• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.6
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• pp.1-9
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• 2017

Spiral reinforcement in a circular column plays an effective role in the ductile behavior of a column through position fixing and buckling restraining of the longitudinal reinforcement, and confining core-concrete. Each country has suggested the minimum volumetric ratio of spiral reinforcement in order to secure the ductility of concrete columns. The minimum volumetric ratio of spiral reinforcement suggested by ACI 318-14 and the national concrete structure design standard was developed based on the theory of Richard et al. (1928); furthermore it has been used until now. However, their theory cannot consider the effects of high strength concrete and high strength reinforcement, and arrangement condition of the spiral reinforcement. In this study, a modified minimum volumetric ratio equation is suggested, which is required to improve the ductility of reinforced concrete circular columns and to recover their stress. The modified minimum volumetric ratio equation suggested here considers the effect of the compressive strength of concrete, the yield strength of spiral reinforcement, the cross sectional area of columns, the pitch of spiral reinforcements and the diameter of spiral reinforcement. In this paper, the validity of the minimum volumetric ratios from ACI 318-14 and this study was investigated and compared based on the results of uniaxial compression experiment for specimens in which the material strength and the spiral reinforcements ratio were used as variables. In the end of the study, the modification method for the suggested equation was examined.

• KSBB Journal
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• v.24 no.3
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• pp.321-326
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• 2009

This study was to optimize the medium components for astaxanthin production in Paracoccus sp. through surface response methodology. A screening test was first conducted on 5 medium components using a Plackett-Burman design, from which $MgSO_4$ and yeast extract were identified as the significant factors affecting astaxanthin production. These significant factors were optimized by central composite design of experiments and response surface methodology, as 2.83 g/L $MgSO_4$ and 7.02 g/L yeast extract, respectively. The expected astaxanthin concentration with these optimized medium compositions were 0.925 mg/L. In flask culture, the experimentally obtained concentration of astaxantin was 1.021 mg/L, where it had been 0.4 mg/L before optimization.

• KSBB Journal
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• v.24 no.3
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• pp.303-311
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• 2009

A scaling up study for the exopolysaccharide (EPS) production by submerged culture of Ganoderma lucidum was carried out in jar fermenter systems (2.6, 20 and 75 L) under bi-staged pH process. Profiles of dissolved oxygen (DO) and volumetric coefficient of oxygen transfer ($k_La$) as a function of operating variables (agitation speed and aeration rate) was investigated, and a correlation between $k_La$ and operating variables was analysed statistically. Under bi-staged pH process, no limitation of DO was observed at agitation speeds tested in the range of 200 and 600 rpm, and the highest EPS production was obtained at the level of DO of $40{\sim}80%$. From the regression analysis, the relation between $k_La$, gas velocity (Vs), stirrer speed (N) and impeller diameter (Di) could be expressed as : $$k_La=0.555{\times}Vs^{0.42}{\times}(N^3{\times}Di^2)^{0.33}\;(R^2=0.925,\;p<0.05)$$ It was found that under 2.6 L jar fermenter, the optimum agitation speed and aeration rate was 400 rpm and 1 vvm, respectively, obtaining the EPS production of 15.43 g/L. Under the submerged cultivation of G. lucidum in jar fermenters of $2.6{\sim}75\;L$, the similar EPS yields at each fermenter were achieved during scaling up based on $k_La$, and $k_La$ value for maximum EPS production was $85.4{\pm}26.70\;h^{-1}$.

• Journal of Radiation Protection and Research
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• v.30 no.2
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• pp.69-75
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• 2005

Gas avalanche microdetectors, such as micro-strip gas chamber (MSGC), micro-gap chamber (MGC), micro-dot chamber (MDOT), etc., are operated under high voltage to induce large electron avalanche signal around micro-size anodes. Therefore, the anodes are highly exposed to electrical damage, for example, sparking because of the interaction between high electric field strength and charge multiplication around the anodes. Gas electron multiplier (GEM) is a charge preamplifying device in which charge multiplication can be confined, so that it makes that the charge multiplication region can be separate from the readout micro-anodes in 9as avalanche microdetectors possible. Primary electron collection efficiency is an important measure for the GEM performance. We have defined that the primary electron collection efficiency is the fractional number of electron trajectories reaching to the collection plane from the drift plane through the GEM holes. The electron trajectories were estimated based on 3-dimensional (3D) finite element method (FEM). In this paper, we present the primary electron collection efficiency with respect to various GEM operation parameters. This simulation work will be very useful for the better design of the GEM.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.4
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• pp.401-412
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• 2003

In this paper, a broadband phase shifter structure using a new switched network was proposed. A new reference network is composed of coupled lines and 45$^{\circ}$open and short stubs, which are shunted at the edge points of a main line, respectively, A delay network is composed of only a standard transmission line. It is possible to design a broadband 180$^{\circ}$phase shifter that phase dispersive characteristics by an impedance ratio R of coupled lines and greater phase dispersive characteristics by characteristic impedances Zm, Zs of a main line and stubs are used together. By considering a structure symmetry, the even and odd mode analysis was performed to obtain theoretical S-parameters of the proposed phase shifter. Also, through computer simulation on the basis of derived equations, design graphs were presented to optimally design a 180$^{\circ}$broadband phase shifter. Design graphs provide the values of characteristic impedances Zm, Zs, and I/O match and phase bandwidths. To verify electrical performances of the broadband phase shifter proposed in this paper, low different 180$^{\circ}$phase shifters, operated at the center frequency 3 GHz were designed and fabricated using design graphs, and were experimented. One of them was designed as a standard Schiffman structure to compare with electrical performances. Measured results of each phase shifter to satisfy simultaneously design conditions of I/O match （VSWR=1.15:1) and maximum phase deviation $({\varepsilon}_{{\Delta}{\phi}}＝{\pm}2^{\circ})$ were well in agreement with corresponding simulation results over impedance match and phase error bandwidths, and showed broadband characteristics.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.3 s.106
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• pp.249-258
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• 2006

In this letter, we propose a novel printed helix antenna for RFID reader in UHF band. The printed strip line of the antenna is first wound up outside a polygonal shaped layer and then the winding continues on an inner layer to control the overall gain and the radiation pattern. In addition, the winding pitch angles on each layer have either negative or positive values resulting in the broad CP bandwidth. The detail structure of the antenna was optimized using Pareto genetic algorithm(GA), so as to obtain excellent performances for RFID reader antennas. The optimized two-layered polygonal helix was fabricated on the cardboard of a flexible substrate and the performances were measured and compared with the simulations. The fabricated antenna was made up of copper tape which can adhere to a flexible cardboard and had 21.4 % matching bandwidth, 31.9 % CP bandwidth, readable range of $5.5m^2$ with kr=3.2. Also based on the current distribution of the strip line of the antenna and sensitivity of the antenna bents points, we confirmed that the antenna has the quarter-wave transformer near the feed for the broad matching bandwidth and radiates the traveling wave for the broad CP bandwidth using the bent strip line.

• Journal of the Society of Naval Architects of Korea
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• v.30 no.1
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• pp.125-133
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• 1993

Most studies on the vibration analysis of a beam-column with ends elastically restrained and various intermediate constraints have been based on the Euler beam theory, which is inadequate for beam-columns of low slenderness ratios. In this paper, analytical methods for vibration and dynamic sensitivity of a Timoshenko beam-column with ends elastically restrained and various intermediate constraints are presented. Firstly, an exact solution method is shown. Since the exact method requires considerable computational effort, a Rayleigh-Ritz analysis is also investigated. In the latter two kinds of trial functions are examined for comparisions : eigenfunctions of the base system(the system without intermediate constraints) and polynomials having properties corresponding to the eigenfunctions of the base system. The results of some numerical Investigations show that the Rayleigh-Ritz analysis using the characteristic polynomials is competitive with the exact solutions in accuracy, and that it is much more efficient in computations than using the eigenfunctions of the base system, especially in the dynamic sensitivity analysis. In addition, the prediction of the changes of natural frequencies due to the changes of design variables based on the first order sensitivity is in good agreements with that by the ordinary reanalysis as long as the changes of design variables are moderate.

• Food Science and Preservation
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• v.18 no.5
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• pp.755-763
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• 2011

This study was conducted to monitor the quality characteristics Citrus unshiu ethanolic extracts by a response surface methodology. In extraction conditions based on the central composite design with variations in ethanol concentration (0~100%), extraction temperature($35\sim95^{\circ}C$), and ratio of solvent to sample(20 mL/g). The maximum value of yield was 36.31% at $93.18^{\circ}C$, 67.13% of ethanol concentration. The extraction yield and total polyphenol content were improved with the increase of ethanol concentration than extraction temperature. Total flavonoid content was improved with the increase of extraction temperature than ethanol concentration. The coefficients of determinations($R^2$) were 0.8646(p<0.1) and 0.9153(p<0.05) in electron donating ability and hesperidin content, respectively. Estimated conditions for the maximized extraction including yield, total polyphenol content, total flavonoid content, electron donating ability, and hesperidin content were 55~73% in ethanol concentration, $89\sim95^{\circ}C$ in extraction temperature, and 20 mL/g in ratio of solvent to sample.

• The Journal of Engineering Research
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• v.2 no.1
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• pp.113-123
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• 1997

The purpose of this paper is an optimum design of the shaped Cassegrainian antenna system for the base station. The process of the shaped Cassegrainian antenna design is as follows : 1) the aperture field distribution is determined so as to meet design specifications, 2) a proper design parameter is selected, 3) extracting of the dimension data for the main and sub-reflector antenna To do these, Hansen's distribution is chosen as the aperture field, and the far-field pattern from the aperture is predicted by the angular spectrum. Firstly, the aperture field distribution is designed to satisfy the specification for design frequency, it is confirmed if this distribution meet the specification for another frequency band. The main- and the sub-reflectors are synthesized so as for the given beamwaveguide feed pattern to be transformed into the prescribed aperture distribution. The designed system has circular aperture, left-right symmetry and no tilted structure. The continuous surface functions of reflectors are obtained by adopting the global interpolation technique to the discrete reflector profiles. Jacobi polynomial-sinusoidal is used as the basis function. A Ka-band Cassegrainian antenna operates over 17.7 – 20.2 GHz for down-link band and 27.5 – 30 GHz for up-link band is designed.

• Korean Journal of Food Science and Technology
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• v.29 no.5
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• pp.947-954
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• 1997

Selected physical properties of cornmeal extrudates fortified with dairy products and extrusion process by $CO_2$ gas injection were analysed. Dairy products including whole milk powder, whey protein concentrate non-fat dry milk, and sodium caseinate were tested at the addition of 10% and 20%, based on cornmeal weight. $CO_2$ gas was injected to the barrel at the pressure of 0.7 and 1.4 MPa. Specific mechanical energy (SME) input was decreased by the addition of dairy products. Sodium caseinate had a little effect on decreasing the SME input, however whole milk powder tremendously reduced SME input when the concentration increased. An increase in milk product content resulted in increasing the piece density at the injection pressure of 0.7 MPa. At both 10% and 20% milk product content, the piece density was lowest at the injection pressure of 0.7 MPa. The sectional expansion index was highest at the injection pressure of 0.7 MPa. However, the specific length was constantly increased with the increase in $CO_2$ injection pressure. Water absorption index was decreased and water solubility index was increased by the addition of milk products. The injection pressure of $CO_2$ was optimum at 0.7 MPa. The addition of whole milk powder limited to puff the melt, but the other milk products tested resulted in puffing with $CO_2$ injection to 1.4 MPa.