Search results for "Acoustics and Ultrasonics"
showing 10 items of 270 documents
Evaluation of viscoelastic constants of metallic materials by laser-ultrasonics at elevating temperature
2002
The main objective of this study is the determination of elastic moduli and viscosity coefficients of metals at elevating temperature up to melting point. More specifically, it involves the analysis of the propagation of acoustic waves generated and detected simultaneously by laser-ultrasonic for the measurement of longitudinal and shear velocities. This preliminary work primarily concerns Tin (Sn) metal known for its low melting point and attenuation coefficient.
Simultaneous laser generation and laser ultrasonic detection of the mechanical breakdown of a coating–substrate interface
2001
Abstract The present study deals with information that could be obtained by real-time contactless monitoring of the normal displacement, due to the propagation of the longitudinal waves generated by nanosecond pulsed laser irradiation, through a transparent and porous ceramic coating deposited on a metallic substrate. These displacements were recorded in real-time at the rear surface of the specimens using a laser heterodyne interferometer and were correlated with the different steps of laser/material interaction (thermoelastic interactions, fracture of the coating–substrate interface and coating expulsion). An analytical model was developed to establish a relation between the longitudinal …
Effects of high power ultrasound treatments on the phenolic, chromatic and aroma composition of young and aged red wine
2019
Abstract In this study, the effects of both ultrasonic bath and probe treatments on the phenolic, chromatic and aroma composition of young red wine Cabernet Sauvignon were studied and modeled by artificial neural networks (ANNs). Moreover, the effect of high power ultrasound (HPU) along with antioxidants addition (sulfur dioxide and glutathione) was investigated during 6 months of aging in bottles. Lower amplitude and temperature, shorter treatment duration and particularly lower frequency showed a more favorable and milder effect on the chemical composition of wine. In the case of the ultrasonic probe treatment, similar effect was achieved primarily by a larger probe diameter as well as lo…
Bengali nasal vowels: Lexical representation and listener perception
2022
This paper focuses on the question of the representation of nasality as well as speakers’ awareness and perceptual use of phonetic nasalisation by examining surface nasalisation in two types of vowels in Bengali: underlying nasal vowels (CṼC) and nasalised vowels before a nasal consonant (CVN). A series of three cross-modal forced-choice experiments was used to investigate the hypothesis that only unpredictable nasalisation is stored and that this sparse representation governs how listeners interpret vowel nasality. Visual full-word targets were preceded by auditory primes consisting of CV segments of CVC words with nasal vowels ([tʃɑ̃] for [tʃɑ̃d] ‘moon’), oral vowels ([tʃɑ] for [tʃɑl] ‘un…
Liver Steatosis and Fibrosis in OSA patients After Long-term CPAP Treatment: A Preliminary Ultrasound Study.
2015
In cases of morbid obesity, obstructive sleep apnea (OSA) was associated with biopsy-proven liver damage. The role of non-invasive techniques to monitor liver changes during OSA treatment with continuous positive airway pressure (CPAP) is unknown. We used non-invasive ultrasound techniques to assess liver steatosis and fibrosis in severe OSA patients at diagnosis and during long-term CPAP treatment. Fifteen consecutive patients with severe OSA (apnea hypopnea index 52.5 ± 19.1/h) were studied by liver ultrasound and elastography (Fibroscan) at 6-mo (n = 3) or 1-y (n = 12) follow-up. Mean age was 49.3 ± 11.9 y, body mass index (BMI) was 35.4 ± 6.4 kg/m(2). Adherence to CPAP was ≥5 h/night. A…
DOSE–RESPONSE RELATIONSHIPS BETWEEN WHOLE-BODY VIBRATION AND LUMBAR DISK DISEASE—A FIELD STUDY ON 388 DRIVERS OF DIFFERENT VEHICLES
1998
Abstract In a longitudinal study, the dose–response relationships between long term occupational exposure to whole-body vibration and degenerative processes in the lumbar spine caused by the lumbar disks were examined. From 1990 to 1992, 388 vibration-exposed workers from different driving jobs were examined medically and by lumbar X-ray. For each individual, a history of all exposure conditions was recorded, and a cumulative vibration dose was calculated allowing comparisons between groups of low, middle, and high intensity of exposure. 310 subjects were selected for a follow-up four years later, of whom 90·6% (n=281) agreed to participate. In comparing the exposure groups, the results ind…
Impact of local order and stoichiometry on the ultrafast magnetization dynamics of Heusler compounds
2015
Nowadays, a wealth of information on ultrafast magnetization dynamics of thin ferromagnetic films exists in the literature. Information is, however, scarce on bulk single crystals, which may be especially important for the case of multi-sublattice systems. In Heusler compounds, representing prominent examples for such multi-sublattice systems, off-stoichiometry and degree of order can significantly change the magnetic properties of thin films, while bulk single crystals may be generally produced with a much more well-defined stoichiometry and a higher degree of ordering. A careful characterization of the local structure of thin films versus bulk single crystals combined with ultrafast demag…
Interface magnetization of ultrathin epitaxial Co2FeSi(110)/Al2O3films
2007
Element-specific magnetic properties of ultrathin epitaxial Co2FeSi(110) films were measured using x-ray magnetic circular dichroism (XMCD). The epitaxial Heusler films were grown by RF magnetron sputtering on substrates. The magnetization of thicker films as determined by XMCD is smaller than expected for a half-metallic material. In addition, the magnetization decreases considerably for films thinner than 10 nm. The thickness dependence of the magnetic moment can be described by introducing a certain number of dead layers representing a deficiency of magnetization at the interfaces. Quantitative evaluation results in a dead layer thickness of 0.8 nm at room temperature, consisting of a te…
Quantitative Ultrasound Bone Measurements in Pre-Pubertal Children with Type 1 Diabetes
2011
This case-control study aimed to assess bone status in children with type 1 diabetes mellitus (T1DM). Fifty-seven pre-pubertal patients (37 boys, aged 7.9 ± 2.5 years, T1DM duration 3.1 ± 1.6 years) and 171 age-matched healthy controls (111 boys) were studied. Quantitative ultrasound (QUS) was used to measure amplitude dependent speed of sound (Ad-SoS) at hand phalanges (expressed as standard deviation score [SDS]). Anthropometric and disease-related data (including mean HbA(1c) from whole T1DM duration [T], last year [Y], examination day [D]) were collected. Mean Ad-SoS SDS in patients -0.13 ± 1.32 (95% confidence interval [CI] -0.48, 0.22) was similar to that of controls. Subgroups discri…
Comparison of three ultrasonic axial transmission methods for bone assessment.
2005
Abstract This study compared three approaches to bone assessment using ultrasonic axial transmission. In 41 fresh human radii, velocity of the first arriving signal was measured with a commercial device (Sunlight Omnisense ™ ) operating at 1.25 MHz, a prototype based on 1-MHz bidirectional axial transmission and a low-frequency (200 kHz) prototype, also measuring the velocity of a slower wave. Cortical and trabecular bone mineral density, cortical thickness and cross-sectional area were determined by peripheral quantitative computed tomography. Significant but modest correlation between velocities reflects differences in the nature of the propagating waves and methodological differences. Of…