多路输出DC-DC电路设计

为了将单一输入电压变换为多路稳压输出,设计了基于LTC1624和AMS1117的DC-DC变换电路,该电路能够将铅酸蓄电池12V输入电压经过DC-DC变换后得到5V、3.3V和1.8V三路输出电压,经测试,设计的DC-DC电路输出电压稳定可靠.该电路应用于某温度测试系统的不同模块供电,电路性能满足系统要求.     

Issues and opportunities in accelerator mass spectrometry for stable isotopes

Accelerator mass spectrometry (AMS) has developed in the last 30 years many notable applications to the spectrometry of radioisotopes, particularly in radiocarbon dating. The instrumentation science of trace element AMS (TEAMS) that analyzes stable isotopes, also called Accelerator SIMS or MegaSIMS, while unique in many features, has also shared in many of these significant advances and has pushed TEAMS sensitivity to concentration levels surpassing many competing mass spectroscopic technologies. This review examines recent instrumentation developments, the capabilities of the new instrumentation and discernable trends for future development.     

加速器质谱测量93Zr的刻度研究

A method of determination for ⁹³Zr/⁹²Zr ratio by multi-collector inductively plasma mass spectrometry (MC-ICP-MS) was described in this paper. A ⁹³Zr/⁹²Zr ratio of (2.75±0.07)×10^－5 was obtained in the original sample for AMS measurement and its relative standard error was 2.5%. Considered the contribute of above-thermal neutron, a calculated ⁹³Zr/⁹²Zr ratio of 2.56×10^－5 was obtained and it was according with measurement of the result. The results showed that it can be used for AMS measurement standards sample preparation. A series 93Zr standards sample for AMS measurement were diluted by irradiated sample with enriched 92Zr.     

先进制造环境下的集成质量保证系统

通过分析当前先进制造技术（ＡＭＴ）的发展状况和制造业面临的市场环境,阐述了研究计算机集成质量保证（ＣＩＱ）系统的意义,并研究了面向ＡＭＴ实际应用的ＣＩＱ系统。实现了对先进制造技术中影响产品质量的三个重要阶段的控制,完成了系统总体结构和信息流程的设计。     

微量样品的AMS^14C年代测量

微量样品的AMS14C年代测量具有十分重要的意义,特别是对于一些珍贵的考古样品或含碳量极少的地质样品尤其如此。近两年来,北京大学AMS研究小组对系统和测量方法进行了一系列的研究和改进工作。包括改进制样流程、提高离子源样品利用率、优化整个束线的传输和改进数据获取与处理系统。已成功地测量了一系列小于100μg的微量样品。     

A Black-Box Iterative Solver Based on a Two-Level Schwarz Method

We propose a black-box parallel iterative method suitable for solving both elliptic and certain non-elliptic problems discretized on unstructured meshes. The method is analyzed in the case of the second order elliptic problems discretized on quasiuniform P1 and Q1 finite element meshes. The numerical experiments confirm the validity of the proved convegence estimate and show that the method can successfully be used for more difficult problems (e.g. plates, shells and Helmholtz equation in high-frequency domain.) Received: July 28, 1997; revised June 20, 1999     

Partial Linearization of One Class of the Nonlinear Total Least Squares Problem by Using the Inverse Model Function

In this paper we consider a special nonlinear total least squares problem, where the model function is of the form . Using the fact that after an appropriate substitution, the model function becomes linear in parameters, and that the symmetry preserves the distances, this nonlinear total least squares problem can be greatly simplified. In this paper we give the existence theorem, propose an efficient algorithm for searching the parameters and give some numerical examples. Received: June 30, 1997; revised October 31, 1998     

Coupling of Nonconforming Finite Elements and Boundary Elements II: A Posteriori Estimates and Adaptive Mesh-Refinement

The coupling of nonconforming finite element and boundary element methods was established in Part I of this paper, where quasi-optimal a priori error estimates are provided. In the second part, we establish sharp a posteriori error estimates and so justify adaptive mesh-refining algorithms for the efficient numerical treatment of transmission problems with the Laplacian in unbounded domains. Received: January 26, 1998; revised February 10, 1999     

Energy Optimization of Algebraic Multigrid Bases

We propose a fast iterative method to optimize coarse basis functions in algebraic multigrid by minimizing the sum of their energies, subject to the condition that linear combinations of the basis functions equal to given zero energy modes, and subject to restrictions on the supports of the coarse basis functions. For a particular selection of the supports, the first iteration gives exactly the same basis functions as our earlier method using smoothed aggregation. The convergence rate of the minimization algorithm is bounded independently of the mesh size under usual assumptions on finite elements. The construction is presented for scalar problems as well as for linear elasticity. Computational results on difficult industrial problems demonstrate that the use of energy minimal basis functions improves algebraic multigrid performance and yields a more robust multigrid algorithm than smoothed aggregation. Received: March 9, 1998; revised January 25, 1999