Laser Doppler velocimetry uses the frequency shift produced by the Doppler effect to measure velocity. It can be used to monitor blood flow or other tissue movement in the body. Laser speckle is a random interference effect that gives a grainy appearance to objects illuminated by laser light. If the object consists of individual moving scatterers (such as blood cells), the speckle pattern fluctuates. These fluctuations provide information about the velocity distribution of the scatterers. It can be shown that the speckle and Doppler approaches are different ways of looking at the same phenomenon. Both these techniques measure at a single point. If a map of the velocity distribution is required, some form of scanning must be introduced. This has been done for both time-varying speckle and laser Doppler. However, with the speckle technique it is also possible to devise a full-field technique that gives an instantaneous map of velocities in real time. This review article presents the theory and practice of these techniques using a tutorial approach and compares the relative merits of the scanning and full-field approaches to velocity map imaging. The article concludes with a review of reported applications of these techniques to blood perfusion mapping and imaging.

/pdf/laser-doppler-speckle-and-related-techniques-for-blood-2tg3to9jwf.pdf

Laser Doppler, speckle and related techniques for blood perfusion mapping and imaging

In particle image velocimetry experiments where optical access is limited or in microscale geometries, it may be desirable to illuminate the entire test section with a volume of light, as opposed to a two-dimensional sheet of light. With volume illumination, the depth of the measurement plane must be defined by the focusing characteristics of the recording optics. A theoretical expression for the depth of the two-dimensional measurement plane is derived and it is shown to agree well with experimental observations. Unfocused particle images, which lie outside the measurement plane, create background noise that decreases the signal-to-noise ratio of the particle-image fields. Results show that the particle concentration must be chosen judiciously in order to balance the desired spatial resolution and signal-to-noise ratio of the particle-image field.

https://iopscience.iop.org/article/10.1088/0957-0233/11/6/326/pdf

Volume illumination for two-dimensional particle image velocimetry

We have used the technique of laser-Doppler velocimetry to study the transition to turbulence in a fluid contained between concentric cylinders with the inner cylinder rotating The experiment was designed to test recent proposals for the number and types of dynamical regimes exhibited by a flow before it becomes turbulent For different Reynolds numbers the radial component of the local velocity was recorded as a function of time in a computer, and the records were then Fourier-transformed to obtain velocity power spectra The first two instabilities in the flow, to time-independent Taylor vortex flow and then to time-dependent wavy vortex flow, are well known, but the present experiment provides the first quantitative information on the subsequent regimes that precede turbulent flow Beyond the onset of wavy vortex flow the velocity spectra contain a single sharp frequency component and its harmonics; the flow is strictly periodic As the Reynolds number is increased, a previously unobserved second sharp frequency component appears at R/Rc = 10·1, where Rc is the critical Reynolds number for the Taylor instability The two frequencies appear to be irrationally related; hence this is a quasi-periodic flow A chaotic element appears in the flow at R/Rc ≃ 12, where a weak broadband component is observed in addition to the sharp components; this flow can be described as weakly turbulent As R is increased further, the component that appeared at R/Rc= 10·1 disappears at R/Rc = 19·3, and the remaining sharp component disappears at R/Rc = 21·9, leaving a spectrum with only the broad component and a background continuum The observance of only two discrete frequencies and then chaotic flow is contrary to Landau's picture of an infinite sequence of instabilities, each adding a new frequency to the motion However, recent studies of nonlinear models with a few degrees of freedom show a behaviour similar in most respects to that observed

https://www.math.fsu.edu/~moore/SeminarFiles/GollubVortex79.pdf

Dynamical instabilities and the transition to chaotic Taylor vortex flow

The evolution of particle image velocimetry (PIV) from its various roots is discussed. The importance of these roots and their influence on different trends in the speciality are described. The state-of-the-art of the technique today is overviewed and illustrated by reference to recent, seminal publications describing both the development and application of PIV.

Particle image velocimetry: A review

An automatic technique for estimating and modeling the glottal flow derivative source waveform from speech, and applying the model parameters to speaker identification, is presented. The estimate of the glottal flow derivative is decomposed into coarse structure, representing the general flow shape, and fine structure, comprising aspiration and other perturbations in the flow, from which model parameters are obtained. The glottal flow derivative is estimated using an inverse filter determined within a time interval of vocal-fold closure that is identified through differences in formant frequency modulation during the open and closed phases of the glottal cycle. This formant motion is predicted by Ananthapadmanabha and Fant (1982) to be a result of time-varying and nonlinear source/vocal tract coupling within a glottal cycle. The glottal flow derivative estimate is modeled using the Liljencrants-Fant (1986) model to capture its coarse structure, while the fine structure of the flow derivative is represented through energy and perturbation measures. The model parameters are used in a Gaussian mixture model speaker identification (SID) system. Both coarse- and fine-structure glottal features are shown to contain significant speaker-dependent information. For a large TIMIT database subset, averaging over male and female SID scores, the coarse-structure parameters achieve about 60% accuracy, the fine-structure parameters give about 40% accuracy, and their combination yields about 70% correct identification. Finally, in preliminary experiments on the counterpart telephone-degraded NTIMIT database, about a 5% error reduction in SID scores is obtained when source features are combined with traditional mel-cepstral measures.

/pdf/modeling-of-the-glottal-flow-derivative-waveform-with-2ffomnn38b.pdf

Modeling of the glottal flow derivative waveform with application to speaker identification

Laser Systems in Flow Measurement

The Musician's Guide to Acoustics

The application of the lattice Boltzmann model to simulating nonlinear propagative acoustic waves is considered. The lattice Boltzmann model, and its application to the study of nonlinear sound propagation, are discussed. Lattice Boltzmann simulations of the development of a shock front are performed when a sound wave is emitted from a high-amplitude sinusoidal source. For a number of parameters, representing different physical situations, the wave development is compared with inviscid shock theory and with the solution of Burgers' equation for a fully viscous fluid. The simulations show good agreement with Burgers' equation and with the inviscid theory when propagation at high Reynolds number is considered. These results suggest that the lattice Boltzmann model is a useful technique for studying a range of problems in nonlinear acoustics.

/pdf/lattice-boltzmann-bgk-simulation-of-nonlinear-sound-waves-2tqxnwraxn.pdf

Lattice Boltzmann BGK simulation of nonlinear sound waves: the development of a shock front

https://www.pure.ed.ac.uk/ws/files/57167230/Numerical_Investigation_of_Vertical_Axis_Tidal_Turbines_with_Sinusoidal_Pitching_Blades.pdf

Numerical investigation of vertical-axis tidal turbines with sinusoidal pitching blades

1. Sounds and Sweet Airs 2. Family Relationships 3. Woodwind Instruments with Reeds 4. The Flute Family 5. Bugles and Horns 6. Trumpets and Trombones 7. Percussion Instruments 8. Stringed Instruments Played with a Bow 9. Plucked and Hammered Stringed Instruments 10. Clavichord and Harpsichord 11. The Pianoforte 12. The Pipe Organ 13. Electroacoustic, Electromechanical and Electronic Instruments

Clive A. Greated

Papers

Laser Systems in Flow Measurement

The Musician's Guide to Acoustics

Lattice Boltzmann BGK simulation of nonlinear sound waves: the development of a shock front

Numerical investigation of vertical-axis tidal turbines with sinusoidal pitching blades

Musical Instruments: History, Technology and Performance of Instruments of Western Music