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PubMed2002

Flexural vibration of perforated plates and porous elastic materials under acoustic loading.

This paper presents a method of theoretical treatment of acoustic coupling due to flexural vibration of perforated plates and plates of porous elastic materials. The analytical model is developed by introducing flow continuity at the plate surface in a spatially mean sense and air-solid interaction within the plate material. To demonstrate the method of application, some fundamental acoustic problems based on a classical thin-plate theory are analyzed and discussed in relation to the interactive effect of flexural vibration and plate permeability. For acoustic radiation from a vibrating plate excited by a harmonic point-force, the attenuation effect of power radiation appears at frequencies below the critical frequency of coincidence. In the problem of sound absorption of a perforated plate or a plate of porous elastic material backed by an air layer, as permeability decreases, the effect of plate vibration increases. For perforated absorber systems including plate vibration effects, the trend of variation from ordinary theory depends on plate thickness.

Journal Article↗
PubMed2000

Free localized vibrations of a semi-infinite cylindrical shell

Free vibrations of a semi-infinite cylindrical shell, localized near the edge of the shell are investigated. The dynamic equations in the Kirchhoff-Love theory of shells are subjected to asymptotic analysis. Three types of localized vibrations, associated with bending, extensional, and super-low-frequency semi-membrane motions, are determined. A link between localized vibrations and Rayleigh-type bending and extensional waves, propagating along the edge, is established. Different boundary conditions on the edge are considered. It is shown that for bending and super-low-frequency vibrations the natural frequencies are real while for extensional vibrations they have asymptotically small imaginary parts. The latter corresponds to the radiation to infinity caused by coupling between extensional and bending modes.

Journal Article↗
PubMed2002

Watching vibrational energy transfer in liquids with atomic spatial resolution.

Ultrafast spectroscopy was used to study vibrational energy transfer between vibrational reporter groups on different parts of a molecule in a liquid. When OH stretching vibrations of different alcohols were excited by mid-infrared laser pulses, vibrational energy was observed to move through intervening CH2 or CH groups, taking steps up and down in energy, ending up at terminal CH3 groups. For each additional CH2 group in the path between OH and CH3, the time for vibrational energy transfer increased by about 0.4 picosecond.

Journal Article↗
PubMed1999

Enhanced reactivity of highly vibrationally excited molecules on metal surfaces

The chemical dynamics of highly vibrationally excited molecules have been studied by measuring the quantum state-resolved scattering probabilities of nitric oxide (NO) molecules on clean and oxygen-covered copper (111) surfaces, where the incident NO was prepared in single quantum states with vibrational energies of as much as 300 kilojoules per mole. The dependence of vibrationally elastic and inelastic scattering on oxygen coverage strongly suggests that highly excited NO (v = 13 and 15) reacts on clean copper (111) with a probability of 0.87 +/- 0.05, more than three orders of magnitude greater than the reaction probability of ground-state NO. Vibrational promotion of surface chemistry on metals (up to near-unit reaction probability) is possible despite the expected efficient relaxation of vibrational energy at metal surfaces.

Journal Article↗
PubMed2000

Vibrational promotion of electron transfer.

By using laser methods to prepare specific quantum states of gas-phase nitric oxide molecules, we examined the role of vibrational motion in electron transfer to a molecule from a metal surface free from the complicating influence of solvation effects. The signature of the electron transfer process is a highly efficient multiquantum vibrational relaxation event, where the nitrogen oxide loses hundreds of kilojoules per mole of energy on a subpicosecond time scale. These results cannot be explained simply on the basis of Franck-Condon factors. The large-amplitude vibrational motion associated with molecules in high vibrational states strongly modulates the energetic driving force of the electron transfer reaction. These results show the importance of molecular vibration in promoting electron transfer reactions, a class of chemistry important to molecular electronics devices, solar energy conversion, and many biological processes.

Journal Article↗
PubMed2004

Importance of direction of vibration on the onset of Soret-driven convection under gravity or weightlessness.

This paper considers the influence of the direction of vibration on the stability threshold of two-dimensional Soret-driven convection. The configuration is an infinite layer filled with a binary mixture, which can be heated from below or from above. The limiting case of high-frequency and small-amplitude vibration is considered for which the time-averaged formulation has been adopted. The linear stability analysis of the quasi-mechanical equilibrium shows that the problem depends on five non-dimensional parameters. These include the thermal Rayleigh number (Ra(T)), the vibrational parameter (R), the Prandtl number (Pr), the Lewis number (Le), the separation ratio (S) and the orientation of vibration with respect to the horizontal heated plate (alpha). For different sets of parameters, the bifurcation diagrams are plotted Ra(c) = f(S) and k(c) = g(S), which are the critical thermal Rayleigh and the critical wave numbers, respectively. Our results indicate that, relative to the classical case of static gravity, vibration may affect all regions in Ra(c)-S stability diagram. In the case of mono-cellular convection, by using a regular perturbation method, a closed-form relation for the critical Rayleigh number is found. Several physical situations in the presence or in the absence of gravity (micro-gravity) are discussed.

Journal Article↗
PubMed2003

Effects of aging on vibration detection thresholds at various body regions.

BACKGROUND: The ability to detect sinusoidal vibrations on the skin surface is dependent on the activation of two classes of receptors. The density of such receptors varies across the skin surface and is a factor in determining the sensory acuity of each skin area. However, the acuity of many sensory systems is known to deteriorate with advancing age. The aim of this study was to determine if vibrotactile sensibility of several skin surfaces deteriorated equally with advancing age. METHODS: Vibration detection thresholds for two frequencies of vibration (30 Hz and 200 Hz) were determined using a method of limits protocol, in two groups of healthy adults, one group aged 17 to 27 years and the other aged 55 to 90 years. Sinusoidal vibrations were generated by a computer and delivered to the skin surface via the probe (diameter = 2 mm) of a mechanical vibrator. Four skin sites (palmar surface of the tip of the middle finger, volar surface of the forearm, lateral aspect of the shoulder, cheek just caudal to the zygoma) were tested. RESULTS: The fingertip was the most sensitive site for vibrotactile detection at both frequencies in a substantial majority of subjects. The older group of subjects showed significantly higher detection thresholds for both frequencies at all sites, except the fingertip, when compared to young subjects. CONCLUSION: The study confirms the deterioration of vibrotactile acuity at several skin sites previously reported in the literature. However, there appears to be no significant reduction in vibrotactile detection at the fingertips in older subjects. This may reflect the high receptor density of this area, or the functional importance of vibrotactile sensibility of the fingertips or some combination of both of these factors.

Journal Article↗
PubMed2002

The effect of vibration noise in space relevant experiments.

The experiments performed were initiated as a part of the post-flight investigations after the "PROTO" experiment performed on IML-1. The present experiments were performed with protoplasts prepared using the same standard isolation procedures as for the IML-1. The protoplasts were vibrated for 24 h with and without air bubbles in the protoplast cultivation bags and in the range of 1 to 20 Hz with 4 mm amplitude. The vibrations were found to have a negative effect on the viability of the protoplasts in bags without air bubbles and the vibration threshold seemed to lie around 20 Hz. Air bubbles are likely to cause cavitation-like conditions, thus increasing the mechanical strain on the free-floating protoplasts. During the 30 days microgravity mode on the ISS, mechanical vibrations would not be expected to have a significant influence on potential protoplast experiments. Experiments with durations overlapping the rendezvous and reboost mode may be exposed to critical vibration levels.

Journal Article↗
PubMed1998

[The vibration-rotational analysis of the high resolution ir spectrum of the CH3D molecule].

High-resolution Fourier transform spectra of the band of the CH3D molecule near 6428cm(-1) have been recorded on a BRUKER IFS 120HR Fourier-transform spectrometer with multipass cell with a length of 20m, an unapodized resolution of 0.004cm(-1) was achieved. Vibration-rotation analysis in Local-mode can provide accurate enough initial values to predict the band origins. The vibration-rotation transitions of CH3D molecule were assigned by using the ground state combination differences and least-squares fitted to yield ten vibration-rotation constants for the band of CH3D molecule near 6428cm(-1). Vibration assignment in Normal-mode and Local-mode expressed that the band of CH3D molecule near 6428cm(-1) is 3V2 vibration states of CH3D molecule.

English Abstract↗
PubMed2006

[The analysis of vibrational structure of the electronic spectra of diatomic molecules].

On the basis of the spectrum term of a electronic rotational-vibrational energy level, the law of vibrational band sequences and progressions in diatomic molecules was analysed. According to the law, the Deslandres table and its nature were summarized. How to indicate the measured values of a electronic-vibrational spectrum was illustrated by taking the Swan band spectra of the C2 molecule as an example. In the example, the measured values were put in order which formed the Deslandres table in terms of the law of vibrational structure. The authors can gain some important data, such as anharmonicity constants and harmonic oscillator frequencies in different vibrational states, concerning the band spectra of molecules. Furthermore, the formula of wave numbers of every band spectrum was derived.

English Abstract↗
PubMed1983

Evaluation of specific pick-ups and preamplifiers for the recording of heart vibrations.

Experiments have shown that pick-ups used for the recording of heart vibrations (apexcardiography, phonocardiography) can influence the vibrations of the soft tissue chest wall to which they are applied. This influence is most pronounced in the medium and high frequency range (10 . . . . . 1000 Hz). Owing to the mechanical loading effect of the pick-up on the chest wall, the vibrations are attenuated and distorted. This is also shown with respect to pure mass loading of the chest wall. The loading effect on the chest wall (coupling function) has been studied by us in the frequency-domain as well as in the time-domain on 6 normal subjects who were in the recumbent position. Typical parameters of the coupling function have been established in relation to mass loading. An empirical formula has been found for the degree of attenuation of the vibrations caused by the load. In order to perform these investigations, a special seismic pick-up FYSPac2 has been constructed which will load the tissue to a slight degree only. Its mass is 1 g and it has a flat frequency response up to 1 kHz and a high sensitivity (12 pC m-1s2). The problem of the vibration measurement on soft tissue is discussed here in its whole context: the loading effect of the pick-up, the sensitivity (and bandwidth) of the pick-up as well as the quality of the preamplifier as regards its transfer characteristics and its electronic noise level.(ABSTRACT TRUNCATED AT 250 WORDS)

Amplifiers, Electronic↗
PubMed2026

Occupationally relevant vibrations and the brain: frequency-dependent proteomics signatures in a rat model.

INTRODUCTION: Occupational exposure to whole-body vibration (WBV), particularly in agricultural environments, has been associated with adverse cognitive and physiological effects. This study examined the neurophysiological impact of WBV in a rat model at 4 Hz and 30 Hz, frequencies representative of off-road and on-road vehicle operation. METHODOLOGY: Forty-four Sprague-Dawley rats were assigned to control (0 Hz), low-frequency (4 Hz), or high-frequency (30 Hz) vibration conditions. After three days of exposure, brain tissues were collected and analyzed using mass spectrometry-based proteomics to identify differentially expressed proteins. RESULTS: Proteomic profiling revealed distinct, frequency-dependent alterations in brain protein expression. Compared with controls, 32 cognition-related proteins were differentially regulated at 4 Hz and 29 at 30 Hz, with 13 differing between the two vibration conditions. Principal component analysis showed clear separation among groups, indicating unique proteomic signatures for each exposure frequency. Functional enrichment and protein-protein interaction analyses demonstrated involvement of synaptic plasticity, cytoskeletal organization, calcium regulation, and neurotransmitter release. Exposure to 4 Hz was associated with the upregulation of proteins involved in calcium homeostasis and synaptic integrity, suggesting potential disruption of cognitive processes. In contrast, 30 Hz increased the expression of proteins related to axonal guidance and neuroprotection, indicating a less clearly adverse response that may reflect adaptive or potentially beneficial effects. DISCUSSION: These findings provide new insight into biological mechanisms underlying WBV-induced cognitive changes and underscore the importance of vibration frequency in shaping neurophysiological outcomes. They also establish a foundation for future studies integrating proteomics with behavioural assessments in animals and humans.

Animals↗
PubMed1987

Stapes vibration produced by the output transducer of an implantable hearing aid. Experimental study.

The function of the output transducer of an implantable hearing aid was assessed by applying it to the stapes head in seven fresh human cadaver temporal bones while observing vibration of the stapes under a microscope with the use of a stroboscope and a video measuring system. The transducer was a 5 X 1.2 X 0.6-mm piezoelectric ceramic bimorph with attached metal holder. Transmission changed with the amount of force holding the transducer tip on the head of the stapes. An optimal connection between the vibrator and stapes produced better transmission than a tight or loose connection. Gluing the connection with cyanoacrylate cement decreased transmission in the optimal connection, produced no change in the tight connection, and improved transmission in the loose connection. Comparison of stapes displacement produced by the vibrator at 1 kHz with that produced by normal middle-ear sound transmission revealed that the vibrator-induced stapes displacement for a 1 V peak-to-peak input was equivalent to that produced by a sound stimulus of 90-dB sound pressure level at the tympanic membrane.

Ear Ossicles↗
PubMed1995

Thyroarytenoid muscle activity and infraglottic aspect of canine vocal fold vibration.

OBJECTIVES: To investigate the effect of contraction of the thyroarytenoid (TA) muscle on the location of the mucosal upheaval (MU) and to estimate the location of the MU in relation to the histologic structure of the vocal fold. BACKGROUND: The MU is a small mucosal ridge arising on the lower surface of the vocal fold during phonation and is thought to be the lower border of the vibrating structure. METHODS: Vibrations were elicited under three conditions: during bilateral TA muscle contraction, without TA muscle stimulation, and during vocal fold lengthening. The vibrations were recorded from the tracheal side by high-speed cinematography or videotape recording combined with stroboscopic illumination. The larynx was prepared for histologic observation in the frontal plane. Tattooed marks on the lower surface of the vocal fold were used to locate macroscopically observed landmarks with reference to microscopic structures. RESULTS: The MU shifted laterally toward the tracheal side during TA muscle contraction. When the vocal fold was lengthened, the MU shifted medially toward the free edge. Histologic examination showed that the MU in the absence of TA muscle contraction arose slightly above the area where the muscular layer approached the epithelial layer. CONCLUSION: When the TA muscle contracts, the vibrating area expands toward the tracheal side, and a more dynamic mucosal wave occurs in the vertical direction. We believe that a part of the body and the cover are probably involved in the vibratory movement of the vocal fold.

Animals↗
PubMed1998

Normal distributions of thermal and vibration sensory thresholds.

The distributions of sensory thresholds were estimated in a healthy population while controlling for potential covariates. Using the method of levels and the two-alternative forced choice, thermal and vibration thresholds respectively were measured in the hand and foot of 148 subjects. Age was uniformly distributed between 20 and 86 years. Independent effects of age, gender, height, and skin temperature were estimated using multiple linear regression. Parametric and nonparametric methods were used to estimate the distributions of interest. Significant age-related increases were observed for all vibration thresholds (P < 0.0001), and for thermal thresholds in the foot (P < 0.0002). Percentiles were estimated for thermal thresholds in the hand and age-adjusted continuous distributions were calculated for all other thresholds. Height was positively associated with vibration thresholds in the foot (P < 0.003), and appropriate corrections were made. Our results provide reference values for thermal and vibration sensory thresholds in a healthy population, allowing for the accurate diagnosis of disordered sensory function.

Adult↗
PubMed1994

Digital nerve conduction velocity as a sensitive indication of peripheral neuropathy in vibration syndrome.

Digital nerve conduction velocities in the median and ulnar nerves were measured in order to obtain a more accurate indication of peripheral nerve impairment induced by hand-arm vibration. The subjects were 26 patients with vibration syndrome and 28 healthy controls, both groups of about the same age. Two pairs of surface electrodes were attached to the finger and one pair was positioned on the palm, while electrical stimulation was applied to the nerve at the wrist and elbow. Then sensory nerve conduction velocities were antidromically measured within the finger, and also from the wrist to the palm and from the elbow to the wrist. Slowed conduction within the finger was mostly found among the patients. The slowing was also encountered from the wrist to the palm across the carpal tunnel. Abnormalities were observed in the digital nerve segment in about 50-70% of the patients, and in the wrist-to-palm segment in about 10-25% of them. The present study indicates that digital nerve impairment predominantly occurs in the vibration-exposed patients, and that measurement of digital nerve conduction velocity can be a useful objective means to detect peripheral neuropathy in vibration syndrome.

Aged↗
PubMed1993

Vibration white finger.

Vibration white finger (VWF) occurs in workers who use vibrating tools. On exposure to vibration or cold, patients experience blanching, numbness and pain in the fingers due to exaggerated vasoconstriction. This may involve both central sympathetic hyper-reactivity and local vasoactive factors. In advanced cases, hypertrophy of vascular smooth muscle causes arterial occlusion and ulceration. Diagnostic tests for VWF are unreliable. In early cases, cessation of vibration exposure arrests the progression of disease and may cause symptom remission. Patients with VWF should keep themselves warm, especially their hands, which they should place in warm water at intervals during the day; they should not smoke. Vasoactive drugs may be beneficial in some patients. In the UK, Industrial Injuries Disablement Benefit and compensation are sometimes available. Improved design of tools and restrictions on their operating time have been the main factors leading to a worldwide decline in the incidence of VWF since the early 1970s.

Age Factors↗
PubMed2006

Computationally-assisted approach to the vibrational spectra of molecular crystals: study of hydrogen-bonding and pseudo-polymorphism.

A new computationally-assisted methodology (PiMM), which accounts for the effects of intermolecular interactions in the crystal, is applied to the complete assignment of the Raman and infrared vibrational spectra of room temperature forms of crystalline caffeine, theobromine, and theophylline. The vibrational shifts due to crystal packing interactions are evaluated from ab initio calculations for a set of suitable molecular pairs, using the B3LYP/6-31G* approach. The proposed methodology provides an answer to the current demand for a reliable assignment of the vibrational spectra of these methyl-xanthines, and clarifies several misleading assignments. The most relevant intermolecular interactions in each system and their effect on the vibrational spectra are considered and discussed. Based on these results, significant insights are obtained for the structure of caffeine in the anhydrous form (stable at room temperature), for which no X-ray structure has been reported. A possible structure based on C((8))--H...N((9)) and C((1,3))--H...O intermolecular interactions is suggested.

Caffeine↗