Coupling Of Vibrational Modes Research Articles

High-Pressure Stability of Energetic Crystal of Dihydroxylammonium 5,5'-Bistetrazole-1,1'-diolate: Raman Spectroscopy and DFT Calculations.

The vibrational and structural behavior of a novel, energetic crystal, dihydroxylammonium 5,5'-bistetrazole-1,1'-diolate (TKX-50), was examined over a broad pressure range to elucidate its structural and chemical stability at high pressures. Raman measurements were performed on single crystals compressed to 50 GPa in a diamond anvil cell, and data were obtained over the entire frequency range of TKX-50 Raman activity. The Raman spectroscopy results were complemented by density functional theory (DFT) calculations to provide vibrational mode assignments and to gain insight into pressure effects on the vibrational and crystal response of TKX-50. Several features were observed in Raman spectra measured in the ranges 4-10, 10-13, and 32-36 GPa. We suggest that the changes between 32 and 36 GPa may be associated with a phase transformation. In addition, a number of vibrational modes showed intensity exchange and avoided crossing of vibrational frequency at various pressures, characteristic of the coupling of modes. Despite all these pressure effects, the compression of TKX-50 to 50 GPa and the subsequent release of pressure did not result in any irreversible spectral changes, demonstrating its remarkable chemical stability. DFT calculations, using the PBE functional with an empirical dispersion correction by the Grimme, PBE-D method, were used to calculate pressure effects on Raman frequencies and unit cell parameters. The calculated Raman shifts to 20 GPa are in good overall agreement with the measured shifts over a broad range of frequencies. The calculations also show that TKX-50 exhibits anisotropic compressibility, with a highly incompressible response along the a axis. The calculated bulk modulus, a measure of average stiffness, of TKX-50 is significantly higher than the calculated or measured bulk moduli of other energetic crystals. We suggest that the strong intermolecular interactions and the coupling of vibrational modes may potentially contribute to the shock insensitivity of TKX-50. This work demonstrates the robust high-pressure response of TKX-50, making this crystal attractive for practical applications.

Helium nanodroplet study of the hydrogen-bonded OH vibrations in HCl-H₂O clusters.

Mixed (HCl)N(H2O)M clusters have been assembled in He droplets from the constituting molecules. Spectra of the clusters were obtained in the range of hydrogen-bonded OH vibrations (3100-3700 cm(-1)) by infrared laser depletion spectroscopy. The observed bands were assigned to cyclic hydrogen-bonded aggregates containing up to two HCl and three H2O molecules. The obtained frequencies are in good agreement with the results of harmonic quantum chemical calculations upon appropriate uniform shifts mimicking anharmonic corrections. Although larger clusters containing up to six water molecules were also produced in the droplets, their spectra were found to contribute to the unresolved signal in the range 3250-3550 cm(-1). The fact that no narrow bands could be unambiguously assigned to the mixed clusters containing more than three water molecules may indicate that such clusters exist in many isomeric forms that lead to overlapped and unresolved bands giving rise to broad structureless features. Another possible explanation includes the formation of elusive zwitterionic clusters, whose bands may have considerable breadth due to electrostatic coupling of different vibrational modes and concomitant intramolecular vibrational relaxation.

Real-time multianalyte biosensors based on interference-free multichannel monolithic quartz crystal microbalance.

In this work, we design, fabricate and characterize a new interference-free multichannel monolithic quartz crystal microbalance (MQCM) platform for bio-sensing applications. Firstly, interference due to thickness-shear vibration mode coupling between channels in MQCM array is effectively suppressed by interposing a polydimethylsiloxane wall between adjacent QCM electrodes on a quartz substrate to form inverted-mesa-like structure. In addition, the electrical coupling due to the electrical impedance of solution is diminished by extending the flow path between them with an extended-design flow channel. The electrical testing results show that individual QCM signal is unaffected by those of adjacent channels under liquid loading, signifying the achievement of interference-free MQCM. The MQCM is applied for multi-analyte biosensing of IgG and HSA. The anti-IgG and anti-HSA are separately immobilized on two adjacent QCM electrodes, which are subsequently blocked with BSA to avoid unspecific binding. The MQCM biosensors are tested with single- and double-analyte solutions under continuous flow of buffer. The IgG and HSA QCM sensors only show frequency shift responses to their corresponding analytes and there are very small cross frequency shifts due to remnant unspecific binding. Moreover, MQCM sensors show approximately linear frequency shift response with analyte concentration. Therefore, the developed MQCM platform is promising for real-time interference-free label-free detection and quantification of multiple bio-analytes.

Length dependence of the resonant magnetoelectric effect in Ni/Pb(Zr,Ti)O3/Ni long cylindrical composites

Magnetoelectric (ME) effect was studied in the long cylindrical Ni/Pb(Zr,Ti)O3/Ni layered composites prepared by electroless deposition. Three significant resonant peaks have been observed in the dependence of the ME voltage coefficient on the magnetic field frequency. The height of the composite cylinder has an important impact on the ME effect. With the height of the cylinder increase, the value of ME coefficient at static or low-frequency case increases, while the resonant frequencies decrease. Furthermore, the ME effect at the individual resonant frequencies can be weakened or enhanced due to the coupling of radial and axial vibration modes. The experimental values of resonant frequencies are in good agreement with the calculated ones. The results are useful for magnetoelectric devices with controllable multifrequency operation.

Three-dimensional modeling for predicting the vibration modes of twin ball screw driving table

As a redundant drive mechanism, twin ball screw feed system has the advantage of high stiffness and little yaw vibration in the feeding process, while leads to increased difficulty with vibration characteristics analysis and structure optimization. Only low-dimensional structure and dynamics parameters are considered in the existing research, the complete and effective model for predicting the table’s vibrations is lacked. A three-dimensional(3D) mechanical model of twin ball screw driving table is proposed. In order to predict the vibration modes of the table quantitatively, an analytical formulation following a comprehensive approach is developed, where the drive system is modeled as a lumped mass-spring system, and the Lagrangian method is used to obtain the table’s independent and coupled axial, yaw, and pitch vibration modes. The frequency variation of each mode is studied for different heights of the center of gravity, nut positions and table masses by numerical simulations. Modal experiment is carried out on the Z-axis feed table of the horizontal machining center MCH63. The results show that for each mode, the error between the estimated and the measured frequencies is less than 13%. The independent and coupled vibration modes are in accordance with the experimental results, respectively. The proposed work can serve a better understanding of the table’s dynamics and be beneficial for optimizing the structure parameters of twin ball screw drive system in the design stage.

Vibration Mitigation without Dissipative Devices: First Large-Scale Testing of a State Switched Inducer

A new passive device for mitigating cable vibrations is proposed and its efficiency is assessed on 45-meter long taut cables through a series of free and forced vibration tests. It consists of a unilateral spring attached perpendicularly to the cable near the anchorage. Because of its ability to change the cable dynamic behaviour through intermittent activation, the device has been called state switched inducer (SSI). The cable behaviour is shown to be deeply modified by the SSI: the forced vibration response is anharmonicc and substantially reduced in amplitude whereas the free vibration decay is largely sped up through a beating phenomenon. The vibration mitigation effect is mainly due to the activation and coupling of various vibration modes, as evidenced in the response spectra of the equipped cable. This first large-scale experimental campaign shows that the SSI outperforms classical passive devices, thus paving the way to a new kind of low-cost vibration mitigation systems which do not rely on dissipation.

Changes in Coupled Vibration Frequencies and Modes of Wall-Cavity Systems Induced by Stiffness Variation in the Structure

Changes in Coupled Vibration Frequencies and Modes of Wall-Cavity Systems Induced by Stiffness Variation in the Structure

Finite element simulation of implant surgery for vocal cord paralysis

As surgeons do not have effective prediction on the the implant surgery for vocal cord paralysis,resulting in high rate of failure,the finite element method was used for preoperative simulation.Through Computed Tomography(CT) data of larynx,the 3D geometric model of vocal cords and glottis trachea was extracted by Mimics,and then imported into ANSYS-Fluent to simulate the vocal vibration mode and airflow dynamic coupling characteristics before and after implanted surgery.The experimental data and clinical statistics data were compared to prove the feasibility of the finite element analysis techniques for implant surgery simulation of vocal cord paralysis.The experimental result can provide support for the design of surgery program.

Resonant frequency and damping of a coupled resonant system measured by apparent dissipation factor frequency spectra

This paper proposes a novel scheme to study the resonance of a vibration mode of a complex system by investigating the apparent dissipation factor frequency spectrum (ADFFS) of another coupled vibration mode. We demonstrate that the resonant absorption peak in ADFFS of one vibration mode is proportional to the displacement amplitude square of another coupled vibration mode from both energy dissipation and dynamics. Two coupled micro-cantilevers are experimentally shown that the ADFFS of one micro-cantilever could be applied to obtain the resonant frequency and the damping of the other coupled micro-cantilever.

Finite Element Analysis for Coupling Vibrations of Liquid-Filled Pipe and Support Structure System

t is made the system vibration analysis complexity that the coupling between the fluid-filled pipes and its support structure. Based on the finite element method, the liquid-filled pipe and a supporting structure are firstly modeled respectively. The obtained two sub-system models are then combined using their common nodes displacement. Based on the combined system, the coupled vibration characteristics of the liquid-filled pipe and the supporting structure system are analyzed. The analysis results show that, the strong coupling vibration modes are existed in the support structure and liquid-filled pipe system. If we change the mass and stiffness of pipe, some orders of vibration performance will change obviously, especially for those controlled by the pipe. However, for the vibration decided by the support structure, it is uselessly to change the mass matrix or stiffness matrix of the pipe.

Investigation of thermal conductivity of graphite flake/poly (p-phenylene sulfide) composite by experimental measurement and non-equilibrium molecular dynamics simulation

The thermal conductivities (TC) of graphite flake (GF)/poly (p-phenylene sulfide) (PPS) composites at different GF weight fractions were investigated by experimental measurement and by non-equilibrium molecular dynamics simulation (NEMD). In the experiment, at GF weight fractions lower than 10%, the TC values of samples fabricated by the hot press and injection methods are very close, while the TC values of those from the hot press method are relatively higher at GF weight fractions higher than 20%. From SEM micrographs, it reveals that the GFs distribute uniformly within the PPS matrix for samples prepared by the hot press method, while gradient distributions of GFs are found for the injection method samples. The results of non-equilibrium molecular dynamics simulation confirm the influence of GF weight fractions on the TC value and are in excellent agreement with the results for the hot press method. The enhancement of TC can be attributed to the coupling of GF and PPS vibration modes, which can be seen from our MD simulation results. Finally, an empirical equation, the Maxwell-Eucken model, can be used to predict TC variations at different GF weight fractions once the GF TC value is derived from the MD simulation results. The TC values predicted by the Maxwell-Eucken model agree well with those by experimental and MD simulation approaches.

Relaxation and Dissociation Following Photoexcitation of the (μ-N2)[Mo(N[t-Bu]Ar)3]2 Dinitrogen Cleavage Intermediate

Frequency resolved pump-probe spectroscopy was performed on isolated (μ-N(2))[Mo(N[t-Bu]Ar)(3)](2) (Ar = 3,5-C(6)H(3)Me(2)), an intermediate formed in the reaction of Mo(N[t-Bu]Ar)(3) to bind and cleave dinitrogen. Evidence is presented for 300 fs internal conversion followed by subpicosecond vibrational cooling on the ground electronic state in competition with bond dissociation. Fast cooling following photoexcitation leads to a relatively low overall dissociation yield of 5%, in quantitative agreement with previous work [Curley, J. J.; Cooke, T. R.; Reece, S. Y.; Mueller, P.; Cummins, C. C. J. Am. Chem. Soc. 2008, 130, 9394]. Coupling of vibrational modes to the excitation and internal conversion results in a nonthermal distribution of energy following conversion, and this provides sufficient bias to allow the nitrogen cleavage reaction to compete with breaking of the Mo-NN bond despite a higher energetic barrier on the ground state.

Electronic and Vibrational Coherences in Algal Light-Harvesting Proteins

We present broadband two-dimensional electronic spectra of a light- harvesting protein from photosynthetic algae. Analysis of the spectra show that the amplitude of the main cross peak oscillates as a function of the waiting time period. Both electronic coupling and intramolecular vibrational modes, and their mixture, can lead to such oscillations. Using predictions based on models of four-level systems, we describe ways to distinguish electronic from vibrational contributions to the coherence and find that both types of coupling contribute to the measured dynamics.

Rigid-Elastic Coupled Dynamics and its Application

According to energy conservation law, the functional of quasi-variational principle of rigid-elastic coupled dynamics is established. Quasi-stationary value conditions of quasi-variational principle of rigid-elastic coupled dynamics are derived. The governing equations of rigid-elastic coupled dynamics are obtained. As an application of rigid-elastic coupled dynamics, an approach of coupled vibration mode determined of unrestrained beam is established. The coupled vibration mode and coupled frequency are studied by the approach.

Quantum Calculations of Intramolecular IR Spectra of Ice Models Using Ab Initio Potential and Dipole Moment Surfaces.

We report the IR spectra of two forms of ice in the monomer bend and OH-stretching regions, using recently developed ab initio potential and dipole moment surfaces for arbitrarily many water monomers. Coupling and anharmonicity of the intramolecular vibrational modes are taken into account using coupled three-mode variational calculations, within the local-monomer model. Spectra for the surface and core regions of these ice models are presented. The calculated spectra for the core region, with no adjustments, are in good agreement with experiment for the intramolecular OH-stretch and bend regions. Our analysis also shows a significant contribution from the overtone of the monomer bend to the OH-stretch region of the spectra.

Ground-State Features in the THz Spectra of Molecular Clusters of β-HMX

We present calculations of absorption spectra arising from molecular vibrations at THz frequencies for molecular clusters of the explosive HMX using density functional theory (DFT). The features of these spectra can be shown to follow from the coupling of vibrational modes. In particular, the coupling among ground-state vibrational modes provides a reasonable molecular-level interpretation of spectral features associated with the vibrational modes of molecular clusters. THz excitation from the ground state is associated with frequencies that characteristically perturb molecular electronic states, in contrast to frequencies, which are usually substantially above the mid-infrared (mid-IR) range, that can induce appreciable electronic-state transition. Owing to this characteristic of THz excitation, one is able to make a direct association between local oscillations about ground-state minima of molecules, either isolated or comprising a cluster, and THz absorption spectra. The DFT software program GAUSSIAN was used for the calculations of the absorption spectra presented here.

Temperature dependence of Mg-H local vibrational modes in heavily doped InN:Mg

We have studied the temperature dependence and anharmonic coupling of the local vibrational modes (LVMs) associated with Mg-H complexes in heavily doped InN:Mg. Two main LVM peaks are observed which are probably related to two different H-impurity bond lengths. The temperature dependence of the higher-frequency mode, which exhibits a monotonic frequency downshift and broadening with increasing temperature, can be explained by LVM dephasing due to acoustic phonon scattering. The lower-frequency mode displays an anomalous behavior as its frequency decreases initially and then starts to increase linearly above room temperature. The anharmonic coupling of the lower-frequency mode to a molecular mode of the impurity complex is suggested as a possible cause for this behavior.

Relating normal vibrational modes to local vibrational modes with the help of an adiabatic connection scheme

Information on the electronic structure of a molecule and its chemical bonds is encoded in the molecular normal vibrational modes. However, normal vibrational modes result from a coupling of local vibrational modes, which means that only the latter can provide detailed insight into bonding and other structural features. In this work, it is proven that the adiabatic internal coordinate vibrational modes of Konkoli and Cremer [Int. J. Quantum Chem. 67, 29 (1998)] represent a unique set of local modes that is directly related to the normal vibrational modes. The missing link between these two sets of modes are the compliance constants of Decius, which turn out to be the reciprocals of the local mode force constants of Konkoli and Cremer. Using the compliance constants matrix, the local mode frequencies of any molecule can be converted into its normal mode frequencies with the help of an adiabatic connection scheme that defines the coupling of the local modes in terms of coupling frequencies and reveals how avoided crossings between the local modes lead to changes in the character of the normal modes.

Vibrational Fano resonances in dipole-bound anions

This paper explores Fano resonances due to non-adiabatic coupling of vibrational modes and the electron continuum in dipole-bound anions. We adopt a simple one-electron model consisting of a point dipole and an auxiliary potential to represent the electron interaction with the neutral core. Nuclear motion is added by assuming that harmonic vibrations modulate the dipole moment. When the model is parameterized to simulate key features of the water tetramer anion, the resultant photodetachment lineshape closely resembles that observed experimentally and analyzed as a Fano resonance with a parameter q close to -1. Other parameterizations are explored for the model and it is found that large changes in the auxiliary potential are required to change the sign of q. This is consistent with the experimental finding that q is negative for all water cluster sizes studied.

Electrostatically coupled vibration modes in unimorph complementary microcantilevers

To extend the tuning capabilities of radio frequency devices, coupled microelectromechanical systems are often employed. In this letter, we demonstrate piezoelectrically actuated, electrically tuneable resonator systems based on coupled micromechanical oscillators operating in a flexural vibration mode. The substantial enhancement in electrostatic coupling was achieved due to the implementation of lateral nanogaps of 100-200 nm between single resonator bars. This allows for resonator synchronization and precise system frequency tuning by over a factor of two, relative to its initial value. Additionally, a simple electro-mechanical model has been developed to describe the dynamic behavior of the electrostatically coupled oscillators.