Dense Wave Research Articles

Evolution of a two-layer fluid for solitary waves propagating over a submarine trench

The induced density-stratified fluid motion of a solitary wave propagating over a submarine trench was investigated numerically and experimentally. A new laboratory experiment in a two-dimensional wave flume on dense fluid transport and flow fields inside and around the trench was reported using a measurement framework of laser-induced fluorescence (LIF) and particle image velocimetry (PIV) techniques. A 3D Navier–Stokes numerical model was applied to trace the dense fluid transport using the volume of fluid method. Good agreements were obtained between experiments and computed results. The calibrated model was then used to examine the transport processes of the various dense fluids. Particular attention is paid to the evolution of vortices induced by solitary waves. The results indicate that transported height of dense fluid around the windward trench wall decreases when the dense fluid density increases or wave nonlinearity decreases. The dense fluid is allowed to be transported toward the upstream of the trench when a denser fluid or lower wave nonlinearity is considered. The presence of strong vortical structure and vorticity strength was observed as the dense fluid density decreases or wave nonlinearity increases. Quantitative analyses also demonstrate that either density of dense fluid or wave nonlinearity significantly affects the transport process of the dense fluid.

Dense plasma heating and shock wave generation by a beam of fast electrons

Hot electrons created in laser plasma interaction at laser intensities 1−10 PW cm−2 in shock ignition scheme can deposit their energy in the shell of the target, augmenting the strength of the ignitor shock. Here, we present a model that describes the effect of the spatial profile of fast electron energy deposition on the dynamics of shock wave formation. A criterion of a strong shock formation is obtained for an arbitrary electron beam distribution function. It is shown that the time and the position of the shock formation are defined by the electron average stopping range, while the strength of the shock decreases as the width of electron energy distribution increases. The latter feature is explained by the fast electron target preheat. The conclusions of theoretical model are confirmed in numerical simulations. The pressure, the strength of the shock, and the efficiency of shock generation are calculated for different electron distributions with the same average stopping range.

Stochastic Geometry Modeling and Analysis of Multi-Tier Millimeter Wave Cellular Networks

In this paper, a new mathematical framework to the analysis of millimeter wave cellular networks is introduced. Its peculiarity lies in considering realistic path-loss and blockage models, which are derived from recently reported experimental data. The path-loss model accounts for different distributions of line-of-sight and non-line-of-sight propagation conditions and the blockage model includes an outage state that provides a better representation of the outage possibilities of millimeter wave communications. By modeling the locations of the base stations as points of a Poisson point process and by relying on a noise-limited approximation for typical millimeter wave network deployments, simple and exact integral as well as approximated and closed-form formulas for computing the coverage probability and the average rate are obtained. With the aid of Monte Carlo simulations, the noise-limited approximation is shown to be sufficiently accurate for typical network densities. The proposed mathematical framework is applicable to cell association criteria based on the smallest path-loss and on the highest received power. It accounts for beamforming alignment errors and for multi-tier cellular network deployments. Numerical results confirm that sufficiently dense millimeter wave cellular networks are capable of outperforming micro wave cellular networks, both in terms of coverage probability and average rate.

A Study of various Trends and Enabling Technologies in Radio over Fiber (RoF) Systems

This paper surveys the various trends and techniques developed and used in the radio over fiber technology. Also a detailed study of some of the techniques like RoF-PON networks, orthogonal frequency division multiplexing (OFDM), optical millimeter wave generation, Dense wave length division multiplexing (DWDM) has been done and the impact due to emergence of these technologies has been evaluated, suggesting the future scope of these technologies in the field of RoF communication systems.

Performance Analysis of Four Wave Mixing: A Non-Linear Effect in Optical fibers

Linear effects in Optical fibers are caused due to the refractive index of the optical medium's dependence on the intensity of light. One of the prominent non-linear effects in Optical fibers is the Four-wave mixing (FWM) phenomenon. FWM effect is resonant when the phase matching condition is satisfied. It only occurs for particular combinations of fiber dispersion and signal frequencies. The FWM is a very unpleasant transmission phenomenon occurring in a transparent optical network based on Dense Wave Division Multiplexing, but it could be used advantageously for implementing optical devices such as wavelength converters, parametric amplifiers, optical de-multiplexers, chromatic dispersion compensators, as well as signal to noise regenerators. This paper discusses the effect of channel spacing, laser power, and dispersion, length of the optical fiber and the variation of input power to compensate the effect of FWM when implemented in a short haul environment. General Terms

Anisotropy beneath a highly extended continental rift

AbstractWe have employed shear wave splitting techniques to image anisotropy beneath the D'Entrecasteaux Islands, in southeastern Papua New Guinea. Our results provide a detailed picture of the extending continent that lies immediately ahead of a propagating mid‐ocean ridge tip; we image the transition from continental to oceanic extension. A dense shear wave splitting data set from a 2010 to 2011 passive‐source seismic deployment is analyzed using single and multichannel methods. Splitting delay times of 1–1.5 s are observed and fast axes of anisotropy trending N‐S, parallel to rifting direction, predominate the results. This trend is linked to lattice‐preferred orientation of olivine, primarily in the shallow convecting mantle, driven by up to 200 km of N‐S continental extension ahead of the westward‐propagating Woodlark Rift. This pattern differs from several other continental rifts that evince rift‐strike‐parallel fast axes and is evident despite the complex recent tectonic history. We contend that across most of this rift, the unusually high rate and magnitude of extension has been sufficient to produce a regime change to a mid‐ocean‐ridge‐like mantle fabric. Stations in the south of our array show more complex splitting that might be related to melt or to complex inherited structure at the edge of the extended region.

Scattering amplitude of a single fracture under uniaxial stress

Remotely sensing the properties of fractures has applications ranging from exploration geophysics to hazard monitoring. Newly developed capabilities to measure the in-plane component of dense laser-based ultrasound wave fields allow us to test the applicability of a linear slip model to describe fracture properties. In particular, we estimate the diameter, and the normal and tangential compliance of a fracture from the measured scattering amplitudes of P and S waves in the laboratory. Finally, we show that the normal compliance decreases linearly with increasing uniaxial static stress in the plane of the fracture, but that our measurements of the SV scattered field do not show significant changes in the tangential compliance. © The Authors 2014. Published by Oxford University Press on behalf of The Royal Astronomical Society.

SUPERNOVA-TRIGGERED MOLECULAR CLOUD CORE COLLAPSE AND THE RAYLEIGH-TAYLOR FINGERS THAT POLLUTED THE SOLAR NEBULA

A supernova is a likely source of short-lived radioisotopes (SLRIs) that were present during the formation of the earliest solar system solids. A suitably thin and dense supernova shock wave may be capable of triggering the self-gravitational collapse of a molecular cloud core while simultaneously injecting SLRIs. Axisymmetric hydrodynamics models have shown that this injection occurs through a number of Rayleigh-Taylor (RT) rings. Here we use the FLASH adaptive mesh refinement (AMR) hydrodynamics code to calculate the first fully three dimensional (3D) models of the triggering and injection process. The axisymmetric RT rings become RT fingers in 3D. While ~ 100 RT fingers appear early in the 3D models, only a few RT fingers are likely to impact the densest portion of the collapsing cloud core. These few RT fingers must then be the source of any SLRI spatial heterogeneity in the solar nebula inferred from isotopic analyses of chondritic meteorites. The models show that SLRI injection efficiencies from a supernova several pc away fall at the lower end of the range estimated for matching SLRI abundances, perhaps putting them more into agreement with recent reassessments of the level of 60Fe present in the solar nebula.

Gaussian Convergence for Stochastic Acceleration of Particles in the Dense Spectrum Limit

The velocity of a passive particle in a one-dimensional wave field is shown to converge in law to a Wiener process, in the limit of a dense wave spectrum with independent complex amplitudes, where the random phases distribution is invariant modulo π/2 and the power spectrum expectation is uniform. The proof provides a full probabilistic foundation to the quasilinear approximation in this limit. The result extends to an arbitrary number of particles, founding the use of the ensemble picture for their behaviour in a single realization of the stochastic wave field.

Sparse and dense spiral waves in heterogeneous excitable media

Dynamic behaviors of sparse and dense spirals are investigated numerically based on a Barkley model in heterogeneous excitable media. It is found that the rotating frequency of sparse spiral wave decreases rapidly with b increasing and then tends to saturation, which is different from that of dense spiral wave. The period and wavelength of dense spiral wave increase with the increase of parameter or the size R of localized inhomogeneity, which depends more sensitively on the size R than those of sparse sprial wave. The change of the speed of dense spiral wave tip with R is opposite to that of the sparse spiral wave tip. In addition, inhomogeneous effect gives rise to a defect point in arm of each of the two spiral waves when or b increases above a critical value.

A new breaking wave height direct estimator from video imagery

Breaker height is a key parameter of nearshore processes and the demand for a continuous remote estimator is pressing. In this paper we present a standalone remote video-based method that estimates wave height at the breakpoint. Individual breaking events are first identified from changes in optical properties and wave height is further derived from the optical signature at the onset of breaking. An extended validation is performed using a dense wave basin dataset. The results show the ability of the method to measure individual breaker heights (9% of mean error, 18% RMS). In addition, the unique combination of in situ and remotely sensed data allows the estimation of two other breaking-related parameters, the height-to-depth ratio and wave front face slope, which show a substantial amount of dispersion. Because nearshore video systems are rapidly spreading over world coasts, this low-cost remote breaker height estimator should encounter large interest in coastal engineering studies.

Uganda's National Transmission Backbone Infrastructure Project: Technical Challenges and the Way Forward

Several publications have identified technical challenges facing Uganda's National Transmission Backbone Infrastructure project. This research addresses the technical limitations of the National Transmission Backbone Infrastructure project, evaluates the goals of the project, and compares the results against the technical capability of the backbone. The findings of the study indicate a bandwidth deficit, which will be addressed by using dense wave division multiplexing repeaters, leasing bandwidth from private companies. Microwave links for redundancy, a Network Operation Center for operation and maintenance, and deployment of wireless interoperability for microwave access as a last-mile solution are also suggested.

Rapidly installed temporary gauging for hurricane waves and surge, and application to Hurricane Gustav

Hurricanes can produce extreme nearshore waves and surge, but permanent gauging stations are often much sparser than is desired. This paper describes the rationale behind and outline for rapidly installed temporary coastal gauges, and presents results during Hurricane Gustav (2008). Within 48 h prior to landfall, twenty self-recording pressure gauges were deployed in depths of 1.4–23 m over more than 700 km of coastline, using helicopters to cover the large distances. Results showed a complex picture that was strongly dependent on location. East of the Mississippi Delta, open coast waves were large, and surge reached 3.8 m NAVD88 in marshes. West of the delta but near landfall, waves and surge were generally smaller as the river levees blocked flow from East to West. West of landfall, both waves and surge were very small and the most prominent feature was a water level drawdown that reached 1.5 m. Wave spectra varied strongly depending both on location and time from landfall. This type of rapid gauging program is straightforward to duplicate: with multiple localized deployment centers to ensure coverage, dense nearshore hurricane wave and surge records could increase substantially in the future.

Characteristics of Light Reflected from a Dense Ionization Wave with a Tunable Velocity

An optically dense ionization wave (IW) produced by two femtosecond (approximately 10/30 fs) laser pulses focused cylindrically and crossing each other may become an efficient coherent x-ray converter in accordance with the Semenova-Lampe theory. The resulting velocity of a quasiplane IW in the vicinity of pulse intersection changes with the angle between the pulses from the group velocity of ionizing pulses to infinity allowing a tuning of the wavelength of x rays and their bunching. The x-ray spectra after scattering of a lower frequency and long coherent light pulse change from the monochromatic to high order harmoniclike with the duration of the ionizing pulses.

Investigation on modified FWM suppression methods in DWDM optical communication system

The focus of this paper is to investigate the methods for Four Wave Mixing (FWM) suppression. Modified techniques equal and unequal-channel spacing with polarization, equal channel spacing with alternate channel delay, optical coupling and varied laser power have been proposed to reduce the impact of FWM on Dense Wave Length Division Multiplexing (DWDM) optical communication system. Further the comparison of reduction of FWM for existing and proposed techniques has been discussed by varying the dispersion of fiber from 0 to 16 ps/nm/km. It has been observed that the suggested techniques are simpler to design optical communication system and superior to the existing methods.

Non-intrusive polarization dependent loss monitoring in fiber-optic transmission systems

A method for non-intrusively monitoring the polarization dependent loss (PDL) of an installed fiber-optic transmission system is proposed using live dense wave division multiplexing (DWDM)-based traffic as the probing signal. The method extracts the statistical parameters of system PDL from the measured partial PDL data. Field measurements of PDL were performed on long-haul DWDM systems deployed in Sprint’s network and the results validated our theoretical model.

Phase retarders for dense wave division multiplexing using two parallel mirrors coated with a single layer thin film

This paper presents the design of quarter-wave retarders for the dense wave division multiplexing using parallel mirrors coated with a single layer. The output light from the device is parallel to the input light and displaced by a distance d. The quarter-wave retarder's total reflection is in the range of 83%. Error analysis on the design is also presented. Error analysis shows how changes on the angle of incident light and the thin film thicknesses affect the design of the retarders.

Momentum Distribution Dynamics of a Tonks-Girardeau Gas: Bragg Reflections of a Quantum Many-Body Wave Packet

The momentum distribution (MD) dynamics of a Tonks-Girardeau (TG) gas is studied in the context of Bragg reflections of a many-body wave packet. We find strong suppression of a Bragg reflection peak for a large and dense TG wave packet; our observation illustrates the dependence of the MD on the interactions and wave function symmetry. The MD is calculated from the reduced single-particle density matrix (RSPDM). We develop a method for calculating the RSPDM of a TG gas, which is operative for a large number of particles, and does not depend on the external potential and the state of the system. The method is based on a formula expressing the RSPDM via a dynamically evolving single-particle basis.

Stabilization of the fan instability: Electron flux relaxation

This paper presents some relevant simulation results on the interaction between electrostatic waves and suprathermal electron fluxes at anomalous cyclotron and Landau resonances. In particular, the case of a dense and continuous wave spectrum is studied. It is shown that, after the waves excited by the fan instability at anomalous cyclotron resonances have reached a first saturation stage due to particle trapping, the process of “dynamical resonance merging” takes place, which leads to a strong amplification of the waves’ amplitudes. The Landau resonances do not play an essential role in the total energy exchange between the particles and the waves, as they mainly help to smooth the peaks rising during the evolution of the electron parallel velocity distribution and contribute to damping. Moreover, the paper shows that at the asymptotic stage of the interaction, when the waves’ amplitudes are saturated and the electron flux is relaxed, some physical features clearly do not fit the predictions of the well-known quasilinear theory. The careful examination of a huge number of trajectories of particles moving in the effective field of the wave packet allows to state that most of the particles involved in the resonant interactions are trapped by several waves simultaneously. In this so-called “multitrapping” process, the particles perform complex oscillatory motions which are far from what is expected from the quasilinear theory, where the diffusive behavior of the particles in the velocity space results from small successive random steps.

Influences of Electroacupuncture on the Expression of Insulin-like Growth Factor-1 Following Focal Cerebral Ischemia in Monkeys

It is known that electro-acupuncture (EA) has neuroprotective effects on cerebral ischemia, however, whether insulin-like growth factor-1 (IGF-1) as a potent nerve regeneration agent involved is unknown. Therefore, the aim of the present study was to investigate the neuroprotective effects of EA against cerebral ischemia whether influence IGF-1 expression following the middle cerebral artery occlusion (MCAO) in monkeys. The results indicated that after occlusion of MCA, the IGF-1mRNA and protein expression was down-regulated. EA, given 15 minutes after occlusion of MCA and lasted for 1 h between the acupuncture points Baihui Point (GV. 20) and Renzhong Point (GV. 26) with a dense-sparse waveforms, which can be transformed into each other when dense or sparse wave is terminated, attenuated brain edema, decreased the infarct area, up-regulated IGF-1mRNA and protein expression. These results implied that EA is effective to extenuate cerebral ischemic injuries and up-regulating the endogenous IGF-1 expression following MCA occlusion in monkeys, which might be an important mechanism of neuroprotective effects of EA against cerebral ischemia.