234 research outputs found
A cross-layer analysis of TCP/link adaptation technologies over free-space optical links with Markov error model
No full textThis paper presents a comprehensive cross-layer framework on the performance of transmission control protocol (TCP) over a free-space optical (FSO) link, which employs automatic repeat request (ARQ) and adaptive modulation and coding (AMC) schemes. Not similar to conventional works in the literature of FSO, we conduct a Markov error model to accurately capture effects of burst errors caused by atmospheric turbulence on cross-layer operations. From the framework, we quantify the impacts of different parameters/settings of ARQ, AMC, and the FSO link on TCP throughput performance. We also discuss several optimization aspects for TCP performance.
Design and Analysis of Sliding Window ARQ Protocols With Rate Adaptation for Burst Transmission Over FSO Turbulence Channels
No full textThis paper studies a cross-layer design of error-control protocols with rate adaptation for a free-space optical (FSO) burst transmission over atmospheric turbulence channels. Specifically, sliding window automatic repeat request (ARQ) protocols are designed so that the window size is determined by the burst duration. This facilitates an effective operation for sliding window protocols with the adaptive rate (AR) transmission over atmospheric turbulence channels. To analyze performance of the design, the time-varying behavior of the atmospheric turbulence channels, modeled by the popular gamma gamma (GG) distribution, is captured to develop the burst error model. An embedded Markov model, which is formulated in the discrete time defined by the burst duration, is analyzed based on the developed burst error model. Using the queueing analysis, the frame loss rate, average delay, and system throughput are analytically derived. Numerical results quantitatively demonstrate the impact of atmospheric turbulence on the system performance and support the optimal selection of system parameters over turbulence conditions. Monte Carlo simulations are also performed to validate the analytical results, and an excellent agreement between the analytical and simulation results is confirmed.
도시협곡에서의 바람유동과 오염물질 이송에 관한 수치적 연구
Get PDF학위논문 (박사) -- 서울대학교 대학원 : 공과대학 건설환경공학부, 2021. 2. Van Thinh Nguyen.In this thesis, a numerical model based on an open source CFD package OpenFOAM is developed in order to investigate the flow pattern and pollutant dispersion in urban street canyons with different geometry configurations. In the new model, the pollutant transport driven by airflow is modelled by the scalar transport equation coupling with the momentum equations for airflow, which are deduced from the RANS (Reynolds Averaged Navier-Stokes) equations. The turbulent flow calculation has been calibrated by various two-equation turbulence closure models, such as standard k-ε, RNG k-ε, realizable k-ε, k-ω, k-ω SST, to select a practical and efficient turbulence model to reasonably capture the flow pattern. There are two approaches for the scalar transport equation to calculate the turbulent scalar flux term: Standard Gradient Diffusion Hypothesis (SGDH) approach and Generalized Gradient Diffusion Hypothesis (GGDH) approach. The GGDH approach shows better results than the SGDH approach, and it overcome the limitation of the SGDH approach caused by time consuming calibration of the turbulent Schmidt number.
The numerical model has been validated against different well-known laboratory experiments in regard to various aspect ratios (a relationship between the building height and the width of street canyon), and different building roof shapes (flat, shed, gable, and round). The comparisons between the numerical simulations and experimental measurements show a good agreement on the flow pattern and pollutant distribution. The numerical model has also provided reasonable agreement with experiment data in three-dimensional problem. It shows the ability of the new numerical model, which can be applied to investigate the wind flow and pollutant dispersion in real urban street area.
Eventually, the numerical model has been applied to a real urban street canyon, the Shinjuku special ward of Tokyo; which contains a large number of skyscrapers, and poses several interesting wind engineering problems including how the wind shed will affect pedestrians nearby and the microclimate of the surrounding region. The simulation results show that the new model can capture the wind flow in the Shinjuku urban street canyon.본 연구에서는 상이한 지형조건의 도시협곡에서의 공기 흐름과 오염확산 양상을 연구하기 위해, 오픈소스 CFD 프로그램인 OpenFOAM 을 기반으로 하는 수치모델을 개발하였다. 수치모의에서 바람유동에 의해 발생하는 오염물질 이송은 운동량 방정식과 연동되는 스칼라 수송 방정식에 의해 기술되며, 운동량 방정식은 RANS(Reynolds Averaged Navier-Stokes) 방정식을 차용하였다. 난류흐름은 다양한 two-equation 난류모형들을 적용하여 본 연구에 적용할 수 있는 실용적이고 효율적인 최적의 난류모형을 선정하였다. 스칼라 수송 방정식에서는 난류 확산항을 기술하는 다음과 같은 두 가지 방법이 있다: Standard Gradient Diffusion Hypothesis(SGDH)와 Generalized Gradient Diffusion Hypothesis(GGDH). 연구 결과, GGDH 방식이 SGDH 방식보다 더 나은 결과를 도출하였으며 각기 다른 실험조건마다 난류 슈미트 수를 조정해주어야 하는 SGDH 방식의 한계를 극복하였다.
수치모델은 다양한 종횡비(도시협곡 내 빌딩의 높이와 너비의 비율)와 지붕 형상(flat, shed, gable, and round)에 대해 수행된 저명한 실험실 실험결과와 비교 및 검증하였다. 수치모델결과와 실험실 실험결과를 비교한 결과, 흐름과 오염물질 분포 양상이 상당히 일치함을 확인할 수 있었다. 또한 수치모델결과는 3차원 실험조건에서도 실험결과와 합리적인 범위에서 일치하였으며, 이는 본 연구에서 개발된 수치모델이 실제 도시협곡 내 기류와 오염물질 이송을 연구하기 위해 적용될 수 있음을 나타낸다.
마지막으로 본 연구에서 제시되는 수치모델은, 수많은 고층빌딩들을 포함하며 wind shed가 인근 보행자들과 주변지역의 미세기후에 어떻게 영향을 끼치는지 등 몇 가지 흥미로운 공기역학적 문제들이 내포되어 있는 일본 도쿄의 신주쿠 지역을 대상으로 적용되었다. 본 연구의 수치모의결과는 개발된 수치모델이 신주쿠 도시협곡의 실제 공기흐름을 재현할 수 있음을 보여준다.ABSTRACT i
TABLE OF CONTENTS iii
NOMENCLATURE vi
1. INTRODUCTION 1
1.1. Motivation of the work 1
1.2. Necessity and Objectives 5
1.3. Structure of thesis 7
2. LITERRATURE REVIEW 9
2.1. Flow characteristics of idealized street canyon 15
2.2. The influence of wind condition 18
2.3. Turbulence transfer between a street canyon and the atmosphere 20
2.4. Characteristics of pollutant dispersion inside street canyon 21
2.5. The influence of geometry of street canyons 23
2.6. Schmidt number 25
2.7. Three-dimensional modelling 26
2.8. CFD modelling of street canyon flow 27
3. METHODOLOGY 31
3.1. Reynolds-Averaged Navier-Stokes Equation (RANS) 31
3.2. Turbulence models and validation 33
3.2.1. The standard k-ε model 34
3.2.2. The RNG k-ε model 36
3.2.3. The realizable k-ε model 37
3.2.4. The k-ω model 38
3.2.5. The SST k-ω model 38
3.2.6. Validation of RANS models 39
3.3. Scalar transport equation and the implementation of code 44
3.3.1. Standard Gradient Diffusion Hypothesis (SGDH) 44
3.3.2. Generalized Gradient Diffusion Hypothesis (GGDH) 46
3.3.3. Implementation of the scalar transport equation in OpenFOAM 47
3.3.4. Validation of the SGDH approach 50
3.3.5. Validation of the GGDH approach 51
3.4. Initial and boundary condition 52
3.4.1. Boundary type 52
3.4.2. Boundary position 53
3.4.3. Inlet boundary profile 54
4. VALIDATION OF CFD MODELS 58
4.1. Studying the flow characteristics in street canyon with different aspect ratios by comparison to Li (2008)s experiment 58
4.1.1. Description of experiment setup 58
4.1.2. Street canyon of AR = 1 60
4.1.3. Street canyon of AR = 2 66
4.1.4. Street canyon of AR = 0.5 71
4.2. Studying the air dispersion in various roof shapes by validating against Kastner-Klein and Plate (1999)s experiment 77
4.2.1. Description of the experiment setup 77
4.2.2. Validation and discussion 80
4.3. Validation of round-shaped roof against the measurement data from Llaguno-Munitxa et al.s experiment (2017) 82
4.4. Validation against CEDVAL data to study the flow characteristics for 3-D isolated building 85
4.4.1. Simulation setup 85
4.4.2. Validation of the isolated rectangular building simulation 88
5. APPLICATION – A CASE STUDY OF AIRFLOW AND POLLUTANT DISPERSION IN SHINJUKU URBAN AREA IN TOKYO 93
6. CONCLUSIONS AND FUTURE WORK 102
6.1. To develop a reliable and economic tool to study flow in urban street canyon 102
6.2. To study the impact of various roof shapes and different aspect ratios on air flow and pollutant dispersion in street canyons. 102
6.2.1. Effect of aspect ratios on flow patterns 102
6.2.2. Effect of roof shapes on the flow patterns and pollutant distribution 104
6.3. To develop a method to adjust accurately Schmidt number 106
6.4. Application to a real urban area 107
6.5. Future work 107
REFERENCE 109
Appendix – Implementation of a solver in OpenFoam 123
초록 138Docto
Restless Legs Syndrome in Psoriasis: A Multicenter Study on Its Prevalence, Severity, and Impact on Patients
Get PDFChuyen Thi Hong Nguyen, Nguyet Huu Minh Nguyen, Trung The Van Department of Dermatology, University of Medicine and Pharmacy at Ho Chi Minh City, 700000, VietnamCorrespondence: Chuyen Thi Hong Nguyen, Department of Dermatology, University of Medicine and Pharmacy at Ho Chi Minh City, 217 Hong Bang Street, Ward 11, District 5, Ho Chi Minh City, Vietnam, Tel +84 28 38566154, Email [email protected]: Psoriasis is a chronic inflammatory skin disease often associated with multiple comorbidities, including restless leg syndrome (RLS). However, the prevalence and impact of RLS on quality of life and clinical outcomes in patients with psoriasis remain underexplored, particularly in Asian populations. In this study, we compared the prevalence of RLS in patients with psoriasis and healthy controls and evaluated the association between RLS and quality of life, sleep disturbances, and clinical severity of psoriasis.Patients and Methods: This multicenter, cross-sectional study involved 212 participants (106 patients with psoriasis and 106 healthy controls) and was conducted from March to July 2024 at three major hospitals in Ho Chi Minh City, Vietnam. RLS was diagnosed according to the International Restless Leg Syndrome Study Group (IRLSSG) criteria. The RLS severity, sleep quality, quality of life, and psoriasis severity were assessed using the Restless Legs Syndrome Rating Scale, Pittsburgh Sleep Quality Index, Dermatology Life Quality Index, and Psoriasis Area and Severity Index (PASI), respectively.Results: The prevalence of RLS was significantly higher in patients with psoriasis than in healthy controls. Patients with psoriasis and RLS exhibited significantly poorer sleep quality and a greater impact on quality of life than those without RLS. The RLS group exhibited a higher PASI score, indicating more severe psoriasis. A strong positive correlation was observed between PASI and RLS severity.Conclusion: RLS is significantly more prevalent in patients with psoriasis and is associated with worse sleep quality, greater impairment of quality of life, and increased psoriasis severity. Early screening for RLS in patients with psoriasis using the IRLSSG criteria may facilitate timely intervention and improve outcomes.Keywords: psoriasis vulgaris, restless legs syndrome, restless legs syndrome study group, Pittsburgh Sleep Quality Index, Dermatology Life Quality Inde
The emerging legal framework for private sector development in Viet Nam's transitional economy
Get PDFA major objective of Viet Nam's transition to a market economy has been to reactivate the private sector in a mixed economy. Several new laws have been introduced in the past five years to implement this policy and to create an enabling environment for the private sector. The author reviews some of the more important laws and regulations that affect Viet Nam's private sector activities, including laws on real property, intellectual property, companies, domestic investment, foreign investment, bankruptcy, contracts, and dispute resolution. Anti-monopoly law has not yet been introduced in Viet Nam. The issue of competition is addressed in the context of trade law, the relative roles of the state and private sector, and restrictions in company law. These areas all establish the foundation of a legal framework for a market economy. The author concludes that Viet Nam's legal framework, like China's, is still influenced by ideology, which causes problems in such areas as private ownership of real property and with such fundamental legal concepts as"due process of law."It is noted that the private sector is constrained by the lack of an independent judiciary, the absence of private land ownership, other uncertainties in property law that limit the develpoment of financial markets, and the inherent bias of the system in favor of the state sector (and collective ownership). Also noted is a law-abiding attitude, equally important to development has been slow to develop. The author goes on to point out that the foreign investment process is too complicated, and its company law too restrictive. A first priority should be to strreamline regulations, as well as liberalize trade policy and increase efforts in privatization of state enterprises. In this respect the author notes that export processing zones may be a useful interim instrument to attract foreign investment but should be phased out over time. More important in the long term is a good investment climate resting on a strong legal foundation.Legal Products,Environmental Economics&Policies,Banks&Banking Reform,Municipal Housing and Land,Municipal Financial Management,Environmental Economics&Policies,Banks&Banking Reform,Municipal Housing and Land,Legal Products,Municipal Financial Management
Exploring learning styles in the online environment: A comprehensive review
Get PDFUnderstanding learning styles has become increasingly important in the realm of education, particularly with the rise of personalized and learner-centered approaches facilitated by advancements in science and technology. This article aims to address the research gap in comprehensively understanding learning styles in the contemporary online context. By consolidating and examining learning styles within the online environment, this study seeks to contribute to the existing body of knowledge and facilitate evidence-based practices. The research questions that guide this study focus on identifying prevailing patterns and tendencies, evaluating academic journals with significant author interest, uncovering emerging themes, and identifying influential scholarly articles. The study employs the PRISMA research model and utilizes the Scopus database for source selection. The inclusion and exclusion criteria ensure the selection of relevant articles published between 2016 and 2023, which underwent evaluation and peer review and are written in English. The data coding and analysis process involves organizing and cleansing the selected articles before analyzing them using the VosViewer tool. The results and discussion section presents trends in the publication of learning styles in the online environment over the years and identifies the academic journals that have garnered significant interest in this field. The abstract concludes by emphasizing the importance of this study in shedding light on evolving trends, informing decision-making processes, and fostering a deeper understanding of learning styles in the digital era. Keywords: Learning styles; online learning; digital environment; personalized education; PRISMA DOI: 10.7176/JEP/15-6-05 Publication date: May 30th 202
Volume No 04 Issue No 04 (2020)
No full text[1] Hung, Bui Thanh (2020). Assessment of Recruitment Records using Machine Learning Approach. International Journal of Machine Learning and Networked Collaborative Engineering, 4(04) pp 143-151.
doi : https://doi.org/10.30991/IJMLNCE.2020v04i04.001
[2] Bui,Thien Xuan, Bui,Chuyen Van, Nguyen,Lao, Nguyen,Pha Xuan, Huy, Ha Nguyen Cuong (2020). The Ripening of Pineapple Fruits. International Journal of Machine Learning and Networked Collaborative Engineering, 4(04) pp 152-161.
doi : https://doi.org/10.30991/IJMLNCE.2020v04i04.002
[3] Trong,Nguyen Thanh, Kien,Luong Gia, Tran,Thi T. T., Duong,Hieu N., Hoa,Tran Van, Nam,Thoai (2020). Improving the Performance of One-shot Face Recognition by using Data Augmentation. International Journal of Machine Learning and Networked Collaborative Engineering, 4(04) pp 162-170.
doi : https://doi.org/10.30991/IJMLNCE.2020v04i04.003
[4] Hung,Bui Thanh (2020). Vietnamese Voice Classification based on Deep Learning Approach. International Journal of Machine Learning and Networked Collaborative Engineering, 4(04) pp 171-180.
doi : https://doi.org/10.30991/IJMLNCE.2020v04i04.004
[5] Thai, Dang Nguyen Ha, Quang, Dat Nguyen (2020). Compare model multi-input RNN, LSTM and GRU for prediction of irrigation canal\u27s water level in Red river delta, North Vietnam. International Journal of Machine Learning and Networked Collaborative Engineering, 4(04) pp 181-188.
doi : https://doi.org/10.30991/IJMLNCE.2020v04i04.005  
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Development of Geodetic Imaging Techniques and Machine Learning for Marsh Observation
No full textAccurate characterization of marsh elevation and landcover evolution is important for coastal management and conservation. With recent advances in the application of high-resolution geodetic remote sensing techniques, accurate and rapid acquisition of topographic and geomorphic data is possible at a fine spatial resolution over large spatial extent. These techniques include airborne-based methods, such as Airborne Laser Scanning (ALS) and Unmanned Aircraft System (UAS) photogrammetry using Structure-from-Motion (SfM), and ground-based methods, such as Terrestrial Laser Scanning (TLS). Products such as Digital Elevation Models (DEMs), above ground biomass, and fractional vegetation cover produced by these high-resolution measurement techniques are revolutionizing and accelerating our understanding of geomorphological processes and landform transformations. Hyperspatial three-dimensional (3D) point cloud data generated by TLS and UAS-SfM can provide sampling of the marsh scene at previously unforeseen spatial detail. However, these data have different characteristics and different representations of the underlying terrain and landcover. While there are differences, the challenges associated with these technologies are large data sets, often larger than 100 million points for a study area. Given their size and complexity, terrain mapping and extraction of relevant information from the complex 3D point cloud cannot be done without the use of intelligent algorithms. This research develops advanced geodetic imaging and computational techniques to better resolve spatial patterns in marsh elevation and landcover over larger spatial extents than is feasible using standard field surveying methods. This includes: (1) Development of a novel unsupervised learning method for robust segmentation of TLS point cloud data acquired in marshes into homogeneous features (clusters) to reduce scene complexity for measurement and monitoring of surface and vegetation evolution. (2) Assessment and evaluation of the transferability and adaptability of the unsupervised learning method developed for a 3D point cloud derived from TLS data to a 3D point cloud derived from UAS-SfM. (3) Development of ensemble neural networks for modelling DEM uncertainty. These networks are able to estimate DEM error, and then apply the DEM correction to every raster cell while providing an uncertainty for every correction. Furthermore, these networks can be applied to any 3D point cloud with a flexibility in the number and selection of model inputs, any type of geomatics measurements, and applicable to any type of environments. This work combines TLS and UAS-SfM measurements of a coastal marsh with the development and application of machine learning. The novel machine learning methods are developed to segment multi-perspective 3D point clouds and to correct DEMs while quantifying the spatial variability of the tolerance interval of the predictions (DEM uncertainty). The resulting information allows for enhanced change detection analysis of short-term marsh surface evolution in varying regimes. The developed computational techniques are generalizable to a wide range of coastal problems beyond marsh observations that rely on 3D point cloud data from a variety of scanning and imaging modalities, whether derived from lidar, UAS photogrammetry, or other survey methods. The resultant methods can be applied to estimate change detection uncertainty and monitor marsh evolution with these surveying technologies. In return, this can help support regional management of marshes in terms of understanding their short-term dynamics and long-term resilience
Using Spectral Graph Theory to Analyze Gene Expression Networks
Get PDFThis paper covers the potential applications of using the spectral analysis of a graph’s Laplacian matrix to gene co-expression networks. The general idea is to take publically available genetic data from cancer studies, organize them into gene co-expression networks, and analyze them using Spectral Graph theory. The publically available cancer study data includes files that show the occurrence of several different genes within a single person’s genetic data (given by fragments per kilobase million). The research takes the data of several patients and organizes them into a table. From there, each gene’s occurrence is measured against every other gene’s occurrence using Pearson correlation values, resulting in another table of pairs of genes and their correlation values. For each line, a gene, another gene, and their Pearson correlation value are represented in three columns corresponding to each aforementioned piece of data. Only genes that have a Pearson correlation value above a certain threshold were added to this file so that the file represents only significant correlations between genes. This file could be interpreted as an edge list for a gene co-expression network, which is a graph showing connections between genes. Each gene represents a single node of the graph, and every line of the file contained the connection between two genes, this connection being the edge between two nodes. With the file able to be interpreted as a graph, Spectral Graph theory concepts applied to it very naturally, allowing us to extract the second-smallest eigenvalue of the graph’s Laplacian matrix and the degree of zero eigenvalues, which gave us an understanding of the graph’s structure
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