Browsing by Issue Date, starting with "2002-10-15"

Now showing 1 - 20 of 74351

Resonant tunneling into a quantum dot embedded inside a microcavity
(2002-10-15)
Chen, YN
;
Chuu, DS
;
電子物理學系
;
Department of Electrophysics
We propose to measure the Purcell effect by observing the current through a semeiconductor quantum dot embedded in a microcavity. An electron and a hole are injected separately into the quantum structure to form an exciton and then recombine radiatively. The stationary current is shown to be altered if one varies the cavity length or the exciton energy gap. Therefore, the Purcell effect can be observed experimentally by measuring the current through the quantum structure. In addition, we also find that super-radiance of excitons between quantum dots may also be observed in an electrical way.
Harmonic mode locking and multiple pulsing in a soft-aperture Kerr-lens mode-locked Ti : sapphire laser
(2002-10-15)
Lin, JH
;
Hsieh, WF
;
Wu, HH
;
光電工程學系
;
Department of Photonics
We report the observation of harmonic mode locking and multiple pulse operations in a soft-aperture Kerr-lens mode-locked Ti:sapphire laser by varying the total intra-cavity dispersion. Second, third, and fourth order harmonic mode locking as well as multiple pulsing with interpulse separation ranging from femtosecond to nanosecond are observed. The laser is characterized in these regimes in terms of wavelength, bandwidth, pulsewidth, average and peak powers as functions of group velocity dispersion. By introducing a loss difference term into gain dynamic analysis, we conclude that gain depletion and recovery mechanisms are responsible for the underlying physics of current observations. (C) 2002 Elsevier Science B.V. All rights reserved.
X-ray scattering study of crystallization behavior in homoepitaxial growth of SrTiO3 films
(2002-10-15)
Lee, HY
;
Chang, WD
;
Hsu, CH
;
Liang, KS
;
Lee, JY
X-ray reflectivity and grazing incidence crystal truncation rod (CTR) measurements were employed to characterize the microstructure and crystallization behavior of homoepitaxial SrTiO3 (STO) films deposited on polished SrTiO3 (0 0 1) substrates by pulse laser deposition technique. X-ray scattering results indicate that room temperature grown STO film has a density approximately 11.1% lower than that of bulk STO and shows poor epitaxial relation with the substrate. Subsequent annealing at 760 degreesC for 20 s appeared to transform the film into two-layer structure, with the density of the layer right above the substrate approaching to its bulk value, while the density of the top 15.5 Angstrom thick layer reducing to near 45% of bulk STO. The annealing process also leads to an increase of lateral lattice constant together with the growth of domain size. The appearance of interference fringes of the CTR after annealing, which is also observed at the film grown at 760 degreesC, clearly demonstrates the development of epitaxy upon short time annealing. (C) 2002 Elsevier Science B.V. All rights reserved.
Efficient generation of continuous-wave yellow light by single-pass sum-frequency mixing of a diode-pumped Nd : YVO4 dual-wavelength laser with periodically poled lithium niobate
(2002-10-15)
Chen, YF
;
Tsai, SW
;
Wang, SC
;
Huang, YC
;
Lin, TC
We report efficient generation of cw yellow light by use of single-pass sum-frequency mixing from a diode-pumped Nd:YVO4 dual-wavelength laser with periodically poled lithium niobate. A diode-pumped Nd:YVO4 dual-wavelength laser is implemented with a three-mirror cavity, and the optimum oscillation condition is obtained from theoretical analysis. We extracted 78 mW of power at 593 run from 1.2 W at 1064 nm and from 1.0 W at 1342 nm in a beam with excellent quality. The output power could probably be increased to similar to92 mW by antireflection. coating of the crystal. (C) 2002 Optical Society of America.
A novel phase-noise-suppressed and delay-time-tunable mode-locked erbium-doped fiber laser
(2002-10-15)
Lin, GR
;
Lai, Y
;
光電工程學系
;
Department of Photonics
A phase-noise-suppressed and delay-time-tunable actively mode-locked erbium-doped fiber ring laser is demonstrated by using voltage-controlled and frequency-discriminated phase shifter as an inherent timing module. By changing the voltage from -3.35 to 3.6 V, the maximum tuning range of phase and delay-time of 500 MHz optical pulse-train from the laser can be up to 340degrees (similar to1.9pi) and 1.9 ns (nearly 1 period), respectively. Optimized responsivity and tuning deviation are 0.27 ps/mV and less than or equal to 4%. The single-sided-band phase the laser operated at feedback controlled mode is significantly reduced to -100 dBc/Hz (measured at frequency of 10 kHz offset from center), which is at least 10 dB smaller than that of the laser operated at free-running mode. (C) 2002 Published by Elsevier Science B.V.
Characteristics of photogenerated bipolar terahertz radiation in biased photoconductive switches
(2002-10-15)
Lin, PI
;
Chen, SF
;
Wu, KH
;
Juang, JY
;
Uhn, TM
The characteristics of the optically induced bipolar terahertz (THz) radiation from biased semi-insulating GaAs photoconductive switches were investigated using a free-space electrooptic sampling technique, The emitted radiation shows a nearly symmetrical waveform with a broad-band frequency spectrum spanning over 0.1-3 THz, which displays essentially no dependence on the optical excitation fluence or strength of biased field. However, it does slightly depend on the file emitter gap spacing. The dynamics of the emitted THz transient is in agreement with the optically induced ultrafast charge transport process driven by the biased field.
Energy states and magnetization in nanoscale quantum rings
(2002-10-15)
Voskoboynikov, O
;
Li, YM
;
Lu, HM
;
Shih, CF
;
Lee, CP
In this paper we calculate electron energy states and magnetization for torus shaped nanoscale quantum rings with external magnetic fields. We use the three-dimensional effective one-band Hamiltonian, the energy and position-dependent quasiparticle effective mass approximation, and the Ben Daniel-Duke boundary conditions. The dependence of the energy spectrum on the sizes and shapes of the quantum rings was calculated and the result agrees with experimental observations. Penetration of the magnetic field into torus region results in an aperiodic oscillation of magnetization at zero temperature. It saturates with the increasing of the magnetic field strength.
Design and synthesis of activity probes for glycosidases
(2002-10-17)
Tsai, CS
;
Li, YK
;
Lo, LC
;
應用化學系
;
Department of Applied Chemistry
[GRAPHICS] A new synthetic route was developed for the preparation of activity probe 1 for beta-glucosidase in this study. The key glycosidation step begins with benzyl p-hydroxyphenylacetate. Benzylic functionalization for the construction of the trapping device was achieved at later stages. Probe 1 was shown to be able to label the target enzyme. This cassette-like design offers great flexibility for future alterations. It would allow the synthetic scheme to expand to other glycosidase probes with different linker/reporter combinations.
詩歌節開唱方塊字起舞
(2002-10-19)
陳盈珊
如歌的行板在中山堂低迴
(2002-10-19)
蔡惠萍
用於印刷微波積體電路之平面式模轉換器
(2002-10-21)
莊晴光
;
李振榮
一種用於印刷微波積體電路之平面式模轉換器，包含：一矩形波導，一微帶線饋入電路及一微帶線饋出電路。該矩形波導之內部填充複數個介質層，各該介質層上下彼此緊鄰相接，其中最上層介質層之頂面、最下層介質層之底面及各該介質層之左、右側面，有金屬材料覆蓋於其上，該最下層介質層其介質常數最大、厚度最厚，除了該最下層介質層以外之各該介質層之前端及後端各有一矩形孔徑，各該前端之矩形孔徑上下緊鄰，各該後端之矩形孔徑上下緊鄰。
詩歌節今夜畫下句點
(2002-10-26)
陳盈珊
詩歌節壓軸詩人化身煉金術士
(2002-10-26)
台北訊
On-off switching of edge direct tunneling currents in metal-oxide-semiconductor field-effect transistors
(2002-10-28)
Chen, MJ
;
Lu, MP
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
On-off switching behaviors or two-level random telegraph signals (RTS) are measured in the low voltage (-1.4 0V
A single mutation converts the nucleotide specificity of phenol sulfotransferase from PAP to AMP
(2002-10-29)
Hsiao, YS
;
Yang, YS
;
生物科技學系
;
Department of Biological Science and Technology
Sulfotransferases (STs) catalyze all the known biological sulfonations, in which a sulfuryl group from a common sulfonate donor such as 3'-phosphoadenosine 5-phosphosulfate (PAPS) is transferred to a nucleophilic acceptor. In addition to PAPS, phenol sulfotransferase (PST), a member of the ST family, utilizes other nucleotides as substrates with much less catalytic efficiency [Lin, E. S., and Yang, Y. S. (2000) Biochem. Biophys. Res. Commun. 271, 818-822]. Six amino acid residues of PST have been chosen for mutagenesis studies on the basis of a model of PST and its sequence alignment with those of available cytosolic and membrane-anchored STs. Systematic analyses of the mutants reveal that Ser134 is important for the regulation of nucleotide specificity between 3'-phosphoadenosine 5'-phosphate (PAP) and adenosine 5'-monophosphate (AMP). Kinetic studies also indicate that Ser134 plays a key role in nucleotide binding (K-m) but not in catalysis (k(cat)). Consequently, the catalytic efficiency (k(cat)/K-m) of PST can be altered by 5 orders of magnitude with a mutation of Ser134. Moreover, the change in nucleotide specificity from PAP to AMP can be achieved by mutation of Ser134 to any of the following residues: Glu, Gln, Arg, and His. Roles of Lys44, Arg126, and Arg253, which interact directly with the 5'- and 3'-phosphate of PAP, were also investigated by mutagenesis and kinetic experiments. On the basis of these findings, we suggest that Ser134 is the key residue that enables PST to discriminate PAP from AMP.
石頭臉上的苔蘚皺紋--管管答客問
(2002-10-31)
管管
石頭臉上的苔蘚皺紋--管管答客問
(2002-10-31)
管管
石頭臉上的苔蘚皺紋--管管答客問
(2002-10-31)
管管
石頭臉上的苔蘚皺紋--管管答客問
(2002-10-31)
管管
石頭臉上的苔蘚皺紋--管管答客問
(2002-10-31)
管管