Oscillatory Decay Research Articles

A Euler-lagrange Model of dynamic internal friction

A Euler-Lagrange model of dynamic internal friction is proposed and is shown to match the frequency and decay of oscillations in both simple extension (pull) and cantilever beam experiments. The proposed dynamic internal frictional stress, τij, is proportional to the rate of change of the engineering stress, σ˙ij. i.e.τij=μmσ˙ij,with μm the dynamic internal friction coefficient. A single value of the dynamic internal friction coefficient is shown to match the results of the experiments for a number of different geometries of the silicon rubber, Dragon SkinTM. Dragon SkinTM is used in skin effects for movies and in prosthetics and cushioning applications. It is chosen here because of its ease of preparation and relatively simple non-linear stress-strain response. Because of these characteristics, it provides a simple starting place for simulating more complicated synthetic rubber and biological materials, which are used in a myriad of commercial applications.

Interband and Intraband Hot Carrier-Driven Photocatalysis on Plasmonic Bimetallic Nanoparticles: A Case Study of Au-Cu Alloy Nanoparticles.

Photoexcited nonthermal electrons and holes in metallic nanoparticles, known as hot carriers, can be judiciously harnessed to drive interesting photocatalytic molecule-transforming processes on nanoparticle surfaces. Interband hot carriers are generated upon direct photoexcitation of electronic transitions between different electronic bands, whereas intraband hot carriers are derived from nonradiative decay of plasmonic electron oscillations. Due to their fundamentally distinct photogeneration mechanisms, these two types of hot carriers differ strikingly from each other in terms of energy distribution profiles, lifetimes, diffusion lengths, and relaxation dynamics, thereby exhibiting remarkably different photocatalytic behaviors. The spectral overlap between plasmon resonances and interband transitions has been identified as a key factor that modulates the interband damping of plasmon resonances, which regulates the relative populations, energy distributions, and photocatalytic efficacies of intraband and interband hot carriers in light-illuminated metallic nanoparticles. As exemplified by the Au-Cu alloy nanoparticles investigated in this work, both the resonant frequencies of plasmons and the energy threshold for the d-to-sp interband transitions can be systematically tuned in bimetallic alloy nanoparticles by varying the compositional stoichiometries and particle sizes. Choosing photocatalytic degradation of Rhodamine B as a model reaction, we elaborate on how the variation of the particle sizes and compositional stoichiometries profoundly influences the photocatalytic efficacies of interband and intraband hot carriers in Au-Cu alloy nanoparticles under different photoexcitation conditions.

Decoupling Plasmonic Hot Carrier from Thermal Catalysis via Electrode Engineering.

Increased attention has been directed toward generating nonequilibrium hot carriers resulting from the decay of collective electronic oscillations on metal known as surface plasmons. Despite numerous experimental endeavors, demonstrating hot carrier-mediated photocatalysis without a heating contribution has proven challenging, particularly for single electron transfer reactions where the thermal contribution is generally detrimental. An innovative engineering solution is proposed to enable single electron transfer reactions with plasmonics. It consists of a photoelectrode designed as an energy filter and photocatalysis performed with light function modulation instead of continuously. The photoelectrode, consisting of FTO/TiO2 amorphous (10 nm)/Au nanoparticles, with TiO2 acting as a step-shape energy filter to enhance hot electron extraction and charge-separated state lifetime. The extracted hot electrons were directed toward the counter electrode, while the hot holes performed a single electron transfer oxidation reaction. Light modulation prevented local heat accumulation, effectively decoupling hot carrier catalysis from the thermal contribution.

PMUs data based detection of oscillatory events and identification of their associated variable: Estimation of information measures approach

Information theory can be a useful tool for quantifying the perturbations in the associated state variables at the time of disturbance occurrence. The study introduces a framework for the spectral decomposition of multivariate information measures to detect initiation of low frequency oscillations (LFOs), caused due to physical events in the power grid. A frequency-specific quantification of the information is shared between a target variable and two source variables from their time series data. Initially, the approach is applied on different synthetic test signals having different oscillatory frequency modes and decay time constant. Then, approach is extended on PMUs signals. The combination of cross-spectral and information-theoretic approaches is applied for the multi-variable analysis of PMUs signals from the same bus. The interdependence among the frequency, voltage angle and voltage magnitude, corresponding to specific oscillations, manifested due to cause-effect relationships obtained in terms of statistics is estimated. The dynamics in terms of unique (interaction), redundant and synergetic information is determined with the contribution from two of these three signals as source variables to target variable (frequency/voltage angle). This provides a direct coupling to identify driver-response relationships between source variables and target variable to indicate the onset of LFOs, following physical events in power network. The extension of approach among the variables from different buses aids to identify the responsible area of event occurrence.

Transient dynamics of magneto-optic rotation with elliptically polarized light

In this paper, we analyze the transient behavior of nonlinear magneto-optical rotation in a 87Rb vapor cell. Our focus is on optimizing the optical rotation signal by identifying influential factors. We investigate the impact of cell temperature on alkali atom density and consider characteristics of the light field, such as polarization direction, frequency, intensity, and beam diameter. Low scanning magnetic field rates produce the usual absorption signal, whereas high rates show an asymmetric transient response with oscillatory decay. To further investigate this phenomenon, we evaluate signal amplitude and resonant peaks along the x-, y-, and z-axis directions. Notably, we establish a one-dimensional quadratic equation that describes the relationship between magnetic field scan rate and signal amplitude/peak value. Our findings facilitate the quick evaluation of cell performance, provide insights into the dynamics of ground-state coherence generation, and have potential applications in detecting transient spin coupling or monitoring magnetic fields.

On a Rayleigh Structure in Temperature Waves

Abstract The hyperbolic temperature wave is investigated as a Rayleigh-like wave that contains mixed transverse and longitudinal components. This allows the absolute ratio of the longitudinal to transverse interfering components to vary in space & time, with increasing the frequency of this wave. Such a variation is demonstrated, for the first time, to exhibit an initial smooth build up with increasing the frequency, to be followed by an asymptotic temporally oscillatory decay towards zero. A main result of this work is that heat transport can be enhanced by vibration only at low frequencies.

Wave mechanics in an ionic liquid mixture.

Experimental measurements of interactions in ionic liquids and concentrated electrolytes over the past decade or so have revealed simultaneous monotonic and oscillatory decay modes. These observations have been hard to interpret using classical theories, which typically allow for just one electrostatic decay mode in electrolytes. Meanwhile, substantial progress in the theoretical description of dielectric response and ion correlations in electrolytes has illuminated the deep connection between density and charge correlations and the multiplicity of decay modes characterising a liquid electrolyte. The challenge in front of us is to build connections between the theoretical expressions for a pair of correlation functions and the directly measured free energy of interaction between macroscopic surfaces in experiments. Towards this aim, we here present measurements and analysis of the interactions between macroscopic bodies across a fluid mixture of two ionic liquids of widely diverging ionic size. The measured oscillatory interaction forces in the liquid mixtures are significantly more complex than for either of the pure ionic liquids, but can be fitted to a superposition of two oscillatory and one monotonic mode with parameters matching those of the pure liquids. We discuss this empirical finding, which hints at a kind of wave mechanics for interactions in liquid matter.

Research on the vibration mechanism of compressor complex exhaust pipeline based on transient flow

The periodic exhaust of the compressor often induces gas flow fluctuations within the pipeline, leading to vibrations. Excessive vibration can lead to fatigue, cracks, loosening of components, and resulting in local leakage, which may easily lead to fire, explosion, and secondary hazards. Therefore, in this paper, a computational model for the transient flow field of the compressor exhaust pipeline was established, using the pulse excitation method and Fluent software, the natural frequencies of the gas column in the pipeline were calculated, and the patterns of oscillation decay of the gas column wave propagating back and forth within three exhaust pipes were researched. The mechanism behind the pipeline pressure pulsation and the influence of pipeline structural parameters on the natural frequencies of the gas column were explored. The calculation results show that the first-order natural frequency of the gas column is very close to the double frequency of the compressor excitation frequency at 3.33Hz, and the second-order natural frequency of the gas column is very close to the quadruple frequency of the compressor excitation frequency at 3.33Hz, which may cause significant pipeline vibrations. Altering the pipeline structure, especially when influenced by airflow branching after a tee junction, results in complex changes in the natural frequencies of the gas column. Furthermore, the structural natural frequencies of the pipeline were obtained through the finite element. It has been observed that resonance phenomena exist among the structural natural frequencies and their harmonics of the pipeline and the natural frequencies of the gas column and their harmonics, as well as multiples of the excitation frequency. These results lay the foundation for understanding the vibration mechanism of the pipeline and finding ways to reduce vibration.

Spatio-temporal mapping and long-term evolution of debris flow activity after a high magnitude earthquake

A high-magnitude earthquake can trigger substantial amounts of co-seismic debris and unstable hillslopes in mountainous regions, which leads to a significant increase in the frequency and magnitude of post-earthquake debris flows. The long-term impacts of earthquakes on the debris flow activity have not been fully understood, primarily because of a lack of multi-temporal mapping inventories of debris flow activity. Therefore, it is crucial to analyze the spatio-temporal evolution of debris flow activities and their driving factors after the 2008 Wenchuan earthquake for disaster risk management and mitigation from a dynamic perspective. We used the fusion of remote sensing data to develop the first systematic multi-temporal inventory of debris flow activity to quantify changes in spatial and temporal activity of post-earthquake debris flows from 2008 to 2021. Subsequently, we examined the control of material sources, topographic and hydrological factors on the evolution of post-earthquake debris flow activities. A close relationship between the decline in debris flow activity and the reduced active material sources was observed in both time and space, so the supply capacity of hillslope deposits after the earthquake was the first-order indicator controlling post-earthquake debris flow activity. With the progressive depletion and stabilization of co-seismic landslide materials over time, topographic and hydrological factors occupied a dominant role in the occurrence of debris flow. In general, an oscillatory decay pattern of debris flow activity over time was observed after the 2008 Wenchuan earthquake. We observed that the period of post-earthquake debris flow activity varied considerably in different regions attributed to the magnitude of the earthquake, and the geological and climatic environments. Based on the debris flow channel disturbances, the dynamic evolution of landslide materials and hydrodynamics, we divided the debris flow active period after the Wenchuan earthquake into three phases: high activity period (lasting 2 ∼ 5 years), medium activity period (lasting 3 ∼ 10 years), and low activity period (lasting 9 ∼ 18 years). Following the above three activity periods, the debris flow activity will evolve into a steady period. We also proposed a quantitative model for debris flow activeness in the main Wenchuan earthquake-affected area, which predicts that the activeness of debris flows will tend to pre-earthquake levels in 46 years following the earthquake.

Decay rates of convergence for Fokker-Planck equations with confining drift

We consider Fokker-Planck equations in the whole Euclidean space, driven by Levy processes, under the action of confining drifts, as in the classical Ornstein-Ulhenbeck model. We introduce a new PDE method to get exponential or sub-exponential decay rates, as time goes to infinity, of zero average solutions, under some diffusivity condition on the Levy process, which includes the fractional Laplace operator as a model example. Our approach relies on the long time oscillation estimates of the adjoint problem and applies to (the possible superposition of) both local and nonlocal diffusions, as well as to strongly or weakly confining drifts. Our results extend, with a unifying perspective, many previous works based on different analytic or probabilistic methods, with several interesting connections. On one hand, we make a link between the (nonlinear) PDE methods used for the long time behavior of Hamilton-Jacobi equations and the decay estimates of Fokker-Planck equations; on another hand, we give a purely analytical approach towards some oscillation decay estimates which were obtained so far only with probabilistic coupling methods.

Investigation on the unsteady ventilation performance of oscillating jet air supply through both spontaneous vortex street effect and active modulation

Ventilation is one of the most vital measures to create a healthy and comfortable indoor environment, significantly influencing indoor air quality and building energy consumption. The conventional steady-state airflow field of a ventilated room, if not reasonably configured, is prone to cause air stagnation in certain regions, whereas the unsteady airflow improves the mixing effect, which favors the dispersion and purging of indoor air pollutants. This paper proposes a method to induce an unstable air flow field utilizing the spontaneous Karman vortex street effect on the air-supply jet and swinging modulation. The quasi-periodicity of the airflow field and its influence on the indoor pollutant purging effect were investigated. The effects of air velocity oscillation and pollutant concentration decay in a ventilated room were studied through experimental measurements and computational fluid dynamics analysis. The results show that the transverse oscillation jet has a dominant period of 1.6 s and the longitudinal oscillation jet has a dominant period of 2.987 s, and both jets have a width about twice that of the free jet. The airborne pollutant discharge efficiency of the oscillating jet was higher than that of the free jet at the occupancy level, and the longitudinal oscillating jet purged pollutants faster than the transverse oscillating jet. This study reveals that oscillating jets can provide an option to create periodic flow fields and improve the efficiency of ventilation.

Large-eddy simulation of a lean-premixed hydrogen flame in a low-swirl combustor under combustion instability

Large-eddy simulation (LES) of a lean-premixed hydrogen turbulent jet flame with combustion instability (CI) in a low-swirl combustor (LSC) is performed by employing a dynamically thickened flame model with a detailed chemical reaction model with 9 chemical species and 20 reactions, and the LES validity and the CI characteristics are investigated in detail. The results show that the present LES can accurately reproduce the experimentally observed characteristics of the CI such as intensity, frequency, sporadic decay of pressure oscillations, and a flame–flow interaction inducing the periodic transitions of an inverted conical flame structure and a flat flame structure in the LSC. The sporadic decay of pressure oscillations and the flame–flow interaction are caused by the temporal decoupling of pressure and heat release rate and the periodic outward and inward deflections of the inflow, which is associated with the flow behavior in the upstream injector channel, respectively.

Seismic metasurface on an orthorhombic elastic half-space.

The article is studying a seismic meta-surface in the case of an oscillatory system arranged on the surface of an orthorhombic elastic half-space. The approach is based on the asymptotic hyperbolic-elliptic formulation for the Rayleigh wave excited by prescribed surface loading. The latter results in hyperbolic equations for surface displacements, with the right-hand sides involving the loading components. The derived model allows a formulation for the meta-surface in the form of a periodic spring-mass system attached to the surface as a hyperbolic equation for the horizontal displacement, with smooth contact stresses emerging from averaging the effect of a regular array of oscillators. The associated dispersion relation is constructed and illustrated numerically for both cases of exponential and oscillatory decay.

A Mechanism Underpinning the Bioenergetic Metabolism-Regulating Function of Gold Nanocatalysts.

Bioenergetic deficits are known to be significant contributors to neurodegenerative diseases. Nevertheless, identifying safe and effective means to address intracellular bioenergetic deficits remains a significant challenge. This work provides mechanistic insights into the energy metabolism-regulating function of colloidal Au nanocrystals, referred to as CNM-Au8, that are synthesized electrochemically in the absence of surface-capping organic ligands. When neurons are subjected to excitotoxic stressors or toxic peptides, treatment of neurons with CNM-Au8 results in dose-dependent neuronal survival and neurite network preservation across multiple neuronal subtypes. CNM-Au8 efficiently catalyzes the conversion of an energetic cofactor, nicotinamide adenine dinucleotide hydride (NADH), into its oxidized counterpart (NAD+ ), which promotes bioenergy production by regulating the intracellular level of adenosine triphosphate. Detailed kinetic measurements reveal that CNM-Au8-catalyzed NADH oxidation obeys Michaelis-Menten kinetics and exhibits pH-dependent kinetic profiles. Photoexcited charge carriers and photothermal effect, which result from optical excitations and decay of the plasmonic electron oscillations or the interband electronic transitions in CNM-Au8, are further harnessed as unique leverages to modulate reaction kinetics. As exemplified by this work, Au nanocrystals with deliberately tailored structures and surfactant-free clean surfaces hold great promise for developing next-generation therapeutic agents for neurodegenerative diseases.

Attenuating dynamics of strongly interacting fermionic superfluids in SYK solvable models

Quench dynamics of fermionic superfluids are an active topic both experimentally and theoretically. Using the BCS theory, such non-equilibrium problems can be reduced to nearly independent spin dynamics, only with a time-dependent mean-field pairing term. This results in persisting oscillations of the pairing strength in certain parameter regimes. However, experiments have observed that the oscillations decay rapidly when the interaction becomes strong, such as in the unitary Fermi gas [Phys. Rev. Res. 3, 023205 (2021)]. Theoretical analysis on this matter is still absent. In this work, we construct an SYK-like model to analyze the effect of strong interactions in a one-dimensional BCS system. We employ the large-NN approximation and a Green’s function-based technique to solve the equilibrium problem and quench dynamics. Our findings reveal that a strong SYK interaction suppresses the pairing order. Additionally, we verify that the system quickly thermalizes with SYK interactions, whether it involves intrinsic pairing order or proximity effect, resulting in a rapid decay of the oscillation strength. The decay rates exhibit different scaling laws against SYK interaction, which can be understood in terms of the Boltzmann equation. This work represents a first step towards understanding the attenuating dynamics of strongly interacting fermionic superfluids.

Speed-up of traveling waves by negative chemotaxis

We consider the traveling wave speed for Fisher-KPP (FKPP) fronts under the influence of repulsive chemotaxis and provide an almost complete picture of its asymptotic dependence on parameters representing the strength and length-scale of chemotaxis. Our study is based on establishing the convergence to the porous medium FKPP traveling wave and a hyperbolic FKPP-Keller-Segel traveling wave in certain asymptotic regimes. In this way, it clarifies the relationship between three equations that have each garnered intense interest on their own. Our proofs involve a variety of techniques ranging from entropy methods and decay of oscillations estimates to a general description of the qualitative behavior to the hyperbolic FKPP-Keller-Segel equation. For this latter equation, we, as a part of our limiting arguments, establish a new explicit lower bound on the minimal traveling wave speed and provide a novel construction of traveling waves that extends the known existence range to all parameter values.

Effects of Internal Boundary Layers and Sensitivity on Frequency Response of Shells of Revolution

New applications introduced capsule designs with features that have not been fully analysed in the literature. In this study, thin shells of revolution are used to model drug delivery capsules both with closed and open designs including perforations. The effects of internal boundary layers and sensitivity on frequency response are discussed in the special case with symmetric concentrated load. The simulations are carried out using high-order finite element method and the frequency response is computed with a very accurate low-rank approximation. Due to the propagation of the singularities induced by the concentrated loads, the most energetic responses do not necessarily include a pinch-through at the point of action. In sensitive configurations, the presence of regions with elliptic curvature leads to strong oscillations at lower frequencies. The amplitudes of these oscillations decay as the frequencies increase. For efficient and reliable analysis of such structures, it is necessary to understand the intricate interplay of loading types and geometry, including the effects of the chosen shell models.

Effective binding potential from Casimir interactions: the case of the Bose gas

We consider the thermal Casimir effect in ideal Bose gases, where the dispersion relation involves both terms quadratic and quartic in momentum. We demonstrate that if macroscopic objects are immersed in such a fluid in spatial dimensionality and at the critical temperature , the Casimir force acting between them is characterized by a sign which depends on the separation D between the bodies and changes from attractive at large distances to repulsive at smaller separations. In consequence, an effective potential which binds the two objects at a finite separation arises. We demonstrate that for odd integer dimensionality , the Casimir energy is a polynomial of degree in D −2. We point out a very special role of dimensionality d = 3, where we derive a strikingly simple form of the Casimir energy as a function of D at Bose–Einstein condensation. We discuss crossover between monotonous and oscillatory decay of the Casimir interaction above the condensation temperature.

Oscillation decay of a pendulum by an air jet

A heavy pendulum oscillating in a vertical air jet is studied in this short communication. Different jet Reynolds number and initial inclination angle of the pendulum are considered. As the jet Reynolds number increases, it is always observed that the time taken by the pendulum to reach the final equilibrium vertical state reduces. The suction pressure induced by the streamlines of the air jet deflected by the pendulum aids the gravitational restoring force. The subsequent increase in the frictional damping force from the pivot of the pendulum is shown to be responsible for this behavior. A theoretical model along with numerical results corroborate this conclusion.

Optimization of neural-network model using a meta-heuristic algorithm for the estimation of dynamic Poisson’s ratio of selected rock types

This research focuses on the predictive modeling between rocks' dynamic properties and the optimization of neural network models. For this purpose, the rocks' dynamic properties were measured in terms of quality factor (Q), resonance frequency (FR), acoustic impedance (Z), oscillation decay factor (α), and dynamic Poisson’s ratio (v). Rock samples were tested in both longitudinal and torsion modes. Their ratios were taken to reduce data variability and make them dimensionless for analysis. Results showed that with the increase in excitation frequencies, the stiffness of the rocks got increased because of the plastic deformation of pre-existing cracks and then started to decrease due to the development of new microcracks. After the evaluation of the rocks’ dynamic behavior, the v was estimated by the prediction modeling. Overall, 15 models were developed by using the backpropagation neural network algorithms including feed-forward, cascade-forward, and Elman. Among all models, the feed-forward model with 40 neurons was considered as best one due to its comparatively good performance in the learning and validation phases. The value of the coefficient of determination (R2 = 0.797) for the feed-forward model was found higher than the rest of the models. To further improve its quality, the model was optimized using the meta-heuristic algorithm (i.e. particle swarm optimizer). The optimizer ameliorated its R2 values from 0.797 to 0.954. The outcomes of this study exhibit the effective utilization of a meta-heuristic algorithm to improve model quality that can be used as a reference to solve several problems regarding data modeling, pattern recognition, data classification, etc.