Browsing by Author "Lin, Shih-Yen"

Now showing 1 - 20 of 72

A Fast and Accurate Algorithm for Diffeomorphic and Symmetric Non-rigid Registration of Brain Magnetic Resonance Images
(2015-01-01)
Lin, Shih-Yen
;
Chen, Yong-Sheng
;
Chen, Li-Fen
;
交大名義發表
;
資訊工程學系
This paper proposes a non-rigid, symmetric and diffeomorphic algorithm for the registration of MR images. A log-Euclidean framework was used to model diffeomorphisms. Multiple features were used to enhance the speed of the proposed algorithm, including compactly supported Wendland\'s basis functions as models of velocity fields, a greedy optimization strategy, and a coarse-to-fine hierarchical framework. Symmetry was ensured through the invertibility of diffeomorphisms and the symmetry of the objective function and optimization algorithm. The proposed algorithm was evaluated using the results of 1560 pairwise registrations of 40 T1-weighted MRIs in the LPBA40 dataset. Our results demonstrated that the proposed algorithm is diffeomorphic with sub-voxel accuracy in terms of symmetry. The proposed algorithm outperforms 14 other registration algorithms in terms of speed (compared with diffeomorphic algorithms) and accuracy.
A Single InN Nanopillar Photodetector with Extended Infrared Response Grown by MOCVD
(2016)
Hsu, Lung-Hsing
;
Kuo, Chien-Ting
;
Cheng, Yuh-Jen
;
Chen, Kuan-Chao
;
Kuo, Hao-Chung
An extended infrared photoresponse is observed in a high quality InN pillar/p-GaN photodetector with self-assembly epitaxy grown by LP-MOCVD. The IR portion photocurrent as high as 14.2% can be measured via AM1.5G solar simulated spectra.
A ZnO/InN/GaN Heterojunction Photodetector with Extended Infrared Response
(2015)
Hsu, Lung-Hsing
;
Hsu, Shun-Chieh
;
Lee, Hsin-Ying
;
Tsai, Yu-Lin
;
Lin, Da-Wei
An extended infrared photoresponse is observed in a ZnO/InN/GaN heterojunction diode with InN grown by MOCVD. The external quantum efficiency is measured between 1200 and 1800 nm and can be as high as 3.55%.
Absorption enhancement in type-II coupled quantum rings due to existence of quasi-bound states
(2018-01-01)
Hsieh, Chi-Ti
;
Lin, Shih-Yen
;
Chang, Shu-Wei
;
光電工程學系
;
Department of Photonics
The absorption of type-II nanostructures is often weaker than type-I counterpart due to spatially separated electrons and holes. We model the bound-to-continuum absorption of type-II quantum rings (QRs) using a multiband source-radiation approach using the retarded Green function in the cylindrical coordinate system. The selection rules due to the circular symmetry for allowed transitions of absorption are utilized. The bound-to continuum absorptions of type-II GaSb coupled and uncoupled QRs embedded in GaAs matrix are compared here. The GaSb QRs act as energy barriers for electrons but potential wells for holes. For the coupled QR structure, the region sandwiched between two QRs forms a potential reservoir of quasi-bound electrons. Electrons in these states, though look like bound ones, would ultimately tunnel out of the reservoir through barriers. Multiband perfectly-matched layers are introduced to model the tunneling of quasi-bound states into open space. Resonance peaks are observed on the absorption spectra of type-II coupled QRs due to the formation of quasi-bound states in conduction bands, but no resonance exist in the uncoupled QR. The tunneling time of these metastable states can be extracted from the resonance and is in the order of ten femtoseconds. Absorption of coupled QRs is significantly enhanced as compared to that of uncoupled ones in certain spectral windows of interest. These features may improve the performance of photon detectors and photovoltaic devices based on type-II semiconductor nanostructures.
Attention and Functional Connectivity Among Patients With Early-Stage Subcortical Ischemic Vascular Disease and Alzheimer's Disease
(2020-08-13)
Tu, Min-Chien
;
Hsu, Yen-Hsuan
;
Yang, Jir-Jei
;
Huang, Wen-Hui
;
Deng, Jie Fu
The current study compared attention profiles and functional connectivity of frontal regions in patients with early-stage subcortical ischemic vascular disease (SIVD) and Alzheimer's disease (AD). Twenty patients with SIVD, 32 patients with AD, and 23 subjects with normal cognition (NC) received cognition and resting-state functional MRI (rs-fMRI) evaluations. The Cognitive Abilities Screening Instrument (CASI) was used to assess global cognition, and simple attention, processing speed, divided attention, and vigilance/sustained attention were evaluated using the Digit Span Forward, Trail Making Test, Symbol Digit Modality Test, and Conners Continuous Performance Test, respectively. Voxel-based regional homogeneity (ReHo) derived from rs-fMRI data was analyzed to identify significant clusters, which were further correlated with attention profiles. Although the patients with SIVD and AD had comparable global cognitive ability, those with SIVD exhibited worse divided attention and vigilance/sustained attention than those with AD. Compared with the NC group, the patients with SIVD exhibited decreased ReHo within the right middle frontal gyrus (MFG) and left anterior cingulate gyrus (ACG), whereas the patients with AD exhibited increased ReHo within the right orbital part of frontal regions. Correlations between these three clusters with attention exhibited distinct patterns according to the dementia subtype, as did attention indices with significance in predicting global cognition. In summary, our study suggested that worse attention performance was associated with functional disconnection within the frontal regions among patients with SIVD than in those with AD. Frontal functional disconnection may underlie the pathogenesis responsible for defective divided attention, vigilance/sustained attention, and notable within-group variations identified in SIVD.
Broadband InGaAs-capped InAs/GaAs quantum-dot infrared photodetector with Bi-modal dot height distributions
(2012-08-01)
Lin, Wei-Hsun
;
Lin, Shih-Yen
;
光電工程學系
;
Department of Photonics
The influence of quantum-dot (QD) height distribution on the detection wavelengths of InGaAs-capped quantum-dot infrared photodetectors (QDIPs) is investigated. For devices with 2.8 and 2.0 mono-layer (ML) InAs coverage, 7.6 and 10.4 mu m detection wavelengths are observed. The results suggest that reduced dot height would result in a longer detection wavelength. By using 2.4 ML InAs QDs with bi-modal dot height distributions, a 6-12 mu m broadband QDIP is achieved with the combination of similar to 8 and similar to 10 mu m peak detection wavelengths contributed by the larger and smaller InAs QDs. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4745052]
Broadband Quantum-Dot Infrared Photodetector
(2010-07-01)
Lin, Wei-Hsun
;
Tseng, Chi-Che
;
Chao, Kuang-Ping
;
Kung, Shu-Yen
;
Lin, Shih-Yen
In this letter, we report the five-period quantum-dot infrared photodetectors (QDIPs) with a bi-stacked quantum-dot (QD) structure for a wide and relatively flat detection response ranging from 4 to 11 m with high responsivities. The bi-stacked QD structure consists of a standard InAs QD and an InGaAs-capped InAs QD layer separated by a 50-nm GaAs barrier layer. The device exhibits a wide detection window in the range of 4-11 mu m with high responsivities, which suggests that similar responsivities can be obtained for the standard QD and the InGaAs-capped QD layers in the mid-wavelength (MWIR) and long-wavelength (LWIR) infrared ranges, respectively. The results are advantageous for the development of broadband QDIPs covering MWIR and LWIR ranges based on the stacked QD structures.
Compact microdisk cavity laser with type-II GaSb/GaAs quantum dots
(2011-01-31)
Hsu, K. S.
;
Chiu, T. T.
;
Lin, Wei-Hsun
;
Chen, K. L.
;
Shih, M. H.
Microdisk lasers with active region made of type-II GaSb/GaAs quantum dots on the GaAs substrate have been demonstrated. A microdisk cavity with diameter of 3.9 mu m was fabricated from a 225-nm-thick GaAs layer filled with GaSb quantum dots. Lasing at wavelengths near 1000 nm at 150 K was achieved for this microdisk. A high threshold characteristic temperature of 77 K was also observed. It is found that the lasing wavelength matches closely with the first-order whispering-gallery mode of the cavity as obtained from the finite-element method simulation. (c) 2011 American Institute of Physics. [doi: 10.1063/1.3543839]
Current Enhancement and Bipolar Current Modulation of Top-Gate Transistors Based on Monolayer MoS2 on Three-Layer WxMo1-xS2
(2018-07-25)
Chen, Kuan-Chao
;
Jian, Cing-Yu
;
Chen, Yi-Jia
;
Lee, Si-Chen
;
Chang, Shu-Wei
We demonstrated the top-gate transistors composed of monolayer MoS2 grown on three-layer alloys MoxW1-xS2 prepared by sequential sulfurization of predeposited transition metal films. The elemental mapping of the alloy indicates a uniform distribution of both cations Mo and W in the grown samples. Surprisingly, we find that the drain current of transistors could be enhanced by 2 orders of magnitude as the composition of Mo increases, whereas the gate-controlled current modulation turns bipolar and ultimately vanishes. These features might originate from the formation of in-gap defect states, with modest activation energy for transport and moderate hopping probability for current conduction, or a reduced electronic band gap of the conducting channel because of strain.
Effects of signal averaging, gradient encoding scheme, and spatial resolution on diffusion kurtosis imaging: An empirical study using 7T MRI
(2019-11-01)
Chiang, Chia-Wen
;
Lin, Shih-Yen
;
Cho, Kuan-Hung
;
Wu, Kuo-Jen
;
Wang, Yun
Background Although diffusion gradient directions and b-values have been optimized for diffusion kurtosis imaging (DKI), little is known about the effect of signal averaging on DKI reliability. Purpose To evaluate how signal averaging influences the reliability of DKI indices using two gradient encoding schemes with three spatial resolutions. Study Type Prospective. Animal Model Fifteen naive Sprague-Dawley rats. Field Strength/Sequence DKI was performed at 7T using two schemes (30 directions with three b-values [30d-3b] and six directions with 15 b-values [6d-15b]), three resolutions, and eight repetitions. Assessment DKI reliability was assessed using voxelwise relative error (sigma) and test-retest error of fractional anisotropy (FA), mean diffusivity (MD), and mean kurtosis (MK) within gray matter (GM) and white matter (WM). The number of excitations (NEX) was optimized by considering DKI reliability. The influence of the partial volume effect (PVE) was also assessed. Statistical Test One-way analysis of variance. Results The 30d-3b scheme, compared with the 6d-15b scheme, exhibited apparently smaller sigma(FA) and sigma(MK) (eg, at NEX 1, in GM, for three resolutions, sigma(FA): 19.9-38.2% vs. 34.2-61.4%, sigma(MK): 6.9-11.4% vs. 14.1-15.4%) and similar sigma(MD) (all differences between two schemes <1.6%). The optimal NEX was determined as 2 for enabling a reliable measurement of DKI-derived indices. The PVE at the lowest resolution apparently increased sigma(FA) for both schemes (19.9% for 30d-3b and 34.2% for 6d-15b) and sigma(MK) for the 6d-15b scheme (14.7%) in GM, and exerted lower effects on MK values for the 30d-3b scheme (P > 0.05). Data Conclusion A higher number of diffusion directions would benefit FA and MK estimation. A higher spatial resolution helps to reduce PVE. By using the 30d-3b scheme, MK is considered a robust index to reflect microstructural changes in GM and WM. We propose a systematic approach to determine the optimal DKI protocols for appropriate preclinical settings. Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;50:1593-1603.
Enhanced Absorption Due to Formation of Quasi-Bound States in Type-II Coupled Quantum Rings
(2018-03-01)
Hsieh, Chi-Ti
;
Lin, Shih-Yen
;
Chang, Shu-Wei
;
光電工程學系
;
Department of Photonics
The absorption of type-II nanostructures is often weaker than type-I counterpart due to spatially indirect optical transitions. This phenomenon limits the application of type-II nanostructures in photon detections. In this paper, we show that with proper arrangements of conduction barriers, the formation of quasi-bound states can significantly boost up the absorption of type-II coupled quantum rings. Meanwhile, the rapid tunneling of electrons in these leaky states should make the corresponding external quantum efficiency comparable to that of single (uncoupled) rings. These featuresmay improve the performance of photon detectors based on type-II semiconductor nanostructures.
Enhanced normal-incident absorption of quantum-dot infrared photodetectors with smaller quantum dots
(2008-07-01)
Tseng, Chi-Che
;
Chou, Shu-Ting
;
Chen, Yi-Hao
;
Chen, Cheng-Nan
;
Lin, Wei-Hsun
Ten-period InAs-GaAs quantum-dot (QD) infrared photodetectors grown under different In adatom supply procedures are investigated. Two In adatom supply procedures of In shutter 1) always opened and 2) periodically opened/closed are adopted in this letter. Larger QD sizes in both height and diameter and more uniform size distribution are observed for samples grown under an In shutter periodically opened/closed condition. The device with QDs grown under the In shutter always opened condition has revealed shorter detection wavelengths and enhanced normal incident absorption. The phenomenon shows that beside the increase of energy difference between confinement states, smaller QD sizes would also enhance the normal incident absorption predicted for the theoretically zero-dimensional QD structures.
Enhancement of field-effect mobility in molybdenum-disulfide transistor through the treatment of low-power oxygen plasma
(2016-09)
Chen, Kuan-Chao
;
Wu, Chong-Rong
;
Chang, Xiang-Rui
;
Chang, Shu-Wei
;
Lee, Si-Chen
We experimentally demonstrate that the treatment with low-power oxygen plasma can raise the field-effect mobility in molybdenum-sulfide (MoS2) transistors from 0.01 to 9.6 cm(2)V(-1)s(-1), which is an increment of about three orders of magnitude. The decrease in threshold voltage and the increase in the drain current of the devices indicate that the electron density increases significantly after the mild plasma treatment. The emergence of Mo-O characteristics but the suppression of Mo-S features on the X-ray photoelectron spectrum of the plasma-treated sample suggests that a portion of the MoS2 film becomes conductive molybdenum oxide. This transformation may considerably upgrade the performance of MoS2 transistors. (C) 2016 The Japan Society of Applied Physics
Enhancement of operation temperature of InAs/GaAs quantum-dot infrared photodetectors with hydrogen-plasma treatment
(2009-09-01)
Lin, Wei-Hsun
;
Tseng, Chi-Che
;
Chao, Kuang-Ping
;
Lin, Shih-Yen
;
Wu, Meng-Chyi
Postprocess hydrogen treatment is performed over fabricated ten-period InAs/GaAs quantum-dot infrared photodetectors. While keeping similar spectral responses at the same applied voltage, a reduced dark current is observed for the H-plasma-treated device, which is attributed to the suppression of surface leakage-current induced by surface damage during device processing. The significant reduction in dark current also enhanced the operation temperature of the device up to 100 K. Also observed are the smoothed-out mesa edges after the H-plasma treatment, which results in trapezoidal mesa edges. In this case, a longer propagation length in the device of the reflected incident light at the mesa edge would enhance the normal-incident absorption ratio of the H-plasma-treated device. (C) 2009 American Vacuum Society. [DOI:10.1116/1.3196781]
Fermi-level shifts in graphene transistors with dual-cut channels scraped by atomic force microscope tips
(2014-01-13)
Lin, Meng-Yu
;
Chen, Yen-Hao
;
Su, Chen-Fung
;
Chang, Shu-Wei
;
Lee, Si-Chen
We investigate the electronic properties of p-type graphene transistors on silicon dioxide with dual-cut channels that were scraped using atomic force microscope tips. In these devices, the current is forced to squeeze into the path between the two cuts rather than flow directly through the graphene sheet. We observe that the gate voltages with minimum current shift toward zero bias as the sizes of the dual-cut regions increase. These phenomena suggest that the Fermi levels in the dual-cut regions are shifted toward the Dirac points after the mechanical scraping process. (C) 2014 AIP Publishing LLC.
Field effect of in-plane gates with different gap sizes on the Fermi level tuning of graphene channels
(2014-05-05)
Lin, Meng-Yu
;
Chen, Yen-Hao
;
Wang, Cheng-Hung
;
Su, Chen-Fung
;
Chang, Shu-Wei
Tuning of the Fermi level is investigated in graphene channels using two in-plane gates with significantly different-sized isolating gaps. While the n-type tuning was achievable in both schemes, the wide-gap device had an enhanced minimum drain current and less prominent current modulation than the narrow-gap device. In addition, further p-type tuning was not observed in the wide-gap device at negative gate biases. These phenomena indicated that both devices had distinct field-strength dependences and Fermi level tuning effects, which may be critical for the practical design of devices. (C) 2014 AIP Publishing LLC.
Functional Correlates of Resting-State Connectivity in the Default Mode Network of Heroin Users on Methadone Treatment and Medication-Free Therapeutic Community Program
(2019-06-06)
Kuo, Li-Wei
;
Lin, Pei-Sheng
;
Lin, Shih-Yen
;
Liu, Ming-Fang
;
Jan, Hengtai
The treatment of heroin addiction is a complex process involving changes in addictive behavior and brain functioning. The goal of this study was to explore the brain default mode network (DMN) functional connectivity using resting-state functional magnetic resonance imaging (rs-fMRI) and decision-making performance based on the Cambridge gambling task in heroin-dependent individuals undergoing methadone treatment (MT, n = 11) and medication-free faith-based therapeutic community program (TC, n = 11). The DMN involved the medial prefrontal cortex (mPFC), left inferior parietal lobe (IPLL), right inferior parietal lobe (IPLR), and posterior cingulate cortex (PCC) subregions for all participants in both the MT and TC groups. Compared with MT, TC had an increased functional connectivity in IPLL-IPLR and IPLR-PCC and decreased functional connectivity in mPFC-IPLL and IPLL-PCC. Both groups exhibited no significant difference in the regional rs-fMRI metric [i.e., amplitude of low-frequency fluctuation (ALFF)]. In the analysis of the neural correlates for decision-making performance, risk adjustment was positively associated with ALFF in IPLL for all participants considering the group effects. The involvement of IPL in decision-making performance and treatment response among heroin-dependent patients warrants further investigation.
GaSb/GaAs quantum dots and rings grown under periodical growth mode by using molecular beam epitaxy
(2015-09-01)
Chen, Hsuan-An
;
Shih, Tung-Chuan
;
Tang, Shiang-Feng
;
Weng, Ping-Kuo
;
Gau, Yau-Tang
GaSb/GaAs quantum dots (QDs) and quantum rings (QRs) are investigated. By using periodical growth interrupts, precise coverage control can be achieved for GaSb QD growth by using a single Ga source. With direct As irradiation to the substrate surface during the post soaking time, the soaking time can be effectively reduced while full ring morphologies and room-temperature QR luminescence can still be obtained by using this method. (C) 2015 Elsevier B.V. All rights reserved.
Graphene films grown at low substrate temperature and the growth model by using MBE technique
(2013-09-01)
Lin, Meng-Yu
;
Guo, Wei-Ching
;
Wu, Meng-Hsun
;
Wang, Pro-Yao
;
Lee, Si-Chen
By depositing atomic C atoms on the grained Cu foil by using molecular beam epitaxy technique (MBE), high-quality graphene is obtained at low substrate temperature 300 degrees C. A model of initial graphene flake formation as crystal seeds and following lateral graphene growth is established to explain the growth mechanisms. After atomic C atom deposition, no significant difference is observed before and after MBE growth. The results suggest that the deposition of atomic C atoms will not improve the crystalline quality of pre-formed C films. The low substrate temperature required would be advantageous for the practical application of graphene. (c) 2013 Elsevier B.V. All rights reserved.
Graphitic carbon film formation under Ni templates by radio-frequency sputtering for transparent electrode applications
(2011-11-01)
Lin, Meng-Yu
;
Sheng, Yung-Shuan
;
Chen, Shu-Han
;
Su, Ching-Yuan
;
Li, Lain-Jong
An alternate approach to the preparation of transfer-free graphitic carbon films is proposed in this paper. Using a standard radio-frequency sputtering system and a high-temperature annealing procedure, graphitic carbon films are prepared under Ni templates. The results demonstrate that carbon precipitation occurs at both Ni template interfaces. With repeated annealing procedures at 1100 degrees C, a sheet resistance of 1.36 x 10(4) Omega/square can be achieved. Selective carbon film deposition has also been developed via pattern formation on the Ni templates. The results indicate the potential application of this method to transparent electrode formation. (C) 2011 American Vacuum Society. [DOI: 10.1116/1.3646481]