Evaluation of the vibrational modes of the human skull as it relates to bone-conducted sound

Analytic and numerical models are used to study bone-conducted sound and how it relates to the vibrational modes of the human skull. The analytic model is based on the solution to the acoustic and elastic wave equations and the constraining boundary conditions for a fluid-filled elastic sphere. Both models predict that most of the acoustic energy of bone-conducted sound exists in the form of surface wave vibrations at the interface between two acoustic media rather than in the bone or cranial chamber. These surface waves have phase speeds much slower than the bulk sound speed for bone. The analytic model, based on spherical elastic shells, predicts a phase speed of 775 m/s and the first resonance frequency at 1500 Hz while the numerical solution yields approximate phase speeds of 450 m/s and provides a visual display of the surface waves and diffraction effects.     

三质点单自由度非线性振动特性分析

设计一个非线性振动实验装置，建立系统的动力学方程，用计算机数值计算并画出相图和运动图，对非线性振动的性质进行了分析。     

Experimental determination of vibrational anharmonic contributions

This article deals with the experimental determination of separate vibrational anharmonic contributions to the self‐energy of phonons in any crystals based on temperature dependence of their Raman spectra. We propose a new approach to find each anharmonic contribution by using special temperature points. We apply the approach to diamond, silicon, and crystalline α‐S₈ and show that our results for summarized anharmonicity in diamond and silicon are in good agreement with the values obtained previously for these systems by other researchers. Copyright © 2013 John Wiley & Sons, Ltd.     

Lattice vibrational analysis of polyacene

Within an extended Su-Schrieffer-Heeger model, we made a lattice vibrational analysis of polyacene. In a singly-charged polyacene, the ground state contains an interchain-coupled polaron of quasi-D2h symmetry, around which we found thirteen localized modes in total. Among these localized modes, five (three B2u and two B3u) are infrared active, six (four Ag and two B1g) modes are Raman active, and the other two localized modes are asymmetric, which are both infrared active and Raman active. For the case a charged polaron is coupled with a neutral soliton in a finite polyacene chain, the vibrational modes are also calculated to display the coupling effect between self-trapping excitations on phonons. It is found that the localized phonons are determined mainly by the charged polaron, but the number and frequencies of the localized modes are influenced by the existence of the neutral soliton.     

A vibrational analysis of trichloroiodomethane

The infrared and Raman spectra of CCl₃I have been recorded. Band assignments have been made on the basis of the infrared results, and the Raman spectrum has been interpreted in terms of the fundamentals of CCl₃I, with additional bands being assigned to decomposition products of CCl₃I. A Urey-Bradley force constant calculation has been made, transferring results from the earlier work of Ngai and Mann.     

Numerical analysis of ultrasonic transmission and absorption of oblique plane waves through the human skull.

Ultrasonic transmission and absorption of oblique plane waves through the human skull are analyzed numerically for frequencies ranging from 1/2 to 1 MHz. These frequencies are optimum for noninvasive ultrasound therapy of brain disorders where numerical predictions of skull transmission are used to set the phase and amplitude of source elements in the phased array focusing system. The idealized model of the skull is a three-layer solid with ivory outer and inner layers and a middle marrow layer. Each layer is modeled as a flat, homogeneous, isotropic, linear solid with effective complex wave speeds to account for focused energy losses due to material damping and scattering. The model is used to predict the amplitude and phase of the transmitted wave and volumetric absorption. Results are reported for three different skull thicknesses: 3 mm, 6 mm, and 9 mm. Thickness resonances are observed in the transmitted wave for 3 mm skulls at all frequencies and for the 6 mm skulls below 0.75 MHz. Otherwise, the transmission is dominated by the direct wave. Skull phase errors due to shear waves are shown to minimally degrade the power at the focus for angles of incidence up to 20 degrees from normal even for low material damping. The location of the peak volumetric absorption occurs either in the outer ivory or middle marrow layer and shown to vary due to wave interference.     

Experimental investigation of vibrational excitations in230Th

Nuclear levels in²³⁰Th have been investigated in the decay of²³⁰Pa, the²³⁰Th(d, pn) reaction and the²³²Th(p, t) reaction. TheK =0 ₁ ⁺ , 2 ₁ ⁺ , and 2 ₂ ⁺ bands with band heads at 635, 781, and 1010 keV were observed up to the 8⁺, 9⁺, and 7⁺ levels, respectively. A second excited 0⁺ level was identified at 1297 keV which might be interpreted as the usual shape-oscillation. The branching ratios of theE2 transitions from the 0 ₁ ⁺ , 2 ₁ ⁺ , and 2 ₂ ⁺ bands are explained in the framework of the rotational model by taking into account the coupling of these bands with the ground-state band, and the coupling between the 0 ₁ ⁺ and 2 ₁ ⁺ band. A strong enhancement ofE2 transitions from the 2 ₁ ⁺ to the 0 ₁ ⁺ band reported earlier is not confirmed. For the octupole vibrations withK =0^–, 1^–, and 2^– theE1 branching ratios are analyzed in terms of the Coriolis coupling of these bands. An almost complete experimental set ofE1 transition moments from these negative-parity bands to the 0 _g ⁺ , 0 ₁ ⁺ , and 2 ₁ ⁺ bands was obtained. It is suggested that octupole correlations might be important in explaining theseE1 moments.We appreciate the help of Mr. Assmus with the proton irradiations and the financial support of the Kernforschungszentrum Karlsruhe GmbH. This work was supported by the Deutsche Forschungsgemeinschaft (grants Bo 1109/1-1, Gr 894/2-1, Gu 179/3-1 and He 1316/2-3) and by the Volkswagen Stiftung.     

Free vibrational characteristics of isotropic coupled cylindrical-conical shells

This paper presents the free vibrational characteristics of isotropic coupled conical-cylindrical shells. The equations of motion for the cylindrical and conical shells are solved using two different methods. A wave solution is used to describe the displacements of the cylindrical shell, while the displacements of the conical sections are solved using a power series solution. Both Donnell-Mushtari and Flügge equations of motion are used and the limitations associated with each thin shell theory are discussed. Natural frequencies are presented for different boundary conditions. The effect of the boundary conditions and the influence of the semi-vertex cone angle are described. The results from the theoretical model presented here are compared with those obtained by previous researchers and from a finite element model.     

Experimental study of vibrational behavior of laminated annular disks

The purpose of this paper is to present an experimental study of the vibrational behavior of laminated annular disks, and effects of laminations on the vibrations of the disks. The vibrations of a series of solid annular disks were calculated using the finite-element method in order to provide a basis for comparison with experimental data. An extensive range of experiments was performed on both a series of solid disks and a series of laminated disks under a range of normal clamping pressures. Based on the calculated and experimental results, it was found that the vibrational behavior of the laminated disks was dominated by that of the individual disk, of which the laminated disks were composed. Laminations had great effects on the vibrational behavior of the laminated disks and the effects depended upon the mode type, the clamping pressure, and the number of disk assembly. Laminations increased damping and reduced the amplitude of frequency response function for both the transverse modes and in-plane modes of disks. The resonant frequency of transverse modes shifted higher because of the effects of laminations. For the in-plane vibrational modes, the effects on the resonant frequency could be neglected and the resonant frequency could be considered to be a constant.     

Experimental and theoretical studies of the vibrational spectra of CHD2Br

The dideuterated form of methyl bromide, CHD₂Br, has been synthesized and the gas-phase infrared spectra investigated in the range 400–10,000?cm^–1 using a medium-resolution FTIR spectrometer. The nine fundamental bands have been characterized in detail. Six of them, i.e. ν ₁, ν ₄, ν ₅, ν ₇, ν ₈ and ν ₉, have been rotationally analysed through the assignment of the partially resolved structure of the ^PQ_K and ^RQ_K cluster of lines and the spectroscopic parameters have been derived in the symmetric top limit approximation. Among the fundamental levels, anharmonic resonance occurs between ν ₇/ν ₄?+?ν ₈ and ν ₈/ν ₆?+?ν ₉. An isotopic ^79/81Br shift was found for ν ₆ and in the more complex region of the ν ₈ fundamental. High-quality ab initio calculations – carried out at coupled cluster level [CCSD(T)] employing the correlation-consistent basis set of Dunning (cc-pVTZ) – were performed to determine quadratic, cubic and quartic (semidiagonal) force constants. Using these constants and applying second-order vibrational perturbation theory (VPT2), with allowance for resonances (when necessary), permitted us to identify and assign, in addition to the fundamentals, about 70 overtones and combination bands up to three quanta.     

Application of holographic interferometry to the vibrational analysis of the harpsichord

This paper presents an original piece of research using holographic interferometry as a quantitative optical diagnostic. The object under investigation was the soundboard of a harpsichord. The results obtained show that it is possible to measure the spatial vibrational behaviour of the whole soundboard with an accuracy of better than 170 nm. Several features which characterize the vibration behaviour of the soundboard have been visualized including a discontinuity created by a crack which has resulted in a phase change of the interferometric fringes. Finally, the theoretical model response of the harpsichord soundboard is determined and compared to our holographic measurement.     

Experimental analysis of spectral characteristics of antiresonant guiding photonic crystal fibers

Both numerical and experimental analyses are carried out to investigate the spectral characteristics of antiresonant guiding photonic crystal fibers. The transmission minima were observed at the wavelengths where LP(ml) (m相似文献   

Quantum chemical analysis of vibrational spectra of methylphenylcarbamate

We present results of ab initio and DFT calculations of the structure, potential function of internal rotation of the methyl group, and vibrational frequencies and intensities in IR and Raman spectra of methylphenylcarbamate. The calculations were carried out in different basis sets in the HF, MP2, and DFT/B3LYP approximations with partial force field scaling. The influence of the phenyl substituent on structural and spectral characteristics of the urethane group has been analyzed. Calculated characteristics of vibrational spectra show satisfactory agreement with experimental values.     

Spectrally dispersed femtosecond CARS investigation of vibrational characteristics in ethanol

Spectrally dispersed femtosecond time‐resolved coherent anti‐Stokes Raman spectroscopy is applied to study the ultrafast vibrational dynamics in ethanol at room temperature. The anti‐Stokes intensities were monitored as a function of delay time and wavenumber. By simply changing the timing of the laser pulses, the vibrational dynamics between the excited Raman transitions in ethanol molecules can be tracked and detected. Copyright © 2014 John Wiley & Sons, Ltd.     

Investigation of vibrational characteristics in BBO crystals by femtosecond CARS

Femtosecond time-resolved coherent anti-Stokes Raman spectroscopy (CARS) is utilized to study the ultrafast vibrational dynamics in BBO crystals at room temperature. Time-resolved two-beam and three-beam CARS are detected. The vibrational dephasing time is analyzed and the changes of vibrational mode intensities with the polarization of pump pulses are observed.     

Time-averaged moire method for in-plane vibrational analysis

A new method is proposed for the determination of the in-plane displacement components of bodies subjected to cyclic loading. The recording on a photographic film is done statically, with exposure times longer than the period of vibration (time-average). A grating printed on the body surface is perturbed by the motion and the displacements are analyzed by photographing the grating lines. For relatively small amplitudes of vibration an alternative technique is proposed requiring the use of a master. Fringes are then photographed directly. In this case it is convenient to use a carrier which can be obtained by rotation of the master over the surface of the vibrating body. It is proposed to use Fourier filtering to convert frequency variation moiré fringes to the conventional intensity variation fringes. The application of the method is illustrated with the determination of u and ν components of displacement in a ring and in a disk subjected to cyclic diametral compression. As do other time-averaged methods, the proposed method has the advantage of permitting the static study of vibration phenomena.     

Generalized skeletal approximation in the analysis of vibrational spectra of polymers

A mathematical procedure is given for analyzing the low-frequency region of the vlbrational spectrum for a defective polymer; this reduces the order of the secular equation to the number of degrees of freedom of the atoms forming the skeleton. As a result, the matrices for the kinetic and potential energies become frequency-dependent, and they describe the vibrations of the skeleton at frequencies near zero, with the nodes bearing lumped masses equal to the masses of the repeating units.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 41–47, November, 1978.     

Finite element three-dimensional analysis of the vibrational behaviour of the Langevin-type transducer

The vibrational behaviour of the Langevin transducer is usually analysed using 1D Mason model which is valid when the lateral dimensions of the transducer are smaller than a quarter wavelength at the fundamental longitudinal resonance. In this work a 3D finite element analysis of the Langevin transducer's behaviour operating in the underwater sonar range of frequencies (30-140 kHz) is presented. Several samples with total length greater, comparable to, and smaller than the diameter of the transducer are analysed. For each sample, the resonance frequencies in the observed frequency range are computed and compared with those obtained experimentally from the measurements carried out using several in-house built prototypes. For the most important aspect ratios the resonance displacement distributions are presented and discussed. The results obtained permit to gain insight into the coupling phenomenon between thickness-extensional and radial modes and suggest that in practical applications transducers with diameters comparable to or greater than total length of the active stack can also be used. The trade-off between the efficiency and power handling ability for different designs is also discussed.     

Enhanced ultrasound transmission through the human skull using shear mode conversion

A new transskull propagation technique, which deliberately induces a shear mode in the skull bone, is investigated. Incident waves beyond Snell's critical angle experience a mode conversion from an incident longitudinal wave into a shear wave in the bone layers and then back to a longitudinal wave in the brain. The skull's shear speed provides a better impedance match, less refraction, and less phase alteration than its longitudinal counterpart. Therefore, the idea of utilizing a shear wave for focusing ultrasound in the brain is examined. Demonstrations of the phenomena, and numerical predictions are first studied with plastic phantoms and then using an ex vivo human skull. It is shown that at a frequency of 0.74 MHz the transskull shear method produces an amplitude on the order of--and sometimes higher than--longitudinal propagation. Furthermore, since the shear wave experiences a reduced overall phase shift, this indicates that it is plausible for an existing noninvasive transskull focusing method [Clement, Phys. Med. Biol. 47(8), 1219-1236 (2002)] to be simplified and extended to a larger region in the brain.