No abstract available

[en] For the last two decades, applications of finite element analysis have tremendously reshaped the metal forming and manufacturing industries. Today, this method is commonly employed as an effective tool to help engineers (1) in conceptual development or virtual prototyping phase precisely predict the behavior of the part to be formed so that the tools can be correctly designed and (2) in product improvement phase correctly and effectively identify the root causes of product defects and provide solutions. These demands, however, have not been well satisfied, mostly because of the difficulties in the complex nonlinearities and boundary conditions in metal forming, implementation of accurate and sophisticated solution methodologies and an accurate material response through appropriate constitutive equations. Approximations and limitations of the programs may not result in the desirable accuracy sought from the simulation and therefore may lead the engineers in a dilemma in interpretation of simulation results. This paper presents and discusses a number of commonly met issues, including prediction of workpiece fracture and influence of material characteristics and friction conditions on such fracture occurrence, in process modeling of a cold extrusion forming method with a hope that these issues can be solved more successfully when the finite element programs have been further advanced

[en] In this work, a rhodamine derivative was synthesized and grafted onto the surface of an up-conversion host of β-NaYF₄:Yb³⁺/Er³⁺, resulting in a Hg(II)-sensing system. The obtained nanocomposite was fully characterized and studied by electron microscopy images, wide-angle XRD diffraction patterns, IR spectra and thermogravimetry, which confirmed the successful construction of the nanocomposite. The analysis on absorption and emission spectra suggested that the up-conversion host could efficiently excite the probe, which was later proved by the emission decay characteristics. The sensing performance of the nanocomposite towards Hg(II) was studied by steady emission spectra. It was found that the fluorescence from the probe increased with the increasing Hg(II) concentration, showing an “off–on” effect. In addition, the fluorescence enhancement effect could be activated only by Hg(II), suggesting that the nanocomposite owned a high selectivity towards Hg(II). -- Highlights: • A Hg(II) sensing system owing high accuracy and good selectivity was reported. • An up-conversion host of β-NaYF₄:Yb³⁺/Er³⁺ served as the excitation core. • A rhodamine-based probe was grafted onto the surface of the excitation source. • The fluorescence enhancement effect could be activated only by Hg(II)

[en] In this paper, we reported an “off–on” optical sensor for Hg(II) detection using upconversion β-NaYF₄:Yb³⁺/Er³⁺ nanobars as the excitation source and a rhodamine derivative as the probe. The nanocomposite was characterized and studied by electron microscopy, XRD analysis, IR spectra, thermogravimetry and photophysical measurements. The energy transfer mechanism between the upconversion excitation source and the rhodamine based probe was analyzed by their emission/excitation spectra and excited state lifetime comparison. Experimental results suggested that the upconversion emission form the excitation source could effectively excite the probe. The sensing performance of the nanocomposite towards Hg(II) was also studied. It was found that the emission intensity of the nanocomposite increased with the increasing Hg(II) concentration, showing an “off–on” phenomenon. In addition, the emission signal of the nanocomposite was immune to other metal ions, providing a high selectivity towards Hg(II). -- Highlights: • An “off–on” optical sensor for Hg(II) detection was constructed. • Upconversion β-NaYF₄:Yb³⁺/Er³⁺ was used as the excitation source. • A rhodamine derivative was connected to β-NaYF₄:Yb³⁺/Er³⁺ as the probe. • The nanocomposite and its sensing performance were fully studied

No abstract available

[en] In recent years, a new technique to detect the characteristic X-ray from projectile ions in accelerator mass spectrometry has been developed. When bombarding a target with heavy ions, characteristic X-ray from these ions and from the target element(s) are emitted, from which it is possible to analyse the element of the projectile ions. If the mass of the ions are known, the isobars can be identified, which is important for heavy isotope analysis and ion beam impurity analysis. To optimize the X-ray yield, the ion velocity and target composition must be well chosen. This can be achieved if the experiment is done in the velocity domain where the formation of quasi-molecules is the main process for X-ray production

[en] Highlights: • A refrigerant composition matching method for N_2–CH_4 expansion processes. • Efficiency improvements for propane pre-cooled N_2–CH_4 expansion processes. • The process shows good adaptability to varying natural gas compositions. - Abstract: An expansion process with a pre-cooling system is simulated and optimised by Aspen HYSYS and MATLAB"™. Taking advantage of higher specific refrigeration effect of methane and easily reduced refrigeration temperature of nitrogen, the designed process adopts N_2–CH_4 as a mixed refrigerant. Based on the different thermodynamic properties and sensitivity difference of N_2 and CH_4 over the same heat transfer temperature range, this work proposes a novel method of matching refrigerant composition which aims at single-stage or multi-stage series expansion liquefaction processes with pre-cooling systems. This novel method is applied successfully in propane pre-cooled N_2–CH_4 expansion process, and the unit power consumption is reduced to 7.09 kWh/kmol, which is only 5.35% higher than the global optimised solutions obtained by genetic algorithm. This novel method can fulfil the accomplishments of low energy consumption and high liquefaction rate, and thus decreases the gap between the mixed refrigerant and expansion processes in energy consumption. Furthermore, the high exergy efficiency of the process indicates good adaptability to varying natural gas compositions.

No abstract available

[en] ¹²⁶Sn is a long-lived beta emitting radionuclide. Artificially produced ¹²⁶Sn has entered our environment through nuclear weapons testing and releases from reprocessing plants and may locally lead to strongly enhanced ¹²⁶Sn concentrations. So the long lived 126Sn may have implications on the nuclear pollution in our environment. Further more, in supernova explosions ¹²⁶Sn is predominantly produced by rapid neutron capture (r process). The live ¹²⁶Sn observed in primitive meteorites can imply that some live nuclear material was present at an early stage of the solar system formation. But the primary difficulty in the determination of the ¹²⁶Sn concentration is the interference of the stable isobar ¹²⁶Te. AMS is one of the most important methods to detect minute amounts of ¹²⁶Sn.This work was carried out using the HI-13 tandem accelerator at CIAE National lab. SnF₃-ions from the negative ion source were injected into the accelerator whose terminal voltage is 8.7 MV. Sn¹⁰⁺ ions were selected by an analyzing magnet and finally counted selectively using a ΔE-E gas ionization detector. A preliminary result of ¹²⁶Sn/Sn=1.2.10^-8 has been obtained for a ¹²⁶SnO₂ sample produced from spent U fuel. Further improvement is needed for the AMS measurement of ¹²⁶Sn.

[en] The basic principle and the last developments of accelerator mass spectrometry are described. Its applications in the fields of geosciences, biomedicine, environmental science and nuclear astrophysics are also discussed. (authors)