Periodic Oscillations Research Articles

Calibrated models for effective clustering: Discriminating operation schedules in occupied buildings

AbstractEuropean directives advocate for end-users to be aware of their energy consumption. However, individual energy monitoring tools, such as energy meters or cost allocators, are not always affordable or technically feasible to install. Therefore, the development of virtual tools that enable the study of energy consumption in existing buildings is necessary. Virtual sensors, particularly based on white-box models, offer the opportunity to recreate these behaviours. When calibrated with measured data, white-box models, which incorporate detailed building physics, become increasingly valuable for designing energy-efficient buildings. This research explores a novel approach to identifying building’s load period directly from energy data generated by these calibrated models. The volume of data generated by white-box models can be overwhelming for visual analysis, but the hypothesis here is that analysing this data through clustering techniques can reveal patterns related to occupant behaviour and operational schedules. By feeding indoor temperature data into the calibrated model and analysing the resulting energy outputs, the research proposes a method to identify the heating, ventilation and air conditioning (HVAC) system operation schedule, free oscillation periods and non-recurrent events. Validation is achieved by comparing the identified periods with actual measured data. This methodology enables the development of a virtual sensor for cost allocation, which minimises the need for physical sensor deployment while complying with European Union directives. The research not only demonstrates high accuracy but also the potential to outperform measured schedule. This suggests the ability of the method to identify missing sensor data or other factors affecting temperature curves, enabling fault detection and diagnostics (FDD). Consequently, this opens doors for setting optimised operation schedules that balance energy efficiency with occupant comfort.

Dynamical analysis of bursting in a system with a discontinuous boundary involving two state variables

Abstract This paper investigates the bursting oscillations and the underlying dynamical mechanisms of a non-smooth system with a discontinuous boundary that involves two state variables. A slow-fast non-smooth system is established after modifying the Chua’s circuit. By applying the variable substitution, the system with a boundary involving two state variables is transformed into a system where the boundary involves only a single state variable. The topological equivalence between the systems before and after the transformation is demonstrated. The stability analysis is performed on the transformed system, and the bifurcation conditions are given. Six types of bursting oscillation patterns under different parameter settings are presented. The bifurcation transition mechanisms of these bursting patterns are revealed using two-dimensional transformed phase diagrams. It is found that an increase in the excitation amplitude leads to changes in the transition patterns of the system trajectory between point and cycle, resulting in the formation of a ‘sticking’ special spiking state. This spiking state involves multiple limit cycle attractors and an equilibrium branch. The magnitude of the excitation amplitude also affects the slow passage effect of the system, determining whether the trajectory undergoes periodic oscillations at the Hopf bifurcation point.

Reassessing the involvement of the CREB pathway in the circadian clock of Drosophila melanogaster

Circadian clocks are ubiquitous in almost all organisms on Earth and many key genes are highly conserved among species. In the mammalian suprachiasmatic nucleus, the cAMP response element binding protein (CREB) pathway is known to play a crucial role in conveying light-input to the transcription of clock genes. The fruit fly Drosophila melanogaster also expresses two Creb proteins, CrebA and CrebB, which have been associated with the circadian clock. For example, Drosophila Creb has been suggested to constitute a molecular link between neuronal excitability and clock gene transcription. In this study we subjected flies with clock cell specific CrebA or CrebB mutations to circadian behavioral and bioluminescence assays. Surprisingly, we found that neither loss of CrebA or CrebB did affect free-running locomotor behavior, rhythmic period oscillations in clock neurons, or light-dependent synchronization. In conclusion our findings question the conserved circadian role of the Creb pathway in Drosophila and encourage further studies to elucidate its potential function within insect circadian clocks.

Optimal control of glucose-insulin dynamics via delay differential model with fractional-order

This paper proposes a delay differential model with fractional order for glucose-insulin endocrine, metabolic regulation model, incorporating beta-cell dynamics to regulate and maintain bloodstream insulin concentration. In the model, two time delays are involved, namely δg and δι, which represent delayed insulin secretion and delayed glucose reduction. A moderate hyperglycemia results in beta-cell growth (negative feedback), while a severe hyperglycemia results in beta-cell reduction (positive feedback). When a time delay passes a bifurcation point, Hopf bifurcation occurs. It is evident from biological findings that the model exhibits periodic oscillations. Furthermore, we present an optimal control problem for external insulin infusions to minimize prolonged high blood sugar levels. Numerical simulations have validated the theoretical results.

A novel late-stage oscillating discharge current for plasma regulation and its effect in material removal in electrical discharge machining

Abstract Improving the material removal rate (MRR) has recently become one of the most important issues in electrical discharge machining. During the discharge process, a large portion of molten material cannot be sufficiently expelled from the molten pool but re-solidifies, ultimately resulting in low energy utilization and machining efficiency. Unlike existing methods that primarily focus on optimizing general discharge parameters, this study aims to enhance molten material expulsion and MRR through discharge plasma regulation by employing a redesigned late-stage oscillating discharge current. During a single-pulse discharge process, this kind of discharge current firstly remains constant to ensure stable heat transfer from the plasma to the workpiece, then transitions to periodic oscillations to enhance plasma movement and facilitate molten material expulsion. High-speed plasma observations and heat-flow coupling simulations are conducted to analyze the effects of the discharge currents on material removal, and the optimal oscillation start time is obtained. Experimental results in machining stainless steel demonstrate that the use of the late-stage oscillating discharge current, in comparison to the conventional rectangular discharge current, results in a 74% increase in material removal volume per unit of energy and a 56% in average recast layer thickness.

Growth-dependent concentration gradient of the oscillating Min system in Escherichia coli.

Cell division in Escherichia coli is intricately regulated by the MinD and MinE proteins, which form oscillatory waves between cell poles. These waves manifest as concentration gradients that reduce MinC inhibition at the cell center, thereby influencing division site placement. This study explores the plasticity of the MinD gradients resulting from the interdependent interplay between molecular interactions and diffusion in the system. Through live cell imaging, we observed that as cells elongate, the gradient steepens, the midcell concentration decreases, and the oscillation period stabilizes. A one-dimensional model investigates kinetic rate constants representing various molecular interactions, effectively recapitulating our experimental findings. The model reveals the nonlinear dynamics of the system and a dynamic equilibrium among these constants, which underlie variable concentration gradients in growing cells. This study enhances quantitative understanding of MinD oscillations within the cellular environment. Furthermore, it emphasizes the fundamental role of concentration gradients in cellular processes.

Freely rising or falling of a sphere in a square tube at intermediate Reynolds numbers

The motion of a sphere freely rising or falling in a 5d (d is the diameter of the sphere) square tube was numerically studied for the sphere-to-fluid density ratio ranging from 0.1 to 2.3 (0.1 ≤ ρs/ρ ≤ 2.3, ρs is the density of spheres and ρ the fluid density) and Galileo number from 140 to 230 (140 ≤ Ga ≤ 230). We report that Hopf bifurcation occurs at Gacrit ≈ 157, where both the heavy and light spheres lose stability. The helical motion is widely seen for all spheres at Ga > 160 resulting from a double-threaded vortex interacting with the tube walls, which becomes irregular at Ga ≥ 190 where heavy spheres act differently from their counterparts; that is, heavy spheres change their helical directions alternately while light spheres exhibit helical trajectories with jaggedness in connection with the shedding of the double-threaded vortices. This is because of the difference in inertia between the heavy and light spheres. We also checked the oscillation periods for the helical motion of the spheres. They show opposite variations with ρs/ρ for the two types of spheres. Light spheres (ρs/ρ ≤ 0.7) reach a zigzagging regime at Ga ≥ 200 where a vortex loop (hairpin-like vortical structure) is formed which may develop into a vortex ring downstream at small ρs/ρ. This might be the first time a transition from the helical motion to the zigzagging motion for heavy spheres (ρs/ρ ≥ 1.8) has been reported. Finally, we examined the dependence of both the terminal Reynolds number and the drag coefficient of the spheres on the Galileo number.

Application of oscillating elastic surfaces for heat transfer enhancement from heat dissipating electronic chips

The present study investigates the possibility of heat transfer enhancement from discrete heat sources by an oscillating elastic surface. The three liquid cooled heat sources are located on the bottom surface of a rectangular channel and are influenced by oscillation of the upper surface. Finite element simulations are carried out at several Reynolds numbers in the laminar flow regime for two different cases of oscillation by cosine and step loads with various periods and amplitudes. It is observed that oscillation of the channel surface alters the direction of the pressure gradient and causes backflow and several vortices along the channel. It also leads to the thermal boundary layer disturbance and flow acceleration on the heat sources and consequently intensifies the heat transfer. Results indicate that reducing the period of the oscillations improves the flow mixing and thus increases the heat transfer rate to an optimum value. Further decrease in the period has a reverse effect on the heat transfer enhancement. Maximum heat transfer enhancement of 223.4 %, 162.2 %, 137.8 %, and 150.5 % are obtained for Reynolds numbers of 200, 600, 1000, and 1400, respectively. It is worth mentioning that the heat transfer enhancement is achieved at the expense of a considerable pressure drop increase. The overall performance factor implies that the heat transfer enhancement dominates the pressure drop increase only at low amplitudes and periods of oscillations. Comparison between the cosine and step loads reveals that the cosine and step forces exhibit better heat transfer performance at low and high periods, respectively.

Experimental study on hydrogen pipeline leakage: Negative pressure wave characteristics and inline detection method

This paper presents an experimental study on a potential safety system for hydrogen fuel cells. It focuses on early leakage detection and localization. This would enable effective system response to avoid the effects of catastrophic loss of containment. Experimental results are presented from a pipeline setup wherein the leak is identified utilizing inline pressure sensors and flowmeters. The investigations involve recorded data at two leak locations at different initial pressures, mass flow rates, and leak diameters. The leak detection technique is based on analysis of the negative pressure wave (NPW) intensity and propagation duration, denoted as peak-to-peak amplitude (Δh) and oscillation period (Δτ). They are extracted from filtered pressure records' first derivative (dp/dt). Δh and Δτ increase as the initial mass flow rate and leak diameter decrease. Therefore, this approach is advantageous for detecting leaks from tiny cross-sections. Δh and Δτ measured at two leak positions at different lengths from the system inlet increase at a higher initial flow rate of 1.0 g/s, but they exhibit opposite behavior at a lower rate (0.42 g/s). Increasing the sampling rate in the dp/dt-time graphs enhances the precision of leak localization. Calculation results show an effective leakage localization with an accuracy of 15 mm (2.5%). The leak flow rate during nitrogen leakage tests is about three times that of hydrogen, and it has higher Δh (about two times at 10 bar).

A Precursor to Solar Prominence Eruptions: Detection and Analysis of EUV Prominence Oscillations

The eruption of prominences can have a significant influence on the solar–terrestrial environment. However, accurately predicting these eruptions remains a challenge. We apply automated detection methods for extreme ultraviolet (EUV) prominences observed by the twin spacecraft from the Solar Terrestrial Relations Observatory (STEREO) mission and the Solar Dynamics Observatory near Earth. We study an event, during 2011 March, when each STEREO spacecraft is in quadrature with respect to the Earth. For two time ranges, we obtain longitudinal height profiles as a function of time. We also track the corresponding EUV filaments across the solar disk, which reveal the emergence of ultra-long-period oscillations in the EUV filament channels. Our analysis shows a correlation between the prominence’s increasing height and the oscillation periods, suggesting a potential link to the subsequent eruption observed by the STEREO spacecraft off-limb. These findings offer new insights into prominence dynamics and may pave the way for improved eruption prediction.

Model for Determining Earth's Gravitational Acceleration on a Mathematical Pendulum

Gravity is an accelerating property of the earth that causes objects to fall freely. The acceleration of gravity is not the same at every place on the Earth's surface. To measure the Earth's gravity (small g), scientists can use various techniques, such as dropping a mass from a certain height and measuring the time it takes to fall to the ground or using a mathematical pendulum to measure the period of oscillation and use it to calculate the acceleration due to gravity. In this paper, a study of the mathematical pendulum in the measurement of the Earth's gravitational acceleration is conducted, and the measurement experiment is illustrated. Method To measure the length of the pendulum, you must have a ruler, meter stick, or tape measure. At the top end of the string, start the measurement at the point where the string rotates out of place. Then, measure up to the center of the pendulum, which is the object hanging on the string. From the results of this study, it can be concluded that the value of the period of a pendulum is affected by several factors, including the length of the rope used and the angle of initial deviation, while the factors that do not affect the period are the mass and diameter of the pendulum.

Wind Velocity Induced Stable and Unstable Periodic Oscillations in a Harmonically Excited Aeroelastic Energy Harvester

Wind Velocity Induced Stable and Unstable Periodic Oscillations in a Harmonically Excited Aeroelastic Energy Harvester

LDOS of electron pair and the role of the Pauli exclusion principle

The local density of states (LDOS) for a pair of non-relativistic electrons, influenced by repulsive Coulomb forces, is expressed in term of one-dimensional integrals over Whittaker functions. The computation of the electron pair's LDOS relies on a two-particle Green's function (GF), a generalization of the one-particle GF applicable to a charged particle in an attractive Coulomb potential. By incorporating electron spins and considering the Pauli exclusion principle, the resulting LDOS consists of two components: one originating from an exchange-even two-particle GF and the other from an exchange-odd two-particle GF. The calculated LDOS reveals its dependence on both inter-electron distance and energy. The pseudo-LDOS, derived from the two-body contribution to the LDOS, is examined. This term ensures complete LDOS suppression atr = 0, exhibiting a limited spatial extent, and the reasons for its emergence are elucidated. It is shown that for energies exceeding the effective Hartree energy and inter-electron distances beyond the effective Bohr radius, the impact of many-body contributions to the LDOS can be disregarded. The induced LDOS for an electron pair subjected to an attractive contact potential in two dimensions is evaluated. At small distancesafrom the potential center, a predicted relative difference in LDOS between even and odd state pair reaches approximately 8%. The calculated LDOS is compared with available experimental findings from a two-dimensional electron gas (2DEG). Both exhibit similar oscillation periods; however, the LDOS of the electron pair decays as1/a3, significantly faster than the1/adecay observed for free electrons in a 2DEG.

The Paleo‐Serchio River: history of floods between Lucca and Pisa during the Roman period

ABSTRACTThe reconstruction of flood frequency beyond the Instrumental Era is challenging and mostly based on historical sources, but it rarely covers more than the last 1000 years when abundant documentation is preserved. To investigate the long‐term trends in flooding and obtain insight into current climatic changes it is necessary to extend these data to a larger number of rivers beyond the Instrumental Era and available period of historical documentation. In this paper we reconstruct the paleoflood record for the Roman Period of the Serchio River (Auser in antiquity, located in Northern Tuscany, Central Italy) using geoarcheological data. The complex hydrological evolution of the river and the development of the important cities of Lucca and Pisa on the river bank allowed an important collection of data, showing a prominent peak in flood activity during the 1st century ce, which seems to correspond to an increase in regional rainfall interpreted from speleothem proxies. A secondary peak is present in the 6th century ce, which corresponds locally with an increase in precipitation recorded by speleothems. The phases of increased flooding, when compared with present‐day synoptical meteorological conditions, probably developed during a period of negative North Atlantic Oscillation (NAO) Index, and it is partially supported by comparison with paleoproxies for NAO. These findings confirm that an extensive collection of geoarcheological data, supported by geological and geomorphological investigation, represents a powerful tool to be integrated with historical data for the reconstruction of floods. The concomitance of local paleohydrological proxies can help in disentangling the origin of the signal from other causes.

Data-driven stabilization of an oscillating flow with linear time-invariant controllers

This paper presents advances towards the data-based control of periodic oscillator flows, from their fully developed regime to their equilibrium stabilized in closed loop, with linear time-invariant (LTI) controllers. The proposed approach directly builds upon the iterative method of Leclercq et al. (J. Fluid Mech., vol. 868, 2019, pp. 26–65) and provides several improvements for an efficient online implementation, aimed at being applicable in experiments. First, we use input–output data to construct an LTI mean transfer functions of the flow. The model is subsequently used for the design of an LTI controller with linear quadratic Gaussian synthesis, which is practical to automate online. Then, using the controller in a feedback loop, the flow shifts in phase space and oscillations are damped. The procedure is repeated until equilibrium is reached, by stacking controllers and performing balanced truncation to deal with the increasing order of the compound controller. In this article, we illustrate the method for the classic flow past a cylinder at Reynolds number $Re=100$ . Care has been taken such that the method may be fully automated and hopefully used as a valuable tool in a forthcoming experiment.

Periodic Gamma-Ray Modulation of the Blazar PG 1553+113 Confirmed by Fermi-LAT and Multiwavelength Observations

A 2.1 yr periodic oscillation of the gamma-ray flux from the blazar PG 1553+113 has previously been tentatively identified in ∼7 yr of data from the Fermi Large Area Telescope. After 15 yr of Fermi sky-survey observations, doubling the total time range, we report >7 cycle gamma-ray modulation with an estimated significance of 4σ against stochastic red noise. Independent determinations of oscillation period and phase in the earlier and the new data are in close agreement (chance probability <0.01). Pulse timing over the full light curve is also consistent with a coherent periodicity. Multiwavelength new data from Swift X-Ray Telescope, Burst Alert Telescope, and UVOT, and from KAIT, Catalina Sky Survey, All-Sky Automated Survey for Supernovae, and Owens Valley Radio Observatory ground-based observatories as well as archival Rossi X-Ray Timing Explorer satellite-All Sky Monitor data, published optical data of Tuorla, and optical historical Harvard plates data are included in our work. Optical and radio light curves show clear correlations with the gamma-ray modulation, possibly with a nonconstant time lag for the radio flux. We interpret the gamma-ray periodicity as possibly arising from a pulsational accretion flow in a sub-parsec binary supermassive black hole system of elevated mass ratio, with orbital modulation of the supplied material and energy in the jet. Other astrophysical scenarios introduced include instabilities, disk and jet precession, rotation or nutation, and perturbations by massive stars or intermediate-mass black holes in polar orbit.

Constraints on axionlike ultralight dark matter from observations of the HL Tauri protoplanetary disk

Dark matter may consist of axionlike particles (ALPs). When polarized electromagnetic radiation passes through the dark-matter media, interaction with background ALPs affects the polarization of photons. The condensate of axionic dark matter experiences periodic oscillations, and the period of the oscillations is of the order of years for ultralight dark matter. This would result in observable periodic changes in the polarization plane, determined by the phases of the ALP field at the Earth and at the source. In this paper, we use recent polarimetric observations of the HL Tauri protoplanetary disk performed in different years to demonstrate the lack of changes of polarization angles, and hence to constrain masses and photon couplings of the hypothetical axionlike ultralight dark matter. Published by the American Physical Society 2024

Anomalous Oscillation Modes of Superfluid Pendant Droplets.

Droplets should exhibit various dynamical phenomena when adhered to a surface; not all of them are realized in classical fluids. Visualization of superfluid ^{4}He pendant droplets revealed that the droplets were horizontally translated on a flat surface, bouncing off at the corner, known as the Noether mode that reflects the translation symmetry. The droplets exhibited another mode in vertical oscillations with high amplitude that included oscillation of the droplet edge. The oscillation period remained constant even as the droplets grew, exhibiting an anomalously weak size dependence. The high mobility of the droplet edges owing to the superfluidity was a crucial factor for the appearance of these anomalous modes.

Quantum Flutter from Nonlinear Luttinger Liquid perspective

Abstract Quantum flutter is a ubiquitous phenomenon which can be observed from the fast moving impurity&amp;#xD;injected into a fermionic or bosonic medium of quantum liquid. In this scenario, one usually consider&amp;#xD;a medium of a fully polarized state and inject a spin-flipped impurity as the initial state. When the&amp;#xD;initial velocity of the impurity is beyond the intrinsic sound velocity of the medium, the impurity&amp;#xD;momentum dramatically exhibits a long-lived periodic oscillation with the periodicity remaining&amp;#xD;invariant with respect to the initial velocity. In this letter, we show that such a novel phenomenon&amp;#xD;can be explained by a linear Luttinger liquid coupled to a deep hole in the Fermi sea. Once the&amp;#xD;deep hole excitations are involved and the impurity momentum surpass the Fermi momentum,&amp;#xD;the propagator thus displays a periodic oscillation after a quick relaxation decay. The oscillation&amp;#xD;periodicity is solely determined by the energy of the deepest hole excitation. Our result provides&amp;#xD;deep insights into the dynamical behavior of quantum impurities immersed into one-dimensional&amp;#xD;quantum liquids.

Comprehensive evaluation of nine evapotranspiration products from remote sensing, gauge upscaling and land surface model over China.

Benefiting from the advancements in monitoring and measuring terrestrial evapotranspiration (ET), diverse ET products have been proliferated. This study evaluated nine ET products from three types, namely remote sensing-based retrievals (GLEAM, PML and PLSH), gauge-based upscaling (FCCRU, FCGSW and FCWFD) and land surface model-based reanalysis (ERA5-Land, GLDAS and MERRA) over China and its seven climate zones. Both spatial and temporal change trends in ET were investigated, and period feature were analyzed. Then, in-situ ET observations were used for validating the performances of ET products. The results demonstrate that all products show comparable performances in spatial distribution over China, but the mean ET values present evident discrepancies (433-563 mm/a). Among them, reanalysis ET products reproduce higher ET, but with less difference. In terms of climate sub-regions, the most significant discrepancies are located in QT. In addition, PLSH, MERRA and GLDAS present substantial increasing trends, while all three gauge-based upscaling ET products display decreasing trends. Regionally, all the ET products show positive trends in QT. Moreover, most of ET products present apparent periodic oscillation ranging from 2.0-5.5 year scales. At point scale, most ET products perform well at NMG and CBS sites (CC > 0.80, RMSE < 20 mm/month). However, general underestimations appear in northwestern China sites (HB and DX), and systematical overestimation exist in southern China sites (DHS and XSBN). By comparison, remote sensing-based ET products performs best, followed by gauge-based upscaling ET, comparatively, reanalysis-based ET products have poorest performances against in-situ ET observations. This study can provide valuable reference information for the selection of proper ET datasets for the hydrological simulation and analysis over China.