Thermal depth

The lithium dopant in ZnO may occupy interstitial sites (Lk) or may substitute for the Zn site (Lizn) acting as a shallow donor or as an accepter, respectively. The optical depth, measured from the edge of the valence band, amounts to about 1 eV and the thermal depths to 0.2 - 0.4 eV. ... 

Like viscous depth, thermal depth is a function of the ultrasound frequency, oi. The... 

The difference between the viscous depth and the thermal depth provides an answer to the observed differences between emulsions and solid particle dispersions. These parameters characterize the penetra tion of the shear wave and thermal wave, respectively, into the liquid. Particles oscillating in the sound wave generate these waves which damp in the particle vicinity. The characteristic distance for the shear wave amplitude to decay is the viscous depth 5y. The corresponding distance for the thermal wave is the thermal depth 5. The following expressions give these parameter values in dilute systems ... 

The relationship between <5y and 5 has been considered before. For instance, McClements plots thermal depth and viscous depth versus frequency (4). It is easy to show that viscous depth is 2.6 times more than thermal depth in aqueous dispersions (15). As a result, the particle viscous... 

Photothermal spectroscopy may be used to measure physical and chemical properties of sample as a function of depth. This depth profiling may be thermal, spectroscopic, or a composite of the two. Thermal depth profiling is achieved by irradiating the sample at opaque wavelengths. The magnitude and phase of the surface temperature is measured at several modulation frequencies and subsurface properties are deduced by subsequent data analysis. 

This paper deals with the control of weld depth penetration for cylinders in gold-nickel alloy and tantalum. After introducing the experimental set-up and the samples description, the study and the optimization of the testing are presented for single-sided measurements either in a pulse-echo configuration or when the pump and the probe laser beams are shifted (influence of a thermal phenomenon), and for different kind of laser impact (a line or a circular spot). First, the ultrasonic system is used to detect and to size a flat bottom hole in an aluminium plate. Indeed, when the width of the hole is reduced, its shape is nearly similar to the one of a slot. Then, the optimization is accomplished for... 

Then, the weld depths penetration are controlled in a pulse-echo configuration because the weld bead (of width 2 mm) disturbs the detection when the pump and the probe beams are shifted of 2.2 mm. The results are presented in figure 8 (identical experimental parameters as in figure 7). The slow propagation velocities for gold-nickel alloy involve that the thermal component does not overlap the ultrasonic components, in particular for the echo due to the interaction with a lack of weld penetration. The acoustic response (V shape) is still well observed both for the slot of height 1.7 mm and for a weld depth penetration of 0.8 mm (lack of weld penetration of 1.7 mm), even with the weld bead. This is hopeful with regard to the difficulties encountered by conventional ultrasound in the case of the weld depths penetration. 

This definition is in terms of a pool of liquid of depth h, where z is distance normal to the surface and ti and k are the liquid viscosity and thermal diffusivity, respectively [58]. (Thermal diffusivity is defined as the coefficient of thermal conductivity divided by density and by heat capacity per unit mass.) The critical Ma value for a system to show Marangoni instability is around 50-100. 

Some solid materials are very intractable to analysis by standard methods and cannot be easily vaporized or dissolved in common solvents. Glass, bone, dried paint, and archaeological samples are common examples. These materials would now be examined by laser ablation, a technique that produces an aerosol of particulate matter. The laser can be used in its defocused mode for surface profiling or in its focused mode for depth profiling. Interestingly, lasers can be used to vaporize even thermally labile materials through use of the matrix-assisted laser desorption ionization (MALDI) method variant. 

Thermal imaging is sensitive to iafrared radiation that detects temperature changes over the surface of a part when heat has been appHed. Thermal diffusion ia a soHd is affected by variatioa ia composition or by the preseace of cracks, voids, delamiaatioas, etc the effects are detected by surface temperature changes. Defects cannot be detected if their depth below the surface is more than two to three times their diameter. Nondestmctive testing has been primarily used for composites and analysis of adhesive bonds or welds. Several studies are documented ia the Hterature (322—327). 

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