Low Vibrational Modes Research Articles

Effect of vibrational modes on electron transfer directionality: Photosynthetic reaction centers.

It is shown in the example of the photosynthetic reaction centers (RCs) that the electron transfer can be directed by vibrational modes into the needed site where it is localized. In the case of the RC, it is the low vibrational mode that produces such an effect. We find that the electron transfer unidirectionality in the photosynthetic reaction center can be determined by the asymmetry in the reorganization energy of the vibrational modes at high temperatures. We also numerically solve generalized master equationsfor various vibration relaxation times. The results are compared with the solution of master equations. It is shown that for small relaxation times, the non-Markovian electron transfer kinetics gives similar results as the Markovian approximation, but the results are significantly different for the long vibration relaxation times.

Prediction of Lower and Higher Modes of Vibration for Kirchhoff’s Plates Using Transcendental and Polynomial Functions via Semi-analytical Method

Prediction of Lower and Higher Modes of Vibration for Kirchhoff’s Plates Using Transcendental and Polynomial Functions via Semi-analytical Method

Dynamic Behavior of the Inertial Platform Related to the Research Facility Building Laser and Gamma at ELI-NP Bucharest

This paper aims to study the vibration of the large inertial platform from the Laser + Gamma building that is part of the ELI-NP project. In order to ensure a precisely positioned radiation beam, it is necessary that the shocks and vibrations coming from the external environment are damped or absorbed until they reach the work installations. This is ensured by the platform on which the devices are positioned, a platform that is supported on spring batteries and shock absorbers. A rigid body model is developed in this regard and a comparison with the finite element model of the concrete platform is conducted. It has been found that low vibration modes can be obtained with the help of the rigid model, which also has the advantage of simplicity and very little time is required to obtain results.

Vibration reduction of cables with pendulum-type elastic metamaterials

Elastic metamaterials (EMMs) have been used to reduce the vibration of various mechanical structures. Recent studies have proposed methods to reduce the vibration of cables and space tethers by introducing pendulum-type EMMs. However, the vibration absorption characteristics in the bandgaps of pendulum-type EMMs need to be investigated in relation to the local resonances of the unit cell structure because only beams among the unit cell structure were considered. Furthermore, it is necessary to improve the vibration reduction performance of the pendulum-type EMMs by allocating as many bandgaps as possible in the frequency range of interest. In this study, the effect of the dynamic characteristics of the coupled structure with the same configuration as the unit cell structure including the ring or annular plate as well as the beam were investigated in depth. Further, based on these results, an improved pendulum-type EMM with multiple bandgaps in the frequency range of interest was developed, which is well suited for most practical applications in mechanical systems where the influence of low vibration modes is dominant. The vibration reduction performance and the effect of the bandgaps of the pendulum-type EMM with an annular plate were verified through comparison between the experimental and simulation results. The frequency response experiments and simulation results were consistent in terms of the resonant peak frequencies outside the bandgaps and the low response amplitude within the bandgaps. Moreover, the experimentally visualized and simulated operational deflection shapes showed that the cable hardly vibrates at the frequency within the bandgap; at this frequency, the operational deflection shape of the annular plate is very similar to the mode shape of the vibration mode of the coupled structure.

Global Analysis of Heme Proteins Elucidates the Correlation between Heme Distortion and the Heme-Binding Pocket.

Heme proteins play diverse and important biological roles, from electron transfer and chemical catalysis to oxygen transport and/or storage. Although the distortion of heme porphyrin correlates with the physical properties of heme, such as the redox potential and oxygen affinity, the relationship between heme distortion and the heme protein environment is unclear. Here, we tested the hypothesis that the protein environment of the heme-binding pocket determines heme distortion (conformation). We analyzed the correlations between the amino acid composition of the heme-binding pocket and the magnitude of heme distortion along 12 vibrational modes using machine learning. A correlation was detected in the three lowest vibrational modes. Analysis of heme distortions in nearly the same environments of the heme-binding pocket supported this notion. Our analyses indicate that the heme-binding pocket environment is a major factor impacting the distortion of heme porphyrin along the three lowest vibrational modes. In addition, statistical analysis of the distortion of heme porphyrin revealed that the peaks of distributions of the ruffling and breathing distortions are shifted from 0 (the equilibrium structure). Both the ruffling and breathing distortions are correlated with the redox potential of heme, so that heme molecules with these distortions have a lower redox potential than planar molecules. These findings explain the structure-function relationship of heme.

Three-dimensional vibration patterns of alto saxophone reeds measured on different mouthpieces under mimicked realistic playing conditions.

In single reed musical instruments, vibrations of the reed, in conjunction with the geometry of the mouthpiece and the acoustic feedback of the instrument, play an essential role in sound generation. Up until now, three-dimensional (3D) reed vibration patterns have only been studied under external acoustic stimulation, or at a single note and lip force. This paper investigates vibration patterns of saxophone reeds under imitated realistic playing conditions. On different notes displacement measurements on the entire optically accessible part of the reed are performed using stroboscopic digital image correlation. These vibration data are decomposed onto the harmonic frequencies of the generated note pitch and into the operational modes. Motion data as a function of time are shown on single points. All points on the reed predominantly move in phase, corresponding to the first flexural mode of the reed. At higher note harmonics very low amplitude higher vibration modes are superimposed on the fundamental mode. Mouthpiece characteristics and lip force influence the vibration patterns. Vibration patterns differ strongly from earlier measurements on free vibrating reeds. Results show that single-point measurements on the tip of the reed can give a good indication of the 3D vibration amplitude, also at higher note pitches.

Damage identification of steel-concrete composite beams based on modal strain energy changes through general regression neural network

This paper presents a novel method for damage identification of steel-concrete composite beams based on modal strain energy (MSE) changes through general regression neural network (GRNN). A finite element (FE) model was developed using two Euler-Bernoulli beam elements as steel beam and concrete slab layers which are coupled by incorporating a deformable shear connection layer distributed at their interface. The connection layer was modelled as a uniform spring that enables both longitudinal slip and vertical uplift between the two components. The FE model was validated using experimental results of a full-scale composite beam in the laboratory. Three damage indices were defined as the elemental stiffness reduction in the steel, concrete and shear connection layers, respectively. A damage identification approach was developed to investigate the sensitivity of eigenvalues to damage in the composite interface. Then, MSEs change ratios were selected as the features for identifying structural damage in the composite layers. Principle component analysis was utilised to reduce the dimensionality of the large data features obtained from modal analysis leading to determining the main features for structural damage identification. The low dimensional data were employed as the input for the GRNN. Different damage cases were investigated, and the damage vectors were defined as the outputs of GRNN. The results show that the proposed method is efficient and reliable to identify damage in the composite beam with a few low vibration modes, even though small damage in the composite layers does not significantly affect these modes.

Optimal design of two viscous dampers for multi-mode control of a cable covering broad frequency range

For the conventional design of viscous dampers attached to cables, only the first few modes are of interest. However, a recent cable vibration event occurred on the Sutong Bridge highlights that the higher mode vibrations of cables also need to be controlled. To this end, a novel optimal design of two viscous dampers near to a cable anchorage is explored which can broaden the control frequency range covering both the lower and higher modes. In the proposed design scheme, the one damper nearest to the cable anchorage is targeted for lower-mode control and the other damper is targeted for higher-mode control. The mode shape characteristics of a cable with two viscous dampers, which is prerequisite for optimal damper design, are investigated. Based on that, the optimal design of the two dampers in a cable is simply reduced to two individual designs of one single viscous damper, which can lower the design complexity. The control performance of the proposed design both for lower and higher vibration modes is numerically validated by a cable on the Sutong Bridge and compared with the conventional design considering only lower vibration modes. Finally, the effects of parametric variations of the two dampers in the proposed design are discussed. It is shown that the proposed design using two dampers can both increase damping ratios of cables for lower and higher vibration modes, and the acceleration response of the cable is effectively reduced to around 60% of that using the conventional design.

Nonlinear interaction of longitudinal and transverse vibrations of a rod at an internal combinational resonance in view of opto-thermal excitation of N/MEMS

In this paper, the character of coupled longitudinal-flexural vibrations of a rod is investigated in the case of an internal combinational resonance between two flexural and lower longitudinal vibration modes. An approximate analytical solution is obtained by a multiple time-scales method applied directly to a system of nonlinear partial differential equations. It is shown that the initial perturbation in the longitudinal direction can effectively excite bending vibration modes, which, on the whole, leads to a longitudinal-transverse beating regime with noticeable amplitudes. It is noted that the period and amplitude of these beats substantially depend on the frequency detuning parameter between the sum of the bending vibration frequencies and the longitudinal vibration frequency. This effect can be used as a new principle of operation of opto-thermally excited N/MEMS resonant sensors.

Evaluation of TMD Performance in Footbridges Using Human Walking Probabilistic Models

Footbridges are generally slender and lightweight structures with low stiffness, designed to support dynamic loads generated by crowds. Therefore, these structures are exposed to vibration problems related to the resonance of human walking step frequencies and the lower vibration modes. To mitigate these problems, one of the most applied corrective strategies is the installation of tuned mass damper (TMD) systems that aim at the vibration reduction of the footbridge’s dominant mode. A fundamental matter in both the footbridge and the TMD design is the pedestrian load modelling, generally considered as a deterministically moving force or a biodynamic model. However, as human gait is a random process, the deterministic models can lead to non-realistic results, directly affecting the TMD system efficiency. In contrast, the use of probabilistic distributions to simulate the human walk randomness can lead to more reliable time series predictions. In this paper, a random walk (RW) algorithm is developed and applied to simulate different crowd scenarios using a simplified plane model of a coupled human-structure-TMD system. In each scenario, the TMD efficiency in reducing the vibration amplitudes is assessed. Results highlight the importance of considering the walking randomness and pedestrians’ dynamic properties in the TMD design.

Photoluminescence line shapes for color centers in silicon carbide from density functional theory calculations

Silicon carbide with optically and magnetically active point defects offers unique opportunities for quantum technology applications. Since interaction with these defects commonly happens through optical excitation and de-excitation, a complete understanding of their light-matter interaction in general and optical signatures, in particular, is crucial. Here, we employ quantum mechanical density functional theory calculations to investigate the photoluminescence lineshapes of selected, experimentally observed color centers (including single vacancies, double vacancies, and vacancy impurity pairs) in 4H-SiC. The analysis of zero-phonon lines as well as Huang-Rhys and Debye-Waller factors are accompanied by a detailed study of the underlying lattice vibrations. We show that the defect lineshapes are governed by strong coupling to bulk phonons at lower energies and localized vibrational modes at higher energies. Generally, good agreement to the available experimental data is obtained, and thus we expect our theoretical work to be beneficial for the identification of defect signatures in the photoluminescence spectra and thereby advance the research in quantum photonics and quantum information processing.

Vibration analysis of post-buckled fluid-conveying functionally graded pipe

The vibration of post-buckled fluid-conveying pipe made of functionally graded material is analyzed. The pipe material properties are assumed to be graded in the thickness direction according to power-law distribution. An exact solution is obtained for the post-buckling deformation of the fluid-conveying functionally graded pipe with various boundary conditions. The linear vibration problem is solved around the first buckled configuration and the natural frequencies of the three lowest vibration modes are obtained. The influences of power-law exponent, initial tension, fluid density and fluid velocity on the static deflection and free vibration frequencies are studied.

Analysis of Strength Stiffness and Modes for Bus Body Frame

In this paper, the bus body frame is made as a research object. The finite element model of bus body frame is built in Hypermesh software. The static strength and stiffness of bus body frame under four typical working conditions are calculated by Nastran solver. Modal analysis is carried out by Lanczos method, low natural frequency and vibration mode are obtained. The analysis of results show that the strength and stiffness of bus body frame must meet design requirement, and the modal frequency is also within the design range. According to finite element analysis, the development cycle of new product is reduced, and theoretical basis for later model improvement and optimal design is provided.

Research on Lightweight Design and Finite Element Analysis of a 9 Meter Bus Body Frame

The finite element model of a 10 meter bus body frame is built in Hypermesh software. The static force and modes of bus body frame under four typical working conditions are calculated by Nastran solver. The simulation of results show that the strength, stiffness, low natural frequency and vibration mode of bus body frame satisfy design requirement, and have enough potential reserve. Under the premise of ensuring the strength, stiffness and modal characteristics of bus body, the bus structure and dimensional parameters of parts are optimized to realize the lightweight design of bus body frame. The weight reduction rate of the optimized body frame is 10.57%, which verifies the feasibility of the optimized scheme.

Torsional ductility spectrum for predicting ductility distribution in simple asymmetric‐plan structures

SummaryAn analytical procedure is developed for predicting the ductility demands in simple asymmetric‐plan structures under earthquake ground motions. The procedure governs regular structures dominated by the lower vibration modes where inelastic response occurs only at the bases of first story columns and at the beam ends, in conformance with the capacity design principles. Torsional ductility spectra are generated for expressing the maximum ductility response of torsionally coupled, generic, single‐story, 2‐degree‐of‐freedom inelastic parametric systems. Five parameters characterize the parametric systems: first mode period, uncoupled frequency ratio, stiffness eccentricity, stiff‐to‐flexible edge strength ratio, and ductility reduction factor. A surrogate modeling approach is developed for converting the properties of the actual systems to those of the parametric system. Mean maximum ductilities of torsionally stiff, equally stiff, and torsionally flexible systems are calculated under a set of design spectrum compatible strong motions for the possible combinations of characteristic parameters. The results obtained from case studies revealed reasonable accuracy of the estimations. The results have indicated that the flexible side frames of torsionally stiff and equally stiff code conforming designs are mainly responsible for providing the intended ductility and energy dissipation capacity whereas the stiff side frames play a secondary role, particularly when the stiff edge is significantly stronger than the flexible edge. However, ductility demands in torsionally flexible systems are significantly larger at both sides compared with torsionally stiff systems.

Microwave-Driven Hexagonal-to-Monoclinic Transition in BiPO4: An In-Depth Experimental Investigation and First-Principles Study.

Present theoretical and experimental work provides an in-depth understanding of the morphological, structural, electronic, and optical properties of hexagonal and monoclinic polymorphs of bismuth phosphate (BiPO4). Herein, we demonstrate how microwave irradiation induces the transformation of a hexagonal phase to a monoclinic phase in a short period of time and, thus, the photocatalytic performance of BiPO4. To complement and rationalize the experimental results, first-principles calculations have been performed within the framework of density functional theory. This was aimed at obtaining the geometric, energetic, and structural parameters as well as vibrational frequencies; further, the electronic properties (band structure diagram and density of states) of the bulk and corresponding surfaces of both the hexagonal and monoclinic phases of BiPO4 were also acquired. A detailed characterization of the low vibrational modes of both the hexagonal and monoclinic polymorphs is key to explaining the irreversible phase transformation from hexagonal to monoclinic. On the basis of the calculated values of the surface energies, a map of the available morphologies of both phases was obtained by using Wulff construction and compared to the observed scanning electron microscopy images. The BiPO4 crystals obtained after 16-32 min of microwave irradiation provided excellent photodegradation of Rhodamine B under visible-light irradiation. This enhancement was found to be related to the surface energy and the types of clusters formed on the exposed surfaces of the morphology. These findings provide details of the hexagonal-to-monoclinic phase transition in BiPO4 during microwave irradiation; further, the results will assist in the design of electronic devices with higher efficiency and reliability.

An Effective Approach for Damage Identification in Beam-Like Structures Based on Modal Flexibility Curvature and Particle Swarm Optimization

In this paper, a computationally simple approach for damage localization and quantification in beam-like structures is proposed. This method is in consonance with applying modal flexibility curvature (MFC) and particle swarm optimization (PSO) algorithm. Analytical studies in the literature have revealed that changes in the modal flexibility curvature can be considered as a sensitive and suitable criterion for identifying damage in the beam-like structures. Modal flexibility curvature can be calculated utilizing central difference approximation, based on entries of the modal flexibility matrix. The PSO algorithm, as a powerful optimization tool, is employed in order to minimize the error function which is formulated as an error function between the measured modal flexibility curvatures of the damaged structure and those calculated from the analytical structure. To demonstrate the efficiency of the method, two beam-like structures under different damage scenarios are studied. In addition, the robustness of presented method is investigated only when the first several modal data are available. It is observed that the proposed approach is able to localize and quantify various damage cases only by a few lower vibrational modes and also, it is low-sensitive to measurement noise.

Synchrotron spectroscopy of the CSH-bending and CH3-rocking bands of methyl mercaptan

The CSH-bending and CH3-rocking infrared bands of CH3SH have been investigated in Fourier transform spectra recorded at 0.001 cm−1 resolution employing synchrotron radiation at the Canadian Light Source in Saskatoon. The relative band strengths and structures are quite different from those of the CH3OH methanol analogue, with the CSH bend being very weak and both the in-plane and out-of-plane CH3 rocks being strong with intensities greater than the C–S stretch. The CSH bend has parallel a-type character with no detectable b-type component. The out-of-plane CH3 rock is a purely c-type perpendicular band, whereas the in-plane rock is of mixed a/b character. Sub-bands have been assigned for A and E torsional species up to about K = 10 for each vibrational mode, providing upper-state term values from which K-reduced substate origins were determined. For the CSH bend, the origins follow the customary oscillatory torsional pattern as a function of K with a sharply reduced amplitude of 0.362 cm−1 compared to the 0.653 cm−1 for the ground state. The torsional energy curves for the out-of-plane rock are also well-behaved but have inverted ordering of the A–E torsional splitting components and a larger amplitude of 1.33 cm−1. In contrast, the substate origins for the in-plane rock are scattered over a range of about 2 cm−1 without clear oscillatory structure. Several instances of coupling among the lower modes and the ground state via resonances between accidentally near-degenerate levels have been observed and characterized. Ab initio calculations are found to give a good representation of the frequency and relative intensity patterns for the lower vibrational modes.

The role of Al doping on ZnO nanowire evolution and optical band gap tuning

In this work, the morphological transformation and band gap modulation of ZnO by Aluminum doping has been investigated. Pure ZnO and Aluminum doped Zinc oxide (Al:ZnO) nanostructure have been fabricated using hydrothermal method on the seed layer coated FTO substrates. The prepared samples were investigated with such analytical techniques as Raman spectroscopy, Field Emission scanning electron microscope (FESEM), Photoluminescence (PL) and spectrophotometer. Raman spectra revealed E2 (high) and E1 (low) vibrational modes for pure ZnO. However, a successive shift in E2 (high) mode towards higher wavenumbers has been observed by placing ZnO with different concentration of Aluminum nitrate nano-hydrate solution (0.1 mM, 0.2 mM and 0.3 mM) confirming the sequential Al incorporation in the ZnO nanostructure. SEM results show the morphological transformation from a typical hexagonal ZnO nano-wire to petal shaped nano-rods with the increase of Al concentration. The optical properties have been investigated using the photoluminescence (PL) and optical transmission. In the PL spectra, pure ZnO nanostructure has UV peak with higher intensity compared to the visible peak. However, the addition of Al in the ZnO causes enhanced emission in the visible region compared to the UV emission. The addition of Al in ZnO nanostructure also modifies the optical band gap of ZnO from 3.2 to 3.15 eV.

Analysis of spatial vibrations of piezoceramic eccentric cylindrical shells interacting with an annular fluid layer

The work is devoted to a numerical study of the behavior of vertically oriented eccentric (non-coaxial) electroelastic shells, containing a fluid in the gap between them. The solution of the problem is found in the framework of a three-dimensional formulation using the finite element method. The shells are made of the piezoelectric material polarized in the radial direction. Thin-walled structures are considered in the framework of the classical theory based on the Kirchhoff – Love hypotheses, as well as the equations of linear electroelasticity. The distribution of the electric potential through the thickness is assumed linear. The fluid is considered within the framework of a potential theory. The study of the low natural frequencies and vibration modes is carried out for different variants of the boundary conditions at the edges of the shells, the level of fluid in the gap and the eccentricity of the inner shell. The influence of the electric boundary conditions specified on the parts of the shells surfaces covered with electrodes is estimated.