Practical Control of a Ball-Screw-Driven Stage for Long-Range Nanometer Positioning

A DC motor and ball-screw-driven stage is studied for long-range nanometer positioning.The closed-loop system with high-gain PID controller is specially designed for high-precision point-to-point (PTP) positioning.A particular input shape of the closed-loop system is proposed to avoid overshoot and vibration by taking into account the nonlinear characteristics of the feed drive.Friction modeling and identification are avoided and the effect of friction is greatly suppressed by the controller.Experimental and simulated results demonstrate long-range nanometer positioning is achieved without overshoot.In PTP positioning from 10 mm down to 5 nm,the positioning error is within ±5 nm and response dynamic is satisfactory.     

新自由主义中的政府与市场理论述评

作为凯恩斯主义的反对者,新自由主义以抵制政府干涉,提倡自由市场竞争的面目出现,在一定程度上被看做是对古典自由主义的复辟,但它绝不仅仅是对古典"放任自由"的一种简单继承。对新自由主义主流学派关于政府与市场理论进行考察,理清新自由主义理论思想,从而对其有一个更客观的认识和评价。     

ZrO2对CaO-SiO2系玻璃析晶的影响

通过DSC曲线研究了不同含量的ZrO2对CaO-SiO2系玻璃析晶的影响,根据JMA方程计算动力学参数(如析晶活化能E、频率因子ν、晶化指数n)。从计算结果可以看出,随着ZrO2含量的增加,析晶活化能E减少,而频率因子ν和晶化指数n增加。当ZrO2含量为7%时,E值最小:235.58kJ/mol;n值最大:4.70。说明ZrO2在CaO-SiO2玻璃体系是有效的晶核剂。     

Preparation and characterization of polyelectrolyte copolymers containing methyl methacrylate and 2-hydroxyethyl methacrylate. I. Polymers based on methacrylic acid

Acidic polyelectrolyte copolymers containing 2-hydroxyethyl methacrylate (HEMA), methyl methacrylate (MMA), and methacrylic acid (MAA) were prepared by free radical polymerization to high conversion in solution. Copolymer yields were obtained by gravimetry (all in the 30–50% range), relative molecular weights estimated by intrinsic viscosity measurements (all in the 50–70 cc/g range), tacticity by ¹³C nuclear magnetic resonance (NMR) spectroscopy (all polymers predominantly syndiotactic with some atactic content), and composition by acid/base titrations in conjunction with ¹H-NMR spectroscopy (all close to the monomer charge ratios). Acid strengths or apparent pKa's were examined as a function of extent of ionization. Measurements performed in water indicated that the compact/extended coil transformation in predominantly syndiotactic polymethacrylic acid occurs also in copolymers of similar tacticity containing moderate to high concentrations of MAA. The apparent pKa of such polymers containing only small amounts of MAA did not vary with extent of ionization, indicating a low degree of interaction between the acid groups. In copolymer pairs containing similar amounts of MAA but differing HEMA and MMA contents, the polymer containing more HEMA appeared the stronger acid, presumably due to a better solvation of that polymer which would increase the net spatial charge–charge separation and decrease cooperative effects that lead to suppressed ionization.     

LogGAN: a Log-level Generative Adversarial Network for Anomaly Detection using Permutation Event Modeling

Information Systems Frontiers - System logs that trace system states and record valuable events comprise a significant component of any computer system in our daily life. Each log contains...     

Analytical investigation on thermal-induced warpage behavior of ultrathin chip-on-flex (UTCOF) assembly

The serious warpage issues of ultrathin chip-on-flex (UTCOF) assembly induced by mismatched thermal stresses have greatly affected the mechanical stability and reliability of emerging ultrathin chip packaging technology. Currently, a theoretical prediction as a convenient and straightforward approach is still lacked for describing effectively the thermal-mechanical behavior of UTCOF during the adhesive curing and cooling process. In consideration of the adhesive thickness approximating to ultrathin chip and flexible substrate thickness, we develop a layerwise-model of ultrathin chip-adhesive-flex structure under plain strain condition, where the behavior of thick adhesive bonding can be described precisely through increasing the subdivided mathematical plies. Further, the analytical results show that the concave and convex forms of ultrathin chip warpage yield at the end of the curing and cooling process respectively. Meanwhile, the effects of its structure dimensions and material properties are also revealed for discussing a way to relieve the extent of ultrathin chip warpage. Additionally, in order to verify the validity of the theoretical prediction, we also introduce the corresponding numerical technique and experimental method. These results suggest that a kind of rigid and ultrathin flexible substrate such as metal foil should be adopted for small warpage of ultrathin assembly.     

Phase diagrams and thermodynamics of the systems ZrO2-CaO and ZrO2-MgO

The partial phase diagrams of the systems ZrO₂-CaO and ZrO₂-MgO were determined using precision lattice parameter measurements in order to check uncertainties reported in the literature. The results are in general agreement with the previous investigations by Hellmann and Stubican [83HeI], Grain [67Gra], and Sim and Stubican [87Sim]. Enthalpies of formation of the fluorite cubic solid solution and the Ca₂6Zr₁₉O₄₄ ordered phase, with reference to the monoclinic zirconia and the periclase forms of CaO and MgO, were measured calorimetrically. Assessment of the thermodynamic properties of these two systems shows that it is appropriate to model the systems with a simple single cation sublattice model. The eutectoid of the cubic phase in ZrO₂-CaO, according to both the optimization and the experimental results, is located at 1412 ± 50 K and 16.2 ±1.0 mol% CaO and in the ZrO₂-MgO binary at 1678 ± 5 K and 13.1 ± 0.5 mol% MgO. The calculated phase diagrams are presented for comparison with the experimental results.     

中国的稀有金属

本文简要介绍了中国稀有金属在研究、生产方面的发展概况。