关键词： 机械扰动   富营养化   水质指标   溶解氧   正交试验  

摘要： 湖泊、水库以及流动不好的河流等水体可以通过提高溶解氧来改善其富营养状况，机械微弱扰动增氧是其中一种有效的方法，但其溶解氧动力学研究不够深入，工程化装置也少有开发。\n 本文选取3种结构相似，但倾角、盘面比和R处弦长等结构参数不同的机械扰动桨叶，安装在3个容积、初始状态相同的试验水池，用1个空白池作参照，在相同的工况下，研究水质指标和动力学情况:\n (1)分析水体富营养化成因和改善方法，确定试验方法，以水温、溶氧量、酸碱度、化学需氧量等水质指标，评价不同机械微弱扰动对水质的影响。\n (2)应用FLUENT软件，采用多重参考系法(MRF)对机械扰动作用下的水池流场进行数值模拟，并用流速仪进行校验，对比、分析水体运动同水质指标的关系。\n (3)对影响扰动桨性能的结构参数进行正交试验，并对影响显著的结构参数进行了优化，开发出一种以太阳能为动力的机械扰动装置。\n 通过以上研究，得到:\n (1)藻类生长旺盛期（2012年7月至9月），对溶氧影响较大，经过47天后，试验水池溶解氧达到相对稳定，三个扰动池稳定后的表层溶解氧平均值分别为6.4mg/L、7.1mg/L、9.6mg/L，底层溶解氧平均值分别为6.2mg/L、6.9mg/L、9.5mg/L;空白水池的表层和底层溶解氧值为5.6mg/L和5.3mg/L。\n 藻类衰亡期，对溶氧影响较小时段（2012年12月至2013年1月），三个扰动池和空白池的表层溶解氧平均值分别为6.0mg/L、6.7mg/L、7.6mg/L、3.7mg/L，底层溶解氧平均值分别为5.9mg/L、6.6mg/L、7.5mg/L、3.6mg/L，倾角、盘面比和R处弦长较大的扰动桨对溶氧影响最大，水质改善效果最好。\n (2)空白对比池的化学需氧量最大，水质最差。而在三个扰动池中，3号扰动池的化学需氧量最小，1号扰动池的化学需氧量最大，说明倾角、盘面比和R处弦长均大的扰动桨对水池水质的改善效果最好。\n (3)扰动桨产生轴向流，可以使水体形成循环。微弱扰动情况下的溶解氧推动力来源于水池表层富氧水与底层贫氧水的相互交换，交换速度越快，扩散作用越强，溶解氧水平越高，化学需氧量水平越低，水质改善越明显。\n (4)正交试验结果表明，盘面比对导流筒出口截面平均流速有显著影响，倾斜角、R处弦长这两个因素对导流筒出口截面平均流速无显著影响，对有显著影响的盘面比进行回归分析，得到优化后的盘面比参数。

关键词： 柔性   机械手   动力学   逆动力学  

摘要： 针对柔性机械手动力学,重点从离散方法、建立数学模型、解决逆动力学问题三方面综述了国内外的研究情况,同时对离散的多种方法、建立模型的多种方法和逆动力学求解的多种方法各种方法进行了对比分析,并指出其优缺点。最后探讨了这一领域的发展方向和需要解决的问题。

关键词： 大学生物理竞赛   动力学   填空题  

摘要： 每年一届的全国部分地区(原名北京市)大学生物理竞赛到目前已举办过28届,关于竞赛问题的讨论鲜有报道,并且多停留在表面。本文对2011年该竞赛中的一道动力学和机械振动的综合性填空题给出了详细的解题过程,并给出了一些建议。

关键词： 穿孔器件   挤压膜阻尼   分子动力学仿真   微谐振器   微结构封装  

摘要： 气体阻尼是微谐振器振动微结构能量损耗的重要机制。微谐振器中振动微结构的灵敏度和分辨率均与气体阻尼有关。为了提高微谐振器（如共振传感器、振动陀螺仪等）的灵敏度和分辨率，通常将振动微结构封装在低压环境下并在振动微结构表面制造穿孔以减小气体阻尼。\n 当微谐振器的振动微结构平行于基底电极且振动方向垂直于基底平面时，振动微结构与基底平面形成的间隙中的气体薄膜就会受到周而复始的挤压，由此就产生挤压膜阻尼。挤压膜阻尼是气体阻尼的一种。在低压环境下，对于挤压膜阻尼的研究通常有两种途径:一是基于连续介质模型并结合使用有效黏度系数，二是利用分子动力学理论。目前，对于未穿孔器件挤压膜阻尼的研究已经相当完善，但是对于穿孔器件挤压膜阻尼的研究仍然有很多不足，尤其是使用分子动力学仿真方法研究穿孔微机械谐振器件的挤压膜阻尼仍然处于空白。\n 2004年，Hutcherson（2004 ***.141726-1733）提出一种分子动力学算法来研究微谐振器件的挤压膜阻尼，但是Hutcherson的分子动力学算法仅对未穿孔的器件有效。本文在Hutcherson研究工作的基础上针对穿孔微机械谐振器件的挤压膜阻尼提出一种新的分子动力学算法。该算法利用MATLAB语言编写的仿真程序搜集振动穿孔微结构与间隙中气体分子之间的能量交换以计算微谐振器的品质因数。同时又在有效黏度系数的基础上运用有限元仿真方法计算穿孔微机械谐振器的品质因数，并将分子动力学算法的计算结果与有限元仿真结果以及Kwok的实验结果相比较，以验证分子动力学算法的精确度。最后利用分子动力学算法和有限元仿真方法详细分析了克努森数、穿孔比以及振动频率和振幅对穿孔微机械谐振器件挤压膜阻尼的影响，并总结概括了分子动力学算法的局限性。

关键词： Poly(ester-ether-imide)   thermal degradation   kinetics   thermal stability   mechanical properties  

摘要： A novel poly(ester-ether-imide) (PEEI) based on N,N-bis(2-hydroxyethyl)-pyromellitimide unit was synthesized via a conventional two-stage procedure with 1,4-butanediol (BD), dimethyl terephthalate (DMT) and poly(tetramethylene glycol) (PTMG1000). The structures of imide dihydric alcohol and PEEI were confirmed by FT-IR and H-1-NMR spectra, respectively. The thermal properties and mechanical properties were investigated. The results show PEEI possesses good mechanical properties and excellent thermal stability with the 5% weight loss temperature of the PEEI at 367.3 degrees C, and melting temperature of hard segments (T-mh) at 209.7 degrees C. In addition, the kinetic parameters of thermal degradation of the PEEI were studied by thermogravimetric analysis (TGA) at different heating rates. The activation energy of the solid-state process was determined to be 174.83 and 175.83 kJ/mol using Kissinger and FlynnWallOzawa methods, respectively. The degradation mechanism model of PEEI was determined bythe Coats-Redfern method. Compared with the values obtained from the Kissinger and FlynnWallOzawa methods, the actual reaction mechanism of the novel PEEI is a F-1 type (Random nucleation with one nucleus on the individual particle nucleation) and growth model with integral g(a)=ln(1a)).

关键词： 弹簧刚度   曳引电梯   动力学分析   曳引钢丝绳   机械   曳引轮绳槽   隔振装置   电梯运行  

摘要： 电梯的绳头弹簧是一个安装在曳引钢丝绳与轿厢之间的隔振装置，其主要作用是：消耗曳引机、钢丝绳振动产生的能量；当曳引轮绳槽磨损造成节径差较大或各根钢丝绳长度伸长有差异时，仍能保持各根钢丝绳能承受一定的力，有力的均衡作用。因此配置合适刚度的绳头弹簧对电梯运行的安全性和舒适性非常重要。

关键词： mechanical properties   high carbon steel   wires   conventional and hydrodynamic dies   redundant strain  

摘要： In the paper the influence of the hydrodynamic die on mechanical properties has been assessed. The drawing process of phi 5,5 mm wires to the final wire of phi 2,5 mm was conducted in 7 passes, in industrial conditions, by means of a modern Koch multi-die drawing machine. The drawing speed in the last passes was 8,2 m/s. On the basis of numerical analyses wire drawing process, the redundant strain of wires has been determined. In the case of the wires drawn with hydrodynamic dies the increase of plasticity properties have been noted. It has been shown that the increase of strength properties in wires drawn with conventional die is related to the occurrence in their bigger redundant strain.

关键词： Axially moving beams   Post-buckling analysis   Divergence   Nonlinear dynamics   Stability  

摘要： The thermo-mechanical nonlinear dynamics of a buckled axially moving beam is numerically investigated, with special consideration to the case with a three-to-one internal resonance between the first two modes. The equation of motion of the system traveling at a constant axial speed is obtained using Hamilton's principle. A closed form solution is developed for the post-buckling configuration for the system with an axial speed beyond the first instability. The equation of motion over the buckled state is obtained for the forced system. The equation is reduced into a set of nonlinear ordinary differential equations via the Galerkin method. This set is solved using the pseudo-arclength continuation technique to examine the frequency response curves and direct-time integration to construct bifurcation diagrams of Poincar, maps. The vibration characteristics of the system at points of interest in the parameter space are presented in the form of time histories, phase-plane portraits, and Poincar, sections.

关键词： metals   nanocontacts   nanowires   surface   electronic structure   electronic density functional theory   first-principle molecular dynamics   computer simulation  

摘要： The atomic and electronic structures of AgAuAg, AuAgAg, and AuCoCo mixed nanocontacts are investigated by the method of first-principle molecular dynamics. The characteristic interatomic distances in contacts depending on their component composition are determined. The interrelationship between the structural and electronic properties of mixed nanocontacts is shown. The formation of stable bonds between the atoms of various elements in the contact chain, which makes it possible to explain the cause of stabilization and an increase in the contact strength at large interatomic distances is found. It is shown that the addition of Co atoms into pure-gold nanocontacts increases their strength (increases the breaking force of the contact), while the addition of Ag atoms leads to an increase in the range of interatomic distances at which the existence of the nanocontact is possible.

关键词： BEDSORES   ANTIPSYCHOTIC drugs   ANALYSIS of variance   CORRELATION (Statistics)   FALLS (Accidents)   FRACTURES   LIFTING & carrying (Human mechanics)   MEDICAL care -- Evaluation   MULTIVARIATE analysis   NURSE administrators   NURSING care facilities   QUESTIONNAIRES   FINANCING of research   RESTRAINT of patients   STATISTICS   DATA analysis   SECONDARY analysis   TRANSPORTATION of patients   DATA analysis software   DESCRIPTIVE statistics   RISK factors   THERAPEUTIC use  

摘要： Objective: To determine associations between long-term care powered mechanical lift (PML) availability and mobility-related resident outcomes. Methods: Long-term care directors of nursing (N = 271) nationwide gave facility information on the PML availability and the lifting policy to which we linked data on mobility-related resident outcomes from the Centers for Medicare & Medicaid Services Minimum Data Set Quality Indicators. Results: Four of six Centers for Medicare & Medicaid Services derived resident indicators improved with the PML number but were maximal for the sit stand lift use. In facilities with the fewest lifts, 16% of residents had pressure ulcers and 4% were bedfast. In facilities with the maximum number of lifts, only 10% had pressure ulcers (P = 0.000) and 2% were bedfast (P = 0.002). Although falls were more frequent with more lift use, this risk was blunted by a comprehensive safe lift program. Conclusion: The PML availability is associated with benefits to resident outcomes, and accompanying risks are mitigated by safe lift policies.