Degree Of Nonlinear Coupling Research Articles

Experimental study on the effect of an oyster reef on the nonlinear characteristics of irregular waves

As a “marine ecological engineer”, the oyster reefs not only perform important ecological functions, but also reduce the damage caused by waves to protective structures such as seawalls. However, oyster reefs in shallow water change the nonlinear characteristics of waves and affect sediment transport and coastal evolution. Based on Fourier spectrum and analysis of Wavelet Transform, the influence of artificial bag oyster reefs on the energy and nonlinear phase coupling of irregular waves are studied through physical experiment. The results show that oyster reefs have a substantial effect on the energy of primary harmonic, which transfer to higher harmonics through triad interactions, and a considerable reduction in primary harmonic energy and an increase in higher harmonics energy are reflected in the energy spectra. The transmission spectrum behind the oyster reefs shows three peaks at primary, secondary and third harmonics. The bicoherence spectrum indicates that the peaks at secondary and third harmonics mainly result from the self-coupling of the primary harmonics and phase coupling between the primary and secondary harmonics respectively. As the water depth increases, the degree of nonlinear coupling between wave components decreases, which leads to the energy of wave components at different frequencies increases. With increasing top width, the length of the shoaling region increases, and the growth of triad nonlinear interactions are observed in wavelet-based bicoherence spectra, resulting in the spectral peak energy decreasing while the secondary harmonics energy increasing in the spectrum. Finally, the potential application of an ecological system composed by “oyster reefs + mangroves” is discussed. As the effect of water depth on wave energy is much greater than that of top width, in artificial oyster reef construction, it is recommended that keep the oyster reefs non-submerged in terms of wave dissipation. Further studies should take the dynamic growth effect of oyster reefs into account.

Nonlinear Effects in Gravity Waves Propagating in Shallow Water

Nonlinear energy transfers due to triad interactions change the characteristics of the wave-field in the shoaling region. The degree of nonlinear coupling is examined using numerical simulations based on an accurate set of deterministic evolution equations for the propagation of fully dispersive weakly nonlinear waves. The model validation, using existing experimental measurements for wave transformation over a shoal, showed that it accurately predicts nonlinear energy transfer for irregular waves with large wave-numbers. The bound higher harmonics and nonlinear statistical measures, i.e. the wave skewness and asymmetry, are well simulated by the model in both the shoaling and deshoaling regions. Numerical simulation of steep waves in shallow water with the Ursell number O(1), showed that nonlinear dispersion and phase locking lead to triad interactions even on a horizontal bottom. Nonlinear energy transfers in monochromatic waves lead to rapid spatial recurrence of the primary wave amplitudes. This is in contrast to the case of irregular waves where the Fourier coefficients of the wave-field do not recur due to the presence of innumerable interactions, which are expected to cancel resulting in no spatial evolution of the wave spectrum.

A Risk Profile for Information Fusion Algorithms

E.T. Jaynes, originator of the maximum entropy interpretation of statistical mechanics, emphasized that there is an inevitable trade-off between the conflicting requirements of robustness and accuracy for any inferencing algorithm. This is because robustness requires discarding of information in order to reduce the sensitivity to outliers. The principal of nonlinear statistical coupling, which is an interpretation of the Tsallis entropy generalization, can be used to quantify this trade-off. The coupled-surprisal, -lnκ(p)≡-(pκ-1)/κ , is a generalization of Shannon surprisal or the logarithmic scoring rule, given a forecast p of a true event by an inferencing algorithm. The coupling parameter κ=1-q, where q is the Tsallis entropy index, is the degree of nonlinear coupling between statistical states. Positive (negative) values of nonlinear coupling decrease (increase) the surprisal information metric and thereby biases the risk in favor of decisive (robust) algorithms relative to the Shannon surprisal (κ=0). We show that translating the average coupled-surprisal to an effective probability is equivalent to using the generalized mean of the true event probabilities as a scoring rule. The metric is used to assess the robustness, accuracy, and decisiveness of a fusion algorithm. We use a two-parameter fusion algorithm to combine input probabilities from N sources. The generalized mean parameter ‘alpha’ varies the degree of smoothing and raising to a power Νβ with β between 0 and 1 provides a model of correlation.

Nonlinear statistical coupling

By considering a nonlinear combination of the probabilities of a system, a physical interpretation of Tsallis statistics as representing the nonlinear coupling or decoupling of statistical states is proposed. The escort probability is interpreted as the coupled probability, with Q = 1 − q defined as the degree of nonlinear coupling between the statistical states. Positive values of Q have coupled statistical states, a larger entropy metric, and a maximum coupled-entropy distribution of compact-support coupled-Gaussians. Negative values of Q have decoupled statistical states and for − 2 < Q < 0 a maximum coupled-entropy distribution of heavy-tail coupled-Gaussians. The conjugate transformation between the heavy-tail and compact-support domains is shown to be Q ˆ = − 2 Q 2 + Q for coupled-Gaussian distributions. This conjugate relationship has been used to extend the generalized Fourier transform to the compact-support domain and to define a scale-invariant correlation structure with heavy-tail limit distribution. In the present paper, we show that the conjugate is a mapping between the source of nonlinearity in non-stationary stochastic processes and the nonlinear coupling which defines the coupled-Gaussian limit distribution. The effects of additive and multiplicative noise are shown to be separable into the coupled- variance and the coupling parameter Q, providing further evidence of the importance of the generalized moments.

The 8-hour tide in the mesosphere and lower thermosphere over the UK, 1988–2004

Horizontal winds in the mesosphere and lower thermosphere at a height of ∼90–95 km have been measured by a VHF meteor radar in Castle Eaton, UK (52.6°N, 2.2°W). The measurements span the 16-year interval from January 1988 to January 2004. The complete dataset has been used to investigate the 8-h (terdiurnal) tide which at this latitude appears as a persistent feature of the atmosphere. Instantaneous amplitudes can be as large as ∼25 m s −1. However, the monthly mean values are smaller and range from ∼1 to ∼9 m s −1. A clear seasonal behaviour is evident, in which the largest amplitudes are observed in autumn and early winter (September–November) and the smallest amplitudes are observed in early summer (May). In general, the phase difference between the zonal and meridional components is close to 2 h, indicating a circularly polarised motion. Conspicuous inter-annual variability is seen in both the amplitude and phase of the tide. On shorter timescales the amplitude of the tide sometimes exhibits a periodic modulation at frequencies associated with planetary waves (particularly the 2-day wave), indicating a degree of non-linear coupling between the tide and planetary waves. Comparisons with observations made by another meteor radar at Esrange (68°N, 21°E) in the Arctic suggest that at higher latitudes the winter time amplitude maximum is absent below heights of ∼95 km.

RF nonlinear interactions in living cells-I: nonequilibrium thermodynamic theory.

Some biological experiments report effects that depend on low frequency modulation of a radiofrequency (RF) carrier. Such effects require nonlinear responses in biological preparations, which we show could be observed with great generality by the unique frequency signatures that would appear in the scattered RF energy. Following Illinger [Illinger (1982): Bioelectromagnetics 3:9-16], we considered a two part physical system. The greater part, dominated by the properties of water, interacts linearly with the RF field and is described by equilibrium thermodynamics. However, another, much smaller part, e.g., certain biological molecules and molecular subgroups, supports nonlinear interactions and is described by nonequilibrium thermodynamics. For example, a nonlinear interaction might result from scattering of RF photons from oscillators located in a region of strong field gradients, such as at membrane surfaces. A second nonlinear mechanism could appear if stress (elastic) waves were launched within the confines of the exposure vessel by RF heating. Amplitude modulation at angular frequency Omega of a carrier wave with angular frequency omega (omega << omega) produces two peaks in elastic stress in the cell structure during each period; that is, there is "full-wave demodulation." As a result of coherent nonlinear charge motion, modulation products could appear at frequencies omega +/- 2 omega and, in general, at omega +/- n 2 omega (n = 1, 2, em leader ) if vibrational harmonics at 2 n omega also are excited. Although in principle microwaves can alter the stability of a thermodynamic system by pumping a chemical transition, the degree of nonlinear coupling required for an observable instability is so great that its probability is effectively zero, unless field intensity is extremely high. A companion paper suggests an extremely sensitive method and the related instrumentation for detection of the spectrum scattered by living cells during exposure to amplitude modulated RF energy.

On the Evolution of Isolated, Nonlinear Vortices

The evolution of an isolated, axially symmetric vortex is calculated with a quasi-geostrophic, adiabatic, hydrostatic. β-plane, two vertical mode model. The circumstances of greatest interest are those of weak friction and large vortex amplitude (strong nonlinearity). Systematic studies are made of the consequences of varying the frictional coefficient, the vortex amplitude, the vortex radius (relative to the deformation radius), the degree of nonlinear coupling between the two vertical modes and the initial vertical structure of the vortex. Results of note include the following. Within the approximation of a single vertical mode model (i.e., in the absence of modal coupling), a baroclinic vortex has an increased westward and a finite meridional propagation speed when its amplitude is greater than infinitesimal. Both of these speeds, however, are limited by the wave speeds (as determined from infinitesimal amplitude theory) of the weak dispersion field outside the vortex. The vortex amplitude decay rate, in the limit of strong nonlinearity, is governed by the frictional coefficient rather than dispersion. When vertical modal coupling is included, the vortex propagation and decay rate can be altered. Asymptotically in time, the vortex approaches a state of deep compensation (i.e., beneath a shallow thermocline, there is no flow in phase with the upper ocean vortex), with a propagation velocity less rapid in the westward direction and more rapid in the meridional direction (compared to a single mode vortex), and with a decay rate again controlled by the friction coefficient. At earlier times, however, more bizarre behavior can occur; for example, a vortex with initially pure baroclinic mode vertical structure can behave as an eastward-propagating vortical modon for a brief interval. This study focuses on vortices whose baroclinic component is of only one sign (a positive temperature extremum in the thermocline); however, because of a symmetry of the model chosen (in particular due to its quasi-geostrophic assumption), these solutions can be simply reinterpreted to apply to vortices of both signs.