Drag on a sphere accelerating rectilinearly in an elastico-viscous fluid

The exact solution for the drag on a sphere moving in an arbitrary manner along a rectilinear path in an otherwise-still elastico-viscous fluid of infinite extent is presented. The Fourier transform technique is used to derive the solution. This technique is based on the fact that drag on an accelerating body can be obtained by integrating the drag on an oscillating body over all possible frequencies. The solution is also expressed in terms of infinite series which is suitable for numerical evaluation of the drag. The solution for the drag on a sphere suddenly brought to uniform motion is presented as an example of this study.     

Transformation of Reference Spheres by an Aberration Free and Infinitely Large Optical System in the Fresnel Approximation

Imaging of a complex distribution by a thin lens is studied and generalized by analysing the imaging process of a complex distribution defined on an off-axis object sphere in an optical system. First, imaging of an object in an elementary system is considered, and then the considerations for the system being a combination of the elementary systems are presented. The general rule of reference spheres transformation is introduced. It is shown that complex distributions given on an off-axis object sphere are fully reconstructed on an image sphere of the system with a change of scale only. The relations between the parameters of the object and image spheres are determined. Some examples of the applications of the transforming rule are given.     

Drag on a sphere accelerating rectilinearly in a maxwell fluid

The exact solution for the drag on a sphere moving in an arbitrary manner along a rectilinear path in an otherwise still Maxwell fluid of infinite extent is presented. The method of solution is that used by Landau and Lifshitz. This technique is based on the fact that drag on an accelerating body can be obtained by integrating the drag on an oscillating body over all possible frequencies. The solutions for the drag for some particular type of accelerating motions are also presented. Discussion on the limits of applicability of the solution is also presented.     

Resolution of aplanatic systems with various semiapertures, viewed from the two sides of the diffracting aperture

With the vector plane-wave spectrum and stationary phase method, a rigorous vector diffraction model of an aplanatic system when the polarized point source is at an arbitrary location on the optical axis is presented. The computer simulation is used to discuss in detail the effects of various angular semiapertures on the object and image sides on the resolution. Results show that angular semiapertures on the object and image sides have an obvious effect on the resolution and image fields, which indicates that the classical Wolf theory [Proc. R. Soc. London, Ser. A253, 358 (1959)] cannot be applied to the study of imaging properties of an aplanatic system when the point source is not located at infinity in the direction of the axis.     

A model for the spread and control of pandemic influenza in an isolated geographical region

In the event of an influenza pandemic, the most probable way in which the virus would be introduced to an isolated geographical area is by an infected traveller. We use a mathematical model, structured on the location at which infection occurs and based on published parameters for influenza, to describe an epidemic in a community of one million people. The model is then modified to reflect a variety of control strategies based on social distancing measures, targeted antiviral treatment and antiviral prophylaxis and home quarantine, and the effectiveness of the strategies is compared. The results suggest that the only single strategy that would be successful in preventing an epidemic (with R0=2.0) is targeted antiviral treatment and prophylaxis, and that closing schools combined with either closing work places or home quarantine would only prevent such an epidemic if these strategies were combined with a modest level of antiviral coverage.     

汽车排气消声器的降噪优化设计

以控制汽车加速噪声为背景，通过对某微型卡车排气消声器的测试分析结果，提出相应的改进措施。在利用数值模拟优化的基础上，完善改进方案。台架试验证明改进后的消声器插入损失增加7.1dB（A），而背压没有明显变化。整车加速噪声试验证明改进后的消声器可以使整车加速噪声降低2dB（A），降噪效果显著。     

Non-autonomous normal forms for Hamiltonian systems

A method for calculating normal forms for non-autonomous periodically perturbed Hamiltonian systems is developed. The solution for an autonomous Hamiltonian normal form is well known, and involves the solution of a homological equation on the vector space of homogeneous scalar polynomials. An algorithm is presented for generating an analogous non-autonomous homological equation using Lie transforms. Solution of this equation will generate a normal form for the non-autonomous Hamiltonian. Although this equation is defined on an infinite-dimensional space, it is shown that the problem can be reduced to an equivalent one on a finite-dimensional space. A solution can then be found in an analogous way to the solution for the autonomous problem. It is also shown that the normal form satisfies invariance properties. Finally, an example problem is presented to illustrate the solution technique.     

The sagnac effect in optically active media

The propagation of a plane, homogeneous and transverse electromagnetic wave through an optically active medium, at rest in an inertial frame or on a uniformly rotating disc, is studied here. This problem is associated with the well known Sagnac effect. The shift of fringe order one in an interferometer due to the rotation is calculated. The solution of the resulting eigenvalue problem is based on a perturbation technique in which only terms up to the first order in the rotation and the optical activity coefficient are retained.     

Multimodal brain tumor detection and classification using deep saliency map and improved dragonfly optimization algorithm

In the last decade, there has been a significant increase in medical cases involving brain tumors. Brain tumor is the tenth most common type of tumor, affecting millions of people. However, if it is detected early, the cure rate can increase. Computer vision researchers are working to develop sophisticated techniques for detecting and classifying brain tumors. MRI scans are primarily used for tumor analysis. We proposed an automated system for brain tumor detection and classification using a saliency map and deep learning feature optimization in this paper. The proposed framework was implemented in stages. In the initial phase of the proposed framework, a fusion-based contrast enhancement technique is proposed. In the following phase, a tumor segmentation technique based on saliency maps is proposed, which is then mapped on original images based on active contour. Following that, a pre-trained CNN model named EfficientNetB0 is fine-tuned and trained in two ways: on enhanced images and on tumor localization images. Deep transfer learning is used to train both models, and features are extracted from the average pooling layer. The deep learning features are then fused using an improved fusion approach known as Entropy Serial Fusion. The best features are chosen in the final step using an improved dragonfly optimization algorithm. Finally, the best features are classified using an extreme learning machine (ELM). The experimental process is conducted on three publically available datasets and achieved an improved accuracy of 95.14, 94.89, and 95.94%, respectively. The comparison with several neural nets shows the improvement of proposed framework.     

一种道路交通安全神经网络评价模型的构建

在综合分析国内外交通安全评价研究的基础上,针对中国道路交通安全现状,提出了基于一个城市行政分区的道路交通安全评价指标和评价模型,并针对我国城市道路交通安全的现状及存在问题,提出了采用基础数据、交通安全管理、公众安全评价3个方面共17项指标组成的面向城市道路交通安全可持续发展的评价指标集;构建了基于BP神经网络的评价模型;并结合算例详细分析了其计算方法。     

基于神经网络的组合预报模型及其应用

时间序列预报是神经网络的一个应用领域,多数研究集中在神经网络直接预报方面。本文从故障预报角度研究了神经网络组合预报模型,由神经网络给出常规预报方法的最佳组合。首先从函数逼近角度阐述这种模型的理论依据,在此基础上给出了模型的评价指标和神经网络的有效训练算法,最后给出在空间推进系统上的应用实例。     

标准和标准化概念的多学科观点(之五)--Brunsson和Busch的社会学观点

本文首先分别介绍Brunsson N和Busch L关于标准化的主要社会学观点,包括标准是某个人或机构为其他人或其他机构给出的建议或处方,标准是支撑社会运行的规则之一,标准与人的行为准则、法律之间的关系,标准的分类和主要特征等等。笔者对他们的观点进行了深入讨论,认为标准是规则以及标准是现实世界的处方的观点对认识标准的本质有重要意义,并提出创新和标准在人类社会发展过程中是一对不可分割的核心要素。     

Polarization distribution control of anisotropic electromagnetic Gaussian-Schell model beams on free propagation by exploiting correlation properties at the source plane

When propagating in free space, the transversal distribution of the degree of polarization of an anisotropic electromagnetic Gaussian-Schell model (AEGSM) beam will generally undergo a complex evolution process. We find that this transversal distribution of the degree of polarization of an AEGSM beam can be controlled by exploiting the partial correlation properties of the source. The main research of our paper falls into two parts. First, the concept of analogical propagation of the transversal distribution of the degree of polarization is proposed, and the condition for an AEGSM beam having an analogical propagation is obtained. When an AEGSM beam is on analogical propagation, the distribution of the degree of polarization on any cross section of the beam is always similar to that on the source plane, except that the size of the distribution pattern will expand continuously as the propagation distance increases. Second, the far-field transversal distribution of the degree of polarization is considered, and the condition for the far-field transversal polarization distribution of an AEGSM beam to be always of circularly symmetric shape, no matter how complicated it is on the source, is obtained. Our research is expected to find applications in areas that make use of the polarization properties of random electromagnetic beams.     

Scorch arisen prediction through elastomer flow in extrusion die

The thermal and kinetic behaviour of an elastomer flow inside an extrusion die is numerically investigated. The aim is to control scorch arisen and reduce the heating time in the mould by using viscous dissipation phenomena in order to improve the rubber compound curing efficiency. A three dimensional model, using the particle tracking technique, is developed in order to get thermal, velocity and kinetic fields through the flow. Three common geometries of an elastomer forming process are modeled: a straight runner, a bend zone and a bifurcation. This simulation is applied on the case of an EPDM (ethylene propylene diene monomer) flow. The thermal and rheological properties are experimentally characterized. The influence of viscous dissipation on the reaction progress of the melt is studied on several process conditions. Many criterions relevant for thermal and cure homogeneity are proposed in order to quantify the performance of geometry modifications.     

Partial disassembly sequencing considering acquired end-of-life product age distributions

Uncertainty management is a priority in remanufacturing operations due to uncertain end-of-life (EoL) product quality, quantity and return timing. Ignoring EoL product uncertainty can result in inefficient remanufacturing operations. In this work, an approach is developed that addresses the impact of EoL product quality uncertainty on partial disassembly sequences. Disassembly is performed on nearly all EoL products, yet it is vulnerable to uncertain EoL product quality, defined in this work as the remaining value of an EoL product compared to original equipment manufacturer standards. The developed approach converges to an optimal or near-optimal partial disassembly sequence provided that information regarding acquired EoL product age distributions is known and correlates to EoL product quality. A mathematical framework is introduced to evaluate disassembly sequences based on profit standard deviation and profit probability as well as the traditionally used expected profit. The approach is tested on an example case study to investigate the impact of uncertain quality on the optimal or near-optimal disassembly sequence, expected profit, profit standard deviation and profit probability.     

Transduction dependent optimization of electromechanical parameters for electrostatically actuated MEMS/NEMS resonators

This paper demonstrates an accurate model to predict the overall effective mass in micro- and nanomechanical resonators with non-uniform deformation along the transduction area. The model is verified experimentally through parameter extraction on various types of resonators with an error less than 3% well within the bounds dictated by manufacturing tolerances. Based on the model, an optimization of transduction electrode designs is proposed for micro- and nanomechanical resonators vibrating in the fabrication plane.     

Edge delamination in an orthotropic bimaterial consisting of a thin film and a substrate

This paper investigates edge delamination in an orthotropic layered structure composed of a thin film and a substrate under a temperature change. An edge interface crack is analyzed for two configurations in which it emerges from an interior or corner edge of the film. Special attention is paid to the effects of orthotropic material constants on delamination cracking. The necessary material parameters involved in the energy release rate and mode mixity for the interface crack are found based on a modified Stroh formalism. The explicit dependence of the energy release rate and mode mixity on one orthotropic parameter for the film is discovered using an orthotropy rescaling technique. The effects of other material parameters on the energy release rate and mode mixity are examined numerically, and the growth and arrest of edge interface cracks are discussed based on an energy criterion.     

考虑乘客不完全理性行为的轨道交通车站应急疏散方法研究

针对突发事件下城市轨道交通车站的客流疏散问题，考虑乘客的不完全理性决策行为，提出基于前景理论的疏散客流分配方法。首先，将车站内部结构网络化为有向图，利用图的深度优先遍历算法求解得到有效路径集合。然后考虑乘客的不完全理性行为，建立基于前景理论的疏散客流分配模型，并利用连续平均法进行求解。最后以成都太升南路地铁站为例，设置应急疏散场景进行模型应用，并利用AnyLogic将基于前景理论的配流结果和基于乘客完全理性的用户均衡配流结果进行仿真对比。结果表明，基于前景理论的客流分配方法得到的配流结果更符合实际应急疏散结果。     

Stationary heat conduction in an anisotropic slab containing a crack

The stationary temperature field in an anisotropic slab containing an internal longitudinal crack is investigated. On each face of the slab the temperature is presumed to have an arbitrary variation in one direction, while on the crack surface either heat flux or temperature is prescribed. The problem is reduced to a pair of Fredholm integral equations which can be solved numerically. As an illustrative example, the temperature distribution is computed for a slab having a temperature rise on one face and containing a central crack across which no heat is transferred. Numerical results are given for orthotropic and isotropic slabs with various ratios of crack length to slab thickness.     

Elastodynamic Doppler effects and wave energy partition by a sliding interface

Wave reflection and refraction at a sliding interface are discussed. The regular dynamic friction rule, Coulomb’s law, is assumed for the sliding interface. Doppler frequency shift is found, and it depends on the ratio of a sliding velocity to an apparent horizontal velocity of an incident wave. Wave energy partition by the sliding interface is also discussed. In the case of an incident P-wave, a transmitted/refracted P-wave gets the major part of the incident wave energy. On the other hand, in the case of an incident SV-wave, a reflected SV-wave gets most of incident wave energy. It is also found an energy supply or loss by the sliding interface. It strongly depends on the friction coefficient and on the sliding direction. Further, it is shown that there is no possibility for detecting the sliding velocity by means of Doppler frequency shift.