• Transactions of the Korean Society of Automotive Engineers
• /
• v.12 no.3
• /
• pp.192-203
• /
• 2004

The AA5182/polypropylene/AA5182 (AA/PP/AA) sandwich sheets have been developed for the application for automotive body panels in the future light weight vehicles with significant weight reduction. It has been reported that the 5182 aluminum sheet shows Luders band because of dissolved Mg atoms that causes fabrication process problem, especially surface roughness. The examination of serration behavior has been made after the tensile deformation of the AA/PP/AA sandwich sheets as well as that of the 5182 aluminum skin at room and elevated temperatures. All sandwich sheets and the 5182 aluminum skin showed serration phenomena on their flow curves. However, the magnitude of the serration was significantly diminished in the sandwich sheet with the high volume fraction of the polypropylene core. According to the results of the surface roughness analysis after the tensile test, the sandwich sheet evidently showed lower Luders band depth than the 5182 aluminum skin. Strain rate sensitivity, m-value, of the 5182 aluminum skin was -0.006. By attaching this skin with polypropylene core which has relatively large positive value, 0.050, m-value of the sandwich sheets was changed to the positive value. The serration reduction of the sandwich sheets was quantitatively investigated in the point of the effect on the polypropylene core thickness variation, that on the strain rate sensitivity. It was found that the serration reduction degree from the experimental results of the sandwich sheet was higher than that from the calculated values by the rule of mixture based on volume fraction of the skins and the core.

• Proceedings of the KWS Conference
• /
• 2004.05a
• /
• pp.234-236
• /
• 2004

The purpose of this study is to establish the predictive equation of welding distortion at the thick AA5083 alloy weldment. In order to do it, the extensive FE analysis was peformed to identify the principal factor controlling welding distortion. Based on the results, the predictive equations of transverse shrinkage and angular distortion at the thick AA5083 alloy weldment were formulated as the function of heat intensity (Q), in-plane(Di) and bending(Db) rigidity.

• Journal of the Korean Magnetics Society
• /
• v.5 no.3
• /
• pp.203-209
• /
• 1995

A study of the dependence of the magnetoresistance in $glass\[Cu_{x\AA}\NiFe_{50\AA}\Cu_{x\AA}\Co_{50\AA}](X;\=\;8,\;10,\;14,\;18,\;22,\;26,\;28,\;38,\;48,\;58\;\AA,\;N\;=\;2,\;3,\;4,\;10,\;20)$ multilayers prepared by dc magnetron sputtering on the interlayer thickness of Cu (X), the number of multylayer(N) and annealing temperature has been performed. Resistance measurement were made by four terminal method, and the magnetic field applied to perpendicular and parallel for the current. The maximum magnetoresistance(MR) ratio(%) was appeared in the vicinity of $10\;\AA$ in Cu layer, and it was oscillated with the thickness of Cu. The MR ratio was increased with the number of layers N, however the ratio for the N = 4 layers decreased rather than the N = 3 layers. The dependence of the ratio on the annealing temperature was increased to $250^{\circ}C$.

• Journal of the Korean Magnetics Society
• /
• v.9 no.6
• /
• pp.301-305
• /
• 1999

NiFe(60$\AA$)/Co(5$\AA$)/Cu(60$\AA$)/Co(30$\AA$) spin valve thin films were patterned into magnetoresistive random access memory (MRAM) cells by a conventional optical lithography process and their output and switching properties were characterized with respect to the cell size and geometry. When 1 mA of constant sense current was applied to the cells, a few or a few tens of mV of output voltage was measured within about 30 Oe of external magnetic field, which is an adequate output property for the commercializing of competitive MRAM devices. In order to resolve the problem of increase in the switching thresholds of magnetic layers with the downsizing of MRAM cells, a new approach using the controlled shape anisotropy was suggested and interpreted by a simple calculation of anisotropy energies of magnetic layers consisting of the cells. This concept gave a reduced switching threshold in NiFe(60$\AA$)/Co(5$\AA$) layer consisting of the patterned cells from about 15 Oe to 5 Oe and it was thought that this concept would be much helpful for the realization of competitive MRAM devices.

• Journal of The Korean Astronomical Society
• /
• v.8 no.1
• /
• pp.11-14
• /
• 1975

Photoelectric observations were made of four N stars (HD 51208, HD 75021, V 1942 Sgr, and RU Vir) at careful1y chosen discrete wavelengths between $7000{\AA}\;and\;11000{\AA}$ with $30{\AA}$ bandpass width. Their effective temperatures have been derived by fitting the black-body radiation curve to the observed continuum intensities at $7800{\AA},\;9000{\AA}\;and\;10800{\AA}$. The resulting temperature ranges from $2500^{\circ}K\;to\;2900^{\circ}K.$. It is probable that almost all the N stars belong to this range of temperature. However, the temperatures of very red N stars can not be well determined due to large variability and redistribution of their radiation energy arising from the graphite shells around them.

• Carbon letters
• /
• v.5 no.2
• /
• pp.51-54
• /
• 2004

Isotropic pitch-based carbon fiber was isothermally activated in $CO_2$ atmosphere. Structural parameters of the isotropic carbon fibers and activated carbon fibers (ACFs) were evaluated by X-ray diffraction (XRD). The $d_{002}$ and La of the carbon fibers were measured to be 4.04 ${\AA}$ and 23.6 ${\AA}$ and those of ACFs were 4.29 ${\AA}$ and 22.7 ${\AA}$, respectively, representing less ordered through activation process. The pores in the ACFs were characterized by BET, and they showed super-high specific surface area of maximum value 3,495 $m^2/g$ from average pore size of 8.3 ${\AA}$ at 59% burn-off. It was recognized that 8-9 ${\AA}$ was optimum range of pore size for efficient creation of high specific surface area. The average size of the pores formed at higher temperature ($1100^{\circ}C$) was larger than that of the pores formed at lower temperature ($900^{\circ}C$).

• Bulletin of the Korean Space Science Society
• /
• 2008.10a
• /
• pp.24.2-24.2
• /
• 2008

We have examined the relative contributions of representative space weather proxies (geomagnetic aa index) to global warming (Global temperature anomaly) and compared them with that of green house effect characterized CO2 content from 1868 to 2005. For this we used Hadcrut3 temperature anomaly (Ta) data, aa index taken at two anti-podal subauroral stations (Canberra Australia and hartland England), and the CO2 data come from historical ice core records. From the comparison between Ta and aa index, we found several interesting results: (1) the linear correlation coefficient between two parameters increases until 1990 and then decreases rapidly, and (2) the scattered plots between two parameters shows different patterns before and after 1990. A partial correlation of Ta and two quantities (aa, CO2) also shows that the geomagnetic effect (aa index) is dominant until about 1990 and the CO2 effect becomes much more important after then. These results imply that the green house effect become very important since at least 1990. For a further analysis, we simply assume that Ta (total) = Ta (aa) + Ta (CO2) and made a linear regression between Ta and aa index from 1868 to 1990. A linear model is then made from the linear regression between energy consumption (a proxy of CO2 effect) and Ta (total) - Ta (aa) since 1990. This linear model makes it possible to predict the temperature anomaly in 2030, about 1 degree higher than the present temperature, which is much larger than in the previous century.

• Preventive Nutrition and Food Science
• /
• v.4 no.3
• /
• pp.203-208
• /
• 1999

The effect of the polyunsaterated fatty acids, linoleic acid(LA), arachidonic acid(AA) and conjugated dienoic linoleic acid(CLA) on IEC-6 cells (rat intestinal cell)proliferation and cell transduction have been determined in vitro. IEC-6 cells proliferation was assessed by cell growth and [3H]-thymidine incroporation analysis. At 10 μM concentration , the proliferationof cells supplemented with AA or LA was significantly higher than that of CLA. [3H]-thymidine uptake showed the same results. LA and AA increased [3H]-thymidine uptake more than CLA. The stimulatory effect of LA or AA was even more pronounced in the presence of IGF. Both cell number analysis and [3H]-thymidine incorporation revealed that IEC-6 cell proliferation was influenced differently by exogenous free fatty acids, in which AA or LA stimulated IEC-6 cell proliferation and CLA inhibited it. Tyorosine phosphorylation provides a key switch to regulate celluar acitivity in response to extracellular stimuli. At 20 μM and 10μM, AA with IGF-1 stimulated protein tyrosine phophorylation in IEC-6 cells, but LA's impact was less than that of AA. CLA and CLA with IGF-1 inhibited protein tyrosine phosphorylation in IEC-6 cells. These results suggest there is a possible correlation between cell proliferation and IGF receptor tyrosine knase activity driven by AA.

• Korean Journal of Materials Research
• /
• v.13 no.11
• /
• pp.742-748
• /
• 2003

The structural parameters such as Lc, La and d of $CO_2$activated isotropic carbon fibers(ACFs) were obtained from XRD in order to understand a development mechanism of micropores. And the structural parameters were compared with specific surface area(SSA) data. The $d_{002}$, Lc, and La of the original fiber were measured to be 4.04$\AA$, 6.2$\AA$, and 23.6$\AA$, respectively. Carbonization of outer-parts and oxidization of inner-parts of the original fibers were far from completeness. It was observed that the structural changes of the ACFs during activation take place severely, therefore the carbonization and the oxidization of the fibers take place simultaneous with pore developments. The $d_{002}$ of the ACFs was increased to be 2.80$\AA$, and the La of the ACFs was decreased to be 17.0$\AA$ by activation. It was shown that the pores are developed continuously from the outer-parts to the inner-parts of the fibers, therefore the SSA increases as a result of the development of pores fully to the inner-parts of the fiber when the burn-off degree was over :39%. It seems that the (002) planes of crystallites contribute to the micropore wall related to the super high SSA.SSA.

• Steel and Composite Structures
• /
• v.28 no.6
• /
• pp.759-766
• /
• 2018

Friction Stir Welding (FSW) is a solid-state process, where the objects are joined together without reaching their melting point. It has been shown that this method is a suitable way to join dissimilar aluminium alloys. The current article employed hole drilling technique to measure the residual stress distribution experimentally in different zones of dissimilar aluminium alloys AA6061-T6 and AA7075-T6 Butt welded using FSW. Results are compared with those of similar AA6061-T6 plates joined using a conventional fusion welding method called tungsten inert gas (TIG). Also, the evolution of the residual stresses in the thickness direction was investigated, and it was found that the maximum residual stresses are below the yield strength of the material in the shoulder region. It was also revealed that the longitudinal residual stresses in the joint were much larger than the transverse residual stresses. Meanwhile, Vickers micro hardness measurements were performed in the cross-section of the samples. The largest hardness values were observed in the stir zone (SZ) adjacent to the advancing side whereas low hardness values were measured at the HAZ of both alloys and the SZ adjacent to the retreating side.