An effective approach for parameter determination of the digital phase-locked loop in the z-domain

In digital communication systems, typical methodologies in determining loop parameters of the digital phase-locked loop (DPLL) are based on the mapping transformation from the analog domain to the digital domain. However, such transform based algorithms are relatively complicated and not straightforward, and they also cause the problem that loop parameters are affected by the pre-detection integration time greatly. To solve these issues, an effective direct method of determining loop parameters of the second-order DPLL in the z-domain is proposed in this paper. Through ascertaining specific positions of the closed-loop system function's poles inside the right-hand side of the z-plane's unit circle, unknown parameters are calculated directly and flexibly in this method, which enables the DPLL to acquire good low-pass filtering characteristic and system stability. This novel method not only reduces the complexity of solving the parameters, but also eliminates the effect of the pre-detection integration time on loop parameters. Simulation results are provided to confirm the feasibility of the proposed method and to show that the DPLL obtained by this method achieves the similar tracking performance to the discretized PLL.     

Analysis of deformation induced martensitic transformation in stainless steels

Abstract

Many studies monitoring the formation of martensite during the tensile deformation of austenite report data which are, in principle, affected by both the applied stress and the resulting plastic strain. It is not clear in these circumstances whether the transformation is stress induced (i.e. the stress provides a mechanical driving force) or whether the generation of defects during deformation helps nucleate martensite in a scenario better described as strain induced transformation. The authors demonstrate in the present work that a large amount of published data relating the fraction of martensite to plastic strain can in fact be described in terms of the pure thermodynamic effect of applied stress.     

昙华林历史街区改造的反思

从武汉昙华林历史价值出发,结合国内创意产业园的成功案例,对造成昙华林被创意改造后的得失进行了分析,就其改造的规模、定位、功能、手法、配套等方面进行专项研究,最后尝试探寻昙华林历史街区改造的正确思路与方法,为昙华林开创一条复兴之路。     

Precipitation behaviors in a quenched high Nb-containing TiAl alloy during annealing

The precipitation of γ phase and heterogeneous nucleation of ω_o phase within β_o phase areas are common phenomena in TiAl alloys. However, detailed explanation on the corresponding phase transformation mechanisms is still lacking. In this study, the precipitation behaviors of γ and ω_o phases in a quenched Ti-45Al-8.5Nb-0.2W-0.2B-0.02Y alloy are investigated. The results show that large γ grains form after quenching whereas small γ particles can directly nucleate within the remaining β_o phase during annealing. Semi-coherent interfaces are observed between γ and β_o phases and the average distance between dislocations is evaluated. The heterogeneous nucleation of ω_o phase at the lamellar colony boundary is imaged by HRTEM. Edge-to-edge method is used to calculate the orientation relationship between γ and ω_o phases. The γ phase grows up faster than ω_o phase within the β_o phase areas during annealing at 800 °C.     

建筑物内振动源变频改造前后楼板振动测试与分析

针对采取简单减振措施后的设备振动仍然会引起楼板明显振感的情况,在进行原因分析后,通过改变振动源工作频率,并取得了良好的减振效果。     

铁路曲线坐标法拨距约束优化方法研究

在铁路曲线整正中,不同组合的曲线要素得到的拨距值也不同,拨距优化可以选配更加合理的曲线要素,使拨量最小.在传统优化方法的基础上,研究了利用乘子法对坐标法拨距优化的方法,建立了对称优化数学模型,推导出相关的计算公式,并编制了相应的计算程序,将其优化结果与传统优化方法结果进行比较.结果表明:利用乘子法优化方法计算简便,得到的拨距与传统优化方法的拨距符合程度较高,且总拨距值更小,可以为铁路线路的养护维修提供参考.     

发现·转化：基于问题驱动的城市住宅课程教学实践探索

在中国房地产快速发展背景下，“城市住宅设计”教学中容易出现重点不清，以及学生对设计素材抄袭的问题。文章针对以住宅设计原理的掌握为主的教学要求，进行了“基于问题驱动的城市住宅课程设计”的实践探索。力图通过一条“问题驱动”的设计链条，引导问题的“发现”，控制问题的 “转化”，帮助学生结合设计条件对城市住宅进行主动的思考以及有目的的设计，以促成教学目标的达成。这样的教学方法有利于学生实现设计创新，并能够开拓具有社会角度的专业视野。     

煤炭装卸系统增设筛分设备的改造方法

在简单介绍煤炭专业化连续输送系统和煤炭筛分设备知识的基础上,结合天津港煤码头公司卸车系统筛分设备改造的相关内容,阐述了在传统煤炭连续输送系统中进行煤炭筛分设备改造的方法。     

Effect of Co addition on the martensitic transformation and magnetocaloric effect of Ni–Mn–Al ferromagnetic shape memory alloys

A series of Ni_50−xCo_xMn₃₂Al₁₈ (x = 3, 4, 5, 6, 7, and 8) alloys were prepared by the arc melting method. The martensitic transformation (MT) shifts to a lower temperature with increasing Co concentration and can be tuned to occur from a ferromagnetic austenite to a weak-magnetic martensite in the range of 6 ≤ x ≤ 8. The field-induced metamagnetic behavior was realized in Ni₄₂Co₈Mn₃₂Al₁₈ sample in which a large magnetic entropy change of 7.7 J/kg K and an effective refrigerant capacity value of 112 J/kg were obtained under the field of 60 kOe. The large magnetocaloric effect and adjustable MT temperature suggest that Ni–Co–Mn–Al alloys should have promising potential as magnetic refrigerants.     

设备检修企业改革发展与转型升级的思考

文章就攀钢集团内部维修企业存在的问题进行了剖析,提出了在市场条件下维修企业改革调整和转型升级的思路.