湖南省体育高考乒乓球专项的教学与探析

在湖南省体育高考培训班的教学过程中,通过观察法、访谈法、文献资料法、数据统计法发现高考生体育老师的专业水平、学生乒乓球技术的基础、学生选择的握拍法、左推右攻和搓中侧身突击的教学顺序、动作的步法移动、学生心理素质的培养、发球机稳定性的选择对学生的成绩都有着至关重要的影响。该文在研究乒乓球高考规则的基础上,通过对不同学生面对的不同问题,总结出最有利于学生拿高分的教学方法。

艺术体操个人成套中结合旋转的动力性动作剖析

结合旋转的动力性动作(R)是艺术体操个人成套中常见的难度类型之一。文章采用文献资料法、录像解析法对2020年莫斯科艺术体操大奖赛个人单项决赛四个单项前三名共计12套成套中结合旋转的动力性动作进行分析研究,此次比赛基本代表了现阶段国际艺术体操的最高水平。为客观掌握高水平运动员结合旋转的动力性动作的现状与国际化发展趋势,文章通过细分各项器械R的附加标准类型,统计高水平运动员对各个加分点的运用情况,归纳其编排规律,阐释其经典成分,同时总结非常见的加分标准类型,将其作为创新性动作编排的备选组成元素,使成套动作在观赏性和难度得分方面达到新高度。

Multi-degree-of-freedom coupling dynamic characteristic of TBM disc cutter under shock excitation

When the tunneling boring machine(TBM) cutterhead tunnels, the excessive vibration and damage are a severe engineering problem, thereby the anti-vibration design is a key technology in the disc cutter system. The structure of disc cutter contains many joint interfaces among cutter ring, cutter body, bearings and cutter shaft. On account of the coupling for dynamic contact and the transfer path among joint interface, mechanical behavior of disc cutter becomes extremely complex under the impact of heavy-duty, which puts forward higher requirements for disc cutter design. A multi-degree-of-freedom coupling dynamic model, which contains a cutter ring, a cutter body, two bearings and cutter shaft, is established, considering the external stochastic excitations, bearing nonlinear contact force, multidirectional mutual coupling vibration, etc. Based on the parameters of an actual project and the strong impact external excitations, the modal properties and dynamic responses are analyzed, as well as the cutter shaft and bearings' loads and load transmission law are obtained. Numerical results indicate the maximum radial and axial cutter ring amplitudes of dynamic responses are 0.568 mm and 0.112 mm; the maximum radial and axial vibration velocities are 41.1 mm/s and 38.9 mm/s; the maximum radial and axial vibration accelerations are 94.7 m/s2 and 58.6 m/s2; the maximum swing angle and angular velocity of cutter ring are 0.007° and 0.0074 rad/s, respectively. Finally, the maximum load of bearing roller is 40.3 k N. The proposed research lays a foundation for structure optimization design of disc cutter and cutter base, as well as model selection, modification and fatigue life of the cutter bearing.

Identification of the development stage-specific factors in mouse fetal liver binding to the human β-globin gene promoter

In order to elucidate the molecular mechanisms of globin gene expression during embryonic development, the nuclear extracts from mouse hematopoietic tissue at different stages of development have been prepared. By using DNase I footprinting and gel mobility shift assays, the binding of protein factors in these extracts to the human βglobin promoter was analyzed. The differences in the binding patterns of protein factors during development were observed. An erythroid-specific and stage-specific nuclear protein in the nuclear extract from d 18 mouse fetal liver was identified, which can bind to the sequence (from -66bp to -90bp) of human β-globin promoter. We therefore speculate that the function of this cis-acting element may be similar to stage selector element (SSE) in chieken βA- promoter.

Structural Synthesis and Workspaces of Serial Robotic Chains with 7 Axes

Redundant serial robot kinematic chains with seven axes are an extension of classical 6-axis ones. The structural synthesis of these structures is useful to provide a working basis, including for the promotion of new structures with 7 axes, besides some already existing and applied structures. This paper summarizes kinematic chain structures using a combinatorial method by listing all possible variants of the structures with 7 axes, obtained by adding a rotational or translational coupling, in a parallel or perpendicular position, against the guiding structure with 6 axes consisting of two distinct modules： positioning module （3 axes） and orientation module （3 axes）. Representation of proper workspaces can help the designer in choosing the structure with maximum functionality for a given application.

Control strategy for energy recovery system in hybrid forklift

After analyzing the working condition of the conventional diesel forklift,an energy recovery system in hybrid forklift is considered and its simulation model is built.Then,the control strategy for the proposed energy recovery system is discussed,which is validated and evaluated by simulation.The simulation results show that the proposed control strategy can achieve balance of the power and keep the state of charge(SOC) of ultra capacitor in a reasonable range,and the fuel consumption can be reduced by about 20.8% compared with the conventional diesel forklift.Finally,the feasibility of the simulation results is experimentally verified based on the lifting energy recovery system.

Strategically supported cooperation in dynamic games with coalition structures

The problem of strategic stability of long-range cooperative agreements in dynamic games with coalition structures is investigated. Based on imputation distribution procedures, a general theoretical framework of the differential game with a coalition structure is proposed. A few assumptions about the deviation instant for a coalition are made concerning the behavior of a group of many individuals in certain dynamic environments.From these, the time-consistent cooperative agreement can be strategically supported by ε-Nash or strong ε-Nash equilibria. While in games in the extensive form with perfect information, it is somewhat surprising that without the assumptions of deviation instant for a coalition, Nash or strong Nash equilibria can be constructed.

Tuning the molecular size of site-specific interferon-polymer conjugate for optimized antitumor efficacy

The covalent attachment of protein-resistant polymers to therapeutic proteins is a widely used method for extending their in vivo half-lives; however, the effect of molecular weight of polymer on the in vitro and in vivo functions of protein-polymer conjugates has not been well elucidated. Herein we report the effect of molecular weight of poly（oligo（ethylene glycol） methyl ether methacrylate） （POEGMA） on the in vitro and in vivo properties of C-termi- nal interferon-alpha （IFN）-POEGMA conjugates. Increasing the molecular weight of POEGMA decreased the in vitro activity of IFN-ct but increased its thermal stability and in vivo pharmacokinetics. Intriguingly, the in vivo antitumor efficacy of IFN-a was increased by increasing the POEGMA molecular weight from ca. 20 to 60 kDa, but was not further increased by increasing the molecular weight of POEGMA from ca. 60 to 100 kDa due to the neutralization of the improved pharmacokinetics and the reduced in vitro activity. This finding offers a new viewpoint on the molecular size rationale for designing next-generation protein-polymer conjugates, which may benefit patients by reducing admin- istration frequency and adverse reactions, and improving therapeutic efficacy.