Design and Implementation of a Full-Duplex Pipelined MAC Protocol for Multihop Wireless Networks

In multihop wireless networks, data packets are forwarded from a source node to a destination node through intermediate relay nodes. With half-duplex relay nodes, the end-to-end delay performance of a multihop network degrades as the number of hops increases, because the relay nodes cannot receive and transmit at the same time. Full-duplex relay nodes can reduce their per-hop delay by starting to forward a packet before the whole packet is received. In this paper, we propose a pipelined medium access control (PiMAC) protocol, which enables the relay nodes on a multihop path to simultaneously transmit and receive packets for full-duplex forwarding. For pipelined transmission over a multihop path, it is important to suppress both the self-interference of each relay node with the full-duplex capability and the intra-flow interference from the next relay nodes on the same path. In the PiMAC protocol, each relay node can suppress both the self- and intra-flow interference for full-duplex relaying on the multihop path by estimating the channel coefficients and delays of the interference during a multihop channel acquisition phase. To evaluate the performance of the PiMAC protocol, we carried out extensive simulations and software-defined radio-based experiments

Analysis of Ionic Domains on a Proton Exchange Membrane Using a Numerical Approximation Model Based on Electrostatic Force Microscopy

Understanding the ionic channel network of proton exchange membranes that dictate fuel cell performance is crucial when developing proton exchange membrane fuel cells. However, it is difficult to characterize this network because of the complicated nanostructure and structure changes that depend on water uptake. Electrostatic force microscopy (EFM) can map surface charge distribution with nano-spatial resolution by measuring the electrostatic force between a vibrating conductive tip and a charged surface under an applied voltage. Herein, the ionic channel network of a proton exchange membrane is analyzed using EFM. A mathematical approximation model of the ionic channel network is derived from the principle of EFM. This model focusses on free charge movement on the membrane based on the force gradient variation between the tip and the membrane surface. To verify the numerical approximation model, the phase lag of dry and wet Nafion is measured with stepwise changes to the bias voltage. Based on the model, the variations in the ionic channel network of Nafion with different amounts of water uptake are analyzed numerically. The mean surface charge density of both membranes, which is related to the ionic channel network, is calculated using the model. The difference between the mean surface charge of the dry and wet membranes is consistent with the variation in their proton conductivity. © 2021 by the authors. Licensee MDPI, Basel, Switzerland. Author keywords1

Comparison of standard-setting methods for the Korean Radiological Technologist Licensing Examination: Angoff, Ebel, bookmark, and Hofstee

Purpose This study aimed to compare the possible standard-setting methods for the Korean Radiological Technologist Licensing Examination, which has a fixed cut score, and to suggest the most appropriate method. Methods Six radiological technology professors set standards for 250 items on the Korean Radiological Technologist Licensing Examination administered in December 2016 using the Angoff, Ebel, bookmark, and Hofstee methods. Results With a maximum percentile score of 100, the cut score for the examination was 71.27 using the Angoff method, 62.2 using the Ebel method, 64.49 using the bookmark method, and 62 using the Hofstee method. Based on the Hofstee method, an acceptable cut score for the examination would be between 52.83 and 70, but the cut score was 71.27 using the Angoff method. Conclusion The above results suggest that the best standard-setting method to determine the cut score would be a panel discussion with the modified Angoff or Ebel method, with verification of the rated results by the Hofstee method. Since no standard-setting method has yet been adopted for the Korean Radiological Technologist Licensing Examination, this study will be able to provide practical guidance for introducing a standard-setting process

Epidemics of enterovirus infection in Chungnam Korea, 2008 and 2009

Previously, we explored the epidemic pattern and molecular characterization of enteroviruses isolated in Chungnam, Korea from 2005 to 2006. The present study extended these observations to 2008 and 2009. In this study, enteroviruses showed similar seasonal prevalent pattern from summer to fall and age distribution to previous investigation. The most prevalent month was July: 42.9% in 2008 and 31.9% in 2009. The highest rate of enterovirus-positive samples occurred in children < 1-year-old-age. Enterovirus-positive samples were subjected to sequence determination of the VP1 region, which resolved the isolated enteroviruses into 10 types in 2008 (coxsackievirus A4, A16, B1, B3, echovirus 6, 7, 9, 11, 16, and 30) and 8 types in 2009 (coxsackievirus A2, A4, A5, A16, B1, B5, echovirus 11, and enterovirus 71). The most prevalent enterovirus serotype in 2008 and 2009 was echovirus 30 and coxsackievirus B1, respectively, whereas echovirus 18 and echovirus 5 were the most prevalent types in 2005 and 2006, respectively. Comparison of coxsackievirus B1 and B5 of prevalent enterovirus type in Korea in 2009 with reference strains of each same serotype were conducted to genetic analysis by a phylogenetic tree. The sequences of coxsackievirus B1 strains segregated into four distinct clusters (A, B, C, and D) with some temporal and regional sub-clustering. Most of Korean coxsackievirus B1 strains in 2008 and 2009 were in cluster D, while only "Kor08-CVB1-001CN" was cluster C. The coxsackievirus B5 strains segregated in five distinct genetic groups (clusters A-E) were supported by high bootstrap values. The Korean strains isolated in 2001 belonged to cluster D, whereas Korean strains isolated in 2005 and 2009 belonged to cluster E. Comparison of the VP1 amino acid sequences of the Korean coxsackievirus B5 isolates with reference strains revealed amino acid sequence substitutions at nine amino acid sequences (532, 562, 570, 571, 576-578, 582, 583, and 585)

Updates on the genetic variations of Norovirus in sporadic gastroenteritis in Chungnam Korea, 2009-2010

Previously, we explored the epidemic pattern and molecular characterization of noroviruses (NoVs) isolated in Chungnam, Korea in 2008, and the present study extended these observations to 2009 and 2010. In Korea, NoVs showed the seasonal prevalence from late fall to spring, and widely detected in preschool children and peoples over 60 years of age. Epidemiological pattern of NoV was similar in 2008 and in 2010, but pattern in 2009 was affected by pandemic influenza A/H1N1 2009 virus. NoV-positive samples were subjected to sequence determination of the capsid gene region, which resolved the isolated NoVs into five GI (2, 6, 7, 9 and 10) and eleven GII genotypes (1, 2, 3, 4, 6, 7, 8, 12, 13, 16 and 17). The most prevalent genotype was GII.4 and occupied 130 out of 211 NoV isolates (61.6%). Comparison of NoV GII.4 of prevalent genotype in these periods with reference strains of the same genotype was conducted to genetic analysis by a phylogenetic tree. The NoV GII.4 strains were segregated into seven distinct genetic groups, which are supported by high bootstrap values and previously reported clusters. All Korean NoV GII.4 strains belonged to either VI cluster or VII cluster. The divergence of nucleotide sequences within VI and VII intra-clusters was > 3.9% and > 3.5%, respectively. The "Chungnam(06-117)/2010" strain which was isolated in June 2010 was a variant that did not belong to cluster VI or VII and showed 5.8-8.2%, 6.2-8.1% nucleotide divergence with cluster VI and VII, respectively

Toroidal-Shaped Coils for a Wireless Power Transfer System for an Unmanned Aerial Vehicle

Unmanned aerial vehicles (UAVs) using communications, sensors, and navigation equipment will play a key role in future warfare. Currently, UAVs are monitored to prevent misfire and accidents, and the conventional method adopted uses wires for data transmission and power supply. The repeated connection and disconnection of cables increases maintenance time and harms the connector. For convenience and stability, a wireless power transfer system to power UAVs is needed. Unlike other wireless power transfer (WPT) applications, the size of the receiving coils must be small, so that the WPT systems can be embedded inside space-limited UAVs. The small size reduces the coupling coefficient and transfer efficiency between the transmitting and the receiving coils. In this study, we propose a toroidal-shaped coil for a WPT system for UAVs with high coupling coefficient with minimum space requirements. For validation, conventional coils and the proposed toroidal-shaped coil were used and their coupling coefficient and power transfer efficiency were compared using simulated and measured results. The simulated and measured results were strongly correlated, confirming that the proposed WPT system significantly improved efficiency with negligible change in the space requirement

High-performance quantum dot light-emitting diodes using crosslinked hole transport materials based on dibenzo[b,d]furan

Solution-processed(용액 공정); High-performance QLEDs(고효율 양자점 발광 다이오드); Cross-linkable hole transport material(열 가교성 전공 수송 물질); Blend(혼합); Small molecule(단분자)Ⅰ. Introduction 1 Ⅱ. Theorical Background 5 2.1 Qunatum dot light-emitting diodes (QLEDs) 5 2.1.1 Quantum Dots (QDs) 5 2.1.2 Core Structure of QDs 5 2.1.3 Surface Passivation of QDs 6 2.2 Device Structure of QLEDs 7 2.2.1 All-Organic Materials Device Structure 7 2.2.2 Hybrid Materials Device Structure 8 2.2.3 All-Inorganic Materials Device Structure 8 2.3 QLEDs Device Mechanisms 8 2.3.1 Molecular Orbitals of Electrons 8 2.3.2 Charge Transfer and Recombination Mechanisms 10 2.4 Progress in Device Configuration 12 2.4.1 Top-Emitting QLEDs 12 2.4.2 Inverted QLEDs with All-Solution Processing 13 2.4.3 Tandem QLEDs 14 2.5 Fabrication of QLEDs devices 15 2.5.1 Vacuum process 15 2.5.1.1 Physical vapor deposition 15 2.5.1.2 Chemical Vapor Deposition 17 2.5.2 Solution process 18 2.5.2.1 spin coating 18 2.5.2.2 inkjet printing 19 2.6 Strategies for Enhancing QLEDs Devices 20 2.6.1 Enhancing QD Structure 20 2.6.2 Optimizing Device Architecture 21 2.6.2.1 Attaining Charge Equilibrium via a Hole Transport Materials 21 2.6.2.2 Attaining Charge Equilibrium via an Electron-Blocking Layer 23 2.6.2.3 Establishing Charge Equilibrium through a Hole-Spacing Layer 23 2.7 The uses of hole transport materials for solution process 24 2.7.1 Solvent resistance 24 2.7.2 Enhancing the properties of hole transport materials 24 2.7.2.1 Double hole transport layers 25 2.7.2.2 Blending hole transport materials 25 Ⅲ. Experimental methods 26 3.1 Materials and Characterization 26 3.2 Device fabrication 26 3.2.1 Fabrication of green QLEDs 26 3.2.2 Fabrication of hole only device 27 Ⅳ. Results and discussion 28 4.1 Blend crosslinked HTMs 28 4.2 Cross-linking test 29 4.3 Optical properties 30 4.4 UPS Analysis 33 4.5 Charge balance analysis 36 4.6 TRPL Analysis 37 4.7 AFM Analysis 38 4.8 Contact angle 40 4.9 QLEDs device performance 41 4.10 Lifetime measurement 46 Ⅴ. Conclusion 47 REFERENCES 48 SUMMARY 51MasterdCollectio

The political economy of social investment policies: evidence from the OECD countries

Since the mid-1990s, Organisation for Economic Co-operation and Development (OECD) countries have developed social investment policies that include active labour market policies (ALMPs) and work-family policies (WFPs). Employing qualitative as well as quantitative methods, this thesis investigates the effectiveness and determinants of social investment policies. The first paper tests the Matthew effect of social investment in terms of employment. It shows the existence of so-called Matthew effect that childcare and training benefit medium-educated workers in getting jobs more than lower- and higher-educated workers in fifteen European countries in the period 1992-2013. The second paper, motivated by the intersectionality between class and gender, explores whether WFPs have the negative consequences in terms of gender equality and how the effects are different by women’s education level. This means the welfare state paradox and gendered trade-offs argument. Using macro-level data on fifteen European countries for 1992-2013, this paper finds that childcare and maternity and parental leave increase gender occupational segregation. Unlike the first and second papers, the third paper, focusing training, investigates the causal mechanism of how different skill preferences and different attitudes over training costs between employers, trade unions, and the state. An in-depth case study of South Korea shows that segmentalist coalitions of the three players play important role in changing institutions, skill formation systems, resulting in either an incremental institutional change or a transformative change of institutions. Three broader contributions can be suggested. First, social investment policies may bear on the recent growth of atypical employment and dualisation of the labour market. Second, the WFPs in particular may be related to the growth of glass ceiling and female ghettos with possibly considerable gender inequality. Third, the detrimental distributional outcomes may be contingent upon unequal power relations between political actors and their segrementalist cross-class coalitions

Privacy-Preserving Federated Learning Using Homomorphic Encryption

Federated learning (FL) is a machine learning technique that enables distributed devices to train a learning model collaboratively without sharing their local data. FL-based systems can achieve much stronger privacy preservation since the distributed devices deliver only local model parameters trained with local data to a centralized server. However, there exists a possibility that a centralized server or attackers infer/extract sensitive private information using the structure and parameters of local learning models. We propose employing homomorphic encryption (HE) scheme that can directly perform arithmetic operations on ciphertexts without decryption to protect the model parameters. Using the HE scheme, the proposed privacy-preserving federated learning (PPFL) algorithm enables the centralized server to aggregate encrypted local model parameters without decryption. Furthermore, the proposed algorithm allows each node to use a different HE private key in the same FL-based system using a distributed cryptosystem. The performance analysis and evaluation of the proposed PPFL algorithm are conducted in various cloud computing-based FL service scenarios

Privacy-Preserving Federated Learning Using Homomorphic Encryption

Federated learning (FL) is a machine learning technique that enables distributed devices to train a learning model collaboratively without sharing their local data. FL-based systems can achieve much stronger privacy preservation since the distributed devices deliver only local model parameters trained with local data to a centralized server. However, there exists a possibility that a centralized server or attackers infer/extract sensitive private information using the structure and parameters of local learning models. We propose employing homomorphic encryption (HE) scheme that can directly perform arithmetic operations on ciphertexts without decryption to protect the model parameters. Using the HE scheme, the proposed privacy-preserving federated learning (PPFL) algorithm enables the centralized server to aggregate encrypted local model parameters without decryption. Furthermore, the proposed algorithm allows each node to use a different HE private key in the same FL-based system using a distributed cryptosystem. The performance analysis and evaluation of the proposed PPFL algorithm are conducted in various cloud computing-based FL service scenarios