• Transactions on Electrical and Electronic Materials
• /
• v.7 no.4
• /
• pp.189-195
• /
• 2006

The microstructure, electrical and dielectric properties, and stability against DC accelerated aging stress of the varistors, which are composed of quaternary system $ZnO-Pr_6O_{11}CoO-Cr_2O_3-based$ ceramics, were investigated for different $La_2O_3$ contents. The increase of $La_2O_3$ content led to more densified ceramics, whereas abruptly decreased the nonlinear properties by incorporating beyond 1.0mol%. The highest nonlinearity was obtained from 0.5mol% $La_2O_3$, with the nonlinear coefficient of 81.6 and the leakage current of $0.1{\mu}A$. The varistors doped with 0.5mol% $La_2O_3$ exhibited high stability, in which the variation rates of breakdown voltage, nonlinear coefficient, leakage current, dielectric constant, and dissipation factor were -1.1%, -3.7%, +100%, +1.4%, and +8.2%, respectively, for stressing state of $0.95V_{1mA}/150^{\circ}C/24h$.

• Journal of Sensor Science and Technology
• /
• v.17 no.3
• /
• pp.203-209
• /
• 2008

Thick film formaldehyde (HCHO) gas sensors were fabricated by using $La_1_{-x}Sr_xMO_3$ (M= Fe, Co, Mn) ceramics. The powders of $La_1_{-x}Sr_xMO_3$ (M=Fe, Co, Mn) were synthesized by conventional solid-state reaction method. By using the $La_1_{-x}Sr_xMO_3$ (M=Fe, Co, Mn) paste, the thick-film formaldehyde sensors were prepared on the alumina substrate by silkscreen printing method. The experimental results revealed that $La_1_{-x}Sr_xMO_3$ (M= Fe, Co, Mn) ceramic powder has a perovskite structure and the thick-film sensor shows excellent gas-sensing characteristics to formaldehyde gas (sensitivity of $La_{0.8}Sr_{0.2}FeO_3$, S= 14.7 at operating temperature of $150^{\circ}C$ in 50 ppm HCHO ambient).

• Journal of Yeungnam Medical Science
• /
• v.10 no.1
• /
• pp.212-217
• /
• 1993

Since discovery of X-rays, radiotherapy has evolved into one of the most scientific branches of medicine and has established its role as the primary line or the secondary line of attack, after surgery, in the treatment of malignant cancers. Nowadays its importance is illustrated by the fact that as many as 70 per cent of all pastients with cancer will receive radiation therapy at sometime during their disease process. Biologic effects of X-rays began to be apparant soon after the discovery by Roentgen in 1895. In clinical radiotherapy, the biologic endpoint of most importance is loss of cellular reproductive ability or clonogenicity. One of the commonest ways to assess cell survival is to use an in vitro plating assay. We analyzed radiation effect on colony formation of HaLa.S3(SC) cell line and obtained results are as follows: The plating efficiency is 0.464. The shape of cell survival curve is similar to multi-target plus single hit component model. Estimated values of Do, Dq, and extrapolation number are 150 cGy, 80 cGy and 1.7 respectively. We reported these experimental data with review of literature.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2001.07a
• /
• pp.705-708
• /
• 2001

The effect of grinding on the synthesis of LaAO$_3$ceramics was investigated. The mixture ground by plantary ball mill showed 70nm particle size (wet ball mill or unground=0.5 $\mu$m). Monophase LaAlO$_3$powders were formed when ground samples were heated at 100$0^{\circ}C$, however unground samples required temperatures above 130$0^{\circ}C$. Density of the ground samples sintered at 140$0^{\circ}C$ showed 98.3% of theoretical density (unground=93.5% at 150$0^{\circ}C$). Dielectric constant of the ground samples($\varepsilon$r=22.4) showed higher values than that of the unground samples($\varepsilon$r=20.32). Temperature coefficient of capacitance($\tau$$_{c}$) and dielectric loss (tan$\delta$) of the ground samples were similar to those of unground samples.s.

• Korean Journal of Materials Research
• /
• v.16 no.7
• /
• pp.416-421
• /
• 2006

The varistor properties of ZPCCL-based ceramics were investigated at different $La_2O_3$ contents in the range of $0{\sim}2.0$ mol%. As $La_2O_3$ content increased, the ceramic density greatly increased in the range of $4.71{\sim}5.77\;g/cm^3$ and the varistor voltage greatly decreased in the range of $503.5{\sim}9.4$ V. The varistor with 0.5 mol% $La_2O_3$ exhibited good nonlinearity, in which the nonlinear exponent is 81.6 and the leakage current is 0.2 ${\mu}A$. Furthermore, the varistors exhibited the high electrical stability, with $%{\Delta}V_{1mA}=-1.1%,%{\Delta}{\alpha}=-3.7%$, and $%{\Delta}I_L=+100%$ for DC accelerated aging stress condition of 0.95 $V_{1mA}/150^{\circ}C/24$ h.

• Journal of Korean Society of Forest Science
• /
• v.90 no.1
• /
• pp.10-18
• /
• 2001

Experiments were conducted to compare ozone sensitivity among clones. Ten clones of Papulus deltoides Marsh. were exposured in walk-in type chambers to charcoal-filtered air, 50ppb, 100ppb, and 150ppb ozone for 8h $day^{-1}$ for 21 consecutive days. Occurrence of premature leaf-fall, and visible foliar injury expressed as adaxial stipple were measured after termination of ozone exposure for 3 weeks. Rate of premature leaf-fall increased progressively according to ozone exposure levels. As a result, rate of premature leaf-fall was estimated over 50% at 150ppb ozone. In the charcoal-filtered air and 50ppb ozone treatments, visible foliar injury was not found. But injury was estimated as LA; 17.3%, AA; 6.5%, and LAA; 1.6% to 100ppb ozone treatment and LA; 34.1%, AA; 17.5%, and LAA; 7.4% to 150ppb ozone treatment. Clonal differences of sensitivity within the species were manifested by significant clone differences of adaxial stipple(LAA) in 100ppb and 150ppb ozone treatments.

• Proceedings of the KIEE Conference
• /
• 1999.07d
• /
• pp.1753-1755
• /
• 1999

$LaCoO_3$ thick-film sensors were fabricated on alumina substrate by screen printing method. The sensitivity for gases was investigated by varying the heat treatment temperature of the films. X-Ray Diffractions and SEM photographs were used to examine their structural properties. The sensitivity of $LaCoO_3$ thick-film for CO gas was much better than for $C_4H_{10}$, $NH_3$ and NO gases. The best condition of heat treatment was $800^{\circ}C$ and the optimal operating temperature of $LaCoO_3$ thick-film for the highest sensitivity was $150^{\circ}C$. Sensitivities of the $LaCoO_3$ thick-film at 500ppm and l000ppm for CO gas were 72% and 95%, respectively.

• Korean Journal of Materials Research
• /
• v.19 no.9
• /
• pp.494-498
• /
• 2009

The thermoluminescent phosphors of LiYSi$O_4$ containing rare earth metal(La) dopants of 1 wt.%5 wt.% were prepared, and their TL characteristics have been investigated as a function of parameters such as the doping level and the heating rate. The grain size and cooling temperature of the highly sensitive LiYSi$O_4$: La phosphors have been investigated. The glow curve of LiYSi$O_4$: La has two peaks ($P_1,\;P_2$), and the peak height ratio of the two peaks is called $P_2/P_1$; here, the main peak is $P_2$. Experimental results indicate that the peak height ratios of the glow curve for LiYSi$O_4$: La are clearly correlated with the grain size and cooling temperature. The maximum $P_2/P_1$ ratio 3.25, the maximum sensitivity was observed for a grain size between 100-150 ${\mu}m$. The intensity of the TL peak of the phosphors was linearly proportion to the dose of X-rays.

• Journal of the Korean Ceramic Society
• /
• v.43 no.6 s.289
• /
• pp.383-388
• /
• 2006

The varistor properties and DC accelerated aging characteristics of $ZnO-Pr_{6}O_{11}-CoO-Cr_{2}O_{3}$-based varistors were investigated at different $La_{2}O_3$ contents in the range of $0{\sim}2.0mol%$. The varistors doped with 0.5 mol% $La_{2}O_3$ exhibited good nonlinearity, with 81.6 in nonlinear coefficient. Increasing the $La_{2}O_3$ content further to 2.0 mol% caused the sintered density to increase, and the breakdown voltage and nonlinearity to decrease abruptly. The varistors with 0.5 mol% $La_{2}O_3$ exhibited the high electrical stability, with -1.14% in variation rate of breakdown voltage, -3.7% in variation rate of nonlinear coefficient, and +100% in variation rate of leakage current for specified DC accelerated aging stress condition (95% of breakdown voltage/$150^{\circ}C$/24 h).

• Advances in nano research
• /
• v.3 no.2
• /
• pp.55-66
• /
• 2015

Crystalline $Ce^{3+}$ co-doped $LaPO_4$:RE ($RE=Dy^{3+}$, $Tb^{3+}$, $Eu^{3+}$, $Sm^{3+}$) and mix doped rare earth ions of $Dy^{3+}$, $Tb^{3+}$ and $Eu^{3+}$ were prepared by the polyol method at $150^{\circ}C$. Strongly enhance luminescence intensity is obtained with the co-doping of $Ce^{3+}$ with $LaPO_4$:$Dy^{3+}$ and $LaPO_4$:$Tb^{3+}$ due to charge transfer (CT) occurring from $Ce^{3+}$ to $Dy^{3+}$ and $Ce^{3+}$ to $Tb^{3+}$, where as there is no significant changes in luminescence intensity of $Ce^{3+}$ co-doped $Eu^{3+}$ and $Sm^{3+}$ doped $LaPO_4$ samples. The luminescence color can be tuned from green to white by varying the excitation wavelength for the mix ions $Ce^{3+}$, $Dy^{3+}$, $Tb^{3+}$ and $Eu^{3+}$ doped with $LaPO_4$.