• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2002.07a
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• pp.25-37
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• 2002

The most important industrial application of gamma radiation in characterizing green compacts is the determination of the density. Examples are given where this method is applied in manufacturing technical components in powder metallurgy. The requirements imposed by modern quality management systems and operation by the workforce in industrial production are described. The accuracy of measurement achieved with this method is demonstrated and a comparison is given with other test methods to measure the density. The advantages and limitations of gamma ray densitometry are outlined. The gamma ray densitometer measures the attenuation of gamma radiation penetrating the test parts (Fig. 1). As the capability of compacts to absorb this type of radiation depends on their density, the attenuation of gamma radiation can serve as a measure of the density. The volume of the part being tested is defined by the size of the aperture screeniing out the radiation. It is a channel with the cross section of the aperture whose length is the height of the test part. The intensity of the radiation identified by the detector is the quantity used to determine the material density. Gamma ray densitometry can equally be performed on green compacts as well as on sintered components. Neither special preparation of test parts nor skilled personnel is required to perform the measurement; neither liquids nor other harmful substances are involved. When parts are exhibiting local density variations, which is normally the case in powder compaction, sectional densities can be determined in different parts of the sample without cutting it into pieces. The test is non-destructive, i.e. the parts can still be used after the measurement and do not have to be scrapped. The measurement is controlled by a special PC based software. All results are available for further processing by in-house quality documentation and supervision of measurements. Tool setting for multi-level components can be much improved by using this test method. When a densitometer is installed on the press shop floor, it can be operated by the tool setter himself. Then he can return to the press and immediately implement the corrections. Transfer of sample parts to the lab for density testing can be eliminated and results for the correction of tool settings are more readily available. This helps to reduce the time required for tool setting and clearly improves the productivity of powder presses. The range of materials where this method can be successfully applied covers almost the entire periodic system of the elements. It reaches from the light elements such as graphite via light metals (AI, Mg, Li, Ti) and their alloys, ceramics ($AI_20_3$, SiC, Si_3N_4, $Zr0_2$, ...), magnetic materials (hard and soft ferrites, AlNiCo, Nd-Fe-B, ...), metals including iron and alloy steels, Cu, Ni and Co based alloys to refractory and heavy metals (W, Mo, ...) as well as hardmetals. The gamma radiation required for the measurement is generated by radioactive sources which are produced by nuclear technology. These nuclear materials are safely encapsulated in stainless steel capsules so that no radioactive material can escape from the protective shielding container. The gamma ray densitometer is subject to the strict regulations for the use of radioactive materials. The radiation shield is so effective that there is no elevation of the natural radiation level outside the instrument. Personal dosimetry by the operating personnel is not required. Even in case of malfunction, loss of power and incorrect operation, the escape of gamma radiation from the instrument is positively prevented.

• Journal of Preventive Medicine and Public Health
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• v.20 no.1 s.21
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• pp.97-113
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• 1987

This study was carried out to know physical growth and development, physical and nutritional indices and body fat weight and so forth by semi-longitudinal research method to measure body height, body weight, chest girth and sitting height of 260 of general high school and 306 of vocational high school 3rd grade students who are living in Seoul and born from 1966 March 1st to 1967 Feb.28th. The results are as follows: 1) Physical growth and development Growth in terms of body height showed one step straight linear development, andthat of body weight showed two step straight linear development in each section in high school. The age of cross over between two sexes of general high school students was between 10.6 to 12. 3 years in body height, between 10.8 to 13 years in body weight, between 11.2 to 14.6 years in chest girth and between 10 to 13 years in sitting height. The age of cross over between two sexes of vocational high school students was between 10.5 to 12.5 years in body height, between 10.5 to 12.5 years in body weight, between 10.5 to 12.5 years in chest girth and between 10.5 to 12.5 years in sitting height. In this periods, female group was superior to male group and after that male group was superior to female group again. The growth of vocational school students was superior to that of general school students in both sexes in terms of body height and body weight significantly. 2) Physical growth and nutritional indices In all cases of relative body weight, relative chest girth and relative sitting height, it was found to be increasing thereafter with advancing ages. In cases of $R{\"{o}}hrer$ index and Kaup index, it was found to be reaching to normal state thereafter with advancing ages. In each case of Vervaeck and Pelidisi index, it was found to be increasing and reaching to normal state thereafter with advancing ages. 3) Total body fat by vital measuring method Average values of body surface area, body volume and body density are measured indirectly by using the body height and body weight as Table 12, 13 and 14. The rate of body fat weight of general high school students was from minimum $11.96{\pm}3.53%(3.33{\pm}1.10kg$) to maximum $18.25{\pm}6.46%(9.08{\pm}2.01kg$) in male and from $25.88{\pm}3.62%(7.96{\pm}0.78kg$) to $43.00{\pm}7.22%(12.91{\pm}1.21kg$) in female. The rate of body fat weight of vocational high school students was from minimum $11.20{\pm}2.88%(3.32{\pm}1.13kg$) to maximum $17.16{\pm}5.88(10.83{\pm}3.16kg$) in male and from minimum $25.11{\pm}2.26%(7.91{\pm}0.89kg$) to maximum $42.16{\pm}7.96%(13.22{\pm}1.75kg$) in female.

• Nuclear Engineering and Technology
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• v.3 no.3
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• pp.148-154
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• 1971

Some formulae have been derived for the handy calculation of the formation of radioisotope when a reactor is operated regularly on a usual on-off pattern. In particular, the case of isotope production with the present operation condition of tile Korean reactor, which is in operation for 8.2 hours from Monday to Thursday and is not operated on friday and Sunday but is back in operation on Saturday only for 3.2 hours, is discussed herein with special emphasis. Should there be no secondary nuclear reaction resulting in the transformation of produced nuclide, the formula for the calculation of its activity could be derived as follows: (equation omitted) where A: activity (dps), $\Phi$： neutron flux (n cm$^{-2}$ sec$^{-1}$ ), No : number of atoms before the irradiation, $\sigma$ : activation cross section ($\textrm{cm}^2$), λ : disintegration constant of the radioactiveisotope formed (hr$^{-1}$ ), t : elapsed time of target in the reactor (hr), n : number of elasped days of target in the reactor, m : number of days from the first day of sample irradiation to Friday, s, r, q: number of weekday of Friday, Saturday and Sunday, respectively. Since the above formula consists of many invariables on the whole, the activity of each radioisotope to be produced can he easily and conveniently made available from the chart in advance which is made of the invariable terms calculated.

• Journal of the Korean Society of Safety
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• v.23 no.2
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• pp.87-97
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• 2008

The Ilsun Bridge is the world's longest box girder bridge(801m) with corrugated steel webs and has the widest width($21.2{\sim}30.9m$: tri-cellular cross section) among these kinds of composite girder bridges. It has fourteen spans(50m, 10 at 60m, 50m, 2 at 50.5m) where twelve spans are erected by the incremental launching method and two spans by full staging method. Special topics related to the structural safety of prestressed concrete box girder bridge with corrugated steel web in construction stage and service were reviewed. Investigations focus on the span-to-depth ratio, shear stress of corrugated steel webs and optimization of tile length of steel launching nose. The span-to-depth ratio of Ilsun bridge has been found to be well-planned while the corrugated steel web has been designed highly conservative and it has been observed that the conventional nose-deck interaction equation do not fit well with corrugated steel web bridges. As a result, detailed construction stage analysis was performed to check the stress levels and the safety of preceding design conditions. Finally, from the design review of Ilsun bridge, this study suggests optimal design issues which should be of interest in designing a prestressed concrete box girder bridge with corrugated steel webs.

• Proceedings of the Korean Geotechical Society Conference
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• 2001.03a
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• pp.167-174
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• 2001

Reflection method using ultrasonic source has been attempted to obtain the information about tunnel lining structures composed of lining, shotcrete, water barrier and voids at the back of lining. In this work, two different types of sources, i.e. single-pulse source and sweep source, can be used. Single-pulse source with short time duration has the frequency content whose amplitudes tend to be concentrated around the dominant frequency, whereas sweep source with long time duration denotes a flat distribution of relatively larger amplitude over a broad frequency band, although the peak to peak amplitude of single-pulse source wavelet is equivalent to that of sweep source one. In traditional seismic application, a single-pulse source(weight drop, dynamite) is typically used. However, to investigate the fine structure, as it is the case in the tunnel lining structure, the sweep wavelet can be also a desirable source waveform primarily due to the higher energy over a broad frequency band. For the investigation purposes of sweep source, a physical modeling is a useful tool, especially to study problems of wave propagation in the fine layered media. The main purpose of this work was using a physical modeling technique to explore the applicability of sweep source to the delineation of inner layer boundaries. To this end, a two-dimensional physical model analogous to the lining structure was built and a special ultrasonic sweep source was devised. The measurements were carried out in the sweep frequency range 10 ∼ 60 KHz, as peformed in the regular reflection survey(e.g. roll-along technique). The measured data were further rearranged with a proper software (cross-correlation). The resulting seismograms(raw data) showed quitely similar features to those from a single-pulse source, in which high frequency content of reflection events could be considerably emphasized, as expected. The data were further processed by using a regular data processing system "FOCUS" and the results(stack section) were well associated with the known model structure. In this context, it is worthy to note that in view of measuring condition the sweep source would be applied to benefit the penetration of high frequency energy into the media and to enhance the resolution of reflection events.

• Membrane Journal
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• v.18 no.1
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• pp.84-93
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• 2008

Poly(vinylidene fluoride) has received much attention in the last several years for the lithium secondary batteries. In this study, to enhance the porosity, PVdF was prepared by phase inversion method using as an additive, PEG (poly(ethylene glycol)), with N,N-dimethylformamid as a solvent. The pores are generated during the solvent and non-solvent exchange process in the coagulation bath filled with non-solvent (distilled water). The surface and cross-section of the membranes were observed with a scanning electron microscopy (SEM). The mechanical property of the membrane was determined by using an universal testing machine (UTM) and thermal property was verified by heat shrinkage. Uniformed sponge structure of PVdF-PEG membrane for the lithium secondary batteries was prepared with 10 wt% of PEG concentration in the PVdF-PEG solution. Porosity, elongation and tensile strengh of the membrane were 87%, 75.45%, and 275. 27 MPa respectively.

• Journal of Korean Society of Steel Construction
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• v.26 no.1
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• pp.55-68
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• 2014

In this study, the beam-to column connections of concrete-encased-and-filled steel tube columns were tested under cyclic loading. Two specimens using steel beams and two specimens using precast concrete beams were tested. The dimension of the column cross section was $670mm{\pm}670mm$. The beam depths were 488mm and 588mm for the steel beams and 700mm for the precast concrete beams. The longitudinal bar ratios of the precast concrete beams were 1.1% and 1.5%. For the connections to the steel beams, continuity plates were used in the tube columns. For the connections to the PC beams, couplers were used for beam re-bar connections. The test results showed that except for a specimen, deformation capacities of the specimens were greater than 4% rotation angle, which is the requirement for the Special Moment Frame. Particularly, specimens using precast concrete beam showed excellent performances in the strength, deformation, and energy dissipation.

• Journal of agriculture & life science
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• v.52 no.6
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• pp.1-12
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• 2018

This study was conducted to analyze the openness of erosion control dams situated near mountain stream. The ecological functions of erosion control dams analyzed by such openness for adequately protect and manage the diversity of species and to prevent disasters. The obtained results were as follows. When structurally modifying or changing non-permeable, gravity type dams with a passing rate of less than 1% into open-type dams, the passing rate increased by about 77 times more from 0.72% to 55.8%. Except for closed, gravity type erosion control dams that are constructed with a special purpose such as creating sand deposits and reservoirs, there is a need to construct and improve the dams into permeable type dams that can relatively satisfactorily perform various functions such as carrying soil and sand to the downstream region and create a ecological corridor upstream and downstream for fish and amphibians. The openness based on the blocking height of the erosion control dam varies depending upon the height of the base part and the depth of the substructural part. It must be designed based on the on-site conditions and the purpose of the construction. The functional types of erosion control dams based on the open form of the cross-section as follows: the fish traffic type, flood control type, reservoir type for forest fire control), non-permeability type for soil and rock blocking, net type for blocking the rock flow and the particle screen type.

• Economic and Environmental Geology
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• v.11 no.4
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• pp.127-141
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• 1978

The major structures characteristic of the Taebaegsan sedimentary basin were regionally analyzed with special reference to its southeastern extension to the Yeonhwa-Ulchin district of economic interest in zinc-lead mineralization. The basin geometry, basement setting, sedimentary components, and the characteristics of deformation and igneous activity of the Taebaegsan basin differ basically from those of the adjacent mobile belt of the Ogcheon geosyncline, although the latter affected the basin's western side considerably. The subrectangular shape of the Taebaegsan basin reflects the checkered pattern of basement-block arrangement, and the carbonate-dominated lithologic components of the basin-fill indicate a cratonic depositional setting, which is comparable to some of the North American mid-continental craton. The Taebaegsan basin, however, has somewhat been less stable than the North American megacraton that is reflected in the former's thicker sedimentary fill and steeper faults of later deformation, showing a tendency to increase in thickness close to the basement-block boundaries, which may indicate contacts of possibly detached cratonic blocks of Precambrian age; these weak zones of block boundaries have been the loci of repeated sedimentation, deformation and related igneous intrusions. A series of downthrown or uplifted tilted blocks, in which the Cambro-Ordovician sedimentary wedges and the late Cretaceous to early Tertiary igneous intrusives are involved, occurs intermittently across the Yeonhwa-Ulchin district in a noticeable pattern of en echelon type. These sedimentary wedges are correlated to the Cambro-Ordovician section of the Hambaeg syncline to the west in stratigraphy and lithology, and are considered to have resulted from the northeastern and/or northwestern cross-faulting of the pre-existing syncline belt of easterly trend, extended from the main portion of the Hambaeg syncline. These structural junctions (or intersections) of the earlier syncline belt and the later cross-faults have been acted as a guide to ascending igneous materials and hydrothermal ore-forming fluids to form a zone of zinc-lead skarn deposits across the Yeonhwa-Ulchin district showing a stepwise recurrence of these deposits toward the east.

• Journal of Bio-Environment Control
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• v.22 no.1
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• pp.27-33
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• 2013

In order to provide basic data for the development of a controlled environment cultivation system and standardization of the structures, structural status and improvement methods were investigated for the fruit tree greenhouses of grape, pear, and peach. The greenhouses for citrus and grape cultivation are increasing while pear and persimmon greenhouses are gradually decreasing due to the advance of storage facilities. In the future, greenhouse cultivation will expand for the fruit trees which are more effective in cultivation under rain shelter and are low in storage capability. Fruit tree greenhouses were mostly complying with standards of farm supply type models except for a pear greenhouse and a large single-span peach greenhouse. It showed that there was no greenhouse specialized in each species of fruit tree. Frame members of the fruit tree greenhouses were mostly complying with standards of the farm supply type model or the disaster tolerance type model published by MIFAFF and RDA. In most cases, the concrete foundations were used. The pear greenhouse built with the column of larger cross section than the disaster tolerance type. The pear greenhouse had also a special type of foundation with the steel plate welded at the bottom of columns and buried in the ground. As the results of the structural safety analysis of the fruit tree greenhouses, the grape greenhouses in Gimcheon and Cheonan and the peach greenhouses in Namwon and Cheonan appeared to be vulnerable for snow load whereas the peach greenhouse in Namwon was not safe enough to withstand wind load. The peach greenhouse converted from a vegetable growing facility turned out to be unsafe for both snow and wind loads. Considering the shape, height and planting space of fruit tree, the appropriate size of greenhouses was suggested that the grape greenhouse be 7.0~8.0 m wide and 2.5~2.8 m high for eaves, while 6.0~7.0 m wide and 3.0~3.3 m of eaves height for the pear and peach greenhouses.