A FLEXIBLE OBJECTIVE-CONSTRAINT APPROACH AND A NEW ALGORITHM FOR CONSTRUCTING THE PARETO FRONT OF MULTIOBJECTIVE OPTIMIZATION PROBLEMS

In this article, a novel scalarization technique, called the improved objective-constraint approach, is introduced to find efficient solutions of a given multiobjective programming problem. The presented scalarized problem extends the objective-constraint problem. It is demonstrated that how adding variables to the scalarized problem, can lead to find conditions for (weakly, properly) Pareto optimal solutions. Applying the obtained necessary and sufficient conditions, two algorithms for generating the Pareto front approximation of bi-objective and three-objective programming problems are designed. These algorithms are easy to implement and can achieve an even approximation of (weakly, properly) Pareto optimal solutions. These algorithms can be generalized for optimization problems with more than three criterion functions, too. The effectiveness and capability of the algorithms are demonstrated in test problems.

The Application of Permanent Magnet Synchronous Motor with Small Electrical Time Constant in Fiber Positioner

With the development of cutting-edge multi-object spectrographs,fiber positioners located in the focal plane are being scaled down in size,and miniature hollow-cup Permanent Magnet motors are now being considered as a suitable replacement for Faulhaber Precistep stepper motors.However,the small electrical time constant of such coreless motors poses a challenge,as the problem of severe commutation torque ripple in a fiber positioner running a position loop has been tricky.To overcome this challenge,it is advised to increase the Pulse Width Modulation(PWM)frequency as much as possible to mitigate the effects of the current fluctuation.This must be done while ensuring adequate resolution of the PWM generator.By employing a voltage open-loop field-oriented control based on a modulation frequency of 1 MHz,the drive current only costs 25 m A under a 3.3 V power supply.The sine degree of phase current is immaculate,and the repeat positioning accuracy can reach 2μm.Moreover,it is possible to further shrink the bill of devices and the layout area of the Printed Circuit Board,especially in sizesensitive applications.This device has been developed under the new generation of The Large Sky Area MultiObject Fiber Spectroscopic Telescope.

Flow and sound fields of scaled high-speed trains with different coach numbers running in long tunnel

Segregated incompressible large eddy simulation and acoustic perturbation equations were used to obtain the flow field and sound field of 1:25 scale trains with three,six and eight coaches in a long tunnel,and the aerodynamic results were verified by wind tunnel test with the same scale two-coach train model.Time-averaged drag coefficients of the head coach of three trains are similar,but at the tail coach of the multi-group trains it is much larger than that of the three-coach train.The eight-coach train presents the largest increment from the head coach to the tail coach in the standard deviation(STD)of aerodynamic force coefficients:0.0110 for drag coefficient(Cd),0.0198 for lift coefficient(Cl)and 0.0371 for side coef-ficient(Cs).Total sound pressure level at the bottom of multi-group trains presents a significant streamwise increase,which is different from the three-coach train.Tunnel walls affect the acoustic distribution at the bottom,only after the coach number reaches a certain value,and the streamwise increase in the sound pressure fluctuation of multi-group trains is strengthened by coach number.Fourier transform of the turbulent and sound pressures presents that coach number has little influence on the peak frequencies,but increases the sound pressure level values at the tail bogie cavities.Furthermore,different from the turbulent pressure,the first two sound pressure proper orthogonal decomposition(POD)modes in the bogie cavities contain 90%of the total energy,and the spatial distributions indicate that the acoustic distributions in the head and tail bogies are not related to coach number.

Combining Medical Care with Elderly Care

With the continuous expansion of the demand in China for the integration of medical care and elderly care,more social capital will be directed into this field.A LTHOUGHT answers to the question“What is happiness?”may vary among young people,for most senior citizens the answer is by and large the same:to be looked after properly.

Twin Paradox and Proper Time

Professors Mohazzbi and Luo [1] published “Despite several attempts have been made to explain the twin paradox … none of the explanations … resolved the paradox. If the paradox can be ever resolved, it requires a much deeper understanding … of the theory of relativity”. The deeper understanding of resolving the paradox is by applying more explicit definitions of proper time interval, Lorentz transform, time dilation, and aging time.

Correction to:Bottomonium suppression in heavy‑ion collisions and the in‑medium strong force

Correction to:NUCL SCI TECH(2023)34:63 https://doi.org/10.1007/s41365-023-01213-3 While typesetting,reference[16]in the list has not been properly placed in the proof.The orders of the references[13-16]were mistaken by the production.The correct order of the references is.

IGBT Temperature Field Monitoring Based on Reduced-order Model

With the rapid development of the world economy,IGBT has been widely used in motor drive and electric energy conversion.In order to timely detect the fatigue damage of IGBT,it is necessary to monitor the junction temperature of IGBT.In order to realize the fast calculation of IGBT junction temperature,a finite element method of IGBT temperature field reduction is proposed in this paper.Firstly,the finite element calculation process of IGBT temperature field is introduced and the linear equations of finite element calculation of temperature field are derived.Temperature field data of different working conditions are obtained by finite element simulation to form the sample space.Then the covariance matrix of the sample space is constructed,whose proper orthogonal decomposition and modal extraction are carried out.Reasonable basis vector space is selected to complete the low dimensional expression of temperature vector inside and outside the sample space.Finally,the reduced-order model of temperature field finite element is obtained and solved.The results of the reduced order model are compared with those of the finite element method,and the performance of the reduced-order model is evaluated from two aspects of accuracy and rapidity.

Deep Learning Applied to Computational Mechanics:A Comprehensive Review,State of the Art,and the Classics

Three recent breakthroughs due to AI in arts and science serve as motivation:An award winning digital image,protein folding,fast matrix multiplication.Many recent developments in artificial neural networks,particularly deep learning(DL),applied and relevant to computational mechanics(solid,fluids,finite-element technology)are reviewed in detail.Both hybrid and pure machine learning(ML)methods are discussed.Hybrid methods combine traditional PDE discretizations with ML methods either(1)to help model complex nonlinear constitutive relations,(2)to nonlinearly reduce the model order for efficient simulation(turbulence),or(3)to accelerate the simulation by predicting certain components in the traditional integration methods.Here,methods(1)and(2)relied on Long-Short-Term Memory(LSTM)architecture,with method(3)relying on convolutional neural networks.Pure ML methods to solve(nonlinear)PDEs are represented by Physics-Informed Neural network(PINN)methods,which could be combined with attention mechanism to address discontinuous solutions.Both LSTM and attention architectures,together with modern and generalized classic optimizers to include stochasticity for DL networks,are extensively reviewed.Kernel machines,including Gaussian processes,are provided to sufficient depth for more advanced works such as shallow networks with infinite width.Not only addressing experts,readers are assumed familiar with computational mechanics,but not with DL,whose concepts and applications are built up from the basics,aiming at bringing first-time learners quickly to the forefront of research.History and limitations of AI are recounted and discussed,with particular attention at pointing out misstatements or misconceptions of the classics,even in well-known references.Positioning and pointing control of a large-deformable beam is given as an example.

Proper orthogonal decomposition based seismic source wavefield reconstruction for finite element reverse time migration

The large storage requirement is a critical issue in cross-correlation imaging-condition based reverse time migration(RTM),because it requires the operation of the source and receiver wavefields at the same time.The boundary value method(BVM),based on the finite difference method(FDM),can be used to reconstruct the source wavefield in the reverse time propagation in the same way as the receiver wavefield,which can reduce the storage burden of the RTM data.Considering that the FDM cannot well handle models with discontinuous material properties and rough interfaces,we develop a source wavefield reconstruction strategy based on the finite element method(FEM),using proper orthogonal decomposition(POD)to enhance computational efficiency.In this method,we divide the whole time period into several segments,and construct the POD basis functions to get a reduced order model(ROM)for the source wavefield reconstruction in each segment.We show the corresponding quantitative analysis of the storage requirement of the POD-FEM.Numerical tests on the homogeneous model show the effectiveness of the proposed method,while the layered model and part of the Marmousi model tests indicate that the POD-FEM can keep an excellent balance between computational efficiency and memory usage compared with the full-stored method(FSM)and the BVM,and can be effectively applied in imaging.

基于CFD降阶的非线性气动弹性稳定性分析

为了快速寻找基于CFD/CSD的非线性气弹系统的颤振边界,根据Lyapunov稳定性理论对非线性流固耦合系统进行稳定性分析。首先通过微扰理论对非线性流固耦合系统处理建立近似线性化状态空间方程,再通过POD(Proper Orthogonal Decomposition)方法将高维状态空间方程降阶为便于分析的降阶系统,根据系统所有特征值即可判定原始非线性系统稳定性。Lyapunov稳定性理论主要针对非线性系统,在实现过程中采用了POD降阶的方法,与大多数对降阶系统稳定性判定不同,其数学理论上是反映原始非线性流固耦合系统稳定性。POD降阶方法从系统内部流场出发,可以较好反映系统内部特性。二维三维算例仿真结果验证了该方法预测颤振边界的正确性,分析发现,在亚音速阶段,稳定性主要由于结构模态主导;而在跨音速和超音速流动阶段,气弹稳定性主要由受流体特性影响。

基于POD的大涡模拟入流脉动合成方法研究

针对并行计算特点,发展适用于流体并行计算的大涡模拟(Large Eddy Simulation,LES)入流脉动直接合成方法。基于特征正交分解(Proper Orthogonal Decomposition,POD)型谱表示法合成入流面主要网格点脉动风速时程,采用有限元形函数空间插值获得入流面所有网格点风速时程,采用UDF(User Defined Functions)编程实现Fluent软件平台流体并行计算时合成的脉动风速时程读入及赋值。进行B类1:500缩尺比风场内宽高比1:6的单体方形截面高层建筑非定常绕流LES计算,将数值模拟所得风剖面、风速谱及结构风压系数统计值、自谱、相干性等,与刚性模型测压风洞试验及文献数值模拟结果比较。研究表明,该合成方法可较好模拟紊流风场,预测结构风荷载具有一定精度。

New crystal structure and physical properties of TcB from first-principles calculations

By combining first-principles calculations with the particle swarm optimization algorithm, we predicted a hexagonal Pˉ3m1 structure for Tc B, which is energetically more favorable than the previously reported WC-type and Cmcm structures.The new phase is mechanically and dynamically stable, as confirmed by its phonon and elastic constants calculations.The calculated mechanical properties show that it is an ultra-incompressible and hard material. Meanwhile, the elastic anisotropy is investigated by the shear anisotropic factors and ratio of the directional bulk modulus. Density of states analysis reveals that the strong covalent bonding between Tc and B atoms plays a leading role in forming a hard material. Additionally, the compressibility, bulk modulus, Debye temperature, Gruneisen parameter, specific heat, and thermal expansion coefficient of Tc B are also successfully obtained by using the quasi-harmonic Debye model.

(π)_1空间中一类非线性算子方程的逼近可解性

首先在(π)1空间的闭集上证明了凝聚映射必为A-Proper映射,进而证明了型如f(x)-λx=0方程当f为弱内向k-集压缩映射且λ>k时是弱逼近可解的,若f为李普希兹型映射,方程还是强逼近可解的.它们推广与改进了[1-3]中一些重要结论.

A Model for Mechanical Property Evaluation of the Periodic Porous Low-k Materials by SAW

The influence of the distribution of nano-pores on the mechanical properties evaluation of porous low-k films by surface acoustic waves （SAW） is studied. A theoretical SAW propagation model is set up to characterize the periodic porous dielectrics by transversely isotropic symmetry. The theoretical deductions of SAW propagating in the low-k film/Si substrate layered structure are given in detail. The dispersive characteristics of SAW in differ- ent propagation directions and the effects of the Young＇s moduli E, E′ and shear modulus G′ of the films on these dispersive curves are found. Computational results show that E′ and G′ cannot be measured along the propagation direction that is perpendicular to the nano-pores＇ direction.

A-proper映射拓扑度的应用

利用A-proper映射拓扑度的基本性质,在投影完备的M enger PN-空间中研究了一些方程解的存在性。

一类非紧映象的不动点及固有值存在定理

本文讨论了一类非紧映象──Ｐγ一紧映象拓扑度的有关性质，并由此导出了其固有值、不动点存在的判定定理，本文所得结论为［１］、［２］中相应结论的推广。

一种D-ProPer保护框架下的差分隐私数据发布方法

差分隐私保护框架是实现差分隐私的基础环境。文中研究了满足PDP保护的Pro Per框架并对其改进应用到分布式环境中,提出了D-Pro Per差分隐私保护框架。在此框架下,针对GS分组划分方法在划分存在离群点的数据集时会造成巨大误差的问题,提出了满足ε差分隐私的S-GS数据发布方法。该方法是在原有GS划分方法的基础上引进差值集这一概念用于对数据集中存在的离群点进行判定,并对其进行针对性的划分,并进行了两组S-GS方法与GS方法的对比实验。实验结果表明,在拥有大量离群点的数据集中S-GS方法比GS方法有更强的算法鲁棒性以及更好的数据可用性。

Abnormal splenic artery diameter/hepatic artery diameter ratio in cirrhosis-induced portal hypertension

AIM:To determine an optimal cutoff value for abnormal splenic artery diameter/proper hepatic artery diameter(S/P) ratio in cirrhosis-induced portal hypertension.METHODS:Patients with cirrhosis and portal hypertension(n = 770) and healthy volunteers(n = 31) underwent volumetric computed tomography threedimensional vascular reconstruction to measure the internal diameters of the splenic artery and proper hepatic artery to calculate the S/P ratio.The cutoff value for abnormal S/P ratio was determined using receiver operating characteristic curve analysis,and the prevalence of abnormal S/P ratio and associations between abnormal S/P ratio and major complications of portal hypertension were studied using logistic regression.RESULTS:The receiver operating characteristic analysis showed that the cutoff points for abnormal splenic artery internal diameter and S/P ratio were > 5.19 mm and > 1.40,respectively.The sensitivity,specificity,positive predictive value,and negative predictive value were 74.2%,45.2%,97.1%,and 6.6%,respectively.The prevalence of an abnormal S/P ratio in the patients with cirrhosis and portal hypertension was 83.4%.Patients with a higher S/P ratio had a lower risk of developing ascites [odds ratio(OR) = 0.708,95%CI:0.508-0.986,P = 0.041] and a higher risk of developing esophageal and gastric varices(OR = 1.483,95%CI:1.010-2.175,P = 0.044) and forming collateral circulation(OR = 1.518,95%CI:1.033-2.230,P = 0.034).After splenectomy,the portal venous pressure and maximum and mean portal venous flow velocities were reduced,while the flow rate and maximum and minimum flow velocities of the hepatic artery were increased(P < 0.05).CONCLUSION:The prevalence of an abnormal S/P ratio is high in patients with cirrhosis and portal hypertension,and it can be used as an important marker of splanchnic hemodynamic disturbances.

PROPER CONDITIONS OF MESHING FOR Hy-Vo SILENT CHAIN AND SPROCKET

Proper meshing of Hy-Vo silent chain and sprocket is important for realizing the transmission of the silent chain with more efficiency and less noise. Based on the study of the meshing theory of the Hy-Vo silent chain with the sprocket and the roll cutting machining principle of the sprocket with the hob, the proper conditions of the meshing for the Hy-Vo silent chain and the sprocket are put forward with the variable pitch characteristic of the Hy-Vo silent chain taken into consideration, and the proper meshing design method on the condition that the value of the link tooth pressure angle is unequal to the value of the sprocket tooth pressure angle is studied. Experiments show that this new design method is feasible. In addition, the design of the pitch, the sprocket tooth pressure angle and the fillet radius of the sprocket addendum circle are studied. It is crucial for guiding the design of the hob which cuts the Hy-Vo silent chain sprocket.

BENSON PROPER EFFICIENCY IN THE NEARLY CONE-SUBCONVEXLIKE VECTOR OPTIMIZATION WITH SET-VALUED FUNCTIONS

Some properties of convex cones are obtained and are used to derive several equivalent conditions as well as another important property for nearly cone-subconvexlike set-valued functions. Under the assumption of nearly cone-subconvexlikeness,a Lagrangian multiplier theorem on Benson proper efficiency is presented. Related results are generalized.