We analyze the dynamics of a two-dimensional system constituted by two masses subjected to elastic, gravitational and viscous forces and constrained by a moving frictional mono-lateral surface. The model exhibits a time-varying dynamics capable of reproducing the hopping phenomenon, an unwanted phenomenon observed in many applications such as the motion of a robotic arm on a surface or that of a wiper on a windscreen. The system dynamics, besides being affected by geometrical non-linearities, has a non-smooth nature due to the impact and friction laws involved in the model. The complexity of the resulting equations and of the transition conditions require the problem to be solved numerically. Various periodic motions are found and the effect of varying the system parameters, in particular the friction coefficient, is investigated. Finally, simulations are used to gain some insight the behavior of the windscreen wiper. 相似文献
The superior capability of wavefront manipulation makes metasurfaces a promising platform for implementing high-density information storage and multifold optical encryption. Although some metasurfaces have realized information encryption, it is still challenging to implement polarization-encrypted grayscale images in both linear and nonlinear channels. Here, a novel approach to realize multichannel linear and nonlinear information encryptions is proposed based on nonlinear Malus metasurfaces composed of single-sized meta-atoms, in which the polarization states of the linear and nonlinear signals can be decoupled. As a proof of concept, two distinct grayscale images with different polarizations have been encrypted in the fundamental and second harmonic wave channels simultaneously. Besides, by further introducing the nonlinear Pancharatnam-Berry phase, a tri-channel polarization encrypted metasurface with a multi-level grayscale image in the near field and two holographic images in the far field has been experimentally demonstrated at the second harmonic frequency. This work provides more degrees of freedom for multichannel information storage and opens an avenue for optical information encryption in both linear and nonlinear regimes. 相似文献
We study some properties of the SU(1, 1) Perelomov number coherent states. The Schrödinger's uncertainty relationship is evaluated for a position and momentum-like operators (constructed from the Lie algebra generators) in these number coherent states. It is shown that this relationship is minimized for the standard coherent states. We obtain the time evolution of the number coherent states by supposing that the Hamiltonian is proportional to the third generator K0 of the su(1, 1) Lie algebra. Analogous results for the SU(2) Perelomov number coherent states are found. As examples, we compute the Perelomov coherent states for the pseudoharmonic oscillator and the two-dimensional isotropic harmonic oscillator. 相似文献
Due to high reflectivity and high resolution of X-ray pulses, diamond is one of the most popular Bragg crystals serving as the reflecting mirror and mono-chromator in the next generation of free electron lasers(FELs).The energy deposition of X-rays will result in thermal heating, and thus lattice expansion of the diamond crystal,which may degrade the performance of X-ray FELs. In this paper, the thermal loading effect of diamond crystal for X-ray FEL oscillators has been systematically studied by combined simulation with Geant4 and ANSYS, and its dependence on the environmental temperature, crystal size, X-ray pulse repetition rate and pulse energy are presented. Our results show that taking the thermal loading effects into account, X-ray FEL oscillators are still robust and promising with an optimized design. 相似文献
Rectangular arrays of pyramidal recesses coated by silver film are investigated by means of polarization‐resolved nonlinear microscopy at 900 nm fundamental wavelength, demonstrating strong dependence of the dipole‐allowed SHG upon the lattice parameters. The plasmonic band gap causes nearly complete SHG suppression in arrays of 650 nm periodicity, whereas a sharp resonance at 550 nm periodicity is observed due to excitation of band edge Bloch states at fundamental frequency, accompanied by symmetry‐constrained interactions with similar modes at the second‐harmonic frequency. Additionally, coupling with modes at the bottom side of the silver film may lead to extraordinary optical transmission, opening a channel for SHG from the highly nonlinear GaAs substrate. Changing the lattice geometry enables SHG intensity modulation over three orders of magnitude, while the effective nonlinear anisotropy can be continuously switched between the two lattice directions, reaching values as high as ±0.96.
In this paper, we present order invariance theoretical results for weighted quasi-arithmetic means of a monotonic series of numbers. The quasi-arithmetic mean, or Kolmogorov–Nagumo mean, generalizes the classical mean and appears in many disciplines, from information theory to physics, from economics to traffic flow. Stochastic orders are defined on weights (or equivalently, discrete probability distributions). They were introduced to study risk in economics and decision theory, and recently have found utility in Monte Carlo techniques and in image processing. We show in this paper that, if two distributions of weights are ordered under first stochastic order, then for any monotonic series of numbers their weighted quasi-arithmetic means share the same order. This means for instance that arithmetic and harmonic mean for two different distributions of weights always have to be aligned if the weights are stochastically ordered, this is, either both means increase or both decrease. We explore the invariance properties when convex (concave) functions define both the quasi-arithmetic mean and the series of numbers, we show its relationship with increasing concave order and increasing convex order, and we observe the important role played by a new defined mirror property of stochastic orders. We also give some applications to entropy and cross-entropy and present an example of multiple importance sampling Monte Carlo technique that illustrates the usefulness and transversality of our approach. Invariance theorems are useful when a system is represented by a set of quasi-arithmetic means and we want to change the distribution of weights so that all means evolve in the same direction. 相似文献
