共查询到19条相似文献,搜索用时 46 毫秒
1.
In this paper, we systematically study the phase boundary Tc(\vec H) of a hexagonal-prism superconducting network in an external magnetic field \vec H of arbitrary magnitude and direction. The result indicates that the phase boundary of the hexagonal-prism superconducting circuit varies more sharply than that of the cubic circuit. The potential applications of the hexagonal-prism superconducting circuit are also discussed. 相似文献
2.
Critical behaviours and magnetic properties of three-dimensional bond and anisotropy dilution Blume——Capel model in the presence of an applied field 下载免费PDF全文
This paper studies the critical behaviours and magnetic properties of
three-dimensional bond and anisotropy dilution Blume--Capel model (BCM) in the
presence of an applied field within the effective field theory. The trajectory of
tricritical point, reentrant transitions and degenerate patterns of anisotropy are
obtained both for the bond and the anisotropy dilutions. The global phase diagrams
demonstrate unusually reentrant phenomena. The temperature dependences of
magnetization curves undergo remarkable spin glass behaviour at low temperatures,
and transform from ferromagnetism to paramagnetism at high temperature in applied
fields. Temperature dependence of magnetic susceptibility curve is in qualitative
agreement with experimental result. 相似文献
3.
Properties of the ground state in a spin—2 transverse Ising model with the presence of a srystal field 下载免费PDF全文
The properties of the ground state in the spin-2 transverse Ising model with the presence of a crystal of a crystal field are studied by using the effective-field theory with correlations,The longitudinal and transverse magnetizations,the phase diagram and the internal energy in the ground state are given numerically for a honeycomb lattice(z=3). 相似文献
4.
The scaling of the flowfield in a gas--gas combustion
chamber is investigated theoretically, numerically and
experimentally. To obtain the scaling criterion of the gas--gas
combustion flowfield, formulation analysis of the three-dimensional
(3D) Navier--Stokes equations for a gaseous multi-component mixing
reaction flow is conducted and dimensional analysis on the gas--gas
combustion phenomena is also carried out. The criterion implies that
the size and the pressure of the gas--gas combustion chamber can be
changed. Based on the criterion, multi-element injector chambers
with different geometric sizes and at different chamber pressures
ranging from 3~MPa to 20~MPa are numerically simulated. A
multi-element injector chamber is designed and hot-fire tested at
five chamber pressures from 1.64~MPa to 3.68~MPa. Wall temperature
measurements are used to understand the similarity of combustion
flowfields in the tests. The results have verified the similarities
between combustion flowfields under different chamber pressures and
geometries, with the criterion applied. 相似文献
5.
Erhan Albayrak 《中国物理 B》2012,21(6):67501-067501
The random crystal field(RCF) effects are investigated on the phase diagrams of the mixed-spins 1/2 and 3/2 Blume-Capel(BC) model on the Bethe lattice.The bimodal random crystal field is assumed and the recursion relations are employed for the solution of the model.The system gives only the second-order phase transitions for all values of the crystal fields in the non-random bimodal distribution for given probability.The randomness does not change the order of the phase transitions for higher crystal field values,i.e.,it is always second-order,but it may introduce first-order phase transitions at lower negative crystal field values for the probability in the range about 0.20 and 0.45,which is only the second-order for the non-random case in this range.Thus our work claims that randomness may be used to induce first-order phase transitions at lower negative crystal field values at lower probabilities. 相似文献
6.
<正>The scattering of scalar light wave from a random medium with a correlation function of Gaussian-Schell model distribution is studied.It is shown that the properties of the scattered field,i.e.,the spectral density and the spectral degree of coherence of the scattered field,are closely related to the properties of the scattering medium,including the scaled effective radius and the scaled correlation length of the correlation function. 相似文献
7.
The combined effects of Lvy noise and immune delay on the extinction behavior in a tumor growth model are explored. The extinction probability of tumor with certain density is measured by exit probability. The expression of the exit probability is obtained using the Taylor expansion and the infinitesimal generator theory. Based on numerical calculations, it is found that the immune delay facilitates tumor extinction when the stability index α < 1, but inhibits tumor extinction when the stability index α > 1. Moreover, larger stability index and smaller noise intensity are in favor of the extinction for tumor with low density. While for tumor with high density, the stability index and the noise intensity should be reduced to promote tumor extinction. 相似文献
8.
Application of higher-order KdV——mKdV model with higher-degree nonlinear terms to gravity waves in atmosphere 下载免费PDF全文
Higher-order Korteweg-de Vries (KdV)-modified KdV (mKdV) equations
with a higher-degree of nonlinear terms are derived from a simple
incompressible non-hydrostatic Boussinesq equation set in atmosphere
and are used to investigate gravity waves in atmosphere. By taking
advantage of the auxiliary nonlinear ordinary differential equation,
periodic wave and solitary wave solutions of the fifth-order
KdV--mKdV models with higher-degree nonlinear terms are obtained
under some constraint conditions. The analysis shows that the
propagation and the periodic structures of gravity waves depend on
the properties of the slope of line of constant phase and atmospheric
stability. The Jacobi elliptic function wave and solitary wave
solutions with slowly varying amplitude are transformed into
triangular waves with the abruptly varying amplitude and breaking
gravity waves under the effect of atmospheric instability. 相似文献
9.
It is shown that the Imry–Ma theorem stating that in space dimensions d < 4 the introduction of an arbitrarily small concentration of defects of the “random local field” type in a system with continuous symmetry of the n-component vector order parameter (O(n) model) leads to long-range order collapse and to the occurrence of a disordered state is not true if the anisotropic distribution of the defect-induced random local field directions in the space of the order parameter gives rise to the effective anisotropy of the “easy axis” type. In the case of a weakly anisotropic field distribution, in space dimensions 2 ≤ d < 4 there exists some critical defect concentration, above which the inhomogeneous Imry–Ma state can exist as an equilibrium one. At a lower defect concentration, long-range order takes place in the system. In the case of a strongly anisotropic field distribution, the Imry–Ma state is suppressed completely and long-range order state takes place at any defect concentration. 相似文献
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采用Kim模型,利用耦合溶质场的相场模型对Al-2-mole-Cu合金等温凝固过程中多晶粒相互影响下枝晶的生长过程进行数值模拟,为了提高计算效率,采用差分去实现宏微观场之间的耦合.研究了不同过冷度对多晶粒枝晶形貌和溶质分布的影响,结果表明:成分过冷对枝晶生长速度和溶质分配有着重大的影响,溶质元素Cu在固液界面前沿重新分布,结果导致实际热过冷减小,进而影响枝晶的生长和溶质向外层的扩散,致使相互接触的枝晶产生萎缩而其余没有受到抑制的枝晶生长方向产生择优现象.
关键词:
相场法
模拟
择优生长
等温凝固
二元合金 相似文献
13.
Numerical study of growth competition between twin grains during directional solidification by using multi-phase field method 下载免费PDF全文
A multi-phase field model is established to simulate the growth competition and evolution behavior between seaweed and columnar dendrites during directional solidification.According to the effects of surface tension and interfacial energy,we quantitatively analyze the influences of factors such as inclination angles,pulling velocity,and anisotropic strength on twin growth.The results demonstrate that the pulling velocity and anisotropic strength have an important influence on the morphology and evolution of the seaweed and dendritic growth.The low pulling velocity and anisotropic strength are both key parameters for maintaining the stable morphology of seaweed during competitive growth in a bicrystal,showing that the lateral branching behavior is the root of the dendrites that can ultimately dominate the growth.And it is clarified that the lateral branching behavior and lateral blocking are the root causes of the final dominant growth of dendrites.With the increase of anisotropy strength,the seaweed is eliminated fastest in case 1,the seaweed is transformed into degenerate dendritic morphology,and eliminates the seaweed by promoting the generation and lateral growth of the lateral branches of the dendrites.The increase of pulling velocity is to increase the undercooling of favorable oriented grain and accelerate the growth rate of dendrites,thus producing more new primary dendrites for lateral expansion and accelerating the elimination rate of unfavorable oriented grain. 相似文献
14.
采用耦合群体动力学方法与元胞自动机方法建立了细化处理条件下铝合金凝固微观组织演变的数值模型.该模型考虑了a-Al的非均匀形核过程、晶粒的初始球形长大以及之后的枝晶生长过程.利用建立的模型模拟了Al-5Ti-1B中间合金细化工业纯铝凝固组织演变过程.结果表明:形核初始阶段,熔体中存在充足数量的有效形核粒子, a-Al形核率随着熔体过冷度的增大逐渐增高;形核开始不久后, a-Al的异质形核过程由熔体中有效形核粒子数量控制,直到再辉发生,形核停止.模拟分析了中间合金添加量以及熔体冷却速度对工业纯铝凝固组织演变过程的影响,模拟结果与实验结果相符,验证了模型的准确性. 相似文献
15.
在二元合金相场模型研究的基础上,进行扩展获得了多元合金相场模型.以Al-Si-Mg三元合金为例,采用该相场模型实现了逼真地模拟多元合金凝固过程的等轴枝晶生长,得到了二次或更高次晶臂生长等复杂的枝晶形貌.随着第三组元Mg含量的减少,枝晶的二次枝晶越发达,枝晶中溶质的偏析越严重,枝晶尖端的生长速率和半径越大,与丁二腈-丙酮体系中枝晶尖端生长速率、半径随溶质浓度变化关系的理论计算和实验结果相符合.另外,枝晶初生晶臂中心的溶质浓度最低,在被二次晶臂包围的界面区域的溶质浓度最高;固液界面区域具有较大的浓度梯度,其中枝晶尖端前沿的梯度最大.
关键词:
相场法
多元合金
凝固过程
枝晶生长 相似文献
16.
ZHENG Renrong CHEN Zhiqian & ZHU Shunquan . Department of Physics Shanghai Normal University Shanghai China . Department of Physics Southwest Normal University Chongqing China . Department of Computer Electric Technology Shanghai Business School Shanghai China 《中国科学G辑(英文版)》2005,48(4):431-441
1 IntroductionThe superconductivity of small metallic grains has been attracting a lot of attentions. On one hand, Anderson[1] predicted that the superconductivity would disappear if a me- tallic grain was so small that the spaces between the nearest neighbor energy levels in the system became larger than the energy gap of the bulk metallic superconductor; On the other hand, it was found in experiments made in the 1960s[2] that the critical tem- perature of superconductivity of small metallic … 相似文献
17.
基于Ginzberg-Landau理论,发展了一个与WBM模型和KKS模型一致的新相场模型.并利用该相场模型与溶质场耦合计算,以Al-65%Cu合金为例模拟了不同过冷度条件下,二元合金凝固过程的等轴枝晶生长过程.研究过冷度对二元合金等温凝固过程的等轴枝晶生长以及溶质场分布的影响.结果表明:随着过冷度的增大,枝晶的二次枝晶更加发达,浓度Peclet数和枝晶尖端的生长速率增大,而枝晶尖端的曲率半径减小,枝晶前沿的溶质富集现象也更严重;另外,计算结果与Ivantsov理论符合较好.
关键词:
相场法
枝晶生长
溶质场
Ivantsov理论 相似文献
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本文研究了在非均匀磁场尘埃等离子体中不规则尘埃颗粒的复杂运动, 包括圆滚运动、尖头圆滚运动、圆周运动以及波浪运动等. 放置在电极上的圆柱形磁铁的主要作用是改变鞘层的径向分布, 进而对颗粒产生径向约束, 使尘埃颗粒悬浮于圆柱形磁铁周围, 其磁场并不足以磁化颗粒使其做圆滚运动. 通过与球形尘埃颗粒的对比实验发现, 圆滚运动是不规则尘埃颗粒在等离子体中特有的一种运动. 我们提出了一种新的机理: 由于不规则颗粒的自旋而引起的横向反Magnus力对颗粒的圆滚运动起了重要的作用. 文中通过受力分析定性地对实验中观察到的非球形颗粒的各种运动给出了合理的解释. 相似文献