Disturbance Frequency Research Articles

A Cross-Sectional Study of Sleep Disturbances in Children and Adolescents With Abdominal Pain-Associated Disorders of Gut-Brain Interaction.

The aims of the current study were to determine the frequencies of specific sleep disturbances in youth with abdominal pain-associated disorders of gut-brain interaction (AP-DGBIs) and to assess relationships with psychological dysfunction. This was a retrospective evaluation of 226 consecutive patients diagnosed with an AP-DGBI. All had undergone a systematic evaluation of gastrointestinal symptoms, the Sleep Disturbance Scale for Children, and the Behavior Assessment System for Children. Disorders of initiation and maintenance of sleep (DIMS; 40%) and disorders of excessive daytime somnolence (DOES; 14%) were each present in more than 10% of the patients. Both DIMS and DOES scores were more likely to be elevated in patients with anxiety and/or depression scores in the at-risk or elevated-risk ranges. Sleep disorders are common in youth with AP-DGBIs and are associated with anxiety and depression, even in those patients with anxiety and depression in the at-risk range.

Determination of the natural frequencies of the above-ground sections of pipelines transporting an incompressible fluid

Under certain conditions, above-ground sections of pipelines are subject to vibration. Increasing the vibration amplitudes beyond the limits can cause the object to fail. In order to assess the vibration resistance of pipelines and to find the most effective ways of detuning from the resonant frequencies of disturbances, it is necessary to determine the natural frequencies of oscillations and the characteristics of the oscillation processes. The authors of the article developed a mathematical model to determine the frequency of free vibrations of above-ground pipeline sections, taking into account the influence of internal pressure and the velocity of the pumped fluid. As a result, a numerical solution based on the Bubnov-Galerkin method was obtained and a sufficient number of series elements in the approximate solution was determined. The authors performed numerical experiments. These showed that the frequencies should be determined for each section under specific conditions according to the pumping mode.

Cross-flow vortex-induced vibrations of a top tensioned riser subjected to boundary disturbances with frequencies close to vortex shedding

In the present paper, the effects of external disturbances on cross-flow vortex-induced vibrations (VIVs) of a top tensioned riser are investigated based on a wake oscillator model. Two different flow conditions, namely uniform and linearly sheared profiles, and different combinations of disturbance frequency and amplitude were considered. Simulation results showed that synchronization between VIV and disturbance can occur when the disturbance frequency approaches the Strouhal frequency or when the disturbance amplitude is significant. This synchronization leads to a significant increase in riser response and the commonly used industry practice of simulating VIV and disturbance independently and summing both could underestimate the actual fatigue rate in such condition. However, in certain cases where VIV did not lock onto the disturbance, it was found that the disturbance could suppress the VIV and the industry practice tends to overestimate the fatigue rate.

Directional modifier adaptation based on input selection for real-time optimization

Modifier adaptation (MA) is commonly used for economic optimization of systems under model uncertainty. In MA, gradient correction terms require estimation through perturbations, thus delaying the optimization procedure. A directional modifier adaptation method is proposed whereby a subset of available gradient corrections are made. An algorithm that evaluates possible adaptation strategies and chooses those with the largest economic effect is proposed, thereby allowing economical operation with less delay. The proposed scheme, named dMAIS, is deployed on the Williams-Otto process where it is found to outperform MA if not inhibited by filtering. Systems can also suffer from constraint violation if uncertainty is present, hampering safety and profitability. An adjustment step is proposed as part of dMAIS, whereby gradients are used to drive the plant to constraint satisfaction. The adjustments are studied in an evaporator case with a product quality constraint whereby dMAIS is shown to result in infrequent violations leading to higher throughput. The proposed approach was also compared to standard directional MA in the evaporator case study, where it was found to be economically beneficial. The benefits of dMAIS are observed most saliently for systems with increasing disturbance frequency.

Islanded Wind Farm Microgrid Stability Control using Synchronverter Algorithm

Indonesia is an archipelagic country with many remote islands. Supplying electricity is difficult in some remote islands in Indonesia, such as Adaut regency of west Maluku. One solution to solve this electricity supply problem is the creation of a microgrid system. However, the application of renewable energy on microgrids can lead to several technical challenges, such as frequency disturbances and voltage instability. Therefore, a control algorithm that can maintain the system stability is required. One recently developed algorithm is the synchronverter. In this study, the synchronverter is used to maintain network stability on an islanded wind farm based microgrid. As a result, we asses the microgrid stability responses with the synchronverter algorithm or a conventional synchronous generator to evaluate the microgrid stability performance. The outcomes of this study indicate that the synchronverter algorithm can maintain the stability of microgrid even it is interrupted by intermittent wind speed input and load changes.

The Impact of Sleep Quality on Cognitive Function in Community-Dwelling Older Adults

Introduction: Given the high prevalence of poor sleep quality in late adulthood, older adults might be involved with different physical, mental and social consequences of this disorder. Current research was conducted to examine the association between sleep quality and cognitive function in community-dwelling older adults.
 
 Methods: This cross-sectional study was carried out on 800 community-dwelling people aged ≥ 60 years living in Amirkola, North of Iran. The participants were selected by simple random sampling method. Mini-Mental State Examination, and the Pittsburgh Sleep Quality Index (PSQI) were used for data collection. Seven components of the sleep quality were categorized into the four groups (very good, relatively good, relatively poor, and very poor condition). The participants were divided into the two groups based on their cognitive function, and sleep quality was compared between these two groups. Mann-Whitney, Spearman's correlation analysis, Chi-square, Pearson's correlation test and Logistic regression analysis were used to analyze the collected data.
 
 Results: Mean PSQI score among the older adults with normal and abnormal cognitive function was 5.5 ± 3.2 and 5.8 ± 3.3, respectively (p = 0.508). Poor sleep quality was slightly more prevalent in the elderly with cognitive dysfunction (p = 0.775). Logistic regression analysis revealed age (adjusted OR = 1.06; 95% CI: 1.03-1.08; p < 0.001) and level of education (adjusted OR = 0.14; 95% CI: 0.09-0.20; p < 0.001) had a significant impact on cognitive function; PSQI score (p = 0.254), gender (p = 0.661), and administration of sleeping drugs showed no significant effect (p = 0.081).
 
 Conclusion: Among different components of sleep quality, a significant positive association was observed between the frequency of sleep disturbances with cognitive function in older adults; furthermore, older age and lower level of education showed a significant negative effect on cognitive function.

Adaptive Power Reserve Control for Photovoltaic Power Plants Based on Local Inertia in Low-Inertia Power Systems

Retirement of thermal power plants and growth in the capacity of power electronics based renewable energy sources reduce the inertia of power systems, making them more sensitive to frequency disturbances. The shortfall of system inertia cannot be compensated by the remaining synchronous generators and alternative solutions are required. Photovoltaic power plants (PVPPs) can provide frequency support services through the application of flexible power point tracking methods and power reserves. This paper proposes a power reserve distribution method based on local inertia across the PVPPs of a power system aimed at enhancing the system frequency response compared to fixed power reserve levels, especially in weaker and less meshed networks. A multi-level adaptive power reserve control for different system inertia levels is also proposed. The performance of the methods against different frequency events is validated through extensive real-time simulations based on benchmark network models.

Impact by the operating and structural parameters of a screen on the technological parameters of vibratory basalt sieving

Purpose is to identify a dependence of basalt raw material fine screening upon the operating and structural parameters of sieving equipment. Methods. The research results have been obtained relying upon comparative analysis of basalt raw material fine screening upon the operating and structural parameters of sieving equipment. In this regard, the analyzed grading efficiency characteristics were defined for three densities of basalt rock mass mined in open pits. They are γ = 1.4 g/сm3 for tuff; γ = 2.2 g/сm3 for lava-breccia; and γ = 2.6 g/сm3 for basalt. The rock mass components are extracted selectively and processed separately. Findings. Expediency of complex mining and processing of three basalt rock mass components (being tuff, lava-breccia, and basalt) as well as their selective treatment has been identified. Mathematical modelling has helped generate regression models of fine basalt raw material sieving upon the operating and structural parameters of a screen. The regression models as well as the represented calculation results are indicative of strong correlation between the efficiency of fine basalt raw material screening and the factors involved by the regression models (i.e. rock mass density; inclination angle of a disturbance force of a vibration exciter of a screen; inclination angle of a screen effector; mesh size; specific load on a screen; disturbance frequency of a screen drive; and a screen length). Originality. For the first time, dependencies of fine basalt raw material sieving efficiency upon the operating and structural parameters of a screen have been modelled mathematically. Based upon the multifactor experiment, ideas have been developed concerning the fine grading process; selection of boundaries of each parameter control; and determination of the efficiency as well as a law of changes in technological parameters while controlling them. Practical implications. Use of the findings will help make adequate solutions while selecting instrumental conditions of an operation schedule to prepare basalt raw material for its integrated processing.

Spruce- and beech-dominated primary forests in the western Carpathians differ in terms of forest structure and bird assemblages, independently of disturbance regimes

Mountain spruce- and beech-dominated forests (SDPF and BDPF) are of major importance in temperate Europe. However, information on the differences between their historical disturbance regimes, structures, and biodiversity is still incomplete. To address this knowledge gap, we established 118 circular research plots across 18 primary forest stands. We analysed the disturbance history of the last 250 years by dendrochronological methods and calculated disturbance frequency, severity, and timing. We also measured forest structure (DBH, tree density, volume of deadwood, and other parameters). Breeding bird populations were examined by point count method during the spring seasons 2017–2018 (SDPF) and 2019–2020 (BDPF). Using direct ordination analysis, we compared the disturbance history, structure and bird assemblage in both forest types. While no differences were found regarding disturbance regimes between forest types, forest structure and bird assemblages were significantly different. SDPF had a significantly higher density of cavities and higher canopy openness, while higher tree species richness and more intense regeneration was found in BDPF. Bird assemblage showed higher species richness in BDPF, but lower total abundance. Most bird species which occurred in both forest types were more numerous in spruce-dominated forests, but more species occurred exclusively in BDPF. Further, some SDPF- preferring species were found in naturally disturbed patches in BDPF. We conclude that although natural disturbances are important drivers of primary forest structures, differences in the bird assemblages in the explored primary forest types were largely independent of disturbance regimes.

Effect of wave disturbance on the fluid dynamics of the pump turbine in a seawater pumped storage hydroplant

Compared with conventional pumped-storage hydroplants, seawater pumped-storage hydroplants are constructed in a complex marine environment. The wave disturbance may affect the safety operation of the pump turbine in the seawater pumped hydroplant via affecting the level of the free water surface. To explore the effect of wave disturbance on the operation of the pump turbine in a seawater pumped-storage hydroplant, assuming that the wave disturbance follows a sine function, on the basis of Airy’s micro-amplitude wave theory and the comprehensive characteristic curve of a pump turbine, we use sliding grid technology and the SST k–ω turbulence model to simulate the dynamics of fluid in a full-flow channel. In this study, the unsteady flow field, Q-criterion vorticity, relative pressure pulsation amplitude, and frequency of pressure pulsation are analyzed to determine the internal flow field and pressure pulsation under different wave disturbance conditions and operating loads. The results show that both the pressure pulsation in the pump turbine and its frequency domain are affected by the wave disturbance. In addition, the turbulent flow with a large flow rate tends to produce higher relative pressure pulsation under wave disturbance. Due to the large flow rate and strong static and dynamic interference in the vaneless area, the relative amplitude of the pressure pulsation is significantly affected by wave disturbance. Furthermore, the low-frequency pressure pulsation of the draft tube is superimposed with the wave disturbance frequency.

A Double Interpolation and Mutation Interval Reconstruction LMD and Its Application in Fault Diagnosis of Reciprocating Compressor

The accuracy and stability of the envelope estimation function are enduring issues throughout the research process of LMD. This paper presents double interpolation and mutation interval reconstruction local mean decomposition (DIMIRLMD) to improve the stability of the demodulation process and the accuracy of PF components. DIMIRLMD first proposes a mutation interval reconstruction envelope algorithm using extreme symmetry points to suppress the demodulation mutation phenomenon, which disturbs the stability of the demodulation process, and then selects the optimal PF component from a double interpolation PF component library based on the index of orthogonality (IO) for a better hierarchical property. DIMIRLMD was employed to analyze the simulation signal and vibration signal of a reciprocating compressor in an oversized bearing clearance state, and the results illustrate its performances are more excellent than those of three other LMD methods. Furthermore, the envelope frequency spectrum obtained from the proposed LMD presents a clear double rotation fault frequency and lower noise disturbance.

THE EFFECT OF SEDATION STRATEGY ON THE FREQUENCY OF POSTOPERATIVE ARRHYTHMIAS AFTER CARDIAC SURGERIES WITH BYPASS

Introduction: Postoperative arrhythmias are a frequent problem after surgical interventions, both noncardiac and cardiac surgeries. A 20% higher frequency of rhythm disturbances occurs in patients after cardiac surgery. Postoperative arrhythmia has many variations. Such arrhythmias include atrial fibrillation, atrial flutter, ventricular arrhythmias, and bradyarrhythmias. There are many conflicting facts about the effect of sedative drugs, which are most often used at the moment: propofol, dexmedetomidine, on reducing the frequency of postoperative arrhythmias. Purpose: To analyze whether there is a difference in the frequency of postoperative arrhythmia in patients in different groups sedated with propofol, dexmedetomidine and their combination. Materials and methods: This is a randomized controlled parallel study. The study included 356 patients over 18 years of age who underwent cardiac surgeries operative treatment. 194 patients were analyzed. Statistical data processing was carried out on the basis of GraphPad Prism 9.0 software. Results: Of the total number of patients in the propofol sedation group without prior rhythm disturbance, in whom arrhythmia was detected in the postoperative period, n=13 patients were registered. In the dexmedetomidine sedation group, postoperative arrhythmia was observed in 8 patients, which is also 50 % of the total number of patients in this group. Among 8 patients in whom postoperative arrhythmia was registered, 5 patients did not have rhythm problems before surgery. Of the total number of patients in the group of sedation with a combination of drugs without previous rhythm disturbance, postoperative arrhythmia was detected in 19 patients. When analyzing the frequency of postoperative arrhythmias, no difference in the frequency of postoperative arrhythmias has been detected in all three sedation strategies (p=0.1107). Conclusions: According to the data we obtained, no difference was found in the frequency of postoperative arrhythmias in patients after cardiac surgery in any of the sedation groups (p=0.1107).

The Impact of Flood Frequency on the Heterogeneity of Floodplain Surface Soil Properties

Floodplain soils are subject to quasi-periodic flood disturbances. This flooding serves to enrich floodplain soils, increasing their fertility and often making them ideal locations for agriculture. However, what is less well understood is how the frequency of flooding impacts on soil fertility and the diversity of soil character. This study investigates how flood frequency influences the heterogeneity (assessed using 26 physical and geochemical soil properties) of floodplain soils in a semi-arid floodplain wetland system in New South Wales, Australia. The study includes an investigation of soil properties across four flood frequency (or disturbance frequency) categories ranging from frequent through to infrequent flood disturbance. Thirty samples were collected from each zone and the physical and geochemical soil data were analyzed using a suite of univariate and multivariate statistical tests. The results show that sites subject to an intermediate level of flood disturbance have a greater level of diversity in soil properties than those sites subject to frequent flood disturbances. These results reflect those of the Intermediate Disturbance Hypothesis, an ecological theory that posits the highest biological diversity will also be found in intermediately disturbed environments and suggests that there might be physical habitat drivers of biological diversity in intermediately disturbed floodplains.

Feedforward resonance control for the European X-ray free electron laser high duty cycle upgrade

The High Duty Cycle (HDC) upgrade is a proposed improvement to the existing European X-ray Free Electron Laser (EuXFEL) to extend the pulsed RF duty factor from the actual value of around 1% to more than 5% up to Continuous Wave (CW). To implement this upgrade, the loaded quality factor (QL) of the superconducting cavities will increase by more than one order of magnitude. This will result in shrinking the cavity bandwidth to values as low as a few Hertz. Since the Lorentz Force Detuning (LFD) experienced during the accelerating field buildup is of hundreds of Hertz, the Low-Level RF (LLRF) system has to accurately track and control the cavity resonance frequency to obtain the desired accelerating gradient. Moreover, ponderomotive instabilities have to be suppressed to achieve stability during beam acceleration. Since LFD is a repetitive disturbance in cavity frequency, the correction to its effects can be implemented as a feedforward compensation on the piezoelectric tuners of the cavity. Initial results on the simulation of feedforward resonance control in the HDC regime are discussed in this proceeding.

Analysis and Design of Direct Force Control for Robots in Contact with Uneven Surfaces

Robots executing contact tasks are essential in a wide range of industrial processes such as polishing, welding, debugging, drilling, etc. Force control is indispensable in these type of tasks since it is required to keep the interaction force (between the robot and the environment/surface) within acceptable values. In this paper, we present a methodology to analyze and to design the force control system needed to regulate the force as close as possible to the desired value. The proposed methods are presented using a widely used generic contact task consisting of exerting a desired force on the normal direction to the surface while a desired velocity/position is tracked on the tangent direction to the surface. The analysis considers environments/surfaces with certain uneven characteristics, i.e., not perfectly flat. The uneven characteristic is studied using ramp or sinusoidal signals disturbing the position on the normal direction to the surface, and we present how the velocity on the tangent direction is related with the slope of the ramp or the frequency of the sinusoidal disturbance. Then, we provide a method to design the force controller that keeps the force error within desired limits and preserves stability, despite the uneven surface. Furthermore, considering the relation between the disturbance (ramp or sinusoidal) and the tangent velocity, we present a method to compute the maximum velocity for which the task can be executed. Simulations exemplifying and verifying the proposed methods are presented.

High precision structured H∞ control of a piezoelectric nanopositioning platform.

The inherent weakly damped resonant modes of the piezoelectric nanopositioning platform and the presence of model uncertainty seriously affect the performance of the system. A structured H∞ design is used in this paper to solve the accuracy and robustness problems respectively using a two-loop control structure. The multiple performance requirements of the system are constituted into an H∞ optimization matrix containing multi-dimensional performance diagonal decoupling outputs, and an inner damping controller d is set according to the damping of the resonant modes; the second-order robust feedback controller is preset in the inner loop to improve the robustness of the system; the tracking controller is connected in series in the outer loop to achieve high accuracy scanning; finally, the structured H∞ controller is designed to meet the multiple performance requirements. To verify the effectiveness of the proposed structured H∞ control, simulation comparison experiments are done with the integral resonant control (IRC) and H∞ controller. The results demonstrate that the designed structured H∞ controller achieves higher tracking accuracy compared to the IRC and H∞ controllers under grating input signals of 5, 10, and 20 Hz. Moreover, it has good robustness under 600g and 1000g loads and high frequency disturbances close to the resonant frequency of the system, meeting multiple performance requirements. Compared with the traditional H∞ control, yet with lower complexity and transparency, which is more suitable for engineering practice applications.

A Disturbance Frequency Index in Earthquake Forecast Using Radio Occultation Data

Earthquake forecasting is the process of forecasting the time, location, and magnitude of an earthquake, hoping to gain some time to prepare to reduce the disasters caused by earthquakes. In this paper, the possible relationship between the maximum electron density, the corresponding critical frequency, and the occurrence of earthquakes is explored by means of radio occultation data based on mechanism analysis and actual earthquake-nearby data. A new disturbance frequency index is proposed in this paper as a novel method to help forecast earthquakes. Forecasting of the location and timing of earthquakes is based on the connection between proven new frequency distributions and earthquakes. The effectiveness of this index is verified by backtracking observation around the 2022 Ya’an earthquake. Using this index, occultation data can forecast the occurrence of earthquakes five days ahead of detection, which can help break the bottleneck in earthquake forecasting.

The implications of seasonal climatic effects for managing disturbance dependent populations under a changing climate

Abstract The frequency of ecological disturbances, such as fires, is changing due to changing land use and climatic conditions. Disturbance‐adapted species may thus require the manipulation of disturbance regimes to persist. However, the effects of changes in other abiotic factors, such as climatic conditions, are frequently disregarded in studies of such systems. Where climatic effects are included, relatively simple approaches that disregard seasonal variation in the effects are typically used. We compare predictions of population persistence using different fire return intervals (FRIs) under recent and predicted future climatic conditions for the rare fire‐dependent herb Eryngium cuneifolium. We used functional linear models (FLMs) to estimate the cumulative effect of climatic variables across the annual cycle, allowing the strength and direction of the climatic impacts to differ over the year. We then estimated extinction probabilities and minimum population sizes under past and forecasted future climatic conditions and a range of FRIs. Under forecasted climate change, E. cuneifolium is predicted to persist under a much broader range of FRIs, because increasing temperatures are associated with faster individual growth. Climatic impacts on fecundity do not result in a temporal trend in this vital rate due to antagonistic seasonal effects operating through winter and summer temperatures. These antagonistic seasonal climatic effects highlight the importance of capturing the seasonal dependence of climatic effects when forecasting their future fate. Synthesis. Awareness of the potential effects of climate change on disturbance‐adapted species is necessary for developing suitable management strategies for future environmental conditions. However, our results suggest that widely used simple methods for modelling climate impacts, that disregard seasonality in such effects, may produce misleading inferences.

Decision Algorithm Based on the Modified Bellman Equation to Deal With EMI-Induced Errors in Hamming-Based Communications

This article presents a decision-making algorithm based on a modified version of the Bellman equation to deal with electromagnetic interference errors in a communication channel inside a harsh electromagnetic reverberant environment. The Bellman equation is a fundamental concept in decision-making problems such as Markov decision processes. Such processes model decision making in situations where the outcomes are partly random and partly controlled by an agent (decision maker). Recent studies have implemented Markov decision processes as a tool for risk assessment in areas such as robotics or aviation. However, so far, no research has been reported that uses the Bellman equation or Markov decision processes to deal with risks related to electromagnetic disturbances. In our study, a wired communication channel that uses non-return-to-zero-level data encoding and Hamming code for error detection and correction is disturbed. First, the packet error rate (PER) is calculated and compared with and without the proposed algorithm for different electromagnetic disturbance frequencies and bit rates. The gain is compared at different PERs when the algorithm's parameters (called rewards) are optimized and when these are set as random. Finally, the influence of the rewards and the maximum number of resends on the algorithm's performance is also studied.

A Disturbance Decoupling Generalized Proportional–Integral Observer Design for Robust Sensor Fault Detection

This paper presents a novel disturbance decoupling generalized proportional-integral observer (DD-GPIO) for the early detection of sensor faults in dynamic systems subject to external semi-stationary periodic disturbances. The focus is to reduce the adverse impacts caused by the disturbance whose spectrum is uneven with some dominant frequencies. This achieved in a two-stage design procedure. In the first stage of zero-assignment, the additional zeros introduced by the state transition matrix of GPIO are allocated near the disturbance frequencies to construct a rank-deficient disturbance transfer function matrix (DFTM) relating from the disturbances to the fault detection residuals. In the second stage, an additional gain matrix is applied to the output estimation error before the error is fed into the GPIO. The additional matrix can be designed by using the eigenvector of zero eigenvalue of the rank deficient DFTM, such that the periodic perturbations can be completely decoupled from the fault detection residual for better performance in fault detection. The conditions to achieve disturbance decoupling is given. Finally, a novel condition number-based sensitivity objective is proposed to optimize the DD-GPIO's poles. Simulation and a two-wheeled robot experiment illustrate the outperformance of the DD-GPIO in decoupling periodic disturbances and detecting minor sensor faults.