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At least 1,027 records · Page 57Linked to original sources

PubMed2003

Hidden corrosion detection in aircraft aluminum structures using laser ultrasonics and wavelet transform signal analysis.

Preliminary results of hidden corrosion detection in aircraft aluminum structures using a noncontact laser based ultrasonic technique are presented. A short laser pulse focused to a line spot is used as a broadband source of ultrasonic guided waves in an aluminum 2024 sample cut from an aircraft structure and prepared with artificially corroded circular areas on its back surface. The out of plane surface displacements produced by the propagating ultrasonic waves were detected with a heterodyne Mach-Zehnder interferometer. Time-frequency analysis of the signals using a continuous wavelet transform allowed the identification of the generated Lamb modes by comparison with the calculated dispersion curves. The presence of back surface corrosion was detected by noting the loss of the S(1) mode near its cutoff frequency. This method is applicable to fast scanning inspection techniques and it is particularly suited for early corrosion detection.

Aircraft↗

PubMed2003

Ultrasonic and IR study of intermolecular association through hydrogen bonding in ternary liquid mixtures.

Complex formation in ternary liquid mixtures of dimethylsulfoxide (DMSO) with phenol and o-cresol in carbontetrachloride has been studied by measuring ultrasonic velocity at 2 MHz, in the concentration range of 0.019-0.162 (in mole fraction of DMSO) at varying temperatures of 20, 30 and 40 degrees C. Using measured values of ultrasonic velocity, other parameters such as adiabatic compressibility, intermolecular free length, molar sound velocity, molar compressibility, specific acoustic impedance and molar volume have been evaluated. These parameters have been utilized to study the solute-solute interactions in these systems. The ultrasonic velocity shows a maxima and adiabatic compressibility a corresponding minima as a function of concentration for these mixtures. The results indicate the occurrence of complex formation between unlike molecules through intermolecular hydrogen bonding between oxygen atom of DMSO molecule and hydrogen atom of phenol and o-cresol molecules. The excess values of adiabatic compressibility and intermolecular free length have also been evaluated. The variation of both these parameters with concentration also indicates the possibility of the complex formation in these systems. Further, to investigate the presence of O-HO bond complexes and the strength of molecular association with concentrations, the infrared spectra of both the systems, DMSO-phenol and DMSO-o-cresol, have been recorded for various concentrations at room temperature (20 degrees C). The results obtained using infrared spectroscopy for both the systems also support the occurrence of complex formation through intermolecular hydrogen bonding in these ternary liquid mixtures.

Carbon Tetrachloride↗

PubMed2003

Thin-disk piezoceramic ultrasonic motor. Part I: design and performance evaluation.

The purpose of this study is to gain the knowledge and experience in the design of thin-disk piezoceramic-driving ultrasonic actuator dedicated. In this paper, the design and construction of an innovative ultrasonic actuator is developed as a stator, which is a composite structure consisting of piezoceramic (PZT) membrane bonded on a metal sheet. Such a concentric PZT structure possesses the electrical and mechanical coupling characteristics in flexural wave. The driving ability of the actuator comes from the mechanical vibration of extension and shrinkage of a metal sheet due to the converse piezoelectric effect, corresponding to the frequency of a single-phase AC power. By applying the constraints on the specific geometry positions on the metal sheet, the various behaviors of flexural waves have been at the different directions. The rotor is impelled by the actuator with rotational speeds of 600 rpm in maximum using a friction-contact mechanism. Very high actuating and braking abilities are obtained. This simple and inexpensive structure of actuator demonstrates that the mechanical design of actuator and rotor could be done separately and flexibly according to the requirements for various applications. And, its running accuracy and positioning precision are described in Part II.A closed loop servo positioning control i.e. sliding mode control (SMC) is used to compensate automatically for nonlinearly mechanical behaviors such as dry friction, ultrasonic vibrating, slip-stick phenomena. Additionally, SMC scheme has been successfully applied to position tracking to prove the excellent robust performance in noise rejection.

Ceramics↗

PubMed2003

The detectability of kissing bonds in adhesive joints using ultrasonic techniques.

This paper concerns a study of the detectability of dry contact kissing bonds in adhesive joints using three ultrasonic inspection techniques. Conventional normal incidence longitudinal and shear wave inspection were conducted on dry contact kissing bonds using a standard damped ultrasonic transducer and an electro-magnetic acoustic transducer (EMAT) respectively. The detectability of the dry contact kissing bonds was assessed by calculating the reflection coefficient of the imperfect interface at varying loads for a number of surface roughnesses. A high power ultrasonic method was also employed to determine the non-linear behavior of the adhesive interface. The non-linearity of the interface was determined by the ratio of the amplitudes of the first harmonic and fundamental frequencies of the transmitted waveform. It was found that the high power technique showed the greatest sensitivity to these kissing bonds at low contact pressures, however at high loads conventional longitudinal wave testing was more sensitive. It was also noted that a combination of two or more techniques could provide enhanced information about the kissing bond compared to a single technique alone.

Adhesives↗

PubMed1998

Characterising ultrasonic physiotherapy systems by performance and safety now internationally agreed.

The IEC 1689 standard specifies: methods of measurement, characterisation of the output performance, requirements for safety due to the ultrasonic field generated, characteristics to be declared by manufacturers and acceptance criteria for aspects of performance. For the characterisation, reference as well as routine testing methods are described. Important parameters such as effective radiating area (AER), beam nonuniformity ratio (RBN) (characterising 'hot-spots': potentially harmful to patients) and beam type have been re-defined. The quality, reproducibility and accuracy of measurements of AER are significantly improved compared to those in IEC 150 (which is now replaced) and the FDA 1050.10 (USA) standards. As a result, values of effective intensity are shown to be significantly higher than those obtained using the FDA 1050.10 (USA) definitions. As it may be expected that the new standard will be implemented worldwide, this problem is just a matter of time. The standard discussed above specifies the need for acoustic power measurement with an accuracy of more than 15%. However, several investigations carried out over the last ten years show a lack of proper facilities to calibrate the acoustic output power at physiotherapy levels. A project to investigate the complications and to produce definitive guidance for therapy-level power measurements is funded by the EC and has been started recently. Future activities will be undertaken to estimate the expected temperature rise in tissue due to the ultrasonic field. Such a figure may result in an improved judgement of the ultrasonic safety aspects of physiotherapy systems.

Acoustics↗

PubMed1998

Microparticle manipulation in millimetre scale ultrasonic standing wave chambers.

Ultrasonic standing wave chambers with acoustic pathlengths of 1.1 and 0.62 mm have been constructed. The chambers were driven at frequencies over the range 0.66-12.2 MHz. The behaviour of 2 microns diameter latex microparticles and 5 microns diameter yeast in the chambers has been elucidated. One (flow) chamber had a downstream laminar flow expansion section to facilitate observation of concentrated particle bands formed in the ultrasonic field. A second (microscopy) chamber allowed direct observation of band formation in the field and their characterisation by confocal scanning laser microscopy. Clear band formation occurs when the chamber pathlength is a multiple of half wavelengths at the driving frequency, so that the chamber rather than the transducer resonance has the most influence on band formation in this system. Band formation occurred in half-wavelength steps from a position one quarter of a wavelength off the transducer to a band at a similar distance from the reflector. Ordered band formation was preserved by the laminar flow in the expansion chamber, although bands that formed very close to the wall were dissipated downstream. The microscopy chamber provided evidence of significant lateral particle concentration within bands in the pressure nodal planes. The approaches described will be applicable to the manipulation of smaller particles in narrower chambers at higher ultrasonic frequencies.

Acoustics↗

PubMed2000

Nonlinear propagation in ultrasonic fields: measurements, modelling and harmonic imaging.

In high amplitude ultrasonic fields, such as those used in medical ultrasound, nonlinear propagation can result in waveform distortion and the generation of harmonics of the initial frequency. In the nearfield of a transducer this process is complicated by diffraction effects associated with the source. The results of a programme to study the nonlinear propagation in the fields of circular, focused and rectangular transducers are described, and comparisons made with numerical predictions obtained using a finite difference solution to the Khokhlov-Zabolotskaya-Kuznetsov (or KZK) equation. These results are extended to consider nonlinear propagation in tissue-like media and the implications for ultrasonic measurements and ultrasonic heating are discussed. The narrower beamwidths and reduced side-lobe levels of the harmonic beams are illustrated and the use of harmonics to form diagnostic images with improved resolution is described.

Nonlinear Dynamics↗

PubMed2000

Viability of yeast cells in well controlled propagating and standing ultrasonic plane waves.

Recent studies have shown that there is no loss of cell viability when the cells are subjected to ultrasonic standing wave fields in acoustic cell retention systems. These systems are characterised by waves that spatially vary in pressure amplitude in the direction of sound propagation. In this work an anechoic 'one-dimensional' sonication chamber has been developed that produces propagating waves, which differ from standing waves in that the pressure amplitude remains constant as the wave travels in a medium with negligible attenuation. The viability of yeast cell suspensions as a function of treatment time was investigated during exposure to both standing and propagating wave fields with frequencies slightly above 2 MHz. The influence of 12% (vol/vol) of ethanol in water on the spatial arrangement of the cells in suspension was also studied. Changes in yeast cell morphology caused by the different types of suspension media and the ultrasonic treatment were examined by transmission electron microscopy (TEM). The agglomeration of yeast cells within the pressure nodal planes appears to minimise damaging effects due to ultrasonic fields.

Cell Survival↗

PubMed2002

"Weak" ultrasonic pre-treatment on anaerobic digestion of flocculated activated biosolids.

This study examined how "weak" ultrasonic pre-treatment affects anaerobic digestion of waste biosolids, treated with a cationic polyelectrolyte flocculant. In relation to pre-treatment, the term "weak" used refers to the fact that the total ultrasonic energy input to biosolids is insufficient to fully disrupt its floc structure or the cell walls, as described in the literature. Methane production potential, floc characteristics (size, morphology and zeta-potential) and process parameters (chemical oxygen demands and oxidative-reductive potentials) were monitored, as the digestion was tested. The presence of polyelectrolyte flocculants enhanced methane production within 6 days of digestion (phase I), but inhibited the digestion thereafter (phase II). Following pre-treatment by sonication (0.33 W/mL, 20 min), the methane productions of both original and flocculated biosolids significantly increased. The underlying mechanisms of weak ultrasonic pre-treatment are discussed.

Bacteria, Anaerobic↗

PubMed1990

Effect of varying the ultrasonic power setting on canal preparation.

The purpose of this study was to evaluate the effect of instrumenting root canals using an ultrasonic device (Enac) at different power levels on the prepared canal shape and instrumentation time, and to compare these results with those obtained using a standardized hand instrumentation technique. The mesial canals (120) of 60 human mandibular first and second molars were randomly assigned to one of six groups. In groups A through D, the canals were instrumented using the Enac ultrasonic unit at different power settings (1, 2, 3, and 5, respectively). Group E was hand instrumented. Group F served as uninstrumented controls. The roots were then sectioned horizontally and the canal shapes examined, as was the mesiodistal canal diameter as it relates to the external root surface. Instrumentation time for each group was recorded. Ultrasonic instrumentation at the different power settings was significantly faster than hand instrumentation (p less than 0.001). However, the difference between the different power levels was not significant. There were no significant differences between the different groups as to the effect on the prepared canal shape. The only problem arising from using the Enac at a power level more than the recommended (5) was the greater tendency to break size #15 files during instrumentation. Using the Enac at power level 3 provided satisfactory instrumentation capability with minimal risk of file breakage.

Dental Pulp Cavity↗

PubMed1991

Effectiveness of halothane used with ultrasonic or hand instrumentation to remove gutta-percha from the root canal.

This study compared halothane and chloroform used with hand or ultrasonic instrumentation to remove gutta-percha and sealer from root canals. Apically extruded debris, residual debris, time for filling removal, and amount of solvent used were determined. The differences in extruded apical debris and radiographically visible residual debris were not significant (p greater than 0.05). Ultrasonic instrumentation required significantly less time to remove the root canal filling than did hand instrumentation (p = 0.02). The only significant difference in the amount of solvent used occurred when the ultrasonic-chloroform group was compared with the hand instrumentation-chloroform group (p = 0.05). Halothane was found to be an acceptable alternative to chloroform for removing gutta-percha and sealer from the obturated root canal.

Analysis of Variance↗

PubMed1989

Obturation quality utilizing ultrasonic cleaning and sealer placement followed by lateral condensation with gutta-percha.

The quality of canal obturation utilizing ultrasonic or hand instrument sealer placement followed by lateral condensation with gutta-percha was investigated. This in vitro study using the mesial roots of human mandibular molars showed the ultrasonic method of sealer placement resulted in a more thorough coverage of canal walls than when the sealer was placed with hand instruments. The difference was statistically significant (p less than 0.005). Ultrasonic sealer placement may be safely and effectively utilized when obturating a complex root canal system.

Bismuth↗

PubMed1996

A new ultrasonic canal preparation system with electronic monitoring of file tip position.

A new ultrasonic root canal preparation system has been developed that electronically monitors the location of the file tip during all instrumentation procedures. The Root ZX has been adapted for this purpose, and its filter circuit effectively cuts out the large spike noise of the ultrasonic unit. During enlargement of the canal, the ultrasonic vibration of the file can be stopped at any desired position on the meter. Extracted human tooth models with electronically measurable canals were used to test the device. Pre- and postoperative shapes of the root canals were evaluated using contact microradiography. The autostop mechanism worked correctly. Using a weak power and fine files, straightening, ledge formation, and file breakage were minimal. It seems that this system minimized the danger of overinstrumentation and could be safely applied in clinical practice.

Dental Instruments↗

PubMed1997

An experimental study of the removal of cemented dowel-retained cast cores by ultrasonic vibration.

A technique for the removal of cemented post-cores by means of ultrasonic vibration was studied clinically and histologically. The removal time was measured for 80 extracted human teeth, including 40 single-rooted teeth and 40 multiple rooted ones and then statistically analyzed. The periapical tissue reaction to the ultrasonic vibration was also examined histologically in dogs. The best result was achieved when lateral vibration was simultaneously given by 2 removal tips using 2 ultrasonic generators. There was little harmful influence on the periodontal tissue, excluding a transient reversible reaction.

Animals↗

PubMed1999

A scanning electron microscopic study of in vivo ultrasonic root-end preparations.

The purpose of this in vivo study was to evaluate root-ends for cracks after root resection and again after ultrasonic root-end preparation in patients undergoing endodontic surgery. Endodontic surgery was performed on 25 roots from 20 patients. In vivo vinyl polysiloxane impressions were made after root resection and again after ultrasonic root-end preparations. Epoxy resin casts were made from the impressions and scanning electron micrographic examination of the root-end replicas was performed. There was no evidence of cracks after root resection. One incomplete canal crack was evident after ultrasonic root-end preparation.

Apicoectomy↗

PubMed1991

The effects of 5-HT receptor ligands on ultrasonic calling in mouse pups.

The influence of a range of drugs acting at various 5-HT receptor sites on the ultrasonic calling of mouse pups was assessed. Calling was decreased by the novel anxiolytics buspirone, ipsapirone and gepirone, and by TFMPP, spiperone, ritanserin and GR 38032F. In contrast, 8-OH-DPAT, DOI and quipazine increased the rate of calling. These effects on ultrasonic calling were independent of sedative or thermoregulatory actions of these drugs. Present data provide further support for the view that ultrasonic calling can be used to assess novel compounds for possible anxiolytic or anxiogenic properties.

Animals↗

PubMed1984

Vaginal scent marking: effects on ultrasonic calling and attraction of male golden hamsters.

Male hamsters were tested for their responses to areas that had been scent marked by intact or vaginectomized females to determine the effects of naturally deposited vaginal secretions on male behavior. In the first experiment males produced more ultrasonic courtship calls when investigating areas marked by intact females than areas scented by vaginectomized females, demonstrating that vaginal marks facilitate such calling. In a wind-tunnel preference test situation in which scent-marked alleys and clean alleys served as sources of odor, males approached the scented alley first if it had been freshly marked by intact females but not if it had been scented by vaginectomized females or other males. Thus, the odors of vaginal marks are sufficient to attract males over short distances. After males entered these alleys they showed a preference for odors of both intact and vaginectomized females over no odors, but still spent significantly more time investigating the odors of intact females than those of vaginectomized females. These experiments indicate that vaginal secretions are one of the primary cues that elicit male courtship calling, and the small quantities of vaginal secretions deposited by females in vaginal marks are sufficient to elicit ultrasonic calling and attract males over short distances. Thus it is likely that vaginal scent marking and ultrasonic calling by females interact to facilitate attraction and location of mates during courtship.

Animals↗

PubMed2004

Scopolamine effects on ultrasonic vocalization emission and behavior in the neonatal mouse.

Developmental alterations of the cholinergic system can lead to short- and long-term detrimental consequences for brain function. In order to study the cholinergic modulation of behavior in the neonatal mouse, we characterized ultrasonic vocalizations and spontaneous behavior of 5- and 8-day old CD-1 Swiss mice after i.p. administration of the muscarinic antagonist scopolamine (doses, 0.8 and 2 mg/kg) during both a first isolation of 30 min and a re-isolation of 5 min, occurring immediately after a brief reunion with the mother. As concerns the first isolation, on PND 5, only scopolamine 0.8m g/kg increased the number of ultrasonic vocalizations and, on PND 8, both doses increased it in a dose-dependent fashion. Scopolamine effects on spontaneous behavior were very limited on PND 5, but markedly evident on PND 8, the high dose increasing activity profile. Independently from treatment, the brief reunion with the mother had no effects on mouse ultrasound emission during re-isolation. The present results show that the cholinergic system plays a role in inhibiting rodent pup USV emission and spontaneous behavior and suggest that the analysis of spontaneous behavior and, in particular, of the number of ultrasonic vocalizations represents a valuable tool to detect precocious developmental alterations of the cholinergic function in the mouse, the most used animal species to model human health disorders.

Age Factors↗