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81.
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
82.
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
83.
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
84.
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
85.
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
86.
Young Jun Kwak Hye Ryoung Park Myoung Youp Song 《Metals and Materials International》2018,24(2):423-432
Zn(BH4)2 made in our former investigation and Ni were mixed with MgH2 to promote the hydrogen absorption and release features of Mg. A 96 w/o MgH2 + 2 w/o Ni + 2 w/o Zn(BH4)2 sample [named MgH2–4NZ] was prepared by milling in a planetary ball mill in a hydrogen atmosphere. The proportion of the additive was small (4 w/o) in order to increase hydrogen absorbing and releasing rates without majorly sacrificing the hydrogen-storage capacity. The hydrogen absorption and release features of the MgH2–4NZ were inspected in detail and compared with those of 99 w/o MgH2 + 1 w/o Zn(BH4)2 [named MgH2–1Z] and 95 w/o MgH2 + 2.5 w/o Ni + 2.5 w/o Zn(BH4)2 [named MgH2–5NZ] samples. The activation of the MgH2–4NZ was not required. The MgH2–4NZ had a useful hydrogen-storage capacity (the quantity of hydrogen absorbed after 60 min) of about 5.5 w/o at the first cycle. At the first cycle, the MgH2–4NZ absorbed 3.84 w/o hydrogen after 5 min and 5.47 w/o hydrogen after 60 min at 593 K in 12 bar hydrogen. The MgH2–4NZ had a higher releasing rate, larger amounts of hydrogen absorbed and released after 60 min, and a better cycling capability than the MgH2–1Z. Staying of Ni (as Mg2Ni) and a larger amount of Zn among particles is believed to have led to the better cycling capability of the MgH2–4NZ. 相似文献
87.
88.
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
89.
Power allocation for secondary users (SUs) in cognitive networks is an important issue to ensure the SUs’ quality of service. When the mutual interference between the primary users (PUs) and the SUs is taken into consideration, it is wanted to achieve the conflict-free power allocation while synchronously maximizing the capacity of the secondary network. In this paper, the optimal power allocation problem is considered in orthogonal frequency division multiplexing cognitive networks. The single SU case is primarily formulated as a constrained optimization problem. On this basis, the multiple SUs case is then studied and simulated in detail. During the analysis, the mutual interference among the PUs and the SUs is comprehensively formulated as the restrictions on the SU’s transmission power and the optimization problems are finally resolved by iterative water-filling algorithms. Consequently, the proposed power allocation scheme restrains the interference to the primary network, as well as maximizing the capacity of the secondary network. Specifying the multiple-SUs case, simulation results are exhibited in a simplified scenario to confirm the efficiency of the proposed water-filling algorithm, and the influence of the mutual interference on the power allocation and the system capacity is further illustrated. 相似文献
90.
Selective catalytic reduction (SCR) of NOx with ammonia using metal-exchanged molecular sieves with a chabazite structure has recently been commercialized on diesel vehicles. One of the commercialized catalysts, i.e., Cu-SSZ-13, has received much attention for both practical and fundamental studies. For the latter, the particularly well-defined structure of this zeolite is allowing long-standing issues of the catalytically active site for SCR in metal-exchanged zeolites to be addressed. In this review, recent progress is summarized with a focus on two areas. First, the technical significance of Cu-SSZ-13 as compared to other Cu ion-exchanged zeolites (e.g., Cu-ZSM-5 and Cu-beta) is highlighted. Specifically, the much enhanced hydrothermal stability for Cu-SSZ-13 compared to other zeolite catalysts is addressed via performance measurements and catalyst characterization using several techniques. The enhanced stability of Cu-SSZ-13 is rationalized in terms of the unique small pore structure of this zeolite catalyst. Second, the fundamentals of the catalytically active center; i.e., the chemical nature and locations within the SSZ-13 framework are presented with an emphasis on understanding structure–function relationships. For the SCR reaction, traditional kinetic studies are complicated by intra-crystalline diffusion limitations. However, a major side reaction, nonselective ammonia oxidation by oxygen, does not suffer from mass-transfer limitations at relatively low temperatures due to significantly lower reaction rates. This allows structure–function relationships that are rather well understood in terms of Cu ion locations and redox properties. Finally, some aspects of the SCR reaction mechanism are addressed on the basis of in situ spectroscopic studies. 相似文献