197,017 research outputs found
Evaluation of thermal stresses in planar solid oxide fuel cells as a function of thermo-mechanical properties of component materials
No full textFuel cells are the direct energy conversion devices which convert the chemical energy of a
fuel to electrical energy with much greater efficiency than conventional devices. Solid Oxide
Fuel Cell (SOFC) is one of the various types of available fuel cells; wherein the major
components are made of inherently brittle ceramics. Planar SOFC have the advantages of
high power density and design flexibility over its counterpart tubular configuration.
However, structural integrity, mechanical reliability, and durability are of great concern for
commercial applications of these cells. The stress distribution in a cell is a function of
geometry of fuel cell, temperature distribution, external mechanical loading and a mismatch
of thermo-mechanical properties of the materials in contact. The mismatch of coefficient of
thermal expansion and elastic moduli of the materials in direct contact results in the
evolution of thermal stresses in the positive electrode/electrolyte/negative electrode (PEN)
assembly during manufacturing and operating conditions (repeated start up and shut down
steps) as well. It has long been realized and demonstrated that the durability and reliability of
SOFCs is not only determined by the degradation in electrochemical performance but also
by the ability of its component materials to withstand the thermal stresses.
In the present work, an attempt has been made to evaluate the thermal stresses as a function
of thermal and mechanical properties of the component materials assuming contribution
from other factors such as thermal gradient, mechanical loading and in-service loading
conditions is insignificant. Materials used in the present study include the state of art anode (Ni-YSZ), electrolyte(YSZ) and cathode materials(LM and LSM) of high temperature SOFC
and also the ones being suggested for intermediate temperature SOFC Ni-SCZ as an anode,
GDC and SCZ as electrolyte and LSCF as the cathode. Variation of thermo-mechanical
properties namely coefficient of thermal expansion, and elastic and shear moduli were
studied using thermo-mechanical analyzer and resonant ultrasound spectroscope respectively
in 25-900��C temperature range. A non-linear variation in elastic and shear moduli- indicative
of the structural changes in the studied temperature range was observed for most of the
above mentioned materials. Coefficient of thermal expansion (CTE) was also found to
increase non-linearly with temperature and sensitive to the phase transformations occurring
in the materials. Above a certain temperature (high temperature region- above 600��C), a
significant contribution from chemical expansion of the materials was also observed.
In order to determine thermal stress distribution in the positive electrode, electrolyte,
negative electrode (PEN) assembly, CTE and elastic and shear moduli of the component
materials were incorporated in finite element analysis at temperature of concern. For the
finite element analysis, anode supported configuration of PEN assembly (of 100mm x
100mm) was considered with 1mm thick anode, 10��m electrolyte and 30��m cathode. The
results have indicated that cathode and anode layer adjacent to cathode/electrolyte and
electrolyte/anode interface respectively are subjected to tensile stresses at the operating
temperature of HT-SOFC (900��C) and IT-SOFC (600��C). However, the magnitude of
stresses is much higher in the former case (500MPa tensile stress in cathode layer) when
compared with the stress level in IT-SOFC (178MPa tensile stress in cathode layer). These
high stresses might have been resulted from the higher CTE of cathode when compared with
the adjacent electrolyte. However, it is worth mentioning here that in the present work, we
have not considered any contribution from the residual stresses arising from fabrication and
the stress relaxation from softening of the glass sealant
Evaluation of the adhesion of fiber posts cemented using different adhesive approaches
No full textThe aim of this study was to investigate the adhesion of fiber posts cemented with luting agents that utilize three currently available adhesive approaches: etch-and-rinse, self-etch, and self-adhesive. Forty-two intact single-rooted human premolars were used in the study. Teeth were divided into six groups. In each group, a different resin cement with its adhesive system (if needed) and a fiber post were used. The groups were classified, according to the adhesive approach, into the following three categories. (i) Etch-and-rinse groups: Calibra resin cement/XPBond adhesive + self-curing activator (SCA)/RadiX Fiber Post (Dentsply Caulk), FluoroCore 2 core build-up material/XPBond + SCA/RadiX Fiber Post (Dentsply Caulk), and MultiCore Flow luting and core build-up material/Excite DSC adhesive/FRC Postec Plus fiber post (Ivoclar Vivadent). (ii) Self-etch group: Panavia F 2.0/ED primer (Kuraray)/RadiX Fiber Post (Dentsply Caulk). (iii) Self-adhesive groups: experimental self-adhesive cement/RadiX Fiber Post (Dentsply Caulk), and RelyX Unicem/RelyX Fiber Post (3M ESPE). The adhesion between the post and the root canal walls was assessed using the 'thin-slice' push-out test. In the test arrangement used, the self-etching approach may offer less favourable adhesion to root canal dentin in comparison with etch-and-rinse and self-adhesive approache
Multiband Optical Networks Control and Provisioning
No full textThis paper presents viable solutions for the control of a multi-band optical network. NETCONF and augmented OpenConfig YANG data models are adopted to configure and monitor the state of network devices. Both connection provisioning and Quality of transmission estimation account for Stimulated Raman Scattering
Leading Women Entrepreneurs of Thailand
No full text"Marriage is like an elephant-- the husband is the front legs that choose the direction, the wife the back legs, providing the power!" – Thai Legend\ud
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Introduction\ud
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The Thai legend above illustrates the important yet veiled role of women in Thai society. Women comprise 46% of the labour force, 26% of senior officials, legislators and managers (UNDP, 2006), and nearly 50% of the entrepreneurs (Minniti, Allen & Langowitz, 2006) in Thailand. Most of these women are running small companies, but a handful head large, growth-oriented entrepreneurial firms. In this chapter, we profile four leading Thai women who have been recognized with the highly prestigious "Leading Women Entrepreneurs of the World" (LWEW) award: Kobkarn Wattanavranangkul , Khungying Pornthip Narongdej, Supapan Pichaironarongsongkram and Supaluck Umpujh.\ud
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Despite the awareness of female entrepreneurs’ role in economic development (OECD, 2000), there has been limited academic attention (Baker, Aldrich & Liou 1997; de Bruin, Brush & Welter 2006), particularly to highly successful "gazelle" entrepreneurs. Extant female entrepreneurship research has explored a range of topics including gender differences (e.g. Birley, 1989; Hisrish & Brush, 1984), performance (e.g. Fasci & Valdez, 1998) and financing (e.g. O’Gorman & Terjesen, 2005). Researchers have called for studies of entrepreneurship that take into account the role of culture (Hayton, George & Zahra, 2002) and are of a qualitative nature (Gartner & Birley, 2002; Davidsson, 2004).\ud
This chapter proceeds as follows. We begin by providing an overview of enterprise and female entrepreneurship in Thailand. Next, we describe relational theory in the context of female entrepreneurship, paying particular attention to the role of family. Following a description of the data and methodology, we review four case studies of Thai "gazelle" entrepreneurs. Following a discussion of key themes, we conclude with implications and suggestions for future research
Repair potential of a laboratory-processed nano-hybrid resin composite
No full textThe purpose of this study was to compare the 24-h composite-to-composite microtensile bond strength of Gradia Forte (GF) repaired with the same or a different material after different surface treatments. Different groups were set up, in which composite blocks of GF were subjected to the following treatments: Group 1, sandblasting with 50-microm aluminum oxide and 37% phosphoric acid etching (PA); Group 2, bur roughening and etching with 37% PA; Group 3, etching with 37% PA only. In all groups, a bonding resin was used as an intermediate agent prior to layering of the repair material (Gradia Direct (GD), Gradia (G), or GF). Bond strengths were then determined and analysed statistically. Scanning electron microscopy (SEM) evaluation of substrates and bonded interfaces was also performed. Surface treatment (P < 0.001) and repair materials (P < 0.001) were factors that significantly affected repair strength, whereas their interaction (P = 0.31) had no significant effect. Group 3 showed significantly superior repair strength to Groups 1 and 2, whereas Group 2 showed significantly weaker repair strength to Groups 1 and 3. Irrespective of surface treatment, GD and G gave similar results, which were better than those obtained using GF. The lowest probability of failure was found for GD and G in Group 3, whereas the highest was found for GF in Groups 1 and 2. Premature failures occurred mainly with G and GF. No pre-testing failures were found in the sandblasting/GD subgroup. Surface-treated composites showed different textures under SEM, whereas composite-repair bonds showed comparable interfacial feature
Multicarrier Transmission Optimization in Elastic Optical Networks
No full textThis study investigates the trade-off between Quality of Transmission (QoT) performance and spectrum efficiency through low-margin operation of multicarriers. Margin reduction is enabled by implementing tight filtering and slight subcarriers overlap. Experiments conducted on a Software Defined Networking (SDN)-controlled Elastic Optical Network (EON) testbed demonstrate spectrum-efficient multicarriers composed of three subcarriers, achieving savings of up to 22% in spectrum occupation for 80 km optical connections
Experimental Optimization of Power-Aware Super-Channels in Elastic Optical Networks
No full textPower-Aware super-channel optimization is experimentally demonstrated using a 600Gbit/s transponder in the SDN-controlled Elastic Optical Network. The trade-off between power consumption and spectrum efficiency is investigated by operating super-channels at nominal and low-margin conditions. Results show that physical layer and operational modes impact power consumption regardless of the spectrum efficiency. Experiments on 800 Gbit/s super-channels show 7% power saving when super-channels are operated at nominal spectrum usage
Experimental Optimization of Spectrum-Efficient Super-Channels in Elastic Optical Networks
No full textAutomatic super-channel optimization is experimentally demonstrated using a 600Gb/ s transponder in the SDN-controlled Elastic Optical Network. Margin reduction while guaranteeing Quality of Transmission allows for a spectrum occupation reduction of 25%
Neural Network-Based Control of TDFA
No full textThe complexity of controlling optical amplifiers with multiple pumps, like Thulium-Doped Fiber Amplifiers (TDFAs), stems from the need to select the optimal pumping to ensure proper operation (e.g., maintaining a constant target output power). Therefore, an experimental demonstration of neural network-assisted SDN control of TDFA configuration is presented. The proposed optimization enables efficient automated TDFA control, resulting in an RMSE of 0.23 dBm between target and actual output power
Dr. Duane M. Jackson, Morehouse College, July 2011
No full textThis video is a conversation with Dr. Duane M. Jackson. Dr. Jackson talks about his paper, "Recall and the Serial Position Effect: The Role of Primacy and Recency on Accounting Students' Performance." Jackie Daniel, AUC Woodruff Library, is the interviewer
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