Seaport Throughput Analysis and Global Risk Management by Using Effective Decision‐Making Theory: A Case Study of Vietnamese Ports

TRUONG NGOC CUONG 한국해양대학교 대학원 2022 국내박사

Recently, globalisation has spurred the importance of seaport operations and terminal capacity in the supply chain networks. Seaports play a vital role in the economy of many countries and regions in which ports must be operated in an efficient way for mitigating supply chain risk. Understanding the underlying mechanism of port operation and optimizing profits is essential business objective for port authorities. As matter of fact, port interaction is a nonlinear dynamic process with much complex behavior. Several socioeconomic factors influenced port throughput such as the gross domestic product, fixed assets investments, imports, and exports, etc. Moreover, seaport ecosystems can no longer be the isolated nodes in which they dynamically interact with each other at only a local scale in regional port governance; but within the globally integrated networks of complex supply chains. Thus, it is beneficial to understand the underlying dynamics of complex seaport networks. By analysing chaotic system in port management, the managers can gain better insights into the complex and nonlinear properties of the port interactions in the real market then the optimal management solution can be undertaken. In this dissertation, the port operation system is considered by utilizing four dimensions of the fractional Lotka-Volterra model. First, the dynamic behaviours of the port operation system are investigated by using nonlinear techniques such as equilibrium evaluation, bifurcation, Lyapunov, and time series investigation. The dynamical analysis indicates that the port competition system shows a complex and highly nonlinear behaviour, notably illustrating unstable equilibria and even chaotic phenomena. Next, based on dynamical analysis results, novel multi-criteria decision-making techniques realized by the neural network prediction controller (NNPC) and adaptive fractional-order super-twisting sliding mode control (AFOSTSM) have been utilized for dealing with throughput dynamics under parametric perturbations and external disturbances. Particularly, the active control algorithms are implemented to ensure the recovery strategy for the throughput growth trend of Vietnam ports against system uncertainty and external disturbance. The case study has confirmed the efficacy of the proposed strategy by using system dynamics and control theory. The simulation results show that the average growth rates of container throughput can be ensured up to 7.46% by exploiting the proposed method. The presented method can be also utilized for providing managerial insights and solutions for efficient port operations. In addition, the control strategies with neural network forecasting can help managers obtain timely and cost-effective decision-making policy for port operations against unprecedented disruptions such as the Covid-19 pandemic.

INVESTIGATION OF FRICTION CHARACTERISTICS OF 2D MATERIALS USING ATOMIC FORCE MICROSCOPY

TRAN KHAC BIEN CUONG 울산대학교 2014 국내석사

ABSTRACT Investigation of Friction Characteristics of 2D Materials Using Atomic Force Microscopy Tran Khac Bien Cuong School of Mechanical Engineering The Graduate School University of Ulsan Two-dimensional (2-D) crystal, including single or few atomic layers of molybdenum disulfide (MoS2) and graphene, have recently attracted a lot of interest for fundamental studies due to their remarkable electrical and mechanical properties. Based on the presence of the bandgap or the strong ambipolar electric effect, single and a few layers MoS2 and graphene have a great potential in micro- and nano-electromechanical systems (MEMS and NEMS). Furthermore, due to the low friction characteristics of MoS2 and graphite, they may have a great potential as a protective layer in MEMS and NEMS applications. However, fundamental friction characteristics of these materials are not clearly understood yet. Therefore, in order to understand friction characteristic of these 2D materials at nano-scale not only from the fundamental tribological point of view but also from their practical applications point of view, a more thorough study of friction characteristics of these atomically thin MoS2 and graphene under various conditions is needed. Raman microscopy has been a powerful technique useful for study of vibrational properties and electronic structure of nano materials, particularly for investigation of number of layer of MoS￢2 and graphene based on their “finger-print” peaks frequencies. Due to the thermal effect, the laser treatment parameters (laser power and laser treatment time) must be carefully taken into account for both data interpretation and specimen modification. However, thermal effect on these 2D materials is not completely explored, particularly on the friction characteristic. In this work, Raman microscopy is not only used for number of layer determination but also used for specimen treatment, by varying the laser excitation parameters, we created different thermal condition in the surface of the specimens. By doing so, we systematically investigated the thermal effects on friction characteristic of the atomically thin MoS2 and graphene by using the friction force microscopy (FFM). The experimental results show that both single layer MoS2 and graphene exhibited exceedingly low friction coefficients, of about 0.06 and 0.04 respectively, which make them promising candidates for protective layer application. It was also found that friction decreased with a factor of 0.4 as the number of layer increased from single layer to bulk (more than 20 layers), as expected. As for the thermal effect, formations of adsorbates on MoS2 are observed, depending on the laser treatment conditions. It is postulated that thermal conditions affect the formation of particle. As a consequence, the friction was significantly increased due to the formation of particles. The AFM manipulation of formed particles suggests that those are adsorbates from the atmospheric environment. However, such thermal effect is not significantly observed for graphene. These experimental results may help to gain a fundamental understanding of friction characteristic of atomically thin MoS2 and graphene and to understand the thermal effects on these 2D materials.

Effect of tocopheryl polyethylene glycol succinate 1000 (TPGS) on solubility enhancement, oral bioavailability enhancement and percutaneous absorption of (S)-zaltoprofen

Cuong, Pham Viet 忠南大學校 大學院 2016 국내석사

본 연구에서, (S)-잘토프로펜 ((S)-ZPF)의 용해도, 경구 생체이용률, 피부 자체와 지질을 제거한 피부를 통한 경피 투과 실험에 대한 D-알파토코페롤 폴리에틸렌글리콜 1000 숙시네이트 (TPGS)의 영향을 조사하였다. TPGS, 2-히드록시프로필 베타사이클로덱스트린 (HPCD), 유기용매, 알코올류 용액, TPGS를 함유한 혼합용매 등의 48가지 용매에 대한 (S)-ZPF의 용해도를 조사하였다. 물에 대한 용해도와 비교하여 TPGS는 (S)-ZPF의 용해도를 484배 증가시켰다. 또한, 우리는 유럽의약국 가이드라인에 따라 액체-액체 추출법을 이용하여 실험용 흰 쥐 혈장에서 (S)-ZPF의 밸리데이션된 분석 방법을 개발하였고 역상 크로마토그래피 컬럼과 키랄 크로마토그래피 컬럼을 이용하여 혈장 내 (S)-ZPF의 잠재적인 대사적 상호 변환을 평가하였다. 실험용 흰 쥐 혈장 내 (S)-ZPF은 0.1~75 µg/mL 범위에서 직선성을 나타냈고 R2 = 0.9998이었다. 최저정량한계는 0.1 µg/mL이고 상대표준편차는 6% 이내였다. 반면에, (R)- 잘토프로펜 ((R)-ZPF)과 (RS)- 잘토프로펜으로부터 (S)-ZPF은 0.5~37.5 µg/mL 범위에서 직선성을 나타냈고 각각 R2 = 0.9996, R2 = 0.9997을 나타냈다. 약동학적 결과는 (S)-ZPF의 경구 생체이용률이 실험용 흰 쥐 그룹 (TPGS 그룹, HPCD 그룹, 물 그룹) 중 TPGS 그룹 (물 그룹과 비교하여 (S)-ZPF의 AUC0-24h가 1.75배 증가)에서 가장 높았으며, (S)-ZPF의 용해도와 경구 생체이용률 사이의 상관계수 (R2 = 0.97)도 높았다. 다른 한편으로, TPGS는 미셀 가용화에 의해 (S)-ZPF의 용해도를 상당히 증가시킬 수 있었다. 그러나, 피부 자체와 지질을 제거한 피부에서 (S)-ZPF의 투과를 증가시키지는 않았다. 피부와 전달체 및 클로로포름/메탄올 용매 사이에서 TPGS의 영향을 알아보기 위해 FT-IR로 평가하였고 이는 (S)-ZPF의 투과 결과가 뒷받침되었다. 그러나, 에탄올은 TPGS와 비교하여 각질층에서 free-form (S)-ZPF의 농도를 증가시킴으로써 (S)-ZPF의 투과를 더욱 효과적으로 증가시켰다. 또한, 모든 용액 (5% (w/v) TPGS 용액, 40% (v/v) 에탄올 용액, 40% (v/v) 에탄올 용액 내 5% (w/v) TPGS)에서 지질을 제거한 피부 각질층으로의 (S)-ZPF 분배는 피부 자체의 각질층보다 높았다. In this study, the influence of D-alpha tocopheryl polyethylene glycol 1000 succinate (TPGS) on solubility, oral bioavailability, and percutaneous permeation of (S)-zaltoprofen ((S)-ZPF) through intact and delipidized skin were investigated. The solubility of (S)-ZPF in forty eight solvents was investigated, such as TPGS, 2-hydroxypropyl-β-cyclodextrin (HPCD), water-soluble organic solvents, ethanol solutions and mixtures of solvents containing TPGS. TPGS denoted as a vehicle having capability to solubilize (S)-ZPF with a 484-fold increase compared to aqueous solubility. The validated analytical method of (S)-ZPF in rat plasma by liquid-liquid extraction as the guidance of European Medicines Agency was developed, and the potential metabolic inter-conversion of (S)-ZPF in plasma using a reversed and a chiral HPLC column was successfully evaluated. For pure (S)-ZPF in rat plasma, response was linear over the calibration ranges of 0.1~75 µg/mL with R2 of 0.9998. The lower limit of quantification was 0.1 µg/mL, and the variation for the quality control samples was within 6%. Meanwhile, the linearity was shown in the calibration ranges of 0.5~37.5 µg/mL with R2 of 0.9996 and 0.9997 for (R)-ZPF and (S)-ZPF from (RS)-ZPF. The pharmacokinetics results showed oral bioavailability of (S)-ZPF was the highest in TPGS group (a 1.75-fold increase in AUC0-24h of (S)-ZPF compared to that in water group) among three studied rat groups including TPGS group, HPCD group, and water group with a strong coefficient of correlation (R2=0.97) between solubilization and oral bioavailability of (S)-ZPF. On the other hand, TPGS was able to significantly enhance the solubility of (S)-ZPF by micellar solubilization. But it was not responsible for the enhancement of (S)-ZPF penetration for intact and delipidized skin. The important role of interfacial coverage by TPGS in hindering intact and delipidized SC, molecular changes in SC lipids evaluated by FTIR after vehicle and chloroform/methanol solvent treatment also supported for the result of permeation of (S)-ZPF. However, ethanol was more effective in enhancing penetration of (S)-ZPF by increasing the free-form concentration of (S)-ZPF and extraction of SC lipids in comparison with TPGS. Also, the partitioning of (S)-ZPF from studied solutions (5% (w/v) TPGS solution, 40% (v/v) ethanol solution, and 5% (w/v) TPGS in 40% (v/v) ethanol solution) into powdered delipidized SC was always higher than that into powdered intact SC.

Sonochemical synthesis and characterization of perovskite La1-xSrxMnO₃nanoparticles

Cuong, Phan Van 경북대학교 대학원 2008 국내석사

본 논문은 Sonochemical 방법으로 합성된 직경 40 ~ 80 nm 크기의 페로브스카이트 La_(1-x)Sr_(x)MnO₃ (x = 0.1, 0.2, 그리고 0.3) 나노 입자들의 특성에 대해 연구하였다. La_(1-x)Sr_(x)MnO₃ (LSMO) 나노입자들은 950 ℃ 에서 10 시간 동안의 열처리를 통하여 결정성을 효과적으로 향상 시키고 불순물 상 (phase)을 제거할 수 있었다. 시료들은 단결정상의 R3c 구조를 가졌다. LSMO 나노입자들의 상자성-강자성 천이 온도 (Tc) 와 절연체-금속 천이 온도 (Tp)는 x 값에 따라 변하였다. x 의 값이 0.3 일 때 Tc 및 Tp 가 각각 377 K 및 264 K 로 최대값을 가졌다. 지금까지 다른 연구그룹들에 의해 발표된 LSMO 나노 입자들에 비해 더 낮은 저항값과, 더 높은상자성-강자성 천이 온도를 보였다. LSMO 나노입자들의 열처리 효과는 750 ℃ 에서 1050 ℃ 까지 체계적으로 연구 하였다. 샘플들의 입자크기, 저항과 상자성- 강자성 천이 온도는 열처리 온도에 크게 의존 하였다. 열처리 온도가 증가함에 따라 시료들의 저항이 감소하였고, 절연체-금속 천이되는 온도는 증가하였다. 열처리 온도 증가에 비례하여 자화가 증가 되었고, 상자성-강자성 천이 온도도 증가하였다. We present a very simple sonochemical method for synthesis of La_(1-x)Sr_(x)MnO₃ (x = 0.1, 0.2, and 0.3) nanoparticles having perovskite structure with particle size in the range of 40~80 nm. After the LSMO NPs preparation, an annealing at 950℃ for 10 h in air is very effective to enhance the crystallinity and to remove the impurities. The samples are close to a single phase perovskite structure of R3c symmetry. The ferromagnetic transition temperature (Tc) and metal-insulator transition temperature (Tp) of the LSMO NPs increase in conjunction with the doping level x in La_(1-x)Sr_(x)MnO₃ nanoparticles. The maxima of Tc (377 K) and Tp (264 K) occur at x = 0.3. Our samples show that the resitivity and ferromagnetic-paramagnetic transition temperature are lower and higher than that of some other nanosize preparation methods. The annealing effects of La_(0.7)Sr_(0.3)MnO₃ NPs are systematically studied from 750℃ to 1050℃. Experimental results show that the particle size, resistivity, and ferromagnetic transition temperature of the samples strongly depend on the annealing temperature. A substantial decrease in resistivity and an enhancement in the insulator-metal transition temperature are found on increasing the annealing temperature. Furthermore, the enhancement in magnetization and paramagnetic-ferromagnetic transition temperatures have been observed as the annealing temperature increases.

생물 복잡계에서 피이드백 조절 기능

CUONG NGUYEN 충북대학교 2009 국내박사

Gene regulatory networks, collections of biological molecular species and their interactions, operate as on-off switches and rheostats regulating protein synthesis in a cell. They play crucial roles in every processes of life, including cell differentiation, metabolism, the cell cycle and signal transduction by properly responding to the external environment, optimizing the cell at a given time for survival in the environment. The gene regulatory networks are composed of various dynamic feedback loops, and regulate the protein synthesis through mutual cooperation between the feedback loops. In this thesis, we analyzed the organization of gene transcriptional regulation and dynamic properties of the gene regulatory networks. At first, I analyzed the positional organization of the gene transcriptional regulation, and observed the presence of operon-like motif structures in eukaryotic cells. For dynamic analysis of gene regulatory networks, we studied the feedback loop motifs across cell cycle regulatory networks, a part of gene regulatory network, of yeast and mammalian and frog egg cells. The feedback loops cooperate with each others by interlocking (sharing output signal) or coupling (sharing regulator). I observed that the interlocked positive feedback loops provides diverse multi-stability, and could be used as joint toggle switches with flexible controllability as well as robustness. I also observed that the coupled feedback positive loops provide time locked dynamical events. Finally I have discussed on the possibility of applying the dynamic properties of feedback loops to understand the dynamic mechanism of cell cycle regulation and various check point regulations. 여러 가지 생체 분자의 집합체와 그들간의 상호 작용으로 이루어진 유전자 조절 네트워크는 유전자 생성물인 단백질의 합성을 조절하는 여러 가지 스위치 혹은 조절 소자로써 유전자 단위에서 세포 기능을 조절하는 기능을 맡고 있다. 이러한 네트워크는 세포 분화, 대사과정, 세포 주기, 외부 환경 신호에 적절히 반응하는 신호 전달, 주어진 환경에서 생존하기 위한 세포의 적응 등 생명 현상의 모든 과정에서 핵심적인 역할을 하고 있다. 이들 네트워크의 특징은 무수히 많은 동력학 피이드백 고리로 구성되어 있으며 이들 피이드백 고리 사이의 상호 협력을 통하여 단백질 합성을 조절을 하고 있다는 것이다. 본 학위 논문에서는 유전자 조절 네트워크의 유전자 발현 상호 작용 분석과 동력학 특성 분석을 다룬다. 먼저 진핵 세포의 유전자 발현 연결 구조 분석을 통하여 오페론과 같은 모티브 구조가 있음을 밝혔다. 다음으로 유전자 조절 네트워크의 동력학 특성 분석으로 효모 세포, 포유류, 개구리 알 세포 등에서 나타나는 세포 주기 조절 네트워크에 나타나는 피이드백 고리 모티브에 대한 동력학 특성을 분석하였다. 세포 주기 조절 네트워크에서는 이러한 피이드백 고리가 서로 엉켜 있거나 상호작용을 함으로써 서로 협력하고 있다. 엉켜 있는 양성 피이드백 고리는 다양하고 유연성이 있는 토우글 스위치로 작동하고 있으며, 서로 상호 작용하는 피이드백 고리는 시간적으로 강하게 서로 연결된 동적 신호 발생 장치로써 작용함을 밝혔다. 마지막으로 피이드백 고리의 동력학 특성으로부터 세포 주기 조절 그리고 다양한 체크 포인트 조절 원리를 이해하고자 하는 시도를 하였다.

Wide band-gap and high conductivity ZnO-based transparent films grown by RF magnetron sputtering : effects of Mg, Be, and Ga doping and process parameters

Cuong, Hoang Ba Chonnam National University 2017 국내박사

ZnO and its alloy ZnMgO have gained much attention for applications in ultraviolet photodetectors, photo-catalyst, transparent conductive electrodes, and electronic devices. The increase of the band-gap in Zn1-xMgxO alloys with added Mg facilitates tunable control of the conduction band alignment and the Fermi-level position. However, the maximal conductivity achieved by doping decreases considerably at higher Mg concentrations, which limits practical application of this material as a wide-gap transparent conductive oxide. This study suggests that the Mg content, band-gap energy, and structural phase in sputter-deposited ZnMgO films could be tailored over a wide range by controlling the growth temperature and sputtering ambient, which opens up an important research direction on deep UV materials. The Mg content in the films and the band-gap energy showed a strong dependence on the growth temperature and sputtering ambient, increasing with the growth temperature or decreasing by the oxygen addition into the plasma ambient. In this work, a wurtzite ZnMgO film with a wide band gap of 4.53 eV and a high Mg content of XMg = 0.53 was realized for the first time by sputtering the Zn0.7Mg0.3O alloy targets with Mg contents of 0.3 – 0.35 below 200 oC under a pure Ar ambient. The structural phase exhibits a dependence on the growth temperature, and the solubility limit of Mg in the single wurtzite ZnMgO phase without phase segregation was estimated at 0.53 – 0.56 and was confirmed to reduce with the growth temperature, possibly due to the lower formation Gibbs free energy of MgO than ZnO and the difference in the growth condition. Next, the quaternary ZnMgBeO films with co-doped Mg and Be were prepared using an RF magnetron sputtering to avoid phase segregation, and the effects of oxygen partial pressure within the Ar process plasma on the optical, structural, and electrical properties ZnMgBeO films were investigated in detail. It was observed that the optical energy bandgap (Eg) values of the ZnMgBeO films substantially decrease with the oxygen addition, from 5.3 eV to 4.3 eV as the oxygen partial pressure increases from zero to one. The full-width-at-half-maximum (FWHM) values of the (0002) XRD peaks drastically decrease with the addition of a small amount of oxygen but then increase with further oxygen addition. All the films had very high sheet resistance, 1.3-1.4 G/. It was also observed that the concentration of Zn within the films significantly increased with the oxygen addition, which was proposed to be mainly responsible for the observed decrease in Eg. It was also proposed that the FWHM change due to the oxygen addition may be attributable to three factors, film composition, grain size, and point defect density, as confirmed by results of TEM and XPS investigations. On the other hand, Ga has been chosen to improve the conductivity of the ZnO-based TCMs, as the element shows well-matched ionic size and covalent radii with the Zn ions, minimizing lattice deformations of the ZnO matrix even at high doping concentration. Ga heavily-doping of ZnO films has been studied to take advantage of the Brustein-Moss effect and to obtain a high conductivity and an extended Eg simultaneously. Sputter growth of highly conductive Ga-doped ZnO films with abnormally wide band-gap (Eg) is discussed in detail, as well as the accompanying defect behavior. It was observed that the optical Eg and the conductivity increased as the working pressure of the Ar plasma decreases. The ZnGaO films with Eg of 3.95 eV and resistivity of 2×10-4 Ω∙cm was obtained by simply lowering the working pressure to 0.3 Pa, which represent the highest Eg value so far reported for the ZnO-based transparent conducting materials with a resistivity lower than 10-3 Ω∙cm. It was proposed that this phenomenon may be attributed to the improved crystalline quality and the increased amount of the Ga incorporation into the Zn sites and the oxygen vacancy concentration. It was also suggested that the oxygen vacancy acts as the electron donor for the sputtered ZnO and ZnGaO films. In a final study, transparent conductive ZnMgGaO films were sputter-grown on sapphire at lower working pressure in an effort to silmuneously improve the conductivity and the optical band-gap. However, the conductivity of the films decreases markedly at high Mg doping level, the Zn0.93Mg0.03Ga0.04O film have a Hall mobility (μ) of 18.8 cm2/VS and a carrier concentration of 1.1×1021 cm-3, yielding a resistivity of 3×10-4 Ω.cm, while the Zn0.66Mg0.3Ga0.04O film possesses significantly worse electrical properties (μ = 1.82 cm2/VS, n = 2×1017 cm-3, and ρ = 23.6 Ω.cm). It is demonstrated that the formation of acceptor-like compensating defects such as Zn vacancies and/or other complexes increases with the increasing Mg content, decreasing the free electron concentration and the mobility through the ionized impurity scattering. XPS investigation proves that the oxygen vacancies also decrease with increasing Mg content, resulting in the films with high resistivity at high Mg doping level. The ZnMgGaO films were post-annealed in Zn vapor to introduce point defects – Zn interstitial and lead to increase the carrier concentration of the films. It was suggested that oxygen ions emerge at the surface of the films and combine with zinc atoms from vapor to form ZnO on the surface, and the electrons given up at the surface by the incorporated zinc atoms convert the newly formed oxygen vacancies then migrate in to the annealed films. Zinc interstitials could also form since the surrounding zinc vapor is an obvious source of zinc atoms that could diffuse into the crystal. As a result, the annealed ZnMgGaO films with Eg = 3.97 eV and the resistivity of 1.6×10-4 Ω.cm could be obtained after post-treatment in Zn vapor ambient. The ZnMgGaO films at high Mg doping level could also be obtained after annealed in Zn vapor with an Eg = 4.26 eV and the resistivity of 4×10-3 Ω.cm, which presents a promising candidate for transparent electrode in the UV optoelectronic application.

Development of lubrication method to improve service life of twisted string actuator

Cuong, Huu Che 중앙대학교 대학원 2019 국내석사

Twisted string actuators (TSAs) have been efficiently applied in various fieldsof mechanical engineering. The string component of the TSAs convertsrotational motion to a linear motion since the length of the string decreases asit is twisted. However, the performance of TSAs is critically limited in realworld applications due to the poor durability of the string. Up to date, thereare only few studies that actively investigate twisted string’s lifetimecharacteristics and develop a method to improve its service time. In this study,a novel lubrication method using a polytetrafluoroethylene (PTFE) film and amixture of polyalphaolefin (PAO) grease and WS2 lubricant powder wasdeveloped to extend the service time of TSA strings. By applying thelubrication method, 124% enhancement in the lifetime was obtained. Variouslifetime characteristics of pre-twisted TSA strings were also obtained underdifferent testing conditions. The lifetime of the string decreased with anincrease of load, initial arm angle, or stroke. The string was frequentlyruptured at the Y-junction near the hook. The effects of environmentaltemperature and humidity on the life cycle of TSA were also investigated. A large deviation in the string lifetime data was observed at increasedtemperatures. The effect of humidity variation on the life cycle of TSA stringswas relatively small, compared with the temperature effect. Twisted String Actuators (TSAs)는 기계공학의 다양한 분야에서 유용하게 적용되어 왔다. 끝단이 회전하면서 스트링이 꼬여 총 길이가 줄어드는 원리를 통해, TSAs의 스트링은 회전 동작을 선형 동작으로 변환시키는 기능을 한다. 그러나 스트링의 낮은 내구성 때문에 TSAs를 제품으로 구현하기에는 기술적 한계가 존재해왔다. 최근까지 TSA 스트링의 수명특성과 내구성을 향상방안에 대한 연구는 소수에 불과했으며, 본격적 연구는 이제 태동기이다. 본 연구에서는, TSA 스트링의 수명을 향상시키기 위하여 polytetrafluoroethylene (PTFE) 필름과 polyalphaolefin (PAO) 윤활유와 WS2 윤활제 분말의 혼합물을 사용하는 새로운 윤활법을 개발하였다. 개발된 윤활법을 적용할 경우 스트링 수명이 124% 향상되는 것이 실험적으로 확인되었다. 또한 다양한 구동 조건에서 TSA 스트링의 수명 특성을 구하였다. 하중, 초기각도 또는 스트링의 구동 스트로크가 늘어남에 따라 스트링 수명이 감소하는 현상이 관찰되었다. 주로 스트링 양단의 후크 근처 Y자 접합부에서 국부적 마찰 집중에 의해 스트링의 파단이 발생하였다. 구동환경이 스트링 수명에 미치는 영향을 확인하기 위해, 온도와 습도를 변화시키면서TSA 수명을 측정하였다. 그 결과, 온도 상승에 의해 수명 특성이 불안정해지는 경향이 측정되었다. 습도에 의한 수명 변화는 온도에 의한 영향보다 상대적으로 작았다.

(An) optimal spectrum access control in cognitive radio networks

Cuong, Do The Kyung Hee University 2014 국내박사

Cognitive Radio (CR) is a promising technology to solve the spectrum scarcity problem and to increase spectrum efficiency. By using spectrum sensing and databases, one is able to obtain information about and utilize white space spectrum. Spectrum costs, which tend to be high for wireless service providers, can then be reduced significantly by using dynamic spectrum access. Most dynamic spectrum approaches are connected to a three-tier model of the dynamic spectrum market, which includes three network entities: spectrum owners, secondary service providers and Secondary Users. Therefore, wireless service provider should focus on understanding how they can benefit from using cognitive radio. With interest increasingly centered on real-time application, spectrum access control that considers delay as a critical quality of service (QoS) metric has become more important. In this thesis, we focus on the equilibrium behaviors of SUs in a strategic queueing system, where arriving users can take the delay and other metrics into account for strategic decision making. In order to control the spectrum access in an effective manner, an spectrum access control design should take into account of both the traffic statistics of the primary users and the secondary users. In this research track, based on pricing mechanism, queueing theory, game theory and optimization theory, several spectrum access schemes are devised elegantly to achieve optimal performance. In this dissertation, we consider two approaches to derive optimal spectrum access schemes in cognitive radio network. The first approach is based on the pricing approach which is widely used as an effective means for spectrum access control in cognitive radio networks. We study the pricing effect on the equilibrium behaviors of selfish secondary users’ data packets which are served by a cognitive radio base station. From the secondary users’ point of view, a spectrum access decision on whether to join the queue of the base station or not is characterized through an individual optimal strategy that is joining the queue with a joining probability. This strategy also requires each secondary user to know the average queueing delay, which is a non-trivial problem. Here, we provide queueing delay analysis by using the M/G/1 queue with breakdown. From the base station’s point of view, we consider a duopoly market based on the two paradigms: the opportunistic dynamic spectrum access (O-DSA) and the mixed O-DSA & dedicated dynamic spectrum access (D-DSA). In the first paradigm, two co-located opportunistic-spectrum BSs utilize free spectrum-holes to serve the secondary users. Then, we show the advantages of the cooperative scenario due to the unique solution that can be obtained in a distributed manner by using the dual decomposition algorithms. For the second paradigm, there are one opportunistic-spectrum base station and one dedicated-spectrum base station. We study a price competition between two base stations as a Stackelberg game. The cooperative behavior between two base stations is modeled as a bargaining game. In both paradigms, bargaining revenues of the cooperation are always higher than those due to competition in both cases. Extensive numerical analysis is used to validate our derivation. The second approach is queue-based approach that is used in a hybrid overlay/underlay and multiple channels cognitive radio system. The first system, a hybrid overlay/underlay cognitive radio system, is modeled as a M/M/1 queue where the rate of arrival and the service capacity are subject to Poisson alternations. Each packet as a customer arriving at the queue of the system makes a decision to join or balk the queue. Upon arrival, the individual decision of each packet is optimized based on its observation about the queue length and the state of system. It is shown that the individually optimal strategy for joining the queue is characterized by a threshold of queue length. Thus, the individual optimal threshold of queue length is analyzed in detail in this thesis. For the second system, the multiple channels cognitive radio system, we propose is a lightweight probability-based spectrum decision scheme which distributes the packets into multiple channels in a minimizing queueing delay manner. Compare with the sensing-based spectrum decision scheme, the probability-based spectrum decision scheme has been shown to yield a shorter queuing delay time in cognitive radio system. However, the former scheme had cumbersome algorithms and slowly converging speed. In this thesis, by introducing Lagrange function, we propose a lightweight algorithm with the computational effort O(N) to define the optimal distribution probability vector. Numerical results demonstrate a high degree of accuracy for the derived expressions.

Role of activating transcription factor (ATF)-3 in bacterial infections

Cuong, Nguyen Thach Sungkyunkwan University 2015 국내박사

Enhancement of K factor in eschbach-knox error diffusion algorithm

Cuong, Nguyen Quoc 안동대학교 대학원 2007 국내석사