• Geophysics and Geophysical Exploration
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• v.12 no.1
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• pp.121-131
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• 2009

In recent years, microtremor array observations have been used for estimation of shear-wave velocity structures. One of the methods is the conventional spatial autocorrelation (SPAC) method, which requires simultaneous recording at least with three or four sensors. Modified SPAC methods such as 2sSPAC, and linear array methods, allow estimating shear-wave structures by using only two sensors, but suffer from instability of the spatial autocorrelation coefficient for frequency ranges higher than 1.0 Hz. Based on microtremor measurements from four different size triangular arrays and four same-size triangular and linear arrays, we have demonstrated the stability of SPAC coefficient for the frequency range from 2 to 4 or 5 Hz. The phase velocities, obtained by fitting the SPAC coefficients to the Bessel function, are also consistent up to the frequency 5 Hz. All data were processed by the SPAC method, with the exception of the spatial averaging for the linear array cases. The arrays were deployed sequentially at different times, near a site having existing Parallel Seismic (PS) borehole logging data. We also used the imaginary part of the SPAC coefficients as a data-quality indicator. Based on perturbations of the autocorrelation spectrum (and in some cases on visual examination of the record waveforms) we divided data into so-called 'reliable' and 'unreliable' categories. We then calculated the imaginary part of the SPAC spectrum for 'reliable', 'unreliable', and complete (i.e. 'reliable' and 'unreliable' datasets combined) datasets for each array, and compared the results. In the case of insufficient azimuthal distribution of the stations (the linear array) the imaginary curve shows some instability and can therefore be regarded as an indicator of insufficient spatial averaging. However, in the case of low coherency of the wavefield the imaginary curve does not show any significant instability.

• Journal of the Korean Magnetics Society
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• v.16 no.1
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• pp.6-10
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• 2006

The sulphur spinel $FeCr_{2-x}M_xS_4$(M=Ga, In) have been studied with Mossbauer spectroscopy, x-ray diffraction (XRD), and vibrating sample magnetometer. The XRB patterns for samples $FeCr_{2-x}M_xS_4$(M=Ga, In: x=0.1, 0.3) reveal a single phase, which the Ga and In ions are partially occupied to the tetrahedral (A) site. The Neel temperature for the Ga substituted samples increases from 180 to 188 K, with increase from x=0.1 to 0.3. While, it decreases from 173 to 160 K, for the In substituted samples of the x=0.1 and 0.3, respectively. The Mossbauer spectra were collected from 4.2 K to room temperature. We have analyzed the Mossbauer spectra using eight Lorentzian lines fitting method for the $FeCr_{2-x}In_xS_4$(x=0.1) at 4.2 K, yielding the 1311owing results; $H_{hf}=146.0kOe,\;{\Delta}E_Q=1.88mm/s,\;\theta=36^{\circ},\;\phi=0^{\circ},\;\eta=0.6$, and R=1.9. The Ga ions enter into the both sites octahedral (B) and tetrahedral (A), simultaneously the same amounts of Fe ions migrate from the A to the B site, this result is an agreement with XRD results, too. The ${\Delta}E_Q$ of the A and B site in Mossbauer spectra of the samples $FeCr_{2-x}Ga_xS_4$(x=0.3) are 0.83 and 2.94mm/s, respectively. While they are 0.56 and 2.36mm/s for the $FeCr_{2-x}In_xS_4$(x=0.3). It is noticeable that the ${\Delta}E_Q$ for the Ga doped samples are larger than that of the corresponding In doped samples, in spite of the larger ionic radius for In ions. The bond lengths of Cr-S, for the Ga and In doped samples (x=0.3) are found to be 2.41 and $2.43\;{\AA}$, respectively. We interpret that the larger covalence effect from the smaller bond length induces a large asymmetric charge distribution. Finally, it gives a large quadrupole interaction.

• Journal of Korean Society of Environmental Engineers
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• v.32 no.2
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• pp.165-174
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• 2010

The numerical modeling of a coal gasification reaction occurring in an entrained flow coal gasifier is presented in this study. The purposes of this study are to develop a reliable evaluation method of coal gasifier not only for the basic design but also further system operation optimization using a CFD(Computational Fluid Dynamics) method. The coal gasification reaction consists of a series of reaction processes such as water evaporation, coal devolatilization, heterogeneous char reactions, and coal-off gaseous reaction in two-phase, turbulent and radiation participating media. Both numerical and experimental studies are made for the 1.0 ton/day entrained flow coal gasifier installed in the Korea Institute of Energy Research (KIER). The comprehensive computer program in this study is made basically using commercial CFD program by implementing several subroutines necessary for gasification process, which include Eddy-Breakup model together with the harmonic mean approach for turbulent reaction. Further Lagrangian approach in particle trajectory is adopted with the consideration of turbulent effect caused by the non-linearity of drag force, etc. The program developed is successfully evaluated against experimental data such as profiles of temperature and gaseous species concentration together with the cold gas efficiency. Further intensive investigation has been made in terms of the size distribution of pulverized coal particle, the slurry concentration, and the design parameters of gasifier. These parameters considered in this study are compared and evaluated each other through the calculated syngas production rate and cold gas efficiency, appearing to directly affect gasification performance. Considering the complexity of entrained coal gasification, even if the results of this study looks physically reasonable and consistent in parametric study, more efforts of elaborating modeling together with the systematic evaluation against experimental data are necessary for the development of an reliable design tool using CFD method.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.12
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• pp.715-732
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• 2009

This article reviews the papers published in the Korean Journal of Air-Conditioning and Refrigeration Engineering during 2008. It is intended to understand the status of current research in the areas of heating, cooling, ventilation, sanitation, and indoor environments of buildings and plant facilities. Conclusions are as follows. (1) Research trends in thermal and fluid engineering have been surveyed in the categories of general fluid flow, fluid machinery and piping, new and renewable energy, and fire. Well-developed CFD technologies were widely applied in developing facilities and their systems. New research topics include fire, fuel cell, and solar energy. Research was mainly focused on flow distribution and optimization in the fields of fluid machinery and piping. Topics related to the development of fans and compressors had been popular, but were no longer investigated widely. Research papers on micro heat exchangers using nanofluids and micro pumps were also not presented during this period. There were some studies on thermal reliability and performance in the fields of new and renewable energy. Numerical simulations of smoke ventilation and the spread of fire were the main topics in the field of fire. (2) Research works on heat transfer presented in 2008 have been reviewed in the categories of heat transfer characteristics, industrial heat exchangers, and ground heat exchangers. Research on heat transfer characteristics included thermal transport in cryogenic vessels, dish solar collectors, radiative thermal reflectors, variable conductance heat pipes, and flow condensation and evaporation of refrigerants. In the area of industrial heat exchangers, examined are research on micro-channel plate heat exchangers, liquid cooled cold plates, fin-tube heat exchangers, and frost behavior of heat exchanger fins. Measurements on ground thermal conductivity and on the thermal diffusion characteristics of ground heat exchangers were reported. (3) In the field of refrigeration, many studies were presented on simultaneous heating and cooling heat pump systems. Switching between various operation modes and optimizing the refrigerant charge were considered in this research. Studies of heat pump systems using unutilized energy sources such as sewage water and river water were reported. Evaporative cooling was studied both theoretically and experimentally as a potential alternative to the conventional methods. (4) Research papers on building facilities have been reviewed and divided into studies on heat and cold sources, air conditioning and air cleaning, ventilation, automatic control of heat sources with piping systems, and sound reduction in hydraulic turbine dynamo rooms. In particular, considered were efficient and effective uses of energy resulting in reduced environmental pollution and operating costs. (5) In the field of building environments, many studies focused on health and comfort. Ventilation. system performance was considered to be important in improving indoor air conditions. Due to high oil prices, various tests were planned to examine building energy consumption and to cut life cycle costs.

• The korean journal of orthodontics
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• v.27 no.4 s.63
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• pp.607-621
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• 1997

GRP was known as the modulator of Pain transmission in central nervous system and local effector to peripheral tissue causing vasodilation, increased blood flow, modulation of immune sysem, stimulation of endothelial cell proliferation, and stimulation of bone formation. Numerous study, therefore, were done to elucidate involvement of CGRP to tooth movement. To investgate the response of CGRP immunoreactive nerve cells according to cell size in trigeminal ganglion during tooth movement, immunohistochemical study was performed using rat. Experimental rats(9 weeks old, 210 gm) were divided as six groups(normal(n=6), 3 hour group(n=5), 12 hour group(n=4), 1 day group(n=5), 3 day group(n=5), 7 day group(n=5)), and were applied orthodontic force (approximately 30 gm) to upper right maxillary molar. After frozen sections of trigeminal ganglions were immunostained using rabbit antisera, the changes of CGRP immunoreactive cells in regard to cell size distribution(small cell(upto $20{\mu}m$), medium cell($20-35{\mu}m$), large cell(above $35{\mu}m$)) were observed. The results were as follows 1. The percentage of CGRP immunoreactive cells to all nerve cells in trigeminal ganglion was 33.0% in normal control group, was decreased to 24.5% in 1 day group, and was increased to 41.8% in 7 day group. 2. The percentage of small, medium, and large cells expressing CGRP immunoreactivity in normal trigeminal ganglion to all CGRP immunoreactive cells were 51.3%, 44.0%, 4.7%, respectively. 3. The percentage of small cells with CGRP immunoreactivity to all CGRP immunopositive cells was increased in 3 hour and 12 hour groups. 4. The percentage of medium cells with CGRP immunoreactivity was increaed in 3 day and 7 day groups. 5. The percentage of large cells with CGRP immunoreactivity was increaed in 7 day group. Conclusively, the small cells with CGRP immunoreactivity in trigeminal ganglion respond to orthodontic force during initial phase of tooth movement, and later the medium and large cells with CGRP immunoreactivity respond

• Advances in pediatric surgery
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• v.9 no.1
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• pp.45-51
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• 2003

A nationwide survey on choledochal cyst was undertaken among 39 members of the Korean Association of Pediatric Surgeons. The members were required to complete a questionnaire and the case registration form for each patient during the five year period of 1997 to 2001. Three hundred and forty eight patients were registered from 32 institutions. The average number of patients per surgeon was one to two every year. The male to female ratio was 1:3.4. The age of patients on diagnosis was $49.0{\pm}44.4$ months. The geographic distribution was 34.8% in Seoul and Kyoungki-do, 33.3% in Kyoungsang-do, 17.9% in Cholla-do, and 8.5% in Choongchung-do, in order of frequency. The three common clinical presentations were abdominal pain (63.8%), vomiting (35.3%), and jaundice (29.1%). Only seven patients (2%) presented with classic triad, and 25 patients were diagnosed by antenatal ultrasonographic examination. According to the Todani Classification, 238 patients (7l.3%) were type 1, 3 (0.9%) type 11, and 93 (27.8%) type IV. At the time of the operation, three important associated conditions were choledocholithiasis in 45 patients (15.1%), liver fibrosis (Grade 1-4) in 35, and previous operative procedure for biliary diseases in 10. Associated anomalies were observed in 13 patients (3.8%). Three hundred thirty nine (98.8%) of 343 lesions were treated by Cyst excision and Roux-Y hepaticoiejunostomy. One hundred seventy-six patients had an anomalous arrangement of the pancreatobiliary ductal system (APBD): APBD was not in 92 patients, biliary duct joined to the pancreatic duct in 51, and pancreatic duct joined to the biliary duct in 26. There were 8.5% early, and 7.7% late phase operative complications. The major complications were bleeding, anastomotic leakage, and acute pancreatitis. The combination of acute abdomen and choledochal cyst may suggest spontaneous rupture. Because of the development of late intrahepatic bile duct stones, long term follow up after cyst excision and hepaticojejunostomy is required. The optimal time of surgical intervention should also be considered in the situation of routine use of antenatal ultrasonographic examination. This is the first review of the choledochal cyst in Korea and provides baseline data for future comparisons.

• Tuberculosis and Respiratory Diseases
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• v.45 no.1
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• pp.169-175
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• 1998

Background: Heliox is known to decrease $PaCO_2$ in patients with increased airway resistance by increasing minute ventilation and reducing work of breathing(WOB). Besides these effect, heliox is expected to decrease functional anatomic dead space owing to improvement of peak expiratory flow rate(PEFR) and enhancement of gas distribution. We investigated whether heliox can decrease $PaCO_2$ even at the same minute ventilation (VE) and WOB with $N_2-O_2$ to speculate the effect of the heliox on the anatomic dead space. Material and Method: The subjects were 8 mechanically ventilated patients with asthma or upper airway obstruction(M : F=5 : 3, $68{\pm}10$years) who were under neuromuscular paralysis. The study was consisted of three 15-minutes phases: basal $N_2-O_2$ heliox and washout Heliox was administered via the low pressure inlet of servo 900C, and respiratory parameters were measured by pulmonary monitor(CP-100 pulmonary monitor, Bicore, Irvine, CA, USA). To obtain the same tidal volume(Vt) in heliox phase, the Vt on monitor was adjusted by the factor of relative flow rate of heliox to $N_2-O_2$. Dead space was calculated by Bohr equation. Results: 1) Vt, VE, peak inspiratory pressure(PIP) and peak inspiratory flow rate(PIFR) were not different between $N_2-O_2$ and heliox. 2) PEFR was higher on heliox($0.52{\pm}0.19$L/sec) than $N_2-O_2$($0.44{\pm}0.13$L/sec)(p=0.024). 3) $PaCO_2$(mmHg) were decreased with heliox($56.1{\pm}14.1$) compared to $N_2-O_2$($60.5{\pm}15.9$)(p=0.027). 4) Dead space ventilation(%) were decreased with heliox($73{\pm}9$ with $N_2-O_2$ and $71{\pm}10$ with heliox)(p=0.026). Conclusion: Heliox decreased $PaCO_2$ even at the same VE and WOB with $N_2-O_2$, and the effect was considered to be related with the reduction of anatomic dead space.

• Journal of Korean Society of Forest Science
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• v.89 no.3
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• pp.310-322
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• 2000

The objectives of this study were to classify the types of vegetation in Pinus densiflora for. erecta stands. The study sites were located at Sokwang-Ri, Mt. Chungok(1,276m), Uljin, Mt. Kumma(1,017m) and Mt. Eungbong(1,267m). Two hundred thirty releves were classified and explained by phytosociological analysis(the method of ZM schools), and the results were summarized as follows. Pinus densiflora for. erecta stands were classified into Vaccinium koreanum community, Rhododendron micranthum community, Quercus dentata community, Acer pseudosieboldianum community, and Typical community. Quercus dentata community was divided into Festuca ovina group, Robinia pseudoacacia group, and Typical group, and Acer pseudosieboldianum community was divided into Hydrangea serrata for. acuminata group, Disporum smilacinum group, Magnolia sieboldii group, Carpinus laxiflora group, and Typical group, and Typical community was divided into Melampyrum roseum group and Typical group. And some groups were divided into 7 subgroups. Therefore, Pinus densiflora for. erecta stands had total of 16 vegetation units, out of those units, Vaccinium koreanum community distributed all over the studied areas. While Rhododendron micranthum community distributed mainly at Sokwang-Ri and Mt. Chungok. Therefore it was considered to be useful indicator in determining the range of afforestation and natural distribution of Pius densiflora for. erecta stands. The classified vegetation units were investigated by using of coincidence method. The results indicated that Quercus dentata community distributed mainly below 100 meters at the sea level, while other communities distributed above 350 meters at the sea level. According to the correlations between vegetation units and topography, Vaccinium koreanum and Rhododendron micranthum communities distributed mainly above middle slope areas, Quercus dentata community distributed mainly from lower slope to upper slope areas, Acer pseudosieboldianum community distributed mainly between valley and lower slope areas, and Typical community distributed mainly above upper slope areas. According to the correlations between vegetation units and 5 study areas, Quercus dentata community was distributed in the region of Uljin, and other communities were evenly distributed over other studied areas. According to the correlations between the units and aspects, all communities occurred all aspects, but most of the communities tended to be more distributed at south slopes than at north slopes, which meant that the relic stands of Pinus densiflora for. erecta were remained largely as patch phase status at south slopes.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.25 no.6
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• pp.346-361
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• 2013

This article reviews the papers published in the Korean Journal of Air-Conditioning and Refrigeration Engineering during 2012. It is intended to understand the status of current research in the areas of heating, cooling, ventilation, sanitation, and indoor environments of buildings and plant facilities. The conclusions are as follows : (1) The research works on thermal and fluid engineering have been reviewed as groups of fluid machinery, pipes and valves, fuel cells and power plants, ground-coupled heat pumps, and general heat and mass transfer systems. Research issues are mainly focused on new and renewable energy systems, such as fuel cells, ocean thermal energy conversion power plants, and ground-coupled heat pump systems. (2) Research works on the heat transfer area have been reviewed in the categories of heat transfer characteristics, pool boiling and condensing heat transfer, and industrial heat exchangers. Researches on heat transfer characteristics included the results for natural convection in a square enclosure with two hot circular cylinders, non-uniform grooved tube considering tube expansion, single-tube annular baffle system, broadcasting LED light with ion wind generator, mechanical property and microstructure of SA213 P92 boiler pipe steel, and flat plate using multiple tripping wires. In the area of pool boiling and condensing heat transfer, researches on the design of a micro-channel heat exchanger for a heat pump, numerical simulation of a heat pump evaporator considering the pressure drop in the distributor and capillary tubes, critical heat flux on a thermoexcel-E enhanced surface, and the performance of a fin-and-tube condenser with non-uniform air distribution and different tube types were actively carried out. In the area of industrial heat exchangers, researches on a plate heat exchanger type dehumidifier, fin-tube heat exchanger, an electric circuit transient analogy model in a vertical closed loop ground heat exchanger, heat transfer characteristics of a double skin window for plant factory, a regenerative heat exchanger depending on its porous structure, and various types of plate heat exchangers were performed. (3) In the field of refrigeration, various studies were executed to improve refrigeration system performance, and to evaluate the applicability of alternative refrigerants and new components. Various topics were presented in the area of refrigeration cycle. Research issues mainly focused on the enhancement of the system performance. In the alternative refrigerant area, studies on CO2, R32/R152a mixture, and R1234yf were performed. Studies on the design and performance analysis of various compressors and evaporator were executed. (4) In building mechanical system research fields, twenty-nine studies were conducted to achieve effective design of mechanical systems, and also to maximize the energy efficiency of buildings. The topics of the studies included heating and cooling, HVAC system, ventilation, renewable energy systems, and lighting systems in buildings. New designs and performance tests using numerical methods and experiments provide useful information and key data, which can improve the energy efficiency of buildings. (5) In the fields of the architectural environment, studies for various purposes, such as indoor environment, building energy, and renewable energy were performed. In particular, building energy-related researches and renewable energy systems have been mainly studied, reflecting interests in global climate change, and efforts to reduce building energy consumption by government and architectural specialists. In addition, many researches have been conducted regarding indoor environments.

• Proceedings of the Membrane Society of Korea Conference
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• 1999.07a
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• pp.39-42
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• 1999

Perfluoropolymers represent the ultimate resistance to hostile chemical environments and high service temperature, attributed to the presence of fluorine in the polymer backbone, i.e. to the high bond energy of C-F and C-C bonds of fluorocarbons. Copolymers of Tetrafluoroethylene (TEE) and 2, 2, 4Trifluoro-5Trifluorometoxy- 1, 3Dioxole (TTD), commercially known as HYFLON AD, are amorphous perfluoropolymers with glass transition temperature (Tg)higher than room temperature, showing a thermal decomposition temperature exceeding 40$0^{\circ}C$. These polymer systems are highly soluble in fluorinated solvents, with low solution viscosities. This property allows the preparation of self-supported and composite membranes with desired membrane thickness. Symmetric and asymmetric perfluoropolymer membranes, made with HYFLON AD, have been prepared and evaluated. Porous and not porous symmetric membranes have been obtained by solvent evaporation with various processing conditions. Asymmetric membranes have been prepared by th wet phase inversion method. Measure of contact angle to distilled water have been carried out. Figure 1 compares experimental results with those of other commercial membranes. Contact angles of about 120$^{\circ}$for our amorphous perfluoropolymer membranes demonstrate that they posses a high hydrophobic character. Measure of contact angles to hexandecane have been also carried out to evaluate the organophobic character. Rsults are reported in Figure 2. The observed strong organophobicity leads to excellent fouling resistance and inertness. Porous membranes with pore size between 30 and 80 nanometers have shown no permeation to water at pressures as high as 10 bars. However high permeation to gases, such as O2, N2 and CO2, and no selectivities were observed. Considering the porous structure of the membrane, this behavior was expected. In consideration of the above properties, possible useful uses in th field of gas- liquid separations are envisaged for these membranes. A particularly promising application is in the field of membrane contactors, equipments in which membranes are used to improve mass transfer coefficients in respect to traditional extraction and absorption processes. Gas permeation properties have been evaluated for asymmetric membranes and composite symmetric ones. Experimental permselectivity values, obtained at different pressure differences, to various single gases are reported in Tab. 1, 2 and 3. Experimental data have been compared with literature data obtained with membranes made with different amorphous perfluoropolymer systems, such as copolymers of Perfluoro2, 2dimethyl dioxole (PDD) and Tetrafluorethylene, commercialized by the Du Pont Company with the trade name of Teflon AF. An interesting linear relationship between permeability and the glass transition temperature of the polymer constituting the membrane has been observed. Results are descussed in terms of polymer chain structure, which affects the presence of voids at molecular scale and their size distribution. Molecular Dyanmics studies are in progress in order to support the understanding of these results. A modified Theodoru- Suter method provided by the Amorphous Cell module of InsightII/Discover was used to determine the chain packing. A completely amorphous polymer box of about 3.5 nm was considered. Last but not least the use of amorphous perfluoropolymer membranes appears to be ideal when separation processes have to be performed in hostile environments, i.e. high temperatures and aggressive non-aqueous media, such as chemicals and solvents. In these cases Hyflon AD membranes can exploit the outstanding resistance of perfluoropolymers.