Activation reduction following an eccentric contraction impairs torque steadiness in the isometric steady-state

Background:The isometric steady-state following active lengthening is associated with greater torque production and lower activation,as measured by electromyographic activity(EMG),in comparison with a purely isometric contraction(ISO)at the same joint angle.This phenomenon is termed residual force enhancement(RFE).While there has been a great deal of research investigating the basic mechanisms of RFE,little work has been performed to understand the everyday relevance of RFE.The purpose of this study was to investigate whether neuromuscular control strategies differ between ISO and RFE by measuring torque steadiness of the human ankle plantar flexors.Methods:Following ISO maximal voluntary contractions in 12 males(25±4 years),an active lengthening contraction was performed at 15°/s over a 30°ankle excursion,ending at the same joint angle as ISO(5°dorsiflexion;RFE).Surface EMG of the tibialis anterior and soleus muscles was recorded during all tasks.Torque steadiness was determined as the standard deviation(SD)and coefficient of variation(CV)of the torque trace in the ISO and RFE condition during activation-matching(20%and 60%integrated EMG)and torque-matching(20%and 60%maximal voluntary contraction)experiments.Two-tailed,paired t tests were used,within subjects,to determine the presence of RFE/activation reduction(AR)and whether there was a difference in torque steadiness between ISO and RFE conditions.Results:During the maximal and submaximal conditions,there was 5%-9%RFE with a 9%-11%AR(p<0.05),respectively,with no difference in antagonist coactivation between RFE and ISO(p>0.05).There were no differences in SD and CV of the torque trace for the 20%and60%activation-matching or the 60%and maximal torque-matching trials in either the RFE or ISO condition(p>0.05).During the 20%torquematching trial,there were～37%higher values for SD and CV in the RFE as compared with the ISO condition(p<0.05).A significant moderate-to-strong negative relationship was identified between the reduction in torque steadiness following active lengthening and the accompanying AR(p<0.05).Conclusion:It appears that while the RFE-associated AR provides some improved neuromuscular economy,this comes at the cost of increased torque fluctuations in the isometric steady-state following active lengthening during submaximal contractions.

POSITIVE CLASSICAL SOLUTIONS OF DIRICHLET PROBLEM FOR THE STEADY RELATIVISTIC HEAT EQUATION

In this paper,for a bounded C2 domain,we prove the existence and uniqueness of positive classical solutions to the Dirichlet problem for the steady relativistic heat equation with a class of restricted positive C2 boundary data.We have a non-existence result,which is the justification for taking into account the restricted boundary data.There is a smooth positive boundary datum that precludes the existence of the positive classical solution.

A Fixed-Point Fast Sweeping WENO Method with Inverse Lax-Wendroff Boundary Treatment for Steady State of Hyperbolic Conservation Laws

Fixed-point fast sweeping WENO methods are a class of efficient high-order numerical methods to solve steady-state solutions of hyperbolic partial differential equations(PDEs).The Gauss-Seidel iterations and alternating sweeping strategy are used to cover characteristics of hyperbolic PDEs in each sweeping order to achieve fast convergence rate to steady-state solutions.A nice property of fixed-point fast sweeping WENO methods which distinguishes them from other fast sweeping methods is that they are explicit and do not require inverse operation of nonlinear local systems.Hence,they are easy to be applied to a general hyperbolic system.To deal with the difficulties associated with numerical boundary treatment when high-order finite difference methods on a Cartesian mesh are used to solve hyperbolic PDEs on complex domains,inverse Lax-Wendroff(ILW)procedures were developed as a very effective approach in the literature.In this paper,we combine a fifthorder fixed-point fast sweeping WENO method with an ILW procedure to solve steadystate solution of hyperbolic conservation laws on complex computing regions.Numerical experiments are performed to test the method in solving various problems including the cases with the physical boundary not aligned with the grids.Numerical results show highorder accuracy and good performance of the method.Furthermore,the method is compared with the popular third-order total variation diminishing Runge-Kutta(TVD-RK3)time-marching method for steady-state computations.Numerical examples show that for most of examples,the fixed-point fast sweeping method saves more than half CPU time costs than TVD-RK3 to converge to steady-state solutions.

Fourier neural operator with boundary conditions for efficient prediction of steady airfoil flows

An efficient data-driven approach for predicting steady airfoil flows is proposed based on the Fourier neural operator(FNO),which is a new framework of neural networks.Theoretical reasons and experimental results are provided to support the necessity and effectiveness of the improvements made to the FNO,which involve using an additional branch neural operator to approximate the contribution of boundary conditions to steady solutions.The proposed approach runs several orders of magnitude faster than the traditional numerical methods.The predictions for flows around airfoils and ellipses demonstrate the superior accuracy and impressive speed of this novel approach.Furthermore,the property of zero-shot super-resolution enables the proposed approach to overcome the limitations of predicting airfoil flows with Cartesian grids,thereby improving the accuracy in the near-wall region.There is no doubt that the unprecedented speed and accuracy in forecasting steady airfoil flows have massive benefits for airfoil design and optimization.

A Fourth-Order Unstructured NURBS-Enhanced Finite Volume WENO Scheme for Steady Euler Equations in Curved Geometries

In Li and Ren(Int.J.Numer.Methods Fluids 70:742–763,2012),a high-order k-exact WENO finite volume scheme based on secondary reconstructions was proposed to solve the two-dimensional time-dependent Euler equations in a polygonal domain,in which the high-order numerical accuracy and the oscillations-free property can be achieved.In this paper,the method is extended to solve steady state problems imposed in a curved physical domain.The numerical framework consists of a Newton type finite volume method to linearize the nonlinear governing equations,and a geometrical multigrid method to solve the derived linear system.To achieve high-order non-oscillatory numerical solutions,the classical k-exact reconstruction with k=3 and the efficient secondary reconstructions are used to perform the WENO reconstruction for the conservative variables.The non-uniform rational B-splines(NURBS)curve is used to provide an exact or a high-order representation of the curved wall boundary.Furthermore,an enlarged reconstruction patch is constructed for every element of mesh to significantly improve the convergence to steady state.A variety of numerical examples are presented to show the effectiveness and robustness of the proposed method.

基于贝叶斯优化支持向量回归的流线型箱梁颤振气动外形优化方法

为解决风洞试验耗时费力和计算流体动力学(CFD)计算量大的问题,提出了一套新型流线型箱梁断面颤振性能气动外形优化方法.以风嘴参数为设计变量,利用CFD获取断面三分力系数,以准定常理论估算的颤振临界风速为优化目标.根据贝叶斯优化支持向量回归构建代理模型,利用混合加点法更新模型,通过寻优算法确定最优断面.以虎门大桥为例,得到桥梁在可行域内颤振性能最佳的断面方案.结果表明,风嘴升高,颤振临界风速先增后减,相对高度为0.6时整体性能较优,相对高度为0.7时可获得最优断面.底板宽增加,颤振性能显著降低,下斜腹板倾角为14°~16°时颤振性能最优.断面优化后桥梁颤振临界风速相比原始断面提升约31%.

基于压力衰减法的低渗透储层高温敏感性评价实验

低渗透油气藏在钻完井过程中易受到损害且难以解除,而利用传统的稳态驱替法评价低渗透储层损害存在适用性差及实验效率低等技术局限。为此,基于压力脉冲衰减法基本原理,分析了上游压力衰减规律及其与岩心渗透率的关系,以岩心损害前后压力脉冲衰减时间为评价指标,建立了适用于低渗透储层损害评价的实验设备与方法,并利用渤海湾盆地渤中凹陷深部低渗透砂岩岩心,开展了室温和150℃高温条件下的敏感性实验。研究结果表明:(1)当实验条件一定时,压力衰减时间仅与岩心的渗透率有关,压力脉冲衰减法可在无需计算渗透率的情况下对低渗透岩心的损害程度进行评价;(2)实验设备组成简单且操作便捷,避免了复杂的渗透率计算及其带来的误差,实验所需时间远低于常规的稳态法且可重复性良好,在低渗透气藏、特低渗透及超低渗透油藏具有很好的适用性;(3)高温环境明显加剧了储层的敏感性损害,深部高温储层损害特征及技术对策研究需要充分考虑高温的影响。结论认为,该认识解决了传统低渗透储层敏感性评价方法适用性差的难题,为高温低渗透储层保护技术对策研究提供了实验方法支撑和理论依据。

High-Intensity Interval Training v/s Steady-State Cardio in Rehabilitation of Neurological Patients

Neuropathy is nerve damage that can cause chronic neuropathic pain, which is challenging to cure and has a significant financial burden. Exercise therapies, including High-Intensity Interval Training (HIIT) and steady-state cardio, are being explored as potential treatments for neuropathic pain. This systematic review compares the effectiveness of HIIT and steady-state cardio for improving function in neurological patients. This article provides an overview of the systematic review conducted on the effects of exercise on neuropathic patients, with a focus on high-intensity interval training (HIIT) and steady-state cardio. The authors conducted a comprehensive search of various databases, identified relevant studies based on predetermined inclusion criteria, and used the EPPI automation application to process the data. The final selection of studies was based on validity and relevance, with redundant articles removed. The article reviews four studies that compare high-intensity interval training (HIIT) to moderate-intensity continuous training (MICT) on various health outcomes. The studies found that HIIT can improve aerobic fitness, cerebral blood flow, and brain function in stroke patients;lower diastolic blood pressure more than MICT and improve insulin sensitivity and skeletal muscle mitochondrial content in obese individuals, potentially helping with the prevention and management of type 2 diabetes. In people with multiple sclerosis, acute exercise can decrease the plasma neurofilament light chain while increasing the flow of the kynurenine pathway. The available clinical and preclinical data suggest that further study on high-intensity interval training (HIIT) and its potential to alleviate neuropathic pain is justified. Randomized controlled trials are needed to investigate the type, intensity, frequency, and duration of exercise, which could lead to consensus and specific HIIT-based advice for patients with neuropathies.

石英光纤近红外波段γ辐照效应实验研究

为提高某光学干涉测量系统的耐辐射能力,开展耐辐射光纤选型实验。以剂量率为0.5 Gy·s^(-1)的稳态γ射线和剂量率为5.0×10^(9) Gy·s^(-1)、脉冲宽度约20 ns的瞬态强γ射线为辐照源,获得掺锗、掺氟耐辐射单模光纤和常规G.652光纤在工作波长1550 nm、注入光功率40 mW工况下的辐射感生损耗,结果表明,实验获得的在线辐射感生损耗数据真实可靠;在稳态γ射线作用下,掺锗和掺氟耐辐射光纤的性能差异不大,辐射感生损耗小于17 dB·km^(-1),随着辐射时间的增加,辐射损耗呈现饱和,耐辐射光纤的性能均优于常规单模G.652通信光纤;在瞬态强γ射线作用下,两个不同型号掺氟光纤的性能最优,辐射感生损耗峰值分别为471.5 dB·km^(-1)和608.6 dB·km^(-1),恢复通信时长约μs量级。掺锗光纤的瞬态辐照性能最差,辐射感生损耗峰值为2691.3 dB·km^(-1),在μs时间尺度维持感生损耗饱和状态。

复杂边界条件下半球壳受迫振动响应分析

基于半解析法求解得到中厚半球壳的稳态振动与瞬态振动响应。基于一阶剪切变形理论推导球壳结构能量表达式,引入Jacobi多项式和傅里叶级数表示半球壳结构的轴向和径向位移,利用Ritz法得到半球壳的稳态振动响应,与有限元法结果对比验证了本文方法的有可行性。在此基础上,对半球壳在不同边界条件、截顶角和壳体厚度下稳态振动与瞬态振动特性规律进行了分析总结。

喷雾热解法加热壁温对铈锆固溶体生产过程的影响

【目的】为了探究喷雾热解过程中加热壁温对铈锆固溶体生产过程的影响,分析热解炉内的流量场和浓度场的变化情况,实现对热解炉的设计优化。【方法】采用数值模拟的方法,建立喷雾热解炉的物理模型,分别探讨加热壁温对铈锆固溶体在热解炉的不同阶段及热解炉中水蒸气分布和HCl分布的影响。【结果】当热解温度为850℃时,液滴的反应主要分2个阶段,在炉膛高度为0~0.05 m处,为加热蒸发阶段,在炉膛高度为0.05~0.6 m处,为稳态热解阶段。当炉壁温度为550~650℃时,在炉膛高度为0.9 m处温度变化放缓,喷雾处于稳定热解阶段;而壁温在750~850℃时,在炉膛高度为0.6 m处温度变化放缓;当壁温为850℃时,在炉膛高度为0.1~0.6 m处的温度曲线斜率最大,液滴达到稳定蒸发阶段的时间缩短,水分蒸发变快,热解时间变短。【结论】炉壁加热区的温度越高,HCl生成的速度越快,速度的最大值越小,在炉膛高度为0.4 m处速度变化最大,达到1.6 m/s左右;并且整体HCl生成的量随温度的升高而增大,平均速度变化随着热空气温度的升高而减小。

改进高斯过程的客车侧风工况下气动造型优化研究

高速客车的行驶安全性受侧风影响较大,为改善高速客车的气动特性和行驶稳定性,提出了一种改进的高斯过程回归模型对客车进行气动造型优化。该模型中,使用一种自动核构造算法,根据数据特征自动构造核函数,采用基于万有引力加速机理的自适应遗传算法对超参数进行优化,克服了传统近似模型精度低的问题。结果表明:改进高斯过程回归模型的预测值均位于95%置信区间,精度较高,实际应用中能够减少仿真和实验的次数,具有较好的工程实用价值。基于协同优化的思想对客车气动造型进行优化,客车的气动升力系数降低了22.56%,侧向力系数降低了18.53%,气动阻力系数降低了4.51%。

京津冀产业结构演进的碳减排灵敏度分析

以产业结构优化助推京津冀稳增长与碳达峰目标协同并进为研究目的,运用岭回归探究京津冀产业结构演进的碳减排灵敏度并筛选调控路径,预测减排潜力,验证协同减排效应。结果表明:(1)提升第一产业比例及第二、三产业劳均产出有助于北京、天津提前碳达峰;提升第二产业比例及劳均产出有助于河北提前碳达峰。(2)北京、河北调控后的减排潜力显著提升,说明两地可协调推进增长和减排,天津则难以协调。2030年后,京津冀调控后的减排潜力在50%以上,说明降低碳强度主要依托于产业结构演进。(3)随着京津冀产业结构高度协同演进,产业协同趋势显著,能源消费碳排放量呈倒“U”型趋势,优化京津冀产业结构高度可为区域协同减排赋能增效。

基于笼屉结构的机载高能激光系统光学中舱温度适应性研究

相较于车载、舰载设备,机载设备受体积及工作环境的限制,发展较为缓慢。针对机载设备的轻小型化要求,系统采用“光路堆叠”思想,提出笼屉式分层结构,实现了系统体积的要求。因光学中舱中包含精跟踪及主激光支路,温度变化时各支路间的光轴一致性难以保证,导致跟踪目标发生偏移,主激光支路无法对目标进行精确打击,严重影响系统的工作。为解决上述问题,对光学中舱进行有限元仿真分析,研究光学中舱在20±5℃情况下各镜片的变形。对镜片变形中影响光轴偏折的刚体位移进行提取计算,计算出单个镜片的偏转角度。根据反射棱镜安装误差理论对各支路间的光轴偏移量进行计算,分析精跟踪支路与主激光支路光轴一致性偏差。经过仿真分析,系统精跟踪支路与主激光支路光轴方位偏差为109.634μrad,俯仰偏差为132.952μrad。在实验室中进行25℃温度实验,结果表明,系统精跟踪支路与主激光支路光轴方位偏差为104.019μrad,俯仰偏差为125.009μrad,与仿真结果误差分别为5.40%、6.35%,验证了仿真结果的合理性。

浅谈安培环路定理的使用

通过应用安培环路定理求解了有限长载流直导线的磁感应强度,说明了“有限长度”的数学条件和物理背景.从麦克斯韦方程的积分形式和微分形式,讨论了安培环路定理的使用场景,阐明了非对称电流密度分布情况下求解稳恒磁场的基本思想——边界条件确定磁场,并拓展至应用高斯定理求解非对称电荷密度分布静电场问题.

多种听力学检测方法在未引出听性脑干反应患儿诊断中的价值

目的探讨多种听力学检测方法在听性脑干反应(ABR)最大输出未引出患儿的听力学诊断中的应用价值。方法回顾性分析69例(138耳)ABR最大强度未引出患儿的临床资料,年龄42天到5岁,平均1岁6个月,鼓室导抗图均为A型或正向单峰,声反射均未引出,影像学检查内耳无畸形。69例患儿均进行ABR、耳蜗微音电位(CM)、畸变产物耳声发射(DPOAE)和听性稳态反应(ASSR)测试。结果69例138耳中,8例16耳(11.59%)记录到CM,其中10耳(7.25%)记录到DPOAE,0.5、1、2、4 kHz ASSR反应阈值分别为83.2±13.1、82.9±13.0、75.3±12.4、63.1±9.1 dB nHL,结合其他检查结果诊断为听神经病。余61例(122耳)CM和DPOAE均未引出,0.5、1、2、4 kHz的ASSR引出率分别为82.3%、81.9%、76.9%、60.2%,其中20耳ASSR各频率均未引出,102耳至少一个频率引出,0.5、1、2、4 kHz ASSR反应阈分别为93.2±6.1、99.8±7.0、105.4±5.4、108.2±9.8 dB nHL,诊断为极重度感音神经性聋。结论对于ABR最大输出强度未引出的患儿,CM和/或DPOAE引出且ASSR各频率反应阈低于感音神经性聋患儿,有助于听神经病的诊断;CM和DPOAE均未引出有助于极重度感音神经性聋的诊断,ASSR测试有助于评估其残余听力。

稳态渗流下非饱和土涵洞竖向土压力的迭代解与简化

为描述稳态渗流下不同类别非饱和土涵洞的竖向土压力变化,应用圆弧小主应力轨迹法和Mohr应力圆获得考虑土拱效应的滑移面土压力系数,继而基于非饱和土的有效应力强度公式与吸应力理论,由水平薄层单元的竖向力平衡分别建立稳态渗流下上埋式/沟埋式非饱和土涵洞竖向土压力的迭代解,给出应用步骤并开展对比验证与方法拓展,最后结合吸应力沿深度分布规律提出涵洞竖向土压力的简化实用公式。研究结果表明:涵洞竖向土压力迭代解能合理反映土体类别、水分蒸发、降雨入渗和土拱效应的综合影响,并得到文献现场实测和理论公式数据的正确性验证以及对非饱和土涵洞的适用性;涵洞竖向土压力实用公式可显式表达且精度良好,方便估算不同稳态渗流下涵洞主要荷载;砂土涵洞可忽略非饱和特性影响而按饱和土计算竖向土压力,粉土和黏土涵洞可简化吸应力沿深度为线性分布;上埋式涵洞土拱负效应使得竖向土压力增大,而沟埋式涵洞土拱正效应使得竖向土压力减小。

高速平板边界层中定常条带的前缘感受性

来流湍流度较高时,自由流涡波可在边界层内激发流向条带结构,并引起边界层的旁路(bypass)转捩。本文采用调和线性化Navier-Stokes方程(harmonic linearized Navier-Stokes,HLNS)方法模拟平板边界层条带对自由流涡波的前缘感受性,并通过直接数值模拟验证了HLNS方法的可靠性。针对马赫数4.8的高速平板边界层,分析了零频涡波激发定常条带的前缘感受性过程及定常条带的演化规律。研究结果表明,边界层外的自由流涡扰动对边界层条带的发展存在持续的激励作用;对于固定展向波数的自由流涡波,法向波数为0时激发的条带幅值最大;自由流涡波的法向波数在小于临界角度时仅影响条带的幅值,而不影响条带扰动的形函数剖面。随着当地雷诺数的增加,条带的幅值演化和形函数剖面呈现出很好的相似性;当地无量纲展向波数β=0.18时,归一化幅值最大。

混合现实场景下结合SSVEP与眼动追踪的脑控机械臂系统

针对混合现实场景下脑控机械臂系统交互性差、指令集小的问题,设计了一种结合稳态视觉诱发电位(SSVEP)和眼动追踪技术的混合现实脑控机械臂系统。该系统通过眼动追踪技术实现目标区域的初选,而SSVEP信号则被用于在初选区域内识别最终的目标指令。在不增加刺激类别数量的前提下扩大了指令集,并根据受试者的视线停留区域实现异步控制。离线实验结果表明,在使用相同刺激类别数量的情况下,增加视觉刺激目标数量不会对分类准确率产生显著影响。通过在线实验验证了系统的适用性,相较于使用单一SSVEP范式的机械臂控制系统,所提出的系统具有更好的交互性和更大的指令集。

不同稳态工况对同步调相机单相短路后暂态温升的影响

同步调相机可在系统故障时为特高压直流换流站提供暂态无功支持,以保持系统电压稳定,防止直流换相失败,但调相机的高无功输出也会导致其温升增加,运行能力受限。系统故障前同步调相机的初始工况是影响其暂态温升和运行能力的一个重要因素,为研究系统低电压时调相机暂态温升与初始工况之间的关系,该文将调相机的电磁场、温度场与电网模型耦合,计算调相机不同稳态工况下的定转子损耗和温度分布;以线路单相短路故障引起的系统低电压为例,研究调相机初始工况对暂态温升的影响。在考虑各结构件最大容许温度的条件下,揭示调相机单相短路持续时间随初始工况的变化规律。研究结果为提升调相机在系统低电压下的暂态运行能力提供技术支持。