A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

A universal constitutive equation between the heat flux vector and the temperature gradient is proposed to cover the fundamental behaviors of diffusion (macroscopic in both space and time), wave (macroscopic in space but microscopic in time), phonon-electron interactions (microscopic in both space and time), and pure phonon scattering The model is generalized from the dual-phase-lag concept accounting for the laging behavior in the high-rate response While the phase lag of the heat flux captures the small-scale response in time, the phase lag of the temperature gradient captures the small-scale response in space The universal form of the energy equation facilitates identifications of the physical parameters governing the transition from one mechanism (such as diffusion or wave) to another (the phonon-electron interaction)

A Unified Field Approach for Heat Conduction From Macro- to Micro-Scales

The flow of homogeneous fluids through porous media: analogies with other physical problems

Hydrogen sensors are of increasing importance in connection with the development and expanded use of hydrogen gas as an energy carrier and as a chemical reactant. There are an immense number of sensors reported in the literature for hydrogen detection and in this work these sensors are classified into eight different operating principles. Characteristic performance parameters of these sensor types, such as measuring range, sensitivity, selectivity and response time are reviewed and the latest technology developments are reported. Testing and validation of sensor performance are described in relation to standardisation and use in potentially explosive atmospheres so as to identify the requirements on hydrogen sensors for practical applications.

Hydrogen Sensors - A review

The dependence of the strength of the electron-phonon coupling and the electron heat capacity on the electron temperature is investigated for eight representative metals, Al, Cu, Ag, Au, Ni, Pt, W, and Ti, for the conditions of strong electron-phonon nonequilibrium. These conditions are characteristic of metal targets subjected to energetic ion bombardment or short-pulse laser irradiation. Computational analysis based on first-principles electronic structure calculations of the electron density of states predicts large deviations (up to an order of magnitude) from the commonly used approximations of linear temperature dependence of the electron heat capacity and a constant electron-phonon coupling. These thermophysical properties are found to be very sensitive to details of the electronic structure of the material. The strength of the electron-phonon coupling can either increase (Al, Au, Ag, Cu, and W), decrease (Ni and Pt), or exhibit nonmonotonic changes (Ti) with increasing electron temperature. The electron heat capacity can exhibit either positive (Au, Ag, Cu, and W) or negative (Ni and Pt) deviations from the linear temperature dependence. The large variations of the thermophysical properties, revealed in this work for the range of electron temperatures typically realized in femtosecond laser material processing applications, have important implications for quantitative computational analysis of ultrafast processes associated with laser interaction with metals.

Electron-phonon coupling and electron heat capacity of metals under conditions of strong electron-phonon nonequilibrium

Boundary and inertia effects on flow and heat transfer in porous media

This work studies heat transfer mechanisms during ultrafast laser heating of metals from a microscopic point of view. The heating process is composed of three processes: the deposition of radiation energy on electrons, the transport of energy by electrons, and the heating of the material lattice through electron-lattice interactions. The Boltzmann transport equation is used to model the transport of electrons and electron lattice interactions. The scattering term of the Boltzmann equation is evaluated from quantum mechanical considerations, which shows the different contributions of the elastic and inelastic electron-lattice scattering processes on energy transport. By solving the Boltzmann equation, a hyperbolic two-step radiation heating model is rigorously established. It reveals the hyperbolic nature of energy flux carried by electrons and the nonequilibrium between electrons and the lattice during fast heating processes. Predictions from the current model agree with available experimental data during subpicosecond laser heating. 20 refs., 7 figs., 2 tabs.

Chuen-Lin Tien

Papers

Boundary and inertia effects on flow and heat transfer in porous media

Heat transfer mechanisms during short-pulse laser heating of metals

Femtosecond laser heating of multi-layer metals—I. Analysis

Boundary and inertia effects on convective mass transfer in porous media

Femtosecond laser heating of multi-layer metals. ii: experiments