驱动马达定向运动的随机动力学模型

本文在非对称周期势中考虑驱动马达的机械化学耦合,基于布朗马达的工作原理,利用MATLAB数值模拟驱动马达在一定实验条件下的运动特征.我们首先模拟了单个驱动马达的位移和速度随时间变化的图像,然后分别计算了多个驱动马达运动的平均速度,最后计算了不同负载力条件下马达运动速度的系综平均值.模拟结果表明驱动马达在定向运动中存在等待态和行走态,行走步长约为8.2nm,且马达运动具有一定的随机性.通过与实验比较,发现模型计算结果与实验吻合.     

Changes in the Effective Parameters of Averaged Motion in Nonlinear Systems Subject to Noise

We discuss how the effective parameters characterising averaged motion in nonlinear systems are affected by noise (random fluctuations). In this approach to stochastic dynamics, the stochastic system is replaced by its deterministic equivalent but with noise-dependent parameters. We show that it can help to resolve certain paradoxes and that it has a utility extending far beyond its usual application in passing from the microscopic equations of motion to the macroscopic ones. As illustrative examples, we consider the diode-capacitor circuit, a Brownian ratchet, and a generic stochastic resonance system. In the latter two cases we calculate for the first time their effective parameters of averaged motion as functions of noise intensity. We speculate that many other stochastic problems can be treated in a similar way. PACS: 05.10.Gg, 05.40.-a, 05.40.Jc     

Will Small Particles Exhibit Brownian Motion in the Quantum Vacuum?

The Brownian motion of small particles interacting with a field at a finite temperature is a well-known and well-understood phenomenon. At zero temperature, even though the thermal fluctuations are absent, quantum fields still possess vacuum fluctuations. It is then interesting to ask whether a small particle that is interacting with a quantum field will exhibit Brownian motion when the quantum field is assumed to be in the vacuum state. In this paper, we study the cases of a small charge and an imperfect mirror interacting with a quantum scalar field in (1 + 1) dimensions. Treating the quantum field as a classical stochastic variable, we write down a Langevin equation for the particles. We show that the results we obtain from such an approach agree with the results obtained from the fluctuation-dissipation theorem. Unlike the finite temperature case, there exists no special frame of reference at zero temperature and hence it is essential that the particles do not break Lorentz invariance. We find that that the scalar charge breaks Lorentz invariance, whereas the imperfect mirror does not. We conclude that small particles such as the imperfect mirror will exhibit Brownian motion even in the quantum vacuum, but this effect can be so small that it may prove to be difficult to observe it experimentally.     

Expansion of the Glauber equation of motion in terms of cumulants powers

We present an expansion of the Glauber equation of motion in terms of cumulants of the effective fields. We show that we recover a part of the fluctuations with a simple third order expansion. We illustrate the method with an application to the 2D square lattice Ising model with nearest neighbors. For the special case of perturbed non gaussian effective fields, we show that only the first cumulants are significative. Furthermore it can be shown that the resulting distribution is closer to the normal distribution than the unperturbed fields one. It leads to the conclusion that we can consistently truncate the expansion of the exact Glauber equation of motion.     

Describing intrinsic noise in Chua's circuit

In this Letter we demonstrate that intrinsic inevitable noise effects, existing in realistic experiments with electronic circuits, are properly described theoretically using a Gaussian noise. For this we integrate numerically the equations of motion from the Chua circuit using a fourth-order stochastic Runge–Kutta integrator. Periodic structures in parameter space, related to periodic motion, start to be destroyed when the noise intensity is increased and vanish at a critical intensity value, for which only chaotic motion remains. We find the appropriate noise intensity interval which satisfactorily reproduces the parameter space from the corresponding experiment and it is in remarkable agreement with the estimated experimental noise. Present achievements should be applicable to describe noise effects in a wide number of electronic circuits.     

Interior symmetries of hadrons:SO(3,2) as a spectrum-generating group

In this work, we study some applications of the spectrum-generating group (SGG) formalism to obtain the mass-spin spectra of hadrons. The possibility of classifying (medium-energy) hadrons in terms of a symmetry group defining the center-of-mass motion and an SGG defining the interior motion is discussed. After considering the defining commutation relations and equations of motion of the generators of the SGG, it is shown how the hadronic spectral information is obtained through a Hamiltonian that is a constraint relation between the generators of the symmetry group and those of the SGG.     

When can a classical electron accelerate without radiating?

A classical point electron radiates when it accelerates. However, there are classical electron models with extended charge distributions which can accelerate and/or deform without radiating. Can a model be contrived that will undergo radiationless motion while accelerating (on the average) over a distance large compared to its size? The answer is no: we prove that the “center” of the electron is always closer than the electron “diameter” to a fictitious point undergoing constant-velocity motion, if the electron's motion is radiationless.     

Creep motion in a granular pile exhibiting steady surface flow

We investigate experimentally granular piles exhibiting steady surface flow. Below the surface flow, it has been believed that a "frozen" bulk region exists, but our results show no such frozen bulk. We report here that even the particles in layers deep in the bulk exhibit very slow flow and that such motion can be detected at an arbitrary depth. The mean velocity of the creep motion decays exponentially with depth, and the characteristic decay length is approximately equal to the particle size and is independent of the flow rate. It is expected that the creep motion we have seen is observable in all sheared granular systems.     

Asymmetry in colloidal diffusion near a rigid wall

The three-dimensional motion of single colloidal particles close to a plane wall is measured by optical microscopy. In accordance with classical theoretical predictions, we find an asymmetric motion of the particles in the directions parallel and perpendicular to the wall. We also find that, close to the wall, the distribution functions of perpendicular steps are asymmetric, being shorter toward the wall and longer away from it.     

空间相机调焦机构运动同步性误差分析

研究了空间相机调焦机构的运动同步性误差对成像质量的影响。针对某型空间相机的大尺寸焦面调焦机构,分析了运动同步性误差产生的原因。按照其光学系统参数计算得出当系统光学传递函数下降不超过5％时,调焦机构运动同步性误差的最大允许值为0.02 mm。针对其采用的调焦机构,推导出运动同步性误差计算公式,并计算得到该调焦机构的最大运动同步性误差为0.015 mm。最后,对该调焦机构进行了实际测试。测试结果显示,该调焦机构的运动同步性误差在振动实验前后分别为0.012和0.013 mm,表明该机构的运行非常稳定。理论分析以及实验结果证明了该调焦机构完全满足应用要求。     

Influence of dark energy on time-like geodesic motion in Schwarzschild spacetime

In this paper we investigate the influence of the dark energy on the time-like geodesic motion of a particle in Schwarzschild spacetime by analysing the behaviour of the effective potential which appears in an equation of motion. For the non-radial time-like geodesics, we find a bound orbit when the particle energy is in an appropriate range, and also find another possible orbit, which is that the particle drops straightly into the singularity of a black hole or escapes to infinity. For the radial time-like geodesics, we find an unstable circular orbit when the particle energy is the critical value, in which case it is possible for the particle to escape to infinity.     

Tunnel effect in the motion of deformable wavelets

In a previous paper it was shown that the tunnel effect does not occur in the motion of an undeformable wavelet which we obtained by solving the Schrödinger equation and interpreted as representing a single particle. In the present supplementary paper we solve the same Schrödinger equation while modifying one of the restrictive conditions assumed previously, and obtain wavelets which deform in force fields. Tunnel effects are seen in the motion of these deformable wavelets. An apparent inaccuracy pointed out mathematically in these solutions is shown to be insignificant under conditions which are feasible in the physical sense.     

Dislocations in two-dimensional liquid foams

In this analysis we make the analogy between the dislocations in metals and the behaviour of 2D liquid foams in the presence of external forces. It is shown that the edge defect which appears in metals can also be introduced in a similar manner in 2D liquid foams and that the motion of this defect through the foam can occur by the process of T1 transformations. The analogy leads to the motion of local cells as opposed to the motion of a row of cells. That is, the T1 process occurs ‘locally’ and the ‘defect’, primarily introduced here as an edge dislocation, can move through the whole 2D liquid foam through the local motion of these edge dislocations. These defects as in the theory of metals lead to the reduction of the critical stress required for the ‘slipping’ of the 2D liquid foam. Furthermore, since it is these defects which are responsible for the behaviour of the 2D liquid foam to external forces and since it will be the motion of these defects which is related to the motion of the cells, it is possible, again through the analogy with ‘slipping’ in metals to determine the strain rate. The result is given as strain rate = ϱ b 〈V〉.     

Active Brownian motion tunable by light

Active Brownian particles are capable of taking up energy from their environment and converting it into directed motion; examples range from chemotactic cells and bacteria to artificial micro-swimmers. We have recently demonstrated that Janus particles, i.e.?gold-capped colloidal spheres, suspended in a critical binary liquid mixture perform active Brownian motion when illuminated by light. In this paper, we investigate in more detail their swimming mechanism, leading to active Brownian motion. We show that the illumination-borne heating induces a local asymmetric demixing of the binary mixture, generating a spatial chemical concentration gradient which is responsible for the particle's self-diffusiophoretic motion. We study this effect as a function of the functionalization of the gold cap, the particle size and the illumination intensity: the functionalization determines what component of the binary mixture is preferentially adsorbed at the cap and the swimming direction (towards or away from the cap); the particle size determines the rotational diffusion and, therefore, the random reorientation of the particle; and the intensity tunes the strength of the heating and, therefore, of the motion. Finally, we harness this dependence of the swimming strength on the illumination intensity to investigate the behavior of a micro-swimmer in a spatial light gradient, where its swimming properties are space-dependent.     

Particle Motion and Perturbed Dynamical System in Warped Product Spacetimes

In this paper we have used the dynamical systems analysis to study the dynamics of a five-dimensional universe in the form of a warped product spacetime with a spacelike dynamic extra dimension. We have decomposed the geodesic equations to get the motion along the extra dimension and have studied the associated dynamical system when the cross-diagonal element of the Einstein tensor vanishes, and also when it is non-vanishing. Introducing the concept of an energy function along the phase path in terms of the extra-dimensional coordinate, we have examined how the energy function depends on the warp factor. The energy function serves as a measure of the amount of perturbation of geodesic paths along the extra dimension in the region close to the brane. Then we studied the geodesic motion under a conventional metric perturbation in the form of homothetic motion and conformal motion and examined the nature of critical points for a Mashhoon-Wesson-type metric, for timelike and null geodesics when the cross-diagonal term of the Einstein tensor vanishes. Finally we investigated the motion for null and timelike geodesics under the condition when the cross-diagonal element of the Einstein tensor is non-vanishing and examined the effects of perturbation on the critical points of the dynamical system.     

The flyby anomaly and the effect of a topological torsion current

A new variational technique determines the general condition of equilibrium of a rotating gravitational or electromagnetic system (or both) and provides a modified dynamical equation of motion from where it emerges a so-far unforseen topological torsion current (TTC) (Pinheiro, 2013) [63]. We suggest that the TTC may explain, in a simple and direct way, the anomalous acceleration detected in spacecrafts during close planetary flybys. In addition, we theorize that TTC may represent a novel relationship between linear momentum and angular motion through the agency of a vector potential.     

基于Harris角点全局运动估计的场景锁定算法

场景锁定技术是视频跟踪领域的一个关键技术,需要对图像的全局运动进行估计,常用的运动估计算法由于计算量大、对噪声敏感等因素很难得到实际应用。为了减少运动估计的计算量,提高全局运动估计的精度,提出了一种基于Harris角点全局运动估计的场景锁定方法。将图像分成4×4的16个块,选取每个块中响应值最大的角点,以参考图像角点周围矩形块与待匹配图像进行匹配,然后利用RANSAC算法对角点进行一致性检测,利用最小二乘法解算全局运动参数,最后计算图像之间的累积运动。实验结果表明,该算法运动估计精度高,稳定性好,能较好地实现场景锁定。     

刚体一般运动的描述

刚体的一般运动是刚体运动学中最复杂的一类运动,其求解通常需要借助欧拉定理或沙勒定理.通过这两个定理,我们可以把刚体的一般运动分解成较简单的定轴转动和平动.本文主要应用代数理论中的正交矩阵描述刚体的运动,并用代数语言分析了定点转动的本征问题,证明了欧拉定理.随后,将刚体的定点转动进行分解,并给出了物理图像和推导结论,完成...