北华航天工业学院，坐落于河北省廊坊市，是国家国防科技工业局、中国航天科技集团有限公司、中国航天科工集团有限公司、河北省人民政府四方共建高校，入选河北省2011计划、高等学校特色专业建设点、国家级大学生创新创业训练计划、数据中国“百校工程”；CDIO工程教育联盟、应用技术大学（学院）联盟成员单位，“十三五”应用型本科产教融合发展工程建设高校，国务院学位委员会批准的硕士学位授予单位，服务国家特殊需求人才培养项目硕士专业学位试点单位，河北省院士工作站建站单位，河北省应用技术大学研究会会长，河北省转型发展试点高校，河北省本科高校转型发展示范学校。学校始建于1978年，前身为廊坊精密机械工业学校。1983年5月组建为航天工业职工大学。1984年8月更名为华北航天工业学校。1985年11月学校改制为普通高等工程专科学校，定名为华北航天工业学院。先后隶属于第八机械工业总局、第七机械工业部、航天工业部、航空航天工业部、航天工业总公司。1999年划转到河北省，实行“中央与地方共建、以地方管理为主”的管理体制“。2004年7月，教育部正式批准北华升格为普通本科院校，更名为北华航天工业学院。据2020年7月学校官网显示，学校占地面积近800亩，分东、西两个校区，总建筑面积36万平方米；馆藏纸质图书100余万册；设有14个教学单位，47个本科专业；有1个一级学科硕士点，2个专业学位硕士点；教职工近1000名；全日制研究生、普通本专科在校生12000余人。
To perform station keeping of a platform connected by a massless extra-long tethered sailcraft with respect to (w.r.t.) the Earth in the Sun–Earth system enables envisaged space missions. The position of the platform could be balanced and controlled exploiting the nature of the dumbbell tethered system in the three-body dynamical environment by placing the platform and sailcraft with modulatable lightness number within and beyond the Sun–Earth L1 point respectively. This propulsionless scheme merely utilizing surrounding gravitational environment and modulatable solar pressure for station keeping is worth exploring. In this work, nonlinear dynamics considering positions of the platform and sailcraft along the Sun–Earth line is established in the Sun–Earth elliptical restricted three-body system (SEER3BS). Equilibria of the tethered system are analyzed parametrically as a reference for parameter selection for performing closed-loop dynamic analysis. Sliding mode control scheme is applied to station keeping of the platform. The tether’s tension is a force directly applied to the platform, and is determined by the platform-sail distance, which is adjustable by varying the sailcraft’s lightness number. Transient and steady-state dynamic responses of closed-loop system are investigated respectively. Specific time histories of physical variables such as the Earth-platform and Earth-sail distances, the elastic elongation, tension and strain of the tether, and the sailcraft’s lightness number, are presented to verify the effectiveness of the controller. Moreover, influences of the system’s dimensionless circular frequency on transient dynamic responses are studied as an example to show the existence of feasible/infeasible parameter ranges. Furtherly, envelopes of elastic tensions and strains, the Earth-sail distance, and the required lightness number are given in steady-state closed-loop dynamic responses. Influences of parameters such as the platform’s mass, the dimensionless circular frequency, the natural length of the tether, and the Earth-platform distance on the envelopes of the preceding physical variables are explored to give the feasible parameter ranges in a comprehensive manner. The corresponding discussion and suggestions on parameter selection are also given.
In this study, the method combining numerical simulation with experimental verification was adopted to investigate the influence laws of pouring temperature (650 680 °C) and casting–forging interval time (3 12 s) on the initial solid fraction distribution during forging, microstructure evolution, formation of casting defects, and mechanical properties of Al-Cu alloy, and the intrinsic correlation mechanism between process parameters and alloy properties was clarified. By means of density measurement, X-ray non-destructive testing, metallographic microscopic observation, scanning electron microscopy (SEM) analysis, and mechanical property testing, the microstructural and performance characteristics of the alloy under different process parameters were systematically characterized. The results show that the pouring temperature exerts a significant influence on the alloy forming quality by regulating the distribution of the initial solid fraction during forging, and the casting–forging interval time determines the solidification state of the alloy at the time of forging intervention. When the pouring temperature is 660 °C, 56.3
Penetration depth is a critical indicator of joint quality in laser welding. However, conventional continuous wave and pulsed modes suffer from excessive heat input and uncontrollable melt pool dynamics, resulting in limited penetration and porosity defects. Although continuous wave power modulation has been employed to synergistically enhance penetration and suppress defects, its stepwise regulation lacks sufficient precision. This study proposes a novel pulsed laser welding process based on spatially resolved energy element control, enabling precise regulation of melt pool behavior through site-specific energy delivery. Compared with conventional constant-energy welding, the proposed approach reduced peak temperature in the far field by 22.47 °C, increased average molten depth by 82.27 μm, and decreased porosity by 2.62–40.18
This study investigates the dynamics of a dissolved oxygen–plankton system described by reaction-diffusion equations incorporating two discrete delays. Under certain conditions, the system admits three equilibria. Crossing curves are constructed on the two-delay plane to analyze the stability of the positive equilibrium and the existence of Hopf bifurcation. Moreover, the normal form on the center manifold near the Hopf bifurcation point is derived. Numerical simulations are carried out to verify the theoretical findings and reveal that a double Hopf bifurcation may emerge at the intersection of the bifurcation curves.
This study systematically explores the impact and underlying mechanism of supply chain finance on supply chain resilience through theoretical analysis and empirical testing, utilizing data from Shanghai and Shenzhen A-share listed companies from 2011 to 2023. The findings reveal that supply chain finance significantly and positively promotes the enhancement of supply chain resilience. Environmental uncertainty perception partially mediates the relationship between supply chain finance and supply chain resilience. Moreover, the resilience-boosting effect of supply chain finance exhibits significant regional disparities. In the eastern region, the effect is more pronounced due to well-established financial infrastructure and mature industrial chains. In the central region, driven by policy support and industrial upgrading, the effect stands out more prominently. Conversely, in the western region, the effect has not yet fully materialized, constrained by uneven distribution of financial resources and inadequate industrial chain inadequate supporting facilities.
