Fast Wave Speed Research Articles

Multistage lithospheric drips control active basin formation within an uplifting orogenic plateau

According to GNSS/INSAR measurements, the Konya Basin in Central Anatolia is undergoing rapid subsidence within an uplifting orogenic plateau. Further, geophysical studies reveal thickened crust under the basin and a fast seismic wave speed anomaly in the underlying mantle, in addition to a localised depression in calculated residual topography (down to 280 m) over the Konya Basin, based on gravity-topography considerations. Using scaled laboratory (analogue) experiments we show that the active formation of the Konya Basin may be accounted for by the descent of a mantle lithospheric drip causing local circular-shaped surface subsidence. We interpret that the Konya Basin is developing through a secondary drip pulse that is contemporaneous with broad plateau uplift caused by a larger-scale lithospheric drip since the Miocene. The research reveals that basin evolution and plateau uplift may be linked in a multistage process of lithospheric removal during episodic development of orogenic systems.

Poroelastic model of the lungs at low frequencies predicted by Biot's theory

Biot's theory of poroelastic wave propagation inherently lends itself to elucidate the characteristics of a biphasic medium comprising solid and fluid components, such as biological tissues. One of the intricately complex biological tissues that remains poorly understood is the lungs since their properties diversify significantly through their pore geometries affected by inspiratory positive airway pressure (IPAP) and applied frequency range. One hypothesizes that the vibroacoustic behaviour of the lungs can be predicted by Biot's theory, as the nature of the lungs aligns with the principles of the theory at low frequencies. This study aims to analytically investigate the vibroacoustic behaviour of the lungs, considering 10 and 20-cm H;2O IPAP. Utilizing a fractional derivative formulation, one predicts the complex-valued shear wave speed, as well as the fast and slow compression wave speeds, for frequencies ranging from 5 to 100 Hz. A 3D digital thorax twin study using these predicted wave speeds, particularly at 28 Hz and 20 cm H;2O IPAP, is validated against experimental data from the literature. Consequently, applying Biot's theory provides a valuable framework for understanding the dynamic vibroacoustic behaviour of the lung tissues in response to varying IPAP and low frequencies.

Discrepancies in the Properties of a Coronal Mass Ejection on Scales of 0.03 au as Revealed by Simultaneous Measurements at Solar Orbiter and Wind: The 2021 November 3–5 Event

Simultaneous in situ measurements of coronal mass ejections (CMEs), including both plasma and magnetic field, by two spacecraft in radial alignment have been extremely rare. Here, we report on one such CME measured by Solar Orbiter (SolO) and Wind on 2021 November 3–5, while the spacecraft were radially separated by a heliocentric distance of 0.13 au and angularly by only 2.2°. We focus on the magnetic cloud (MC) part of the CME. We find notable changes in the R and N magnetic field components and in the speed profiles inside the MC between SolO and Wind. We observe a greater speed at the spacecraft farther away from the Sun without any clear compression signatures. Since the spacecraft are close to each other and computing fast magnetosonic wave speed inside the MC, we rule out temporal evolution as the reason for the observed differences, suggesting that spatial variations over 2.2° of the MC structure are at the heart of the observed discrepancies. Moreover, using shock properties at SolO, we forecast an arrival time 2 hr 30 minutes too late for a shock that is just 5 hr 31 minutes away from Wind. Predicting the north–south component of the magnetic field at Wind from SolO measurements leads to a relative error of 55%. These results show that even angular separations as low as 2.2° (or 0.03 au in arc length) between spacecraft can have a large impact on the observed CME properties, which raises the issue of the resolutions of current CME models, potentially affecting our forecasting capabilities.

The development of rifting and magmatism in the multiply rifted Turkana Depression, East Africa: Evidence from surface-wave analysis of crustal and uppermost mantle structure

The Turkana Depression separates the uplifted Ethiopian and East African Plateaus. It was the site, in Mesozoic times, of a failed episode of NE–SW-oriented rifting (the Anza Rift), but now hosts E–W-oriented Nubia–Somalia separation at the junction between the Main Ethiopian Rift in the north and the Eastern Rift to the south. However, the time-integrated effect of these rifting phases on crustal and lithospheric mantle architecture and thermal structure is poorly understood. Utilising data from new seismograph networks in the Turkana Depression and northern Tanzania Craton, we produce a detailed anisotropic crustal and uppermost mantle shear-wave velocity model of the region. Within the Tanzania Craton, slightly lower uppermost mantle wavespeeds (4.4–4.5 km/s) compared to neighbouring regions, and coincident rift-parallel crustal anisotropy, imply the Nyanza Rift developed in relatively weak mobile belt lithosphere between two refractory Archean blocks. At upper-crustal (≲10 km) depths in the Turkana Depression, the slowest velocities (≲3.2 km/s) are attributed to thick Mesozoic-age sedimentary basins. Nowhere within the Depression is the mid-to-lower crust or lithospheric mantle associated with wavespeeds as slow, or seismic anisotropy as strong, as that observed below the melt-rich central and northern Main Ethiopian Rift (MER) and Ethiopian Plateau further north. High upper mantle wavespeeds (≳4.5 km/s), coinciding with the broadening of MER-rifting into southern Ethiopia, confirm the presence of refractory Proterozoic lithosphere acting as a rheological boundary to rift development. Thinned crustal zones associated with failed Mesozoic Anza rifting are also underlain by fast wavespeed (>4.5 km/s) mantle lithosphere, implying this area has resisted significant thermomechanical modification from Miocene-Recent extension and magmatism. Pre-existing crustal thin zones do not, therefore, necessarily represent zones of plate-weakness where subsequent phases of rifting will develop.

Density polarization effect of spin-up and spin-down electrons on magnetosonic solitons in a dense plasma with oblique magnetic field

Nonlinear wave propagation of fast and slow magnetosonic waves is investigated in a magnetized quantum plasma with spin polarization effects of degenerate electrons. The multi-fluid quantum magnetohydrodynamic model is considered and two separate fluid dynamic equations for degenerate electrons i.e. spin-up and spin-down states (Pauli paramagnetism) with their different Fermi pressures. The ions are assumed to be classical and external magnetic field lies in a plane. The magnetization energy and current density of electrons due to the spin-1/2 effects are included in the momentum equation of the degenerate electrons and Maxwell equations, respectively. A Korteweg-de-Vries (KdV) equation is derived for nonlinear magnetosonic waves in a dense magnetized plasma with the inclusion of electron spin effects and oblique external magnetic field. The electron inertial effect (which causes wave dispersion) of both spin-up and spin-down state electrons is also included in the model. It is found that electron spin polarization density has significant effects on the phase speed and soliton structures (i.e. its width and amplitude) of fast (hump) and slow (dip) magnetosonic waves in a dense magnetized plasma. The present theoretical study along with the obtained numerical results may have possible applications towards many realistic astrophysical scenarios.

A New P‐Wave Tomographic Model (CAP22) for North America: Implications for the Subduction and Cratonic Metasomatic Modification History of Western Canada and Alaska

AbstractOur understanding of the present‐day state and evolution of the Canadian and Alaskan mantle is hindered by a lack of absolute P‐wavespeed constraints that provide complementary sensitivity to composition in conjunction with existing S‐wavespeed models. Consequently, cratonic modification, orogenic history of western North America and complexities within the Alaskan Proto‐Pacific subduction system remain enigmatic. One challenge concerns the difficulties in extracting absolute arrival‐time measurements from often‐noisy data recorded by temporary seismograph networks required to fill gaps in continental and global databases. Using the Absolute Arrival‐time Recovery Method (AARM), we extract >180,000 new absolute arrival‐time residuals from seismograph stations across Canada and Alaska and combine these data with USArray and global arrival‐time data from the contiguous US and Alaska. We develop a new absolute P‐wavespeed tomographic model, CAP22, spanning North America that significantly improves resolution in Canada and Alaska over previous models. Slow wavespeeds below the Canadian Cordillera sharply abut fast wavespeeds of the continental interior at the Rocky Mountain Trench in southwest Canada. Slow wavespeeds below the Mackenzie Mountains continue farther inland in northwest Canada, indicating Proterozoic‐Archean metasomatism of the Slave craton. Inherited tectonic lineaments colocated with this north‐south wavespeed boundary suggest that both the crust and mantle may control Cordilleran orogenic processes. In Alaska, fast upper mantle wavespeeds below the Wrangell Volcanic Field favor a conventional subduction related mechanism for volcanism. Finally, seismic evidence for the subducted Kula and Yukon slabs indicate tectonic reconstructions of western North America may require revision.

A 3D crustal shear speed model of the Auckland volcanic field, New Zealand, from multi-component ambient noise tomography

We present a 3D shear-wave speed model of the crust in the intra-plate Auckland Volcanic Field (AVF), that provides new depth information on the basement geology and is a step towards determining lithospheric controls on volcanism of the AVF, within the Zealandia continent. Beneath the AVF, our model finds a mid-crustal contact of the upturning ophiolite-rich Dun Mountain-Maitai Terrane (DMT), and the western end of the accretionary Waipapa (Caples) Terranes which are dominated by terrigenous sedimentary rocks. Westward and at depth, the DMT presents as a high-speed, thick, and horizontal part of the Gondwana-ward verging syncline seen in the DMT elsewhere in New Zealand. Along the western side of the Junction Magnetic Anomaly (which indicates the presence of the DMT), a major vertical discontinuity probably marks the contact between the horizontal DMT and the Waipapa (Caples) Terranes. The Waipapa (Caples) Terrane contain a large wedge-shaped low-speed zone tapering eastward and extending NNW-SSE alongside the DMT. In addition, the model identifies a sharp vertical discontinuity at the eastern edge of the AVF that extends from the near-surface through the low-speed wedge. We interpret this discontinuity as a relatively young subvertical fault with a significant downthrow to the west. It appears to be a reactivation of a fault zone inherited from the break-up of Gondwana. The model also imaged the largest massif of crystalline ultramafic rocks in the DMT that causes the Takapuna Gravity Anomaly and the NE striking Port Waikato-Mangatangi cross-fault system. The strike directions of the faults mirror a rhombic-rectangular fault grid inherited from the breakaway of Zealandia from Gondwana.The shear speed model was produced using frequency-time analysis of multi-component Rayleigh wave Green's functions, reversible-jump Markov chain Monte Carlo inversion of group arrival times, and the inversion of dispersion relations for shear speed as a function of depth. Plain language summaryA 3D model of shear wave speeds in the crust provides new information on the geological structure beneath the Auckland Volcanic Field (AVF). The field is positioned above the contact between ocean floor rocks of the Dun Mountain-Maitai Terrane (DMT) in the west with fast wave speeds and a prominent wedge-shaped low-speed zone in the sandstone-dominated Waipapa/Caples Terrane in the east. The model images a fold structure of the DMT similar to that seen throughout New Zealand and at depth delineates the contact as a major sub-vertical discontinuity. A second vertical discontinuity just east of the AVF is very abrupt, is also oriented NNW-SSE and is probably caused by faulting. The model has also imaged the NE-oriented Port Waikato-Mangatangi cross-fault system in the south of the region and the large massif of coarse-grained intrusive rocks in the DMT that causes the previously recognised Takapuna gravity anomaly.

Control of diffusion-driven pattern formation behind a wave of competency

In certain biological contexts, such as the plumage patterns of birds and stripes on certain species of fishes, pattern formation takes place behind a so-called “wave of competency”. Currently, the effects of a wave of competency on the patterning outcome are not well-understood. In this study, we use Turing’s diffusion-driven instability model to study pattern formation behind a wave of competency, under a range of wave speeds. Numerical simulations show that in one spatial dimension a slower wave speed drives a sequence of peak splittings in the pattern, whereas a higher wave speed leads to peak insertions. In two spatial dimensions, we observe stripes that are either perpendicular or parallel to the moving boundary under slow or fast wave speeds, respectively. We argue that there is a correspondence between the one- and two-dimensional phenomena, and hypothesize that (as others have) pattern formation behind a wave of competency can account for the pattern organization observed in many biological systems.

Use of the Normalized Design Parameters for Designing a Strip Speaker Operated by the Traveling-Wave Control Method

A strip speaker is the simplified panel speaker adopting a thin beam as the radiator, which is operated under the traveling-wave control method (TCM) with three actuators. The structural resonances are suppressed fundamentally by nullifying the reflected bending waves near the boundary, thus radiating a smooth sound spectrum in a wide frequency band. This study develops the design guidelines for such TCM-controlled strip speakers by investigating the effect of design variables on acoustic performances, such as the effective frequency range and the radiation efficiency. To this end, the acoustic performances are normalized by the size and physical properties of the beam so that a parametric study in the normalized domain can generalize the conditions for the desired acoustic performances. The result shows that the effective frequency range becomes wider when the beam material has a fast wave speed, and the radiation efficiency is enhanced as the beam density decreases. It is found that the two acoustic performances require a trade-off in selecting the actuator location and beam thickness. The suggested design procedure is validated using acrylic and aluminum beams having the same size. The aluminum beam has a faster wave speed, thus covering the effective bandwidth of 5800 Hz, 2.5 times wider than the acrylic case. On the other hand, the acrylic beam has five times higher radiation efficiency due to its low density. As a result, one can select the dimension and material of the beam appropriately to achieve the desired acoustic performance by using the suggested design method.

Fundamental diagrams of commercial adaptive cruise control: Worldwide experimental evidence

Experimental measurements on commercial adaptive cruise control (ACC) vehicles are becoming increasingly available from around the world, providing an unprecedented opportunity to study the traffic flow characteristics that arise from this technology. This paper adds new experimental evidence to this knowledge base and presents a comprehensive empirical study on the ACC equilibrium behaviors via the resulting fundamental diagrams. We find that, like human-driven vehicles, ACC systems display a linear equilibrium spacing-speed relationship (within the range of available data) but the key parameters of these relationships can differ significantly from human-driven traffic depending on input settings. At the minimum ACC headway setting, equilibrium capacities in excess of 3500 vehicles per hour are observed, together with an extremely fast equilibrium wave speed of 100 kilometers per hour. These fast waves are unfamiliar to human drivers, and may pose a safety risk. The results also suggest that ACC jam spacing can be much larger than in human traffic, which reduces the network storage capacity.

Constraining the 410-km discontinuity and slab structure in the Kuril subduction zone with triplication waveforms

SUMMARYThe detailed structure near the 410-km discontinuity provides key constraints of the dynamic interactions between the upper mantle and the lower mantle through the mantle transition zone (MTZ) via mass and heat exchange. Meanwhile, the temperature of the subducting slab, which can be derived from its fast wave speed perturbation, is critical for understanding the mantle dynamics in subduction zones where the slab enters the MTZ. Multipathing, i.e. triplicated, body waves that bottom near the MTZ carry rich information of the 410-km discontinuity structure and can be used to constrain the discontinuity depth and radial variations of wave speeds across it. In this study, we systematically analysed the trade-off between model parameters in triplication studies using synthetic examples. Specifically, we illustrated the necessity of using array-normalized amplitude. Two 1-D depth profiles of the wave speed below the Tatar Strait of Russia in the Kuril subduction zone are obtained. We have observed triplications due to both the 410-km discontinuity and the slab upper surface. And, seismic structures for these two interfaces are simultaneously inverted. Our derived 410-km discontinuity depths for the northern and southern regions are at 420$\pm $15 and 425$\pm $15 km, respectively, with no observable uplift. The slab upper surface is inverted to be located about 50–70 km below the 410-km discontinuity. This location is between the depths of the 1 and 2 per cent P-wave speed perturbation contours of a regional 3-D full-waveform inversion (FWI) model, but we found twice the wave speed perturbation amplitude. A wave speed increase of 3.9–4.6 per cent within the slab, compared to 2.0–2.4 per cent from the 3-D FWI model, is necessary to fit the waveforms with the shortest period of 2 s, indicating that high-frequency waves are required to accurately resolve the detailed structures near the MTZ.

Seismic Tomographic Imaging of the Eastern Mediterranean Mantle: Implications for Terminal‐Stage Subduction, the Uplift of Anatolia, and the Development of the North Anatolian Fault

AbstractThe Eastern Mediterranean captures the east‐west transition from active subduction of Earth's oldest oceanic lithosphere to continental collision, making it an ideal location to study terminal‐stage subduction. Asthenospheric‐ or subduction‐related processes are the main candidates for the region's ∼2 km uplift and Miocene volcanism; however, their relative importance is debated. To address these issues, we present new P and S wave relative arrival‐time tomographic models that reveal fast anomalies associated with an intact Aegean slab in the west, progressing to a fragmented, partially continental, Cyprean slab below central Anatolia. We resolve a gap between the Aegean and Cyprean slabs, and a horizontal tear in the Cyprean slab below the Central Anatolian Volcanic Province. Below eastern Anatolia, the completely detached “Bitlis” slab is characterized by fast wave speeds at ∼500 km depth. Assuming slab sinking rates mirror Arabia‐Anatolia convergence rates, the Bitlis slab's location indicates an Oligocene (∼26 Ma) break‐off. Results further reveal a strong velocity contrast across the North Anatolian Fault likely representing a 40–60 km decrease in lithospheric thickness from the Precambrian lithosphere north of the fault to a thinned Anatolian lithosphere in the south. Slow uppermost‐mantle wave speeds below active volcanoes in eastern Anatolia, and ratios of P to S wave relative traveltimes, indicate a thin lithosphere and melt contributions. Positive central and eastern Anatolian residual topography requires additional support from hot/buoyant asthenosphere to maintain the 1–2 km elevation in addition to an almost absent lithospheric mantle. Small‐scale fast velocity structures in the shallow mantle above the Bitlis slab may therefore be drips of Anatolian lithospheric mantle.

Properties of Trans-fast Magnetosonic Jets in Black Hole Magnetospheres

Abstract Traveling across several orders of magnitude in distance, relativistic jets from strong gravity regions to asymptotic flat spacetime regions are believed to consist of several general relativistic magnetohydrodynamic (GRMHD) processes. We present a semianalytical approach for modeling the global structures of a trans-fast magnetosonic relativistic jet, which should be ejected from a plasma source near a black hole in a funnel region enclosed by dense accreting flow and a disk corona around the black hole. Our model consistently includes the inflow and outflow part of the GRMHD solution along the magnetic field lines penetrating the black hole horizon. After the rotational energy of the black hole is extracted electromagnetically by the negative energy GRMHD inflow, the huge electromagnetic energy flux propagates from the inflow to the outflow region across the plasma source, and in the outflow region, the electromagnetic energy converts to the fluid kinetic energy. Eventually, the accelerated outflow must exceed the fast magnetosonic wave speed. We apply the semianalytical trans-fast magnetosonic flow model to the black hole magnetosphere for both parabolic and split-monopole magnetic field configurations and discuss the general flow properties, that is, jet acceleration, jet magnetization, and the locations of some characteristic surfaces of the black hole magnetosphere. We have confirmed that, at large distances, the GRMHD jet solutions are in good agreement with the previously known trans-fast special relativistic magnetohydrodynamic jet properties, as expected. The flexibility of the model provides a prompt and heuristic way to approximate the global GRMHD trans-fast magnetosonic jet properties.

Geophysics: The buoyancy of Earth's deep mantle.

The physical nature of two regions called large low-shear-velocity provinces at the base of Earth's mantle is uncertain. A measurement of their density has implications for our understanding of mantle dynamics. See Article p.321 The interior composition of Earth can be estimated by imaging seismic waves changing speed as they travel through different materials, but some anomalies in the deep mantle remain challenging to explain. Fast wave speed anomalies appear in areas with a history of subduction, indicating relatively cold and dense mantle material driving downward flow. However, slow wave speed anomalies in the form of large domes above the core–mantle boundary remain contentious—in particular their net buoyancy. Harriet Lau and co-authors estimate Earth's deep mantle buoyancy using GPS-based measurements of the daily deformation of Earth in response to the gravitational pull of the Sun and the Moon. They show that the mean excess density across the bottom two-thirds of these lower-mantle domes is about 0.5 per cent. The authors conclude that these structures are enriched with high-density chemical components, probably originating from subducted oceanic plates or primordial material associated with Earth's formation.

An FCT finite element scheme for ideal MHD equations in 1D and 2D

This paper presents an implicit finite element (FE) scheme for solving the equations of ideal magnetohydrodynamics in 1D and 2D. The continuous Galerkin approximation is constrained using a flux-corrected transport (FCT) algorithm. The underlying low-order scheme is constructed using a Rusanov-type artificial viscosity operator based on scalar dissipation proportional to the fast wave speed. The accuracy of the low-order solution can be improved using a shock detector which makes it possible to prelimit the added viscosity in a monotonicity-preserving iterative manner. At the FCT correction step, the changes of conserved quantities are limited in a way which guarantees positivity preservation for the density and thermal pressure. Divergence-free magnetic fields are extracted using projections of the FCT predictor into staggered finite element spaces forming exact sequences. In the 2D case, the magnetic field is projected into the space of Raviart–Thomas finite elements. Numerical studies for standard test problems are performed to verify the ability of the proposed algorithms to enforce relevant constraints in applications to ideal MHD flows.

Traveling Pulses in a Nonlocal Equation Arising Near a Saddle-Node Infinite Cycle Bifurcation

We formally derive a simple normal form for the dynamics of a nonlocally coupled neural field model when the local dynamics is near a saddle-node infinite cycle (SNIC) bifurcation. The derivation produces a nonlocally coupled scalar model which does not satisfy the comparison principle (ordered initial data produces ordered dynamical solutions). We prove the existence of unique traveling waves for the corresponding nonlocal evolution problem with a new tool that does not use the comparison principle. We obtain sharp estimates for the speed of fast and slow waves and compare these to numerical results.

Thick lithosphere, deep crustal earthquakes and no melt: a triple challenge to understanding extension in the western branch of the East African Rift

Geodynamic models predict that rifting of thick, ancient continental lithosphere should not occur unless it is weakened by heating and magmatic intrusion. Therefore, the processes occurring along sections of the western branch of the East African Rift, where ∼150 km thick, Palaeoproterozoic lithosphere is rifting with no surface expression of magmatism, are a significant challenge to understand. In an attempt to understand the apparently amagmatic extension we probed the regional uppermost mantle for signatures of thermal alteration using compressional (Vp) and shear (Vs) wave speeds derived from Pn and Sn tomography. Pervasive thermal alteration of the uppermost mantle and possibly the presence of melt can be inferred beneath the Rungwe volcanic centre, but no signatures on a similar scale were discerned beneath amagmatic portions of the western rift branch encompassing the southern half of the Lake Tanganyika rift and much of the Rukwa rift. In this region, Vp and Vs wave speeds indicate little, if any, heating of the uppermost mantle and no studies have reported dyking. Vp/Vs ratios are consistent with typical, melt-free, olivine-dominated upper mantle. Although our resolution limit precludes us from imaging potential localised magmatic intrusions with dimensions of tens of kilometres, the absence of surface volcanism, the amagmatic upper crustal rupture known to have occurred at disparate locations on the western branch, the presence of lower crustal seismicity and the low temperatures implied by the fast seismic wave speeds in the lower crust and uppermost mantle in this region suggests possible amagmatic extension. Most dynamic models predict that this should not happen. Indeed even with magmatic intrusion, rifting of continental lithosphere >100 km thick is considered improbable under conditions found on Earth. Yield strength envelopes confirm that currently modelled stresses are insufficient to produce the observed deformation along these portions of the rift system. Stresses arising from the gravitational force related to the uplift of the East African Plateau provide only one-eighth of the minimum stress necessary to produce observed lower crustal earthquakes in the western branch. We expect that some of this disparity may be accounted for by considering smaller scale bending stresses and dynamic feedbacks between brittle and elastic deformation and between faulting, topography and weathering that are not currently included in models of the East African Rift.

Falling liquid films on a slippery substrate with Marangoni effects

This paper investigates the dynamics of liquid films of mean thickness h0 flowing down a uniformly heated slippery substrate. The dimensionless slippery length β is small and is assumed to have the same order as the film parameter ∊=h0/l where l is a typical wave length. A weighted-residual model and a Benney-type model are derived to discuss the influences of slippery length β, Reynolds number Re, Marangoni number M and Biot number Bi on the dynamics of the film. It is found that, when Reynolds number is small (Re<1) and the wall is non-slip, the Benney-type model, weighted-residual model are in good agreements with the linearized Navier–Stokes equations (LNS). However, when the wall is slip or the Reynolds number is moderate, the Benney-type model does not agree with LNS. Our results show that, for a small slippery effect at the substrate, the weighted-residual model compares well with LNS at moderate Re. It demonstrates that the weighted-residual model is more reasonable than the Benney-type model. A critical Reynolds number obtained by the weighted-residual model for this system is Rec=35(1-3β)46(7-67β+159β2)Wek2+cotα-3MBi2(1+Bi)2 (α is the inclined angle and We is the Weber number). Linear stability analysis shows that, the instability is enhanced as the slippery length β and the Reynolds number Re increase. In the long-wave range, the linear wave speed c=1+2β. When the wall is heated, the instability is reinforced. The instability is impeded when the substrate is cooled. Nonlinear analysis by the traveling wave solutions shows that, the wave speed and wave height of traveling waves are promoted by the slippery and fluid inertial effects. Nonlinear study shows that the traveling wave speed is promoted by a heated substrate and is reduced by a cooled substrate. It shows that the speed of fast waves is larger than the linear wave speed and the higher the wave is the faster it travels. Direct numerical simulation of the weighted residual model supports the linear stability analysis and the nonlinear analysis of traveling wave solutions.

Seismic wave speed structure of the Ontong Java Plateau

The Ontong Java Plateau (OJP) represents the result of a significant event in the Earth's geologic history. Limited geophysical and geochemical data, as well as the plateau's relative isolation in the Pacific ocean, have made interpretation of the modern day geologic structure and its 120 Ma formation history difficult.Here we present the highest resolution image to date of the wave speed structure of the OJP region. We use a data set that combines Rayleigh waves extracted from both ambient noise and earthquake waveforms and an iterative finite-frequency tomography methodology. The combination of datasets allow us to best exploit the limited station distribution in the Pacific and image wave speed structures between 35 km and 300 km into the Earth.We image a region of fast shear wave speeds, greater than 4.75 km/s, that extends to greater than 100 km beneath the plateau. The wave speeds are similar to as observed in cratonic environments and are consistent with a compositional anomaly that resulted from the residuum of eclogite entrainment during the plateau's formation.The combination of our imaged wave speed structure and previous geochemical work suggest that a surfacing plume head entrained eclogite from the deep mantle and accounts for the anomalous buoyancy characteristics of the plateau and observed fast wave speeds.

N2와Characteristics of AlN Thin Films by Magnetron Sputtering System Using Reactive Gases of N2 and NH3

Aluminum nitride, a compound semiconductor, has a Wurtzite structure; good material properties such as high thermal conductivity, great electric conductivity, high dielectric breakdown strength, a wide energy band gap (6.2eV), a fast elastic wave speed; and excellent in thermal and chemical stability. Furthermore, the thermal expansion coefficient of the aluminum nitride is similar to those of Si and GaAs. Due to these characteristics, aluminum nitride can be applied to electric packaging components, dielectric materials, SAW (surface acoustic wave) devices, and photoelectric devices. In this study, we surveyed the crystallization and preferred orientation of AlN thin films with an X-ray diffractometer. To fabricate the AlN thin film, we used the magnetron sputtering method with N2, NH3 and Ar. According to an increase in the partial pressures of N2 and NH3, Al was nitrified and deposited onto a substrate in a molecular form. When AlN was fabricated with N2, it showed a c-axis orientation and tended toward a high orientation with an increase in the temperature. On the other hand, when AlN was fabricated with NH3, it showed a-axis orientation. This result is coincident with the proposed mechanism. We fabricated AlN thin films with an a-axis orientation by controlling the sputtering electric power, NH3 pressure, deposition speed, and substrate temperature. According to the proposed mechanism, we also fabricated AlN thin films which demonstrated high a- axis and c-axis orientations.