Artificial Disturbances Research Articles

The Effect of Submergence and Eutrophication on the Trait’s Performance of Wedelia Trilobata over Its Congener Native Wedelia Chinensis

Climate change and artificial disturbance may lead to increased submergence and eutrophication near a riparian zone and the shift of terrestrial plants into a riparian zone. In this study, the responses of terrestrial invasive Wedelia trilobata (WT) and congener native Wedelia chinensis (WC) plants were examined under submergence and eutrophication. A greenhouse experiment was conducted in which ramets of WT and WC were investigated under two levels of submergence (S1 and S2) and three levels of nutrients (N1, N2 and N3) along with two cultures (mono and mixed). Submergence (S) did not affect the morphological traits of both the species but nutrients (N), culture (C) and their interaction, along with submergence, had a significant effect on the morphological traits of both the species. The growth of WC under high submergence and high nutrients was decreased compared with low nutrients (N1, N2) but WT maintained its growth in monoculture. In mixed culture, low submergence (S1) and low nutrients (N1, N2) made WC more dominant but high submergence (S2) and high nutrients (N3) made WT more successful than WC due to its high phenotypic plasticity and negative effect of competition intensity. It was concluded that both species survive and grow well under submergence and eutrophication, but high submergence and eutrophication provide better conditions for WT to grow well.

Degradation of multi-thread gravel-bed rivers in medium-high mountain settings: Quantitave analysis and possible solutions

Multi-thread gravel-bed rivers in Europe have undergone distinctive changes in morphology related to progressive narrowing and incision during the last 100 years. In many cases, the post-effects of multi-thread channel transformations are associated with sediment deficits caused by channelization, damming, or land use changes. Similar trends of channel narrowing and incision can be observed in the Morávka River in the Czech Carpathians, where damming, in particular, has led to sediment deficits and decreases in flood events. Evaluation of the planform dynamics of vegetation in the active channel, lateral and vertical erosion in the channel and calculations of the dominant discharge were used as tools to define potential measures for the protection and sustainability of the close-to-natural multi-thread Morávka River channel. The successive vegetation rapidly colonised originally non-vegetated gravel-bar patches, controlling sediment material reinforcement. This process strongly contributed to a decrease in the number of gravel bars in recent decades and a decline in multi-thread channel dynamics. The total volumes of approximately 36,000 m3 and 3000 m3 of sediment material were eroded in an approximately 1-km-long reach during a high-magnitude flood (with ~20-year recurrence interval of mean daily discharge) and the ordinal high-flow event (with ~1-year recurrence interval of mean daily discharge), respectively, which led to an overall sediment material deficit in the studied reach. No single value of dominant discharge for sediment transport was found by bedload transport simulations because the volumes of transported material continuously increased with the magnitude of a particular discharge and its duration. Based on these findings, the main potential measures for the protection and sustainability of multi-thread channels are recommended. The artificial disturbance of successive vegetation cover on gravel bars and the occurrence of artificial flooding are crucial factors that could increase the multi-thread Morávka River channel dynamics. The artificial supply of gravel- and cobble-sized sediment material is necessary to stop the propagation of the ‘hungry water effect’ and incision due to the present sediment deficit in the studied reach.

Advanced analytics of elastic adhesive bonds by means of in situ computed tomography

This paper addresses optimization of parameters and measuring setups for in situ computed tomography measurements on marker particle-filled adhesives. The focus of this work was to increase the detail detectability and discriminability between used marker particles and surrounding adhesive compound even for materials with a high X-ray attenuation. Therefore, it is necessary to reduce the effects of artifacts like scattered X-rays and beam hardening, respectively. A key benefit of being able to distinguish different materials clearly improves the correct interpretation of the reconstructed three-dimensional volume significantly, while a reduction of artificial disturbances enhances the possibility to visualize previously overlaid undetected details, e.g. air voids. Performing in situ computed tomography measurements by applying the optimized parameter setups, cavitation formation was observed investigating the particle behavior of specimens modified with glass beads as marker particles under applied load. An achieved bonding enhancement by using a coupling agent as pre-treatment for glass beads was also proven by means of in situ computed tomography. Furthermore, the parameter setups optimized for bulk specimen could be adapted on material combinations, e.g. single-lap shear specimen, by adjusting a few parameters. Additional experiments demonstrate that computed tomography measurements can also be used for analytical purposes, for instance to evaluate the mixing quality of the so-called QUADRO™ or 2C mixers for two-component adhesives.

Coastal Landscape Vulnerability Analysis in Eastern China-Based on Land-Use Change in Jiangsu Province.

The unreasonable land use in rapid urbanization areas induced by large-scale urban construction activities have caused massive ecological issues. In this study, landscape vulnerability index (LVI) and landscape human interference index (LHAI) were originally addressed and calculated using multi-temporal land-use data from 2000 to 2015. Then, the spatial-temporal relationship assessment model of landscape fragility caused by human activities were constructed for each county of Jiangsu Province, China, so as to analyze the spatial distribution of landscape vulnerability and determine the impacts of artificial disturbance on landscape vulnerability. The results showed: (1) The number of counties with middle and high landscape vulnerability increased from 20 in 2000 to 27 in 2015 with a peak value (33) in 2010. (2) Counties with high-intensity human activities showed an upward trend. (3) Land use generally has a significant and diverse impact on landscape vulnerability. At the county level, the LVI was positively correlated with the LHAI before 2010 and was followed by a negative correlation of them. As concluded from this study, a total of four sub-regions (continuous benefit zones, variable benefit zones, continuous harmful zones, and variable harmful zones) have been identified for sustainable landscape management in the future. (4) The LVI suggests that the landscape vulnerability in Jiangsu did not continue to deteriorate in the study period. Further, accelerated land exploitation has produced a positive impact on regional economic development and ecological protection. This study provided an effective method set for analyzing the environmental impacts caused by human activities and promoting future ecosystem management in coastal areas.

Conjugate heat transfer model for feedback control and state estimation in a volumetric solar receiver

Open volumetric solar receivers (VSRs) are a promising technology for concentrated solar power plants due to their capability to provide heat using ambient air as the working fluid operating at temperatures over 700°C. Nevertheless, VSRs are challenged by the unsteadiness and high intensity of the radiation flux, which may cause unreliable or unsafe outflow temperatures, and may compromise the lifetime of the porous ceramic absorbers due to extreme thermal loads, thermal shock or thermal fatigue. We propose a data assimilation framework to address these matters using blower actuation, measurements from sensors located in the outflow stream of air, and a model for the conjugate heat transfer in an open VSR. We formulate said model and compare it against full three-dimensional CFD simulations to show that it captures the relevant dynamics while reducing the computational cost enough to allow for online calculations. A linear quadratic Gaussian (LQG) controller is used with the model to perform simultaneous state estimation and feedback control in three simulated scenarios. Our framework proves capable of stabilizing outflow air temperatures during the passing of a cloud, estimating the radiation flux hitting the absorber during daily operation, monitoring temperature cycling in the solid matrix, and avoiding extreme temperature gradients during start-up procedures. Artificial noise and disturbances are added to the system for all scenarios and the LQG controller proves to be robust, rejecting disturbances and attenuating noise, as well as compensating for model uncertainty.

Fluorescent thermal imaging of a quench in insulated and non-insulated REBCO-wound pancake coils following a heater pulse at 77 K

High temperature superconductors (HTS)-wound coils are being developed for use in motors, generators as well as magnet applications. Determining the stability and safe operating margins of such coils still poses challenges. While the recently introduced no-insulation winding method provides a remedy for many problems, it comes with its own limitations. For comparison, we have wound two pancake coils from HTS coated conductors with the insulated and non-insulated winding techniques. Both coils were coated with a fluorescent, temperature-sensitive coating, which allowed monitoring the surface temperatures during operation. The coils were cooled to 77 K via a combination of conduction and gas cooling, and their electrical and thermal behaviour was observed in operation. Here we present the normal transition of both coils caused by an artificially introduced instability due to a surface-mounted, resistive heater element. In the insulated coil, the localized disturbance caused a local transition of the superconductor to the normal conducting state, triggering a thermal runaway. Merely the turns in contact with the artificial disturbance heated up, while the rest of the coil remained in the superconducting state. In the non-insulated coil—although a much longer heater pulse was required—the normal transition started from the weakest point of the coil (around the bobbin) and the whole coil was heating thereafter, with the centre heating more.

Historical sedimentation at an artificial lake margin, Bangudae Petroglyphs site, SE Korea

The Bangudae Petroglyphs is Korea’s National Treasure No. 285, carved on a vertical rock face on the riverside of a mountain stream (Daegokcheon) near Ulsan. Since the construction of the Sayeon Dam in the downstream area in 1965, the petroglyphs was repeatedly flooded and submerged, raising concerns of erosion and water damage of the prehistoric rock-art motifs. Recent excavation of the fluvial sediments in front of the petroglyphs provided an opportunity to investigate the changes in sedimentation pattern before and after the construction of the dam and the consequences of human activity on natural environments. Sedimentological observations of trench sections and radiocarbon, OSL, and garbage dating of sediments reveal that the sediments comprises gravelly to sandy fluvial sediments in the lower part that accumulated since the early to middle Holocene or early to middle Neolithic Era until 1965. Above this, 25 units of alternating horizontally laminated sand and massive, mottled mud with abundant rootlets occur. This sand/mud sequence is interpreted to have accumulated after the construction of the Sayeon Dam in 1965, which caused repetitive flooding and submergence of the study area every year or two. The alternations of horizontally laminated sand and massive mud are interpreted to have resulted from rainfall-induced floods and subsequent suspension settling of fines in stagnant water after the area was inundated and temporarily transformed into a lacustrine margin setting. Afterwards, the depositional site was exposed and vegetated until the next flood event. Comparison of the deposit features with the precipitation data in Ulsan area, the water level data of the Sayeon Dam, and age data suggests that this flood-related sedimentation occurred almost every year until 2005 when the water level of the Sayeon Dam was lowered permanently because of the construction of another dam in the upstream section of the stream. This study thus provides a good example of a dramatic environmental change of a mountain stream caused by artificial disturbance of a river system due to construction of dams and an example of high-resolution sedimentary records of meteorologically induced floods in an artificial lake margin.

Assessing the slake durability of red stratum sandstone in different solution environments by a novel dual rotation test

This paper proposed a novel dual rotation slaking test with minimum mechanical and artificial disturbance that can better correlate slaking characteristics. The robustness of the proposed method was validated through a comparison of the results of the proposed test with those of the standard slake durability test. Theoretical analysis was conducted to reveal the micro-mechanism of the air-breakage phenomenon of red stratum sandstone from the perspective of surface tension, then the possibility of employing surfactant as a restrainer to retard slaking was proposed. Finally, the dual rotation slaking test was employed to evaluate the effect of various chemical additives in the slaking fluid on the durability of the red stratum sandstone. Test results showed that the surfactant sodium dodecyl sulphate (SDS) could retard deterioration by reducing the air-breakage phenomenon at its critical micelle concentration (CMC, 0.05 mol/L). Sodium chloride (NaCl) and magnesium chloride (MgCl2) can inhibit mineral dissolution through the common ion effect. The precipitation generated by sodium carbonate (Na2CO3) and potassium carbonate (K2CO3) acts as cement, increasing the durability of the red stratum sandstone. However, acidic agents generated by the hydrolysis of Al2(SO4)3 make the minerals highly susceptible to be attacked, and the significant volumetric expansion of the precipitated calcium sulphate (CaSO4) in sodium sulphate (Na2SO4) solution can contribute to the breakdown of the red stratum sandstone.

Pioneer root invasion and fibrous root development into disturbed soil space observed with a flatbed scanner method

Fine roots with thick diameter preferentially elongated into disturbed soil space, indicating positive invasion of pioneer roots that recolonize distal root systems. Fine roots and their morphological traits are related to below-ground resource dynamics at physiological and ecological levels. Established approaches for investigating fine root dynamics inevitably cause artificial soil disturbance due to root excavation or instrument installation into the soil. Soil disturbance can have considerable effects on fine root dynamics. The aim of the present study was to clarify the temporal changes of morphological traits of fine roots produced after soil disturbance. The flatbed scanner method was employed in cypress (Chamaecyparis obtusa Endl.) and deciduous oak (Quercus serrata Thunb.) stands, and changes in length and diameter of elongated roots were measured for 4 years after soil disturbance. In both stands, specific trends of diameter and length production of fine roots were observed. Root length production increased extensively, and diameter was greater in an initial phase after soil disturbance. However, temporal patterns varied between the two stands. Soil disturbance affected fine root dynamics for a longer duration in the cypress stand, but more intensively in the oak stand. These results indicate that soil disturbance can affect fine root morphology and can induce invasion of thick fine roots, which are traditionally grouped as pioneer roots. Moreover, the results showed high length production continued for a longer period than that of larger diameter roots, suggesting recolonization of fine root systems by elongating pioneer roots followed by the branching of absorptive fibrous roots in order to recover root uptake capacity lost due to soil disturbance.

Vertical Pollution Characteristics and Sources of Polycyclic Aromatic Hydrocarbons in a Heterogeneous Unsaturated Zone Under a Coking Plant

Six deep sampling boreholes are used for studying the sources and vertical distribution of 16 polycyclic aromatic hydrocarbons (PAHs) in an abandoned coking plant. The maximum depth of soil sampling ranged from 9.5-42 m. The present study analyzes the distribution characteristics and sources of PAHs in addition to the important factors affecting migration of PAHs in the unsaturated zone. Results showed that the maximum values of total PAHs range of 134.79-11266.81 mg·kg-1 at vertical depths ranging from 1-5 m. We found that 2+3 rings dominated total PAHs and that the highest content was Nap. Results also showed that the main source of PAH pollution was coal combustion. Coal tar pitch and different oils from deep processing of tar played an important role in PAH pollution. The gravel layer served as a good infiltration channel for pollutants, and the sand lens below 20 m depth became the main enrichment layer for PAHs through adsorption and interception. Oils and wastewater from discharge and leaching of chemicals contributed to the migration of PAHs through inter-miscibility and competitive adsorption, which led to deep soil pollution. Soil layers above 1 m depth were affected by artificial disturbance, rainfall leaching, and degradation, and the unsaturated zone below 30 m depth was affected by leaching from groundwater. Consequently, the ratio of low to high rings first increased before decreasing with increased depth of the unsaturated zone. The types of pollution sources, rock particle sizes, organic matter content, and hydrogeological conditions all affected the vertical distribution and migration of PAHs.

Mass strandings of discinid brachiopod shells related to artificial habitat disturbance

Mass strandings of discinid brachiopod shells related to artificial habitat disturbance

Kalman filter and sliding mode observer in artificial pancreas: an in-silico comparison

Observers are essential in artificial pancreas systems, either for states or disturbance estimation. Kalman filters based on the Hovorka model are largely applied for this purpose. However, simpler approaches can be used too. We intend to analyze whether the observer structure, the applied model and the individualization of the model parameters affect the estimation accuracy. We perform an in-silico comparison between two Kalman filters and a sliding mode observer, as observer structures previously proposed in the field. All observers are implemented in population and individualized versions of the Hovorka and the simpler Identifiable Virtual Patient models. To tune the Kalman filters, a genetic algorithm based framework was developed. The results indicate that the choice of the model has a larger effect on the outcome than the choice of the observer structure. Finally, the observer based on the Hovorka model does not always perform the most accurate estimation given the higher difficulty during the identification of its parameters.

Learning nonlinear robust control as a data-driven zero-sum two-player game for an active suspension system

Abstract An optimal robust control data-driven learning solution is proposed for an active suspension system. The problem is formulated as a zero-sum two-player differential game (ZS-TP-DG), where the optimal control law and the worst-case disturbance control law must be searched for. The distinctive features of the proposed solution are: a Q-learning-like data-driven model-free (with unknown process dynamics) algorithm relying on collected input-state data from the process; neural networks being used as generic function approximators; validation on an active suspension system that is easily amenable to artificial road profile disturbance generation. The superiority of the ZS-TP-DG controller over another optimal controller learned in a disturbance-free context is validated and proven.

The Role of Water and Lithology on the Deformation and Failure of an Anaclinal Rock Slope in a Hydropower Reservoir

A series of settlement, cracking, and collapse of the Zhengjiaping slope has been increasingly developing since October 2015 during impoundment at the Dagangshan Hydropower Station. It is a dangerous signal, which means thatlandslide potential will be existed for the Zhengjiaping slope and poses greatthreat to the operation of hydropower station and traffic safety. Related slope protection measures and research studies have been implemented accordingly in the Zhengjiaping slope to prevent and control adverse influences on property security and human life in the reservoir area. In order to understand the geological and hydrological settings of the Zhengjiaping slope and its surroundings, a field investigation was carried out to determine the lithological composition and toppling/sliding deformation characteristics using exploratory adit and site boreholes. The large deformation process in the apparently deformed area was analyzed using borehole inclinometers and global navigation satellite systems (GNSS). It was found that the apparently deformed area zone was characterized by crushed rock masses, with only a small amount of slope deposits and the sliding deformation occurring in Zone I. The deformation process of the reservoir landslide was considered to be a complex integration of the geological effects of various adverse factors. Impoundment and heavy rainfall are the direct causes of sliding deformation. During the preparation of the basic conditions for sliding, lithology, tectonic activity, and artificial disturbances play an important role, including the sliding mass and the sliding surface zone.

First SWARM Observations of the Artificial Ionospheric Plasma Disturbances and Field‐Aligned Currents Induced by the SURA Power HF Heating

AbstractA series of experiments were conducted with a conjunction between the midlatitude SURA ionospheric heating facility and the multisatellite SWARM mission. We present the first observations made by SWARM on the plasma perturbations and electric currents induced in the F2 region ionosphere by the high‐power high‐frequency O‐mode radio wave pumping. In the heated region, significant effects include a localized increase of the electron temperature accompanied by stratification of the electron density and the magnetic signatures of field‐aligned currents (FACs). The spatial structure and amplitude of FACs indicate that the current system is likely associated with the unipolar diffusion and excitation of eddy electric currents in the ionosphere. Similar effects are revealed in the laboratory experiment but not previously observed in space.

Spatial Patterns in Different Stages of Regeneration after Clear-Cutting of a Black Locust Forest in Central China

Estimating underlying mechanisms and dynamics from observed tree patterns can provide guidance for plantation management. Robinia pseudoacacia can reproduce via clonally produced ramets, leading to a complex distribution of stems. Three second generation plots and three third generation plots (each plot 50 m × 50 m) were established across a wide age range after clear-cutting in a Robinia pseudoacacia plantation in central China. We measured spatial coordinates, diameter at breast height (DBH) or diameter at basal stem, and heights of all recruits, as well as the coordinates and base diameter of all stumps, in six plots. The spatial pattern in different plots and the spatial relation between stumps and regenerations after clear-cutting were analyzed. To estimate the underlying processes of the observed patterns, we fitted Matérn and Variance-Gamma cluster processes to the observed dataset. The results revealed that the percentage of ramets from stumps decreasing with age in the two types of stands (from 40.4% to 30.1%, from 57.6% to 35.7%), and trees exhibited an aggregated distribution in all plots, but the degree of aggregation exhibited a decreasing trend with age, and aggregation occurred at different scale. Furthermore, a large proportion of ramets had their nearest neighbor at a short distance (<1 m) based on analysis of the nearest neighbour function. The bivariate analysis revealed that the spatial relation between stumps and ramets changed with age, and a repulsion trend was found between them in all the six plots. The Variance-Gamma process with covariate of Cartesian coordinates fitted the observed patterns better than others. The observed pattern was likely driven by root dispersal limitation, seed dispersal limitation, human disturbance, and intraspecific competition. Spatial patterns are important characteristics in forest stand structure, and understanding the pattern change and its underlying mechanisms could allow for better timing of artificial disturbances to optimize stand structure and promote stand growth.

Output Feedback Model Predictive Control With Steady-State Target Calculation For Fuzzy Systems

In this article, an output feedback model predictive control for fuzzy systems to track a time-varying steady-state target is presented. The steady-state target is calculated through a steady-state target calculation (SSTC) module, which is combined with the controller in the lower layer designing based on the linear time invariant model. The presence of SSTC makes the recursive feasibility as well as the stability difficult to guarantee. This article presents a promising approach by specifying the solution of SSTC as a function of estimated artificial disturbance, designing the robust invariant set offline and including the invariance condition in SSTC. Hence, the proposed approach in this article guarantees that if SSTC optimization problem is feasible, then the dynamic controller steers the system to the time-varying steady-state target. Furthermore, in order to reduce the conservativeness of the proposed approach, a heuristic online approach with N free control moves is proposed where the invariant set specified offline is acting as a terminal region for the dynamic controller. A numerical example is given to show the effectiveness of the proposed approach.

Heuristic open-loop output feedback model predictive control for control of intermittent transonic wind tunnel

For intermittent transonic wind tunnel (ITWT), Mach number and total pressure are crucial features of the flow field in the test section. However, they are typically difficult to control due to system nonlinearities, uncertainties, coupling and delays. This paper proposes an output feedback model predictive control (MPC) strategy to ensure the tracking of Mach number and total pressure of the ITWT to a specified reference trajectory. The proposed approach includes open-loop prediction, steady state target calculation (SSTC) and dynamic control, where the lower layer dynamic control tracks the steady state target obtained from the upper SSTC layer. By adding an artificial disturbance in the identified linear parameter varying (LPV) model for ITWT, and utilizing the resulting LPV model in both SSTC and dynamic control layers, a heuristic open-loop output feedback MPC approach is proposed. The experimental results for the control of Mach number and total pressure for ITWT demonstrate the effectiveness of the proposed approach.

Evolution of artificial disturbances in swept wing supersonic boundary layer

Experimental data on the evolution of artificial controlled travelling disturbances in a three-dimensional supersonic boundary layer on a 45° swept wing at Mach number 2.0 is presented. Artificial disturbances were introduced in the boundary layer using a periodical glow discharge with a frequency of 20 kHz. Pulsations of the boundary layer were measured with a constant-temperature hot-wire anemometer and the probe moved parallel and not parallel to the leading edge of the model. In both cases spatial-temporal and spectral-wave characteristics of the wave train development were obtained and quantitatively compared with each other. This paper discusses the suitability of the method for measuring fluctuations fields when the probe is moving not parallel to the leading edge of the model.

Experimental investigation of the natural and controlled disturbance development in a supersonic boundary layer on the swept wing

The results of investigation of the transverse flow inhomogeneity effect on the natural and controlled disturbance development in 3D supersonic boundary layer are considered. The transition curves were measured on a model of a smooth swept wing and on a swept wing with roughness elements of two configurations. The influence of periodic surface roughness on the growth of natural pulsations (without using a discharge) in the boundary layer is determined. In experiments with artificial disturbances it is found that the periodic modulation of mean flow can lead to stabilization of controlled disturbances in supersonic boundary layer on a swept wing. It was found out that the weak flow inhomogeneity can influence the effectiveness of the active/passive technology of supersonic boundary layer transition control, including the surface microroughness on a swept wing.