Multiple Stable Points Research Articles

Analysis and Experiments of a Pendulum Vibration Energy Harvester With a Magnetic Multi-Stable Mechanism

This work couples a magnetic multi-stable mechanism to a pendulum vibration energy harvester so as to widen its bandwidth, especially in low-frequency operation. Multiple stable points are formed by a movable permanent magnet installed on the pendulum and two fixed permanent magnets installed symmetrically on the base of the energy harvester. Thus, the pendulum can swing between the stable points at two sides, which causes large motion amplitude and power generation. In designing the prototype of the energy harvester, dynamical modeling and potential energy analysis are carried out to achieve a low threshold for snap through. An experimental setup is developed and a series of comparative experiments are implemented to investigate prototype performance. It is shown that the energy harvester with the fixed magnets can generate a noticeable normalized induced voltage at 0.7 Hz, while the energy harvester without the fixed magnets requires the excitation frequency of 1.0 Hz to reach a similar level. The electrical outputs varying with vibration acceleration and load resistance are also examined. In general, the experimental results verify the effectiveness of the proposed structure on enlarging frequency bandwidth. This work can provide a promising candidate of energy harvesting for low-frequency applications such as ocean wave.

Research on the Evolution Path and Influence Factors of Core Enterprise Oriented Entrepreneurship Ecosystem Under the Government Regulation

The core enterprise oriented entrepreneurship ecosystem plays an important role in promoting the sustainable development of innovation and entrepreneurship and realizing the multi-agent win-win symbiosis. Based on the structure of the core enterprise oriented entrepreneurship ecosystem, this paper constructs an evolutionary game model with the participation of core enterprises, start-up enterprises and the government, analyzes the equilibrium point and corresponding stability conditions for the evolutionary game model, and carries out a simulation analysis on different stability conditions from the aspects of the initial willingness of the participants, the intensity of the subsidy and punishment, the cost and benefit of the strategy selection. The results show that: (1) In order to achieve different equilibrium states, different stability conditions should be satisfied, and there may be multiple stable points under each stability condition. (2) The initial intention will positively affect the subject’s positive strategy selection, and negatively affect the subject’s negative strategy selection. (3) The strategy selections of core enterprises, start-up enterprises and the government will be affected by many factors, and different factors have different influences on the directions and degrees of the main strategy selections. Based on these conclusions, we can build a unified information platform, set up a moderately high, flexible reward and punishment mechanism, and build a multi-party collaborative governance system. In addition, we can also use the stability conditions to judge the development status of the ecosystem to promote the formation of the ideal core enterprise oriented entrepreneurship ecosystem.

What Does It Mean to Successfully Conserve a (Vertebrate) Species?

The conservation of species is one of the foundations of conservation biology. Successful species conservation has often been defined as simply the avoidance of extinction. We argue that this focus, although important, amounts to practicing conservation at the “emergency room door,” and will never be a sufficient approach to conserving species. Instead, we elaborate a positive definition of species conservation on the basis of six attributes and propose a categorization of different states of species conservation using the extent of human management and the degree to which each of the attributes is conserved. These states can be used to develop a taxonomy of species “recovery” that acknowledges there are multiple stable points defined by ecological and social factors. “With this approach, we hope to contribute to a new, optimistic conservation biology that is not based on underambitious goals and that seeks to create the conditions under which Earth's biological systems can thrive.

Experimental confirmation of multiple community states in a marine ecosystem

Small changes in environmental conditions can unexpectedly tip an ecosystem from one community type to another, and these often irreversible shifts have been observed in semi-arid grasslands, freshwater lakes and ponds, coral reefs, and kelp forests. A commonly accepted explanation is that these ecosystems contain multiple stable points, but experimental tests confirming multiple stable states have proven elusive. Here we present a novel approach and show that mussel beds and rockweed stands are multiple stable states on intertidal shores in the Gulf of Maine, USA. Using broad-scale observational data and long-term data from experimental clearings, we show that the removal of rockweed by winter ice scour can tip persistent rockweed stands to mussel beds. The observational data were analyzed with Anderson's discriminant analysis of principal coordinates, which provided an objective function to separate mussel beds from rockweed stands. The function was then applied to 55 experimental plots, which had been established in rockweed stands in 1996. Based on 2005 data, all uncleared controls and all but one of the small clearings were classified as rockweed stands; 37% of the large clearings were classified as mussel beds. Our results address the establishment of mussels versus rockweeds and complement rather than refute the current paradigm that mussel beds and rockweed stands, once established, are maintained by site-specific differences in strong consumer control.

Stochastic networks with multiple stable points

This paper analyzes stochastic networks consisting of a set of finite capacity sites where different classes of individuals move according to some routing policy. The associated Markov jump processes are analyzed under a thermodynamic limit regime, that is, when the networks have some symmetry properties and when the number of nodes goes to infinity. An intriguing stability property is proved: under some conditions on the parameters, it is shown that, in the limit, several stable equilibrium points coexist for the empirical distribution. The key ingredient of the proof of this property is a dimension reduction achieved by the introduction of two energy functions and a convenient mapping of their local minima and saddle points. Networks with a unique equilibrium point are also presented.

The Fouling Community at Beaufort, North Carolina: A Study in Stability

The stability of natural communities can only be studied by asking, How does a local resident adult assemblage respond to the perturbations it experiences? One must measure perturbations directly and independently of the community response. One must be alert to perturbations which potentially or actually add to, as well as subtract from, the resident adult assemblage. The appropriate time scale will depend on the perturbation frequency and the community response, if any. This approach to stability is applied to the fouling community at Beaufort, North Carolina. Multiple stable points, resident assemblages resistant to recruitment (Sutherland 1974), are common and are evidence for persistence stability. However, most eventually disappear because of continued recruitment of other species, overgrowth, sloughing off, or senility. Thus there is ample evidence for instability in the community (Sutherland and Karlson 1977) especially if one compares the species composition of winter assemblages. However, with ...

A three-year study of benthos of muddy environments in Port Phillip Bay, Victoria

Samples taken four times a year over three years (1973–1975) at three widely separate stations in muddy environments in Port Phillip Bay were used to compare species diversity and composition of the benthic community between areas, seasons and years. Analysis of variance of five community statistics: the number of individuals, the number of species, Shannon's diversity and two evenness measures; showed that differences between the three stations and between years contributed the largest fractions of the variance in number of individuals and species but little to diversity or evenness. Seasonal differences contributed negligibly to variance in any statistic except diversity. Smallscale spatial patchiness (from replicate samples within stations) contributed a significant fraction of variance to all five statistics. The fauna at all stations was dominated by the deposit-feeding bivalve Theora fragilis and the decapod shrimp Callianassa limosa; only minor species were restricted to single stations. The density of few species varied seasonally but several were more abundant in some years than others. Hierarchical classification using the Canberra metric dissimilarity coefficient grouped samples into station groups. Use of the Bray-Curtis coefficient grouped some samples by station and some by season and it was concluded that the main differences between stations were in overall species composition, not in the densities of dominant species. Temporal changes in community structure were non-seasonal but, rather, were irregular changes occurring at single stations. Differences in fauna between stations were related in part to small differences in sediment-type but not to physico-chemical features of the overlying water. The irregular fluctuations in density of the common species and in the identity of the minor species suggest that multiple-stable points in community structure may exist for the silty-clay community. The two major species seemed not to have altered each other's environment over the sampling period. Considerable variation in species composition may occur in soft-bottom benthos in the absence of marked environmental perturbations.

Multiple Stable Points in Natural Communities

Evidence is presented which indicates the importance of historical events in determining the structure of a variety of natural communities. In the fouling community at Beaufort, North Carolina, the order of larval recruitment determined which species monopolized the available space during initial community development. In other systems, community structure could be explained only by referring to the specific historical events which determined the presence or absence of important consumers. Since history was relevant to the observed community structure, multiple stable points are an undeniable reality in space and time in these systems.

Ecosystem stability: A result from an abstract simulation

An abstract model of an ecosystem is presented which incorporates both population dynamic and energy flow concepts and attempts to avoid the simple assumptions of the Lotka-Volterra or mass-action types of equation. The model allows simulation of very complex foodwebs, involving all trophic levels, with 50 or more species. The results indicate unusual stability features for such models; for systems with a range of species numbers, multiple stable points (or limits cycles) are found in which all species survive. Various views of the relationship between stability and species diversity are reconciled by the following conclusion of the study. “With increasing species numbers in an ecosystem similar to that described here, there is an increase in stable points due to compensating adjustments with increasing food web complexity, however stability declines, in the sense that the equilibrium points become less aggregated in the vector field.”