stokes (RANS) Volume of Fluid (VOF) code (Flow-3D) was adopted for CFD computations. The computed results were compared with experimental data to check the validity of the model. Numerical results showed that the direct three dimensional (3D) simulation method can deliver accurate results for wave run-up over rubble mound breakwaters. The results showed that the placement pattern of antifer units had a great impact on values of wave run-up so that by changing the placement pattern from regular to double pyramid can reduce the wave run-up by approximately 30%. Analysis was done to investigate the influences of surface roughness, energy dissipation in the pores of the armour layer and reduced wave run-up due to inflow into the armour and stone layer.

Numerical investigation of the interaction between a planar shock wave with square and triangular bubbles containing different gases

NASA Astrophysics Data System (ADS)

Igra, Dan; Igra, Ozer

2018-05-01

The interaction between a planar shock wave and square and triangular bubbles containing either SF6, He, Ar, or CO2 is studied numerically. It is shown that, due to the existing large differences in the molecular weight, the specific heat ratio, and the acoustic impedance between these gases, different wave patterns and pressure distribution inside the bubbles are developed during the interaction process. In the case of heavy gases, the velocity of the shock wave propagating along the bubble inner surface is always less than that of the incident shock wave and higher than that of the transmitted shock wave. However, in the case of the light gas (He), the fastest one is the transmitted shock wave and the slowest one is the incident shock wave. The largest pressure jump is witnessed in the SF6 case, while the smallest pressure jump is seen in the helium case. There are also pronounced differences in the deformation of the investigated bubbles; while triangular bubbles filled with either Ar, CO2, or SF6 were deformed to a crescent shape, the helium bubble is deformed to a trapezoidal shape with three pairs of vortices emanating from its surface.

Prediction of the Acoustic Field Associated with Instability Wave Source Model for a Compressible Jet

NASA Technical Reports Server (NTRS)

Golubev, Vladimir; Mankbadi, Reda R.; Dahl, Milo D.; Kiraly, L. James (Technical Monitor)

2002-01-01

This paper provides preliminary results of the study of the acoustic radiation from the source model representing spatially-growing instability waves in a round jet at high speeds. The source model is briefly discussed first followed by the analysis of the produced acoustic directivity pattern. Two integral surface techniques are discussed and compared for prediction of the jet acoustic radiation field.

Erosion patterns in a sediment layer

NASA Astrophysics Data System (ADS)

Daerr, Adrian; Lee, Peter; Lanuza, José; Clément, Éric

2003-06-01

We report here on a laboratory-scale experiment which reproduces a rich variety of natural patterns with few control parameters. In particular, we focus on intriguing rhomboid structures often found on sandy shores and flats. We show that the standard views based on water surface waves do not explain the phenomenon, and we evidence a different mechanism based on mud avalanche instability.

Vacillations induced by interference of stationary and traveling planetary waves

NASA Technical Reports Server (NTRS)

Salby, Murry L.; Garcia, Rolando R.

1987-01-01

The interference pattern produced when a traveling planetary wave propagates over a stationary forced wave is explored, examining the interference signature in a variety of diagnostics. The wave field is first restricted to a diatomic spectrum consisting of two components: a single stationary wave and a single monochromatic traveling wave. A simple barotropic normal mode propagating over a simple stationary plane wave is considered, and closed form solutions are obtained. The wave fields are then restricted spatially, providing more realistic structures without sacrificing the advantages of an analytical solution. Both stationary and traveling wave fields are calculated numerically with the linearized Primitive Equations in a realistic basic state. The mean flow reaction to the fluctuating eddy forcing which results from interference is derived. Synoptic geopotential behavior corresponding to the combined wave and mean flow fields is presented, and the synoptic signature in potential vorticity on isentropic surfaces is examined.

Sound pressure distribution within natural and artificial human ear canals: forward stimulation.

PubMed

Ravicz, Michael E; Tao Cheng, Jeffrey; Rosowski, John J

2014-12-01

This work is part of a study of the interaction of sound pressure in the ear canal (EC) with tympanic membrane (TM) surface displacement. Sound pressures were measured with 0.5-2 mm spacing at three locations within the shortened natural EC or an artificial EC in human temporal bones: near the TM surface, within the tympanic ring plane, and in a plane transverse to the long axis of the EC. Sound pressure was also measured at 2-mm intervals along the long EC axis. The sound field is described well by the size and direction of planar sound pressure gradients, the location and orientation of standing-wave nodal lines, and the location of longitudinal standing waves along the EC axis. Standing-wave nodal lines perpendicular to the long EC axis are present on the TM surface >11-16 kHz in the natural or artificial EC. The range of sound pressures was larger in the tympanic ring plane than at the TM surface or in the transverse EC plane. Longitudinal standing-wave patterns were stretched. The tympanic-ring sound field is a useful approximation of the TM sound field, and the artificial EC approximates the natural EC.

Waving and skewing: how gravity and the surface of growth media affect root development in Arabidopsis.

PubMed

Oliva, Michele; Dunand, Christophe

2007-01-01

Arabidopsis seedlings growing on inclined agar surfaces exhibit characteristic root behaviours called 'waving' and 'skewing': the former consists of a series of undulations, whereas the latter is a deviation from the direction of gravity. Even though the precise basis of these growth patterns is not well understood, both gravity and the contact between the medium and the root are considered to be the major players that result in these processes. The influence of these forces on root surface-dependent behaviours can be verified by growing seedlings at different gel pitches: plants growing on vertical plates present roots with slight waving and skewing when compared with seedlings grown on plates held at minor angles of < 90 degrees . However, other factors are thought to modulate root growth on agar; for instance, it has been demonstrated that the presence and concentration of certain compounds in the medium (such as sucrose) and of drugs able to modify the plant cell cytoskeleton also affect skewing and waving. The recent discovery of an active role of ethylene on surface-dependent root behaviour, and the finding of new mutants showing anomalous growth, pave the way for a more detailed description of these phenomena.

Seismic site characterization of an urban dedimentary basin, Livermore Valley, California: Site tesponse, basin-edge-induced surface waves, and 3D simulations

USGS Publications Warehouse

Hartzell, Stephen; Leeds, Alena L.; Ramirez-Guzman, Leonardo; Allen, James P.; Schmitt, Robert G.

2016-01-01

Thirty‐two accelerometers were deployed in the Livermore Valley, California, for approximately one year to study sedimentary basin effects. Many local and near‐regional earthquakes were recorded, including the 24 August 2014 Mw 6.0 Napa, California, earthquake. The resulting ground‐motion data set is used to quantify the seismic response of the Livermore basin, a major structural depression in the California Coast Range Province bounded by active faults. Site response is calculated by two methods: the reference‐site spectral ratio method and a source‐site spectral inversion method. Longer‐period (≥1  s) amplification factors follow the same general pattern as Bouguer gravity anomaly contours. Site response spectra are inverted for shallow shear‐wave velocity profiles, which are consistent with independent information. Frequency–wavenumber analysis is used to analyze plane‐wave propagation across the Livermore Valley and to identify basin‐edge‐induced surface waves with back azimuths different from the source back azimuth. Finite‐element simulations in a 3D velocity model of the region illustrate the generation of basin‐edge‐induced surface waves and point out strips of elevated ground velocities along the margins of the basin.

Surface-wave potential for triggering tectonic (nonvolcanic) tremor

USGS Publications Warehouse

Hill, D.P.

2010-01-01

Source processes commonly posed to explain instances of remote dynamic triggering of tectonic (nonvolcanic) tremor by surface waves include frictional failure and various modes of fluid activation. The relative potential for Love- and Rayleigh-wave dynamic stresses to trigger tectonic tremor through failure on critically stressed thrust and vertical strike-slip faults under the Coulomb-Griffith failure criteria as a function of incidence angle is anticorrelated over the 15- to 30-km-depth range that hosts tectonic tremor. Love-wave potential is high for strike-parallel incidence on low-angle reverse faults and null for strike-normal incidence; the opposite holds for Rayleigh waves. Love-wave potential is high for both strike-parallel and strike-normal incidence on vertical, strike-slip faults and minimal for ~45?? incidence angles. The opposite holds for Rayleigh waves. This pattern is consistent with documented instances of tremor triggered by Love waves incident on the Cascadia mega-thrust and the San Andreas fault (SAF) in central California resulting from shear failure on weak faults (apparent friction, ????? 0.2). However, documented instances of tremor triggered by surface waves with strike-parallel incidence along the Nankai megathrust beneath Shikoku, Japan, is associated primarily with Rayleigh waves. This is consistent with the tremor bursts resulting from mixed-mode failure (crack opening and shear failure) facilitated by near-lithostatic ambient pore pressure, low differential stress, with a moderate friction coefficient (?? ~ 0.6) on the Nankai subduction interface. Rayleigh-wave dilatational stress is relatively weak at tectonic tremor source depths and seems unlikely to contribute significantly to the triggering process, except perhaps for an indirect role on the SAF in sustaining tremor into the Rayleigh-wave coda that was initially triggered by Love waves.

Surface-wave potential for triggering tectonic (nonvolcanic) tremor-corrected

USGS Publications Warehouse

Hill, David P.

2012-01-01

Source processes commonly posed to explain instances of remote dynamic triggering of tectonic (nonvolcanic) tremor by surface waves include frictional failure and various modes of fluid activation. The relative potential for Love- and Rayleigh-wave dynamic stresses to trigger tectonic tremor through failure on critically stressed thrust and vertical strike-slip faults under the Coulomb-Griffith failure criteria as a function of incidence angle are anticorrelated over the 15- to 30-km-depth range that hosts tectonic tremor. Love-wave potential is high for strike-parallel incidence on low-angle reverse faults and null for strike-normal incidence; the opposite holds for Rayleigh waves. Love-wave potential is high for both strike-parallel and strike-normal incidence on vertical, strike-slip faults and minimal for ~45° incidence angles. The opposite holds for Rayleigh waves. This pattern is consistent with documented instances of tremor triggered by Love waves incident on the Cascadia megathrust and the San Andreas fault (SAF) in central California resulting from shear failure on weak faults (apparent friction is μ* ≤ 0:2). Documented instances of tremor triggered by surface waves with strike-parallel incidence along the Nankai megathrust beneath Shikoku, Japan, however, are associated primarily with Rayleigh waves. This is consistent with the tremor bursts resulting from mixed-mode failure (crack opening and shear failure) facilitated by near-lithostatic ambient pore pressure, low differential stress, with a moderate friction coefficient (μ ~ 0:6) on the Nankai subduction interface. Rayleigh-wave dilatational stress is relatively weak at tectonic tremor source depths and seems unlikely to contribute significantly to the triggering process, except perhaps for an indirect role on the SAF in sustaining tremor into the Rayleigh-wave coda that was initially triggered by Love waves.

SEQUENCING of TSUNAMI WAVES: Why the first wave is not always the largest?

NASA Astrophysics Data System (ADS)

Synolakis, C.; Okal, E.

2016-12-01

We discuss what contributes to the `sequencing' of tsunami waves in the far field, that is, to the distribution of the maximum sea surface amplitude inside the dominant wave packet constituting the primary arrival at a distant harbour. Based on simple models of sources for which analytical solutions are available, we show that, as range is increased, the wave pattern evolves from a regime of maximum amplitude in the first oscillation to one of delayed maximum, where the largest amplitude takes place during a subsequent oscillation. In the case of the simple, instantaneous uplift of a circular disk at the surface of an ocean of constant depth, the critical distance for transition between those patterns scales as r 30 /h2 where r0 is the radius of the disk and h the depth of the ocean. This behaviour is explained from simple arguments based on a model where sequencing results from frequency dispersion in the primary wave packet, as the width of its spectrum around its dominant period T0 becomes dispersed in time in an amount comparable to T0 , the latter being controlled by a combination of source size and ocean depth. The general concepts in this model are confirmed in the case of more realistic sources for tsunami excitation by a finite-time deformation of the ocean floor, as well as in real-life simulations of tsunamis excited by large subduction events, for which we find that the influence of fault width on the distribution of sequencing is more important than that of fault length. Finally, simulation of the major events of Chile (2010) and Japan (2011) at large arrays of virtual gauges in the Pacific Basin correctly predicts the majority of the sequencing patterns observed on DART buoys during these events. By providing insight into the evolution with time of wave amplitudes inside primary wave packets for far field tsunamis generated by large earthquakes, our results stress the importance, for civil defense authorities, of issuing warning and evacuation orders of sufficient duration to avoid the hazard

Sequencing of tsunami waves: why the first wave is not always the largest

NASA Astrophysics Data System (ADS)

Okal, Emile A.; Synolakis, Costas E.

2016-02-01

This paper examines the factors contributing to the `sequencing' of tsunami waves in the far field, that is, to the distribution of the maximum sea surface amplitude inside the dominant wave packet constituting the primary arrival at a distant harbour. Based on simple models of sources for which analytical solutions are available, we show that, as range is increased, the wave pattern evolves from a regime of maximum amplitude in the first oscillation to one of delayed maximum, where the largest amplitude takes place during a subsequent oscillation. In the case of the simple, instantaneous uplift of a circular disk at the surface of an ocean of constant depth, the critical distance for transition between those patterns scales as r_0^3 / h^2 where r0 is the radius of the disk and h the depth of the ocean. This behaviour is explained from simple arguments based on a model where sequencing results from frequency dispersion in the primary wave packet, as the width of its spectrum around its dominant period T0 becomes dispersed in time in an amount comparable to T0, the latter being controlled by a combination of source size and ocean depth. The general concepts in this model are confirmed in the case of more realistic sources for tsunami excitation by a finite-time deformation of the ocean floor, as well as in real-life simulations of tsunamis excited by large subduction events, for which we find that the influence of fault width on the distribution of sequencing is more important than that of fault length. Finally, simulation of the major events of Chile (2010) and Japan (2011) at large arrays of virtual gauges in the Pacific Basin correctly predicts the majority of the sequencing patterns observed on DART buoys during these events. By providing insight into the evolution with time of wave amplitudes inside primary wave packets for far field tsunamis generated by large earthquakes, our results stress the importance, for civil defense authorities, of issuing warning and evacuation orders of sufficient duration to avoid the hazard inherent in premature calls for all-clear.

Role of surface plasmon polaritons and other waves in the radiation of resonant optical dipole antennas

PubMed Central

Jia, Hongwei; Liu, Haitao; Zhong, Ying

2015-01-01

The radiation of an electric dipole emitter can be drastically enhanced if the emitter is placed in the nano-gap of a metallic dipole antenna. By assuming that only surface plasmon polaritons (SPPs) are excited on the antenna, we build up an intuitive pure-SPP model that is able to comprehensively predict the electromagnetic features of the antenna radiation, such as the total or radiative emission rate and the far-field radiation pattern. With the model we can distinguish the respective contributions from SPPs and from other surface waves to the antenna radiation. It is found that for antennas with long arms that support higher-order resonances, SPPs provide a dominant contribution to the antenna radiation, while for other cases, the contribution of surface waves other than SPPs should be considered. The model reveals an intuitive picture that the enhancement of the antenna radiation is due to surface waves that are resonantly excited on the two antenna arms and that are further coupled into the nano-gap or scattered into free space. From the model we can derive a phase-matching condition that predicts the antenna resonance and the resultant enhanced radiation. The model is helpful for a physical understanding and intuitive design of antenna devices. PMID:25678191

Strait of Gibraltar as seen from STS-58

NASA Image and Video Library

1993-10-20

STS058-73-009 (18 Oct-1 Nov 1993) --- Atlantic water flowing with the tide through the Strait of Gibraltar into the Mediterranean generates internal waves as depicted in this photo. The incoming cool, less dense Atlantic water flows over the warm, more saline Mediterranean water. As the tide moves into the Strait of Gibraltar it encounters the Camarinal Sill, which is like a cliff under water, south of Camarinal Point, Spain. Internal waves are generated at the Sill and travel along the density boundary between the Atlantic water and the Mediterranean water. Internal waves have very little effect on the sea surface, except for gentle slopes and slight differences in roughness. We can see them in the Space Shuttle photos because of sunglint which reflects off the water. Internal waves smooth out some of the capillary waves at the surface in bands. The sun reflects more brightly from these smooth areas showing us the pattern of the underwater waves. The Bay of Cadiz on the southwest coast of Spain, the Rock of Gibraltar, and the Moroccan coast are also visible in this photo.

An effective noise-suppression technique for surface microseismic data

USGS Publications Warehouse

Forghani-Arani, Farnoush; Willis, Mark; Haines, Seth S.; Batzle, Mike; Behura, Jyoti; Davidson, Michael

2013-01-01

The presence of strong surface-wave noise in surface microseismic data may decrease the utility of these data. We implement a technique, based on the distinct characteristics that microseismic signal and noise show in the τ‐p domain, to suppress surface-wave noise in microseismic data. Because most microseismic source mechanisms are deviatoric, preprocessing is necessary to correct for the nonuniform radiation pattern prior to transforming the data to the τ‐p domain. We employ a scanning approach, similar to semblance analysis, to test all possible double-couple orientations to determine an estimated orientation that best accounts for the polarity pattern of any microseismic events. We then correct the polarity of the data traces according to this pattern, prior to conducting signal-noise separation in the τ‐p domain. We apply our noise-suppression technique to two surface passive-seismic data sets from different acquisition surveys. The first data set includes a synthetic microseismic event added to field passive noise recorded by an areal receiver array distributed over a Barnett Formation reservoir undergoing hydraulic fracturing. The second data set is field microseismic data recorded by receivers arranged in a star-shaped array, over a Bakken Shale reservoir during a hydraulic-fracturing process. Our technique significantly improves the signal-to-noise ratios of the microseismic events and preserves the waveforms at the individual traces. We illustrate that the enhancement in signal-to-noise ratio also results in improved imaging of the microseismic hypocenter.

Monitoring of surface-fatigue crack propagation in a welded steel angle structure using guided waves and principal component analysis

NASA Astrophysics Data System (ADS)

Lu, Mingyu; Qu, Yongwei; Lu, Ye; Ye, Lin; Zhou, Limin; Su, Zhongqing

2012-04-01

An experimental study is reported in this paper demonstrating monitoring of surface-fatigue crack propagation in a welded steel angle structure using Lamb waves generated by an active piezoceramic transducer (PZT) network which was freely surface-mounted for each PZT transducer to serve as either actuator or sensor. The fatigue crack was initiated and propagated in welding zone of a steel angle structure by three-point bending fatigue tests. Instead of directly comparing changes between a series of specific signal segments such as S0 and A0 wave modes scattered from fatigue crack tips, a variety of signal statistical parameters representing five different structural status obtained from marginal spectrum in Hilbert-huang transform (HHT), indicating energy progressive distribution along time period in the frequency domain including all wave modes of one wave signal were employed to classify and distinguish different structural conditions due to fatigue crack initiation and propagation with the combination of using principal component analysis (PCA). Results show that PCA based on marginal spectrum is effective and sensitive for monitoring the growth of fatigue crack although the received signals are extremely complicated due to wave scattered from weld, multi-boundaries, notch and fatigue crack. More importantly, this method indicates good potential for identification of integrity status of complicated structures which cause uncertain wave patterns and ambiguous sensor network arrangement.

Solubility Interactions and the Design of Chemically Selective Sorbent Coatings for Chemical Sensors and Arrays

DTIC Science & Technology

1990-07-27

sorptionpiezoelectric sorption 63 detector, surface acoustic wave, pattern recognition, array, 16. PRICE CODE molecular recognition , 17. SECURITY...1 PIEZOELECTRIC SORPTION DETECTORS ........................................................... 6 SOLUBILITY... SORPTION AND LINEAR SOLVATION ENERGY RELATIONSHIPS (LSER) ................................................................................... 9

The role of Internal Solitary Waves on deep-water sedimentary processes: the case of up-slope migrating sediment waves off the Messina Strait.

PubMed

Droghei, R; Falcini, F; Casalbore, D; Martorelli, E; Mosetti, R; Sannino, G; Santoleri, R; Chiocci, F L

2016-11-03

Subaqueous, asymmetric sand waves are typically observed in marine channel/canyon systems, tidal environments, and continental slopes exposed to strong currents, where they are formed by current shear resulting from a dominant unidirectional flow. However, sand-wave fields may be readily observed in marine environments where no such current exists; the physical processes driving their formation are enigmatic or not well understood. We propose that internal solitary waves (ISWs) induced by tides can produce an effective, unidirectional boundary "current" that forms asymmetric sand waves. We test this idea by examining a sand-wave field off the Messina Strait, where we hypothesize that ISWs formed at the interface between intermediate and surface waters are refracted by topography. Hence, we argue that the deflected pattern (i.e., the depth-dependent orientation) of the sand-wave field is due to refraction of such ISWs. Combining field observations and numerical modelling, we show that ISWs can account for three key features: ISWs produce fluid velocities capable of mobilizing bottom sediments; the predicted refraction pattern resulting from the interaction of ISWs with bottom topography matches the observed deflection of the sand waves; and predicted migration rates of sand waves match empirical estimates. This work shows how ISWs may contribute to sculpting the structure of continental margins and it represents a promising link between the geological and oceanographic communities.

The role of Internal Solitary Waves on deep-water sedimentary processes: the case of up-slope migrating sediment waves off the Messina Strait

NASA Astrophysics Data System (ADS)

Droghei, R.; Falcini, F.; Casalbore, D.; Martorelli, E.; Mosetti, R.; Sannino, G.; Santoleri, R.; Chiocci, F. L.

2016-11-01

Subaqueous, asymmetric sand waves are typically observed in marine channel/canyon systems, tidal environments, and continental slopes exposed to strong currents, where they are formed by current shear resulting from a dominant unidirectional flow. However, sand-wave fields may be readily observed in marine environments where no such current exists; the physical processes driving their formation are enigmatic or not well understood. We propose that internal solitary waves (ISWs) induced by tides can produce an effective, unidirectional boundary “current” that forms asymmetric sand waves. We test this idea by examining a sand-wave field off the Messina Strait, where we hypothesize that ISWs formed at the interface between intermediate and surface waters are refracted by topography. Hence, we argue that the deflected pattern (i.e., the depth-dependent orientation) of the sand-wave field is due to refraction of such ISWs. Combining field observations and numerical modelling, we show that ISWs can account for three key features: ISWs produce fluid velocities capable of mobilizing bottom sediments; the predicted refraction pattern resulting from the interaction of ISWs with bottom topography matches the observed deflection of the sand waves; and predicted migration rates of sand waves match empirical estimates. This work shows how ISWs may contribute to sculpting the structure of continental margins and it represents a promising link between the geological and oceanographic communities.

Investigation of phononic crystals for dispersive surface acoustic wave ozone sensors

NASA Astrophysics Data System (ADS)

Westafer, Ryan S.

The object of this research was to investigate dispersion in surface phononic crystals (PnCs) for application to a newly developed passive surface acoustic wave (SAW) ozone sensor. Frequency band gaps and slow sound already have been reported for PnC lattice structures. Such engineered structures are often advertised to reduce loss, increase sensitivity, and reduce device size. However, these advances have not yet been realized in the context of surface acoustic wave sensors. In early work, we computed SAW dispersion in patterned surface structures and we confirmed that our finite element computations of SAW dispersion in thin films and in one dimensional surface PnC structures agree with experimental results obtained by laser probe techniques. We analyzed the computations to guide device design in terms of sensitivity and joint spectral operating point. Next we conducted simulations and experiments to determine sensitivity and limit of detection for more conventional dispersive SAW devices and PnC sensors. Finally, we conducted extensive ozone detection trials on passive reflection mode SAW devices, using distinct components of the time dispersed response to compensate for the effect of temperature. The experimental work revealed that the devices may be used for dosimetry applications over periods of several days.

Northern Hemisphere Winter Climate Response to Greenhouse Gas, Ozone, Solar and Volcanic Forcing

NASA Technical Reports Server (NTRS)

Shindell, Drew T.; Schmidt, Gavin A.; Miller, Ron L.; Rind, David; Hansen, James E. (Technical Monitor)

2001-01-01

The Goddard Institute for Space Studies (GISS) climate/middle atmosphere model has been used to study the impacts of increasing greenhouse gases, polar ozone depletion, volcanic eruptions, and solar cycle variability. We focus on the projection of the induced responses onto Northern Hemisphere winter surface climate. Changes in the model's surface climate take place largely through enhancement of existing variability patterns, with greenhouse gases, polar ozone depletion and volcanic eruptions primarily affecting the Arctic Oscillation (AO) pattern. Perturbations descend from the stratosphere to the surface in the model by altering the propagation of planetary waves coming up from the surface, in accord with observational evidence. Models lacking realistic stratospheric dynamics fail to capture these wave flux changes. The results support the conclusion that the stratosphere plays a crucial role in recent AO trends. We show that in our climate model, while ozone depletion has a significant effect, greenhouse gas forcing is the only one capable of causing the large, sustained increase in the AO observed over recent decades. This suggests that the AO trend, and a concurrent strengthening of the stratospheric vortex over the Arctic, are very likely anthropogenic in origin.

Rogue waves and large deviations in deep sea.

PubMed

Dematteis, Giovanni; Grafke, Tobias; Vanden-Eijnden, Eric

2018-01-30

The appearance of rogue waves in deep sea is investigated by using the modified nonlinear Schrödinger (MNLS) equation in one spatial dimension with random initial conditions that are assumed to be normally distributed, with a spectrum approximating realistic conditions of a unidirectional sea state. It is shown that one can use the incomplete information contained in this spectrum as prior and supplement this information with the MNLS dynamics to reliably estimate the probability distribution of the sea surface elevation far in the tail at later times. Our results indicate that rogue waves occur when the system hits unlikely pockets of wave configurations that trigger large disturbances of the surface height. The rogue wave precursors in these pockets are wave patterns of regular height, but with a very specific shape that is identified explicitly, thereby allowing for early detection. The method proposed here combines Monte Carlo sampling with tools from large deviations theory that reduce the calculation of the most likely rogue wave precursors to an optimization problem that can be solved efficiently. This approach is transferable to other problems in which the system's governing equations contain random initial conditions and/or parameters.

Ginzburg-Landau equation as a heuristic model for generating rogue waves

NASA Astrophysics Data System (ADS)

Lechuga, Antonio

2016-04-01

Envelope equations have many applications in the study of physical systems. Particularly interesting is the case 0f surface water waves. In steady conditions, laboratory experiments are carried out for multiple purposes either for researches or for practical problems. In both cases envelope equations are useful for understanding qualitative and quantitative results. The Ginzburg-Landau equation provides an excellent model for systems of that kind with remarkable patterns. Taking into account the above paragraph the main aim of our work is to generate waves in a water tank with almost a symmetric spectrum according to Akhmediev (2011) and thus, to produce a succession of rogue waves. The envelope of these waves gives us some patterns whose model is a type of Ginzburg-Landau equation, Danilov et al (1988). From a heuristic point of view the link between the experiment and the model is achieved. Further, the next step consists of changing generating parameters on the water tank and also the coefficients of the Ginzburg-Landau equation, Lechuga (2013) in order to reach a sufficient good approach.

Wave Pattern Peculiarities of Different Types of Explosions Conducted at Semipalatinsk Test Site

NASA Astrophysics Data System (ADS)

Sokolova, Inna

2014-05-01

The historical seismograms of the explosions conducted at the STS in 1949 - 1989 are of great interest for the researchers in the field of monitoring. Large number of air (86), surface (30) and underground nuclear explosions were conducted here in boreholes and tunnels (340). In addition to nuclear explosions, large chemical explosions were conducted at the Test Site. It is known that tectonic earthquakes occur on the Test Site territory and near it. Since 2005 the Institute of Geophysical Researches conducts works on digitizing the historical seismograms of nuclear explosions. Currently, the database contains more than 6000 digitized seismograms of nuclear explosions used for investigative monitoring tasks, major part of them (4000) are events from the STS region. Dynamic parameters of records of air, surface and underground nuclear explosions, as well as large chemical explosions with compact charge laying were investigated for seismic stations located on the territory of Kazakhstan using digitized records of the STS events. In addition, the comparison between salvo wave pattern and single explosions was conducted. The records of permanent and temporary seismic stations (epicentral distances range 100 - 800 km) were used for the investigations. Explosions spectra were analyzed, specific features of each class of events were found. The seismograms analysis shows that the wave pattern depends significantly on the explosion site and on the source type.

On mass transport in porosity waves

NASA Astrophysics Data System (ADS)

Jordan, Jacob S.; Hesse, Marc A.; Rudge, John F.

2018-03-01

Porosity waves arise naturally from the equations describing fluid migration in ductile rocks. Here, we show that higher-dimensional porosity waves can transport mass and therefore preserve geochemical signatures, at least partially. Fluid focusing into these high porosity waves leads to recirculation in their center. This recirculating fluid is separated from the background flow field by a circular dividing streamline and transported with the phase velocity of the porosity wave. Unlike models for one-dimensional chromatography in geological porous media, tracer transport in higher-dimensional porosity waves does not produce chromatographic separations between relatively incompatible elements due to the circular flow pattern. This may allow melt that originated from the partial melting of fertile heterogeneities or fluid produced during metamorphism to retain distinct geochemical signatures as they rise buoyantly towards the surface.

Underwater refraction-polarization patterns of skylight perceived by aquatic animals through Snell's window of the flat water surface.

PubMed

Horváth, G; Varjú, D

1995-06-01

The grass shrimp (Palaemonetes vulgaris) orients itself by means of the polarization pattern of the sky visible through Snell's window of the water surface. The celestial polarization pattern viewed from water is distorted and modified because of refraction and repolarization of skylight at the air-water interface. This work provides a quantitative account of the repolarization of skylight transmitted through a flat water surface. The degree and direction of linear polarization, the transmissivity and the shape of the refraction-polarization oval are calculated at the air-water interface as functions of the polarization characteristics and the incident angle of partially linearly polarized incoming light. Two-dimensional patterns of linear polarization ellipses and of the degree and direction of polarization of skylight are presented for different zenith distances of the sun. The corresponding underwater refraction-polarization patterns are computed. Transmissivity patterns of a flat water surface are calculated for unpolarized light of an overcast sky and for partially polarized light of clear skies as a function of the zenith distance of the sun. The role of these refraction-polarization patterns in orientation and polarization vision of the grass shrimp (P. vulgaris) and rainbow trout (Oncorhyncus mykiss) is reviewed. The effects of cloud cover, surface waves and water turbidity on the refraction-polarization patterns are briefly discussed.

Marble Ageing Characterization by Acoustic Waves

NASA Astrophysics Data System (ADS)

Boudani, Mohamed El; Wilkie-Chancellier, Nicolas; Martinez, Loïc; Hébert, Ronan; Rolland, Olivier; Forst, Sébastien; Vergès-Belmin, Véronique; Serfaty, Stéphane

In cultural heritage, statue marble characterization by acoustic waves is a well-known non-destructive method. Such investigations through the statues by time of flight method (TOF) point out sound speeds decrease with ageing. However for outdoor stored statues as the ones in the gardens of Chateau de Versailles, ageing affects mainly the surface of the Carrara marble. The present paper proposes an experimental study of the marble acoustic properties variations during accelerated laboratory ageing. The surface degradation of the marble is reproduced in laboratory for 29 mm thick marble samples by using heating/cooling thermal cycles on one face of a marble plate. Acoustic waves are generated by 1 MHz central frequency contact transducers excited by a voltage pulse placed on both sides of the plate. During the ageing and by using ad hoc transducers, the marble samples are characterized in transmission, along their volume by shear, compressional TOF measurements and along their surface by Rayleigh waves measurements. For Rayleigh waves, both TOF by transducers and laser vibrometry methods are used to detect the Rayleigh wave. The transmission measurements point out a deep decrease of the waves speeds in conjunction with a dramatic decrease of the maximum frequency transmitted. The marble acts as a low pass filter whose characteristic frequency cut decreases with ageing. This pattern occurs also for the Rayleigh wave surface measurements. The speed change in conjunction with the bandwidth translation is shown to be correlated to the material de-structuration during ageing. With a similar behavior but reversed in time, the same king of phenomena have been observed trough sol-gel materials during their structuration from liquid to solid state (Martinez, L. et all (2004). "Chirp-Z analysis for sol-gel transition monitoring". Ultrasonics, 42(1), 507-510.). A model is proposed to interpret the acoustical measurements

General mechanism involved in subwavelength optics of conducting microstructures: charge-oscillation-induced light emission and interference.

PubMed

Huang, Xian-Rong; Peng, Ru-Wen

2010-04-01

Interactions between light and conducting microstructures or nanostructures can result in a variety of novel phenomena, but their underlying mechanisms have not been completely understood. From calculations of surface charge density waves on conducting gratings and by comparing them with classical surface plasmons, we revealed a general yet concrete picture regarding the coupling of light to free electron oscillation on structured conducting surfaces that can lead to oscillating subwavelength charge patterns (i.e., structured surface plasmons). New wavelets emitted from these light sources then destructively interfere to form evanescent waves. This principle, usually combined with other mechanisms, is mainly a geometrical effect that can be universally involved in light scattering from all periodic and non-periodic structures containing free electrons. This picture may provide clear guidelines for developing conductor-based nano-optical devices.

Helioseismology.

ERIC Educational Resources Information Center

Leibacher, John W.; And Others

1985-01-01

Helioseismology (similar to geophysicists' study of seismic waves) makes it possible to penetrate the sun's opaque brilliance by measuring surface oscillations. Their pattern and period hold clues to temperature, structure, composition, and dynamics of the sun's interior. Scientists have used data to build models (evolved mathematically) to…

Land surface and atmospheric conditions associated with heat waves over the Chickasaw Nation in the South Central United States

NASA Astrophysics Data System (ADS)

Lee, Eungul; Bieda, Rahama; Shanmugasundaram, Jothiganesh; Basara Richter, Heather

2016-06-01

Exposure to extreme heat was reconstructed based on regional land-atmosphere processes from 1979 to 2010 in the South Central U.S. The study region surrounds the Chickasaw Nation (CN), a predominantly Native American population with a highly prevalent burden of climate-sensitive chronic diseases. Land surface and atmospheric conditions for summer heat waves were analyzed during spring (March-April-May, MAM) and summer (June-July-August, JJA) based on the Climate and Ocean: Variability, Predictability, and Change maximum temperature definition for heat wave frequency (HWF). The spatial-temporal pattern of HWF was determined using empirical orthogonal function (EOF) analysis and the corresponding principle component time series of the first EOF of HWF. Statistically significant analyses of observed conditions indicated that sensible heat increased and latent heat fluxes decreased with high HWF in the South Central U.S. The largest positive correlations of sensible heat flux to HWF and the largest negative correlations of latent heat flux to HWF were specifically observed over the CN. This is a significantly different energy transfer regime due to less available soil moisture during the antecedent MAM and JJA. The higher sensible heat from dry soil could cause significant warming from the near surface (>2.0°C) to the lower troposphere (>1.5°C), and accumulated boundary layer heat could induce the significant patterns of higher geopotential height and enhance anticyclonic circulations (negative vorticity anomaly) at the midtroposphere. Results suggested a positive land-atmosphere feedback associated with heat waves and called attention to the need for region-specific climate adaptation planning.

Land surface and atmospheric conditions associated with heat waves in the South Central United States

NASA Astrophysics Data System (ADS)

Lee, Eungul; Bieda, Rahama; Shanmugasundaram, Jothiganesh; Richter, Heather

2017-04-01

Exposure to extreme heat was reconstructed based on regional land-atmosphere processes from 1979 to 2010 in the South Central U.S. The study region surrounds the Chickasaw Nation (CN), a predominantly Native American population with a highly prevalent burden of climate-sensitive chronic diseases. Land surface and atmospheric conditions for summer heat waves were analyzed during spring (March-April-May, MAM) and summer (June-July-August, JJA) based on the Climate and Ocean: Variability, Predictability, and Change maximum temperature definition for heat wave frequency (HWF). The spatial-temporal pattern of HWF was determined using empirical orthogonal function (EOF) analysis and the corresponding principle component time series of the first EOF of HWF. Statistically significant analyses of observed conditions indicated that sensible heat increased and latent heat fluxes decreased with high HWF in the South Central U.S. The largest positive correlations of sensible heat flux to HWF and the largest negative correlations of latent heat flux to HWF were specifically observed over the CN. This is a significantly different energy transfer regime due to less available soil moisture during the antecedent MAM and JJA. The higher sensible heat from dry soil could cause significant warming from the near surface (> 2.0°C) to the lower troposphere (> 1.5°C), and accumulated boundary layer heat could induce the significant patterns of higher geopotential height and enhance anticyclonic circulations (negative vorticity anomaly) at the midtroposphere. Results suggested a positive land-atmosphere feedback associated with heat waves and called attention to the need for region-specific climate adaptation planning.

The synoptic setting and possible energy sources for mesoscale wave disturbances

NASA Technical Reports Server (NTRS)

Uccellini, Louis W.; Koch, Steven E.

1987-01-01

Published data on 13 cases of mesoscale wave disturbances and their environment were examined to isolate common features for these cases and to determine possible energy sources for the waves. These events are characterized by either a singular wave of depression or wave packets with periods of 1-4 h, horizontal wavelengths of 50-500 km, and surface-pressure perturbation amplitudes of 0.2-7.0 mb. These wave events are shown to be associated with a distinct synoptic pattern (including the existence of a strong inversion in the lower troposphere and the propagation of a jet streak toward a ridge axis in the upper troposphere) while displaying little correlation with the presence of convective storm cells. The observed development of the waves is consistent with the hypothesis that the energy source needed to initiate and sustain the wave disturbances may be related to a geostrophic adjustment process associated with upper-tropospheric jet streaks.

A Factor Affecting Transonic Leading-edge Flow Separation

NASA Technical Reports Server (NTRS)

Wood, George P; Gooderum, Paul B

1956-01-01

A change in flow pattern that was observed as the free-stream Mach number was increased in the vicinity of 0.8 was described in NACA Technical Note 1211 by Lindsey, Daley, and Humphreys. The flow on the upper surface behind the leading edge of an airfoil at an angle of attack changed abruptly from detached flow with an extensive region of separation to attached supersonic flow terminated by a shock wave. In the present paper, the consequences of shock-wave - boundary layer interaction are proposed as a factor that may be important in determining the conditions under which the change in flow pattern occurs. Some experimental evidence in support of the importance of this factor is presented.

Global multiresolution models of surface wave propagation: comparing equivalently regularized Born and ray theoretical solutions

NASA Astrophysics Data System (ADS)

Boschi, Lapo

2006-10-01

I invert a large set of teleseismic phase-anomaly observations, to derive tomographic maps of fundamental-mode surface wave phase velocity, first via ray theory, then accounting for finite-frequency effects through scattering theory, in the far-field approximation and neglecting mode coupling. I make use of a multiple-resolution pixel parametrization which, in the assumption of sufficient data coverage, should be adequate to represent strongly oscillatory Fréchet kernels. The parametrization is finer over North America, a region particularly well covered by the data. For each surface-wave mode where phase-anomaly observations are available, I derive a wide spectrum of plausible, differently damped solutions; I then conduct a trade-off analysis, and select as optimal solution model the one associated with the point of maximum curvature on the trade-off curve. I repeat this exercise in both theoretical frameworks, to find that selected scattering and ray theoretical phase-velocity maps are coincident in pattern, and differ only slightly in amplitude.

Free motion scanning system

DOEpatents

Sword, Charles K.

2000-01-01

The present invention relates to an ultrasonic scanner system and method for the imaging of a part system, the scanner comprising: a probe assembly spaced apart from the surface of the part including at least two tracking signals for emitting radiation and a transmitter for emitting ultrasonic waves onto a surface in order to induce at least a portion of the waves to be reflected from the part, at least one detector for receiving the radiation wherein the detector is positioned to receive the radiation from the tracking signals, an analyzer for recognizing a three-dimensional location of the tracking signals based on the emitted radiation, a differential converter for generating an output signal representative of the waveform of the reflected waves, and a device such as a computer for relating said tracking signal location with the output signal and projecting an image of the resulting data. The scanner and method are particularly useful to acquire ultrasonic inspection data by scanning the probe over a complex part surface in an arbitrary scanning pattern.

Initial observations from seismometers frozen into a borehole through the McMurdo Ice Shelf.

NASA Astrophysics Data System (ADS)

Prior, David; Eccles, Jennifer; Cooper, Joanna; Craw, Lisa; van Haastrecht, Laurine; Hamish Bowman, M.; Stevens, Craig; Gamble Rosevear, Madi; Hulbe, Christina; Gorman, Andrew; Horgan, Huw; Pyne, Alex

2017-04-01

A seismometer cable with two, three-component seismometers was frozen into a hot water borehole through the McMurdo Ice Shelf at Windless Bight in late December 2016. The seismometers are at 39m and 189m depth. The upper seismometer lies just below the firn-ice transition ( 37m) and very close to sea level ( 38m). The lower seismometer is positioned 30m above the base of the ice shelf ( 222m). The seismometers froze in within 40 (upper) to 60 (lower) hours of the last reaming operation. The temperature evolution during freezing is complicated, particularly for the lower seismometer. The complications are interpreted as the result of brine expulsion and brine pocket migration. We conducted an active source experiment using the frozen-in seismometers together with a surface seismometer and four lines of geophones radiating from the borehole, at 45-degree angles, to a distance of 240m. Sources included a traditional hammer and surface plate, two types of hammer activated surface shear wave sources (for hard and soft surfaces) and a hammer activated borehole source. The frozen-in seismometers show excellent separation of P - wave and S - wave arrivals for all sources, particularly on the lower seismometer. The surface shear sources give clearer separation of arrivals on the vertical and horizontal components. For some source to receiver geometries the surface shear sources give no P - wave arrival on the horizontal seismometer components and a very strong S - wave arrival that is partitioned between the horizontal components in correspondence with the source orientation. The borehole source (at 3 to 10m in the firn) also gives clearer separation of P - wave and S - wave arrivals compared to a surface hammer and plate. The frozen-in seismometers were also used to listen for natural events in the ice. Comparing the same events recorded at the surface and at depth, the latter are much less noisy than the former, leading to more clear interpretation. As in the active source experiments, P-wave and S-wave arrivals are clear and the partitioning onto different components (vertical and horizontal) is very clear. Using seismology to interpret the physical properties of ice masses is dependent on quality data. The patterns of anisotropy related to ice crystallographic preferred orientations (CPOs) are particularly rich for S - waves and the ability to measure S - wave velocities and shear wave splitting is of particular importance in using seismology to constrain CPOs. Our initial observations suggest that seismometers frozen-in at depth, together with artificial sources with controlled shear wave kinematics have great potential to help us constrain ice CPOs and resultant plastic anisotropy through seismic data.

Inexpensive Ultrasound Demonstrations as Analogs of Radio Diffraction in the field : Huygens Probe Bistatic experiment on Titan and the Sea Interferometer (Invited)

NASA Astrophysics Data System (ADS)

Lorenz, R. D.

2013-12-01

The wave nature of electromagnetic radiation can be exploited in a number of astronomical and remote sensing methods, but is often challenging to visualize in the classroom. One approach with conveniently-inexpensive components is to use sound as an analog. Readily-available ultrasonic transducers at 40 kHz can be driven with a 555 oscillator and received intensity detected with an op-amp and visualized with a digital voltmeter, a lightbulb, or even acoustically. The wavelength of 9mm is convenient for tabletop experiments, with a relevant example being Lloyds Mirror, the interference of a direct wave from a source just above a surface with the reflected wave. As a distant receiver moves in angle through this interference pattern, a series of peaks and nulls in recorded intensity can be interpreted as the height of the transmitter and the reflectivity (i.e. with some assumptions, the roughness) of the reflecting surface. This $10 experiment will be demonstrated at the poster. Such an observation was (serendipitously) made in 2005 after the landing of the Huygens probe on the surface of Titan, where the radio signal measured by Cassini as it set on the horizon as seen from the probe underwent sharp dips in strength that were inverted into a precise measurement of the post-impact probe height. A similar technique in reverse was applied a half century earlier in early Australian radio astronomy to measure the position and width of astrophysical sources from a single clifftop antenna. Ultrasound can be convenient to emulate other radio work, exploiting Doppler effects and (for pulsed sources, like those used in rangers for amateur robotics) propagation time rather than diffraction. Some experiments on tracking Frisbees as an analog for measuring planetary winds by tracking descent probes, and on bistatic delay/Doppler scatterometry as in the CYGNSS GPS-based experiment to measure hurricane winds via sea state, will also be discussed. Huygens probe on the surface of Titan. The interference pattern constrained Titan surface properties Ultrasound pattern is a function of geometry and surface covering

Frequency-controls of electromagnetic multi-beam scanning by metasurfaces.

PubMed

Li, Yun Bo; Wan, Xiang; Cai, Ben Geng; Cheng, Qiang; Cui, Tie Jun

2014-11-05

We propose a method to control electromagnetic (EM) radiations by holographic metasurfaces, including to producing multi-beam scanning in one dimension (1D) and two dimensions (2D) with the change of frequency. The metasurfaces are composed of subwavelength metallic patches on grounded dielectric substrate. We present a combined theory of holography and leaky wave to realize the multi-beam radiations by exciting the surface interference patterns, which are generated by interference between the excitation source and required radiation waves. As the frequency changes, we show that the main lobes of EM radiation beams could accomplish 1D or 2D scans regularly by using the proposed holographic metasurfaces shaped with different interference patterns. This is the first time to realize 2D scans of antennas by changing the frequency. Full-wave simulations and experimental results validate the proposed theory and confirm the corresponding physical phenomena.

Interferometric synthetic aperture radar: Building tomorrow's tools today

USGS Publications Warehouse

Lu, Zhong

2006-01-01

A synthetic aperture radar (SAR) system transmits electromagnetic (EM) waves at a wavelength that can range from a few millimeters to tens of centimeters. The radar wave propagates through the atmosphere and interacts with the Earth’s surface. Part of the energy is reflected back to the SAR system and recorded. Using a sophisticated image processing technique, called SAR processing (Curlander and McDonough, 1991), both the intensity and phase of the reflected (or backscattered) signal of each ground resolution element (a few meters to tens of meters) can be calculated in the form of a complex-valued SAR image representing the reflectivity of the ground surface. The amplitude or intensity of the SAR image is determined primarily by terrain slope, surface roughness, and dielectric constants, whereas the phase of the SAR image is determined primarily by the distance between the satellite antenna and the ground targets, slowing of the signal by the atmosphere, and the interaction of EM waves with ground surface. Interferometric SAR (InSAR) imaging, a recently developed remote sensing technique, utilizes the interaction of EM waves, referred to as interference, to measure precise distances. Very simply, InSAR involves the use of two or more SAR images of the same area to extract landscape topography and its deformation patterns.

Sound pressure distribution within natural and artificial human ear canals: Forward stimulation

PubMed Central

Ravicz, Michael E.; Tao Cheng, Jeffrey; Rosowski, John J.

2014-01-01

This work is part of a study of the interaction of sound pressure in the ear canal (EC) with tympanic membrane (TM) surface displacement. Sound pressures were measured with 0.5–2 mm spacing at three locations within the shortened natural EC or an artificial EC in human temporal bones: near the TM surface, within the tympanic ring plane, and in a plane transverse to the long axis of the EC. Sound pressure was also measured at 2-mm intervals along the long EC axis. The sound field is described well by the size and direction of planar sound pressure gradients, the location and orientation of standing-wave nodal lines, and the location of longitudinal standing waves along the EC axis. Standing-wave nodal lines perpendicular to the long EC axis are present on the TM surface >11–16 kHz in the natural or artificial EC. The range of sound pressures was larger in the tympanic ring plane than at the TM surface or in the transverse EC plane. Longitudinal standing-wave patterns were stretched. The tympanic-ring sound field is a useful approximation of the TM sound field, and the artificial EC approximates the natural EC. PMID:25480061

Surface electrical properties experiment. [for Taurus-Littrow region of the moon on Apollo 17

NASA Technical Reports Server (NTRS)

Simmons, G.

1974-01-01

The Surface Electrical Properties Experiment (SEP) was flown to the moon in December 1972 on Apollo 17 and used to explore a portion of the Taurus-Littrow region. SEP used a relatively new technique, termed radio frequency interferometry (RFI). Electromagnetic waves were radiated from two orthogonal, horizontal electric dipole antennas on the surface of the moon at frequencies of 1, 2, 4, 8, 16, and 32 Mhz. The field strength of the EM waves was measured as a function of distance with a receiver mounted on the Lunar Roving Vehicle and using three orthogonal, electrically small, loops. The interference pattern produced by the waves that travelled above the moon's surface and those that travelled below the surface was recorded on magnetic tape. The tape was returned to earth for analysis and interpretation. Several reprints, preprints, and an initial draft of the first publication of the SEP results are included. These documents provide a rather complete account of the details of the theory of the RFI technique, of the terrestrial tests of the technique, and of the present state of our interpretation of the Apollo 17 data.

Visualizing weakly bound surface Fermi arcs and their correspondence to bulk Weyl fermions

PubMed Central

Batabyal, Rajib; Morali, Noam; Avraham, Nurit; Sun, Yan; Schmidt, Marcus; Felser, Claudia; Stern, Ady; Yan, Binghai; Beidenkopf, Haim

2016-01-01

Fermi arcs are the surface manifestation of the topological nature of Weyl semimetals, enforced by the bulk-boundary correspondence with the bulk Weyl nodes. The surface of tantalum arsenide, similar to that of other members of the Weyl semimetal class, hosts nontopological bands that obscure the exploration of this correspondence. We use the spatial structure of the Fermi arc wave function, probed by scanning tunneling microscopy, as a spectroscopic tool to distinguish and characterize the surface Fermi arc bands. We find that, as opposed to nontopological states, the Fermi arc wave function is weakly affected by the surface potential: it spreads rather uniformly within the unit cell and penetrates deeper into the bulk. Fermi arcs reside predominantly on tantalum sites, from which the topological bulk bands are derived. Furthermore, we identify a correspondence between the Fermi arc dispersion and the energy and momentum of the bulk Weyl nodes that classify this material as topological. We obtain these results by introducing an analysis based on the role the Bloch wave function has in shaping quantum electronic interference patterns. It thus carries broader applicability to the study of other electronic systems and other physical processes. PMID:27551687

High-resolution electrical mapping of porcine gastric slow-wave propagation from the mucosal surface.

PubMed

Angeli, T R; Du, P; Paskaranandavadivel, N; Sathar, S; Hall, A; Asirvatham, S J; Farrugia, G; Windsor, J A; Cheng, L K; O'Grady, G

2017-05-01

Gastric motility is coordinated by bioelectrical slow waves, and gastric dysrhythmias are reported in motility disorders. High-resolution (HR) mapping has advanced the accurate assessment of gastric dysrhythmias, offering promise as a diagnostic technique. However, HR mapping has been restricted to invasive surgical serosal access. This study investigates the feasibility of HR mapping from the gastric mucosal surface. Experiments were conducted in vivo in 14 weaner pigs. Reference serosal recordings were performed with flexible-printed-circuit (FPC) arrays (128-192 electrodes). Mucosal recordings were performed by two methods: (i) FPC array aligned directly opposite the serosal array, and (ii) cardiac mapping catheter modified for gastric mucosal recordings. Slow-wave propagation and morphology characteristics were quantified and compared between simultaneous serosal and mucosal recordings. Slow-wave activity was consistently recorded from the mucosal surface from both electrode arrays. Mucosally recorded slow-wave propagation was consistent with reference serosal activation pattern, frequency (P≥.3), and velocity (P≥.4). However, mucosally recorded slow-wave morphology exhibited reduced amplitude (65-72% reduced, P<.001) and wider downstroke width (18-31% wider, P≤.02), compared to serosal data. Dysrhythmias were successfully mapped and classified from the mucosal surface, accorded with serosal data, and were consistent with known dysrhythmic mechanisms in the porcine model. High-resolution gastric electrical mapping was achieved from the mucosal surface, and demonstrated consistent propagation characteristics with serosal data. However, mucosal signal morphology was attenuated, demonstrating necessity for optimized electrode designs and analytical algorithms. This study demonstrates feasibility of endoscopic HR mapping, providing a foundation for advancement of minimally invasive spatiotemporal gastric mapping as a clinical and scientific tool. © 2016 John Wiley & Sons Ltd.

Surface Waves as Major Controls on Particle Backscattering in Southern California Coastal Waters

NASA Astrophysics Data System (ADS)

Henderikx Freitas, F.; Fields, E.; Maritorena, S.; Siegel, D.

2016-02-01

Satellite observations of particle loads and optical backscattering coefficients (bbp) in the Southern California Bight (SCB) have been thought to be driven by episodic inputs from storm runoff. Here we show however that surface waves have a larger role in controlling remotely sensed bbp values than previously considered. More than 14 years of 2-km resolution SeaWiFS, MODIS and MERIS satellite imagery spectrally-merged with the Garver-Siegel-Maritorena bio-optical model were used to assess the relative importance of terrestrial runoff and surface wave forcings in determining changes in particle load in the SCB. The space-time distributions of particle backscattering at 443nm and chlorophyll concentration estimates from the model were analyzed using Empirical Orthogonal Function analysis, and patterns were compared with several environmental variables. While offshore values of bbp are tightly related to chlorophyll concentrations, as expected for productive Case-1 waters, values of bbp in a 10km band near the coast are primarily modulated by surface waves. The relationship with waves holds throughout all seasons and is most apparent around the 40m isobath, but extends offshore until about 100m in depth. Riverine inputs are associated with elevated bbp near the coast mostly during the larger El Nino events of 1997/1998 and 2005. These findings are consistent with bio-optical glider and field observations from the Santa Barbara Channel taken as part of the Santa Barbara Coastal Long-Term Ecological Research and Plumes and Blooms programs. The implication of surface waves determining bbp variability beyond the surf zone has large consequences for the life cycle of many marine organisms, as well as for the interpretation of remote sensing signals near the coast.

Measuring sea surface height with a GNSS-Wave Glider

NASA Astrophysics Data System (ADS)

Morales Maqueda, Miguel Angel; Penna, Nigel T.; Foden, Peter R.; Martin, Ian; Cipollini, Paolo; Williams, Simon D.; Pugh, Jeff P.

2017-04-01

A GNSS-Wave Glider is a novel technique to measure sea surface height autonomously using the Global Navigation Satellite System (GNSS). It consists of an unmanned surface vehicle manufactured by Liquid Robotics, a Wave Glider, and a geodetic-grade GNSS antenna-receiver system, with the antenna installed on a mast on the vehicle's deck. The Wave Glider uses the differential wave motion through the water column for propulsion, thus guaranteeing an, in principle, indefinite autonomy. Solar energy is collected to power all on-board instrumentation, including the GNSS system. The GNSS-Wave Glider was first tested in Loch Ness in 2013, demonstrating that the technology is capable of mapping geoid heights within the loch with an accuracy of a few centimetres. The trial in Loch Ness did not conclusively confirm the reliability of the technique because, during the tests, the state of the water surface was much more benign than would normally be expect in the open ocean. We now report on a first deployment of a GNSS-Wave Glider in the North Sea. The deployment took place in August 2016 and lasted thirteen days, during which the vehicle covered a distance of about 350 nautical miles in the north western North Sea off Great Britain. During the experiment, the GNSS-Wave Glider experienced sea states between 1 (0-0.1 m wave heights) and 5 (2.5-4 m wave heights). The GNSS-Wave Glider data, recorded at 5 Hz frequency, were analysed using a post-processed kinematic GPS-GLONASS precise point positioning (PPP) approach, which were quality controlled using double difference GPS kinematic processing with respect to onshore reference stations. Filtered with a 900 s moving-average window, the PPP heights reveal geoid patterns in the survey area that are very similar to the EGM2008 geoid model, thus demonstrating the potential use of a GNSS-Wave Glider for marine geoid determination. The residual of subtracting the modelled or measured marine geoid from the PPP signal combines information about dynamic topography and sea state. GNSS-Wave Glider data will next be validated against concurrent and co-located satellite altimetry data from the Jason-1, Jason-2, CryoSat-2 and AltiKa missions.

Earth Observations taken by Expedition 38 crewmember

NASA Image and Video Library

2014-01-28

ISS038-E-036501 (28 Jan. 2014) --- This wide field-of-view image photographed by an Expedition 38 crew member on the International Space Station shows an east-west swath of the southwestern Indian Ocean. Two remote islands, part of the French Southern and Antarctic Lands, appear in the center of the image. Possession Island (right center) and East Island (center) are both only 18 kilometers long. A smaller island, Ile aux Cochons (Pigs Island), lies 100 kilometers to the west. Each island has set up V-shaped trains of waves, like bow waves, as the air flows over the islands from the west (right to left). The bow-wave patterns are overlaid on the low regional stratus (blanket) cloud that is so common in the southern Indian Ocean at 50 degrees south latitude. This view was taken from more than 400 kilometers above the sea surface and reveals relationships that could not be readily understood by someone standing on one of the islands. For example, larger and higher islands produce larger waves. So the largest are being generated by Possession Island (934 meters above sea level at the highest point), and East Island, versus much smaller waves developed downwind of the tiny Ile de Pingouins (340 meters above sea level high, invisible below the cloud deck). Other patterns also can be detected. Waves in an upper layer can be seen casting shadows onto a lower layer (lower left). In the top half of the image the waves are making thicker and thinner zones in the clouds of the lower layer. Wave trains from Possession Island and Ile aux Cochons are interacting in a cross-hatch pattern (center).

The role of Internal Solitary Waves on deep-water sedimentary processes: the case of up-slope migrating sediment waves off the Messina Strait

PubMed Central

Droghei, R.; Falcini, F.; Casalbore, D.; Martorelli, E.; Mosetti, R.; Sannino, G.; Santoleri, R.; Chiocci, F. L.

2016-01-01

Subaqueous, asymmetric sand waves are typically observed in marine channel/canyon systems, tidal environments, and continental slopes exposed to strong currents, where they are formed by current shear resulting from a dominant unidirectional flow. However, sand-wave fields may be readily observed in marine environments where no such current exists; the physical processes driving their formation are enigmatic or not well understood. We propose that internal solitary waves (ISWs) induced by tides can produce an effective, unidirectional boundary “current” that forms asymmetric sand waves. We test this idea by examining a sand-wave field off the Messina Strait, where we hypothesize that ISWs formed at the interface between intermediate and surface waters are refracted by topography. Hence, we argue that the deflected pattern (i.e., the depth-dependent orientation) of the sand-wave field is due to refraction of such ISWs. Combining field observations and numerical modelling, we show that ISWs can account for three key features: ISWs produce fluid velocities capable of mobilizing bottom sediments; the predicted refraction pattern resulting from the interaction of ISWs with bottom topography matches the observed deflection of the sand waves; and predicted migration rates of sand waves match empirical estimates. This work shows how ISWs may contribute to sculpting the structure of continental margins and it represents a promising link between the geological and oceanographic communities. PMID:27808239

Nanoscale topographic pattern formation on Kr{sup +}-bombarded germanium surfaces

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

Perkinson, Joy C.; Madi, Charbel S.; Aziz, Michael J.

2013-03-15

The nanoscale pattern formation of Ge surfaces uniformly irradiated by Kr{sup +} ions was studied in a low-contamination environment at ion energies of 250 and 500 eV and at angles of 0 Degree-Sign through 80 Degree-Sign . The authors present a phase diagram of domains of pattern formation occurring as these two control parameters are varied. The results are insensitive to ion energy over the range covered by the experiments. Flat surfaces are stable from normal incidence up to an incidence angle of {theta} = 55 Degree-Sign from normal. At higher angles, the surface is linearly unstable to the formationmore » of parallel-mode ripples, in which the wave vector is parallel to the projection of the ion beam on the surface. For {theta} {>=} 75 Degree-Sign the authors observe perpendicular-mode ripples, in which the wave vector is perpendicular to the ion beam. This behavior is qualitatively similar to those of Madi et al. for Ar{sup +}-irradiated Si but is inconsistent with those of Ziberi et al. for Kr{sup +}-irradiated Ge. The existence of a window of stability is qualitatively inconsistent with a theory based on sputter erosion [R. M. Bradley and J. M. Harper, J. Vac. Sci. Technol. A 6, 2390 (1988)] and qualitatively consistent with a model of ion impact-induced mass redistribution [G. Carter and V. Vishnyakov, Phys. Rev. B 54, 17647 (1996)] as well as a crater function theory incorporating both effects [S. A. Norris et al., Nat. Commun. 2, 276 (2011)]. The critical transition angle between stable and rippled surfaces occurs 10 Degree-Sign -15 Degree-Sign above the value of 45 Degree-Sign predicted by the mass redistribution model.« less

The Role of Different Plant Soil-Water Feedbacks in Models of Dryland Vegetation Patterns

NASA Astrophysics Data System (ADS)

Silber, M.; Bonetti, S.; Gandhi, P.; Gowda, K.; Iams, S.; Porporato, A. M.

2017-12-01

Understanding the processes underlying the formation of regular vegetation patterns in arid and semi-arid regions is important to assessing desertification risk under increasing anthropogenic pressure. Various modeling frameworks have been proposed, which are all capable of generating similar patterns through self-organizing mechanisms that stem from assumptions about plant feedbacks on surface/subsurface water transport. We critically discuss a hierarchy of hydrology-vegetation models for the coupled dynamics of surface water, soil moisture, and vegetation biomass on a hillslope. We identify distinguishing features and trends for the periodic traveling wave solutions when there is an imposed idealized topography and make some comparisons to satellite images of large-scale banded vegetation patterns in drylands of Africa, Australia and North America. This work highlights the potential for constraining models by considerations of where the patterns may lie on a landscape, such as whether on a ridge or in a valley.

Acoustic scattering of a Bessel vortex beam by a rigid fixed spheroid

NASA Astrophysics Data System (ADS)

Mitri, F. G.

2015-12-01

Partial-wave series representation of the acoustic scattering field of high-order Bessel vortex beams by rigid oblate and prolate spheroids using the modal matching method is developed. The method, which is applicable to slightly elongated objects at low-to-moderate frequencies, requires solving a system of linear equations which depends on the partial-wave index n and the order of the Bessel vortex beam m using truncated partial-wave series expansions (PWSEs), and satisfying the Neumann boundary condition for a rigid immovable surface in the least-squares sense. This original semi-analytical approach developed for Bessel vortex beams is demonstrated for finite oblate and prolate spheroids, where the mathematical functions describing the spheroidal geometry are written in a form involving single angular (polar) integrals that are numerically computed. The transverse (θ = π / 2) and 3D scattering directivity patterns are evaluated in the far-field for both prolate and oblate spheroids, with particular emphasis on the aspect ratio (i.e., the ratio of the major axis over the minor axis of the spheroid) not exceeding 3:1, the half-cone angle β and order m of the Bessel vortex beam, as well as the dimensionless size parameter kr0. Periodic oscillations in the magnitude plots of the far-field scattering form function are observed, which result from the interference of the reflected waves with the circumferential (Franz') waves circumnavigating the surface of the spheroid in the surrounding fluid. Moreover, the 3D directivity patterns illustrate the far-field scattering from the spheroid, that vanishes in the forward (θ = 0) and backward (θ = π) directions. Particular applications in underwater acoustics and scattering, acoustic levitation and the detection of submerged elongated objects using Bessel vortex waves to name a few, would benefit from the results of the present investigation.

Laser-driven high-frequency vibrations of metal blister surface

NASA Astrophysics Data System (ADS)

Kononenko, T. V.; Sinyavsky, M. N.; Konov, V. I.; Sentis, M.

2013-09-01

Time-resolved interferometric microscopy was applied to investigate laser-induced blistering of a titanium film on a silica substrate. Ablation of the titanium/silica interface by single 0.7 ns pulses within a certain fluence range results in local exfoliation of the metal film from the substrate avoiding, however, complete film destruction. Time-dependent transformation of the metal surface profile was reconstructed from the interference patterns within 0-13 ns time delay range. Transverse annular waves with typical amplitude of one hundred of nanometers and estimated traveling speed of few kilometers per second were revealed on the blister surface. The wave occurrence was attributed to fast inhomogeneous bending of the film covering the expanding blister. The resultant high-frequency (˜1 GHz) vibrations of the metal surface provide intensive inertial forces when such metalized target is used for blister-based laser-induced forward transfer of nanopowders and organic molecules.

Evidence against a charge density wave on Bi(111)

DOE PAGES

Kim, T. K.; Wells, J.; Kirkegaard, C.; ...

2005-08-18

The Bi(111) surface was studied by scanning tunneling microscopy (STM), transmission electron microscopy (TEM) and angle-resolved photoemission (ARPES) in order to verify the existence of a recently proposed surface charge density wave (CDW). The STM and TEM results to not support a CDW scenario at low temperatures. Thus the quasiparticle interference pattern observed in STM confirms the spin-orbit split character of the surface states which prevents the formation of a CDW, even in the case of good nesting. The dispersion of the electronic states observed with ARPES agrees well with earlier findings. In particular, the Fermi contour of the electronmore » pocket at the centre of the surface Brillouin zone is found to have a hexagonal shape. However, no gap opening or other signatures of a CDW phase transition can be found in the temperature-dependent data.« less

Mutations in Arabidopsis thaliana genes involved in the tryptophan biosynthesis pathway affect root waving on tilted agar surfaces

NASA Technical Reports Server (NTRS)

Rutherford, R.; Gallois, P.; Masson, P. H.

1998-01-01

Arabidopsis thaliana roots grow in a wavy pattern upon a slanted surface. A novel mutation in the anthranilate synthase alpha 1 (ASA1) gene, named trp5-2wvc1, and mutations in the tryptophan synthase alpha and beta 1 genes (trp3-1 and trp2-1, respectively) confer a compressed root wave phenotype on tilted agar surfaces. When trp5-2wvc1 seedlings are grown on media supplemented with anthranilate metabolites, their roots wave like wild type. Genetic and pharmacological experiments argue that the compressed root wave phenotypes of trp5-2wvc1, trp2-1 and trp3-1 seedlings are not due to reduced IAA biosynthetic potential, but rather to a deficiency in L-tryptophan (L-Trp), or in a L-Trp derivative. Although the roots of 7-day-old seedlings possess higher concentrations of free L-Trp than the shoot as a whole, trp5-2wvc1 mutants show no detectable alteration in L-Trp levels in either tissue type, suggesting that a very localized shortage of L-Trp, or of a L-Trp-derived compound, is responsible for the observed phenotype.

Rapid determination of floral aroma compounds of lilac blossom by fast gas chromatography combined with surface acoustic wave sensor.

PubMed

Oh, Se Yeon; Shin, Hyun Du; Kim, Sung Jean; Hong, Jongki

2008-03-07

A novel analytical method using fast gas chromatography combined with surface acoustic wave sensor (GC/SAW) has been developed for the detection of volatile aroma compounds emanated from lilac blossom (Syringa species: Syringa vulgaris variginata and Syringa dilatata). GC/SAW could detect and quantify various fragrance emitted from lilac blossom, enabling to provide fragrance pattern analysis results. The fragrance pattern analysis could easily characterize the delicate differences in aromas caused by the substantial difference of chemical composition according to different color and shape of petals. Moreover, the method validation of GC/SAW was performed for the purpose of volatile floral actual aroma analysis, achieving a high reproducibility and excellent sensitivity. From the validation results, GC/SAW could serve as an alternative analytical technique for the analysis of volatile floral actual aroma of lilac. In addition, headspace solid-phase microextraction (HS-SPME) GC-MS was employed to further confirm the identification of fragrances emitted from lilac blossom and compared to GC/SAW.

Surface wave scattering from sharp lateral discontinuities

NASA Astrophysics Data System (ADS)

Pollitz, Fred F.

1994-11-01

The problem of surface wave scattering is re-explored, with quasi-degenerate normal mode coupling as the starting point. For coupling among specified spheroidal and toroidal mode dispersion branches, a set of coupled wave equations is derived in the frequency domain for first-arriving Rayleigh and Love waves. The solutions to these coupled wave equations using linear perturbation theory are surface integrals over the unit sphere covering the lateral distribution of perturbations in Earth structure. For isotropic structural perturbations and surface topographic perturbations, these solutions agree with the Born scattering theory previously obtained by Snieder and Romanowicz. By transforming these surface integrals into line integrals along the boundaries of the heterogeneous regions in the case of sharp discontinuities, and by using uniformly valid Green's functions, it is possible to extend the solution to the case of multiple scattering interactions. The proposed method allows the relatively rapid calculation of exact second order scattered wavefield potentials for scattering by sharp discontinuities, and it has many advantages not realized in earlier treatments. It employs a spherical Earth geometry, uses no far field approximation, and implicitly contains backward as well as forward scattering. Comparisons of asymptotic scattering and an exact solution with single scattering and multiple scattering integral formulations show that the phase perturbation predicted by geometrical optics breaks down for scatterers less than about six wavelengths in diameter, and second-order scattering predicts well both the amplitude and phase pattern of the exact wavefield for sufficiently small scatterers, less than about three wavelengths in diameter for anomalies of a few percent.

Coherent Structures and Evolution of Vorticity in Short-Crested Breaking Surface Waves

NASA Astrophysics Data System (ADS)

Kirby, James; Derakhti, Morteza

2017-11-01

We employ a multi-phase LES/VOF code to study turbulence and coherent structures generated during breaking of short-crested surface water waves. We examine the evolution of coherent vortex structures evolving at the scale of the width of the breaking event, and their long-time interaction with smaller vortex loops formed by the local instability of the breaking crest. Long-time results are often characterized by the detachment of the larger scale vortex loop from the surface and formation of a closed vortex ring. The evolution of circulation for the vortical flow field is examined. The initial concentration of forcing close to the free surface leads to spatial distributions of both span-wise and vertical vorticity distributions which are concentrated close to the surface. This result, which persists into shallow water, is at odds with the basic simplicity of the Peregrine mechanism, suggesting that even shallow flows such as the surf zone should be regarded as being forced (in dissipative situations) by a wave-induced surface stress rather than a uniform-over-depth body force. The localized forcing leads to the development of a complex pattern of stream-wise vorticity, comparable in strength to the vertical and span-wise components, and also persist into shallow water. NSF OCE-1435147.

Morphological evolution of thin polymer film on chemically patterned substrates

NASA Astrophysics Data System (ADS)

Singh, Satya Pal

2018-05-01

In this paper work, pattern formation in ultra thin polymer film, adsorbed on chemically patterned substrates, is reported under strong confinement. The observations indicate for the strong influence of the surface attraction over evolution of spindoal waves, leading to the flattening of the film. But, the film appears to be torn apart in strip or nano fiber like structures, because of coalescences of the monomers at the free ends of the chains. The beads at the free ends of the chain are relatively more mobile. The chain diffusion towards attractive part of the chemically patterned surfaces is clearly seen. Prewetting or crystallization like phenomena seems to appear resulting into formation of strips with coexistence of molten phase drops at the top of the ruptured film. The investigation mimics spindoal dewetting because of the fact that the rupturing occurs in case of strong attractive surface. The investigation is of technical importance as it highlights the formation of nano scale strips and fibers though in a quasi equilibrium case.

Root-growth behavior of the Arabidopsis mutant rgr1. Roles of gravitropism and circumnutation in the waving/coiling phenomenon

NASA Technical Reports Server (NTRS)

Mullen, J. L.; Turk, E.; Johnson, K.; Wolverton, C.; Ishikawa, H.; Simmons, C.; Soll, D.; Evans, M. L.

1998-01-01

In this study we investigated the kinetics of the gravitropic response of the Arabidopsis mutant rgr1 (reduced root gravitropism). Although the rate of curvature in rgr1, which is allelic to axr4, was smaller than in the wild type (ecotype Wassilewskija), curvature was initiated in the same region of the root, the distal elongation zone. The time lag for the response was unaffected in the mutant; however, the gravitropic response of rgr1 contained a feature not found in the wild type: when roots growing along the surface of an agar plate were gravistimulated, there was often an upward curvature that initiated in the central elongation zone. Because this response was dependent on the tactile environment of the root, it most likely resulted from the superposition of the waving/coiling phenomenon onto the gravitropic response. We found that the frequency of the waving pattern and circumnutation, a cyclic endogenous pattern of root growth, was the same in rgr1 and in the wild type, so the waving/coiling phenomenon is likely governed by circumnutation patterns. The amplitudes of these oscillations may then be selectively amplified by tactile stimulation to provide a directional preference to the slanting.

Interferometric imaging of nonlocal electromechanical power transduction in ferroelectric domains.

PubMed

Zheng, Lu; Dong, Hui; Wu, Xiaoyu; Huang, Yen-Lin; Wang, Wenbo; Wu, Weida; Wang, Zheng; Lai, Keji

2018-05-22

The electrical generation and detection of elastic waves are the foundation for acoustoelectronic and acoustooptic systems. For surface acoustic wave devices, microelectromechanical/nanoelectromechanical systems, and phononic crystals, tailoring the spatial variation of material properties such as piezoelectric and elastic tensors may bring significant improvements to the system performance. Due to the much slower speed of sound than speed of light in solids, it is desirable to study various electroacoustic behaviors at the mesoscopic length scale. In this work, we demonstrate the interferometric imaging of electromechanical power transduction in ferroelectric lithium niobate domain structures by microwave impedance microscopy. In sharp contrast to the traditional standing-wave patterns caused by the superposition of counterpropagating waves, the constructive and destructive fringes in microwave dissipation images exhibit an intriguing one-wavelength periodicity. We show that such unusual interference patterns, which are fundamentally different from the acoustic displacement fields, stem from the nonlocal interaction between electric fields and elastic waves. The results are corroborated by numerical simulations taking into account the sign reversal of piezoelectric tensor in oppositely polarized domains. Our work paves ways to probe nanoscale electroacoustic phenomena in complex structures by near-field electromagnetic imaging.

River Plumes in Sunglint, Sarawak, Borneo

NASA Technical Reports Server (NTRS)

1991-01-01

The sunglint pattern along the coast of Sarawak (3.0N, 111.5E) delineates the boundry of fresh water river plumes as they flow into the South China Sea. The fresh water lens (boundry between fresh and sea water) overides the saline and more dense sea water and oils, both natural and man made, collect along the convergence zones and dampen wave action. As a result, the smoother sea surface appears bright in the sunglint pattern.

Ripple pattern formation on silicon surfaces by low-energy ion-beam erosion: Experiment and theory

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

Ziberi, B.; Frost, F.; Rauschenbach, B.

The topography evolution of Si surfaces during low-energy noble-gas ion-beam erosion (ion energy {<=}2000 eV) at room temperature has been studied. Depending on the ion-beam parameters, self-organized ripple patterns evolve on the surface with a wavelength {lambda}<100 nm. Ripple patterns were found to occur at near-normal ion incidence angles (5 deg. -30 deg.) with the wave vector oriented parallel to the ion-beam direction. The ordering and homogeneity of these patterns increase with ion fluence, leading to very-well-ordered ripples. The ripple wavelength remains constant with ion fluence. Also, the influence of ion energy on the ripple wavelength is investigated. Additionally itmore » is shown that the mass of the bombarding ion plays a decisive role in the ripple formation process. Ripple patterns evolve for Ar{sup +},Kr{sup +}, and Xe{sup +} ions, while no ripples are observed using Ne{sup +} ions. These results are discussed in the context of continuum theories and by using Monte Carlo simulations.« less

Controlling the influence of elastic eigenmodes on nanomagnet dynamics through pattern geometry

NASA Astrophysics Data System (ADS)

Berk, C.; Yahagi, Y.; Dhuey, S.; Cabrini, S.; Schmidt, H.

2017-03-01

The effect of the nanoscale array geometry on the interaction between optically generated surface acoustic waves (SAWs) and nanomagnet dynamics is investigated using Time-Resolved Magneto-Optical Kerr Effect Microscopy (TR-MOKE). It is demonstrated that altering the nanomagnet geometry from a periodic to a randomized aperiodic pattern effectively removes the magneto-elastic effect of SAWs on the magnetization dynamics. The efficiency of this method depends on the extent of any residual spatial correlations and is quantified by spatial Fourier analysis of the two structures. Randomization allows observation and extraction of intrinsic magnetic parameters such as spin wave frequencies and damping to be resolvable using all-optical methods, enabling the conclusion that the fabrication process does not affect the damping.

Improving the analysis of biogeochemical patterns associated with internal waves in the strait of Gibraltar using remote sensing images

NASA Astrophysics Data System (ADS)

Navarro, Gabriel; Vicent, Jorge; Caballero, Isabel; Gómez-Enri, Jesús; Morris, Edward P.; Sabater, Neus; Macías, Diego; Bolado-Penagos, Marina; Gomiz, Juan Jesús; Bruno, Miguel; Caldeira, Rui; Vázquez, Águeda

2018-05-01

High Amplitude Internal Waves (HAIWs) are physical processes observed in the Strait of Gibraltar (the narrow channel between the Atlantic Ocean and the Mediterranean Sea). These internal waves are generated over the Camarinal Sill (western side of the strait) during the tidal outflow (toward the Atlantic Ocean) when critical hydraulic conditions are established. HAIWs remain over the sill for up to 4 h until the outflow slackens, being then released (mostly) towards the Mediterranean Sea. These have been previously observed using Synthetic Aperture Radar (SAR), which captures variations in surface water roughness. However, in this work we use high resolution optical remote sensing, with the aim of examining the influence of HAIWs on biogeochemical processes. We used hyperspectral images from the Hyperspectral Imager for the Coastal Ocean (HICO) and high spatial resolution (10 m) images from the MultiSpectral Instrument (MSI) onboard the Sentinel-2A satellite. This work represents the first attempt to examine the relation between internal wave generation and the water constituents of the Camarinal Sill using hyperspectral and high spatial resolution remote sensing images. This enhanced spatial and spectral resolution revealed the detailed biogeochemical patterns associated with the internal waves and suggests local enhancements of productivity associated with internal waves trains.

Holographic studies of shock waves within transonic fan rotors

NASA Technical Reports Server (NTRS)

Benser, W. A.; Bailey, E. E.; Gelder, T. F.

1974-01-01

NASA has funded two separate contracts to apply pulsed laser holographic interferometry to the detection of shock patterns in the outer span regions of high tip speed transonic rotors. The first holographic approach used ruby laser light reflected from a portion of the centerbody just ahead of the rotor. These holograms showed the bow wave patterns upstream of the rotor and the shock patterns just inside the blade row near the tip. The second holographic approach, on a different rotor, used light transmitted diagonally across the inlet annulus past the centerbody. This approach gave a more extensive view of the region bounded by the blade leading and trailing edges, by the part span shroud and by the blade tip. These holograms showed the passage shock emanating from the blade leading edge and a moderately strong conical shock originating at the intersection of the part span shroud leading edge and the blade suction surface.

From antinode clusters to node clusters: the concentration-dependent transition of floaters on a standing Faraday wave.

PubMed

Sanlı, Ceyda; Lohse, Detlef; van der Meer, Devaraj

2014-05-01

A hydrophilic floating sphere that is denser than water drifts to an amplitude maximum (antinode) of a surface standing wave. A few identical floaters therefore organize into antinode clusters. However, beyond a transitional value of the floater concentration ϕ, we observe that the same spheres spontaneously accumulate at the nodal lines, completely inverting the self-organized particle pattern on the wave. From a potential energy estimate we show (i) that at low ϕ antinode clusters are energetically favorable over nodal ones and (ii) how this situation reverses at high ϕ, in agreement with the experiment.

Diagnosing the leading mode of interdecadal covariability between the Indian Ocean sea surface temperature and summer precipitation in southern China

NASA Astrophysics Data System (ADS)

Liu, Jingpeng; Ren, Hong-Li; Li, Weijing; Zuo, Jinqing

2018-03-01

Precipitation in southern China during boreal summer (June to August) shows a substantial interdecadal variability on the timescale longer than 8 years. In this study, based on the analysis of singular value decomposition, we diagnose the leading mode of interdecadal covariability between the observational precipitation in southern China and the sea surface temperature (SST) in the Indian Ocean. Results indicate that there exist a remarkable southern China zonal dipole (SCZD) pattern of interdecadal variability of summer precipitation and an interdecadal Indian Ocean basin mode (ID-IOBM) of SST. It is found that the SCZD is evidently covaried with the ID-IOBM, which may induce anomalous inter-hemispheric vertical circulation and atmospheric Kelvin waves. During the warm phase of the ID-IOBM, an enhanced lower-level convergence and upper-level divergence exist over the tropical Indian Ocean, which is a typical Gill-Matsuno-type response to the SST warming. Meanwhile, the accompanied upper-level outflow anomalies further converge over the Indo-China peninsula, resulting in a lower-level anticyclone that contributes to reduction of the eastward moisture transport from the Bay of Bengal to the west part of southern China. In addition, the Kelvin wave-like pattern, as a response of the warm ID-IOBM phase, further induces the lower-level anticyclonic anomaly over the South China Sea-Philippines. Such an anticyclonic circulation is favorable for more water vapor transport from the East China Sea into the east part of southern China. Therefore, the joint effects of the anomalous inter-hemispheric vertical circulation and the Kelvin wave-like pattern associated with the ID-IOBM may eventually play a key role in generating the SCZD pattern.

Root Growth Patterns and Morphometric Change Based on the Growth Media

NASA Astrophysics Data System (ADS)

Schultz, Eric R.; Paul, Anna-Lisa; Ferl, Robert J.

2016-12-01

Arabidopsis thaliana roots skew with minimal waving in the microgravity environment of the International Space Station. Root skewing and root waving have been studied on the ground as well as in spaceflight, but often using different media types. In this study, Arabidopsis seedlings were grown on nutrient media plates that were comprised of various gelling agents with varied hardness in order to better assess these media for spaceflight research experiments. ImageJ was used to quantify the root morphology of 8-dayold seedlings, while R was used to perform statistical analyses. Root growth was drastically different between Difco agar, agarose, and Phytagel. Additionally, root waving masked skewing in certain media. Regression analysis revealed overall patterns when organized by hardness but also revealed that differences in media type had more of an impact on root growth than hardness itself. Different arrangements of media around the root tip revealed that roots grown on the media surface were longer and had fewer waves per millimeter than roots grown embedded in media. The implications for spaceflight research are discussed.

Artificial excitation of ELF waves with frequency of Schumann resonance

NASA Astrophysics Data System (ADS)

Streltsov, A. V.; Guido, T.; Tulegenov, B.; Labenski, J.; Chang, C.-L.

2014-11-01

We report results from the experiment aimed at the artificial excitation of extremely low-frequency (ELF) electromagnetic waves with frequencies corresponding to the frequency of Schumann resonance. Electromagnetic waves with these frequencies can form a standing pattern inside the spherical cavity formed by the surface of the Earth and the ionosphere. In the experiment the ELF waves were excited by heating the ionosphere with X-mode HF electromagnetic waves generated at the High Frequency Active Auroral Research Program (HAARP) facility in Alaska. The experiment demonstrates that heating of the ionosphere can excite relatively large-amplitude electromagnetic waves with frequencies in the range 7.8-8.0 Hz when the ionosphere has a strong F layer, the frequency of the HF radiation is in the range 3.20-4.57 MHz, and the electric field greater than 5 mV/m is present in the ionosphere.

Gravity shear waves atop the cirrus layer of intense convective storms

NASA Technical Reports Server (NTRS)

Stobie, J. G.

1975-01-01

Recent visual satellite photographs of certain intense convective storms have revealed concentric wave patterns. A model for the generation and growth of these waves is proposed. The proposed initial generating mechanism is similar to the effect noticed when a pebble is dropped into a calm pond. The penetration of the tropopause by overshooting convection is analogous to the pebble's penetration of the water's surface. The model for wave growth involves instability due to the wind shear resulting from the cirrus outflow. This model is based on an equation for the waves' phase speed which is similar to the Helmholtz equation. It, however, does not assume an incompressible atmosphere, but rather assumes density is a logarithmic function of height. Finally, the model is evaluated on the two mid-latitude and three tropical cases. The data indicate that shearing instability may be a significant factor in the appearance of these waves.

Numerical Study of Interaction of a Vortical Density Inhomogeneity with Shock and Expansion Waves

NASA Technical Reports Server (NTRS)

Povitsky, A.; Ofengeim, D.

1998-01-01

We studied the interaction of a vortical density inhomogeneity (VDI) with shock and expansion waves. We call the VDI the region of concentrated vorticity (vortex) with a density different from that of ambiance. Non-parallel directions of the density gradient normal to the VDI surface and the pressure gradient across a shock wave results in an additional vorticity. The roll-up of the initial round VDI towards a non-symmetrical shape is studied numerically. Numerical modeling of this interaction is performed by a 2-D Euler code. The use of an adaptive unstructured numerical grid makes it possible to obtain high accuracy and capture regions of induced vorticity with a moderate overall number of mesh points. For the validation of the code, the computational results are compared with available experimental results and good agreement is obtained. The interaction of the VDI with a propagating shock wave is studied for a range of initial and induced circulations and obtained flow patterns are presented. The splitting of the VDI develops into the formation of a non-symmetrical vortex pair and not in a set of vortices. A method for the analytical computation of an overall induced circulation Gamma(sub 1) as a result of the interaction of a moving VDI with a number of waves is proposed. Simplified, approximated, expressions for Gamma(sub 1) are derived and their accuracy is discussed. The splitting of the VDI passing through the Prandtl-Meyer expansion wave is studied numerically. The obtained VDI patterns are compared to those for the interaction of the VDI with a propagating shock wave for the same values of initial and induced circulations. These patterns have similar shapes for corresponding time moments.

Origin of seasonal predictability for summer climate over the Northwestern Pacific

PubMed Central

Kosaka, Yu; Xie, Shang-Ping; Lau, Ngar-Cheung; Vecchi, Gabriel A.

2013-01-01

Summer climate in the Northwestern Pacific (NWP) displays large year-to-year variability, affecting densely populated Southeast and East Asia by impacting precipitation, temperature, and tropical cyclones. The Pacific–Japan (PJ) teleconnection pattern provides a crucial link of high predictability from the tropics to East Asia. Using coupled climate model experiments, we show that the PJ pattern is the atmospheric manifestation of an air–sea coupled mode spanning the Indo-NWP warm pool. The PJ pattern forces the Indian Ocean (IO) via a westward propagating atmospheric Rossby wave. In response, IO sea surface temperature feeds back and reinforces the PJ pattern via a tropospheric Kelvin wave. Ocean coupling increases both the amplitude and temporal persistence of the PJ pattern. Cross-correlation of ocean–atmospheric anomalies confirms the coupled nature of this PJIO mode. The ocean–atmosphere feedback explains why the last echoes of El Niño–Southern Oscillation are found in the IO-NWP in the form of the PJIO mode. We demonstrate that the PJIO mode is indeed highly predictable; a characteristic that can enable benefits to society. PMID:23610388

The effect of artificial rain on backscattered acoustic signal: first measurements

NASA Astrophysics Data System (ADS)

Titchenko, Yuriy; Karaev, Vladimir; Meshkov, Evgeny; Goldblat, Vladimir

The problem of rain influencing on a characteristics of backscattered ultrasonic and microwave signal by water surface is considered. The rain influence on backscattering process of electromagnetic waves was investigated in laboratory and field experiments, for example [1-3]. Raindrops have a significant impact on backscattering of microwave and influence on wave spectrum measurement accuracy by string wave gauge. This occurs due to presence of raindrops in atmosphere and modification of the water surface. For measurements of water surface characteristics during precipitation we propose to use an acoustic system. This allows us obtaining of the water surface parameters independently on precipitation in atmosphere. The measurements of significant wave height of water surface using underwater acoustical systems are well known [4, 5]. Moreover, the variance of orbital velocity can be measure using these systems. However, these methods cannot be used for measurements of slope variance and the other second statistical moments of water surface that required for analyzing the radar backscatter signal. An original design Doppler underwater acoustic wave gauge allows directly measuring the surface roughness characteristics that affect on electromagnetic waves backscattering of the same wavelength [6]. Acoustic wave gauge is Doppler ultrasonic sonar which is fixed near the bottom on the floating disk. Measurements are carried out at vertically orientation of sonar antennas towards water surface. The first experiments were conducted with the first model of an acoustic wave gauge. The acoustic wave gauge (8 mm wavelength) is equipped with a transceiving antenna with a wide symmetrical antenna pattern. The gauge allows us to measure Doppler spectrum and cross section of backscattered signal. Variance of orbital velocity vertical component can be retrieved from Doppler spectrum with high accuracy. The result of laboratory and field experiments during artificial rain is presented. The estimates of roughness parameters variability during precipitation are obtained. The first measurements of rain influencing on cross section and Doppler spectrum of backscattered acoustic signal was carried out. The obtained results were compared with calculations based on the theoretical model. Acknowledgments. The reported study was supported by RFBR, research project No. 14-05-31517 mol_a. References 1. Bliven Larry, Branger Hubert, Sobieski Piotr, Giovanangeli Jean-Paul, An analysis of scatterometer returns from a water surface agitated by artificial rain : evidence that ring-waves are the mean feature, Intl. Jl. of Remote Sensing, Vol. 14, n 12, 1993, pp. 2315-2329, 1993 2. Sobieski Piotr, Craeye Christophe, Bliven Larry, A Relationship Between Rain Radar Reflectivity and Height Elevation Variance of Ringwaves due to the Impact of Rain on the Sea Surface, Radio Science, AGU, 44, RS3005, 1-20, 2009 3. Weissman, D. E., and M. A. Bourassa, Measurements of the Effect of Rain-induced Sea Surface Roughness on the Satellite Scatterometer Radar Cross Section, IEEE Trans. Geosci. Remote Sens., 46, 2882-2894, 2008 4. B. Brumley, La Jolla, E.Terray, B.String, «System and method for measuring wave directional spectrum and wave height», USA Patent N US 2004/0184350 A1,23 September 2004 5. James H. Churchill, Albert J. Plueddemann, Stephen M. Faluotico, «Extracting Wind Sea and Swell from Directional Wave Spectra derived from a bottom-mounted ADCP», Woods Hole Oceanographic Institution, Technical Report WHOI-2006-13 6. V. Yu. Karaev, M. B. Kanevsky, E. M. Meshkov, Measuring the parameters of sea-surface roughness by underwater acoustic systems: discussion of the device concept, Radiophysics and Quantum Electronics, V. 53, I. 9-10. pp. 569-579, 2011

Identification marking by means of laser peening

DOEpatents

Hackel, Lloyd A.; Dane, C. Brent; Harris, Fritz

2002-01-01

The invention is a method and apparatus for marking components by inducing a shock wave on the surface that results in an indented (strained) layer and a residual compressive stress in the surface layer. One embodiment of the laser peenmarking system rapidly imprints, with single laser pulses, a complete identification code or three-dimensional pattern and leaves the surface in a state of deep residual compressive stress. A state of compressive stress in parts made of metal or other materials is highly desirable to make them resistant to fatigue failure and stress corrosion cracking. This process employs a laser peening system and beam spatial modulation hardware or imaging technology that can be setup to impress full three dimensional patterns into metal surfaces at the pulse rate of the laser, a rate that is at least an order of magnitude faster than competing marking technologies.

Anisotropic tomography of the European lithospheric structure from surface wave studies

NASA Astrophysics Data System (ADS)

Nita, Blanka; Maurya, Satish; Montagner, Jean-Paul

2016-06-01

We present continental-scale seismic isotropic and anisotropic imaging of shear wave upper-mantle structure of tectonically diversified terranes creating the European continent. Taking into account the 36-200 s period range of surface waves enables us to model the deep subcontinental structure at different vertical scale-lengths down to 300 km. After very strict quality selection criteria, we have obtained phase wave speeds at different periods for fundamental Rayleigh and Love modes from about 9000 three-component seismograms. Dispersion measurements are performed by using Fourier-domain waveform inversion technique named "roller-coaster-type" algorithm. We used the reference model with a varying average crustal structure for each source-station path. That procedure led to significant improvement of the quality and number of phase wave speed dispersion measurements compared to the common approach of using a reference model with one average crustal structure. Surface wave dispersion data are inverted at depth for retrieving isotropy and anisotropy parameters. The fast axis directions related to azimuthal anisotropy at different depths constitute a rich database for geodynamical interpretations. Shear wave anomalies of the horizontal dimension larger than 200 km are imaged in our models. They correlate with tectonic provinces of varying age-provenance. Different anisotropy patterns are observed along the most distinctive feature on our maps-the bordering zone between the Palaeozoic and Precambrian Europe. We discuss the depth changes of the lithosphere-asthenosphere boundary along the profiles crossing the chosen tectonic units of different origin and age: Fennoscandia, East European Craton, Anatolia, Mediterranean subduction zones. Within the flat and stable cratonic lithosphere, we find traces of the midlithospheric discontinuity.

Numerical Study of Nonlinear Structures of Locally Excited Marangoni Convection in the Long-Wave Approximation

NASA Astrophysics Data System (ADS)

Wertgeim, Igor I.

2018-02-01

We investigate stationary and non-stationary solutions of nonlinear equations of the long-wave approximation for the Marangoni convection caused by a localized source of heat or a surface active impurity (surfactant) in a thin horizontal layer of a viscous incompressible fluid with a free surface. The distribution of heat or concentration flux is determined by the uniform vertical gradient of temperature or impurity concentration, distorted by the imposition of a slightly inhomogeneous heating or of surfactant, localized in the horizontal plane. The lower boundary of the layer is considered thermally insulated or impermeable, whereas the upper boundary is free and deformable. The equations obtained in the long-wave approximation are formulated in terms of the amplitudes of the temperature distribution or impurity concentration, deformation of the surface, and vorticity. For a simplification of the problem, a sequence of nonlinear equations is obtained, which in the simplest form leads to a nonlinear Schrödinger equation with a localized potential. The basic state of the system, its dependence on the parameters and stability are investigated. For stationary solutions localized in the region of the surface tension inhomogeneity, domains of parameters corresponding to different spatial patterns are delineated.

A comparison of thermocouple and infrared thermographic analysis of temperature rise on the root surface during the continuous wave of condensation technique.

PubMed

Mc Cullagh, J J; Setchell, D J; Gulabivala, K; Hussey, D L; Biagioni, P; Lamey, P J; Bailey, G

2000-07-01

This study was designed to use two methods of temperature measurement to analyse and quantify the in vitro root surface temperature changes during the initial stage of the continuous wave technique of obturation of 17 single-rooted premolar teeth with standard canal preparations. A model was designed to allow simultaneous temperature measurement with both thermocouples and an infrared thermal imaging system. Two thermocouples were placed on the root surface, one coronally and the other near the root apex. A series of thermal images were recorded by an infrared thermal imaging camera during the downpack procedure. The mean temperature rises on the root surface, as measured by the two thermocouples, averaged 13.9 degrees C over the period of study, whilst the infrared thermal imaging system measured an average rise of 28.4 degrees C at the same sites. Temperatures at the more apical point were higher than those measured coronally. After the first wave of condensation, the second activation of the plugger in the canal prior to its removal always resulted in a secondary rise in temperature. The thermal imaging system detected areas of greater temperature change distant from the two selected thermocouple sites. The continuous wave technique of obturation may result in high temperatures on the external root surface. Infrared thermography is a useful device for mapping patterns of temperature change over a large area.

Artificial Excitation of Schumann Resonance with HAARP

NASA Astrophysics Data System (ADS)

Streltsov, A. V.; Chang, C. L.

2014-12-01

We report results from the experiment aimed at the artificial excitation of extremely-low-frequency (ELF) electromagnetic waves with frequencies corresponding to the frequency of Schumann resonance (typically, 7.5 - 8.0 Hz frequency range). Electromagnetic waves with these frequencies can form a standing pattern inside the spherical cavity formed by the surface of the earth and the ionosphere. In the experiment the ELF waves were excited by heating the ionosphere with X-mode HF electromagnetic waves generated by the High Frequency Active Auroral Research Program (HAARP) facility in Alaska. The experiment demonstrates that heating of the ionosphere can excite relatively large-amplitude electromagnetic waves with frequencies in the range of the Schumann resonance, when the ionosphere has a strong F-layer and an electric field greater than 5 mV/m is present in the E-region.

Spatiotemporal chaos involving wave instability.

PubMed

Berenstein, Igal; Carballido-Landeira, Jorge

2017-01-01

In this paper, we investigate pattern formation in a model of a reaction confined in a microemulsion, in a regime where both Turing and wave instability occur. In one-dimensional systems, the pattern corresponds to spatiotemporal intermittency where the behavior of the systems alternates in both time and space between stationary Turing patterns and traveling waves. In two-dimensional systems, the behavior initially may correspond to Turing patterns, which then turn into wave patterns. The resulting pattern also corresponds to a chaotic state, where the system alternates in both space and time between standing wave patterns and traveling waves, and the local dynamics may show vanishing amplitude of the variables.

Spatiotemporal chaos involving wave instability

NASA Astrophysics Data System (ADS)

Berenstein, Igal; Carballido-Landeira, Jorge

2017-01-01

In this paper, we investigate pattern formation in a model of a reaction confined in a microemulsion, in a regime where both Turing and wave instability occur. In one-dimensional systems, the pattern corresponds to spatiotemporal intermittency where the behavior of the systems alternates in both time and space between stationary Turing patterns and traveling waves. In two-dimensional systems, the behavior initially may correspond to Turing patterns, which then turn into wave patterns. The resulting pattern also corresponds to a chaotic state, where the system alternates in both space and time between standing wave patterns and traveling waves, and the local dynamics may show vanishing amplitude of the variables.

Visualizing the Vibration of Laryngeal Tissue during Phonation Using Ultrafast Plane Wave Ultrasonography.

PubMed

Jing, Bowen; Tang, Shanshan; Wu, Liang; Wang, Supin; Wan, Mingxi

2016-12-01

Ultrafast plane wave ultrasonography is employed in this study to visualize the vibration of the larynx and quantify the vibration phase as well as the vibration amplitude of the laryngeal tissue. Ultrasonic images were obtained at 5000 to 10,000 frames/s in the coronal plane at the level of the glottis. Although the image quality degraded when the imaging mode was switched from conventional ultrasonography to ultrafast plane wave ultrasonography, certain anatomic structures such as the vocal folds, as well as the sub- and supraglottic structures, including the false vocal folds, can be identified in the ultrafast plane wave ultrasonic image. The periodic vibration of the vocal fold edge could be visualized in the recorded image sequence during phonation. Furthermore, a motion estimation method was used to quantify the displacement of laryngeal tissue from hundreds of frames of ultrasonic data acquired. Vibratory displacement waveforms of the sub- and supraglottic structures were successfully obtained at a high level of ultrasonic signal correlation. Moreover, statistically significant differences in vibration pattern between the sub- and supraglottic structures were found. Variation of vibration amplitude along the subglottic mucosal surface is significantly smaller than that along the supraglottic mucosal surface. Phase delay of vibration along the subglottic mucosal surface is significantly smaller than that along the supraglottic mucosal surface. Copyright © 2016 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

Characteristics of Quasi-Biennial Oscillation simulation in the Meteorological Research Institute earth system model

NASA Astrophysics Data System (ADS)

Yoshida, K.; Naoe, H.

2016-12-01

Whether climate models drive Quasi-Biennial Oscillation (QBO) appropriately is important to assess QBO impact on climate change such as global warming and solar related variation. However, there were few models generating QBO in the Coupled Model Intercomparison Project Phase 5 (CMIP5). This study focuses on dynamical structure of the QBO and its sensitivity to background wind pattern and model configuration. We present preliminary results of experiments designed by "Towards Improving the QBO in Global Climate Models (QBOi)", which is derived from the Stratosphere-troposphere processes and their role in climate (SPARC), in the Meteorological Research Institute earth system model, MRI-ESM2. The simulations were performed in present-day climate condition, repeated annual cycle condition with various CO2 level and sea surface temperatures, and QBO hindcast. In the present climate simulation, zonal wind in the equatorial stratosphere generally exhibits realistic behavior of the QBO. Equatorial zonal wind variability associated with QBO is overestimated in upper stratosphere and underestimated in lower stratosphere. In the MRI-ESM2, the QBO behavior is mainly driven by gravity wave drag parametrization (GWDP) introduced in Hines (1997). Comparing to reanalyses, shortage of resolved wave forcing is found especially in equatorial lower stratosphere. These discrepancies can be attributed to difference in wave forcing, background wind pattern and model configuration. We intend to show results of additional sensitivity experiments to examine how model configuration and background wind pattern affect resolved wave source, wave propagation characteristics, and QBO behavior.

Validation and Performance Comparison of Numerical Codes for Tsunami Inundation

NASA Astrophysics Data System (ADS)

Velioglu, D.; Kian, R.; Yalciner, A. C.; Zaytsev, A.

2015-12-01

In inundation zones, tsunami motion turns from wave motion to flow of water. Modelling of this phenomenon is a complex problem since there are many parameters affecting the tsunami flow. In this respect, the performance of numerical codes that analyze tsunami inundation patterns becomes important. The computation of water surface elevation is not sufficient for proper analysis of tsunami behaviour in shallow water zones and on land and hence for the development of mitigation strategies. Velocity and velocity patterns are also crucial parameters and have to be computed at the highest accuracy. There are numerous numerical codes to be used for simulating tsunami inundation. In this study, FLOW 3D and NAMI DANCE codes are selected for validation and performance comparison. Flow 3D simulates linear and nonlinear propagating surface waves as well as long waves by solving three-dimensional Navier-Stokes (3D-NS) equations. FLOW 3D is used specificaly for flood problems. NAMI DANCE uses finite difference computational method to solve linear and nonlinear forms of shallow water equations (NSWE) in long wave problems, specifically tsunamis. In this study, these codes are validated and their performances are compared using two benchmark problems which are discussed in 2015 National Tsunami Hazard Mitigation Program (NTHMP) Annual meeting in Portland, USA. One of the problems is an experiment of a single long-period wave propagating up a piecewise linear slope and onto a small-scale model of the town of Seaside, Oregon. Other benchmark problem is an experiment of a single solitary wave propagating up a triangular shaped shelf with an island feature located at the offshore point of the shelf. The computed water surface elevation and velocity data are compared with the measured data. The comparisons showed that both codes are in fairly good agreement with each other and benchmark data. All results are presented with discussions and comparisons. The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement No 603839 (Project ASTARTE - Assessment, Strategy and Risk Reduction for Tsunamis in Europe)

Molecular Genetics of Root Thigmoresponsiveness in Arabidopsis thaliana

NASA Technical Reports Server (NTRS)

Masson, Patrick H.

2002-01-01

The molecular mechanisms that allow plant roots to use gravity and touch as growth guides are investigated. We are using a molecular genetic strategy in Arabidopsis thaliana to study these processes. When Arabidopsis thaliana seedlings grow on tilted hard-agar surfaces, their roots develop a wavy pattern of growth which appears to derive from a succession of left-handed and right-handed circumnutation-like processes triggered by gravity and touch stimulation (Okada and Shimura, 1990; Rutherford et al., 1998; Rutherford and Masson, 1996). Interestingly, mutations that affect root waving on tilted hard-agar surfaces can be identified and characterized. Some of these mutations affect root gravitropism, while others appear to be responsible for the production of abnormal waves (no waves, compressed or square waves, coils) without affecting gravitropism. The specific objectives of this project were to functionally characterize two genes (WVD2 and WVD6) which are required for root waving on tilted agar surfaces, but not for root gravitropism. Specific objectives included a physiological and cytological analysis of the mutants, and molecular cloning and characterization of the corresponding genes. As summarized in this paper, we have reached these objectives. We have also identified and partially characterized other mutations that affect root skewing on hard-agar surfaces (sku5-1 and ago1), and have completed our work on the root-wave phenotype associated with mutations in genes of the tryptophan biosynthesis pathway (Lynn et al., 1999; Rutherford et al., 1998; Sedbrook et al., 2000, 2002). We briefly describe our progress on the cloning and characterization of WVD6, WVD2 and SKU5, and provide a list of papers (published, or in preparation) that derived from this grant. We also discuss the biological implications of our findings, with special emphasis on the analysis of WVD2.

On the Effect of Rigid Swept Surface Waves on Turbulent Drag

NASA Technical Reports Server (NTRS)

Denison, M.; Wilkinson, S. P.; Balakumar, P.

2015-01-01

Passive turbulent drag reduction techniques are of interest as a cost effective means to improve air vehicle fuel consumption. In the past, rigid surface waves slanted at an angle from the streamwise direction were deemed ineffective to reduce skin friction drag due to the pressure drag that they generate. A recent analysis seeking similarities to the spanwise shear stress generated by spatial Stokes layers suggested that there may be a range of wavelength, amplitude, and orientation in which the wavy surface would reduce turbulent drag. The present work explores, by experiments and Direct Numerical Simulations (DNS), the effect of swept wavy surfaces on skin friction and pressure drag. Plates with shallow and deep wave patterns were rapid-prototyped and tested using a drag balance in the 7x11 inch Low-Speed Wind Tunnel at the NASA LaRC Research Center. The measured drag o set between the wavy plates and the reference at plate is found to be within the experimental repeatability limit. Oil vapor flow measurements indicate a mean spanwise flow over the deep waves. The turbulent flow in channels with at walls, swept wavy walls and spatial Stokes spanwise velocity forcing was simulated at a friction Reynolds number of two hundred. The time-averaged and dynamic turbulent flow characteristics of the three channel types are compared. The drag obtained for the channel with shallow waves is slightly larger than for the at channel, within the range of the experiments. In the case of the large waves, the simulation over predicts the drag. The shortcomings of the Stokes layer analogy model for the estimation of the spanwise shear stress and drag are discussed.

Baja California, Mexico

NASA Technical Reports Server (NTRS)

1989-01-01

Sunglint on the surface of the Sea of Cortez near the island of Tiburon (28.5 N, 112.5W) reveals intricate patterns of internal waves under the placid surface. Mexico's state of Sonora and the Sonora Desert is on the mainland and the state of Baja California consists of the entire peninsula. The large bay on the Pacific side of Baja is Laguna Ojo de Libre (Bay of Whales) which is a breeding area for the Pacific Grey Whales.

Thirty-four years of Hawaii wave hindcast from downscaling of climate forecast system reanalysis

NASA Astrophysics Data System (ADS)

Li, Ning; Cheung, Kwok Fai; Stopa, Justin E.; Hsiao, Feng; Chen, Yi-Leng; Vega, Luis; Cross, Patrick

2016-04-01

The complex wave climate of Hawaii includes a mix of seasonal swells and wind waves from all directions across the Pacific. Numerical hindcasting from surface winds provides essential space-time information to complement buoy and satellite observations for studies of the marine environment. We utilize WAVEWATCH III and SWAN (Simulating WAves Nearshore) in a nested grid system to model basin-wide processes as well as high-resolution wave conditions around the Hawaiian Islands from 1979 to 2013. The wind forcing includes the Climate Forecast System Reanalysis (CFSR) for the globe and downscaled regional winds from the Weather Research and Forecasting (WRF) model. Long-term in-situ buoy measurements and remotely-sensed wind speeds and wave heights allow thorough assessment of the modeling approach and data products for practical application. The high-resolution WRF winds, which include orographic and land-surface effects, are validated with QuickSCAT observations from 2000 to 2009. The wave hindcast reproduces the spatial patterns of swell and wind wave events detected by altimeters on multiple platforms between 1991 and 2009 as well as the seasonal variations recorded at 16 offshore and nearshore buoys around the Hawaiian Islands from 1979 to 2013. The hindcast captures heightened seas in interisland channels and around prominent headlands, but tends to overestimate the heights of approaching northwest swells and give lower estimates in sheltered areas. The validated high-resolution hindcast sets a baseline for future improvement of spectral wave models.

Ultrasonic Surface Measurements for the investigation of superficial alteration of natural stones

NASA Astrophysics Data System (ADS)

Meier, Thomas; Auras, Michael; Bilgili, Filiz; Christen, Sandra; Cristiano, Luigia; Krompholz, Rolf; Mosca, Ilaria; Rose, David

2013-04-01

Seismic waveform analysis is applicable also to the centimeter and decimeter scale for non-destructive testing of pavement, facades, plaster, sculptures, or load-bearing structures like pillars. Mostly transmission measurements are performed and travel-times of first arriving P-waves are considered that have limited resolution for the upper centimeters of an object. In contrast, surface measurements are well suited to quantify superficial alterations of material properties e.g. due to weathering. A number of surface measurements have been carried out in the laboratory as well as on real structures in order to study systematically the information content of ultrasonic waveforms and their variability under real conditions. As a preposition for ultrasonic waveform analysis, reproducible, broad-band measurements have to be carried out with a definite radiation pattern and an about 1 mm accuracy of the measurement geometry. We used special coupling devices for effective ultrasonic surface measurements in the laboratory as well as at real objects. Samples of concrete with varying composition and samples of natural stone - marble, tuff, and sandstone - were repeatedly weathered and tested by ultrasonic measurements. The resistance of the samples to weathering and the penetration depth of the weathering are analyzed. Furthermore, material specific calibration curves for changes in velocities of elastic waves due to weathering can be obtained by these tests. Tests on real structures have been carried out for marble (Schlossbrücke, Berlin) and sandstone (Porta Nigra, Trier). Altogether, these test measurements show clearly that despite of the internal inhomogeneity of many real objects, their surface roughness and topography especially ultrasonic Rayleigh waves are well suited to study material alterations in the upper centimeters. Dispersion of Rayleigh waves may be inverted for shear-wave velocity as a function of depth.

A Mechanism for Land-Atmosphere Feedback Involving Planetary Wave Structures

NASA Technical Reports Server (NTRS)

Koster, Randal D.; Chang, Yehui; Schubert, Siegfried D.

2014-01-01

While the ability of land surface conditions to influence the atmosphere has been demonstrated in various modeling and observational studies, the precise mechanisms by which land-atmosphere feedback occurs are still largely unknown particularly the mechanisms that allow land moisture state in one region to affect atmospheric conditions in another. Such remote impacts are examined here in the context of atmospheric general circulation model (AGCM) simulations, leading to the identification of one potential mechanism: the phase-locking and amplification of a planetary wave through the imposition of a spatial pattern of soil moisture at the land surface. This mechanism, shown here to be relevant in the AGCM, apparently also operates in nature, as suggested by supporting evidence found in reanalysis data.

Recent advances in particle and droplet manipulation for lab-on-a-chip devices based on surface acoustic waves.

PubMed

Wang, Zhuochen; Zhe, Jiang

2011-04-07

Manipulation of microscale particles and fluid liquid droplets is an important task for lab-on-a-chip devices for numerous biological researches and applications, such as cell detection and tissue engineering. Particle manipulation techniques based on surface acoustic waves (SAWs) appear effective for lab-on-a-chip devices because they are non-invasive, compatible with soft lithography micromachining, have high energy density, and work for nearly any type of microscale particles. Here we review the most recent research and development of the past two years in SAW based particle and liquid droplet manipulation for lab-on-a-chip devices including particle focusing and separation, particle alignment and patterning, particle directing, and liquid droplet delivery.

Analytical coupled-wave model for photonic crystal surface-emitting quantum cascade lasers.

PubMed

Wang, Zhixin; Liang, Yong; Yin, Xuefan; Peng, Chao; Hu, Weiwei; Faist, Jérôme

2017-05-15

An analytical coupled-wave model is developed for surface-emitting photonic-crystal quantum cascade lasers (PhC-QCLs). This model provides an accurate and efficient analysis of full three-dimensional device structure with large-area cavity size. Various laser properties of interest including the band structure, mode frequency, cavity loss, mode intensity profile, and far field pattern (FFP), as well as their dependence on PhC structures and cavity size, are investigated. Comparison with numerical simulations confirms the accuracy and validity of our model. The calculated FFP and polarization profile well explain the previously reported experimental results. In particular, we reveal the possibility of switching the lasing modes and generating single-lobed FFP by properly tuning PhC structures.

Chladni Patterns on Drumheads: A ``Physics of Music'' Experiment

NASA Astrophysics Data System (ADS)

Worland, Randy

2011-01-01

In our "Physics of Music" class for non-science majors, we have developed a laboratory exercise in which students experiment with Chladni sand patterns on drumheads. Chladni patterns provide a kinesthetic, visual, and entertaining way to illustrate standing waves on flat surfaces and are very helpful when making the transition from one-dimensional systems, such as string and wind instruments, to the two-dimensional membranes and plates of the percussion family. Although the sand patterns attributed to Ernst Florens Friedrich Chladni (1756-1827) are often demonstrated for this purpose using metal plates,2-4 the use of drumheads offers several pedagogical and practical advantages in the lab.

Pattern formation for NO+N H3 on Pt(100): Two-dimensional numerical results

NASA Astrophysics Data System (ADS)

Uecker, Hannes

2005-01-01

The Lombardo-Fink-Imbihl model of the NO+NH3 reaction on a Pt(100) surface consists of seven coupled ordinary differential equations (ODE) and shows stable relaxation oscillations with sharp transitions in the relevant temperature range. Here we study numerically the effect of coupling of these oscillators by surface diffusion in two dimensions. We find different types of patterns, in particular phase clusters and standing waves. In models of related surface reactions such clustered solutions are known to exist only under a global coupling through the gas phase. This global coupling is replaced here by relatively fast diffusion of two variables which are kinetically slaved in the ODE. We also compare our simulations with experimental results and discuss some shortcomings of the model.

Surface acoustic wave diffraction driven mechanisms in microfluidic systems.

PubMed

Fakhfouri, Armaghan; Devendran, Citsabehsan; Albrecht, Thomas; Collins, David J; Winkler, Andreas; Schmidt, Hagen; Neild, Adrian

2018-06-26

Acoustic forces arising from high-frequency surface acoustic waves (SAW) underpin an exciting range of promising techniques for non-contact manipulation of fluid and objects at micron scale. Despite increasing significance of SAW-driven technologies in microfluidics, the understanding of a broad range of phenomena occurring within an individual SAW system is limited. Acoustic effects including streaming and radiation force fields are often assumed to result from wave propagation in a simple planar fashion. The propagation patterns of a single SAW emanating from a finite-width source, however, cause a far richer range of physical effects. In this work, we seek a better understanding of the various effects arising from the incidence of a finite-width SAW beam propagating into a quiescent fluid. Through numerical and experimental verification, we present five distinct mechanisms within an individual system. These cause fluid swirling in two orthogonal planes, and particle trapping in two directions, as well as migration of particles in the direction of wave propagation. For a range of IDT aperture and channel dimensions, the relative importance of these mechanisms is evaluated.

Three-dimensional simulations of ground motions in the San Bernardino Valley, California, for hypothetical earthquakes on the San Andreas Fault

USGS Publications Warehouse

Frankel, A.

1993-01-01

Three-dimensional finite difference simulations of elastic waves in the San Bernardino Valley were performed for two hypothetical earthquakes on the San Andreas fault: a point source with moment magnitude M5 and an extended rupture with M6.5. A method is presented for incorporating a source with arbitrary focal mechanism in the grid. Synthetics from the 3-D simulations are compared with those derived from 2-D (vertical cross section) and 1-D (flat-layered) models. The synthetic seismograms from the 3-D and 2-D simulations exhibit large surface waves produced by conversion of incident S waves at the edge of the basin. Seismograms from the flat-layered model do not contain these converted surface waves and underestimate the duration of shaking. Maps of maximum ground velocities occur in localized portions of the basin. The location of the largest velocities changes with the rupture propagation direction. Contours of maximum shaking are also dependent on asperity positions and radiation pattern. -from Author

Application of RMS for damage detection by guided elastic waves

NASA Astrophysics Data System (ADS)

Radzieński, M.; Doliński, Ł.; Krawczuk, M.; dot Zak, A.; Ostachowicz, W.

2011-07-01

This paper presents certain results of an experimental study related with a damage detection in structural elements based on deviations in guided elastic wave propagation patterns. In order to excite guided elastic waves within specimens tested piezoelectric transducers have been applied. As excitation signals 5 sine cycles modulated by Hanning window have been used. Propagation of guided elastic waves has been monitored by a scanning Doppler laser vibrometer. The time signals recorded during measurement have been utilised to calculate the values of RMS. It has turned out that the values of RMS differed significantly in damaged areas from the values calculated for the healthy ones. In this way it has become possible to pinpoint precisely the locations of damage over the entire measured surface. All experimental investigations have been carried out for thin aluminium or composite plates. Damage has been simulated by a small additional mass attached on the plate surface or by a narrow notch cut. It has been shown that proposed method allows one to localise damage of various shapes and sizes within structural elements over the whole area under investigation.

Standing waves, clustering, and phase waves in 1D simulations of kinetic relaxation oscillations in NO+NH 3 on Pt(1 0 0) coupled by diffusion

NASA Astrophysics Data System (ADS)

Uecker, Hannes

2004-04-01

The Lombardo-Imbihl-Fink (LFI) ODE model of the NO+NH 3 reaction on a Pt(1 0 0) surface shows stable relaxation oscillations with very sharp transitions for temperatures T between 404 and 433 K. Here we study numerically the effect of linear diffusive coupling of these oscillators in one spatial dimension. Depending on the parameters and initial conditions we find a rich variety of spatio-temporal patterns which we group into four main regimes: bulk oscillations (BOs), standing waves (SW), phase clusters (PC), and phase waves (PW). Two key ingredients for SW and PC are identified, namely the relaxation type of the ODE oscillations and a nonlocal (and nonglobal) coupling due to relatively fast diffusion of the kinetically slaved variables NH 3 and H. In particular, the latter replaces the global coupling through the gas phase used to obtain SW and PC in models of related surface reactions. The PW exist only under the assumption of (relatively) slow diffusion of NH 3 and H.

Chemical waves in the O2 + H2 reaction on a Rh(111) surface alloyed with nickel. I. Photoelectron emission microscopy

NASA Astrophysics Data System (ADS)

Smolinsky, Tim; von Boehn, Bernhard; Imbihl, Ronald

2018-04-01

Chemical waves that arise in the H2 + O2 reaction on a bimetallic Rh(111)/Ni surface have been studied in the 10-6 and 10-5 mbar range at T = 773 K with photoelectron emission microscopy (PEEM), low-energy electron diffraction (LEED), and Auger electron spectroscopy (AES). Nickel coverages of 0.3, 0.6, and 1.0 monolayers were investigated. Coadsorbed with some oxygen, Ni starts to penetrate the Rh bulk region substantially only beyond 900 K. In the 10-5 mbar range, chemical waves are characterized by three distinct gray levels in PEEM. This number reduces to only two levels in the 10-6 mbar range. In situ LEED showed the periodic appearance of a (n × 1) (n = 8, 10) pattern during chemical waves which was assigned to a 2D-Ni oxide. With in situ AES, one observes that the bright phase in PEEM correlates with a high Ni coverage and the dark phase with a low Ni coverage.

Recording polarization gratings with a standing spiral wave

NASA Astrophysics Data System (ADS)

Vernon, Jonathan P.; Serak, Svetlana V.; Hakobyan, Rafik S.; Aleksanyan, Artur K.; Tondiglia, Vincent P.; White, Timothy J.; Bunning, Timothy J.; Tabiryan, Nelson V.

2013-11-01

A scalable and robust methodology for writing cycloidal modulation patterns of optical axis orientation in photosensitive surface alignment layers is demonstrated. Counterpropagating circularly polarized beams, generated by reflection of the input beam from a cholesteric liquid crystal, direct local surface orientation in a photosensitive surface. Purposely introducing a slight angle between the input beam and the photosensitive surface normal introduces a grating period/orientation that is readily controlled and templated. The resulting cycloidal diffractive waveplates offer utility in technologies requiring diffraction over a broad range of angles/wavelengths. This simple methodology of forming polarization gratings offers advantages over conventional fabrication techniques.

Enhanced Sensitivity of Wireless Chemical Sensor Based on Love Wave Mode

NASA Astrophysics Data System (ADS)

Wang, Wen; Oh, Haekwan; Lee, Keekeun; Yang, Sangsik

2008-09-01

A 440 MHz wireless and passive Love-wave-based chemical sensor was developed for CO2 detection. The developed device was composed of a reflective delay line patterned on 41° YX LiNbO3 piezoelectric substrate, a poly(methyl methacrylate) (PMMA) waveguide layer, and Teflon AF 2400 sensitive film. A theoretical model is presented to describe wave propagation in Love wave devices with large piezoelectricity and to allow the design of an optimized structure. In wireless device testing using a network analyzer, infusion of CO2 into the testing chamber induced large phase shifts of the reflection peaks owing to the interaction between the sensing film and the test gas (CO2). Good linearity and repeatability were observed at CO2 concentrations of 0-350 ppm. The obtained sensitivity from the Love wave device was approximately 7.07° ppm-1. The gas response properties of the fabricated Love-wave sensor in terms of linearity and sensitivity were provided, and a comparison to surface acoustic wave devices was also discussed.

Parameter-free determination of the exchange constant in thin films using magnonic patterning

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

Langer, M.; Wagner, K.; Fassbender, J.

2016-03-07

An all-electrical method is presented to determine the exchange constant of magnetic thin films using ferromagnetic resonance. For films of 20 nm thickness and below, the determination of the exchange constant A, a fundamental magnetic quantity, is anything but straightforward. Among others, the most common methods are based on the characterization of perpendicular standing spin-waves. These approaches are however challenging, due to (i) very high energies and (ii) rather small intensities in this thickness regime. In the presented approach, surface patterning is applied to a permalloy (Ni{sub 80}Fe{sub 20}) film and a Co{sub 2}Fe{sub 0.4}Mn{sub 0.6}Si Heusler compound. Acting as amore » magnonic crystal, such structures enable the coupling of backward volume spin-waves to the uniform mode. Subsequent ferromagnetic resonance measurements give access to the spin-wave spectra free of unquantifiable parameters and, thus, to the exchange constant A with high accuracy.« less

Coastal loading and transport of Escherichia coli at an embayed beach in Lake Michigan

USGS Publications Warehouse

Ge, Z.; Nevers, M.B.; Schwab, D.J.; Whitman, R.L.

2010-01-01

A Chicago beach in southwest Lake Michigan was revisited to determine the influence of nearshore hydrodynamic effects on the variability of Escherichia coli (E. coli) concentration in both knee-deep and offshore waters. Explanatory variables that could be used for identifying potential bacteria loading mechanisms, such as bed shear stress due to a combined wave-current boundary layer and wave runup on the beach surface, were derived from an existing wave and current database. The derived hydrodynamic variables, along with the actual observed E. coli concentrations in the submerged and foreshore sands, were expected to reveal bacteria loading through nearshore sediment resuspension and swash on the beach surface, respectively. Based on the observation that onshore waves tend to result in a more active hydrodynamic system at this embayed beach, multiple linear regression analysis of onshore-wave cases further indicated the significance of sediment resuspension and the interaction of swash with gull-droppings in explaining the variability of E. coli concentration in the knee-deep water. For cases with longshore currents, numerical simulations using the Princeton Ocean Model revealed current circulation patterns inside the embayment, which can effectively entrain bacteria from the swash zone into the central area of the embayed beach water and eventually release them out of the embayment. The embayed circulation patterns are consistent with the statistical results that identified that 1) the submerged sediment was an additional net source of E. coli to the offshore water and 2) variability of E. coli concentration in the knee-deep water contributed adversely to that in the offshore water for longshore-current cases. The embayed beach setting and the statistical and numerical methods used in the present study have wide applicability for analyzing recreational water quality at similar marine and freshwater sites. ?? 2010 American Chemical Society.

Apparatus for measuring surface movement of an object that is subjected to external vibrations

DOEpatents

Kotidis, Petros A.; Woodroffe, Jaime A.; Rostler, Peter S.

1997-01-01

A system for non-destructively measuring an object and controlling industrial processes in response to the measurement is disclosed in which an impulse laser generates a plurality of sound waves over timed increments in an object. A polarizing interferometer is used to measure surface movement of the object caused by the sound waves and sensed by phase shifts in the signal beam. A photon multiplier senses the phase shift and develops an electrical signal. A signal conditioning arrangement modifies the electrical signals to generate an average signal correlated to the sound waves which in turn is correlated to a physical or metallurgical property of the object, such as temperature, which property may then be used to control the process. External, random vibrations of the workpiece are utilized to develop discernible signals which can be sensed in the interferometer by only one photon multiplier. In addition the interferometer includes an arrangement for optimizing its sensitivity so that movement attributed to various waves can be detected in opaque objects. The interferometer also includes a mechanism for sensing objects with rough surfaces which produce speckle light patterns. Finally the interferometer per se, with the addition of a second photon multiplier is capable of accurately recording beam length distance differences with only one reading.

Method and apparatus for measuring surface movement of a solid object that is subjected to external vibrations

DOEpatents

Schultz, Thomas J.; Kotidis, Petros A.; Woodroffe, Jaime A.; Rostler, Peter S.

1995-01-01

A system for non-destructively measuring an object and controlling industrial processes in response to the measurement is disclosed in which an impulse laser generates a plurality of sound waves over timed increments in an object. A polarizing interferometer is used to measure surface movement of the object caused by the sound waves and sensed by phase shifts in the signal beam. A photon multiplier senses the phase shift and develops an electrical signal. A signal conditioning arrangement modifies the electrical signals to generate an average signal correlated to the sound waves which in turn is correlated to a physical or metallurgical property of the object, such as temperature, which property may then be used to control the process. External, random vibrations of the workpiece are utilized to develop discernible signals which can be sensed in the interferometer by only one photon multiplier. In addition the interferometer includes an arrangement for optimizing its sensitivity so that movement attributed to various waves can be detected in opaque objects. The interferometer also includes a mechanism for sensing objects with rough surfaces which produce speckle light patterns. Finally the interferometer per se, with the addition of a second photon multiplier is capable of accurately recording beam length distance differences with only one reading.

Method and apparatus for measuring surface movement of an object using a polarizing interfeometer

DOEpatents

Schultz, Thomas J.; Kotidis, Petros A.; Woodroffe, Jaime A.; Rostler, Peter S.

1995-01-01

A system for non-destructively measuring an object and controlling industrial processes in response to the measurement is disclosed in which an impulse laser generates a plurality of sound waves over timed increments in an object. A polarizing interferometer is used to measure surface movement of the object caused by the sound waves and sensed by phase shifts in the signal beam. A photon multiplier senses the phase shift and develops an electrical signal. A signal conditioning arrangement modifies the electrical signals to generate an average signal correlated to the sound waves which in turn is correlated to a physical or metallurgical property of the object, such as temperature, which property may then be used to control the process. External, random vibrations of the workpiece are utilized to develop discernible signals which can be sensed in the interferometer by only one photon multiplier. In addition the interferometer includes an arrangement for optimizing its sensitivity so that movement attributed to various waves can be detected in opaque objects. The interferometer also includes a mechanism for sensing objects with rough surfaces which produce speckle light patterns. Finally the interferometer per se, with the addition of a second photon multiplier is capable of accurately recording beam length distance differences with only one reading.

Method and apparatus for measuring surface movement of an object using a polarizing interferometer

DOEpatents

Schultz, T.J.; Kotidis, P.A.; Woodroffe, J.A.; Rostler, P.S.

1995-05-09

A system for non-destructively measuring an object and controlling industrial processes in response to the measurement is disclosed in which an impulse laser generates a plurality of sound waves over timed increments in an object. A polarizing interferometer is used to measure surface movement of the object caused by the sound waves and sensed by phase shifts in the signal beam. A photon multiplier senses the phase shift and develops an electrical signal. A signal conditioning arrangement modifies the electrical signals to generate an average signal correlated to the sound waves which in turn is correlated to a physical or metallurgical property of the object, such as temperature, which property may then be used to control the process. External, random vibrations of the workpiece are utilized to develop discernible signals which can be sensed in the interferometer by only one photon multiplier. In addition the interferometer includes an arrangement for optimizing its sensitivity so that movement attributed to various waves can be detected in opaque objects. The interferometer also includes a mechanism for sensing objects with rough surfaces which produce speckle light patterns. Finally the interferometer per se, with the addition of a second photon multiplier is capable of accurately recording beam length distance differences with only one reading. 38 figs.

Method and apparatus for measuring surface movement of a solid object that is subjected to external vibrations

DOEpatents

Schultz, T.J.; Kotidis, P.A.; Woodroffe, J.A.; Rostler, P.S.

1995-04-25

A system for non-destructively measuring an object and controlling industrial processes in response to the measurement is disclosed in which an impulse laser generates a plurality of sound waves over timed increments in an object. A polarizing interferometer is used to measure surface movement of the object caused by the sound waves and sensed by phase shifts in the signal beam. A photon multiplier senses the phase shift and develops an electrical signal. A signal conditioning arrangement modifies the electrical signals to generate an average signal correlated to the sound waves which in turn is correlated to a physical or metallurgical property of the object, such as temperature, which property may then be used to control the process. External, random vibrations of the workpiece are utilized to develop discernible signals which can be sensed in the interferometer by only one photon multiplier. In addition the interferometer includes an arrangement for optimizing its sensitivity so that movement attributed to various waves can be detected in opaque objects. The interferometer also includes a mechanism for sensing objects with rough surfaces which produce speckle light patterns. Finally the interferometer per se, with the addition of a second photon multiplier is capable of accurately recording beam length distance differences with only one reading. 38 figs.

Apparatus for measuring surface movement of an object that is subjected to external vibrations

DOEpatents

Kotidis, P.A.; Woodroffe, J.A.; Rostler, P.S.

1997-04-22

A system for non-destructively measuring an object and controlling industrial processes in response to the measurement is disclosed in which an impulse laser generates a plurality of sound waves over timed increments in an object. A polarizing interferometer is used to measure surface movement of the object caused by the sound waves and sensed by phase shifts in the signal beam. A photon multiplier senses the phase shift and develops an electrical signal. A signal conditioning arrangement modifies the electrical signals to generate an average signal correlated to the sound waves which in turn is correlated to a physical or metallurgical property of the object, such as temperature, which property may then be used to control the process. External, random vibrations of the workpiece are utilized to develop discernible signals which can be sensed in the interferometer by only one photon multiplier. In addition the interferometer includes an arrangement for optimizing its sensitivity so that movement attributed to various waves can be detected in opaque objects. The interferometer also includes a mechanism for sensing objects with rough surfaces which produce speckle light patterns. Finally the interferometer per se, with the addition of a second photon multiplier is capable of accurately recording beam length distance differences with only one reading. 38 figs.

Thermal radiation scanning tunnelling microscopy

NASA Astrophysics Data System (ADS)

de Wilde, Yannick; Formanek, Florian; Carminati, Rémi; Gralak, Boris; Lemoine, Paul-Arthur; Joulain, Karl; Mulet, Jean-Philippe; Chen, Yong; Greffet, Jean-Jacques

2006-12-01

In standard near-field scanning optical microscopy (NSOM), a subwavelength probe acts as an optical `stethoscope' to map the near field produced at the sample surface by external illumination. This technique has been applied using visible, infrared, terahertz and gigahertz radiation to illuminate the sample, providing a resolution well beyond the diffraction limit. NSOM is well suited to study surface waves such as surface plasmons or surface-phonon polaritons. Using an aperture NSOM with visible laser illumination, a near-field interference pattern around a corral structure has been observed, whose features were similar to the scanning tunnelling microscope image of the electronic waves in a quantum corral. Here we describe an infrared NSOM that operates without any external illumination: it is a near-field analogue of a night-vision camera, making use of the thermal infrared evanescent fields emitted by the surface, and behaves as an optical scanning tunnelling microscope. We therefore term this instrument a `thermal radiation scanning tunnelling microscope' (TRSTM). We show the first TRSTM images of thermally excited surface plasmons, and demonstrate spatial coherence effects in near-field thermal emission.

Deformation of Tibetan lithosphere and asthenosphere as inferred from broadband surface waves

NASA Astrophysics Data System (ADS)

Agius, Matthew; Lebedev, Sergei

2014-05-01

The numerous seismic stations deployed across Tibet and the surrounding regions in recent years have greatly increased the data coverage across the Plateau. Despite the numerous studies of its crust, however, how the convergence of northward moving India and stable Eurasia is accommodated today is still debated. Regarding the lateral distribution of deformation, end-member models invoke deformation at narrow boundaries between "rigid blocks" and, alternatively, "continuous deformation" with viscous behaviour of the lithosphere. Regarding the vertical distribution of deformation, end-member models include "vertically coherent deformation" within the entire lithospheric thickness, and "channel flow" in which mechanically weak mid-lower crust undergoes flow that is distinctly different from the motions of the (stronger) layers above and below. Broad-band surface waves provide resolving power from the upper crust down to the asthenosphere, for both isotropic-average shear-wave speeds (proxies for composition and temperature) and the radial and azimuthal shear-wave anisotropy (indicative of the patterns of deformation and flow). We measured highly accurate Love- and Rayleigh-wave phase-velocity curves in broad period ranges (5-200 s) for a few tens of pairs and groups of stations across Tibet, combining, in each case, hundreds of inter-station measurements, made with cross-correlation and waveform-inversion methods. Robust shear-velocity profiles were then determined by series of non-linear inversions, yielding depth-dependent ranges of shear speeds and radial anisotropy consistent with the data. Azimuthal anisotropy in the crust and upper mantle was determined by surface-wave tomography and, also, by sub-array analysis targeting the anisotropy amplitude. The Tibetan middle crust is characterised by very low shear-wave speeds, as observed previously, however with strong variations across the plateau. The mid-crustal low-velocity zone, probably indicating partial melt and low viscosity, shows particularly low wave speeds in northern Tibet (3.08-3.43 km/s). The similarity of phase-velocity curves for neighbouring station pairs across large regions within Tibet and the coherent pattern of anisotropy within them suggest that deformation is diffused across broad areas. The maximum extension directions, derived from crustal azimuthal anisotropy, show W-E and NW-SE fast directions in central and eastern Tibet, respectively. The correlation of azimuthal anisotropy with the surface strain indicates that the dominant pattern of deformation in the middle crust is the same as that in the upper crust. Furthermore, the close agreement of anisotropy and the extensional component of the current strain rate field with the traces of sutures implies that the dominant deformation mechanism within the plateau has not changed since the initiation of continental collision and is still governed by the northward push of India. A warm Tibetan lithosphere and asthenosphere lay beneath the north-central and north-eastern plateau. SSW-NNE asthenospheric flow beneath north-eastern Tibet is evidenced by azimuthal anisotropy constrained by our data, with the fast-propagation direction parallel to that of India's plate motion. This suggests that the flow is associated with India's northward subduction beneath the Tibetan lithosphere and asthenosphere under the central and eastern plateau. The distributed, multi-layered azimuthal anisotropy beneath Tibet, with different fast-propagations directions in the crust and asthenospheric mantle, accounts for the complexity of published shear-wave splitting observations.

Root-Growth Behavior of the Arabidopsis Mutant rgr11

PubMed Central

Mullen, Jack L.; Turk, Ed; Johnson, Karin; Wolverton, Chris; Ishikawa, Hideo; Simmons, Carl; Söll, Deiter; Evans, Michael L.

1998-01-01

In this study we investigated the kinetics of the gravitropic response of the Arabidopsis mutant rgr1 (reduced root gravitropism). Although the rate of curvature in rgr1, which is allelic to axr4, was smaller than in the wild type (ecotype Wassilewskija), curvature was initiated in the same region of the root, the distal elongation zone. The time lag for the response was unaffected in the mutant; however, the gravitropic response of rgr1 contained a feature not found in the wild type: when roots growing along the surface of an agar plate were gravistimulated, there was often an upward curvature that initiated in the central elongation zone. Because this response was dependent on the tactile environment of the root, it most likely resulted from the superposition of the waving/coiling phenomenon onto the gravitropic response. We found that the frequency of the waving pattern and circumnutation, a cyclic endogenous pattern of root growth, was the same in rgr1 and in the wild type, so the waving/coiling phenomenon is likely governed by circumnutation patterns. The amplitudes of these oscillations may then be selectively amplified by tactile stimulation to provide a directional preference to the slanting. PMID:9847088

Interfacial instabilities in vibrated fluids

NASA Astrophysics Data System (ADS)

Porter, Jeff; Laverón-Simavilla, Ana; Tinao Perez-Miravete, Ignacio; Fernandez Fraile, Jose Javier

2016-07-01

Vibrations induce a range of different interfacial phenomena in fluid systems depending on the frequency and orientation of the forcing. With gravity, (large) interfaces are approximately flat and there is a qualitative difference between vertical and horizontal forcing. Sufficient vertical forcing produces subharmonic standing waves (Faraday waves) that extend over the whole interface. Horizontal forcing can excite both localized and extended interfacial phenomena. The vibrating solid boundaries act as wavemakers to excite traveling waves (or sloshing modes at low frequencies) but they also drive evanescent bulk modes whose oscillatory pressure gradient can parametrically excite subharmonic surface waves like cross-waves. Depending on the magnitude of the damping and the aspect ratio of the container, these locally generated surfaces waves may interact in the interior resulting in temporal modulation and other complex dynamics. In the case where the interface separates two fluids of different density in, for example, a rectangular container, the mass transfer due to vertical motion near the endwalls requires a counterflow in the interior region that can lead to a Kelvin-Helmholtz type instability and a ``frozen wave" pattern. In microgravity, the dominance of surface forces favors non-flat equilibrium configurations and the distinction between vertical and horizontal applied forcing can be lost. Hysteresis and multiplicity of solutions are more common, especially in non-wetting systems where disconnected (partial) volumes of fluid can be established. Furthermore, the vibrational field contributes a dynamic pressure term that competes with surface tension to select the (time averaged) shape of the surface. These new (quasi-static) surface configurations, known as vibroequilibria, can differ substantially from the hydrostatic state. There is a tendency for the interface to orient perpendicular to the vibrational axis and, in some cases, a bulge or cavity is induced that leads to splitting (fluid separation). We investigate the interaction of these prominent interfacial instabilities in the absence of gravity, concentrating on harmonically vibrated rectangular containers of fluid. We compare vibroequilibria theory with direct numerical simulations and consider the effect of surfaces waves, which can excite sloshing motion of the vibroequilibria. We systematically investigate the saddle-node bifurcation experienced by a symmetric singly connected vibroequilibria solution, for sufficiently deep containers, as forcing is increased. Beyond this instability, the fluid rapidly separates into (at least) two distinct masses. Pronounced hysteresis is associated with this transition, even in the presence of gravity. The interaction of vibroequilibria and frozen waves is investigated in two-fluid systems. Preparations for a parabolic flight experiment on fluids vibrated at high frequencies are discussed.

Mechanism of single-pulse ablative generation of laser-induced periodic surface structures

NASA Astrophysics Data System (ADS)

Shugaev, Maxim V.; Gnilitskyi, Iaroslav; Bulgakova, Nadezhda M.; Zhigilei, Leonid V.

2017-11-01

One of the remarkable capabilities of ultrashort polarized laser pulses is the generation of laser-induced periodic surface structures (LIPSS). The origin of this phenomenon is largely attributed to the interference of the incident laser wave and surface electromagnetic wave that creates a periodic absorption pattern. Although, commonly, LIPSS are produced by repetitive irradiation of the same area by multiple laser pulses in the regime of surface melting and resolidification, recent reports demonstrate the formation of LIPSS in the single-pulse irradiation regime at laser fluences well above the ablation threshold. In this paper, we report results of a large-scale molecular dynamics simulation aimed at providing insights into the mechanisms of single-pulse ablative LIPSS formation. The simulation performed for a Cr target reveals an interplay of material removal and redistribution in the course of spatially modulated ablation, leading to the transient formation of an elongated liquid wall extending up to ˜600 nm above the surface of the target at the locations of the minima of the laser energy deposition. The upper part of the liquid wall disintegrates into droplets while the base of the wall solidifies on the time scale of ˜2 ns, producing a ˜100 -nm-tall frozen surface feature extending above the level of the initial surface of the target. The properties of the surface region of the target are modified by the presence of high densities of dislocations and vacancies generated due to the rapid and highly nonequilibrium nature of the melting and resolidification processes. The insights into the LIPSS formation mechanisms may help in designing approaches for increasing the processing speed and improving the quality of the laser-patterned periodic surface structures.

Wavelength dependence of picosecond laser-induced periodic surface structures on copper

NASA Astrophysics Data System (ADS)

Maragkaki, Stella; Derrien, Thibault J.-Y.; Levy, Yoann; Bulgakova, Nadezhda M.; Ostendorf, Andreas; Gurevich, Evgeny L.

2017-09-01

The physical mechanisms of the laser-induced periodic surface structures (LIPSS) formation are studied in this paper for single-pulse irradiation regimes. The change in the LIPSS period with wavelength of incident laser radiation is investigated experimentally, using a picosecond laser system, which provides 7-ps pulses in near-IR, visible, and UV spectral ranges. The experimental results are compared with predictions made under the assumption that the surface-scattered waves are involved in the LIPSS formation. Considerable disagreement suggests that hydrodynamic mechanisms can be responsible for the observed pattern periodicity.

Spatial Evolution of Resonant Harmonic Mode Triads in a Blasius Boundary Layer

NASA Technical Reports Server (NTRS)

Davila, Jose B.; King, Rudolph A.

2007-01-01

Blasius boundary layer evolution is studies by means of bicoherence calculations. The layer is acoustically excited at the T-S frequency to provide a controlled transition. Measurements are made using a smooth surface as well as various roughness patterns. The bicoherence calculations are used to determine the extent to which frequency resonant velocity fluctuation waves can participate in energy exchange. The emphasis is on downstream variation of the individual interactions among harmonic modes. A limited picture of the role of quadratic wave interactions is revealed.

Compact Submillimeter-Wave Receivers Made with Semiconductor Nano-Fabrication Technologies

NASA Technical Reports Server (NTRS)

Jung, C.; Thomas, B.; Lee, C.; Peralta, A.; Chattopadhyay, G.; Gill, J.; Cooper, K.; Mehdi, I.

2011-01-01

Advanced semiconductor nanofabrication techniques are utilized to design, fabricate and demonstrate a super-compact, low-mass (<10 grams) submillimeter-wave heterodyne front-end. RF elements such as waveguides and channels are fabricated in a silicon wafer substrate using deep-reactive ion etching (DRIE). Etched patterns with sidewalls angles controlled with 1 deg precision are reported, while maintaining a surface roughness of better than 20 nm rms for the etched structures. This approach is being developed to build compact 2-D imaging arrays in the THz frequency range.

Self-referenced interferometer for cylindrical surfaces.

PubMed

Šarbort, Martin; Řeřucha, Šimon; Holá, Miroslava; Buchta, Zdeněk; Lazar, Josef

2015-11-20

We present a new interferometric method for shape measurement of hollow cylindrical tubes. We propose a simple and robust self-referenced interferometer where the reference and object waves are represented by the central and peripheral parts, respectively, of the conical wave generated by a single axicon lens. The interferogram detected by a digital camera is characterized by a closed-fringe pattern with a circular carrier. The interference phase is demodulated using spatial synchronous detection. The capabilities of the interferometer are experimentally tested for various hollow cylindrical tubes with lengths up to 600 mm.

Quadrupedal gaits in hexapod animals - inter-leg coordination in free-walking adult stick insects.

PubMed

Grabowska, Martyna; Godlewska, Elzbieta; Schmidt, Joachim; Daun-Gruhn, Silvia

2012-12-15

The analysis of inter-leg coordination in insect walking is generally a study of six-legged locomotion. For decades, the stick insect Carausius morosus has been instrumental for unravelling the rules and mechanisms that control leg coordination in hexapeds. We analysed inter-leg coordination in C. morosus that freely walked on straight paths on plane surfaces with different slopes. Consecutive 1.7 s sections were assigned inter-leg coordination patterns (which we call gaits) based on footfall patterns. Regular gaits, i.e. wave, tetrapod or tripod gaits, occurred in different proportions depending on surface slopes. Tetrapod gaits were observed most frequently, wave gaits only occurred on 90 deg inclining slopes and tripod gaits occurred most often on 15 deg declining slopes, i.e. in 40% of the sections. Depending on the slope, 36-66% of the sections were assigned irregular gaits. Irregular gaits were mostly due to multiple stepping by the front legs, which is perhaps probing behaviour, not phase coupled to the middle legs' cycles. In irregular gaits, middle leg and hindleg coordination was regular, related to quadrupedal walk and wave gaits. Apparently, front legs uncouple from and couple to the walking system without compromising middle leg and hindleg coordination. In front leg amputees, the remaining legs were strictly coordinated. In hindleg and middle leg amputees, the front legs continued multiple stepping. The coordination of middle leg amputees was maladapted, with front legs and hindlegs performing multiple steps or ipsilateral legs being in simultaneous swing. Thus, afferent information from middle legs might be necessary for a regular hindleg stepping pattern.

Retinal Wave Patterns Are Governed by Mutual Excitation among Starburst Amacrine Cells and Drive the Refinement and Maintenance of Visual Circuits

PubMed Central

Xu, Hong-Ping; Burbridge, Timothy J.; Ye, Meijun; Chen, Minggang; Ge, Xinxin; Zhou, Z. Jimmy

2016-01-01

Retinal waves are correlated bursts of spontaneous activity whose spatiotemporal patterns are critical for early activity-dependent circuit elaboration and refinement in the mammalian visual system. Three separate developmental wave epochs or stages have been described, but the mechanism(s) of pattern generation of each and their distinct roles in visual circuit development remain incompletely understood. We used neuroanatomical, in vitro and in vivo electrophysiological, and optical imaging techniques in genetically manipulated mice to examine the mechanisms of wave initiation and propagation and the role of wave patterns in visual circuit development. Through deletion of β2 subunits of nicotinic acetylcholine receptors (β2-nAChRs) selectively from starburst amacrine cells (SACs), we show that mutual excitation among SACs is critical for Stage II (cholinergic) retinal wave propagation, supporting models of wave initiation and pattern generation from within a single retinal cell type. We also demonstrate that β2-nAChRs in SACs, and normal wave patterns, are necessary for eye-specific segregation. Finally, we show that Stage III (glutamatergic) retinal waves are not themselves necessary for normal eye-specific segregation, but elimination of both Stage II and Stage III retinal waves dramatically disrupts eye-specific segregation. This suggests that persistent Stage II retinal waves can adequately compensate for Stage III retinal wave loss during the development and refinement of eye-specific segregation. These experiments confirm key features of the “recurrent network” model for retinal wave propagation and clarify the roles of Stage II and Stage III retinal wave patterns in visual circuit development. SIGNIFICANCE STATEMENT Spontaneous activity drives early mammalian circuit development, but the initiation and patterning of activity vary across development and among modalities. Cholinergic “retinal waves” are initiated in starburst amacrine cells and propagate to retinal ganglion cells and higher-order visual areas, but the mechanism responsible for creating their unique and critical activity pattern is incompletely understood. We demonstrate that cholinergic wave patterns are dictated by recurrent connectivity within starburst amacrine cells, and retinal ganglion cells act as “readouts” of patterned activity. We also show that eye-specific segregation occurs normally without glutamatergic waves, but elimination of both cholinergic and glutamatergic waves completely disrupts visual circuit development. These results suggest that each retinal wave pattern during development is optimized for concurrently refining multiple visual circuits. PMID:27030771

Autogenic and Allogenic: Emergent Coastline Patterns Interact With Forcing Variations

NASA Astrophysics Data System (ADS)

Murray, A. B.; Alvarez Antolinez, J. A.; Mendez, F. J.; Moore, L. J.; Wood, J.; Farley, G.

2017-12-01

A range of coastline shapes can emerge from large-scale morphodynamic interactions. Coastline shape determines local wave influences. Local wave influences (fluxes of alongshore momentum), determine sediment fluxes, and gradients in these sediment fluxes, in turn, alter coastline shape. Modeling studies show that such feedbacks lead to an instability, and to subsequent finite-amplitude interactions, producing self-organized patterns and emergent structures including sandwaves, capes, and spits (e.g. Ashton and Murray, 2006; Ashton et al., 2015); spiral bays on rocky coastlines (e.g. Barkwith et al., 2014); and convex, spit-bounded coastlines (Ells et al., in prep.). Coastline shapes depend sensitively on wave climate, defined as the angular distribution of wave influences on alongshore sediment transport. Therefore, shifts in wave climate arising from shifts in storms (decadal scale fluctuations or longer-term trends) will tend to change coastline shape. Previous efforts have detected changing coastline shape, likely related to changing influence from hurricane-generated waves, as expressed in changes in the location and intensity of coastal erosion zones along the cuspate capes in North Carolina, USA (Moore et al., 2013). These efforts involved the assumption that coastline response to changing forcing occurs in a quasi-equilibrium manner. However, in some cases coastline responses can exhibit long-term memory and path dependence (Thomas et al., 2016). Recently, we have hindcast the wave climate affecting the North Carolina coast since 1870, using a series of statistical analyses to downscale from basin-scale surface pressure fields to regional deep-water wave climate, and then a numerical transformation to local offshore wave climate. We used this wave climate as input for the Coastline Evolution Model (CEM). The results show that the emergent coastline features respond to decadal-scale shifts in wave climate, but with time lags that complicate the relationship between forcing and coastline shape. Comparisons between model predictions and observed shoreline-change patterns support the suggestion that the relationship between emergent coastline behaviours (autogenic processes) and external influences (autogenic forcing) involves such memory effects (Antolinez et al., in revision).

Bandwidth broadening of a graphene-based circular polarization converter by phase compensation.

PubMed

Gao, Xi; Yang, Wanli; Cao, Weiping; Chen, Ming; Jiang, Yannan; Yu, Xinhua; Li, Haiou

2017-10-02

We present a broadband tunable circular polarization converter composed of a single graphene sheet patterned with butterfly-shaped holes, a dielectric spacer, and a 7-layer graphene ground plane. It can convert a linearly polarized wave into a circularly polarized wave in reflection mode. The polarization converter can be dynamically tuned by varying the Fermi energy of the single graphene sheet. Furthermore, the 7-layer graphene acting as a ground plane can modulate the phase of its reflected wave by controlling the Femi energy, which provides constructive interference condition at the surface of the single graphene sheet in a broad bandwidth and therefore significantly broadens the tunable bandwidth of the proposed polarization converter.

EASI - EQUILIBRIUM AIR SHOCK INTERFERENCE

NASA Technical Reports Server (NTRS)

Glass, C. E.

1994-01-01

New research on hypersonic vehicles, such as the National Aero-Space Plane (NASP), has raised concerns about the effects of shock-wave interference on various structural components of the craft. State-of-the-art aerothermal analysis software is inadequate to predict local flow and heat flux in areas of extremely high heat transfer, such as the surface impingement of an Edney-type supersonic jet. EASI revives and updates older computational methods for calculating inviscid flow field and maximum heating from shock wave interference. The program expands these methods to solve problems involving the six shock-wave interference patterns on a two-dimensional cylindrical leading edge with an equilibrium chemically reacting gas mixture (representing, for example, the scramjet cowl of the NASP). The inclusion of gas chemistry allows for a more accurate prediction of the maximum pressure and heating loads by accounting for the effects of high temperature on the air mixture. Caloric imperfections and specie dissociation of high-temperature air cause shock-wave angles, flow deflection angles, and thermodynamic properties to differ from those calculated by a calorically perfect gas model. EASI contains pressure- and temperature-dependent thermodynamic and transport properties to determine heating rates, and uses either a calorically perfect air model or an 11-specie, 7-reaction reacting air model at equilibrium with temperatures up to 15,000 K for the inviscid flowfield calculations. EASI solves the flow field and the associated maximum surface pressure and heat flux for the six common types of shock wave interference. Depending on the type of interference, the program solves for shock-wave/boundary-layer interaction, expansion-fan/boundary-layer interaction, attaching shear layer or supersonic jet impingement. Heat flux predictions require a knowledge (from experimental data or relevant calculations) of a pertinent length scale of the interaction. Output files contain flow-field information for the various shock-wave interference patterns and their associated maximum surface pressure and heat flux predictions. EASI is written in FORTRAN 77 for a DEC VAX 8500 series computer using the VAX/VMS operating system, and requires 75K of memory. The program is available on a 9-track 1600 BPI magnetic tape in DEC VAX BACKUP format. EASI was developed in 1989. DEC, VAX, and VMS are registered trademarks of the Digital Equipment Corporation.

Evolution of wave patterns and temperature field in shock-tube flow

NASA Astrophysics Data System (ADS)

Kiverin, A. D.; Yakovenko, I. S.

2018-05-01

The paper is devoted to the numerical analysis of wave patterns behind a shock wave propagating in a tube filled with a gaseous mixture. It is shown that the flow inside the boundary layer behind the shock wave is unstable, and the way the instability develops fully corresponds to the solution obtained for the boundary layer over a flat plate. Vortical perturbations inside the boundary layer determine the nonuniformity of the temperature field. In turn, exactly these nonuniformities define the way the ignition kernels arise in the combustible mixture after the reflected shock interaction with the boundary layer. In particular, the temperature nonuniformity determines the spatial limitations of probable ignition kernel position relative to the end wall and side walls of the tube. In the case of low-intensity incident shocks the ignition could start not farther than the point of first interaction between the reflected shock wave and roller vortices formed in the process of boundary layer development. Proposed physical mechanisms are formulated in general terms and can be used for interpretation of the experimental data in any systems with a delayed exothermal reaction start. It is also shown that contact surface thickening occurs due to its interaction with Tollmien-Schlichting waves. This conclusion is of importance for understanding the features of ignition in shock tubes operating in the over-tailored regime.

Sediment Transport over a Dredge Pit, Sandy Point Southeast, west flank of the Mississippi River during Summer Upcoast Currents: a Coupled Wave, Current and Sediment Numerical Model

NASA Astrophysics Data System (ADS)

Chaichitehrani, N.; Li, C.; Xu, K.; Bentley, S. J.; Miner, M. D.

2017-12-01

Sandy Point southeast, an elongated sand resource, was dredged in November 2012 to restore Pelican Island, Louisiana. Hydrodynamics and wave propagation patterns along with fluvial sediments from the Mississippi River influence the sediment and bottom boundary layer dynamics over Sandy Point. A state-of-the-art numerical model, Delft3D, was implemented to investigate current variations and wave transformation on Sandy Point as well as sediment transport pattern. Delft3d FLOW and WAVE modules were coupled and validated using WAVCIS and NDBC data. Sediment transport model was run by introducing both bed and river sediments, consisted of mainly mud and a small fraction of sand. A sediment transport model was evaluated for surface sediment concentration using data derived from satellite images. The model results were used to study sediment dynamics and bottom boundary layer characteristics focused on the Sandy Point area during summer. Two contrasting bathymetric configurations, with and without the Sandy Point dredge pit, were used to conduct an experiment on the sediment and bottom boundary layer dynamics. Preliminary model results showed that the presence of the Sandy Point pit has very limited effect on the hydrodynamics and wave pattern at the pit location. Sediments from the Mississippi River outlets, especially in the vicinity of the pit, get trapped in the pit under the easterly to the northeasterly upcoast current which prevails in August. We also examined the wave-induced sediment reworking and river-borne fluvial sediment over Sandy Point. The effect of wind induced orbital velocity increases the bottom shear stress compared to the time with no waves, relatively small wave heights (lower than 1.5 meters) along the deepest part of the pit (about 20 meters) causes little bottom sediment rework during this period. The results showed that in the summertime, river water is more likely the source of sedimentation in the pit.

Tropospheric Waves, Jet Streams, and United States Weather Patterns. Resource Paper No. 11.

ERIC Educational Resources Information Center

Harman, Jay R.

Intended as a supplement to undergraduate college geography courses, this resource paper reviews the mechanism by which surface weather features are linked with the mid-atmospheric circulation within the westerly wind belt. Specifically, vertical atmospheric motions associated with certain aspects of the upper tropospheric flow, including jet…

Experimental investigation of linear and nonlinear wave systems: A quantum chaos approach

NASA Astrophysics Data System (ADS)

Neicu, Toni

2002-09-01

An experimental and numerical study of linear and nonlinear wave systems using methods and ideas developed from quantum chaos is presented. We exploit the analogy of the wave equation for the flexural modes of a thin clover-shaped acoustic plate to the stationary solutions of the Schrodinger wave equation for a quantum clover-shaped billiard, a generic system that has regular and chaotic regions in its phase space. We observed periodic orbits in the spectral properties of the acoustic plate, the first such definitive acoustic experiment. We also solved numerically the linear wave equation of the acoustic plate for the first few hundred eigenmodes. The Fourier transform of the eigenvalues show peaks corresponding to the principal periodic orbits of the classical billiard. The signatures of the periodic orbits in the spectra were unambiguously verified by deforming one edge of the plate and observing that only the peaks corresponding to the orbits that hit this edge changed. The statistical measures of the eigenvalues are intermediate between universal forms for completely integrable and chaotic systems. The density distribution of the eigenfunctions agrees with the Porter-Thomas formula of chaotic systems. The viscosity dependence and effects of nonlinearity on the Faraday surface wave patterns in a stadium geometry were also investigated. The ray dynamics inside the stadium, a paradigm of quantum chaos, is completely chaotic. The majority of the observed patterns of the orbits resemble three eigenstates of the stadium: the bouncing ball, longitudinal, and bowtie patterns. We observed many disordered patterns that increase with the viscosity. The experimental results were analyzed using recent theoretical work that explains the suppression of certain modes. The theory also predicts that the perimeter dissipation is too strong for whispering gallery modes, which contradicts our observations of these modes for a fluid with low viscosity. Novel vortex patterns were observed in a strongly nonlinear, dissipative granular system of vertically vibrated rods. Above a critical packing fraction, moving domains of nearly vertical rods were seen to coexist with horizontal rods. The vertical domains coarsen to form several large vortices, which were driven by the anisotropy and inclination of the rods.

Modeling contact angle hysteresis of a liquid droplet sitting on a cosine wave-like pattern surface.

PubMed

Promraksa, Arwut; Chen, Li-Jen

2012-10-15

A liquid droplet sitting on a hydrophobic surface with a cosine wave-like square-array pattern in the Wenzel state is simulated by using the Surface Evolver to determine the contact angle. For a fixed drop volume, multiple metastable states are obtained at two different surface roughnesses. Unusual and non-circular shape of the three-phase contact line of a liquid droplet sitting on the model surface is observed due to corrugation and distortion of the contact line by structure of the roughness. The contact angle varies along the contact line for each metastable state. The maximum and minimum contact angles among the multiple metastable states at a fixed viewing angle correspond to the advancing and the receding contact angles, respectively. It is interesting to observe that the advancing/receding contact angles (and contact angle hysteresis) are a function of viewing angle. In addition, the receding (or advancing) contact angles at different viewing angles are determined at different metastable states. The contact angle of minimum energy among the multiple metastable states is defined as the most stable (equilibrium) contact angle. The Wenzel model is not able to describe the contact angle along the three-phase contact line. The contact angle hysteresis at different drop volumes is determined. The number of the metastable states increases with increasing drop volume. Drop volume effect on the contact angles is also discussed. Crown Copyright © 2012. Published by Elsevier Inc. All rights reserved.

On near-source earthquake triggering

USGS Publications Warehouse

Parsons, T.; Velasco, A.A.

2009-01-01

When one earthquake triggers others nearby, what connects them? Two processes are observed: static stress change from fault offset and dynamic stress changes from passing seismic waves. In the near-source region (r ??? 50 km for M ??? 5 sources) both processes may be operating, and since both mechanisms are expected to raise earthquake rates, it is difficult to isolate them. We thus compare explosions with earthquakes because only earthquakes cause significant static stress changes. We find that large explosions at the Nevada Test Site do not trigger earthquakes at rates comparable to similar magnitude earthquakes. Surface waves are associated with regional and long-range dynamic triggering, but we note that surface waves with low enough frequency to penetrate to depths where most aftershocks of the 1992 M = 5.7 Little Skull Mountain main shock occurred (???12 km) would not have developed significant amplitude within a 50-km radius. We therefore focus on the best candidate phases to cause local dynamic triggering, direct waves that pass through observed near-source aftershock clusters. We examine these phases, which arrived at the nearest (200-270 km) broadband station before the surface wave train and could thus be isolated for study. Direct comparison of spectral amplitudes of presurface wave arrivals shows that M ??? 5 explosions and earthquakes deliver the same peak dynamic stresses into the near-source crust. We conclude that a static stress change model can readily explain observed aftershock patterns, whereas it is difficult to attribute near-source triggering to a dynamic process because of the dearth of aftershocks near large explosions.

The impact of North Atlantic wind and cyclone trends on European precipitation and significant wave height in the Atlantic.

PubMed

Trigo, Ricardo M; Valente, Maria A; Trigo, Isabel F; Miranda, Pedro M A; Ramos, Alexandre M; Paredes, Daniel; García-Herrera, Ricardo

2008-12-01

An analysis of the frequency of cyclones and surface wind velocity for the Euro-Atlantic sector is performed by means of an objective methodology. Monthly and seasonal trends of cyclones and wind speed magnitude are computed and trends between 1960 and 2000 evaluated. Results reveal a significant frequency decrease (increase) in the western Mediterranean (Greenland and Scandinavia), particularly in December, February, and March. Seasonal and monthly analysis of wind magnitude trends shows similar spatial patterns. We show that these changes in the frequency of low-pressure centers and the associated wind patterns are partially responsible for trends in the significant height of waves. Throughout the extended winter months (October-March), regions with positive (negative) wind magnitude trends, of up to 5 cm/s/year, often correspond to regions of positive (negative) significant wave height trends. The cyclone and wind speed trends computed for January-March are well matched by the corresponding trends in significant wave height, with February being the month with the highest trends (negative south of lat 50 degrees N up to -3 cm/year, and positive up to 5 cm/year just north of Scotland). Trends in European precipitation are assessed using the Climatic Research Unit data set. The results of the assessment emphasize the link with the corresponding tendencies of cyclone frequencies. Finally, it is shown that these changes are associated, to a large extent, with the preferred phases of major large-scale atmospheric circulation modes, particularly with the North Atlantic Oscillation, the eastern Atlantic pattern, and the Scandinavian pattern.

Retinal Wave Patterns Are Governed by Mutual Excitation among Starburst Amacrine Cells and Drive the Refinement and Maintenance of Visual Circuits.

PubMed

Xu, Hong-Ping; Burbridge, Timothy J; Ye, Meijun; Chen, Minggang; Ge, Xinxin; Zhou, Z Jimmy; Crair, Michael C

2016-03-30

Retinal waves are correlated bursts of spontaneous activity whose spatiotemporal patterns are critical for early activity-dependent circuit elaboration and refinement in the mammalian visual system. Three separate developmental wave epochs or stages have been described, but the mechanism(s) of pattern generation of each and their distinct roles in visual circuit development remain incompletely understood. We used neuroanatomical,in vitroandin vivoelectrophysiological, and optical imaging techniques in genetically manipulated mice to examine the mechanisms of wave initiation and propagation and the role of wave patterns in visual circuit development. Through deletion of β2 subunits of nicotinic acetylcholine receptors (β2-nAChRs) selectively from starburst amacrine cells (SACs), we show that mutual excitation among SACs is critical for Stage II (cholinergic) retinal wave propagation, supporting models of wave initiation and pattern generation from within a single retinal cell type. We also demonstrate that β2-nAChRs in SACs, and normal wave patterns, are necessary for eye-specific segregation. Finally, we show that Stage III (glutamatergic) retinal waves are not themselves necessary for normal eye-specific segregation, but elimination of both Stage II and Stage III retinal waves dramatically disrupts eye-specific segregation. This suggests that persistent Stage II retinal waves can adequately compensate for Stage III retinal wave loss during the development and refinement of eye-specific segregation. These experiments confirm key features of the "recurrent network" model for retinal wave propagation and clarify the roles of Stage II and Stage III retinal wave patterns in visual circuit development. Spontaneous activity drives early mammalian circuit development, but the initiation and patterning of activity vary across development and among modalities. Cholinergic "retinal waves" are initiated in starburst amacrine cells and propagate to retinal ganglion cells and higher-order visual areas, but the mechanism responsible for creating their unique and critical activity pattern is incompletely understood. We demonstrate that cholinergic wave patterns are dictated by recurrent connectivity within starburst amacrine cells, and retinal ganglion cells act as "readouts" of patterned activity. We also show that eye-specific segregation occurs normally without glutamatergic waves, but elimination of both cholinergic and glutamatergic waves completely disrupts visual circuit development. These results suggest that each retinal wave pattern during development is optimized for concurrently refining multiple visual circuits. Copyright © 2016 the authors 0270-6474/16/363872-16$15.00/0.

Thin-film Faraday patterns in three dimensions

NASA Astrophysics Data System (ADS)

Richter, Sebastian; Bestehorn, Michael

2017-04-01

We investigate the long time evolution of a thin fluid layer in three spatial dimensions located on a horizontal planar substrate. The substrate is subjected to time-periodic external vibrations in normal and in tangential direction with respect to the plane surface. The governing partial differential equation system of our model is obtained from the incompressible Navier-Stokes equations considering the limit of a thin fluid geometry and using the long wave lubrication approximation. It includes inertia and viscous friction. Numerical simulations evince the existence of persistent spatially complex surface patterns (periodic and quasiperiodic) for certain superpositions of two vertical excitations and initial conditions. Additional harmonic lateral excitations cause deformations but retain the basic structure of the patterns. Horizontal ratchet-shaped forces lead to a controllable lateral movement of the fluid. A Floquet analysis is used to determine the stability of the linearized system.

Surface-Wave Tomographic Studies of the Hudson Bay Lithosphere: Implications for Paleoproterozoic Tectonic Processes and the Assembly of the Canadian Shield

NASA Astrophysics Data System (ADS)

Darbyshire, F. A.

2015-12-01

Hudson Bay is a shallow intracratonic basin that partially conceals the Trans-Hudson Orogen (THO) in northern Canada. The THO is thought to be a Himalayan-scale Paleoproterozoic orogenic event that was an important component of assembly of the Canadian Shield, marking the collision of the Archean Superior and Western Churchill plates. Until recently, only global and continental-scale seismic tomographic models had imaged the upper-mantle structure of the region, giving a broad but relatively low-resolution picture of the thick lithospheric keel. The Hudson Bay Lithospheric Experiment (HuBLE) investigated the present-day seismic structure beneath Hudson Bay and its surroundings, using a distributed broadband seismograph network installed around the periphery of the Bay and complemented by existing permanent and temporary seismographs further afield. This configuration, though not optimal for body-wave studies which use subvertical arrivals, is well-suited to surface wave tomographic techniques, with many paths crossing the Bay. As there is little seismicity in the region around the Canadian Shield, two-station measurements of teleseismic Rayleigh wave phase velocity formed the principal data set for lithospheric studies. The interstation measurements were combined in a linearized tomographic inversion for maps of phase velocity and azimuthal anisotropy at periods of 20-200 s; these maps were then used to calculate a pseudo-3D anisotropic upper-mantle shear-wavespeed model of the region. The model shows thick (~180-260 km), seismically fast lithosphere across the Hudson Bay region, with a near-vertical 'curtain' of lower wavespeeds trending NE-SW across the Bay, likely associated with more juvenile material trapped between the Archean Superior and Churchill continental cores during the THO. The lithosphere is layered, suggesting a 2-stage formation process. Seismic anisotropy patterns vary with depth; a circular pattern in the uppermost mantle wrapping around the Hudson Bay basin is superseded in the lower lithosphere by a pattern that mirrors THO-related structures within the crust; the lower layer thus likely formed when stress patterns related to the THO were still active.

Transition of torque pattern in undulatory locomotion due to wave number variation in resistive force dominated media

NASA Astrophysics Data System (ADS)

Ding, Yang; Ming, Tingyu

2016-11-01

In undulatory locomotion, torque (bending moment) is required along the body to overcome the external forces from environments and bend the body. Previous observations on animals using less than two wavelengths on the body showed such torque has a single traveling wave pattern. Using resistive force theory model and considering the torque generated by external force in a resistive force dominated media, we found that as the wave number (number of wavelengths on the locomotor's body) increases from 0.5 to 1.8, the speed of the traveling wave of torque decreases. When the wave number increases to 2 and greater, the torque pattern transits from a single traveling wave to a two traveling waves and then a complex pattern that consists two wave-like patterns. By analyzing the force distribution and its contribution to the torque, we explain the speed decrease of the torque wave and the pattern transition. This research is partially supported by the Recruitment Program of Global Young Experts (China).

Holographic studies of shock waves within transonic fan rotors

NASA Technical Reports Server (NTRS)

Benser, W. A.; Bailey, E. E.; Gelder, T. F.

1973-01-01

Pulsed laser holographic interferometry has been applied to the detection of shock patterns in the outer span regions of high tip speed transonic rotors. The first holographic approach used ruby laser light reflected from a portion of the centerbody just ahead of the rotor. These holograms showed the bow wave patterns upstream of the rotor and the shock patterns just inside the blade row near the tip. Much of the region of interest was in the shadow of the blade leading edge and could not be visualized. The second holographic approach, on a different rotor, used light transmitted diagonally across the inlet annulus past the centerbody. This approach gave a more extensive view of the region bounded by the blade leading and trailing edges, by the part span shroud and by the blade tip. These holograms showed the passage shock emanating from the blade leading edge and a moderately strong conical shock originating at the intersection of the part span shroud leading edge and the blade suction surface. Reasonable details of the shock patterns were obtained from holograms which were made without extensive rig modifications.

Wave Propagation and Localization via Quasi-Normal Modes and Transmission Eigenchannels

NASA Astrophysics Data System (ADS)

Wang, Jing; Shi, Zhou; Davy, Matthieu; Genack, Azriel Z.

2013-10-01

Field transmission coefficients for microwave radiation between arrays of points on the incident and output surfaces of random samples are analyzed to yield the underlying quasi-normal modes and transmission eigenchannels of each realization of the sample. The linewidths, central frequencies, and transmitted speckle patterns associated with each of the modes of the medium are found. Modal speckle patterns are found to be strongly correlated leading to destructive interference between modes. This explains distinctive features of transmission spectra and pulsed transmission. An alternate description of wave transport is obtained from the eigenchannels and eigenvalues of the transmission matrix. The maximum transmission eigenvalue, τ1 is near unity for diffusive waves even in turbid samples. For localized waves, τ1 is nearly equal to the dimensionless conductance, which is the sum of all transmission eigenvalues, g = Στn. The spacings between the ensemble averages of successive values of lnτn are constant and equal to the inverse of the bare conductance in accord with predictions by Dorokhov. The effective number of transmission eigenvalues Neff determines the contrast between the peak and background of radiation focused for maximum peak intensity. The connection between the mode and channel approaches is discussed.

Wave Propagation and Localization via Quasi-Normal Modes and Transmission Eigenchannels

NASA Astrophysics Data System (ADS)

Wang, Jing; Shi, Zhou; Davy, Matthieu; Genack, Azriel Z.

Field transmission coefficients for microwave radiation between arrays of points on the incident and output surfaces of random samples are analyzed to yield the underlying quasi-normal modes and transmission eigenchannels of each realization of the sample. The linewidths, central frequencies, and transmitted speckle patterns associated with each of the modes of the medium are found. Modal speckle patterns are found to be strongly correlated leading to destructive interference between modes. This explains distinctive features of transmission spectra and pulsed transmission. An alternate description of wave transport is obtained from the eigenchannels and eigenvalues of the transmission matrix. The maximum transmission eigenvalue, τ1 is near unity for diffusive waves even in turbid samples. For localized waves, τ1 is nearly equal to the dimensionless conductance, which is the sum of all transmission eigenvalues, g = Στn. The spacings between the ensemble averages of successive values of lnτn are constant and equal to the inverse of the bare conductance in accord with predictions by Dorokhov. The effective number of transmission eigenvalues Neff determines the contrast between the peak and background of radiation focused for maximum peak intensity. The connection between the mode and channel approaches is discussed.

Multiple-frequency acoustic wave devices for chemical sensing and materials characterization in both gas and liquid phase

DOEpatents

Martin, Stephen J.; Ricco, Antonio J.

1993-01-01

A chemical sensor (1) includes two or more pairs of interdigital electrodes (10) having different periodicities. Each pair is comprised of a first electrode (10a) and a second electrode (10b). The electrodes are patterned on a surface of a piezoelectric substrate (12). Each pair of electrodes may launch and receive various acoustic waves (AW), including a surface acoustic wave (SAW), and may also launch and receive several acoustic plate modes (APMs). The frequencies associated with each are functions of the transducer periodicity as well as the velocity of the particular AW in the chosen substrate material. An AW interaction region (13) exists between each pair of electrodes. Circuitry (20, 40) is used to launch, receive, and monitor the propagation characteristics of the AWs and may be configured in an intermittent measurement fashion or in a continuous measurement fashion. Perturbations to the AW velocity and attenuation are recorded at several frequencies and provide the sensor response.

Island wake produced by Antipodes Islands south of New Zealand

NASA Image and Video Library

1973-12-16

SL4-137-3655 (16 Dec. 1973) --- An island wake produced by the Antipodes Islands in the ocean current south of New Zealand is seen in this photograph taken from the Skylab space station in Earth orbit. A Skylab 4 crewmen took the picture with a hand-held 70mm Hasselblad camera. The bow wave pattern is quite evident and can be used to determine the current speed from the angle of the bow wave if the propagation speed of the surface wave is known. Also, evident is the darker band extending downstream from the island tens of miles. This is the actual wake of the island. The existence of water color differences from within to outside a turbulent island wake may indicate a temperature difference, with cooler water being stirred to the surface in the wake. This temperature difference could be used to drive a thermo-electric type generator to reduce small islands' dependence on imported oil for power generation. Photo credit: NASA

How to Join a Wave: Decision-Making Processes in Shimmering Behavior of Giant Honeybees (Apis dorsata)

PubMed Central

Kastberger, Gerald; Weihmann, Frank; Hoetzl, Thomas; Weiss, Sara E.; Maurer, Michael; Kranner, Ilse

2012-01-01

Shimmering is a collective defence behaviour in Giant honeybees (Apis dorsata) whereby individual bees flip their abdomen upwards, producing Mexican wave-like patterns on the nest surface. Bucket bridging has been used to explain the spread of information in a chain of members including three testable concepts: first, linearity assumes that individual “agent bees” that participate in the wave will be affected preferentially from the side of wave origin. The directed-trigger hypothesis addresses the coincidence of the individual property of trigger direction with the collective property of wave direction. Second, continuity describes the transfer of information without being stopped, delayed or re-routed. The active-neighbours hypothesis assumes coincidence between the direction of the majority of shimmering-active neighbours and the trigger direction of the agents. Third, the graduality hypothesis refers to the interaction between an agent and her active neighbours, assuming a proportional relationship in the strength of abdomen flipping of the agent and her previously active neighbours. Shimmering waves provoked by dummy wasps were recorded with high-resolution video cameras. Individual bees were identified by 3D-image analysis, and their strength of abdominal flipping was assessed by pixel-based luminance changes in sequential frames. For each agent, the directedness of wave propagation was based on wave direction, trigger direction, and the direction of the majority of shimmering-active neighbours. The data supported the bucket bridging hypothesis, but only for a small proportion of agents: linearity was confirmed for 2.5%, continuity for 11.3% and graduality for 0.4% of surface bees (but in 2.6% of those agents with high wave-strength levels). The complimentary part of 90% of surface bees did not conform to bucket bridging. This fuzziness is discussed in terms of self-organisation and evolutionary adaptedness in Giant honeybee colonies to respond to rapidly changing threats such as predatory wasps scanning in front of the nest. PMID:22662123

How to join a wave: decision-making processes in shimmering behavior of Giant honeybees (Apis dorsata).

PubMed

Kastberger, Gerald; Weihmann, Frank; Hoetzl, Thomas; Weiss, Sara E; Maurer, Michael; Kranner, Ilse

2012-01-01

Shimmering is a collective defence behaviour in Giant honeybees (Apis dorsata) whereby individual bees flip their abdomen upwards, producing Mexican wave-like patterns on the nest surface. Bucket bridging has been used to explain the spread of information in a chain of members including three testable concepts: first, linearity assumes that individual "agent bees" that participate in the wave will be affected preferentially from the side of wave origin. The directed-trigger hypothesis addresses the coincidence of the individual property of trigger direction with the collective property of wave direction. Second, continuity describes the transfer of information without being stopped, delayed or re-routed. The active-neighbours hypothesis assumes coincidence between the direction of the majority of shimmering-active neighbours and the trigger direction of the agents. Third, the graduality hypothesis refers to the interaction between an agent and her active neighbours, assuming a proportional relationship in the strength of abdomen flipping of the agent and her previously active neighbours. Shimmering waves provoked by dummy wasps were recorded with high-resolution video cameras. Individual bees were identified by 3D-image analysis, and their strength of abdominal flipping was assessed by pixel-based luminance changes in sequential frames. For each agent, the directedness of wave propagation was based on wave direction, trigger direction, and the direction of the majority of shimmering-active neighbours. The data supported the bucket bridging hypothesis, but only for a small proportion of agents: linearity was confirmed for 2.5%, continuity for 11.3% and graduality for 0.4% of surface bees (but in 2.6% of those agents with high wave-strength levels). The complimentary part of 90% of surface bees did not conform to bucket bridging. This fuzziness is discussed in terms of self-organisation and evolutionary adaptedness in Giant honeybee colonies to respond to rapidly changing threats such as predatory wasps scanning in front of the nest.

Phase-coherent elastic scattering of electromagnetic waves from a random array of resonant dielectric ridges on a dielectric substrate: Weak roughness limit

NASA Astrophysics Data System (ADS)

Danila, B.; McGurn, A. R.

2005-03-01

A theoretical discussion is given of the diffuse scattering of p -polarized electromagnetic waves from a vacuum-dielectric interface characterized by a one-dimensional disorder in the form of parallel, Gaussian shaped, dielectric ridges positioned at random on a planar semi-infinite dielectric substrate. The parameters of the surface roughness are chosen so that the surface is characterized as weakly rough with a low ridge concentration. The emphasis is on phase coherent features in the speckle pattern of light scattered from the surface. These features are determined from the intensity-intensity correlation function of the speckle pattern and are studied as functions of the frequency of light for frequencies near the dielectric frequency resonances of the ridge material. In the first part of the study, the ridges on the substrate are taken to be identical, made from either GaAs, NaF, or ZnS. The substrate for all cases is CdS. In a second set of studies, the heights and widths of the ridges are statistically distributed. The effects of these different types of randomness on the scattering from the random array of dielectric ridges is determined near the dielectric resonance frequency of the ridge material. The work presented is an extension of studies [A. B. McGurn and R. M. Fitzgerald, Phys. Rev. B 65, 155414 (2002)] that originally treated only the differential reflection coefficient of the diffuse scattering of light (not speckle correlation functions) from a system of identical ridges. The object of the present work is to demonstrate the effects of the dielectric frequency resonances of the ridge materials on the phase coherent features found in the speckle patterns of the diffusely scattered light. The dielectric frequency resonances are shown to enhance the observation of the weak localization of electromagnetic surface waves at the random interface. The frequencies treated in this work are in the infrared. Previous weak localization studies have concentrated mainly on the visible and ultraviolet.

Passive tire pressure sensor and method

DOEpatents

Pfeifer, Kent Bryant; Williams, Robert Leslie; Waldschmidt, Robert Lee; Morgan, Catherine Hook

2006-08-29

A surface acoustic wave device includes a micro-machined pressure transducer for monitoring tire pressure. The device is configured having a micro-machined cavity that is sealed with a flexible conductive membrane. When an external tire pressure equivalent to the cavity pressure is detected, the membrane makes contact with ridges on the backside of the surface acoustic wave device. The ridges are electrically connected to conductive fingers of the device. When the detected pressure is correct, selected fingers on the device will be grounded producing patterned acoustic reflections to an impulse RF signal. When the external tire pressure is less than the cavity reference pressure, a reduced reflected signal to the receiver results. The sensor may further be constructed so as to identify itself by a unique reflected identification pulse series.

Passive tire pressure sensor and method

DOEpatents

Pfeifer, Kent Bryant; Williams, Robert Leslie; Waldschmidt, Robert Lee; Morgan, Catherine Hook

2007-09-04

A surface acoustic wave device includes a micro-machined pressure transducer for monitoring tire pressure. The device is configured having a micro-machined cavity that is sealed with a flexible conductive membrane. When an external tire pressure equivalent to the cavity pressure is detected, the membrane makes contact with ridges on the backside of the surface acoustic wave device. The ridges are electrically connected to conductive fingers of the device. When the detected pressure is correct, selected fingers on the device will be grounded producing patterned acoustic reflections to an impulse RF signal. When the external tire pressure is less than the cavity reference pressure, a reduced reflected signal to the receiver results. The sensor may further be constructed so as to identify itself by a unique reflected identification pulse series.

Spall Fracture Patterns for the Heterophase Cu-Al-Ni Alloy in Ultrafine- and Coarse-Grained States Exposed to a Nanosecond Relativistic High-Current Electron Beam

NASA Astrophysics Data System (ADS)

Dudarev, E. F.; Markov, A. B.; Mayer, A. E.; Bakach, G. P.; Tabachenko, A. N.; Kashin, O. A.; Pochivalova, G. P.; Skosyrskii, A. B.; Kitsanov, S. A.; Zhorovkov, M. F.; Yakovlev, E. V.

2013-05-01

A comparative study of spall fracture patterns for the heterophase Cu - 8.45% Al - 5.06% Ni alloy (аt.%) in ultrafine- and coarse-grained states under shock-wave loading using the "SINUS-7" electron accelerator is carried out. For electron energy of 1.4 MeV, pulse duration of 50 ns, and power density of 1.6·1010 W/cm2, the shock wave amplitude was 8 GPa and the strain rate was ~2·105 s-1. It is established that the thickness of the spalled layer increased for both grained structures, and the degree of plastic strain decreased with increasing target thickness. Based on experimental data obtained and results of theoretical calculations, it is demonstrated that the spall strength of ultrafine- and coarse-grained structures is ~3 GPa. The data on the grained structure at different distances from the spall surface and spall fraction patterns and mechanism are presented.

Material fabrication using acoustic radiation forces

DOEpatents

Sinha, Naveen N.; Sinha, Dipen N.; Goddard, Gregory Russ

2015-12-01

Apparatus and methods for using acoustic radiation forces to order particles suspended in a host liquid are described. The particles may range in size from nanometers to millimeters, and may have any shape. The suspension is placed in an acoustic resonator cavity, and acoustical energy is supplied thereto using acoustic transducers. The resulting pattern may be fixed by using a solidifiable host liquid, forming thereby a solid material. Patterns may be quickly generated; typical times ranging from a few seconds to a few minutes. In a one-dimensional arrangement, parallel layers of particles are formed. With two and three dimensional transducer arrangements, more complex particle configurations are possible since different standing-wave patterns may be generated in the resonator. Fabrication of periodic structures, such as metamaterials, having periods tunable by varying the frequency of the acoustic waves, on surfaces or in bulk volume using acoustic radiation forces, provides great flexibility in the creation of new materials. Periodicities may range from millimeters to sub-micron distances, covering a large portion of the range for optical and acoustical metamaterials.

Dynamics in Layer Models of Solid Flame Propagation

NASA Technical Reports Server (NTRS)

Aldushin, A. P.; Bayliss, A.; Matkowsky, B. J.; Gokoglu, S. (Technical Monitor)

2000-01-01

Self-propagating high-temperature synthesis (SHS) is a process in which combustion waves, e.g., "solid flames", which are considered here, are employed to synthesize desired materials. Like many other systems, SHS is a pattern forming system. The problem of describing experimentally observed patterns and of predicting new, as yet unobserved, patterns continues to attract the attention of scientists and mathematicians due to the fundamental significance of the phenomena in combustion in particular, and in nonlinear science in general. Here, we analyze the dynamics of solid flame propagation in a 2D region by considering the region to be composed of parallel, identical layers aligned along the direction of propagation and having thermal contact. Each layer is then described by wave propagation in 1D, with the transverse Laplacian replaced by a term describing heat exchange between neighboring layers. This configuration is the simplest model of a 2D system because it accounts, in a simple way, for the principal feature of the problem, i.e., heat exchange between neighbors in the transverse direction. For simplicity, we describe the situation for two layers. Because the layers are identical, uniformly propagating waves in each layer must be identical, independent of the heat exchange rate alpha. When the Zeldovich number Z exceeds a critical value Z(sub c), which depends on alpha, uniformly propagating waves become unstable. The stability diagram for the two coupled layers reproduces that for the full 2D problem after appropriate identification of parameters in the two problems. Depending on parameter values, we determine three different steady-state dynamical behaviors (though additional behaviors are also expected to occur). The three behaviors are: (i) waves in each layer which pulsate in phase as they propagate, so that together they form a single pulsating propagating wave; (ii) the waves in each layer are no longer identical, and antiphase pulsations occur, with the two waves alternately advancing and receding as they propagate. This wave is the analog of the spinning wave on the surface of a circular cylinder; (iii) finally, there is a region of bistability between the in phase and antiphase waves. with each having its own domain of attraction, so that which of the two behaviors occur depends on the condition of initiation of the wave. The results of our computations indicate a qualitative similarity in the behavior of combustion waves in the layer model and in the full 2D model. Specifically, due to the similarity between the small alpha wave behavior in the layer model and the large diameter behavior in the model of waves on the surface of a cylinder, we are able to predict the behavior of the mean velocity for the waves on the cylinder, where computations of the full problem can be rather difficult. We also compute solutions for three or more layers. The results of our computations prompt us to predict that, while planar uniformly propagating waves are unstable, the wave will be quasiplanar, i.e., the resulting spinning waves have very low amplitude hot spots, and travel with the velocity close to that of the uniformly propagating wave. Such waves may be difficult to distinguish from uniformly propagating waves in experiments. We also find that for both the layer model and full 2D problem, steady-state time-dependent waves, e.g., pulsating and spinning wave, have a conserved quantity H which characterizes the excess energy in the wave, just as in the case of uniformly propagating waves. The quantity H, which is generated by dissipation, does not vary in time and is proportional to the diffusivity and caloricity of the system, and inversely proportional to the mean wave velocity.

Left atrial pressure pattern without a-wave in sinus rhythm after cardioversion affects the outcomes after catheter ablation for atrial fibrillation.

PubMed

Kishima, Hideyuki; Mine, Takanao; Takahashi, Satoshi; Ashida, Kenki; Ishihara, Masaharu; Masuyama, Tohru

2018-04-24

The a-wave in left atrial pressure (LAP) is often not observed after cardioversion (CV). We hypothesized that repeated atrial fibrillation (AF) occurs in patients who do not show a-wave pattern after CV. We investigated the impact of "LAP pattern without a-wave" on the outcome after catheter ablation (CA) for AF. We studied 100 patients (64 males, age 66 ± 8 years, 42 with non-paroxysmal AF) who underwent CA for AF. Sustained- or induced-AF were terminated with internal CV, and LAP was measured during sinus rhythm (SR) after CV. LAP pattern without a-wave was defined as absence of a-wave (the "a-wave" was defined as a protruding part by 0.2 mmHg or more from the baseline) in LAP wave form. AF was terminated with CV in all patients. Recurrent AF was detected in 35/100 (35%) during the follow-up period (13.1 ± 7.8 month). Univariate analysis revealed higher prevalence of LAP pattern without a-wave (71 vs. 17%, P < 0.0001), larger left atrial volume, elevated E wave, and decreased deceleration time as significant variables. On multivariate analysis, LAP pattern without a-wave was only independently associated with recurrent AF (P = 0.0014, OR 9.865, 95% CI 2.327-54.861). Moreover, patients with LAP pattern without a-wave had a higher risk of recurrent AF than patients with a-wave (25/36 patients, 69 vs. 10/64 patients, 16%, log-rank P < 0.0001). Left atrial pressure pattern without a-wave in sinus rhythm after cardioversion could predict recurrence after catheter ablation for AF.

Vibration characteristics of aluminum surface subjected to ultrasonic waves and their effect on wetting behavior of solder droplets.

PubMed

Ma, Lin; Xu, Zhiwu; Zheng, Kun; Yan, Jiuchun; Yang, Shiqin

2014-03-01

The vibration characteristics of an aluminum surface subjected to ultrasonic waves were investigated with a combination of numerical simulation and experimental testing. The wetting behavior of solder droplets on the vibrating aluminum surface was also examined. The results show that the vibration pattern of the aluminum surface is inhomogeneous. The amplitude of the aluminum surface exceeds the excitation amplitude in some zones, while the amplitude decreases nearly to zero in other zones. The distribution of the zero-amplitude zones is much less dependent on the strength of the vibration than on the location of the vibration source. The surface of the liquid solder vibrates at an ultrasonic frequency that is higher than the vibration source, and the amplitude of the liquid solder is almost twice that of the aluminum surface. The vibration of the surface of the base metal (liquid solder) correlates with the oxide film removal effect. Significant removal of the oxide film can be achieved within 2s when the amplitude of the aluminum surface is higher than 5.4 μm or when the amplitude of the liquid solder surface is higher than 10.2 μm. Copyright © 2013 Elsevier B.V. All rights reserved.

Self-calibrated active pyrometer for furnace temperature measurements

DOEpatents

Woskov, Paul P.; Cohn, Daniel R.; Titus, Charles H.; Surma, Jeffrey E.

1998-01-01

Pyrometer with a probe beam superimposed on its field-of-view for furnace temperature measurements. The pyrometer includes a heterodyne millimeter/sub-millimeter-wave or microwave receiver including a millimeter/sub-millimeter-wave or microwave source for probing. The receiver is adapted to receive radiation from a surface whose temperature is to be measured. The radiation includes a surface emission portion and a surface reflection portion which includes the probe beam energy reflected from the surface. The surface emission portion is related to the surface temperature and the surface reflection portion is related to the emissivity of the surface. The simultaneous measurement of surface emissivity serves as a real time calibration of the temperature measurement. In an alternative embodiment, a translatable base plate and a visible laser beam allow slow mapping out of interference patterns and obtaining peak values therefor. The invention also includes a waveguide having a replaceable end portion, an insulating refractory sleeve and/or a source of inert gas flow. The pyrometer may be used in conjunction with a waveguide to form a system for temperature measurements in a furnace. The system may employ a chopper or alternatively, be constructed without a chopper. The system may also include an auxiliary reflector for surface emissivity measurements.

Climatology of Global Swell-Atmosphere Interaction

NASA Astrophysics Data System (ADS)

Semedo, Alvaro

2016-04-01

At the ocean surface wind sea and swell waves coexist. Wind sea waves are locally generated growing waves strongly linked to the overlaying wind field. Waves that propagate away from their generation area, throughout entire ocean basins, are called swell. Swell waves do not receive energy from local wind. Ocean wind waves can be seen as the "gearbox" between the atmosphere and the ocean, and are of critical importance to the coupled atmosphere-ocean system, since they modulate most of the air-sea interaction processes and exchanges, particularly the exchange of momentum. This modulation is most of the times sea-state dependent, i.e., it is a function of the prevalence of one type of waves over the other. The wave age parameter, defined as the relative speed between the peak wave and the wind (c_p⁄U_10), has been largely used in different aspects of the air-sea interaction theory and in practical modeling solutions of wave-atmosphere coupled model systems. The wave age can be used to assess the development of the sea state but also the prevalence (domination) of wind sea or swell waves at the ocean surface. The presence of fast-running waves (swell) during light winds (at high wave age regimes) induces an upward momentum flux, directed from the water surface to the atmosphere. This upward directed momentum has an impact in the lower marine atmospheric boundary layer (MABL): on the one hand it changes the vertical wind speed profile by accelerating the flow at the first few meters (inducing the so called "wave-driven wind"), and on the other hand it changes the overall MABL turbulence structure by limiting the wind shear - in some observed and modeled situations the turbulence is said to have "collapse". The swell interaction with the lower MABL is a function of the wave age but also of the swell steepness, since steeper waves loose more energy into the atmosphere as their energy attenuates. This interaction can be seen as highest in areas where swells are steepest, but also where the wind speed is lowest and consequently the wave age is high. A detailed global climatology of the wave age and swell steepness parameters, based on the ECMWF (European Centre for Medium-Range Weather Forecasts) ERA-Interim reanalysis is presented. It will be shown, in line with previous studies, that the global climatological patterns of the wave age confirm the global dominance of the World Ocean by swell waves. The areas of the ocean where the highest interaction of swell waves and the lower atmosphere can be expected are also presented.

High-order rogue waves of the Benjamin-Ono equation and the nonlocal nonlinear Schrödinger equation

NASA Astrophysics Data System (ADS)

Liu, Wei

2017-10-01

High-order rogue wave solutions of the Benjamin-Ono equation and the nonlocal nonlinear Schrödinger equation are derived by employing the bilinear method, which are expressed by simple polynomials. Typical dynamics of these high-order rogue waves are studied by analytical and graphical ways. For the Benjamin-Ono equation, there are two types of rogue waves, namely, bright rogue waves and dark rogue waves. In particular, the fundamental rogue wave pattern is different from the usual fundamental rogue wave patterns in other soliton equations. For the nonlocal nonlinear Schrödinger equation, the exact explicit rogue wave solutions up to the second order are presented. Typical rogue wave patterns such as Peregrine-type, triple and fundamental rogue waves are put forward. These high-order rogue wave patterns have not been shown before in the nonlocal Schrödinger equation.

Climate change and heat waves in Paris and London metropolitan areas

NASA Astrophysics Data System (ADS)

Dousset, B.

2010-12-01

Summer warming trends in Western and Central Europe and in Mediterranean regions are increasing the incidence, intensity, and duration of heat waves. Those extreme events are especially deadly in large cities, owing to high population densities, surface characteristics, heat island effects, anthropogenic heat and pollutants. In August 2003, a persistent anticyclone over Western Europe generated a heat wave of exceptional strength and duration with an estimated death toll of 70,000, including 4678 in the Paris region. A series of NOAA-AVHRR satellite thermal images over the Paris and London metropolitan areas, were used to analyze Land Surface Temperature (LST) and its related mortality. In the Paris region, LSTs were merged with land use and cover data to identify risk areas, and thermal indicators were produced at the addresses of ~ 500 elderly people to assess diurnal heat exposure. Results indicate: (i) contrasting night time and daytime heat island patterns related to land use and surface characteristics; (ii) the relation between night-time heat islands and heat waves intensity; (iii) the impact of elevated minimal temperatures on excess mortality, with a 0.5 °C increase doubling the risk of death, (in the temperature range of the heatwave); iv) the correlation between the spatial distribution of highest night-time LSTs and that of highest mortality ratios; and v) the significant impact of urban parks in the partitioning between latent and sensible surface heat fluxes, despite a prior warm and dry spring. Near-real time satellite monitoring of heat waves in urban areas improve our understanding of the LST processes and spatial variability, and of the related heat stress and mortality. These observations provide criteria for warning systems, contingency policies and planning, and climate adaptation and mitigation strategies.

Non-invasive localization of atrial ectopic beats by using simulated body surface P-wave integral maps

PubMed Central

Godoy, Eduardo J.; Lozano, Miguel; Martínez-Mateu, Laura; Atienza, Felipe; Saiz, Javier; Sebastian, Rafael

2017-01-01

Non-invasive localization of continuous atrial ectopic beats remains a cornerstone for the treatment of atrial arrhythmias. The lack of accurate tools to guide electrophysiologists leads to an increase in the recurrence rate of ablation procedures. Existing approaches are based on the analysis of the P-waves main characteristics and the forward body surface potential maps (BSPMs) or on the inverse estimation of the electric activity of the heart from those BSPMs. These methods have not provided an efficient and systematic tool to localize ectopic triggers. In this work, we propose the use of machine learning techniques to spatially cluster and classify ectopic atrial foci into clearly differentiated atrial regions by using the body surface P-wave integral map (BSPiM) as a biomarker. Our simulated results show that ectopic foci with similar BSPiM naturally cluster into differentiated non-intersected atrial regions and that new patterns could be correctly classified with an accuracy of 97% when considering 2 clusters and 96% for 4 clusters. Our results also suggest that an increase in the number of clusters is feasible at the cost of decreasing accuracy. PMID:28704537

A highly attenuating and frequency tailorable annular hole phononic crystal for surface acoustic waves.

PubMed

Ash, B J; Worsfold, S R; Vukusic, P; Nash, G R

2017-08-02

Surface acoustic wave (SAW) devices are widely used for signal processing, sensing and increasingly for lab-on-a-chip applications. Phononic crystals can control the propagation of SAW, analogous to photonic crystals, enabling components such as waveguides and cavities. Here we present an approach for the realisation of robust, tailorable SAW phononic crystals, based on annular holes patterned in a SAW substrate. Using simulations and experiments, we show that this geometry supports local resonances which create highly attenuating phononic bandgaps at frequencies with negligible coupling of SAWs into other modes, even for relatively shallow features. The enormous bandgap attenuation is up to an order-of-magnitude larger than that achieved with a pillar phononic crystal of the same size, enabling effective phononic crystals to be made up of smaller numbers of elements. This work transforms the ability to exploit phononic crystals for developing novel SAW device concepts, mirroring contemporary progress in photonic crystals.The control and manipulation of propagating sound waves on a surface has applications in on-chip signal processing and sensing. Here, Ash et al. deviate from standard designs and fabricate frequency tailorable phononic crystals with an order-of-magnitude increase in attenuation.

Surface elastic wave detectors

NASA Technical Reports Server (NTRS)

Lawson, R. L.

1971-01-01

The potential applications of acoustic surface wave technology to multiplex communication systems such as data-bus, are examined. The goals are primarily to characterize certain aspects of surface wave trapped delay lines, surface wave modulation techniques, and surface wave applications that are relevant to the evaluation of surface wave devices in multiplex systems. The results indicate that there is a potential for the application of surface wave technology in data-bus type systems.

Surface wave chemical detector using optical radiation

DOEpatents

Thundat, Thomas G.; Warmack, Robert J.

2007-07-17

A surface wave chemical detector comprising at least one surface wave substrate, each of said substrates having a surface wave and at least one measurable surface wave parameter; means for exposing said surface wave substrate to an unknown sample of at least one chemical to be analyzed, said substrate adsorbing said at least one chemical to be sensed if present in said sample; a source of radiation for radiating said surface wave substrate with different wavelengths of said radiation, said surface wave parameter being changed by said adsorbing; and means for recording signals representative of said surface wave parameter of each of said surface wave substrates responsive to said radiation of said different wavelengths, measurable changes of said parameter due to adsorbing said chemical defining a unique signature of a detected chemical.

View of atmospheric wave patterns by effect of island on wind currents

NASA Image and Video Library

1973-12-14

SL4-137-3632 (February 1974) --- A photograph taken from the Skylab space station in Earth orbit illustrating an atmospheric wave pattern by the affect of a small mountainous island on wind currents. Various patterns can be seen downwind of small islands. Often a Von Karmon vortex can be seen which appears as a spiral pattern. Multiple vortices have been photographed on previous missions. This photograph illustrates a "bow wave" pattern which extends for hundreds of miles downwind from the island. The island itself is often clear when a wave pattern is formed downstream. This particular pattern is very symmetrical. These wave patterns are most common in the South Pacific. This picture was taken by a Skylab 4 crewmen using a hand-held 70mm Hasselblad camera. Photo credit: NASA

Sound recovery via intensity variations of speckle pattern pixels selected with variance-based method

NASA Astrophysics Data System (ADS)

Zhu, Ge; Yao, Xu-Ri; Qiu, Peng; Mahmood, Waqas; Yu, Wen-Kai; Sun, Zhi-Bin; Zhai, Guang-Jie; Zhao, Qing

2018-02-01

In general, the sound waves can cause the vibration of the objects that are encountered in the traveling path. If we make a laser beam illuminate the rough surface of an object, it will be scattered into a speckle pattern that vibrates with these sound waves. Here, an efficient variance-based method is proposed to recover the sound information from speckle patterns captured by a high-speed camera. This method allows us to select the proper pixels that have large variances of the gray-value variations over time, from a small region of the speckle patterns. The gray-value variations of these pixels are summed together according to a simple model to recover the sound with a high signal-to-noise ratio. Meanwhile, our method will significantly simplify the computation compared with the traditional digital-image-correlation technique. The effectiveness of the proposed method has been verified by applying a variety of objects. The experimental results illustrate that the proposed method is robust to the quality of the speckle patterns and costs more than one-order less time to perform the same number of the speckle patterns. In our experiment, a sound signal of time duration 1.876 s is recovered from various objects with time consumption of 5.38 s only.

Upper Mantle Shear Wave Structure Beneath North America From Multi-mode Surface Wave Tomography

NASA Astrophysics Data System (ADS)

Yoshizawa, K.; Ekström, G.

2008-12-01

The upper mantle structure beneath the North American continent has been investigated from measurements of multi-mode phase speeds of Love and Rayleigh waves. To estimate fundamental-mode and higher-mode phase speeds of surface waves from a single seismogram at regional distances, we have employed a method of nonlinear waveform fitting based on a direct model-parameter search using the neighbourhood algorithm (Yoshizawa & Kennett, 2002). The method of the waveform analysis has been fully automated by employing empirical quantitative measures for evaluating the accuracy/reliability of estimated multi-mode phase dispersion curves, and thus it is helpful in processing the dramatically increasing numbers of seismic data from the latest regional networks such as USArray. As a first step toward modeling the regional anisotropic shear-wave velocity structure of the North American upper mantle with extended vertical resolution, we have applied the method to long-period three-component records of seismic stations in North America, which mostly comprise the GSN and US regional networks as well as the permanent and transportable USArray stations distributed by the IRIS DMC. Preliminary multi-mode phase-speed models show large-scale patterns of isotropic heterogeneity, such as a strong velocity contrast between the western and central/eastern United States, which are consistent with the recent global and regional models (e.g., Marone, et al. 2007; Nettles & Dziewonski, 2008). We will also discuss radial anisotropy of shear wave speed beneath North America from multi-mode dispersion measurements of Love and Rayleigh waves.

Density Wave Signatures In VIMS Spectral Data

NASA Astrophysics Data System (ADS)

Nicholson, Philip D.; Hedman, M. M.; Cassini VIMS Team

2012-10-01

Spectral scans of Saturn's rings by the Cassini VIMS instrument have revealed both regional and local variations in the depths of the water ice bands at 1.5 and 2.0 microns, which have been interpreted in terms of variations in regolith grain size and the amount of non-icy "contaminants" (Filacchione et al. 2012; Hedman et al. 2012). Noteworthy among the local variations are distinctive patterns associated with the four strong density waves in the A ring. Within each wavetrain there is a peak in band strength relative to the surrounding material, while extending on both sides of the wave is a "halo" of reduced band strength. The typical width of these haloes is 400-500 km, about 2-3 times the visible extent of the density waves. The origin of these features is unknown, but may involve enhanced collisional erosion in the wave zones and transport of the smaller debris into nearby regions. A similar pattern of band depth variations is also seen at several locations in the more opaque B ring in association with the strong 3:2 ILRs of Janus, Pandora and Prometheus. The former shows a pattern just like its siblings in the A ring, while the latter two resonances show haloes, but without central peaks. In each case, the radial widths of the halo approaches 1000 km, but stellar occultation profiles show no detectable density wavetrain. We suggest that this spectral signature may be a useful diagnostic for the presence of strong density waves in regions where the rings are too opaque for occultations to reveal a typical wave profile. More speculatively, the displacement of the haloes' central radii from the calculated ILR locations of 600-700 km could imply a surface density in the central B ring in excess of 500 g/cm^2. This research was supported by the Cassini/Huygens project.

Direct Femtosecond Laser Surface Structuring with Optical Vortex Beams Generated by a q-plate

PubMed Central

JJ Nivas, Jijil; He, Shutong; Rubano, Andrea; Vecchione, Antonio; Paparo, Domenico; Marrucci, Lorenzo; Bruzzese, Riccardo; Amoruso, Salvatore

2015-01-01

Creation of patterns and structures on surfaces at the micro- and nano-scale is a field of growing interest. Direct femtosecond laser surface structuring with a Gaussian-like beam intensity profile has already distinguished itself as a versatile method to fabricate surface structures on metals and semiconductors. Here we present an approach for direct femtosecond laser surface structuring based on optical vortex beams with different spatial distributions of the state of polarization, which are easily generated by means of a q-plate. The different states of an optical vortex beam carrying an orbital angular momentum ℓ = ±1 are used to demonstrate the fabrication of various regular surface patterns on silicon. The spatial features of the regular rippled and grooved surface structures are correlated with the state of polarization of the optical vortex beam. Moreover, scattered surface wave theory approach is used to rationalize the dependence of the surface structures on the local state of the laser beam characteristics (polarization and fluence). The present approach can be further extended to fabricate even more complex and unconventional surface structures by exploiting the possibilities offered by femtosecond optical vector fields. PMID:26658307

The seasonal march of the equatorial Pacific upper-ocean and its El Niño variability

NASA Astrophysics Data System (ADS)

Gasparin, Florent; Roemmich, Dean

2017-08-01

Based on two modern data sets, the climatological seasonal march of the upper-ocean is examined in the equatorial Pacific for the period 2004-2014, because of its large contribution to the total variance, its relationship to El Niño, and its unique equatorial wave phenomena. Argo provides a broadscale view of the equatorial Pacific upper-ocean based on subsurface temperature and salinity measurements for the period 2004-2015, and satellite altimetry provides synoptic observations of the sea surface height (SSH) for the period 1993-2015. Using either 11-year (1993-2003/2004-2014) time-series for averaging, the seasonal Rossby waves stands out clearly and eastward intraseasonal Kelvin wave propagation is strong enough in individual years to leave residuals in the 11-year averages, particularly but not exclusively, during El Niño onset years. The agreement of altimetric SSH minus Argo steric height (SH) residuals with GRACE ocean mass estimates confirms the scale-matching of in situ variability with that of satellite observations. Surface layer and subsurface thermohaline variations are both important in determining SH and SSH basin-wide patterns. The SH/SSH October-November maximum in the central-eastern Pacific is primarily due to a downward deflection of the thermocline (∼20 m), causing a warm subsurface anomaly (>1 °C), in response to the phasing of downwelling intraseasonal Kelvin and seasonal Rossby waves. Compared with the climatology, the stronger October-November maximum in the 2004-2014 El Niño composites is due to higher intraseasonal oscillations and interannual variability. Associated with these equatorial wave patterns along the thermocline, the western warm/fresh pool waters move zonally at interannual timescales through zonal wind stress and pressure gradient fluctuations, and cause substantial fresh (up to 0.6 psu) and warm (∼1 °C higher than the climatology) anomalies in the western-central Pacific surface-layer during the El Niño onset year, and of the opposite sign during the termination year. These El Niño-related patterns are then analyzed focusing on the case of the onset of the strong 2015/2016 episode, and are seen to be around two times larger than that in the 2004-2014 El Niño composites. The present work exploits the capabilities of Argo and altimetry to update and improve the description of the physical state of the equatorial Pacific upper-ocean, and provides a benchmark for assessing the accuracy of models in representing equatorial Pacific variability.

Impacts of short-time scale water column variability on broadband high-frequency acoustic wave propagation

NASA Astrophysics Data System (ADS)

Eickmeier, Justin

Acoustical oceanography is one way to study the ocean, its internal layers, boundaries and all processes occurring within using underwater acoustics. Acoustical sensing techniques allows for the measurement of ocean processes from within that logistically or financially preclude traditional in-situ measurements. Acoustic signals propagate as pressure wavefronts from a source to a receiver through an ocean medium with variable physical parameters. The water column physical parameters that change acoustic wave propagation in the ocean include temperature, salinity, current, surface roughness, seafloor bathymetry, and vertical stratification over variable time scales. The impacts of short-time scale water column variability on acoustic wave propagation include coherent and incoherent surface reflections, wavefront arrival time delay, focusing or defocusing of the intensity of acoustic beams and refraction of acoustic rays. This study focuses on high-frequency broadband acoustic waves, and examines the influence of short-time scale water column variability on broadband high-frequency acoustics, wavefronts, from 7 to 28 kHz, in shallow water. Short-time scale variability is on the order of seconds to hours and the short-spatial scale variability is on the order of few centimeters. Experimental results were collected during an acoustic experiment along 100 m isobaths and data analysis was conducted using available acoustic wave propagation models. Three main topics are studied to show that acoustic waves are viable as a remote sensing tool to measure oceanographic parameters in shallow water. First, coherent surface reflections forming striation patterns, from multipath receptions, through rough surface interaction of broadband acoustic signals with the dynamic sea surface are analyzed. Matched filtered results of received acoustic waves are compared with a ray tracing numerical model using a sea surface boundary generated from measured water wave spectra at the time of signal propagation. It is determined that on a time scale of seconds, corresponding to typical periods of surface water waves, the arrival time of reflected acoustic signals from surface waves appear as striation patterns in measured data and can be accurately modelled by ray tracing. Second, changes in acoustic beam arrival angle and acoustic ray path influenced by isotherm depth oscillations are analyzed using an 8-element delay-sum beamformer. The results are compared with outputs from a two-dimensional (2-D) parabolic equation (PE) model using measured sound speed profiles (SSPs) in the water column. Using the method of beamforming on the received signal, the arrival time and angle of an acoustic beam was obtained for measured acoustic signals. It is determined that the acoustic ray path, acoustic beam intensity and angular spread are a function of vertical isotherm oscillations on a time scale of minutes and can be modeled accurately by a 2-D PE model. Third, a forward problem is introduced which uses acoustic wavefronts received on a vertical line array, 1.48 km from the source, in the lower part of the water column to infer range dependence or independence in the SSP. The matched filtering results of received acoustic wavefronts at all hydrophone depths are compared with a ray tracing routine augmented to calculate only direct path and bottom reflected signals. It is determined that the SSP range dependence can be inferred on a time scale of hours using an array of hydrophones spanning the water column. Sound speed profiles in the acoustic field were found to be range independent for 11 of the 23 hours in the measurements. A SSP cumulative reconstruction process, conducted from the seafloor to the sea surface, layer-by-layer, identifies critical segments in the SSP that define the ray path, arrival time and boundary interactions. Data-model comparison between matched filtered arrival time spread and arrival time output from the ray tracing was robust when the SSP measured at the receiver was input to the model. When the SSP measured nearest the source (at the same instant in time) was input to the ray tracing model, the data-model comparison was poor. It was determined that the cumulative sound speed change in the SSP near the source was 1.041 m/s greater than that of the SSP at the receiver and resulted in the poor data-model comparison. In this study, the influences on broadband acoustic wave propagation in the frequency range of 7 to 28 kHz of spatial and temporal changes in the oceanography of shallow water regions are addressed. Acoustic waves can be used as remote sensing tools to measure oceanographic parameters in shallow water and data-model comparison results show a direct relationship between the oceanographic variations and acoustic wave propagations.

Out-of-plane stretching for simultaneous generation of different morphological wrinkles on a soft matter

NASA Astrophysics Data System (ADS)

Li, Xin; Zhao, Zhi-Jun; Park, Sang-Hu

2016-07-01

This study demonstrates a simple and flexible out-of-plane induced mechanical stretching method for generating labyrinthic, waving, and straight orderly microscale directional wrinkles. Different complex wrinkling patterns were fabricated simultaneously using a UV-curable thin layer of resin NOA-68T that was coated on a soft foundation. Then an out-of-plane pre-straining deformation was applied by a specially designed punch to generate internal elastic instabilities. The surface wrinkling pattern characteristics (shapes and size) changed according to the amount of punch stroke (pre-strain) and the cross-sectional shape of the punch. This study confirms the usefulness of this method for controlling and generating local wrinkling patterns for diverse applications. As an example, the contact angles of a water droplet on a local area of the same pattern were measured to identify the change in wettability with respect to different wrinkling shapes. This method can be utilized in topographical tunable wrinkle fabrication for local surface modification.

Fabrication of a highly oriented line structure on an aluminum surface and the nanoscale patterning on the nanoscale structure using highly functional molecules

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

Watanabe, Y.; Kato, H.; Takemura, S.

2009-07-15

The surface of an Al plate was treated with a combination of chemical and electrochemical processes for fabrication of surface nanoscale structures on Al plates. Chemical treatments by using acetone and pure water under supersonic waves were conducted on an Al surface. Additional electrochemical process in H{sub 2}SO{sub 4} solution created a finer and oriented nanoscale structure on the Al surface. Dynamic force microscopy (DFM) measurement clarified that the nanoscale highly oriented line structure was successfully created on the Al surface. The line distance was estimated approximately 30-40 nm. At the next stage, molecular patterning on the highly oriented linemore » structure by functional molecules such as copper phthalocyanine (CuPc) and fullerene C{sub 60} was also conducted. CuPc or C{sub 60} molecules were deposited on the highly oriented line structure on Al. A toluene droplet containing CuPc molecules was cast on the nanostructured Al plate and was extended on the surface. CuPc or C{sub 60} deposition on the nanostructured Al surface proceeded by evaporation of toluene. DFM and x-ray photoemission spectroscopy measurements demonstrated that a unique molecular pattern was fabricated so that the highly oriented groove channels were filled with the functional molecules.« less

Journal and Wave Bearing Impedance Calculation Software

NASA Technical Reports Server (NTRS)

Hanford, Amanda; Campbell, Robert

2012-01-01

The wave bearing software suite is a MALTA application that computes bearing properties for user-specified wave bearing conditions, as well as plain journal bearings. Wave bearings are fluid film journal bearings with multi-lobed wave patterns around the circumference of the bearing surface. In this software suite, the dynamic coefficients are outputted in a way for easy implementation in a finite element model used in rotor dynamics analysis. The software has a graphical user interface (GUI) for inputting bearing geometry parameters, and uses MATLAB s structure interface for ease of interpreting data. This innovation was developed to provide the stiffness and damping components of wave bearing impedances. The computational method for computing bearing coefficients was originally designed for plain journal bearings and tilting pad bearings. Modifications to include a wave bearing profile consisted of changing the film thickness profile given by an equation, and writing an algorithm to locate the integration limits for each fluid region. Careful consideration was needed to implement the correct integration limits while computing the dynamic coefficients, depending on the form of the input/output variables specified in the algorithm.

Anomalous refraction of light through slanted-nanoaperture arrays on metal surface

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

Kim, Myungji; Jung, Yun Suk; Xi, Yonggang

2015-09-07

We report a nanoapertured metal surface that demonstrates anomalous refraction of light for a wide range of incident angles. A nanoslit aperture is designed to serve as a tilted vertical-dipole whose radiation pattern orients to a glancing angle direction to substrate. An array of such slanted nanoslits formed in a metal film redirects an incident beam into the direction of negative refraction angle: the aperture-transmitted wave makes a far-field propagation to the tilt-oriented direction of radiation pattern. The thus-designed nanoaperture array demonstrates the −1st order diffraction (i.e., to the negative refraction-angle direction) with well-suppressed background transmission (the zero-order direct transmissionmore » and other higher-order diffractions). Engineering the radiation pattern of nanoaperture offers an approach to overcoming the limits of conventional diffractive/refractive optics and complementing metasurface-based nano-optics.« less

Low-energy Auger electron diffraction: influence of multiple scattering and angular momentum

NASA Astrophysics Data System (ADS)

Chassé, A.; Niebergall, L.; Kucherenko, Yu.

2002-04-01

The angular dependence of Auger electrons excited from single-crystal surfaces is treated theoretically within a multiple-scattering cluster model taking into account the full Auger transition matrix elements. In particular the model has been used to discuss the influence of multiple scattering and angular momentum of the Auger electron wave on Auger electron diffraction (AED) patterns in the region of low kinetic energies. Theoretical results of AED patterns are shown and discussed in detail for Cu(0 0 1) and Ni(0 0 1) surfaces, respectively. Even though Cu and Ni are very similar in their electronic and scattering properties recently strong differences have been found in AED patterns measured in the low-energy region. It is shown that the differences may be caused to superposition of different electron diffraction effects in an energy-integrated experiment. A good agreement between available experimental and theoretical results has been achieved.

A CMB polarization primer

NASA Astrophysics Data System (ADS)

Hu, Wayne; White, Martin

1997-10-01

We present a pedagogical and phenomenological introduction to the study of cosmic microwave background (CMB) polarization to build intuition about the prospects and challenges facing its detection. Thomson scattering of temperature anisotropies on the last scattering surface generates a linear polarization pattern on the sky that can be simply read off from their quadrupole moments. These in turn correspond directly to the fundamental scalar (compressional), vector (vortical), and tensor (gravitational wave) modes of cosmological perturbations. We explain the origin and phenomenology of the geometric distinction between these patterns in terms of the so-called electric and magnetic parity modes, as well as their correlation with the temperature pattern. By its isolation of the last scattering surface and the various perturbation modes, the polarization provides unique information for the phenomenological reconstruction of the cosmological model. Finally we comment on the comparison of theory with experimental data and prospects for the future detection of CMB polarization.

Upper mantle structure of shear-waves velocities and stratification of anisotropy in the Afar Hotspot region

NASA Astrophysics Data System (ADS)

Sicilia, D.; Montagner, J.-P.; Cara, M.; Stutzmann, E.; Debayle, E.; Lépine, J.-C.; Lévêque, J.-J.; Beucler, E.; Sebai, A.; Roult, G.; Ayele, A.; Sholan, J. M.

2008-12-01

The Afar area is one of the biggest continental hotspots active since about 30 Ma. It may be the surface expression of a mantle "plume" related to the African Superswell. Central Africa is also characterized by extensive intraplate volcanism. Around the same time (30 Ma), volcanic activity re-started in several regions of the African plate and hotspots such as Darfur, Tibesti, Hoggar and Mount Cameroon, characterized by a significant though modest volcanic production. The interactions of mantle upwelling with asthenosphere, lithosphere and crust remain unclear and seismic anisotropy might help in investigating these complex interactions. We used data from the global seismological permanent FDSN networks (GEOSCOPE, IRIS, MedNet, GEO- FON, etc.), from the temporary PASSCAL experiments in Tanzania and Saudi Arabia and a French deployment of 5 portable broadband stations surrounding the Afar Hotspot. A classical two-step tomographic inversion from surface waves performed in the Horn of Africa with selected Rayleigh wave and Love wave seismograms leads to a 3D-model of both S V velocities and azimuthal anisotropy, as well as radial SH/ SV anisotropy, with a lateral resolution of 500 km. The region is characterized by low shear-wave velocities beneath the Afar Hotspot, the Red Sea, the Gulf of Aden and East of the Tanzania Craton to 400 km depth. High velocities are present in the Eastern Arabia and the Tanzania Craton. The results of this study enable us to rule out a possible feeding of the Central Africa hotspots from the "Afar plume" above 150-200 km. The azimuthal anisotropy displays a complex pattern near the Afar Hotspot. Radial anisotropy, although poorly resolved laterally, exhibits S H slower than S V waves down to about 150 km depth, and a reverse pattern below. Both azimuthal and radial anisotropies show a stratification of anisotropy at depth, corresponding to different physical processes. These results suggest that the Afar hotspot has a different and deeper origin than the other African hotspots (Darfur, Tibesti, Hoggar). These latter hotspots can be traced down to 200 km from S-wave velocity but have no visible effect on radial and azimuthal anisotropy.

A delayed action oscillator shared by biennial, interannual, and decadal signals in the Pacific Basin

USGS Publications Warehouse

White, Warren B.; Tourre, Y.M.; Barlow, M.; Dettinger, M.

2003-01-01

Biennial, interannual, and decadal signals in the Pacific basin are observed to share patterns and evolution in covarying sea surface temperature (SST), 18??C isotherm depth (Z18), zonal surface wind (ZSW), and wind stress curl (WSC) anomalies from 1955 to 1999. Each signal has warm SST anomalies propagating slowly eastward along the equator, generating westerly ZSW anomalies in their wake. These westerly ZSW anomalies produce cyclonic WSC anomalies off the equator which pump baroclinic Rossby waves in the western/central tropical North Pacific Ocean. These Rossby waves propagate westward, taking ???6, ???12, and ???36 months to reach the western boundary near ???7??N, ???12??N, and ???18??N on biennial, interannual, and decadal period scales, respectively. There, they reflect as equatorial coupled waves, propagating slowly eastward in covarying SST, Z18, and ZSW anomalies, taking ???6, ???12, and ???24 months to reach the central/eastern equatorial ocean. These equatorial coupled waves produce a delayed-negative feedback to the warm SST anomalies there. The decrease in Rossby wave phase speed with latitude, the increase in meridional scale of equatorial SST anomalies with period scale, and the associated increase in latitude of Rossby wave forcing are consistent with the delayed action oscillator (DAO) model used to explain El Nin??o. However, this is not true of the western-boundary reflection of Rossby waves into slow equatorial coupled waves. This requires modification of the extant DAO model. We construct a modified DAO model, demonstrating how the various mechanisms and the size and sources of their delays yield the resulting frequency of each signal.

Confinement of surface state electrons in self-organized Co islands on Au(111)

NASA Astrophysics Data System (ADS)

Schouteden, Koen; Lijnen, Erwin; Janssens, Ewald; Ceulemans, Arnout; Chibotaru, Liviu F.; Lievens, Peter; Van Haesendonck, Chris

2008-04-01

We report on detailed low temperature scanning tunneling spectroscopy measurements performed on nanoscale Co islands on Au(111) films. At low coverages, Co islands self-organize in arrays of mono- and bilayer nanoscale structures that often have an hexagonal shape. The process of self-organization is induced by the Au(111) 'herringbone' reconstruction. By means of mapping of the local density of states with lock-in detection, electron standing wave patterns are resolved on top of the atomically flat Co islands. The surface state electrons are observed to be strongly confined laterally inside the Co nanosized islands, with their wavefunctions reflecting the symmetry of the islands. To complement the experimental work, particle-in-a-box calculations were performed. The calculations are based on a newly developed variational method that can be applied to '2D boxes' of arbitrary polygonal shape. The experimental patterns are found to fit nicely to the calculated wavefunctions for a box having a symmetry corresponding to the experimental island symmetry. The small size of the Co islands under study (down to 7.7 nm2) is observed to induce a strong discretization of the energy levels, with very large energy separations between the eigenstates up to several 100 meV. The observed standing wave patterns are identified either as individual eigenstates or as a 'mixture' of two or more energetically close-lying eigenstates of the cobalt island. Additionally, the Co surface state appears not to be limited to mono- and bilayer islands, but this state remains observable for multilayered islands up to five monolayers of Co.

Measurements of shock-induced guided and surface acoustic waves along boreholes in poroelastic materials

NASA Astrophysics Data System (ADS)

Chao, Gabriel; Smeulders, D. M. J.; van Dongen, M. E. H.

2006-05-01

Acoustic experiments on the propagation of guided waves along water-filled boreholes in water-saturated porous materials are reported. The experiments were conducted using a shock tube technique. An acoustic funnel structure was placed inside the tube just above the sample in order to enhance the excitation of the surface modes. A fast Fourier transform-Prony-spectral ratio method is implemented to transform the data from the time-space domain to the frequency-wave-number domain. Frequency-dependent phase velocities and attenuation coefficients were measured using this technique. The results for a Berea sandstone material show a clear excitation of the fundamental surface mode, the pseudo-Stoneley wave. The comparison of the experimental results with numerical predictions based on Biot's theory of poromechanics [J. Acoust. Soc. Am. 28, 168 (1956)], shows that the oscillating fluid flow at the borehole wall is the dominant loss mechanism governing the pseudo-Stoneley wave and it is properly described by the Biot's model at frequencies below 40 kHz. At higher frequencies, a systematic underestimation of the theoretical predictions is found, which can be attributed to the existence of other losses mechanisms neglected in the Biot formulation. Higher-order guided modes associated with the compressional wave in the porous formation and the cylindrical geometry of the shock tube were excited, and detailed information was obtained on the frequency-dependent phase velocity and attenuation in highly porous and permeable materials. The measured attenuation of the guided wave associated with the compressional wave reveals the presence of regular oscillatory patterns that can be attributed to radial resonances. This oscillatory behavior is also numerically predicted, although the measured attenuation values are one order of magnitude higher than the corresponding theoretical values. The phase velocities of the higher-order modes are generally well predicted by theory.

Planar time-resolved PIV for velocity and pressure retrieval in atmospheric boundary layer over surface waves.

NASA Astrophysics Data System (ADS)

Troitskaya, Yuliya; Kandaurov, Alexander; Sergeev, Daniil; Bopp, Maximilian; Caulliez, Guillemette

2017-04-01

Air-sea coupling in general is important for weather, climate, fluxes. Wind wave source is crucially important for surface waves' modeling. But the wind-wave growth rate is strongly uncertain. Using direct measurements of pressure by wave-following Elliott probe [1] showed, weak and indefinite dependence of wind-wave growth rate on the wave steepness, while Grare et.al. [2] discuss the limitations of direct measurements of pressure associated with the inability to measure the pressure close to the surface by contact methods. Recently non-invasive methods for determining the pressure on the basis of technology of time-resolved PIV are actively developed [3]. Retrieving air flow velocities by 2D PIV techniques was started from Reul et al [4]. The first attempt for retrieving wind pressure field of waves in the laboratory tank from the time-resolved PIV measurements was done in [5]. The experiments were performed at the Large Air-Sea Interaction Facility (LASIF) - MIO/Luminy (length 40 m, cross section of air channel 3.2 x 1.6 m). For 18 regimes with wind speed up to 14 m/s including presence of puddle waves, a combination of time resolved PIV technique and optical measurements of water surface form was applied to detailed investigation of the characteristics of the wind flow over the water surface. Ammonium chloride smoke was used for flow visualization illuminated by two 6 Wt blue diode lasers combined into a vertical laser plane. Particle movement was captured with high-speed camera using Scheimpflug technique (up to 20 kHz frame rate with 4-frame bursts, spatial resolution about 190 μm, field of view 314x12 mm). Velocity air flow field was retrieved by PIV images processing with adaptive cross-correlation method on the curvilinear grid following surface wave form. The resulting time resolved instantaneous velocity fields on regular grid allowed us to obtain momentum fluxes directly from measured air velocity fluctuations. The average wind velocity patterns were retrieved using conditional averaging with phase like in [5]. Basing on these data we then retrieve the pressure field and find the air-sea interaction parameters. Peculiarity of these experiments was the presence of noticeable modulation of the waves, so we describe peculiarities of the pressure distribution over a wave-train. This work was supported by the Russian Foundation of Basic Research (project codes 16-05-00839, 16-55-52025, 15-35-20953), President Grant for young scientists MK-2041.2017.5, Russian Science Foundation (Agreements 14-17-00667, 15-17-20009) and FP7 Collaborative Project No. 612610. References 1. Saveliev I., et. al. (2011) J. Phys. Oceanogr. 41. 1328-1344. 2. Grare, L., et. al. (2013) J. Fluid Mech., 722, 5-50. 3. van Oudheusden B.W. (2013) Meas. Sci. Technol. 24. 032001 (32pp) 4. Reul N., et.al. (1999) Phys. Fluids. 11. 1959-1961. 5. Troitskaya Yu., et. al.(2011). J. Phys. Oceanogr., 41, 1421-1454

Dynamics of the Trans-Neptune Region: Apsidal Waves in the Kuiper Belt

NASA Technical Reports Server (NTRS)

Ward, William R.; Hahn, Joseph M.

1998-01-01

The role of apsidal density waves propagating in a primordial trans-Neptune disk (i.e., Kuiper belt) is investigated. It is shown that Neptune launches apsidal waves at its secular resonance near 40 AU that propagate radially outward, deeper into the particle disk. The wavelength of apsidal waves is considerably longer than waves that might be launched at Lindblad resonances, because the pattern speed, g(sub s), resulting from the apsis precession of Neptune is much slower than its mean motion, Omega(sub s). If the early Kuiper belt had a sufficient surface density, sigma, the disk's wave response to Neptune's secular perturbation would have spread the disturbing torque radially over a collective scale lambda(sub *) approx. = r(2(mu)(sub d)Omega/ absolute value of r dg/dr)(sup 1/2), where mu(sub d)equivalent pi(sigma)r(exp 2)/(1 solar mass) and Omega(r) and g(r) are respectively the mean motion and precession frequency of the disk particles. This results in considerably smaller eccentricities at resonance than had the disk particles been treated as noninteracting test particles. Consequently, particles are less apt to be excited into planet-crossing orbits, implying that the erosion timescales reported by earlier test-particle simulations of the Kuiper belt may be underestimated. It is also shown that the torque the disk exerts upon the planet (due to its gravitational attraction for the disk's spiral wave pattern) damps the planet's eccentricity and further inhibits the planet's ability to erode the disk. Key words: celestial mechanics, stellar dynamics - comets: general minor planets, asteroids

Linking North American Summer Ozone Pollution Episodes to Subseasonal Atmospheric Variability

NASA Astrophysics Data System (ADS)

White, E. C.; Watt-Meyer, O.; Kushner, P. J.; Jones, D. B. A.

2017-12-01

Ozone concentrations in the planetary boundary layer (PBL) are positively correlated with surface air temperature due to shared influences including incident solar radiation and PBL stagnancy, as well as the temperature-sensitive emission of ozone precursor compounds. While previous studies have linked heat waves in North America to modes of subseasonal atmospheric variability, such analyses have not been applied to summertime ozone pollution episodes. This study investigates a possible link between subseasonal atmospheric variability in reanalysis data and summertime ozone pollution episodes identified in almost thirty years of in-situ measurements from the Air Quality System (AQS) network in the United States. AQS stations are grouped into regions likely to experience simultaneous extreme ozone concentrations using statistical clustering methods. Composite meteorological patterns are calculated for ozone episodes in each of these regions. The same analysis is applied to heat waves identified in AQS temperature records for comparison. Local meteorological features during typical ozone episodes include extreme temperatures and reduced cloud cover related to anomalous synoptic-scale anticyclonic circulation aloft. These anticyclonic anomalies are typically embedded in wave trains extending from the North Pacific to North Atlantic. Spectral analysis of these wave trains reveals that low-frequency standing waves play a prominent role. These long-lived circulation patterns may provide a means to increase air quality prediction lead-times and to estimate the frequency of ozone pollution episodes under climate change.

Strait of Gibraltar seen from STS-66

NASA Technical Reports Server (NTRS)

1994-01-01

Swift currents flow through the Strait of Gibraltar, producing complicated patterns in the surface waters. Some of those patterns are highlighted in the sunglint in this photograph. The Mediterranian Sea is on the upper right, the Atlantic Ocean in in the lower left. Few features can be seen on the Mediterranian side, but current shears (straight lines coming off Spain), several sets of internal waves (impinging on the Spanish continental shelf) and ship wakes can be seen on the Atlantic side, west of Cadiz. Both Tangier and Cadiz show up in the sunglint as well.

Earth observations taken by the Expedition 14 crew

NASA Image and Video Library

2007-03-10

ISS014-E-16597 (10 March 2007) --- Isles of Scilly, United Kingdom is featured in this image photographed by an Expedition 14 crewmember on the International Space Station. The Isles of Scilly, an archipelago of approximately 150 islands, is located some 44 kilometers southwest of the westernmost point of England (Land's End). According to scientists, the islands are an erosional remnant of an ancient granite intrusion, and are notable because they have been inhabited for over 4000 years. Historical and geological evidence cited by NASA scientists on the Isles indicates that many of the islands were larger and/or connected in the recent past--this could be due to local subsidence, rising sea levels, or a combination of both factors. Even today, it is possible to walk between certain islands during low tides. The Isles have been designated a United Kingdom Area of Outstanding Natural Beauty due to their unique landscape, ecology, and historical significance. The potential effect of rising sea level on the Isles is a primary concern for both long-term ecosystem health and human habitability. This image illustrates the geographic configuration of the archipelago, and its effect on ocean wave patterns. Long linear swells oriented northeast-southwest and moving to the southeast (from upper left to lower right) are diffracted (bent) as they approach the coastlines and small shoals of the Isles. The wave diffraction forms complex interacting surface patterns--this is most clearly visible southwest of St. Mary's island (left). The dominant ocean wave pattern resumes to the southeast of St. Mary's, but with an additional northwest-southeast oriented pattern superimposed, possibly due to winds originating in the English channel to the east (not shown). Suspended, tan-colored sediments visible within and around the archipelago are locally derived from continuing wave erosion of the granite forming the islands and remobilization of beach sands. Bright white areas in the photograph are waves breaking on shoals.

Optimal ciliary beating patterns

NASA Astrophysics Data System (ADS)

Vilfan, Andrej; Osterman, Natan

2011-11-01

We introduce a measure for energetic efficiency of single or collective biological cilia. We define the efficiency of a single cilium as Q2 / P , where Q is the volume flow rate of the pumped fluid and P is the dissipated power. For ciliary arrays, we define it as (ρQ) 2 / (ρP) , with ρ denoting the surface density of cilia. We then numerically determine the optimal beating patterns according to this criterion. For a single cilium optimization leads to curly, somewhat counterintuitive patterns. But when looking at a densely ciliated surface, the optimal patterns become remarkably similar to what is observed in microorganisms like Paramecium. The optimal beating pattern then consists of a fast effective stroke and a slow sweeping recovery stroke. Metachronal waves lead to a significantly higher efficiency than synchronous beating. Efficiency also increases with an increasing density of cilia up to the point where crowding becomes a problem. We finally relate the pumping efficiency of cilia to the swimming efficiency of a spherical microorganism and show that the experimentally estimated efficiency of Paramecium is surprisingly close to the theoretically possible optimum.

An Effective Quality Control of Pharmacologically Active Volatiles of Houttuynia cordata Thunb by Fast Gas Chromatography-Surface Acoustic Wave Sensor.

PubMed

Oh, Se Yeon

2015-06-03

Fast gas chromatography-surface acoustic wave sensor (GC/SAW) has been applied for the detection of the pharmacological volatiles emanated from Houttuynia cordata Thunb which is from South Korea. H. cordata Thunb with unpleasant and fishy odors shows a variety of pharmacological activities such as anti-microbial, anti-inflammatory, anti-cancer, and insect repellent. The aim of this study is to show a novel quality control by GC/SAW methodology for the discrimination of the three different parts of the plant such as leaves, aerial stems, and underground stems for H. cordata Thunb. Sixteen compounds were identified. β-Myrcene, cis-ocimene and decanal are the dominant volatiles for leaves (71.0%) and aerial stems (50.1%). While, monoterpenes (74.6%) are the dominant volatiles for underground stems. 2-Undecanone (1.3%) and lauraldehyde (3.5%) were found to be the characteristic components for leaves. Each part of the plant has its own characteristic fragrance pattern owing to its individual chemical compositions. Moreover, its individual characteristic fragrance patterns are conducive to discrimination of the three different parts of the plant. Consequently, fast GC/SAW can be a useful analytical method for quality control of the different parts of the plant with pharmacological volatiles as it provides second unit analysis, a simple and fragrant pattern recognition.

Earth Observations taken by the Expedition 13 crew

NASA Image and Video Library

2006-05-09

ISS013-E-16599 (9 May 2006) --- Wave sets and tidal currents in the Gulf of California are featured in this image photographed by an Expedition 13 crewmember on the International Space Station. In this image, sunglint off the Gulf of California gives the water a silver-gray appearance rather than the usual azure blue color. The sunglint allows us to see several active features which would not be visible otherwise. In this view of Punta Perihuete, Mexico we can see three major features: biological or man-made oils floating on the surface; the out-going tidal current; and complex wave patterns. The oils on the surface are recognizable as light grey, curved and variable-width streamers shaped by the local winds and currents. Plankton, fish, natural oil seeps and boats dumping bilges are all potential sources for these oils.

Emergent thermodynamics in a system of macroscopic, chaotic surface waves

NASA Astrophysics Data System (ADS)

Welch, Kyle J.

The properties of conventional materials are inextricably linked with their molecular composition; to make water flow like wine would require changing its molecular identity. To circumvent this restriction, I have constructed and characterized a two-dimensional metafluid, so-called because its constitutive dynamics are derived not from atoms and molecules but from macroscopic, chaotic surface waves excited on a vertically agitated fluid. Unlike in conventional fluids, the viscosity and temperature of this metafluid are independently tunable. Despite this unconventional property, our system is surprisingly consistent with equilibrium thermodynamics, despite being constructed from macroscopic, non-equilibrium elements. As a programmable material, our metafluid represents a new platform on which to study complex phenomena such as self-assembly and pattern formation. We demonstrate one such application in our study of short-chain polymer analogs embedded in our system.

Separation of platelets from whole blood using standing surface acoustic waves in a microchannel.

PubMed

Nam, Jeonghun; Lim, Hyunjung; Kim, Dookon; Shin, Sehyun

2011-10-07

Platelet separation from blood is essential for biochemical analyses and clinical diagnosis. In this article, we propose a method to separate platelets from undiluted whole blood using standing surface acoustic waves (SSAWs) in a microfluidic device. A polydimethylsiloxane (PDMS) microfluidic channel was fabricated and integrated with interdigitated transducer (IDT) electrodes patterned on a piezoelectric substrate. To avoid shear-induced activation of platelets, the blood sample flow was hydrodynamically focused by introducing sheath flow from two side-inlets and pressure nodes were designed to locate at side walls. By means of flow cytometric analysis, the RBC clearance ratio from whole blood was found to be over 99% and the purity of platelets was close to 98%. Conclusively, the present technique using SSAWs can directly separate platelets from undiluted whole blood with higher purity than other methods.

Nonlinear modulation near the Lighthill instability threshold in 2+1 Whitham theory

NASA Astrophysics Data System (ADS)

Bridges, Thomas J.; Ratliff, Daniel J.

2018-04-01

The dispersionless Whitham modulation equations in 2+1 (two space dimensions and time) are reviewed and the instabilities identified. The modulation theory is then reformulated, near the Lighthill instability threshold, with a slow phase, moving frame and different scalings. The resulting nonlinear phase modulation equation near the Lighthill surfaces is a geometric form of the 2+1 two-way Boussinesq equation. This equation is universal in the same sense as Whitham theory. Moreover, it is dispersive, and it has a wide range of interesting multi-periodic, quasi-periodic and multi-pulse localized solutions. For illustration the theory is applied to a complex nonlinear 2+1 Klein-Gordon equation which has two Lighthill surfaces in the manifold of periodic travelling waves. This article is part of the theme issue `Stability of nonlinear waves and patterns and related topics'.

Dispersion Energy Analysis of Rayleigh and Love Waves in the Presence of Low-Velocity Layers in Near-Surface Seismic Surveys

NASA Astrophysics Data System (ADS)

Mi, Binbin; Xia, Jianghai; Shen, Chao; Wang, Limin

2018-03-01

High-frequency surface-wave analysis methods have been effectively and widely used to determine near-surface shear (S) wave velocity. To image the dispersion energy and identify different dispersive modes of surface waves accurately is one of key steps of using surface-wave methods. We analyzed the dispersion energy characteristics of Rayleigh and Love waves in near-surface layered models based on numerical simulations. It has been found that if there is a low-velocity layer (LVL) in the half-space, the dispersion energy of Rayleigh or Love waves is discontinuous and ``jumping'' appears from the fundamental mode to higher modes on dispersive images. We introduce the guided waves generated in an LVL (LVL-guided waves, a trapped wave mode) to clarify the complexity of the dispersion energy. We confirm the LVL-guided waves by analyzing the snapshots of SH and P-SV wavefield and comparing the dispersive energy with theoretical values of phase velocities. Results demonstrate that LVL-guided waves possess energy on dispersive images, which can interfere with the normal dispersion energy of Rayleigh or Love waves. Each mode of LVL-guided waves having lack of energy at the free surface in some high frequency range causes the discontinuity of dispersive energy on dispersive images, which is because shorter wavelengths (generally with lower phase velocities and higher frequencies) of LVL-guided waves cannot penetrate to the free surface. If the S wave velocity of the LVL is higher than that of the surface layer, the energy of LVL-guided waves only contaminates higher mode energy of surface waves and there is no interlacement with the fundamental mode of surface waves, while if the S wave velocity of the LVL is lower than that of the surface layer, the energy of LVL-guided waves may interlace with the fundamental mode of surface waves. Both of the interlacements with the fundamental mode or higher mode energy may cause misidentification for the dispersion curves of surface waves.

A Multiscale Nested Modeling Framework to Simulate the Interaction of Surface Gravity Waves with Nonlinear Internal Gravity Waves

DTIC Science & Technology

2015-09-30

We aim at understanding the impact of tidal , seasonal, and mesoscale variability of the internal wave field and how it influences the surface waves ...Interaction of Surface Gravity Waves with Nonlinear Internal Gravity Waves Lian Shen St. Anthony Falls Laboratory and Department of Mechanical...on studying surface gravity wave evolution and spectrum in the presence of surface currents caused by strongly nonlinear internal solitary waves

Generation of Customizable Micro-wavy Pattern through Grayscale Direct Image Lithography

PubMed Central

He, Ran; Wang, Shunqiang; Andrews, Geoffrey; Shi, Wentao; Liu, Yaling

2016-01-01

With the increasing amount of research work in surface studies, a more effective method of producing patterned microstructures is highly desired due to the geometric limitations and complex fabricating process of current techniques. This paper presents an efficient and cost-effective method to generate customizable micro-wavy pattern using direct image lithography. This method utilizes a grayscale Gaussian distribution effect to model inaccuracies inherent in the polymerization process, which are normally regarded as trivial matters or errors. The measured surface profiles and the mathematical prediction show a good agreement, demonstrating the ability of this method to generate wavy patterns with precisely controlled features. An accurate pattern can be generated with customizable parameters (wavelength, amplitude, wave shape, pattern profile, and overall dimension). This mask-free photolithography approach provides a rapid fabrication method that is capable of generating complex and non-uniform 3D wavy patterns with the wavelength ranging from 12 μm to 2100 μm and an amplitude-to-wavelength ratio as large as 300%. Microfluidic devices with pure wavy and wavy-herringbone patterns suitable for capture of circulating tumor cells are made as a demonstrative application. A completely customized microfluidic device with wavy patterns can be created within a few hours without access to clean room or commercial photolithography equipment. PMID:26902520

Prospects for Jovian seismological observations following the impact of comet Shoemaker-Levy 9

NASA Technical Reports Server (NTRS)

Deming, Drake

1994-01-01

The impact of each fragment of comet SL-9 will produce a downward-propagating pressure wave which will travel at the sound speed through the jovian interior. Since the sound speed increases with depth, most of the energy in the pressure pulse will be strongly refracted and return to the surface, as recently computed by Marley (1994). This wave may in principle be observable as it propagates into the stratosphere, using sufficiently sensitive thermal infrared imaging. If so, it will provide a unique opportunity to constrain models of the jovian interior. This paper extends Marley's calculations to include the effect of the limited spatial resolution which will be characteristic of real observations. The wave pattern on the disk will consist of closely spaced regions of alternating temperature increases and decreases. Spatial averaging will significantly reduce the observed amplitude for resolutions attainable using earth-based telescopes, but the waves should remain above the detection limit.

Subwavelength and directional control of flexural waves in zone-folding induced topological plates

NASA Astrophysics Data System (ADS)

Chaunsali, Rajesh; Chen, Chun-Wei; Yang, Jinkyu

2018-02-01

Inspired by the quantum spin Hall effect shown by topological insulators, we propose a plate structure that can be used to demonstrate the pseudospin Hall effect for flexural waves. The system consists of a thin plate with periodically arranged resonators mounted on its top surface. We extend a technique based on the plane-wave expansion method to identify a double Dirac cone emerging due to the zone-folding in frequency band structures. This particular design allows us to move the double Dirac cone to a lower frequency than the resonating frequency of local resonators. We then manipulate the pattern of local resonators to open subwavelength Bragg band gaps that are topologically distinct. Building on this method, we verify numerically that a waveguide at an interface between two topologically distinct resonating plate structures can be used for guiding low-frequency, spin-dependent one-way flexural waves along a desired path with bends.

An experimental investigation of the impingement of a planar shock wave on an axisymmetric body at Mach 3

NASA Technical Reports Server (NTRS)

Brosh, A.; Kussoy, M. I.

1983-01-01

An experimental study of the flow caused by a planar shock wave impinging obliquely on a cylinder is presented. The complex three dimensional shock wave and boundary layer interaction occurring in practical problems, such as the shock wave impingement from the shuttle nose on an external fuel tank, and store carriage interference on a supersonic tactical aircraft were investigated. A data base for numerical computations of complex flows was also investigated. The experimental techniques included pressure measurements and oil flow patterns on the surface of the cylinder, and shadowgraphs and total and static pressure surveys on the leeward and windward planes of symmetry. The complete data is presented in tabular form. The results reveal a highly complex flow field with two separation zones, regions of high crossflow, and multiple reflected shocks and expansion fans.

Integrated modeling of the dynamic meteorological and sea surface conditions during the passage of Typhoon Morakot

NASA Astrophysics Data System (ADS)

Lee, Han Soo; Yamashita, Takao; Hsu, John R.-C.; Ding, Fei

2013-01-01

In August 2009, Typhoon Morakot caused massive flooding and devastating mudslides in the southern Taiwan triggered by extremely heavy rainfall (2777 mm in 4 days) which occurred during its passage. It was one of the deadliest typhoons that have ever attacked Taiwan in recent years. In this study, numerical simulations are performed for the storm surge and ocean surface waves, together with dynamic meteorological fields such as wind, pressure and precipitation induced by Typhoon Morakot, using an atmosphere-waves-ocean integrated modelling system. The wave-induced dissipation stress from breaking waves, whitecapping and depth-induced wave breaking, is parameterized and included in the wave-current interaction process, in addition to its influence on the storm surge level in shallow water along the coast of Taiwan. The simulated wind and pressure field captures the characteristics of the observed meteorological field. The spatial distribution of the accumulated rainfall within 4 days, from 00:00 UTC 6 August to 00:00 UTC 10 August 2009, shows similar patterns as the observed values. The 4-day accumulated rainfall of 2777 mm at the A-Li Shan mountain weather station for the same period depicted a high correlation with the observed value of 2780 mm/4 days. The effects of wave-induced dissipation stress in the wave-current interaction resulted in increased surge heights on the relatively shallow western coast of Taiwan, where the bottom slope of the bathymetry ranges from mild to moderate. The results also show that wave-breaking has to be considered for accurate storm surge prediction along the east coast of Taiwan over the narrow bank of surf zone with a high horizontal resolution of the model domain.

Surface-Wave Pulse Routing around Sharp Right Angles

NASA Astrophysics Data System (ADS)

Gao, Z.; Xu, H.; Gao, F.; Zhang, Y.; Luo, Y.; Zhang, B.

2018-04-01

Surface-plasmon polaritons (SPPs), or localized electromagnetic surface waves propagating on a metal-dielectric interface, are deemed promising information carriers for future subwavelength terahertz and optical photonic circuitry. However, surface waves fundamentally suffer from scattering loss when encountering sharp corners in routing and interconnection of photonic signals. Previous approaches enabling scattering-free surface-wave guidance around sharp corners are limited to either volumetric waveguide environments or extremely narrow bandwidth, being unable to guide a surface-wave pulse (SPP wave packet) on an on-chip platform. Here, in a surface-wave band-gap crystal implemented on a single metal surface, we demonstrate in time-domain routing a surface-wave pulse around multiple sharp right angles without perceptible scattering. Our work not only offers a solution to on-chip surface-wave pulse routing along an arbitrary path, but it also provides spatiotemporal information on the interplay between surface-wave pulses and sharp corners, both of which are desirable in developing high-performance large-scale integrated photonic circuits.

Effects of Sea-Surface Waves and Ocean Spray on Air-Sea Momentum Fluxes

NASA Astrophysics Data System (ADS)

Zhang, Ting; Song, Jinbao

2018-04-01

The effects of sea-surface waves and ocean spray on the marine atmospheric boundary layer (MABL) at different wind speeds and wave ages were investigated. An MABL model was developed that introduces a wave-induced component and spray force to the total surface stress. The theoretical model solution was determined assuming the eddy viscosity coefficient varied linearly with height above the sea surface. The wave-induced component was evaluated using a directional wave spectrum and growth rate. Spray force was described using interactions between ocean-spray droplets and wind-velocity shear. Wind profiles and sea-surface drag coefficients were calculated for low to high wind speeds for wind-generated sea at different wave ages to examine surface-wave and ocean-spray effects on MABL momentum distribution. The theoretical solutions were compared with model solutions neglecting wave-induced stress and/or spray stress. Surface waves strongly affected near-surface wind profiles and sea-surface drag coefficients at low to moderate wind speeds. Drag coefficients and near-surface wind speeds were lower for young than for old waves. At high wind speeds, ocean-spray droplets produced by wind-tearing breaking-wave crests affected the MABL strongly in comparison with surface waves, implying that wave age affects the MABL only negligibly. Low drag coefficients at high wind caused by ocean-spray production increased turbulent stress in the sea-spray generation layer, accelerating near-sea-surface wind. Comparing the analytical drag coefficient values with laboratory measurements and field observations indicated that surface waves and ocean spray significantly affect the MABL at different wind speeds and wave ages.

Role of electromagnetic wave in mode selection of magnetically driven instabilities

NASA Astrophysics Data System (ADS)

Dan, J. K.; Ren, X. D.; Duan, S. C.; Ouyang, K.; Chen, G. H.; Huang, X. B.

2014-12-01

The fundamental wavelength of the instability along two 25-μm-diameter aluminum wires using a 100 ns rise time, 220 kA pulsed power facility is measured for two different load configurations. In one case the wires are perpendicular to end surface of electrodes, and in another case the wires are oblique to electrode's end surface. The primary diagnostic used to measure time revolution of instability wavelength and amplitude is laser shadowgraphy. The role of end surface of electrodes appears to be responsible for the differences in dominant wavelength of instability between two types of load configurations. The experimental results that the fundamental wavelength in oblique case is about one half of that in perpendicular case indicates the ionic electromagnetic waves may play a key role in mode selection of magnetically driven instabilities. Conclusions drew from this paper may help us to understand the original reason why instabilities along wires manifest itself as a quasiperiodic pattern.

Design of a variable-line-spacing grating pattern for spectrometers based on a grating Fresnel device.

PubMed

Li, Xinghui; Zhang, Jinchao; Zhou, Qian; Ni, Kai; Pang, Jinchao; Tian, Rui

2016-04-01

In this Letter, we propose a variable-line-spacing (VLS) grating pattern for a hybrid diffractive device termed a grating Fresnel (G-Fresnel) lens, which is used in spectrometers to improve spectral resolution over a wide spectral range. The VLS grating pattern disperses light of specific wavelengths with a different angle and position such that the aberration caused by the Fresnel surface can be compensated for. In this manner, high resolution can be achieved over a relatively wide spectral range. The VLS grating pattern is designed based on the least wave-change principle and simulated by ZEMAX. Results reveal that the VLS G-Fresnel device allows a subnanometer resolution over a spectral range of 200 nm.

Two-dimensional wave patterns of spreading depolarization: Retracting, re-entrant, and stationary waves

NASA Astrophysics Data System (ADS)

Dahlem, Markus A.; Graf, Rudolf; Strong, Anthony J.; Dreier, Jens P.; Dahlem, Yuliya A.; Sieber, Michaela; Hanke, Wolfgang; Podoll, Klaus; Schöll, Eckehard

2010-06-01

We present spatio-temporal characteristics of spreading depolarizations (SD) in two experimental systems: retracting SD wave segments observed with intrinsic optical signals in chicken retina, and spontaneously occurring re-entrant SD waves that repeatedly spread across gyrencephalic feline cortex observed by laser speckle flowmetry. A mathematical framework of reaction-diffusion systems with augmented transmission capabilities is developed to explain the emergence and transitions between these patterns. Our prediction is that the observed patterns are reaction-diffusion patterns controlled and modulated by weak nonlocal coupling such as long-range, time-delayed, and global coupling. The described spatio-temporal characteristics of SD are of important clinical relevance under conditions of migraine and stroke. In stroke, the emergence of re-entrant SD waves is believed to worsen outcome. In migraine, retracting SD wave segments cause neurological symptoms and transitions to stationary SD wave patterns may cause persistent symptoms without evidence from noninvasive imaging of infarction.

Interactions of side (left and right ovary) with the number of follicles per ovary and with the intraovarian relationships between dominant follicle and corpus luteum in heifers.

PubMed

Ginther, O J; Hoffman, M M

2016-09-01

The interactions between side of ovary (left ovary [LO] and right ovary [RO]) and number of follicles per ovary and between side and intraovarian patterns were studied in heifers with two follicular waves (anovulatory wave 1 and ovulatory wave 2). Intraovarian patterns were on the basis of location of the dominant follicle (DF) and corpus luteum (CL) and were termed DF-CL, DF, CL, and devoid. The frequency of the DF-CL intraovarian pattern was greater for the RO than for the LO in wave 1 (80 of 121; P < 0.0004) and in wave 2 (54 of 83; P < 0.006). For each wave, the DF of the DF-CL and DF patterns was more often in the RO for the ipsilateral relationship (e.g., wave 1: 66% vs. 48%; P < 0.01) and in the LO for the contralateral relationship (52% vs. 34%; P < 0.01). An interaction between side and pattern (P < 0.05) for number of follicles in wave 2 that attained 6 mm was from a greater number in RO than in LO when a DF was present (DF-CL and DF patterns). An interaction of side and pattern for the number of wave 2 regressing subordinate follicles that recovered (increased in diameter) and became part of the subsequent wave 1 was greater (P < 0.05) for LO than for RO for the DF pattern but not for the CL pattern. An effect of side or an interaction that involved side was not found for the greater dimensions and blood flow for both the DF and CL of the DF-CL pattern. Results indicated that side interacted with ovarian pattern for number of DF-CL patterns, side of DF, number of follicles per ovary, and recovery of regressing wave 2 follicles. The hypothesis was supported that some aspects of follicle dynamics reflect an interaction of side and intraovarian pattern. Future studies on the effect of side on luteal or follicle dynamics could be incomplete or misleading if intraovarian patterns are ignored. Copyright © 2016 Elsevier Inc. All rights reserved.

Improvement of infrared single-photon detectors absorptance by integrated plasmonic structures

PubMed Central

Csete, Mária; Sipos, Áron; Szalai, Anikó; Najafi, Faraz; Szabó, Gábor; Berggren, Karl K.

2013-01-01

Plasmonic structures open novel avenues in photodetector development. Optimized illumination configurations are reported to improve p-polarized light absorptance in superconducting-nanowire single-photon detectors (SNSPDs) comprising short- and long-periodic niobium-nitride (NbN) stripe-patterns. In OC-SNSPDs consisting of ~quarter-wavelength dielectric layer closed by a gold reflector the highest absorptance is attainable at perpendicular incidence onto NbN patterns in P-orientation due to E-field concentration at the bottom of nano-cavities. In NCAI-SNSPDs integrated with nano-cavity-arrays consisting of vertical and horizontal gold segments off-axis illumination in S-orientation results in polar-angle-independent perfect absorptance via collective resonances in short-periodic design, while in long-periodic NCAI-SNSPDs grating-coupled surface waves promote EM-field transportation to the NbN stripes and result in local absorptance maxima. In NCDAI-SNSPDs integrated with nano-cavity-deflector-array consisting of longer vertical gold segments large absorptance maxima appear in 3p-periodic designs due to E-field enhancement via grating-coupled surface waves synchronized with the NbN stripes in S-orientation, which enable to compensate fill-factor-related retrogression. PMID:23934331

Intraseasonal Variability of the Indian Monsoon as Simulated by a Global Model

NASA Astrophysics Data System (ADS)

Joshi, Sneh; Kar, S. C.

2018-01-01

This study uses the global forecast system (GFS) model at T126 horizontal resolution to carry out seasonal simulations with prescribed sea-surface temperatures. Main objectives of the study are to evaluate the simulated Indian monsoon variability in intraseasonal timescales. The GFS model has been integrated for 29 monsoon seasons with 15 member ensembles forced with observed sea-surface temperatures (SSTs) and additional 16-member ensemble runs have been carried out using climatological SSTs. Northward propagation of intraseasonal rainfall anomalies over the Indian region from the model simulations has been examined. It is found that the model is unable to simulate the observed moisture pattern when the active zone of convection is over central India. However, the model simulates the observed pattern of specific humidity during the life cycle of northward propagation on day - 10 and day + 10 of maximum convection over central India. The space-time spectral analysis of the simulated equatorial waves shows that the ensemble members have varying amount of power in each band of wavenumbers and frequencies. However, variations among ensemble members are more in the antisymmetric component of westward moving waves and maximum difference in power is seen in the 8-20 day mode among ensemble members.

The boreal winter Madden-Julian Oscillation's influence on summertime precipitation in the greater Caribbean

NASA Astrophysics Data System (ADS)

Curtis, Scott; Gamble, Douglas W.

2016-07-01

Precipitation totals in the greater Caribbean are known to be affected by interannual variability. In particular, dry conditions in the spring-summer have been physically linked to the positive phase of North Atlantic Oscillation (NAO) in the literature. In this study, it was found through regression analysis that an active Madden-Julian Oscillation (MJO) in winter geographically focused over the Maritime Continent contributes to a positive NAO in March via the generation of Rossby waves in the Northern Hemisphere. Specifically, a negative Pacific-North American pattern develops in the winter and transitions to an Atlantic pattern in spring. The positive NAO is a transient feature of this evolving wave train, but a center of significant positive 200 hPa geopotential heights is entrenched over the southeast U.S. throughout the February to May time period and is manifested as high pressure at the surface. The southern flank of this system increases the speeds of the trade winds and leads to a cooling of the Caribbean sea surface temperatures and, thus, convection suppression and reduced precipitation. Thus, this study advances our understanding of the climate of the greater Caribbean by using climate teleconnections to relate the MJO to rainfall in the region.

Noninvasive, three-dimensional full-field body sensor for surface deformation monitoring of human body in vivo

NASA Astrophysics Data System (ADS)

Chen, Zhenning; Shao, Xinxing; He, Xiaoyuan; Wu, Jialin; Xu, Xiangyang; Zhang, Jinlin

2017-09-01

Noninvasive, three-dimensional (3-D), full-field surface deformation measurements of the human body are important for biomedical investigations. We proposed a 3-D noninvasive, full-field body sensor based on stereo digital image correlation (stereo-DIC) for surface deformation monitoring of the human body in vivo. First, by applying an improved water-transfer printing (WTP) technique to transfer optimized speckle patterns onto the skin, the body sensor was conveniently and harmlessly fabricated directly onto the human body. Then, stereo-DIC was used to achieve 3-D noncontact and noninvasive surface deformation measurements. The accuracy and efficiency of the proposed body sensor were verified and discussed by considering different complexions. Moreover, the fabrication of speckle patterns on human skin, which has always been considered a challenging problem, was shown to be feasible, effective, and harmless as a result of the improved WTP technique. An application of the proposed stereo-DIC-based body sensor was demonstrated by measuring the pulse wave velocity of human carotid artery.

Confining standing waves in optical corrals.

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

Babayan, Y.; McMahon, J. M.; Li, S.

2009-03-01

Near-field scanning optical microscopy images of solid wall, circular, and elliptical microscale corrals show standing wave patterns confined inside the structures with a wavelength close to that of the incident light. The patterns inside the corrals can be tuned by changing the size and material of the walls, the wavelength of incident light, and polarization direction for elliptical corrals. Finite-difference time-domain calculations of the corral structures agree with the experimental observations and reveal that the electric and magnetic field intensities are out of phase inside the corral. A theoretical modal analysis indicates that the fields inside the corrals can bemore » attributed to p- and s-polarized waveguide modes, and that the superposition of the propagating and evanescent modes can explain the phase differences between the fields. These experimental and theoretical results demonstrate that electromagnetic fields on a dielectric surface can be controlled in a predictable manner.« less

Development of indirect EFBEM for radiating noise analysis including underwater problems

NASA Astrophysics Data System (ADS)

Kwon, Hyun-Wung; Hong, Suk-Yoon; Song, Jee-Hun

2013-09-01

For the analysis of radiating noise problems in medium-to-high frequency ranges, the Energy Flow Boundary Element Method (EFBEM) was developed. EFBEM is the analysis technique that applies the Boundary Element Method (BEM) to Energy Flow Analysis (EFA). The fundamental solutions representing spherical wave property for radiating noise problems in open field and considering the free surface effect in underwater are developed. Also the directivity factor is developed to express wave's directivity patterns in medium-to-high frequency ranges. Indirect EFBEM by using fundamental solutions and fictitious source was applied to open field and underwater noise problems successfully. Through numerical applications, the acoustic energy density distributions due to vibration of a simple plate model and a sphere model were compared with those of commercial code, and the comparison showed good agreement in the level and pattern of the energy density distributions.

Polarization-dependent thin-film wire-grid reflectarray for terahertz waves

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

Niu, Tiaoming; School of Information Science and Engineering, Lanzhou University, Lanzhou 730000; Upadhyay, Aditi

2015-07-20

A thin-film polarization-dependent reflectarray based on patterned metallic wire grids is realized at 1 THz. Unlike conventional reflectarrays with resonant elements and a solid metal ground, parallel narrow metal strips with uniform spacing are employed in this design to construct both the radiation elements and the ground plane. For each radiation element, a certain number of thin strips with an identical length are grouped to effectively form a patch resonator with equivalent performance. The ground plane is made of continuous metallic strips, similar to conventional wire-grid polarizers. The structure can deflect incident waves with the polarization parallel to the stripsmore » into a designed direction and transmit the orthogonal polarization component. Measured radiation patterns show reasonable deflection efficiency and high polarization discrimination. Utilizing this flexible device approach, similar reflectarray designs can be realized for conformal mounting onto surfaces of cylindrical or spherical devices for terahertz imaging and communications.« less

Laser Imaging of Airborne Acoustic Emission by Nonlinear Defects

NASA Astrophysics Data System (ADS)

Solodov, Igor; Döring, Daniel; Busse, Gerd

2008-06-01

Strongly nonlinear vibrations of near-surface fractured defects driven by an elastic wave radiate acoustic energy into adjacent air in a wide frequency range. The variations of pressure in the emitted airborne waves change the refractive index of air thus providing an acoustooptic interaction with a collimated laser beam. Such an air-coupled vibrometry (ACV) is proposed for detecting and imaging of acoustic radiation of nonlinear spectral components by cracked defects. The photoelastic relation in air is used to derive induced phase modulation of laser light in the heterodyne interferometer setup. The sensitivity of the scanning ACV to different spatial components of the acoustic radiation is analyzed. The animated airborne emission patterns are visualized for the higher harmonic and frequency mixing fields radiated by planar defects. The results confirm a high localization of the nonlinear acoustic emission around the defects and complicated directivity patterns appreciably different from those observed for fundamental frequencies.

Bifocal Fresnel Lens Based on the Polarization-Sensitive Metasurface

NASA Astrophysics Data System (ADS)

Markovich, Hen; Filonov, Dmitrii; Shishkin, Ivan; Ginzburg, Pavel

2018-05-01

Thin structured surfaces allow flexible control over propagation of electromagnetic waves. Focusing and polarization state analysis are among functions, required for effective manipulation of radiation. Here a polarization sensitive Fresnel zone plate lens is proposed and experimentally demonstrated for GHz spectral range. Two spatially separated focal spots for orthogonal polarizations are obtained by designing metasurface pattern, made of overlapping tightly packed cross and rod shaped antennas with a strong polarization selectivity. Optimized subwavelength pattern allows multiplexing two different lenses with low polarization crosstalk on the same substrate and provides a control over focal spots of the lens only by changing of the polarization state of the incident wave. More than a wavelength separation between the focal spots was demonstrated for a broad spectral range, covering half a decade in frequency. The proposed concept could be straightforwardly extended for THz and visible spectra, where polarization-sensitive elements utilize localized plasmon resonance phenomenon.

Observation of giant Goos-Hänchen and angular shifts at designed metasurfaces

PubMed Central

Yallapragada, Venkata Jayasurya; Ravishankar, Ajith P.; Mulay, Gajendra L.; Agarwal, Girish S.; Achanta, Venu Gopal

2016-01-01

Metasurfaces with sub-wavelength features are useful in modulating the phase, amplitude or polarization of electromagnetic fields. While several applications are reported for light manipulation and control, the sharp phase changes would be useful in enhancing the beam shifts at reflection from a metasurface. In designed periodic patterns on metal film, at surface plasmon resonance, we demonstrate Goos-Hanchen shift of the order of 70 times the incident wavelength and the angular shifts of several hundred microradians. We have designed the patterns using rigorous coupled wave analysis (RCWA) together with S-matrices and have used a complete vector theory to calculate the shifts as well as demonstrate a versatile experimental setup to directly measure the shifts. The giant shifts demonstrated could prove to be useful in enhancing the sensitivity of experiments ranging from atomic force microscopy to gravitational wave detection. PMID:26758471

Transmittance enhancement of sapphires with antireflective subwavelength grating patterned UV polymer surface structures by soft lithography.

PubMed

Lee, Soo Hyun; Leem, Jung Woo; Yu, Jae Su

2013-12-02

We report the total and diffuse transmission enhancement of sapphires with the ultraviolet curable SU8 polymer surface structures consisting of conical subwavelength gratings (SWGs) at one- and both-side surfaces for different periods. The SWGs patterns on the silicon templates were transferred into the SU8 polymer film surface on sapphires by a simple and cost-effective soft lithography technique. For the fabricated samples, the surface morphologies, wetting behaviors, and optical characteristics were investigated. For theoretical optical analysis, a rigorous coupled-wave analysis method was used. At a period of 350 nm, the sample with SWGs on SU8 film/sapphire exhibited a hydrophobic surface and higher total transmittance compared to the bare sapphire over a wide wavelength of 450-1000 nm. As the period of SWGs was increased, the low total transmittance region of < 85% was shifted towards the longer wavelengths and became broader while the diffuse transmittance was increased (i.e., larger haze ratio). For the samples with SWGs at both-side surfaces, the total and diffuse transmittance spectra were further enhanced compared to the samples with SWGs at one-side surface. The theoretical optical calculation results showed a similar trend to the experimentally measured data.

Characteristics and present trends of wave extremes in the Mediterranean Sea

NASA Astrophysics Data System (ADS)

Pino, Cosimo; Lionello, Piero; Galati, Maria Barbara

2010-05-01

Wind generated surface waves are an important factor characterizing marine storminess and the marine environment. This contribution considers characteristics and trends of SWH (Significant Wave Height) extremes (both high and low extremes, such as dead calm duration are analyzed). The data analysis is based on a 44-year long simulation (1958-2001) of the wave field in the Mediterranean Sea. The quality of the model simulation is controlled using satellite data. The results show the different characteristics of the different parts of the basin with the variability being higher in the western (where the highest values are produced) than in the eastern areas of the basin (where absence of wave is a rare condition). In fact, both duration of storms and of dead calm episodes is larger in the east than in the west part of the Mediterranean. The African coast and the southern Ionian Sea are the areas were exceptional values of SWH are expected to occur in correspondence with exceptional meteorological events. Significant trends of storm characteristics are present only in sparse areas and suggest a decrease of both storm intensity and duration (a marginal increase of storm intensity is present in the center of the Mediterranean). The statistics of extremes and high SWH values is substantially steady during the second half of the 20th century. The influence of the large-scale teleconnection patterns (TlcP) that are known to be relevant for the Mediterranean climate on the intensity and spatial distribution of extreme SWH (Significant Wave Height) has been investigated. The analysis was focused on the monthly scale analysing the variability of links along the annual cycle. The considered TlcP are the North Atlantic Oscillation, the East-Atlantic / West-Russian pattern and the Scandinavian pattern and their effect on the intensity and the frequency of high/low SWH conditions. The results show it is difficult to establish a dominant TlcP for SWH extremes, because all 4 patterns considered are important for at least few months in the year and none of them is important for the whole year. High extremes in winter and fall are more influenced by the TlcPs than in other seasons and low extremes.

Vertical shear-wave velocity profiles generated from spectral analysis of surface waves : field examples

DOT National Transportation Integrated Search

2003-04-01

Surface wave (Rayleigh wave) seismic data were acquired at six separate bridge sites in southeast Missouri. Each acquired surface wave data set was processed (spectral analysis of surface waves; SASW) and transformed into a site-specific vertical she...

Three-Dimensional Velocity Structure in Southern California from Teleseismic Surface Waves and Body Waves.

NASA Astrophysics Data System (ADS)

Prindle-Sheldrake, K. L.; Tanimoto, T.

2003-12-01

Analysis of teleseismic waves generated by large earthquakes worldwide across the Southern California TriNet Seismic Broadband Array has yielded high quality measurements of both surface waves and body waves. Rayleigh waves and Love waves were previously analyzed using a spectral fitting technique (Tanimoto. and Prindle-Sheldrake, GRL 2002; Prindle-Sheldrake and Tanimoto, submitted to JGR), producing a three-dimensional S-wave velocity structure. Features in our velocity structure show some regional contrasts with respect to the starting model (SCEC 2.2), which has detailed crustal structure, but laterally homogeneous upper mantle structure. The most prominent of which is a postulated fast velocity anomaly located west of the Western Transverse Ranges that could be related to a rotated remnant plate from Farallon subduction. Analysis indicates that, while Rayleigh wave data are mostly sensitive to mantle structure, Love wave data require some modifications of crustal structure from SCEC 2.2 model. Recent advances in our velocity structure focus on accommodation of finite frequency effect, and the addition of body waves to the data. Thus far, 118 events have been analyzed for body waves. A simple geometrical approach is used to represent the finite frequency effect in phase velocity maps. Due to concerns that, for seismic phases between 10-100 seconds, structure away from the ray theoretical is also sampled by a propagating surface wave, we have adopted a technique which examines a normal mode formula in its asymptotic limit (Tanimoto, GRL 2003 in press). An ellipse, based on both distance from source to receiver and wavelength, can be used to approximate the effect on the structure along the ray path and adjacent structure. Three models were tested in order to select the appropriate distribution within the ellipse; the first case gives equal weight to all blocks within the ellipse; case 2 incorporates a Gaussian function which falls off perpendicular to the ray path, allowing the amplitude to peak at the receiver; case 3 is the same as case 2, yet removes the effect of the peak at the receiver. A major improvement is that the locale under consideration has expanded due to the effect of ray paths spreading over a larger area than the ray theoretical. Comparison of the three techniques yields very similar results, and all techniques show an exceptional correlation to the ray theoretical phase velocity maps. After analyzing our data in terms of the finite frequency effect, we find that little change has occurred as a result of employing this technique other than expanding our region of study. P-wave measurements were obtained from the data set for 118 events. Preliminary results show systematic patterns. We have successfully measured 30 S-wave events which we plan to incorporate into our velocity structure. Our goal is to proceed with a joint inversion of P-waves, S-waves and Surface waves for a collective Southern California velocity structure.

Dispersion analysis of passive surface-wave noise generated during hydraulic-fracturing operations

USGS Publications Warehouse

Forghani-Arani, Farnoush; Willis, Mark; Snieder, Roel; Haines, Seth S.; Behura, Jyoti; Batzle, Mike; Davidson, Michael

2014-01-01

Surface-wave dispersion analysis is useful for estimating near-surface shear-wave velocity models, designing receiver arrays, and suppressing surface waves. Here, we analyze whether passive seismic noise generated during hydraulic-fracturing operations can be used to extract surface-wave dispersion characteristics. Applying seismic interferometry to noise measurements, we extract surface waves by cross-correlating several minutes of passive records; this approach is distinct from previous studies that used hours or days of passive records for cross-correlation. For comparison, we also perform dispersion analysis for an active-source array that has some receivers in common with the passive array. The active and passive data show good agreement in the dispersive character of the fundamental-mode surface-waves. For the higher mode surface waves, however, active and passive data resolve the dispersive properties at different frequency ranges. To demonstrate an application of dispersion analysis, we invert the observed surface-wave dispersion characteristics to determine the near-surface, one-dimensional shear-wave velocity.

The Effects of Realistic Geological Heterogeneity on Seismic Modeling: Applications in Shear Wave Generation and Near-Surface Tunnel Detection

NASA Astrophysics Data System (ADS)

Sherman, Christopher Scott

Naturally occurring geologic heterogeneity is an important, but often overlooked, aspect of seismic wave propagation. This dissertation presents a strategy for modeling the effects of heterogeneity using a combination of geostatistics and Finite Difference simulation. In the first chapter, I discuss my motivations for studying geologic heterogeneity and seis- mic wave propagation. Models based upon fractal statistics are powerful tools in geophysics for modeling heterogeneity. The important features of these fractal models are illustrated using borehole log data from an oil well and geomorphological observations from a site in Death Valley, California. A large part of the computational work presented in this disserta- tion was completed using the Finite Difference Code E3D. I discuss the Python-based user interface for E3D and the computational strategies for working with heterogeneous models developed over the course of this research. The second chapter explores a phenomenon observed for wave propagation in heteroge- neous media - the generation of unexpected shear wave phases in the near-source region. In spite of their popularity amongst seismic researchers, approximate methods for modeling wave propagation in these media, such as the Born and Rytov methods or Radiative Trans- fer Theory, are incapable of explaining these shear waves. This is primarily due to these method's assumptions regarding the coupling of near-source terms with the heterogeneities and mode conversion. To determine the source of these shear waves, I generate a suite of 3D synthetic heterogeneous fractal geologic models and use E3D to simulate the wave propaga- tion for a vertical point force on the surface of the models. I also present a methodology for calculating the effective source radiation patterns from the models. The numerical results show that, due to a combination of mode conversion and coupling with near-source hetero- geneity, shear wave energy on the order of 10% of the compressional wave energy may be generated within the shear radiation node of the source. Interestingly, in some cases this shear wave may arise as a coherent pulse, which may be used to improve seismic imaging efforts. In the third and fourth chapters, I discuss the results of a numerical analysis and field study of seismic near-surface tunnel detection methods. Detecting unknown tunnels and voids, such as old mine workings or solution cavities in karst terrain, is a challenging prob- lem in geophysics and has implications for geotechnical design, public safety, and domestic security. Over the years, a number of different geophysical methods have been developed to locate these objects (microgravity, resistivity, seismic diffraction, etc.), each with varying results. One of the major challenges facing these methods is understanding the influence of geologic heterogeneity on their results, which makes this problem a natural extension of the modeling work discussed in previous chapters. In the third chapter, I present the results of a numerical study of surface-wave based tunnel detection methods. The results of this analysis show that these methods are capable of detecting a void buried within one wavelength of the surface, with size potentially much less than one wavelength. In addition, seismic surface- wave based detection methods are effective in media with moderate heterogeneity (epsilon < 5 %), and in fact, this heterogeneity may serve to increase the resolution of these methods. In the fourth chapter, I discuss the results of a field study of tunnel detection methods at a site within the Black Diamond Mines Regional Preserve, near Antioch California. I use a com- bination of surface wave backscattering, 1D surface wave attenuation, and 2D attenuation tomography to locate and determine the condition of two tunnels at this site. These results compliment the numerical study in chapter 3 and highlight their usefulness for detecting tunnels at other sites.

Scattered surface wave energy in the seismic coda

USGS Publications Warehouse

Zeng, Y.

2006-01-01

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

Application of interface waves for near surface damage detection in hybrid structures

NASA Astrophysics Data System (ADS)

Jahanbin, M.; Santhanam, S.; Ihn, J.-B.; Cox, A.

2017-04-01

Guided waves are acoustic waves that are guided by boundaries. Depending on the structural geometry, guided waves can either propagate between boundaries, known as plate waves, or propagate on the surface of the objects. Many different types of surface waves exist based on the material property of the boundary. For example Rayleigh wave in solid - air, Scholte wave in solid - liquid, Stoneley in solid - solid interface and many other different forms like Love wave on inhomogeneous surfaces, creeping waves, etc. This research work is demonstrating the application of surface and interface waves for detection of interfacial damages in hybrid bonded structures.

Regional Climate Variability Under Model Simulations of Solar Geoengineering

NASA Astrophysics Data System (ADS)

Dagon, Katherine; Schrag, Daniel P.

2017-11-01

Solar geoengineering has been shown in modeling studies to successfully mitigate global mean surface temperature changes from greenhouse warming. Changes in land surface hydrology are complicated by the direct effect of carbon dioxide (CO2) on vegetation, which alters the flux of water from the land surface to the atmosphere. Here we investigate changes in boreal summer climate variability under solar geoengineering using multiple ensembles of model simulations. We find that spatially uniform solar geoengineering creates a strong meridional gradient in the Northern Hemisphere temperature response, with less consistent patterns in precipitation, evapotranspiration, and soil moisture. Using regional summertime temperature and precipitation results across 31-member ensembles, we show a decrease in the frequency of heat waves and consecutive dry days under solar geoengineering relative to a high-CO2 world. However in some regions solar geoengineering of this amount does not completely reduce summer heat extremes relative to present day climate. In western Russia and Siberia, an increase in heat waves is connected to a decrease in surface soil moisture that favors persistent high temperatures. Heat waves decrease in the central United States and the Sahel, while the hydrologic response increases terrestrial water storage. Regional changes in soil moisture exhibit trends over time as the model adjusts to solar geoengineering, particularly in Siberia and the Sahel, leading to robust shifts in climate variance. These results suggest potential benefits and complications of large-scale uniform climate intervention schemes.

Two-dimensional single-cell patterning with one cell per well driven by surface acoustic waves

PubMed Central

Collins, David J.; Morahan, Belinda; Garcia-Bustos, Jose; Doerig, Christian; Plebanski, Magdalena; Neild, Adrian

2015-01-01

In single-cell analysis, cellular activity and parameters are assayed on an individual, rather than population-average basis. Essential to observing the activity of these cells over time is the ability to trap, pattern and retain them, for which previous single-cell-patterning work has principally made use of mechanical methods. While successful as a long-term cell-patterning strategy, these devices remain essentially single use. Here we introduce a new method for the patterning of multiple spatially separated single particles and cells using high-frequency acoustic fields with one cell per acoustic well. We characterize and demonstrate patterning for both a range of particle sizes and the capture and patterning of cells, including human lymphocytes and red blood cells infected by the malarial parasite Plasmodium falciparum. This ability is made possible by a hitherto unexplored regime where the acoustic wavelength is on the same order as the cell dimensions. PMID:26522429

Investigation on the real-time prediction of ground motions using seismic records observed in deep boreholes

NASA Astrophysics Data System (ADS)

Miyakoshi, H.; Tsuno, S.

2013-12-01

The present method of the EEW system installed in the railway field of Japan predicts seismic ground motions based on the estimated earthquake information about epicentral distances and magnitudes using initial P-waves observed on the surface. In the case of local earthquakes beneath the Tokyo Metropolitan Area, however, a method to directly predict seismic ground motions using P-waves observed in deep boreholes could issue EEWs more simply and surely. Besides, a method to predict seismic ground motions, using S-waves observed in deep boreholes and S-wave velocity structures beneath seismic stations, could show planar distributions of ground motions for train operation control areas in the aftermath of earthquakes. This information is available to decide areas in which the emergency inspection of railway structures should be performed. To develop those two methods, we investigated relationships between peak amplitudes on the surface and those in deep boreholes, using seismic records of KiK-net stations in the Kanto Basin. In this study, we used earthquake accelerograms observed in boreholes whose depths are deeper than the top face of Pre-Neogene basement and those on the surface at 12 seismic stations of KiK-net. We selected 243 local earthquakes whose epicenters are located around the Kanto Region. Those JMA magnitudes are in the range from 4.5 to 7.0. We picked the on-set of P-waves and S-waves using a vertical component and two horizontal components, respectively. Peak amplitudes of P-waves and S-waves were obtained using vertical components and vector sums of two horizontal components, respectively. We estimated parameters which represent site amplification factors beneath seismic stations, using peak amplitudes of S-waves observed in the deep borehole and those on the surface, to minimize the residuals between calculations by the theoretical equation and observations. Correlation coefficients between calculations and observations are high values in the range from 0.8 to 0.9. This result suggests that we could predict ground motions with the high accuracy using peak amplitudes of S-waves in deep boreholes and site amplification factors based on S-wave velocity structures. Also, we estimated parameters which represent radiation coefficients and the P/S velocity ratios around hypocentral regions, using peak amplitudes of P-waves and S-waves observed in deep boreholes, to minimize the residuals between calculations and observations. Correlation coefficients between calculations and observations are slightly lower values in the range from 0.7 to 0.9 than those for site amplification factors. This result suggests that the variability of radiation patterns for individual earthquakes affects the accuracy to predict ground motions using P-waves in deep boreholes.

Terahertz pulse generation from metal nanoparticle ink

NASA Astrophysics Data System (ADS)

Kato, Kosaku; Takano, Keisuke; Tadokoro, Yuzuru; Phan, Thanh Nhat Khoa; Nakajima, Makoto

2016-11-01

Terahertz pulse generation from metallic nanostructures irradiated by femtosecond laser pulses is of interest because the conversion efficiency from laser pulses to terahertz waves is increased by the local field enhancement resulting from the plasmon oscillation. In this talk we present our recent study on terahertz generation from metal nanoparticle ink. We baked a silver nanoparticle ink spin-coated onto a glass coverslip in various temperatures. On the surface of the baked ink, bumpy nanostructures are spontaneously formed, and the average size of bumps depends on the baking temperature. These structures are expected to lead to local field enhancement and then large nonlinear polarizations on the surface. The baked ink was irradiated by the output of regeneratively amplified Ti:sapphire femtosecond laser at an incidence angle of 45°. Waveforms of generated terahertz pulses are detected by electro-optical sampling. The generation efficiency was high when the average diameter of bumps was around 100 nm, which is realized when the ink is baked in 205 to 235°C in our setup. One of our next research targets is terahertz wave generation from micro-patterned metallic nanoparticle ink. It is an advantage of the metal nanoparticle ink that by using inkjet printers one can fabricate various patterns with micrometer scales, in which terahertz waves have a resonance. Combination of microstructures made by a printer and nanostructure spontaneously formed in the baking process will provide us terahertz emitters with unique frequency characteristics.

Influence of San Gabriel submarine canyon on narrow-shelf sediment dynamics, southern California

USGS Publications Warehouse

Karl, Herman A.

1980-01-01

A conceptual model attributes the PTC to modification of shelf circulation patterns by San Gabriel Canyon. Surface waves diverge over the canyon head resulting in differential wave set up at the shore face. This forces back turbid nearshore water for a distance of a few kilometers toward the canyon. At some point on the shelf, seaward nearshore flow overlaps offshore currents generated or modified by internal waves focused onto the shelf by the canyon and/or turbulent eddies produced by flow separation in currents moving across the canyon axis. At times, these subtle processes overprint tidal and wind-driven currents and thereby create the PTC. The model suggests that canyons heading several kilometers from shore can have a regulatory effect on narrow-shelf sediment dynamics.

The Effect of Surface Topography on the Nonlinear Dynamics of Rossby Waves

NASA Technical Reports Server (NTRS)

Abarzhi, S. I.; Desjardins, O.; Pitsch, H.

2003-01-01

Boussinesq convection in rotating systems attracts a sustained attention of the fluid dynamics community, because it has intricate non-linear dynamics (Cross & Hohenberg 1993) and plays an important role in geophysical and astrophysical applications, such as the motion of the liquid outer core of Earth, the Red Spot in Jupiter, the giant cells in the Sun etc. (Alridge et al. 1990). A fundamental distinction between the real geo- and astrophysical problems and the idealized laboratory studies is that natural systems are inhomogeneous (Alridge et al. 1990). Heterogeneities modulate the flow and influence significantly the dynamics of convective patterns (Alridge et al. 1990; Hide 1971). The effect of modulations on pattern formation and transition to turbulence in Boussinesq convection is far from being completely understood (Cross & Hohenberg 1993; Aranson & Kramer 2002). It is generally accepted that in the liquid outer core of the Earth the transport of the angular momentum and internal heat occurs via thermal Rossby waves (Zhang et al. 2001; Kuang & Bloxham 1999). These waves been visualized in laboratory experiments in rotating liquid-filled spheres and concentric spherical shells (Zhang et al. 2001; Kuang & Bloxham 1999). The basic dynamical features of Rossby waves have been reproduced in a cylindrical annulus, a system much simpler than the spherical ones (Busse & Or 1986; Or & Busse 1987). For convection in a cylindrical annulus, the fluid motion is two-dimensional, and gravity is replaced by a centrifugal force, (Busse & Or 1986; Or & Busse 1987). Hide (1971) has suggested that the momentum and heat transport in the core might be influenced significantly by so-called bumps, which are heterogeneities on the mantle-core boundary. To model the effect of surface topography on the transport of momentum and energy in the liquid outer core of the Earth, Bell & Soward (1996), Herrmann & Busse (1998) and Westerburg & Busse (2001) have studied the nonlinear dynamics of thermal Rossby waves in a cylindrical annulus with azimuthally modulated height.

Storm-driven sediment transport in Massachusetts Bay

USGS Publications Warehouse

Warner, J.C.; Butman, B.; Dalyander, P.S.

2008-01-01

Massachusetts Bay is a semi-enclosed embayment in the western Gulf of Maine about 50 km wide and 100 km long. Bottom sediment resuspension is controlled predominately by storm-induced surface waves and transport by the tidal- and wind-driven circulation. Because the Bay is open to the northeast, winds from the northeast ('Northeasters') generate the largest surface waves and are thus the most effective in resuspending sediments. The three-dimensional oceanographic circulation model Regional Ocean Modeling System (ROMS) is used to explore the resuspension, transport, and deposition of sediment caused by Northeasters. The model transports multiple sediment classes and tracks the evolution of a multilevel sediment bed. The surficial sediment characteristics of the bed are coupled to one of several bottom-boundary layer modules that calculate enhanced bottom roughness due to wave-current interaction. The wave field is calculated from the model Simulating WAves Nearshore (SWAN). Two idealized simulations were carried out to explore the effects of Northeasters on the transport and fate of sediments. In one simulation, an initially spatially uniform bed of mixed sediments exposed to a series of Northeasters evolved to a pattern similar to the existing surficial sediment distribution. A second set of simulations explored sediment-transport pathways caused by storms with winds from the northeast quadrant by simulating release of sediment at selected locations. Storms with winds from the north cause transport southward along the western shore of Massachusetts Bay, while storms with winds from the east and southeast drive northerly nearshore flow. The simulations show that Northeasters can effectively transport sediments from Boston Harbor and the area offshore of the harbor to the southeast into Cape Cod Bay and offshore into Stellwagen Basin. This transport pattern is consistent with Boston Harbor as the source of silver found in the surficial sediments of Cape Cod Bay and Stellwagen Basin.

Seasonality of P wave microseisms from NCF-based beamforming using ChinArray

NASA Astrophysics Data System (ADS)

Wang, Weitao; Gerstoft, Peter; Wang, Baoshan

2018-06-01

Teleseismic P wave microseisms produce interference signals with high apparent velocity in noise cross-correlation functions (NCFs). Sources of P wave microseisms can be located with NCFs from seismic arrays. Using the vertical-vertical component NCFs from a large-aperture array in southwestern China (ChinArray), we studied the P wave source locations and their seasonality of microseisms at two period bands (8-12 and 4-8 s) with an NCF-based beamforming method. The sources of P, PP and PKPbc waves are located. The ambiguity between P and PP source locations is analysed using averaged significant ocean wave height and sea surface pressure as constraints. The results indicate that the persistent P wave sources are mainly located in the deep oceans such as the North Atlantic, North Pacific and Southern Ocean, in agreement with previous studies. The Gulf of Alaska is found to generate P waves favouring the 8-12 s period band. The seasonality of P wave sources is consistent with the hemispheric storm pattern, which is stronger in local winter. Using the identified sources, arrival times of the interference signals are predicted and agree well with observations. The interference signals exhibit seasonal variation, indicating that body wave microseisms in southwestern China are from multiple seasonal sources.

Experimental verification of electrostatic boundary conditions in gate-patterned quantum devices

NASA Astrophysics Data System (ADS)

Hou, H.; Chung, Y.; Rughoobur, G.; Hsiao, T. K.; Nasir, A.; Flewitt, A. J.; Griffiths, J. P.; Farrer, I.; Ritchie, D. A.; Ford, C. J. B.

2018-06-01

In a model of a gate-patterned quantum device, it is important to choose the correct electrostatic boundary conditions (BCs) in order to match experiment. In this study, we model gated-patterned devices in doped and undoped GaAs heterostructures for a variety of BCs. The best match is obtained for an unconstrained surface between the gates, with a dielectric region above it and a frozen layer of surface charge, together with a very deep back boundary. Experimentally, we find a  ∼0.2 V offset in pinch-off characteristics of 1D channels in a doped heterostructure before and after etching off a ZnO overlayer, as predicted by the model. Also, we observe a clear quantised current driven by a surface acoustic wave through a lateral induced n-i-n junction in an undoped heterostructure. In the model, the ability to pump electrons in this type of device is highly sensitive to the back BC. Using the improved boundary conditions, it is straightforward to model quantum devices quite accurately using standard software.

Numerical simulation of turbulent convective flow over wavy terrain

NASA Astrophysics Data System (ADS)

Dörnbrack, A.; Schumann, U.

1993-09-01

By means of a large-eddy simulation, the convective boundary layer is investigated for flows over wavy terrain. The lower surface varies sinusoidally in the downstream direction while remaining constant in the other. Several cases are considered with amplitude δ up to 0.15 H and wavelength λ of H to 8 H, where H is the mean fluid-layer height. At the lower surface, the vertical heat flux is prescribed to be constant and the momentum flux is determined locally from the Monin-Obukhov relationship with a roughness length z o=10-4 H. The mean wind is varied between zero and 5 w *, where w * is the convective velocity scale. After rather long times, the flow structure shows horizontal scales up to 4 H, with a pattern similar to that over flat surfaces at corresponding shear friction. Weak mean wind destroys regular spatial structures induced by the surface undulation at zero mean wind. The surface heating suppresses mean-flow recirculation-regions even for steep surface waves. Short surface waves cause strong drag due to hydrostatic and dynamic pressure forces in addition to frictional drag. The pressure drag increases slowly with the mean velocity, and strongly with δ/ H. The turbulence variances increase mainly in the lower half of the mixed layer for U/w *>2.

Superconducting states of topological surface states in β-PdBi2 investigated by STM/STS

NASA Astrophysics Data System (ADS)

Iwaya, Katsuya; Okawa, Kenjiro; Hanaguri, Tetsuo; Kohsaka, Yuhki; Machida, Tadashi; Sasagawa, Takao

We investigate superconducting (SC) states of topological surface states in β-PdBi2 using very low temperature STM. Characteristic quasiparticle interference patterns strongly support the existence of the spin-polarized surface states at the Fermi level in the normal state. A fully-opened SC gap well described by the conventional BCS model is observed, indicating the SC gap opening at the spin-polarized Fermi surfaces. Considering a possible mixing of odd- and even parity orbital functions in C4v group symmetry lowered from D4h near the surface, we suggest that the SC gap consists of the mixture of s- and p-wave SC gap functions in the two-dimensional state.

Spin flip statistics and spin wave interference patterns in Ising ferromagnetic films: A Monte Carlo study.

PubMed

Acharyya, Muktish

2017-07-01

The spin wave interference is studied in two dimensional Ising ferromagnet driven by two coherent spherical magnetic field waves by Monte Carlo simulation. The spin waves are found to propagate and interfere according to the classic rule of interference pattern generated by two point sources. The interference pattern of spin wave is observed in one boundary of the lattice. The interference pattern is detected and studied by spin flip statistics at high and low temperatures. The destructive interference is manifested as the large number of spin flips and vice versa.

Time-domain full-waveform inversion of Rayleigh and Love waves in presence of free-surface topography

NASA Astrophysics Data System (ADS)

Pan, Yudi; Gao, Lingli; Bohlen, Thomas

2018-05-01

Correct estimation of near-surface seismic-wave velocity when encountering lateral heterogeneity and free surface topography is one of the challenges to current shallow seismic. We propose to use time-domain full-waveform inversion (FWI) of surface waves, including both Rayleigh and Love waves, to solve this problem. We adopt a 2D time-domain finite-difference method with an improved vacuum formulation (IVF) to simulate shallow-seismic Rayleigh wave in presence of free-surface topography. We modify the IVF for SH-wave equation for the simulation of Love wave in presence of topographic free surface and prove its accuracy by benchmark tests. Checkboard model tests are performed in both cases when free-surface topography is included or neglected in FWI. Synthetic model containing a dipping planar free surface and lateral heterogeneity was then tested, in both cases of considering and neglecting free-surface topography. Both checkerboard and synthetic models show that Rayleigh- and Love-wave FWI have similar ability of reconstructing near-surface structures when free-surface topography is considered, while Love-wave FWI could reconstruct near-surface structures better than Rayleigh-wave when free-surface topography is neglected.

The 2010 Pakistan Flood and Russian Heat Wave: Teleconnection of Hydrometeorological Extremes

NASA Technical Reports Server (NTRS)

Lau, William K. M.; Kim, Kyu-Myong

2012-01-01

In this paper, preliminary results are presented showing that the two record-setting extreme events during 2010 summer (i.e., the Russian heat wave-wildfires and Pakistan flood) were physically connected. It is found that the Russian heat wave was associated with the development of an extraordinarily strong and prolonged extratropical atmospheric blocking event in association with the excitation of a large-scale atmospheric Rossby wave train spanning western Russia, Kazakhstan, and the northwestern China-Tibetan Plateau region. The southward penetration of upper-level vorticity perturbations in the leading trough of the Rossby wave was instrumental in triggering anomalously heavy rain events over northern Pakistan and vicinity in mid- to late July. Also shown are evidences that the Russian heat wave was amplified by a positive feedback through changes in surface energy fluxes between the atmospheric blocking pattern and an underlying extensive land region with below-normal soil moisture. The Pakistan heavy rain events were amplified and sustained by strong anomalous southeasterly flow along the Himalayan foothills and abundant moisture transport from the Bay of Bengal in connection with the northward propagation of the monsoonal intraseasonal oscillation.

Cyclodextrin-based microsensor for volatile organic compounds

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

Swanson, B.I.; Li, D.Q.

1996-12-31

The direct covalent attachment of modified {alpha}- and {beta}-cyclodextrin on oxide surfaces has been studied for application in chemical sensors. First, oxide surfaces were treated with a silane coupling layer followed by the addition of cyclodextrin to form a self-assembled monolayer (SAM) of host receptors. Second, the oxide surfaces were reacted with a sol-gel (SG) precursor based on cyclodextrin structure to form a thick film with defined hydrophobic cyclodextrin cavities. The sensing properties of both films (SAM and SG) were examined with surface acoustic wave (SAW) measurement platform. Molecular interactions between an organic guest and a host thin-film on amore » 200 MHZ SAW resonator are being studied as a method of tracking and recognizing the presence of volatile organics. Surface acoustic wave sensors based on the inclusion chemistry of the bucket-type (cyclodextrin) molecules, were capable of detecting volatile organic compounds (VOCs) down to ppb levels. Because the nature of the interactions is moderate but noncovalent, detection of these VOCs was possible using a reversible real-time mode. Pattern recognition with an array of complementary microsensors appears to be a viable approach for identifying and quantifying VOCs. Recent results using optical waveguides for sensor transduction will also be discussed.« less

SITE AMPLIFICATION OF EARTHQUAKE GROUND MOTION.

USGS Publications Warehouse

Hays, Walter W.

1986-01-01

When analyzing the patterns of damage in an earthquake, physical parameters of the total earthquake-site-structure system are correlated with the damage. Soil-structure interaction, the cause of damage in many earthquakes, involves the frequency-dependent response of both the soil-rock column and the structure. The response of the soil-rock column (called site amplification) is controversial because soil has strain-dependent properties that affect the way the soil column filters the input body and surface seismic waves, modifying the amplitude and phase spectra and the duration of the surface ground motion.

Experimental observation of standing interfacial waves induced by surface waves in muddy water

NASA Astrophysics Data System (ADS)

Maxeiner, Eric; Dalrymple, Robert A.

2011-09-01

A striking feature has been observed in a laboratory wave tank with a thin layer of clear water overlying a layer of mud. A piston-type wave maker is used to generate long monochromatic surface waves in a tank with a layer of kaolinite clay at the bottom. The wave action on the mud causes the clay particles to rise from the bottom into the water column, forming a lutocline. As the lutocline approaches the water surface, a set of standing interfacial waves form on the lutocline. The interfacial wave directions are oriented nearly orthogonal to the surface wave direction. The interfacial waves, which sometimes cover the entire length and width of the tank, are also temporally subharmonic as the phase of the interfacial wave alternates with each passing surface wave crest. These interfacial waves are the result of a resonant three-wave interaction involving the surface wave train and the two interfacial wave trains. The interfacial waves are only present when the lutocline is about 3 cm of the water surface and they can be sufficiently nonlinear as to exhibit superharmonics and a breaking-type of instability.

Externally driven magnetic granular layers at a liquid/air interface: self-organization, flows and magnetic order

NASA Astrophysics Data System (ADS)

Snezhko, Alexey

2007-03-01

Collective dynamics and pattern formation in ensembles of magnetic microparticles suspended at the liquid/air interface and subjected to an alternating magnetic field are studied. Experiments reveal a new type of nontrivially ordered dynamic self-assembled structures (``snakes'') emerging in such systems in a certain range of field magnitudes and frequencies. These remarkable structures are directly related to surface waves in the liquid generated by the collective response of magnetic microparticles to the alternating magnetic field. In addition, a large-scale vortex flows are induced in the vicinity of the dynamic structures. Some features of the self-localized snake structures can be understood in the framework of an amplitude equation for parametric waves coupled to the conservation law equation describing the evolution of the magnetic particle density. Self-assembled snakes have a complex magnetic order: the segments of the snake exhibit long-range antiferromagnetic ordering mediated by the surface wave, while each segment is composed of ferromagnetically aligned chains of microparticles. A phenomenological model describing magnetic behavior of the magnetic snakes in external magnetic fields is proposed.

Surface plasmon enhanced cell microscopy with blocked random spatial activation

NASA Astrophysics Data System (ADS)

Son, Taehwang; Oh, Youngjin; Lee, Wonju; Yang, Heejin; Kim, Donghyun

2016-03-01

We present surface plasmon enhanced fluorescence microscopy with random spatial sampling using patterned block of silver nanoislands. Rigorous coupled wave analysis was performed to confirm near-field localization on nanoislands. Random nanoislands were fabricated in silver by temperature annealing. By analyzing random near-field distribution, average size of localized fields was found to be on the order of 135 nm. Randomly localized near-fields were used to spatially sample F-actin of J774 cells (mouse macrophage cell-line). Image deconvolution algorithm based on linear imaging theory was established for stochastic estimation of fluorescent molecular distribution. The alignment between near-field distribution and raw image was performed by the patterned block. The achieved resolution is dependent upon factors including the size of localized fields and estimated to be 100-150 nm.

On the generation of internal wave modes by surface waves

NASA Astrophysics Data System (ADS)

Harlander, Uwe; Kirschner, Ian; Maas, Christian; Zaussinger, Florian

2016-04-01

Internal gravity waves play an important role in the ocean since they transport energy and momentum and the can lead to mixing when they break. Surface waves and internal gravity waves can interact. On the one hand, long internal waves imply a slow varying shear current that modifies the propagation of surface waves. Surface waves generated by the atmosphere can, on the other hand, excite internal waves by nonlinear interaction. Thereby a surface wave packet consisting of two close frequencies can resonate with a low frequency internal wave (Phillips, 1966). From a theoretical point of view, the latter has been studied intensively by using a 2-layer model, i.e. a surface layer with a strong density contrast and an internal layer with a comparable weak density contrast (Ball, 1964; Craig et al., 2010). In the present work we analyse the wave coupling for a continuously stratified fluid using a fully non-linear 2D numerical model (OpenFoam) and compare this with laboratory experiments (see Lewis et al. 1974). Surface wave modes are used as initial condition and the time development of the dominant surface and internal waves are studied by spectral and harmonic analysis. For the simple geometry of a box, the results are compared with analytical spectra of surface and gravity waves. Ball, F.K. 1964: Energy transfer between external and internal gravity waves. J. Fluid Mech. 19, 465. Craig, W., Guyenne, P., Sulem, C. 2010: Coupling between internal and surface waves. Natural Hazards 57, 617-642. Lewis, J.E., Lake, B.M., Ko, D.R.S 1974: On the interaction of internal waves and surfacr gravity waves, J. Fluid Mech. 63, 773-800. Phillips, O.M. 1966: The dynamics of the upper ocean, Cambridge University Press, 336pp.

Seismic Technology Adapted to Analyzing and Developing Geothermal Systems Below Surface-Exposed High-Velocity Rocks Final Report

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

Hardage, Bob A.; DeAngelo, Michael V.; Ermolaeva, Elena

The objective of our research was to develop and demonstrate seismic data-acquisition and data-processing technologies that allow geothermal prospects below high-velocity rock outcrops to be evaluated. To do this, we acquired a 3-component seismic test line across an area of exposed high-velocity rocks in Brewster County, Texas, where there is high heat flow and surface conditions mimic those found at numerous geothermal prospects. Seismic contractors have not succeeded in creating good-quality seismic data in this area for companies who have acquired data for oil and gas exploitation purposes. Our test profile traversed an area where high-velocity rocks and low-velocity sedimentmore » were exposed on the surface in alternating patterns that repeated along the test line. We verified that these surface conditions cause non-ending reverberations of Love waves, Rayleigh waves, and shallow critical refractions to travel across the earth surface between the boundaries of the fast-velocity and slow-velocity material exposed on the surface. These reverberating surface waves form the high level of noise in this area that does not allow reflections from deep interfaces to be seen and utilized. Our data-acquisition method of deploying a box array of closely spaced geophones allowed us to recognize and evaluate these surface-wave noise modes regardless of the azimuth direction to the surface anomaly that backscattered the waves and caused them to return to the test-line profile. With this knowledge of the surface-wave noise, we were able to process these test-line data to create P-P and SH-SH images that were superior to those produced by a skilled seismic data-processing contractor. Compared to the P-P data acquired along the test line, the SH-SH data provided a better detection of faults and could be used to trace these faults upward to the boundaries of exposed surface rocks. We expanded our comparison of the relative value of S-wave and P-wave seismic data for geothermal applications by inserting into this report a small part of the interpretation we have done with 3C3D data across Wister geothermal field in the Imperial Valley of California. This interpretation shows that P-SV data reveal faults (and by inference, also fractures) that cannot be easily, or confidently, seen with P-P data, and that the combination of P-P and P-SV data allows VP/VS velocity ratios to be estimated across a targeted reservoir interval to show where an interval has more sandstone (the preferred reservoir facies). The conclusion reached from this investigation is that S-wave seismic technology can be invaluable to geothermal operators. Thus we developed a strong interest in understanding the direct-S modes produced by vertical-force sources, particularly vertical vibrators, because if it can be demonstrated that direct-S modes produced by vertical-force sources can be used as effectively as the direct-S modes produced by horizontal-force sources, geothermal operators can acquire direct-S data across many more prospect areas than can be done with horizontal-force sources, which presently are limited to horizontal vibrators. We include some of our preliminary work in evaluating direct-S modes produced by vertical-force sources.« less

Simulation of the light emission properties of patterned metal-based nanostructures for ultra-high density optical storage

NASA Astrophysics Data System (ADS)

Li, Weijun; Zhu, Yaping; Luo, Jun; Peng, Sha; Lei, Yu; Tong, Qing; Zhang, Xinyu; Xie, Changsheng

2015-10-01

Current researches show that the surface plasmon-polariton modes (SPPMs) in metallic nanostructures can lead to a powerful localization of guided light signals, which is generally as small as a few nanometers and thus far beyond the diffraction limit of electromagnetic waves in dielectric media. In this paper, our attention is paid to the modeling and simulation of particular kinds of patterned metal-based nanostructure fabricated over several common wafers such as typical silicon dioxide. The nanostructures are designed for concentrating and delivering incident light energy into nanoscale regions. In our research, the factors, for instance, optical materials, patterned nano-structures, the distance arrangement between adjacent single nanopattern, and the frequency of incident electromagnetic wave, are taken as variables, and further the CST microwave studio is used to simulate optical behaviors of the devices developed by us. By comparing the transmittance and electric field intensity distribution in small area, the nano-light-emission effects are analyzed, and the conditions for obtaining near-field nanospots have been chosen.

On the modeling of the bottom particles segregation with non-linear diffusion equations: application to the marine sand ripples

NASA Astrophysics Data System (ADS)

Tiguercha, Djlalli; Bennis, Anne-claire; Ezersky, Alexander

2015-04-01

The elliptical motion in surface waves causes an oscillating motion of the sand grains leading to the formation of ripple patterns on the bottom. Investigation how the grains with different properties are distributed inside the ripples is a difficult task because of the segration of particle. The work of Fernandez et al. (2003) was extended from one-dimensional to two-dimensional case. A new numerical model, based on these non-linear diffusion equations, was developed to simulate the grain distribution inside the marine sand ripples. The one and two-dimensional models are validated on several test cases where segregation appears. Starting from an homogeneous mixture of grains, the two-dimensional simulations demonstrate different segregation patterns: a) formation of zones with high concentration of light and heavy particles, b) formation of «cat's eye» patterns, c) appearance of inverse Brazil nut effect. Comparisons of numerical results with the new set of field data and wave flume experiments show that the two-dimensional non-linear diffusion equations allow us to reproduce qualitatively experimental results on particles segregation.

Surface waves in the western Taiwan coastal plain from an aftershock of the 1999 Chi-Chi, Taiwan, earthquake

USGS Publications Warehouse

Wang, G.-Q.; Tang, G.-Q.; Boore, D.M.; Van Ness, Burbach; Jackson, C.R.; Zhou, X.-Y.; Lin, Q.-L.

2006-01-01

Significant surface waves were recorded in the western coastal plain (WCP) of Taiwan during the 1999 Chi-Chi, Taiwan, earthquake and its series of aftershocks. We study in detail the surface waves produced by one aftershock (20 September 1999, 18hr 03m 41.16sec, M 6.2) in this paper. We take the Chelungpu-Chukou fault to be the eastern edge of the WCP because it marks a distinct lateral contrast in seismic wave velocities in the upper few kilometers of the surface. For many records from stations within the WCP, body waves and surface waves separate well in both the time domain and the period domain. Long-period (e.g., >2 sec) ground motions in the plain are dominated by surface waves. Significant prograde Rayleigh wave particle motions were observed in the WCP. The observed peak ground velocities are about 3-5 times larger than standard predictions in the central and western part of the plain. Observed response spectra at 3 sec, 4 sec, and 5 sec at the center of the plain can be 15 times larger than standard predictions and 10 times larger than the predictions of Joyner (2000) based on surface wave data from the Los Angeles basin. The strong surface waves were probably generated at the boundary of the WCP and then propagated toward the west, largely along radial directions relative to the epicenter. The geometry of the boundary may have had a slight effect on propagation directions of surface waves. Group velocities of fundamental mode Rayleigh and Love waves are estimated using the multiple filter analysis (MFA) technique and are refined with phase matched filtering (PMF). Group velocities of fundamental mode surface waves range from about 0.7 km/sec to 1.5 km/sec for the phases at periods from 3 sec to 10 sec. One important observation from this study is that the strongest surface waves were recorded in the center of the plain. The specific location of the strongest motions depends largely on the period of surface waves rather than on specific site conditions or plain structures. Accordingly, we conjecture that surface waves could be generated in a wide area close to boundaries of low-velocity sedimentary wave guides. In the case studied in this article the area can be as wide as 30 km (from the Chelungpu fault to the center of the plain). Surface waves converted by P and S waves at different locations would overlap each other and add constructively along their propagation paths. As a result, the surface waves would get stronger and stronger. Beyond a certain distance to the boundary, no more surface waves would be generated. Consequently, no more local surface waves would be superimposed into the invasive surface waves, and the surface waves would tend to decay in amplitude with distance.

Development of Biological Acoustic Impedance Microscope and its Error Estimation

NASA Astrophysics Data System (ADS)

Hozumi, Naohiro; Nakano, Aiko; Terauchi, Satoshi; Nagao, Masayuki; Yoshida, Sachiko; Kobayashi, Kazuto; Yamamoto, Seiji; Saijo, Yoshifumi

This report deals with the scanning acoustic microscope for imaging cross sectional acoustic impedance of biological soft tissues. A focused acoustic beam was transmitted to the tissue object mounted on the "rear surface" of plastic substrate. A cerebellum tissue of rat and a reference material were observed at the same time under the same condition. As the incidence is not vertical, not only longitudinal wave but also transversal wave is generated in the substrate. The error in acoustic impedance assuming vertical incidence was estimated. It was proved that the error can precisely be compensated, if the beam pattern and acoustic parameters of coupling medium and substrate had been known.

Giant honeybees ( Apis dorsata) mob wasps away from the nest by directed visual patterns

NASA Astrophysics Data System (ADS)

Kastberger, Gerald; Weihmann, Frank; Zierler, Martina; Hötzl, Thomas

2014-11-01

The open nesting behaviour of giant honeybees ( Apis dorsata) accounts for the evolution of a series of defence strategies to protect the colonies from predation. In particular, the concerted action of shimmering behaviour is known to effectively confuse and repel predators. In shimmering, bees on the nest surface flip their abdomens in a highly coordinated manner to generate Mexican wave-like patterns. The paper documents a further-going capacity of this kind of collective defence: the visual patterns of shimmering waves align regarding their directional characteristics with the projected flight manoeuvres of the wasps when preying in front of the bees' nest. The honeybees take here advantage of a threefold asymmetry intrinsic to the prey-predator interaction: (a) the visual patterns of shimmering turn faster than the wasps on their flight path, (b) they "follow" the wasps more persistently (up to 100 ms) than the wasps "follow" the shimmering patterns (up to 40 ms) and (c) the shimmering patterns align with the wasps' flight in all directions at the same strength, whereas the wasps have some preference for horizontal correspondence. The findings give evidence that shimmering honeybees utilize directional alignment to enforce their repelling power against preying wasps. This phenomenon can be identified as predator driving which is generally associated with mobbing behaviour (particularly known in selfish herds of vertebrate species), which is, until now, not reported in insects.

Morphology of ductile metals eroded by a jet of spherical particles impinging at normal incidence

NASA Technical Reports Server (NTRS)

Veerabhadra Rao, P.; Young, S. G.; Buckley, D. H.

1983-01-01

Scanning electron microscopy and energy-dispersive X-ray spectroscopy are used, together with surface profile measurements, in the present morphological study of the erosion of an aluminum alloy and copper by the normal impact of spherical glass erodent particles. The morphology of the damage pattern is a manifestation of the flow pattern of erodent particles, and yields insight into the mechanisms that may be active at different stages of erosion. The simultaneous appearance of radial cracks and concentric rings is reported, together with wave crests which contain an accumulation of metallic flakes. A preliminary analysis is advanced to explain the formation of the various damage patterns observed.

Distinct winter patterns of tropical Pacific convection anomaly and the associated extratropical wave trains in the Northern Hemisphere

NASA Astrophysics Data System (ADS)

Ding, Shuoyi; Chen, Wen; Graf, Hans-F.; Guo, Yuanyuan; Nath, Debashis

2017-11-01

In this paper, distinct patterns of boreal winter convection anomalies over the tropical Pacific and associated wave trains in the extratropics are addressed. The first leading mode (EOF1) of convection anomalies as measured by outgoing longwave radiation demonstrates an east-west oscillation of deep convection with centers over the equatorial central Pacific (CP) and over the tropical western North Pacific and the Maritime Continent. The second leading mode (EOF2) is also a dipole pattern with opposite centers straddling 170°W, possibly modifying EOF1 to some extent. Combining the first two leading modes, five major categories of tropical convection anomalies can be identified for the period 1979/80-2012/13. The comparison between these five categories and the corresponding SST anomaly patterns indicates a nonlinear relationship between convection and SST. The combination of EOF1 and EOF2 with in-phase PCs exhibits an east-west dipole pattern with opposite signs over west of the dateline and the Maritime Continent. The negative phase of the two PCs, named La Niña pattern, induces a negative Pacific/North American—positive North Atlantic Oscillation teleconnection in the extratropics. Approximately opposite responses can be detected in its positive phase, named CP El Niño pattern. The negative PC2 superposing positive PC1, named EP El Niño pattern, shows the strongest convection anomalies with enhanced (depressed) convection over the eastern (western) Pacific and leads to a Tropical/Northern Hemisphere-like teleconnection pattern and an anomalous anticyclone extending from the North Pacific to the North Atlantic. The positive PC2 with neutral PC1, named western CP pattern, shows weakly enhanced convection to the west of the dateline as a response to local SST warming around the dateline. This convection anomaly pattern, although weak, is important and excites a northeastward wave train from the tropics to Greenland, resulting in surface air temperature cooling covering the northeastern North America and warmer and wetter conditions over Western Europe.

Three-component ambient noise beamforming in the Parkfield area

NASA Astrophysics Data System (ADS)

Löer, Katrin; Riahi, Nima; Saenger, Erik H.

2018-06-01

We apply a three-component beamforming algorithm to an ambient noise data set recorded at a seismic array to extract information about both isotropic and anisotropic surface wave velocities. In particular, we test the sensitivity of the method with respect to the array geometry as well as to seasonal variations in the distribution of noise sources. In the earth's crust, anisotropy is typically caused by oriented faults or fractures and can be altered when earthquakes or human activities cause these structures to change. Monitoring anisotropy changes thus provides time-dependent information on subsurface processes, provided they can be distinguished from other effects. We analyse ambient noise data at frequencies between 0.08 and 0.52 Hz recorded at a three-component array in the Parkfield area, California (US), between 2001 November and 2002 April. During this time, no major earthquakes were identified in the area and structural changes are thus not expected. We compute dispersion curves of Love and Rayleigh waves and estimate anisotropy parameters for Love waves. For Rayleigh waves, the azimuthal source coverage is too limited to perform anisotropy analysis. For Love waves, ambient noise sources are more widely distributed and we observe significant and stable surface wave anisotropy for frequencies between 0.2 and 0.4 Hz. Synthetic data experiments indicate that the array geometry introduces apparent anisotropy, especially when waves from multiple sources arrive simultaneously at the array. Both the magnitude and the pattern of apparent anisotropy, however, differ significantly from the anisotropy observed in Love wave data. Temporal variations of anisotropy parameters observed at frequencies below 0.2 Hz and above 0.4 Hz correlate with changes in the source distribution. Frequencies between 0.2 and 0.4 Hz, however, are less affected by these variations and provide relatively stable results over the period of study.

Particle separation by phase modulated surface acoustic waves.

PubMed

Simon, Gergely; Andrade, Marco A B; Reboud, Julien; Marques-Hueso, Jose; Desmulliez, Marc P Y; Cooper, Jonathan M; Riehle, Mathis O; Bernassau, Anne L

2017-09-01

High efficiency isolation of cells or particles from a heterogeneous mixture is a critical processing step in lab-on-a-chip devices. Acoustic techniques offer contactless and label-free manipulation, preserve viability of biological cells, and provide versatility as the applied electrical signal can be adapted to various scenarios. Conventional acoustic separation methods use time-of-flight and achieve separation up to distances of quarter wavelength with limited separation power due to slow gradients in the force. The method proposed here allows separation by half of the wavelength and can be extended by repeating the modulation pattern and can ensure maximum force acting on the particles. In this work, we propose an optimised phase modulation scheme for particle separation in a surface acoustic wave microfluidic device. An expression for the acoustic radiation force arising from the interaction between acoustic waves in the fluid was derived. We demonstrated, for the first time, that the expression of the acoustic radiation force differs in surface acoustic wave and bulk devices, due to the presence of a geometric scaling factor. Two phase modulation schemes are investigated theoretically and experimentally. Theoretical findings were experimentally validated for different mixtures of polystyrene particles confirming that the method offers high selectivity. A Monte-Carlo simulation enabled us to assess performance in real situations, including the effects of particle size variation and non-uniform acoustic field on sorting efficiency and purity, validating the ability to separate particles with high purity and high resolution.

A new point contact surface acoustic wave transducer for measurement of acoustoelastic effect of polymethylmethacrylate.

PubMed

Lee, Yung-Chun; Kuo, Shi Hoa

2004-01-01

A new acoustic transducer and measurement method have been developed for precise measurement of surface wave velocity. This measurement method is used to investigate the acoustoelastic effects for waves propagating on the surface of a polymethylmethacrylate (PMMA) sample. The transducer uses two miniature conical PZT elements for acoustic wave transmitter and receiver on the sample surface; hence, it can be viewed as a point-source/point-receiver transducer. Acoustic waves are excited and detected with the PZT elements, and the wave velocity can be accurately determined with a cross-correlation waveform comparison method. The transducer and its measurement method are particularly sensitive and accurate in determining small changes in wave velocity; therefore, they are applied to the measurement of acoustoelastic effects in PMMA materials. Both the surface skimming longitudinal wave and Rayleigh surface wave can be simultaneously excited and measured. With a uniaxial-loaded PMMA sample, both acoustoelastic effects for surface skimming longitudinal wave and Rayleigh waves of PMMA are measured. The acoustoelastic coefficients for both types of surface wave motions are simultaneously determined. The transducer and its measurement method provide a practical way for measuring surface stresses nondestructively.

Seasonal variability of atmospheric surface layer characteristics and weather pattern in Qatar

NASA Astrophysics Data System (ADS)

Samanta, Dhrubajyoti; Cheng, Way Lee; Sadr, Reza

2016-11-01

Qatar's economy is based on oil and gas industry, which are mostly located in coastal regions. Therefore, better understanding of coastal weather, characteristics of surface layer and turbulence exchange processes is much needed. However, the turbulent atmospheric layer study in this region is severely limited. To support the broader aim and study long term precise wind information, a micro-meteorological field campaign has been carried out in a coastal location of north Qatar. The site is based on a 9 m tower, installed at Al Ghariya in the northern coast of Qatar, equipped with three sonic anemometers, temperature-humidity sensor, radiometer and a weather station. This study shows results based on the period August 2015 to July 2016. Various surface layer characteristics and modellings coefficients based on Monin Obukhov similarity theory is studied for the year and seasonal change is noted. Along with the seasonal variabilities of different weather parameters also observed. We hope this long term field observational study will be very much helpful for research community especially for modelers. In addition, two beach and shoreline monitoring cameras installed at the site could give first time information on waves and shoreline changes, and wind-wave interaction in Qatar. An Preliminary Analysis of Wind-Wave Interaction in Qatar in the Context of Changing Climate.

A cdk1 gradient guides surface contraction waves in oocytes.

PubMed

Bischof, Johanna; Brand, Christoph A; Somogyi, Kálmán; Májer, Imre; Thome, Sarah; Mori, Masashi; Schwarz, Ulrich S; Lénárt, Péter

2017-10-11

Surface contraction waves (SCWs) in oocytes and embryos lead to large-scale shape changes coupled to cell cycle transitions and are spatially coordinated with the cell axis. Here, we show that SCWs in the starfish oocyte are generated by a traveling band of myosin II-driven cortical contractility. At the front of the band, contractility is activated by removal of cdk1 inhibition of the RhoA/RhoA kinase/myosin II signaling module, while at the rear, contractility is switched off by negative feedback originating downstream of RhoA kinase. The SCW's directionality and speed are controlled by a spatiotemporal gradient of cdk1-cyclinB. This gradient is formed by the release of cdk1-cyclinB from the asymmetrically located nucleus, and progressive degradation of cyclinB. By combining quantitative imaging, biochemical and mechanical perturbations with mathematical modeling, we demonstrate that the SCWs result from the spatiotemporal integration of two conserved regulatory modules, cdk1-cyclinB for cell cycle regulation and RhoA/Rok/NMYII for actomyosin contractility.Surface contraction waves (SCWs) are prominent shape changes coupled to cell cycle transitions in oocytes. Here the authors show that SCWs are patterned by the spatiotemporal integration of two conserved modules, cdk1-cyclinB for cell cycle regulation and RhoA/Rok/NMYII for actomyosin contractility.

Refinement and Pattern Formation in Neural Circuits by the Interaction of Traveling Waves with Spike-Timing Dependent Plasticity

PubMed Central

Bennett, James E. M.; Bair, Wyeth

2015-01-01

Traveling waves in the developing brain are a prominent source of highly correlated spiking activity that may instruct the refinement of neural circuits. A candidate mechanism for mediating such refinement is spike-timing dependent plasticity (STDP), which translates correlated activity patterns into changes in synaptic strength. To assess the potential of these phenomena to build useful structure in developing neural circuits, we examined the interaction of wave activity with STDP rules in simple, biologically plausible models of spiking neurons. We derive an expression for the synaptic strength dynamics showing that, by mapping the time dependence of STDP into spatial interactions, traveling waves can build periodic synaptic connectivity patterns into feedforward circuits with a broad class of experimentally observed STDP rules. The spatial scale of the connectivity patterns increases with wave speed and STDP time constants. We verify these results with simulations and demonstrate their robustness to likely sources of noise. We show how this pattern formation ability, which is analogous to solutions of reaction-diffusion systems that have been widely applied to biological pattern formation, can be harnessed to instruct the refinement of postsynaptic receptive fields. Our results hold for rich, complex wave patterns in two dimensions and over several orders of magnitude in wave speeds and STDP time constants, and they provide predictions that can be tested under existing experimental paradigms. Our model generalizes across brain areas and STDP rules, allowing broad application to the ubiquitous occurrence of traveling waves and to wave-like activity patterns induced by moving stimuli. PMID:26308406

Refinement and Pattern Formation in Neural Circuits by the Interaction of Traveling Waves with Spike-Timing Dependent Plasticity.

PubMed

Bennett, James E M; Bair, Wyeth

2015-08-01

Traveling waves in the developing brain are a prominent source of highly correlated spiking activity that may instruct the refinement of neural circuits. A candidate mechanism for mediating such refinement is spike-timing dependent plasticity (STDP), which translates correlated activity patterns into changes in synaptic strength. To assess the potential of these phenomena to build useful structure in developing neural circuits, we examined the interaction of wave activity with STDP rules in simple, biologically plausible models of spiking neurons. We derive an expression for the synaptic strength dynamics showing that, by mapping the time dependence of STDP into spatial interactions, traveling waves can build periodic synaptic connectivity patterns into feedforward circuits with a broad class of experimentally observed STDP rules. The spatial scale of the connectivity patterns increases with wave speed and STDP time constants. We verify these results with simulations and demonstrate their robustness to likely sources of noise. We show how this pattern formation ability, which is analogous to solutions of reaction-diffusion systems that have been widely applied to biological pattern formation, can be harnessed to instruct the refinement of postsynaptic receptive fields. Our results hold for rich, complex wave patterns in two dimensions and over several orders of magnitude in wave speeds and STDP time constants, and they provide predictions that can be tested under existing experimental paradigms. Our model generalizes across brain areas and STDP rules, allowing broad application to the ubiquitous occurrence of traveling waves and to wave-like activity patterns induced by moving stimuli.

Preliminary study of internal wave effects to chlorophyll distribution in the Lombok Strait and adjacent areas

NASA Astrophysics Data System (ADS)

Arvelyna, Yessy; Oshima, Masaki

2005-01-01

This paper studies the effect of internal wave in the Lombok Strait to chlorophyll distribution in the surrounded areas using ERS SAR, ASTER, SeaWiFS and AVHRR-NOAA images data during 1996-2004 periods. The observation results shows that the internal waves were propagated to the south and the north of strait and mostly occurred during transitional season from dry to wet and wet season (rainy season) between September to December when the layers are strongly stratified. Wavelet transform of image using Meyer wavelet analysis is applied for internal wave detection in ERS SAR and ASTER images, for symmetric extension of data at the image boundaries, to prevent discontinuities by a periodic wrapping of data in fast algorithm and space-saving code. Internal wave created elongated pattern in detail and approximation of image from level 2 to 5 and retained value between 2-4.59 times compared to sea surface, provided accuracy in classification over than 80%. In segmentation process, the Canny edge detector is applied on the approximation image at level two to derive internal wave signature in image. The proposed method can extract the internal wave signature, maintain the continuity of crest line while reduce small strikes from noise. The segmentation result, i.e. the length between crest and trough, is used to compute the internal wave induced current using Korteweg-de Vries (KdV) equation. On ERS SAR data contains surface signature of internal wave (2001/8/20), we calculated that internal wave propagation speed was 1.2 m/s and internal wave induced current was 0.56 m/s, respectively. From the observation of ERS SAR and SeaWiFS images data, we found out that the distribution of maximum chlorophyll area at southern coastline off Bali Island when strong internal wave induced current occurred in south of the Lombok Strait was distributed further to westward, i.e. from 9.25°-10.25°LS, 115°-116.25°SE to 8.8°-10.7°LS, 114.5°-116°SE, and surface chlorophyll concentration near coastal area, i.e. area 8.8°-9.25° LS, 114.5°-115°SE, increased. The preliminary result of this study concludes that the internal waves presumably affect chlorophyll distribution to westward (from 9.25°-10.25°LS, 115°-116.25°SE to 8.8°-10.7°LS, 114.5°-116°SE) in the south coast off Bali Island and increase surface chlorophyll concentration near coastal area (8.8°-9.25° LS, 114.5°-115°SE).

Warm Season Subseasonal Variability and Climate Extremes in the Northern Hemisphere: The Role of Stationary Rossby Waves

NASA Technical Reports Server (NTRS)

Schubert, Siegfried; Wang, Hailan; Suarez, Max

2010-01-01

This study examines the nature of boreal summer subseasonal atmospheric variability based on the new NASA Modern-Era Retrospective analysis for Research and Applications (MERRA) for the period 1979-2010. An analysis of the June, July and August subseasonal 250hPa v-wind anomalies shows distinct Rossby wave-like structures that appear to be guided by the mean jets. On monthly subseasonal time scales, the leading waves (the first 10 rotated empirical orthogonal functions or REOFs of the 250hPa v-wind) explain about 50% of the Northern Hemisphere vwind variability, and account for more than 30% (60%) of the precipitation (surface temperature) variability over a number of regions of the northern middle and high latitudes, including the U.S. northern Great Plains, parts of Canada, Europe, and Russia. The first REOF in particular, consists of a Rossby wave that extends across northern Eurasia where it is a dominant contributor to monthly surface temperature and precipitation variability, and played an important role in the 2003 European and 2010 Russian heat waves. While primarily subseasonal in nature, the Rossby waves can at times have a substantial seasonal mean component. This is exemplified by REOF 4 which played a major role in the development of the most intense anomalies of the U.S. 1988 drought (during June) and the 1993 flooding (during July), though differed in the latter event by also making an important contribution to the seasonal mean anomalies. A stationary wave model (SWM) is used to reproduce some of the basic features of the observed waves and provide insight into the nature of the forcing. In particular, the responses to a set of idealized forcing functions are used to map the optimal forcing patterns of the leading waves. Also, experiments to reproduce the observed waves with the SWM using MERRA-based estimates of the forcing indicate that the wave forcing is dominated by sub-monthly vorticity transients.

Thermospheric Extension of the Quasi 6-day Wave Observed by the TIMED Satellite

NASA Astrophysics Data System (ADS)

Gan, Q.; Oberheide, J.

2017-12-01

The quasi 6-day wave is one of the most prevailing planetary waves in the mesosphere and lower thermosphere (MLT) region. Its peak amplitude can attain 20-30 m/s in low-latitude zonal winds at around equinoxes. Consequently, it is anticipated that the 6-day wave can induce not only significantly dynamic effects (via wave-mean flow and wave-wave interactions) in the MLT, but also have significant impacts on the Thermosphere and Ionosphere (T-I). The understanding of the 6-day wave impact on the T-I system has been advanced a lot due to the recent development of whole atmosphere models and new satellite observations. Three pathways were widely proposed to explain the upward coupling due to the 6-day wave: E-region dynamo modulation, dissipation and nonlinear interaction with thermal tides. The current work aims to show a comprehensive pattern of the 6-day wave from the mesosphere up to the thermosphere/ionosphere in neutral fields (temperature, 3-D winds and density) and plasma drifts. To achieve this goal, we carry out the 6-day wave diagnostics by two different means. Firstly, the output of a one-year WACCM+DART run with data assimilation is analyzed to show the global structure of the 6-day wave in the MLT, followed by E-P flux diagnostics to elucidate the 6-day wave source and wave-mean flow interactions. Secondly, we produce observation-based 6-day wave patterns throughout the whole thermosphere by constraining modeled (TIME-GCM) 6-day wave patterns with observed 6-day wave patterns from SABER and TIDI in the MLT region. This allows us to fill the 110-400 km gap between remote sensing and in-situ satellites, and to obtain more realistic 6-day wave plasma drift patterns.

Solar flare leaves sun quaking

NASA Astrophysics Data System (ADS)

1998-05-01

Dr. Alexander G. Kosovichev, a senior research scientist from Stanford University, and Dr. Valentina V. Zharkova from Glasgow (United Kingdom) University found the tell-tale seismic signature in data on the Sun's surface collected by the Michelson Doppler Imager onboard the Solar and Heliospheric Observatory (SOHO) spacecraft immediately following a moderate-sized flare on July 9, 1996. "Although the flare was a moderate one, it still released an immense amount of energy," said Dr. Craig Deforest, a researcher with the SOHO project. "The energy released is equal to completely covering the Earth's continents with a yard of dynamite and detonating it all at once." SOHO is a joint project of the European Space Agency and NASA. The finding is reported in the May 28 issue of the journal Nature, and is the subject of a press conference at the spring meeting of the American Geophysical Union in Boston, Mass., May 27. The solar quake that the science team recorded looks much like ripples spreading from a rock dropped into a pool of water. But over the course of an hour, the solar waves traveled for a distance equal to 10 Earth diameters before fading into the fiery background of the Sun's photosphere. Unlike water ripples that travel outward at a constant velocity, the solar waves accelerated from an initial speed of 22,000 miles per hour to a maximum of 250,000 miles per hour before disappearing. "People have looked for evidence of seismic waves from flares before, but they didn't have a theory so they didn't know where to look," says Kosovichev. Several years ago Kosovichev and Zharkova developed a theory that can explain how a flare, which explodes in space above the Sun's surface, can generate a major seismic wave in the Sun's interior. According to the currently accepted model of solar flares, the primary explosion creates high-energy electrons (electrically charged subatomic particles). These are funneled down into a magnetic flux tube, an invisible tube of magnetic energy, and produce X-rays, microwaves and a shock wave that heats the solar surface. Kosovichev and Zharkova developed a theory that predicts the nature and magnitude of the shock waves that this beam of energetic electrons should create when they slam down into the solar atmosphere. Although their theory directed them to the right area to search for the seismic waves, the waves that they found were 10 times stronger than they had predicted. "They were so strong that you can see them in the raw data," Kosovichev says. The solar seismic waves appear to be compression waves like the "P" waves generated by an earthquake. They travel throughout the Sun's interior. In fact, the waves should recombine on the opposite side of the Sun from the location of the flare to create a faint duplicate of the original ripple pattern, Kosovichev predicts. Now that they know how to find them, the SOHO scientists say that the seismic waves generated by solar flares should allow them to verify independently some of the conditions in the solar interior that they have inferred from studying the pattern of waves that are continually ruffling the Sun's surface. SOHO is part of the International Solar-Terrestrial Physics (ISTP) program, a global effort to observe and understand our star and its effects on our environment. The ISTP mission includes more than 20 satellites, coupled with with ground-based observatories and modeling centers, that allow scientists to study the Sun, the Earth, and the space between them in unprecedented detail. ISTP is a joint program of NASA, ESA, Japan's Institute for Astronautical Science, and Russia's Space Research Institute. Still images of the solar quake can be found at the following internet address: FTP://PAO.GSFC.NASA.GOV/newsmedia/QUAKE/ For further information, please contact : ESA Public Relations Division Tel:+33(0)1.53.69.71.55 Fax: +33(0)1.53.69.76.90 3

Rogue-wave pattern transition induced by relative frequency.

PubMed

Zhao, Li-Chen; Xin, Guo-Guo; Yang, Zhan-Ying

2014-08-01

We revisit a rogue wave in a two-mode nonlinear fiber whose dynamics is described by two-component coupled nonlinear Schrödinger equations. The relative frequency between two modes can induce different rogue wave patterns transition. In particular, we find a four-petaled flower structure rogue wave can exist in the two-mode coupled system, which possesses an asymmetric spectrum distribution. Furthermore, spectrum analysis is performed on these different type rogue waves, and the spectrum relations between them are discussed. We demonstrate qualitatively that different modulation instability gain distribution can induce different rogue wave excitation patterns. These results would deepen our understanding of rogue wave dynamics in complex systems.

The influence of El Niño-Southern Oscillation (ENSO) cycles on wave-driven sea-floor sediment mobility along the central California continental margin

USGS Publications Warehouse

Storlazzi, Curt D.; Reid, Jane A.

2010-01-01

Ocean surface waves are the dominant temporally and spatially variable process influencing sea floor sediment resuspension along most continental shelves. Wave-induced sediment mobility on the continental shelf and upper continental slope off central California for different phases of El Niño-Southern Oscillation (ENSO) events was modeled using monthly statistics derived from more than 14 years of concurrent hourly oceanographic and meteorologic data as boundary input for the Delft SWAN wave model, gridded sea floor grain-size data from the usSEABED database, and regional bathymetry. Differences as small as 0.5 m in wave height, 1 s in wave period, and 10° in wave direction, in conjunction with the spatially heterogeneous unconsolidated sea-floor sedimentary cover, result in significant changes in the predicted mobility of continental shelf surficial sediment in the study area. El Niño events result in more frequent mobilization on the inner shelf in the summer and winter than during La Niña events and on the outer shelf and upper slope in the winter months, while La Niña events result in more frequent mobilization on the mid-shelf during spring and summer months than during El Niño events. The timing and patterns of seabed mobility are addressed in context of geologic and biologic processes. By understanding the spatial and temporal variability in the disturbance of the sea floor, scientists can better interpret sedimentary patterns and ecosystem structure, while providing managers and planners an understanding of natural impacts when considering the permitting of offshore activities that disturb the sea floor such as trawling, dredging, and the emplacement of sea-floor engineering structures.

The picosecond structure of ultra-fast rogue waves

NASA Astrophysics Data System (ADS)

Klein, Avi; Shahal, Shir; Masri, Gilad; Duadi, Hamootal; Sulimani, Kfir; Lib, Ohad; Steinberg, Hadar; Kolpakov, Stanislav A.; Fridman, Moti

2018-02-01

We investigated ultrafast rogue waves in fiber lasers and found three different patterns of rogue waves: single- peaks, twin-peaks, and triple-peaks. The statistics of the different patterns as a function of the pump power of the laser reveals that the probability for all rogue waves patterns increase close to the laser threshold. We developed a numerical model which prove that the ultrafast rogue waves patterns result from both the polarization mode dispersion in the fiber and the non-instantaneous nature of the saturable absorber. This discovery reveals that there are three different types of rogue waves in fiber lasers: slow, fast, and ultrafast, which relate to three different time-scales and are governed by three different sets of equations: the laser rate equations, the nonlinear Schrodinger equation, and the saturable absorber equations, accordingly. This discovery is highly important for analyzing rogue waves and other extreme events in fiber lasers and can lead to realizing types of rogue waves which were not possible so far such as triangular rogue waves.

Characterization of the Goubau line for testing beam diagnostic instruments

NASA Astrophysics Data System (ADS)

Kim, S. Y.; Stulle, F.; Sung, C. K.; Yoo, K. H.; Seok, J.; Moon, K. J.; Choi, C. U.; Chung, Y.; Kim, G.; Woo, H. J.; Kwon, J.; Lee, I. G.; Choi, E. M.; Chung, M.

2017-12-01

One of the main characteristics of the Goubau line is that it supports a low-loss, non-radiated surface wave guided by a dielectric-coated metal wire. The dominant mode of the surface wave along the Goubau line is a TM01 mode, which resembles the pattern of the electromagnetic fields induced in the metallic beam pipe when the charged particle beam passes through it. Therefore, the Goubau line can be used for the preliminary bench test and performance optimization of the beam diagnostic instruments without requiring charged particle beams from the accelerators. In this paper, we discuss the basic properties of the Goubau line for testing beam diagnostic instruments and present the initial test results for button-type beam position monitors (BPMs). The experimental results are consistent with the theoretical estimations, which indicates that Goubau line allows effective testing of beam diagnostic equipment.

Anisotropic surface wave tomography in the Horn of Africa.

NASA Astrophysics Data System (ADS)

Sicilia, D.; Montagner, J. P.; Debayle, E.; Leveque, J. J.; Cara, M.; Lepine, J. C.; Beucler, E.; Sebai, A.

2003-04-01

One of the largest continental hotspot is located in the Afar Depression, in East of Africa. It has been advocated to be the surface expression of the South-West African Superswell, which is the antipode of the Pacific Superswell in the framework of the mantle degree 2 pattern. We performed an anisotropic surface wave tomography in the Horn of Africa in order to image the seismic structure beneath the region. Data were collected from the permanent IRIS and GEOSCOPE networks and from the PASSCAL experiment in Tanzania and Saudi Arabia. We supplemented our data base with a French deployment of 5 portable broadband stations surrounding the Afar Hotspot. Path average phase velocities are obtained using a method based on a least-squares minimization (Beucler et al., 2002). The data are corrected from the effect of the crust according to the a priori 3SMAC model (Nataf et Ricard, 1996). 3D-models of velocity, radial and azimuthal anisotropies are inverted for. We find low velocities beneath the Red Sea, the Gulf of Aden, the South East of the Tanzania Craton, the Hotspot and Central Africa. High velocities are present in the eastern Arabia and the Tanzania Craton. These results are in agreement with the anisotropic model of Debayle et al.(2002). The flow pattern can be derived from fast axis directions of seismic anisotropy. The anisotropy model beneath Afar displays a complex pattern, in which the hotspot seems to play a perturbating role. The azimuthal anisotropy shows that the Afar plume might be interpreted as feeding other hotspots in central Africa. The directions of fast axis are in good agreement with the results of previous SKS studies performed in the region (Gao et al., 1997; Wolfe et al., 1999; Barruol and Ismail, 2001).

Calculation of Seismic Waves from Explosions with Tectonic Stresses and Topography

NASA Astrophysics Data System (ADS)

Stevens, J. L.; O'Brien, M.

2017-12-01

We investigate the effects of explosion depth, tectonic stresses and topography on seismic waves from underground nuclear explosions. We perform three-dimensional nonlinear calculations of an explosion at several depths in the topography of the North Korean test site. We also perform a large number of two-dimensional axisymmetric calculations of explosions at depths from 150 to 1000 meters in four earth structures, with compressive and tensile tectonic stresses and with no tectonic stresses. We use the representation theorem to propagate the results of these calculations and calculate seismic waves at regional and teleseismic distances. We find that P-waves are not strongly affected by any of these effects because the initial downgoing P-wave is unaffected by interaction with the free surface. Surface waves, however, are strongly affected by all of these effects. There is an optimal depth at which surface waves are maximized at the base of a mountain and at or slightly below normal containment depth. At deeper depths, increasing overburden pressure reduces the surface waves. At shallower depths, interaction with the free surface reduces the surface waves. For explosions inside a mountain, displacement of the sides of the mountain reduces surface waves. Compressive prestress reduces surface waves substantially, while tensile prestress increases surface waves. The North Korean explosions appear to be at an optimal depth, in a region of extension, and beneath a mountain, all of which increase surface wave amplitudes.

Laser mode conversion into a surface plasma wave in a metal coated optical fiber

NASA Astrophysics Data System (ADS)

Liu, C. S.; Kumar, Gagan; Tripathi, V. K.

2006-07-01

An optical fiber, coated with thin metal film, supports two distinct kinds of waves, viz., body waves that propagate through the fiber as transverse magnetic (TM) and transverse electric modes, and surface plasma waves that propagate on metal free space interface. When the metal has a ripple of suitable wave number q, a body wave of frequency ω and propagation constant kz induces a current at ω ,kz+q in the ripple region that resonantly derives a surface plasma wave. When the metal surface has metallic particles attached to it and molecules are adsorbed on them, the surface plasma wave undergoes surface enhanced Raman scattering with them. The scattered signals propagate backward as a TM body wave and can be detected.

Compact portable diffraction moire interferometer

DOEpatents

Deason, Vance A.; Ward, Michael B.

1989-01-01

A compact and portable moire interferometer used to determine surface deformations of an object. The improved interferometer is comprised of a laser beam, optical and fiber optics devices coupling the beam to one or more evanescent wave splitters, and collimating lenses directing the split beam at one or more specimen gratings. Observation means including film and video cameras may be used to view and record the resultant fringe patterns.

Experimental Study of Shock Wave Interference Heating on a Cylindrical Leading Edge. Ph.D. Thesis

NASA Technical Reports Server (NTRS)

Wieting, Allan R.

1987-01-01

An experimental study of shock wave interference heating on a cylindrical leading edge representative of the cowl of a rectangular hypersonic engine inlet at Mach numbers of 6.3, 6.5, and 8.0 is presented. Stream Reynolds numbers ranged from 0.5 x 106 to 4.9 x 106 per ft. and stream total temperature ranged from 2100 to 3400 R. The model consisted of a 3" dia. cylinder and a shock generation wedge articulated to angles of 10, 12.5, and 15 deg. A fundamental understanding was obtained of the fluid mechanics of shock wave interference induced flow impingement on a cylindrical leading edge and the attendant surface pressure and heat flux distributions. The first detailed heat transfer rate and pressure distributions for two dimensional shock wave interference on a cylinder was provided along with insight into the effects of specific heat variation with temperature on the phenomena. Results show that the flow around a body in hypersonic flow is altered significantly by the shock wave interference pattern that is created by an oblique shock wave from an external source intersecting the bow shock wave produced in front of the body.

In Pursuit of Internal Waves

NASA Astrophysics Data System (ADS)

Peacock, Thomas

2014-11-01

Orders of magnitude larger than surface waves, and so powerful that their generation impacts the lunar orbit, internal waves, propagating disturbances of a density-stratified fluid, are ubiquitous throughout the ocean and atmosphere. Following the discovery of the phenomenon of ``dead water'' by early Arctic explorers and the classic laboratory visualizations of the curious St. Andrew's Cross internal wave pattern, there has been a resurgence of interest in internal waves, inspired by their pivotal roles in local environmental and global climate processes, and their profound impact on ocean and aerospace engineering. We detail our widespread pursuit of internal waves through theoretical modeling, laboratory experiments and field studies, from the Pacific Ocean one thousand miles north and south of Hawaii, to the South China Sea, and on to the Arctic Ocean. We also describe our recent expedition to surf the most striking internal wave phenomenon of them all: the Morning Glory cloud in remote Northwest Australia. This work was supported by the National Science Foundation through a CAREER Grant OCE-064559 and through Grants OCE-1129757 and OCE-1357434, and by the Office of Naval Research through Grants N00014-09-1-0282, N00014-08-1-0390 and N00014-05-1-0575.

The structure and large-scale organization of extreme cold waves over the conterminous United States

NASA Astrophysics Data System (ADS)

Xie, Zuowei; Black, Robert X.; Deng, Yi

2017-12-01

Extreme cold waves (ECWs) occurring over the conterminous United States (US) are studied through a systematic identification and documentation of their local synoptic structures, associated large-scale meteorological patterns (LMPs), and forcing mechanisms external to the US. Focusing on the boreal cool season (November-March) for 1950‒2005, a hierarchical cluster analysis identifies three ECW patterns, respectively characterized by cold surface air temperature anomalies over the upper midwest (UM), northwestern (NW), and southeastern (SE) US. Locally, ECWs are synoptically organized by anomalous high pressure and northerly flow. At larger scales, the UM LMP features a zonal dipole in the mid-tropospheric height field over North America, while the NW and SE LMPs each include a zonal wave train extending from the North Pacific across North America into the North Atlantic. The Community Climate System Model version 4 (CCSM4) in general simulates the three ECW patterns quite well and successfully reproduces the observed enhancements in the frequency of their associated LMPs. La Niña and the cool phase of the Pacific Decadal Oscillation (PDO) favor the occurrence of NW ECWs, while the warm PDO phase, low Arctic sea ice extent and high Eurasian snow cover extent (SCE) are associated with elevated SE-ECW frequency. Additionally, high Eurasian SCE is linked to increases in the occurrence likelihood of UM ECWs.

An algorithm for power line detection and warning based on a millimeter-wave radar video.

PubMed

Ma, Qirong; Goshi, Darren S; Shih, Yi-Chi; Sun, Ming-Ting

2011-12-01

Power-line-strike accident is a major safety threat for low-flying aircrafts such as helicopters, thus an automatic warning system to power lines is highly desirable. In this paper we propose an algorithm for detecting power lines from radar videos from an active millimeter-wave sensor. Hough Transform is employed to detect candidate lines. The major challenge is that the radar videos are very noisy due to ground return. The noise points could fall on the same line which results in signal peaks after Hough Transform similar to the actual cable lines. To differentiate the cable lines from the noise lines, we train a Support Vector Machine to perform the classification. We exploit the Bragg pattern, which is due to the diffraction of electromagnetic wave on the periodic surface of power lines. We propose a set of features to represent the Bragg pattern for the classifier. We also propose a slice-processing algorithm which supports parallel processing, and improves the detection of cables in a cluttered background. Lastly, an adaptive algorithm is proposed to integrate the detection results from individual frames into a reliable video detection decision, in which temporal correlation of the cable pattern across frames is used to make the detection more robust. Extensive experiments with real-world data validated the effectiveness of our cable detection algorithm. © 2011 IEEE

Wake of inertial waves of a horizontal cylinder in horizontal translation

NASA Astrophysics Data System (ADS)

Machicoane, Nathanaël; Labarre, Vincent; Voisin, Bruno; Moisy, Frédéric; Cortet, Pierre-Philippe

2018-03-01

We analyze theoretically and experimentally the wake behind a horizontal cylinder of diameter d horizontally translated at constant velocity U in a fluid rotating about the vertical axis at a rate Ω . Using particle image velocimetry measurements in the rotating frame, we show that the wake is stabilized by rotation for Reynolds number Re =U d /ν much larger than in a nonrotating fluid. Over the explored range of parameters, the limit of stability is Re ≃(275 ±25 )/Ro , with Ro =U /2 Ω d the Rossby number, indicating that the stabilizing process is governed by the Ekman pumping in the boundary layer. At low Rossby number, the wake takes the form of a stationary pattern of inertial waves, similar to the wake of surface gravity waves behind a ship. We compare this steady wake pattern to a model, originally developed by Johnson [E. R. Johnson, J. Fluid Mech. 120, 359 (1982), 10.1017/S0022112082002808], assuming a free-slip boundary condition and a weak streamwise perturbation. Our measurements show quantitative agreement with this model for Ro ≲0.3 . At larger Rossby number, the phase pattern of the wake is close to the prediction for an infinitely small line object. However, the wake amplitude and phase origin are not correctly described by the weak-streamwise-perturbation model, calling for an alternative model for the boundary condition at moderate rotation rate.

Enhanced Sensitivity of a Surface Acoustic Wave Gyroscope

NASA Astrophysics Data System (ADS)

Zhang, Yanhua; Wang, Wen

2009-10-01

In this paper, we present an optimal design and performance evaluation of a surface acoustic wave (SAW) gyroscope. It consists of a two-port SAW resonator (SAWR) and a SAW sensor (SAWS) structured using a delay line pattern. The SAW resonator provides a stable reference vibration and creates a standing wave, and the vibrating metallic dot array at antinodes of the standing wave induces the second SAW in the normal direction by the Coriolis force, and the SAW sensor is used to detect the secondary SAW. By using the coupling of modes (COM), the SAW resonator was simulated, and the effects of the design parameters on the frequency response of the device were investigated. Also, a theoretical analysis was performed to investigate the effect of metallic dots on the frequency response of the SAW device. The measured frequency response S21 of the fabricated 80 MHz two-port SAW resonator agrees well with the simulated result, that is, a low insertion loss (˜5 dB) and a single steep resonance peak were observed. In the gyroscopic experiments using a rate table, optimal metallic dot thickness was determined, and the sensitivity of the fabricated SAW gyroscope with an optimal metallic dot thickness of ˜350 nm was determined to be 3.2 µV deg-1 s-1.

Furnace control apparatus using polarizing interferometer

DOEpatents

Schultz, Thomas J.; Kotidis, Petros A.; Woodroffe, Jaime A.; Rostler, Peter S.

1995-01-01

A system for non-destructively measuring an object and controlling industrial processes in response to the measurement is disclosed in which an impulse laser generates a plurality of sound waves over timed increments in an object. A polarizing interferometer is used to measure surface movement of the object caused by the sound waves and sensed by phase shifts in the signal beam. A photon multiplier senses the phase shift and develops an electrical signal. A signal conditioning arrangement modifies the electrical signals to generate an average signal correlated to the sound waves which in turn is correlated to a physical or metallurgical property of the object, such as temperature, which property may then be used to control the process. External, random vibrations of the workpiece are utilized to develop discernible signals which can be sensed in the interferometer by only one photon multiplier. In addition the interferometer includes an arrangement for optimizing its sensitivity so that movement attributed to various waves can be detected in opaque objects. The interferometer also includes a mechanism for sensing objects with rough surfaces which produce speckle light patterns. Finally the interferometer per se, with the addition of a second photon multiplier is capable of accurately recording beam length distance differences with only one reading.

Polarizing optical interferometer having a dual use optical element

DOEpatents

Kotidis, P.A.; Woodroffe, J.A.; Rostler, P.S.

1995-04-04

A system for nondestructively measuring an object and controlling industrial processes in response to the measurement is disclosed in which an impulse laser generates a plurality of sound waves over timed increments in an object. A polarizing interferometer is used to measure surface movement of the object caused by the sound waves and sensed by phase shifts in the signal beam. A photon multiplier senses the phase shift and develops an electrical signal. A signal conditioning arrangement modifies the electrical signals to generate an average signal correlated to the sound waves which in turn is correlated to a physical or metallurgical property of the object, such as temperature, which property may then be used to control the process. External, random vibrations of the workpiece are utilized to develop discernible signals which can be sensed in the interferometer by only one photon multiplier. In addition the interferometer includes an arrangement for optimizing its sensitivity so that movement attributed to various waves can be detected in opaque objects. The interferometer also includes a mechanism for sensing objects with rough surfaces which produce speckle light patterns. Finally the interferometer per se, with the addition of a second photon multiplier is capable of accurately recording beam length distance differences with only one reading. 38 figures.

Process control system using polarizing interferometer

DOEpatents

Schultz, T.J.; Kotidis, P.A.; Woodroffe, J.A.; Rostler, P.S.

1994-02-15

A system for nondestructively measuring an object and controlling industrial processes in response to the measurement is disclosed in which an impulse laser generates a plurality of sound waves over timed increments in an object. A polarizing interferometer is used to measure surface movement of the object caused by the sound waves and sensed by phase shifts in the signal beam. A photon multiplier senses the phase shift and develops an electrical signal. A signal conditioning arrangement modifies the electrical signals to generate an average signal correlated to the sound waves which in turn is correlated to a physical or metallurgical property of the object, such as temperature, which property may then be used to control the process. External, random vibrations of the workpiece are utilized to develop discernible signals which can be sensed in the interferometer by only one photon multiplier. In addition the interferometer includes an arrangement for optimizing its sensitivity so that movement attributed to various waves can be detected in opaque objects. The interferometer also includes a mechanism for sensing objects with rough surfaces which produce speckle light patterns. Finally the interferometer per se, with the addition of a second photon multiplier is capable of accurately recording beam length distance differences with only one reading. 38 figures.

Polarizing optical interferometer having a dual use optical element

DOEpatents

Kotidis, Petros A.; Woodroffe, Jaime A.; Rostler, Peter S.

1995-01-01

A system for non-destructively measuring an object and controlling industrial processes in response to the measurement is disclosed in which an impulse laser generates a plurality of sound waves over timed increments in an object. A polarizing interferometer is used to measure surface movement of the object caused by the sound waves and sensed by phase shifts in the signal beam. A photon multiplier senses the phase shift and develops an electrical signal. A signal conditioning arrangement modifies the electrical signals to generate an average signal correlated to the sound waves which in turn is correlated to a physical or metallurgical property of the object, such as temperature, which property may then be used to control the process. External, random vibrations of the workpiece are utilized to develop discernible signals which can be sensed in the interferometer by only one photon multiplier. In addition the interferometer includes an arrangement for optimizing its sensitivity so that movement attributed to various waves can be detected in opaque objects. The interferometer also includes a mechanism for sensing objects with rough surfaces which produce speckle light patterns. Finally the interferometer per se, with the addition of a second photon multiplier is capable of accurately recording beam length distance differences with only one reading.

Process control system using polarizing interferometer

DOEpatents

Schultz, Thomas J.; Kotidis, Petros A.; Woodroffe, Jaime A.; Rostler, Peter S.

1994-01-01

A system for non-destructively measuring an object and controlling industrial processes in response to the measurement is disclosed in which an impulse laser generates a plurality of sound waves over timed increments in an object. A polarizing interferometer is used to measure surface movement of the object caused by the sound waves and sensed by phase shifts in the signal beam. A photon multiplier senses the phase shift and develops an electrical signal. A signal conditioning arrangement modifies the electrical signals to generate an average signal correlated to the sound waves which in turn is correlated to a physical or metallurgical property of the object, such as temperature, which property may then be used to control the process. External, random vibrations of the workpiece are utilized to develop discernible signals which can be sensed in the interferometer by only one photon multiplier. In addition the interferometer includes an arrangement for optimizing its sensitivity so that movement attributed to various waves can be detected in opaque objects. The interferometer also includes a mechanism for sensing objects with rough surfaces which produce speckle light patterns. Finally the interferometer per se, with the addition of a second photon multiplier is capable of accurately recording beam length distance differences with only one reading.

Furnace control apparatus using polarizing interferometer

DOEpatents

Schultz, T.J.; Kotidis, P.A.; Woodroffe, J.A.; Rostler, P.S.

1995-03-28

A system for nondestructively measuring an object and controlling industrial processes in response to the measurement is disclosed in which an impulse laser generates a plurality of sound waves over timed increments in an object. A polarizing interferometer is used to measure surface movement of the object caused by the sound waves and sensed by phase shifts in the signal beam. A photon multiplier senses the phase shift and develops an electrical signal. A signal conditioning arrangement modifies the electrical signals to generate an average signal correlated to the sound waves which in turn is correlated to a physical or metallurgical property of the object, such as temperature, which property may then be used to control the process. External, random vibrations of the workpiece are utilized to develop discernible signals which can be sensed in the interferometer by only one photon multiplier. In addition the interferometer includes an arrangement for optimizing its sensitivity so that movement attributed to various waves can be detected in opaque objects. The interferometer also includes a mechanism for sensing objects with rough surfaces which produce speckle light patterns. Finally the interferometer per se, with the addition of a second photon multiplier is capable of accurately recording beam length distance differences with only one reading. 38 figures.

Far-Field Simulation of the Hawaiian Wake: Sea Surface Temperature and Orographic Effects(.

NASA Astrophysics Data System (ADS)

Hafner, Jan; Xie, Shang-Ping

2003-12-01

Recent satellite observations reveal far-reaching effects of the Hawaiian Islands on surface wind, cloud, ocean current, and sea surface temperature (SST) that extend leeward over an unusually long distance (>1000 km). A three-dimensional regional atmospheric model with full physics is used to investigate the cause of this long wake. While previous wind wake studies tend to focus on regions near the islands, the emphasis here is the far-field effects of SST and orography well away from the Hawaiian Islands. In response to an island-induced SST pattern, the model produces surface wind and cloud anomaly patterns that resemble those observed by satellites. In particular, anomalous surface winds are found to converge onto a zonal band of warmer water, with cloud liquid water content enhanced over it but reduced on the northern and southern sides. In the vertical, a two-cell meridional circulation develops of a baroclinic structure with the rising motion and thicker clouds over the warm water band. The model response in the wind and cloud fields supports the hypothesis that ocean atmosphere interaction is crucial for sustaining the island effects over a few thousand kilometers.Near Hawaii, mountains generate separate wind wakes in the model lee of individual islands as observed by satellites. Under orographic forcing, the model simulates the windward cloud line and the southwest-tilted cloud band leeward of the Big Island. In the far field, orographically induced wind perturbations are found to be in geostrophic balance with pressure anomalies, indicative of quasigeostrophic Rossby wave propagation. A shallow-water model is developed for disturbances trapped in the inversion-capped planetary boundary layer. The westward propagation of Rossby waves is found to increase the wake length significantly, consistent with the three-dimensional simulation.

An Oceanic General Circulation Model (OGCM) investigation of the Red Sea circulation: 2. Three-dimensional circulation in the Red Sea

NASA Astrophysics Data System (ADS)

Sofianos, Sarantis S.; Johns, William E.

2003-03-01

The three-dimensional circulation of the Red Sea is studied using a set of Miami Isopycnic Coordinate Ocean Model (MICOM) simulations. The model performance is tested against the few available observations in the basin and shows generally good agreement with the main observed features of the circulation. The main findings of this analysis include an intensification of the along-axis flow toward the coasts, with a transition from western intensified boundary flow in the south to eastern intensified flow in the north, and a series of strong seasonal or permanent eddy-like features. Model experiments conducted with different forcing fields (wind-stress forcing only, surface buoyancy forcing only, or both forcings combined) showed that the circulation produced by the buoyancy forcing is stronger overall and dominates the wind-driven part of the circulation. The main circulation pattern is related to the seasonal buoyancy flux (mostly due to the evaporation), which causes the density to increase northward in the basin and produces a northward surface pressure gradient associated with the downward sloping of the sea surface. The response of the eastern boundary to the associated mean cross-basin geostrophic current depends on the stratification and β-effect. In the northern part of the basin this results in an eastward intensification of the northward surface flow associated with the presence of Kelvin waves while in the south the traditional westward intensification due to Rossby waves takes place. The most prominent gyre circulation pattern occurs in the north where a permanent cyclonic gyre is present that is involved in the formation of Red Sea Outflow Water (RSOW). Beneath the surface boundary currents are similarly intensified southward undercurrents that carry the RSOW to the sill to flow out of the basin into the Indian Ocean.

3D shear wave velocity structure revealed with ambient noise tomography on a DAS array

NASA Astrophysics Data System (ADS)

Zeng, X.; Thurber, C. H.; Wang, H. F.; Fratta, D.

2017-12-01

An 8700-m Distributed Acoustic Sensing (DAS) cable was deployed at Brady's Hot Springs, Nevada in March 2016 in a 1.5 by 0.5 km study area. The layout of the DAS array was designed with a zig-zag geometry to obtain relatively uniform areal and varied angular coverage, providing very dense coverage with a one-meter channel spacing. This array continuously recorded signals of a vibroseis truck, earthquakes, and traffic noise during the 15-day deployment. As shown in a previous study (Zeng et al., 2017), ambient noise tomography can be applied to DAS continuous records to image shear wave velocity structure in the near surface. To avoid effects of the vibroseis truck operation, only continuous data recorded during the nighttime was used to compute noise cross-correlation functions for channel pairs within a given linear segment. The frequency band of whitening was set at 5 to 15 Hz and the length of the cross-correlation time window was set to 60 second. The phase velocities were determined using the multichannel analysis of surface waves (MASW) methodology. The phase velocity dispersion curve was then used to invert for shear wave velocity profiles. A preliminarily velocity model at Brady's Hot Springs (Lawrence Livermore National Laboratory, 2015) was used as the starting model and the sensitivity kernels of Rayleigh wave group and phase velocities were computed with this model. As the sensitivity kernel shows, shear wave velocity in the top 200 m can be constrained with Rayleigh wave group and phase velocities in our frequency band. With the picked phase velocity data, the shear wave velocity structure can be obtained via Occam's inversion (Constable et al., 1987; Lai 1998). Shear wave velocity gradually increases with depth and it is generally faster than the Lawrence Livermore National Laboratory (2015) model. Furthermore, that model has limiting constraints at shallow depth. The strong spatial variation is interpreted to reflect the different sediments and sediment thicknesses in the near surface. Shear wave velocities in the northeast corner of the tested area is high whereas loose soil reduces shear wave velocities in the central part of the tested area. This spatial variation pattern is very similar to the results obtained with the ambient noise tomography using the 238-geophone array used the experiment.

Excitation of high-frequency surface waves with long duration in the Valley of Mexico

NASA Astrophysics Data System (ADS)

Iida, Masahiro

1999-04-01

During the 1985 Michoacan earthquake (Ms = 8.1), large-amplitude seismograms with extremely long duration were recorded in the lake bed zone of Mexico City. We interpret high-frequency seismic wave fields in the three geotechnical zones (the hill, the transition, and the lake bed zones) in the Valley of Mexico on the basis of a systematic analysis for borehole strong motion recordings. We make identification of wave types for real seismograms. First, amplitude ratios between surface and underground seismograms indicate that predominant periods of the surface seismograms are largely controlled by the wave field incident into surficial layers in the Valley of Mexico. We interpret recorded surface waves as fundamental-mode Love waves excited in the Mexican Volcanic Belt by calculating theoretical amplification for different-scale structures. Second, according to a cross-correlation analysis, the hill and transition seismograms are mostly surface waves. In the lake bed zone, while early portions are noisy body waves, late portions are mostly surface waves. Third, using two kinds of surface arrays with different station intervals, we investigate high-frequency surface-wave propagation in the lake bed zone. The wave propagation is very complicated, depending upon the time section and the frequency band. Finally, on the basis of a statistical time series model with an information criterion, we separate S- and surface-wave portions from lake bed seismograms. Surface waves are dominant and are recognized even in the early time section. Thus high-frequency surface waves with long duration in the Valley of Mexico are excited by the Mexican Volcanic Belt.

Cell and module formation research area

NASA Technical Reports Server (NTRS)

Bickler, D. B.

1982-01-01

Metallization is discussed. The influence of hydrogen on the firing of base-metal pastes in reducing atmospheres is reported. A method for optimization of metallization patterns is presented. A process sequence involving an AR coating and thick-film metallization system capable of penetrating the AR coating during firing is reported. Design and construction of the NMA implantation machine is reported. Implanted back-surface fields and NMA primary (front) junctions are discussed. The use of glass beads, a wave-soldering device, and ion milling is reported. Processing through the module fabrication and environmental testing of its design are reported. Metallization patterns by mathematical optimization are assessed.

Ground Based Studies of Gas-Liquid Flows in Microgravity Using Learjet Trajectories

NASA Technical Reports Server (NTRS)

Bousman, W. S.; Dukler, A. E.

1994-01-01

A 1.27 cm diameter two phase gas-liquid flow experiment has been developed with the NASA Lewis Research Center to study two-phase flows in microgravity. The experiment allows for the measurement of void fraction, pressure drop, film thickness and bubble and wave velocities as well as for high speed photography. Three liquids were used to study the effects of liquid viscosity and surface tension, and flow pattern maps are presented for each. The experimental results are used to develop mechanistically based models to predict void fraction, bubble velocity, pressure drop and flow pattern transitions in microgravity.

Measurement of the configuration of a concave surface by the interference of reflected light

NASA Technical Reports Server (NTRS)

Kumazawa, T.; Sakamoto, T.; Shida, S.

1985-01-01

A method whereby a concave surface is irradiated with coherent light and the resulting interference fringes yield information on the concave surface is described. This method can be applied to a surface which satisfies the following conditions: (1) the concave face has a mirror surface; (2) the profile of the face is expressed by a mathematical function with a point of inflection. In this interferometry, multilight waves reflected from the concave surface interfere and make fringes wherever the reflected light propagates. Interference fringe orders. Photographs of the fringe patterns for a uniformly loaded thin silicon plate clamped at the edge are shown experimentally. The experimental and the theoretical values of the maximum optical path difference show good agreement. This simple method can be applied to obtain accurate information on concave surfaces.

Ambient Noise Tomography at Regional and Local Scales in Southern California using Rayleigh Wave Phase Dispersion and Ellipticity

NASA Astrophysics Data System (ADS)

Berg, E.; Lin, F. C.; Qiu, H.; Wang, Y.; Allam, A. A.; Clayton, R. W.; Ben-Zion, Y.

2017-12-01

Rayleigh waves extracted from cross-correlations of ambient seismic noise have proven useful in imaging the shallow subsurface velocity structure. In contrast to phase velocities, which are sensitive to slightly deeper structure, Rayleigh wave ellipticity (H/V ratios) constrains the uppermost crust. We conduct Rayleigh wave ellipticity and phase dispersion measurements in Southern California between 6 and 18 second periods, computed from multi-component ambient noise cross-correlations using 315 stations across the region in 2015. Because of the complimentary sensitivity of phase velocity and H/V, this method enables simple and accurate resolution of near-surface geological features from the surface to 20km depth. We compare the observed H/V ratios and phase velocities to predictions generated from the current regional models (SCEC UCVM), finding strong correspondence where the near-surface structure is well-resolved by the models. This includes high H/V ratios in the LA Basin, Santa Barbara Basin and Salton Trough; and low ratios in the San Gabriel, San Jacinto and southern Sierra Nevada mountains. Disagreements in regions such as the Western Transverse Ranges, Salton Trough, San Jacinto and Elsinore fault zones motivate further work to improve the community models. A new updated 3D isotropic model of the area is derived via a joint inversion of Rayleigh phase dispersions and H/V ratios. Additionally, we examine azimuthal dependence of the H/V ratio to ascertain anisotropy patterns for each station. Clear 180º periodicity is observed for many stations suggesting strong shallow anisotropy across the region including up to 20% along the San Andreas fault, 15% along the San Jacinto Fault and 25% in the LA Basin. To better resolve basin structures, we apply similar techniques to three dense linear geophone arrays in the San Gabriel and San Bernardino basins. The three arrays are composed by 50-125 three-component 5Hz geophones deployed for one month each with 15-25km apertures to image basin structure, important for seismic hazard analysis and ground motion predictions. Clear Rayleigh and Love wave signals are extracted. We determine Love wave dispersion and Rayleigh wave H/V and phase dispersion measurements. The preliminary basin models from inverting surface wave measurements will be presented.

Dynamic interaction of CO/H 2O mixtures with gold nanocrystals: Real-time imaging and local chemical probing

NASA Astrophysics Data System (ADS)

Visart de Bocarmé, Thierry; Chau, Thoi-Dai; Kruse, Norbert

2006-09-01

The dynamic interaction of pure gold nanocrystals ("tips") with H 2O/CO gas mixtures was studied by means of video-field ion microscopy (FIM). While imaging with nano-scale resolution selected areas of the equivalent of ˜200 atomic Au sites were analysed for their chemical composition using short field pulses and injecting respective ions into a time-of-flight mass spectrometer (pulsed field desorption mass spectrometry, PFDMS). At room temperature the exposure of a clean Au sample to water gas at 10 -4 Pa, in the presence of an electric field of ˜10 V/nm, led to water adsorption and formation of bright patterns in FIM. Additional exposure to CO gas at 5 × 10 -3 Pa led to the removal of the water layer. This was associated with the occurrence of bright wave fronts which ignited simultaneously in several regions of the Au surface with no preference for a certain crystallographic surface plane. In some cases wave fronts were seen to collide resulting in more complicated patterns such as concentric rings. Surface areas free of water appeared with low brightness. The phenomena were completely reversible. PFDMS demonstrated water ions to be responsible for image formation. Surface hydroxyl was also detected mass spectrometrically and respective ion intensities decreased during the titration with CO. The results suggest that gold nanocrystals, in the absence of oxidic support materials, may be active in the reaction between water and CO at temperatures as low as 300 K and in the presence of an electric field of ˜10 V/nm.

Utilization of high-frequency Rayleigh waves in near-surface geophysics

USGS Publications Warehouse

Xia, J.; Miller, R.D.; Park, C.B.; Ivanov, J.; Tian, G.; Chen, C.

2004-01-01

Shear-wave velocities can be derived from inverting the dispersive phase velocity of the surface. The multichannel analysis of surface waves (MASW) is one technique for inverting high-frequency Rayleigh waves. The process includes acquisition of high-frequency broad-band Rayleigh waves, efficient and accurate algorithms designed to extract Rayleigh-wave dispersion curves from Rayleigh waves, and stable and efficient inversion algorithms to obtain near-surface S-wave velocity profiles. MASW estimates S-wave velocity from multichannel vertical compoent data and consists of data acquisition, dispersion-curve picking, and inversion.

Submesoscale features and their interaction with fronts and internal tides in a high-resolution coupled atmosphere-ocean-wave model of the Bay of Bengal

NASA Astrophysics Data System (ADS)

Jensen, Tommy G.; Shulman, Igor; Wijesekera, Hemantha W.; Anderson, Stephanie; Ladner, Sherwin

2018-03-01

Large freshwater fluxes into the Bay of Bengal by rainfall and river discharges result in strong salinity fronts in the bay. In this study, a high-resolution coupled atmosphere-ocean-wave model with comprehensive physics is used to model the weather, ocean circulation, and wave field in the Bay of Bengal. Our objective is to explore the submesoscale activity that occurs in a realistic coupled model that resolves mesoscales and allows part of the submesoscale field. Horizontal resolution in the atmosphere varies from 2 to 6 km and is 13 km for surface waves, while the ocean model is submesoscale permitting with resolutions as high as 1.5 km and a vertical resolution of 0.5 m in the upper 10 m. In this paper, three different cases of oceanic submesoscale features are discussed. In the first case, heavy rainfall and intense downdrafts produced by atmospheric convection are found to force submesoscale currents, temperature, and salinity anomalies in the oceanic mixed layer and impact the mesoscale flow. In a second case, strong solitary-like waves are generated by semidiurnal tides in the Andaman Sea and interact with mesoscale flows and fronts and affect submesoscale features generated along fronts. A third source of submesoscale variability is found further north in the Bay of Bengal where river outflows help maintain strong salinity gradients throughout the year. For that case, a comparison with satellite observations of sea surface height anomalies, sea surface temperature, and chlorophyll shows that the model captures the observed mesoscale eddy features of the flow field, but in addition, submesoscale upwelling and downwelling patterns associated with ageostrophic secondary circulations along density fronts are also captured by the model.

Molecular genetics of root gravitropism and waving in Arabidopsis thaliana

NASA Technical Reports Server (NTRS)

Sedbrook, J.; Boonsirichai, K.; Chen, R.; Hilson, P.; Pearlman, R.; Rosen, E.; Rutherford, R.; Batiza, A.; Carroll, K.; Schulz, T.;

Observation of low-frequency acoustic surface waves in the nocturnal boundary layer.

PubMed

Talmadge, Carrick L; Waxler, Roger; Di, Xiao; Gilbert, Kenneth E; Kulichkov, Sergey

2008-10-01

A natural terrain surface, because of its porosity, can support an acoustic surface wave that is a mechanical analog of the familiar vertically polarized surface wave in AM radio transmission. At frequencies of several hundred hertz, the acoustic surface wave is attenuated over distances of a few hundred meters. At lower frequencies (e.g., below approximately 200 Hz) the attenuation is much less, allowing surface waves to propagate thousands of meters. At night, a low-frequency surface wave is generally present at long ranges even when downward refraction is weak. Thus, surface waves represent a ubiquitous nighttime transmission mode that exists even when other transmission modes are weak or absent. Data from recent nighttime field experiments and theoretical calculations are presented, demonstrating the persistence of the surface wave under different meteorological conditions. The low-frequency surface wave described here is the "quasiharmonical" tail observed previously in nighttime measurements but not identified by S. Kulichkov and his colleagues (Chunchuzov, I. P. et al. 1990. "On acoustical impulse propagation in a moving inhomogeneous atmospheric layer," J. Acoust. Soc. Am. 88, 455-461).

High Density Waves of the Bacterium Pseudomonas aeruginosa in Propagating Swarms Result in Efficient Colonization of Surfaces

PubMed Central

Du, Huijing; Xu, Zhiliang; Anyan, Morgen; Kim, Oleg; Leevy, W. Matthew; Shrout, Joshua D.; Alber, Mark

2012-01-01

This work describes a new, to our knowledge, strategy of efficient colonization and community development where bacteria substantially alter their physical environment. Many bacteria move in groups, in a mode described as swarming, to colonize surfaces and form biofilms to survive external stresses, including exposure to antibiotics. One such bacterium is Pseudomonas aeruginosa, which is an opportunistic pathogen responsible for both acute and persistent infections in susceptible individuals, as exampled by those for burn victims and people with cystic fibrosis. Pseudomonas aeruginosa often, but not always, forms branched tendril patterns during swarming; this phenomena occurs only when bacteria produce rhamnolipid, which is regulated by population-dependent signaling called quorum sensing. The experimental results of this work show that P. aeruginosa cells propagate as high density waves that move symmetrically as rings within swarms toward the extending tendrils. Biologically justified cell-based multiscale model simulations suggest a mechanism of wave propagation as well as a branched tendril formation at the edge of the population that depends upon competition between the changing viscosity of the bacterial liquid suspension and the liquid film boundary expansion caused by Marangoni forces. Therefore, P. aeruginosa efficiently colonizes surfaces by controlling the physical forces responsible for expansion of thin liquid film and by propagating toward the tendril tips. The model predictions of wave speed and swarm expansion rate as well as cell alignment in tendrils were confirmed experimentally. The study results suggest that P. aeruginosa responds to environmental cues on a very short timescale by actively exploiting local physical phenomena to develop communities and efficiently colonize new surfaces. PMID:22947877

Formation and propagation of Love waves in a surface layer with a P-wave source. Technical report

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

Florence, A.L.; Miller, S.A.

The objective of this research is to investigate experimentally, and support with theoretical calculations, the formation and propagation of Love waves from a P-wave source due to scattering at material heterogeneities. The P-wave source is a spherical piezoelectric crystal cast in a surface layer of rock simulant overlaying a higher impedance granite substrate. Excitation of the piezoelectric crystal with a known voltage applies a spherical compressional pulse of known amplitude to the surrounding medium. Lateral heterogeneities cast in the surface layer convert incident P-wave energy into shear waves. The horizontally polarized shear waves (SH waves) trapped in the surface layermore » wave guide are the Love waves we will measure at the surface.« less

Internal solitary waves on the Saya de Malha bank of the Mascarene Plateau: SAR observations and interpretation

NASA Astrophysics Data System (ADS)

New, A. L.; Magalhaes, J. M.; da Silva, J. C. B.

2013-09-01

Energetic Internal Solitary Waves (ISWs) were recently discovered radiating from the central region of the Mascarene Plateau in the south-western Indian Ocean (da Silva et al., 2011). SAR imagery revealed the two-dimensional structure of the waves which propagated for several hundred kilometres in deep water both to the east and west of a sill, located near 12.5°S, 61°E between the Saya de Malha and Nazareth banks. These waves were presumed to originate from the disintegration of a large lee wave formed on the western side of the sill at the time of maximum barotropic flow to the west. In the present paper we focus instead on ISWs propagating in the shallow water above the Saya da Malha (SM) bank (to the north of the sill), rather than on those propagating in deep water (here denominated as type-I or -II waves if propagating to the west or east respectively). Analysis of an extended SAR image dataset reveals strong sea surface signatures of complex patterns of ISWs propagating over the SM bank arising from different sources. We identify three distinct types of waves, and propose suitable generation mechanisms for them using synergy from different remotely sensed datasets, together with analyses of linear phase speeds (resulting from local stratification and bathymetry). In particular, we find a family of ISWs (termed here A-type waves) which results from the disintegration of a lee wave which forms on the western slopes of SM. We also identify two further wave trains (B- and C-type waves) which we suggest result from refraction of the deep water type-I and -II waves onto the SM bank. Therefore, both B- and C-type waves can be considered to result from the same generation source as the type-I and -II waves. Finally, we consider the implications of the ISWs for mixing and biological production over the SM bank, and provide direct evidence, from ocean colour satellite images, of enhanced surface chlorophyll over a shallow topographic feature on the bank, which is consistent with the breaking of the ISWs.

Shear Wave Structure of Mount St. Helens, WA Region From Ambient Noise, Earthquake Surface Waves and Receiver Functions

NASA Astrophysics Data System (ADS)

Crosbie, K.; Abers, G. A.; Mann, M. E.; Janiszewski, H. A.; Creager, K. C.; Kiser, E.; Ulberg, C. W.; Denlinger, R. P.; Moran, S. C.

2017-12-01

Mount St. Helens (MSH) lies 50 km trenchward of the main arc front in Cascadia. The imaging Magma Under St. Helens (iMUSH) experiment probes its magmatic plumbing system in the mid to lower crust to understand how magmas could be generated in this setting. A 70-element broadband array was deployed for 2 years with a 10 km station spacing and 100 km aperture. Ambient noise and earthquake surface waves provide fundamental-mode Rayleigh wave phase velocity maps of the region from 0.01 to 0.18 Hz. From these, shear velocity (Vs) is estimated from 0 to 80 km depth. Initial attempts at integrating ambient-noise and earthquake datasets have been complicated by the lower resolution of earthquake-derived phase velocities compared to ambient noise, and care is being taken to minimize this incompatibility. Joint inversions with receiver functions help resolve these ambiguities and velocity contrasts across interfaces. For depths of 0-5 km, fast Vs zones (3.3 km/s) are imaged that correspond well with mapped plutons (Spud Mountain and Spirit Lake). Crust at 10-30 km depth has higher Vs (>3.9 km/s) west of MSH than east and north of it (Vs < 3.7 km/s). Crustal temperature variations from a cold forearc to a hot volcanic crust could partly explain this crustal velocity pattern. However, the exceedingly high Vs west of MSH requires a strong change in crustal composition, most likely revealing the east edge of the mafic Siletzia terrane with a predicted Vs similar to that observed. Just below the Moho, Vs variations are much smaller. The resulting Vs contrast across the Moho from surface waves and receiver functions is weak in the forearc and strong beneath the arc volcanoes. This pattern was previously interpreted as due to a serpentinized cold nose of the mantle. However, the anomalously high crustal velocities we observe west of MSH contribute to this forearc Moho absence more than mantle velocity variations, indicating that crustal geology enhances or dominates an effect attributed to mantle hydration. These results confirm that MSH lies on the edge of a notably cold forearc, exactly where crustal composition varies markedly. This sharp crustal terrane boundary immediately west of MSH may help localize volcanism.

Connection between the Silk Road Pattern in July and the following January temperature over East Asia

NASA Astrophysics Data System (ADS)

He, Shengping; Liu, Yang; Wang, Huijun

2017-04-01

This study investigates a cross-seasonal influence of the Silk Road Pattern (SRP) in July and discusses the related mechanism. Both the reanalysis and observational datasets indicate that the July SRP is closely related to the following January temperature over East Asia during 1958/59-2001/02. Linear regression results reveal that, following a higher-than-normal SRP index in July, the Siberian high, Aleutian low, Urals high, East Asian trough, and meridional shear of the East Asian jet intensify significantly in January. Such atmospheric circulation anomalies are favorable for northerly wind anomalies over East Asia, leading to more southward advection of cold air and causing a decrease in temperature. Further analysis indicates that the North Pacific sea surface temperature anomalies (SSTAs) might play a critical role in storing the anomalous signal of the July SRP. The significant SSTAs related to the July SRP weaken in October and November, re-emerge in December, and strengthen in the following January. Such an SSTA pattern in January can induce a surface anomalous cyclone over North Pacific and lead to dominant convergence anomalies over northwestern Pacific. Correspondingly, significant divergence anomalies appear, collocated in the upper-level troposphere in situ. Due to the advection of vorticity by divergent wind, which can be regarded as a wave source, a stationary Rossby wave originates from North Pacific and propagates eastward to East Asia, leading to temperature anomalies through its influence on the large-scale atmospheric circulation.

Estimation of Sea Level variations with GPS/GLONASS-Reflectometry Technique: Case Study at Stationary Oceanographic Platform in the Black Sea

NASA Astrophysics Data System (ADS)

Kurbatov, G. A.; Padokhin, A. M.

2017-12-01

In the present work we study GNSS - reflectometry methods for estimation of sea level variations using a single GNSS-receiver, which are based on the multipath propagation effects (interference pattern in SNR of GNSS signals at small elevation angles) caused by the reflection of navigational signals from the sea surface. The measurements were carried out in the coastal zone of Black Sea at the Stationary Oceanographic Platform during one-week campaign in the summer 2017. GPS/GLONASS signals at two working frequencies of both systems were used to study sea level variations which almost doubled the amount of observations compared to GPS-only tide gauge. Moreover all the measurements were conducted with 4-antenna GNSS receiver providing the opportunity for different orientations of antennas including zenith and nadir looking ones as well as two horizontally oriented ones at different azimuths. As the reference we used data from co-located wire wave gauge which showed good correspondence of both datasets. Though tidal effects are not so pronounced for the Black Sea, the described experimental setup allowed to study the effects of sea surface roughness, driven by meteorological conditions (e.g. wind waves), as well as antenna directivity pattern effects on the observed interference patterns of GPS/GLONASS L1/L2 signals (relation of the main spectral peak to the noise power) and the quality of sea level estimations.

Topographic Influence on Near-Surface Seismic Velocity in southern California

NASA Astrophysics Data System (ADS)

Lin, J. C.; Moon, S.; Meng, L.; Davis, P. M.

2016-12-01

Near-surface seismic velocity is commonly used to determine subsurface rock structure, properties, and ground-motion amplification. The spatial distribution of Vs30 (shear-wave seismic velocity in the top 30 m of Earth's crust) has been inferred based on the correlations of measured Vs30 with rock types and topographic slopes. Inference of Vs30 based on topographic slopes relies on the assumption that mechanically strong rocks tend to have steep slopes. The topographic slopes can thus be used to infer bedrock strength and seismic velocity. However, due to limited accessibility and logistical difficulties, there are few Vs30 measurements in sites of crystalline rocks that have measurable topographic variations. Thus, the variability of Vs30 with topographic slope for crystalline rocks has not been addressed systematically. In order to examine the local variabilities in near-surface seismic velocity in southern California, we measured the spatial distributions of near-surface seismic velocity at two sites: one in the San Gabriel Mountains (SGM) and one in the San Bernardino Mountains (SBM). Both sites are composed of predominantly crystalline rocks with topographic slopes that range from 0.2 to 0.5. We conducted seismic refraction surveys using sledgehammer-induced impacts on a steel plate along seismic lines that were oriented roughly N-S, 240 m in length with a spacing of 5 m, and with topographic variation including both a local hilltop and valley. Using first P-wave arrivals, we constructed a P-wave seismic tomography down to 50 m. Our results show that P-wave seismic velocity in the SGM site varies significantly within hillslopes and does not linearly correlate with slope, while P-wave seismic velocity in the SBM site shows little variation in the hillslope. In the SGM site, the Vs30 beneath the valley is 25% faster than the Vs30 beneath the hillslope. These results suggest that the local variability of seismic velocity depends on differences in sediment thickness, bedrock fractures, and weathering patterns.

Coplanar electrowetting-induced stirring as a tool to manipulate biological samples in lubricated digital microfluidics. Impact of ambient phase on drop internal flow patterna)

PubMed Central

Davoust, Laurent; Fouillet, Yves; Malk, Rachid; Theisen, Johannes

2013-01-01

Oscillating electrowetting on dielectrics (EWOD) with coplanar electrodes is investigated in this paper as a way to provide efficient stirring within a drop with biological content. A supporting model inspired from Ko et al. [Appl. Phys. Lett. 94, 194102 (2009)] is proposed allowing to interpret oscillating EWOD-induced drop internal flow as the result of a current streaming along the drop surface deformed by capillary waves. Current streaming behaves essentially as a surface flow generator and the momentum it sustains within the (viscous) drop is even more significant as the surface to volume ratio is small. With the circular electrode pair considered in this paper, oscillating EWOD sustains toroidal vortical flows when the experiments are conducted with aqueous drops in air as ambient phase. But when oil is used as ambient phase, it is demonstrated that the presence of an electrode gap is responsible for a change in drop shape: a pinch-off at the electrode gap yields a peanut-shaped drop and a symmetry break-up of the EWOD-induced flow pattern. Viscosity of oil is also responsible for promoting an efficient damping of the capillary waves which populate the surface of the actuated drop. As a result, the capillary network switches from one standing wave to two superimposed traveling waves of different mechanical energy, provided that actuation frequency is large enough, for instance, as large as the one commonly used in electrowetting applications (f ∼ 500 Hz and beyond). Special emphasis is put on stirring of biological samples. As a typical application, it is demonstrated how beads or cell clusters can be focused under flow either at mid-height of the drop or near the wetting plane, depending on how the nature of the capillary waves is (standing or traveling), and therefore, depending on the actuation frequency (150 Hz–1 KHz). PMID:24404038

Ocean waves and turbulence as observed with an adaptive coherent multifrequency radar

NASA Technical Reports Server (NTRS)

Gjessing, D. T.; Hjelmstad, J.

1984-01-01

An adaptive coherent multifrequency radar system is developed for several applications. The velocity distribution (Doppler spectrum) and spectral intensity of 15 different irregularity scales (waves and turbulence) can be measured simultaneously. Changing the azimuth angle of the antennas at regular intervals, the directivity of the wave/turbulence pattern on the sea surface can also be studied. A series of measurements for different air/sea conditions are carried out from a coast based platform. Experiments in the Atlantic are also performed with the same equipment making use of the NASA Electra aircraft. The multifrequency radar allows the measurement of the velocity distribution (""coherent and incoherent component'') associated with 15 different ocean irregularity scales simultaneously in a directional manner. It is possible to study the different air/sea mechanisms in some degree of detail.

Micropatterned photoalignment for wavefront controlled switchable optical devices

NASA Astrophysics Data System (ADS)

Glazar, Nikolaus

Photoalignment is a well-established technique for surface alignment of the liquid crystal director. Previously, chrome masks were necessary for patterned photoalignment but were difficult to use, costly, and inflexible. To extend the capabilities of photoalignment we built an automated maskless multi-domain photoalignment device based on a DMD (digital multimirror device) projection system. The device is capable of creating arbitrary photoalignment patterns with micron-sized features. Pancharatnam-Berry phase (PB-phase) is a geometric phase that arises from cyclic change of polarization state. By varying the azimuthal anchoring angle in a hybrid-aligned liquid crystal cell we can control the spatial variation of the PB-phase shift. Using our automated photoalignment device to align the liquid crystal arbitrary wave front manipulations are possible. The PB-phase shift effect is maximized when the cell is tuned to have a half-wave retardation and disappears at full-wave retardation, so the cell can be switched on and off by applying a voltage. Two wavefront controlled devices developed using this technique will be discussed: A switchable liquid crystal phase shift mask for creating sub-diffraction sized photolithographic features, and a transparent diffractive display that utilizes a switchable liquid crystal diffraction grating.

Characterization of the surface wave variability in the California Current region from satellite altimetry.

NASA Astrophysics Data System (ADS)

Villas Boas, A. B.; Gille, S. T.; Mazloff, M. R.

2016-02-01

Surface gravity waves play a crucial role in upper-ocean dynamics, and they are an important mechanism by which the ocean exchanges energy with the overlying atmosphere. Surface waves are largely wind forced and can also be modulated by ocean currents via nonlinear wave-current interactions, leading to either an amplification or attenuation of the wave amplitude. Even though individual waves cannot be detected by present satellite altimeters, surface waves have the potential to produce a sea-state bias in altimeter measurements and can impact the sea-surface-height spectrum at high wavenumbers or frequencies. Knowing the wave climatology is relevant for the success of future altimeter missions, such as the Surface Water and Ocean Topography (SWOT). We analyse the seasonal, intra-annual and interannual variability of significant wave heights retrieved from over two decades of satellite altimeter data and assess the extent to which the variability of the surface wave field in the California Current region is modulated by the local wind and current fields.

Marangoni-induced symmetry-breaking pattern selection on viscous fluids

NASA Astrophysics Data System (ADS)

Shen, Li; Denner, Fabian; Morgan, Neal; van Wachem, Berend; Dini, Daniele

2016-11-01

Symmetry breaking transitions on curved surfaces are found in a wide range of dissipative systems, ranging from asymmetric cell divisions to structure formation in thin films. Inherent within the nonlinearities are the associated curvilinear geometry, the elastic stretching, bending and the various fluid dynamical processes. We present a generalised Swift-Hohenberg pattern selection theory on a thin, curved and viscous films in the presence of non-trivial Marangoni effect. Testing the theory with experiments on soap bubbles, we observe the film pattern selection to mimic that of the elastic wrinkling morphology on a curved elastic bilayer in regions of slow viscous flow. By examining the local state of damping of surface capillary waves we attempt to establish an equivalence between the Marangoni fluid dynamics and the nonlinear elastic shell theory above the critical wavenumber of the instabilities and propose a possible explanation for the perceived elastic-fluidic duality. The authors acknowledge the financial support of the Shell University Technology Centre for fuels and lubricants.

Climate variations in northern North America (6000 BP to present) reconstructed from pollen and tree-ring data

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

Diaz, H.F.; Andrews, J.T.; Short, S.K.

The characteristic anomaly patterns of modern surface temperature and precipitation are compared to tree-ring indices (0-300 yr) and fossil pollen (0-6000 yr) variations in northern North America. The data base consists of 245 climate stations, 55 tree-ring chronologies, 153 modern pollen collections, and 39 fossil pollen sites. A few areas exhibit relatively high climatic sensitivity, displaying generally consistent patterns during alternate warm and cold periods, regardless of time scales. The surface changes are related to the redistribution (i.e., changes in the mean position and strength) of the planetary-scale waves and to north-south shifts in the mean boundary of the Arcticmore » Front. The zone where the largest changes occur is typically located along the mean present-day boundary between Arctic and Pacific airstreams. Establishing plausible relationships between vegetation responses and concomitant changes in atmospheric circulation patterns increases our confidence that the paleoclimatic signals are indeed related to large-scale circulation changes.« less

Frequency lock-in and phase synchronization of vortex shedding behind circular cylinder due to surface waves

NASA Astrophysics Data System (ADS)

Gunnoo, Hans; Abcha, Nizar; Ezersky, Alexander

2016-02-01

The influence of harmonic surface wave on non-regular Karman Vortex Street is investigated. In our experiments, Karman Street arises behind a vertical circular cylinder in a water flow and harmonic surface waves propagating upstream. It is found that surface waves can modify regimes of shedding in Karman Street: frequency lock-in and synchronization of vortex shedding can arise. Intensive surface waves can excite symmetric vortex street instead of chess-like street, and completely suppress shedding behind the cylinder. It is shown experimentally that such effects occur if frequency of harmonic surface wave is approximately twice higher than the frequency of vortex shedding. Region of frequency lock-in is found on the plane amplitude-frequency of surface wave.

Nonlinear Internal Waves on the Inner Shelf: Observations Using a Distributed Temperature Sensing (DTS) System.

NASA Astrophysics Data System (ADS)

Davis, K. A.; Reid, E. C.; Cohen, A. L.

2016-02-01

Internal waves propagating across the continental slope and shelf are transformed by the competing effects of nonlinear steepening and dispersive spreading, forming nonlinear internal waves (NLIWs) that can penetrate onto the shallow inner shelf, often appearing in the form of bottom-propagating nonlinear internal bores or boluses. NLIWs play a significant role in nearshore dynamics with baroclinic current amplitudes on the order of that of wind- and surface wave-driven flows and rapid temperature changes on the order of annual ranges. In June 2014 we used a Distributed Temperature Sensing (DTS) system to give a continuous cross-shelf view of nonlinear internal wave dynamics on the forereef of Dongsha Atoll, a coral reef in the northern South China Sea. A DTS system measures temperature continuously along the length of an optical fiber, resolving meter-to-kilometer spatial scales. This unique view of cross-shelf temperature structure made it possible to observe internal wave reflection, variable propagation speed across the shelf, bolus formation and dissipation. Additionally, we used the DTS data to track internal waves across the shallow fore reef and onto the reef flat and to quantify spatial patterns in temperature variability. Shoaling internal waves are an important process affecting physical variability and water properties on the reef.

Multifrequency synthesis and extraction using square wave projection patterns for quantitative tissue imaging.

PubMed

Nadeau, Kyle P; Rice, Tyler B; Durkin, Anthony J; Tromberg, Bruce J

2015-11-01

We present a method for spatial frequency domain data acquisition utilizing a multifrequency synthesis and extraction (MSE) method and binary square wave projection patterns. By illuminating a sample with square wave patterns, multiple spatial frequency components are simultaneously attenuated and can be extracted to determine optical property and depth information. Additionally, binary patterns are projected faster than sinusoids typically used in spatial frequency domain imaging (SFDI), allowing for short (millisecond or less) camera exposure times, and data acquisition speeds an order of magnitude or more greater than conventional SFDI. In cases where sensitivity to superficial layers or scattering is important, the fundamental component from higher frequency square wave patterns can be used. When probing deeper layers, the fundamental and harmonic components from lower frequency square wave patterns can be used. We compared optical property and depth penetration results extracted using square waves to those obtained using sinusoidal patterns on an in vivo human forearm and absorbing tube phantom, respectively. Absorption and reduced scattering coefficient values agree with conventional SFDI to within 1% using both high frequency (fundamental) and low frequency (fundamental and harmonic) spatial frequencies. Depth penetration reflectance values also agree to within 1% of conventional SFDI.

Multifrequency synthesis and extraction using square wave projection patterns for quantitative tissue imaging

PubMed Central

Nadeau, Kyle P.; Rice, Tyler B.; Durkin, Anthony J.; Tromberg, Bruce J.

2015-01-01

Abstract. We present a method for spatial frequency domain data acquisition utilizing a multifrequency synthesis and extraction (MSE) method and binary square wave projection patterns. By illuminating a sample with square wave patterns, multiple spatial frequency components are simultaneously attenuated and can be extracted to determine optical property and depth information. Additionally, binary patterns are projected faster than sinusoids typically used in spatial frequency domain imaging (SFDI), allowing for short (millisecond or less) camera exposure times, and data acquisition speeds an order of magnitude or more greater than conventional SFDI. In cases where sensitivity to superficial layers or scattering is important, the fundamental component from higher frequency square wave patterns can be used. When probing deeper layers, the fundamental and harmonic components from lower frequency square wave patterns can be used. We compared optical property and depth penetration results extracted using square waves to those obtained using sinusoidal patterns on an in vivo human forearm and absorbing tube phantom, respectively. Absorption and reduced scattering coefficient values agree with conventional SFDI to within 1% using both high frequency (fundamental) and low frequency (fundamental and harmonic) spatial frequencies. Depth penetration reflectance values also agree to within 1% of conventional SFDI. PMID:26524682

Clinical significance of J-wave in elite athletes.

PubMed

Pelliccia, Antonio; Quattrini, Filippo M

2015-01-01

The J-wave pattern on 12-lead ECG is traditionally defined as a positive deflection at junction between the end of the QRS and the beginning of the ST-segment. This pattern has recently been associated with increased risk for idiopathic ventricular fibrillation in the absence of cardiovascular disease. The interest for the clinical significance of J-wave pattern as a potential ECG hallmark of high risk for cardiac arrest has recently been reinforced by the growing practice of ECG screening, such as occurs in large population of young competitive athletes. The available scientific evidence shows that the J-wave pattern is relatively common in trained athletes (ranging from 14% to 44%) and, differently from subjects who suffered from ventricular fibrillation, commonly localized in lateral leads while it is relatively rare to be found in inferior leads. Furthermore the J-wave pattern has been demonstrated to be a dynamic phenomenon related to the training status, with the larger prominence at the peak of training and with an inverse relation between magnitude of J-wave and heart rate. In addition the J-wave pattern is usually associated with other ECG changes, such as increased QRS voltages and ST-segment elevation, as well as LV remodeling, suggesting that it likely represents another expression of the physiologic athlete's heart. Finally the scientific data available demonstrated that during a medium follow-up period the J-wave pattern does not convey risk for adverse cardiac events, including sudden death or ventricular tachyarrhythmias. Copyright © 2015 Elsevier Inc. All rights reserved.

Influence of changing surface temperature gradients on mid-latitudinal circulation and western hemispheric summer temperature extremes

NASA Astrophysics Data System (ADS)

Kornhuber, Kai; Hoffmann, Peter; Coumou, Dim

2017-04-01

Many recent summers in the Northern hemisphere (NH) mid-latitudes have seen severe heatwaves (2003, 2004, 2009, 2010, 2012, 2015, (Black et al. 2004; Diffenbaugh & Scherer 2013; Russo et al. 2014; Hoy et al. 2016)). During many of those extremes the mid-latitudinal tropospheric circulation was characterized by an amplified, quasi-stationary and hemispheric wave pattern with a dominant influence of wavenumber seven (Coumou et al. 2014; Petoukhov et al. 2016; Kornhuber et al. 2016). Analyzing NH summer reanalysis data we show that the position where these heat extremes occur is not arbitrary. If the amplitude of wave seven is large, the wave gets "locked" in a specific preferred phase position. As a consequence of this phase-locking behavior some regions are more likely to experience extreme weather during high-amplitude events. Meridional wind speeds associated with the preferred phase are particularly strong over longitudes of the western hemisphere (180°W - 40°E) leading to positive temperature anomalies over the US and Western Europe. Using a widely-used blocking-index we demonstrate that longitudes over these regions experience an increased probability of blocking during high amplitude wave seven events. We show that during the above mentioned extreme summers, amplified waves were locked in their preferred phase-position creating the right dynamical background condition for severe heatwaves to occur. Further, regression analyses reveal that a pronounced Ocean - Land temperature contrast (Tdiff) and weak poleward surface temperature gradient (dT/dy) are associated with an amplified wave seven in its preferred phase-position. Our study suggests that the observed positive trend in Tdiff and negative trend in dT/dy favors the occurrence of high-amplitude, quasi-stationary wave seven in its preferred phase position and therefore persistent heatwaves in the US and western Europe.

The frictional response of patterned soft polymer surfaces

NASA Astrophysics Data System (ADS)

Rand, Charles J.

2008-10-01

Friction plays an intricate role in our everyday lives, it is therefore critical to understand the underlying features of friction to better help control and manipulate the response anywhere two surfaces in contact move past each other by a sliding motion. Here we present results targeting a thorough understanding of soft material friction and how it can be manipulated with patterns. We found that the naturally occurring length scale or periodicity (lambda) of frictionally induced patterns, Schallamach waves, could be described using two materials properties (critical energy release rate Gc and complex modulus (E*), i.e. lambdainfinity Gc /E*). Following this, we evaluated the effect of a single defect at a sliding interface. Sliding over a defect can be used to model the sliding from one feature to another in a patterned surface. Defects decreased the sliding frictional force by as much as 80% sliding and this decrease was attributed to changes in tangential stiffness of the sliding interface. The frictional response of surface wrinkles, where multiple edges or defects are acting in concert, was also evaluated. Wrinkles were shown to decrease friction (F) and changes in contact area (A) could not describe this decrease. A tangential stiffness correction factor (fx) and changes in the critical energy release rate were used to describe this deviation (F infinity Gc *A*fx/ℓ, where ℓ is a materials defined length scale of dissipation). This scaling can be used to describe the friction of any topographically patterned surface including the Gecko's foot, where the feature size is smaller than ℓ and thus replaces ℓ, increasing the friction compared to a flat surface. Also, mechanically-induced surface defects were used to align osmotically driven surface wrinkles by creating stress discontinuities that convert the global biaxial stress state to local uniaxial stresses. Defect spacing was used to control the alignment process at the surface of the wrinkled rigid film/soft elastomer interface. These aligned wrinkled surfaces can be used to tune the adhesion and friction of an interface. The work presented here gives insight into tuning the friction of a soft polymeric surface as well as understanding the friction of complex hierarchical structures.

Shear Wave Imaging of Breast Tissue by Color Doppler Shear Wave Elastography.

PubMed

Yamakoshi, Yoshiki; Nakajima, Takahito; Kasahara, Toshihiro; Yamazaki, Mayuko; Koda, Ren; Sunaguchi, Naoki

2017-02-01

Shear wave elastography is a distinctive method to access the viscoelastic characteristic of the soft tissue that is difficult to obtain by other imaging modalities. This paper proposes a novel shear wave elastography [color Doppler shear wave imaging (CD SWI)] for breast tissue. Continuous shear wave is produced by a small lightweight actuator, which is attached to the tissue surface. Shear wave wavefront that propagates in tissue is reconstructed as a binary pattern that consists of zero and the maximum flow velocities on color flow image (CFI). Neither any modifications of the ultrasound color flow imaging instrument nor a high frame rate ultrasound imaging instrument is required to obtain the shear wave wavefront map. However, two conditions of shear wave displacement amplitude and shear wave frequency are needed to obtain the map. However, these conditions are not severe restrictions in breast imaging. This is because the minimum displacement amplitude is [Formula: see text] for an ultrasonic wave frequency of 12 MHz and the shear wave frequency is available from several frequencies suited for breast imaging. Fourier analysis along time axis suppresses clutter noise in CFI. A directional filter extracts shear wave, which propagates in the forward direction. Several maps, such as shear wave phase, velocity, and propagation maps, are reconstructed by CD SWI. The accuracy of shear wave velocity measurement is evaluated for homogeneous agar gel phantom by comparing with the acoustic radiation force impulse method. The experimental results for breast tissue are shown for a shear wave frequency of 296.6 Hz.

Teleconnection between sea ice in the Barents Sea in June and the Silk Road, Pacific-Japan and East Asian rainfall patterns in August

NASA Astrophysics Data System (ADS)

He, Shengping; Gao, Yongqi; Furevik, Tore; Wang, Huijun; Li, Fei

2018-01-01

In contrast to previous studies that have tended to focus on the influence of the total Arctic sea-ice cover on the East Asian summer tripole rainfall pattern, the present study identifies the Barents Sea as the key region where the June sea-ice variability exerts the most significant impacts on the East Asian August tripole rainfall pattern, and explores the teleconnection mechanisms involved. The results reveal that a reduction in June sea ice excites anomalous upward air motion due to strong near-surface thermal forcing, which further triggers a meridional overturning wave-like pattern extending to midlatitudes. Anomalous downward motion therefore forms over the Caspian Sea, which in turn induces zonally oriented overturning circulation along the subtropical jet stream, exhibiting the east-west Rossby wave train known as the Silk Road pattern. It is suggested that the Bonin high, a subtropical anticyclone predominant near South Korea, shows a significant anomaly due to the eastward extension of the Silk Road pattern to East Asia. As a possible descending branch of the Hadley cell, the Bonin high anomaly ultimately triggers a meridional overturning, establishing the Pacific-Japan pattern. This in turn induces an anomalous anticyclone and cyclone pair over East Asia, and a tripole vertical convection anomaly meridionally oriented over East Asia. Consequently, a tripole rainfall anomaly pattern is observed over East Asia. Results from numerical experiments using version 5 of the Community Atmosphere Model support the interpretation of this chain of events.

Teleconnection between Sea Ice in the Barents Sea in June and the Silk Road, Pacific-Japan and East Asian Rainfall Patterns in August

NASA Astrophysics Data System (ADS)

He, S.; Gao, Y.; Furevik, T.; Huijun, W.; Li, F.

2017-12-01

In contrast to previous studies that have tended to focus on the influence of the total Arctic sea-ice cover on the East Asian summer tripole rainfall pattern, the present study identifies the Barents Sea as the key region where the June sea-ice variability exerts the most significant impacts on the East Asian August tripole rainfall pattern, and explores the teleconnection mechanisms involved. The results reveal that a reduction in June sea ice excites anomalous upward air motion due to strong near-surface thermal forcing, which further triggers a meridional overturning wave-like pattern extending to midlatitudes. Anomalous downward motion therefore forms over the Caspian Sea, which in turn induces zonally oriented overturning circulation along the subtropical jet stream, exhibiting the east-west Rossby wave train known as the Silk Road pattern. It is suggested that the Bonin high, a subtropical anticyclone predominant near South Korea, shows a significant anomaly due to the eastward extension of the Silk Road pattern to East Asia. As a possible descending branch of the Hadley cell, the Bonin high anomaly ultimately triggers a meridional overturning, establishing the Pacific-Japan pattern. This in turn induces an anomalous anticyclone and cyclone pair over East Asia, and a tripole vertical convection anomaly meridionally oriented over East Asia. Consequently, a tripole rainfall anomaly pattern is observed over East Asia. Results from numerical experiments using version 5 of the Community Atmosphere Model support the interpretation of this chain of events.

Magnetic antenna excitation of whistler modes. IV. Receiving antennas and reciprocity

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

Stenzel, R. L., E-mail: stenzel@physics.ucla.edu; Urrutia, J. M.

Antenna radiation patterns are an important property of antennas. Reciprocity holds in free space and the radiation patterns for exciting and receiving antennas are the same. In anisotropic plasmas, radiation patterns are complicated by the fact that group and phase velocities differ and certain wave properties like helicity depend on the direction of wave propagation with respect to the background magnetic field B{sub 0}. Interference and wave focusing effects are different than in free space. Reciprocity does not necessarily hold in a magnetized plasma. The present work considers the properties of various magnetic antennas used for receiving whistler modes. Itmore » is based on experimental data from exciting low frequency whistler modes in a large uniform laboratory plasma. By superposition of linear waves from different antennas, the radiation patterns of antenna arrays are derived. Plane waves are generated and used to determine receiving radiation patterns of different receiving antennas. Antenna arrays have radiation patterns with narrow lobes, whose angular position can be varied by physical rotation or electronic phase shifting. Reciprocity applies to broadside antenna arrays but not to end fire arrays which can have asymmetric lobes with respect to B{sub 0}. The effect of a relative motion between an antenna and the plasma has been modeled by the propagation of a short wave packet moving along a linear antenna array. An antenna moving across B{sub 0} has a radiation pattern characterized by an oscillatory “whistler wing.” A receiving antenna in motion can detect any plane wave within the group velocity resonance cone. The radiation pattern also depends on loop size relative to the wavelength. Motional effects prevent reciprocity. The concept of the radiation pattern loses its significance for wave packets since the received signal does not only depend on the antenna but also on the properties of the wave packet. The present results are of fundamental interest and of relevance to loop antennas in space.« less

Reconstructing surface wave profiles from reflected acoustic pulses using multiple receivers.

PubMed

Walstead, Sean P; Deane, Grant B

2014-08-01

Surface wave shapes are determined by analyzing underwater reflected acoustic signals collected at multiple receivers. The transmitted signals are of nominal frequency 300 kHz and are reflected off surface gravity waves that are paddle-generated in a wave tank. An inverse processing algorithm reconstructs 50 surface wave shapes over a length span of 2.10 m. The inverse scheme uses a broadband forward scattering model based on Kirchhoff's diffraction formula to determine wave shapes. The surface reconstruction algorithm is self-starting in that source and receiver geometry and initial estimates of wave shape are determined from the same acoustic signals used in the inverse processing. A high speed camera provides ground-truth measurements of the surface wave field for comparison with the acoustically derived surface waves. Within Fresnel zone regions the statistical confidence of the inversely optimized surface profile exceeds that of the camera profile. Reconstructed surfaces are accurate to a resolution of about a quarter-wavelength of the acoustic pulse only within Fresnel zones associated with each source and receiver pair. Multiple isolated Fresnel zones from multiple receivers extend the spatial extent of accurate surface reconstruction while overlapping Fresnel zones increase confidence in the optimized profiles there.

Basinwide response of the Atlantic Meridional Overturning Circulation to interannual wind forcing

NASA Astrophysics Data System (ADS)

Zhao, Jian

2017-12-01

An eddy-resolving Ocean general circulation model For the Earth Simulator (OFES) and a simple wind-driven two-layer model are used to investigate the role of momentum fluxes in driving the Atlantic Meridional Overturning Circulation (AMOC) variability throughout the Atlantic basin from 1950 to 2010. Diagnostic analysis using the OFES results suggests that interior baroclinic Rossby waves and coastal topographic waves play essential roles in modulating the AMOC interannual variability. The proposed mechanisms are verified in the context of a simple two-layer model with realistic topography and only forced by surface wind. The topographic waves communicate high-latitude anomalies into lower latitudes and account for about 50% of the AMOC interannual variability in the subtropics. In addition, the large scale Rossby waves excited by wind forcing together with topographic waves set up coherent AMOC interannual variability patterns across the tropics and subtropics. The comparisons between the simple model and OFES results suggest that a large fraction of the AMOC interannual variability in the Atlantic basin can be explained by wind-driven dynamics.

Synchronization of Large Josephson-Junction Arrays by Traveling Electromagnetic Waves

NASA Astrophysics Data System (ADS)

Galin, M. A.; Borodianskyi, E. A.; Kurin, V. V.; Shereshevskiy, I. A.; Vdovicheva, N. K.; Krasnov, V. M.; Klushin, A. M.

2018-05-01

Mutual synchronization of many Josephson junctions is required for superradiant enhancement of the emission power. However, the larger the junction array is, the more difficult is the synchronization, especially when the array size becomes much larger than the emitted wavelength. Here, we study experimentally Josephson emission from such larger-than-the-wavelength Nb /NbSi /Nb junction arrays. For one of the arrays we observe a clear superradiant enhancement of emission above a threshold number of active junctions. The arrays exhibit strong geometrical resonances, seen as steps in current-voltage characteristics. However, radiation patterns of the arrays have forward-backward asymmetry, which is inconsistent with the solely geometrical resonance (standing-wave) mechanism of synchronization. We argue that the asymmetry provides evidence for an alternative mechanism of synchronization mediated by unidirectional traveling-wave propagation along the array (such as a surface plasmon). In this case, emission occurs predominantly in the direction of propagation of the traveling wave. Our conclusions are supported by numerical modeling of Josephson traveling-wave antenna. We argue that such a nonresonant mechanism of synchronization opens a possibility for phase locking of very large arrays of oscillators.

Dynamics of the Venus atmosphere

NASA Technical Reports Server (NTRS)

Ingersoll, A. P.

1992-01-01

The superrotation of the Venus atmosphere is a major unanswered problem in planetary science. At cloud-top levels (65-70 km altitude) the atmosphere rotates with a five-day period, corresponding to an equatorial wind speed of 90 m/s. Angular velocity is roughly constant on spherical shells, and decreases linearly with altitude to zero at the surface. The direction of rotation is the same as that of the solid planet, which is retrograde--opposite to the direction of orbital motion, but the 5-day period is short compared to the 243-day spin period of the solid planet or to the mean solar day, which is 117 Earth-days at the surface. The problem with the superrotation is that shearing stresses tend to transfer angular momentum downward, and would slow the atmosphere until it is spinning with the solid planet. Some organized circulation pattern is counteracting the tendency, but the pattern has not been identified. A simple Hadley-type circulation cannot do it because such a circulation is zonally symmetric and Hide's Theorem states that in an axisymmetric circulation an extremum in angular momentum per unit mass M can exist only at the surface. Venus violates the last condition, having a maximum of retrograde M on the equator at 70-80 km altitude. This leaves waves and eddies to maintain the superrotation but the length scales and forcing mechanisms for these motions need to be specified. Possible forcing mechanisms associated with waves, eddies and tides are discussed.

[Effects of forest regeneration patterns on the quantity and chemical structure of soil solution dissolved organic matter in a subtropical forest.

PubMed

Yuan, Xiao Chun; Lin, Wei Sheng; Pu, Xiao Ting; Yang, Zhi Rong; Zheng, Wei; Chen, Yue Min; Yang, Yu Sheng

2016-06-01

Using the negative pressure sampling method, the concentrations and spectral characte-ristics of dissolved organic matter (DOM) of soil solution were studied at 0-15, 15-30, 30-60 cm layers in Castanopsis carlesii forest (BF), human-assisted naturally regenerated C. carlesii forest (RF), C. carlesii plantation (CP) in evergreen broad-leaved forests in Sanming City, Fujian Pro-vince. The results showed that the overall trend of dissolved organic carbon (DOC) concentrations in soil solution was RF>CP>BF, and the concentration of dissolved organic nitrogen (DON) was highest in C. carlesii plantation. The concentrations of DOC and DON in surface soil (0-15 cm) were all significantly higher than in the subsurface (30-60 cm). The aromatic index (AI) was in the order of RF>CP>BF, and as a whole, the highest AI was observed in the surface soil. Higher fluorescence intensity and a short wave absorption peak (320 nm) were observed in C. carlesii plantation, suggesting the surface soil of C. carlesii plantation was rich in decomposed substance content, while the degree of humification was lower. A medium wave absorption peak (380 nm) was observed in human-assisted naturally regenerated C. carlesii forest, indicating the degree of humification was higher which would contribute to the storage of soil fertility. In addition, DOM characte-ristics in 30-60 cm soil solution were almost unaffected by forest regeneration patterns.

Compact portable diffraction moire interferometer

DOEpatents

Deason, V.A.; Ward, M.B.

1988-05-23

A compact and portable moire interferometer used to determine surface deformations of an object. The improved interferometer is comprised of a laser beam, optical and fiber optics devices coupling the beam to one or more evanescent wave splitters, and collimating lenses directing the split beam at one or more specimen gratings. Observations means including film and video cameras may be used to view and record the resultant fringe patterns. 7 figs.

Performances estimation of a rotary traveling wave ultrasonic motor based on two-dimension analytical model.

PubMed

Ming, Y; Peiwen, Q

2001-03-01

The understanding of ultrasonic motor performances as a function of input parameters, such as the voltage amplitude, driving frequency, the preload on the rotor, is a key to many applications and control of ultrasonic motor. This paper presents performances estimation of the piezoelectric rotary traveling wave ultrasonic motor as a function of input voltage amplitude and driving frequency and preload. The Love equation is used to derive the traveling wave amplitude on the stator surface. With the contact model of the distributed spring-rigid body between the stator and rotor, a two-dimension analytical model of the rotary traveling wave ultrasonic motor is constructed. Then the performances of stead rotation speed and stall torque are deduced. With MATLAB computational language and iteration algorithm, we estimate the performances of rotation speed and stall torque versus input parameters respectively. The same experiments are completed with the optoelectronic tachometer and stand weight. Both estimation and experiment results reveal the pattern of performance variation as a function of its input parameters.

Estimation of near-surface shear-wave velocities and quality factors using multichannel analysis of surface-wave methods

NASA Astrophysics Data System (ADS)

Xia, Jianghai

2014-04-01

This overview article gives a picture of multichannel analysis of high-frequency surface (Rayleigh and Love) waves developed mainly by research scientists at the Kansas Geological Survey, the University of Kansas and China University of Geosciences (Wuhan) during the last eighteen years by discussing dispersion imaging techniques, inversion systems, and real-world examples. Shear (S)-wave velocities of near-surface materials can be derived from inverting the dispersive phase velocities of high-frequency surface waves. Multichannel analysis of surface waves—MASW used phase information of high-frequency Rayleigh waves recorded on vertical component geophones to determine near-surface S-wave velocities. The differences between MASW results and direct borehole measurements are approximately 15% or less and random. Studies show that inversion with higher modes and the fundamental mode simultaneously can increase model resolution and an investigation depth. Multichannel analysis of Love waves—MALW used phase information of high-frequency Love waves recorded on horizontal (perpendicular to the direction of wave propagation) component geophones to determine S-wave velocities of shallow materials. Because of independence of compressional (P)-wave velocity, the MALW method has some attractive advantages, such as 1) Love-wave dispersion curves are simpler than Rayleigh wave's; 2) dispersion images of Love-wave energy have a higher signal to noise ratio and more focused than those generated from Rayleigh waves; and 3) inversion of Love-wave dispersion curves is less dependent on initial models and more stable than Rayleigh waves.

a Model for the Dynamical Behavior of Patterned Thin Film Structures on Silicon

NASA Astrophysics Data System (ADS)

Every, A. G.; Maznev, A. A.

2010-02-01

Metrology of metal-dielectric thin film structures fabricated on silicon wafers has emerged as a major application area of laser ultrasonics. The measurements are oftentimes performed on structures comprised of periodic line arrays, which as regards their dynamical behavior, form a distinct class of phononic crystals. Recently reported measurements of laser-generated surface acoustic modes in Cu-SiO2 line arrays on silicon have uncovered a number of interesting phenomena. The goal of this paper is to provide a simple theoretical model capturing the salient features of the experiment and leading to a better understanding of the physical nature of the observed phenomena. The structure is simulated by a uniform layer on a substrate with periodic mass loading applied to its upper surface, and is treated by the plane wave expansion method. We establish that the large bandgap observed inside the Brillouin zone originates from the hybridization of the Rayleigh and Sezawa modes of the film-substrate structure. The displacement pattern in the Rayleigh and Sezawa waves explains their strong interaction, leading to a larger bandgap than the ones formed at the zone boundary. Unexpectedly low radiation loss of the hybridized Rayleigh-Sezawa mode in the "supersonic" domain, is also reproduced by the model.

Analysis of dispersion and attenuation of surface waves in poroelastic media in the exploration-seismic frequency band

USGS Publications Warehouse

Zhang, Y.; Xu, Y.; Xia, J.

2011-01-01

We analyse dispersion and attenuation of surface waves at free surfaces of possible vacuum/poroelastic media: permeable-'open pore', impermeable-'closed pore' and partially permeable boundaries, which have not been previously reported in detail by researchers, under different surface-permeable, viscous-damping, elastic and fluid-flowing conditions. Our discussion is focused on their characteristics in the exploration-seismic frequency band (a few through 200 Hz) for near-surface applications. We find two surface-wave modes exist, R1 waves for all conditions, and R2 waves for closed-pore and partially permeable conditions. For R1 waves, velocities disperse most under partially permeable conditions and least under the open-pore condition. High-coupling damping coefficients move the main dispersion frequency range to high frequencies. There is an f1 frequency dependence as a constant-Q model for attenuation at high frequencies. R1 waves for the open pore are most sensitive to elastic modulus variation, but least sensitive to tortuosities variation. R1 waves for partially permeable surface radiate as non-physical waves (Im(k) < 0) at low frequencies. For R2 waves, velocities are slightly lower than the bulk slow P2 waves. At low frequencies, both velocity and attenuation are diffusive of f1/2 frequency dependence, as P2 waves. It is found that for partially permeable surfaces, the attenuation displays -f1 frequency dependence as frequency increasing. High surface permeability, low-coupling damping coefficients, low Poisson's ratios, and low tortuosities increase the slope of the -f1 dependence. When the attenuation coefficients reach 0, R2 waves for partially permeable surface begin to radiate as non-physical waves. ?? 2011 The Authors Geophysical Journal International ?? 2011 RAS.

Spatial eigenmodes and synchronous oscillation: co-incidence detection in simulated cerebral cortex.

PubMed

Chapman, Clare L; Wright, James J; Bourke, Paul D

2002-07-01

Zero-lag synchronisation arises between points on the cerebral cortex receiving concurrent independent inputs; an observation generally ascribed to nonlinear mechanisms. Using simulations of cerebral cortex and Principal Component Analysis (PCA) we show patterns of zero-lag synchronisation (associated with empirically realistic spectral content) can arise from both linear and nonlinear mechanisms. For low levels of activation, we show the synchronous field is described by the eigenmodes of the resultant damped wave activity. The first and second spatial eigenmodes (which capture most of the signal variance) arise from the even and odd components of the independent input signals. The pattern of zero-lag synchronisation can be accounted for by the relative dominance of the first mode over the second, in the near-field of the inputs. The simulated cortical surface can act as a few millisecond response coincidence detector for concurrent, but uncorrelated, inputs. As cortical activation levels are increased, local damped oscillations in the gamma band undergo a transition to highly nonlinear undamped activity with 40 Hz dominant frequency. This is associated with "locking" between active sites and spatially segregated phase patterns. The damped wave synchronisation and the locked nonlinear oscillations may combine to permit fast representation of multiple patterns of activity within the same field of neurons.

Theory and Application of Auger and Photoelectron Diffraction and Holography

NASA Astrophysics Data System (ADS)

Chen, Xiang

This dissertation addresses the theories and applications of three important surface analysis techniques: Auger electron diffraction (AED), x-ray photoelectron diffraction (XPD), and Auger and photoelectron holography. A full multiple-scattering scheme for the calculations of XPD, AED, and Kikuchi electron diffraction pattern from a surface cluster is described. It is used to simulate 64 eV M_{2,3}VV and 913 eV L_3VV AED patterns from Cu(001) surfaces, in order to test assertions in the literature that they are explicable by a classical "blocking" and channeling model. We find that this contention is not valid, and that only a quantum mechanical multiple-scattering calculation is able to simulate these patterns well. The same multiple scattering simulation scheme is also used to investigate the anomalous phenomena of peak shifts off the forward-scattering directions in photo -electron diffraction patterns of Mg KLL (1180 eV) and O 1s (955 eV) from MgO(001) surfaces. These shifts are explained by calculations assuming a short electron mean free path. Similar simulations of XPD from a CoSi_2(111) surface for Co-3p and Si-2p normal emission agree well with experimental diffraction patterns. A filtering process aimed at eliminating the self -interference effect in photoelectron holography is developed. A better reconstructed image from Si-2p XPD from a Si(001) (2 times 1) surface is seen at atomic resolution. A reconstruction algorithm which corrects for the anisotropic emitter waves as well as the anisotropic atomic scattering factors is used for holographic reconstruction from a Co-3p XPD pattern from a CoSi_2 surface. This new algorithm considerably improves the reconstructed image. Finally, a new reconstruction algorithm called "atomic position recovery by iterative optimization of reconstructed intensities" (APRIORI), which takes account of the self-interference terms omitted by the other holographic algorithms, is developed. Tests on a Ni-C-O chain and Si(111)(sqrt{3} times sqrt{3})B surface suggest that this new method may overcome the twin image problem in the traditional holographic methods, reduce the artifacts in real space, and even separately identify the chemical species of the scatterers.

A new dynamical index for classification of cold surge types over East Asia

NASA Astrophysics Data System (ADS)

Park, Tae-Won; Ho, Chang-Hoi; Jeong, Jee-Hoon; Heo, Jin-Woo; Deng, Yi

2015-11-01

The cold surges over East Asia can be classified into wave-train type and blocking type according to their dynamic origins. In the present study, two dynamic indices are proposed to objectively identify cold surge types using potential temperature ( θ) on the dynamic tropopause at 2-potential vorticity units (2-PVU) surface. The two indices are designed to represent primary characteristics of the two types of cold surge. The wave-train index ( WI) is defined as a difference of anomalous θ on the 2-PVU surface between the western North Pacific and northeast China, which captures a southward (northward) intrusion of cold (warm) air mass related to the trough-ridge pattern. The blocking index ( BI) is defined as a difference of anomalous θ between the subarctic region and northeast China, which indicates air mass overturning related to a reversal of the usual meridional θ gradient commonly observed in the occurrence of blocking type cold surge. Composite analyses based on the distribution of the WI and BI clearly demonstrate the dynamic evolutions of corresponding cold surge types. The wave-train cold surge is associated with a southeastward expansion of the Siberian High and northerly wind near surface, which is caused by growing baroclinic waves. During the blocking cold surge, a geopotential height dipole indicating the subarctic blocking and deepening of East Asian coastal trough induces a southward expansion of the Siberian High and northeasterly wind. Compared to the wave-train type, the blocking cold surge exhibits a longer duration and stronger intensity. In the new framework of these dynamic indices, we can detect a third type of cold surge when both the wave-train and the blocking occur together. In addition, we can exclude the events that do not have the essential features of the upper tropospheric disturbances or the subarctic anticyclonic circulation, which are responsible for cold surge occurrence, using the new indices.

Seismic anisotropy and large-scale deformation of the Eastern Alps

NASA Astrophysics Data System (ADS)

Bokelmann, Götz; Qorbani, Ehsan; Bianchi, Irene

2013-12-01

Mountain chains at the Earth's surface result from deformation processes within the Earth. Such deformation processes can be observed by seismic anisotropy, via the preferred alignment of elastically anisotropic minerals. The Alps show complex deformation at the Earth's surface. In contrast, we show here that observations of seismic anisotropy suggest a relatively simple pattern of internal deformation. Together with earlier observations from the Western Alps, the SKS shear-wave splitting observations presented here show one of the clearest examples yet of mountain chain-parallel fast orientations worldwide, with a simple pattern nearly parallel to the trend of the mountain chain. In the Eastern Alps, the fast orientations do not connect with neighboring mountain chains, neither the present-day Carpathians, nor the present-day Dinarides. In that region, the lithosphere is thin and the observed anisotropy thus resides within the asthenosphere. The deformation is consistent with the eastward extrusion toward the Pannonian basin that was previously suggested based on seismicity and surface geology.

Nanosecond laser-induced ablation and laser-induced shockwave structuring of polymer foils down to sub-μm patterns

NASA Astrophysics Data System (ADS)

Lorenz, P.; Bayer, L.; Ehrhardt, M.; Zimmer, K.; Engisch, L.

2015-03-01

Micro- and nanostructures exhibit a growing commercial interest where a fast, cost-effective, and large-area production is attainable. Laser methods have a great potential for the easy fabrication of surface structures into flexible polymer foils like polyimide (PI). In this study two different concepts for the structuring of polymer foils using a KrF excimer laser were tested and compared: the laser-induced ablation and the laser-induced shock wave structuring. The direct front side laser irradiation of these polymers allows the fabrication of different surface structures. For example: The low laser fluence treatment of PI results in nano-sized cone structures where the cone density can be controlled by the laser parameters. This allows inter alia the laser fabrication of microscopic QR code and high-resolution grey-tone images. Furthermore, the laser treatment of the front side of the polymer foil allows the rear side structuring due to a laserinduced shock wave. The resultant surface structures were analysed by optical and scanning electron microscopy (SEM) as well as white light interferometry (WLI).

Cyclic fluctuations of water level as a basis for determining aquifer transmissibility

USGS Publications Warehouse

Ferris, John G.

1952-01-01

In coastal areas, wells near bodies of tidal water frequently exhibit sinusoidal fluctuations of water level, in response to periodic changes of tidewater stage.  Inland, the regulation of a surface reservoir often produces correlative changes of ground-water stage in wells adjacent either to the reservoir or to its attendant stream.  As the stage of the surface water rises, the head upon the subaqueous outcrop of the aquifer increases and thereby either increases the rate of inflow to the aquifer or reduces the rate of outflow therefrom.  The increase in recharge or reduction in discharge results in a general recovery of water level in the aquifer. On the subsequent falling stage this pattern is reversed.  When the stage of the surface body fluctuates as a simple harmonic motion a train of sinusoidal waves is propagated shoreward through the sub-outcrop of the aquifer.  With increasing distance from the sub-outcrop, the amplitude of the transmitted wave decreases and the time lag of a given maximum or minimum increases.

Utilizing the NASA and NOAA Joint Ocean Surface Topography Mission to Assess Patterns and Trends in Sea-Surface Height in the U.S. Affiliated Pacific Islands

NASA Astrophysics Data System (ADS)

Fitzgerald, S. S.; Walker, K. A.; Courtright, A. B.; Young, I. J.

2017-12-01

The United States Affiliated Pacific Islands (USAPI) are home to a population of low-lying coral atolls which are extremely vulnerable to sea level rise. Coastal infrastructure like groundwater reservoirs, harbor operations, and sewage systems, as well as natural coastal features such as reefs and beach ecosystems, are most vulnerable during inundation events. These Pacific Islanders face increasing hazards as coastal flooding infiltrates freshwater resources and may even lead to displacement. The two main components of inundation include tidal fluctuations and sea level anomalies; however, low-lying atolls are also vulnerable to the additional influence of waves. This study created a climatology of significant wave height in the Republic of the Marshall Islands (RMI), and incorporated this dataset with tides and sea level anomalies to create a novel approach to assessing inundation flood risk in the RMI. The risk metric was applied to the RMI as a study site with the goal of assessing wider-scale applicability across the rest of the USAPI. The inclusion of wave height and wave direction as a crucial component of the risk metric will better inform USAPI coastal-managers for future inundation events and disaster preparedness. In addition to the risk metric, a wave-rose atlas was created for decision-makers in the RMI. This study highlights the often-overlooked region of the Pacific and demonstrates the application of the risk metric to specific examples in the RMI.