• Journal of Positioning, Navigation, and Timing
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• 제10권4호
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• pp.371-377
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• 2021

This research proposes the best combination of tropospheric delay models for Korean Positioning System (KPS). The overall results are based on real observation data of Japanese Quasi-Zenith satellite system (QZSS), whose constellation is similar to the proposed constellation of KPS. The tropospheric delay models are constructed as the combinations of three types of zenith path delay (ZPD) models and four types of mapping functions (MFs). Two sets of International GNSS Service (IGS) stations with the same receiver are considered. Comparison of observation residuals reveals that the ZPD models are more influential to the measurement model rather than MFs, and that the best tropospheric delay model is the combination of GPT3 with 5 degrees grid and Vienna Mapping Function 1 (VMF1). While the bias of observation residual depends on the receivers, it still remains to be further analyzed.

• 대한토목학회논문집
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• 제38권2호
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• pp.283-294
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• 2018

정확한 보행자 지체 모형은 보행자 중심의 신호교차로 평가에 있어 핵심 요소이다. 신호화된 보행자 횡단보도에서 녹색시간동안 보행자 횡단 행태는 매우 다양하며, 보행자의 도착 행태는 임의도착과 보행군으로 구성된다. 따라서 정확한 보행자 지체를 산정하기 위해서는 보행자의 횡단과 도착 행태가 고려되어야 한다. 이러한 필요성에도 불구하고, 도로용량편람(HCM)은 보행자 도착과 횡단 행태를 반영하지 않은 간략한 보행자 지체모형을 권고하고 있다. 이러한 이유로, 보행자 중심적인 신호교차로의 설계 및 운영에 대한 의사결정을 위해서는 다양한 신호화된 단일 횡단보도 및 신호교차로에 적합한 보행자 지체 모형이 요구되고 있다. 본 연구에서는 보행자의 도착과 횡단 행태를 기반으로 새로운 보행자 지체모형을 제시한다. 제안되는 모형은 신호화된 단일 횡단보도 보행자 지체모형과 신호교차로 보행자 지체모형으로 구성된다. 단일 횡단보도 지체모형은 보행자 녹색시간 동안 보행자 횡단 행태를 기반으로 개발되었다. 신호교차로 지체모형은 보행자 횡단과 보행군 도착 행태를 기반으로 개발되었다. 수치 모의실험을 통한 평가결과, 제안되는 지체모형은 다양한 보행자 횡단과 도착 행태를 고려하기 때문에 HCM 모형의 과대/과소추정 문제를 효과적으로 해결할 수 있음을 보였다.

• Management Science and Financial Engineering
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• 제12권1호
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• pp.1-34
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• 2006

In this paper, the impact of information sharing, possibly with some delay, on costs in a simple supply chain in which there are two participants, a single retailer and a single manufacturer, is considered. When participants in the supply chain do not use fully integrated EDI, some delay associated with information sharing is inevitable. A mathematical model that allows us to quantify the cost incurred by the manufacturer in the supply chain under information sharing, possibly with some delay, vs. no information sharing is presented. From this model, some managerial implications are gleaned.

• Journal of applied mathematics & informatics
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• 제28권5_6호
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• pp.1379-1393
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• 2010

In this paper, a stage-structured predator prey model (stage structure on prey) with two discrete time delays has been discussed. The two discrete time delays occur due to maturation delay and gestation delay. Linear stability analysis for both non-delay as well as with delays reveals that certain thresholds have to be maintained for coexistence. Numerical simulation shows that the system exhibits Hopf bifurcation, resulting in a stable limit cycle.

• Kyungpook Mathematical Journal
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• 제62권1호
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• pp.119-132
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• 2022

Virotherapy is an effective method for the treatment of cancer. The oncolytic virus specifically infects the lyse cancer cell without harming normal cells. There is a time delay between the time of interaction of the virus with the tumor cells and the time when the tumor cells become infectious and produce new virus particles. Several types of viruses are used in virotherapy and the delay varies with the type of virus. This delay can play an important role in the success of virotherapy. Our present study is to explore the impact of this delay in cancer virotherapy through a mathematical model based on delay differential equations. The partial success of virotherapy is guarenteed when one gets a stable non-trivial equilibrium with a low level of tumor cells. There exits Hopf-bifurcation by considering the delay as bifurcation parameter. We have estimated the length of delay which preserves the stability of the non-trivial equilibrium point. So when the delay is less than a threshold value, we can predict partial success of virotherapy for suitable sets of parameters. Here numerical simulations are also performed to support the analytical findings.

• Journal of applied mathematics & informatics
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• 제27권1_2호
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• pp.385-400
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• 2009

The adverse effect of harmful plankton on the marine ecosystem is a topic of deep concern. To investigate the role of such phytoplankton, a mathematical model containing distinct dynamical equations for toxic and non-toxic phytoplankton is analyzed. Stability analysis of the resulting three equation model is carried out. A continuous time variation in toxin liberation process is incorporated into the model and a stability analysis of the resulting delay model is performed. The distributed delay model is then extended to include the spatial distribution of plankton and the delay-diffusion model is analyzed with spatial and spatiotemporal kernels. Conditions for diffusion-driven instability in both the cases are derived and compared to explore the significance of these kernels. Numerical studies are performed to justify analytical findings.

• 대한교통학회지
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• 제21권2호
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• pp.107-118
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• 2003

미국 도로용량편람(HCM)은 도심부 신호 교차로 운영상태 평가를 돕기 위하여 지체도 추정 수리모형을 제시하고 있다. 2000년도 개정판 HCM모형은 전문가들의 최근(up-to-date) 연구결과가 반영된 것이며 많은 교통공학자들에 의해 실무 및 연구에 활용되고 있다. HCM은 비보호 좌회전 움직임의 경우, 별도의 부가절차를 통해 포화교통류율을 보정할 것을 제시하고 있다. 그러나 HCM 지체도 산정 모형식은 보호현시 직진 움직임을 기준으로 설계된 모형이기 때문에 비보호 좌회전 움직임의 지체도를 과소 추정하는 문제점을 내제한다. 본 논문에서는 (1)HCM지체도 모형의 설계과정을 검토하고 (2)이를 토대로 HCM 지체도모형을 통한 비보호 좌회전 지체도 추정에 문제가 있음을 지적하고 (3)새로운 비보호 좌회전 지체도 추정 수리모형을 제안한다. 다양한 교통상황. 제어상황을 현장실험에서 통제함에 어려움이 있어 모의실험을 통한 제안모형의 검증을 수행하였다. 검증을 위해 마련된 120가지 경우의 다양한 비보호 좌회전 교통상황에서 (1)CORSIM 모의실험 지체도, (2)HCM 모형추정 지체도, (3)제안된 모형추정 지체도를 비교하였으며, 비교분석 결과 모의실험 지체도를 기준으로 HCM지체도 추정모형은 설명력이 0.47로, 제안된 모형의 설명력은 0.77로 분석되었다.

• Asian Pacific Journal of Cancer Prevention
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• 제17권sup3호
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• pp.167-174
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• 2016

One of the major causes of morbidity and mortality in breast cancer patients is delay in seeking help. Leventhal's self-regulation model provides an appropriate framework to assess delay in seeking help. The aim of this study was to investigate the relationship between "illness perception" and "help seeking delay" in breast cancer patients based on Leventhal's self-regulation model. In this correlational descriptive study with convenience sampling conducted in 2013, participants were 120 women with breast cancer who were diagnosed in the last year and referred to chemotherapy and radiotherapy centers in Rasht, Iran. Data collection scales included demographic data, Revised Illness Perception Questionnaire (IPQ-R)and a researcher made questionnaire to measure the delay in seeking help. Pre-hospital delay (help seeking delay) was evaluated in 3 phases (assessment, disease, behavior). The data were analyzed using SPSS-19. The mean (SD) age calculated for the patients was $47.3{\pm}10.2$. Some 43% of the patients had a high school or higher education level and 82% were married. The "pre-hospital delay" was reported ${\geq}3months$. Logistic regression analysis showed that none of the illness perception components were correlated with appraisal and behavioral delay phases. In the illness delay phase, "time line" (p-value =0.04) and "risk factors"(p-value=0.03) had significant effects on reducing and "psychological attributions" had significant effects on increasing the delay (p-value =0.01). "Illness coherence" was correlated with decreased pre-hospital patient delay (p-value<0.01). Women's perceptions of breast cancer influences delay in seeking help. In addition to verifying the validity of Leventhal's self-regulation model in explaining delay in seeking help, the results signify the importance of the "illness delay phase" (decision to seek help) and educational interventions-counseling for women in the community.

• Journal of Communications and Networks
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• 제6권4호
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• pp.352-361
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• 2004

In this paper, we study how to achieve the maximum capacity under delay constraints for large mobile wireless networks. We develop a systematic methodology for studying this problem in the asymptotic region when the number of nodes n in the network is large. We first identify a number of key parameters for a large class of scheduling schemes, and investigate the inherent tradeoffs among the capacity, the delay, and these scheduling parameters. Based on these inherent tradeoffs, we are able to compute the upper bound on the maximum per-node capacity of a large mobile wireless network under given delay constraints. Further, in the process of proving the upper bound, we are able to identify the optimal values of the key scheduling parameters. Knowing these optimal values, we can then develop scheduling schemes that achieve the upper bound up to some logarithmic factor, which suggests that our upper bound is fairly tight. We have applied this methodology to both the i.i.d. mobility model and the random way-point mobility model. In both cases, our methodology allows us to develop new scheduling schemes that can achieve larger capacity than previous proposals under the same delay constraints. In particular, for the i.i.d. mobility model, our scheme can achieve (n-1/3/log3/2 n) per-node capacity with constant delay. This demonstrates that, under the i.i.d. mobility model, mobility increases the capacity even with constant delays. Our methodology can also be extended to incorporate additional scheduling constraints.

• 전자공학회논문지 IE
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• 제48권3호
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• pp.1-9
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• 2011

본 연구는 submicrometer CMOS 인버터의 신호 전달 지연에 대한 모사로서 출력 전류 파형을 삼각형 모양으로 근사하고 두 개의 실험적 변수를 사용하여 구현 하였다. 본 모사의 결과는 HSPICE 결과와 매우 부합된 결과를 보인다. 모델의 시뮬레이션 결과 인버터 지연 값과 jitter의 최대 오류치는 각각 0.6%와 2.8% 이하의 결과를 보인다. 앞선 연구자들의 결과와 비교해 볼 때 본 연구의 모사는 작은 동작 전압에서 더 나은 결과를 보이는 특성을 가지고 있다. 이러한 모사의 결과를 실험적으로 증명하기 위해 인버터 체인을 제작 하였고 인버터 지연과 jitter 특성을 평가하였다. 제작된 시료의 결과는 새로운 모델과 매우 근사한 값을 보인다.