1,721,139 research outputs found
Large-Scale Network Imputation and Prediction of Traffic Volume Based on Multi-Source Data Collection System
No full textWhile newly developed traffic detectors were actively deployed to improve the accuracy and coverage of collecting city-wise traffic state information, the rapid transition of the traffic management system caused the problems of massive data corruption. For the practical application of recovering the missing values, the deep learning-based imputation technique is used, which relies on prediction performance with the consideration of dynamic spatial and temporal characteristics in the traffic state information. However, the existing method requires an assumption that the given data is a complete dataset from a single source based on the experiments evaluated on a small scale or long stream of freeways. In this paper, we propose a multivariable spatio-temporal learning technique based on multi-source traffic state information, which was realized by adopting Attention-based Spatial-Temporal Graph Convolutional Networks(ASTGCN). The proposed imputation method cooperatively aggregates spatial and temporal correlation from two different types of detectors into an integrated framework, which allows us to predict missing volume regardless of the missing rate. Moreover, the study was conducted on a large-scale network that contains the entire road characteristics. Daejeon city has served as a case study to demonstrate the performance, and the results show that the mean absolute error of the proposed method is under 12 veh/5-min. Our work indicates that multi-source traffic state information can be utilized to impute city-wide missing traffic volume
Organic complementary ring oscillators using a functional polymer interfacial layer for highly improved oscillation frequency
No full textWe report the improved oscillation frequency of the organic complementary ring oscillators by balancing mobilities of p- and n-type organic field-effect transistors (OFETs) with a functional polymer interfacial layer. By employing poly (methyl methacrylate) (PMMA) as the interfacial layer, the balanced performance of the p- and n-type OFETs was achieved, which resulted in the improved performance of the complementary inverters. With the PMMA interfacial layer, the noise margin was increased from 35 % to 80 % of 1/2 supply voltage, and the maximum gain was 1.5 times higher than the one of the complementary inverter without the interfacial layer. The oscillation frequency of the organic complementary ring oscillators was remarkably improved from 106.7 Hz to 1.4 kHz. The polymer interfacial layer to balance the performance of p- and n-type OFETs is found to be a simple and efficient way to facilitate the operation of the organic complementary ring oscillators.OAIID:RECH_ACHV_DSTSH_NO:T201633259RECH_ACHV_FG:RR00200001ADJUST_YN:EMP_ID:A076109CITE_RATE:1.43DEPT_NM:전기·정보공학부EMAIL:[email protected]_YN:YN
Top-Gate Field-Effect Transistor as a Testbed for Evaluating the Photostability of Organic Photovoltaic Polymers
No full text© 2022 Wiley-VCH GmbHLight-induced performance degradation in organic solar cells (OSCs) is a major impediment to their commercialization. As the photostability of OSCs strongly depends on the material's properties, the most effective solution for this concern is to develop a photostable material. However, the wide variety of causes of photo-instability in a standard multilayered OSC structure complicates the evaluation of photostability of newly developed materials. To address this challenge, a top-gate field-effect transistor (FET) as a testbed for evaluating the photostability of OSC materials is proposed. This device test platform minimizes the internal and external origins of photo-instability by employing a fluoropolymer gate dielectric. The photostability of an OSC material incorporated in this FET testbed can be evaluated by monitoring light-induced mobility degradation. Two types of common donor polymers with similar chemical structures and crystallinity are employed as test materials, and their photostability is evaluated. The test results correspond to the photostability measurements conducted in the standard OSC structure, validating the proposed FET testbed. The proposed FET testbed enables rapid evaluation of the photostability of a newly developed OSC material, thereby providing timely feedback to material scientists. This boosts the development of photostable OSC materials.N
Efficient computation of elliptic gabriel graph
No full textSearching neighboring points around a point in a point set has been important for various applications and there have been extensive studies such as the minimum spanning tree, relative neighborhood graph, Delaunay triangulation, Gabriel graph, and so on. Observing the fact that the previous approaches of neighbor search may possibly sample severely biased neighbors in a set of unevenly distributed points, an elliptic Gabriel graph has recently been proposed. By extending the influence region from a circle to an ellipse, the elliptic Gabriel graph generalizes the ordinary Gabriel graph. Hence, the skewness in the sampled neighbors is rather reduced. In this paper, we present a simple observation which allows to compute the correct elliptic Gabriel graph efficiently by reducing the search space. © Springer-Verlag Berlin Heidelberg 2006
Origin of the Mixing Ratio Dependence of Power Conversion Efficiency in Bulk Heterojunction Organic Solar Cells with Low Donor Concentration
No full textWe studied the origin of the improvement in device performance of thermally evaporated bulk heterojunction organic photovoltaic devices (OPVs) with low donor concentration. Samples with three different donor-acceptor mixing ratios, 0:10 (C70-only), 1:9 (low-doped) and 3:7 (high-doped), were fabricated with 1,1-bis-(4-bis(4-methyl-phenyl)-amino-phenyl)-cyclohexane (TAPC):C70. The power conversion efficiencies (PCEs) of these samples were 1.14%, 2.74% and 0.69%, respectively. To determine why the low-doped device showed a high PCE, we measured various properties of the devices in terms of the effective energy band gap, activation energy, charge carrier mobility and recombination loss. We found that the activation energy for charge carrier transport was increased as we increased the TAPC concentration in the blends whereas the hole and electron mobilities became more balanced as the TAPC concentration was increased. Furthermore, the recombination loss parameter alpha (from the light intensity dependence) remained alpha to approximately 0.9 in the low-doped device, but it decreased to alpha to approximately 0.77 in the high-doped device, indicating a large recombination loss as a result of space charge. Therefore, the improved PCE of low-doped OPVs can be attributed to the balance between carrier mobilities with no increase in recombination loss.This work was supported by the Human Resources Development Program of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea government Ministry of Knowledge Economy (No. 20124010203170).OAIID:oai:osos.snu.ac.kr:snu2013-01/102/0000029430/6SEQ:6PERF_CD:SNU2013-01EVAL_ITEM_CD:102USER_ID:0000029430ADJUST_YN:NEMP_ID:A076109DEPT_CD:430CITE_RATE:1.149FILENAME:journal of nanoscience and nanotechnology 13, 7982 (dec, 2013).pdfDEPT_NM:전기·정보공학부EMAIL:[email protected]_YN:YCONFIRM:
Photocurable propyl-cinnamate-functionalized polyhedral oligomeric silsesquioxane as a gate dielectric for organic thin film transistors
No full textA polyhedral oligomeric silsesquioxane (POSS)-based insulating material with photocurable propyl-cinnamate groups (POSS-CYNNAM) was designed and synthesized through simple single step reaction for use as a gate dielectric in organic thin-film transistors (OTFT). POSS-CYNNAM was soluble in common organic solvents and formed a smooth thin film after spin-casting. A thin film of POSS-CYNNAM was cross-linked and completely solidified under UV irradiation without the use of additives such as photoacid generators or photoradical initiators. ITO/insulator/Au devices were fabricated and characterized to measure the dielectric properties of POSS-CYNNAM thin films, such as leakage current and capacitance. A pentacene-based OTFT using the synthesized insulator as the gate dielectric layer was fabricated on the transparent indium tin oxide (ITO) electrode, and its performance was compared to OTFTs using thermally cross-linked poly(vinyl phenol) (PVP) as the insulator. The fabricated POSS-CYNNAM OTFT showed a comparable performance to devices based on the PVP insulator with 0.1 cm(2)/Vs of the field effect mobility and 4.2 x 10(5) of an on/off ratio.This work was supported by a National Science Foundation (NRF) grant funded by the Korea government (MEST) (No. 2011-0011122) through GCRC-SOP (Grant No. 2011-0030668).OAIID:oai:osos.snu.ac.kr:snu2013-01/102/0000029430/7SEQ:7PERF_CD:SNU2013-01EVAL_ITEM_CD:102USER_ID:0000029430ADJUST_YN:YEMP_ID:A076109DEPT_CD:430CITE_RATE:3.836FILENAME:organic electronics 14, 2315 (sep, 2013).pdfDEPT_NM:전기·정보공학부EMAIL:[email protected]_YN:YCONFIRM:
Highly Efficient and Bright Inverted Top‐Emitting InP Quantum Dot Light‐Emitting Diodes Introducing a Hole‐Suppressing Interlayer
No full textInP quantum dots (QDs) based light-emitting diodes (QLEDs) are considered as one of the most promising candidates as a substitute for the environmentally toxic Cd-based QLEDs for future displays. However, the device architecture of InP QLEDs is almost the same as the Cd-based QLEDs even though the properties of Cd-based and InP-based QDs are quite different in their energy levels and shapes. Thus, it is highly required to develop a proper device structure for InP-based QLEDs to improve the efficiency and stability. In this work, efficient, bright, and stable InP/ZnSeS QLEDs based on an inverted top emission QLED (ITQLED) structure by newly introducing a "hole-suppressing interlayer" are demonstrated. The green-emitting ITQLEDs with the hole-suppressing interlayer exhibit a maximum current efficiency of 15.1-21.6 cd A(-1) and the maximum luminance of 17 400-38 800 cd m(-2), which outperform the recently reported InP-based QLEDs. The operational lifetime is also increased when the hole-suppressing interlayer is adopted. These superb QLED performances originate not only from the enhanced light-outcoupling by the top emission structure but also from the improved electron-hole balance by introducing a hole-suppressing interlayer which can control the hole injection into QDs.N
Large-Scale Network Imputation and Prediction of Traffic Volume Based on Multi-Source Data Collection System
No full textAlthough newly developed traffic detectors were actively deployed to improve the accuracy and coverage of collecting city-wise traffic state information, the rapid transition of the traffic management system caused the problems of massive data corruption. For the practical application of recovering the missing values, the deep learning-based imputation technique is used, which relies on prediction performance with the consideration of dynamic spatial and temporal characteristics in the traffic state information. However, the existing method requires an assumption that the given data comprise a complete dataset from a single source based on the experiments evaluated on a small scale or long stream of freeways. In this paper, we propose a multi-variable spatio-temporal learning technique based on multi-source traffic state information, which was realized by adopting Attention-based Spatial-Temporal Graph Convolutional Networks (ASTGCN). The proposed imputation method cooperatively aggregates spatial and temporal correlation from two different types of detectors into an integrated framework, which allows us to predict missing volume regardless of the missing rate. Moreover, the study was conducted on a large-scale network that contains the entire road characteristics. Daejeon city has served as a case study to demonstrate the performance, and the results show that the mean absolute error of the proposed method is under 12 vehicles/5 min. Our work indicates that multi-source traffic state information can be utilized to impute city-wide missing traffic volume.
"Positive Incentive" Approach To Enhance the Operational Stability of Quantum Dot-Based Light-Emitting Diodes
No full textBalanced charge injection promises high efficiency of quantum dot-based light-emitting diodes (QD-LEDs). The most widely used approach to realize charge injection balance impedes the injection rate of the dominant charge carrier with energetic barriers. However, these approaches often accompany unwanted outcomes (e.g., the increase in operation voltage) that sacrifice the operational stability of devices. Herein, a "positive incentive" approach is proposed to enhance the efficiency and the operational stability of QD-LEDs. Specifically, the supply of hole, an inferior carrier than its counterpart, is facilitated by adopting a thin fullerene (C-60) interlayer at the interface between the hole injection layer (MoOx) and hole transport layer (4,4'-bis(9-carbazolyl)-1,1'-biphenyl). The C-60 interlayer boosts the hole current by eliminating the universal energy barrier, lowers the operation voltage of QD-LEDs, and enhances the charge balance in the QD emissive layer within the working device. Consequently, QD-LEDs benefitting from the adoption of the C-60 interlayer exhibit significantly enhanced device efficiency and operation stability. Grounded on the quantitative assessment of the charge injection imbalance within the QD emissive layer, the impact of electrical parameters of QD-LEDs on their optoelectronic performance and operational stability is also discussed.N
Electrical-Stress-Induced Threshold Voltage Instability in Solution-Processed ZnO Thin-Film Transistors: An Experimental and Simulation Study
No full textIn this paper, we present the experimental and simulation results of the stress-recovery characteristics of solution-processed ZnO thin-film transistors under gate bias and current stress conditions. Under both stress conditions, we invariably observed a positive threshold voltage shift (Delta V(T)) that is initially associated with changes in the values of subthreshold slope and off-current, which later becomes constant on prolonging the stress time. However, Delta V(T) was less for current stress, compared with gate bias stress. This stress-induced Delta V(T) is speculated to be caused by defect creation in the active layer and charge trapping at the semiconductor-dielectric interface. Following a stretched exponential model, at room temperature, a characteristics time of 1.6 x 10(3) -3.6 x 10(3) s during stress and 7.7 x 10(3) -15.7 x 10(3) s during recovery was obtained under all gate bias and current stress conditions. The Delta V(T)-time measurements performed under various temperatures yield an activation energy of similar to 0.5 and similar to 0.7 eV for the stress and recovery periods, respectively. The device simulation indicates that Delta V(T) is mainly caused by the increase in acceptorlike defects of the density of states in the ZnO channel layer. Furthermore, it was found that the deep lying states are responsible for the change in the value of inverse subthreshold slope
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