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Gerald J Diebold

Publications and source records attributed to Gerald J Diebold.

9 recordsLinked to original sources
PubMed2006

Transient gratings generated by particulate suspensions: the uniformly irradiated sphere and the point source.

Expressions for the time dependence of the state variables in a transient grating experiment carried out on suspensions of particles can be determined by integration over space of the solutions for the temperature and photoacoustic pressure for a single particle. The method relies on independent computation of the thermal and acoustic modes of wave motion which are combined to give the temperature, pressure, and density in the grating as a function of time. Calculations are given for the uniformly irradiated droplet and the point source, the latter including the effects of a temperature-dependent thermal expansion coefficient. Transient grating experiments are reported in colloidal Pt that show features described in the calculation.

Journal Article↗
PubMed2005

Mathematical analysis of thermal diffusion shock waves.

Thermal diffusion, also known as the Ludwig-Soret effect, refers to the separation of mixtures in a temperature gradient. For a binary mixture the time dependence of the change in concentration of each species is governed by a nonlinear partial differential equation in space and time. Here, an exact solution of the Ludwig-Soret equation without mass diffusion for a sinusoidal temperature field is given. The solution shows that counterpropagating shock waves are produced which slow and eventually come to a halt. Expressions are found for the shock time for two limiting values of the starting density fraction. The effects of diffusion on the development of the concentration profile in time and space are found by numerical integration of the nonlinear differential equation.

Journal Article↗
PubMed2005

Thermal diffusion shock waves.

The Ludwig-Soret effect or thermal diffusion, which refers to the separation of liquid mixtures in a temperature gradient, is governed by a nonlinear, partial differential equation in space and time. It is shown here that the solution to the nonlinear differential equation for a binary mixture predicts the existence of shock waves completely analogous to fluid shocks and obeys an expression for the shock velocity that is an exact analogue of the Rankine-Hugoniot relations. Direct measurements of the time dependent, spatial absorption profile of a suspension of nanometer sized particles subjected to a sinusoidal temperature field generated by a pair of continuous laser beams, as well as self-diffraction experiments, show motion of the particles in agreement with the predictions of nonlinear theory.

Journal Article↗
PubMed2005

Imaging with the ultrasonic vibration potential: A theory for current generation.

The current in a circuit produced by a time-varying polarization generated by an object within a body in response to the passage of ultrasound (US) is found through solution to Maxwell's equations. Current generation is modelled in a body with uniform dielectric constant and conductivity where a finite region within the body produces an ultrasonic vibration potential. The results of the calculation form the mathematical basis for imaging through use of the ultrasonic vibration potential.

Electric Conductivity↗
PubMed2004

Acoustically modulated x-ray phase contrast imaging.

We report the use of ultrasonic radiation pressure with phase contrast x-ray imaging to give an image proportional to the space derivative of a conventional phase contrast image in the direction of propagation of an ultrasonic beam. Intense ultrasound is used to exert forces on objects within a body giving displacements of the order of tens to hundreds of microns. Subtraction of images made with and without the ultrasound field gives an image that removes low spatial frequency features and highlights high frequency features. The method acts as an acoustic 'contrast agent' for phase contrast x-ray imaging, which in soft tissue acts to highlight small density changes.

Acoustics↗
PubMed2004

Thermal diffusion in a sinusoidal temperature field.

Separation of liquid mixtures in a thermal gradient, known as the Ludwig-Soret effect or thermal diffusion, is governed by a nonlinear, partial differential equation. It is shown here that the nonlinear differential equation for a binary mixture can be reduced to a Hamiltonian system of equations and that a solution can be obtained for the linear problem. The calculation gives a closed form expression for the space and time dependence of the concentration profile of the mixture, valid at short times.

Journal Article↗
PubMed2003

Internally excited acoustic resonator for photoacoustic trace detection.

The quantum-cascade laser can be used as an infrared source for a small portable photoacoustic trace gas detector. The device that we describe uses a quantum-cascade laser without collimating optics mounted inside an acoustic resonator. The laser is positioned in the center of a longitudinal resonator at a pressure antinode and emits radiation along the length of the resonator exciting an axially symmetric longitudinal acoustic mode of an open-ended cylindrical resonator. Experiments are reported with an 8-microm, quasi-cw-modulated, room-temperature laser used to detect N2O.

Journal Article↗
PubMed2002

The photoacoustic effect generated by an incompressible sphere.

An incompressible sphere with a vanishing thermal expansivity suspended in a fluid can generate a photoacoustic effect when the heat deposited in the sphere by a light beam diffuses into the surrounding liquid causing it to expand and launch a sound wave. The properties of the photoacoustic effect for the sphere are found using a Green's function solution to the wave equation for pressure with Neumann boundary conditions. The results of the calculation show that the acoustic wave for fast heat liberation is an outgoing compressive pulse followed by a reflected pulse whose time profile is modified as a result of frequency dependent reflection from the sphere. For slow heat release by the sphere, the photoacoustic effect is shown to be proportional to the first time derivative of the heat flux at the particle-fluid interface.

Acoustics↗