Pulse Disturbance Research Articles

Fuzzy Swing Up Control and Optimal State Feedback Stabilization for Self-Erecting Inverted Pendulum

This paper presents the realisation of self-erecting inverted pendulum controls via two switched control approaches, a rule based fuzzy control for swing up inverted pendulum rod to pose upright position from downright position and an optimal state feedback control for stabilization as pendulum on upright position close to its equilibrium vertical line. The aim of this study is to solve two important problems on self-erecting inverted pendulum; swing up and stability in its upright balance position. Simulation and experimental results showed that control methods enabled the inverted pendulum swinging up and reaching its stable attitude in upright position even though small impulse and pulse disturbances were given.

Disturbance Rejection Control Using a Novel Velocity Fusion Estimation Method for Levitation Control Systems

Magnetic levitation has been applied to maglev trains and magnetic suspension wind tunnel. However, there are some problems with the existing levitation control. For example, it is difficult to extract smooth velocity signals from the gap sensor with noise. The classical differentiator is susceptible to noise, which makes the levitation system sometimes vibrate. The accuracy and stability of levitation control need to be improved. The velocity fusion estimation method (VFE) is proposed to extract the velocity signal from the gap and acceleration sensor, which is theoretically derived to prove that it reduced the noise of the velocity signal. Then disturbance rejection control(DRC) is proposed that add VFE into classical levitation control. Because of the high-quality velocity signal and accelerometer’s fast responsiveness, it makes DRC have many advantages. The advantages of using the proposed control structure are that it improved the control accuracy of the target gap and resisted disturbance effectively. Air-gap fluctuations in levitation systems can be reduced in transient pulse disturbance test, white noise disturbance test, and external force disturbance test when it applies the proposed control method. The effectiveness and advantages of the proposed control method are verified by the simulation and experiments.

Performance Improvement of Semicontrolled Open-Winding PMSGs Based on Virtual Zero-Crossing Detection and Segment Injection of Third-Order Harmonic Current

The semicontrolled open-winding permanent magnet synchronous generators (OW-PMSGs) with a common dc bus system have received more attention in recent years due to its advantages of reduced cost and simpler power supply. Good control performances could be achieved under the zero power factor angle (PFA). However, current clamping problem is normally presented under non-zero PFA condition, resulting in unexpected torque pulsations and voltage pulse disturbances. Meanwhile, misjudgment of voltage vectors and subsequent deteriorations in steady-state performances can be observed at current zero-crossing points. In order to improve the control performances of semicontrolled OW-PMSGs, a virtual zero-crossing detection method is proposed in this paper to effectively suppress the oscillation of voltage vectors at current zero-crossing points. In addition, a segment injection strategy of third-order harmonic current is proposed. With the proposed strategy adopted, the current clamping problem can be successfully solved, and more importantly, the torque ripple and third-order harmonic current could be simultaneously suppressed. Relevant experimental validations and performance comparisons based on a 2.3-kW semicontrolled OW-PMSG system are presented to verify the proposed control strategies.

Fully Connected Clustering Based Software Defined Control System and Node Failure Analysis

This paper proposes a Software Defined Control System (SDCS), which is a fully distributed controller scheme based on a fully connected cluster. The characteristic of SDCS is that the control task is virtualized into multiple Virtual Control Tasks (VCTs) and distributed on nodes with capabilities of computing and memory in the wireless network, there is no core node in the control system. The topologies of the wireless networks are inherently unstable, through constructing a Set of Migratable Nodes (SMN), a dynamic mapping relationship between VCTs and nodes to cope with the impact of potential network node failures on the function and performance of the control system is established. By equating the mapping relationship adjustment process to an external square wave pulse disturbance, the stability of the system under changing the mapping relationship is analyzed. In the scheme, the wireless network itself acts as a dynamic distributed controller, instead of using a particular core node to execute the control task, the distributed design of the controller and the dynamic mapping relationship above enhance the flexibility and the reliability of the control system. The digital simulation analysis is carried out in the MATLAB/Simulink environment, the results demonstrate the availability and effectiveness of the proposed scheme.

Connectance and nestedness as stabilizing factors in response to pulse disturbances in adaptive antagonistic networks

Understanding how network architectures are related to community robustness is essential to investigating the effects of disturbances on biological systems. Regarding the perturbations that are observed in disturbance regimes, frequency and intensity are two main descriptors, specifically for those events with short duration. Here, I used the architecture of 45 real-world weighted bipartite networks to assess whether network size, connectance, and nestedness are related to the effects of pulse disturbances in antagonistic communities. Networks were simulated under five scenarios with different combinations of frequency and intensity of perturbations. The dynamics of resource-consumer interactions followed the adaptive interaction switching behavior, which is the key topological process underlying most of the architectures of antagonistic webs. As opposed to most studies considering the effects of disturbances as species extinctions explicitly, the effects of disturbances here were modeled as changes in the abundance of consumers following immediate reductions in the abundance of resources. Simulations revealed that community robustness to pulse disturbances increased with both connectance and nestedness overall, with no effect of network size. Community networks with highly connected and nested topologies were more robust to disturbances, particularly under high frequency and intensity perturbations. By considering disturbances that are not directly related to species’ extinctions, this study provides valuable insights that connectance and nestedness have an important stabilizing role in ecological networks.

The effects of forest cover and disturbance on torrential hazards: large-scale evidence from the Eastern Alps

Global human population growth, limited space for settlements and a booming tourism industry have led to a strong increase of human infrastructure in mountain regions. As this infrastructure is highly exposed to natural hazards, a main role of mountain forests is to regulate the environment and reduce hazard probability. However, canopy disturbances are increasing in many parts of the world, potentially threatening the protection function of forests. Yet, large-scale quantitative evidence on the influence of forest cover and disturbance on natural hazards remains scarce to date. Here we quantified the effects of forest cover and disturbance on the probability and frequency of torrential hazards for 10 885 watersheds in the Eastern Alps. Torrential hazard occurrences were derived from a comprehensive database documenting 3768 individual debris flow and flood events between 1986 and 2018. Forest disturbances were mapped from Landsat satellite time series analysis. We found evidence that forests reduce the probability of natural hazards, with a 25 percentage point increase in forest cover decreasing the probability of torrential hazards by 8.7%± 1.2%. Canopy disturbances generally increased the probability of torrential hazard events, with the regular occurrence of large disturbance events being the most detrimental disturbance regime for natural hazards. Disturbances had a bigger effect on debris flows than on flood events, and press disturbances were more detrimental than pulse disturbances. We here present the first large scale quantification of forest cover and disturbance effects on torrential hazards. Our findings highlight that forests constitute important green infrastructure in mountain landscapes, efficiently reducing the probability of natural hazards, but that increasing forest disturbances can weaken the protective function of forests.

Recovery ability of lowshore sessile assemblages in a highly contaminated post-industrial area

The inheritance of environmental contamination left by abandoned industrial plants is widespread globally. Here we compared the patterns of recovery of lowshore algal and invertebrate assemblages between the post-industrial site of Bagnoli-Coroglio and four reference sites distributed along the coast in the Gulf of Naples, southern Tyrrhenian Sea. The structure of whole assemblages, richness of taxa and abundance of individual taxa were followed during one year since an event of experimental disturbance consisting in the removal of all erect organisms from the rocky substrate. Our main findings suggest that the examined benthic assemblages recovered effectively and quickly after a pulse disturbance and, contrarily to initial expectations, that this ability was comparable between the post-industrial site and the reference sites. This result is discussed in terms of several plausible processes and mechanisms, including the general capability of intertidal organisms to recover from physical disturbance, the potential high level of environmental stress affecting the reference sites too, the chance that the most intense impacts of contamination remained restricted to the sediments of the post-industrial site without propagating to adjacent rocky habitats, and the large natural variability of reference sites that may have masked weak effects of the historical contamination. Irrespective of the actual causes, we emphasize the need for including natural variability of the examined system in any future restoration interventions, to guarantee representation of the range of variation of target organisms and of their underlying processes, and to avoid confounding the intended post-industrial impact with the effects of other natural and anthropogenic processes.

Resilience of Natural Phytoplankton Communities to Pulse Disturbances from Micropollutant Exposure and Vertical Mixing

Freshwaters are increasingly exposed to complex mixtures of pharmaceutical and personal care products (PPCPs) from municipal wastewater, which are known to alter freshwater communities' structure and functioning. However, their interaction with other disturbances and whether their combined effects can impact ecological resilience (i.e., the ability of a system to tolerate disturbances without altering the system's original structure and processes) remain unexplored. Using in situ mesocosms in 2 lakes with different nutrient levels (mesotrophic and eutrophic), we assessed whether a pulse exposure to sublethal concentrations of 12 PPCPs affects the ecological resilience of natural phytoplankton communities that experienced an abrupt environmental change involving the destabilization of the water column through mixing. Such mixing events are predicted to increase as the effects of climate change unfold, leading to more frequent storms, which disrupt stratification in lakes and force communities to restructure. We assessed their combined effects on community metrics (biomass, species richness, and composition) and their relative resilience using 4 indicators (cross-scale, within-scale, aggregation length, and gap length), inferred from phytoplankton communities by discontinuity analysis. The mixing disturbance alone had negligible effects on the community metrics, but when combined with chemical contaminants significant changes were measured: reducing total biomass, species richness, and altered community composition of phytoplankton. Once these changes occurred, they persisted until the end of the experiment (day 20), when the communities' structures from the 2 highest exposure levels diverged from the controls. The resilience indicators were not affected by PPCPs but differed significantly between lakes, with lower resilience found in the eutrophic lake. Thus, PPCPs can significantly alter community structures and reinforce mechanisms that maintain ecosystems in a "degraded state." Environ Toxicol Chem 2019;38:2197-2208. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Multi-Decadal Change in Reef-Scale Production and Calcification Associated With Recent Disturbances on a Lizard Island Reef Flat

Climate change is threatening the persistence of coral reef ecosystems resulting in both chronic and acute impacts which include higher frequency and severity of cyclones, warming sea surface temperatures, and ocean acidification. This study measured net ecosystem primary production (NEP) and net ecosystem calcification (NEC) on a reef flat after the most severe El Nino-driven mass bleaching event on Australia’s Great Barrier Reef (GBR) in 2016 and again in 2018 after another consecutive bleaching event in 2017. Our results indicate that reef metabolism is altered as result of both the continuing press disturbance of ocean acidification and severe pulse disturbances (cyclones and bleaching events). In 2016, NEP was within the range of values reported in past studies, however it declined in 2018. NEC over a 12-h period was lower in 2016 than 2018; but when compared with past studies there was a severe decline in daytime net calcification from 2008-2009, to 2016 followed by an increase in 2018 (but still NEC remained lower than values reported in 2008-2009). Conversely, nighttime net calcification was similar to that reported in 2009 indicating nighttime dissolution did not increase over the past decade. Overall coral cover remained stable following recent disturbances, however algal turf was the dominant benthic component on the reef flat, while calcifiers (corals and calcified algae) were minor components (< 20% of total benthic cover). This study documented changes in community function following major pulse disturbances (bleaching events and cyclones) within the context of ongoing OA at the same location over the last decade. Repeated pulse disturbances could jeopardize the persistence of the reef flat as a net calcifying entity, with the potential for cascading effects on other ecosystem services.

Shifting baselines in coastal forests: Rising seas transform plant communities from the ‘ground’ up

Increases in the rate of sea level rise are likely to result in changes to disturbance-adapted coastal forests and associated freshwater resources over the next several decades. In this study, we investigated how the press disturbance of two decades of sea level rise altered island hydrology and interacted with pulse disturbances (frequent hurricane impacts) to alter coastal forest composition and structure. The research was conducted on two low-elevation islands located within the lower Florida Keys: Big Pine and Upper Sugarloaf Keys. Groundwater salinity and vegetation structure and composition were sampled in the early 1990s prior to impact from two hurricanes – Hurricanes Georges (1998) and Wilma (2005) – and again in 2012/2013 in permanent plots inside and outside the boundaries of the islands’ freshwater lenses. Using linear mixed effects modeling, we examined whether groundwater salinity varied over time among locations, and investigated whether this variation was reflected in changes in forest structure and composition in three height strata. The results of this analysis revealed that groundwater salinity underlying plots outside the freshwater lens increased over the two decades, while salinity of groundwater at plots inside the freshwater lens remained stable. The greatest shift in composition occurred in the understory strata along a gradient of increasing salinity, and plots located outside the freshwater lens gained species typical of tidally-influenced buttonwood forest and lost glycophytic species. Viewed against the background of recurring hurricane impacts, these findings suggest that sea level rise is currently altering both groundwater resources and the composition of coastal forests in the Florida Keys. Similar dynamics should be observed in low-lying coastal forests within ocean basins subject to increased tropical cyclone activity. Management of these island coastal forests must now consider the continually shifting nature of the resource in light of acceleration in sea level rise.

Quantifying the risk of irreversible degradation for ecosystems: A probabilistic method based on Bayesian inference

Abstract Ecosystem degradation is usually abrupt and unexpected shifts in ecosystem states that cannot be easily reversed. Some ecosystems might be subject to high risks of irreversible degradation (RID) because of strong undesirable resilience. In this study, we propose a probabilistic method to quantify RID by measuring the probability of the recovering threshold being unattainable under real world scenarios. Bayesian inference was used for parameter estimations and the posteriors were used to calculate the threshold for recovery and thereby the probability of it being unattainable, i.e., RID. We applied this method to lake eutrophication as an example. Our case study supported our hypothesis that ecosystems could be subject to high RID, as shown by the lake having a RID of 72% at the whole lake level. Spatial heterogeneity of RID was significant and certain regions were more susceptible to irreversible degradation, whereas others had higher chances of recovery. This spatial heterogeneity provides opportunities for mitigation because targeting regions with lower RID is more effective. We also found that pulse disturbances and ecosystem-based solutions had positive influences on lowering the RID. Pulse disturbances had the most significant influence on regions with higher RID, while ecosystem-based solutions performed best for regions with moderate RID, reducing RID to almost 0. Our method provides a practical framework to identify sensitive regions for conservation as well as opportunities for mitigation, which is applicable to a wide range of ecosystems. Our findings highlighted the worst scenario of irreversible degradation by providing a quantitative measure of the risk, thus raising further requirements and challenges for sustainability.

Vectors with autonomy: what distinguishes animal-mediated nutrient transport from abiotic vectors?

Animal movements are important drivers of nutrient redistribution that can affect primary productivity and biodiversity across various spatial scales. Recent work indicates that incorporating these movements into ecosystem models can enhance our ability to predict the spatio-temporal distribution of nutrients. However, the role of animal behaviour in animal-mediated nutrient transport (i.e. active subsidies) remains under-explored. Here we review the current literature on active subsidies to show how the behaviour of active subsidy agents makes them both ecologically important and qualitatively distinct from abiotic processes (i.e. passive subsidies). We first propose that animal movement patterns can create similar ecological effects (i.e. press and pulse disturbances) in recipient ecosystems, which can be equal in magnitude to or greater than those of passive subsidies. We then highlight three key behavioural features distinguishing active subsidies. First, organisms can transport nutrients counter-directionally to abiotic forces and potential energy gradients (e.g. upstream). Second, unlike passive subsidies, organisms respond to the patterns of nutrients that they generate. Third, animal agents interact with each other. The latter two features can form positive- or negative-feedback loops, creating patterns in space or time that can reinforce nutrient hotspots in places of mass aggregations and/or create lasting impacts within ecosystems. Because human-driven changes can affect both the space-use of active subsidy species and their composition at both population (i.e. individual variation) and community levels (i.e. species interactions), predicting patterns in nutrient flows under future modified environmental conditions depends on understanding the behavioural mechanisms that underlie active subsidies and variation among agents' contributions. We conclude by advocating for the integration of animal behaviour, animal movement data, and individual variation into future conservation efforts in order to provide more accurate and realistic assessments of changing ecosystem function.

A theory of pulse dynamics and disturbance in ecology.

We propose four postulates as the minimum set of logical propositions necessary for a theory of pulse dynamics and disturbance in ecosystems: (1) resource dynamics characterizes the magnitude, rate, and duration of resource change caused by pulse events, including the continuing changes in resources that are the result of abiotic and biotic processes; (2) energy flux characterizes the energy flow that controls the variation in the rates of resource assimilation across ecosystems; (3) patch dynamics characterizes the distribution of resource patches over space and time, and the resulting patterns of biotic diversity, ecosystem structure, and cross‐scale feedbacks of pulses processes; and (4) biotic trait diversity characterizes the evolutionary responses to pulse dynamics and, in turn, the way trait diversity affects ecosystem dynamics during and after pulse events. We apply the four postulates to an important class of pulse events, biomass‐altering disturbances, and derive seven generalizations that predict disturbance magnitude, resource trajectory, rate of resource change, disturbance probability, biotic trait diversification at evolutionary scales, biotic diversity at ecological scales, and functional resilience. Ultimately, theory must define the variable combinations that result in dynamic stability, comprising resistance, recovery, and adaptation.

Antibiotic disturbance affects aquatic microbial community composition and food web interactions but not community resilience.

Notwithstanding the fundamental role that environmental microbes play for ecosystem functioning, data on how microbes react to disturbances are still scarce, and most factors that confer stability to microbial communities are unknown. In this context, antibiotic discharge into the environment is considered a worldwide threat for ecosystems with potential risks to human health. We therefore tested resilience of microbial communities challenged by the presence of an antibiotic. In a continuous culture experiment, we compared the abundance, composition and diversity of microbial communities undisturbed or disturbed by the constant addiction of tetracycline in low (10µg/L) or intermediate (100µg/L) concentration (press disturbance). Further, the bacterial communities in the three treatments had to face the sudden pulse disturbance of adding an allochthonous bacterium (Escherichia coli). Tetracycline, even at low concentrations, affected microbial communities by changing their phylogenetic composition and causing cell aggregation. This, however, did not coincide with a reduced microbial diversity, but was mainly caused by a shift in dominance of specific bacterial families. Moreover, the less disturbed community (10µg/L tetracycline) was sometimes more similar to the control and sometimes more similar to heavily disturbed community (100µg/L tetracycline). All in all, we could not see a pattern where the communities disturbed with antibiotics were less resilient to a second disturbance introducing E. coli, but they seemed to be able to buffer the input of the allochthonous strain in a similar manner as the control.

Sea Level Rise and the Dynamics of the Marsh-Upland Boundary

During sea level rise, salt marshes transgress inland invading low-lying forests, agricultural fields, and suburban areas. This transgression is a complex process regulated by infrequent storms that flood upland ecosystems increasing soil salinity. As a result upland vegetation is replaced by halophyte marsh plants. Here we present a review of the main processes and feedbacks regulating the transition from upland ecosystems to salt marshes. The goal is to provide a process-based framework that enables the development of quantitative models for the dynamics of the marsh-upland boundary. Particular emphasis is given to the concept of ecological ratchet, combining the press disturbance of sea level rise with the pulse disturbance of storms.

The three regimes of spatial recovery.

An enduring challenge for ecology is identifying the drivers of ecosystem and population stability. In a spatially explicit context, key features to consider are landscape spatial structure, local interactions, and dispersal. Substantial work has been done on each of these features as a driver of stability, but little is known on the interplay between them. Missing has been a more integrative approach, able to map and identify different dynamical regimes, predicting a system's response to perturbations. Here we first consider a simple scenario, i.e., the recovery of a homogeneous metapopulation from a single localized pulse disturbance. The analysis of this scenario reveals three fundamental recovery regimes: Isolated Regime when dispersal is not significant, Rescue Regime when dispersal mediates recovery, and Mixing Regime when perturbations spread throughout the system. Despite its simplicity, our approach leads to remarkably general predictions. These include the qualitatively different outcomes of various scenarios of habitat fragmentation, the surprising benefits of local extinctions on population persistence at the transition between regimes, and the productivity shifts of metacommunities in a changing environment. This study thus provides context to known results and insight into future directions of research.

Insights into Long-Term Toxicity of Triclosan to Freshwater Green Algae in Lake Erie

This study explored the long-term impacts of a pulse disturbance of triclosan on five nontarget green algae in Lake Erie. Comprehensive analyses were performed using multiple physiological end points at community and subcellular scales. The toxic mechanism of triclosan in a wide range of concentrations was analyzed. The diverse sensitivity of algae species and complex interrelationships among multiple end points were revealed. The results showed the taxonomic groups of algae were the key issue for sensitivity difference. High doses of triclosan caused irreversible damage on algae, and environmentally relevant doses initiated either inhibition or stimulation. Smaller cells had higher sensitivity to triclosan, while larger cells had a wider size variation after exposure. Colonial cells were less sensitive than unicells. For chlorophyll, there were better dose-response relationships in Chlorococcum sp., Chlamydomonas reinhardtii CPCC 12 and 243 than Asterococcus superbus and Eremosphaera viridis. For chlorophyll fluorescence, Fv/ Fm was the most sensitive parameter, and qN was more sensitive than qP. Triclosan showed long-term effects on biochemical components, such as lipids, proteins, and nucleic acids. The findings will be helpful for a systematic and complete assessment of triclosan toxicity in natural waters and the development of appropriate strategies for its risk management.

Effect of laser intensity on microwave radiation generated in nanosecond laser-plasma interactions

Microwave radiation in several gigahertz frequency band is a common phenomenon in laser-plasma interactions. It can last hundreds of nanoseconds and cause huge electromagnetic pulse disturbances to electrical devices in experiments. It has been found that the microwave radiation might originate from the oscillation of charged chambers, the return current on target holders, the dipole radiation, the quadrupole radiation, and the electron bunch emitted from the plasma to the vacuum. The microwave radiation waveform, frequency spectrum, and intensity depend on many factors such as laser pulse, target, and chamber parameter. To distinguish the microwave radiation mechanisms, the influence of the experimental parameters on the radiation characteristics should be investigated systematically. In this paper we investigate the microwave radiation influenced by the laser intensity in nanosecond laser-plasma interactions. It is found that the microwave radiation intensity varies nonmonotonically with the laser intensity. For the lower laser intensity, the radiation intensity first increases and then decreases with laser intensity increasing, the radiation field continuously oscillates in tens of nanoseconds, and the radiation spectrum contains two components below and above 0.3 GHz, respectively. For the higher laser intensity, the radiation intensity increases with the laser intensity increasing, the radiation field has a unipolar radiation lasting tens of nanoseconds, and the radiation spectrum mainly includes the component below 0.3 GHz. The waveform and spectrum analysis show that these phenomena are due to the difference of the radiation mechanisms at different laser intensities. The frequency component below and above 0.3 GHz are induced by the electron bunch emitted from the plasma to the vacuum and the dipole radiation respectively. At low laser intensity, both the dipole radiation and the electron bunch emitted from the plasma contribute to the microwave radiation. At high laser intensity, the microwave radiation is mainly produced by the electron beam emitted from the plasma to the vacuum. This work is significant for understanding the microwave radiation mechanisms in nanosecond laser-plasma interactions, and implies the potential to provide a reference to the diagnosing of the escape electrons and the sheath field on the target surface by the microwave radiation in laser-plasma interaction.

Post-fire consequences for leaf breakdown in a tropical stream

Abstract Aim Wildfire is a natural pulsed disturbance in landscapes of the Savannah Biome. This study evaluates short-term post-fire effects on leaf litter breakdown, the invertebrate community and fungal biomass of litter from three different vegetal species in a tropical stream. Methods Senescent leaves of Inga laurina, Protium spruceanum and Rircheria grandis (2 ± 0.1 g dry mass) were individually placed in litter bags (30 × 30 cm: 10 mm coarse mesh and 0.5 mm fine mesh) and submerged in the study stream before and after fire. Replicate bags (n = 4; individually for each species, sampling time, fire event and mesh size) were then retrieved after 20 and 40 days and washed to separate the invertebrates before fire event and again immediately after fire. Disks were cut from leaves to determine ash-free dry mass, while the remaining material was oven-dried to determine dry mass. Results The pre-fire mean decomposition coefficient (k = -0.012 day-1) was intermediate compared to that reported for other savannah streams, but post-fire it was lower (k = -0.007 day-1), due to decreased allochthonous litter input and increased autochthones production. Intermediate k values for all qualities of litter post-fire may indicate that fire is equalizing litter quality in the stream ecosystem. The abundance of scrapers was found to be more important than fungal biomass or shredder abundance, probably due to their functioning in leaf fragmentation while consuming periphyton growing on leaf litter. Conclusions Theses results indicate that fire can modify the relationships within decomposer communities in tropical stream ecosystems.

Multistability of Spiking Regimes in a Model of a Laser with Delayed-Feedback

We use the methods of asymptotic analysis to obtain finite-dimensional maps, whose dynamics determines the dynamics of relaxation oscillations in a laser model with optoelectronic feedback. The coexistence of cycles and chaotic attractors is demonstrated. Switching of spiking regimes by pulsed disturbance of pumping in a certain oscillation phase is discussed.