Image Dipole Model Research Articles

Symmetry-tailored patterns and polarizations of single-photon emission

Abstract Due to small optical mode volumes and linear polarizations of surface-plasmon-polariton (SPP) resonant modes in metallic antennas, it is very difficult to obtain complex emission patterns and polarizations for single-photon emitters. Herein, nonresonant enhancement in a silver nanowire is used to both enhance emission rates and extract a z-oriented dipole, and then the symmetry of metallic nanostructures is proposed to tailor the patterns and polarizations of single-photon emission. The emission pattern of a quantum dot located close to a metallic nanostructure with a symmetric axis is split into multiple flaps. The number of splitting flaps is equal to the order of the symmetric axis. Moreover, the electric vectors of the emitted photons become centrally symmetric about the symmetric axis. The above phenomena are well explained by both a simulation and an image dipole model. The structural-symmetry-tailoring mechanism may open up a new avenue in the design of multifunctional and novel quantum-plasmonic devices.

Controllability of Flux-Pinned Docking Interface

The flux-pinned docking interface (FPDI) is composed of an YBCO high-temperature superconductor bulk and an electromagnet (EM). They are installed on the spherical target spacecraft module and another spherical tracking spacecraft module, respectively. This novel docking interface can enable the active control of the docking process to become an additional option rather than a necessary option. The vertical force between two flux-pinned spacecraft modules (FPSMs) can be analytically calculated based on the improved image dipole model. The controllability of the FPDI is achieved through varying current flowing through the EM. Two FPSMs can be linked or detached by changing the direction of current. The distinct equilibrium connection state of two FPSMs can be transformed by changing the current intensity. The orbital dynamic docking equation of two FPSMs is established based on Clohessy–Wiltshire's equation. The numerical calculation based on the Runge–Kutta algorithm can calculate the derived dynamic docking equation. The simulated consequence shows that proportional-derivative active feedback control applied to this docking interface can effectively suppress the vibration amplitude and significantly shorten the settling time, which suggests that this potential novel docking interface can be readily controlled.

Connection stiffness and dynamical docking process of flux pinned spacecraft modules

This paper describes a novel kind of potential flux pinned docking system that consists of guidance navigation and control system, the traditional extrusion type propulsion system, and a flux pinned docking interface. Because of characteristics of passive stability of flux pinning, the docking control strategy of flux pinned docking system only needs a series of sequential control rather than necessary active feedback control, as well as avoidance of hazardous collision accident. The flux pinned force between YBaCuO (YBCO) high temperature superconductor bulk and permanent magnet is able to be given vent based on the identical current loop model and improved image dipole model, which can be validated experimentally. Thus, the connection stiffness between two flux pinned spacecraft modules can be calculated based on Hooke's law. This connection stiffness matrix at the equilibrium position has the positive definite performance, which can validate the passively stable connection of two flux pinned spacecraft modules theoretically. Furthermore, the relative orbital dynamical equation of two flux pinned spacecraft modules can be established based on Clohessy-Wiltshire's equations and improved image dipole model. The dynamical docking process between two flux pinned spacecraft modules can be obtained by way of numerical simulation, which suggests the feasibility of flux pinned docking system.

Lateral Force and Lateral Connection Stiffness of Flux Pinned Docking Interface

Another novel flux pinned docking interface consisting of an YBCO high temperature superconductor bulk and two electromagnets is designed in order to improve the connection stiffness of this docking interface and the detailed control strategy of the docking process is introduced. Using this novel docking interface, two spacecraft modules appear with a noncontacting connection status through intervehicle interaction, but with the characteristics of passive stability. The identical current loop model is proposed based on the Ampere current loop hypothesis to treat the magnetic field of the cylindrical permanent magnet that may be installed in the flux pinned docking interface, and the improved image dipole model is adopted with the intention of analyzing the flux pinned lateral force of the novel docking interface theoretically. Additionally, the experiment data of the flux pinned lateral force between a YBCO high temperature superconductor bulk and a cylindrical NdFeB permanent magnet is collected. The theoretical calculation and experimental data both show an initial decrease then increase with the increase of lateral displacement. Moreover, the theoretical analysis compared to the corresponding experimental data indicates that the improved image dipole model is an effective approach. Furthermore, the flux pinned lateral connection stiffness is obtained based on Hooke’s law, showing that this stiffness initially decreases then increases as the lateral displacement that is larger than zero increases.

Study on Flux Pinned Vertical Force between High-Temperature Superconductor and Permanent Magnet

The flux pinned force attracts our eyes, where the levitating system is widely investigated for the transportable application. Although plenty of experiments can lead to many significant consequences, the mechanism has been not understood completely since the enormously complicated behavior and quantum effect involve. In this paper, in order to calculate the flux pinned force analytically, the image-dipole model is adopted and improved and the simple and precise expression of magnetic strength is utilized, so the flux pinned vertical force can be calculated in analytical form. In addition, the experimental data in case of zero field-cooling and field-cooling experiment can be collected in our experimental table and the comparison is completed between the precise and simple formula and the experimental data, the precise version of expression fro flux pinned vertical force can correspond to the experimental data well.

Study on Flux-Pinned Interaction between High-Temperature Superconductor and Permanent Magnet and Flux-Pinning’s Self-Stability

Flux pinned effect (FPE) takes place in high-temperature superconductors (HTSC) when being cooled below critical temperature in magnetic field and appears the self-stable with resisting the disturbing and recovering the initial equilibrium position , even in the failure of control, which is ideal for the activities of spacecraft. In order to investigate the special phenomenon, the image-dipole model (IDM) for interaction and spring-damper model (SDM) for system are adopted in this paper. IDM are based on two assumed images and SDM linked with flux-pinned interface is based on virtual spring and damper. Two models effectively deal with the flux-pinning and give some clear expressions. When moving along single orient, this paper demonstrates the pairs’ self-stability based on two models.

Electromagnetic ion cyclotron waves stimulated by modest magnetospheric compressions

The relationship between sudden impulses and enhancements or onset of Pc 1 at high‐latitude ground stations is well established. It has been proposed that increased hot proton temperature anisotropy resulting from convection during magnetospheric compression is responsible for the enhancement in Pc 1 emissions via generation of electromagnetic ion cyclotron (EMIC) waves in the dayside outer equatorial magnetosphere (e.g., Olson and Lee, 1983). We use AMPTE/CCE magnetic field and particle data to test this suggestion. Compression‐induced Pc 1 events are very common in the AMPTE/CCE data set: among isolated sudden (<5 min) magnetic field increases of 10 nT or greater in the 8‐16 MLT/L > 6 region, 47% are associated with EMIC wave onset at the satellite. Compressions energize particles via earthward convection, so the association of local Pc 1 onsets with compressions may be either a temporal effect or merely the result of inward transport to the spacecraft of plasma previously unstable to EMIC waves. EMIC waves occur 10‐20% of the time in the outer magnetosphere, which is considerably less than the occurrence rate of Pc 1 with compressions, suggesting that convection alone does not account for compression Pc 1 onset. To test whether the plasma is more unstable to EMIC waves after compressions than before, the proton distribution (1‐300 keV) measured at the peak of the compression is used together with an image dipole model to calculate the distribution that would result from adiabatic expansion back to the precompression state. Comparison of the EMIC wave growth rates from the measured compression and extrapolated expansion distributions provide an indication of the compression‐induced enhancement of EMIC wave activity. Differences in wave growth of several orders of magnitude are found, indicating significant increases in EMIC wave activity. The results suggest that enhancements in dynamic pressure pump the energetic proton distributions in the outer magnetosphere, driving EMIC waves. Waves are expected to be generated most readily close to the magnetopause, and transient pressure pulses may be associated with bursts of EMIC waves, which would be observed on the ground in association with ionospheric transient signatures.

Molecule Adsorbed on Metal Surface–Role of Electron-Hole Excitation in Metal–

Fano's treatment for the interaction between a discrete level and a continuum state is used to calculate the eigenstates of molecules adsorbed on a metal surface, where both surface plasmon and electron-hole pair excitations due to the Coulomb field of the molecular dipole are taken into account. Spectral density of states of adsorbed molecules shows more broadened structure than that calculated by a simple image dipole model. The role of electron-hole excitations on the Raman scattering of adsorbed molecules is then investigated.

Surface enhanced Raman spectra: A critical review of the image dipole description

Recent experiments have demonstrated enhancements of several orders of magnitude for Raman scattering of pyridine and other molecules adsorbed on a silver surface. One explanation which has been proposed is an image dipole model, in which a point dipole is mirrored in the metal, with the mirror image inducing an additional dipole in the adsorbed species and thus changing its effective polarizability αeff. In this paper we suggest that the large enhancements obtained from such a point dipole description result from the use of an symptotic theory at unphysically short distances. We demonstrate this through a model calculation of αeff of a hydrogen atom near a mirror surface. A point dipole approximation gives a divergent αeff near a critical distance Rc from the surface, while a more exact self-consistent Hartree calculation (including the finite extent of the hydrogen charge cloud) gives only a slight enhancement or even a de-enhancement near Rc.

Mathematical models of the open magnetosphere: Application to dayside auroras

Two static mathematical models of the open or Dungey model of the magnetosphere are constructed. The process of construction is similar to that for early closed magnetosphere models, such as the Taylor-Hones model. The first model in fact is simply an addition of an interplanetary field in arbitrary direction to a Taylor-Hones image dipole model. In order to preserve the shape of the magnetosphere at high latitudes, and to partially exclude the exterior field, another model is constructed with the magnetopause approximated by a diamagnetic sphere. We find that there are some interplanetary field lines connected to the earth for all orientations of the interplanetary field other than strictly northward, and that the maximum number of connected field lines occurs with a due southward field. For an average spiral hose angle of the interplanetary field, the dayside neutral point occurs on the magnetopause at about 10 o'clock local time. Dayside auroras, convection patterns, and other phenomena may exhibit symmetry about this local time. For a positive (negative) interplanetary field sector, energetic, anisotropic particle fluxes should have direct access to the northern (southern) polar caps, as is supported by many recent observations.

Sudden impulses in the magnetosphere observed by Explorer 12

Explorer 12 magnetic data show that a positive sudden impulse on the ground is accompanied by an increase in the field strength everywhere within the magnetosphere. Similarly, a negative sudden impulse on the ground is associated with a decrease in the field strength in the magnetosphere. Evidence is also found that the magnetospheric boundary moves outward at the time of a negative sudden impulse. The rise, and fall, time of a sudden impulse is the same everywhere in the magnetosphere (including that portion close to the boundary) and on the ground. Hence this time can be interpreted as the time in which the compression or the expansion of the magnetosphere takes place. The speed of propagation of the field variations through the magnetosphere seems to be close to the hydromagnetic wave speed. The magnitude of a sudden impulse at the satellite level relative to that on the ground is better explained by a magnetospheric model with a curved boundary than by an image dipole model.