Effects Of Environmental Disturbances Research Articles

Robust fuzzy controller design for dynamic positioning system of ships

This paper presents a robust fuzzy controller design approach for dynamic positioning (DP) system of ships using optimal H∞ control techniques. The H∞ control technique is used to exterminate the effects of environmental disturbances. Firstly, a Takagi-Sugeno (TS) fuzzy model is applied to approximate the nonlinear DP system. Next, linear matrix inequality (LMI) and general eigenvalue problem (GEVP) methods are employed to find a positive definite matrix and controller gains. The stability of the controller is proven by using Lyapunov stability theorems. A positive definite matrix is determined by solving LMI equations using robust control toolbox available in MATLAB. The obtained positive definite matrix proves that the designed fuzzy controller is stable. Finally, a uniformly ultimately bound (UUB) and control performance for the dynamic position system is guaranteed. Simulation is carried out, and results are presented to validate the effectiveness and performance of the proposed control system.

Effects of environmental disturbance on phenotypic variation: an integrated assessment of canalization, developmental stability, modularity, and allometry in lizard head shape.

When populations experience suboptimal conditions, the mechanisms involved in the regulation of phenotypic variation can be challenged, resulting in increased phenotypic variance. This kind of disturbance can be diagnosed by using morphometric tools to study morphological patterns at different hierarchical levels and evaluate canalization, developmental stability, integration, modularity, and allometry. We assess the effect of urbanization on phenotypic variation in the common wall lizard (Podarcis muralis) by using geometric morphometrics to assess disturbance to head shape development. The head shapes of urban lizards were more variable and less symmetric, suggesting that urban living is more likely to disturb development. Head shape variation was congruent within and across individuals, which indicated that canalization and developmental stability are two related phenomena in these organisms. Furthermore, urban lizards exhibited smaller mean head sizes, divergent size-shape allometries, and increased deviation from within-group allometric lines. This suggests that mechanisms regulating head shape allometry may also be disrupted. The integrated evaluation of several measures of developmental instability at different hierarchical levels, which provided in this case congruent results, can be a powerful methodological guide for future studies, as it enhances the detection of environmental disturbances on phenotypic variation and aids biological interpretation of the results.

Meiofauna and its sedimentary environment as an integrated indication of anthropogenic disturbance to sandy beach ecosystems

The accuracy and applicability of the Nematode/Copepod index (N/C) in monitoring the effects of environmental disturbances is controversial. In this study, we used an integrated approach that includes both meiofauna and the sedimentary environment to demonstrate a tourism-induced disturbance gradient among sampled beaches. We also analysed the relationships between meiofauna and environmental factors. The results showed that disturbed beaches were characterised by high values of meiofauna abundance, chlorophyll a content, total organic carbon content and N/C but lower levels of dissolved oxygen. The chlorophyll a and dissolved oxygen contents were found to be the most important factors for explaining the disturbance gradient amongst the beaches. The N/C index had a positive relationship with chlorophyll a and a negative relationship with dissolved oxygen. There was no significant relationship between N/C index and total organic carbon content.

Improving environmental noise suppression for micronewton force sensing based on electrostatic by injecting air damping.

A micro/nano force can be traced to the International System of Units by means of an electrostatic force balance weight system. However, the micro/nano force measurement system is susceptible to environmental disturbances. Various methods have been proposed to reduce the effect of environmental disturbances and obtain high resolution and fast response. In this paper, we introduce a combination of air damping and inherent damping from the internal molecular friction of spring suspension. This will optimize system stability and improve environmental noise suppression. Results from the air damping model show that the damping ratio increases from 0.0005 to 0.1, which improves the vibration resistance. We found that the system with air damping has the advantages of fast response and low scatter.

Sensitivity of food webs to nitrogen pollution: a study of three transitional water ecosystems embedded in agricultural landscapes

1 - Transitional water ecosystems constitute extremely complex and productive environments, a preferred route of migrating birds and optimal nursery locations for many fish species. In these interesting environments, descriptors of trophic relationships between species in a web have been suggested as potential integrative and sensitive endpoints for anthropogenic pressure. 2 - To better understand the effects of environmental disturbance on the resident macroinvertebrate assemblage structure, we analysed food webs in three neighbouring transitional water ecosystems located along the Thyrrenian coastal area of Central Italy (Lake Caprolace, Lake Fogliano and Lake Sabaudia), which are affected by different inputs of nitrates from agricultural, farming and urban activities. 3 - Macrozoobenthos, aquatic macrophytes and attached macroalgae, leaf detritus from sediments and suspended organic matter in the water column were sampled at four sites in each ecosystem and stable isotope analysis (C and N) was carried out in order to describe trophic pathways and the food web structure. 4 - a15N values of macroinvertebrates increased from Caprolace to Sabaudia according to increasing nitrate concentration derived from organic sources. Macrozoobenthic assemblages varied in species composition with the lowest biodiversity found in Sabaudia, the most polluted ecosystem. Also proportion of primary consumers, predators and omnivorous species varied, with cascade effects on food web topology and nutrient flow pathways. 5 - In particular, omnivorous and generalist predators were more numerous in Sabaudia, where food chains were longer and webs less compartmentalised than in Caprolace and Fogliano. In Sabaudia a lower level of web robustness to species loss was also observed. 6 - These results suggest that nitrogen pollution can be responsible of evident changes in the architecture of biodiversity between ecosystems, determining less robust trophic structures with strong implication for biodiversity management and conservation.

Effect of environmental disturbance on the population of sandflies and leishmania transmission in an endemic area of Venezuela.

The exploitation of new wilderness areas with crops is increasing and traditional crop substitution has been modified by new more productive crops. The results show the anthropogenic disturbance effect on the sandflies population and Leishmania transmission in endemic areas of Venezuela. Three agroecosystems with variable degrees of ecological disturbance, forest (conserved), cacao (fragmented), and orangery (disturbed), were selected. Four methods to sandfly capture were used; the specimens were identified and infected with Leishmania. Diversity, population structure, ANOVA, Tukey test, and simple correlation analysis were carried out. Shannon traps were able to capture 94.7% of the total sandflies, while CDC light traps, Sticky traps, and direct suction just captured 2.2%, 1.2%, and 0.9%, respectively. The results showed the effect of ecological disturbance degree on the composition of sandflies and population structure, revealing a dominance level increased but decreased on the diversity and richness of sandflies species in the greatest ecological disturbance area in relation to areas with less organic disturbance. Environments more disturbed cause adaptability of certain species such as Lutzomyia gomezi and Lutzomyia walkeri. These changes on the composition of sandflies population and structure emerging species could cause increasing of leishmaniasis transmission.

Dung beetle communities as biological indicators of riparian forest widths in southern Brazil

Riparian forests provide important habitat for many wildlife species and are sensitive to landscape change. Among terrestrial invertebrates, dung beetles have been used to investigate the effects of environmental disturbances on forest structure and diversity. Since many studies demonstrated a negative response of dung beetle communities to increasing forest fragmentation, and that most dung beetle species had a more pronounced occurrence during warmest seasons, three hypotheses were tested: (1) Scarabaeinae richness, abundance, diversity and evenness are lower in thinner riparian zone widths than in wider widths during the warmest seasons; (2) Scarabaeinae richness and abundance are positively influenced by leaf litter coverage and height and canopy cover; and (3) Scarabaeinae composition varies with the reduction in riparian vegetation and among annual seasons. We selected four fragments with different riparian zone widths in three secondary streams in southern Brazil. In each fragment, four sampling periods were carried out seasonally between spring 2010 and winter 2011. We collected dung beetles using pitfall traps with two types of bait. We collected 1289 specimens distributed among 29 species. In spring and summer, dung beetle richness was higher in fragments with the widest riparian zone than in those with a thinner riparian zone, and it did not vary between fragments in fall and winter seasons. Dung beetle abundance did not differ among fragments with different riparian zone widths, but it was higher in spring and summer than fall and winter. Richness and abundance were positively influenced by leaf litter. While dung beetle diversity was higher in fragments with wider riparian zone widths than in those with thinner widths, the evenness was similar among fragments. Dung beetle composition differed between the fragments with the widest and thinnest riparian zones, and it also varied among the seasons. Our results suggest that decreased riparian zones affect negatively to dung beetle community structure in southern Brazil. Fragments with thinner riparian zones had lower beetle richness in warmest seasons and an altered community composition. In this sense, the dung beetles are potentially good indicators of riparian forest fragmentation since some species were indicators of a particular riparian zone width. From a conservation perspective, our results demonstrate that the new Brazilian Forest Code will greatly jeopardize not only the terrestrial and aquatic biodiversity of these ecosystems, but also countless other ecological functions.

Unity through nonlinearity: a unimodal coral–nutrient interaction

The magnitude and direction of biological effects of environmental disturbances can vary considerably, especially among studies that use presence/absence manipulations. Because nonlinearities (e.g., humped relationships) are common in biological systems, this heterogeneity in effects may arise if systems are similar in their responses but specific studies use few (e.g., two) levels, or a narrow range, of a factor. To test whether nonlinearity can explain heterogeneous responses to a common environmental disturbance, I examined the effect of nutrient enrichment on coral growth, which has been previously shown using simple (e.g., two-level) manipulations to yield positive, negative, or neutral responses. I subjected corals (Porites) to a nutrient gradient in situ for 28 days. Coral growth rate increased (2.4-fold) then decreased (2.7-fold) with enrichment, returning to near-ambient values at the highest nutrient levels. This unimodal response could explain disparities among past findings and provides a compelling case for using regression designs to understand heterogeneity within ecological interactions.

Advanced Aperture Synthesis by Wave-Front Combination in Generalized Phase-Shifting Interferometry

An approach to improve the image quality by aperture synthesis in generalized phase-shifting interferometry is proposed. The aperture of the holographic system is enlarged by increasing the recording area to receive a more diffusive spectrum by moving a singular CCD. The sub-object wave fronts are combined with the index of their intensities. This method can avoid the negative effect of environmental disturbance and improve the synthesis efficiency by hundreds of times. The optical experiments have shown that it is simple and robust to stitch the complex object wave front accurately and to improve the imaging quality greatly, especially for the recording of large scale objects.

The Effects of Environmental Disturbances on Tumor Growth

In this study, the analytic expressions of the steady probability distribution of tumor cells were established based on the steady state solution to the corresponding Fokker-Planck equation. Then, the effects of two uncorrelated white noises on tumor cell growth were investigated. It was found that the predation rate plays the main role in determining whether or not the noise is favorable for tumor growth.

Mathematical modeling, optimal design and control of an SCR reactor for NOx removal

The elimination of nitrogen oxides (NOx) is an important issue for global environment. This paper deals with the model development, optimal design and feedback control of an SCR (selective catalytic reduction) reactor for NOx removal. A 3D dynamic simulation model for use to investigate the reaction behavior and the transport phenomena in the catalytic filter of the SCR reactor is proposed. To estimate the model's kinetic parameters from experimental data, an optimization technique that integrates Taguchi method, a real-coded genetic algorithm and a neural network auxiliary model is developed. With the proposed dynamic model, we investigated the effects of the key parameters, such as the gas hourly space velocity, operating temperature and the amount of ammonium used, on the NOx conversion and NH3 slip phenomena. To improve the NOx abatement performance, the proposed optimization technique is then applied to search for a set of best operation conditions for the SCR reactor. The obtained results indicate that the optimized SCR can achieve the NOx reduction rate up to 99.93%, which is over 9% better in performance than the previously reported one in the literature. Besides, the optimal operating temperature is considerably lower and the emission of ammonium from the reactor is insignificant. Compared with conventional designs, the proposed design is much better in energy savings and is environment-friendly. To attenuate the negative effects of environmental disturbances on reactor's performance, we implemented a direct adaptive control strategy to the SCR reactor. The stability of the control system is theoretically guaranteed with a Lyapunov-based approach. Extensive simulation results show that the learning-type, nonlinear control strategy presents significantly much better NOx reduction performance than a conventional IMC-PI controller, especially when facing process uncertainties and disturbances.

Oscillator phase noise: systematic construction of an analytical model encompassing nonlinearity

This paper offers a derivation of phase noise in oscillators resulting in a closed-form analytic formula that is both general and convenient to use. This model provides a transparent connection between oscillator phase noise and the fundamental device physics and noise processes. The derivation accommodates noise and nonlinearity in both the resonator and feedback circuit, and includes the effects of environmental disturbances. The analysis clearly shows the mechanism by which both resonator noise and electronics noise manifest as phase noise, and directly links the manifestation of phase noise to specific sources of noise, nonlinearity, and external disturbances. This model sets a new precedent, in that detailed knowledge of component-level performance can be used to predict oscillator phase noise without the use of empirical fitting parameters.

Enhanced Resolution of Lossy Interferometry by Coherent Amplification of Single Photons

In the quantum sensing context most of the efforts to design novel quantum techniques of sensing have been constrained to idealized, noise-free scenarios, in which effects of environmental disturbances could be neglected. In this work, we propose to exploit optical parametric amplification to boost interferometry sensitivity in the presence of losses in a minimally invasive scenario. By performing the amplification process on the microscopic probe after the interaction with the sample, we can beat the losses' detrimental effect on the phase measurement which affects the single-photon state after its interaction with the sample, and thus improve the achievable sensitivity.

Natural habitat change, commercial fishing, climate, and dispersal interact to restructure an Alaskan fish metacommunity

The metacommunity concept has recently been described to account for the roles of dispersal in regulating community structure. Despite its strong theoretical basis, there exist few large-scale and long-term examples of its applicability in aquatic ecosystems. In this study we used a long-term dataset (1961-2007) on the relative abundances of the dominant limnetic fishes from two interconnected lakes to investigate the synergistic effects of naturally declining lake volume (approximately 50% in 50 years), climate variation, fishery management, and dispersal on community composition. We found a marked shift in fish community composition and variability during a period of rapid natural habitat change; however, the change was most apparent in the downstream, more stable lake of the system rather than at the site of disturbance. Multivariate analysis suggested significant shifts in community composition and variability in the downstream lake. Results indicated that the community composition in both lakes was best explained by habitat loss in the upper watershed and the number of spawning adult sockeye salmon the previous year (reflecting both natural processes and commercial fishing). Furthermore, communities exhibited site-specific responses to climatic conditions (e.g., index of the Pacific Decadal Oscillation), whereby the upper lake responded to climate within a given year and with a 1-year time lag, whereas the downstream community responded only with a 1-year lag. We attribute this difference largely to downstream dispersal and recruitment of fish from the upper lake. Thus, we suggest that the interconnected nature of the communities in this system provides a useful and large-scale example of the metacommunity concept, whereby the effects of environmental disturbance on community structure ultimately depend on the effects of these disturbances on dispersal among ecosystems.

Modelling the thermal response of permafrost terrain to right-of-way disturbance and climate warming

Field observations from a permafrost thermal monitoring network in the Norman Wells pipeline corridor Northwest Territories, and thermal modelling have been utilized to gain insights into the relative effects that both environmental disturbance associated with vegetation clearance and ongoing climate warming have on the ground thermal regime in the vicinity of a right-of-way (ROW). This analysis was conducted to generate information that may aid engineering design of northern development projects, the assessment of environmental impacts associated with these projects and the development of related environmental monitoring and management plans. The separate and combined effects of environmental disturbance and climate change on the ground thermal regime beneath and adjacent to a ROW in an area of discontinuous permafrost are investigated using a two-dimensional finite element thermal model. A simplified soil profile consisting of one metre of peat overlying a fine-grained mineral soil is considered. A limited set of scenarios consider the effect of: ROW clearing alone; ROW clearing followed by vegetation recovery; ROW clearing combined with climate warming of 0.5 °C per decade; and ROW clearing followed by vegetation recovery combined with climate warming. Simulation results for warm thin permafrost (mean annual ground temperature above − 1 °C; 20 m thick) indicate that the combined effects of ROW disturbance and climate warming are likely to result in permafrost degradation within 20 to 40 years, and ROW-disturbance effects may extend off-ROW under scenarios of climate warming. In colder and thicker permafrost (mean annual ground temperature below − 1 °C; 50 m thick), the combined effect of climate warming and ROW disturbance will not likely lead to talik formation within 50 years, although seasonal thaw penetration will increase. For the range in ground thermal conditions considered, the results of the simulations indicate that the effects of ROW disturbance outweigh those associated with climate warming in the initial 10 to 15 years following disturbance, although climate warming becomes important over longer time periods. Climate warming and its influence on the ground thermal regime should therefore be incorporated into the design of northern development projects (and assessment of associated environmental impacts) expected to operate over two decades or more and where ground instability associated with permafrost thawing is a concern.

Modeling the effects of environmental disturbance on wildlife communities: avian responses to prescribed fire

Prescribed fire is a management tool used to reduce fuel loads on public lands in forested areas in the western United States. Identifying the impacts of prescribed fire on bird communities in ponderosa pine (Pinus ponderosa) forests is necessary for providing land management agencies with information regarding the effects of fuel reduction on sensitive, threatened, and migratory bird species. Recent developments in occupancy modeling have established a framework for quantifying the impacts of management practices on wildlife community dynamics. We describe a Bayesian hierarchical model of multi-species occupancy accounting for detection probability, and we demonstrate the model's usefulness for identifying effects of habitat disturbances on wildlife communities. Advantages to using the model include the ability to estimate the effects of environmental impacts on rare or elusive species, the intuitive nature of the modeling, the incorporation of detection probability, the estimation of parameter uncertainty, the flexibility of the model to suit a variety of experimental designs, and the composite estimate of the response that applies to the collection of observed species as opposed to merely a small subset of common species. Our modeling of the impacts of prescribed fire on avian communities in a ponderosa pine forest in Washington indicate that prescribed fire treatments result in increased occupancy rates for several bark-insectivore, cavity-nesting species including a management species of interest, Black-backed Woodpeckers (Picoides arcticus). Three aerial insectivore species, and the ground insectivore, American Robin (Turdus migratorius), also responded positively to prescribed fire, whereas three foliage insectivores and two seed specialists, Clark's Nutcracker (Nucifraga columbiana) and the Pine Siskin (Carduelis pinus), declined following treatments. Land management agencies interested in determining the effects of habitat manipulations on wildlife communities can use these methods to provide guidance for future management activities.

Intelligent adaptive control and monitoring of band sawing using a neural-fuzzy system

In bandsaw machines, it is desired to feed the bandsaw blade into the workpiece with an appropriate feeding force in order to perform an efficient cutting operation. This can be accomplished by controlling the feed rate and thrust force by accurately detecting the cutting resistance against the bandsaw blade during cutting operation. In this study, a neural-fuzzy-based force model for controlling band sawing process was established. Cutting parameters were continuously updated by a secondary neural network, to compensate the effect of environmental disturbances. Required feed rate and cutting speed were adjusted by developed fuzzy logic controller. Results of cutting experiments using several steel specimens show that the developed neural-fuzzy system performs well in real time in controlling cutting speed and feed rate during band sawing. A material identification system was developed by using the measured cutting forces. Materials were identified at the beginning of the cutting operation and cutting force model was updated by using the detected material type. Consequently, cutting speed and feed rate were adjusted by using the updated model. The new methodology is found to be easily integrable to existing production systems.

Flesh flies species (Diptera: Sarcophagidae) from a grassland and a woodland in a Nature Reserve of Buenos Aires, Argentina

Temporal changes of flesh flies abundance were simultaneously recorded at monthly intervals during a year in a woodland and in a grassland at the "Reserva Ecológica Costanera Sur" (RECS), Buenos Aires city, Argentina. Samples were taken at monthly intervals (February 2004-January 2005). Hourly captures of adult flies (10:00 am - 04:00 pm) were taken each sampling date with a hand net. Temperature was recorded at each hourly capture. The baits used were 200 g of rotten cow liver and 200 g of fresh dog faeces. Records of abundance included only species whose abundance was > or = 30 individuals accumulated during the whole sampling period. Considering overall abundance, a non-parametric Chi-square test was used to estimate deviations of an expected habitat and bait preference ratios of 1:1. The same criterion was applied to include species in a contingency table to describe their seasonality. The final matrix included four species whose associations to seasons were analyzed by using a Correspondence Analysis. To normalize the data, a log 10 (n+1) transformation was applied prior to the analysis of correlation. Pearson product-moment correlations were used to examine the relationship between flesh-fly abundance with temperature and habitat preference. The entire sample accumulated 1 305 individuals and 18 species. The flies were more abundant in the grassland than in the woodland. Microcerella muehni, Oxysarcodexia paulistanensis, O. varia and Tricharaea (Sarcophagula) occidua exhibited the higher relative abundance, representing the remaining species less than 8% of the entire sample. Most of the recorded species showed preference for faces as bait. Concerning the dominant species, all of them but M. muehni, a suggestively termophobic species, prevailed in late spring-summer. The observed species arrangement at both sites indicates low species diversity and equitability and high information per individual in the average. The referred community traits would indicate the possible effects of environmental disturbance due to the proximity of study sites to dense urban settlements.

Desplazamientos de la iguana verde, Iguana iguana (Squamata: Iguanidae) durante la estación seca en La Palma, Veracruz, México

The green iguana (Iguana iguana) is said to be primarily sedentary, although the females travel long distances to nest. Displacement patterns must be known to help predict the effects of environmental disturbance on iguanas' survival. We studied nesting season (February-July) movements in La Palma, Los Tuxtlas, Veracruz, Mexico (18 degrees 33' N, 95 degrees 03' W). Individual movements and activity were monitored by radio tracking. The transmitters were implanted surgically in eight adult iguanas (four males and four females). Snout vent length (SVL) was used to determine the relationship between size of the body and size of home range. To estimate the size of home range, three or more points were used. Minimum convex polygons estimates of home range were calculated with McPAAL. The iguanas were radio-located between 23 and 30 occasions, mainly in trees (56% between 3-9 m); only 4% were localized under a height of 3 m (forest floor). The occupation area mean was larger for males (9,158.06+/-3,025.3 m2 vs. 6,591.24+/-4,001.1 m2) although the differences were not significant (t= 0.51, p>0.05). SVL was correlated with home range (r= 0.76; gl= 7; p<0.05). Breeding males defended their home range vigorously against other adult males. We observed one separate male home range and large portions of overlap between the sexes. The home range generally formed a conglomerate of polygons and only two had linear shapes along the river: apparently iguanas use the riparian vegetation for foraging. The females display two strategies for nesting: 1) moving to the sandy area near the sea or, 2) laying eggs near the river, in loam. Iguanas responded to habitat fragmentation and reduction by modifying their nesting strategy.

Optimal Control Laws for Momentum-Wheel Desaturation Using Magnetorquers

E ARTH-pointing satellites are expected to maintain the localvertical/local-horizontal attitude in the presence of environmental disturbance effects. In many applications this is achieved by using momentum-wheel systems which continuously exchange angular momentum with the spacecraft (SC) body. Because of secular external disturbances, such as the aerodynamic and solar radiation pressure torque, thewheel will accumulate (or lose) angular momentum, drifting towards its maximum (or minimum) allowed speed limits. Hence, suitable control of the wheel’s angular momentum is required to counteract the influence of a persisting external disturbance torque. An external control torque must be applied to perform the wheel’s momentum dumping and force the angular velocity back into its allowable limits. Magnetic attitude control of spinning and momentum biased SC is one of the earliest techniques employed in attitude stabilization [1–4]. A number of relevant studies on wheel’s momentum dumping using magnetorquers are available, both for low earth orbiting (LEO) SC [5–11] and higher altitude satellites [12–14]. Whereas reaction thrusters allow rapid momentum dumping with a large propellant consumption, the use of magnetorquers provides a cheaper desaturation maneuver, without the use of any propellant. In this Note we derive the control laws for a satellite equippedwith magnetic dipoles which allow an optimal momentum-wheel desaturation. To this end, we minimize a cost function taking into account both the maneuvering time and the power consumption. The problem is solved through an indirect approach, and the dependence of the optimal control law on the SC orbital parameters and its characteristics is discussed. Also, the minimum time and the minimum power problem are solved by using a semi-analytical and a closed-form solution, respectively. A number of numerical simulations based on the proposed methodology have been applied to theALMASatMicrosatellite [15], whose program was established and developed at the University of Bologna in 2003.