Oscillation Phenomenon Research Articles

Effect of temporal increase in equivalence ratio on combustion instability of a lean-premixed swirling hydrogen flame

The effect of temporal increase in the equivalence ratio on the combustion instability of a lean-premixed low-swirl hydrogen jet flame in a low-swirl combustor (LSC) is investigated in detail using a high-fidelity Large-Eddy Simulation (LES). The equivalence ratio is linearly increased from 0.3 to 0.5 over a duration of 0.4 s. The results show that the pressure oscillation amplitude in the combustor increases significantly when the equivalence ratio at the combustor inlet (ERCI) exceeds 0.42, and the maximum pressure amplitude and the combustion instability mode exhibit trends consistent with those in a previous experiment and numerical simulation conducted with the same LSC setup at a fixed equivalence ratio of 0.39. Temporal variations in the equivalence ratio and consequently the temperature inside the combustor cause the drastic amplification of pressure oscillation (when the ERCI exceeds 0.42) whose amplitude is larger than that at the fixed equivalence ratio (= 0.39). Prior to the onset of this exceptionally strong combustion instability, a transient irregular oscillation phenomenon comprising instantaneous changes in the pressure oscillation frequency is observed. While the pressure oscillations in the combustor and in the injector channel are in phase after the onset of strong combustion instability, they are in opposite phases during the occurrence of the irregular oscillation phenomenon prior to the onset of strong combustion instability. This irregular oscillation phenomenon predicted by the LES may play a crucial role in the mechanism of transition from stable combustion to combustion instability.

Baryon acoustic scale at zeff = 0.166 with the SDSS blue galaxies

ABSTRACT The baryon acoustic oscillations (BAOs) phenomenon provides a unique opportunity to establish a standard ruler at any epoch in the history of the evolving universe. The key lies in identifying a suitable cosmological tracer to conduct the measurement. In this study, we focus on quantifying the sound horizon scale of BAO in the Local Universe. Our chosen cosmological tracer is a sample of blue galaxies from the Sloan Digital Sky Survey (SDSS), positioned at the effective redshift $z_{{\rm eff}} = 0.166$. Utilizing Planck-CMB input values for redshift-to-distance conversion, we derive the BAO scale $s_{{\rm BAO}} = 100.28 ^{+10.79} _{-22.96}$ Mpc h−1 at the 1$\sigma$ confidence level. Subsequently, we extrapolate the BAO signal scale in redshift space: $\Delta z_{{\rm BAO}}(z_{\rm eff}=0.166)=0.0361^{+0.00262}_ {-0.0055}$. This measurement holds the potential to discriminate among dark energy models within the Local Universe. To validate the robustness of our methodology for BAO scale measurement, we conduct three additional BAO analyses using different cosmographic approaches for distance calculation from redshifts. These tests aim to identify possible biases or systematics in our measurements of $s_{{\rm BAO}}$. Encouragingly, our diverse cosmographic approaches yield results in statistical agreement with the primary measurement, indicating no significant deviations. Conclusively, our study contributes with a novel determination of the BAO scale in the Local Universe, at $z_{{\rm eff}} = 0.166$, achieved through the analysis of the SDSS blue galaxies cosmic tracer.

Exploring Spatial and Temporal Patterns in the Debrecen Solar Faculae Database: Part I

Photospheric faculae are markers of the solar magnetic field, appearing as bright regions along the edges of granules on the Sun’s surface. Using data from the Debrecen Solar Faculae Database, we investigated the spatiotemporal distribution of photospheric faculae between 2010 May 1 and 2014 December 31 and found the following. (i) At lower latitudes, there is an enhanced abundance of faculae appearing as stripes at given Carrington longitudes, which are interpreted as indicative of the presence of active longitudes. (ii) At higher latitudes, we identified so-called crisscross patterns of facular appearance. These patterns are likely the result of faculae in regions situated along the boundaries of supergranules. Last but not least, (iii) various periods of oscillatory phenomena were identified in this facular data set, including a longer periodic range consistent with the quasi-biennial oscillations and shorter ones with periods of 4–12 days. Our findings are supported by the visualization of a simple heuristic thought experiment and more complex dynamo simulations, strengthening the proposed interpretation of the three observed solar phenomena reported.

Design principles and control of non-cooperative oscillatory enzymatic reactions

Oscillatory phenomena are often observed in enzyme systems due to feedback regulation, with a classic motif for persistent oscillation being a three-component negative feedback loop. Delay and high cooperativity are proposed as essential for the oscillation in these motifs. This study focuses on designing and optimizing oscillatory biochemical reactions using three-node enzymatic networks without cooperativity. Our findings revealed that improving the specificity constant – the so-called kinetic efficiency – and selecting the optimal topology can greatly increase the probability and frequency of oscillation in biochemical reactions. Inspired by pharmacology, various moderators were utilized to enhance the specificity constant, demonstrating how various oscillatory regimes can be reached with a given topology.

Marangoni Convection Velocity in Nonlinear Hanging-Droplet Vibration Phenomena

The Marangoni effect involves a mass transfer along an interface between two phases owing to the gradient of the interfacial tension. The flow caused by this phenomenon is called Marangoni convection, a complex phenomenon that involves mass transfer processes, such as surfactant adsorption/desorption processes, solvent dissolution phenomena, and viscous dissipation processes. Therefore, the strength of the convection depends on the various thermodynamic and physical properties of the fluids. In this study, we experimentally investigated the relationship between the Marangoni convection generated inside a hanging oil droplet and the interfacial tension of the oil droplet in an aqueous phase by the particle image velocimetry method. This convection velocity depended on the initial value of the interfacial tension in the oil–water interfacial tension oscillation phenomenon accompanied by the expansion and contraction of the hanging drop. Additionally, the droplet oscillation frequency decreased as the Marangoni convection velocity increased. Furthermore, continuous convection, which is unlike Marangoni convection, was observed within this spontaneously expanding and contracting hanging-droplet system. This buoyant convection was caused by the mutual dissolution of the hanging-droplet oil phase and the surrounding aqueous phase.

Experimental study on the combustion and pressure drop characteristics of a pintle injector for LOX/kerosene rocket engine

Pintle injectors have attracted much attention in recent years for their excellent throttling and combustion performance. However, the combustion characteristics of cryogenic propellant on pintle injectors with varying operating conditions remain unclear. A LOX/kerosene throttleable rocket engine with a fuel-centered liquid-liquid pintle injector was designed and its pressure drop and combustion characteristics were tested. The pintle engine achieved stable combustion with the total flow rate and oxygen-fuel mixture ratio varying from 59 to 559 g/s and from 0.73 to 1.02. A calculation model for the gas ratio in the LOX channel of the pintle injector was established. The deviation of measurements from the calculated values did not exceed ±10%. The vaporization of LOX from the pintle injector in the hot test was calculated and the positive correlation between gas ratio and combustion efficiency was analyzed. For the phenomenon of low-frequency oscillation of pressure in the hot tests, the source and development process of the oscillation were studied by FFT. The primary frequency and amplitude of low-frequency oscillation had been discovered to exhibit a positive correlation with the gas ratio. Low pressure drop of injection was the main cause of low-frequency oscillation. The strong vaporization of LOX under low operating conditions made the combustion efficiency remain in a high range even if low-frequency oscillation was observed. This work can provide a reference for the design of pintle injectors for cryogenic liquid rocket engines that can be deeply throttled.

Metabolic Oscillation Phenomena in Clostridia Species—A Review

Clostridia are interesting candidates for biotechnological applications due to their diverse and unique metabolic abilities. Particularly in continuous fermentation processes, productivity-decreasing metabolic oscillations have been reported in many species. The resulting process instability and reduced productivity can be a serious hurdle for the development of industrially feasible processes. This review highlights the current state of knowledge about oscillatory metabolic phenomena in Clostridia, including the mechanisms, assumed and proven, behind those oscillations and methods to mitigate the phenomena if applicable. The nature of observed metabolic oscillations in Clostridia is diverse, including a wide range of periods of oscillation and different parameters in which the oscillation is observed. Some phenomena remain to be investigated further, while others are already well understood. However, knowledge of mechanisms is a very valuable asset in overcoming the metabolic oscillation to create a stable process.

A control algorithm to follow the limitations of an electric vehicle motor using the Tm4 Sumo drive as an example

A control algorithm to follow the limitations of an electric vehicle motor using the Tm4 Sumo drive as an example

Phenomenon of reverberation intensity oscillation observed in shallow-water reverberation experiment

Reverberation has always been a disturbance for active sonar. In the Yellow Sea reverberation experiment conducted in July 2014, the motion of the soliton internal wave was recorded by the temperature sensor attached to the vertical array. The effect of the soliton internal wave on reverberation was investigated from both the temperature chain and the reverberation static experiment. Through the processing of the data in this section, it is found that the soliton internal wave can cause the generation of clutter and the oscillation phenomenon of the average reverberation intensity, and the subsequent research can realize the acoustic telemetry to forecast the internal wave and further improve the performance of the active sonar.

Gravitational wave oscillations in bimetric cosmology

Unlike general relativity, in bimetric gravity linear gravitational waves do not evolve as free fields. In this theory there are two types of tensor perturbations, whose interactions are inherited from non-trivial couplings between two dynamical metric tensor fields in the Hassan-Rosen action, and are responsible for the phenomenon of bigravity oscillations. In this work, we analyze the dynamics of cosmological tensor modes in bimetric gravity on sub-horizon scales and close to the general relativity limit. In this limit, the system has a characteristic length scale L that is strictly contained within the comoving Hubble radius. Thus, depending on the magnitude of the comoving wavelength λ relative to L, we identify two regimes of interest where the system can be studied analytically: (i) deep sub-horizon modes with λ ≪ L, whose dynamics can be studied using multiple scale analysis and are characterized by small and slowly evolving super-imposed perturbations; (ii) sub-horizon modes with λ ≫ L, where the dynamics is characterized by fast super-imposed oscillations that can be studied using asymptotic techniques for highly oscillatory problems. Furthermore, our analysis represents a substantial improvement compared to previous analyses based on a generalization of the WKB method, which, as we show, is ill-suited to study the system at hand.

Wave resonance mitigation using a rigid submerged breakwater in a varying-width channel

This paper digs deeper into the phenomenon of wave oscillation that is caused by external forces, such as air pressure and seismic vibrations. This would eventually lead to potentially dire consequences, particularly in coastal areas. In order to solve this issue, this study focuses on adding a rigid breakwater at the bottom of the basin to minimize the aforementioned damages. We will be looking at a semi-closed basin with triangular width and either constant or triangular depth, to which is added one block of the submerged breakwater with smooth and rough surfaces. We will employ the modified shallow water equations to obtain the analytical natural period for each basin type. After that, numerical simulations are carried out to check the presence of resonance phenomena in each basin. Additionally, the study investigates the crucial role of the friction coefficient in preventing resonance in basins with rough-surfaced submerged breakwaters. The aim is to explore whether a single block of smooth-surfaced submerged breakwater is sufficient to eliminate resonance or whether other conditions are necessary to halt the resonance phenomenon in each basin. Ultimately, the findings of this study hold potential benefits for individuals involved in the planning and construction of harbors and protective structures. By gaining a deeper understanding of wave oscillation and resonance in semi-closed basins, the research aims to contribute valuable insights for creating more effective and resilient coastal protection measures.

Detection of limit cycle signatures of El Niño in models and observations using reservoir computing

While the physics of the El Niño–Southern Oscillation (ENSO) phenomenon in the Tropical Pacific is quite well understood, there is still debate on several more fundamental aspects. The focus of this paper is on one of these issues that deals with whether ENSO variability, within the recharge-discharge oscillator theory arising from a stochastic Hopf bifurcation, is subcritical or supercritical. Using a Reservoir Computing method, we develop a criticality index as an indicator for the presence of a limit cycle in noisy time series. The utility of this index is shown in three members of a hierarchy of ENSO models: a conceptual box model, the classical Zebiak-Cane model and a state-of-the-art Global Climate Model. Finally, the criticality index is determined from observations, leading to the result that ENSO variability appears to be subcritical.

How to develop modelling competence for Vietnamese students

Developing modeling competence is an educational objective in many countries such as “SEP 2: Developing and Using Models” in Next Generation Science Standards (NGSS). In Vietnam, the new physics-education curriculum has clearly defined the key learning outcomes, including modeling-competence elements as well. Experiencing modelling cycle is an effective way to develop modelling competence for students. Our recent work studies which tool is suitable for students and how to integrate this tool in modelling activities. This paper presents the use of Coach 7 modelling software to investigate common physics phenomenon of oscillations, shows feasibility and effectiveness of these activities via tryout.

Generation and Suppression of Pendant Droplet Oscillation in Electron Beam Directed Energy Deposition

Electron beam–directed energy deposition (EB–DED) has emerged as a promising wire-based metal additive manufacturing technique. However, the effects of EBs on pendant droplets at wire tips have not yet been determined. The aim of this study is to enhance the understanding of this action by analyzing the mechanism of droplet oscillation. The pendant droplet oscillation phenomenon hinders the stable transfer of droplets to the molten pool and limits the feasibility of manufacturing complex lattice structures by EB–DED. Hence, another aim of this study is to create an oscillation suppression method. An escalating asymmetric amplitude is the main characteristic of droplet oscillation. The primary oscillation-inducing force is the recoil force generated from the EB-acted local surface of the droplet. The physical mechanism of this force is the rapid increase and uneven distribution of the local surface temperature caused by the partial action of the EB. The prerequisites for droplet oscillation include vacuum conditions, high power densities, and bypass wire feeding processes. The proposed EB–dynamic surrounding melting (DSM) method can be applied to conveniently and effectively suppress oscillations, enable the accurate transfer of droplets to the molten pool, and achieve stable processes for preparing the strut elements of lattice structures. Lowering the temperature and improving the uniformity of its distribution are the mechanisms of oscillation suppression in EB–DSM. In this study, the physical basis for interpreting the mechanism by which EBs act on droplets and the technical basis for using EB–DED to prepare complex lattice structure parts are provided.

A knitted smart sneaker system based on piezoresistive strain sensing for stride counting

Currently, smart shoes are not as common as other wearable devices such as fitness trackers or smartwatches. However, with the continuous improvement in sensor and IOT technologies, it is expected that shoes with smart capabilities will catch up with the other popular wearables. The emergence of 3D knitting and its subsequent application in footwear manufacture has revolutionized the shoe manufacturing process. The use of knitwear allows for shoe parts such as the upper or the sole (insole, Strobel sole, midsole and/or outer sole) to be tailored with specific areas having different characteristics and providing different functions with low production effort. This study presents the design and manufacture of a knitted smart sneaker for cadence mensuration. The specified part of the sneaker is knitted with silverplated polyester yarn to serve as a strain sensor. During the weight-bearing and release phases of the foot, while walking, this strain sensor is stressed and relaxed by this oscillatory phenomenon thus allowing footstep data to be measured. Stride estimate tests were carried out and the results established that strides taken by a user can accurately be correlated to the readings of the system. This study is the first to develop a smart shoe-sensing system where the sensor is inherently embedded within the shoe upper.

Dynamic vibration absorber for the mitigation of potential wheel polygonization at trams

Polygonal wheels are a widespread problem in the railway industry. Oscillation phenomena appearing at the wheelset may provide an environment where the wheel polygonization is promoted essentially. The flexibility of the wheelset was highlighted as an important influence on these phenomena in curves with a small radius of curvature at trams in recent studies. A dynamic vibration absorber applied on the wheelset may reduce oscillations at the wheelset significantly and is studied as a potential mitigation measure of wheel polygonization. A basic system model, representing a wheelset with non-driven independently rotating wheels, is used to investigate the mechanism and performance of this passive remedy. Influences of different parameter combinations of the absorber are discussed systematically. The efficiency of the dynamic vibration absorber is analysed further with a more detailed multibody system model of a two-axle tram bogie. Results reveal that an adequately tuned absorber might significantly reduce the possible development and further evolution of predominant polygonal orders. Additionally, basic guidelines for the design of the dynamic vibration absorber applied at the wheelset are pointed out.

An investigation of the on-board microwave radiometer of satellite Altimetry for studying the atmosphere variability

Since its first launching, the ability of satellite Altimetry in providing reliable and accurate ocean geophysical information of the sea surface height (SSH), significant wave height (SWH), and wind speed has been proven by numerous researchers, as it was designed for observing the ocean dynamics through nadir range measurement between satellite and the sea surface. However, to achieve high level accuracy, environmental and geophysical effects on the range measurement must be accurately determined and corrected, particularly the effects from the atmospheric water vapor which can divert altimeter range up to 3–45 cm. Thus, satellite Altimetry is originally equipped with the on-board microwave radiometer to measure the water vapour content for correcting the range measurement. To our knowledge, no one has attempted to apply the on-board radiometer for atmospheric studies. In this present work, we attempt to optimize the on-board radiometer data for studying the atmosphere variability due to the El Niño–Southern Oscillation (ENSO) phenomena. We convert the on-board water vapor data into the precipitable water vapour (PWV), and we then investigate whether the derived PWV can capture the variability of ocean–atmosphere phenomena due to ENSO as accurate as the conventional Altimetry-derived sea level anomaly (SLA). Based on our analysis using the empirical orthogonal function (EOF), the results show convincing argument that Altimetry-derived PWV are reliable in examining the atmospheric fluctuation as the correlation of its primary principal component time series (PC1) with Oceanic Nino Index (ONI) is higher (0.87) than SLA (0.80). These results may reinforce the confidence in the ability of satellite Altimetry for ocean–atmospheric studies.Graphical

Prehispanic Arid Zone Farming: Hybrid Flood and Irrigation Systems along the North Coast of Peru

As arid lands expand across the globe, scholars increasingly turn to the archaeological record for examples of sustainable farming in extreme environments. The arid north coast of Peru was the setting of early and intensive irrigation-based farming; it is also periodically impacted by sudden, heavy rainfall related to the El Niño Southern Oscillation (ENSO) phenomenon. While the sociopolitical effects, technologies, and engineering expertise of these irrigation systems have been thoroughly examined and theorized, little is known about how farmers managed periods of water stress. The aim of this study is to test whether arid zone farming was supported by hybrid, intermittent flood and perennial water source systems in the prehispanic past. An arroyo in the Chicama Valley was selected for preliminary data collection, and these data are presented here: (1) drone photography of the arroyo capturing the aftermath of a recent (2023) rain event; and (2) potassium (K) soil test kit results from samples collected near suspected prehispanic check dam features in the same area. The paper combines these data with comparative examples from the literature to suggest that the prehispanic features functioned as water-harvesting infrastructure. The paper concludes that sustainable, arid zone farming can be supported by hybrid, intermittent flood and perennial water source systems.

Using a New Phenomenon of Electronic Oscillations Near the Positive Electrode to Generate Powerful Microwave Radiation

A novel microwaves generator scheme is introduced, where electrons perform oscillations within the electric field of a positively charged electrode. This phenomenon is based on a recently developed theory of the interaction of electrons with electric fields, which predicts the presence of a repulsive force acting on an electron near strongly positively charged bodies. Along with the usual attractive force acting at a distance, this newly discovered repulsive force causes specific oscillations of electrons in the vicinity of a positively charged electrode, leading to the generation of electromagnetic radiation. The proposed generator represents a new variant of a vircator, wherein a virtual cathode is formed in front of, rather than behind, a positively charged anode.

Triple dip La-Nina, unorthodox circulation and unusual spin in air quality of India

The recent La-Nina phase of the El Nino Southern Oscillation (ENSO) phenomenon unusually lasted for third consecutive year, has disturbed global weather and linked to Indian monsoon. However, our understanding on the linkages of such changes to regional air quality is poor. We hereby provide a mechanism that beyond just influencing the meteorology, the interactions between the ocean and the atmosphere during the retreating phase of the La-Niña produced secondary results that significantly influenced the normal distribution of air quality over India through disturbed large-scale wind patterns. The winter of 2022–23 that coincided with retreating phase of the unprecedented triple dip La-Niña, was marred by a mysterious trend in air quality in different climatological regions of India, not observed in recent decades. The unusually worst air quality over South-Western India, whereas relatively cleaner air over the highly polluted North India, where levels of most toxic pollutant (PM2.5) deviating up to about ±30 % from earlier years. The dominance of higher northerly wind in the transport level forces influx and relatively slower winds near the surface, trapping pollutants in peninsular India, thereby notably increasing PM2.5 concentration. In contrast, too feeble western disturbances, and unique wind patterns with the absence of rain and clouds and faster ventilation led to a significant improvement in air quality in the North. The observed findings are validated by the chemical-transport model when forced with the climatology of the previous year. The novelty of present research is that it provides an association of air quality with climate change. We demonstrate that the modulated large-scale wind patterns linked to climatic changes may have far-reaching consequences even at a local scale leading to unusual changes in the distribution of air pollutants, suggesting ever-stringent emission control actions.