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[en] It has been found that effective removal of small particles from silicon wafer surfaces can be achieved by laser-induced airborne plasma shock waves initiated above the surface. This process has demonstrated successfully the removal of 1 μm sized tungsten particles from the surface. Tungsten is known to be one of the most difficult particles to remove using conventional laser cleaning techniques employing direct laser irradiation onto the surface. The area cleaned by the shock waves was over ten times larger than that achieved by conventional laser cleaning. This provides an advantage in speed for cleaning large areas. The cleaning efficiency was strongly dependent on the gap distance between the laser focus (where laser-induced sparking takes place) and the surface. The particle removal began to occur with a gap of 6 mm and the removal efficiency increased significantly with decreasing the gap resulting in a complete removal at 2 mm. The basic idea behind this new cleaning technique and how to apply it for the removal of small particles from surfaces are described. Theoretical considerations about adhesion forces of small particles on the surface and laser-induced shock wave generation are carried out to understand this process. [copyright] 2001 American Institute of Physics
[en] Principal component analysis (PCA) is a popular data analysis method. One of the motivations for using PCA in practice is to reduce the dimension of the original data by projecting the raw data onto a few dominant eigenvectors with large variance (energy). Due to the ubiquity of 1/fα noise in science and engineering, in this Letter we study the prototypical stochastic model for 1/fα processes--the fractional Brownian motion (fBm) processes using PCA, and find that the eigenvalues from PCA of fBm processes follow a power-law, with the exponent being the key parameter defining the fBm processes. We also study random-walk-type processes constructed from DNA sequences, and find that the eigenvalue spectrum from PCA of those random-walk processes also follow power-law relations, with the exponent characterizing the correlation structures of the DNA sequence. In fact, it is observed that PCA can automatically remove linear trends induced by patchiness in the DNA sequence, hence, PCA has a similar capability to the detrended fluctuation analysis. Implications of the power-law distributed eigenvalue spectrum are discussed
[en] The main objectives of this project are to establish the internatinal collaboration basis of optical technolgies between Korean and China through the combination of the Chinese advanced fundamental technologies with the Korea industrialization and commercialization infrastructures, by ways of exchanging scientist and informations, holding joint seminars, cooperative utilization of research resources. On the ground of this establishment, the optical technologies of Korea are supposed to be leveled up to that of the world-most advanced. At the same time, for the improvement of mutual benefit and financial profit of both of the countries, technical support for the investment on the optical industries in the two countries and establishment of foundation for the venture capitals are also the purpose of this project. Because the state-of-the-arts of the Chinese technologies such as aerospace engineering, military defense technology, applications to medical treatments, laser fusion research, and so on, are known to be far above those of Korean and upto one of the most advanced in the world, it is necessary that the acquisition of these technologies, resulting in the enhancement of the levels of domestic technologies in these fields, implementation of joint research projects for technology development as well as the balanced opportunities for commercial product/sales and cooperation should be actively pursued
[en] Manufacturing process of IPS Mock-up was initiated in late of 2003 with DAEWOO Precision industries Company. Manufacturing drawings due to detail drawings are composed of Outer assembly and Inner assembly. Welding of IPS Mock-up was performed by the GMAW(Gas Metal Arc Welding) process. After the welding process, non-destructive examination was conducted. Leak test was performed to the Main cooling water part and Neon gas inter-space gap part by the He gas injection with the pressure of 6.0 kgf/cm2 and 30 minutes holding time. the result was shown that there was no leak at the Neon gas inter-space gap part but leak was occurred at Main cooling water part according to imperfect screw of purge plug. so, it was re-finished and test was performed to certify the leak tightness. To satisfy the HANARO Limiting Operation Condition, IPS should be tested ahead of installation at the HANARO reactor by the use of test facilities. IPS Mock-up and its test facilities will be designed and used for the test of 'HANARO flow tube pressure drop', 'IPS inner pressure drop' and 'IPS inner vibration'
[en] High temperature structures of LMR experience inelastic deformation such as plasticity and creep due to high temperature operating temperature of 530∼550 .deg. C. The generated creep strains are connected with the stress relaxations, redistributions and/or progressive deformations. The superposition of primary and secondary stresses may lead to enhanced creep deformations. The term 'creep ratchetting' refer to the phenomenon where enhanced creep occurs with plasticity ratcheting. The interchange of elastoplastic and creep strains is important for its understanding. Since creep ratcheting is highly nonlinear structural behavior, it is required to secure the proper analysis technique to evaluate inelastic strain due to enhanced creep. In this project, the simplified evaluation method for enhanced creep using core stress concept was investigated and the enhanced creep of pipe subjected to sustained axial tensile loading and transient thermal loading with hold time was evaluated using several analysis models; that is, isotropic hardening model, kinematic hardening model and combined hardening model with Norton's power law creep equation. In addition, the viscoplastic analysis using NONSTA-VP was performed for comparisons. The simplified evaluation method using core stress concept yields conservative result as expected. It is necessary to systematize the simplified evaluation procedure, to analyze the conservatism of the method, and to improve the inelastic analysis techniques including NONSTA-VP
[en] Radon calibration chamber has been constructed to test and calibrate radon and radon progeny detectors at various environmental conditions and to study the characteristic behavior of radon decay products. The size of main room in the chamber is 3.2 mx3.3 mx2.4 m (25.3 m3) and the total volume of the chamber is 39.1 m3. The maximum concentration of radon in the chamber can be maintained up to 250 kBq m-3 and temperature and humidity are controlled in the ranges of (10-40) deg. C and (30-80)%, respectively. The equilibrium factor and unattached fraction of radon progeny are determined at the radon concentration of 2 kBq m-3
[en] The out-of-pile mechanical performance and microstructure of recrystallized Zr.1.5 Nb-S alloy was investigated. The strength of the recrystallized Zr-1.5Nb-O-S alloys was observed to increase with the addition of sulfur over a wide temperature range, from room temperature up to 300 .deg. C. A yield drop and stress serrations due to dynamic strain were observed at room temperature and 300 .deg. C. Wavy and curved dislocations and loosely knit tangles were observed after strained to 0.07 at room temperature, suggesting that cross slip is easier. At 300 .deg. C, however, dislocations were observed to be straight and aligned along the slip plane, suggesting that cross slip is rather difficult. At 300 .deg. C, oxygen atoms are likely to exert a drag force on moving dislocations, intensifying the dynamic strain aging effect. Oxygen atoms segregated at partial dislocations of a screw dislocation with the edge component may hinder the cross slip, resulting in the rather straight dislocations distributed on the major slip planes. Recrystallized Zr-Nb-S alloys exhibited ductile fracture surfaces, supporting the beneficial effect of sulfur in zirconium alloys. Oxidation resistance in air was also found to be improved with the addition of sulfur in Zr-1.5 Nb-O alloys
[en] We investigated the effect of Nb substitution for Ru on the structural and magnetic properties of (Ru1-xNbx)Sr2(Sm1.4Ce0.6)Cu2Oz Samples. X-ray diffraction measurements indicated that nearly single-phase samples are formed in the range from x = 0 to 1.0. The superconducting transition temperature determined from the inflection in the field-cooled magnetic susceptibility decreased only slightly from Tc = 25 K for x = 0 to Tc = 22 K for x = 1.0, in consistent with the change in room temperature thermopower of the samples. However, the Nb substitution for Ru above x 0.25 significantly suppressed the weak ferromagnetic component of the field-cooled magnetic susceptibility. It was also found that the Nb substitution for Ru results in an enhanced diamagnetic susceptibility with Nb content above x = 0.5 in both zero field-cooled and field-cooled magnetization measurements, in contrast to the behavior of the samples with x≤0.5 in which the diamagnetic susceptibility decreases as the Nb content increases.
[en] The cross-sectional anatomy of the intervertebral disc and spinal canal can be studied in detail by computed tomography (CT) which is not invasive and is much simpler than conventional myelography. The shape of the normal disc and distribution of epidural fat pad varied at each disc level and CT findings of the normal disc and spinal canal are essential in diagnosis of herniation or bulging. However, there has been no previous publications providing us with the detailed criteria of normal disc and neural canal cross-sectional anatomy. The present study has been carried out to investigate CT anatomy of the normal distribution of the epidural fat at each lumbar disc level to set up a baseline by which one will be able to judge disc herniation or bulging. The materials consisted of 30 adult volunteers. They were sampled randomly from the individual undergoing a CT study for the reasons other than spinal disease and having no symptoms or signs of the lumbar spinal disease. CT scans were performed with a Siemens Somatom 2 Scanner. Technical factors involved were: Tube voltage 125 kVp, exposure time 10 seconds, 460 mAS, 256 x 256 matrix, and pixel size 0.4 mm. Contiguous 2-mm thick slice of each disc were obtained parallel to the disc plane at 3-mm interval for 5 lumbar disc. The results are follows: 1. The shape of the posterior disc margins at L1-2, L2-3, and L3-4 levels were concave anteriorly in over 90% of the cases compared with the disc margins at L4-5 and L5-S1 where were convex or flat in over 85%. 2. None of the convex disc showed focal nodular protrusion nor were more convex than anterior margin of the disc. 3. The lower lumbar levels, the greater the visibility of the epidural fat pad. The visibility of the epidural fat pad in both lateral recesses was 81.5% at the L4-5 level and 100% at the L5-S1 level. There was no single case in which epidural fat pad was visable in only on side. 4. The visibility of the epidural fat just behind the disc was only 18.5% at the L4-5 level compared with 88% at the L5-S1 level.
[en] In lumbar region the epidural fat pad is relatively abundant so that CT can provides sufficient information in diagnosis of lumbar HNP. Many authors have reported on the CT findings of HNP such as focal nodular protrusion of the posterior disc margin, obliteration of epidural fat pad, impingement of dural sac and nerve root, swelling of nerve root, soft tissue density in the spinal canal and calcification of disc. However there was so previous report describing incidence and reliability of the findings. It is the purpose of the present study to survey the frequency, reliability, and limitation of these CT findings. The clinical material was consisted of 30 operatively proven cases of HNP of the lumbar spine. Each lumbar CT scan was reviewed retrospectively and the findings were analysed by two radiologists independently. There were 20 males and 10 females and the mean age was 36.7 years. Involvement of L4-S5 level was 2.3 times more frequent than that of L5-S1 level. Of 30 cases, 22 were unilateral posterolateral types and 8 cases central or unilateral far lateral types. CT findings observed were nodular protrusion of the posterior margin of the disc, obliteration of epidural fat pad, impingement of dural sac or nerve root, soft tissue density in the spinal canal and calcification in the posterior portion of the protruded disc, in order of decreasing frequency. The conclusions are follows: 1. Nodular protrusion of the posterior disc margin accompanied by obliteration of epidural fat pad was observed in every case. The former findings was designated as direct sign and the latter indirect. 2. Obliteration of the epidural fat appears to be significant in lateral recesses especially when it occurs unilaterally. This was not true, however, in the centrally located fat pad. 3. Impingement of the dural sac and nerve root were observed in 90% and 67%, respectively, and were very helpful in establishing HNP diagnosis when the direct and indirect signs were equivocal. Metrizamide CT scan facilitated the evaluation of the dural sac and nerve root. 4. Soft tissue density in the spinal canal and calcification in the posterior portion of the protruded disc were demonstrated in only 2% and 1% of the case, respectively.