• Korean Journal of Materials Research
• /
• v.25 no.12
• /
• pp.678-682
• /
• 2015

The electrical property of polymer matrix composites with added carbon powder is studied based on the temperature dependency of the conduction mechanism. The temperature coefficient of the resistance of the polymer matrix composites below the percolation threshold (x) changed from negative to positive at 0.20 < x < 0.21; this trend decreased with increasing of the percolation threshold. The temperature dependence of the electrical property(resistivity) of the polymer matrix composites below the percolation threshold can be explained by using a tunneling conduction model that incorporates the effect of the thermal expansion of the polymer matrix composites into the tunneling gap. The temperature coefficient of the resistance of the polymer matrix composites above the percolation threshold has a positive value; its absolute value increased with increasing volume fraction of carbon powder. By assuming that the electrical conduction through the percolating paths is a thermally activated process and by incorporating the effect of thermal expansion into the volume fraction of the carbon power, the temperature dependency of the resistivity above the percolation threshold can be well explained without violating the universal law of conductivity.

• Korean Journal of Materials Research
• /
• v.19 no.12
• /
• pp.644-648
• /
• 2009

Temperature dependency of resistivity of the carbon black-polyethylene composites below and above percolation threshold is studied based on the electrical conduction mechanism. Temperature coefficient of resistance of the composites below percolation threshold changed from minus to plus, increasing volume fraction of carbon black; this trend decreased with increasing volume fraction of carbon black. The temperature dependence of resistivity of the composites below percolation threshold can be explained with a tunneling conduction model by incorporating the effect of thermal expansion of the composites into a tunneling gap. Temperature coefficient of resistance of the composites above percolation threshold was positive and its absolute value increased with increasing volume fraction of carbon black. By assuming that the electrical conduction through percolating paths is a thermally activated process and by incorporating the effect of thermal expansion into the volume fraction of carbon black, the temperature dependency of the resistivity above percolation threshold has been well explained without violating the universal law of conductivity. The apparent activation energy is estimated to be 0.14 eV.

• Journal of Korean Physical Therapy Science
• /
• v.2 no.2
• /
• pp.465-479
• /
• 1995

We randomly assigned 61 healthy subjects(male 14, female 47) to compare the experimental pain threshold and skin temperature between high mode TENS and burst mode TENS. In this study, 61 subjects were divided into three groups ; high mode TENS(n=20), burst mode TENS (n=20), and control group(n=21). Experimental pain thresholds and skin temperatures were measured before, immediately after cessation of stimulation, and at 30 minutes post stimulation. Stimulation was applied to the dorsal surface of the forearm(L14, LI10). Pain thresholds were measured by chronaxie meter. Skin temperature were measured by electrical digital thermometer. The results are as follows ; 1. There were no statistical difference in the pain threshold and skin temperature at before TENS stimulation among the three groups(p>0.05). 2. The pain threshold and skin temperature in burst mode TENS group was significantly higher and longer effect than that in high mode TENS group and control group(p<0.01). 3. The pain threshold in burst mode TENS group decreased to prestimulation levels by 30 minutes poststimulation. 4. The skin temperature in burst mode TENS group decreased to prestimulation levels by 20 minutes poststimulation. 5. The skin temperature was significantly difference among three group at immediately after, and at 30 minutes poststimulation and the skin temperature in burst mode TENS group was significantely higher than that in two groups(p<0.001). 6. The increasing rate of pain threshold in high mode TENS group after immediately cassation of stimulation was 24.3%(p<0.001). 7. The increasing rate of pain threshold in burst mode TENS group after immediately cessation of stimulation was 93.5% (p<0.001).

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.15 no.7
• /
• pp.559-563
• /
• 2002

A threshold voltage model of SiC N-channel MOSFETs for high-temperature and hard radiation environments has been developed and verified by comparing with experimental results. The proposed model includes the difference in the work functions, the surface potential, depletion charges and SiC/$SiO_2$acceptor-like interface state charges as a function of temperature. Simulations of the model shoved that interface slates were the most dominant factor for the threshold voltage decrease as the temperature increase. To verify the model, SiC N-chnnel MOSFETS were fabricated and threshold voltages as a function of temperature were measured and compared wish model simulations. From these comparisons, extracted density of interface slates was $4{\times}10^{12}\textrm{cm}^{-2}eV^{-1}$.

• Proceedings of the Korean Nuclear Society Conference
• /
• 1998.05b
• /
• pp.279-284
• /
• 1998

Applicability of the threshold burnup for rim formation was investigated as a function of temperature by Rest's model. The threshold burnup was the lowest in the intermediate temperature region, while on the other temperature regions the threshold burnup is higher. The rim porosity was predicted by the van der Waals equation based of the rim pore radius of 0.75${\mu}{\textrm}{m}$ and the overpressurization model on rim pores. The calculated centerline temperature is in good agreement with the measured temperature. However, more efforts seem to be necessary for the mechanistic model of the rim effect including rim growth with the fuel burnup.

• Laser Solutions
• /
• v.11 no.4
• /
• pp.13-20
• /
• 2008

The damage threshold measurement of gold films is carried out with ultrashort-pulse laser. An enhanced two temperature model is developed to encounter the limitation of linear modeling during ultrashort pulse laser ablation. In which the electron heat capacity is calculated using a quantum mechanical approach based on a Fermi-Dirac distribution, temperature-dependent electron thermal conductivity valid beyond the Fermi temperature is adopted, and reflectivity and absorption coefficient are estimated by applying a temperature-dependent electron relaxation time. The predicted damage threshold using the proposed enhanced modelclosely agreed with experimental results, demonstrating the importance of considering transient thermal and optical properties in the modeling of ultrashort pulse laser ablation.

• The Transactions of the Korean Institute of Electrical Engineers A
• /
• v.50 no.9
• /
• pp.399-399
• /
• 2001

This paper proposes TAR(Threshold Autoregressive) model for short-term load forecasting including temperature variable. In the scatter diagram of daily peak load versus daily high or low temperature, we can find out that the load-temperature relationship has a negative slope in the lower regime and a positive slope in the upper regime due to the heating and cooling load, respectively. TAR model is adequate for analyzing these phenomena since TAR model is a piecewise linear autoregressive model. In this paper, we estimated and forecasted one day-ahead daily peak load by applying TAR model using this load-temperature characteristic in these regimes. The results are compared with those of linear and quadratic regression models.

• The Transactions of the Korean Institute of Electrical Engineers A
• /
• v.50 no.9
• /
• pp.309-405
• /
• 2001

This paper proposes TAR(Threshold Autoregressive) model for short-term load forecasting including temperature variable. In the scatter diagram of daily peak load versus daily high or low temperature, we can find out that the load-temperature relationship has a negative slope in the lower regime and a positive slope in the upper regime due to the heating and cooling load, respectively. TAR model is adequate for analyzing these phenomena since TAR model is a piecewise linear autoregressive model. In this paper, we estimated and forecasted one day-ahead daily peak load by applying TAR model using this load-temperature characteristic in these regimes. The results are compared with those of linear and quadratic regression models.

• The Korean Journal of Pain
• /
• v.21 no.2
• /
• pp.126-130
• /
• 2008

Background: Females generally have a lower pain and temporal summation threshold than men. However, the results of studies designed to evaluate gender differences in the thresholds of heat pain and the temporal summation have been inconsistent. Newly developed device, CHEPS (Contact Heat Evoked Potential Stimulation) model of PATHWAY, have superiority on its fast rise and return time in temperature. Therefore we investigated gender differences in heat pain and temporal summation threshold. Methods: Forty healthy volunteers (20 males and 20 females) were enrolled in this study. A thermode was applied to the volar side of each volunteer's left forearm and heat pain and the temporal summation threshold was then measured. The heat pain threshold was estimated using the staircase method by starting from $36^{\circ}C$ and then increasing the temperature in $0.5^{\circ}C$ increments. The temporal summation threshold was estimated by applying five successive stimulation of the same temperature starting at $2^{\circ}C$ lower than the heat pain threshold and then increasing the temperature in $0.5^{\circ}C$ increments. Results: The mean heat pain thresholds was found to be $41.63{\pm}1.63^{\circ}C$ for males and $41.60{\pm}1.84^{\circ}C$ for females and the temporal summation thresholds were found to be $40.83{\pm}1.64^{\circ}C$ for males and $40.77{\pm}1.93^{\circ}C$ for females. The differences between males and females were not statistically significant. Conclusions: The result of this study suggested that there are no gender differences in heat pain and temporal summation threshold.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2000.04a
• /
• pp.187-191
• /
• 2000

High temperature creep behaviour of Al-5 wt% Mg alloy reinforced with 7.5% BN flakes was studied. The composite specimens showed two main creep characteristics : (1) the value of the apparent stress exponent of the composite was high and varied with applied stress (2) the apparent activation energy for creep was much larger than that for self-diffusion in aluminum The true stress exponent of the composite was set equal to 5. Temperature dependence of the threshold stress of the composite was very strong. Which could not be rationalized by allowing for the temperature dependence of the elastic modulus change. AIN particles which were incorporated into the Al matrix during fabrication of the composite by the PRIMEXTM method were found to be effective barriers to dislocation motion and to give rise the threshold stress during creep of the composite