46 research outputs found
The role and experimental determination of equivalent mass in complex SEA models
No full textThe application of statistical energy analysis to vibro-acoustic systems of complex geometry has been made practicable by the introduction of the concept of equivalent mass/equivalent volume. Although previous research at the ISVR has shown that these parameters can be directly measured, it has recently been found that the published formulae for carrying out this calculation are not sufficiently accurate. This is because it has been previously incorrectly assumed that the measurement on the subsystem of interest is unaffected by the presence of other attached subsystems. The paper derives the correct expressions for equivalent mass/equivalent volume for the general case of N -connected subsystems. By utilizing these derived expressions, the paper then proceeds to show that the coupling loss factors can be obtained directly in terms of the measured input power and vibration velocity/sound pressure. The paper concludes by showing that the power balance equations can, by utilizing the above expressions, be framed in terms of the subsystem velocities/sound pressures rather than in terms of subsystem energies
La solució a l'escalfament és consumir menys
No full textEl gel de la foto procedeix de l'Antàrtida i es conserva a l'Institut de Ciències del Mar de Barcelona, on Pablo Rodríguez Ros (Cartagena, 1990) realitza la seva investigació. Llicenciat en Ciències Ambientals per la Universitat de Múrcia, acaba d'obtenir una beca de doctorat de La Caixa, un guardó que li permetrà embarcar-se en la primera expedició científica a envoltar completament el continent gelat. [...]Peer reviewe
Development of a hybrid finite element/finite integration model for the UK's national physical laboratory acoustic emission reference facility
No full textS.857-868Recent advances in computer power and signal processing techniques have highlighted the need for a greater understanding of acoustic emission (AE) wave propagation and the interactions with the sensor being used. Complex structures often lead to numerous wave modes being generated which arrive at a surface mounted sensor from different angles of incident and in different planes. To fully understand the signals produced by the sensor, one requires intimate knowledge of the elastic wave propagation through the structure and understanding of the sensors response to the propagating elastic wave. This paper proposes a hybrid method for modelling acoustic emission reference systems in both the electrical and acoustical domain using the finite element (FE) method and the elastodynamic finite integration technique (EFIT). The method for validation of the FE and EFIT methods is detailed and the hybrid method has been tested using inputs to the EFIT code generated in a FE model of a conical piezoelectric transducer excited with an electric charge function. The agreement for both axial and radial displacement components at the opposite sensor loaded surface has been shown to be excellent and only shows small discrepancies after several reflections. The hybrid method shows excellent potential for modelling more complex acoustic emission structures in the future by combining the FE capabilities of modelling piezoelectric material in the electro-mechanical domain and the EFIT capabilities for rapid solutions to large scale linear and non-linear problems
Erratum: Evolution of ultrasonic impulses in chains of spheres using resonant excitation
No full textThis is an erratum for the article 2015 EPL 109 54002. The last name of the co-author L. A. J. Davis was given incorrectly in the published letter. The correct version of the author's name appears above
Simulating Focused Ultrasound with the Boundary Element Method
No full textFocused ultrasound is a non-invasive, non-ionizing technology with great potential for various clinical applications, including thermal ablation of tumors, targeted drug delivery, and neuromodulation. Focused ultrasound uses ultrasound energy to treat tissue deep in the body. Optimizing treatment parameters to achieve desired clinical outcomes while minimizing adverse effects remains a significant challenge. Computational simulations are powerful tools to address this challenge, develop patient-specific treatment plans and general safety guidelines, and optimize ultrasound transducers. This study presents the development of an open-source Python library, named OptimUS, for calculating ultrasound wave propagation in large computational domains in 3D using the boundary element method, specifically for focused ultrasound applications. The numerical calculations only require surface meshes at the scatterers' interfaces to define the model's geometry. Also, the computations are fast and accurate for high-frequency waves through materials with high contrast in density and speed of sound. An intercomparison exercise supports the fidelity of the simulations. Finally, simulations using anatomical models for abdominal applications of focused ultrasound reliably show the aberration of the focus from reflections by ribs and the presence of prefocal hotspots due to the lensing effect of fat layers
The phosphorus-Claisen condensation
No full textInternational audience1,1-Bisphosphorus compounds are easily synthesized through the phosphorus-Claisen (phospha-Claisen) condensation between a phosphorus-stabilized anion and a phosphorus electrophile. The preliminary scope of this reaction is investigated in terms of employable phosphorus reagents. Valuable intermediates are conveniently prepared in a single step. Overall, the method is competitive with multistep procedures which require the preparation of PCl intermediates derived from the P(OR) reagents we instead employ directly, and it delivers complex organophosphorus compounds in moderate to good isolated yields. An example of the intramolecular version of the reaction, the phospha-Dieckmann condensation, is also reported
Evolution of ultrasonic impulses in chains of spheres using resonant excitation
No full textIt is demonstrated that broad-bandwidth ultrasonic signals containing frequency components in excess of 200 kHz can be created in spherical chains using harmonic excitation at 73 kHz. Multiple reflections created a periodic waveform containing both harmonics and sub-harmonics of the original forcing frequency, due to non-linear Hertzian contact. These discrete frequencies represented some of the many allowed non-linear normal modes of vibration of the whole chain. Excitation at a single fixed frequency could thus be used to produce wide-bandwidth impulses for different lengths of spherical chains. Experimental results were in good agreement with theoretical predictions
Bubble dynamics in boiling histotripsy
No full textBoiling histotripsy is a non-invasive, cavitation-based ultrasonic technique which uses a number of millisecond pulses to mechanically fractionate tissue. Though a number of studies have demonstrated the efficacy of boiling histotripsy for fractionation of solid tumours, treatment monitoring by cavitation measurement is not well studied because of the limited understanding of the dynamics of bubbles induced by boiling histotripsy. The main objectives of this work are to (a) extract qualitative and quantitative features of bubbles excited by shockwaves and (b) distinguish between the different types of cavitation activity for either a thermally or a mechanically induced lesion in the liver. A numerical bubble model based on the Gilmore equation accounting for heat and mass transfer (gas and water vapour) was developed to investigate the dynamics of a single bubble in tissue exposed to different High Intensity Focused Ultrasound fields as a function of temperature variation in the fluid. Furthermore, ex vivo liver experiments were performed with a passive cavitation detection system to obtain acoustic emissions. The numerical simulations showed that the asymmetry in a shockwave and water vapour transport are the key parameters which lead the bubble to undergo rectified growth at a boiling temperature of 100°C. The onset of rectified radial bubble motion manifested itself as (a) an increase in the radiated pressure and (b) the sudden appearance of higher order multiple harmonics in the corresponding spectrogram. Examining the frequency spectra produced by the thermal ablation and the boiling histotripsy exposures, it was observed that higher order multiple harmonics as well as higher levels of broadband emissions occurred during the boiling histotripsy insonation. These unique features in the emitted acoustic signals were consistent with the experimental measurements. These features can, therefore, be used to monitor (a) the different types of acoustic cavitation activity for either a thermal ablation or a mechanical fractionation process and (b) the onset of the formation of a boiling bubble at the focus in the course of HIFU exposure
UV-mediated hydrophosphinylation of unactivated alkenes with phosphinates under batch and flow conditions
No full textIn this study, we report an efficient UV-mediated hydrophosphinylation of unactivated alkenes with H-phosphinates and hypophosphorous acid under radical free conditions in batch and in continuous flow.</p
