12,141 research outputs found
Adsorption properties of hydrogen on (10,0) single-walled carbon nanotube through density functional theory
No full textThe density functional theory (DFT) has been used to simultaneously investigate physi-/chemi- sorption properties of hydrogen on the (10,0) single-walled carbon nanotube (SWCNT) walls. Physisorption of H-2 outside the CNT with a vertical orientation to the tube axis above the center of a hexagon surface is the most stable state of physisorption and its binding energy is very weak, -0.792 kcal/mol. In the chemisorp ion of two hydrogen atoms the most stable state is above two adjacent carbon atoms of a hexagon with a C-H bond length of 1.10 Angstrom and one C-H bond energy of -45.761 kcal/mol. Based on these results, we have also investigated the transition state and the reaction pathway from physisorption to chernisorption of hydrogen on the CNT. The energy barrier of the reaction from physisorption to chemisorption is about 78.837 kcal/mol and the reaction is not spontaneous at 0 K. Through the calculations of the Gibbs free energy change from physisorption to chemisorption with temperatures, we learned that it is not easy for the reaction to occur, which is a major obstacle for the practical use of the CNT as a hydrogen storage medium. (C) 2004 Elsevier Ltd. All rights reserved.This research was supported by a grant (code #:
03K1501-02210) from ‘Center for Nanostructured
Materials Technology’ under ‘21st Century Frontier
R&D Programs’ of Ministry of Science and Technology,
Korea
Study on cap closure mechanism of single-walled carbon nanotubes by molecular dynamics
No full textThe closing mechanism of zigzag single-walled carbon nanotubes (SWCNT) was investigated using the molecular dynamics (MD) simulation at the experimental arcdischarge temperature of 3000 K. The (10,0) SWCNT with a diameter of 0.78 nm showed a dome-shape tip which evolved into a saddle-shaped cap that was caused by double heptagon-octagon pairs. In the case of (18,0) SWCNT with a diameter of 1.404 nm, a zipper-like closing mechanism was observed and the flat cap was obtained.This research was performed by the financial support of
‘Center for Nanostructured Materials Technology’ under
‘21st Century Frontier R&D Programs’ of the Ministry of
Science and Technology, Korea
EXPERIMENTAL-VERIFICATION OF SUPERPLASTIC SHEET-METAL FORMING ANALYSIS BY THE FINITE-ELEMENT METHOD
No full textThe numerical result for superplastic sheet-forming simulation is compared with the experimental result to verify the validity of the finite-element code developed. The code calculates the optimum pressure cycle, the deformed shapes, and the distributions of the strain and strain-rate in the blow-forming processes. The calculation deals with the maximization of the strain-rate sensitivity, the protection of the localized deformation, the consistency of the desired strain-rate, and the control of the hour-glass mode and locking phenomenon. The comparison demonstrates the validity of the present algorithm and its results, especially in respect of the optimum pressure cycle, where there is only a slight difference between the two results
Deposition of fluorinated amorphous carbon thin films with low dielectric constant and thermal stability
No full text
MODIFIED MEMBRANE FINITE-ELEMENT FORMULATION CONSIDERING BENDING EFFECTS IN SHEET-METAL FORMING ANALYSIS
No full textA modified membrane finite element formulation is derived to take the bending effect into account for sheet metal forming analysis. The algorithm developed is applied to a cylindrical and a square cup drawing problem to confirm its validity. The results show that the bending effect is appreciable in a class of deep drawing problems. It is also noted that the present algorithm enhances the convergence of a solution procedure and prevents numerical buckling
RDLS-SS-DWT v. 0.9
No full textThis fileset contains the implementation of RDLS-DWT and SS-DWT in JPEG 2000 (RDLS-SS-DWT v. 0.9), which was used in a research described in: R. Starosolski, “Application of reversible denoising and lifting steps to DWT in lossless JPEG 2000 for improved bitrates,” Signal Processing: Image Communication, Vol. 39, Part A, pp. 249-63, DOI: 10.1016/j.image.2015.09.013, 2015 and R. Starosolski, “Skipping selected steps of DWT computation in lossless JPEG 2000 for improved bitrates,” submitted. This software is intended for research purposes only; it is provided "as is"; author makes no warranty of any kind, either express or implied, with respect to this software. <br
Numerical modeling of the multi-stage sheet pair hydroforming process
No full textThe need for reduction of the weight is an important issue in the sheet metal forming industry. The hydroforming process has become an effective manufacturing process, because it can be adapted to the manufacturing of complex structural components into a single body with high structural stiffness. Tube hydroforming has been successfully developed in industry such as in the manufacturing of the components of automotive vehicles. There still, however, remains the constraint of the geometrical shape that can be fabricated by tube hydroforming. In order to improve such a constraint in product shape of the tube hydroforming process and in the formability of conventional sheet metal forming, the hydroforming process of sheet metal has been studied. The sheet pair hydroforming process has been reported to have several important advantages compared with the conventional deep drawing process. Uniform deformation over the whole region is a main advantage in the sheet hydroforming process. However, the deformation of the sheet metal can be concentrated on a small region in the case of rectangular cup with a steep slope in the wall. In this paper, the multi-stage hydroforming process of a sheet pair is proposed in order to increase the formability of a structural parts having a shape like that of an oil pan. For the strict comparison of the proposed process, the blank holding force is controlled by a hydraulic valve to a constant value during deformation. The deformed shape and strain distribution of the manufactured parts with the proposed process are compared with the results of simulation. (C) 2004 Elsevier B.V. All rights reserved
CRAS-CBR: Internal control risk assessment system using case-based reasoning
No full textInformation technology and the Internet have been major drivers for changes in all aspects of business processes and activities. They have brought major changes to the financial statements audit environment as well, which in turn has required modifications in audit procedures. There exist certain difficulties, however, with current audit procedures especially for the assessment of the level of control risk. This assessment is primarily based on the auditors' professional judgment and experiences, not on objective rules or criteria. To overcome these difficulties, we propose a prototype decision support model named CRAS-CBR using case-based reasoning to support auditors in making their professional judgment on the assessment of the level of control risk of the general accounting system in the manufacturing industry. To validate the performance, we compare our proposed model with benchmark performances in terms of classification accuracy for the level of control risk. Our experimental results show that CRAS-CBR outperforms a statistical model and staff auditor performance in average hit ratio
A tension split Hopkinson bar for investigating the dynamic behavior of sheet metals
No full textThe dynamic response of sheet metals at high strain rate is investigated with a tensile split Hopkinson bar test using plate type specimens. The tension split Hopkinson bar inevitably causes some errors in the strain at grips with the plate type specimens, since the grip and specimens disturb the one-dimensional wave propagation in bars. To validate the experiment, the level of error induced from the grips is estimated by comparing the waves acquired from experiments with the Pochhammer-Chree solution. The optimum geometry of the specimen is determined to minimize the loading equilibrium error. High strain rate tensile tests are then performed with auto-body sheet metals in order to construct their appropriate constitutive models for use in crash-worthiness evaluation
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