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The Effect of Calcium and Halide Ions on the Gramicidin A Molecular State and Antimicrobial Activity
(2020-09-01)
Carillo, Kathleen D.
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Lo, Chi-Jen
;
Tzou, Der-Lii M.
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Lin, Yi-Hung
;
Fang, Shang-Ting
Gramicidin A (gA) forms several convertible conformations in different environments. In this study, we investigated the effect of calcium halides on the molecular state and antimicrobial activity of gramicidin A. The molecular state of gramicidin A is highly affected by the concentration of calcium salt and the type of halide anion. Gramicidin A can exist in two states that can be characterized by circular dichroism (CD), mass, nuclear magnetic resonance (NMR) and fluorescence spectroscopy. In State 1, the main molecular state of gramicidin A is as a dimer, and the addition of calcium salt can convert a mixture of four species into a single species, which is possibly a left-handed parallel double helix. In State 2, the addition of calcium halides drives gramicidin A dissociation and denaturation from a structured dimer into a rapid equilibrium of structured/unstructured monomer. We found that the abilities of dissociation and denaturation were highly dependent on the type of halide anion. The dissociation ability of calcium halides may play a vital role in the antimicrobial activity, as the structured monomeric form had the highest antimicrobial activity. Herein, our study demonstrated that the molecular state was correlated with the antimicrobial activity.
Two-Layer Current Sharing Control of Parallel Connected Grid Inverters with Specified Line Impedance Uncertainties
(2019-01-01)
Chen, Yi-Cheng
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Tzou, Ying-Yu
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電控工程研究所
;
Institute of Electrical and Control Engineering
Parallel operation of grid inverters for AC nanogrids requires robust power sharing as well as fast dynamic responses. This paper proposes a two-layer current sharing control scheme for parallel connected inverters with specified uncertainties of line impedances. The inner layer controller is designed to achieve a desired output impedance with specified voltage THD under nonlinear rectifier load. The outer layer controller is designed to provide robust current sharing control by using virtual impedance control with specified line impedance uncertainties. Simulation and experimental verifications have been carried out to illustrate the performance of the proposed two-layer current sharing control scheme.
Heteroepitaxy of Co-Based Heusler Compound/Muscovite for Flexible Spintronics
(2019-09-25)
Chen, Yi-Cheng
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Yen, Min
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Lai, Yu-Hong
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Markou, Anastasios
;
Zhang, Liguo
Materials with high spin-polarization play an important role in the development of spintronics. Co-based Heusler compounds are a promising candidate for practical applications because of their high Curie temperature and tunable half-metallicity. However, it is a challenge to integrate Heusler compounds into thin film heterostructures because of the lack of control on crystallinity and chemical disorder, critical factors of novel behaviors. Here, muscovite is introduced as a growth substrate to fabricate epitaxial Co2MnGa films with mechanical flexibility. The feature of heteroepitaxy is evidenced by the results of X-ray diffraction and transmission electron microscopy. Moreover, high chemical ordering with superior properties is delivered according to the observation of large Hall conductivity (680 Omega(-1) cm(-1)) and highly saturated magnetic moment (similar to 3.93 mu(B)/f.u.), matching well with bulk crystals. Furthermore, the excellence of magnetic and electrical properties is retained under the various mechanical bending conditions. Such a result suggests that the development of Co2MnGa/muscovite heteroepitaxy provides not only a pathway to the thin film heterostructure based on high-quality Heusler compounds but also a new aspect of spintronic applications on flexible substrates.
Thickness dependence of the anomalous Hall effect in thin films of the topological semimetal Co2MnGa
(2019-08-19)
Markou, Anastasios
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Kriegner, Dominik
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Gayles, Jacob
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Zhang, Liguo
;
Chen, Yi-Cheng
Topological magnetic semimetals promise large Berry curvature through the distribution of the topological Weyl nodes or nodal lines and further novel physics with exotic transport phenomena. We present a systematic study of the structural and magnetotransport properties of Co2MnGa films from thin (20 nm) to bulklike behavior (80 nm) in order to understand the underlying mechanisms and the role of topology. The magnetron sputtered Co2MnGa films are L2(1)-ordered showing very good heteroepitaxy and a strain-induced tetragonal distortion. The anomalous Hall conductivity was found to be maximum at a value of 1138 S/cm, with a corresponding anomalous Hall angle of 13%, which is comparatively larger than topologically trivial metals. There is good agreement between the theoretical calculations and the Hall conductivity observed for the 80 nm film, which suggests that the effect is intrinsic. Thus, the Co2MnGa compound manifests as a promising material for topologically driven spintronic applications.
THz emission from organic cocrystalline salt: 2, 6-diaminopyridinium-4-nitrophenolate-4-nitrophenol
(2016-03-07)
Tu, Chien-Ming
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Chou, Li-Hsien
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Chen, Yi-Cheng
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Huang, Ping
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Rajaboopathi, M.
We report few-cycle THz pulses emission from a novel organic crystal 2,6-diaminopyridinium-4-nitrophenolate-4-nitrophenol (DAP(+)NP(-)NP). The observed amplitude of the THz electric field from a DAP(+)NP(-)NP crystal is comparable with that from a ZnTesingle crystal under the same optical pumping conditions. Both the waveform and spectra of the THz radiation from DAP(+)NP(-)NP are similar to those from ZnTe. We conclude that a high quality DAP(+)NP(-)NP crystal would be a high potential candidate in THz generation and applications. (C) 2016 Optical Society of America
Helicity-dependent terahertz emission spectroscopy of topological insulator Sb2Te3 thin films
(2017-11-06)
Tu, Chien-Ming
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Chen, Yi-Cheng
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Huang, Ping
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Chuang, Pei-Yu
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Lin, Ming-Yu
We report on helicity-dependent terahertz emissions that originate from the helicity-dependent photocurrents in topological insulator Sb2Te3 thin films due to ultrafast optical excitation. The polarity of the emitted terahertz radiation is controlled by both the incident angle and the helicity of optical pulses. Using an unprecedented decomposition-recombination procedure in the time domain, the signals of the Dirac fermions are fully separated from bulk contributions. These results provide insights into the optical coupling of topological surface states and open up opportunities for applying helicity-dependent terahertz emission spectroscopy in spintronics.
Large anomalous Nernst effect in thin films of the Weyl semimetal Co2MnGa
(2018-11-19)
Reichlova, Helena
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Schlitz, Richard
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Beckert, Sebastian
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Swekis, Peter
;
Markou, Anastasios
The magneto-thermoelectric properties of Heusler compound thin films are very diverse. Here, we discuss the anomalous Nernst response of Co2MnGa thin films. We systematically study the anomalous Nernst coefficient as a function of temperature, and we show that unlike the anomalous Hall effect, the anomalous Nernst effect in Co2MnGa strongly varies with temperature. We exploit the on-chip thermometry technique to quantify the thermal gradient, which enables us to directly evaluate the anomalous Nernst coefficient. We compare these results to a reference CoFeB thin film. We show that the 50-nm-thick Co2MnGa films exhibit a large anomalous Nernst effect of -2 mu V/K at 300 K, whereas the 10-nm-thick Co2MnGa film exhibits a significantly smaller anomalous Nernst coefficient despite having similar volume magnetizations. These findings suggest that the microscopic origin of the anomalous Nernst effect in Co2MnGa is complex and may contain contributions from skew-scattering, side-jump, or intrinsic Berry phase. In any case, the observed anomalous Nernst coefficient of -2 mu V/K at 300 K is large compared to the values measured in other thin films and makes this material system a very promising candidate for efficient spin-caloritronic devices. Published by AIP Publishing.
Predicting Traffic of Online Advertising in Real-time Bidding Systems from Perspective of Demand-Side Platforms
(2016-01-01)
Lai, Hsu-Chao
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Shih, Wen-Yueh
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Huang, Jiun-Long
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Chen, Yi-Cheng
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資訊工程學系
Online advertising has been all the rage these years. Budget control and traffic prediction turn out to be important issues for the demand-side platforms (DSPs). However, DSPs cannot easily grab the information of audiences and media platforms. Although DSPs might have the information immediately, it is still hard to response the request of advertisements in real-time due to the high volume of features. Therefore, we propose a method predicting traffic of requests from perspective of DSPs. The features we used are simple to be extracted from historical data. The prediction model we chose is regression model with closed-form solution. Both the features and regression model make our prediction adaptive in real-time systems. Our method can detect traffic anomalies and prevent it from overwhelming prediction. Moreover, our method can also keep pace of the trend. Experiment results show that our method's error rate of prediction is about 0.9% in total, and 10% per time unit.
Spectro-temporal Modulation Based Singing Detection Combined with Pitch based Grouping for Singing Voice Separation
(2013-01-01)
Lin, Tse-En
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Hsu, Chung-Chien
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Chen, Yi-Cheng
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Chen, Jian-Hueng
;
Chi, Tai-Shih
A spectro-temporal modulation based singing voice detection cascaded with a Viterbi based pitch tracking algorithm is proposed in this paper for singing-voice separation from monaural recordings. To detect the singing voice, the spectrotemporal modulation energy related to voice harmonics is extracted using a spectro-temporal modulation analysis framework developed for the Fourier spectrogram. Separation of singing -voice from background music is conducted using a binary mask to group estimated harmonics of singing voice. The proposed system is evaluated using MIR-1K dataset and is shown outperforming three other binary-mask based systems in the vocal/music separation task.
On efficiently mining high utility sequential patterns
(2016-11)
Wang, Jun-Zhe
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Huang, Jiun-Long
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Chen, Yi-Cheng
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資訊工程學系
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Department of Computer Science
High utility sequential pattern mining is an emerging topic in pattern mining, which refers to identify sequences with high utilities (e.g., profits) but probably with low frequencies. To identify high utility sequential patterns, due to lack of downward closure property in this problem, most existing algorithms first generate candidate sequences with high sequence-weighted utilities (SWUs), which is an upper bound of the utilities of a sequence and all its supersequences, and then calculate the actual utilities of these candidates. This causes a large number of candidates since SWU is usually much larger than the real utilities of a sequence and all its supersequences. In view of this, we propose two tight utility upper bounds, prefix extension utility and reduced sequence utility, as well as two companion pruning strategies, and devise HUS-Span algorithm to identify high utility sequential patterns by employing these two pruning strategies. In addition, since setting a proper utility threshold is usually difficult for users, we also propose algorithm TKHUS-Span to identify top-k high utility sequential patterns by using these two pruning strategies. Three searching strategies, guided depth-first search (GDFS), best-first search (BFS) and hybrid search of BFS and GDFS, are also proposed to improve the efficiency of TKHUS-Span. Experimental results on some real and synthetic datasets show that HUS-Span and TKHUS-Span with strategy BFS are able to generate less candidate sequences and thus outperform other prior algorithms in terms of mining efficiency.

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