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1.
This paper presents the investigation of the clustering of the intruders in a vertically vibrated granular bed by means of event-driven simulations.The results indicate that the position of intruders in the vertical direction is not a key factor for their aggregation.Energy dissipation of the intruders and host particles are calculated in the process of intruder-host and host-host collisions.The relative energy dissipation of the intruders to that of the host particles is obtained.We find that clustering of the intruders happens when the relative energy dissipation is negative.The conclusion is verified when the restitution coefficient,density and diameter of the intruders are varied.  相似文献   

2.
The macro- and micro-magnetic properties of Fe-Co alloy films eletrodeposited on CaAs(100) are studied by synchrotron radiation x-ray magnetic circular dichroism (XMCD) in combination with the magneto-optical Kerr effect (MOKE) measurements and magnetic force microscopy (MFM). The orbital and spin magnetic moments of each element in the Fe-Co alloy are determined by the sum rules of XMCD. Element-specific hysteresis loops (ESHL) are obtained by recording the La MCD signals as a function of applied magnetic field. MOKE results reveal that the amorphous films are magnetically isotropic in the surface plane. The MFM image shows that the dimension of the magnetic domains is about 1-2 #m, which is much larger than that of the grains, indicating that there are intergranular correlations among these grains. Both ESHL and MOKE hysteresis loops indicate the strong ferromagnetic coupling of Fe and Co in the alloy films.  相似文献   

3.
The mutual control mechanism between magnetization and polarization in multiferroic materials is studied. The system contains a ferromagnetic sublattice and a ferroelectric sublattice. To describe the magneto–electric coupling, we propose a linear coupling Hamiltonian between ferromagnetism and ferroelectricity without microscopic derivation. This coupling enables one to retrieve the hysteresis loops measured experimentally. The thermodynamic properties of the system are calculated, such as the temperature dependences of the magnetization, polarization, internal energy and free energy.The ferromagnetic and ferroelectric hysteresis loops driven by either a magnetic or an electric field are calculated, and the magnetic spin and pseudo-spin are always flipped synchronously under the external magnetic and electric field. Our theoretical results are in agreement with the experiments.  相似文献   

4.
The ferroelectric response of bismuth titanate Bi4Ti3O12(BIT) thin film is studied through a Monte Carlo simulation of hysteresis loops. The ferroelectric system is described by using a Diffour Hamiltonian with three terms: the electric field applied in the z direction, the nearest dipole–dipole interaction in the transversal(x–y) direction, and the nearest dipole–dipole interaction in the direction perpendicular to the thin film(the z axis). In the sample construction, we take into consideration the dipole orientations of the monoclinic and orthorhombic structures that can appear in BIT at low temperature in the ferroelectric state. The effects of temperature, stress, and the concentration of pinned dipole defects are assessed by using the hysteresis loops. The results indicate the changes in the hysteresis area with temperature and stress, and the asymmetric hysteresis loops exhibit evidence of the imprint failure mechanism with the emergence of pinned dipolar defects. The simulated shift in the hysteresis loops conforms to the experimental ferroelectric response.  相似文献   

5.
The investigation of dust particle characteristics in fusion devices has become more and more imperative.In the HL-2A tokamak,the morphologies and compositions of dust particles are analyzed by using scanning electron microscopy(SEM) and energy dispersive x-ray spectroscopy(EDX) with mapping.The results indicate that the sizes of dust particles are in a range from 1 μm to 1 mm.Surprisingly,stainless steel spheres with a diameter of 2.5μm-30 μm are obtained.The production mechanisms of dust particles include flaking,disintegration,agglomeration,and arcing.In addition,dynamic characteristics of the flaking dust particles are observed by a CMOS fast framing camera and simulated by a computer program.Both of the results display that the ion friction force is dominant in the toroidal direction,while the centrifugal force is crucial in the radial direction.Therefore,the visible dust particles are accelerated toriodally by the ion friction force and migrated radially by the centrifugal force.The averaged velocity of the grain is on the order of~100 m/s.These results provide an additional supplement for one of critical plasma-wall interaction(PWI) issues in the framework of the International Thermonuclear Experimental Reactor(ITER) programme.  相似文献   

6.
Molecular dynamic simulations are performed to study the nanoscratching behavior of polymers.The effects of scratching depth,scratching velocity and indenter/polymer interaction strength are investigated.It is found that polymer material in the scratching zone around the indenter can be removed in a ductile manner as the local temperature in the scratching zone exceeds glass transition temperature Tg.The recovery of polymer can be more significant when the temperature approaches or exceeds Tg.The tangential force,normal force and friction coefficient increase as the scratching depth increases.A larger scratching velocity leads to more material deformation and higher pile-up.The tangential force and normal force are larger for a larger scratching velocity whereas the friction coefficient is almost independent of the scratching velocities studied.It is also found that stronger indenter/polymer interaction strength results in a larger tangential force and friction coefficient.  相似文献   

7.
Classical strength criteria are developed based on some empirical assumptions and have been widely used in engineering to predict material strength owing to their simplicity. In some cases, however, considerable discrepancies arise between classicalstrength-criteria-based theoretical predictions and experimental results. Recently, a global nonequilibrium thermodynamics model has made important progress over classical models without resorting to any empirical assumptions. A prominent advance of this rational energy model is that it straightforwardly determines the dissipation energy density function, which is pertinent to inherent material ductility, through simple uniaxial and equi-biaxial tensions. In this study, a brief introduction of the nonequilibrium energy model was followed by systematic experimental investigation to determine the dissipation energy function and predict the material strength of pristine 316 L stainless steel-commonly used in engineering-under complex loadings. The results indicated that the strength contours predicted by the nonequilibrium energy criterion for complex loadings are consistent with the experimental results obtained for biaxial tension, implying that the nonequilibrium thermodynamics model is both reasonable and reliable. The prediction error was presumed to be induced by the anisotropy of the 316 L stainless steel sheets.  相似文献   

8.
In order to solve the problem of deformation and blurred edge in underwater acoustic image segmentation, an approach based on the deformable template is presented. Compared with the energy minimization of the Snake model, the energy function is redefined by adding a shape restriction. This improves the noise-resistance ability so that robustness and high segmentation efficiency are acquired. The energy optimization problem is tackled using the Dijkstra Algorithm. This method has been successfully tested on the filled-in acoustic images. The results show that this algorithm is efficient, precise and very immune to image deformation and noise when compared to results obtained from the Snake model and several traditional optimization methods.  相似文献   

9.
邓茂林  朱位秋 《中国物理》2007,16(6):1510-1515
In this paper the energy diffusion controlled reaction rate in dissipative Hamiltonian systems is investigated by using the stochastic averaging method for quasi Hamiltonian systems. The boundary value problem of mean first- passage time (MFPT) of averaged system is formulated and the energy diffusion controlled reaction rate is obtained as the inverse of MFPT. The energy diffusion controlled reaction rate in the classical Kramers bistable potential and in a two-dimensional bistable potential with a heat bath are obtained by using the proposed approach respectively. The obtained results are then compared with those from Monte Carlo simulation of original systems and from the classical Kraraers theory. It is shown that the reaction rate obtained by using the proposed approach agrees well with that from Monte Carlo simulation and is more accurate than the classical Kramers rate.  相似文献   

10.
姜文宁  陈建平  李新碗  尚韬 《中国物理》2004,13(9):1460-1463
In this paper, amplified double Rayleigh backscattering noise (DRB) in the optical fibre Raman amplifier is analysed. Expressions are presented for both forward pumping and backward pumping schemes. Calculation is performed to show the effective suppression of DRB noise by employing an optical isolator. The optimal position for the isolator is determined and is found to be insensitive to the power levels of the signals and pumps. The results show that a reduction of the DRB noise by almost 2 to 3 orders can be reached.  相似文献   

11.
Problems of dissipation of energy in the contact of bodies made of titanium nickelide are studied by the mechanocycling method. Under normal loading or joint action of normal and shearing forces the dissipation of energy ΔW, determined from the hysteresis loop area enclosed by the dependences pressure q—approach δ and shearing force τ-shift Δ, is several times higher than that of traditional materials, and the dependence τ-Δ is nonmonotonous in character and has some extreme points. The peculiarities in the formation of hysteresis loops are established. The obtained results are explained in the context of thermoelastic martensite transformations and the theory of contact interaction. V. D. Kuznetsov Siberian Physical-Technical Institute at Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 83–87, March, 1999.  相似文献   

12.
A nonlinear vibration isolator is considered to study effectiveness of isolation against harmonic force and displacement excitations. Nonlinearity in the magneto-rheological (MR) fluid based damper as well as in the elastic member is taken into account. The MR-damper has been modeled including Bouc–Wen hysteretic element and the spring is taken to have cubic nonlinearity. Analytical expression for the energy dissipation characteristics of the damper has been derived. Near resonant response of the isolated mass is obtained by a modified averaging technique suitable for hysteretic type nonlinearity present in the system. The performance of the isolators is estimated for various nonlinear stiffness values, both hardening and softening types. Different performance measures are also proposed to judge the performance of the nonlinear isolator.  相似文献   

13.
We study a hysteresis phenomenon in a rotating BEC with a weak link in a quasi-one-dimensional torus by proposing a microscopic theoretical model including a dissipation bath. By analyzing the role of dissipation and the decay rates of all the energy levels, we are able to give a microscopic interpretation of hysteresis recently observed in the experiment and confirm that the hysteresis is the result of the presence of metastable state. In particular, we obtain the hysteresis loops in a quench process just as that in the experiment. We also find that the shape and size of the hysteresis loop change drastically with the strength of the link.  相似文献   

14.
刘清友  罗旭  朱海燕  韩一维  刘建勋 《物理学报》2017,66(10):107501-107501
Jiles-Atherton(J-A)模型在磁化建模领域应用广泛,但不同文献给出的J-A模型并不一致,致使采用不同表达式建立的塑性变形磁化模型存在多种版本,其正确性难以甄别.通过对无磁滞磁化方程、能量守恒方程和等效磁场强度方程的梳理与比较,发现原有模型中存在将磁化强度和无磁滞磁化强度混用、将不可逆磁化能量等效于全部的磁化能量、等效磁场强度中应力磁化项界定不清等问题.在此基础上,对上述方程进行了修正,推导了基于J-A模型的塑性变形磁化修正模型.将修正模型计算结果与原模型计算结果、相关文献中的试验结果进行对比,结果表明:与原有计算模型相比,修正模型计算结果的饱和磁化强度和剩余磁化强度随塑性变形增加而减小,矫顽力随塑性变形增大而增大,达到饱和磁化强度时的外磁场强度随塑性变形增大而增大的趋势有所减弱,更符合试验结果,可更准确地反映塑性变形对材料磁化的影响.  相似文献   

15.
The temperature dependence of minor hysteresis loops of compressively deformed nickel single crystals has been investigated in a wide temperature range below the Curie temperature of 628 K. There exist power-law relations between the field-dependent parameters of minor-loops, and their exponents are independent of both temperature and strain after the compressive deformation. These observations indicate the presence of universal power laws in minor hysteresis loops. The minor-loop coefficients of the power laws show a similar temperature dependence of the coercive force, which is quantitatively related to the dislocation density. These properties of minor hysteresis loops are useful for the accurate and quantitative nondestructive evaluation of age degradation in ferromagnetic materials.  相似文献   

16.
樊康旗  贾建援  朱应敏  刘小院 《物理学报》2007,56(11):6345-6351
基于Hamaker假设、Lennard-Jones势能定律及经典弹性理论建立了一种新型的球体与平面黏着接触的弹性模型,该模型显示黏着力在原子力显微镜(AFM)针尖趋近和撤离样品表面,即加载和卸载的两个过程中存在黏着滞后现象,表明了AFM在轻敲工作模式中存在能量耗散.同时,根据所建的黏着接触弹性模型,建立了AFM在轻敲工作模式下的动力学模型,研究了AFM在轻敲工作模式下的振动幅度、相位差及耗散功率随针尖与样品表面间距的变化规律,仿真结果与现有的实验结果相一致.  相似文献   

17.
P Chaddah  M Manekar 《Pramana》2001,56(5):657-665
We present a model in which metastable supercooled phase and stable equilibrium phase of vortex matter coexist in different regions of a sample. Minor hysteresis loops are calculated with the simple assumption of the two phases of vortex matter having field-independent critical current densities. We use our earlier published ideas that the free energy barrier separating the metastable and stable phases reduces as the magnetic induction moves farther from the first order phase transition line, and that metastable to stable transformations occur in local regions of the sample when the local energy dissipation exceeds a critical value. Previously reported anomalous features in minor hysteresis loops are reproduced, and calculated field profiles are presented.  相似文献   

18.
The effects of adhesion hysteresis in the dynamic‐dissipation curves measured in amplitude‐modulation atomic force microscopy are discussed. Hysteresis in the interaction forces is shown to modify the dynamics of the cantilever leading to different power dissipation curves in the repulsive and attractive regimes. Experimental results together with numerical simulations show that power dissipation, as measured in force microscopy, is not always proportional to the energy dissipated in the tip–sample interaction process. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

19.
Assuming that different energy dissipation mechanisms are at work along hysteresis, a hysteresis loss subdivision procedure has been proposed, using the induction at maximum permeability (around 0.8 T, in electrical steels) as the boundary between the “low-induction” and the “high-induction” regions. This paper reviews the most important results obtained in 10 years of investigation of the effect of microstructure on these components of the hysteresis loss. As maximum induction increases, the “low-induction loss” increases linearly up to 1.2 T, while the “high-induction loss” is zero up to 0.7 T and then increases as a power law with n=5. Low-induction loss behavior is linearly related to Hc between 0.4 and 1.2 T. Grain size has a larger influence on low-induction losses than on high-induction losses. Texture has a much stronger influence on high loss than on low-induction loss, and it is related to the average magnetocrystalline energy. 6.5%Si steel shows smaller hysteresis loss at 1.5 T than 3.5%Si steel only because of its smaler high-induction component. The abrupt increase in hysteresis loss due to very small plastic deformation is strongly related to the high-induction loss component. These results are discussed in terms of energy dissipation mechanisms such as domain wall movement, irreversible rotation and domain wall energy dissipation at domain nucleation and annihilation.  相似文献   

20.
利用动力学加统计模型对200Pb 系统的断前中子的发射进行了模拟。计算结果表明,在核耗散的形变关系(DDND) 确定的情况下,断前中子多重性会随着能级密度坐标关系(DDLDP) 的增强而减少,且该规律主要由第一阶段内断前中子的发射决定。此外,选定DDLDP 而采用核耗散的不同形变关系也都很好地重现了实验数据。为了解释上述现象,提出了研究热核退激的路径分析方法,其主要内容是把核耗散看成是实验粒子在拉伸维度上的阻尼力,而核裂变的动力学过程是该阻尼力和自由能产生的驱动力之间相互竞争的结果。利用该方法对200Pb 系统的断前中子多重性进行了分析,并指出在确定DDND时应考虑DDLDP。Within a certain deformation dependence of nuclear dissipation (DDND), the simulation results about the deexcitation process of 200Pb show that the prescission neutron multiplicities decrease with increasing deformation dependence of level density parameter (DDLDP). Moreover, this pattern is determined by the emission of prescission neutron in the first period of nuclear fission. On the other hand, all of the results from two kinds of different DDNDs can reproduce the experiment data perfectly with a certain DDLDP. In order to illustrate those phenomena, the pathwise analysis method (PAM) is presented in this paper. In the PAM, nuclear dissipation is treated as the damping force on the elongation dimension, whereas the fission dynamics process results from the competition between damping force and the driving force stemming from the nuclear free energy. The prescission neutron multiplicity in the deexcitation process of 200Pb is analyzed, and the results point out that the DDLDP needs to be taken into account in studying the DDND.  相似文献   

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