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1.
本在环形圆对称Josephson结Sine-Gordon方程的基础上,考虑在实际物理环境必然存在热噪声和各种电磁噪声,加入无规随机噪声的影响,对环形结的孤子运动和第一零场台阶进行数据模拟计算,观察磁通孤子在噪声涨落电流作用下的运动情况,发现了不同于理想结的孤子运动模式转变现象,讨论了涨落电流在这些现象中所起的作用,并分析了噪声涨落对环形结各种物理性质的影响。 相似文献
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�ܺ������ݾ����ųڣ���ģ������� 《核聚变与等离子体物理》2018,38(3):309-314
为了更好地研究反常输运,J-TEXT发展了一套相关电子回旋辐射(CECE)系统来测量电子温度涨落。该系统采用频率去相关的结构,通过八道窄带滤波器进行频率选择,其中两道采用带宽为100MHz的定频滤波器,其余六道采用带宽为100~240MHz的钇铁石榴石(YIG)滤波器,YIG滤波器的中心频率为数字可调,增加了系统的灵活性。通过光路的优化,系统的极向分辨率最高可达2.5cm-1。实验结果表明系统性能良好,通过互相关技术可以消除热噪声的影响得到电子温度涨落,并且观测到靠近等离子体芯部的电子温度涨落要小于靠近边缘的电子温度涨落。 相似文献
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为了更好地研究反常输运,J-TEXT发展了一套相关电子回旋辐射(CECE)系统来测量电子温度涨落。该系统采用频率去相关的结构,通过八道窄带滤波器进行频率选择,其中两道采用带宽为100MHz的定频滤波器,其余六道采用带宽为100~240MHz的钇铁石榴石(YIG)滤波器,YIG滤波器的中心频率为数字可调,增加了系统的灵活性。通过光路的优化,系统的极向分辨率最高可达2.5cm-1。实验结果表明系统性能良好,通过互相关技术可以消除热噪声的影响得到电子温度涨落,并且观测到靠近等离子体芯部的电子温度涨落要小于靠近边缘的电子温度涨落。 相似文献
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利用热场动力学的方法研究了具有热噪声的相干态和压缩态中场正交分量的高阶涨落和高阶压缩.利用测量相位算符讨论了这些热化态中相位的高阶涨落.从而得到在有限温度下这些态的低阶及高阶涨落与温度的关系和压缩特性与温度的关系.由于实际的场态总是在一有限的温度下,所以讨论温度对涨落和压缩的影响是很有意义的.
关键词: 相似文献
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建立了自发噪声谱测量系统来研究稀磁半导体(Ga,Mn)As的电学噪声性质.通过测量(Ga,Mn)As材料的自发噪声谱,发现(Ga,Mn)As的自发涨落会随温度升高而逐渐增大,同时,外加磁场会降低(Ga,Mn)As的自发涨落,这来源于外加磁场导致的(Ga,Mn)As磁畴部分有序化.此外,不同频率的噪声随温度的变化规律有很大差异:当频率低于30 kHz的时候,噪声谱和温度的变化关系和热噪声很相似,但数值上明显大于热噪声的值;当频率在30 kHz左右的时候,噪声大小和温度成线性关系;当频率大于30 kHz以后,在相变点附近噪声大小和温度的关系出现了明显的转折,高频高温噪声的大小和热噪声的理论值非常接近.这些结果有助于深入理解(Ga,Mn)As磁性起源的物理机制.
关键词:
自旋电子学
稀磁半导体
自发涨落谱 相似文献
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利用热场动力学的方法研究了介观RLC电路在具有热噪声的真空态下电荷和磁通(电流)的量子涨落.从而得到了有限温度下这一电路在热真空态下的量子涨落与温度的关系.结果表明,介观RLC电路的量子涨落不仅与电路中的元件参量和电路的共振频率ω有关,而且与温度T有关.温度越高,介观RLC电路的量子噪声越大
关键词:
介观RLC电路
热真空态
量子涨落 相似文献
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A new stochastic averaging method for predicting the response of vibro-impact (VI) systems to random perturbations is proposed. First, the free VI system (without damping and random perturbation) is analyzed. The impact condition for the displacement is transformed to that for the system energy. Thus, the motion of the free VI systems is divided into periodic motion without impact and quasi-periodic motion with impact according to the level of system energy. The energy loss during each impact is found to be related to the restitution factor and the energy level before impact. Under the assumption of lightly damping and weakly random perturbation, the system energy is a slowly varying process and an averaged Itô stochastic differential equation for system energy can be derived. The drift and diffusion coefficients of the averaged Itô equation for system energy without impact are the functions of the damping and the random excitations, and those for system energy with impact are the functions of the damping, the random excitations and the impact energy loss. Finally, the averaged Fokker–Plank–Kolmogorov (FPK) equation associated with the averaged Itô equation is derived and solved to yield the stationary probability density of system energy. Numerical results for a nonlinear VI oscillator are obtained to illustrate the proposed stochastic averaging method. Monte-Carlo simulation (MCS) is also conducted to show that the proposed stochastic averaging method is quite effective. 相似文献
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We show that for a quasi 1-d metal the resistivity ? varies with temperature T as 1/sinh (? ω /kBT), ?ω being the energy of the (external) 2kF phonon involved in the scattering process. The theory fits the observed ? vs. T of (TMTSF)2PF6 and other quasi 1-d metals below 60K, where lattice expansion, internal mode scattering and precursor effects of the Peierls transition can be neglected. 相似文献
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Collective intraband charge-density excitations in the quasi-two-dimensional electron system of double GaAs/AlGaAs quantum wells in an external parallel magnetic field B∥ are studied by inelastic light scattering. It has been found that the energy of the excitations under study (acoustic and optical plasmons) exhibits anisotropy depending on the mutual orientation of B∥ and the excitation quasi-momentum k. It is shown theoretically that, in a strong parallel magnetic field, the effects associated with the finite width of the quantum wells dominate over the effects associated with interlayer tunneling and determine the anisotropy of plasmons. The experimental data are compared with a theoretical calculation. 相似文献
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采用随机级数展开的量子蒙特卡罗方法研究二维硬核的玻色-赫伯德模型的热力学性质. 首先通过算符变换将模型映射成为二维反铁磁准海森伯模型. 变换后的模型比通常的海森伯模型多一项, 该项正比于系统的格点总数 N, 对于大粒子数的系统, 该项使模拟耗时指数增加, 所以难以计算大粒子数系统.采用非局域操作循环更新后, 这个困难可以得到很好的解决, 可使粒子数总数增大到几千个.研究结果表明, 粒子数密度在0-0.5范围内增大时, 能量呈递减趋势, 并趋于某一定值, 随着正方晶格系统尺度增大, 能量也随之增大;正方晶格系统尺度一定时, 能量和磁化强度随着温度的升高而增大, 化学势的变化对能量和磁化强度没有影响, 能量随着正方晶格系统尺度增大而增大, 磁化强度却随之减小;正方晶格系统尺度一定时, 化学势的增大对比热没有影响, 随着温度的升高比热出现先增大后减小的趋势, 最后趋于某个值, 达到平衡, 而正方晶格系统尺度越大, 比热曲线增大部分的趋势越大, 减小部分的趋势也更明显, 参照朗道超流理论, 本文模拟的能量和比热曲线趋势与朗道二流体模型下He II的理论研究一致; 不同正方晶格系统尺度的影响不大, 均匀磁化率倒数在0-0.5(J/kB)的低温范围内有很小的波动, J为耦合能, kB为玻尔兹曼常数, 温度在0.5-2 (J/kB)的范围内, 均匀磁化率的倒数随着温度的升高而增大, 且曲线的趋势显示了一种类似近藤行为. 相似文献
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The zeroth-order theory of intermolecular forces is used to derive additivity relations for rotationally averaged molecular dipole properties and dispersion energy constants by assuming that a molecule is comprised of non-interacting atoms or molecules. Some of the additivity rules are new and others, for example the mixture rule for dipole oscillator strength distributions (DOSDs), Bragg's rule for stopping cross sections and Landolt's rule for molecular refractivities, are well known. The additivity rules are tested by using previously constructed DOSDs and reliable values for the dipole oscillator strength sums Sk , Lk and Ik , and dispersion energy constants C 6, for H, N, O, H2, N2, O2, NO, N2O, NH3 and H2O as models. It is found that additivity is generally unreliable for estimating molecular properties corresponding to k < -2. Generally for k ≥ -2 and for C 6, and if the hydrogen molecule is used to represent the hydrogen atom in the additivity rules, the additivity relations yield results that are reliable to within ?20 per cent and the estimates improve substantially as k increases. The effects of molecule formation on DOSDs is examined by comparing the various molecular DOSDs with the sum of the DOSDs for the atoms making up the molecules. Molecule formation results in a net decrease in the amount of dipole oscillator strength for low excitation energies and a compensating net increase for higher energies in a region extending from the absorption threshold to about 100 eV. This is shown to imply that estimates of the stopping average energy I 0, obtained by using bona fide atomic I 0 values, are lower bounds to the correct molecular I 0 results. 相似文献
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M. E. Manley 《哲学杂志》2013,93(21):2467-2473
Since phonons are built on the free energy of electrons, their frequencies can be altered by thermal electronic excitations, implying that thermal electronic excitations can alter the phonon entropy. The effect of this extra phonon entropy on electronic distribution functions and thermodynamic properties is calculated in the limit of classical vibrations. The phonon entropy stabilizes electrons above the Fermi level by more than the usual k B T. The thermodynamic coupling of electron and phonon degrees of freedom allows far more heat capacity than in equivalent independent systems. The method developed is used to explain uranium data from the literature. 相似文献
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Stability Analysis of an Inverted Pendulum Subjected to Combined High Frequency Harmonics and Stochastic Excitations
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Stability of vertical upright position of an inverted pendulum with its suspension point subjected to high frequency harmonics and stochastic excitations is investigated. Two classes of excitations, i.e., combined high frequency harmonic excitation and Gaussian white noise excitation, and high frequency bounded noise excitation, respectively, are considered. Firstly, the terms of high frequency harmonic excitations in the equation of motion of the system can be set equivalent to nonlinear stiffness terms by using the method of direct separation of motions. Then the stochastic averaging method of energy envelope is used to derive the averaged Ito stochastic differential equation for system energy. Finally, the stability with probability 1 of the system is studied by using the largest Lyapunov exponent obtained from the averaged Ito stochastic differential equation. The effects of system parameters on the stability of the system are discussed, and some examples are given to illustrate the efficiency of the proposed procedure. 相似文献
19.
V. A. Sadovnikova 《Bulletin of the Russian Academy of Sciences: Physics》2014,78(7):636-639
It is shown in the theory of finite Fermi systems that giant resonances can be considered as zero-sound excitations in concrete nuclei. Solutions to the zero-sound dispersion equation in symmetric nuclear matter, ωs(k), are obtained. Hydrodynamic models determine the wave vector k A corresponding to giant resonance in a nucleus with atomic number A. The real and imaginary parts of ωs(k A ) compare to the energy and escape width of giant resonance. Calculations are performed for giant dipole resonances. 相似文献
20.
Ulf Larsen 《Physics letters. A》1984,105(6):307-310
It is shown that in one-dimensional stochastic models with gaussian random energy levels along a quantum reaction coordinate the dominant, rate-determining time-scale does not follow the conventional Arrhenius law, but rather has a much stronger temperature dependence, of the form τ ~ exp[(B/kBT)2], where B is proportional to the width of the energy distribution. The new activation law can be ascribed to the large number of energy barriers of varying heights which exist in the random structure, as distinct from the conventional case of a single barrier, leading to the Arrhenius form τ ~ Tp × exp(A/kBT). In systems with random structure and configuration space which are not strictly one-dimensional it is discussed if the thermal energy bias of detailed balance may lead to a kinetics that is essentially restricted to an energetically optimal network at low temperatures, thus leading to an essentially one-dimensional diffusion. Several recent studies of spin glass models appear to support the relevance of this principle, and include the observation of the new activation law in Monte Carlo experiments. 相似文献