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91.
Zinc was introduced into HZSM-5 by chemical vapor deposition (CVD) to investigate the catalytic properties of Zn/HZSM-5 for propane conversion. Irrespective of catalytic precursor or ion exchange method, protons were found to be replaced by Zn ions. However, Zn species in the zeolite were different depending on the precursors used. Although the addition of Zn decreased the intensity of the BrÕnsted acidity, it did not caused the apparent formation of Lewis acid sites unlike Ga/HZSM-5 catalysts. On Zn/HZSM-5, both Zn and protons intervene in propane activation step. 相似文献
92.
Fabrication of a pilot scale module of thin film composite hollow fiber membrane for osmotic pressure‐driven processes 下载免费PDF全文
Polyamide thin film composite hollow fiber membranes have advantages in their unique structure compared to flat sheet membranes. This study examined interfacial polymerization methods for fabricating pilot scale hollow fiber membranes (membrane area: 1.2 m2, number of hollow fiber strands: 1200). For use in osmotic pressure‐driven processes, a one‐pot hydrophilic interfacial polymerization procedure was developed simultaneously to modify the surface property and synthesize polyamide thin film. With the procedure, a pilot scale module has a water flux of 13 LMH using a draw solution of 0.6M NaCl and a feed solution of distilled water through the design of the module configuration. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46110. 相似文献
93.
C. William Ibbs Clarence K. Wong Young Hoon Kwak 《Canadian Metallurgical Quarterly》2001,17(3):159-165
Changes in projects are common and may be deleterious or beneficial—whether you see a change as a conflict or a valuable lesson depends only on your prospective. Project changes affect the cost, the scheduling, and the duration of projects, both directly and indirectly. Despite many articles and much discussion in practice and academic literature, there is a lack of information about systematic approaches to manage project change. This paper introduces a comprehensive project change management system that is founded on five principles: (1) promote a balanced change culture; (2) recognize change; (3) evaluate change; (4) implement change; and (5) continuously improve from lessons learned. By applying this project change management system, project participants can minimize deleterious change and promote beneficial change. 相似文献
94.
Somin Shin Ki Seon Lee Seoung Duck Park Jae Su Kwak 《Journal of Mechanical Science and Technology》2009,23(3):624-630
Heat transfer coefficients were measured in a channel with one side dimpled surface. The sphere type dimples were fabricated,
and the diameter (D) and the depth of dimple was 16 mm and 4 mm, respectively. Two channel heights of about 0.6D and 1.2D,
two dimple configurations were tested. The Reynolds number based on the channel hydraulic diameter was varied from 30000 to
50000. The improved hue detection based transient liquid crystal technique was used in the heat transfer measurement. Heat
transfer measurement results showed that high heat transfer was induced downstream of the dimples due to flow reattachment.
Due to the flow recirculation on the upstream side in the dimple, the heat transfer coefficient was very low. As the Reynolds
increased, the overall heat transfer coefficients also increased. With the same dimple arrangement, the heat transfer coefficients
and the thermal performance factors were higher for the lower channel height. As the distance between the dimples became smaller,
the overall heat transfer coefficient and the thermal performance factors increased.
This paper was recommended for publication in revised form by Associate Editor Yong Tae Kang
Jae Su Kwak received his B.S. and M.S. degrees in Mechanical Engineering from Korea University in 1996 and 1998, respectively. He then
received his Ph.D. from Texas A&M University in 2002. Dr. Kwak is currently an Assistant Professor at the School of Aerospace
and Mechanical Engineering at Korea Aerospace University in Goyang-City, Korea. His main research interests include gas turbine
heat transfer, compact heat exchanger, and enhancement of heat transfer. 相似文献
95.
Junsu Park Byoung Kyu Kwak Eunjoo Bae Jeongjin Lee Kyunghee Choi Jongheop Yi Younghun Kim 《Korean Journal of Chemical Engineering》2009,26(6):1630-1636
Nanotechnology is a rapidly growing field and numerous products containing engineered nanomaterials are already in the market.
With the increasing use of engineered nanomaterials, it is expected to increase the exposures to nanomaterials in the workplace.
However, the researches on the exposure assessment of nanomaterials to humans and the environment are just a beginning step,
as the nanotechnology industries are expanding. Questionnaire surveys conducted by various organizations reveal that many
nanotechnology companies are searching for information on exposure measurement for the protection of workers who handle nanomaterials.
We analyze the trends of researches on the occupational exposure measurement of engineered nanomaterials and investigate the
methodologies of exposure assessment recommended by the related working groups. This work is expected to fill the gaps in
knowledge on the exposure assessment of nanomaterials. 相似文献
96.
Fiber glass reinforced composites like sheet molding compounds (SMC) have recently been widely used in the fabrication of two-piece automobile hoods for passenger cars. In the present investigation, a one-piece composite hood with reinforcing ribs was optimally designed and manufactured by resin transfer molding in order to reduce manufacturing cost. In order to obtain the optimal design, stiffness analyses for deflections due to self-weight, oil canning, and torsion test conditions were carried out by applying the ABAQUS/Standard program. Based on these analyses, the thickness dimension of the composite hood required to maintain a stiffness comparable to a conventional steel hood was determined. For optimization studies of the weight reduction of the currently proposed one-piece composite hood with reinforcing ribs, IDESIGN program was employed. Based on a recursive quadratic programming technique, the thickness dimensions of the reinforcing ribs were optimized. The deflection ratios between fiber glass reinforced composite and conventional steel hoods were minimized in the optimization studies. From the present studies, it was found that the weight saving effect obtained by introducing the optimally designed one-piece composite hood was 37% compared to the conventional steel hood. This ranged approximately from 30 to 40% for composite hoods manufactured by resin transfer molding, depending on the composite materials used. Through these studies, it was confirmed that the one-piece composite hood was a preferable design and manufacture, compared to currently used composite hood made in two pieces, in terms of weight reductions and manufacturing cost without losing the stiffness required. 相似文献
97.
Boo Young Chung Miros?aw J. Skibniewski Henry C. Lucas Jr. Young Hoon Kwak 《Canadian Metallurgical Quarterly》2008,22(6):373-382
Enterprise resource planning (ERP) systems offer many benefits to the engineering–construction industry. Many construction firms recognize the benefits of ERP system implementation; however, they still hesitate to adopt these systems due to high cost, uncertainties, and risks. This study identifies and analyzes critical factors that need to be considered to ensure successful ERP system implementation in the construction industry. First, this paper identifies the factors associated with the success and failure of ERP systems, and provides indicators to evaluate the success of such systems. Then, the paper develops an information system success model to analyze the relationships between factors and success indicators. Finally, the paper provides recommendations for successful ERP systems based on the analysis. The derived success factors should help senior managers in construction firms make better decisions and improve their business value by implementing the most effective EPR systems. 相似文献
98.
Jian Zhi Hu Ja Hun Kwak Zhenguo Yang William Osborn Tippawan Markmaitree Leon L. Shaw 《Journal of power sources》2008,181(1):116-119
Using variable temperature in situ 1H NMR spectroscopy on a mixture of LiNH2 + LiH that was mechanically activated using high-energy ball milling, the dehydrogenation of the LiNH2 + LiH to Li2NH + H2 was investigated. The analysis indicates NH3 release at a temperature as low as 30 °C and rapid reaction between NH3 and LiH at 150 °C. The transition from NH3 release to H2 appearance accompanied by disappearance of NH3 confirms unambiguously the two-step elementary reaction pathway proposed by other workers. 相似文献
99.
Jong Kyu Kim Ki-Jeong Kim Bongsoo Kim Jae Nam Kim Joon Seop Kwak Yong Jo Park Jong-Lam Lee 《Journal of Electronic Materials》2001,30(3):129-133
Effects of surface treatment on the change of band bending at the surface of p-type GaN were studied using synchrotron radiation
photoemission spectroscopy, and the results were used to interpret the reduction of contact resistivity by the surface treatment.
The contact resistivity on p-type GaN decreased from (5.1±1.2)×10−1 to (9.3±3.5)×10−5Ω cm2 by the surface treatment using aqua regia prior to Pt deposition. Surface band bending was reduced by 0.58 eV and 0.87 eV
after the surface treatments by HCl and aqua regia solutions, respectively. The atomic ratio of Ga/N decreased as the photoelectron
detection angle was decreased, indicating that the surface oxide was mainly composed of Ga and O, GaOx, formed during high-temperature annealing for the generation of holes, and Ga vacancies, VGa, were produced below the GaOx layer. Consequently, the aqua regia treatment plays a role in removing GaOx formed on p-type GaN, leading to the shift of the Fermi level toward the energy levels of VGa located near the valence band edge. This causes the decrease of barrier height for the transport of holes, resulting in the
good ohmic contacts to p-type GaN. 相似文献
100.
Jeong Eun Lee Mi Hwa Seo Yoon Hyuk Chang Hae-Soo Kwak 《Journal of the American Oil Chemists' Society》2010,87(2):233-238
The present study was designed to optimize the different conditions for β-cyclodextrin (β-CD) crosslinked by adipic acid on
cholesterol removal from squid liver oil. Different factors were concentrations of crosslinked β-CD, mixing temperature, ratio
of squid liver oil to distilled water, mixing time and mixing speed. It was found that cholesterol removal from squid liver
oil was significantly affected by concentrations of crosslinked β-CD, mixing temperature, ratio of squid liver oil to distilled
water, mixing time and mixing speed. In a recycling study, cholesterol removal from the squid liver oil with recycled crosslinked
β-CD in the first recycling trial was 81.05%, which was slightly lower than that with new crosslinked β-CD (87.06%). In up
to three time trials, over 70% of cholesterol removal was observed. The present study indicated that the optimum conditions
for cholesterol removal from squid liver oil using crosslinked β-CD were a 1:3 ratio of squid liver oil to distilled water,
25% (crosslinked β-CD/distilled water, w/v) crosslinked β-CD concentration, 20 min mixing time, 800 rpm mixing speed and 55 °C
mixing temperature with about 87% cholesterol removal. 相似文献