Search

A study was conducted to analyze the thermal conductivity depth profiles of thermally inhomogeneous materials obtained from the time dependence of the surface temperature after a flash illumination. A neural network technique was utilized. The average reconstruction errors were then examined for different circumstances. Results indicated the flexibility of neural network recognition for inverse problems.

A new neural network technique for reconstructing the depth profile of thermally inhomogeneous materials from a photothermal spectrum is presented. The possibilities and limits of this kind of photothermal depth profiling are examined. The effect of the network architecture and several profile and signal parameters on the reconstruction quality are evaluated. Statistical forecasts are provided for the accuracy of the reconstructed profiles for various levels of Gaussian noise in the signal and at various depths.

The thermal characteristics of layered materials were investigated using a photoacoustic technique. The photoacoustic method was based on thermal waves, which posses other transmission and reflection properties than optical or acoustical waves. This characteristic allows it to obtain data which other techniques cannot. An inversion procedure was effective in obtaining depth information from the photoacoustic signal.

We studied the thermal conductivity, thermal effusivity, and specific heat capacity at constant pressure of the critical binary liquid mixture aniline–cyclohexane near the consolute point, using a photopyroelectric (PPE) technique and adiabatic scanning calorimetry (ASC). According to recent theoretical predictions based on renormalization group theory calculations, a substantial (but not diverging) enhancement in the thermal conductivity in the homogeneous phase near the critical temperature was expected for this binary system near the consolute point. However, within an experimental precision of 0.05%, we found no deviation from linear behavior in the range of 5 K above Tc down to Tc. The specific heat capacity calculated from the results for the thermal conductivity and effusivity is in good agreement with that measured by ASC. For the ASC results, the theoretical power law expression with the Ising critical exponent was fitted to the specific heat capacity both above and below the transition temperature. Good agreement with theory was found both for the amplitude ratio and the two-scale universality. © 2005 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this article, we apply our analytical theory, published earlier in this journal, to obtain information on the earth surface temperature history from some borehole temperature data. Compared to the results of the five different methods applied to the same temperature data, our method seems to be easier, assumption-free, and yields internally consistent results. The results suggest a cooling a few centuries ago, followed by a continuing warming up to these days, in agreement with a little ice age scenario. [ABSTRACT FROM AUTHOR]

Experimental investigations on binary liquid mixtures near the critical mixing point are presently leading to a controversy about the anomaly in the thermal conductivity. A photopyroelectric technique is used to determine the thermal conductivity and the effusivity of the binary liquid mixture n-butoxyethanol–water at its critical concentration near the critical mixing point. It is proven that, contrary to previous reports, there is no critical enhancement in the thermal conductivity. The specific heat capacity is calculated from these results and compared with the results from measurements performed by adiabatic scanning calorimetry. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this paper we report on experimental data for the frequency and temperature dependence of the thermal properties of supercooled glycerol and propylene glycol. By using a photopyroelectric method the specific heat capacity and thermal conductivity were separately determined in a bandwidth of several decades. We have recently shown that the thermal conductivity has no relaxation behavior, which simplifies the analysis of our results. The relaxation behavior of the specific heat capacity is compared with literature results for other physical quantities and a detailed analysis of the temperature dependence of the relaxation parameters is presented. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We investigated the specific heat capacity near the demixing transition of ternary mixtures of water, 3-methylpyridine and sodium bromide as a function of salt concentration. In this system, a crossover from Ising to tricritical behavior caused by the appearance of a new “microheterogeneous” phase was reported from light-scattering measurements [Jacob et al., Phys. Rev. E 58, 2811 (1998)]. We used adiabatic scanning calorimetry, a very sensitive technique for detecting and characterizing phase transitions, to investigate this system and found no specific heat anomaly to be associated with the formation of a new phase. In the one phase region, the critical exponent α is consistent with the Ising value and is incompatible with the tricritical value for all the investigated samples. In the phase-separated region, the values of the exponent are substantially lower and even negative. This is probably caused by the change in salt concentration of the two phases close to the critical point. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Using different photopyroelectric configurations, we have experimentally studied the frequency dependence of the thermal properties of the glass former glycerol near its glass transition. With our method, an unambiguous and separate determination of the frequency dependence of the specific heat capacity and the thermal conductivity is possible. Within experimental uncertainty, in the frequency range from 0.1 Hz to 1100 Hz, unlike the specific heat capacity, the thermal conductivity of glycerol does not show any frequency dependence through the glass transition region. We have also extended the thermal spectroscopy frequency range to 100 kHz, which is one decade higher than other methods. [ABSTRACT FROM AUTHOR]