Browsing by Issue Date, starting with "2020-05-13"

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Dual heterogeneous structures lead to ultrahigh strength and uniform ductility in a Co-Cr-Ni medium-entropy alloy
(2020-05-13)
Du, X. H.
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Li, W. P.
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Chang, H. T.
;
Yang, T.
;
Duan, G. S.
Alloys with ultra-high strength and sufficient ductility are highly desired for modern engineering applications but difficult to develop. Here we report that, by a careful controlling alloy composition, thermomechanical process, and microstructural feature, a Co-Cr-Ni-based medium-entropy alloy (MEA) with a dual heterogeneous structure of both matrix and precipitates can be designed to provide an ultra-high tensile strength of 2.2GPa and uniform elongation of 13% at ambient temperature, properties that are much improved over their counterparts without the heterogeneous structure. Electron microscopy characterizations reveal that the dual heterogeneous structures are composed of a heterogeneous matrix with both coarse grains (10 similar to 30 mu m) and ultra-fine grains (0.5 similar to 2 mu m), together with heterogeneous L1(2)-structured nanoprecipitates ranging from several to hundreds of nanometers. The heterogeneous L1(2) nanoprecipitates are fully coherent with the matrix, minimizing the elastic misfit strain of interfaces, relieving the stress concentration during deformation, and playing an active role in enhanced ductility. Improving both strength and ductility simultaneously in structural metals and alloys remains a challenge. Here, the authors design a heterogeneous structure in a Co-Cr-Ni alloy that results in ultrahigh strength and significant uniform elongation.
Giant Resistivity Change of Transparent ZnO/Muscovite Heteroepitaxy
(2020-05-13)
Yen, Min
;
Lai, Yu-Hong
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Zhang, Chun-Li
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Cheng, Hou-Yung
;
Hsieh, Yi-Ting
The piezoresistive effect has shown a remarkable potential for mechanical sensor applications and been sought for its excellent performance. A great attention was paid to the giant piezoresistive effect and sensitivity delivered by silicon-based nanostructures. However, low thermal stability and complicated fabrication process hinder their practical applications. To overcome these issues and enhance the functionalities, we envision the substantial piezopotential in a zinc oxide (ZnO)/muscovite (mica) heteroepitaxy system based on theoretical consideration and realize it in practice. High piezoresistive effect with giant change of resistivity (-80 to 240%) and large gauge factor (>1000) are demonstrated through mechanical bending. The detailed features of heteroepitaxy, electrical transport, and strain are probed to understand the mechanism of such a giant resistivity change. In addition, a bending model is established to reveal the distribution of strain. Finally, we demonstrate a flex sensor featuring high sensitivity, optical transparency, and two-segment sensing with a great potential toward practical applications. Such an oxide heteroepitaxy exhibits excellent piezoresistive properties and mechanical flexibility. In the near future, the importance of flex sensors will emerge because of the precise control in the automation industries, and our results lead to a new design in the field of flex sensors.
Ultrafast Electron Cooling and Decay in Monolayer WS2 Revealed by Time- and Energy-Resolved Photoemission Electron Microscopy
(2020-05-13)
Li, Yaolong
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Liu, Wei
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Wang, Yunkun
;
Xue, Zhaohang
;
Leng, Yu-Chen
A comprehensive understanding of the ultrafast electron dynamics in two-dimensional transition metal dichalcogenides (TMDs) is necessary for their applications in optoelectronic devices. In this work, we contribute a study of ultrafast electron cooling and decay dynamics in the supported and suspended monolayer WS2 by time- and energy-resolved photoemission electron microscopy (PEEM). Electron cooling in the Q valley of the conduction band is clearly resolved in energy and time, on a time scale of 0.3 ps. Electron decay is mainly via a defect trapping process on a time scale of several picoseconds. We observed that the trap states can be produced and increased by laser illumination under an ultrahigh vacuum, and the higher local optical-field intensity led to the faster increase of trap states. The enhanced defect trapping could significantly modify the carrier dynamics and should be paid attention to in photoemission experiments for two-dimensional materials.
Development of Hybrid Pseudohalide Tin Perovskites for Highly Stable Carbon-Electrode Solar Cells
(2020-05-13)
Rameez, Mohammad
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Lin, Eric Yan-Ru
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Raghunath, Putikam
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Narra, Sudhakar
;
Song, Donghoon
Tin-based perovskites degrade rapidly upon interaction with water and oxygen in air because Sn-I bonds are weak. To address this issue, we developed novel tin perovskites, FASnI((3-x))(SCN)(x) (x = 0, 1, 2, or 3), by employing a pseudohalide, thiocyanate (SCN-), as a replacement for halides and as an inhibitor to suppress the Sn2+/Sn4+ oxidation. The structural and electronic properties of pseudohalide tin perovskites in this series were explored with quantum-chemical calculations by employing the plane-wave density functional theory (DFT) method; the corresponding results are consistent with the experimental results. Carbon-based perovskite devices fabricated with tin perovskite FASnI(SCN)(2) showed about a threefold enhancement of the device efficiency (2.4%) relative to that of the best FASnI(3)-based device (0.9%), which we attribute to the improved suppression of the formation of Sn4+, retarded charge recombination, enhanced hydrophobicity, and stronger interactions between Sn and thiocyanate for FASnI(SCN)(2) than those for FASnI(3). After the incorporation of phenylethyleneammonium iodide (PEAI, 10%) and ethylenediammonium diiodide (EDAI(2), 5%) as coadditives, the FASnI(SCN)(2) device gave the best photovoltaic performance with J(SC) = 20.17 mA cm(-2), V-OC = 322 mV, fill factor (FF) = 0.574, and overall efficiency of power conversion PCE = 3.7%. Moreover, these pseudohalide-containing devices display negligible photocurrent-voltage hysteresis and great stability in ambient air conditions.
Stereospecific Epitaxial Growth of Bilayered Porous Molecular Networks
(2020-05-13)
Fang, Yuan
;
Lindner, Benjamin D.
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Destoop, Iris
;
Tsuji, Takashi
;
Zhang, Zhenzhe
Stereocontrolled multilayer growth of supramolecular porous networks at the interface between graphite and a solution was investigated. For this study, we designed a chiral dehydrobenzo[12]annulene (DBA) building block bearing alkoxy chains substituted at the 2 position with hydroxy groups, which enable van der Waals stabilization in a layer and potential hydrogen-bonding interactions between the layers. Bias voltage-dependent scanning tunneling microscopy (STM) experiments revealed the diastereospecificity of the bilayer with respect to both the intrinsic chirality of the building blocks and the supramolecular chirality of the self-assembled networks. Top and bottom layers within the same crystalline domain were composed of the same enantiomers but displayed opposite supramolecular chiralities.
Deep learning assisted detection of glaucomatous optic neuropathy and potential designs for a generalizable model
(2020-05-14)
Ko, Yu-Chieh
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Wey, Shih-Yu
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Chen, Wei-Ta
;
Chang, Yu-Fan
;
Chen, Mei-Ju
Purpose To evaluate ways to improve the generalizability of a deep learning algorithm for identifying glaucomatous optic neuropathy (GON) using a limited number of fundus photographs, as well as the key features being used for classification. Methods A total of 944 fundus images from Taipei Veterans General Hospital (TVGH) were retrospectively collected. Clinical and demographic characteristics, including structural and functional measurements of the images with GON, were recorded. Transfer learning based on VGGNet was used to construct a convolutional neural network (CNN) to identify GON. To avoid missing cases with advanced GON, an ensemble model was adopted in which a support vector machine classifier would make final classification based on cup-to-disc ratio if the CNN classifier had low-confidence score. The CNN classifier was first established using TVGH dataset, and then fine-tuned by combining the training images of TVGH and DrishtiGS datasets. Class activation map (CAM) was used to identify key features used for CNN classification. Performance of each classifier was determined through area under receiver operating characteristic curve (AUC) and compared with the ensemble model by diagnostic accuracy. Results In 187 TVGH test images, the accuracy, sensitivity, and specificity of the CNN classifier were 95.0%, 95.7%, and 94.2%, respectively, and the AUC was 0.992 compared to the 92.8% accuracy rate of the ensemble model. For the Drishti-GS test images, the accuracy of the CNN, the fine-tuned CNN and ensemble model was 33.3%, 80.3%, and 80.3%, respectively. The CNN classifier did not misclassify images with moderate to severe diseases. Class-discriminative regions revealed by CAM co-localized with known characteristics of GON. Conclusions The ensemble model or a fine-tuned CNN classifier may be potential designs to build a generalizable deep learning model for glaucoma detection when large image databases are not available.
【完美求職系列講座】傻瓜理財法～畢業存出一桶金
(國立陽明大學, 2020-05-15)
陽明電子報編輯小組
【反毒宣導月活動】「藥物濫用防制認知檢測」問卷填答抽獎活動
(國立陽明大學, 2020-05-15)
陽明電子報編輯小組
Resource provisioning towards OPEX optimization in horizontal edge federation
(2020-05-15)
Baghban, Hojjat
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Huang, Ching-Yao
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Hsu, Ching-Hsien
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電子工程學系及電子研究所
;
電機工程學系
Energy consumption is a key performance metric in multi-access edge computing (MEC) system. Therefore, minimizing consumed energy cost is critically essential. The 5G networks deal with edge computing resources so that the operator would face with power supply limitation. Therefore, it may not be able to provide sufficient resources to ever-increasing user's requests. One way to compensate such limitation is to form horizontal edge federation (HEF) so that all participant can share the resource capacities as well as request workloads. Energy efficient and ultra-low latency HEF involves the setting of critical factor in each participant: offloading ratios. The decided offloading ratios must provide satisfactory service level to meet latency and physical resource types capacity constraints demanded by requests. Our proposed problem is an energy efficient operational cost (eOPEX) optimization problem. In this paper, we formulate it as a mixed integer linear program and demonstrate that the problem is NP-hard and proposed a federated multidimensional fractional knapsack based algorithm (FMFK) as our approach. The result shows that the horizontal edge federation based on the FMFK performs better and saves the more e-OPEX as well as serving more input requests compare with the non-federation approach. The experimental results show that our approach save about 40% of e-OPEX specially for high latency sensitive application requests in hotspot zone. It shows around 50% e-OPEX saving in the case of high computation unit cost compare with non-federation approach.
陳右穎教授團隊利用「石墨烯」打造奈米生物晶片，讓診斷治療合而為一
(國立陽明大學, 2020-05-15)
陽明電子報編輯小組
如何縮短診斷與治療的時間差，一直是亟待克服的難題。陽明醫工系陳右穎教授團隊利用奈米材料「石墨烯」，重新打造神經探針晶片深
【懷生社講座】歡迎餵食～兩隻偽浪浪的徒步環台記
(國立陽明大學, 2020-05-15)
陽明電子報編輯小組
Timing jitter reduction of passively Q-switched solid-state lasers by coupling resonance between pumping and firing rates
(2020-05-15)
Chen, Y. F.
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Chien, P. Y.
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Lee, C. C.
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Huang, K. F.
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Liang, H. C.
The coupling resonance between pumping and firing rates is originally proposed to achieve the timing jitter reduction of a Nd : YVO4 laser passively Q-switched with a saturable absorber. When the pumping rate is higher than the spontaneous emission rate, it is experimentally confirmed that the pulse firing rate can be fractionally locked with the pumping rate by controlling the pump power. The locking characteristics of the firing rate display a variety of complex plateaus that can be excellently manifested with the sine-circle map. From numerical analyses, the coupling strength can be verified to be effectively enhanced by reducing the duty cycle of the pumping rate. (C) 2020 Optical Society of America
NiCo2O4/graphene quantum dots (GQDs) for use in e fficient electrochemical energy devices: An electrochemical and X-ray absorption spectroscopic investigation
(2020-05-15)
Chang, Han-Wei
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Fu, Ji-Xuan
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Huang, Yu-Cheng
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Lu, Ying-Rui
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Kuo, Chun-Hong
NiCo2O4/graphene quantum dots (GQDs) were synthesized by the incorporation of GQDs into NiCo2O4 as electrode materials for use in electrochemical energy devices. The electronic structure and the electrochemical performance of NiCo2O4/GQDs were investigated by X-ray absorption spectroscopy (XAS) and electrochemical measurements. The rich redox active sites were revealed on the NiCo2O4/GQDs, which were formed by the strong CeOeNi/Co interaction between NiCo2O4 and GQDs. The synergetic double-layer capacitive and pseudocapacitive properties were suggested to provide favorable electrochemical characteristics. In/ex situ XAS elucidates local electronic and chemical environments and provides insights into the energy storage/conversion mechanisms. Analytical results demonstrate that the NiCo2O4/GQDs have strong oxygen-carbon bridges and have more Ni active sites than does NiCo2O4, favoring metal-to-ligand charge transfer at the interface between NiCo2O4 and GQDs, critically influencing electrochemical performance. This work contributes importantly to the field by elucidating an energy storage/conversion mechanism for electrochemical energy devices.
A permutation-and-backtrack approach for reliability evaluation in multistate information networks
(2020-05-15)
Chen, Shin-Guang
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Lin, Yi-Kuei
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工業工程與管理學系
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Department of Industrial Engineering and Management
Nowadays, people live heavily on information systems to handle their business and schedules. A reliable information system helps people smoothly and efficiently deal with their daily-life affairs. An information system usually consists of connected software and hardware components, and can be modeled by connected graphs. In network theory, such graphs are called multistate information networks. Therefore, the reliability of an information system can be evaluated by network theory, namely network reliability. The most popular approach to evaluate network reliability is the three-stage-approach (TSA), which involves (a) finding all minimal paths (MPs), (b) finding all d-system vectors (d-SVs), and (c) calculating the union probability of d-SVs for reliability. Approaches for creating all MPs has been reported. There is a need for a more efficient approach to generate all d-SVs for such calculation. In this article, an approach based on permutation-and-backtrack facility is proposed to generate all such d-SVs. The efficiency of this approach is generally accepted to be superior to the existing approaches. The proposed approach provides us an efficient, and simple way to speed up TSA as a more powerful tool for evaluating the reliability of multistate information networks. (C) 2020 Elsevier Inc. All rights reserved.
【陽明圖花樹報報Ｘ萬方知識查找】
(國立陽明大學, 2020-05-15)
陽明電子報編輯小組
2020「天下USR大學公民」調查，陽明名列公立中型大學第一
(國立陽明大學, 2020-05-15)
陽明電子報編輯小組
《天下雜誌》日前公布2020年「天下USR大學公民」調查結果，陽明在公立一般中型大學排行中名列第一。對於創校以來即以偏鄉醫療為使
Berezinskii-Kosterlitz-Thouless transition in an Al superconducting nanofilm grown on GaAs by molecular beam epitaxy
(2020-05-15)
Su, Guan-Ming
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Wu, Bi-Yi
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Fan, Yen-Ting
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Kumar, Ankit
;
Chang, Chau-Shing
We have performed extensive transport experiments on a 4 nm thick aluminum (Al) superconducting film grown on a GaAs substrate by molecular beam epitaxy (MBE). Nonlinear current-voltage (I-V) measurements on such a MBE-grown superconducting nanofilm show that V similar to I-3, which is evidence for the Berezinskii-Kosterlitz-Thouless (BKT) transition, both in the low-voltage (T-BKT 1.97 K) and high-voltage regions (T-BKT 2.17 K). In order to further study the two regions where the I-V curves are BKT-like, our experimental data are fitted to the temperature-induced vortices/antivortices unbinding model as well as the dynamical scaling theory. It is found that the transition temperature obtained in the high-voltage region is the correct T-BKT as confirmed by fitting the data to the aforementioned models. Our experimental results unequivocally show that I-V measurements alone may not allow one to determine T-BKT for superconducting transition. Therefore, one should try to fit one's results to the temperature-induced vortices/antivortices unbinding model and the dynamical scaling theory to accurately determine T-BKT in a two-dimensional superconductor.
陽明聯手國體大打造防疫訓練系統，助選手備戰東澳
(國立陽明大學, 2020-05-15)
陽明電子報編輯小組
新型冠狀病毒造成全球大傳染，也導致運動訓練與比賽中斷，包括東京奧運都被迫延後一年舉行。陽明與國立體育大學聯手辦理「東京奧
《私人戰爭》（A Private War）
(國立陽明大學, 2020-05-15)
黃柏威
;
陽明電子報編輯小組
傳統與現代並陳，合校校徽設計初稿公布
(國立陽明大學, 2020-05-15)
陽明電子報編輯小組
秘書室與學生會5月6日晚間共同主辦「陽明交大校徽識別系統設計說明會」，會中公布Ａ、Ｂ兩組分別呈現傳統與現代兩種風格，以及由