Browsing by Issue Date, starting with "2009-05-13"

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Electronic structure of pyrochlore Cd2Re2O7
(2009-05-13)
Huang, Shih-Wen
;
Jeng, Horng-Tay
;
Lin, J-Y
;
Chang, W. J.
;
Chen, J. M.
Detailed band structure calculations have been performed for Cd2Re2O7 in high-, middle- and low-temperature (T) phases. The calculations are based on the observed lattice structures from x-ray diffraction measurements. The spin-orbit interaction is incorporated self-consistently in both the generalized gradient approximation (GGA) and the GGA plus Hubbard U (GGA + U) approaches. It is found that the on-site U has negligible effects on the Re 5d band structures; therefore both the GGA and GGA + U Re 5d band energies agree well with the observed O K-edge x-ray absorption spectroscopy (XAS) spectrum, whereas the Cd 4d band energy observed from photoemission spectroscopy can only be correctly reproduced by GGA + U calculations, indicating the relatively itinerant Re 5d and localized Cd 4d electrons. On the other hand, the spin-orbit coupling gives rise to nontrivial spin and orbital magnetic moments for the middle-T phase. Most unexpectedly, we found that the low-T phase exhibits quasi-two-dimensional Fermi surfaces. The calculated carrier numbers for the three phases are, at least qualitatively, consistent with the measured Hall coefficient.
Electronic structure of pyrochlore Cd(2)Re(2)O(7)
(2009-05-13)
Huang, Shih-Wen
;
Jeng, Horng-Tay
;
Lin, J-Y
;
Chang, W. J.
;
Chen, J. M.
Detailed band structure calculations have been performed for Cd(2)Re(2)O(7) in high-, middle- and low-temperature (T) phases. The calculations are based on the observed lattice structures from x-ray diffraction measurements. The spin-orbit interaction is incorporated self-consistently in both the generalized gradient approximation (GGA) and the GGA plus Hubbard U (GGA + U) approaches. It is found that the on-site U has negligible effects on the Re 5d band structures; therefore both the GGA and GGA + U Re 5d band energies agree well with the observed O K-edge x-ray absorption spectroscopy (XAS) spectrum, whereas the Cd 4d band energy observed from photoemission spectroscopy can only be correctly reproduced by GGA + U calculations, indicating the relatively itinerant Re 5d and localized Cd 4d electrons. On the other hand, the spin-orbit coupling gives rise to nontrivial spin and orbital magnetic moments for the middle-T phase. Most unexpectedly, we found that the low-T phase exhibits quasi-two-dimensional Fermi surfaces. The calculated carrier numbers for the three phases are, at least qualitatively, consistent with the measured Hall coefficient.
A Computational Study on the Adsorption Configurations and Reactions of Phosphorous Acid on TiO2 Anatase (101) and Rutile (110) Surfaces
(2009-05-14)
Raghunath, P.
;
Lin, M. C.
;
應用化學系分子科學碩博班
;
Institute of Molecular science
We report the result of a density functional theory study on the adsorption and decomposition pathways of phosphorous acid (H3PO3) on TiO2 anatase (101) and rutile (110) surfaces. The most stable adsorption structure for H3PO3 and its isomer, HP(O)(OH)(2), is a monodentate adsorption mode for the anatase surface with calculated adsorption energies 23.5 and 38.5 kcal/mol and a bidentate adsorption mode for rutile surface with 26.7 and 36.6 kcal/mol. The mechanisms for the surface reactions of these species have been explicitly elucidated with the computed potential energy surfaces. The barriers for the stepwise H3PO3 H-migration to two nearby bridged O atoms reactions on anatase leads to Ti-OP(OH)O-Ti(a) + 2H-O-b(a) with 7.9 and 6.8 kcal/mol barriers. Even lower activation barriers (1.3 and 2.9 kcal/mol) have been obtained on the rutile (110) surface for the same bond breaking modes. The intermediate Ti-OP(OH)O-Ti(a) thus formed on both surfaces can further decompose via two distinct pathways through H-migration to the P atom and H2O elimination to produce Ti-OP(H)(O)O-Ti(a) and Ti-OPO-Ti(a), respectively. In addition, we have calculated the adsorption and reactions of the dimer of H3PO3 on both surfaces. The most noticeable difference occurs in the energy levels of the H3PO3 reactions on the anatase and rutile surfaces, with the rutile being more reactive than the anatase surface. The predicted adsorption energies show that Ti-OP(OH)O-Ti(a) with two hydrogen atoms on bridged surface oxygen atoms is 47.1 kcal/mol for anatase and 42.4 kcal/mol for rutile; both are low when compared with the Ti-OB(OH)O-Ti(a) on the same surfaces, 140.1 and 134.6 kcal/mol, respectively. Our density of states analysis shows that OB(OH)O has a larger overlap with the TiO2 surface than OP(OH)O has, favoring the former's charge transfer efficiency.
Holographic information recording and reproducing apparatus for the same
(2009-05-14)
Hsieh, Mei-Li
;
Lin, Shiuan-Huei
;
Wang, Jui-Hsin
;
Hsu, Ken-Yuh
;
Chiang, Don-Yau
In a holographic information recording and reproducing apparatus, an optical fiber guides a reference beam toward a recording medium for holographic recording, and a precision rotator is turned, so that the reference beam is incident on the recording medium at different angles and interferes with a data-carrying signal beam to complete the recording of holographic information on the recording medium. To reproduce the holographic information, the optical fiber guides a reading beam, and the reading beam is incident on the recording medium at an angle the same as the reference beam for the recording to reproduce the holographic information stored on the recording medium. With the optical fiber and the precision rotator, a simplified light path system and a wide range of incident angles for the reference and reading beams may be achieved, and the transmissive, reflective, and 90-degree holographic storage techniques may be integrated in one single apparatus.
THREE-DIMENSIONAL MICROPROBE ARRAY
(2009-05-14)
Chiou, Jin-Chern
;
Chang, Chih-Wei
The present invention discloses a three-dimensional microprobe array assembly structure, wherein spacers are used in assembling edge-type microprobe arrays to form a three-dimensional structure, and the spacers reveal conductive pads of the edge-type microprobe arrays to benefit wire bonding. The present invention detects depths and angles and thus increases detection reliability. Besides, in the present invention, the related IC is integrated with the spacer to achieve circuit integration and reduce cost.
A Computational Study on the Adsorption Configurations and Reactions of Phosphorous Acid on TiO(2) Anatase (101) and Rutile (110) Surfaces
(2009-05-14)
Raghunath, P.
;
Lin, M. C.
;
應用化學系分子科學碩博班
;
Institute of Molecular science
We report the result of a density functional theory study on the adsorption and decomposition pathways of phosphorous acid (H(3)PO(3)) on TiO(2) anatase (101) and rutile (110) surfaces. The most stable adsorption structure for H(3)PO(3) and its isomer, HP(O)(OH)(2), is a monodentate adsorption mode for the anatase surface with calculated adsorption energies 23.5 and 38.5 kcal/mol and a bidentate adsorption mode for rutile surface with 26.7 and 36.6 kcal/mol. The mechanisms for the surface reactions of these species have been explicitly elucidated with the computed potential energy surfaces. The barriers for the stepwise H(3)PO(3) H-migration to two nearby bridged O atoms reactions on anatase leads to Ti-OP(OH)O-Ti(a) + 2H-O(b)(a) with 7.9 and 6.8 kcal/mol barriers. Even lower activation barriers (1.3 and 2.9 kcal/mol) have been obtained on the rutile (110) surface for the same bond breaking modes. The intermediate Ti-OP(OH)O-Ti(a) thus formed on both surfaces can further decompose via two distinct pathways through H-migration to the P atom and H(2)O elimination to produce Ti-OP(H)(O)O-Ti(a) and Ti-OPO-Ti(a), respectively. In addition, we have calculated the adsorption and reactions of the dimer of H(3)PO(3) on both surfaces. The most noticeable difference occurs in the energy levels of the H(3)PO(3) reactions on the anatase and rutile surfaces, with the rutile being more reactive than the anatase surface. The predicted adsorption energies show that Ti-OP(OH)O-Ti(a) with two hydrogen atoms on bridged surface oxygen atoms is 47.1 kcal/mol for anatase and 42.4 kcal/mol for rutile; both are low when compared with the Ti-OB(OH)O-Ti(a) on the same surfaces, 140.1 and 134.6 kcal/mol, respectively. Our density of states analysis shows that OB(OH)O has a larger overlap with the TiO(2) surface than OP(OH)O has, favoring the former's charge transfer efficiency.
Equiangular-spiral bent lightpipes with arbitrary bent angle
(2009-05-15)
Chu, Shu-Chun
;
Cheng, Yi-Kai
;
Chern, Jyh-Long
;
光電工程學系
;
Department of Photonics
A recent study proposed the concept of a leakage-free bent lightpipe with an equiangular-spiral shape [S.-C. Chu, J.-L Chern, Opt. Lett. 30 (2005) 3006]. This paper extends the design of a leakage-free equiangular-spiral bent lightpipe with arbitrary-bend-angle and addresses in detail the mathematical formalism required to build such an equiangular-spiral bent lightpipe. Furthermore, a comparison of the proposed equiangular-spiral bent lightpipe and a conventional circular bent lightpipe is provided. Numerical verifications are discussed, and experimental explorations with different bent shapes and angles are carried out for comparison. Results show that equiangular-spiral bent lightpipes with different bent angles exhibit a theoretical 100% transmission with more than 76% efficiency when practically propagating, which is much better than conventional circular bent lightpipes. The output irradiance distributions of bent lightpipes with different bent shapes are also investigated. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.
Removal of Hg(2+) from Aqueous Solution Using a Novel Composite Carbon Adsorbent
(2009-05-15)
Chang, Yu-Hsin
;
Hsieh, Kuo-Huang
;
Chang, Feng-Chih
;
應用化學系
;
Department of Applied Chemistry
A novel composite carbon adsorbent (GCA) has been prepared by immobilizing activated carbon and genipin-crosslinked chitosan into calcium alginate gel beads via entrapment and applied to the removal of mercury (Hg(2+)) ions from aqueous solution (e.g., drinking water). Two bead sizes and two mixing ratios of components were obtained and characterized. Batch experiments were performed to study the Uptake equilibrium and kinetics, of Hg(2+) ions by the GCA. The Hg(2+) adsorption capacity of GCA was found to be dependent of pH and independent of size of the adsorbent. The Hg(2+) adsorption rate of GCA increases with decreasing its bead size. However, both adsorption capacity and rate of GCA for Hg(2+) increase with increasing its chitosan content. Otherwise, it was shown that the GCA has higher Hg(2+) adsorption capacity and rate than activated carbon, which might he caused by the incorporation of chitosan into the GCA. The maximum Hg(2+) adsorption capacity of GCA was found to be 576 mg/g, which is over seven times higher than that of activated carbon. Our results reveal the uniform distribution of activated carbon and chitosan within the alginate gel bead and that Hg(2+) ions can diffuse inside the bead. It also demonstrated the feasibility of using this GCA for Hg(2+) removal at low pH values. The Hg(2+) absorbed beads of the GCA can be effectivelY regenerated and reused using H(2)SO(4). (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 2445-2454, 2009
Removal of Hg2+ from Aqueous Solution Using a Novel Composite Carbon Adsorbent
(2009-05-15)
Chang, Yu-Hsin
;
Hsieh, Kuo-Huang
;
Chang, Feng-Chih
;
應用化學系
;
Department of Applied Chemistry
A novel composite carbon adsorbent (GCA) has been prepared by immobilizing activated carbon and genipin-crosslinked chitosan into calcium alginate gel beads via entrapment and applied to the removal of mercury (Hg2+) ions from aqueous solution (e.g., drinking water). Two bead sizes and two mixing ratios of components were obtained and characterized. Batch experiments were performed to study the Uptake equilibrium and kinetics, of Hg2+ ions by the GCA. The Hg2+ adsorption capacity of GCA was found to be dependent of pH and independent of size of the adsorbent. The Hg2+ adsorption rate of GCA increases with decreasing its bead size. However, both adsorption capacity and rate of GCA for Hg2+ increase with increasing its chitosan content. Otherwise, it was shown that the GCA has higher Hg2+ adsorption capacity and rate than activated carbon, which might he caused by the incorporation of chitosan into the GCA. The maximum Hg2+ adsorption capacity of GCA was found to be 576 mg/g, which is over seven times higher than that of activated carbon. Our results reveal the uniform distribution of activated carbon and chitosan within the alginate gel bead and that Hg2+ ions can diffuse inside the bead. It also demonstrated the feasibility of using this GCA for Hg2+ removal at low pH values. The Hg2+ absorbed beads of the GCA can be effectivelY regenerated and reused using H2SO4. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 2445-2454, 2009
Theoretical and Experimental Investigations of Direct-Detected RF-Tone-Assisted Optical OFDM Systems
(2009-05-15)
Peng, Wei-Ren
;
Wu, Xiaoxia
;
Arbab, Vahid R.
;
Feng, Kai-Ming
;
Shamee, Bishara
In this paper, we propose and experimentally demonstrate a radio frequency (RF)-tone-assisted optical orthogonal frequency-division multiplexing (OFDM) transmission. By inserting an RF tone at the edge of the signal band and biasing the Mach-Zehnder modulator (MZM) at the null point, the proposed system has a better sensitivity and chromatic dispersion (CD) tolerance compared to the previous intensity-modulated single-sideband OFDM (SSB-OFDM). We show analytically that the majority of the linear channel impairments, such as the transmitter, CD, optical filtering, and receiver, can be compensated for by a simple zero-forcing equalizer. Besides, the optimum value of the important parameter, carrier-to-signal-power ratio (CSPR), is analytically obtained and supported via the experimental results. We also observe that the relatively worse sensitivity of the previous SSB-OFDM can be attributed to the limited CSPR. We experimentally demonstrate a 10-Gb/s, 8 quadrature-amplitude modulation (QAM) RF-tone-assisted OFDM transmission, and show that our system has a similar to 5-dB better sensitivity compared to the previous intensity-modulated SSB-OFDM and exhibits a negligible transmission penalty after 260-km uncompensated standard single-mode fiber (SSMF).
Electrochemical reduction of CO2 by Cu2O-catalyzed carbon clothes
(2009-05-15)
Chang, Tin-Yu
;
Liang, Ru-Meng
;
Wu, Pu-Wei
;
Chen, Jing-Yu
;
Hsieh, Yu-Chi
Cu2O cubes with average edge lengths of 640 nm were prepared by a chemical reduction approach. The as-synthesized Cu2O particles were deposited on carbon clothes for electrochemical characterizations in cyclic voltammetry (CV) and potentiostatic measurements. In 0.5 M NaOH electrolytes saturated with N-2 or CO2, both the Cu2O and carbon clothes were stable at the potential range of 0 to -1.7 V. Comparisons in the Current responses from the CV and potentiostatic measurements suggested the Cu2O with notable catalytic abilities for the CO2 reduction. The mass activity was estimated at 0.94 mA/mg. Chemical analysis from gas chromatography confirmed the methanol to be the predominant product. (C) 2009 Elsevier B.V. All rights reserved.
Analysis of GaAs/GaSb/GaAs structures under optical excitation considering surface states as an electron reservoir
(2009-05-15)
Hsieh, Hong-Wen
;
Yen, Shun-Tung
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We present a self-consistent model for the analysis of the carrier distribution, the band profile, and the transition energy of type-II aligned GaAs/GaSb/GaAs structures under optical excitation. The model considers the surface states as an electron reservoir, associated with pinning of the conduction band Fermi level at the midgap. In our model, the optical generated holes in the GaSb quantum well causes a potential well on one side of the GaSb layer, which can efficiently accommodate the optically generated electrons. Accordingly, we derive a relation connecting the excitation power to the carrier density. Using the relation and the effective triangular potential approximation, we obtain a simple formula for the transition energy shift as a function of the excitation power, which follows the cube-root rule quite well. The calculation allows the determination of the band offset of a type-II heterointerface by comparison with data from photoluminescence measurement. The result suggests the unstrained valence band offset of GaSb/GaAs to lie between 0.5 and 0.55 eV. We also present a simplified model for analyzing the electronic and optical properties of type-II heterostructures without the need of a self-consistent calculation.
Estimation of the Bit Error Rate for Direct-Detected OFDM Signals With Optically Preamplified Receivers
(2009-05-15)
Peng, Wei-Ren
;
Feng, Kai-Ming
;
Willner, Alan E.
;
Chi, Sien
;
光電工程學系
In this paper, we provide a numerical bit error rate (BER) estimation approach for direct-detected orthogonal frequency division multiplexing (OFDM) signals in the presence of optical preamplified receivers. The individual BER of each subcarrier is first computed by considering their electrical signal-to-noise ratio (SNR), and then the ensemble BER is derived simply by taking the average of all the subcarriers' BERs. The calculated BER is verified by the conventional error-counting approach with high precision and is still accurate with higher quadratic-amplitude modulation (QAM) formats, even under the influences of the optical filtering and polarization mode dispersion (PMD) effects. Based on our simulation approach, the required extra power budget for 16- and 64-QAM relative to 4-QAM format are found to be similar to 3.8 and 8.2 dB, respectively, at a BER of 10(-9) Furthermore, we use this approach to compare the receiving sensitivities and PMD tolerances for the previous proposed gapped and interleaved radio-frequency (RF)-tone-assisted OFDM systems. The results show that the gapped OFDM has a better sensitivity while the interleaved OFDM has a more PMD-tolerable capability.
Electrochemical reduction of CO(2) by Cu(2)O-catalyzed carbon clothes
(2009-05-15)
Chang, Tin-Yu
;
Liang, Ru-Meng
;
Wu, Pu-Wei
;
Chen, Jing-Yu
;
Hsieh, Yu-Chi
Cu(2)O cubes with average edge lengths of 640 nm were prepared by a chemical reduction approach. The as-synthesized Cu(2)O particles were deposited on carbon clothes for electrochemical characterizations in cyclic voltammetry (CV) and potentiostatic measurements. In 0.5 M NaOH electrolytes saturated with N(2) or CO(2), both the Cu(2)O and carbon clothes were stable at the potential range of 0 to -1.7 V. Comparisons in the Current responses from the CV and potentiostatic measurements suggested the Cu(2)O with notable catalytic abilities for the CO(2) reduction. The mass activity was estimated at 0.94 mA/mg. Chemical analysis from gas chromatography confirmed the methanol to be the predominant product. (C) 2009 Elsevier B.V. All rights reserved.
色序顯示器之色彩資料處理裝置及其方法
(2009-05-16)
黃乙白
;
孫沛立
;
林芳正
;
魏景明
;
謝漢萍
本發明係為一種色序顯示器之色彩資料處理裝置及其方法,本發明之色彩資料處理裝置及其方法配合具有紅光、綠光、藍光及由紅光、綠光或藍光混和之色光等四種背光之色序顯示器,利用該色彩資料處理裝置及其方法處理一色彩資料,得到分別對應四種背光之灰階値,該些灰階値配合該色序顯示器所顯示出之畫面可大幅降低色分離現象,更不會使該畫面失真。
在無線寬頻基地台的延遲與調變感知動態頻寬分配之設備及其方法
(2009-05-16)
林盈達
;
林義能
;
吳哲文
;
賴源正
新一代的無線寬頻系統在高速行動無線網路下可支援高速率且長距離的傳輸。然而連線品質受到長距離及空氣干擾而不穩定,使得及時應用程式面臨嚴峻的考驗。因此,需要一個適當的頻寬分配演算法及設備同時滿足及時應用程式延遲要求且充分利用可用的頻寬來提供差異式服務和公平性。在本發明中提出一個在基地台藉由考慮調適調變及編碼比率與需求急迫性的最高急迫優先演算法來克服上述的問題。在上下行頻寬的動態調節中,分別優先保留其最急迫請求的頻寬,接著根據其餘上下行不急迫請求的需求量比例地分配剩餘頻寬。在上下行獨自分配頻寬給行動裝置階段,則利用一新穎的係數來決定每個需求的急迫性,以最急迫優先的分配方式來反映出延遲保證與公平性。
降低液晶顯示器色分離之顯示方法
(2009-05-16)
林芳正
;
黃乙白
;
魏景明
;
謝漢萍
本發明為一種降低液晶顯示器色分離之顯示方法,其包括下列步驟:產生每一子畫面之控制訊號;以及依序顯示子畫面。本發明係根據欲顯示之畫面的亮暗程度,產生每一子畫面中每一顯示區域之第二背光控制訊號及第二液晶控制訊號,再根據第二背光控制訊號及第二液晶控制訊號依序顯示多彩子畫面及多個單色子畫面,並經由人眼的視覺作用而形成欲顯示之畫面。藉由本發明之實施不但可降低液晶顯示器產生色分離(Color Break Up, CBU)的現象,又可達成兼具高對比、高色彩飽和度、低功率消耗及低製造成本之液晶顯示器。
免手持裝置之音質增強器
(2009-05-16)
白明憲
;
蕭博耀
;
楊鎮懇
本發明係關於一種適用於免手持裝置之音質增强器,包含:一麥克風陣列模組,用以接收一近端聲訊並提高該近端聲訊之指向性及訊噪比;一回音消除模組,用以消除該免手持裝置使用時,至少部分一遠端聲訊回饋至遠端所產生之一回音訊號;及一噪音抑制模組,用以抑制該近端聲訊中之一噪音訊號。藉此,利用前揭本發明之各組成構件,可達到提高免手持裝置所接收聲音訊號的清晰度,並消除回音與噪音,以增進通訊品質之目的。
三維微探針陣列的組裝結構
(2009-05-16)
邱俊誠
;
張志瑋
一種三維微探針陣列的組裝結構,利用墊片(spacer)的概念,疊加單片側向式探針成為三維立體結構,並且使每一片側向式探針之導電片皆於墊片露出,使得導線易於連接,而可同時偵測深度與角度,有效的增進感測可靠度,此外,亦可將相關訊號處理積體電路與墊片整合,更可達到整合電路與降低製造成本的優勢。
全像資訊記錄與讀取裝置
(2009-05-16)
謝美莉
;
林烜輝
;
王瑞鑫
;
許根玉
;
蔣東堯
一種全像資訊記錄與讀取裝置,係利用光纖引導記錄所需之參考光,並搭配旋轉裝置使參考光可以不同角度入射至記錄介質,與攜帶資料之信號光相交干涉後,由全像記錄介質將資訊儲存下來;讀取資料時,再以相同裝置導引讀取光,以記錄時參考光所用的角度入射於全像記錄介質中,即可讀取原儲存資料。由於此發明利用光纖導引參考與讀取光,因此在參考與讀取光路徑上無光學元件阻攔,此舉可簡化參考與讀取光之光路系統;同時,利用光纖導引光線可以大幅度改善此裝置所能改變之角度範圍,並且可整合穿透式、反射式與90度的三種不同形式之全像儲存技術,可為全像材料之測試平台。