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Considering that no current limiting inductances (CLIs) are installed at the end of the DC line in the flexible DC distribution grid, the protections relying on line boundary are no longer applicable. To overcome this problem, the paper proposes a single‐ended protection method independent of line boundary. Firstly, the Peterson equivalent circuit is applied to analyze the amplitude‐time ratio of initial voltage travelling wave (ARIVTW) under internal and external faults. Secondly, the fault direction criterion based on the fault component current and the fault type criterion based on the pole voltage are built. Subsequently, the fault identification criterion is constructed by using the ARIVTW, and the corresponding protection method is formed. Finally, the flexible DC distribution grid is built in PSCAD to verify the proposed method. The simulation results show that the method is robust to fault resistance and noise. Besides, the method realizes the protection of the whole line, which has good selectivity and engineering applicability. [ABSTRACT FROM AUTHOR]

Spatial synchrony in population dynamics can be caused by dispersal or spatially correlated variation in environmental factors like weather (Moran effect). Distinguishing between these mechanisms is challenging for natural populations, and the study of dispersal‐induced synchrony in particular has been dominated by theoretical modelling and laboratory experiments.The goal of the present study was to evaluate the evidence for dispersal as a cause of meso‐scale (distances of tens of kilometres) spatial synchrony in natural populations of the two cyclic geometrid moths Epirrita autumnata and Operophtera brumata in sub‐arctic mountain birch forest in northern Norway.To infer the role of dispersal in geometrid synchrony, we applied three complementary approaches, namely estimating the effect of design‐based dispersal barriers (open sea) on synchrony, comparing the strength of synchrony between E. autumnata (winged adults) and the less dispersive O. brumata (wingless adult females), and relating the directionality (anisotropy) of synchrony to the predominant wind directions during spring, when geometrid larvae engage in windborne dispersal (ballooning).The estimated effect of dispersal barriers on synchrony was almost three times stronger for the less dispersive O. brumata than E. autumnata. Inter‐site synchrony was also weakest for O. brumata at all spatial lags. Both observations argue for adult dispersal as an important synchronizing mechanism at the spatial scales considered. Further, synchrony in both moth species showed distinct anisotropy and was most spatially extensive parallel to the east–west axis, coinciding closely to the overall dominant wind direction. This argues for a synchronizing effect of windborne larval dispersal. Congruent with most extensive dispersal along the east–west axis, E. autumnata also showed evidence for a travelling wave moving southwards at a speed of 50–80 km/year.Our results suggest that dispersal processes can leave clear signatures in both the strength and directionality of synchrony in field populations, and highlight wind‐driven dispersal as promising avenue for further research on spatial synchrony in natural insect populations. [ABSTRACT FROM AUTHOR]

Emerging and invasive pathogens can have long-lasting impacts on susceptible wildlife populations, including localized collapse and extirpation. Management of threatening disease is of widespread interest and requires knowledge of spatiotemporal patterns of pathogen spread., Theory suggests disease spread often occurs via two patterns: homogenous mixing and travelling waves. However, high-resolution empirical data demonstrating localized (within population) disease spread patterns are rare., This study examined the spread of sarcoptic mange (aetiological agent Sarcoptes scabiei) in a population of bare-nosed wombats ( Vombatus ursinus), and investigated whether pathogen spread occurred by homogenous mixing or a travelling wave., Using 7 years of population surveys and 4 years of disease severity surveys, we show that mange was first detected in the east of a wombat population in northern Tasmania, and progressed westward as a travelling wave. Wombat mortality rates reached 100% behind the wave, with a 94% decline in overall wombat abundance within the park., Synthesis and applications. Globally distributed pathogens may have severe impacts on susceptible host species. This is the first study to quantify population-level impacts of sarcoptic mange upon bare-nosed wombats, showing a wave of mange disease which resulted in a dramatic population decline. Successful management of the spread of this and similar pathogens may hinge on the capacity to establish transmission barriers at local or between-population scales. [ABSTRACT FROM AUTHOR]

Aim Time-lagged population synchrony, where spatially separated populations show similar fluctuations in abundance lagged over time, is thought to be driven by dispersal among populations. When dispersal is proportional to population density or positively density dependent, and individuals move readily from population A to population B, then as population A increases, the increased number of dispersers from population A to B will cause a subsequent increase in population B. If true, then time-lagged synchrony should be strongest at a species' typical dispersal distance, because the rate of exchange between populations will be greatest at that distance. Location United Kingdom (U. K.). Time period 1994 - 2013. Major taxa studied Birds (class Aves). Methods We estimated the spatial scale of 1-year-lagged population synchrony for 76 U.K. bird species, using 20 years of bird count data collected at 2,415 locations by the British Breeding Bird Survey. We then compared these spatial scales with published mean natal and breeding dispersal distance estimates (ranging from 0.1 to 25.8 km) for the same species based on an independent, large-scale, mark-recapture dataset of 492,272 bird recaptures in Britain and Ireland. Results We found strong, positive cross-species relationships between the spatial scale of time-lagged synchrony and mean natal and breeding dispersal distance estimates from the mark-recapture study. However, average spatial scales of time-lagged synchrony were more than 60 km longer than those from mark-recapture data, with scales ranging from 5 to 185 km. Main conclusions Ours is the first study to show that the spatial scale of time-lagged synchrony increases with species dispersal distance. The scale of synchrony was larger than expected, probably because mark-recapture data underestimated the real dispersal distances, or because dispersal synchronizes populations at a larger spatial scale than that of dispersal (e.g., through formation of travelling waves), or both. Nevertheless, the strong relative concordance is consistent with the explanation that time-lagged synchrony results from dispersal among populations. [ABSTRACT FROM AUTHOR]

The innovative travelling wave bioreactor (TWB), an orbitally shaken system, developed specifically for cell culture applications, is investigated. In this study, engineering parameters covering power input, mixing time and oxygen mass transfer obtained in two TWB prototypes are presented for the first time. Based on the results, cultivation parameters for CHO suspension cell cultivations were defined. Cell growth and substrate consumption were comparable with a wave-mixed reference bioreactor, which demonstrates the bioreactor's applicability for cultivations of mammalian cell cultures for the first time. [ABSTRACT FROM AUTHOR]

In the travelling wave bioreactor (TWB) an orbital movement is used to set up a quasi-periodic wave motion in the partially filled, toroidal shaped vessel. Based on computational fluid dynamics (CFD) models, this study presents detailed analyses of the fluid flow in the TWB for a wide range of operational conditions. Even though the wave propagation is shown to be greatly influenced by the rotation, it was found that the regular vessel shape facilitates a predominantly tangential flow with low back mixing, irrespective of the operational conditions. Hence, the influence of different bioreactor geometries without and with baffles is examined. The study indicates that CFD models can be used as a valuable tool for bioreactor development, because it provides a deep insight into the bioreactor's hydrodynamics and can help to reduce the number of prototypes. [ABSTRACT FROM AUTHOR]

A new algorithm for busbar protection is proposed based on the Hilbert–Huang transform in this study. The algorithm decomposes currents of all lines connecting to the busbar into intrinsic‐mode functions and calculates the instantaneous amplitude of the first intrinsic mode function (IMF). Then, the instantaneous amplitude is normalised to eliminate the impact of fault initial angle and transition resistance. When a fault occurs on the busbar, the initial travelling waves on head ends of the lines all have great instantaneous amplitudes; when a fault occurs on any line, the travelling wave on the faulted line is of great instantaneous amplitude, whereas the initial travelling waves on healthy lines are of small instantaneous amplitudes. Thus, through analysing the detected instantaneous amplitudes of travelling waves, a new busbar protection scheme can be constructed, which achieves a high reliability relative to other fault‐travel‐wave‐based algorithms. According to simulation results on a 500 kV substation modelled in ATP‐Draw, the graphical preprocessor to ATP‐EMTP windows version, the proposed algorithm is effective in determining various types of faults. [ABSTRACT FROM AUTHOR]

This study presents a novel protection criterion of fault locating in multi‐terminal DC (MTDC) transmission systems. When a fault occurs on the DC transmission line of the MTDC system, the traditional protection cannot locate the fault because there is no smoothing reactor (equipped at the converter output) in the transmission lines. In the circumstance of AC/DC conductor contact (ADCC) fault, the varieties of the transient voltage and current components are given based on the symmetrical fault analysis. According to the Bergeron equation, the travelling wave characteristic is analysed. A new criterion of fault locating using the change rate of the current travelling wave is presented which can reduce the impacts of the related fault on the AC system. Finally, simulation results verify the effectiveness of the proposed protection criterion. [ABSTRACT FROM AUTHOR]

Travelling waves ( TW) are among the most striking ecological phenomena emerging in oscillating populations. Despite much theory, understanding how real-world TW arise remains a challenge for ecology. Herein, we analyse 16-year time series of cyclic vole populations collected at 314 localities covering 2500 km² in France. We found evidence for a linear front TW spreading at a speed of 7.4 km year−1 along a north-west/south-east direction and radiating away from a major landscape discontinuity as predicted by recent theory. The spatial signature of vole dispersal was assessed using genetic data collected at 14 localities. Both data sets were handled using similar autocorrelation approaches. Our results revealed a remarkable congruence of the spatial extent and direction of anisotropy of both demographic and genetic structures. Our results constitute the first empirical evidence that effective dispersal is limited in the direction of TW while most of the individual exchanges occur along the wave front. [ABSTRACT FROM AUTHOR]

Application of travelling wave MR to human body imaging is restricted by the limited peak power of the available RF amplifiers. Nevertheless, travelling wave MR advantages like a large field of view excitation and distant location of transmit elements would be desirable for whole body MRI. In this work, improvement of the [ABSTRACT FROM AUTHOR]

At high magnetic fields the performance of a volume-type body coil inside a human sized MR-scanner is influenced by the waveguide action of the scanner's bore. This can result in undesirable strong radio frequency fields [ABSTRACT FROM AUTHOR]

This study presents the concept of the travelling wave single-use bioreactor, based on an orbitally shaken, annular-shaped vessel. A numerical model was developed for early design studies in order to reduce the number of prototypes. The flow characteristics in two different vessel shapes were investigated. It was shown that the orbital motion combined with the toroidal shape of the bioreactor create the desired wave characteristics in the contents of the vessel. [ABSTRACT FROM AUTHOR]

A novel travelling wave case study is developed to verify a front-tracking model of Kelvin–Helmholtz (K–H) instability of immiscible, incompressible two-fluid flow. In this benchmark comparison, two fluids flow at different velocities in the same parallel horizontal direction, forming travelling waves when the interface between the fluids is set to oscillate in the vertical direction at the inlet. With a specific oscillation frequency, the effect of the inlet velocity difference, or gap, on the interface undulation spatial propagation, such as wave damping or wave amplification is quantitatively analysed. By using a variety of different inlet velocity gaps and oscillation frequencies, the effects of the gap on wave propagation are investigated over a large range of wave numbers. The simulation predictions are compared with the result of the linear stability theory. This comparison represents a comprehensive verification of the current front-tracking model of K–H instability. Copyright © 2007 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Bacterial transport in saturated–unsaturated soils is an important process in environmental science and hydrology. A mechanistic model for bacterial transport in geomaterials is presented here. The model equations comprise a pair of fully coupled non-linear parabolic partial differential equations that describe the concentration of microbes in the liquid water and solid surfaces. The model equations not only describe the bacteria sorption and desorption processes, but also take into account the retention of bacteria at the liquid–water interface and the dynamic reproduction characteristics of the bacteria. The instability and travelling waves for the coupled equations are analysed. Copyright © 2004 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract 1. Recent characterizations of the spatial scale of population dynamics have typically considered patterns at a single scale and ignored the possibility that different patterns may arise at different scales. In this study we assessed population densities of field voles with cyclic dynamics in northern England at 147 sites from three spatial scales on five occasions over a 2·5-year period. 2. The scale over which densities were similar was estimated by comparing the variance of density at the three scales (< 1 km2, 10 km2, and 70 km2) and by using autocorrelation techniques. Closer sites were more similar in density than more distant sites and the autocorrelations suggested that sites up to within 8–20 km had more similar densities and higher population synchrony than the average similarity for all the sampling sites. 3. A generalized additive model fitted to all the data showed that the data supported the hypothesis of a travelling wave of vole densities moving through the study area. The model assumed that the wave moved at a constant speed and in a uniform direction. Estimates of the wave’s speed (14 km year-1) and direction (travelling in a direction of 66° from north) were consistent with the estimates which had previously been calculated from a time series of vole densities covering a much smaller spatial area but a longer temporal scale. 4. The spatio-temporal pattern of vole densities detected over a small spatial scale therefore appears to extend over much larger scales and occurs despite the fragmentation of suitable vole habitat at local (a few square kilometres) and regional (hundreds of square kilometres) scales. [ABSTRACT FROM AUTHOR]

ABSTRACT The power wave had been proposed to handle the power flow of transmission lines with complex-valued characteristic impedance. Although the power wave is commonly used, the straightforward derivation of the power wave had not been presented in the previous paper. In this article, the power wave was reviewed and its straightforward derivation is presented. The definition and the meaning of the power wave became much clearer. Numerical simulations were performed to confirm the physical meaning of several wave definitions, and it was confirmed that only the power wave satisfies consumed power and conjugate matching relation. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:26-28, 2015 [ABSTRACT FROM AUTHOR]

Abstract The fine tuning mechanisms involved in the normal processing of sound in the cochlea are non‐linear, hence combination tones are generated inside the cochlea when a pair of low‐level pure tones with neighbouring frequencies f 1 and f 2 is used as a stimulus. Their detection as sounds in the ear canal proves that they undergo backward propagation in the cochlea and through the middle ear, and the non‐invasive measurement of the combination tone at 2f 1 –f 2 , called the cubic difference tone (CDT), has become a routine method of monitoring cochlear function. In order to gain information on the hypothetical places where CDTs are generated, on their intracochlear levels and propagation velocities, direct measurements of CDT pressure waves were carried out in scala vestibuli and tympani of the first and second turn of the guinea‐pig cochlea. Cubic difference tones at 2f 1 –f 2 varied from 0.75 to 9 kHz and were measured with a miniature piezoresistive transducer. Its high sensitivity allowed the detection of CDTs whenever their levels exceeded 5 dB SPL in the ear canal, i.e. 40 dB SPL (re: 20 μPa) inside the cochlea. The levels of CDTs were similar in scala vestibuli of the first and second turn. Phase comparisons between measurements at 2f 1 –f 2 in the first and second turn allowed determination of the place where the CDT phase was minimum. It provided an estimation of the generation site of the CDT, which appeared to be close to the place tuned to f 2 for stimulus levels lower than 70 dB SPL. Forward and backward travel times from one turn to the other were assessed at several frequencies, and both values were shorter than 0.2 ms. In contrast, the overall ‘round‐trip’ delay of CDTs, measured in the ear canal, was about five times larger, suggesting that local filtering processes... [ABSTRACT FROM AUTHOR]

We analyse spatial population dynamics showing that periodic or period-like chaotic dynamics produce self-organization structures, such as travelling waves. We suggest that self-organized patterns are associated with spatial synchrony patterns that often depend on geographical distance between subpopulations. The population dynamics also show statistical spatial autocorrelation patterns. We contrast our theoretical simulations with empirical data on annual damages in young sapling stands caused by voles. We conclude, on the basis of the periodicity, synchrony, and spatial autocorrelation patterns, and our simulation results, that vole dynamics represent travelling waves in population dynamics. We suggest that because such synchrony patterns are frequently observed in natural populations, spatial self-organization may be more common in population dynamics than reported in the literature. [ABSTRACT FROM AUTHOR]