基于ABAQUS的显式动力学分析方法研究

显式动力学(The Explicit Dynamic)是针对隐式求解器的一个补充,其分析方法对于求解广泛、各类非线性结构力学问题是一个非常有效的工具,显式方法中的单个增量步取决于模型的最高固有频率,与持续时间、载荷类型无关。ABAQUS/Explicit主要用于碰撞、接触以及失效分析。探讨了ABAQUS显式动力学的基本理论、求解的问题,对显示动力学分析方法中的求解算法、稳定时间极限和能量平衡问题进行研究,给出了显示动力学分析的一般性分析方法。通过案例验证了该方法的可行性,应用该方法可有效解决实际工业生产中的碰撞问题、复杂的接触问题以及复杂的后屈曲问题,可为显式动力学分析方法应用于工程实践奠定理论与方法基础。     

Limit Cycles in a Class of Hybrid Dynamical Systems

This paper deals with qualitative analysis of the so-called switched fluid networks. Such networks are used to model communication, computer, and flexible manufacturing systems. We prove that for any deterministic network from a specific class, there exists a finite number of limit cycles attracting all the trajectories of the system. Furthermore, we determine this number. Date received: March 11, 2000. Date revised: January 19, 2001.     

Rapid degradation of the mycotoxin patulin in man quantified by stable isotope dilution assays

The absorption and degradation of the mycotoxin patulin in man was quantified by using a recently developed stable isotope dilution assay. Application of this currently most sensitive method revealed a patulin content less than 200 ng l -1 in the blood serum of five consumers of apple juice. Likewise, no patulin was found in the serum of a volunteer, whose blood was drawn shortly after consumption of a juice containing a maximum tolerable amount of patulin. In further in vitro experiments, the degradation of patulin by reacting it with whole blood was investigated. After addition of 100 μg patulin to 9 ml blood, only 6.1% of the mycotoxin was detected after 2 min. It was concluded, therefore, that even high naturally occurring concentrations of patulin in foods are quickly degraded before reaching other tissues than the gastrointestinal tract.     

Finding nondegenerate Hopf bifurcation points for four-dimensional two-parametric systems

We establish a numerically feasible algorithm to find a simplicial approximation A to a certain part of the boundary of the set of stable (or Hurwitz) polynomials of degree 4. Moreover, we have that . Using this, we build an algorithm to find a piecewise-linear approximation to the intersection curve of a given surface contained in ⁴ with . We have also devised an efficient computer program to perform all these operations. The main motivation is to find the curve of nondegenerate bifurcation points in parameter space for a given 2-parametric Hopf bifurcation problem of dimension 4.     

Limited evidence of zebra mussel (Dreissena polymorpha) consumption by freshwater drum (Aplodinotus grunniens) in Lake Winnipeg

Freshwater drum (Aplodinotus grunniens) may be a predator of the invasive zebra mussel (Dreissena polymorpha), which established in Lake Winnipeg in 2013. In this study, the diets, trophic position, and growth of 51 freshwater drum collected in 2019 (six years post-zebra mussel invasion) were compared to 64 freshwater drum sampled in 2000. Benthic insect larvae were the dominant food items in both years. Although mollusks occur in high densities in Lake Winnipeg, they were only consumed by a few freshwater drum in either sample year. Zebra mussels were not a frequent prey item in 2019 as they were only consumed by four of the sampled freshwater drum. Stable isotope analysis of white muscle tissue yielded similar δ¹³C and δ¹⁵N values in both years and were consistent with a benthic, insectivorous diet. Length-at-age data derived from otoliths revealed that the 2019 population had at least an equal growth rate to the 2000 population. Weight-at-length data suggested that fish condition was greater in 2019 than in 2000, which coincided with increased benthic macroinvertebrate density in Lake Winnipeg. Based on these findings, Lake Winnipeg freshwater drum continue to feed predominantly on insect larvae and not zebra mussels.     

多孔β-TCP陶瓷药物载体的制备与体外释药速率的研究

本文用注浆成形的方法制备了以β-TCP为主晶相的多孔药物载体，体外测定了利福平的释药速率。实验结果表明，利福平在模拟体液中能够达到稳定的释放，可以作为骨结核手术后的辅助治疗。多孔β-TCP药物载体有望成为一种理想的药物缓释载体。     

复杂断块油田特高含水期实现持续稳产的做法

胜利油田临盘采油厂目前开发动用临盘、商河、临南三个油田,区域构造位于渤海湾盆地济阳坳陷惠民凹陷中央隆起带。“九五”末期由于油田相继进入特高含水期,剩余油分布复杂、断块破碎、油水井套损严重、注采完善程度低,造成油田产量连续三年下降。针对严峻的开发形势,进入“十五”以后,通过深化油藏构造、储层、剩余油潜力的研究,强化注采井网的完善。提高了水驱控制程度,增强油田稳产基础,提高采收率。全厂连续三年原油年产量连续稳定在163×104t,取得较好的开发效果和经济效益。     

无线移动网络节点发包概率的演化博弈模型

针对大规模无线移动网络中节点对信道资源的群体性随机博弈问题,在载波侦听多路访问/冲突避免(CSMA/CA)的机制下,建立一种节点发包概率的演化博弈模型。考虑节点成功发送数据包的收益、监听、退避和冲突等成本因素,给出并证明该模型的演化稳定策略(ESS),推导节点发包概率演化的复制动态方程。数值仿真结果表明,该模型能提供更强的ESS,保证在多个移动节点干扰时演化稳定点的鲁棒性。     

Subsoil <Superscript>15</Superscript>N-N<Subscript>2</Subscript>O Concentrations in a Sandy Soil Profile After Application of <Superscript>15</Superscript>N-fertilizer

Studies on emissions of nitrous oxide (N₂O) from agricultural soils mostly focus on fluxes between the soil and the atmosphere or are limited to the atmosphere in the topsoil. However, in soils with shallow water tables, significant N₂O formation may occur closer to the groundwater. The aims of this study were (i) to determine the importance of subsoil N₂O formation in a sandy soil; and (ii) to obtain a quantitative insight in the contribution of subsoil N₂O to the overall losses of N₂O to the environment. We applied ¹⁵N labeled fertilizer at a rate of 5.22 kg ¹⁵N ha⁻¹; 50% as Ca(NO₃)₂ and 50% as NH₄Cl, on a mesic typic Haplaquod seeded with potatoes (Solanum tuberosum L.), and traced soil N₂O concentrations and fluxes over a one-year period. Throughout the year, total N₂O and the amount of ¹⁵N recovered in soil N₂O were highest in the subsoil, with a maximum concentration at 48 cm depth in mid-February of 19900 μl m⁻³ and 24 μg ¹⁵N m⁻³, respectively. The maximum concentration coincided with the highest water-filled pore space of 71%. The cumulative flux of N₂O was 446 g N₂O-N ha⁻¹, the recovery of ¹⁵N in this flux was 0.06%. During the summer, maximum fluxes followed high soil N₂O concentrations. During winter, no such relation was found. We concluded that the formation of N₂O was the highest in the subsoil, largely controlled by water-filled pore space rather than NO₃⁻ concentration or temperature. Although high subsoil N₂O concentrations did not lead to high surface fluxes of N₂O in the winter, artificial draining may lead to high indirect N₂O emissions through supersaturated drainage water.     

旋转导向钻井稳定平台的广义预测控制研究

研究了旋转导向钻井稳定平台的摩擦问题,建立了带摩擦的稳定平台广义被控对象的数学模型。针对稳定平台摩擦的不确定性,为了提高稳定平台系统的控制精度和稳定性,提出了阶梯式广义预测控制算法,既保留了传统广义预测控制的优点,又避免了在线求解逆矩阵,同时使算法的安全性得到了提高。将改进算法应用于稳定平台的工具面角控制,并进行了仿真。仿真结果表明,上述算法具有较高的控制精度和良好的动态性能,并且对时变的摩擦干扰具有较强的抗干扰能力,对系统参数摄动具有良好的鲁棒性。