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Vibrations
Kinds of Vibrations Terms modified by Vibrations Selected AbstractsVibration of a space arc subject to a critical dynamic loadINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 4 2005Lazarus Teneketzis Tenek Abstract The present study concerns the dynamic behaviour of a space arc subject to a midarc vertical buckling load dynamically applied. The arc is discretized with a set of three-dimensional beam finite elements and the non-linear dynamic equation (large displacements) is solved by means of an unconditionally stable time-dependent scheme over time. The vertical excitation gives rise to a very fast and erratic horizontal wave as the structure begins to vibrate in all directions. This horizontal wave has chaotic characteristics as its attractor indicates. Time,displacement curves are obtained for all components of the midarc point. Although the time algorithm was executed here for 2000 time steps, simulation over longer periods of time can reveal the vibration characteristics and even simulate structural failure under the imposed dynamic buckling load for the space arc structure. Copyright © 2004 John Wiley & Sons, Ltd. [source] Modification of polypropylene by melt vibration blending with ultra high molecular weight polyethyleneADVANCES IN POLYMER TECHNOLOGY, Issue 3 2002Kejian Wang Abstract A novel vibration internal mixer was used to prepare polypropylene/ultra high molecular weight polyethylene PP/UHMWPE blends with two additional adjustable processing parameters (vibration frequency and vibration amplitude) as compared with those prepared in the steady mode. Microscopy, mechanical tests, and differential scanning calorimetry showed that vibration influenced the blend morphology and the product properties. The good phase homogeneity of the blends might be due to the variation of shear rate either spatially or temporally in blending. Additionally, the vibration internal mixer could be used to analyze the dependency of viscosity on the shear rate. Vibration enhanced the interpenetration of UHMWPE into PP and vice versa. Subsequently, the formed crystals of two components were connected, and there was epitaxy between PP and UHMWPE crystals. Moreover, the crystalline aggregates, with the amorphous UHMWPE, formed a complex network-like continuous structure, which improved the elongation ratio at the break and the yield strength. The higher the vibration frequency and/or the larger the vibration amplitude at a fixed average rotation speed of the mixer, the more significant these effects were. The larger amount of the connected crystals, especially of , form of PP in the bulk , form PP as well as with the continuous phase structure, led to a higher tensile properties of PP/UHMWPE vibration blended. © 2002 Wiley Periodicals, Inc. Adv Polym Techn 21: 164,176, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/adv.10020 [source] Vibration and Components of Bone StrengthJOURNAL OF BONE AND MINERAL RESEARCH, Issue 9 2004Toshihiro Sugiyama No abstract is available for this article. [source] Effect of 6-Month Whole Body Vibration Training on Hip Density, Muscle Strength, and Postural Control in Postmenopausal Women: A Randomized Controlled Pilot Study,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 3 2004Sabine MP Verschueren Abstract High-frequency mechanical strain seems to stimulate bone strength in animals. In this randomized controlled trial, hip BMD was measured in postmenopausal women after a 24-week whole body vibration (WBV) training program. Vibration training significantly increased BMD of the hip. These findings suggest that WBV training might be useful in the prevention of osteoporosis. Introduction: High-frequency mechanical strain has been shown to stimulate bone strength in different animal models. However, the effects of vibration exercise on the human skeleton have rarely been studied. Particularly in postmenopausal women,who are most at risk of developing osteoporosis,randomized controlled data on the safety and efficacy of vibration loading are lacking. The aim of this randomized controlled trial was to assess the musculoskeletal effects of high-frequency loading by means of whole body vibration (WBV) in postmenopausal women. Materials and Methods: Seventy volunteers (age, 58,74 years) were randomly assigned to a whole body vibration training group (WBV, n = 25), a resistance training group (RES, n = 22), or a control group (CON, n = 23). The WBV group and the RES group trained three times weekly for 24 weeks. The WBV group performed static and dynamic knee-extensor exercises on a vibration platform (35,40 Hz, 2.28,5.09g), which mechanically loaded the bone and evoked reflexive muscle contractions. The RES group trained knee extensors by dynamic leg press and leg extension exercises, increasing from low (20 RM) to high (8 RM) resistance. The CON group did not participate in any training. Hip bone density was measured using DXA at baseline and after the 6-month intervention. Isometric and dynamic strength were measured by means of a motor-driven dynamometer. Data were analyzed by means of repeated measures ANOVA. Results: No vibration-related side effects were observed. Vibration training improved isometric and dynamic muscle strength (+15% and + 16%, respectively; p < 0.01) and also significantly increased BMD of the hip (+0.93%, p < 0.05). No changes in hip BMD were observed in women participating in resistance training or age-matched controls (,0.60% and ,0.62%, respectively; not significant). Serum markers of bone turnover did not change in any of the groups. Conclusion: These findings suggest that WBV training may be a feasible and effective way to modify well-recognized risk factors for falls and fractures in older women and support the need for further human studies. [source] Effect of 8-Month Vertical Whole Body Vibration on Bone, Muscle Performance, and Body Balance: A Randomized Controlled Study,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 5 2003Saila Torvinen MD Abstract Recent animal studies have given evidence that vibration loading may be an efficient and safe way to improve mass and mechanical competence of bone, thus providing great potential for preventing and treating osteoporosis. Randomized controlled trials on the safety and efficacy of the vibration on human skeleton are, however, lacking. This randomized controlled intervention trial was designed to assess the effects of an 8-month whole body vibration intervention on bone, muscular performance, and body balance in young and healthy adults. Fifty-six volunteers (21 men and 35 women; age, 19-38 years) were randomly assigned to the vibration group or control group. The vibration intervention consisted of an 8-month whole body vibration (4 min/day, 3-5 times per week). During the 4-minute vibration program, the platform oscillated in an ascending order from 25 to 45 Hz, corresponding to estimated maximum vertical accelerations from 2g to 8g. Mass, structure, and estimated strength of bone at the distal tibia and tibial shaft were assessed by peripheral quantitative computed tomography (pQCT) at baseline and at 8 months. Bone mineral content was measured at the lumbar spine, femoral neck, trochanter, calcaneus, and distal radius using DXA at baseline and after the 8-month intervention. Serum markers of bone turnover were determined at baseline and 3, 6, and 8 months. Five performance tests (vertical jump, isometric extension strength of the lower extremities, grip strength, shuttle run, and postural sway) were performed at baseline and after the 8-month intervention. The 8-month vibration intervention succeeded well and was safe to perform but had no effect on mass, structure, or estimated strength of bone at any skeletal site. Serum markers of bone turnover did not change during the vibration intervention. However, at 8 months, a 7.8% net benefit in the vertical jump height was observed in the vibration group (95% CI, 2.8-13.1%; p = 0.003). On the other performance and balance tests, the vibration intervention had no effect. In conclusion, the studied whole body vibration program had no effect on bones of young, healthy adults, but instead, increased vertical jump height. Future human studies are needed before clinical recommendations for vibration exercise. [source] Vibration and stability control of robotic manipulator systems consisting of a thin-walled beam and a spinning tip rotorJOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 10 2002Ohseop Song Vibration and stability feedback control of a robotic manipulator modeled as a cantilevered thin-walled beam carrying a spinning rotor at its tip is investigated. The control is achieved via incorporation of adaptive capabilities that are provided by a system of piezoactuators, bonded or embedded into the host structure. Based on converse piezoelectric effect, the piezoactuators produce a localized strain field in response to an applied voltage, and as a result, an adaptive change of vibrational and stability response characteristics is obtained. A feedback control law relating the piezoelectrically induced bending moments at the beam tip with the appropriately selected kinematical response quantities is used, and the beneficial effects of this control methodology upon the closed-loop eigenvibration characteristics and stability boundaries are highlighted. The cantilevered structure modeled as a thin-walled beam, and built from a composite material, encompasses non-classical features, such as anisotropy, transverse shear, and secondary warping, and in this context, a special ply-angle configuration inducing a structural coupling between flapping-lagging and transverse shear is implemented. It is also shown that the directionality property of the material of the host structure used in conjunction with piezoelectric strain actuation capability, yields a dramatic enhancement of both the vibrational and stability behavior of the considered structural system. © 2002 Wiley Periodicals, Inc. [source] Shaking alone, without concurrent aeration, affects the growth characteristics of Escherichia coliLETTERS IN APPLIED MICROBIOLOGY, Issue 2 2007M.A. Juergensmeyer Abstract Aims:, This study investigated the effects of linear vibration on cultures grown in both hard- and soft-sided containers to determine whether vibration alone affected the growth rate. Methods and Results:, Cultures of Escherichia coli were exposed to vibrational acceleration with and without access to additional oxygen. Vibrated cultures grown in hard-sided containers exited lag phase earlier and had a higher final yield than identical unshaken cultures, whether or not the cultures had access to ambient air. Cultures grown in soft-sided containers showed no response to vibration. Conclusions:, Vibration in hard-sided containers decreases the length of the lag phase and increases final OD in E. coli, with or without increased oxygenation. Increased mixing and improved suspension, which result from vibration of cultures in hard-sided containers, are the most likely physical mechanisms for the more favorable culture conditions. Significance and Impact of the Study:, This paper demonstrates that growth enhancement of shaken cultures is a function of the rigidity of the vessel even without aeration of the medium. [source] Effect of whole body vibration in Parkinson's disease: A controlled study,MOVEMENT DISORDERS, Issue 6 2009Pablo Arias PhD Abstract In the search of new strategies to improve the quality of life of Parkinson's disease patients, recent work has reported an amelioration of Parkinsonian symptoms using Whole Body Vibration (WBV). A double-blinded, placebo controlled design was used to evaluate the effect of a 12 WBV sessions-programme on a number of motor and clinical tests in 23 Parkinson's disease patients. Patients were assigned to one of two groups, one receiving WBV and the other a placebo group. At the end of the programme as well as during intra-session evaluation, there was no difference between the experimental (vibration) and placebo groups in any outcomes. These results suggest that reported benefits of vibration are due to a placebo response. © 2009 Movement Disorder Society [source] Vibration prolongs the cortical silent period in an antagonistic muscleMUSCLE AND NERVE, Issue 6 2009Christian Binder MD Abstract We tested whether the silent period, an indicator of inhibitory neuronal activity, is modulated by muscle vibration. Vibration was applied to the right extensor carpi radialis (ECR) muscle in 17 healthy subjects and, as a control experiment, to the dorsal terminal phalanges in 5 subjects. Data before vibration were compared with those during vibration. The cortical silent period (CSP) was evoked by transcranial magnetic stimuli (TMS) during voluntary wrist flexion or during voluntary wrist extension. TMS-evoked motor potentials (MEPs) of the flexor carpi radialis (FCR) muscle were recorded during muscle relaxation. The mixed nerve silent period (MNSP) was obtained by electrical stimulation of the median nerve during wrist flexion. ECR vibration induced a significant prolongation of the CSP in FCR. CSP increases induced by vibration of the dorsal terminal phalanges were significantly less pronounced. In ECR, the CSP tended to be shortened. MEPs and MNSP remained unchanged. We conclude that vibration enhances inhibitory neuronal properties in a non-vibrated antagonistic muscle, presumably at a supraspinal level. These results may be relevant for the treatment of spasticity of the upper extremity. Muscle Nerve, 2009 [source] Vibration of a porouse-cellular circular platePROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2006Ewa Magnucka-Blandzi The subject of investigation is a circular porous-cellular plate under uniform pressure. Mechanical properties of the isotropic porous cellular metal vary accross the thickness of the plate. Middle plane of the plate is its symmetry plane. Fields of diseplacements and stresses with respect the nonlinear hypothesis are described. Basing on Hamilton principle three motion equations of the plate are formulated. These equations are approximately solved. The vibration problem is reduced to the second-order differential equation. Numerical investigations are realised for family of plates. Natural frequencies are determined. The obtained results are shown in Figures. To the end of the investigation comparition analyses with respect to homogeneous plates is presented. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Vibration of the soil caused by a vehicle moving over the randomly uneven surface of a slab trackPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2003H. Grundmann Univ.-Prof. A vehicle which passes an uneven surface of a slab track causes vibrations of the whole system: the vehicle, the slab track and the subsoil. For a given random unevenness ,w of the slab track surface, covariances of the soil surface motion are calculated. [source] Vibration Causes Acute Vascular Injury in a Two-Step Process: Vasoconstriction and Vacuole DisruptionTHE ANATOMICAL RECORD : ADVANCES IN INTEGRATIVE ANATOMY AND EVOLUTIONARY BIOLOGY, Issue 8 2008Sandya R. Govindaraju Abstract Hand,arm vibration syndrome is a vasospastic and neurodegenerative occupational disease. In the current study, the mechanism of vibration-induced vascular smooth muscle cell (SMC) injury was examined in a rat-tail vibration model. Tails of male Sprague Dawley rats were vibrated continuously for 4 hr at 60 Hz, 49 m/s2 with or without general anesthesia. Ventral tail arteries were aldehyde fixed and embedded in epoxy resin to enable morphological analysis. Vibration without anesthesia caused vasoconstriction and vacuoles in the SMC. Anesthetizing rats during vibration prevented vasoconstriction and vacuole formation. Exposing tail arteries in situ to 1 mM norepinephrine (NE) for 15 min induced the greatest vasoconstriction and vacuolation. NE induced vacuoles were twice as large as those formed during vibration. When vibrated 4 hr under anesthesia after pretreatment with NE for 15 min, the SMC lacked vacuoles and exhibited a longitudinal banding pattern of dark and light staining. The extracellular matrix was filled with particulates, which were confirmed by electron microscopy to be cellular debris. The present findings demonstrate that vibration-induced vasoconstriction (SMC contraction) requires functioning central nervous system reflexes, and the physical stress of vibration damages the contracted SMC by dislodging and fragmenting SMC vacuoles. Anat Rec, 291:999,1006, 2008. © 2008 Wiley-Liss, Inc. [source] Aerodynamics of the Human Larynx During Vocal Fold Vibration,THE LARYNGOSCOPE, Issue 12 2005Randall L. Plant MD Abstract Objectives: The goal of this study was to comprehensively analyze the influence of aerodynamics on laryngeal function. Three specific aspects were considered: 1) a multidimensional comparison of the interaction of subglottic pressure, sound intensity, and fundamental frequency; 2) examination of instantaneous changes in subglottic pressure during each glottic cycle; and 3) determination of the threshold subglottic pressure for vocal fold vibration and its dependence on other aerodynamic factors. Study Design: Prospective study with six healthy individuals without history of voice disorders. Methods: The subjects vocalized the vowel sound /i/ with a variety of different intensities, pitch, and sound intensity. Subglottic air pressure, fundamental frequency, sound intensity, and the electroglottography signal were simultaneously measured. Results: Linear relationships were seen in all subjects between subglottic air pressure and sound intensity, although there were large variations in the slopes of these relationships. Rapid variations in subglottic pressure during each glottic cycle were detected, corresponding to the opening of the vocal folds with each individual vibration. Threshold pressures for vocal fold vibration were dependent primarily on sound intensity and fundamental frequency and tended to be higher at vibration onset than at offset. Conclusion: The larynx responded in a predictable pattern to general aerodynamic forces, but there was tremendous variability in its specific behavior. Fundamental frequency and sound intensity tended to increase with subglottic air pressure, but that relationship was not seen consistently in all subjects. The relationship between subglottic air pressure and sound intensity was usually linear, unlike the exponential relationship seen in previous studies. Subglottic pressure was noted to undergo rapid change with each glottic cycle in some, but not all, subjects and was most strongly affected by average subglottic pressure. Phonation threshold air pressure was influenced by the sound intensity and, to a smaller extent, by the fundamental frequency of the voiced sound. [source] Comparative Histology and Vibration of the Vocal Folds: Implications for Experimental Studies in Microlaryngeal Surgery ,THE LARYNGOSCOPE, Issue 5 2000C. Gaelyn Garrett MD Abstract Objectives/Hypothesis To determine the most suitable animal model for experimental studies on vocal fold surgery and function by a histological comparison of the microflap surgical plane and laryngeal videostroboscopy (LVS) in different species of animals. A second goal was to determine how the layered vocal fold structure in humans and three different animal species affects surgical dissection within the lamina propria. Study Design Prospective laboratory. Methods Three larynges each from dogs, monkeys, and pigs were compared with three ex vivo human larynges. Microflap surgery was performed on one vocal fold from each larynx. Both the operated and nonoperated vocal folds were examined histologically using stains specific for elastin, mature collagen, and ground substance. Based on the histological results, LVS was performed on two dogs and two pigs after first performing a tracheotomy for ventilation and airflow through the glottis. Arytenoid adduction sutures were placed to facilitate vocal fold adduction. Results The distributions of the collagen and elastin fibers were found to differ among the species with concentrations varying within species. Unlike the human vocal fold, which has a higher elastin concentration in the deeper layers of the lamina propria, both the pig and the dog had a thin band of elastin concentrated just deep to the basement membrane zone in the superficial layer. Just deep to this thin band, the collagen and the elastin were less concentrated. The monkey vocal fold had a very thin mucosal layer with less elastin throughout the mucosa. The microflap dissections in each of the dog, pig, and human vocal folds were similar, being located within that portion of the superficial lamina propria where the elastin and mature collagen are less concentrated. The microflap plane in the monkey vocal fold was more deeply located near the vocalis fibers. Despite the differences in elastin concentration, the microflap plane in both the dog and the pig was found to be similar to that in humans. The dog anatomy was much more suitable for microsuspension laryngoscopy and stroboscopic examination. The dog vocal folds vibrated in a similar fashion to human vocal folds with mucosal waves and vertical phase differences, features not seen in the pig vocal folds. Conclusions Based on both the histological and stroboscopic results, the dog was believed to be a more suitable animal model for studies on vocal fold surgery, acknowledging that no animal's laryngeal anatomy is identical to that of the human. The dog LVS model presented allows for longitudinal laryngeal studies requiring repeated examinations at multiple time periods with histological correlation applied at sacrifice. [source] ChemInform Abstract: Ab initio Prediction of the Structure and Vibration,Rotation Spectroscopic Properties of Li2OH and Li2OH+.CHEMINFORM, Issue 24 2008Artur Gertych Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Symmetric Stretching Vibration of CH4 in Clathrate Hydrate StructuresCHEMPHYSCHEM, Issue 14 2010Dr. Hiroshi Ohno Movers and shakers: Vibrational states of CH4 molecules encaged in three clathrate hydrate structures are studied (see picture). Guest methane distribution in the structure-H 512 and 435663 host cavities is revealed for the first time. Raman profiles of the CH4 vibration are dependent not only on types of water cages, but also on clathrate structures (guest compositions), suggesting distinctive differences in molecular interactions between the three hydrate systems. [source] Direct Probe of NO Vibration in the Naked Ferric Heme Nitrosyl ComplexCHEMPHYSCHEM, Issue 6 2008Barbara Chiavarino Dr. Vibrational features: The coupling of a free electron laser to a mass spectrometer measures the IR spectrum of iron porphyrin complexes of nitric oxide (see figure). Comparison of the photo-dissociation spectra, identifies the NO vibration at 1842 cm,1. [source] Excitation of the Asymmetric Stretch Vibration of CO2 in OH+CO,H+CO2 ReactionCHEMPHYSCHEM, Issue 4 2006Congyun Shi Dr. CO2vibrations: High excitation in the asymmetric stretch (v3) mode of the CO2 product in the OH+CO reaction has been found (see picture). The strong IR emission was detected by time-resolved Fourier transform infrared (TR-FTIR) emission spectroscopy. The observed vibrational distribution is used for comparison with a variety of theoretical calculations on this reaction. [source] A digital simulation of the vibration of a two-mass two-spring systemCOMPUTER APPLICATIONS IN ENGINEERING EDUCATION, Issue 3 2010Wei-Pin Lee Abstract In this study, we developed a computer program to simulate the vibration of a two-mass two-spring system by using Visual BASIC. Users can enter data for the two-mass two-spring system. The software will derive the eigenvalue problem from the input data. Then the software solves the eigenvalue problem and illustrates the results numerically and graphically on the screen. In addition, the program uses animation to demonstrate the motions of the two masses. The displacements, velocities, and accelerations of the two bodies can be shown if the corresponding checkboxes are selected. This program can be used in teaching courses, such as Linear Algebra, Advanced Engineering Mathematics, Vibrations, and Dynamics. Use of the software may help students to understand the applications of eigenvalue problems and related topics such as modes of vibration, natural frequencies, and systems of differential equations. © 2009 Wiley Periodicals, Inc. Comput Appl Eng Educ 18: 563,573, 2010; View this article online at wileyonlinelibrary.com; DOI 10.1002/cae.20241 [source] Terahertz Time Domain Spectroscopy to Detect Low-Frequency Vibrations of Double-Walled Carbon NanotubesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 27 2010Sunil Kumar Abstract We have measured the frequency-dependent real index of refraction and extinction coefficient (and hence the complex dielectric function) of a free-standing double-walled carbon nanotube film of thickness 200 nm by using terahertz time domain spectroscopy in the frequency range 0.1 to 2.5 THz. The real index of refraction and extinction coefficient have very high values of approximately 52 and 35, respectively, at 0.1 THz, which decrease at higher frequencies. Two low-frequency phonon modes of the carbon nanotubes at 0.45 and 0.75 THz were clearly observed for the first time in the real and imaginary parts of the complex dielectric function along with a broad resonance centred at around 1.45 THz, the latter being similar to that in single-walled carbon nanotubes assigned to electronic excitations. Our experiments bring out a possible application of double-walled carbon nanotube films as a neutral density filter in the THz range. [source] A numerical,analytical combined method for vibration of a beam excited by a moving flexible bodyINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 10 2007Huajiang Ouyang Abstract The vibration of a beam excited by a moving simple oscillator has been extensively studied. However, the vibration of a beam excited by an elastic body with conformal contact has attracted much less attention. This is the subject of the present paper. The established model is more complicated but has a much wider range of applications than the moving-oscillator model. Because the moving body is flexible, the moving loads at the contact interface are not known a priori and must be determined together with the dynamics of the whole system. In this paper, the equation of motion of the beam and the moving body are established separately using a numerical,analytical combined approach. It is found from the numerical results of the simulated example that the vibrations of the moving body and the beam excited by the moving body are significantly influenced by the travelling speed. At very low or very high speeds the dynamic effect is small and the beam deforms to take the shape of its static deflection. Vibrations tend to be greater in the intermediate speed range and the total moving force at the interface of the beam and the moving body can be compressive and tensile. Copyright © 2007 John Wiley & Sons, Ltd. [source] Vibrations of skewed cantilevered triangular, trapezoidal and parallelogram Mindlin plates with considering corner stress singularitiesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 13 2005C. S. Huang Abstract Based on the Mindlin shear deformation plate theory, a method is presented for determining natural frequencies of skewed cantilevered triangular, trapezoidal and parallelogram plates using the Ritz method, considering the effects of stress singularities at the clamped re-entrant corner. The admissible displacement functions include polynomials and corner functions. The admissible polynomials form a mathematically complete set and guarantee the solution convergent to the exact frequencies when sufficient terms are used. The corner functions properly account for the singularities of moments and shear forces at the re-entrant corner and accelerate the convergence of the solution. Detailed convergence studies are carried out for plates of various shapes to elucidate the positive effects of corner functions on the accuracy of the solution. The results obtained herein are compared with those obtained by other investigators to demonstrate the validity and accuracy of the solution. Copyright © 2005 John Wiley & Sons, Ltd. [source] Eddy-current induction in extended metallic parts as a source of considerable torsional momentJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 4 2006Hansjörg Graf PhD Abstract Purpose To examine eddy-current-provoked torque on conductive parts due to current induction from movement through the fringe field of the MR scanner and from gradient switching. Materials and Methods For both cases, torque was calculated for frames of copper, aluminum, and titanium, inclined to 45° to B0 (maximum torque case). Conditions were analyzed in which torque from gravity (legal limit, ASTM F2213-02) was exceeded. Experiments were carried out on a 1.5 T and a 3 T scanner for copper and titanium frames and plates (,50 × 50 mm2). Movement-induced torque was measured at patient table velocity (20 cm/second). Alternating torque from gradient switching was investigated by holding the specimens in different locations in the scanner while executing sequences that exploited the gradient capabilities (40 mT/m). Results The calculations predicted that movement-induced torque could exceed torque from gravity (depending on the part size, electric resistance, and velocity). Two experiments on moving conductive frames in the fringe fields of the scanners confirmed the calculations. For maximum torque case parameters, gradient-switching-induced torque was calculated to be nearly 100 times greater than the movement-induced torque. Well-conducting metal parts located off center vibrated significantly due to impulse-like fast alternating torque characteristics. Conclusion Torque on metal parts from movement in the fringe field is weak under standard conditions, but for larger parts the acceptable limit can be reached with a high static field and increased velocity. Vibrations due to gradient switching were confirmed and may explain the sensations occasionally reported by patients with implants. J. Magn. Reson. Imaging 2006. © 2006 Wiley-Liss, Inc. [source] Good Vibrations: Ambience and Alienation in the Twentieth CenturyJOURNAL OF POPULAR MUSIC STUDIES, Issue 2 2002Stephen Nunns [source] Compaction of Powders due to Vibrations and ShocksPARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 4 2004Roman Linemann Abstract Bulk density and compactibility of bulk materials play an important role in process engineering. Reliable data are required for dimensioning plants and for supplying load data for static design. Furthermore, the data are useful for the production of sintered materials or catalyst beds and the characterization of bulk materials. While compression by normal stress can be reproduced and mathematically described, the influence of shocks and vibrations remains very poorly understood. All known standard methods for bulk material compression under vibrations and shocks are based on individual equipment. The parameters of shocks or vibrations, however, have not yet been defined. Therefore, an investigation was carried out to examine the influence of uniaxial stress and defined shocks and vibrations on bulk material compression. The shocks and vibrations were controlled by an electrodynamic shaker. The first results for highly disperse Kaolin powders are presented. Using the chosen parameters, the random mode and the uniaxial compression cause the highest increase in density. High compression rates can also be obtained by shocks. With sinusoidal vibrations much lower bulk densities can be reached. [source] Aspects Regarding the Conception, Modeling and Implementation of an Articulated Robot in Space with Noises and VibrationsPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2008Virgil Ispas The authors want to conceive and to model a structure of a 6R serial modular industrial robot with six freedom degrees. Some specific points are followed: the direct geometric modelling of the robot using the matrix of rotation method, the given in 3D modelling of the robot, the presentation of its components having some possible applications in the processes of production in the spaces with noises and vibrations. The direct geometrical modelling will be determinate the relative orientation matrices, which express the position of each system Ti, (i=1-6), according to the system Ti,1, also expressing the vectors of relative position of origin Oi of the systems Ti. They will be expressed the orientation of each system Ti in account to the fixed system To attached to the robot base, the set of independent parameters of orientation then are obtained the final equation of the column vector of the generalized coordinates, which express the position and the orientation of the clamping device. The paper presents the two possible applications of the studied robot implementation in a flexible manufacturing cel for the manipulation operations of parts. The robot will be used on the other side for the execution of weld in a points applied to the car carcases. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Vibrations of thin cylindrical shells with a periodic structurePROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2008Barbara Tomczyk Free vibrations of thin linear,elastic Kirchhoff,Love cylindrical shells, having a periodic structure along one direction tangent to the shell midsurface, is considered. In order to take into account the effect of the periodicity cell size in this problem, a new averaged non,asymptotic model of such shells, proposed by Tomczyk (2006), is applied. The new additional higher,order free vibration frequencies dependent on the microstructure size will be derived and discussed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Prevention of Stick-Slip Vibrations by Passive Normal Force ControlPROCEEDINGS IN APPLIED MATHEMATICS & MECHANICS, Issue 1 2003Martin Rudolph The classical stick-slip oscillator is extended by an additional degree of freedom which couples the slipping motion to the normal force. Using this, the effective friction force can be altered without changing the friction-velocity characteristic. The paper deals with the optimization problem of finding parameters of the additional system that prevent stick-slip motion or minimize the amplitude of the residual limit cycle. Another goal is to increase the decay rate of vibration. Results were achieved by numerical integration based on analytical investigations. [source] Observation of Terahertz Vibrations in the Nitrogenase FeMo Cofactor by Femtosecond Pump,Probe Spectroscopy,ANGEWANDTE CHEMIE, Issue 23 2010Ines Delfino Dr. Hochgepumpt: Die Dynamik des durch Resonanz-Raman-Spektroskopie nicht charakterisierbaren FeMo-Cofaktors (siehe Bild) wurde nun mit kohärenter Puls-Schwingungsspektroskopie als Sonde untersucht: Ein Laserpuls mit sichtbarem Licht (15,fs) pumpte die Probe in einen angeregten elektronischen Zustand, und ein zweiter Puls (<10,fs) untersuchte die Änderung in der Transmission als Funktion des Zeitabstands. [source] VLT-CRIRES: "Good Vibrations" Rotational-vibrational molecular spectroscopy in astronomyASTRONOMISCHE NACHRICHTEN, Issue 5 2010H.U. Käufl Abstract Near-Infrared high spectral and spatial resolution spectroscopy offers new and innovative observing opportunities for astronomy. The "traditional" benefits of IR-astronomy , strongly reduced extinction and availability of adaptive optics , more than offset for many applications the compared to CCD-based astronomy strongly reduced sensitivity. Especially in high resolution spectroscopy interferences by telluric lines can be minimized. Moreover for abundance studies many important atomic lines can be accessed in the NIR. A novel spectral feature available for quantitative spectroscopy are the molecular rotational-vibrational transitions which allow for fundamentally new studies of condensed objects and atmospheres. This is also an important complement to radio-astronomy, especially with ALMA, where molecules are generally only observed in the vibrational ground state. Rot-vib transitions also allow high precision abundance measurements , including isotopic ratios , fundamental to understand the thermo-nuclear processes in stars beyond the main sequence. Quantitative modeling of atmospheres has progressed such that the unambiguous interpretation of IR-spectra is now well established. In combination with adaptive optics spectro-astrometry is even more powerful and with VLT-CRIRES a spatial resolution of better than one milli-arcsecond has been demonstrated. Some highlights and recent results will be presented: our solar system, extrasolar planets, star- and planet formation, stellar evolution and the formation of galactic bulges (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||||||||||||||||||||