Domain Wave Research Articles

Radiative transfer modeling in the Earth–Atmosphere system with DART model

The atmosphere strongly affects satellite measurements of Earth surfaces in the optical domain. Modeling this influence is complex. This is typically the case of the “Earth–Atmosphere” radiative coupling in the presence of Earth surfaces with spatially variable optical properties. In that case, it may be very difficult to couple Earth and cloud-free atmosphere radiative transfer models. This explains why an atmosphere module was input into the Earth radiative transfer (R.T.) model DART (Discrete Anisotropic Radiative Transfer) in order to simulate accurately satellite images of natural and urban Earth surfaces. This paper presents how DART simulates the atmosphere R.T. in the short wave and thermal infrared domains. The atmosphere is divided into 3 zones: bottom atmosphere (BA), mid atmosphere (MA) and high atmosphere (HA). The 3D distribution is arbitrary in BA and horizontally constant with any vertical distribution in MA and HA. The “Earth–Atmosphere” R.T. is modeled in 5 stages. 1) Atmosphere R.T. (i.e., atmosphere thermal emission and/or sun radiation scattering). 2) Earth surface R.T. (i.e., Earth thermal emission and/or atmosphere and direct sun radiation scattering). 3) Atmosphere R.T. (i.e., Earth radiation scattering). 4) Earth surface R.T. (i.e., scattering of downward atmosphere radiation). 5) Simulation of satellite reflectance and/or brightness temperature images. The approach takes into account the earth curvature and the atmosphere non-Beer law behavior in the presence of strongly varying spectral properties. It uses optimally located scattering points for improving atmosphere R.T. accuracy, and it reduces computer time through the use of pre-computed transfer functions that transfer radiation between the different atmosphere levels (BA, MA, HA). Moreover, it can simulate automatically an atmosphere geometry that optimizes the trade-off “Computer time–Accuracy” of simulations. The robustness and accuracy of the DART atmosphere modeling were successfully validated with theoretical cases and with the MODTRAN atmosphere R.T. model.

STRUCTURE AND EVOLUTION OF CIRCUMBINARY DISKS AROUND SUPERMASSIVE BLACK HOLE BINARIES

It is generally believed that gaseous disks around supermassive black hole (SMBH) binaries in centers of galaxies can facilitate binary merger and give rise to observational signatures both in electromagnetic and gravitational wave domains. We explore general properties of circumbinary disks by reformulating standard equations for the viscous disk evolution in terms of the viscous angular momentum flux F_J. In steady state F_J is a linear function of the specific angular momentum, which is a generalization of (but is not equivalent to) the standard constant \dot M disk solution. If the torque produced by the central binary is effective at stopping gas inflow and opening a gap (or cavity) in the disk, then the inner part of the circumbinary disk can be approximated as a constant F_J disk. We compute properties of such disks in different physical regimes relevant for SMBH binaries and use these results to understand the gas-assisted evolution of SMBH pairs starting at separations 10^{-4}-10^{-2} pc. We find the following. (1) Pile-up of matter at the inner edge of the disk leads to continuous growth of the torque acting on the binary and can considerably accelerate its orbital evolution compared to the gravitational wave-driven decay. (2) Torque on the binary is determined non-locally and does not in general reflect the disk properties in the vicinity of the binary. (3) Binary evolution depends on the past history of the disk evolution. (4) Eddington limit can be important in circumbinary disks even if they accrete at sub-Eddington rates at late stages of binary evolution. (5) Circumbinary disk self-consistently evolved under the action of the binary torque emits more power and has spectrum different from the spectrum of constant \dot M disk - it is steeper (\nu F_\nu\propto \nu^{12/7}) and extends to shorter wavelength, facilitating its detection.

Competition driven by retinal waves promotes morphological and functional synaptic development of neurons in the superior colliculus.

Prior to eye opening, waves of spontaneous activity sweep across the developing retina. These "retinal waves," together with genetically encoded molecular mechanisms, mediate the formation of visual maps in the brain. However, the specific role of wave activity in synapse development in retino-recipient brain regions is unclear. Here we compare the functional development of synapses and the morphological development of neurons in the superior colliculus (SC) of wild-type (WT) and transgenic (β2-TG) mice in which retinal wave propagation is spatially truncated (Xu HP, Furman M, Mineur YS, Chen H, King SL, Zenisek D, Zhou ZJ, Butts DA, Tian N, Picciotto MR, Crair MC. Neuron 70: 1115-1127, 2011). We use two recently developed brain slice preparations to examine neurons and synapses in the binocular vs. mainly monocular SC. We find that retinocollicular synaptic strength is reduced whereas the number of retinal inputs is increased in the binocular SC of β2-TG mice compared with WT mice. In contrast, in the mainly monocular SC the number of retinal inputs is normal in β2-TG mice, but, transiently, synapses are abnormally strong, possibly because of enhanced activity-dependent competition between local, "small" retinal wave domains. These findings demonstrate that retinal wave size plays an instructive role in the synaptic and morphological development of SC neurons, possibly through a competitive process among retinofugal axons.

Experimental Research on Acoustic Parameters and Saturation of Gas Hydrate-Bearing Sediments

It's very important to control the sensors of ultrasonic and Time Domain Reflectometry when study the relationship between gas hydrate saturation and acoustic parameters in sediments. We combined Ultrasonic Wave and Time Domain Reflectometry in one apparatus to study the acoustic parameters of gas hydrate-bearing sediments in different saturation. The experimental results show that the apparatus is well designed and can work smoothly. Subsequently, we compare the calculated data by time-average equation, Woods equation, Lees weighted equation and Biot-Gassmann Theory by Lee (BGTL) with the observed data in experiments. It suggests that the Lees weighted equation and BGTL are more applicable in our experiments and various sediments.

Computation of Gas Hydrate Saturation Models Based on the Experimental Acoustic Parameters

It is necessary to know gas hydrate saturation in evaluating gas hydrate volume. So far, there are only few models to estimate gas hydrate saturation. These models are often empirical or derived from observed data. Therefore, we need to confirm their legitimacy and get an approach to use the correct model. For the first time, we combine Ultrasonic Wave and Time Domain Reflectometry to study the relationship between gas hydrate saturation and acoustic parameters, which gets fine results. Subsequently, it attempts to compare the calculated data by time-average equation, Wood’s equation, Lee’s weighted equation and BGTL with the observed data in experiments. The results show the experimental method is very effective. It suggests that the Lee’s weighted equation and BGTL are more applicable in our experiments and various sediments.

Nonlinear wave propagation of large amplitude ion-acoustic solitary waves in negative ion plasmas with superthermal electrons

AbstractInvestigation of arbitrary amplitude nonlinear ion-acoustic solitary waves which accompany collisionless positive–negative ion plasmas with high-energy electrons (represented by kappa distribution) is presented. Arbitrary amplitude solitary waves are investigated by deriving an energy-integral equation involving a Sagdeev-like pseudopotential. The existence regions of solitary pulses are, defined precisely, modified by the superthermality of energetic electrons. Furthermore, numerical calculations reveal that both compressive and rarefactive pulses may exist for negative ion mass groups in Titan's atmosphere. The superthermality of energetic electrons are found to modify the existence domains of large amplitude ion-acoustic waves in Titan's atmosphere. The dependence of solitary excitation characteristics on the superthermal parameter, the negative ion concentration, the positive-to-negative ions mass ratio, and the Mach number have been investigated. The present study might be helpful to understand the excitation of fully nonlinear ion-acoustic solitary pulses that may appear in the interplanetary medium and/or in the astrophysical plasmas in general.

Nonlinear dust–ion acoustic waves in a dusty plasma with non-extensive electrons and ions

AbstractUsing the reductive perturbation approach, dust–ion acoustic solitons and double layers (DLs) have been studied in a dust–electron–positron–ion (d-e-p-i) plasma composed of q-distributed electrons and positrons, warm fluid ions, and a fraction of immobile dust grains. Existence domains of either solitary waves or DLs are presented and their parametric dependence determined. It is found that particle non-extensivity, dust concentration and positron concentration may drastically affect these existence domains and may play a key role in defining the polarity of these localized structures. Our results should assist in interpreting the nonlinear structures that may occur in astrophysical environments.

Finite Element Modeling and Design of Rectangular Patch Antenna with Different Feeding Techniques

The finite element modeling of three dimensional structures is important for researchers especially in the field of antennas and other domains of electromagnetic waves. This paper presents a finite element calculations and numerical analysis for the microstrip patch antennas. In this paper, two different designs have been modelled and analyzed and both designs are based on the rectangular patches. The feeding point of one design is inside the patch while the other design contains feeding point outside the patch is T shaped. The computational analysis showed some interesting results for radiation pattern and far field domain. For these designs, the characteristic impedance taken is 50 Ω and the operating frequency domain is 1.4 to 1.7 GHz. The microstrip patch antennas are encapsulated in the inert spherical atmosphere of 20 mm thickness containing air inside it.

Stability Problem of Wave Variable Based Bilateral Control: Influence of the Force Source Design

The wave variable has been proposed to achieve robust stability against the time delay in bilateral control system. However, the influence of the force source on the overall system is still not clear. This paper analyzes this problem and proposes a supplement to the stability analysis for wave variable based bilateral control. Based on the scattering theory, it is pointed out that the design of force source decides the passivity of the two-port network of slave robot. This passivity influences the stability of overall system. Based on the characteristic equation and small gain theorem, it is clear that inappropriate designed force source in encoding the wave variable destroys the stability in the presence of time delay. A wave domain filter makes up for the broken stability. The principle of this reparation is explained in this paper. A reference is also provided by the analysis to design the parameter of the wave domain filter. Experiments prove the correctness and validity.

ON DIVERSITY OF CONFIGURATIONS GENERATED BY EXCITABLE CELLULAR AUTOMATA WITH DYNAMICAL EXCITATION INTERVALS

Excitable cellular automata with dynamical excitation interval exhibit a wide range of space-time dynamics based on an interplay between propagating excitation patterns which modify excitability of the automaton cells. Such interactions leads to formation of standing domains of excitation, stationary waves and localized excitations. We analyzed morphological and generative diversities of the functions studied and characterized the functions with highest values of the diversities. Amongst other intriguing discoveries we found that upper boundary of excitation interval more significantly affects morphological diversity of configurations generated than lower boundary of the interval does and there is no match between functions which produce configurations of excitation with highest morphological diversity and configurations of interval boundaries with highest morphological diversity. Potential directions of future studies of excitable media with dynamically changing excitability may focus on relations of the automaton model with living excitable media, e.g. neural tissue and muscles, novel materials with memristive properties and networks of conductive polymers.

Barkhausen-type noise in the resistance of antiferromagnetic Cr thin films

We present an experimental study of the changes generated on the electrical resistance R(T) of epitaxial Cr thin films by the transformation of quantized spin density wave domains as the temperature is changed. A characteristic resistance noise appears only within the same temperature region where a cooling-warming cycle in R(T) displays hysteretic behavior. We propose an analysis based on an analogy with the Barkhausen noise seen in ferromagnets. There fluctuations in the magnetization M(H) occur when the magnetic field H is swept. By mapping and , where Ψ0 corresponds to the order parameter of the spin density wave, we generalize the Preisach model in terms of a random distribution of resistive hysterons to explain our results. These hysterons are related to distributions of quantized spin density wave domains with different sizes, local energies and number of nodes.

Interaction Between Spin Wave Packets and Domain Wall With Various Propagation Modes and Wall Structures

The interaction between the spin wave (SW) packet and the domain wall (DW) have been numerically studied for various spin wave modes and the DW structures. Micromagnetic simulations reveal that the Neel type DW causes practically similar phase shift Δφ (0.4π ~ 0.6π) for all of the three different SW modes, while the Δφ is considerably enhanced in the case of the interaction with the Bloch type DW. The inductive detection of the DW induced phase shift in the SW, emitted with a pulsed microwave current, is also demonstrated.

Image plane coded aperture for terahertz imaging

In the absence of detector arrays, a single pixel coupled with an image plane coded aperture has been shown to be a practical solution to imaging problems in the terahertz and sub-millimeter wave domains. The authors demonstrate two laboratory, real-time, two-dimensional, sub-millimeter wave imagers that are based on an image plane coded aperture. These active imaging systems consist of a heterodyne source and receiver pair, image forming optics, a coded aperture, data acquisition hardware, and image reconstruction software. In one of the configurations, the target is measured in transmission, while in the other it is measured in reflection. In both configurations, images of the targets are formed on the coded aperture, and linear measurements of the image are acquired as the aperture patterns change. Once a sufficient number of linearly independent measurements are obtained, the image is reconstructed by solving a system of linear equations that is generated from the aperture patterns and the corresponding measurements. The authors show that for image sizes envisioned for many current applications, this image reconstruction technique is computationally efficient and can be implemented in real time. Measurements are collected with these systems, and the reconstruction results are presented and discussed.

An ABC of near Infrared Photon Migration in Tissues: The Diffusive Regime of Propagation

In this paper, the theories commonly used for the study of photon migration through biological tissues and for biomedical applications are reviewed. The concepts of absorption and scattering are introduced with particular reference to biological tissues and to the near infrared wavelength range. In particular, the basic definitions of optical properties and their statistical meaning, the Beer–Lambert law, the modified Beer–Lambert law, the radiative transfer equation and the diffusion equation are examined and described. The main frame of the theories is provided in the time domain, in the continuous wave domain and in the frequency domain and the principal solutions of the radiative transfer equation and of the diffusion equation are reviewed. The propagation of photons through biological tissue can be accurately described with solutions of the radiative transfer equation, while solutions of the diffusion equation are subjected to intrinsic approximations that limit their range of validity. Whenever the solutions of the diffusion equation provide a sufficiently accurate description of photon migration, we have a diffusive regime of propagation and the media where this happens can be denoted as diffusive as well. A rule to identify the diffusive regime of propagation has been provided. For many biological tissues, the diffusive regime of propagation can be established, even near the source, provided the photons have travelled trajectories with lengths greater than four times the transport mean free path.

On Distributed Multirate Control of Direct User-to-User Touch in Networked Haptic Systems with Passive Wave-Domain Communications

This paper investigates the stability and performance of distributed multirate control of direct touch in networked haptic systems that provide users with a remote dynamic proxy of their peer and with passive wave domain communications. The paper considers communication networks with fixed delay and with packet update rate smaller than the update rate of the users' local force feedback loops. After developing a multirate state space model of the direct touch haptic system, the paper uses eigenvalue-based stability analysis to determine the maximum contact stiffness that can be applied to users, as well as the maximum coordination gain that can be used to synchronize the user sites. The analysis predicts that both remote dynamic proxies and passive wave-domain communications make the contact stiffness robust to delay, but only passive wave-domain communications mitigate the negative impact of delay on the coordination gain. In other words, the analysis suggests that passive wave-domain communications should be employed to make the distributed multirate control of direct touch in networked haptic systems stable regardless of the fixed communication delay. However, if power-domain communications are employed, remote dynamic proxies should be used to allow rendering of stiffer contact between users. Experiments in which two users probe each other using similar haptic interfaces validate the analytical results.

NUMERICAL MODELING OF A DUAL PONTOON FLOATING STRUCTURE WITH A LIQUID CONTAINER

A numerical model is developed to investigate the waveinduced dynamic properties of a dual pontoon floating structure (DPFS) with a liquid container on the top. This model has to deal with two kinds of fluid domain: one is the incident wave domain, while the other is the excited fluid domain in a sloshing container. The boundary integral equation method (BIEM) with linear element scheme is applied to forming a 2D fully nonlinear numerical wave tank (NWT). The secondorder Stokes wave theory is adopted to give the velocity on the input boundary. The velocity potential and acceleration potential are solved simultaneously to obtain the contact forces on the DPFS as well as the liquid container. Summing the total external forces on the floating platform, we may form a system of motion equations. To establish an accurate and yet efficient numerical model is the goal of this paper, and it may lay a good foundation for the further study on the renewable wave energy devices or structural motion damping apparatus.

Amplitude equations for reaction-diffusion systems with cross diffusion

Using Taylor series expansion, multiscaling, and further expansion in powers of a small parameter, we develop general amplitude equations for two-variable reaction-diffusion systems with cross-diffusion terms in the cases of Hopf and Turing instabilities. We apply this analysis to the Oregonator and Brusselator models and find that inhibitor cross diffusion induced by the activator and activator cross diffusion induced by the inhibitor have opposite effects in the two models as a result of the different structure of their community matrices. Our analysis facilitates finding regions of supercritical and subcritical bifurcations, as well as wave and antiwave domains and domains of turbulent waves in the case of Hopf instability.

Method of adaptive artificial viscosity

A new finite-difference method for the numerical solution of gas dynamics equations is proposed. This method is a uniform monotonous finite-difference scheme of second-order approximation on time and space outside of domains of shock and compression waves. This method is based on inputting adaptive artificial viscosity (AAV) into gas dynamics equations. In this paper, this method is analyzed for 2D geometry. The testing computations of the movement of contact discontinuities and shock waves and the breakup of discontinuities are demonstrated.

On acoustic and gravity waves in the solar photosphere and their energy transport

Aims. We study acoustic and atmospheric gravity waves in the quiet Sun to estimate their energy transport to the chromosphere. Methods. A two-dimensional time sequence from quiet Sun disc centre was analysed with simultaneous spectroscopic observations in Fe i 5576 A and Fe i 5434 A (both with Lande factor g = 0). We calculated response functions of the velocities for the line minimum shifts and atmospheric transmissions of waves for the two lines. For this, NLTE line formation in granular and intergranular model atmospheres from numerical simulations were performed. For the interpretation of the observed waves and for the estimates of energy fluxes, we assumed adiabatic propagation of plane waves in an isothermal model atmosphere. Fourier analyses of intensity and velocity fluctuations were carried out. They yield power, phase, and coherence as functions of frequency ν (from temporal Fourier transforms) and in thekh−ν plane (from three-dimensional transforms). The power spectra, together with the mass densities at velocity formation heights, give then the energy fluxes. Results. The rms velocities found here in the acoustic and gravity wave domains are lower by a factor ∼1.5 as in earlier work. We therefore admit a factor of 2 for an upward correction of the estimated fluxes. For acoustic waves we find: 1) upward propagating waves are present on the Sun with frequencies up to 14−15 mHz (periods U ≈ 70 s); 2) the approximation of plane adiabatic waves in an isothermal atmosphere appears adequate for estimating the energy fluxes; 3) the acoustic energy fluxes are in the same range as found in our earlier work from ground-based, two-dimensional spectroscopy, 1500−3100 W m −2 at an atmospheric height of ∼380 km and 1300−2700 W m −2 at 570 km. The energy flux carried by gravity waves is difficult to determine. We find: 1) phase and coherence spectra between continuum and velocity fluctuations show that convective overshoot and gravity waves are superimposed. We account for the convective flows using these coherence spectra. 2) At low frequencies, the vertical wavelength Λz can be short (� 300 km), yielding large corrections for atmospheric transmissions (factors >100). We thus exclude from the flux estimates waves with |kz| > 20 Mm −1 and with vertical group velocities υgr,z < 0. 3k m s −1 . They are likely to be strongly reduced in amplitude by radiative damping. 3) With these caveats, the energy fluxes carried by gravity waves are found in the range of 4000−8200 W m −2 at 380 km and 700−1400 W m −2 at 570 km. Gravity waves thus also contribute to the energy transport into the chromosphere.

UWB, Non Dispersive Radiation From the Planarly Fed Leaky Lens Antenna&amp;#x2014; Part 1: Theory and Design

An efficient directive antenna is described that can be used to realize essentially non dispersive links over extremely large bandwidths. The antenna is a significantly enhanced version of previously proposed Leaky Lens antennas that use a frequency independent leaky slot radiation mechanism. A theoretical breakthrough now allows the use of this mechanism also in the presence of purely planar structures. This step allows the realization of the feed of a leaky lens antenna in a unique planar structure that is then glued to a standard circularly symmetric elliptical dielectric lens, as integrated technology requires in the mm and sub-mm wave domains. The first part of this sequence deals with a theoretical breakthrough, the consequent antenna concept and a description of the basic physical mechanisms inside and outside the lens antenna. It is shown that Leaky Lens antennas have the potential to be used to realize antenna links over bands exceeding a decade with minimal dispersion, high efficiency and high directivity. The second part of this sequence deals with the demonstration of these claims via the measurement of two prototypes.