External Fluctuations Research Articles

Study and application of coupling relationship between water-salt-resistivity-soil structure in saline soils in arid and semi-arid areas of northwest China

Widespread saline soils in Northwest China pose a serious threat to the region's ability to use infrastructure safely because they are prone to soil structure damage when subjected to external environmental fluctuations, which in turn affects the stability of the foundations for buildings. The non-destructive approach of measuring resistivity can be used to swiftly reflect the subsoil body's state and make assumptions about its safety. However, the electrical resistivity of the underground soil body can be used to quickly identify unstable areas because the resistivity is influenced by the water content, salt content, and structural characteristics of the soil body. To do this, it is necessary to understand the coupling relationship between various factors. In this study, we first constructed samples with various water, salt, and soil structure characteristics, and then used indoor tests, such as soil resistivity measurement and thermogravimetric analysis, to analyze the multiple factors affecting the resistivity characteristics of the soil. The relationship between soil resistivity and actual saline soil diseases in Northwest China was then further discussed in conjunction with the results of the indoor tests and analyses. subsequently, the resistivity and soil properties have been measured in the field at specific locations in Northwest China where railway roadbeds are diseased. The study's findings can theoretically support a deeper comprehension of the law and mechanism of soil resistivity change, as well as provide assistance for building infrastructure in Northwest China.

Effect of Blade Trimming Length on the Performance of Marine Centrifugal Pump

To study the hydrodynamic characteristics of blade trimming length in centrifugal pumps, Delayed Detached Eddy Simulation (DDES) with nonlinear eddy viscosity was utilized to conduct unsteady calculations on the centrifugal pump. A comprehensive examination of the fluid dynamic properties of the centrifugal pump, including external features, flow conditions, and pressure fluctuations, was carried out. By applying the theory of entropy production, the areas of high energy loss within the centrifugal pump were identified, and the correlations between local entropy production, energy loss, and unsteady flow in different areas with varying blade trimming lengths were analyzed. The results indicate that with the increase in blade trimming length, under rated flow conditions, the head decreases by 1.8%, 3.2%, and 5.7% for different blade trimming lengths, respectively, compared to normal impellers. Similarly, the efficiency decreases by 0.5%, 0.8%, and 1.0% for different blade trimming lengths, respectively. Similar trends were observed under other working conditions as well. As the degree of blade trimming increases, the irreversible losses after the failure of the centrifugal pump also increase significantly, indicating that the flow inside the centrifugal pump becomes disorder. Blade trimming leads to a disorderly fluid flow inside the centrifugal pump, causing an increase in the radial force during operation, which in turn leads to an increase in vibration amplitude and affects its operational stability. Blade trimming failure has a significant impact on the frequency and amplitude of pressure pulsation, resulting in abnormal pressure pulsation and abnormal vibration of the centrifugal pump. Therefore, early warning and diagnosis of blade trimming can be achieved through pressure pulsation monitoring.

A novel approach for the development of edible oleofoams using double network oleogelation systems.

Whipped oleogels (oleofoams) are commonly stabilized by crystalline particles. Still, external factors like temperature fluctuations could change the state of the crystals (phase transitions), leading to the destabilization and disruption of oleofoams. Herein, a double network oleogelation system comprised of a primary crystalline network (using glycerol monostearate) and a secondary colloidal network (stabilized by soy protein isolate-anionic polysaccharides Mailard conjugates) is proposed as a novel strategy to overcome these challenges. It was observed that the incorporation of the secondary network resulted in a lower over-run, but a higher melting point, elasticity, foam stability, and more uniform bubble size distribution. This was explained by the strong interfacial stabilization provided by the colloidal network that can protect the crystalline particle against coarsening and oil drainage. These double network oleofoams, which could retain 41-48 % air (oleogel-based), display great potential for utilization in low-calorie lipid-based products.

Does Economic Policy Uncertainty Explain Exchange Rate Movements in the Economic Community of West African States (ECOWAS): A Panel ARDL Approach

Research proposes that economic policy uncertainty (EPU) leads to exchange rate fluctuations. Given that African countries experience higher levels of uncertainty in developed/emerging markets, we examine the extent to which domestic and foreign EPU affect exchange rates for a panel of 12 ECOWAS countries covering the period 1996–2018. In order to account for non-stationarity, cross-sectional dependence, and heterogeneity, the paper employs the dynamic heterogeneous panel approach. The ECOWAS has a dual currency arrangement ranging from a common currency union (CFA) to floating exchange rates (Non-CFA). To account for this, this study splits the sample data into CFA and Non-CFA areas. In addition, this study considers the role of the global financial crisis in the exchange rate-EPU nexus. Our results show that domestic EPU has a positive effect on exchange rates in the long run for Non-CFA areas. Different from the existing literature, our results suggest that domestic EPU does not explain exchange rate fluctuations in the short run. For all countries, foreign EPU leads to appreciation in the long run and depreciation in the short run. Interestingly, foreign EPU has a more dominant effect on exchange rate fluctuations in the selected countries than domestic EPU. This may reflect the weak institutional framework in these countries, which allows external fluctuations to have a greater impact. Moreover, this could be attributed to the increase in foreign capital flows during the sample period. Thus, these countries must develop effective policies to effectively absorb these external shocks. Results are robust to different proxies of EPU.

Is bedding material a more effective thermal insulator than trap cover for small mammal trapping? A field experiment

Live trapping is a key technique for conducting ecological studies on small mammals. All-metal live traps are popular in monitoring schemes owing to their tested performance, lightweight design (aluminium) and foldability. However, capture represents a stressful situation for small mammals, particularly during cold seasons, when individuals are susceptible to cold weather starvation resulting from low temperature and insufficient food to maintain body temperature. Metal live traps provide limited protection against cold temperatures, and it is often recommended to use covers to buffer external temperature fluctuations and prevent entry of moisture. Here, we compared the insulative performance of a PVC cover designed for Sherman traps and of bedding material, using data loggers to record temperature and humidity inside traps. We conducted different experiments simulating field conditions (traps at night with a heat source inside) and different treatments (cover, bedding material) to test the thermal insulation capacity of three models of widely used commercial traps: Longworth, Sherman, and Heslinga. Our findings indicated that Longworth and Sherman traps were better insulated against ambient air temperature fluctuations than Heslinga traps (+2.0 °C warmer on average). Bedding material was paramount in reducing relative humidity and increasing thermal insulation capacity of traps (+3.1 °C), an effect that was strengthened when a PVC cover was additionally used (+4.2 °C). The covered traps prevented the direct entrance of rain and dew (reducing damp bedding), provided camouflage (reducing thefts), and improved thermal and humidity conditions of traps (potentially increasing survival of captive small mammals). Our results suggest that using covers and bedding materials can improve thermal and humidity conditions within live traps, thus reducing the metabolic costs of thermoregulation and increasing survival chances for trapped small mammals during cold seasons.

Genome-wide transcription landscape of citric acid producing Aspergillus niger in response to glucose gradient.

Aspergillus niger is the main industrial workhorse for global citric acid production. This fungus has complex sensing and signaling pathways to respond to environmental nutrient fluctuations. As the preferred primary carbon source, glucose also acts as a critical signal to trigger intracellular bioprocesses. Currently, however, there is still a knowledge gap in systems-level understanding of metabolic and cellular responses to this vital carbon source. In this study, we determined genome-wide transcriptional changes of citric acid-producing Aspergillus niger in response to external glucose gradient. It demonstrated that external glucose fluctuation led to transcriptional reprogramming of many genes encoding proteins involved in fundamental cellular process, including ribosomal biogenesis, carbon transport and catabolism, glucose sensing and signaling. The major glucose catabolism repressor creA maintained a stable expression independent of external glucose, while creB and creD showed significant downregulation and upregulation by the glucose increase. Notably, several high-affinity glucose transporters encoding genes, including mstA, were greatly upregulated when glucose was depleted, while the expression of low-affinity glucose transporter mstC was glucose-independent, which showed clear concordance with their protein levels detected by in situ fluorescence labeling assay. In addition, we also observed that the citric acid exporter cexA was observed to be transcriptionally regulated by glucose availability, which was correlated with extracellular citric acid secretion. These discoveries not only deepen our understanding of the transcriptional regulation of glucose but also shed new light on the adaptive evolutionary mechanism of citric acid production of A. niger.

Design of proportional integral observer‐based resilient control for periodic piecewise time‐varying systems: The finite‐time case

AbstractThe prime intent of this study is to scrutinize the state estimation and finite‐time (FT) stabilization problems for a class of periodic piecewise time‐varying systems (PPTVSs) in the presence of external disturbances, immeasurable states and gain fluctuations by dint of resilient control. Moreover, the proportional integral observer system is built in line with the output of the PPTVSs to reconstruct the states of the PPTVSs, since the state dynamics of the system are often not measurable. Meanwhile, the output signals are quantized with the use of a logarithmic quantizer prior to being fed into the constructed observer systems. Further, the fluctuations in the controller and observer gain matrices are considered to occur in a random manner and they pursue the pattern of a Bernoulli distributed white sequence. Subsequently, by means of Lyapunov stability theory and the matrix polynomial lemma, the adequate requirements for ascertaining the FT boundedness and IO‐FT stabilization of the addressed system are procured in the context of linear matrix inequalities. Thereupon, on the premise of the established criteria, the gain matrices of the controller and observer are obtained. Ultimately, the simulation results have been showcased including the mass spring damper system to exemplify the efficacy and usefulness of the theoretical conclusions drawn.

A fuzzy control and neural network based rotor speed controller for maximum power point tracking in permanent magnet synchronous wind power generation system

When the wind speed changes significantly in a permanent magnet synchronous wind power generation system, the maximum power point cannot be easily determined in a timely manner. This study proposes a maximum power reference signal search method based on fuzzy control, which is an improvement to the climbing search method. A neural network-based parameter regulator is proposed to address external wind speed fluctuations, where the parameters of a proportional-integral controller is adjusted to accurately monitor the maximum power point under different wind speed conditions. Finally, the effectiveness of this method is verified via Simulink simulation

On asymmetry of magnetic activity and plasma flow temperature in Jupiter’s magnetosphere

Discs of plasma around giant planets are natural laboratories that contain within mechanisms of transferring and keeping energy into the plasma and magnetic field system. Various missions to Jovian planets observed that expansion of plasmadiscs is not adiabatic and plasma temperature is increasing with radial distance. Magnetometer measurements from Juno mission were examined to determine plausibility of turbulent fluctuations as the plasma heating mechanism. Extensive azimuthal map of magnetic activity in Jupiter’s nightside plasmadisc is presented. Observations show that magnetic activity is distributed asymmetrically, with active and quiet regions. This is similar to the asymmetrical distribution of activity observed in Saturn’s magnetosphere. However, comprehensive study of temperature measurements showed that the only systematic change of temperature in magnetospheres of giant planets is in the radial direction. Observed breakfrequency in the magnetometer time series is systematically greater than the ion cyclotron frequency. Examination of the power spectrum points to that the kinetic energy of the corotating plasma as a source of increase of plasma temperature. This study shows that turbulent fluctuations themselves are not good candidates as a plasma heating mechanism. External pressure fluctuation however, can be used to convert kinetic energy of the plasma flow into thermal.

Recent progress of enhanced bubble separation in alkaline water electrolyzer

Alkaline water electrolysis has a large industrial application and development potential in hydrogen energy owing to its high maturity and low cost. However, its moderate energy efficiency, especially caused by bubble effects, inhibits its use for large-scale hydrogen production. To overcome this shortcoming, this review first analyzes the bubble effect and summarizes the external operation methods, such as external field intensification, flow operation, fluctuation operation, and surfactant addition to the electrolyte, to enhance bubble separation in the electrolyzer. Then, electrode and flow channel structure optimization, particularly superhydrophilic and superaerophobic electrodes, and flow channels with varying heights, square column arrangements, and inlet/outlet numbers are highlighted. Finally, future research directions in alkaline water electrolysis technology are suggested to advance the industrial application of large-scale alkaline water electrolysis.

Economic Resilience and Sustainable Finance Path to Development and Convergence in Romanian Counties

Economic resilience and sustainable finance are two interlinked and crucial issues for development and convergence in Romania’s counties increasing cohesion. These issues can contribute to sustainable and balanced growth of local and regional economies and to the reduction of inequalities in regional development. Economic resilience in counties refers to their capacity to adapt and survive in the face of unforeseen economic shocks or challenges, and sustainable finance refers to ensuring responsible management of financial resources to support long-term development and protect the environment. Identifying and understanding the significant variations in economic resilience and sustainable financing between counties is essential for the formulation of regional development policies and strategies. These variations provide valuable information about the vulnerabilities and opportunities of individual counties and guide resource allocation and investment decisions. The research provides new data and relevant information on the significant variations among counties in economic resilience and sustainable financing, using a Markov transition probability matrix and exploratory–visual method. This study on Romanian counties aims to provide valuable information for the formulation of public policies to support balanced economic development across the country. The results showed that economic diversification is essential to increase the resilience of the economy to shocks and fluctuations. Counties that have a diversified economic structure, with multiple sources of income and economic activities, are less vulnerable to the negative impact of economic or natural events. Governance and political stability are key factors in creating a favorable environment for investment and economic development. Well-managed government policies can help maintain macroeconomic stability and increase the resilience of the economy to external fluctuations.

Design of a 15-Level Non-Modular Multilevel-Inverter in a Grid-Connected Solar PV System: A Hybrid ZOA-SNN Technique

In this paper, a hybrid strategy is proposed for an innovative 15-level inverter method for the grid-connected photovoltaic (PV) system. The proposed technique is combined with the Zebra Optimization Algorithm (ZOA) plus the spiking neural network (SNN) and is called the ZOASNN method. The major goals of the ZOASNN approach are to fulfill the power demand of load, lessen harmonics, and improve the PV system power regulation or maximal energy conversion. The multilevel inverter (MLI) is used to operate at symmetrical and asymmetrical configurations aimed at utilizing reduced power components. The proposed ZOASNN controller develops the operating modes of two-generation methods to determine the converter switching states for this purpose. Using this control method, load demands are optimally fulfilled while external disturbances and fluctuations in system parameters are minimized. The proposed strategy is implemented in MATLAB and its performance is estimated with other algorithms, such as the Grasshopper Optimization Algorithm (GOA), the Random Forest Algorithm (RFA), and the Cuckoo Search Algorithm (CSA). The proposed method shows high efficiency, low total harmonics distortion (THD), and lower cost than other existing methods.

In-Loco Optical Spectroscopy through a Multiple Digital Lock-In on a Linear Charge-Coupled Device (CCD) Array.

Accurate and reliable measurements of optical properties are crucial for a wide range of industrial and commercial applications. However, external illumination fluctuations can often make these measurements challenging to obtain. This work proposes a new technique based on digital lock-in processing that enables the use of CCD spectrometers in optical spectroscopy applications, even in uncontrolled lighting conditions. This approach leverages digital lock-in processing, performed on each pixel of the spectrometer's CCD simultaneously, to mitigate the impact of external optical interferences. The effectiveness of this method is demonstrated by testing and recovering the spectrum of a yellow LED subjected to other light sources in outdoor conditions, corresponding to a Signal-to-Noise Ratio of -70.45 dB. Additionally, it was possible to demonstrate the method's applicability for the spectroscopic analysis of gold nanoparticles in outdoor conditions. These results suggest that the proposed technique can be helpful for a wide range of optical measurement techniques, even in challenging lighting conditions.

Sympathetically cooled highly charged ions in a radio-frequency trap with superconducting magnetic shielding

We sympathetically cool highly charged ions (HCI) in Coulomb crystals of Doppler-cooled Be+ ions confined in a cryogenic linear Paul trap that is integrated into a fully enclosing radio-frequency resonator manufactured from superconducting niobium. By preparing a single Be+ cooling ion and a single HCI, quantum logic spectroscopy toward frequency metrology and qubit operations with a great variety of species are enabled. While cooling down the assembly through its transition temperature into the superconducting state, an applied quantization magnetic field becomes persistent, and the trap becomes shielded from subsequent external electromagnetic fluctuations. Using a magnetically sensitive hyperfine transition of Be+ as a qubit, we measure the fractional decay rate of the stored magnetic field to be at the 10−10 s−1 level. Ramsey interferometry and spin-echo measurements yield coherence times of >400 ms, demonstrating excellent passive magnetic shielding at frequencies down to DC.

High-frequency measurement of concentration in an isothermal methane–air gas mixture using spontaneous Raman spectroscopy

A high-frequency (1.5 kHz) spontaneous Raman spectroscopy measurement technique is developed and applied to measure external fluctuations generated in the local concentration of an isothermal binary gas mixture of methane and air. Raman excitation is provided by a high-frequency laser at 527 nm in dual-pulsed mode. The Stokes Raman signal is collected using an EMCCD camera coupled to a high-frequency intensifier as a shutter. The emitted signal is collected over the 596–627 nm wavelength range, which allows for the simultaneous tracking of methane and nitrogen Stokes Q-branch mode signals. Calibration curves are initially obtained for each species ({text{CH}}_{4} and {mathrm{N}}_{2}) based on steady-state concentrations, and further corrected during use to detect local unsteady mixture fluctuations at gas pulsation frequencies up to 250 Hz. The main novelty is the demonstration of Raman spectroscopy for the simultaneous multispecies measurement of unsteady concentrations of gas-phase methane and air mixtures using a laser beam with a high-repetition rate, low energy per pulse, combined with a high-frequency intensifier and a single camera.

Study on nonlinear vibration and primary resonance characteristics of helicopter face gear-planetary gear coupling transmission system

In order to explore the dynamic response and primary resonance characteristics of the gear transmission system of the helicopter main reducer. The face gear-planetary gear torsion-translation vibration dynamics model is established, and the time-varying meshing stiffness, gear backlashes, gear eccentricity error, and friction are considered. The four-order variable-step Runge–Kutta was used to solve the dynamic response of the system, and the nonlinear dynamic characteristics of the system were described by time domain diagram, phase trajectory plane, Poincaré map, 3D frequency spectrum, and bifurcation diagram. Additionally, using the face gear-spur gear system's transmission as an example, the multi-scale method is used to analyze the face gear-spur gear system's primary resonance characteristics. The influence of load fluctuation amplitude, meshing damping, and meshing stiffness on its amplitude-frequency characteristics is also investigated. It is found that when external load excitation frequency changes, the vibration response of the whole system changes synchronously, which exhibits periodic, multi-periodic, and chaotic motion. In addition, according to the primary resonance analysis, the system's stability will be harmed by increasing the external load fluctuations’ amplitude, lowering the meshing damping, and raising the meshing stiffness.

Novel Graphene-Based Materials as a Tool for Improving Long-Term Storage of Cultural Heritage.

The very serious problem of temperature and humidity regulation, especially for small and medium-sized museums, galleries, and private collections, can be mitigated by the introduction of novel materials that are easily applicable and of low cost. Within this study, archive boxes with innovative technology are proposed as "smart" boxes that can be used for storage and transportation, in combination with a nanocomposite material consisting of polyvinyl alcohol (PVA) and graphene oxide (GO). The synthesis and characterization of the PVA/GO structure with SEM, Raman, AFM, XRD, Optical Microscopy, and profilometry are fully discussed. It is shown that the composite material can be integrated into the archive box either as a stand-alone film or attached onto fitting carriers, for example, those made of corrugated board. By applying the PVA/GO membrane this way, even with strong daily temperature fluctuations of ΔT = ±24.1 °C, strong external humidity fluctuations can be reduced by -87% inside the box. Furthermore, these humidity regulators were examined as Volatile Organic Compounds (VOCs) adsorbers since gas pollutants like formic acid, formaldehyde, acetic acid, and acetaldehyde are known to exist in museums and induce damages in the displayed or stored items. High rates of VOC adsorption have been measured, with the highest ones corresponding to formic acid (521% weight increase) and formaldehyde (223% weight increase).

Inherent flexibility design strategy of extractive distillation for binary azeotropic separation

The steady-state design and control studies of extractive distillation (ED) for azeotropic separation has received significant interest in the recent years. These studies however are usually conducted sequentially where the steady-state design is first developed followed by conducting the control analysis. In contrast to existing studies, this work incorporated the operational flexibility into the steady-state design of the ED so that any external fluctuations can be accounted in the early stage of the design. Two case studies are used to exemplify the inherent flexibility design strategy, i.e., the IPA dehydration using dimethyl sulfoxide (DMSO) and ethylene glycol (EG) as entrainer. Each case study is optimized using two different objective function individually, i.e., the total annual cost (TAC) and the flexibility index (FI). Optimizing both cases using TAC as objective function provides a lower TAC relative to the base case, which aligned with existing studies. In contrast, optimizing both cases using FI enables a greater operational flexibility, but such benefit is always accompanied by the increase in the TAC. During the FI optimization, four different uncertainties are considered, i.e., A, B, C, and D, with a combination of ± 20% feed flowrate and IPA feed concentration. For both cases, the operational flexibility limitation was found to lie in the direction of vertex D when the system is experiencing an increase in feed flowrate and a decrease in IPA feed composition. Overall, it was found that using EG provides 2.3 times better operational flexibility in comparison to that using DMSO, as indicated by the higher FI, while using DMSO provides a lower TAC by about 9%. Here, it was also found that using EG provides a lower trade-off in an increase in TAC over using DMSO, when the FI is incorporated into the steady-state design of the ED.

Quantum Anomalous Hall Effects Controlled by Chiral Domain Walls

We report the interplay between two different topological phases in condensed matter physics, the magnetic chiral domain wall (DW), and the quantum anomalous Hall (QAH) effect. It is shown that the chiral DW driven by Dzyaloshinskii–Moriya interaction can divide the uniform domain into several zones where the neighboring zone possesses opposite quantized Hall conductance. The separated domain with a chiral edge state (CES) can be continuously modified by external magnetic field-induced domain expansion and thermal fluctuation, which gives rise to the reconfigurable QAH effect. More interestingly, we show that the position of CES can be tuned by spin current driven chiral DW motion. Several two-dimensional magnets with high Curie temperature and large topological band gaps are proposed for realizing these phenomena. The present work thus reveals the possibility of chiral DW controllable QAH effects.

Numerical analysis of bubble size effect in a gas-liquid two-phase rotodynamic pump by using a bubble coalescence and collapse model

The inlet bubble sizes and their coalescence and collapse behavior are the key factors affecting the performance and transportability of the multiphase pump. In this paper, a bubble coalescence and collapse model is applied for the simulation of a gas-liquid two-phase rotodynamic pump. The external characteristic, gas-liquid flow, phase interaction, and pressure fluctuation are analyzed using computational fluid dynamics (CFD) methods as the inlet bubble diameter d0 varies from 0.1 mm to 2.2 mm. The CFD results show that the pump’s efficiency and pressure rise decrease sharply at 0.1 mm ≤ d0 ≤ 0.4 mm, slow down at 0.4 mm < d0 ≤ 1.3 mm, and become stable at 1.3 mm < d0 ≤ 2.2 mm. The effects of inlet bubble size on flow characteristics in the impeller, such as gas-liquid separation, flow separation, vorticity change rate, and interphase force, are larger than that in the guide vane. The drag is the most significant interphase force at d0 = 0.1 mm, while the lift force plays a dominant role at d0 = 0.7 mm and 1.9 mm. The effect of the turbulent dispersion force is weakest at d0 = 0.1 mm, 0.7 mm, and 1.9 mm. Rotor-stator interaction is the key driver of the pressure fluctuation in the gas-liquid two-phase pump but is restrained by serious phase separation, flow separation, and interphase interaction at the impeller outlet. The most obvious fluctuation occurs near the guide vane inlet at d0 = 0.1 mm, 0.7 mm, and 1.9 mm. The maximum fluctuation at d0 = 0.7 mm and 1.9 mm are 5.98 times and 7.17 times that at d0 = 0.1 mm.