Browsing by Issue Date, starting with "2016-07-26"

Now showing 1 - 20 of 16849

Dynamics of phonons in Sr3Ir4Sn13: an experimental study by ultrafast spectroscopy measurements
(2016-07-26)
Luo, C. W.
;
Cheng, P. C.
;
Tu, C. M.
;
Kuo, C. N.
;
Wang, C. M.
We report a study of ultrafast dynamics of photoexcited electrons and phonons in Sr3Ir4Sn13 using dual-color transient reflectivity change (Delta R/R) measurements. Time resolved optical spectroscopy of collective excitations reveal the marked features near its structural phase transition temperature T* similar or equal to 147 K. Two distinctive oscillatory timescales in Delta R/R have been clearly resolved. The rapid THz-range oscillations are attributed to the dynamics of the optical phonons which strongly correlate to the structural phase transition. The slow GHz-range oscillatory phenomenon which only occurs below about 150 K is associated with the dynamic response of the longitudinal-acoustic phonons. These low-energy phonons show a softening feature on approaching the transition temperature, also indicating a strong relevance to the structural phase transition. The information that we demonstrated would provide a deeper understanding of the structural phase transition in Sr3Ir4Sn13.
Synthesis of a 4,9-Didodecyl Angular-Shaped Naphthodiselenophene Building Block To Achieve High-Mobility Transistors
(2016-07-26)
Tsai, Che-En
;
Yu, Ruo-Han
;
Lin, Fang-Ju
;
Lai, Yu-Ying
;
Hsu, Jhih-Yang
A new tetracyclic 4,9-dialkyl angular-shaped naphthodiselenophene (4,9-alpha-aNDS) was designed and synthesized. The naphthalene core in 4,9-alpha-aNDS is formed by the DBU-induced 6 pi-cyclization of an (E)-1,2-bis(3-(tetradec-1-yn-1-yl)selenophen-2-yl)ethene intermediate followed by the second PtCl2-catalyzed benzannulation. This synthetic protocol allows for incorporating two dodecyl groups regiospecifically at 4,9-positions of the resulting alpha-aNDS. An ordered supramolecular self-assembly formed via noncovalent selenium-selenium interactions with a short contact of 3.5 angstrom was observed in the single-crystal structure of 4,9-alpha-aNDS. The distannylated alpha-aNDS building block was copolymerized with Br-DTFBT and Br-DPP acceptors by Stille cross coupling to form two new donor-acceptor polymers P alpha NDSDTFBT and P alpha NDSDPP, respectively. The bottom-gate/top-contact organic field-effect devices using the PaNDSDTFBT and PaNDSDPP semiconductors accomplished superior hole mobility of 3.77 and 2.17 cm(2) V-1 s(-1), respectively, which are among the highest mobilities reported to date.
Electrochemical and in situ X-ray spectroscopic studies of MnO2/reduced graphene oxide nanocomposites as a supercapacitor
(2016-07-28)
Chang, Han-Wei
;
Lu, Ying-Rui
;
Chen, Jeng-Lung
;
Chen, Chi-Liang
;
Lee, Jyh-Fu
Electrochemical and in situ X-ray absorption spectroscopy (XAS) measurements of various MnO2-coated carbon materials (MnO2/acid-functionalized carbon nanotubes (C-CNT), MnO2/reduced graphene oxide (RGO), and MnO2/RGO-Au electrodes) were conducted to evaluate the supercapacitive performances and electronic structures. MnO2 was deposited on the surface of C-CNT, RGO, and RGO-Au via a spontaneous redox reaction to facilitate the growth of the bulk form of MnO2/C-CNT and the surface forms of MnO2/RGO-based materials. Various forms of MnO2 on the carbon materials exhibited different charge/discharge behaviors. The specific capacitances of the MnO2/RGO and MnO2/RGO-Au electrodes at a current density of 1 A g(-1) were about 433 and 469 F g(-1), respectively; these values are about 1.5 times that of the MnO2/C-CNT (259 F g(-1)) electrode. Specific capacitances of 220 and 281 F g(-1) with retention rates of about 50-60% were obtained from MnO2/RGO and MnO2/RGO-Au, respectively, even at a high current density of 80 A g(-1). Experimental results revealed that the long-term electrochemical stability of the MnO2/RGO-based electrodes (with similar to 90% retention) exceeded that of the MnO2/C-CNT electrode (with similar to 60% retention) after 1000 cycles at a high scan rate of 80 A g(-1). This finding indicates that MnO2/RGO-based electrodes feature excellent cycling stability and rate capacity retention performance. To elucidate the atomic/electronic structures of the MnO2/C-CNT, MnO2/RGO, and MnO2/RGO-Au electrodes during the charge/discharge process, in situ XAS of the Mn K-edge was performed. The MnO2/RGO-based electrodes exhibited the least variations in the pre-peak intensity of the Mn K-edge during the charge/discharge process because a nano-network of MnO2 is homogeneously decorated on the outer surfaces of RGO-based electrodes to facilitate the growth of surface forms of MnO2/RGO and MnO2/RGO-Au. Analytical results further revealed suppression of changes in tunnel size and promotion of insertion/extraction behavior. This work, particularly the combination of cyclic voltammetry with in situ XAS measurements, will be of general value in the fields of nanomaterials and nanotechnology, and in their use in energy storage.
Substrate-induced structures of bismuth adsorption on graphene: a first principles study
(2016-07-28)
Lin, Shih-Yang
;
Chang, Shen-Lin
;
Chen, Hsin-Hsien
;
Su, Shu-Hsuan
;
Huang, Jung-Chun
The geometric and electronic properties of Bi-adsorbed monolayer graphene, enriched by the strong effect of a substrate, are investigated by first-principles calculations. The six-layered substrate, corrugated buffer layer, and slightly deformed monolayer graphene are all simulated. Adatom arrangements are thoroughly studied by analyzing the ground-state energies, bismuth adsorption energies, and Bi-Bi interaction energies of different adatom heights, inter-adatom distance, adsorption sites, and hexagonal positions. A hexagonal array of Bi atoms is dominated by the interactions between the buffer layer and the monolayer graphene. An increase in temperature can overcome a similar to 50 meV energy barrier and induce triangular and rectangular nanoclusters. The most stable and metastable structures agree with the scanning tunneling microscopy measurements. The density of states exhibits a finite value at the Fermi level, a dip at similar to -0.2 eV, and a peak at similar to-0.6 eV, as observed in the experimental measurements of the tunneling conductance.
Reflection Microspectroscopic Study of Laser Trapping Assembling of Polystyrene Nanoparticles at Air/Solution Interface
(2016-07-28)
Wang, Shun-Fa
;
Yuyama, Ken-ichi
;
Sugiyama, Teruki
;
Masuhara, Hiroshi
;
應用化學系
We present the formation of a single nanoparticle assembly with periodic array structure induced by laser trapping of 200 nm polystyrene nanoparticles at air/solution interface of the colloidal heavy water solution. Their trapping and assembling behavior is observed by monitoring transmission and backscattering images and measuring reflection spectra under a microscope. Upon the laser irradiation into the solution surface layer, nanoparticles are gathered at and around the focal spot, and eventually a nanoparticle assembly with the size much larger than the focal volume is formed. The assembly gives structural color in visible range under halogen lamp illumination, indicating that constituent nanoparticles are periodically arrayed. Reflection spectra of the assembly show a reflection band, and its peak position is gradually shifted to short wavelength and the bandwidth becomes narrow with time, depending on the distance from the focal spot. After the laser is switched off, red-shift is observed in the reflection band. These results indicate that nanoparticles are rearranged into a densely packed periodic array during laser irradiation and diffused out to the surrounding solution after turning off the laser. These dynamics are discussed from the viewpoints of the attractive optical trapping force and the electrostatic repulsive force among nanoparticles.
Infrared absorption spectrum of the simplest deuterated Criegee intermediate CD2OO
(2016-07-28)
Huang, Yu-Hsuan
;
Nishimura, Yoshifumi
;
Witek, Henryk A.
;
Lee, Yuan-Pern
;
應用化學系
We report a transient infrared (IR) absorption spectrum of the simplest deuterated Criegee intermediate CD2OO recorded using a step-scan Fourier-transform spectrometer coupled with a multipass absorption cell. CD2OO was produced from photolysis of flowing mixtures of CD2I2, N-2, and O-2 (13 or 87 Torr) with laser light at 308 nm. The recorded spectrum shows close structural similarity with the spectrum of CH2OO reported previously [Y.-T. Su et al., Science 340, 174 (2013)]. The four bands observed at 852, 1017, 1054, and 1318 cm(-1) are assigned to the OO stretching mode, two distinct in-plane OCD bending modes, and the CO stretching mode of CD2OO, respectively, according to vibrational wavenumbers, IR intensities, rotational contours, and deuterium-isotopic shifts predicted with extensive quantum-chemical calculations. The CO-stretching mode of CD2OO at 1318 cm(-1) is blue shifted from the corresponding band of CH2OO at 1286 cm(-1); this can be explained by a mechanism based on mode mixing and isotope substitution. A band near 936 cm(-1), observed only at higher pressure (87 Torr), is tentatively assigned to the CD2 wagging mode of CD2IOO. Published by AIP Publishing.
Structural order and melting of a quasi-one-dimensional electron system
(2016-07-29)
Rees, David G.
;
Beysengulov, Niyaz R.
;
Teranishi, Yoshiaki
;
Tsao, Chun-Shuo
;
Yeh, Sheng-Shiuan
We investigate the influence of confinement on the positional order of a quasi-1D electron system trapped on the surface of liquid helium. We find evidence that the melting of the Wigner solid (WS) depends on the confinement strength, as well as electron density and temperature. A reentrant solid-liquid-solid transition is observed for increasing electron density under constant electrostatic confinement. As the electron row number N-y changes, varying commensurability results in a modulation of the WS order, even when N-y is large (several tens). This is confirmed by Monte Carlo simulations.
Uniqueness: skews bit occurrence frequencies in randomly generated fingerprint libraries
(2016-08)
Chen, Nelson G.
;
分子醫學與生物工程研究所
;
Institute of Molecular Medicine and Bioengineering
Requiring that randomly generated chemical fingerprint libraries have unique fingerprints such that no two fingerprints are identical causes a systematic skew in bit occurrence frequencies, the proportion at which specified bits are set. Observed frequencies (O) at which each bit is set within the resulting libraries systematically differ from frequencies at which bits are set at fingerprint generation (E). Observed frequencies systematically skew toward 0.5, with the effect being more pronounced as library size approaches the compound space, which is the total number of unique possible fingerprints given the number of bit positions each fingerprint contains. The effect is quantified for varying library sizes as a fraction of the overall compound space, and for changes in the specified frequency E. The cause and implications for this systematic skew are subsequently discussed. When generating random libraries of chemical fingerprints, the imposition of a uniqueness requirement should either be avoided or taken into account.
癢
(深河出版有限公司, 2016-08-01)
鄭聖勳
日光調控裝置
(2016-08-01)
陳政寰
一種日光調控裝置包含一光聚焦模組以及一光偏折模組。光聚焦模組用以將入射之一日光會聚於一聚焦區域或鄰近聚焦區域。光偏折模組設置於聚焦區域，並用以將會聚之日光偏折至一目標區域，其中目標區域偏離光聚焦模組之一光軸。上述之日光調控裝置可使太陽能電池、加熱裝置以及光導元件等裝置有較為彈性之設置方式。
Using a Low Fluence Q-Switched 532/1064-nm Nd:YAG Laser for Facial Skin Depigmentation in Asian Patients Outcome and Complication Profile Analysis
(2016-08)
Shen, Jen-Hsiang
;
Chang, Chang-Cheng
;
Chen, Yu-Tsung
;
Hsih, Chao-Jen
;
Huang, Hsin
Background and Objectives: Low fluence Q-switched neodymium-doped yttrium aluminum garnet (Nd:YAG) lasers are widely applied for facial depigmentation. Nonetheless, few reports analyze the general outcome, complications, of single and combined therapy of 532/1064-nm Nd: YAG lasers in Asian patients with Fitzpatrick type IV skin. Study Design/Materials and Methods: We retrospectively reviewed all consecutive patients who completed 5 consecutive sessions at 1-month intervals of treatment with 1064-nm (spot size: 5-7 mm, 1.5-2.0 J/cm(2)) or combined with 532-nm (spot size, 2-3 mm; 0.5-1.5 J/cm(2)) Nd: YAG laser (Laseroptek, Korea) from October 2011 to March 2013. The patients, laser surgeon, and 3 blinded reviewers assessed the outcomes and complications. Improvement was graded as follows: 1, 0%-25%; 2, 26%-50%; 3, 51%-75%; 4, 76-90%; and 5, greater than 90%. Postinflammatory hyperpigmentation (PIH) was documented according to the severity (1, slight; 2, moderate; 3, severe; and 4, extreme). Other post-laser side effects were also documented (eg, scaling, dryness, erythema, and pruritus). Results: Four male patients and 37 female patients were included with a mean age of 38.5 years (SD, 10.1 years). There were no significant differences on patients\', surgeon\'s, or blinded reviewers\' improvement gradings. (4.11 +/- 0.62 vs 4.30 +/- 0.46, P = 0.54; 3.88 +/- 0.66 vs 3.89 +/- 0.31, P = 0.50; 3.30 +/- 0.69 vs 3.74 +/- 0.38, P = 0.34). Transient minor side effect occurred as follows: erythema in 9 (22%), pruritus in 7 (17%), dryness in 6 (15%), and scaling in 6 (15%). There was no risk difference in these side effects between groups. The PIH scores were slight in 10 patients (4 in single and 6 in combined), severe in 4 (3 in single and 1 in combined), and extreme in 1 (single therapy). The PIH incidence also did not differ (33.3%, 35.3%; P = 0.58). Conclusions: We reported satisfactory outcomes after low-fluence Q-switched sole 1064-nmor combined 532/1064-nm therapy. The outcome and complication profiles did not differ between the groups. The PIH incidence was not low, but usually transient. The incidence of severe or extreme PIH was rare.
讀書－《葉榮鐘選集》：編案
(深河出版有限公司, 2016-08-01)
蔡鈺淩
Bifurcation analysis of the behavior of partially wetting liquids on a rotating cylinder
(2016-08)
Lin, Te-Sheng
;
Rogers, Steven
;
Tseluiko, Dmitri
;
Thiele, Uwe
;
應用數學系
We discuss the behavior of partially wetting liquids on a rotating cylinder using a model that takes into account the effects of gravity, viscosity, rotation, surface tension, and wettability. Such a system can be considered as a prototype for many other systems where the interplay of spatial heterogeneity and a lateral driving force in the proximity of a first-or second-order phase transition results in intricate behavior. So does a partially wetting drop on a rotating cylinder undergo a depinning transition as the rotation speed is increased, whereas for ideally wetting liquids, the behavior only changes quantitatively. We analyze the bifurcations that occur when the rotation speed is increased for several values of the equilibrium contact angle of the partially wetting liquids. This allows us to discuss how the entire bifurcation structure and the flow behavior it encodes change with changing wettability. We employ various numerical continuation techniques that allow us to track stable/unstable steady and time-periodic film and drop thickness profiles. We support our findings by time-dependent numerical simulations and asymptotic analyses of steady and time-periodic profiles for large rotation numbers. Published by AIP Publishing.
Quantum-Dot Surface Emitting Distributed Feedback Lasers Using Indium-Tin-Oxide as Top Claddings
(2016-08-01)
Chang, Ting-Yuan
;
Pan, Chien-Hung
;
Hong, Kuo-Bin
;
Lin, Chien-Hung
;
Lin, Gray
We demonstrate InAs/InGaAs quantum-dot surface emitting distributed feedback (SE-DFB) lasers, using an indium-tin-oxide layer as top cladding, which eliminates the regrowth process used in conventional DFB lasers to greatly simplify laser process. The lasing peak near 1.30 mu m realized using the grating period of 375 nm exhibited a 0.13-nm linewidth and a low-temperature red-shift rate of 0.1 nm/K. The laser had a threshold current density of 210 A/cm(2) and a characteristic temperature of 94.6 K. The surface emitting laser light had the divergence angles of less than 1 degrees and 8 degrees similar to 9 degrees along and perpendicular to the grating direction, respectively.
拒絕用完即丟：優衣庫代工廠工人的身體抗爭（2014-2015）
(深河出版有限公司, 2016-08-01)
劉世鼎
;
史唯
Tight Lower Bounds for Channel Hopping Schemes in Cognitive Radio Networks
(2016-08)
Chang, Cheng-Shang
;
Liao, Wanjiun
;
Wu, Tsung-Ying
;
傳播研究所
;
Institute of Communication Studies
In this paper, we consider the two-user multichannel rendezvous problem in a cognitive radio network (CRN) and derive tight lower bounds for maximum time-to-rendezvous (MTTR) and maximum conditional time-to-rendezvous (MCTTR) of various channel hopping (CH) schemes under a channel loading constraint. In the symmetric and synchronous setting, we propose a novel Cycle-Adjustable Channel Hopping (CACH) scheme to achieve the MTTR lower bound (when the channel loading is bounded above by with being a prime power). Thus, the MTTR lower bound is tight and the CACH scheme is optimal in minimizing MTTR among all the symmetric and synchronous CH schemes under the same channel loading constraint. In the asymmetric setting, we show that the classical wait-for-mommy strategy can be used to achieve the MCTTR lower bound, and thus it is optimal. In the symmetric and asynchronous setting, we also show a hierarchical construction of an asynchronous CH sequence by using two smaller asynchronous CH sequences. To further understand the effect of channel loading to the other performance metrics in a CRN, we perform various computer simulations for various CH schemes. Our simulation results show that the average time-to-rendezvous of CACH is independent of the total number of channels, and it is also robust to the disturbance of primary users.
Urban sustainability assessment of Taiwan based on data envelopment analysis
(2016-08)
Yang, Wen-Chi
;
Lee, Yuh-Ming
;
Hu, Jin-Li
;
交大名義發表
;
National Chiao Tung University
The rapid process of urbanization brings forth growing concerns about the sustainability of cities. This study adopts an extended urban metabolism framework to assess urban sustainability and utilizes a data envelopment analysis (DEA) model with undesirable outputs that takes pollutions into account in order to measure the aggregate urban input-output efficiency of Taiwan\'s 22 administrative regions. The model not only compares aggregate urban efficiency, but also identifies which input or output item should be adjusted and what the target values are. The results indicate that Taipei City and Lienchiang County are the most sustainable cities in Taiwan. This study also proposes several indices, categorized as resource efficiency and pollution efficiency. In terms of resource efficiency, the findings present that Taiwan needs to improve its electricity and water efficiencies the most. With regard to pollution efficiency, garbage efficiency performs the best. Finally, industrial structure has a strong influence on resource efficiency and pollution efficiency. (C) 2016 Elsevier Ltd. All rights reserved.
記．憶聖勳：重慶，2015年秋
(深河出版有限公司, 2016-08-01)
趙剛
A Planarized Thermophotovoltaic Emitter With Idealized Selective Emission
(2016-08-01)
Fu, Sze Ming
;
Zhong, Yan Kai
;
Tu, Ming Hsiang
;
Chen, Bo Ruei
;
Lin, Albert
Compared with conventional solar cells, thermophotovoltaics (TPV) can be more efficient and, thus, exceeds the detailed balance efficiency limit. In particular, the emitter of TPV is a critical design since it determines whether the thermalization loss can be reduced and whether the sub-band-gap radiation can be suppressed, as far as the photovoltaic (PV) process is concerned. In this paper, we propose a selective planar emitter composed of alternating ultrathin metal and dielectric layers. An aperiodic dielectric stacking is designed to tailor the emission spectrum by shaping the emission peak and by adjusting the emission wavelength. We show that the peak emission wavelength (lambda(emission)) is adjustable from lambda = 1500 nm to lambda = 2500 nm. Furthermore, the long-wavelength cutoff is very sharp for our proposed emitter structure, and the absorption is suppressed to 0.1 beyond the cutoff. The preliminary experiment is also conducted to fulfill the concept of a fully planar ultrathin refractory metal emitter design, and the result is similar to the calculated ones. We believe that the planar thermal emitter based on ultrathin metals and aperiodic dielectric stacking is very promising for future thermal emission applications since it requires no lithography and etching, provides strong peak emission power, and possesses wide wavelength scalability.
聖勳的德性之美
(深河出版有限公司, 2016-08-01)
呂正惠