• Proceedings of the IEEK Conference
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• 2003.07a
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• pp.230-233
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• 2003

In this paper, it is shown that, in DS/CDMA mobile systems, halving or doubling the spreading factor (HSF or DSE) when retransmission is requested possibly improves the throughput. Given transmit power, DSF essentially decreases probability of packet error (PPE) by increasing the signal energy per information bit. It, however, doubles the time duration needed for transmitting the original packet. On the other hand, HSF increases PPE. It, however halves the time duration required to carry the original packet. Thus, the efficiency of HSF or DSF as a retransmission strategy depends on the amount of increased or reduced PPE after HSF or DSF is selected. With achieving given residual error probability (REP) in CDMA systems, the effective throughput is evaluated in this paper to find conditions with which HSF or DSF achieves better performance than using the original one. Analytic results show that HSF or DSF performs better when relatively small or big changes in their PPE's are present, respectively.

• Asian-Australasian Journal of Animal Sciences
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• v.22 no.2
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• pp.187-193
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• 2009

The present study identified the favorable conditions for isolation, enrichment and in vitro culture of highly purified, undifferentiated pig spermatogonial stem cell (SSC) lines that proliferate for long periods of time in culture. The colonies displayed morphology similar to miceSSC and were positive for markers of SSC (PGP9.5), proliferating germ cell (PigVASA), pre-meiotic germ cell (DAZL) and pluripotency (OCT4, SSEA-1, NANOG, and SOX2) based on immuno-cytochemistry and RT-PCR. The purity of these colonies was confirmed by negative expression of markers for sertoli cell (GATA4 and SOX9), peritubular myoid cell (${\alpha}$-SMA), differentiating spermatogonial and germ cells (c-KIT). The colonies could be maintained with undifferentiated morphology for more than two months and passaged more than 8 times with doubling time between 6-7 days. Taken together, we conclude that pigSSC could be successfully isolated and cultured in vitro and they possess characteristics similar to miceSSC.

• The Journal of Korean Medicine
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• v.25 no.1
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• pp.49-59
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• 2004

Objectives: This paper is to investigate what effects Yeonryunggobondan and Palmijihwangtang have on postponing senility in rat fibroblasts, heart-endothelial cells, mesangial cells. Methods: 1. In vitro Yeonryunggobondan and Palmijihwangtang controlled the growth of fibroblasts, heart-endothelial cells, mesangial cells, extended the PDT of them. 2. After feeding rats the drugs for 2 months, the fibroblasts, heart-endothelial cells, mesangial cells were cultured. Results: 1) In fibroblasts the PDN was incresed and the PDT was decreased at passage-1, 2 by Yeonryunggobondan and Palmijihwangtang(p<0.05). 2) In heart-endothelial cells the PDN was incresed and the PDT was decreased at passage 8 by Yeonryunggobondan and Palmijihwangtang(p<0.05). 3) In mesangial cells the PDN was increased and the PDT was decreased at passage 4 by Yeonryunggobondan, the PDN was incresed at passage 4 by Palmijihwangtang(p<0.05). Conclusions: It is concluded that both Yeonryunggobondan and Palmijihwangtang maybe be conductive to protect and delay the senescence of rat fibroblasts, heart-endothelial cells, mesangial cells.

• The Journal of Asian Finance, Economics and Business
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• v.7 no.9
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• pp.659-672
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• 2020

The outbreak of a recent strain of Coronavirus, known as 'COVID-19', has spread sharply from China across the globe, resulting in a dramatic recession in the global economy. This uncertainty has therefore negatively influenced the business perspective and the various formulated strategies that may not considered such [extreme] circumstances. Using baseline analysis and archival data, this paper reports some of the major implications of COVID-19 on global business and strategy and puts forward suggested research agenda as potential future directions for organizations. In order to survive and remain sustainable, this paper argues that businesses need to revisit their strategies during current COVID-19 crises from three perspectives, including supporting human resources financial commitment, forming cross-functional teams and connecting with their supply chains, as well as investing in corporate social responsibility and doubling down efforts with regard to partnerships. The study also represents a preliminary analysis to the implications of COVID-19 on the business and strategies across the globe and is considered the first such in the field of business, as to date all research papers on COVID-19 have been published in medical-related journals. Directions for future research are also proposed at the end of this study.

• Journal of Advanced Navigation Technology
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• v.13 no.6
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• pp.846-853
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• 2009

This paper presents the design of a high efficiency frequency multiplier with load-pull simulation and analyses the nonlinear distortion of the frequency multiplier. The frequency multiplier shows serious distortion of multiplying signal bandwidth because of nonlinearity when modulated signal is applied, so a digital predistortion with look up table (LUT) is applied to compensate for the distortion of the frequency multiplier. The frequency multiplier is designed to produce 5.8GHz output by doubling the input frequency to be operating at IEEE 802.11a standard wireless LAN. The output spectrum shows 12dB ACPR improvement both at +11MHz, +20MHz offset from center frequency after linearization.

• KSBB Journal
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• v.6 no.1
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• pp.35-43
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• 1991

The production of poly-$\beta$-hydroxybutyrate(PHB) from methanol by batch and fed-batch cultivations of Methylobacterium sp. GL-10 was studied. PHB accumulation was stimulated by the nutrients deficiency including, NH4+, SO42-, and K+. The nitrogen deficiency was the most critical factor for PHB accumulation. In batch cultivation, the maximum cell concentration and PHB content were 1.86g/l and 0.62g/l, respectively, with 1.0%(v/v) of methanol and 0.5g/1 of ammonium sulfate. The mass doubling time of Methylobacterum sp. GL-10 was in the range of 4-5 hrs. The cell growth and PHB accumulation were severely inhibited at the methanol concentration over than 2% (v/v). To overcome methanol Inhibition, constant feeding and intermittent feedillg fed-batch cultivations were adopted, using C/N molar ratio as a control factor. In constant feeding fed-batch process, cell concentration was increased up to 2.67g/1, and PHB yield was enhanced from 0.33 of batch culture to 0.53. The relatively low cell concentration was caused by methanol accumulated in culture broth at late growth phase. To prevent methanol accumulation and to maximize PHB production, DO-state intermittent fed-batch cultivation was attempted. The cell and PHB concentration was reached up to 4.55g/1 and 1.80g/1, respectively. It was possible to maintain methanol concentration low and also to feed nutrient of desired C/N molar ratio.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.48 no.2
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• pp.89-95
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• 1999

This study investigates the population model of the spread of HIV/AIDS which the infection is generated by an infectious individual in a population of susceptible. A mathematical model is presented for the transmission dynamics of HIV infection within the communities of homosexual males. The pattern on the epidemic character of HIV, the causative agent of AIDS, was analysed by the mathematical model of AIDS system which is derived according to the ecological relationship between five epidemilogic states of individuals. The computer simulation was performed using real data and the following conclusions are drawn on the basis of the simulations. 1. The model structure and the algorithm described n the thesis is good. 2. In proportion to increase Ro, the population of AIDS patient increases and the time of its widespread reaches earlier. 3. The AIDS patients will be maximum between 7 and 21 years after an attack of AIDS and widespread between 10 and 20 years. 4. Considering the properties of the incubation periods, the maximum number of infected person is increased, and the attack rate is decreased.

• Transactions of the Society of Information Storage Systems
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• v.1 no.1
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• pp.78-83
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• 2005

The Blu-ray disc as a next generation high density optical medium uses an objective lens of high numerical aperture(NA 0.85) and blue laser in order to increase the recording density. The double layer is also useful for doubling the density. The spherical aberration of Blu-ray disc is very sensitive to the thickness of the disk because of high numerical aperture. This paper suggests a method to compensate the spherical aberration caused by the change of disk thickness, by using the Liquid Crystal lens instead of the Liquid Crystal panel. It was possible to develop both the LC panel generating the optical phase difference and LC lens changing the optical power. In this paper, we analyzed the aberration performance and a position sensitivity of the two type LC elements when the samples deviate from the optical axis of the objective lens. The results of applying this analysis show that the LC lenses rather than the LC panels have a significant assembling tolerance. The theoretical characteristics of the two elements are calculated and compared with the measurement data.

• 유체기계공업학회:학술대회논문집
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• 2005.12a
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• pp.311-317
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• 2005

Measurements of the leakage flow in the shrouded cavity were performed in axial compressor cascades at $Re=2.6{\times}10^5$. This paper describes the effects of the leakage flow tangential velocity on kinematics of the leakage flow in the shrouded cavity and consequent overall loss and exit flow turning at stator blade row downstream. Flow data and flow visualization images consistently indicate that leakage flow circumferentially migrates 2, 4 and 5 blade passages in the direction of rotation for ${\upsilon}_y/c=0.09$, 0.35 and 0.45, respectively where ${\upsilon}_y$ is the leakage tangential velocity and c is the mainstream velocity. The leakage flow contracts to a jet across the seal-tooth resulting in an increase in the leakage axial velocity-doubling the leakage axial velocity in upstream cavity compared to that in the downstream cavity. Consequently, two flow regions are distinguished before and after the seal-tooth. As increasing the leakage tangential velocity, the overall loss downstream of stator blade row decreases and the exit flow turning in the range of span. from the hub endwall to 15% increases while the decreases in the flow turning from 15% to 30% span is observed.

• Journal of Drive and Control
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• v.9 no.2
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• pp.39-45
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• 2012

The NAS 1638 cleanliness classification system was originally developed in 1966 by the US Aircraft Industries of America to both simplify reporting of particle count data and to control the introduction of dirt during the assembly of aircraft fluid systems. The numbers of particles at stated sizes are represented by broad bands where the interval was generally a doubling of contamination. A number of systems have been introduced since this to suit differing requirements. NAS 1638 and AS4059 are used in other industrial sectors such as the Off-shore & Sub-Sea and the Primary Metal Industries. The changes to ISO contamination measurement standards controlled by ISO/TC131/SC6 in 1999 meant that a revision of most of these classification systems was necessary. The body responsible for NAS 1638 decided to withdraw it for new installations and replace it with an update of an existing standard, SAE AS 4059. This paper details the philosophy behind the contamination coding systems, the reasons for the changes to the ISO contamination standards and explains the workings of AS 4059, the replacement for NAS 1638. It goes on to detail the latest changes to this standard.