Disturbance Tolerance Research Articles

Using plant traits to predict the sensitivity of colonizations and extirpations to landscape context.

Theory suggests that species with different traits will respond differently to landscape fragmentation. Studies have shown that the presence of species in fragments of varying size, shape and connectivity is dependent on plant traits related to dispersal ability, persistence and disturbance tolerance. However, the role of traits in determining long-term plant community changes in response to changing landscape context is not well understood. We used data from resurveys of 184 plots to test the ability of nine plant traits to predict colonizations and extirpations between 1968 and 2009 based on the surrounding landscape context. We related apparent colonizations and extirpations to road density, naturally vegetated area and patch shape and then tested for significant relationships between a tendency for positive or negative associations and plant traits. Exotic, herbaceous, annual, shade-intolerant species and species with higher specific leaf area were more likely than others to colonize plots with higher road density, lower amount of naturally vegetated area and higher edge-to-area ratio. However, extirpations were rarely predictable based on traits. The role of landscape context in structuring plant community change over the past four decades in the 184 plots resurveyed was largely mediated by colonization events, suggesting that trait-based extirpations occur with a longer post-fragmentation time lag or, alternatively, that extirpation is more stochastic with respect to plant traits than is colonization.

Association Between Habitat Characteristics, Human Activities, and Anuran Species in a Wetland Agricultural Landscape

Abstract I conducted anuran vocalization surveys in cranberry bogs, drainage ditches, and reservoirs of three active and three abandoned cranberry farms in the New Jersey Pinelands to examine the distribution of four anuran species in three consecutive years. I then applied a multinomial model to quantify their calling intensity and assess the influence of cranberry cultivation activities on each anuran species. I discovered that four species naturally inhabiting the Pinelands exhibited varied responses to cranberry cultivation. The responses ranged from positive to negative depending on the life history characteristics, disturbance tolerance, and especially the breeding season of the species in question. Green frogs (Lithobates (=Rana) clamitans) showed a high abundance in the bog habitats of active farms, where they exhibited prolonged courtship calls in late summer. Fowler's Toads (Anaxyrus (=Bufo) fowleri) exhibited high abundance in the ditches of active farms and the reservoirs of abandoned farms. O...

Robust H-Infinity Stabilization and Resilient Filtering for Discrete-Time Constrained Singular Piecewise-Affine Systems

This paper is concerned with the problem of designing robust H-infinity output feedback controller and resilient filtering for a class of discrete-time singular piecewise-affine systems with input saturation and state constraints. Based on a singular piecewise Lyapunov function combined with S-procedure and some matrix inequality convexifying techniques, the H-infinity stabilization condition is established and the resilient H-infinity filtering error dynamic system is investigated, and, meanwhile, the domain of attraction is well estimated. Under energy bounded disturbance, the input saturation disturbance tolerance condition is proposed; then, the resilient H-infinity filter is designed in some restricted region. It is shown that the controller gains and filter design parameters can be obtained by solving a family of LMIs parameterized by one or two scalar variables. Meanwhile, by using the corresponding optimization methods, the domain of attraction and the disturbance tolerance level is maximized, and the H-infinity performanceγis minimized. Numerical examples are given to illustrate the effectiveness of the proposed design methods.

Fast Sampling Control of Singularly Perturbed Systems with Actuator Saturation andL2Disturbance

We will consider the problem of fast sampling control for singularly perturbed systems subject to actuator saturation andL2disturbance. A sufficient condition for the existence of a state feedback controller is proposed. Under this controller, the boundedness of the trajectories in the presence ofL2disturbances is guaranteed for any singular perturbation parameter less than or equal to a predefined upper bound. To improve the capacity of disturbance tolerance and disturbance rejection, two convex optimization problems are formulated. Finally, a numerical example is presented to demonstrate the effectiveness of the main results of this paper.

Disturbance tolerance and rejection of discrete switched systems with time-varying delay and saturating actuator

This paper is concerned with the problems of disturbance tolerance and rejection of discrete switched systems with time-varying delay and saturating actuator. Using the switched Lyapunov function approach, a sufficient condition for the existence of a state feedback controller is proposed such that the disturbance tolerance capability of the closed-loop system is ensured. By solving a convex optimization problem with linear matrix inequality (LMI) constraints, the maximal disturbance tolerance is estimated. In addition, the problem of disturbance rejection of the closed-loop system is solved. Two examples are given to illustrate the effectiveness of the proposed method.

Chair's summary: Innate and adaptive immune responses in airway disease.

The lungs are constantly exposed to the external environment, which contains myriad particles and molecules that are potentially antigenic. The respiratory immune system must maintain a state of tolerance, discriminating between potentially harmful pathogens that could promote infectious disease while ignoring innocuous particles such as dust or pollen. These immunological control systems develop during early life and are greatly influenced by genetics, infection history, age, and environmental conditions such as smoking, diet, and pollution. Asthma, emphysema, chronic obstructive pulmonary disease (COPD) and pneumonia are thought to occur as a consequence of disruption of these control systems and disturbance of respiratory tolerance. Conversely, excessive immunological tolerance may lead to ineffective clearance of infectious agents such as influenza, tuberculosis, respiratory syncytial virus, or Streptococcus pneumoniae, which in turn may lead to inflammatory lung disease, bronchitis, pneumonia, and sepsis. Respiratory diseases represent an important cause of morbidity and mortality globally, and deaths due to these diseases are increasing worldwide. Moreover, the very young and the elderly are disproportionately represented at the more severe end of the disease spectrum, with asthma being more common in children and COPD and emphysema occurring later in life. It is clear that a better understanding of the basic mechanisms underlying respiratory immune homeostasis is vital to developing novel therapeutic agents and vaccines for disease prevention and control. Traditionally, diseases have been associated specifically with either innate or adaptive immune pathways—for example, innate immunity for infections and COPD or adaptive immune systems for asthma. However, the distinction between the different arms of the immune system is becoming less apparent, and it is clear that most diseases involve contributions from both sides of the immune system. Understanding these interactions is critical in the search for more effective therapies for diseases, which are common and ever-increasing. The focus of the 29th Transatlantic Airway Conference was how innate and adaptive immune system pathways contribute to the development of a variety of lung diseases, such as asthma, COPD, and respiratory infections. The papers that the speakers presented at the meeting covered the broad areas of epithelium–immune system interactions, early effector mechanisms, the influence of the microbiome and host defense mechanisms, and immunomodulatory and regulatory pathways. The talks highlighted novel aspects of the immune system and revealed the complexity of interactions that operate within the lung.

Active Disturbance Rejection Control System Design for a Morphing Wing Structure

AbstractControl system design for a morphing wing structure, which is proposed by NextGen Aeronautics, Inc., is investigated in this paper. The dynamic model of the morphing wing, developed based on the Euler‐Lagrange equation, is nonlinear, multivariable coupled, over‐actuated and uncertain. The allocation‐decoupling controller is designed based on control efficiency and decoupling matrices. For each decoupled subsystem, nonlinear and linear active disturbance rejection control (ADRC) systems are designed and compared. The time‐optimal property and the convergence of nonlinear ADRC are analyzed theoretically based on the isochronic region and Lyapunov theories. The simulation results of the developed control systems show satisfactory performances of decoupling and extreme tolerance of internal uncertainty and external disturbance. The comparison of nonlinear and linear ADRC systems demonstrate that the nonlinear system can provide a little better performance while the linear system can greatly simplify the design procedure. The results indicate that, the methods of control system design proposed in this paper are practical and effective for motion control of complex uncertain dynamical systems.

Finite‐time stability of switched linear systems with subsystems which are not finite‐time stable

Up to now, the potential assumption of most existing results for finite-time stability and finite-time boundedness of switched linear systems is that each subsystem should be finite-time stable or finite-time bounded. If any one subsystem of switched systems is not finite-time stable or finite-time bounded, the previous results may not be true anymore. In this paper, finite-time stability and finite-time boundedness of switched linear systems with subsystems that are not finite-time stable or finite-time bounded are discussed. Sufficient conditions are given under which switched linear systems with subsystems that are not finite-time stable or finite-time bounded is guaranteed to be still finite-time stable or finite-time bounded. The results also show the effect of the switching signals on finite-time stability and finite-time boundedness of switched linear systems. Moreover, finite-time L 2 -gain of switched linear systems with subsystems which are not finite-time bounded is also given to measure its disturbance tolerance capability in the fixed time interval. A numerical example is employed to verify the efficiency of the proposed method.

Reduction of hyperproduction of thyroid autoantibodies in patients without disturbance of the thyroid function: new patents.

A new method of reduction of autoimmune process activity related to the thyroid in patients without signs of thyroiditis is presented in the article (patent of Ukraine No. 103742). New patents and inventions from different countries of the world related to the problem have been analysed. Sixty one patients with a significant disturbance of tolerance to the thyroid antigens in the absence of disturbance of the thyroid function were involved in the research. Twenty two patients with chronic hepatitis C, genotype 1 HCV, receiving antiviral therapy, were also included in the research. Patients were immunized intracutaneously with autoleukocytes for autoimmune process inhibition. After single immunization with autoleukocytes decrease in the level of antibodies against the thyroid antigens was observed in all patients. In some patients without chronic hepatitis C the levels of thyroperoxidase and thyroglobulin antibodies decreased by 50% and more (33.33% and 20.51%, respectively). In patients with ChHC these indices were considerably lower, and the duration of the achieved effect was shorter. However, immunization inhibited activity of immune process in patients with ChHC due to interferon therapy. The suggested method enables to decrease the threat for thyroiditis development even in patients with chronic hepatitis C during antiviral therapy.

$${L}_{2}$$ L 2 -gain analysis and output feedback control for continuous-time switched systems with actuator saturation

This paper is concerned with the problem of \(L_2\)-gain analysis for a class of continuous-time switched systems with actuator saturation. Different from the existing results using the state-dependent switching approach, a linear parameter-varying output feedback controller with the time-dependent switching mechanism is designed such that the overall system is exponentially stable and with disturbance tolerance capacity and \(L_2\) gain. Further, the proposed controller is insured by introducing the slack matrices to have less conservatism, which maximizes the ellipsoid where the state trajectories starting from the origin will remain. Sufficient conditions for the existence of the switching and output feedback control law are derived in terms of linear matrix inequalities. Finally, a practical example is given to show the effectiveness of the proposed method.

Disturbance tolerance and H ∞ control of port-controlled hamiltonian systems in the presence of actuator saturation

This paper investigates the disturbance tolerance and H ∞ control of multi-input Port-Controlled Hamiltonian (PCH) systems in the presence of actuator saturation which may be not openloop stable. A simple condition is derived under which trajectories starting from the origin will remain inside an ellipsoid. The disturbance tolerance ability of the closed-loop system under a given feedback control law is measured by the size of this ellipsoid. Based on the above mentioned condition, the problem of disturbance tolerance can be expressed in the form of the linear matrix inequalities (LMIs) optimization problem with constraints. In addition, an H ∞ control approach is presented to attenuate the disturbances, and disturbance rejection ability in terms of L 2 gain is also determined by the solution of an LMI optimization problem. Study of an illustrative example with simulations shows the effectiveness of the methods proposed.

L2‐gain fault tolerant control of singular Lipschitz systems in the presence of actuator saturation

SummaryIn this paper, the L2‐gain fault tolerant control for a class of singular systems in the presence of Lipschitz nonlinearity and actuator saturation is investigated. Both fixed‐gain controller and adaptive controller are designed such that the closed‐loop system is regular, impulse‐free, and stable. In contrast with our previous work where the saturation avoidance method is adopted, here we resort to the saturation allowance approach to tackle this issue. As a result, the obtained criterion guaranteeing the regularity, impulse‐free, and stability properties does not involve information about the initial state a prior comparing with our previous results. Moreover, the structural constraint on the feedback control gain is removed. An optimization algorithm is formulated to find the largest disturbance tolerance capability. In addition, the L2‐gain performance of the closed‐loop system is also addressed based on the aforementioned results. An example is given to validate the theoretical results. Copyright © 2014 John Wiley & Sons, Ltd.

Robust stabilization and l 2-gain control of uncertain discrete-time constrained piecewise-affine systems

In this paper, the robust stabilization and l 2 gain control are investigated for a class of uncertain discrete-time piecewise-affine systems with input saturation and state constraints. By introducing some auxiliary feedback matrices, the LMI-based local stabilization condition is firstly proposed, where the designed controller can be saturated, and meanwhile, the domain of attraction is well estimated. Under energy bounded disturbance, the disturbance tolerance condition is proposed under which all trajectories starting from the origin will remain inside a bounded state region, then the l 2-gain controller is designed in the restricted region. Finally, numerical examples and simulations illustrate the effectiveness and the reduced conservativeness of the proposed results.

River flooding as a driver of polygon dynamics: modern vegetation data and a millennial peat record from the Anabar River lowlands (Arctic Siberia)

Abstract. The spatial and temporal variability of a low-centred polygon on the eastern floodplain area of the lower Anabar River (72.070° N, 113.921° E; northern Yakutia, Siberia) has been investigated using a multi-method approach. The present-day vegetation in each square metre was analysed, revealing a community of Larix, shrubby Betula, and Salix on the polygon rim, a dominance of Carex and Andromeda polifolia in the rim-to-pond transition zone, and a predominantly monospecific Scorpidium scorpioides coverage within the pond. The total organic carbon (TOC) content, TOC / TN (total nitrogen) ratio, grain size, vascular plant macrofossils, moss remains, diatoms, and pollen were analysed for two vertical sections and a sediment core from a transect across the polygon. Radiocarbon dating indicates that the formation of the polygon started at least 1500 yr ago; the general positions of the pond and rim have not changed since that time. Two types of pond vegetation were identified, indicating two contrasting development stages of the polygon. The first was a well-established moss association, dominated by submerged or floating Scorpidium scorpioides and/or Drepanocladus spp. and overgrown by epiphytic diatoms such as Tabellaria flocculosa and Eunotia taxa. This stage coincides temporally with a period in which the polygon was only drained by lateral subsurface water flow, as indicated by mixed grain sizes. A different moss association occurred during times of repeated river flooding (indicated by homogeneous medium-grained sand that probably accumulated during the annual spring snowmelt), characterized by an abundance of Meesia triquetra and a dominance of benthic diatoms (e.g. Navicula vulpina), indicative of a relatively high pH and a high tolerance of disturbance. A comparison of the local polygon vegetation (inferred from moss and macrofossil spectra) with the regional vegetation (inferred from pollen spectra) indicated that the moss association with Scorpidium scorpioides became established during relatively favourable climatic conditions, while the association dominated by Meesia triquetra occurred during periods of harsh climatic conditions. Our study revealed a strong riverine influence (in addition to climatic influences) on polygon development and the type of peat accumulated.

Biomass and Stored Carbohydrate Compensation after Above-Ground Biomass Removal in a Perennial Herb: Does Environmental Productivity Play a Role?

Many plant species are able to tolerate severe disturbance leading to removal of a substantial portion of the body by resprouting from intact or fragmented organs. Resprouting enables plants to compensate for biomass loss and complete their life cycles. The degree of disturbance tolerance, and hence the ecological advantage of damage tolerance (in contrast to alternative strategies), has been reported to be affected by environmental productivity. In our study, we examined the influence of soil nutrients (as an indicator of environmental productivity) on biomass and stored carbohydrate compensation after removal of aboveground parts in the perennial resprouter Plantago lanceolata. Specifically, we tested and compared the effects of nutrient availability on biomass and carbon storage in damaged and undamaged individuals. Damaged plants of P. lanceolata compensated neither in terms of biomass nor overall carbon storage. However, whereas in the nutrient-poor environment, root total non-structural carbohydrate concentrations (TNC) were similar for damaged and undamaged plants, in the nutrient-rich environment, damaged plants had remarkably higher TNC than undamaged plants. Based on TNC allocation patterns, we conclude that tolerance to disturbance is promoted in more productive environments, where higher photosynthetic efficiency allows for successful replenishment of carbohydrates. Although plants under nutrient-rich conditions did not compensate in terms of biomass or seed production, they entered winter with higher content of carbohydrates, which might result in better performance in the next growing season. This otherwise overlooked compensation mechanism might be responsible for inconsistent results reported from other studies.

Tolerance of human approaches by Common Mynas along an urban-rural gradient

Successful urban colonisation by birds requires tolerance of many disturbances and avoidance of chronic stress and major disruption to critical activities. Habituation may be involved in acquiring tolerance of human proximity, in which case tolerance should vary with the degree of opportunity to learn that most humans do not present a threat and should therefore vary with human population density. We studied Common Mynas (Acridotheres tristis) in the urban, suburban, peri-urban and surrounding rural zones of Melbourne, Australia, to determine whether flight-initiation distance (FID) and time allocated to anti-predator vigilance increased along this gradient from the urban to the rural zone. This gradient encompassed a 143-fold variation in average human population density during daylight hours. Urban and suburban Mynas had a 2.3-5.7 times shorter FID, were 1.6-2.5 times less likely to retreat by flying and were 1.9-3.1 times more likely to flee >5 m than their peri-urban and rural conspecifics. Fleeing behaviour was not strongly correlated with estimated human population density, but exhibited an apparent ‘step’ in response at the suburban-peri-urban divide. Vigilance effort did not vary significantly between zones. This suggested that habituation did not occur with respect to surveillance for people, although surveillance presumably encompassed other predators too. Similar foraging effort and rates of food acquisition among zones could suggest that food abundance per individual was similar in urban and rural environments for Common Mynas, although this requires direct measurement.

Finite‐time stability and finite‐time weighted L 2 ‐gain analysis for switched systems with time‐varying delay

Finite-time stability and finite-time boundedness for a class of switched linear systems with time-varying delay are studied. Sufficient conditions which guarantee switched linear systems with time-varying delay finite-time stable or finite-time bounded are presented. These conditions are delay-dependent and are given in terms of linear matrix inequalities. Average dwell time of switching signals is also given such that switched linear systems are finite-time stable or finite-time bounded. Moreover, finite-time weighted L2 -gain of switched linear systems with time-varying delay are also given to measure its disturbance tolerance capability in the fixed time interval. Detail proofs are accomplished by using multiple Lyapunov-like functions. An example is employed to verify the efficiency of the proposed method.

Disturbance tolerance and rejection of discrete-time stochastic systems with saturating actuators

This paper considers the problems of disturbance tolerance and disturbance rejection capabilities of discrete-time stochastic systems with saturating actuators. We consider two classes of disturbances whose energy and magnitudes are bounded. A simple condition is given under which any trajectories starting from a certain ellipsoid will remain inside an outer ellipsoid. Invariant sets of criteria are presented. Based on the derived condition, the problems of disturbance tolerance and rejection capabilities of the closed-loop system under a given state feedback law are solved. The effectiveness of these results is demonstrated by a simulation example.

Boiled, tumbled, burned, and heated: seed scarification techniques for Munro's globemallow appropriate for large-scale application

Physically dormant seeds of Munro’s globemallow ( Sphaeralcea munroana (Douglas) Spach [Malvaceae]) were scarified by boiling, tumbling, burning, dry-heating, and burning + heating treatments in an attempt to find an effective, operational, largescale treatment for nurseries and restoration activities. Results indicate that out of the tested treatments, seed germination was highest following boiling water scarification (49%). All other treatments did not achieve significant improvements in germination compared to the control. Findings should improve the use of this cool-season peren nial for restoration in the Great Basin, where its effectiveness in soil stabilization; its tolerance of disturbance, drought, and extreme temperatures; and its importance as a food source for animals make it a suitable candidate. In addition, the tested treat ments should serve as a foundation for further method refinement.

The Vigilance Promoting Drug Modafinil Modulates Serotonin Transmission in the Rat Prefrontal Cortex and Dorsal Raphe Nucleus. Possible Relevance for Its Postulated Antidepressant Activity

Modafinil, (RS)-2-(diphenylmethylsulfinyl)acetamide derivative (Modiodal, Provigil), is a vigilance-promoting agent which reduces sleep episodes by improving wakefulness. It is approved by the USA FDA for narcolepsy, shiftwork sleep disorder and obstructive sleep apnoea with residual excessive sleepiness despite optimal use of continuous positive airway pressure. Unlike classical psychostimulants such as amphetamine and amphetamine-like compounds, the awaking effect of modafinil is not associated with a disturbance of nighttime sleep, tolerance, and sensitization. Its precise mechanism of action is still unclear. In animal studies, modafinil and its analogues have been shown to modify dopaminergic, noradrenergic, glutamatergic, GABAergic, serotoninergic, orexinergic, and histaminergic pathways. Besides the approved use in sleep disorders, modafinil has been investigated for the treatment of fatigue, impaired cognition and some symptoms in a number of other disorders. In particular, clinical studies seem to indicate that the drug could be particularly successful in the treatment of depression and its use in major depressive and bipolar disorders, has been suggested. However, the molecular mechanisms underlying this possible effect are still unknown. The present review firstly summarizes the structure-activity relationship studies and the mechanism of action of modafinil and its related compounds. Then, it focuses on data demonstrating that modafinil interacts with serotonin neuronal activity in rat frontal cortex and dorsal raphe nucleus, two brain areas linked together and involved in depression. Preclinical and clinical evidence of a positive interaction between modafinil and classical antidepressant drugs, is also summarized.