[en] This paper on the incorporation of the structural information available from the correlated x-ray computed tomography (CT) scans or magnetic resonance (MR) images to compensate for the effect of photon attenuation in positron emission tomography (PET) that can provide more accurate image reconstruction. Using a surface-fitting technique previously developed in our laboratories, we can now correlate tomographic images from PET, CT, and MR imaging with precise registration; thus, anatomic maps from the correlated CT and MR images become available for PET image reconstruction. These anatomic maps give more accurate estimations of the effect of photon attenuation. Delineation of regions that exhibit distinctly different tissue characteristics can be performed on these anatomic maps. Average attenuation coefficients calculated within each region with appropriate calibration for photon energy and spectrum are then assigned to various regions. These attenuation coefficient maps are reprojected to produce a set of attenuation correction factors for each projection profile

[en] Accurate segmentation of apple targets is one of the most important problems to be solved in the vision system of apple picking robots. This work aimed to solve the difficulties that background targets often bring to foreground targets segmentation, by fusing the visual attention mechanism and the growth rule of seed points. Background targets could be eliminated by extracting the ROI (region of interest) of apple targets; the ROI was roughly segmented on the HSV color space, and then each of the pixels was used as a seed growing point. The growth rule of the seed points was adopted to obtain the whole area of apple targets from seed growing points. The proposed method was tested with 20 images captured in a natural scene, including 54 foreground apple targets and approximately 84 background apple targets. Experimental results showed that the proposed method can remove background targets and focus on foreground targets, while the k-means algorithm and the chromatic aberration algorithm cannot. Additionally, its average segmentation error rate was 13.23%, which is 2.71% higher than that of the k-means algorithm and 2.95% lower than that of the chromatic aberration algorithm. In conclusion, the proposed method contributes to the vision system of apple-picking robots to locate foreground apple targets quickly and accurately under a natural scene. (Author)

[en] The key problem for picking robots is to locate the picking points of fruit. A method based on the moment of inertia and symmetry of apples is proposed in this paper to locate the picking points of apples. Image pre-processing procedures, which are crucial to improving the accuracy of the location, were carried out to remove noise and smooth the edges of apples. The moment of inertia method has the disadvantage of high computational complexity, which should be solved, so convex hull was used to improve this problem. To verify the validity of this algorithm, a test was conducted using four types of apple images containing 107 apple targets. These images were single and unblocked apple images, single and blocked apple images, images containing adjacent apples, and apples in panoramas. The root mean square error values of these four types of apple images were 6.3, 15.0, 21.6 and 18.4, respectively, and the average location errors were 4.9°, 10.2°, 16.3° and 13.8°, respectively. Furthermore, the improved algorithm was effective in terms of average runtime, with 3.7 ms and 9.2 ms for single and unblocked and single and blocked apple images, respectively. For the other two types of apple images, the runtime was determined by the number of apples and blocked apples contained in the images. The results showed that the improved algorithm could extract symmetry axes and locate the picking points of apples more efficiently. In conclusion, the improved algorithm is feasible for extracting symmetry axes and locating the picking points of apples. (Author)

[en] A rather simple process for separating uranium isotope was designed and a relatively high separation factor was obtained at room temperature (α = 1.05). The separation factor may be achieved as high as 2 by this process at cryogenic temperature since the measured (FWHM) value of ν₃ absorption peak at sufficient low temperature is about one-fifth of that at room temperature. Therefore, it may be developed to be a new, practical and economical method for producing enriched uranium

[en] The temperature dependence of critical currents in YBa₂Cu₃O_7-δ superconducting ceramics have been studied following the Ginzburg-Landau theory and the de Gennes proximity effects for a superconductor--normal-conductor interface. Based on an S/N/S weak-link model, critical currents as a function of temperature have been calculated and a model able to describe different kinds of I_c-T characteristics in 1:2:3 ceramics has been developed. A set of four YBa₂Cu₃O_7-δ ceramic samples has been prepared for experimental studies. These samples were annealed under different conditions. Critical currents as a function of temperature have been measured in a high-heat-transfer system. I_c-T characteristics ranging from a quadratic temperature dependence to a temperature dependence of the Josephson-tunneling type have been observed. The experimental I_c-T characteristics fit very well theoretical predictions which include the effects of randomness in the thickness of the nonsuperconducting barriers and the boundary conditions for the samples

[en] The Beijing Electron-Positron Collider (BEPC) serving for both high energy physics experiments and synchrotron radiation application has been well operated for more than 13 years since May 1989. After the luminosity upgrade program from 1999, the performance and stability of the operation were much improved in recent years. The peak luminosity of the BEPC has reached 5.8 x 10³⁰ cm^-2s^-1 at J/ψ energy of 1.55GeV and 1 x 10³¹ cm^-2s^-1 at ψ(2S) energy of 1.84GeV respectively. Over 50 million J/ψ events were accumulated in two years from Sept. 1999 and 14 million ψ(2S) events have been taken in the last run from Sept. 2001 to June 2002. For dedicated synchrotron radiation operation, the maximum beam current is around 120mA with lifetime over 20∼30 hours. In addition, two insertion devices as well as new beamlines were installed in the last summer (2002). Besides, experimental studies for the machine development and BEPCII R and D are being carried out. Improvement on the machine operation system and the database is still under way. It's expected that BEPC will continue to run stably till the mounting of BEPCII starts. The operation and performance of BEPC will be described in this paper in details, and also the presentation will be offered about the operation team, organization system etc. (author)

[en] We have calculated the states associated with valence alternation pair defects in a Te-rich amorphous GeTe random network. Two-fold Te sites and four-fold Ge sites are found to introduce states that are resonant with the valence and conduction bands, respectively. The system has a band gap, but these defect states are in the same energy range as those found by modulated photocurrent experiments. The absence of electron spin resonance signals is still not explained. (author)

[en] The APR1400(Advanced Power Reactor 1400MWe), a next generation nuclear reactor of Korea, is an advanced PWR(Pressurized Water Reactor). APR1400 adopts a DVI (Direct Vessel Injection) system as the advanced feature of the ECCS(Emergency Core Cooling System). Therefore, the DVI system requires an additional safety analysis on the DVI line break LOCA(Loss-of-Coolant Accident) and the conventional analysis models should be estimated and modified for understanding of this accident. Recently, ATLAS(Advanced Thermal-Hydraulic Test Loop for Accident Simulation), a thermalhydraulic integral effect test facility for APR1400, was utilized to simulate the DVI line break accident. Especially, a series of sensitivity tests on DVI line break sizes, 100%, 50% and 25% of the cross section of the DVI nozzle, were carried out with the ATLAS. However, the results of the sensitivity tests with ATLAS were not validated with any other counter-part tests. Thus, the SNUF(Seoul National Univ. Facility) will be utilized to perform the sensitivity test which is similar as the experiment performed with ATLAS for obtaining the valuable counter-part test data. Since the SNUF is a RHRP(Reduced Height Reduced Pressure) test facility, the test conditions of the experiments should be determined with an appropriate scaling method for performing the SNUF experiment. Therefore, in this paper, the test conditions were determined according to the energy scaling method. Also, the test conditions were estimated by the MARS code analysis, which contains comparisons between the prototype and the SNUF at the different break areas: 100%, 50% and 25% of the cross section of the DVI nozzle

[en] The resonant nonlinear refraction in rare-earth-doped solids is studied with femtosecond degenerate pump-probe two-beam coupling spectroscopy. The phase modulation induced by the pump pulses is shown to result in a significant contribution to the differential change of the probe transmission. An ultrafast resonant nonlinear refractive index of the order of 1x10^-18 m2/W is measured in Nd:YVO₄ crystals. [copyright] 2001 American Institute of Physics

[en] Aim: To retrospectively evaluate the criteria for discriminating infiltrative cholangiocarcinoma from benign common bile duct (CBD) stricture using three-dimensional dynamic contrast-enhanced (3D-DCE) magnetic resonance imaging (MRI) combined with magnetic resonance cholangiopancreatography (MRCP) imaging and to determine the predictors for cholangiocarcinoma versus benign CBD stricture. Materials and methods: 3D-DCE MRI and MRCP images in 28 patients with infiltrative cholangiocarcinoma and 23 patients with benign causes of CBD stricture were reviewed retrospectively. The final diagnosis was based on surgical or biopsy records. Two radiologists analysed the MRI images for asymmetry, including the wall thickness, length, and enhancement pattern of the narrowed CBD segment, and upstream CBD dilatation. MRI findings that could be used as predictors were identified by univariate analysis and multivariable stepwise logistic regression analysis. Results: Malignant strictures were significantly thicker (4.4 ± 1.2 mm) and longer (16.7 ± 7.7 mm) than the benign strictures (p < 0.05), and upstream CBD dilatation was larger in the infiltrative cholangiocarcinoma cases (20.7 ± 5.7 mm) than in the benign cases (16.5 ± 5.2 mm; p = 0.018). During both the portal venous and equilibrium phases, hyperenhancement was more frequently observed in malignant cases than in benign cases (p < 0.001). The results of the multivariable stepwise logistic regression analysis showed that both hyperenhancement of the involved CBD during the equilibrium phase and the ductal thickness were significant predictors for malignant strictures. When two diagnostic predictive values were used in combination, almost all patients with malignant strictures (n = 26, 92.9%) and benign strictures (n = 21, 91.3%) were correctly identified; the overall accuracy was 92.2% with correct classifications in 47 of the 51 patients. Conclusion: Infiltrative cholangiocarcinoma and benign CBD strictures could be effectively differentiated using DCE-MRI and MRCP based on hyperenhancement during the equilibrium phase and bile wall thickness of the involved segment