Browsing by Issue Date, starting with "2016-05-23"

Now showing 1 - 20 of 17265

A Novel Metallo-beta-Lactamase Involved in the Ampicillin Resistance of Streptococcus pneumoniae ATCC 49136 Strain
(2016-05-23)
Chang, Chia-Yu
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Lin, Hui-Jen
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Li, Bor-Ran
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Li, Yaw-Kuen
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分子醫學與生物工程研究所
Streptococcus pneumoniae, a penicillin-sensitive bacterium, is recognized as a major cause of pneumonia and is treated clinically with penicillin-based antibiotics. The rapid increase in resistance to penicillin and other antibiotics affects 450 million people globally and results in 4 million deaths every year. To unveil the mechanism of resistance of S. pneumoniae is thus an important issue to treat streptococcal disease that might consequently save millions of lives around the world. In this work, we isolated a streptococci-conserved L-ascorbate 6-phosphate lactonase, from S. pneumoniae ATCC 49136. This protein reveals a metallo-beta-lactamase activity in vitro, which is able to deactivate an ampicillin-based antibiotic by hydrolyzing the amide bond of the beta-lactam ring. The Michaelis parameter (K-m) = 25 mu M and turnover number (k(cat)) = 2 s(-1) were obtained when nitrocefin was utilized as an optically measurable substrate. Through confocal images and western blot analyses with a specific antibody, the indigenous protein was recognized in S. pneumoniae ATCC 49136. The protein-overexpressed S. pneumonia exhibits a high ampicillin-tolerance ability in vivo. In contrast, the protein-knockout S. pneumonia reveals the ampicillin-sensitive feature relative to the wild type strain. Based on these results, we propose that this protein is a membrane-associated metallo-beta-lactamase (MBL) involved in the antibiotic-resistant property of S. pneumoniae.
Electrohydrodynamics of a viscous drop with inertia
(2016-05-23)
Nganguia, H.
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Young, Y. -N.
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Layton, A. T.
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Lai, M. -C.
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Hu, W. -F.
Most of the existing numerical and theoretical investigations on the electrohydrodynamics of a viscous drop have focused on the creeping Stokes flow regime, where nonlinear inertia effects are neglected. In this work we study the inertia effects on the electrodeformation of a viscous drop under a DC electric field using a novel second-order immersed interface method. The inertia effects are quantified by the Ohnesorge number Oh, and the electric field is characterized by an electric capillary number Ca E. Below the critical Ca E, small to moderate electric field strength gives rise to steady equilibrium drop shapes. We found that, at a fixed Ca E, inertia effects induce larger deformation for an oblate drop than a prolate drop, consistent with previous results in the literature. Moreover, our simulations results indicate that inertia effects on the equilibrium drop deformation are dictated by the direction of normal electric stress on the drop interface: Larger drop deformation is found when the normal electric stress points outward, and smaller drop deformation is found otherwise. To our knowledge, such inertia effects on the equilibrium drop deformation has not been reported in the literature. Above the critical Ca E, no steady equilibrium drop deformation can be found, and often the drop breaks up into a number of daughter droplets. In particular, our Navier-Stokes simulations show that, for the parameters we use, (1) daughter droplets are larger in the presence of inertia, (2) the drop deformation evolves more rapidly compared to creeping flow, and (3) complex distribution of electric stresses for drops with inertia effects. Our results suggest that normal electric pressure may be a useful tool in predicting drop pinch-off in oblate deformations.
Geometry-dependent phase, stress state and electrical properties in nickel-silicide nanowires
(2016-05-25)
Wang, C. C.
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Lai, W. T.
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Hsiao, Y. Y.
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Chen, I. H.
;
George, T.
We report that the geometry of single-crystalline Si nanowires (NWs) prior to salicidation at 500 degrees C is the key factor controlling the phase, stress state, and electrical resistivity of the resulting NixSiy NWs of width less than 100 nm. This is a radical departure from previous observations of a single phase formation for nickel silicides generated from the silicidation of bulk Si substrates. The phase transition from NiSi for large NWs (W-Si NW = 250-450 nm) to Ni2Si for small NWs (W-Si NW = 70-100 nm) is well correlated with the observed volumetric expansion and electrical resistivity variation with the NW width. For the extremely small dimensions of NixSiy NWs, we propose that the preeminent, kinetics-based Zhang and d\'Heurle model for salicidation be modified to a more thermodynamically-governed, volume-expansion dependent NixSiy phase formation. A novel, plastic deformation mechanism is proposed to explain the observed, geometry-dependent NixSiy NW phase formation that also strongly influences the electrical performance of the NWs.
Intersystem crossing-branched excited-state intramolecular proton transfer for o-nitrophenol: An ab initio on-the-fly nonadiabatic molecular dynamic simulation
(2016-05-25)
Xu, Chao
;
Yu, Le
;
Zhu, Chaoyuan
;
Yu, Jianguo
;
Cao, Zexing
The 6SA-CASSCF(10, 10)/6-31G (d, p) quantum chemistry method has been applied to perform on-the-fly trajectory surface hopping simulation with global switching algorithm and to explore excited-state intramolecular proton transfer reactions for the o-nitrophenol molecule within low-lying electronic singlet states (S-0 and S-1) and triplet states (T-1 and T-2). The decisive photoisomerization mechanisms of o-nitrophenol upon S-1 excitation are found by three intersystem crossings and one conical intersection between two triplet states, in which T-1 state plays an essential role. The present simulation shows branch ratios and timescales of three key processes via T-1 state, non-hydrogen transfer with ratio 48% and timescale 300 fs, the tunneling hydrogen transfer with ratios 36% and timescale 10 ps, and the direct hydrogen transfer with ratios 13% and timescale 40 fs. The present simulated timescales might be close to low limit of the recent experiment results.
Optimized Spiral Metal-Gallium-Nitride Nanowire Cavity for Ultra-High Circular Dichroism Ultraviolet Lasing at Room Temperature
(2016-05-25)
Liao, Wei-Chun
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Liao, Shu-Wei
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Chen, Kuo-Ju
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Hsiao, Yu-Hao
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Chang, Shu-Wei
Circularly polarized laser sources with small footprints and high efficiencies can possess advanced functionalities in optical communication and biophotonic integrated systems. However, the conventional lasers with additional circular-polarization converters are bulky and hardly compatible with nanophotonic circuits, and most active chiral plasmonic nanostructures nowadays exhibit broadband emission and low circular dichroism. In this work, with spirals of gallium nitride (GaN) nanowires (NWRs) covered by a metal layer, we demonstrated an ultrasmall semiconductor laser capable of emitting circularly-polarized photons. The left-and right-hand spiral metal nanowire cavities with varied periods were designed at ultraviolet wavelengths to achieve the high quality factor circular dichroism metastructures. The dissymmetry factors characterizing the degrees of circular polarizations of the left-and right-hand chiral lasers were 1.4 and -1.6 (+/- 2 if perfectly circular polarized), respectively. The results show that the chiral cavities with only 5 spiral periods can achieve lasing signals with the high degrees of circular polarizations.
Enzyme Catalysis that Paves the Way for S-Sulfhydration via Sulfur Atom Transfer
(2016-05-26)
Huang, Gou-Tao
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Yu, Jen-Shiang K.
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生物科技學系
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生物資訊及系統生物研究所
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Department of Biological Science and Technology
S-sulfhydration is generally anticipated to proceed through the transfer of the SH group (Nu-SH center dot center dot center dot S--R -> Nu(-)center dot center dot center dot HS-S-R). The other route involves the sulfur atom (5) transfer between two sulfhydryl anions (Nu-S-center dot center dot center dot S--R -> Nu(-)center dot center dot center dot S--S-R) and is considered electrostatically unfavorable. Mercaptopyruvate sulfurtransferase (MST, PDB code: 4JGT) catalyzes sulfur transfer from mercaptopyruvate to sulfur acceptors, and the first step of the reaction is the formation of cysteine (Cys248) persulfide via S-sulfhydration. Mechanistic studies on S-sulfhydration in MST using QM/MM methods show that the sulfur atom transfer initialized by the deprotonation of the Ser250/His74/Asp63 triad is kinetically preferred to the SH-promoted sulfur transfer. The calculated barrier of approximately 16 kcal mol(-1) for the S-0 transfer agrees well with experimental results. The electrostatic repulsion during the S-0 transfer can be sophisticatedly reduced by the aid of the Cys248-Gly249-Ser250-Gly251-Val252-Thr253 (CGSGVT) loop. Electrostatic potentials and frontier orbitals are also analyzed for the persulfide anion surrounded by the loop. The sulfur atom transfer which is seldom regarded possible is therefore facilitated with the assistance of the triad and the loop in the enzyme.
Short wavelength enhanced phototransistor with n-doped porous silicon layer
(2016-05-26)
Wang, Yao-Chin
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Lin, Bor-Shyh
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Yang, Zu-Po
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光電學院
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College of Photonics
A phototransistor with aluminium (Al)/porous silicon (Si)/epitaxial-Si structures was proposed and was fabricated and characterised with short wavelength enhanced operating. We proposed the short wavelength response of the Si-based thin film phototransistor; it can be enhanced by introducing thin porous Si (PS) layer as the base region of transistor. The porous process of device manufacture is suitable for applications in design of visible-light sensitive phototransistors. Experimental results showed that the short wavelength responses in the developed devices were enhanced as compared with the Si-based homojunction transistors, this comparably medium optical gain indicated that the developed Al/PSi/epitaxial-Si heterojunction thin film phototransistor got potential for practical Si-based optical-electron integrated-circuit and biophotonics applications.
A theoretical and experimental evaluation of surface roughness variation in trigate metal oxide semiconductor field effect transistors
(2016-05-28)
Hsieh, E. R.
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Chung, Steve S.
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
A gate current variation measurement method is proposed to examine the surface roughness of metal oxide semiconductor field effect transistors (MOSFETs). This gate current variation is demonstrated on the trigate structure MOSFETs. It was found that the standard deviation of oxide-thickness is proportional to the inverse of square-root of device areas, and its slope is defined as the effective surface roughness variation. In particular, for the transistors with varying fin height, this surface roughness effect aggravates with the increasing fin height. More importantly, the gate leakage at off-state, i.e., Vg = 0V, is strongly dependent on the gate dielectric surface roughness and dominates the drain current variations. This gate leakage may serve as a quality measure of a low power and energy efficient integrated circuit, especially for the transistor with 3-dimensional gate structure. The present results provide us better understandings on an additional source of V-th fluctuations, i.e., the surface roughness variation, in addition to the random dopant fluctuation, that we are usually not noticed. In particular, this study also provides us a simple easy-to-use method for the monitoring of oxide quality in the volume production of trigate MOSFETs. Published by AIP Publishing.
臺灣電影　從低谷中爬起
(2016-05-29)
許凱智
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Department of Communication and Technology
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傳播與科技學系
臺灣電影發展多年，過程中遇到許多問題，而臺灣的電影人，是如何準備和面對這些難關？
日本動畫　虛擬中的現實　
(2016-05-29)
梅瑞庭
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Department of Communication and Technology
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傳播與科技學系
以廣播為日本動畫的內涵與影響稍做分析。
一日活力的來源　竹東市場
(2016-05-29)
張家瑋
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Department of Communication and Technology
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傳播與科技學系
一日之計在於晨，民以食為天；早上的市場，滿足人們的胃。
輕小說　不輕鬆
(2016-05-29)
陳緯僑
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Department of Communication and Technology
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傳播與科技學系
一本捧在手上的輕小說，背後其實有許多人的默默付出。
伯特利　看見都市原民困境
(2016-05-29)
林湘芸
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Department of Communication and Technology
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傳播與科技學系
由Malayumu創立的原住民兒童托育機構—伯特利，秉持原住民互助精神實行全人照顧，卻不被法規認同。
食農教育推手　沺源青
(2016-05-29)
許雅筑
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Department of Communication and Technology
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傳播與科技學系
沺源青工作室以實際行動，享受土地與人之間最自然的關係。
隱形殺手　個資安全知多少
(2016-05-29)
楊淑斐
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Department of Communication and Technology
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傳播與科技學系
在大數據的時代，個人資訊就是金錢，你今天保護好你的個資了嗎？
流行樂的新趨勢與主流迷思
(2016-05-29)
吳和謙
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Department of Communication and Technology
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傳播與科技學系
近年來，受到數位化與網路串流科技的影響，流行音樂產業的收益與趨勢受到巨大的威脅與轉變。
總編輯的話
(2016-05-29)
王聖安
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Department of Communication and Technology
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傳播與科技學系
本期為喀報第兩百四十三期，共有二十篇稿件，其中廣播八篇、電視專題六篇、動畫兩篇、照片兩篇以及文字兩篇。
台灣首場　人外獸人ONLY
(2016-05-29)
王鈞鋒
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Department of Communication and Technology
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傳播與科技學系
簡單介紹CU聯盟，以及從二○一五年開始的人外獸人ONLY緣起，以及參加者的感想、問題。
台大藝術季　藝術席捲校園
(2016-05-29)
林謙耘
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Department of Communication and Technology
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傳播與科技學系
台大藝術季今年以星際大戰的ART2 D2作為主題，利用藝術詮釋對於未來的想像。
新一代　新銳設計師的舞台
(2016-05-29)
修瑞韓
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謝萱穎
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Department of Communication and Technology
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傳播與科技學系
新一代設計展為新銳設計師提供一個表現自我的舞台。