Browsing by Issue Date, starting with "2019-04-15"

Now showing 1 - 20 of 7804

A review on airflow management in data centers
(2019-04-15)
Chu, Wen-Xiao
;
Wang, Chi-Chuan
;
機械工程學系
;
Department of Mechanical Engineering
This study provides a review upon airflow management in data centers. Based on the available airflow path, cooling systems in data centers are categorized as long-distance cooling or short-distance cooling systems. Investigations on airflow management include tests in real data center or in simulated data center. Besides, the computational fluid dynamics (CFD) had been widely employed upon the thermal and airflow management of the data centers. For the long-distance cooling system, the airflow management normally adopts raised-floor configuration and hot/cold aisle arrangement. The major problems in airflow management include hot-air recirculation, cold-air bypass, leakages, over-provisioned and under-provisioned air supply, and airflow/temperature non-uniformity. The aforementioned effects often interact with the geometry layout of the data center. Related literatures regarding the effect of plenum depth, perforated tiles, enhanced facility such as induced bypass fans, infrastructure layout, aisle containment and leakage are discussed and compared. In addition, studies on the overhead air supply method are also examined and compared with the raised-floor ones. For the short-distance cooling system, the effect of server layout and heat exchanger layout concerning the airflow uniformity are investigated. It is found that the appropriate management of the original design into centralized server layout can ease the mal-distribution of airflow into the severs by 30%. This review aims to emphasize the criteria of implementing airflow management to data centers that serve as a reference guide for energy saving in data center as far as airflow arrangement is concerned. Moreover, some recommended future research efforts are also addressed.
Composite metal substrate for thin film AlGaInP LED applications
(2019-04-15)
Horng, R. H.
;
Sinha, Shreekant
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Lee, C. P.
;
Feng, H. A.
;
Chung, C. Y.
The fabrication and feasibility assessment of n-side up, thin-epilayer, AlGaInPbased vertical light-emitting-diodes (LEDs; emitting area: 1 mm x 1 mm) with a copperinvar-copper-composite metal (CIC) substrate was obtained by wafer bonding and epilayer transferring technologies. The structure of CIC substrate is a top Cu layer of 20 mu m, a middle Invar layer of 64 mu m, and a bottom Cu layer of 20 mu m. The invar layer consists of Fe and Ni at a ratio of 70% to 30%. The coefficient of thermal expansion for CIC is about 6.1 x 10(-6) /K, which is similar to that of the GaAs substrate (5.7 x 10(-6)/K) and AlGaInP epilayers. Due to the high thermal conductivity (160 W/m-K) of 10(4)-mu m-thick CIC, the high performances of the packaged LEDs are obtained. They present a low red shift phenomenon (from 623 to 642 nm for 100 mA to 1 A) and a high output power 212 mW at 800 mA. The CIC substrate can be extended to fabricate high-efficiency thin film LEDs with conventional vertical electrodes. (c) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
Pulse compression irrespective of fiber dispersion using chirp of transistor lasers
(2019-04-15)
Tung, Chien-Ting
;
Chang, Chi-Hsiang
;
Chang, Shu-Wei
;
Wu, Chao-Hsin
;
光電工程學系
The voltage modulation of transistor lasers (TLs) through Franze-Keldysh absorption can impose an unconventional chirp on optical signals. In this Letter, we model this chirp effect and demonstrate how the output Gaussian pulse is reshaped through optical fibers. It is shown that pre-chirped pulses of TLs may be compressed in fibers with both normal and anomalous dispersions. (C) 2019 Optical Society of America
Flexible, multifunctional neural probe with liquid metal enabled, ultra-large tunable stiffness for deep-brain chemical sensing and agent delivery
(2019-04-15)
Wen, Ximiao
;
Wang, Bo
;
Huang, Shan
;
Liu, Tingyi ''Leo''
;
Lee, Meng-Shiue
Flexible neural probes have been pursued previously to minimize the mechanical mismatch between soft neural tissues and implants and thereby improve long-term performance. However, difficulties with insertion of such probes deep into the brain severely restricts their utility. We describe a solution to this problem using gallium (Ga) in probe construction, taking advantage of the solid-to-liquid phase change of the metal at body temperature and probe shape deformation to provide temperature-dependent control of stiffness over 5 orders of magnitude. Probes in the stiff state were successfully inserted 2 cm-deep into agarose gel "brain phantoms" and into rat brains under cooled conditions where, upon Ga melting, they became ultra soft, flexible, and stretchable in all directions. The current 30 mu m-thick probes incorporated multilayer, deformable microfluidic channels for chemical agent delivery, electrical interconnects through Ga wires, and high-performance electrochemical glutamate sensing. These PDMS-based microprobes of ultra-large tunable stiffness (ULTS) should serve as an attractive platform for multifunctional chronic neural implants.
Correlation of surface processes with characteristic sensing responses of PdO thin films to ethanol
(2019-04-15)
Cheng, I-Kai
;
Wang, Jeng-Han
;
Tsai, Cheng-Yu
;
Chen, Yi-Sheng
;
Pan, Fu-Ming
Gas sensing characteristics of PdO nanoflake thin films exposed to ethanol (EtOH) at temperatures below 250 degrees C was studied. The PdO thin film responses distinctly to 0.15 ppm EtOH in dry air at temperatures above 100 degrees C. A characteristic valley-shaped response feature develops in the early stage of the exposure to EtOH at 150 degrees C and above. Formation of the valley feature is a result of the combined effects of two types of surface processes, which successively modify the sensor conductance in the opposite way. Dehydrogenation of adsorbed EtOH induces reduction of preadsorbed oxygen anions and the PdO substrate, resulting in the drop of the conductance. On the other hand, subsequent adsorption of EtOH and oxygen on newly growing Pd nanoclusters, which develop due to the reduction of the PdO substrate, causes the increase in the conductance. The Pd nanoclusters can be later reoxidized in the EtOH gas mixture, thereby modifying the sensing behavior of the PdO sensor. X-ray photoelectron spectroscopy (XPS), diffusive reflectance infrared Fourier transform spectroscopy (DRIFTS) and temperature programmed desorption (TPD) were used to study adspecies and gaseous species formed in the EtOH gas sensing reactions. On the basis of the characteristic electrical response and chemical characterizations, we proposed the formation mechanism for the characteristic response feature.
Ultraviolet polarized light emitting and detecting dual-functioning device based on nonpolar n-ZnO/i-ZnO/p-AlGaN heterojunction
(2019-04-15)
Dai, Jiangnan
;
Chen, Jingwen
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Li, Xiaohang
;
Zhang, Jun
;
Long, Hanling
We report on the demonstration of a 386 nm light emission and detection dual-functioning device based on nonpolar a-plane n-ZnO/i-ZnO/p-Al0.1Ga0.9N heterojunction under both forward and reverse bias. The electroluminescence intensity under reverse bias is significantly stronger than that under forward bias, facilitated by carrier tunneling when the valence band of p-AlGaN aligns with the conduction band of i-ZnO under reverse bias. Also amid reverse bias, the photodetection was observed and applied in a duplex optical communication device. Optical polarization of the light emission is studied for potential polarization-sensitive device applications. The proposed device provides an important pathway for the multifunctional devices operating in a UV spectrum. (C) 2019 Optical Society of America
Wave representation for asymmetric elliptic vortex beams generated from the astigmatic mode converter
(2019-04-15)
Chen, Y. F.
;
Lai, Y. H.
;
Hsieh, M. X.
;
Hsieh, Y. H.
;
Tu, C. W.
An analytical wave representation is derived to express the asymmetric elliptic vortex beams generated by using an astigmatic mode converter to transform the asymmetric Hermite-Gaussian modes. The effect of the spatial asymmetry on the elliptic vortex beam can be straight forwardly considered in the analytical wave representation. A detailed comparison with experimental intensity patterns and phase structures is made. The good agreement between experimental results and theoretical analyses confirms the characterization and generation of the asymmetric elliptic vortex beams. (C) 2019 Optical Society of America
All Nonmetal Resistive Random Access Memory
(2019-04-16)
Yen, Te Jui
;
Gismatulin, Andrei
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Volodin, Vladimir
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Gritsenko, Vladimir
;
Chin, Albert
Traditional Resistive Random Access Memory (RRAM) is a metal-insulator-metal (MIM) structure, in which metal oxide is usually used as an insulator. The charge transport mechanism of traditional RRAM is attributed to a metallic filament inside the RRAM. In this paper, we demonstrated a novel RRAM device with no metal inside. The N+-Si/SiOx/P+-Si combination forms a N+IP+ diode structure that is different from traditional MIM RRAM. A large high-resistance/low-resistance window of 1.9 x 10(4) was measured at room temperature. A favorable retention memory window of 1.2 x 10(3) was attained for 10(4)s at 85 degrees C. The charge transport mechanism of virgin, high- and low-resistance states can be well modeled by the single Shklovskii-Efros percolation mechanism rather than the charge transport in metallic filament. X-ray photoelectron spectroscopy demonstrated that the value of x in SiOx was 0.62, which provided sufficient oxygen vacancies for set/reset RRAM functions.
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