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111.
We compare the transport properties of electrons in monolayer graphene by modulating the Fermi velocity inside the barrier. A critical transmission angle is found only when the Fermi velocity in the barriers is larger than the one outside the barriers. It is shown that the transmission exhibits periodicity with the incident angle below the critical transmission angle, and attenuates exponentially in the opposite situation. For both situations, peak splitting occurs in the transmission as the number of the velocity barriers increases, and the characteristics of the transmission suggest an interesting application of an excellent band-pass filter. The dependence of the conductance on the Fermi energy through an identical velocity- modulation structure differs wildly with different Fermi velocities of the barrier. The counterpart of the peak splitting is the sharp oscillations in the conductance profile. Furthermore, some oscillations for the multiple barriers are so sharp that the structure may be used as an excellent sensor.  相似文献   
112.
Linear and nonlinear ion acoustic waves in the presence of adiabatically heated ions in magnetized electron-positron-ion plasmas are studied. The Sagdeev potential approach is employed to obtain the energy integral equation in such a mulitcomponent plasma using fluid theory. It is found that electron density humps are formed in the subsonic region in magnetized electron-positron-ion plasmas. The amplitude of electron density hump is decreased with the increase of hot ion temperature in electron-positron-ion plasmas. However, the increase in positron concentration and obliqueness of the wave increases the amplitude of nonlinear structure. The increase in positron concentration also reduces the width of the nonlinear structure in a magnetized multicomponent plasma. The numerical solutions in the form of solitary pulses are also presented for different plasma cases. The results may be applicable to astrophysical plasma situations, where magnetized electron-positron-ion plasma with hot ions can exist.  相似文献   
113.
A.K. Nchange  P. Woafo 《Physica A》2008,387(11):2519-2525
In this paper, we investigate the spatiotemporal dynamics of a bidirectional coupled chain of cells, in which a cell is subjected to an external noise. Noisy oscillations of calcium (Ca2+), that is, a bursting-like phenomenon induced by noise with fluctuations in the baseline values of calcium, are induced in the first cell and propagated along the chain with noise suppression. This phenomenon of noise suppression is further investigated by computing the normalized fluctuation of pulse durations. It is therefore found that the noise induced coherence resonance phenomenon occurs at the cellular level. Coherence biresonance behaviour appears in the transmission of noise induced oscillations at appropriate noise intensity or noise coupling (for low noise intensity) and the information flow in each cell can be simultaneously optimized at the optimal value of noise or coupling.  相似文献   
114.
通过研究发现,内噪声对细胞内钙振荡是有影响的,当体系处于由确定性方程所确定的稳定区域时,如果考虑内噪声的作用,就会有随机的钙振荡发生. 并且这种振荡的行为随着体系尺度的变化出现两个最大值,表明了尺度共振现象的发生. 这种行为是与体系的Canard现象密切相关的. 最佳的体系尺度与真实的细胞体积是相吻合的,并且这种吻合基本不随控制参数的改变而改变.  相似文献   
115.
ABSTRACT

The article deals with the study of plane wave propagation in the thermoelastic medium in the presence of voids. The problem is considered in the context of three-phase-lag model of generalized thermoelasticity. There exists three longitudinal waves, namely elastic (E-mode), thermal (T-mode) and volume fraction (V-mode) in addition to transverse waves which get decoupled from the rest of motion and not affected by thermal and volume fraction fields. The fundamental solution of the system of differential equations in case of steady oscillations in terms of the elementary functions has been constructed. The phase velocity and attenuation coefficient of these waves are computed numerically and presented graphically.  相似文献   
116.
Coupled shape oscillations and translational motion of an incompressible gas bubble in a vibrating liquid container is studied numerically. The bubble oscillation characteristics are mapped based on the bubble Bond number (Bo) and the ratio of the vibration amplitude of the container to the bubble diameter (A/D). At small Bo and A/D, the bubble oscillation is found to be linear with small amplitudes, and at large Bo and A/D, it is nonlinear and chaotic. This chaotic bubble oscillation is similar to those observed in two coupled nonlinear systems, here being the gas inside the bubble and its surrounding liquid. Further increases in the forcing, results in the bubble breakup due to large liquid inertia.  相似文献   
117.
Due to the unique magnetic, mechanical and thermal properties, magnetic nanoparticles(MNPs) have comprehensive applications as the contrast and therapeutic agents in biomedical imaging and magnetic hyperthermia. The linear and nonlinear magnetoacoustic responses determined by the magnetic properties of MNPs have attracted more and more attention in biomedical engineering. By considering the relaxation time of MNPs, we derive the formulae of second harmonic magnetoacoustic responses(2H-MARs) for a cylindrical MNP solution model based on the mechanical oscillations of MNPs in magnetoacoustic tomography with magnetic induction(MAT-MI). It is proved that only the second harmonic magnetoacoustic oscillations can be generated by MNPs under an alternating magnetic excitation. The acoustic pressure of the 2H-MAR is proportional to the square of the magnetic field intensity and exhibits a linear increase with the concentration of MNPs. Numerical simulations of the 2H-MAR are confirmed by the experimental measurements for various magnetic field intensities and solution concentrations using a laser vibrometer. The favorable results demonstrate the feasibility of the harmonic measurements without the fundamental interference of the electromagnetic excitation, and suggest a new harmonic imaging strategy of MAT-MI for MNPs with enhanced spatial resolution and improved signal-to-noise ratio in biomedical applications.  相似文献   
118.
Predicting the onset of non-spherical oscillations of bubbles in soft matter is a fundamental cavitation problem with implications to sonoprocessing, polymeric materials synthesis, and biomedical ultrasound applications. The shape stability of a bubble in a Kelvin-Voigt viscoelastic medium with nonlinear elasticity, the simplest constitutive model for soft solids, is analytically investigated and compared to experiments. Using perturbation methods, we develop a model reducing the equations of motion to two sets of evolution equations: a Rayleigh-Plesset-type equation for the mean (volume-equivalent) bubble radius and an equation for the non-spherical mode amplitudes. Parametric instability is predicted by examining the natural frequency and the Mathieu equation for the non-spherical modes, which are obtained from our model. Our theoretical results show good agreement with published experiments of the shape oscillations of a bubble in a gelatin gel. We further examine the impact of viscoelasticity on the time evolution of non-spherical mode amplitudes. In particular, we find that viscosity increases the damping rate, thus suppressing the shape instability, while shear modulus increases the natural frequency, which changes the unstable mode. We also explain the contributions of rotational and irrotational fields to the viscoelastic stresses in the surroundings and at the bubble surface, as these contributions affect the damping rate and the unstable mode. Our analysis on the role of viscoelasticity is potentially useful to measure viscoelastic properties of soft materials by experimentally observing the shape oscillations of a bubble.  相似文献   
119.
120.
蔡泽民  毕勤胜 《力学季刊》2019,40(3):478-487
当周期激励频率远小于系统固有频率时,会存在快慢耦合效应,与单项激励不同,参外联合激励不仅会导致快子系统平衡曲线和分岔行为的复杂化,也会产生一些特殊的非线性现象,为此,本文以两耦合Hodgkin-Huxley细胞模型为例,引入周期参外联合激励,探讨在频域不同尺度耦合时该系统的簇发振荡的特点及其分岔机制.通过建立相应的快慢子系统,得到慢变参数变化下的快子系统的各种分岔模式以及相应的分岔行为,结合转换相图,揭示耦合系统随激励幅值变化时的动力学行为及其机理.研究表明,在激励幅值较小时,系统表现为概周期振荡,两频率分别近似于快子系统平衡曲线由Hopf分岔引起的两稳定极限环的振荡频率.概周期解随激励幅值的增加进入簇发振荡,导致这些簇发振荡的主要原因是在慢变参数变化的部分区间内,存在唯一稳定的平衡曲线,使得系统的轨迹逐渐趋向该平衡曲线,产生沉寂态,并随着慢变参数的变化,由分岔进入激发态.同时,快子系统中参与簇发振荡的稳定吸引子随激励幅值的变化也会不同,导致不同形式的簇发振荡.另外,与单项激励下的情形不同,联合激励时快子系统的部分稳定吸引子掩埋在其它稳定吸引子内,从而失去对簇发振荡的影响.  相似文献   
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