Hermite WENO-based limiters for high order discontinuous Galerkin method on unstructured grids

A novel class of weighted essentially nonoscillatory （WENO） schemes based on Hermite polynomi- als, termed as HWENO schemes, is developed and applied as limiters for high order discontinuous Galerkin （DG） method on triangular grids. The developed HWENO methodology utilizes high-order derivative information to keep WENO re- construction stencils in the von Neumann neighborhood. A simple and efficient technique is also proposed to enhance the smoothness of the existing stencils, making higher-order scheme stable and simplifying the reconstruction process at the same time. The resulting HWENO-based limiters are as compact as the underlying DG schemes and therefore easy to implement. Numerical results for a wide range of flow conditions demonstrate that for DG schemes of up to fourth order of accuracy, the designed HWENO limiters can simul- taneously obtain uniform high order accuracy and sharp, es- sentially non-oscillatory shock transition.

An empirical behavioral order‑driven model with price limit rules

We propose an empirical behavioral order-driven(EBOD)model with price limit rules,which consists of an order placement process and an order cancellation process.All the ingredients of the model are determined based on the empirical microscopic regularities in the order flows of stocks traded on the Shenzhen Stock Exchange.The model can reproduce the main stylized facts in real markets.Computational experiments unveil that asymmetric setting of price limits will cause the stock price to diverge exponentially when the up price limit is higher than the down price limit and to vanish vice versa.We also find that asymmetric price limits have little influence on the correlation structure of the return series and the volatility series,but cause remarkable changes in the average returns and the tail exponents of returns.Our EBOD model provides a suitable computational experiment platform for academics,market participants,and policy makers.

ENTIRE SOLUTIONS OF HIGHER ORDER DIFFERENTIAL EQUATIONS WITH ENTIRE COEFFICIENTS HAVING THE SAME ORDER

In this paper,we consider entire solutions of higher order homogeneous differential equations with the entire coefficients having the same order,and prove that the entire solutions are of infinite lower order.The properties on the radial distribution,the limit direction of the Julia set and the existence of a Baker wandering domain of the entire solutions are also discussed.

Target reliability index for serviceability limit state of single piles

The objective is to develop an approach for the determination of the target reliability index for serviceability limit state(SLS) of single piles. This contributes to conducting the SLS reliability-based design(RBD) of piles. Based on a two-parameter,hyperbolic curve-fitting equation describing the load-settlement relation of piles, the SLS model factor is defined. Then, taking into account the uncertainties of load-settlement model, load and bearing capacity of piles, the formula for computing the SLS reliability index(βsls) is obtained using the mean value first order second moment(MVFOSM) method. Meanwhile, the limit state function for conducting the SLS reliability analysis by the Monte Carlo simulation(MCS) method is established. These two methods are finally applied to determine the SLS target reliability index. Herein, the limiting tolerable settlement(slt) is treated as a random variable. For illustration, four load test databases from South Africa are compiled again to conduct reliability analysis and present the recommended target reliability indices. The results indicate that the MVFOSM method overestimates βsls compared to that computed by the MCS method. Besides, both factor of safety(FS) and slt are key factors influencing βsls, so the combination of FS and βsls is welcome to be used for the SLS reliability analysis of piles when slt is determined. For smaller slt, pile types and soils conditions have significant influence on the SLS target reliability indices; for larger slt, slt is the major factor having influence on the SLS target reliability indices. This proves that slt is the most key parameter for the determination of the SLS target reliability index.

Limit Cycle Containing Nine Critical Points in its Interior for a Class of Cubic Systems

Discuss a class of real planar cubic systems with a critical point O (0,0) of nine orders and obtain the conditions for its limit cycle surrounding the origin, and prove that when small pertubations of coefficients are made, the critical point O (0,0) of nine orders is split into nine real simple critical points and the limit cycle surrounding the origin becomes the limit cycle containing nine critical points in its interior.

A NOTE ON q-DIFFERENCE OPERATOR AND RELATED LIMIT DIRECTION

The growth of entire functions under the q-difference operators is studied inthis paper, and then some properties of Julia set of entire functions under the higher orderq-difference operators are obtained.

High Order Finite Difference WENO Methods for Shallow Water Equations on Curvilinear Meshes

A high order finite difference numerical scheme is developed for the shallow water equations on curvilinear meshes based on an alternative flux formulation of the weighted essentially non-oscillatory(WENO)scheme.The exact C-property is investigated,and comparison with the standard finite difference WENO scheme is made.Theoretical derivation and numerical results show that the proposed finite difference WENO scheme can maintain the exact C-property on both stationarily and dynamically generalized coordinate systems.The Harten-Lax-van Leer type flux is developed on general curvilinear meshes in two dimensions and verified on a number of benchmark problems,indicating smaller errors compared with the Lax-Friedrichs solver.In addition,we propose a positivity-preserving limiter on stationary meshes such that the scheme can preserve the non-negativity of the water height without loss of mass conservation.

Banach Limits Revisited

Order unit normed linear spaces are a special type of regularly ordered normed linear spaces and therefore the first section is a short collection of the fundamental results on this type of normed linear spaces. The connection between order unit normed linear spaces and base normed linear spaces within the category of regularly ordered normed linear spaces is described in Section 2, and Section 3 at last, contains the results on Banach limits in an arbitrary order unit normed linear space. It is shown that the original results on Banach limits are valid for a greater range.

Design of 15 Gb/s inductorless limiting amplifier with RSSI and LOS indication in 65nm CMOS

A limiting amplifier IC implemented in 65nm CMOS technology and intended for high-speed op- tical fiber communications is described in this paper. The inductorless limiting amplifier incorporates 5-stage 8 dB gain limiting cells with active feedback and negative Miller capacitance, a high speed output buffer with novel third order active feedback, and a high speed full-wave rectifier. The re- ceiver signal strength indictor （RSSI） can detect input signal power with 33dB dynamic range, and the limiting amplifier features a programmable loss of signal （LOS） indication with external resistor. The sensitivity of the limiting amplifier is 5.5mV at BER = 10^ -12 and the layout area is only 0.53 × 0.72 mm^2 because of no passive inductor. The total gain is over 41dB, and bandwidth exceeds 12GHz with 56mW power dissipation.

CONSTRUCTION OF THIRD-ORDER WNND SCHEMEAND ITS APPLICATION IN COMPLEX FLOW

According to the Liu's weighted idea, a space third-order WNND (weighted non-oscillatory, containing no free parameters, and dissipative scheme) scheme was constructed based on the stencils of second-order NND (non-oscillatory, containing no free parameters, and dissipative scheme) scheme. It was applied in solving linear-wave equation, 1D Euler equations and 3D Navier-Stokes equations. The numerical results indicate that the WNND scheme which does not increase interpolated point(compared to NND scheme) has more advantages in simulating discontinues and convergence than NND scheme. Appling WNND scheme to simulating the hypersonic flow around lift-body shows:With the AoA(angle of attack) increasing from 0° to 50°, the structure of limiting streamline of leeward surface changes from unseparating,open-separating to separating, which occurs from the combined-point (which consists of saddle and node points). The separating area of upper wing surface is increasing with the (AoA's) increasing. The topological structures of hypersonic flowfield based on the sectional flow patterns perpendicular to the body axis agree well with Zhang Hanxin's theory. Additionally, the unstable-structure phenomenon which is showed by two saddles connection along leeward symmetry line occurs at some sections when the AoA is bigger than 20°.

Six New Sets of the Non-Elementary Jef-Family-Functions that Are Giving Solutions to Some Second-Order Nonlinear Autonomous ODEs

In this paper, we define some new sets of non-elementary functions in a group of solutions x(t) that are sine and cosine to the upper limit of integration in a non-elementary integral that can be arbitrary. We are using Abel’s methods, described by Armitage and Eberlein. The key is to start with a non-elementary integral function, differentiating and inverting, and then define a set of three functions that belong together. Differentiating these functions twice gives second-order nonlinear ODEs that have the defined set of functions as solutions. We will study some of the second-order nonlinear ODEs, especially those that exhibit limit cycles. Using the methods described in this paper, it is possible to define many other sets of non-elementary functions that are giving solutions to some second-order nonlinear autonomous ODEs.

Describing failure in geomaterials using second-order work approach

Geomaterials are known to be non-associated materials. Granular soils therefore exhibit a variety of failure modes, with diffuse or localized kinematical patterns. In fact, the notion of failure itself can be confusing with regard to granular soils, because it is not associated with an obvious phenomenology. In this study, we built a proper framework, using the second-order work theory, to describe some failure modes in geomaterials based on energy conservation. The occurrence of failure is defined by an abrupt increase in kinetic energy. The increase in kinetic energy from an equilibrium state, under incremental loading, is shown to be equal to the difference between the external second-order work,involving the external loading parameters, and the internal second-order work, involving the constitutive properties of the material. When a stress limit state is reached, a certain stress component passes through a maximum value and then may decrease. Under such a condition, if a certain additional external loading is applied, the system fails, sharply increasing the strain rate. The internal stress is no longer able to balance the external stress, leading to a dynamic response of the specimen. As an illustration, the theoretical framework was applied to the well-known undrained triaxial test for loose soils. The influence of the loading control mode was clearly highlighted. It is shown that the plastic limit theory appears to be a particular case of this more general second-order work theory. When the plastic limit condition is met, the internal second-order work is nil. A class of incremental external loadings causes the kinetic energy to increase dramatically, leading to the sudden collapse of the specimen, as observed in laboratory.

极限下限分析的区域光滑径向点插值法

极限分析的高效数值计算方法在结构设计和安全评定中具有非常重要的作用.为了更加有效地求解极限分析问题,将区域光滑径向点插值法与二阶锥规划相结合,提出了理想弹塑性结构极限下限分析的一种新方法.将问题域离散为简单的三角形背景单元,每个单元进一步划分成若干个光滑域.为了将复杂的域积分转化为简单的边界积分,并且避免计算形函数的导数,采用广义梯度光滑技术对每个光滑域进行应变光滑处理.由于径向点插值法构造的形函数满足Kronecker delta性质,本质边界条件可以直接施加.依据下限定理,在满足以等效积分弱形式表达的自平衡应力场平衡条件的基础上,用二阶锥规划成功构建了极限分析下限法的计算模型,从而可方便地通过基于原始-对偶内点法的数学规划求解器MOSEK直接求解该问题.数值算例结果表明,本文所提方法有效地克服了维数障碍问题,具有较高的计算精度,并且计算结果对网格畸变十分不敏感.

限时促销中消费者冲动购买意愿的认知机制:基于时间压力和前瞻性情绪的实证研究

购物节频繁举办使得消费者对限时促销活动的感知下降,如何应对“造节”泛滥所导致的营销疲态、重新激发市场活力成为业界亟待解决的难题。随着更多情绪消费形式的涌现和消费者购物行为前置化成为趋势,前瞻性情绪正日益成为影响购买行为的重要因素。因此,探究限时促销期间消费者前瞻性情绪的演化过程具有重要现实意义。基于S-O-R分析框架,构建以时间压力为自变量、前瞻性情绪(预期后悔、预期惊喜)为中介变量、冲动购买意愿为因变量的中介模型,并分析产品类型的调节作用。通过两个实验研究发现,限时促销中时间压力对消费者冲动购买意愿具有显著正向影响;产品类型在时间压力和消费者冲动购买意愿之间发挥调节作用;前瞻性情绪在时间压力—产品类型对消费者冲动购买意愿的交互影响中起中介作用,即面对享乐品时,时间压力对消费者产生的前瞻性情绪具有显著正向影响,进而放大了冲动购买意愿的差异;而面对实用品时,时间压力对前瞻性情绪及冲动购买意愿的影响没有显著差异。本研究拓展了S-O-R理论在限时促销领域的应用,从产品类型层面确定了限时促销活动有效发挥作用的边界条件,深化了对前瞻性情绪驱动冲动购买的理解,并为商家优化限时营销策略提供实践指导。

基于Kriging模型与FORM的钢板组合梁桥结构优化设计

考虑材料参数的不确定性以及设计变量多重约束条件的影响,提出了基于可靠性分析的钢板组合梁桥结构优化设计方法。首先,利用拉丁超立方试验设计(Latin hypercube design,LHD)构建试验组合方案,并通过有限元分析获取试验设计组合下的最大挠度响应值。基于获取的训练样本,构建能够表征结构最大挠度值与随机输入之间映射关系的Kriging代理模型。基于建立的代理模型,以钢结构截面积最小化为目标函数,建立符合规范要求与可靠度约束的优化数学模型,并采用一阶可靠性方法(first order reliability method,FORM),实现设计变量优化。通过比较具有相同设计变量上限,但下限分别为初始值的80%和70%两种优化设计方案,评估了两者在相同阈值以及不同阈值下设计变量的优化结果。最后对方案二在阈值为17 mm下的优化结果进行极限状态验算。结果表明:两个优化设计方案在阈值为17 mm下的优化结果更具合理性,并且方案二在同一阈值下具有更高的优化程度。随着阈值增加,优化程度增加,且腹板高度在较大阈值下对结果影响更大,而翼缘宽度在较小阈值下影响更大。

基于实际触发角响应的连续换相失败抑制方法

针对逆变侧交流故障下高压直流(line commutated converter-high voltage direct current,LCC-HVDC)输电系统易引发连续换相失败问题,该文分阶段分析了连续换相失败的产生机理。明确了当产生触发角偏差后,直流电流调节效果与实际触发角不匹配是连续换相失败的重要诱因。同时不对称故障后,负序分量通过极控、阀控两级控制系统对实际触发角造成的影响,增加连续换相失败的风险。因此提出了一种基于实际触发角响应的连续换相失败抑制方法,通过实际触发角修正整流侧电流指令值。与此同时,该方法通过陷波器降低负序电流对极控层触发角指令值的影响,通过相序解耦控制器和换相电压相位补偿降低负序电压对阀控层触发角实际值的影响。该方法能实现动态、自适应的电流指令值调整,提升恢复过程中直流电流与实际触发角的匹配度,提升直流系统抵御连续换相失败能力。在CIGRE标准测试模型和实际工程模型中,验证了理论分析的正确性和优化方法的有效性。

附带STATCOM的HVDC系统改进参考电压控制法

在弱交流系统下对于附带有STATCOM的电网换相换流器高压直流输电(Line Commutated Converter based High Voltage Direct Current, LCC-HVDC)系统,存在着LCC逆变站与STATCOM之间耦合导致LCC-HVDC系统的稳定裕度下降问题,这会减弱LCC-HVDC抑制换相失败的能力。此外,HVDC控制环节之中的电压指令电流控制(voltage dependent current order limiter, VDCOL)环节的输出电流指令大幅剧烈波动还有几率会导致HVDC系统在首次换相失败之后发生后续换相失败。针对上述问题提出了一种“改进参考电压”的思想,对STATCOM和VDCOL的参考电压与输入电压分别进行修正。首先在STATCOM原本的参考电压经过一个“虚拟电抗”之后得到一个新的参考电压,通过这个改进参考电压弱化了STATCOM电压外环控制模块与LCC逆变站的耦合,减小了交流系统等效阻抗的大小,提升了系统对干扰的抵抗能力。然后对VDCOL的输入电压进行改进,新的改进输入电压改善了故障后VDCOL输出电流指令的大幅剧烈波动情况。最后通过三个层次的对照试验,验证了所提方法的有效性。

基于两阶段动态兴趣识别的购买行为预测模型

在线购买预测旨在预测用户的购买行为,为购物网站带来可观的商业价值。针对传统模型学习用户历史行为中隐含的兴趣偏好不准确的问题,提出基于两阶段动态兴趣识别的购买行为预测模型,以预测用户购买商品的概率。首先,模型的第一阶段构建用户-商品的点击频率图,并利用轻量图卷积网络(LightGCN)学习图的上下文特征作为用户的静态兴趣表征;其次,第二阶段采用带有注意力机制的双向门控递归单元(Bi-GRU)探索用户偏好的转化过程;最后,针对潜在的高维特征,建立一个融合动态兴趣和隐含特征的购买预测模型。在2个真实电子商务数据集上的实验结果表明,所提模型与图卷积网络(GCN)模型相比,准确率至少提升0.3个百分点,F1分数至少提升了2.05个百分点。

反事实思维视角下限时促销对旅游直播消费者即时购买意愿的影响机制研究

限时促销作为一种条件促销模式,已成为提升旅游直播营销效果的重要手段,但已有研究较少关注旅游直播领域的限时促销。为弥补现有研究不足,探究旅游直播中限时促销对消费者即时购买决策的影响机制,本文以目标导向行为理论为基础,从反事实思维视角,通过两项情景实验对此进行了剖析,研究发现:(1)旅游直播限时促销能够直接激发消费者的即时购买意愿,其中限时折扣形式比限时赠品效果更好;(2)当消费者具有较强的上行反事实思维时,旅游直播限时促销能够诱发消费者的预期作为后悔,从而降低即时购买意愿;(3)当消费者具有较强的下行反事实思维时,旅游直播限时促销能够诱发消费者的预期不作为后悔,从而提升即时购买意愿。研究结果揭示了旅游直播限时促销所具有的双面性,丰富了旅游直播营销的相关研究,可为旅游企业合理采取网络促销措施提供启示。

A LIMITED ORDER CAPACITY STOCHASTIC INVENTORY MODEL WITH A FIXED COST FOR ORDER: THE DISCOUNTED CASE

This paper considers a single-item, periodic-review inventory model with linear ordercosts, a convex function representing expected one-period costs, nonegative i.i.d. demandsand a fixed cost for order. Stockouts are backordered. All data are stationary Both finiteand infinite horizon problems are treated.