Combined Resonance Research Articles

Reactive oxygen species formation at Pt nanoparticles revisited by electron paramagnetic resonance and electrochemical analysis

A combined electrochemical and electron paramagnetic resonance (EPR) procedure for the study of oxygen reduction reaction (ORR) intermediates generated at Pt nanoparticles (NPs) is validated in this work. Using spin-trap EPR complemented by electrochemical analysis, we show that we can detect and identify the free radicals that are produced during the ORR through trapping with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) which are otherwise difficult to detect. Experiments with 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline-N-oxide (DEPMPO) as spin trap show no evidence of DEPMPO-OOH and indicate that only OH radicals are trapped during the ORR. The results of this study serve as a functional proof-of-concept for further research on the identification of radical ORR intermediates in solution. We propose that our procedure can be used for a more rigorous quantification of free radicals involved in other electrochemical reactions.

An Important Step toward Understanding the Role of Body-based Cues on Human Spatial Memory for Large-Scale Environments

Moving our body through space is fundamental to human navigation; however, technical and physical limitations have hindered our ability to study the role of these body-based cues experimentally. We recently designed an experiment using novel immersive virtual-reality technology, which allowed us to tightly control the availability of body-based cues to determine how these cues influence human spatial memory [Huffman, D. J., & Ekstrom, A. D. A modality-independent network underlies the retrieval of large-scale spatial environments in the human brain. Neuron, 104, 611-622, 2019]. Our analysis of behavior and fMRI data revealed a similar pattern of results across a range of body-based cues conditions, thus suggesting that participants likely relied primarily on vision to form and retrieve abstract, holistic representations of the large-scale environments in our experiment. We ended our paper by discussing a number of caveats and future directions for research on the role of body-based cues in human spatial memory. Here, we reiterate and expand on this discussion, and we use a commentary in this issue by A. Steel, C. E. Robertson, and J. S. Taube (Current promises and limitations of combined virtual reality and functional magnetic resonance imaging research in humans: A commentary on Huffman and Ekstrom (2019). Journal of Cognitive Neuroscience, 2020) as a helpful discussion point regarding some of the questions that we think will be the most interesting in the coming years. We highlight the exciting possibility of taking a more naturalistic approach to study the behavior, cognition, and neuroscience of navigation. Moreover, we share the hope that researchers who study navigation in humans and nonhuman animals will synergize to provide more rapid advancements in our understanding of cognition and the brain.

Myocardial involvement in eosinophilic granulomatosis with polyangiitis evaluated with cardiopulmonary magnetic resonance

Patients with eosinophilic granulomatosis with polyangiitis (EGPA) most commonly die from cardiac causes, however, cardiac involvement remains poorly characterised and the relationship between cardiac and pulmonary disease is not known. This study aimed to characterise myocardial and pulmonary manifestations of EGPA, and their relationship. Prospective comprehensive cardiopulmonary investigation, including a novel combined cardiopulmonary magnetic resonance imaging (MRI) technology, was performed in 13 patients with stable EGPA. Comparison was made with 11 prospectively recruited matched healthy volunteers. Stable EGPA was associated with focal replacement and diffuse interstitial myocardial fibrosis (myocardial extracellular volume 26.9% vs. 24.7%; p = 0.034), which drove a borderline increase in left ventricular mass (56 ± 9 g/m2 vs. 49 ± 8 g/m2; p = 0.065). Corrected QT interval was significantly prolonged and was associated with the severity of myocardial fibrosis (r = 0.582, p = 0.037). Stable EGPA was not associated with increased myocardial capillary permeability or myocardial oedema. Pulmonary tissue perfusion and capillary permeability were normal and there was no evidence of pulmonary tissue oedema or fibrosis. Forced expiratory volume in one second showed a strong inverse relationship with myocardial fibrosis (r = −0.783, p = 0.038). In this exploratory study, stable EGPA was associated with focal replacement and diffuse interstitial myocardial fibrosis, but no evidence of myocardial or pulmonary inflammation or pulmonary fibrosis. Myocardial fibrosis was strongly associated with airway obstruction and abnormal cardiac repolarisation. Further investigation is required to determine the mechanisms underlying the association between heart and lung disease in EGPA and whether an immediate immunosuppressive strategy could prevent myocardial fibrosis formation.

Mechanism and Characteristics of Global Varying Compliance Parametric Resonances in a Ball Bearing

Varying compliance (VC) is an unavoidable form of parametric excitation in rolling bearings and can affect the stability and safety of the bearing and its supporting rotor system. To date, we have investigated VC primary resonance in ball bearings, and in this paper other parametric VC resonance types are addressed. For a classical ball bearing model with Hertzian contact and clearance nonlinearities between the rolling elements and raceway, the harmonic balance and alternating frequency/time domain (HB–AFT) method and Floquet theory are adopted to analyze the VC parametric resonances and their stabilities. It is found that the 1/2-order subharmonic resonances, 2-order superharmonic resonances, and various VC combination resonances, such as the 1-order and 2-order summed types, can be excited, thus resulting in period-1, period-2, period-4, period-8, period-35, quasi-period, and even chaotic VC motions in the system. Furthermore, the bifurcation and hysteresis characteristics of complex VC resonant responses are discussed, in which cyclic fold, period doubling, and the second Hopf bifurcation can occur. Finally, the global involution of VC resonances around bearing clearance-free operations (i.e., adjusting the bearing clearance to zero or one with low interference) are provided. The overall results extend the investigation of VC parametric resonance cases in rolling bearings.

Internal resonances in nonlinear fractionally damped plates of the Uflyand-Mindlin type

In the present paper, the non-linear free vibrations of fractionally damped plates are investigated for the case when its equations of motion involve the rotary inertia and shear deformations via five coupled nonlinear differential equations in terms of three mutually orthogonal displacements and two angles of rotation. The damping features of the surrounding medium are described by the fractional detivative Kelvin-Voigt model. The procedure resulting in decoupling linear parts of governing equations has been proposed, what allows one to utulyze effectively the fractional derivative expansion method for solving the non-linear equations of motion. The occurrence of the internal or combinational resonances has been revealed and classified for plates of the Uflyand-Mindlin type.

Quantification of body fluid compartmentalization by combined time-domain nuclear magnetic resonance and bioimpedance spectroscopy.

The measurement of fluid compartmentalization, or the distribution of fluid volume between extracellular (ECF) and intracellular (ICF) spaces, historically requires complicated, burdensome, and often terminal methodologies that do not permit repeated or longitudinal experiments. New technologies including time-domain nuclear magnetic resonance (TD-NMR)-based methods allow for highly accurate measurements of total body water (TBW) within minutes in a noninvasive manner, but do not permit dissection of ECF versus ICF reservoirs. In contrast, methods such as bioimpedance spectroscopy (BIS) allow dissection of ECF versus ICF reservoirs but are hampered by dependence on many nuanced details in data collection that undermine confidence in experimental results. Here, we present a novel combinatorial use of these two technologies (NMR/BIS) to improve the accuracy of BIS-based assessments of ECF and ICF, while maintaining the advantages of these minimally invasive methods. Briefly, mice undergo TD-NMR and BIS-based measures, and then fat masses as derived by TD-NMR are used to correct BIS outputs. Mice of the C57BL/6J background were studied using NMR/BIS methods to assess the effects of acute furosemide injection and diet-induced obesity on fluid compartmentalization, and to examine the influence of sex, body mass and composition, and diet on TBW, ECF, and ICF. We discovered that in mice, sex and body size/composition have substantial and interactive effects on fluid compartmentalization. We propose that the combinatorial use of NMR/BIS methods will enable a revisioning of the types of longitudinal, kinetic studies that can be performed to understand the impact of various interventions on body fluid homeostasis.

Combined application of DTI and BOLD-MRI in the assessment of renal injury with hyperuricemia.

To explore the value of combined diffusion tensor imaging (DTI) and blood oxygenation level-dependent magnetic resonance imaging (BOLD-MRI) in detecting early renal alterations in patients with hyperuricemia. Seventy-one individuals were enrolled in this study and divided into three groups according to their serum uric acid (SUA) level and clinical symptoms: healthy controls (HC, n = 23), asymptomatic hyperuricemia (AH, n = 22) and gouty arthritis (GA, n = 26). All patients underwent both DTI and BOLD-MRI examination. Renal cortical and medullary ADC, FA and R2* values were calculated, respectively, and compared among the three groups. Correlations between ADC, FA and R2* with estimated glomerular filtration rate (eGFR) and SUA in hyperuricemia were evaluated, respectively. In the renal cortex, the ADC, FA and R2* values of the AH and GA groups were significantly lower than those of the HC groups (p < 0.05). In the renal medulla, the ADC and FA values in AH and GA patients were significantly lower than those in healthy controls (p < 0.05). The R2* value of the GA group significantly decreased, compared to that of the AH and HC groups (p < 0.05). SUA was negatively correlated with cortical ADC, FA and R2* values (p < 0.05) as well as with medullary ADC and FA values. No significant correlation was discovered between the eGFR and ADC, FA and R2* values. The combined evaluation of DTI and BOLD might provide a sensitive and non-invasive approach for detection of renal microstructural alterations and oxygen metabolism abnormality in hyperuricemia.

Stability and combined vibration of gear transmission system in shearer cutting section under multi-parameter excitation

The torsional vibration of the gear device in the shearer permanent magnet semi-direct drive cutting transmission system is easily induced by the end load impact and the internal and external parameter excitation. To solve this problem, taking into account the time-varying meshing stiffness, meshing damping, backlash and dynamic transmission error, the nonlinear torsional dynamic model of the gear system is established by the concentrated mass method. The approximate analytical solution and the stability boundary curve of the gear device in the permanent magnet semi-direct drive cutting drive system of the shearer are obtained under multi-parameter excitation. The system stability parameter threshold is determined. The frequency response equation of steady-state vibration is constructed. The corresponding frequency response curve is drawn, and the combined resonance state of the gear pair under the coupling of internal excitation and external excitation is studied. The effects of static excitation, dynamic excitation, internal excitation and external excitation on the resonance response of the shearer cutting drive system are analyzed to provide guidance for the optimal design of shearer permanent magnet semi-direct drive cutting gear drive system.

Combined resonance in quasi-two-dimensional conductors

A theoretical investigation of the combined resonance of interlayer conductivity and spin magnetization, in conductors with quasi-two-dimensional electronic energy spectra. Analytical expressions are obtained for the surface impedance, magnetic susceptibility, and the resonance interlayer conductivity component caused by Rashba–Dresselhaus spin-orbit interaction, with allowance for spatial dispersion.

Biocompatible Polymer Nanocomposites Integrating Magnetic Polyoxomolybdates for Enhanced MRI and On-Site Activated Photothermal Properties.

This work reports the ionic composition of a PEGylated and chemically crosslinked polyethyleneimine with a gadolinium-coordinated polyoxomolybdate cluster, K17 [Gd(P2 Mo17 O61 )2 ], via electrostatic interaction. The prepared composites form nanoobjects with an average size of ≈27nm at dried state and maintain structural stability in aqueous solution. While the biocompatibility on HeLa cells is demonstrated, the polymer-shielded multifunctional nanoplatform shows both the combined magnetic resonance imaging and redox-triggered photothermal conversion effect. As a contrast agent, the T1 -weighed relaxivity reaches up to 22.77mm-1 s-1 . The photothermal conversion of the prepared composites can be aroused by yielding a broad near infrared (NIR) adsorption through on-site reduction of the glutathione that is enriched in the tumor environment. The high efficiency ≈61.0% under the irradiation of 808nm NIR laser illustrates a distinct treatment capability according to cell counting Kit-8 assay while the obvious inhibition for the growth of tumor cells is observed.

CLASSIFICATION OF INTERNAL RESONANCES IN NONLINEAR FRACTIONALY DAMPED UFLYAND-MINDLIN PLATES

In the present paper, the nonlinear free vibrations of fractionally damped plates are studied, equations of motion of which take the rotary inertia and shear deformations into account and involve fivecoupled nonlinear differentialequations in terms of three mutually orthogonal displacements and two angles of rotation. The procedure resulting in decoupling linear parts of equations has been proposed with further utilization of the generalized method of multiple time scales for solving nonlinear governing equations of motion, in so doing the amplitude functions have been expanded into power series in terms of the small parameter and depend on differenttime scales. The occurrence of the internal or combinational resonances in Uflyand-Mindlinplates has been revealed and classified

Suppression of Complex Hysteretic Resonances in Varying Compliance Vibration of a Ball Bearing

It is traditionally considered that, due to the Hertzian contact force-deformation relationship, the stiffness of rolling bearings has stiffening characteristics, and gradually researchers find that the supporting characteristics of the system may stiffen, soften, and even coexist from them. The resonant hysteresis affects the stability and safety of the system, and its jumping effect can make an impact on the system. However, the ball bearing contains many nonlinearities such as the Hertzian contact between the rolling elements and raceways, bearing clearance, and time-varying compliances (VC), leading great difficulties to clarify the dynamical mechanism of resonant hysteresis of the system. With the aid of the harmonic balance and alternating frequency/time domain (HB-AFT) method and Floquet theory, this paper will investigate the hysteretic characteristics of the Hertzian contact resonances of a ball bearing system under VC excitations. Moreover, the linearized dynamic bearing stiffness of the system will be presented for assessing the locations of VC resonances, and the nonlinear characteristics of bearing stiffness will also be discussed in depth. Our analysis indicates that the system possesses many types of VC resonances such as the primary, internal, superharmonic, and even combination resonances, and the evolutions of these resonances are presented. Finally, the suppression of resonances and hysteresis of the system will be proposed by adjusting the bearing clearance.

Nonlinear mode coupling in a passively isolated mechanical system

Recent studies in passively isolated systems have shown that mode coupling is desirable for better vibration suppression, thus refuting the long-standing rule of modal decoupling. However, these studies have ignored the nonlinearities in the isolators. In this work, we consider stiffness nonlinearity from pneumatic isolators and study the nonlinear forced damped vibrations of a passively isolated ultra-precision manufacturing (UPM) machine. Experimental analysis is conducted to guide the mathematical formulation. The system comprises linearly and nonlinearly coupled in-plane horizontal and rotational motion of the UPM machine with quadratic nonlinear stiffness from the isolators. We present an analytical study using the method of multiple scales and the method of harmonic balance for different cases of external resonances, viz., the primary and the secondary resonances (superharmonic and combined resonances) with 1 : 2 internal resonance between the modes. We further validate our analytical findings using direct numerical integration and observe an excellent match. On extending our analysis, we observe the existence of subcritical, supercritical, and s-shaped bifurcation depending on the location of the isolators and the case of external resonance. Also, the saturation and quasi-saturation phenomenon are observed for the case of resonances close to the higher natural frequency and combined resonance, respectively. A parametric study is conducted to examine the effect of different parameters on the dynamics of the system, and consecutively the critical parameters of the system are identified for different cases of external resonance.

Dynamic analysis of piezoelectric energy harvester under combination parametric and internal resonance: a theoretical and experimental study

In this work, theoretical and experimental analysis of a piezoelectric energy harvester with parametric base excitation is presented under combination parametric resonance condition. The harvester consists of a cantilever beam with a piezoelectric patch and an attached mass, which is positioned in such a way that the system exhibits 1:3 internal resonance. The generalized Galerkin’s method up to two modes is used to obtain the temporal form of the nonlinear electromechanical governing equation of motion. The method of multiple scales is used to reduce the equations of motion into a set of first-order differential equations. The fixed-point response and the stability of the system under combination parametric resonance are studied. The multi-branched non-trivial response exhibits bifurcations such as turning point and Hopf bifurcations. Experiments are performed under various resonance conditions. This study on the parametric excitation along with combination and internal resonances will help to harvest energy for a wider frequency range from ambient vibrations.

Modeling and dynamic study of rotating blades with adjustable stagger angle

A blade with an adjustable stagger angle is a type of blade that is able to partially rotate around its long axis. In fact, while a hub rotates, simultaneously the angle of the blade root section can change. The objective of this research is to develop and analyze a model of rotating cantilever orthotropic blade with adjustable stagger angle. Using Hamilton's principle, the governing partial differential equations are derived. In this formulation, both the Coriolis effects and centrifugal inertia forces are accounted for. First, the extended Galerkin method is utilized to discretize the equations of motion. Then, the multiple scales method is used to investigate the dynamic stability of the rotating blades analytically. Consequently, the possibility of internal resonances between different modes is studied and recognized. Moreover, the influence of various parameters on the instability regions is evaluated in detail, and the results are discussed. For validating the results, the modal characteristics of the system obtained by two methods of extended Galerkin and extended Kantorovich are compared with each other. Additionally, the fourth-order Runge–Kutta algorithm is employed to more deeply understand the dynamic behaviors of the system in the cases of constant and variable stagger angles and the differences between them as well as to prove the validity of the results of multiple scales method. The time histories, phase space diagrams and frequency spectrums are provided. Furthermore, a detailed investigation is carried out to determine the properties of the response under different conditions of the amplitude of the variable angle. As far as we know, the present study is the first attempt to demonstrate the effects of time-varying stagger angle for this class of problems in the literature. A stable motion in the adjustable stagger angle configuration gives a more complicated response. It can be observed that in this dynamic situation, the results are affected by Coriolis, both in quality and quantity. The findings indicate that with a change in the speed, there is a possibility of switching instability zones relative to each other. It is also found that the maximum width of the instability regions among the combination resonances is related to the second spanwise and first chordwise bending modes. The type of instability qualitatively depends on the amplitude of angle.

Analysis of the Combined Cyclotron and Cherenkov Resonances in Metallic Grating Structures

The metallic grating structure is usually used in the Cherenkov maser. In order to further improve the gain and bandwidth of the sheet beam metallic grating waveguide system, the beam can be with initial transverse and axial velocity instead of pure axial velocity. In this situation, the sheet helical beam will interact with several space harmonics waves simultaneously, and then, the combined cyclotron and Cherenkov resonances can be utilized. Based on the linear theory, the “hot” dispersion equation of the sheet beam metallic grating cyclotron maser is derived and calculated. Through the numerical calculations, the contribution of each resonance, and the influence of beam voltage, the magnetic field and transverse to axial velocity ratio on the gain and bandwidth are analyzed. Besides, the effects of the beam voltage and magnetic field on the growth rate are also simulated, which can further verify the accuracy of the theoretical calculations. This analysis shows the potential of the sheet helical beam with a metallic grating waveguide system, which can be further studied and applied in the future.

Asynchronous parametric excitation: validation of theoretical results by electronic circuit simulation

A validation of recent theoretical results on the stability effects of asynchronous parametric excitation is presented. In particular, the coexistence of both resonance and anti-resonance at each combination resonance frequency is to be confirmed on a close-to-experiment simulation model. The simulation model reproduces the experimental setup developed by Schmieg in 1976, remaining the only experimental study on asynchronous excitation to this day. The model consists of two oscillating electronic circuits with feedback-free coupling through parametric excitation. In contrast to a mechanical system, the phase relations of the parametric excitation terms in an electronic system can be easily adjusted. The implementation of the simulation model is performed in the electronic circuit simulation software LTspice. The electronic model itself is first validated against the experimental results obtained by Schmieg and is then used to confirm the theoretical findings. The results of the electronic circuit simulation show excellent qualitative and quantitative agreement with analytical approximations confirming the coexistence of resonance and anti-resonance effects near a combination resonance frequency.

Secondary Resonance Energy Harvesting with Quadratic Nonlinearity

Piezoelectric energy harvesters can transform the mechanical strain into electrical energy. The microelectromechanical transformation device is often composed of piezoelectric cantilevers and has been largely experimented. Most resonances have been developed to harvest nonlinear vibratory energy except for combination resonances. This paper is to analyze several secondary resonances of a cantilever-type piezoelectric energy harvester with a tip magnet. The conventional Galerkin method is improved to truncate the continuous model, an integro-partial differential equation with time-dependent boundary conditions. Then, more resonances on higher-order vibration modes can be obtained. The stable steady-state response is formulated approximately but analytically for the first two subharmonic and combination resonances. The instability boundaries are discussed for these secondary resonances from quadratic nonlinearity. A small damping and a large excitation readily result in an unstable response, including the period-doubling and quasiperiodic motions that can be employed to enhance the voltage output around a wider band of working frequency. Runge–Kutta method is employed to numerically compute the time history for stable and unstable motions. The stable steady-state responses from two different methods agree well with each other. The outcome enriches structural dynamic theory on nonlinear vibration.

Mapping nanoscale dynamic properties of suspended and supported multi-layer graphene membranes via contact resonance and ultrasonic scanning probe microscopies

Graphene’s (GR) remarkable mechanical and electrical properties—such as its Young’s modulus, low mass per unit area, natural atomic flatness and electrical conductance—would make it an ideal material for micro and nanoelectromechanical systems (MEMS and NEMS). However, the difficulty of attaching GR to supports, coupled with naturally occurring internal defects in a few layer GR can significantly adversely affect the performance of such devices. Here, we have used a combined contact resonance atomic force microscopy (CR-AFM) and ultrasonic force microscopy (UFM) approach to characterise and map with nanoscale spatial resolution GR membrane properties inaccessible to most conventional scanning probe characterisation techniques. Using a multi-layer GR plate (membrane) suspended over a round hole, we show that this combined approach allows access to the mechanical properties, internal structure and attachment geometry of the membrane providing information about both the supported and suspended regions of the system. We show that UFM allows the precise geometrical position of the supported membrane-substrate contact to be located and provides an indication of the local variation of its quality in the contact areas. At the same time, we show that by mapping the position sensitive frequency and phase response of CR-AFM response, one can reliably quantify the membrane stiffness, and image the defects in the suspended area of the membrane. The phase and amplitude of experimental CR-AFM measurements show excellent agreement with an analytical model accounting for the resonance of the combined CR-AFM probe-membrane system. The combination of UFM and CR-AFM provide a beneficial combination for the investigation of few-layer NEMS systems based on two dimensional materials.

Simultaneous Resonance and Anti-Resonance in Dynamical Systems Under Asynchronous Parametric Excitation

Abstract Since the discovery of parametric anti-resonance, parametric excitation has also become more prominent for its stabilizing properties. While resonance and anti-resonance are mostly studied individually, there are systems where both effects appear simultaneously at each combination resonance frequency. With a steep transition between them and a high sensitivity of their relative positions, there is a need for a concurrent study of resonance and anti-resonance. The semi-analytical method of normal forms is used to derive approximate analytical expressions describing the magnitude of the stability impact as well as the precise locations of stabilized and destabilized areas. The results reveal that the separate appearance of resonance and anti-resonance is only a special case occurring for synchronous parametric excitation. In particular, in circulatory systems the simultaneous appearance is expected to be much more common.