• Journal of the Korean Society for Precision Engineering
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• v.21 no.9
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• pp.103-110
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• 2004

Pressure ripples yield noise and vibration in hydraulic pipelines, which are inevitably generated by a fluctuation of flow rate in the pump mechanism, and such noise and vibration deteriorate the stability and accuracy of hydraulic systems. To reduce the pressure ripples, accumulator and hydraulic attenuator are normally used. In this study, parallel pipeline with a bent-axis piston pump is introduced to a hydraulic pipe system as a method for reducing the pressure ripples and using the transfer matrix method, the dynamic characteristics of the pipe system are analysed and compared with experimental results. The results show that the phase interference using parallel pipeline with a bent-axis piston pump is effective to reduce the pressure ripples in the hydraulic pipelines.

• Proceedings of the Korean Society of Fisheries Technology Conference
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• 2001.05a
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• pp.319-321
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• 2001

Supply of ntrition-balanced feed is very important for growth of fish, especially for growth of early period of fish. Therefore, most of commercial feeds for larval and juvenile fish are relatively expensive due to high level of the several nutrients to satisfy their requirements for growth. Overfeeding larval fish may increase fish production cost because of larvae feeds high price and deteriorate water quality, eventually reduce growth of fish. (omitted)

• Journal of the Korean institute of surface engineering
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• v.15 no.4
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• pp.208-217
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• 1982

To study the effect of TiC coating on weight change, microhardness, wear and heat - resistance of TiC layer, chemical vapour deposition on the various substrates has been carried out with the gaseous mixture of TiCl4, toluene, and H2 in the temperature range of 900 - 1000$^{\circ}C$. The results obtained are as follows ; (1) There is a limited value of carrier and reductant H2 gas flow rate, above which deteriorate effect on the TiC depoition arises (2) Increased thickness of TiC layer was resulted with increasing temperature and time. Better deposition was obtained with stainless steels and the best results were introduced by cobalt coating of substrates. (3) Wear resistance of the TiC coated specimen improved markedly. Heat resistivity of the coated steel showed excellent result, whereas the coated stainless Steels were infer-ior to the substrate.

• Journal of the Korean Geotechnical Society
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• v.27 no.4
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• pp.77-87
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• 2011

To investigate the effect of drainage spacing and smear on the rate of consolidation and the efficiency of vertical drain method, a series of consolidation tests with a large consolidation chamber and special equipment for inserting mandrels were conducted. As the smeared region increases, total settlement in over-consolidated clay increases whereas apparent change in settlement does not appear in normally consolidated clay. Vertical drain generally accelerates the rate of consolidation, while it could also deteriorate the efficiency of vertical drain method even for the decreasing drainage length and spacing ratio.

• KOREAN JOURNAL OF CROP SCIENCE
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• v.46 no.4
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• pp.317-320
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• 2001

Sweet com seeds deteriorate faster due to low starch content than field com seeds when stored for a long tenn. This study had been conducted to observe the seed deterioration of four different sweet corns in a long tenn storage conditions in room temperature. Four kinds of sweet com genes (sh2, bt, su, and se) were harvested from 15 days to 50 days after silking with 5-day intervals. These seeds were stored in the room temperature and tested for germination percentages from 3 months to 18 months period with 3-month interval. su seeds germinated better than other types of gene. Hybrid Mecca which is sh2 gene germinated better when stored for 3 months to 18 months. For all genes, mean regression equations in relation to storage periods showed linear responses. For regression equation, the slope of sh2 gene was lower than that of su gene. The highest slope value was observed in bt gene showing faster deterioration rate. The rate at which seed deteriorates seems to be affected by the date at which it was harvested. The seeds that were harvested at the optimum time deteriorated more slowly than those which were not.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38B no.10
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• pp.832-842
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• 2013

Cognitive Radio has attracted intensive interests of the researchers, recently. The data rate always increases in the emerging technologies. The increased data rate poses mainly two challenges for spectrum sensing. One is that the state of primary user (PU) is fast and alternatively varying between "on/off" in a spectrum sensing window. The other is that the asynchronicity among the reports in a cooperative spectrum sensing setting becomes more apparent. Both of them would deteriorate the spectrum sensing performance. Thus, we propose an asynchronous cooperative spectrum sensing method to cope with these two challenges. A likelihood ratio test based spectrum sensing is developed for a single cooperator. The likelihood ratio is obtained in the setting of fast varying PU state. The likelihood ratio test is uniformly powerful according to the Neyman-pearson lemma. Furthermore, the asynchronicity among the cooperators are studied. Two sets of fusion weights are discussed for the asynchronous time among cooperators. One is designed based on the condition probability of the PU state variation and the other one is designed based on the queueing theory. The simulation results are provided with different fusion methods. The performance improvements are demonstrated.

• Journal of Korean Society for Quality Management
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• v.47 no.1
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• pp.87-96
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• 2019

Purpose: The purpose of this paper is to determine an optimal production time for economic production quantity model with preventive maintenance and random defective rate as the function of a machinery deteriorates. Methods: If a machinery shifts from "in-control" state to "out-of-control" state, a proportion of defective items being produced increases. It is assumed that time to state shift is a random variable and follows an arbitrary distribution. The elapsed time until process shift decreases stochastically as a production cycle repeats and quasi-renewal process is used to implement for production facilities to deteriorate. Results: When the exponential parameter for exponential distribution increases, the optimal production time increases. When Weibull distribution is considered, the optimal production time is closely affected by the shape parameter of Weibull distribution. Conclusion: A mathematical model is suggested to find optimal production time and optimal number of production cycles and numerical examples are implemented to validate the patterns for changes of optimal times under different parameters assumptions. The real application is implemented using the proposed approach.

• Journal of Electrochemical Science and Technology
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• v.15 no.2
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• pp.253-260
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• 2024

Proton exchange membrane water electrolysis (PEMWE) is an efficient method for utilizing renewable energy sources such as wind and solar powers to produce green hydrogen. For PEMWE powered by renewable energy sources, its durability is a crucial factor in its performance since irregular and fluctuating characteristics of renewable energy sources, especially for wind power, can deteriorate the stability of PEMWE. Triangular voltage cycle is well able to simulate fluctuating wind power, but its effect on the durability has not been investigated extensively. In this study, the performance degradation of the PEMWE cell operated with the triangular voltage cycling was investigated at different ramping rates. The measured current responses during the cycling gradually decreased for both ramping rates, and I-V curve measurements before and after the cycling confirmed the degradation of the performances of PEMWE. For both measurements, the degradation rate was larger for 300 mV s^-1 than 30 mV s^-1, and they were determined as 0.36 and 1.26 mV h^-1 (at the current density of 2 A cm^-2) at the ramping rates of 30 and 300 mV s^-1, respectively. The comparison with other studies on triangular voltage cycling also indicate that an increase in the ramping rate accelerates the deterioration of the PEMWE performance. X-ray photoelectron spectroscopy and transmission electron microscopy results showed that the Ir catalyst was oxidized and did not dissolve during the voltage cycling. This study suggests that the ramping rate of the triangular voltage cycling is an important factor for the evaluation of the durability of PEMWE cells.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.38 no.4
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• pp.302-312
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• 2001

As the data transfer rate between chips gets higher, both crosstalk and SSN (Simultaneous Switching Noise) deteriorate seriously the performance of a system. The proposed interface scheme uses P-CTR and N-CTR(Positive/Negative Constant Transition Rate) which encodes data at both falling and rising edges, where the transition directions of N-CTR and P-CTR are opposite. And the proposed bus system places two P-CTR drivers and two N-CTR drivers alternatively. In the proposed P/N-CTR interface scheme, the signals of neighboring interconnection lines at both sides of a bus will not switch simultaneously in the same direction, which leads to reduction in the maximum crosstalk and SSN compared to conventional interfaces. For verification of noise reduction of the proposed interface scheme, the scheme is applied to several kinds of bit-wide buses with various interconnection structures, and HSPICE simulation was performed with 0.35 ${\mu}{\textrm}{m}$ SPICE parameters. The simulation results show that in the 32-bit or less wide bus, the maximum SSN and crosstalk are reduced to at least 26.78% and 50%, respectively in comparison with the conventional interface scheme.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.44 no.4
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• pp.1-7
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• 2012

The increase of OCC solid content after wet pressing will save drying energy greatly. We applied spacers, which used to increase draining rate and bulk in fiber furnishes, to increase the OCC solid contents. MDF fibers (fibers for making medium density fiberboard) and diatomaceous earth were used as spacers, and added 10% by weight to the OCC fiber furnish. Application of high wet pressing pressure to the mixed furnish of spacers and refined OCC did not deteriorate bulk and drainage rate, but their solid contents were increased to 0.5-1.5% without loss of compressive strength when compared to those of unrefined OCC, which is the furnish normally used for mill commercial practice. It is believed that the spacers caused the rate of solid content increase faster in the mixed furnish with OCC at high wet pressing pressure area than the unrefined OCC furnish did. Little amount of starch addition (0.5%) to the spacers helped to keep the strength properties.