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[en] The AP-0 Target Hall Collection Lens is a pulsed device which focuses anti-protons just downstream of the Target. Since the angles at which the anti-protons depart the Target can be quite large, a very high focusing strength is required to maximize anti-proton capture into the downstream Debuncher Ring. The current design of the Collection Lens was designed to operate with a focusing gradient of 1,000 T/m. However, multiple failures of early devices resulted in lowering the normal operating gradient to about 750 T/m. At this gradient, the Lens design fares much better, lasting several million pulses, but ultimately still fails. A Finite Element Analysis (FEA) has been performed on this Collection Lens design to help determine the cause and/or nature of the failures. The Collection Lens magnetic field is created by passing high current through a central conductor cylinder. A uniform current distribution through the cylinder will create a tangential or azimuthal magnetic field that varies linearly from zero at the center of the cylinder to a maximum at the outer surface of the cylinder. Anti-proton particles passing through this cylinder (along the longitudinal direction) will see an inward focusing kick back toward the center of the cylinder proportional to the magnetic field strength. For the current Lens design a gradient of 1,000 T/m requires a current of about 580,000 amps. Since the DC power and cooling requirements would be prohibitive, the Lens is operated in a pulsed mode. Each pulse is half sine wave in shape with a pulse duration of about 350 microseconds. Because of the skin effect, the most uniform current density actually occurs about two-thirds of the way through the pulse. This means that the maximum current of the pulse is actually higher than that required in the DC case (about 670,000 amps). Since the beam must pass through the central conductor cylinder it must be made of a conducting material that is also very 'transparent' to the beam. For the Collection Lens, this material is lithium (Li). The central conductor cylinder is a lithium cylinder 1 cm in radius and about 14 cm long. Figure 1 shows this cylinder in a cross-section view of the Collection Lens. Surrounding the central cylinder is a jacket of titanium alloy (6Al-4V ELI) called the septum. The septum's purpose is to contain the lithium against various thermal and magnetic forces while allowing cooling (melting point of Li is 180.5 C) by an annular water passage. The ends of the Li cylinder are bound by end windows made of beryllium (Be) and a thin titanium (ti) foil. The foil protects the Be from the corrosive effects of Li and the Be window provides the structural support. The two end windows sit in pockets in the ends of two larger steel cylinders or body halves. The body halves are separated from each other by ceramic spacers. The body halves, septum and end windows are connected to each other by nickel (Ni) seals which preserve the boundary of the lithium conductor. Force required to make these seals is provided by eight Ti 6Al-4V ELI tie rods which traverse the entire assembly. These tie rods also resist magnetic forces that attempt to separate the body halves during the current pulse. There are several insulating components that are used to isolate one side of the lens from the other and force the current through the central Li conductor. The volumes of Li at each end of the central conductor cylinder outside the septum but inside the body halves are called buffer volumes. These buffer volumes serve two roles. One, they provide a low resistance current path to the end of the central conductor cylinder. Two, they provide a volume for Li to expand into during the current pulse. For the latter it is assumed that magnetic forces and thermal strains will force lithium from the central cylinder and into the buffer volumes during the current pulse. There are several loads on the Lens that are developed during a current pulse. High magnetic loads act radially and longitudinally outward on the steel body halves and radially inward on the central conductor cylinder. This latter force on the Li cylinder is termed the magnetic pinch effect and could result in the separation of the Li from the septum inner wall. To prevent this from happening, the Li is actually pre-loaded when the Lens is filled. During the current pulse, ohmic losses heat the various components and create thermal strains. This, coupled with beam losses, create non-uniform displacements and therefore stresses in the Lens components. Finally, the pre-loaded tie rods add yet another load to the Lens. Since the geometry, materials, and loads are so complex and interdependent, an analysis should try to integrate all these aspects in one model if possible. ANSYS finite element code has been utilized in an attempt to do so. The results are hoped to shed light on why the current Collection Lens design fails at high gradient (short term) and low gradient (long term).
[en] Charge-exchange injection by means of carbon foils is a widely used method in accelerators. This paper discusses two critical issues concerning the use of carbon foils: efficiency and lifetime. An energy scaling of stripping efficiency was suggested and compared with measurements. Several factors that determine the foil lifetime--energy deposition, heating, stress and buckling--were studied by using the simulation codes MARS and ANSYS
[en] The decomposition and burning of straw results in serious environmental pollution, and research is needed to improve strategies for straw collection to reduce pollution. This work presents an integrated design of multi-functional rice combine harvester that allows grain harvesting and straw baling. This multi-functional combine harvester could reduce the energy consumption required for rice harvesting and simplify the process of harvesting and baling. The transmission schematic, matching parameters and the rotation speed of threshing cylinder and square baler were designed and checked. Then the evaluation of grain threshing and straw baling were tested on a transverse threshing cylinders device tes rig and straw square bales compression test rig. The test results indicated that, with a feeding rate of 3.0 kg/s, the remaining straw flow rate at the discharge outlet was only 1.22 kg/s, which indicates a variable mass threshing process by the transverse threshing cylinder. Then the optimal diameter, length and rotating speed of multi-functional combine harvester transverse threshing cylinder were 554 mm, 1590 mm, and 850 r/min, respectively. The straw bale compression rotating speed of crank compression slider and piston was 95 r/min. Field trials by the multi-functional combine harvester formed bales with height×width×length of 40×50×54-63 cm, bale mass of 22.5 to 26.0 kg and bale density 206 to 216 kg/m3. This multi-functional combine harvester could be used for stem crops (such as rice, wheat and soybean) grain harvesting and straw square baling, which could reduce labor cost and power consumption.
[en] Rice panicles which have reached a mature state must be harvested, requiring differently specialized threshing devices and operating parameters to achieve favorable threshing and separating results. The primary objective of this study is to design a transverse multi-cylinders device that operates under the most effective possible variables to harvest rice in different states of maturity. The attachment forces between the grain and pedicel on the panicle were measured at different moisture contents. Based on rice agronomic characteristics, a transverse multi-cylinders device test bench was developed to conduct threshing and separating experiments. The threshing and separating capability of each transverse cylinder was tested, and the operating parameters of each threshing cylinder were investigated. Results showed that detachment force decreased from the bottom to the top of the rice panicle. Optimal harvesting time was identified at moisture content of 29.69%, and the best operating parameters combination was cylinder speed of 600, 650 and 700 rpm, and concave clearances of 40, 35 and 40 mm. Combine harvester of transverse multi-cylinder device test results showed an un-threshed grain ratio of 0.64%, un-separated grain ratio of 0.35%, and broken grain ratio of 0.22%, at a feeding rate of 6 kg/s. This research can be used in the future to successfully design transverse multi-cylinders device for small and medium-sized rice combine harvesters. (Author)
[en] Carbon foils are widely used in charge-exchange injection in high intensity hadron accelerators. There are a number of physics issues associated with the use of carbon foils, including stripping efficiency, energy deposition and foil lifetime (temperature rise, mechanical stress and buckling, etc.). This paper will give a brief discussion of these issues
[en] Two-detector coincidence Doppler broadening (CDB) method of positron annihilation radiation is applied to the study of precipitates in metals. As the first step, the CDB spectra for many kinds of elements are measured to obtain the 'fingerprint' of each element for the chemical analysis of the precipitates in metals. Utilizing the fingerprint of Cu, we made chemical analysis of nano-particles formed in the initial stage of thermal aging in a Fe-Cu alloy, and found that the particles are consisting of Cu only and free from vacancies, which demonstrates the usefulness of this method in the study of the precipitates.
[en] Vacancies and vacancy clusters in Ni, Cu, and Fe induced by high- and low-speed deformations are studied systematically by positron annihilation techniques and are compared with those induced by the conventional-rolling. To clarify the nature of the defects, the experimental results are compared with our superimposed-atomic-charge calculations of the positron lifetimes in the vacancy clusters as a function of their size. It is found that the deformation-induced defects in the fcc and bcc metals are significantly distinct. In the fcc metals of Ni and Cu, monovacancies with high number densities are induced by the high- and low-speed deformations and by heavy conventional-rolling (>10% in Ni and >40% in Cu). Vacancy clusters are observed after the high- and low-speed deformation for Ni and after the conventional-rolling for Cu. On the contrary, dislocations and vacancy clusters are introduced in bcc Fe regardless of the type or degree of deformation
[en] A coating of nickel with La2O3 particles was electrodeposited on the surface of γ-TiAl to improve its high-temperature oxidation resistance. The experimental results showed that contrary to the oxidation of bare specimens, the electro-deposited Ni-La2O3 composite-coated ones exhibited much better resistance to both isothermal and cyclic oxidation in air at 1000 and 900 C. For the oxidation of the Ni-La2O3 composite-coated γ-TiAl EPMA/EDX microanalyses revealed that after the composite film had been thoroughly oxidized, a La2O3-rich NiO layer close to the gas-scale interface and two alumina-rich layers, with one beneath the NiO layer and the other adjacent to the γ-TiAl matrix, were produced in the scale. The results indicated that the preferentially formed la2O3-doped NiO layer retarded the growth of rutile and favored the formation of two alumina-rich layers. The mechanism of the effects of the electrodeposited Ni-La2O3 composite on the oxidation behavior of γ-TiAl is discussed in detail
[en] In recent years, the use of ultrasonography (US), X-CT and MRI has reduced the employment of isotopic explorations in the detection of hepatocellular carcinoma (HCC). But sometime the results of US, X-CT or MRI were different and diagnosis was very difficult. This present investigation was aimed to assess the usefulness of delayed hepatobiliary imaging in the diagnosis of HCC in these patients. Forty-eight patients consisting of 33 males and 15 females were entered into the research protocol. The mean age was 46 yr old (range 12-71 yr old). All of the patients were performed by surgery and verified histologically after nuclear examination. The subject was in a supine position under a gamma camera (Elscint, Apex Ap-6) and 555 MBq of Tc-99m-PMT were injected intravenously. The initial scinphotos obtained within 1 min after injection were used to image the blood pool phase. Subsequently, hepatic scans were obtained at 5 min, 1,2 and 5 hr. Anterior, right lateral and posterior hepatic images were recorded. According to the radioactive uptake by the lesion in delayed phase, the negative (no or minor uptake), positive (equal or greater uptake) or very strong positive (almost equal to the activity, of gallbladder) were judged. The positive were considered as diagnostic of HCC. And the very strong positive, were considered as diagnostic of benign hepatoma, such as adenoma or FNH. Thirty-seven of the forty-eight patients were HCC based on histology. Delayed imaging revealed increased or equilibrated uptake of radioactivity by the tumors in 22 of 37 patients with hepatocellular carcinoma. The sensitivity was 59.5%. One patient final diagnosis based on histology was focal nodular regenerative hyperplasia, and only the diagnosis with delayed hepatobiliary imaging before surgery was correct. Compared with US, X-CT and MRI, delayed hepatobiliary imaging had the highest specificity for diagnosis of hepatocellular carcinoma. In recent group, the specificity of Tc-99m-PMT delayed imaging was 100%. Some HCC patients were misdiagnosed as liver cyst, hemangioma or other benign diseases by US, X-CT or MRI. So, these results show that Tc-99m-PMT delayed hepatobiliary imaging is very useful in the diagnosis of hepatocellular carcinoma