Effect Of Thermal Field Research Articles

Electric and Thermal Field Effects in Tissue Around Radiofrequency Electrodes

A study is carried out of the spatial distribution and time dependence of electric and thermal fields in the tissue around a radiofrequency (RF) electrode used in pain therapy. Finite-element calculation of the fields is performed, and results are compared with ex vivo tissue data. Field predictions are made for continuous and for pulsed RF applications. A special RF cannula electrode is constructed with both macro and micro thermocouple sensors to measure both average and rapid, transitory temperature effects. Temperatures and impedances are recorded in liver and egg-white models using signal outputs from a commercially available RF lesion generator. These data are compared with the results of finite-element calculations using electric field equations and the bio-heat equation. Average and pulsatory temperatures at the RF electrode are measured. Rapid temperature spikes during pulsed RF bursts are observed. These data compared well with theoretical calculations using known electrical and thermal tissue parameters. Continuous RF lesioning causes heat destruction of neurons. Pulsed RF lesioning (PRFL) produces heat bursts with temperatures in the range associated with destructive heat lesions. PRFL also produces very high electric fields that may be capable of disrupting neuronal membranes and function. Finite-element calculations agree substantially with the measured data, giving confidence to their predictions of fields around the RF electrode.

Effect of Thermal Field on Interface Step Structures during PVT Growth of (0001)Si 6H-SiC

Effect of Thermal Field on Interface Step Structures during PVT Growth of (0001)Si 6H-SiC

Thermal effects on the morphological stability in a directional solidification system with remote flow

In this paper we investigate the effect of thermal fields on the morphological stability in a directional solidification system with remote flow. We undertake a linear analysis and develop an asymptotic solution for large Schmidt number. The result shows that the system is more stable when the latent heat increases and/or the ratio of conductivity of solid to that of melt gets smaller. The lead/tin alloy is taken for a realistic example and the result shows that the freezing lead/tin system is more stable when the thermal effect is taken into consideration.

Effect of Thermal Field on Residual Stress in Joined Cylindrical Dissimilar Materials. Elastic Analysis of Residual Stress in Nonuniform Thermal Field.

When dissimilar materials are joined at elevated temperature, residual stress is generated around the bonding interface area. Because of the stress concentration at the interface, the strength of the joint is not as great as expected. Many attempts have been made to reduce the residual stress value and to change the residual stress distribution. Many investigations using the finite-element method (FEM) have been carried out to estimate the effects of residual stress on the joining process under a homogeneous thermal field. In this works, the thermal residual stress and the strain were analyzed with FEM under thermal elastic conditions. Namely, numerical analysis was carried out for an electrical conductive ceramic of TiB2-Ni joint under an axisymmetric condition. It was found that the principal residual stress at the edge of the bonding interface was affected by the difference in elevated temperature between the inner and outer sections of the joining materials.

On magneto‐thermoelastic coupled wave propagation

Analytical results are reported on magneto‐thermoelastic coupled wave propagation in a solid medium. The relevant frequency equations have been obtained by solving equations of elasticity, taking into account the effects of thermal field, magnetic field and the electromagnetic equations of Maxwell. The nature of frequency has been discussed in different cases. It is also shown that, if the frequency is sufficiently smaller than a certain critical frequency, the attenuation factor as well as the phase velocity retain the same characteristics as in a purely thermoelastic body, provided the thermoelastic coupling factor is suitably increased.

Thermal-field effects of photon statistics in resonance fluorescence

The photon counting statistics of the fluorescence of a single atom driven by a resonant coherent field has been calculated and the results checked experimentally. The authors examine the effect of detuning the coherent field and/or the effect of an additional thermal field on the photon counting statistics. They work with a master equation that they have used previously and derive exact results for the probability distribution function P(n, tau ) for the emitted photons and for the normalised second factorial moment Q. The subPoissonian character of the photon statistics, for which Q<0, is most pronounced for weak thermal fields or weak detuned coherent fields. For short counting times tau the statistic is dominated by any spontaneous emission that occurs, as expected. Increasing numbers of black-body photons tend to increase the Q values, as might be expected-especially in the case of an initially excited atom-but no simple rule emerges. The recent experiments in the microwave region on Rydberg atoms interacting with thermal radiation in (low-Q) cavities offers the possibility of observing thermal-field effects on the photon counting statistics.

Squeezing in a Rydberg atom maser: effect of damping and thermal field

The 1/ N expansion of the quantum evolution of the N-Rydberg atom maser is extended to include losses and thermal field effects. Small values for squeezing and subpoissonian statistics for the field are obtained for experimentally realistic Q-values and temperatures.

Longitudinal vibrations of a circular cylinder coupled with a thermal field

In this paper the longitudinal vibration of a circular infinite cylinder in presence of a temperature field has been studied. The frequency equation has been obtained for two particular cases, namely constant temperature and zero heat flux on the surface of the cylinder. The resulting equations have been solved for small radii and weak coupling between fields. For the former case no first order thermal effect has been observed. In the latter, expressions have been found for the velocity of propagation and damping factor, which indicate the effect of thermal field on the elastic waves and which coincide, if the lateral contraction is neglected, with those found earlier by Sneddon for the very short and very long wave lengths.