变温度场下提高热线探针标定精度的方法

IFA300热线风速仪系统自带的探针标定风洞由于散热快、低速气流流过时温度锐减,无法完成给定温度、小流量时的探针标定。针对这一结构缺陷,本文提出了通过加热标定风洞侧壁的方式来维持标定气流温度,拓宽了标定低速气流的温度范围。采用重复性的实验研究方法,有效提高了标定结果的准确性。将温度跨度在20℃-58℃之间流体的标定结果的相对偏差控制在1%以内,远高于IFA300热线风速仪的设计精度。为适应对完全封闭腔内流动参数的测试,本文设计制作了一套探针防碰撞控制系统,大幅降低了探针的坏损率,同时实测了封闭腔热壁面不同高度处外法线方向上的温度及平均速度,与文献结果吻合较好。

缓变温度场下正交各向异性椭圆板振动问题

本文联合使用奇异摄动法和Galerkin法求解任意缓变温度场下正交各向异性椭圆板振动问题。给出了椭圆板自由振动频率受热效应影响的显式表示。最后给出算例,具体显示热效应对椭圆板自由振动的影响。

变温度场下楔横轧端头凹心数值模拟研究

目的研究楔横轧凹心产生的原因以及变温度场对端面凹心的影响。方法采用数值模拟的方法,详细分析了楔横轧变形规律下凹心产生的原因。同时利用Deform-3D用户子程序方式,给轧件端部添加一定形式的变温度场,分析了变温度场改善凹心缺陷的机制;研究了变温区表面温度与变温度场长度对凹心深度的影响。结果楔横轧凹心是由轧至极限料头长度Imin时,端面金属变形不均匀引起的,凹心深度随着变温长度的增加和变温区表面温度的减小而减小,结论所提变温度场楔横轧轧制工艺,可以有效改善端面变形的均匀性,添加此变温度场可以有效减小楔横轧凹心深度。

变温度场下CFRP布加固工字钢梁疲劳性能研究

为研究湿热环境下CFRP布加固工字钢梁的加固效果,采用有限元软件ABAQUS进行了变温度场下未加固、一层、三层和五层CFRP布加固工字钢梁的数值模拟,得到了工字钢梁的荷载-温度曲线和疲劳寿命-温度曲线,建立了CFRP布加固工字钢梁的疲劳寿命预测模型。结果表明,CFRP布加固工字钢梁的承载力和疲劳性能受温度的影响,一层、三层、五层CFRP布加固工字钢梁的疲劳寿命增强比例最大分别为157%,266%,370%,极限荷载增强比例最大分别为2.31%,5.53%,8,41%。

不同季节施工对软基上船闸闸首结构的影响

软基上船闸闸首结构作为空间薄壁结构,在施工期混凝土浇筑硬化过程中产生较大热量,易受外界环境温度的影响,产生温度裂缝。因此,采用瞬变温度场和徐变应力场理论,以芒稻船闸闸首结构为例进行三维仿真分析,研究闸首结构在不同季节浇筑的温度和应力情况,分析其产生机理。结果表明,廊道在夏季和秋季浇筑时内部温度最大分别达到46.8、47.1℃,在夏季浇筑时拉应力最大为3.88 MPa,廊道内外边墙及阀门槽等结构突变处极易产生裂缝,应采取措施加以控制,在实际施工中应避免在夏季开始浇筑混凝土。

Temperature field evolution and heat transfer during continual local induction cladding

The evolution of temperature field of the continual motion induction cladding and the depth of heat affected zone are studied in this study.A three-dimensional finite element model for the point type continual induction cladding is established to investigate temperature distributions of fixed and motion induction cladding modes.The novel inductor is designed for cladding of curved surfaces.The modeling reliability is verified by the temperature measurements.The influence of process parameters on the maximum temperature and the generation and transfer of heat are studied.Quantitative calculation is performed to its melting rate to verify the temperature distribution and microstructures.The results show that a good metallurgical bond can be formed between the cladding layer and substrate.The melting rate gradually falls from the top of the cladding layer to the substrate,and the grain size in the substrate gradually rises.The heat affected zone is relatively small compared to integral heating.

Explicit Proof of Equivalence of Two—Point Functions in the Two Formalisms of Thermal Field Theory

We give an explicit proof of equivalence of the two-point function to one-loop order in the two formalisms of thermal theory based on the expressions in the real-time formalism and indicate that the key point of completing the proof is to separate carefully the imaginary part of the zero-temperature loop integral from relevant expressions and this fact will certainly be very useful for examination of the equivalent problem of two formalisms of thermal field theory in other theories, including the one of the propagators for scalar bound states in an NJL model.

Residual stress and welding distortion of Al/steel butt joint by arc-assisted laser welding-brazing

The thermo-elastic.plastic finite element method(FEM)is used to simulate the thermo-mechanical behavior of Al/steel tungsten inert gas(TIG)arc-assisted laser welding-brazing(A-LWB)butt joint.The influence of material nonlinearity,geometrical nonlinearity and work hardening on the welding process is studied,and the differences in the welding temperature field,residual stress and welding distortion by A-LWB and by single laser welding-brazing(SLWB)are analyzed.The results show that the thermal cycle,residual stress distribution and welding distortion by the numerical simulation are in good agreement with the measured data by experiments,which verifies the effectiveness of FEM.Compared with the SLWB,A-LWB can make the high-temperature distribution zone of weld in width direction wider,decrease the transverse tensile stress in the weld and reduce the distribution range of longitudinal tensile stress.And the welding deformation also decreases to some extent.

Numerical Simulation of Coseismic Response and Its Mechanism of Well Water Temperature to Farfield Strong Earthquakes1

Heat flow is inevitably accompanied by temperature change,thus,the water temperature coseismic response during earthquake activity should also obey the laws of thermodynamics.Taking the M S8.0 Wenchuan,Sichuan,China earthquake and the M9.0Tohoku,Japan earthquake as an example,and based on the data of water temperature coseismic responses observed in well ZK26 in Haikou,Hainan Province,China,we investigate the relationship between well water temperature change and heat transfer in the coseismic response process and the relevant thermodynamic mechanism by using the numerical simulation method for thermodynamic equations.Then,through forward modeling,we obtain several simulation curves of water temperature change in response to earthquakes along the well depth at different times.The simulated curves of water temperature change approximately fit the observed curves.Consequently,based on the variation of temperature,we find that the modes of well water temperature coseismic response( ascending,descending or stable) are related to factors such as the location of sensors,distribution and location of heat sources,the span between sensors and heat sources.

A δ-function-like peak in the specific heat of two-dimensional vortex lattice： Monte carlo study

A repulsive vortex\|vortex interaction model was used to numerically study the melting transition of the two\|dimensional vortex system with Monte Carlo method. Then a δ\|function\|like peak in the specific heat was observed and the internal energy showed a sharp drop at the melting temperature, which indicated that there exists a first\|order melting transition at finite temperatures. The Lindemann criterion was also investigated and valid, but different from previous simulation results.

Gap Equations and Effective Potentials at Finite Temperature and Chemical Potential in D—Dimensional Four—Fermion Models

We have proven the general relations between the gap equations obeyed by dynamical fermion mass and thecorresponding effective potentials at finite temperature and chemical potential in D-dimensional four-fermion interactionmodels. This gives an easy approach to get effective potentials directly from the gap equations. We find out explicitexpressions for the effective potentials at zero temperature in the cases of D = 2,3, and 4 for practical use.

Effect of the interfacial electric field on the HER on Pt(111)modified with iron adatoms in alkaline media

The study of the hydrogen evolution reaction(HER)aimed to reach a deeper understanding of the parameters that control the rate of this reaction is of great importance given the technical relevance of hydrogen production as an energy vector in the so-called hydrogen economy.In previous works,laser-induced temperature jump(LITJ)experiments on Pt(111)modified with Ni(OH)_(2)in alkaline media have revealed the importance of the interfacial electric field in the rate of the HER.It was hypothesised that small amounts of Ni(OH)_(2)cause a decrease of the electric field because of a negative shift of the pzfc toward the onset of the hydrogen evolution.In this work,to test the validity of this hypothesis,the study has been extended to Pt(111)surfaces modified with Fe(OH)_(2).The modified surfaces have been studied voltammetrically,and the voltammetric charges have been analysed.The voltammograms show a peak in the hydrogen evolution region that suggest the transformation in the adlayer from Fe(II)to Fe(0).In agreement with the coulometric analysis,the voltammetric features in the OH adsorption region would be related with the oxidation to the+3 valence state.The results obtained with LITJ method reflect the existence of a strong interaction of the Fe oxophilic species with the water molecules,shifting the potential of maximum entropy away from the onset of the HER.Hence,the most catalytic surface is the one with the lowest Fe coverage.

Effects of Electric and Magnetic Fields on Pure Dephasing of Exciton Qubits

In a two-dimensional quantum dot （QD） with parabolic confinement potential, we investigate pure dephasing due to deformation potential exciton-bulk longitudinal acoustic phonons （LAP） interaction for exciton qubits under the influence of external static electric and magnetic fields by adopting the full quantum-mechanical method of Kunihiro Kojima and Akihisa Tomita. The wave function is found and the dependence of the pure dephasing factor on the confinement length of the QD and time and temperature is discussed. We find the external electric and magnetic fields have important effects on pure dephasing of exciton qubits because exciton-LAP interaction increases, leading to more pure dephasing.

整体式挂车支承桥主轴变温挤压成形工艺

根据13 t整体式挂车支承桥主轴产品的结构特点,提出了无缝钢管挤压缩径成形新工艺。通过精确控制温度场梯度,提高无缝钢管变形区的支撑能力,实现端部缩径系数大幅降低。采用数值模拟结合工艺试验的方法,揭示了主轴成形过程中金属的流动状态以及关键工艺参数对产品成形性和壁厚分布的影响规律。结合主轴的形状尺寸要求和变温成形的工艺性,对工艺参数的取值或选择范围进行了优化。在双向挤压液压机上进行了工艺试验并得到了形状尺寸合格的样件,各工序变形区的壁厚分实测数值与数值模拟基本吻合,验证了数值模拟的正确性和工艺的可行性。与传统工艺相比,新工艺实现了挂车主轴少火次、短工艺流程的精密快捷成形。

Reversible magnetocaloric effect and refrigeration capacity enhanced by two successive magnetic transitions in DyB2

A large and reversible magnetocaloric effect is found in the compound DyB2, which is associated with two successive mag- netic transitions： a spin-reorientation-like transition followed by a ferromagnetic-paramagnetic transition. These two transitions appreciably enlarge the magnetic-refrigeration temperature window and yield a huge refrigeration capacity of 610 J kg^-1, with a maximum magnetic entropy change -ASmax of 17 J kg^-1K^-1, at a magnetic-field change of 5 T. The corresponding values for low magnetic-field change of 2 T are 193 J kg^-1 and 7.4 J kg-lK^-1, respectively.

Research Progress on Colossal Anisotropic Magnetoresistive Effect

Perovskite manganites show exotic functionalities due to the coupling between spin, charge, orbital and lattice, such as metal-insulator transition, colossal magnetoresistance （ CMR ） , charge-orbital order and phase separation. Recently, an extraordinary anisotropic magnetoresistance （ AMR ） has been observed in perovskite manganite single crystals. The AMR value is about 2 orders larger than that of the conventional 3E transition metals and alloys, which is attributed to tunable metal-insulator transition temperature modulated by the magnetic field. This result provides a new route for exploring novel AMR materials and their applications.

Revealing intrinsic and extrinsic piezoelectric contributions in phase coexistence system of PbTiO_(3)-BiScO_(3)

PbTiO_(3)-BiScO_(3) ceramics possess high piezoelectricity and high Curie temperature simultaneously,presenting a very promising candidate for high-temperature actuators and transducers.Figuring out the underlying piezoelectric mechanisms is of great importance for its application.Herein,we reveal the quantified intrinsic and extrinsic contributions to the high electrostrain of the morphotropic composition with phase coexistence by employing the advanced in situ electrical biasing high-energy synchrotron X-ray diffraction combined with the STRAP(strain,texture,and Rietveld analysis for piezoceramics from diffraction)methodology.An electric field-induced phase transformation is observed between the coexisting tetragonal and rhombohedral phases.It is found that the tetragonal phase contributes most of the domain switching strain,while the predominant lattice strain is from the rhombohedral phase.With phase fraction changes,the quantitative results demonstrate that the fieldinduced electrostrain is mainly contributed by the intrinsic lattice strain.In contrast,the high irreversible domain switching strain dominates the large remanent strain.It implies that transforming the large remanent strain into reversible strain would be a strategic direction to improve the piezoelectric response.The present results provide a further understanding of the high piezoelectricity and could help to advance the application of PbTiO_(3)-BiScO_(3).