Fluctuation Characteristics Research Articles

Super-resolution radial fluctuations (SRRF) algorithm with better real-time performance

Super-resolution radial fluctuations (SRRF) is a type of statistical analysis based on fluorescence fluctuation characteristics to achieve super-resolution imaging. At present, facing the problems of slow reconstruction speed and weak real-time image processing. For dealing with these issues, parallel computing characteristics of FPGA is employed in this paper to achieve the acceleration of the algorithm. Firstly, the reconstruction process of SRRF algorithm process is split into five sub-modules, which are designed depended on the pipeline design idea. Secondly, the top-level module is designed to accomplish the sub-modules connection for executing the SRRF algorithmic process, while the reconstruction is finished by using the high-density image dataset. Finally, the single-frame image processing time is recorded and analysed in FPGA with the mainstream configuration of PC. The experimental results show that, in terms of the single frame image processing time, SRRF in FPGA is improved by 77.95% compared to PC, with real-time image processing capability under 10 ms image sampling period. In addition, the resolution-scaled Pearson coefficient (RSP) and resolution-scaled error (RSE) values of the reconstruction results in FPGA are similar to those of PC.

Investigating alterations of nutritional constituents, antioxidant abilities, and physicochemicals in aging processes of ginseng sprouts

This study was the first to document the fluctuations of nutritional constituents, antioxidant capacities, and physicochemical characteristics during the aging processes of red ginseng sprouts (RGS) and black ginseng sprouts (BGS) from dried ginseng sprouts (DGS). Total ginsenoside levels differed with 54.72 (DGS) → 57.15 (RGS) and 6.98 (BGS) mg/g, specifically, ginsenoside F2 and Rd2 in RGS remarkably increased with 1.97 → 5.88 and 2.41 → 5.49 mg/g, respectively. Phenolics increased dramatically as 297.02 → 1770.01 (6.0-fold); 1834.94 (6.2-fold) μg/g in DGS → RGS; BGS with abundance contents of benzoic acid (>15.3-fold), chlorogenic acid (>9.5-fold), and catechin (>4.2-fold), whereas amino acids markedly decreased (3686.81 → 1505.00; 364.64 mg/100 g), with arginine showing a significant decrease. Moreover, beneficial factors (total phenolic content: TPC; total flavonoid content: TFC; maillard reaction products: MRP) displayed increase tendencies (approximately 2.0-fold) with BGS > RGS > DGS, and antioxidant patterns significantly increased with potential capacities as follows: ABTS (48.3: DGS → 65.8: RGS; 70.2 %: BGS) > DPPH (18.5 → 44.6; 59.2 %) > hydroxyl (23.2 → 35.4; 39.9 %) > FRAP (0.6 → 1.8; 1.8 %) at 500 μg/mL. In particular, DNA protection exhibited excellent rates of 100 %, in the order of BGS (25 μg/mL) > RGS (50 μg/mL) > DGS (500 μg/mL). These findings suggest that processed ginseng sprouts can be excellent agents for natural antioxidants.

Numerical analysis of pressure fluctuation characteristics of axial flow pump device of edge pump unit in multi-unit pumping station

Numerical analysis of pressure fluctuation characteristics of axial flow pump device of edge pump unit in multi-unit pumping station

Robust Assessment of Hosting Capacity of Renewable Generation in Distribution Systems Considering the Active Network Management

Abstract As the penetration rate of renewable distributed generation (RDG) increases, its random fluctuation characteristics have brought many problems to the safe operation of the active distribution network (ADN), such as voltage over-limit, reverse flow, and deterioration of power quality. Therefore, it has effectively affected the new energy hosting capacity of the ADN. Therefore, the effective assessment of the new energy hosting capacity of the ADN is a key part of the distribution network planning. In order to cope with the random fluctuation characteristics of new energy, this paper presents a two-stage robust assessment method of RDG hosting capacity of distribution networks by considering active network management (ANM) techniques such as network reconfiguration, reactive power compensation and on-load voltage regulation. Finally, the improved IEEE-33 distribution system is used to verify the results. The proposed method has been shown to be effective for evaluating the ADN’s RDG hosting capacity.

Experimental study on the flash boiling spray characteristics and jet fluctuation of high-pressure direct injection liquid ammonia

The high-temperature environment of actual engines significantly influences the characteristics of high-pressure liquid ammonia flash boiling spray and leads to jet instability. Therefore, this study investigated the influence mechanisms of different ambient temperatures on the high-pressure liquid ammonia flash boiling spray characteristics in a constant volume chamber. Simultaneously, it conducted the first exploration of the fluctuation characteristics of liquid ammonia jets, laying a foundation for achieving the stable and efficient combustion. The results indicate that the spray exhibits a three-stage axial development process at different ambient temperatures and ambient pressures, and the non-dimensional empirical formulas for describing the different stages of ammonia were proposed. In high-temperature conditions, the spray area is subject to the synergistic effects of flash boiling and evaporation. During the early stages, the spray development is dominated by flash boiling, leading to a rapid increase in the change rate of the spray area. However, during the later stages, the spray development is dominated by high-temperature evaporation, resulting in a rapid decrease in the change rate of spray area. Therefore, with increasing ambient temperature, the spray area experiences a significant reduction during the later stages. Through an analysis of spray centroid fluctuations at different ambient temperatures, it is evident that with rising ambient temperature, thermal disturbances intensify, leading to an increase in the oscillations deviation of the near-nozzle local region, and the maximum growth rate reaches 59.16%. Regarding different flash boiling stages, the spray centroid fluctuation is more stable during the transition flash boiling stage, with oscillation deviations below 0.02 at all ambient temperatures.

The influence of air distribution ratio on the fluctuation characteristics and stability of horizontal jet diesel non-premixed flame under extreme sub-atmospheric pressures

The burning problem in the plateau environment attracts more and more people’s attention, and the plateau adaptability and flame stability of burner are the focus of recent research. The main purpose of this paper is to reveal the horizontal jet spray flame fluctuation characteristics and stability change rule under extremely low pressure (0.05 MPa) at a high altitude (about 5500 m) inhabited by human beings. Flame morphology and temperature properties were investigated in a low-pressure chamber with different secondary air ratios (23–53 %). It is found that the normalization of the flame trajectory equation is not affected by the ratio of secondary air. The temperature in the flame recirculation zone can be increased by 110 K as the proportion of secondary air increases to 45 %, but the maximum temperature is still lower than 1500 K. A continuous flame image processing method was implemented to define and analyze the flame fluctuation region. The results show that the dimensionless fluctuation parameter γ can predict the flame stability in advance than β. When the secondary air ratio is 40 %, the flame has the largest upward fluctuation; and when it exceeds 45 %, the flame stability becomes worse. This work is the first to obtain the results of the study on flame morphology and stability of horizontal jet spray flame distribution ratio under extremely low atmospheric pressure, which provides a theoretical scientific basis for the design of plateau burner, flame control, and flame stability improvement.

Research on Internal Flow and Pressure Fluctuation Characteristics of Centrifugal Pumps as Turbines with Different Blade Wrap Angles

The use of pumps as turbines has been gaining more and more attention in recent years. The present work mainly investigates the influence of blade wrap angle on the internal flow and pressure fluctuation characteristics of centrifugal pumps as turbines. Five different wrap angles (35°,45°, 55°, 65°, and 75°) for a forward-curved impeller were numerically analyzed under multiple operating conditions. The accuracy of numerical simulation was validated by experimental results. The results show that maximum efficiency is achieved with a blade wrap angle of 35°, and the highest efficiency flow point gradually decreases as the blade wrap angle increases. It is found by conducting entropy production theory analysis that the high-entropy production rate regions in PATs are concentrated in the volute tongue and impeller blade inlet regions, and that the entropy production rate at the impeller inlet region increases and then decreases as the blade wrap angle decreases. In addition, pressure pulsation was affected not only by dynamic and static interference but also by an irregular vortex around the impeller; its magnitude under Qt is higher than 0.8Qt for blade wrap angles of 55° and 75°. The primary frequency of pressure pulsation within the impeller is the axial frequency fn and its multiples, and the frequency with the largest amplitude is 3fn. The periodicity of vortices is closely related to the periodicity of pressure pulsation. And it is suggested that a PAT with a 35° blade wrap angle is advantageous for improving the stability of a turbine.

A study of European wheat price series forecasting based on multiple variants of Holt-Winters and LSTM models

Given the importance of wheat in global food security and agricultural economy, accurate price forecasts are of significant practical significance for growers, the food chain, and government macro-control. Four different time series forecasting models were used in this study, including the traditional Holt-Winters three-parameter exponential smoothing method and three improved models based on the Long Short-Term Memory Network (LSTM): the CNN-LSTM, the GRU, and the VMD-LSTM. By comparing the forecasting effects of these models under the same training and test sets, this study aims to select the best models using the best model for predicting European wheat prices from 2010 to 2023 after training. The results show that the CNN-LSTM model performs the best in predicting the European wheat price series, and the future wheat price will show a slow downward trend, and the CNN-LSTM model combines the feature extraction ability of convolutional neural network and the long-term dependency learning ability of LSTM, which can effectively capture the fluctuation characteristics of the price series and the trend characteristics. The GRU model also shows a better prediction ability, especially in dealing with long-term dependencies. in dealing with long-term dependencies. However, the VMD-LSTM model has certain shortcomings in its prediction effect when facing time series data with large fluctuations in the later period. In addition, the Holt-Winters model predicts that after a period of slow decline, wheat prices may rebound, which may be related to the adjustment of market supply and demand and changes in external factors.

Investigation of fracture-plugging wellbore strengthening: Large scale true tri-axial experiments and field tests

Lost circulation caused by developed natural fracture occurs frequently in tight sandstone formations located in Sichuan Basin, China. Fracture-plugging wellbore strengthening by lost circulation materials (FPWSLCM) is a widely applied fluid loss control technique globally. The upper limit of the pressure-bearing capacity treated using FPWSLCM and the relevant engineering influencing factors needs to be investigated further. In this paper, a self-designed large-scale true tri-axial cell was developed to simulate the fracturing and sealing processes in a cubic sandstone sample (30 cm × 30 cm×30 cm) under anisotropic stress to investigate the effect of lost circulation materials (LCM) and the experimental processes on the formation pressure-bearing capacity. Three homogeneous cubic tight sandstone samples taken from Xujiahe Formation in Sichuan Basin with a central hole were used for the wellbore strengthening experiments with FPWSLCM, which was used to eliminate the heterogeneity effect of the rock. SRIPE (SINOPEC Research Institute of Petroleum Engineering) bridge plugging materials were used as LCM. The results show that the formation pressure-bearing capacity after treatment by FPWSLCM was affected by the initial injection pressure, the intrusion amount of LCM, the pressure holding time, and the injection rate. The formation pressure-bearing capacity did not decrease consistently with the increase of plugging zone instability times, but showed an obvious characteristic of fluctuations; the formation pressure-bearing capacity exceeded the fracturing pressure in some cases. The experimental results could be explained by the stress cage theory. Finally, the modified FPWSLCM was applied as a lost circulation control approach by drilling into the tight sandstone formation in the Shunbei oil field, which has a history of severe loss of fluid circulations. The result of the field test indicated that the modified approaches were more successful than the previous approaches used in other wells in this block. The research results are of great significance for improving the success rate of lost circulation control and a reduction in drilling costs.

Research on day-ahead and intraday scheduling strategy of distribution network based on dynamic partitioning

With the massive participation of new energy in the operation of distribution network (DN), the uncertainties arising from both load and renewable generation have brought challenges to its secure and reliable operation. In this paper, a model of day-ahead and intraday optimal scheduling based on dynamic partitioning (DP) of DN is constructed to realize the refinement of operation in both temporal and spatial dimensions, as well as to improve the reliability of system operation. For the strong fluctuation characteristics of the source-load in DN, the DP is achieved under the premise that the partition structure in each period is tight and the internal power supply has the ability to balance the power fluctuations. In order to improve the regional autonomy of DN, a day-ahead multi-objective optimal scheduling model is constructed based on the DP with the optimization objectives of weak inter-partition power coupling, lowest deficiency rate of flexibility, and lowest operating cost. And a scheme for articulation is proposed to ensure the effective guidance of day-ahead for intraday. Then the intraday dispatch model is constructed by shifting the focus to the incorporate characteristics of DP and quickly smooth the net load fluctuations. Finally, the performance and reliability of the proposed models are verified via case studies.

East Asian winter monsoon intensification over the Northwest Pacific Ocean driven by late Miocene atmospheric CO2 decline.

East Asian winter monsoon (EAWM) activity has had profound effects on environmental change throughout East Asia and the western Pacific. Much attention has been paid to Quaternary EAWM evolution, while long-term EAWM fluctuation characteristics and drivers remain unclear, particularly during the late Miocene when marked global climate and Asian paleogeographic changes occurred. To clarify understanding of late Miocene EAWM evolution, we developed a high-precision 9-million-year-long stacked EAWM record from Northwest Pacific Ocean abyssal sediments based on environmental magnetism, sedimentology, and geochemistry, which reveals a strengthened late Miocene EAWM. Our paleoclimate simulations also indicate that atmospheric CO2 decline played a vital role in this EAWM intensification over the Northwest Pacific Ocean compared to other factors, including central Asian orogenic belt and northeastern Tibetan Plateau uplift and Antarctic ice-sheet expansion. Our results expand understanding of EAWM evolution from inland areas to the open ocean and indicate the importance of atmospheric CO2 fluctuations on past EAWM variability over large spatial scales.

An innovative variable flow control strategy and system performance analysis of a solar collector field

The dynamic changes in the environmental variables and the fluctuation characteristics of the thermal storage temperature have notable influences on the efficiency of solar collector fields. In addition, the optimal flow rate of solar collector fields varies under different combinations of variables and depends primarily on the collector scale and connection form. On this basis, it is imperative to carefully and comprehensively determine and adjust the optimal operating flow rate, considering the specific characteristics of the employed solar collector field under diverse variable combinations. To address this, this study proposes and develops a variable flow control strategy for solar collector fields based on maximizing net income. The presented strategy adjusts the operation flow according to environmental variables and the thermal storage tank temperature. The control principle of the proposed strategy and the corresponding method of obtaining the optimal flow are described. Based on this principle, the optimal flow optimization model is established, and the polynomial function of the optimal flow value is obtained by regression. Using the developed model, several conventional control methods are defined and simulated, and an analysis is performed to compare the collector’s performance under different scenarios. The results indicated that the variable flow control strategy proposed in this study can significantly improve the economic feasibility of solar collector fields. A 100 m2 series–parallel flat-plate solar collector field is considered as an example, and the proposed variable flow control strategy is implemented. As a result, a notable increase in the net income is reported compared to other conventional operation strategies, ranging from 6.70 % to 14.04 % in three different regions, namely Lhasa, Yinchuan, and Xi’an.

Multifractal Analysis of International Energy and Agricultural Markets Under the Influence of Russia–Ukraine Conflict

Taking six representative futures in the international energy and agricultural markets as the research objects, we use multifractal analysis methods to study the fluctuation characteristics, market risks and cross-correlations within and between these markets before and after the outbreak of the Russia–Ukraine conflict in this paper. The empirical results show that both the auto-correlations and cross-correlations have obvious multifractal features. It is confirmed that the multifractal strength and market risks of the international energy markets have weakened, while those of the international agricultural markets have enhanced after the Russia–Ukraine conflict broke out. In addition, the Russia–Ukraine conflict has intensified the strength of the multifractality and the degree of fluctuation complexity between these two classes of international markets. Further, the intrinsic multifractal natures of cross-correlations are tested, and the apparent and intrinsic multifractality before and after the conflict are revealed. Finally, some policy suggestions are put forward based on the empirical results.

Impact of applied potential range on corrosion behavior of stainless steel oxygen evolution electrode under potential cycle loading

We investigated the corrosion behavior of 310S stainless steel anode for alkaline water electrolyzer under various triangle-wave potential cycle loadings by changing the lower (x) and higher (y) vertex potentials to simulate the power fluctuation characteristics of renewable energy sources. The anode was subjected to the loadings of x = 0.5–1.5 and y = 1.8–2.5 V in 7 M KOH solution. The dissolution of Fe and Cr into the electrolyte depended significantly on x. Notably, under conditions of x ≥ 1.35 V, the total dissolution amounts of Fe and Cr after the 20,000 potential cycles decreased to approximately 7 % of the condition where x = 0.5 V. Conversely, y had less influence on the total dissolution amounts. Interestingly, the molar ratios of the eluted Fe and Cr into the electrolyte depended on both x and y, suggesting distinct corrosion behaviors of the stainless steel induced by the potential cycles of x ≤ 1.35 and y = 1.8 V, compared to those at x ≥ 1.35 and y = 2.5 V. These findings suggest the importance of precise potential control of the stainless steel anode in alkaline water electrolysis for preventing potential fluctuation-induced corrosion.

Exploring the Relationship between Wind Patterns and Hospital Admissions Due to Respiratory Symptoms in Children.

Respiratory disorders significantly impact adolescents' health, often resulting in hospital admissions. Meteorological elements such as wind patterns have emerged as potential contributors to respiratory symptoms. However, it remains uncertain whether fluctuations in wind characteristics over extended periods have a tangible impact on respiratory health, particularly in regions characterized by distinct annual wind patterns. Crete is situated in the central-eastern Mediterranean Sea and frequently faces southerly winds carrying Sahara Desert sand from Africa and northerly winds from the Aegean Sea. This retrospective study analyzes long-term wind direction data and their relationship to respiratory symptoms observed in children up to 14 years old admitted at the University Hospital of Heraklion between 2002 and 2010. Symptoms such as headache, dyspnea, dry cough, dizziness, tachypnea, throat ache, and earache were predominantly reported during the presence of southern winds. Fever, productive cough, and chest pain were more frequently reported during northern winds. Cough was the most common symptom regardless of the wind pattern. Southern winds were significantly associated with higher probabilities of productive or non-productive cough, headache, dyspnea, tachypnea, dizziness, earache, and throat ache. Northern winds were related to a higher incidence of productive cough. Rhinitis, asthma, allergies, pharyngitis, and sinusitis were related to southern winds, while bronchiolitis and pneumonia were associated with northern winds. These findings underscore the critical role of local climatic factors, emphasizing their potential impact on exacerbating respiratory conditions in children. Moreover, they point out the need for further research to elucidate the underlying mechanisms and develop targeted interventions for at-risk populations.

Spatio-temporal differentiation characteristics and the influencing factors of PM2.5 emissions from coal consumption in Central Plains Urban Agglomeration

Central Plains urban agglomeration (CPUA) had developed rapidly, but its air pollution was also serious. Despite advances in study on China's PM2.5 emissions from coal consumption (CC), the differentiation characteristics and the affecting variables of PM2.5 in CPUA required further investigation. This paper computed the PM2.5 emissions of each city from 2000 to 2020 using CC data from CPUA, evaluated its spatio-temporal fluctuation characteristics using the spatial autocorrelation and analyzed its influencing factors by combining various indicators through the spatial Durbin model (SDM). The results verified that: (1) There was a trend of rapid increase of PM2.5 emissions from CC; (2) The Moran's I of the PM2.5 emissions from CC showed a significant agglomeration effect; (3) PM2.5 emissions from CC had a strong spillover effect. The recommendations were in this following: (1) The urban pollution regulation and the pace of industrial green transformation should be Strengthened; (2) Close linkages between cities should be established and attention should be paid to pollution management; (3) The spillover of PM2.5 emissions from CC should be lessened and development of environmental governance technology should be enhanced.

Multifractal Characteristics and Displacement Prediction of Deformation on Tunnel Portal Slope of Shallow Buried Tunnel Adjacent to Important Structures

The tunnel portal section is often in extremely weak and fragmented strata, and the deformation of the portal side and slope will affect the stability of the surrounding rock and the tunnel-supporting structure. However, the deformation characteristics and displacement development patterns of slopes in the tunnel portal section are not clear. In this paper, the multifractal characteristics and displacement prediction of the deformation sequence of the tunnel portal slope at of a weak and water-rich shallow buried tunnel adjacent to an important structure are studied in depth. Combined with the deformation characteristics of the tunnel portal slope, a suitable slope monitoring and measurement scheme is designed to analyze the deformation pattern of the tunnel portal slope. Based on the multifractal detrended fluctuation analysis (MF-DFA) method, the multifractal characteristics of the deformation monitoring sequences at each monitoring point of the tunnel portal slope are analyzed. The multifractal characteristics of displacement sequences at different monitoring points of the tunnel portal slope are consistent with the actual monitoring results. Furthermore, the Long Short-Term Memory (LSTM) model is optimized using the Particle Swarm Optimization (PSO) algorithm to predict the deformation of the tunnel portal slope. The results show that the maximum mean square error (MSE) of the horizontal displacement test set prediction results is 0.142, and the coefficient of determination (R2) is higher than 91%. The maximum value of MSE for vertical displacement test set prediction is 0.069, and the R2 are higher than 91%. The study shows that the performance of the PSO-LSTM prediction model can meet the requirements for predicting the displacement of the tunnel portal slope. Based on the MF-DFA method and PSO-LSTM prediction model, the fluctuation characteristics of the displacement value of the tunnel portal section can be accurately identified and the displacement development pattern can be effectively predicted. The conclusions of the study are of great practical significance for the safe construction of the tunnel portal section.

Ab Initio Characterization of the CO2-Water Interface Using Unsupervised Machine Learning for Dimensionality Reduction.

Precise characterization of the supercritical CO2-water interface under high pressure and temperature conditions is crucial for the geological storage of carbon dioxide (CO2) in deep saline aquifers. Molecular dynamics (MD) simulations offer a valuable approach to gaining insight into the CO2-water interface at a microscopic level. However, no attempt has been made to characterize the CO2-water interface with the accuracy afforded by ab initio calculations. In this study, we performed ab initio MD (AIMD) simulations to investigate the structural and dynamical properties of the CO2-water interface, comparing the results with those obtained from classical force-field MD (FF-MD) simulations. Molecular orientation at the interface was well reproduced in both AIMD and FF-MD simulations. Characteristic structural fluctuations of water at the interface were unveiled by applying multidimensional scaling and time-dependent principal component analysis to the AIMD trajectories; however, they were not prominent in the FF-MD simulations. Furthermore, our study demonstrated a marked difference in the residence time of molecules in the interface region between AIMD and FF-MD simulations, indicating that time-dependent properties of the CO2-water interface strongly depend on the description of the intermolecular forces.

A Field Test Study on the Instability of a Pump-Turbine under Turbine Mode

Abstract In the context of increasing demand for flexible operation of hydropower plants, this study analyses the factors leading to instability in a prototype pump turbine under turbine mode, based on experimental data collected on-site. Pressure sensors and accelerometers were installed to compare pressure signals and vibration acceleration signals. The test results show that the characteristics of pressure fluctuation are dominated by three specific factors under different output power. Vibration reaches its maximum value at approximately 30% of the rated output and its minimum value at around 70% of the rated output, and the causes of twice increases in vibration is not the same. These characteristics often indicate potential unsteady flow, vortex-induced vibration, and flow separation, subsequently affecting the stability of the pump turbine. Understanding the conditions and severity of the occurrence of instability characteristics in the unit is of great significance for power plant personnel to adjust the unit’s operation strategy and improve operational efficiency.

Impact of rotor–stator axial spacing on the gas–liquid–solid flow characteristics of a multiphase rotodynamic pump based on the Euler multi-fluid model

Multiphase rotodynamic pumps are used by the oil and gas industry to transport mixed media in pipelines. The characteristics of gas–liquid–solid flow in such pumps are significantly affected by the rotor–stator axial spacing so that further investigation is required. Based on the Euler multi-fluid model, the Computational Fluid Dynamics simulations were conducted in this study on the gas–liquid–solid multiphase rotodynamic pump at the rotor–stator axial spacings of 8, 10, 12, 14, and 16 mm, respectively. Changes in the pump's characteristics of external, multiphase flow, and pressure fluctuation were systematically analyzed by using ANSYS-CFX. The results showed that, an overall decreasing trend for the efficiency and head of the multiphase rotodynamic pump were demonstrated with increases in the rotor–stator axial spacing from 8 to 16 mm, which can be categorized into plummets I, moderation, and plummets II. As the rotor–stator axial spacing increased, the pressurization decreased from the inlet to outlet of guide vane while the aggregation of gas and solid increased. Additionally, vorticity increased and vortex structure was found to be more significant. As a result, the overall performance of the multiphase rotodynamic pump deteriorated. The pressure fluctuation in the multiphase rotodynamic pump was determined by the rotor–stator interaction and multiphase flow under gas–liquid–solid flow conditions, resulting in a non-positive correlation between the pressure fluctuation and the pump's external and internal flow characteristics. The location of maximum pressure fluctuation in the multiphase rotodynamic pump was changed from the impeller outlet to the guide vane inlet with increases in rotor–stator axial spacing.