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By identifying the model of a relativistic spin-half neutral particle which possesses magnetic and electric dipole moments interacting with an electromagnetic field as the [Formula: see text] gauge theory, we study the Anandan phase in [Formula: see text]-dimensional noncommutative space–time by applying the Seiberg–Witten map. We find that up to the first order of the noncommutative parameter, Anandan phase does not receive any corrections due to the spatial noncommutativity. Our result also indicates that phases of either Aharonov–Casher or He–Mckellar–Wilkens effects can receive corrections due to spatial noncommutativity.

We revisit time-independent and time-dependent Aharonov-Bohm effects in the noncommutative space-time by investigating a relativistic spin-half particle in the background of a long-thin magnetic-flux-carried solenoid. Our results show that, up to the first order of the noncommutative parameter, there are no noncommutative corrections on the AB effects for both cases.

Based on the supersymmetry structures, we propose to solve the model of a charged Dirac oscillator interacting with a uniform perpendicular magnetic field on both commutative and noncommutative planes in a unified way by employing unitary transformations. The unitary operators are constructed out of the generators of the supersymmetry structures of the model.

In this paper, symmetric spoof surface plasmon (SSP) mode on the doubly corrugated metal surfaces is indentified as long-range spoof surface plasmon (LRSSP) because of its extreme low propagation loss and symmetric dominant field profile so as short-range SSP (SRSSP) for anti-symmetric mode. Based on theoretical calculation and numerical simulation of finite integration method, symmetric and anti-symmetric SSP modes with various gap sizes between these two identical corrugated metal surfaces are investigated in terahertz (THz) regime and good agreement is realized. Besides, the low loss superiority of LRSSP diminishes along with the increased gap size. This work opens up new avenues to utilize this long-range surface mode in far-infrared, THz or lower frequency band and can find many potential applications such as low-loss waveguide, filters and novel electronic sources.

A terahertz electronic source based on the spoof surface plasmon (SSP) with 2-D subwavelength metallic grating is presented. The SSP dispersion relation of plasmonic grating is derived by a simplified modal expansion method, and the coupling and interaction between the SSP and the electron beam is studied by particle-in-cell simulation. The results reveal that the output performance highly depends on the location of electron beam from grating surface. For an injected electron beam with 19.15 kV and 0.5 A, the SSP output power can reach 22.7 W for the optimized distance of the beam from the grating surface at a frequency near 1 THz for the given structure. Besides, the influence of different electron beam parameters on output power is also investigated and we find that pulse electron beam is preferable than continuous electron beam for good performance. There is an optimized operation frequency for the given beam voltage. Furthermore, output performance can be improved by changing grating structure parameters. By decreasing the grating groove filling factor from 0.8 to 0.2, the SSP output power can be increased from 17.2 to 23.6 W. The SSP power can also be significantly enhanced from 14 to 28.6 W using shallow grating with a groove depth changing from 76 to 56 $\mu \text{m}$ for the optimized operation frequency with the same electron beam. The present work may provide a new avenue to obtain powerful THz electronic sources.

Active polarization rotators are desirable for many applications in photonics. Metasurfaces based on phase-change or magneto-optical materials can do the job, but suffer from long response time or the need for a strong magnetic field. This study reports tunable and omnidirectional polarization rotation using a pair of coupled, perforated metal screens. Here the tuning originates from the near-field coupling of the screens and its dependence on lateral displacement. For millimeter-scale displacement, continuous and efficient polarization rotation from -90 to 90 degrees can be achieved in the microwave band, and the effect could also be extended to the terahertz regime.

The relativistic electron cyclotron maser (ECM) has been successfully applied to generating high-power THz wave. In order to realize the additional advantages of broadband tuning and high efficiency interaction, this paper is devoted to exploring the THz pre-bunched ECM. Other than a conventional open-cavity tunable gyrotron consecutively switching between axial modes to realize frequency tuning, a pre-bunched ECM system operates on the backward traveling-wave resonance to achieve broadband smooth tuning. Especially, an interaction circuit of specified axial profile of beam-wave detuning frequency is built to achieve high efficiency. An optimized 0.1 THz pre-bunched ECM system using an electron beam of 30 kV voltage and 3 A current is predicted to generate broad bandwidth of 10 GHz and efficiency between 10% $\sim$ 25%. The broadband tuning pre-bunched ECM is promising for a new generation of broadband and high-power THz source.

The acceleration efficiency is a key index for charged-particle acceleration process. This paper introduced a method to enhance the acceleration efficiency in slowed circularly polarized wave. The numerical calculation results indicated that with an optimal choice of the taper factor, a significant acceleration efficiency enhancement can be obtained.

Dirac oscillator subjects to an external magnetic field is re-examined. We show that this model can be mapped onto different quantum optics models if one insists to introduce two kinds of phonons which associate with the excitations of Dirac oscillator and magnetic field respectively. The conclusion about chirality quantum phase transition in the paper “Chirality quantum phase transition in the Dirac oscillator” (Bermudez et al. Phys. Rev. A, 77, 063815 2008) is only valid for a specific mapped quantum optics models rather than the Dirac oscillator itself. Thus, the conclusions about chirality quantum phase transitions in this paper are not universal.

The nonlinear theory of slow-wave electron cyclotron masers (ECM) with an initially straight electron beam is developed. The evolution equation of the nonlinear beam electron energy is derived. The numerical studies of the slow-wave ECM efficiency with inclusion of Gaussian beam velocity spread are presented. It is shown that the velocity spread reduces the interaction efficiency.

We show that a Yangian symmetry, namely, Y ( s u ( 2 ) ) , exists in the Dirac equation with spin symmetry when the potential term takes a Coulomb form. We construct the generators of Y ( s u ( 2 ) ) explicitly and get the energy spectrum of this model from the representation theory for Y ( s u ( 2 ) ) . We also show that this model is integrable, from RTT relations.

Pure and Er-doped BiFeO3 nanoparticles were prepared using a sol–gel method. The remanent magnetization was found to increase with increasing Er concentration. Due to the cocontribution of both the ferromagnetic coupling between Er3+ and Fe3+ ions and the suppression of spatial spin structure of BiFeO3, Er substitution is a more effective approach of enhanced magnetization than the other rare-earth (RE) element substitutions. The observed dielectric loss behavior in the doped sample indicated that the leakage current decreased due to the substitution with Er. The evidence of enhanced magnetization and improved leakage in Er-doped BiFeO3 at room temperature makes it a good candidate for potential applications.

The extreme strong near field of spoof surface plasmon (SSP) on the corrugated metal surface is attractive to develop powerful and efficient Terahertz (THz) electronic sources. In this paper, a THz electronic source based on the generation of SSP modes on the asymmetric doubly-corrugated waveguide is studied both theoretically and numerically. Dispersion characteristics of SSP modes on the asymmetric structure are derived and presented by a simplified modal expansion method. Besides, THz electronic sources on this asymmetric doubly-corrugated metallic waveguide are modeled and studied by particle-in-cell simulation based on FDTD algorithm. The results reveal that output power decreases slightly with the asymmetry of doubly-corrugated structure. However, output power can be significantly improved by using an acentric electron beam on the given doubly-corrugated metal surfaces. Our studies on the excitation of SSP modes on the asymmetric doubly-corrugated metal surfaces are instructive to develop this kind of THz electronic sources.

Ho doped BiFeO 3 nanoparticles were synthesized by a sol–gel method, and their magnetic and microwave absorption properties were investigated. X-ray diffraction pattern shows that Ho ions occupy the Bi site in BiFeO 3 . The Ho substitution is found to enhance ferromagnetic properties, which attributed to the destruction of spin cycloid structure and the emergence of exchange interaction between Ho 4 f electrons and Fe 3 d electrons. Microwave magnetic loss also shows an obvious increase in the range of 2–18 GHz for high level substitution, caused mainly by the natural ferromagnetic resonance at microwave frequencies. Furthermore, microwave absorbing bandwidth and intensity are greatly improved due to the better electromagnetic match property of BiFeO 3 with Ho substitution.

A general dispersion relation is derived for a relativistic rectilinear electron beam of arbitrary momentum distributions interacting with a dielectric in a guide magnetic field, on the basis of Maxwell equations and the relativistic Vlasov equation. The instability occurs when the beam velocity exceeds the wave phase velocity in the medium. The linear wave dispersion relation, growth rate, spatial growth rate are studied analytically for delta and Lorentzian distributions of beam momentums in detail. The results are of importance for a new kind of high-power microwave generation or amplification devices based on anomalous Doppler effect.

Modes in cylindrical waveguides with periodic subwavelength metal grating loaded on the inner surface are analyzed by both theory and simulation. Coupling between spoof surface plasmon mode and traditional waveguide mode provides a robust way to build TM 02 single mode operation. Furthermore, a new approach to realize the well-integrated and reciprocal mode conversion between TM 01 mode and TM 02 mode is proposed.

In this paper, a novel terahertz electronic sources based on the interaction between spoof surface plasmons (SSP) and injected electron beam on the doubly-corrugated metasurfaces are studied by particle-in-cell (PIC) simulation. The SSP fields, dispersion and modes on the two identical corrugated surfaces are calculated and then presented theoretically and numerically. Besides, the influence of the separated distance between these two corrugated metal surfaces on different SSP dispersion modes is specifically analyzed. The PIC simulation results show that the output power increases along with the decreased gap distance at the frequency near 1THz for the given variation range. The maximum output power can reach above 1.5W by the same 19.55kV, 1A half duty-cycle electron beam by decreasing gap size from 110μm to 70μm. The obtained SSP power can be increased by decreasing gap size further. The investigations on the excitation and amplification of SSP on the doubly-corrugated metasurfaces will open new venues for the development of electronic sources from microwave to THz regime.

This abstract presents a complete study of dispersion and mode distribution of spoof surface plasmons (SSPs) in planar metal gratings. The subject under investigation is intended for Terahertz wave generation. Because of its characteristics of near field localization of this plasmonic wave and collective resonance effects of electrons in metals, SSPs in this textured metal surface has attracted enormous interest such as potential applications in plasmonic metamaterials (F. J. Garcia-Vidal. et al., J. Opt. A: Pure Appl. Opt, 7, 2005, S97–S101). There are many novel phenomena steam from surface plasmons, such as enhanced total reflection (G. A. Plotz. et al., J. Opt. Soc. Am., 69, 1979, pp.419–422), extraordinary optical transmission (T. W. Ebbesen. et al., Nature, 391, 1998, pp. 667–669), enhanced Raman spectroscopy (P. L. Stiles. et al., Ann. Rev. Chem. 1, 2008, pp. 601–626), superradiant Terahertz Smith-Purcell radiation (Y. M. Shin. et al., Appl. Phys. Lett. 90, 2007, pp. 031502), etc.

A 1 THz vacuum electronic source has been designed and implemented by Particle-in-cell (PIC) simulation based on rectangular grating slow-wave structure (SWS) and half duty cycle electron beam. The dispersion relation and coupling impedance are analyzed numerically. The simulation results predict that this designed 1 THz vacuum source can produce maximum 102 W saturated power at the end of structure with 19.55 kV, 1A electron beam at frequencies between 0.9985–1.0007 THz. The power growth rate is approximately 23.06 W/mm and modulation depth of pulsed electron beam is nearly 2.10% with a 3 dB bandwidth of 1.1GHz. This vacuum source operate without input driving signal and can be developed into compact, powerful, mobile and attainable sheet-beam THz vacuum electronic sources.

The coupling between surface plasmons and free electrons may be used to amplify waves or accelerate particles. Nonetheless, such an interaction is usually weak due to the small interaction length or velocity mismatching. Here a mechanism for enhancing the coupling between plasmonic fields and relativistic electrons is proposed. By using a weakly gradient meta-surface that supports the spoof surface-plasmons (SSP), the phase velocity of SSP mode can be manipulated and quasi-velocity-matching between SSP and electrons may be achieved. The dynamic coupling equations suggest that, due to the strong coupling, the energy can be extracted continuously from the relativistic electrons. The sustained increase of SSP in a narrow frequency band has been demonstrated by the particle-in-cell simulations, where the output power of SSP attains 65 W at 1 THz (with 28 mm interaction length) and the coupling efficiency is enhanced by two orders of magnitude. The results may find potential applications for designing new compact and efficient THz wave sources.

The resonance interaction of a relativistic charged particle in a circularly polarized electromagnetic wave traveling along a uniform magnetic field is considered. The position, momentum and energy of the particle are presented analytically as functions of a free parameter. The results may be of importance for plasma heating, microwave generation or particle acceleration.

A mechanism for electron acceleration by spoof surface-plasmons (SSP) is proposed. By using a specially designed meta-surface with gradient structural size, the SSP and electrons can be accelerated simultaneously along the surface, which gives rise to a long-range and efficient electron-SSP interaction. Compared with the homogeneous meta-surfaces, the increment of electron kinetic energy, ∼19 keV, is enhanced by two orders of magnitude. The effect may be valuable for developing efficient plasmonic electron accelerators.

Based on previous report that the Chinese herb Ligustrum lucidum (LL) extract directly inhibited hepatitis C virus (HCV) replicase (NS5B) activity, the active components of LL extract to inhibit HCV NS5B activity and their inhibition mode were investigated in this study. LL extract was separated using ethyl acetate and thin layer chromatography (TLC). The inhibitory activity of separated fractions on HCV NS5B was analyzed by the inhibitory assay of NS5B activity. The results showed that only fractions 1 and 2 inhibited NS5B activity, and fraction 2 possessed higher inhibitory activity than fraction 1. HPLC analysis combined with inhibitory assays indicated that ursolic acid and oleanolic acid are the active components within fractions 1 and 2 to inhibit NS5B activity, separately. Moreover, oleanolic acid possessed higher inhibitory activity than ursolic acid. Further inhibition mode analysis found that both oleanolic acid and ursolic acid suppressed NS5B activity as noncompetitive inhibitors. The Ki values of ursolic acid and oleanolic acid were about 4.7 microg x mL(-1) (10 micromol x kg(-1)) and 2.5 microg x mL(-1) (5.5 micromol x kg(-1)), respectively. Taken together, these results demonstrated that oleanolic acid and ursolic acid suppressed NS5B activity as noncompetitive inhibitors, implying that the two natural products have potential value for HCV therapy.

Spoof surface plasmons (SSPs) have many potential applications such as imaging and sensing, communications, innovative leaky wave antenna and many other passive devices in the microwave and terahertz (THz) spectrum. The extraordinary properties of SSPs (e.g. extremely strong near field, enhanced beam–wave interaction) make them especially attractive for developing novel THz electronic sources. SSP modes on doubly corrugated metal surfaces are investigated and analyzed both theoretically and numerically in this paper. The analytical SSP dispersion expressions of symmetric and anti-symmetric modes are obtained with a simplified modal field expansion method; the results are also verified by the finite integration method. Additionally, the propagation losses are also considered for real copper surfaces with a limited constant conductivity in a THz regime. It is shown that the asymptotical frequency of the symmetric mode at the Brillouin boundary decreases along with the decreased gap size between these two corrugated metal surfaces while the asymptotical frequency increases for the anti-symmetric mode. The anti-symmetric mode demonstrates larger propagation losses than the symmetric mode. Further, the losses for both symmetric and anti-symmetric modes decrease when this gap size enlarges. By decreasing groove depth, the asymptotical frequency increases for both the symmetric and the anti-symmetric mode, but the variation of propagation losses is more complicated. Propagation losses increase along with the increased period. Our studies on the dispersion characteristics and propagation losses of SSP modes on this doubly corrugated metallic structure with various parameters is instructive for numerous applications such as waveguides, circuitry systems with high integration, filters and powerful electronic sources in the THz regime.

We study the Berry phase of the ground state and excited states in the Lipkin model. Using the Schwinger representation of spin operators, we get the expression for the Berry phase of the ground state in the thermodynamic limit and numerically calculate that of the excited states in finite sizes. We find that the Berry phase of the ground state is nonanalytic, but its derivative (with respect to the control parameter $\ensuremath{\alpha}$, see text) is finite even in the thermodynamic limit. Whereas, for the excited states, the Berry phase tends to be nonanalytic, and its derivative approaches $\ensuremath{\infty}$ in the thermodynamic limit and in the vicinity of the critical point of the excited-state quantum phase transition.

The plasmon coupling in a nanorod dimer obeys the exponential size dependence according to the Universal Plasmon Ruler Equation. However, it was shown recently that such a model does not hold at short nanorod distance (Nano Lett. 2009, 9, 1651). Here we study the nanorod coupling in various cases, including nanorod dimer with the asymmetrical lengths and symmetrical dimer with the varying gap width. The asymmetrical nanorod dimer causes two plasmon modes: one is the attractive lower- energy mode and the other the repulsive high-energy mode. Using a simple coupled LC-resonator model, the position of dimer resonance has been determined analytically. Moreover, we found that the plasmon coupling of symmetrical cylindrical (or rectangular) nanorod dimer is governed uniquely by gap width scaled for the (effective) rod radius rather than for the rod length. A new Plasmon Ruler Equation without using the fitting parameters has been proposed, which agrees well with the FDTD calculations. The method has also been extended to study the plasmonic wave-guiding in a linear chain of gold nanorod particles. A field decay length up to 2700nm with the lateral mode size about 50nm (~wavelength/28) has been suggested., Comment: 31 pages, 6 figures, 58 references

We propose a mechanism for electron acceleration in which circularly polarized electromagnetic waves (CPEMW) propagate along a uniform magnetic field in a medium with a tapered refractive index. Results show that with a decreasing refractive index and a moderate CPEMW electric field, e.g., 1.20 × 108 V/m, the relativistic factor of an electron can go above 14 after it travels 10 cm in the direction of CPEMW propagation. Without tapering of the refractive index, the maximum value of the relativistic factor is less than 2.92 under the same wave and guiding magnetic field conditions. Similar acceleration efficiency is found for electrons with different initial velocities.

The efficiency of slow-wave electron cyclotron masers (ECM) is usually low, thus limiting the practical applications. Here, a method of tapered magnetic field is introduced for the efficiency enhancement of the slow-wave ECM. The numerical calculations show that the tapered magnetic-field method can enhance the efficiency of slow-wave ECM significantly. The effect of beam electron velocity spread on the efficiency has also been studied. Although the velocity spread reduces the efficiency, a great enhancement of efficiency can still be obtained by the tapered magnetic field method.

Various materials have been examined to obtain permittivity and permeability values required for detailed investigations on functional materials like microwave-absorbing and high-permittivity dielectrics. We call for caution when samples exhibit negative imaginary permeability, whether containing a resonance peak or not. In the retrieval procedure, the Fabry-Perot resonance (FPR) can produce a negative imaginary permeability, which should be classified as an extrinsic rather than an intrinsic physical attribute. In particular, for high-loss materials, the implicit FPR would bring a plausible negative imaginary permeability. Here we have listed a dielectric dispersion of FPR behavior for BiFeO3 samples.

This paper presents a novel metamaterial constructed with wires, spheres and hollow slabs (WSHS), which simultaneously exhibits negative permittivity and permeability. An electromagnetic wave simulation is performed based on the proposed metamaterial and shows that a negative refractive index is achieved for this metamaterial. Adjusting the lattice constant of the unit cell is an easy way to manipulate the frequency of negative index of this structure. A left-hand material prism is designed composed of metamaterial unit cells and the simulation on the proposed prism proves the left-hand behavior of the designed metamaterial.

The nonlinear analysis of slow-wave electron cyclotron masers (ECM) based on anomalous Doppler effect in a slab waveguide is presented. A method of tapered refractive index (TRI) is proposed to enhance the efficiency of slow-wave ECM. The numerical calculations show that the TRI method can significantly enhance the efficiency of slow-wave ECM with the frequency ranging from the microwave to terahertz band. The effect of beam velocity spread on the efficiency has also been studied. Although the velocity spread suppresses the efficiency significantly, a great enhancement of efficiency can still be introduced by the TRI method.

The electromagnetic parameters (permittivity and permeability) method, retrieved from the reflection and transmission coefficients of a slab, is presented. Improvements over existing methods, including the determination of the permittivity, permeability and impedance of the slab, are expressed as explicit functions of the S parameters for both the time-dependent factors, eiωt and e−iωt (ω is the angular frequency of the incident electromagnetic wave), and the proper selection of the sign of impedance and the real part of the refractive index. Moreover, based on the retrieving method, the calculations of the electromagnetic parameters of the conventional-material teflon slab standard sample through the experimental data of the S parameters are performed, which confirm the validity of the technique for the retrieval of electromagnetic parameters.

An electron cyclotron maser based on anomalous Doppler effect (ADECM) with an initially axial beam velocity is considered, and the nonlinear equation of beam-wave interaction is presented. With the numerical methods, the nonlinear dynamics of the ADECM is investigated. It is shown that the saturated interaction efficiency of the ADECM approaches 90% and the interaction length for the saturated efficiency spans about 5–20 cm. The results may be of importance for designing a compact device in applications in microwave generations or microwave heating of ceramic laminates.

The self-consistent nonlinear equations, which describe electron cyclotron maser under the condition of anomalous Doppler effect, have been developed. By employing an initially rectilinear electron beam and a guiding static magnetic field, an efficient energy transfer between electrons and microwave can be achieved. The results suggest potential applications in designing a compact and efficient microwave generation/amplification device.

The dispersion relation of relativistic rectilinear electron beam propagating along a guide magnetic field in a dielectric is investigated by cold fluid model. In such a system, due to anomalous Doppler effect, the instability occurs when the electron velocity exceeds the wave phase velocity. The growth rate and spatial growth rate are studied analytically and the nonlinear saturated efficiency is given analytically for the first time. Numerical results show that the saturated efficiency approaches about 10%–30%. The distinctive interaction mechanism is promising for the design of a new kind of compact high-power microwave generation devices.

The relativistic motion of a charged particle in a uniform magnetic field and a circularly polarized electromagnetic wave propagating along the direction of magnetic field is studied. By manipulating the integrals of motion, some typical quantities of particle motion have been presented analytically in terms of explicit functions of three free parameters. The results may be of great importance for high-power microwave generation or particle acceleration.

The nonlinear dynamics of an initially rectilinear electron beam interacting with a retarded transverse circularly polarized electromagnetic wave under the condition of anomalous Doppler effect has been studied. The physical mechanism of the interaction is presented, and nonlinear ordinary equations for electron energy evolutions have been derived and discussed. The numerical calculations show that the interaction efficiency can be very high. The results are of great importance for the design of practical devices.