Effects Of Disturbances Research Articles

Landscape patterns of carbon fluxes in natural and disturbed ice-wedge-polygon tundra

ABSTRACT The degradation of ice-rich permafrost ecosystems due to climate change and infrastructure development strongly impacts carbon exchange dynamics in tundra landscapes. This study investigates the effects of surficial geology and infrastructure disturbances from road dust and flooding on vegetation and trace gas fluxes in polygonal ice-wedge tundra in arctic Alaska. We compared CO2 and CH4 fluxes from closed-chamber measurements at common landform elements (polygon centers, troughs, and rims) at a natural site and a disturbed site within the Prudhoe Bay Oil Field. Relationships among environmental parameters, plant species composition, and trace gas fluxes were assessed through nonmetric multidimensional scaling. Map extrapolations showed spatial variations in midsummer landscape-level ecosystem productivity and CH4 efflux at the various geologic landforms. Highest carbon uptake occurred in ice-rich drained thaw lake basins with aquatic, graminoid-dominated polygon troughs. In contrast, wet, featureless areas associated with more recently drained, ice-poor thaw lake basins showed a net carbon loss even during summer. The damming effect of road infrastructure led to deeply flooded, minimally vegetated troughs with low ecosystem respiration and high CH4 fluxes close to the road. This work highlights the importance of the complex interactions among surficial geology, landform elements, vegetation type, and disturbance factors in understanding carbon exchange dynamics in ice-rich permafrost environments.

Elevation and Human Disturbance Interactively Influence the Patterns of Insect Diversity on the Southeastern Periphery of the Tibetan Plateau.

The maintenance of biodiversity and ecological balance heavily relies on the diversity of insects. In order to investigate the impacts of elevation and human disturbance, as well as their interactions on insect diversity, we conducted an intensive survey of insects in the Hengduan Mountain Range, which is situated on the southeastern periphery of the Tibetan Plateau in China. A total of 50 line transects were established in this study to investigate the impact of elevation and human disturbance on insect diversity and distribution patterns. Designed insect surveys were conducted at various elevations and levels of human disturbance, and statistical methods such as generalized linear modeling and redundancy analysis were employed for data analysis. The results of this study indicated a negative correlation between insect diversity and elevation. Additionally, moderate disturbance was found to have a positive impact on insect diversity to some extent. The explanatory power of the model for the distribution of insect diversity could be improved if elevation and human disturbance were included as an interaction effect into the model, and there were differences in the effects of human disturbances on insect diversity at different elevation levels. The highest insect diversity was observed under low disturbance conditions below elevation of ~2200 m, whereas above this threshold, insect diversity was the highest under moderate disturbance compared to low disturbance. The response of different insect taxa to the interactions of elevation and human disturbance varied. The findings imply that when formulating strategies for managing insect diversity, it is crucial to thoroughly consider the interaction of environmental factors and disturbance response of individual insect taxa.

Event-triggered model-free adaptive sliding-mode heading control for unmanned surface vehicles under DoS attacks

This article investigates event-triggered model-free adaptive sliding-mode heading control issues for unmanned surface vehicles with dual-channel denial of service (DoS) attacks and bounded disturbances. Initially, we establish a redefined output. Meanwhile, we establish a virtual linear data model based on the redefined output and pseudo-partial-derivative technology. In addition, to reduce the effects of the external disturbance, we introduce the sliding mode control method to enhance the system’s robustness against disturbances. Then, an event-triggered communication scheme is developed to reduce the waste of communication resources. Two compensation schemes are formulated to eliminate the effects of dual-channel DoS attacks. So, the main contributions of the presented method are the enhancement of accuracy, reduction of computational burden, and increased robustness, all of which are demonstrated in the simulation section.

Composition and Diversity of Spiders in the Lian-huo Highway (Shangqiu Section) Shelter Forest and Campus Habitat of Henan Province, China

Background: Spider assemblages, which are easily sampled, are useful indicators that can be used to compare the biodiversity of various environments and assess the effects of disturbances on diversity. Because spiders are generally found in forests in high abundance, they form some good model taxa for biodiversity studies. Methods: The present study compares the composition and diversity of spiders in the Lian-Huo highway (Shangqiu section) shelter forest (HS) and campus habitat (CH) of Henan province, China. Sampling were collected from April to June 2018 and fourth time a month, a total of twenty-four samples were collected. Within each habitat type there were eight sites surveyed which represented a wide geographical spread of the habitats. Result: A total of 3725 individual spiders were collected from the two sites, representing 14 families and 23 species. Guild structure analysis of the collected spiders revealed 4 feeding guilds viz, web weavers, Sheet web weavers, Foliage hunter’s spider and Ambush hunters. The abundance of spiders in the campus habitat is significantly higher than that in Lian-Huo highway (Shangqiu section) shelter forestand the Shannon-Wiener index (H’) (HS=3.3827, CH=2.2007), Simpson index (D) (HS=0.8710, CH=0.7391), Evenness index (J) (HS=2.8391, CH=1.7088) and Richness index (E) (HS=0.7462, CH=0.6362) are significantly higher in the campus habitat than in the Lian-Huo highway (Shangqiu section) shelter forest. These results suggest that increasing the complexity of habitat structure and reducing anthropogenic disturbance is a meaningful way to conserve and restore Spiders diversity.

Appraising Supplier Economic Resilience in the Post-COVID Era

Resiliency is the ability to sustain growth and prosper during adverse disruptions. This translates into continuing to provide profitable service with operational efficiency amidst exceptional situations. At the very minimum, company buyers can view a supplier’s financials as that could convey the vital signs of operational stability, which is the underlying platform of resiliency. In this paper, we view a supplier as an operational process and employ process behavior analysis tools combined with analytics to decipher the operational resiliency of two competing companies. We demonstrate how one can glean operational resiliency by viewing several common financial indicators and their behavior over time. High variability in these indicators reflects a firm’s inability to deal with disturbances that may arise from systemic or external causes. In contrast, stable behavior reflects the ability to self-heal and absorb the effects of disturbances. While many more factors and indicators need to be considered to obtain an overall resiliency picture, this analysis focused on several to demonstrate the approach's potential.

The effects of disturbance on woody species composition, structure and regeneration status in the ura natural forest, Guangua district, Awi Zone, Ethiopia

Ethiopia Province has diverse forest resources. However, it has decreased over time, leaving the country's forest with only remnant patches. Therefore, the present study was conducted to examine the species composition, structure and regeneration status of woody plant species along disturbance gradients. To collect the data, the forests were first stratified into low disturbed (LD), moderately disturbed (MD) and heavily disturbed (HD) groups based on information from reconnaissance site visits and consultations with key informants. Three transect lines were laid systematically 200 m apart, and rectangular plots 10 m∗20 m (200 m2) in length were laid at 50 m intervals along each transect, for a total of 27 plots. The DBH and height of all woody individuals with ≥5 cm and ≥2 m were measured. Seedling and sapling data were recorded in four subplots of 2 m∗5 m (10 m2) respectevly in the opposite corner of the main plot. Woody species density, richness, evenness, diversity, frequency and IVI were determined for each disturbance class, and one-way ANOVA and mean comparison tests were used to examine significant differences among disturbance classes. A total of 37 woody species and 27 families were recorded. Based on structural analysis, only Croton macrostachyus exhibited an inverted J shape. It is concluded that woody species composition was affected by human disturbance. Therefore, a concentrated form of forest conservation should be established to protect against excessive human disturbance.

Effects of coal mining disturbance on spatial and temporal distribution of soil water content in Northwest China‐based on 3D EBK model

AbstractNorthwest China is both an important coal storage base and an ecologically fragile area, and soil water content (SWC) is a key factor limiting the ecological development of Northwest China. Revealing the characteristics of spatial and temporal distribution changes of soil water content in mining areas under coal mining disturbance and the influencing mechanism is crucial for the protection of water resources in mining areas. In this study, the soil water content (depth 0–1000 cm) of a typical coal mine subsidence area in the western part of Shendong Coal Group was monitored in situ for 1 year after mining, and the absolute value, variability, and spatial distribution of soil water content were temporally analysed by combining classical statistics, 2D Ordinary Kriging and 3D Empirical Bayesian kriging spatial interpolation. sequence analysis. The results showed that the shallow SWC (0 ~ 60 cm) was distributed horizontally in bands, and gradually increased along the direction from northwest to southeast; with the increase of coal mining time, the absolute value of SWC decreased by 0.81% ~ 33.58%, and the coefficient of variation decreased and then increased, with the range of variation from 2.19% ~ 34.49%. The deep SWC (100 ~ 1000 cm) was stratified vertically and increased with soil depth, and the shallow and deeper soil moisture would gradually migrate to the middle layer under the influence of coal mining. In addition, this paper accurately portrays the three‐dimensional spatial and temporal distribution of soil water content by the 3D EBK model, which further reveals the mechanism of coal mining's influence on soil water content. This study can provide technical and data support for predicting and evaluating the potential impacts of mining activities on the water cycle, and help mining areas to formulate policies for managing and protecting water resources.

Effect of solar wind disturbances on small-amplitude simultaneous Forbush events during solar cycle 23

The transient and rapid reduction in galactic cosmic ray (GCR) flux intensity, commonly referred to as Forbush decrease (FD), is widely used as a mediator variable in searching for solar-terrestrial weather linkages. Whereas literature in the field is replete with high-amplitude (FD(%) ⩾3) FD-based analyses, the empirical connections between low-amplitude (FD(%) ⩽3) events and Sun-Earth variables are seldom tested. It is recently observed that the dearth of such studies might be due to the daunting task of accurate detection/precise timing of FDs and other transient astrophysical events. Using a sensitive version of the FD detection algorithm, we selected 264, 267, and 206 low amplitude (FD(%) ⩽3) FDs from the daily GCR data of Hermanus (HRMS), Newark (NWRK) and Oulu (OULU) neutron monitor stations respectively during solar cycle 23. A total of 80 simultaneous small-amplitude FDs were identified from the three stations with a simple coincident computer code. Statistically significant correlations at 95% confidence level exist between the planetary K-index (Kp), disturbance storm time index (Dst), planetary A-index (Ap), and the corresponding simultaneous small-amplitude FDs at OULU station, but not found in HRMS and NWRK data. These significant links between the weak FDs and the geomagnetic indices (Kp, Dst, and Ap) at OULU station suggest that the parameters (Kp, Dst, and Ap) are likely connected with some common solar activities.

Multi-UAV adaptive super-twisting integral terminal sliding mode formation control

This paper addresses issues such as model uncertainties, actuator failures, and gust disturbances in multi-quadrotor UAV formation flight. An adaptive super-twisting integral terminal sliding mode control method is proposed, incorporating a ‘Leader-Follower’ formation control strategy. The approach includes designing an adaptive super-twisting integral terminal sliding mode controller and a formation adaptive cooperative controller. Additionally, adaptive gains are utilized to manage the effects of actuator failures, gust disturbances, and ground station interference, ensuring safe formation flight. Simulation and experimental results indicate that the proposed controller can track the target trajectory within a finite time and effectively maintain formation flight.

Resistance of plant diversity to road disturbance: Evidence from the Tibetan Plateau

The expansion of road networks in recent decades has drawn considerable attention due to its impact on biodiversity in high-altitude ecosystems. Here, we conducted a comprehensive field survey to investigate the effects of road disturbance on plant diversity in alpine grasslands on the Tibetan Plateau. Our results indicate that road disturbance caused no significant changes in species richness, Shannon–Wiener’s diversity, or Simpson’s diversity, and the alteration in species composition was limited. These findings demonstrate the robust resistance of alpine grassland plant diversity to road disturbance. Plant diversity exhibited more resistance to road disturbance in regions with more hostile environments, such as plateau sub-frigid regions and alpine steppes. Our study suggests that road construction in the Tibetan Plateau poses limited risk to plant biodiversity.

Effect on Top-Coal Mass Failure under Load–Unload Induced by Shield Support

Prior to being released, the top coal of a fully mechanized caving face typically experiences the effects of mining-induced pressure and disturbances from the hydraulic support’s canopy. To investigate the promoting effect of canopy disturbances in the support-controlled area on the damage of top coal during fully mechanized top-coal caving mining, block instability theory and discrete block numerical simulation methods were employed. The instability modes during the initial support and cyclic disturbance stages were analyzed. The fracture evolution and displacement distribution curves were studied for coal bodies with strengths of 3.1 MPa, 15.0 MPa, and 29.5 MPa under the mining influence and support strengths of 0.5 MPa, 1.0 MPa, and 1.5 MPa during the initial support and cyclic disturbance processes. The results showed that during the initial support stage, the instability of the block-structured coal body exhibited four modes as follows: inter-block breakage, inter-block delamination, intra-block fracture expansion, and inter-block sliding. During the cyclic disturbance stage, the coal body instability showed three modes as follows: inter-block sliding, intra-block fracture expansion, and inter-block rotation. The disturbance from the support had little impact on the fragmentation of both low-strength and high-strength coal bodies. However, small support forces combined with multiple cycles of disturbance had an enhancing effect on the instability of medium-strength block-structured top coal.

Anthropogenic disturbance and competitive avoidance shape the coexistence pattern of macaque species in tropical forests

AbstractThe factors that enable the coexistence of closely related species remain a major question in ecology, particularly in human‐disturbed habitats. The effects of anthropogenic disturbance and interspecific competition can exacerbate the decline in populations of competing species. The adoption of different strategies in responding to anthropogenic disturbances and competitive avoidances may create opportunities for competing species to coexist. However, few studies have explored how disturbance and competition interact to shape species coexistence. In this study, we conducted long‐term and large‐scale camera trap surveys comprising 540 sampling sites from 2017 to 2021 at Xishuangbanna, southwestern China, and deployed a spatiotemporal analysis framework to determine the effect of anthropogenic disturbances and competitive avoidances on the coexistence of three sympatric macaque species: Assamese macaque (Macaca assamensis; MA), northern pig‐tailed macaque (M. leonina; ML), and rhesus macaque (M. mulatta; MM). Macaque species exhibited diverse responses to different types of anthropogenic disturbances. The occurrence probability of MM was positively associated with distance to road and relative abundance of human occurrence, and negatively associated with distance to cropland, which reduces the likelihood of sympatry between MM and the other two species due to their opposing responses to road, cropland, and human occurrence. Conversely, the similar responses to road and cropland increase the sympatry between MA and ML. Three macaque species did not avoid each other through shifting space use or their overall daily activity pattern. However, they delayed using the shared site after other species used it to avoid confrontation. We provide evidence that (1) the spatial co‐occurrence pattern of sympatric macaque species was determined by anthropogenic disturbances rather than by competitive spatial avoidance and (2) fine‐scale temporary avoidance is the strategy to alleviate their interspecific competition. These results enhance our understanding of the underlying mechanisms leading to species coexistence of nonhuman primates in human‐disturbed habitats.

Fungal community composition in arthropogenically-active and non-active northern Borneo caves

Fungal studies are scant within this region of Borneo, and the potential effects of anthropogenic disturbance on fungal communities in Sabahan caves have not been explored. This study involved opportunistic sampling of guano, speleothems, and cavern water from four caves in Sabah, Malaysia, categorised according to the level of anthropogenic activity. The dilution method was used for fungal isolation and abundance calculations. Morphological identification of axenic cultures was conducted, and DNA barcoding of the ITS region of cryptic species corroborated identification. A total of 170 axenic cultures were attained, composed of 69 morphological taxonomic units (MTUs), 33 genera, ten orders, and two divisions – Ascomycota and Basidiomycota. Fifty-seven of the 69 MTUs were identified to the species level. The genera Aspergillus and Penicillium were particularly prevalent, with a combined total of 86 isolations (50.6%). Notably, twelve species were documented for the first time in cave ecosystems of Sabah. The average fungal abundance across all substrates and fungal taxa occurrence was found to be higher in samples found in active caves. A significant difference in relative abundance was observed between active and non-active cave conditions. Beta regression modelling indicated that anthropogenic activity is a significant factor influencing the composition of cave fungal communities. While anthropogenic activity seems to affect cave mycobiomes, especially by selecting for ubiquitous fungi, it is likely not the sole influencing determinant of their composition.

The influence of the disturbing effect of roadways through faults on the faults' stability and slip characteristics

AbstractIn order to mitigate the risk of geological disasters induced by fault activation when roadways intersect reverse faults in coal mining, this paper uses a combination of mechanical models with PFC2D software. A mechanical model is introduced to represent various fault angles, followed by a series of PFC2D loading and unloading tests to validate the model and investigate fault instability and crack propagation under different excavation rates and angles. The results show that (1) the theoretical fault model, impacted by roadway advancing, shows a linear reduction in horizontal stress at a rate of −2.01 MPa/m, while vertical stress increases linearly at 4.02 MPa/m. (2) At field excavation speeds of 2.4, 4.8, 7.2, and 9.6 m/day, the vertical loading rates for the model are 2.23, 4.47, 6.70, and 8.93 Pa/s, respectively. (3) Roadway advancement primarily causes tensile‐compressive failures in front of the roadway, with a decrease in tensile cracks as the stress rate increases. (4) An increase in the fault angle leads to denser cracking on the fault plane, with negligible cracking near the fault itself. The dominant crack orientation is approximately 90°, aligned with the vertical stress.

Nanosatellite Design Considerations for a Mission to Explore the Propellant Sloshing Problem

Sloshing Platform for In-Orbit Controller Experimentation is an ambitious, student run mission to design and fly a cubesat to study fluid sloshing in spacecraft. The project will examine zero-g propellant sloshing from an experimental standpoint. Despite the small size and limited payload capacity, we intend to use the cubesat platform to mimic larger spacecraft and implement novel detection and computer vision methods in our analysis. Many modern spacecraft rely on propellant-filled tanks to perform attitude control and station-keeping maneuvers. When a large percentage of the spacecraft’s mass is comprised of liquid propellant, sloshing becomes a critical aspect of spacecraft attitude control and stability. The mission will study the tank/fluid dynamics using new methods to gain an enhanced understanding of low-gravity fluid disturbance effects and improve simulations using equivalent mechanical models (EMMs). Active control of the fluid leading to the reduction of propellant slosh settling times will improve the maneuverability and performance of spacecraft. This paper will focus on satellite payload research and design requirements used to inform other aspects of the SPICEsat design. In this paper, mission objectives will be discussed, numerical simulations for the proposed control algorithms are demonstrated, and a satellite experiment design is presented. Finally, we examine computational fluid dynamics models to validate the satellite design and propellant sensing components of the proposed spacecraft.

An approach to mismatched disturbance rejection control for uncontrollable systems

This study focuses on the problem of optimal mismatched disturbance rejection control for uncontrollable linear discrete-time systems. In contrast to previous studies, by introducing a quadratic performance index such that the regulated state can track a reference trajectory and minimize the effects of disturbances, mismatched disturbance rejection control is transformed into a linear quadratic tracking problem. The necessary and sufficient conditions for the solvability of this problem over a finite horizon and a disturbance rejection controller are derived by solving a forward–backward difference equation. In the case of an infinite horizon, a sufficient condition for the stabilization of the system is obtained under the detectable condition. Additionally, in combination with the generalized extended state observer, a controller design method is proposed, and the stability analysis of the system under this controller is presented. This paper details our novel approach to disturbance rejection. Finally, four examples are provided to demonstrate the effectiveness of the proposed method.

Exploring soil nitrogen and sulfur dynamics: implications for greenhouse gas emissions on the Qinghai-Tibet Plateau.

The Qinghai-Tibet Plateau is particularly vulnerable to the effects of climate change and disturbances caused by human activity. To better understand the interactions between soil nitrogen and sulfur cycles and human activities on the plateau, the distribution characteristics of soil nitrogen and sulfur density and their influencing factors for three soil layers in Machin County at depths of 0-20cm, 0-100cm, and 0-180cm are discussed in this paper. The results indicated that at depths of 0-180cm, soil nitrogen density in Machin County varied between 1.36 and 16.85kg/m2, while sulfur density ranged from 0.37 to 4.61kg/m2. The effects of three factors-geological background, land use status, and soil type-on soil nitrogen and sulfur density were all highly significant (p < 0.01). Specifically, natural factors such as soil type and geological background, along with anthropogenic factors including land use practices and grazing intensity, were identified as decisive in causing spatial variations in soil nitrogen and sulfur density. Machin County on the Tibetan Plateau exhibits natural nitrogen and sulfur sinks; However, it is crucial to monitor the emissions of N2O and SO2 into the atmosphere from areas with high external nitrogen and sulfur inputs and low fertility retention capacities, such as bare land. On this basis, changes in the spatial and temporal scales of the nitrogen and sulfur cycles in soils and their source-sink relationships remain the focus of future research.

Adaptive super-twisted sliding mode trajectory tracking control for quadrotor UAV with prescribed performance based on finite-time disturbance observer

This study proposes a finite-time disturbed observer-based prescribed performance adaptive super-twisted sliding mode trajectory tracking control scheme for quadrotor UAV. Based on the super-twisted sliding mode algorithm, adaptive control, finite-time theory, and prescribed performance control, this scheme aims to achieve stable tracking of a quadrotor UAV along a defined trajectory. This is achieved even when faced with challenges such as modeling uncertainty, external uncertainty, and complex interference environments. Firstly, the coupling between the channels and the disturbance effects are unified as the aggregate disturbance. To address the issue of the adverse impact of aggregate disturbance on system performance, a new finite-time disturbance observer is developed to estimate the overall disturbance. The observer can effectively eliminate the negative effects of the aggregate disturbance without considering the disturbed boundary conditions during the design process. Secondly, the disturbance estimation information and the adaptive super-twisted algorithm are used to construct the adaptive super-twisted sliding mode controllers for the position and attitude loops, respectively. Then, a prescribed performance control is designed to predefined the time for the position loop to effectively suppress the deleterious effects of interference. This ensures that the position system can quickly meet the prescribed tracking requirements. Finally, the stability of the designed trajectory tracking control system is demonstrated using the Lyapunov theorem. Numerical simulation results verify the effectiveness and superiority of the proposed controller.

Composite adaptive neural control for automatic carrier landing system with input saturation and output constraints

This paper investigates the automatic carrier landing control problem in the presence of model uncertainty, airwake disturbances, input saturation, and output constraints. Considering the performance requirements of the carrier-based aircraft, a composite adaptive neural controller is proposed based on the time-varying barrier Lyapunov function and backstepping control techniques. The radial basis function neural network is used to approximate the model uncertainty, where the neural network weight update law incorporating prediction and tracking errors further improves the convergence rate of the neural network and mitigates high-frequency oscillations. Furthermore, an adaptive disturbance compensation model is established to mitigate the adverse effects of airwake disturbances and estimation errors in the neural network. Based on the Lyapunov stability theory, it is proven that the proposed controller maintains the aircraft trajectory within the prescribed constraints and also ensures that all signals in the closed-loop control system are semiglobally uniformly ultimately bounded. Finally, comparative simulations are performed to demonstrate the effectiveness and superiority of the proposed composite adaptive neural control method.

Adaptive immune fuzzy quasi-sliding mode control for leader–follower formation of wheeled mobile robots under uncertainties and disturbances with obstacle avoidance

PurposeThis paper aims to propose a robust kinematic controller based on sliding mode theory designed to solve the trajectory tracking problem and also the formation control using the leader–follower strategy for nonholonomic differential-drive wheeled mobile robots with a PD dynamic controller.Design/methodology/approachTo deal with classical sliding mode control shortcomings, such as the chattering and the requirement of a priori knowledge of the limits of the effects of disturbances, an immune regulation mechanism-inspired approach is proposed to adjust the control effort magnitude adaptively. A simple fuzzy boundary layer method and an adaptation law for the immune portion gain online adjustment are also considered. An obstacle avoidance reactive strategy is proposed for the leader robot, given the importance of the leader in the formation control structure.FindingsTo verify the adaptability of the controller, obstacles are distributed along the reference trajectory, and the simulation and experimental results show the effectiveness of the proposed controller, which was capable of generating control signals avoiding chattering, compensating for disturbances and avoiding the obstacles.Originality/valueThe proposed design stands out for the ability to adapt in a case involving obstacle avoidance, trajectory tracking and leader–follower formation control by nonholonomic robots under the incidence of uncertainties and disturbances and also considering that the immune-based control provided chattering mitigation by adjusting the magnitude of the control effort, with adaptability improved by a simple integral-type adaptive law derived by Lyapunov stability analysis.