Oscillatory Profile Research Articles

The effect of the cell tilting on the temperature oscillation in turbulent Rayleigh–Bénard convection

We experimentally studied the effect of cell tilting on the temperature oscillation in turbulent Rayleigh–Bénard convection. We simultaneously measured the temperature using both in-fluid and in-wall thermistors for Ra=1.7×109 and 5.0×109 at Prandtl number Pr = 5.3. The tilt angles relative to gravity are set to 0°, 0.5°, 1°, 2°, and 7°. It is found that the temperature oscillation intensity measured in-fluid is much stronger than that measured in-wall, because the in-fluid thermistors measure both the large-scale circulation (LSC) and the plumes/plume clusters, while the in-wall thermistors only measure the LSC due to the filter effect of the sidewall. Despite the intensity difference, the obtained azimuthal profiles of the oscillation intensity measured by in-fluid and in-wall share similar spatial distribution, and the spatial distribution can be explained by the torsional motion near the top and bottom plates and the sloshing motion at the mid-height. With the in-fluid measurements, we find that with the increase in the tilt angle, the azimuthal profile of oscillation evolves toward a sawtooth-like profile and the intensity gets more prominent, which implies that the temperature oscillation becomes more coherent. Through a conditional sampling method based on the azimuthal position of LSC, we reveal that the uniformly distributed oscillation intensity in the level cell is the result of the superimposition of the random azimuthal motion and the sloshing motion. Tilting the cell can efficiently disentangle the above-mentioned two types of motions of LSC. Moreover, we found that the frequency of the temperature oscillation increases when the tilt angle increases, while the amplitude of the sloshing motion of the LSC remains unchanged, which is believed to be related to the confinement of the convection cell.

A generically singular type of saddle–node bifurcation that occurs for relativistic shock waves

This paper is concerned with two-parameter families of planar dynamical systems in which a saddle–node bifurcation interacts with a singular perturbation. We identify bifurcation curves along which the non-saddle point switches from node to focus and establish the existence of heteroclinic connections in either case. As an application, the result is used to show the existence of oscillatory shock profiles in a model of relativistic fluid dynamics.

Echoes of axial gravitational perturbations in stars of uniform density* *Supported by the National Natural Science Foundation of China (42230207) and the Brazilian Agencies Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP), Fundação de Amparo à Pesquisa do Estado do Rio de Janeiro (FAPERJ), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Coordenação de Aperfeiçoamento de Pessoal

This study investigates the echoes in axial gravitational perturbations in compact objects. Accordingly, we propose an alternative scheme of the finite difference method implemented in two coordinate systems, where the initial conditions are placed on the axis of the tortoise coordinate with appropriate boundary conditions that fully respect the causality. The scheme is then employed to study the temporal profiles of the quasinormal oscillations in the Schwarzschild black hole and uniform-density stars. When presented as a two-dimensional evolution profile, the resulting ringdown waveforms in the black hole metric are split into reflected and transmitted waves as the initial perturbations evolve and collide with the peak of the effective potential. Meanwhile, for compact stars, quasinormal oscillations might be characterized by echoes. Consistent with the causality arguments, the phenomenon is produced by the gravitational waves bouncing between the divergent potential at the star's center and the peak of the effective potential. The implications of the present study are also discussed herein.

The Dramatic Effect of Water Structure on Hydration Forces and the Electrical Double Layer

Forces between hydrophilic surfaces mediated by water are important in various systems from lipid membranes and solid surfaces to colloids and macromolecules, first discovered as a significant addition to DLVO forces at the nanoscale. These “hydration forces” have been studied in great detail experimentally using osmotic stress measurements, surface force apparatus, and AFM, and they have also been the subject of multiple theories and simulations. One spectacular feature observed in experimental and simulation studies was the nonmonotonic, oscillatory decay in the forces between atomically smooth surfaces. Forces between “rougher” surfaces exhibit only quasi-exponential, monotonic decay. Here we revisit this hydration force problem by exploring the consequences of an extended phenomenological Landau–Ginzburg approach that describes nonlocal correlations in water, linking them with the key features of the wave-number k-dependent nonlocal dielectric function of water. With corresponding boundary conditions, this theory predicts the observed oscillatory decay in hydration force between ideally flat surfaces, the oscillatory mode disappearing with just a tiny roughness of the surfaces (of mean height ca. of the size of a water molecule). This study also brings an important side message. Explanation of these observations appears only possible under an assumption of two modes of polarization in water, consistent with the behavior of the response function, i.e., Lorentzian at small k and resonance-like at higher k. This resolves the “force oscillation–non-oscillation” paradigm, which is a strong, although indirect indication of the existence of these two modes. We also consider other important subjects, such as how the distribution of ions near a charged surface reacts to the propensity for overscreening oscillations due to polarized water. This is important not only for the interactions between charged surfaces but also for the fundamental understanding of the structure of the electrical double layer at electrochemical interfaces. We show that even in dilute electrolytes, the distribution of ions in the vicinity of the polarized interface follows, although not literally, preferential positions corresponding to the potential wells caused by “resonance” water layering. For a sharp interface, the theory predicts that the decaying spatial oscillation profiles extend over a 1 to 2 nm distance from the interface. With the smearing of the interface and the corresponding suppression of the resonance water layering, oscillations in the spatial distribution of ions subside, resulting in a familiar Gouy–Chapman–Stern picture. At longer distances from the interface, whether smeared or not, the ion distribution profiles become Gouy–Chapman-like. The effect of the boundary conditions on water polarization at the interface goes beyond a trivial shift of the potential of zero charge. We show that they can dramatically affect the ion distribution near the charged surface. Last, but not least, we study how the interfacial water layering influences the double layer capacitance and show the effect of the boundary conditions on the slopes of Parsons–Zobel plots, resolving some recently discussed puzzles.

On the oscillations in a nonextensive complex plasma by improved differential transformation method: An application to a damped Duffing equation

In this study, the nonlinear damping oscillations in a complex non-Maxwellian plasma are investigated. For this purpose, the set of fluid equations of the present plasma model is reduced to the Burger-modified Korteweg De Vries equation (BmKdV) equation using a reductive perturbation technique. Using the traveling wave transformation, the BmKdV equation can be reduced to a damped Duffing equation. The numerical solutions to the damped Duffing equation are obtained using multistage differential transformation method (MsDTM). Also, we compared the obtained results to the semi-analytical approximations using the Padé differential transformation (PDTM) method and numerical solution, by the 4th-order Rung Kutta (RK4) method and analytical solution by He’s frequency method. The impact of relevant plasma parameters, namely, negative dust concentrations and ion kinematic viscosity on the profile of dust ion-acoustic oscillations are examined. The suggested mathematical approaches can help many authors for explaining the mystery of their laboratory results. Moreover, the suggested numerical method can be applied for solving higher order nonlinearity oscillations for a long domain.

How Nonlinearity Changes Different Parameters in the Solar Corona

We consider different velocity amplitudes of incident waves to study nonlinearity effects on the plasma parameters around a magnetic null point in the solar corona. This could query the seismological methods used to observe and interpret damping profiles of oscillations of magnetic structures, based on linear theory. To this end, initially symmetric fast magnetoacoustic waves with three different amplitudes are applied to the system to pursue the effect of nonlinearity on the resulting plasma heating and flows. The dynamic evolution is investigated by solving the resistive MHD equations in a Cartesian domain by the PLUTO code. The considered magnetic null point is surrounded by an initially constant density and temperature plasma. Pursuing the partition of different energy components can shed light on our understanding of the energy release mechanisms. It is found that nonlinear behavior could be the reason for the occurring magnetic reconnection and the related excitation of coronal jets. Furthermore, the fully nonlinear simulation run results in a high temperature and a high current density accumulation and less twisting along the wave accumulation direction, which is even higher than the heating at the magnetic null point itself. Moreover, it is found that there is no significant amplification in the velocity profile. This could be related to the fact that there are not any clear correlations between jets and flares. Furthermore, it is illustrated that the period of the oscillations depends on the amplitude of the initial perturbation, obtaining a shorter period for the fully nonlinear case.

Harmonic Balance Analysis of Lur’e Oscillator Network With Non-Diffusive Weak Coupling

The central pattern generator (CPG) is a group of interconnected neurons, existing in biological systems as a control center for oscillatory behaviors. We propose a new approach based on the multivariable harmonic balance to characterize the relationship between the oscillation profile (frequency, amplitude, phase) and interconnections within the CPG, modeled as weakly coupled oscillators. In particular, taking advantage of the weak coupling, we formulate a low-dimensional matrix whose eigenvalue/eigenvector capture the perturbation in the oscillation profile due to the coupling. Then we develop an algorithm to estimate the perturbed oscillation profile of a given CPG, and suggest an optimization to synthesize the interconnections to produce a given oscillation profile.

Fabrication of submillimeter-sized spherical self-oscillating gels and control of their isotropic volumetric oscillatory behaviors.

In this study, we established a fabrication method and analyzed the volumetric self-oscillatory behaviors of submillimeter-sized spherical self-oscillating gels. We validated that the manufactured submillimeter-sized spherical self-oscillating gels exhibited isotropic volumetric oscillations during the Belousov-Zhabotinsky (BZ) reaction. In addition, we experimentally elucidated that the volumetric self-oscillatory behaviors (i.e., period and amplitude) and the oscillatory profiles depended on the following parameters: (1) the molar composition of N-(3-aminopropyl)methacrylamide hydrochloride (NAPMAm) in the gels and (2) the concentration of Ru(bpy)3-NHS solution containing an active ester group on conjugation. These clarified relationships imply that controlling the amount of Ru(bpy)3 in the gel network could influence the gel volumetric oscillation during the BZ reaction. These results of submillimeter-sized and spherical self-oscillating gels bridge knowledge gaps in the current field because the gels with corresponding sizes and shapes have not been systematically explored yet. Therefore, our study could be a cornerstone for diverse applications of (self-powered) gels in various scales and shapes, including soft actuators exhibiting life-like functions.

A maximum principle of the Fourier spectral method for diffusion equations

<abstract><p>In this study, we investigate a maximum principle of the Fourier spectral method (FSM) for diffusion equations. It is well known that the FSM is fast, efficient and accurate. The maximum principle holds for diffusion equations: A solution satisfying the diffusion equation has the maximum value under the initial condition or on the boundary points. The same result can hold for the discrete numerical solution by using the FSM when the initial condition is smooth. However, if the initial condition is not smooth, then we may have an oscillatory profile of a continuous representation of the initial condition in the FSM, which can cause a violation of the discrete maximum principle. We demonstrate counterexamples where the numerical solution of the diffusion equation does not satisfy the discrete maximum principle, by presenting computational experiments. Through numerical experiments, we propose the maximum principle for the solution of the diffusion equation by using the FSM.</p></abstract>

Temporal profiles of cortical oscillations in novice performers for goal-directed aiming in a shooting task

Goal-directed aiming relies on the ability to control attention and visuomotor movements while preparing for motor execution. Research in precision sports has investigated cortical oscillations for supporting expert performance. However, the results may be influenced by adaptive and strategic behaviors after intensive training. Whether and at what time points distinctive oscillations support goal-directed aiming without such training remains elusive. In this electroencephalographic (EEG) study, we investigated how the theta, alpha and beta oscillations change to support accurate aiming before novices took an action. We first conducted a model-based analysis to examine the correlation of cortical oscillations with accurate shooting on a trial-by-trial basis in a within-individual manner. The results showed that alpha and beta oscillations at different time points during the aiming period were better predictors of aiming accuracy. We then compared the oscillatory power for good versus poor performance. The results showed decreases in the alpha and beta power across distributed cortical areas and an increase in the frontal theta power successively before shot release. Moreover, greater intertrial phase coherence was observed for good performance than for poor performance in posterior alpha activity and anterior beta activity during the aiming period. In conclusion, these results advance our understanding of the temporal dynamics of theta, alpha and beta oscillations in orchestrating goal setting, motor preparation and focused attention to monitoring both external and internal states for accurate aiming. Among the three, alpha and beta oscillations are critical for predicting aiming performance and theta oscillations reflect effortful cognitive control.

Impact of Negative Solar Resistance on DC Microgrid Stability: Virtual Damping Voltage and Current Solar Droop Emulated Controller

The negative solar resistance, is highly dependent on the solar operating point. The system will become sluggish and unstable during low irradiance. It is reported that the impact of negative solar resistance is nullified by parallel impedance emulated condition (PIEC). During low irradiance, the system stability has been moved to an unstable position which is not fully resolved by PIEC. In this paper, a virtual inertia-damping voltage and current solar droop emulated controller is proposed to improve the voltage oscillation profile, inertia problem and damping of the DC microgrid system. In DC microgrids, the inherent inertia from DC capacitors is low, thus affecting the bus voltage oscillation during a reduction of irradiance. The oscillation of the system has been increased due to the equivalent impedance by negative solar resistance at lower irradiance. Oscillation’s issue and voltage instability of the PV system have been enhanced by the inner current controller. In addition, the steady-state error of the PV voltage is minimized by the virtual inertia-damping voltage restoration droop controller with PIEC. Performance analysis and dynamic characteristics are discussed through a pole-zero plot for the various conditions of negative solar resistance using virtual inertia-damping voltage and current Solar Droop Emulated Controller. This paper focuses on stability analysis to strengthen the DC microgrid. The performance of the solar controller with bidirectional converter (BDC) controller has been discussed to verify the power management between the system to manage the power for the unbalanced load.

Loss of the Synuclein Family Members Differentially Affects Baseline- and Apomorphine-Associated EEG Determinants in Single-, Double- and Triple-Knockout Mice.

Synucleins comprise a family of small proteins highly expressed in the nervous system of vertebrates and involved in various intraneuronal processes. The malfunction of alpha-synuclein is one of the key events in pathogenesis of Parkinson disease and certain other neurodegenerative diseases, and there is a growing body of evidence that malfunction of other two synucleins might be involved in pathological processes in the nervous system. The modulation of various presynaptic mechanisms of neurotransmission is an important function of synucleins, and therefore, it is feasible that their deficiency might affect global electrical activity detected of the brain. However, the effects of the loss of synucleins on the frequency spectra of electroencephalograms (EEGs) have not been systematically studied so far. In the current study, we assessed changes in such spectra in single-, double- and triple-knockout mice lacking alpha-, beta- and gamma-synucleins in all possible combinations. EEGs were recorded from the motor cortex, the putamen, the ventral tegmental area and the substantia nigra of 78 3-month-old male mice from seven knockout groups maintained on the C57BL/6J genetic background, and 10 wild-type C57BL/6J mice for 30 min before and for 60 min after the systemic injection of a DA receptor agonist, apomorphine (APO). We found that almost any variant of synuclein deficiency causes multiple changes in both basal and APO-induced EEG oscillation profiles. Therefore, it is not the absence of any particular synuclein but rather a disbalance of synucleins that causes widespread changes in EEG spectral profiles.

Neuromorphic model of hippocampus place cells using an oscillatory interference technique for hardware implementation

In this paper, we propose a simplified and robust model for place cell generation based on the oscillatory interference (OI) model concept. Aiming toward hardware implementation in bio-inspired simultaneous localization and mapping (SLAM) systems for mobile robotics, we base our model on logic operations that reduce its computational complexity. The model compensates for parameter variations in the behaviors of the population of constituent theta cells, and allows the theta cells to have square-wave oscillation profiles. The robustness of the model, with respect to mismatch in the theta cell’s base oscillation frequency and gain—as a function of modulatory inputs—is demonstrated. Place cell composed of 48 theta cells with base frequency variations with a 25% standard deviation from the mean and a gain error with 20% standard deviation from the mean only result in a 20% deformations within the place field and 0.24% outer side lobes, and an overall pattern with 0.0015 mean squared error on average. We also present how the model can be used to achieve the localization and path-tracking functionalities of SLAM. Hence, we propose a model for spatial cell formation using theta cells with behaviors that are biologically plausible and hardware implementable for real world application in neurally-inspired SLAM.

Mitochondrial redox environments predict sensorimotor brain-behavior dynamics in adults with HIV

Despite virologic suppression, people living with HIV (PLWH) remain at risk for developing cognitive impairment, with aberrations in motor control being a predominant symptom leading to functional dependencies in later life. While the neuroanatomical bases of motor dysfunction have recently been illuminated, the underlying molecular processes remain poorly understood. Herein, we evaluate the predictive capacity of the mitochondrial redox environment on sensorimotor brain-behavior dynamics in 40 virally-suppressed PLWH and 40 demographically-matched controls using structural equation modeling. We used state-of-the-art approaches, including Seahorse Analyzer of mitochondrial function, electron paramagnetic resonance spectroscopy to measure superoxide levels, antioxidant activity assays and dynamic magnetoencephalographic imaging to quantify sensorimotor oscillatory dynamics. We observed differential modulation of sensorimotor brain-behavior relationships by superoxide and hydrogen peroxide-sensitive features of the redox environment in PLWH, while only superoxide-sensitive features were related to optimal oscillatory response profiles and better motor performance in controls. Moreover, these divergent pathways may be attributable to immediate, separable mechanisms of action within the redox environment seen in PLWH, as evidenced by mediation analyses. These findings suggest that mitochondrial redox parameters are important modulators of healthy and pathological oscillations in motor systems and behavior, serving as potential targets for remedying HIV-related cognitive-motor dysfunction in the future.

Adiabatic inversion in an array of spherical microcrystals under conditions of the Stark effect

A model of the process of adiabatic tracking on a system of size-quantized levels of isolated spherical quantum dots (QDs) in an electric field is proposed, which, due to the Stark effect, creates intervals between levels varied by the field. The method of perturbation theory for degenerate states is used to analyze the splitting and partial lifting of the degeneracy of levels in the lower part of the spectrum of a spherical QD. Using the pseudospin electric dipole vector model, we study the process of adiabatic inversion on a system of selected pairs of QD levels, the energy intervals between which are subject to a monotonous change by an external electric field. The course of the process of adiabatic tracking is analyzed in the case of a linear dependence of the electric field on time, at different values of the amplitude of the radiation pulse field. An asymmetry in the course of change in the amplitude profile of the inversion oscillations is revealed, which can affect the process of detecting non-stationary stimulated amplification. It is pointed out that it is possible to trace the inversion process, when the variation of the resonance detuning can be determined by the selection of the radii of the spherical QDs.

Growth of germanium crystals by time-varying temperature profile, CVT methods

Germanium crystals have been prepared by Chemical Vapour Transport (CVT) to study the influence of the thermal profile on the crystal growth: using the stationary temperature profile, the Linear Time-varying Temperature Profile (LTVTP) and the LTVTP followed by the oscillatory temperature profile in the same run.With the optimization of the growth parameters we have obtained a progressive increase of the crystal sizes and a reduction of the crystalline nuclei during the primary nucleation. The final result was only one crystal grown using the LTVTP associated with oscillatory temperature profile.The crystals morphology observed by scanning electron microscopy showed details of their shape typical of germanium, the cubic structure was confirmed by X-ray diffraction.

Unravelling Contributions of Astrocytic Connexin 43 to the Functional Activity of Brain Neuron-Glial Networks under Hypoxic State In Vitro.

Brain hypoxia remains an Achilles’ heel for public health that must be urgently addressed. Hypoxic damage affects both neurons and glial cells, particularly astrocytes, which are in close dynamic bi-directional communication, and are organized in plastic and tightly regulated networks. However, astroglial networks have received limited attention regarding their influence on the adaptive functional rearrangements of neural networks to oxygen deficiency. Herein, against the background of astrocytic Cx43 gap junction blockade by the selective blocker Gap19, we evaluated the features of spontaneous calcium activity and network characteristics of cells in primary cultures of the cerebral cortex, as well as the expression levels of metabotropic glutamate receptors 2 (mGluR2) and 5 (mGluR5) in the early and late periods after simulated hypoxia in vitro. We showed that, under normoxic conditions, blockade of Cx43 leads to an increase in the expression of metabotropic glutamate receptors mGluR2 and mGluR5 and long-term modulation of spontaneous calcium activity in primary cortical cultures, primarily expressed in the restructuring of the functional architectonics of neuron–glial networks through reducing the level of correlation between cells in the network and the percentage of existing correlated connections between cells. Blocking Cx43 during hypoxic injury has a pronounced neuroprotective effect. Together with the increased expression of mGluR5 receptors, a decrease in mGluR2 expression to the physiological level was found, which suggests the triggering of alternative molecular mechanisms of cell adaptation to hypoxia. Importantly, the blockade of Cx43 in hypoxic damage contributed to the maintenance of both the main parameters of the spontaneous calcium activity of primary cortical cultures and the functional architectonics of neuron–glial networks while maintaining the profile of calcium oscillations and calcium signal communications between cells at a highly correlated level. Our results demonstrate the crucial importance of astrocytic networks in functional brain adaptation to hypoxic damage and could be a promising target for the development of rational anti-hypoxic therapy.

Strain effect on transmission in graphene laser barrier

We investigate the strain effect along armchair and zigzag directions on the tunneling transport of Dirac fermions in graphene laser barrier through a time dependent potential along y-axis. Our system is composed of three regions and the central one is subjected to a deformation of strength S. Based on Dirac equation and the Floquet approach, we determine the eigenvalues and eigenspinors for each region. Using the boundary conditions at interfaces together with the transfer matrix method we identify the transmission in the different Floquet sideband states as a function of the physical parameters. In the strainless case, we show that the transmission of central band decreases for smaller values of the barrier width and rapidly oscillates with different amplitude for larger ones. Whereas the transmission for the first sidebands increases from zero and shows a damped oscillatory profile. It is found that the number of oscillations in all transmission channels reduces with increasing the strength of armchair strain, but becomes more important by switching the deformation to zigzag. Moreover, it is observed the appearance of Fano type resonance peaks by altering the amplitude and the frequency of the laser field.

Physics and Modeling of Multidomain FeFET With Domain Wall-Induced Negative Capacitance

In this article, we present the dynamics and modeling of multidomains in the ferroelectric FET (FeFET). Due to the periodic texture of domains, the electrostatics of the FeFET exhibit an oscillatory conduction band profile. To capture such oscillations, we solve coupled 2-D Poisson’s equation with the net ferroelectric energy density (gradient energy + free energy + depolarization energy) equation. Multidomain dynamics are captured by minimizing the net ferroelectric energy, leading to a thermodynamically stable state. Furthermore, we show that the motion of domain walls originates from local bound charge density in the ferroelectric region, which induces the negative capacitance (NC) effect. The strength of domain wall-induced NC is determined by the gradient energy of the ferroelectric material. FeFET exhibits variability in the drain current with domain period due to the inherent NC effect. Additionally, the impact of domain wall transition (soft <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\rightleftharpoons $ </tex-math></inline-formula> hard) on the device’s electrostatic/transport is also analyzed. The model also accurately captures both nucleations of a new domain and the motion of the domain wall. Furthermore, the model is thoroughly validated against experimental results and phase-field simulations.

Oscillatory and Aperiodic Neural Activity Jointly Predict Language Learning.

Memory formation involves the synchronous firing of neurons in task-relevant networks, with recent models postulating that a decrease in low-frequency oscillatory activity underlies successful memory encoding and retrieval. However, to date, this relationship has been investigated primarily with face and image stimuli; considerably less is known about the oscillatory correlates of complex rule learning, as in language. Furthermore, recent work has shown that nonoscillatory (1/ƒ) activity is functionally relevant to cognition, yet its interaction with oscillatory activity during complex rule learning remains unknown. Using spectral decomposition and power-law exponent estimation of human EEG data (17 women, 18 men), we show for the first time that 1/ƒ and oscillatory activity jointly influence the learning of word order rules of a miniature artificial language system. Flexible word-order rules were associated with a steeper 1/ƒ slope, whereas fixed word-order rules were associated with a shallower slope. We also show that increased theta and alpha power predicts fixed relative to flexible word-order rule learning and behavioral performance. Together, these results suggest that 1/ƒ activity plays an important role in higher-order cognition, including language processing, and that grammar learning is modulated by different word-order permutations, which manifest in distinct oscillatory profiles.