Superconvergence of Direct Discontinuous Galerkin Methods:Eigen-structure Analysis Based on Fourier Approach

This paper investigates superconvergence properties of the direct discontinuous Galerkin(DDG)method with interface corrections and the symmetric DDG method for diffusion equations.We apply the Fourier analysis technique to symbolically compute eigenvalues and eigenvectors of the amplification matrices for both DDG methods with different coefficient settings in the numerical fluxes.Based on the eigen-structure analysis,we carry out error estimates of the DDG solutions,which can be decomposed into three parts:(i)dissipation errors of the physically relevant eigenvalue,which grow linearly with the time and are of order 2k for P^(k)(k=2,3)approximations;(ii)projection error from a special projection of the exact solution,which is decreasing over the time and is related to the eigenvector corresponding to the physically relevant eigenvalue;(iii)dissipative errors of non-physically relevant eigenvalues,which decay exponentially with respect to the spatial mesh sizeΔx.We observe that the errors are sensitive to the choice of the numerical flux coefficient for even degree P^(2)approximations,but are not for odd degree P^(3)approximations.Numerical experiments are provided to verify the theoretical results.

Underdetermined direction of arrival estimation with nonuniform linear motion sampling based on a small unmanned aerial vehicle platform

Uniform linear array(ULA)radars are widely used in the collision-avoidance radar systems of small unmanned aerial vehicles(UAVs).In practice,a ULA's multi-target direction of arrival(DOA)estimation performance suffers from significant performance degradation owing to the limited number of physical elements.To improve the underdetermined DOA estimation performance of a ULA radar mounted on a small UAV platform,we propose a nonuniform linear motion sampling underdetermined DOA estimation method.Using the motion of the UAV platform,the echo signal is sampled at different positions.Then,according to the concept of difference co-array,a virtual ULA with multiple array elements and a large aperture is synthesized to increase the degrees of freedom(DOFs).Through position analysis of the original and motion arrays,we propose a nonuniform linear motion sampling method based on ULA for determining the optimal DOFs.Under the condition of no increase in the aperture of the physical array,the proposed method obtains a high DOF with fewer sampling runs and greatly improves the underdetermined DOA estimation performance of ULA.The results of numerical simulations conducted herein verify the superior performance of the proposed method.

Direction finding of bistatic MIMO radar in strong impulse noise

For bistatic multiple-input multiple-output(MIMO)radar,this paper presents a robust and direction finding method in strong impulse noise environment.By means of a new lower order covariance,the method is effective in suppressing impulse noise and achieving superior direction finding performance using the maximum likelihood(ML)estimation method.A quantum equilibrium optimizer algorithm(QEOA)is devised to resolve the corresponding objective function for efficient and accurate direc-tion finding.The results of simulation reveal the capability of the presented method in success rate and root mean square error over existing direction-finding methods in different application situations,e.g.,locating coherent signal sources with very few snapshots in strong impulse noise.Other than that,the Cramér-Rao bound(CRB)under impulse noise environment has been drawn to test the capability of the presented method.

Evaluation of bronchoscopic direct vision glottis anesthesia method in bronchoscopy

BACKGROUND Fibrobronchoscopy is a common adjunct tool that requires anesthesia and is widely used in the diagnosis and treatment of various respiratory diseases.However,current anesthesia methods,such as spray,nebulized inhalation,and cricothyroid membrane puncture,have their own advantages and disadvantages.Recently,studies have shown that bronchoscopic direct-view glottis anesthesia is a simple and inexpensive method that shortens the examination time and provides excellent anesthetic results.AIM To evaluate the effectiveness of bronchoscopic direct vision glottis anesthesia for bronchoscopy.METHODS The study included 100 patients who underwent bronchoscopy during thoracic surgery.A random number table method was used to divide the patients into control and observation groups(50 patients each).The control and observation groups were anesthetized using the nebulized inhalation and bronchoscopic direct vision glottis method,respectively.Hemodynamic indices[systolic blood pressure(SBP),diastolic blood pressure(DBP),heart rate(HR),and oxygen saturation(SpO_(2))before(T1),5 min after anesthesia(T2),and at the end of the operation(T3)]serum stress hormone indices[norepinephrine(NE),epinephrine(E),adrenocorticotropic hormone(ACTH),and cortisol(Cor)before and after treatment]were compared between the 2 groups.Adverse effects were also RESULTS At T2 and T3,SBP,DBP,and HR were lower in the observation group than the control group,whereas SpO_(2) was higher than the control group[(119.05±8.01)mmHg vs(127.05±7.83)mmHg,(119.35±6.66)mmHg vs(128.39±6.56)mmHg,(84.68±6.04)mmHg vs(92.42±5.57)mmHg,(84.53±4.97)mmHg compared to(92.57±6.02)mmHg,(74.25±5.18)beats/min compared to(88.32±5.72)beats/min,(74.38±5.31)beats/min compared to(88.42±5.69)beats/min,(97.36±2.21)%vs(94.35±2.16)%,(97.42±2.36)%vs(94.38±2.69%],with statistically significant differences(all P<0.05).After treatment,NE,E,ACTH,and Cor were significantly higher in both groups than before treatment,but were lower in the observation group than in the control group[(68.25±8.87)ng/mL vs(93.35±14.00)ng/mL,(53.59±5.89)ng/mL vs(82.32±10.70)ng/mL,(14.32±1.58)pg/mL vs(20.35±3.05)pg/mL,(227.35±25.01)nmol/L vs(322.28±45.12)nmol/L],with statistically significant differences(all P<0.05).The incidence of adverse reactions was higher in the control group than in the observation group[12.00%(12/50)vs 6.00%(3/50)](P<0.05).CONCLUSION The use of bronchoscopic direct vision glottis anesthesia method for bronchoscopy patients is beneficial for stabilizing hemodynamic indices during bronchoscopy and reducing the level of patient stress,with good safety and practicality.

Limitations of Lightning Rods in Preventing Direct Lightning Strikes

Since ancient times,lightning disasters have undoubtedly been an unstoppable threat to humanity.During thunderstorms,lightning often damages objects on the ground,such as buildings and structures.Since Franklin invented the lightning rod in 1752,lightning rods have been used worldwide to prevent direct lightning strikes in various fields such as high-voltage power transmission lines,outdoor chemical sites,highways,land and sea wind farms,and forest lightning fire protection.It has been proven that lightning accidents still occur frequently in places where lightning rods are installed and the protective angle method is used.In order to further study the protective effect of lightning rods and identify the shortcomings of lightning rod protection,negative lightning strikes are taken as the research object,to analyze the limitations of lightning rods in preventing direct lightning strikes from the working principle of lightning rods.

Tensile and tear-type fracture toughness of gypsum material:Direct and indirect testing methods

In this context,four specimens,i.e.(i)circumferentially notched cylindrical torsion(CNCT),(ii)circum-ferentially notched cylindrical direct tension(CNCDT),(iii)edge notch disc bend(ENDB)and(iv)three-point bend beam(3PBB),were utilized to measure the modesⅠandⅢfracture toughness values of gypsum.While the CNCT specimen provides pure modeⅢloading in a direct manner,this pure mode condition is indirectly produced by the ENDB specimen.The ENDB specimen provided lower KⅢc and a non-coplanar(i.e.twisted)fracture surface compared with the CNCT specimen,which showed a planar modeⅢfracture surface.The ENDB specimen is also employed for conducting pure modeⅠ(with different crack depths)and mixed modeⅠ/Ⅲtests.KIc value was independent of the notch depth,and it was consistent with the RILEM and ASTM standard methods.But the modeⅢfracture results were highly sensitive to the notch depth.While the fracture resistance against modeⅢwas significantly lower than that of modeⅠ,the greater work of fracture under modeⅢwas noticeable.

Direct measurement of nonlocal quantum states without approximation

Efficient acquiring information from a quantum state is important for research in fundamental quantum physics and quantum information applications. Instead of using standard quantum state tomography method with reconstruction algorithm, weak values were proposed to directly measure density matrix elements of quantum state. Recently, similar to the concept of weak value, modular values were introduced to extend the direct measurement scheme to nonlocal quantum wavefunction. However, this method still involves approximations, which leads to inherent low precision. Here, we propose a new scheme which enables direct measurement for ideal value of the nonlocal density matrix element without taking approximations. Our scheme allows more accurate characterization of nonlocal quantum states, and therefore has greater advantages in practical measurement scenarios.

FIXED/PREASSIGNED-TIME SYNCHRONIZATION OF QUATERNION-VALUED NEURAL NETWORKS INVOLVING DELAYS AND DISCONTINUOUS ACTIVATIONS: A DIRECT APPROACH

The fixed-time synchronization and preassigned-time synchronization are investigated for a class of quaternion-valued neural networks with time-varying delays and discontinuous activation functions. Unlike previous efforts that employed separation analysis and the real-valued control design, based on the quaternion-valued signum function and several related properties, a direct analytical method is proposed here and the quaternion-valued controllers are designed in order to discuss the fixed-time synchronization for the relevant quaternion-valued neural networks. In addition, the preassigned-time synchronization is investigated based on a quaternion-valued control design, where the synchronization time is preassigned and the control gains are finite. Compared with existing results, the direct method without separation developed in this article is beneficial in terms of simplifying theoretical analysis, and the proposed quaternion-valued control schemes are simpler and more effective than the traditional design, which adds four real-valued controllers. Finally, two numerical examples are given in order to support the theoretical results.

A novel method for geometric quality assurance of rock joint replicas in direct shear testing-Part 2:Validation and mechanical replicability

Each rock joint is unique by nature which means that utilization of replicas in direct shear tests is required in experimental parameter studies.However,a method to acquire knowledge about the ability of the replicas to imitate the shear mechanical behavior of the rock joint and their dispersion in direct shear testing is lacking.In this study,a novel method is presented for geometric quality assurance of replicas.The aim is to facilitate generation of high-quality direct shear testing data as a prerequisite for reliable subsequent analyses of the results.In Part 1 of this study,two quality assurance parameters,smf and V_(Hp100),are derived and their usefulness for evaluation of geometric deviations,i.e.geometric reproducibility,is shown.In Part 2,the parameters are validated by showing a correlation between the parameters and the shear mechanical behavior,which qualifies the parameters for usage in the quality assurance method.Unique results from direct shear tests presenting comparisons between replicas and the rock joint show that replicas fulfilling proposed threshold values of σ_(mf)<0.06 mm and
|V_(Hp100)|
<0.2 mm have a narrow dispersion and imitate the shear mechanical behavior of the rock joint in all aspects apart from having a slightly lower peak shear strength.The wear in these replicas,which have similar morphology as the rock joint,is in the same areas as in the rock joint.The wear is slightly larger in the rock joint and therefore the discrepancy in peak shear strength derives from differences in material properties,possibly from differences in toughness.It is shown by application of the suggested method that the quality assured replicas manufactured following the process employed in this study phenomenologically capture the shear strength characteristics,which makes them useful in parameter studies.

Greedy Randomized Gauss-Seidel Method with Oblique Direction

For the linear least squares problem with coefficient matrix columns being highly correlated, we develop a greedy randomized Gauss-Seidel method with oblique direction. Then the corresponding convergence result is deduced. Numerical examples demonstrate that our proposed method is superior to the greedy randomized Gauss-Seidel method and the randomized Gauss-Seidel method with oblique direction.

火山灰质材料的火山灰活性检测方法综述

本文将火山灰质材料的火山灰活性检测方法分为直接法和间接法两大类。其中,直接法包括石灰吸收值法,火山灰反应程度评定法和酸、碱溶出度法;而间接法包括物理性能法,水化反应放热量法和物理、化学特征参数法。为正确指导火山灰活性检测方法的应用,本文详细介绍并比较了各检测方法的原理和特点。笔者认为,直接法可直接测定出火山灰质材料与Ca(OH)2反应的程度,但其操作和分析过程相对复杂;间接法可通过测定火山灰质材料对体系物化性能的影响或材料自身的物理、化学特征参数来评价其火山灰活性。本文从材料科学的角度厘清了各检测方法的适用对象,认为应根据不同的火山灰质材料的特性选择与其相适应的火山灰活性检测方法。

移动机器人视觉里程计技术研究综述

随着移动机器人技术不断发展,里程计技术已经成为移动机器人实现环境感知的关键技术,其发展水平对提高机器人的自主化和智能化具有重要意义。首先,系统阐述了同步定位与地图构建(Simultaneous localization and mapping,SLAM)中激光SLAM和视觉SLAM的发展近况,阐述了经典SLAM框架及其数学描述,简要介绍了3类常见相机的相机模型及其视觉里程计的数学描述。其次,分别对传统视觉里程计和深度学习里程计的研究进展进行系统阐述。对比分析了近10年来各类里程计算法的优势与不足。另外,对比分析了7种常用数据集的性能。最后,从精度、鲁棒性、数据集、多模态等方面总结了里程计技术面临的问题,从提高算法实时性、鲁棒性等方面展望了视觉里程计的发展趋势为:更加智能化、小型化新型传感器的发展;与无监督学习融合;语义表达技术的提高;集群机器人协同技术的发展。

基于物理信息神经网络的金属表面吸收率测量方法

漫反射金属吸收率的准确测量十分重要且比较困难.量热法可靠性较高,但是参数反演较为困难.为此,建立了一种物理信息神经网络方法.该方法通过神经网络拟合温度上升段曲线,进而获得吸收率.为了验证该方法,开展了数值仿真和实验研究.数值仿真结果表明,该方法适用于吸收率测量,抗干扰能力强,反演精度高,在0.05—0.2的吸收率范围内,最大误差为0.00092.实验以喷砂镀金铝板为被测对象,受表面粗糙度、镀金工艺等影响,这些样品的吸收率处于2%—10%之间,测量重复精度优于1%.基于物理信息神经网络的吸收率测量方法有望成为一种有力的金属表面吸收率测量方法.

基于三维空间面积划分的轨迹相似性度量算法

针对大部分轨迹相似性度量算法无法区分方向相反轨迹的问题,提出了一种基于三维空间面积划分的三维三角分割(3TD)算法。首先,按照3TD算法的时间转换规则将轨迹集的绝对时间序列转变为相对时间序列;然后,在由经度、纬度以及时间三要素构成的三维空间坐标系中,通过划分规则将轨迹间面积分割成若干互不重叠的三角形,累加三角形面积并计算轨迹相似度;最后,在从船舶自动识别系统(AIS)收集的随机采样轨迹数据集上,与最长公共子序列(LCSS)算法和三角分割(TD)算法等进行了对比实验。实验结果表明:3TD算法对实验数据集中异向轨迹识别精确度达到100%;同时该算法面对海量数据集以及轨迹点部分缺失的数据集时,也能维持准确的度量结果以及较高的运算效率,能更好地适应异向轨迹相似度量工作。

智慧供热系统数据运行核查方法研究

高质量数据是智慧供热系统数据分析的前提和分析结论可靠性的保障,计量器具的良好工作状态是获得高质量数据的基础。本文讨论了计量器具的检定、校准及运行核查的区别,研究了智慧供热系统计量器具在线运行核查方法。研究表明:流量计根据其实际安装工作条件,采用安装条件修正系数可解决直管段长度不够带来的测量误差问题;采用基准表法对使用的流量计进行技术性能核查,可正确判别单台流量计的工作状态;示踪法是解决大口径贸易结算表数据质量问题的有效方法。本研究可为及时发现工作异常的计量器具、确保测量数据的准确性及可靠性提供理论指导及技术支撑。

区域水平衡及失衡程度度量方法

区域水平衡量化及诊断是水网工程建设优化和水资源均衡调控的基础,对提升水安全保障能力、支撑经济社会稳定发展、实现人水和谐具有重要意义。本文从空间、时间、结构、过程、总量五个维度解构了区域人水系统的四大平衡,即反映水收入项和支出项定量关系的水收支平衡、体现经济社会供水量与需水量匹配关系的经济社会供需水平衡、结合经济社会-生态系统发展与用水定量关系的经济社会与生态用水平衡、表征人水系统发展状态的人水关系和谐平衡,并提出相应的水平衡度量方法。多角度解析了区域水平衡的失衡状态,提出四大平衡的失衡程度度量方法及区域水平衡的失衡程度综合度量方法。以沁河流域为实例应用和检验了上述方法,结果表明:提出的度量方法具有科学性和适用性,能够应用于区域水平衡研究实践;2019年沁河流域水平衡的失衡度为0.327,处于蓄水量减少、水资源短缺、生态端亏水、水系统受损的中度失衡状态,后续应注重人类涉水行为的管控。研究成果可为区域水平衡评估与调控提供理论支撑,服务国家或区域水平衡策略制定和水网工程规划。

现代产业链韧性评价及提升路径

国际变局加剧产业链发展风险,产业链韧性是建设现代化产业体系和提升产业链安全的重要基础。理解产业链韧性的内涵及影响因素是建立产业链韧性理论分析的基础,构建包括产业链基础能力、产业链抵御能力、产业链链条控制力和产业链创新能力在内的多维评价指标体系,通过熵值法对产业链韧性水平进行测度评价,并与美国、日本、印度等国家进行国际比较。研究发现,支撑中国产业链韧性的主要因素是包括基础设施、劳动力供给在内的产业链基础能力。与发达国家相比,产业链抵御能力和产业链创新能力对产业链韧性提升的贡献相对较低;近年来中国产业链韧性水平总体呈现上升趋势,但是增速放缓。因此,应该加快关键核心技术攻关的产业链创新能力,提升产业链治理能力,积极开展高水平对外开放和推动产业链数字化转型,成为提升中国产业链韧性的主要政策主张。

基于压差法的波向测量方法初步研究

为解决波向测量误差大的问题,本文首次提出了一种基于压差法的波向测量新技术,根据海浪的运动变化规律,在这里巧妙地引进了压差技术,通过对放置在水下一个圆环上多个压力传感器同圆心点上的压差变化进行分析可以得出,圆环上不同方向上的压力传感器同圆心点上的压力传感器之间的差值及相位是随波浪方向变化而变化的,对圆环上不同方向上的压力传感器同圆心点上的压力传感器之间的差值进行分析,找出变化规律与波向的关系,以此得出真实的波向分布。本文通过波浪水池实验验证了该方法的可行性,并通过对实验数据的解析初步得出了压差变化规律与波向的变换关系。

超深勘察钻孔ASR法地应力测试技术应用

宝灵山隧道是某铁路先开段的重难点控制性工程,其中宝灵山DZ-06勘察钻孔深2118.00 m,是该段深度最大的控制性勘察钻孔。在钻孔的2072.53、2084.27 m深度选取合适岩心,采用ASR法(非弹性应变恢复法)开展了地应力测试,并与该钻孔采用水压致裂法获取的地应力结果进行对比,同时验证了ASR法对于估测超深钻孔的三维地应力大小和方向的实用价值。结果表明:在钻孔2072.53~2084.27 m深度范围,ASR法2个测点获取的最大主应力、中间主应力、最小主应力平均值分别为59.70、54.03、30.74 MPa,最大主应力近水平,方向近SN向,说明该区域以水平构造应力为主;ASR法的最大主应力测试结果均值与水压致裂法测试结果回归值一致性很好,最小主应力测试结果均值与水压致裂法测试结果回归值的一致性处于合理范围,两种方法的水平主应力方向测试结果基本一致。

极近距离煤层开采无煤柱自成巷控制方法研究

极近距离煤层传统长壁开采,受上层遗留煤柱和采空区垮落等因素的影响,下煤层开采过程中应力环境复杂、矿压显现剧烈,易诱发巷道围岩大变形。为解决上述问题,提出了极近距离条件下巷道定向切顶–约束高强支护无煤柱自成巷控制方法。通过顶板定向预裂切顶,主动改变顶板悬臂结构,切断采空区向巷道顶板的应力传递。充分利用矿山压力和岩体碎胀特性,取消煤柱留设,结合高强支护加强巷道顶板整体性,共同实现切顶自成巷。建立了极近距离煤层开采覆岩结构模型,计算了下煤层切顶自成巷巷旁支护阻力。以典型极近距离煤层为工程背景,开展了不同开采方法的数值试验对比研究,结果表明,提出的自成巷控制方法使巷道围岩应力降低59.8%,巷道顶板变形减少70.8%,并明确了极近距离煤层开采无煤柱自成巷控制机理。在此基础上,开展了典型极近距离煤层工程设计及现场应用研究,结果表明该方法有效降低了矿压显现程度,保证了自成巷的安全稳定控制。