Electromagnetic fields near plasmonic wedges

The behavior of electromagnetic fields near the edge of a plasmonic wedge is investigated. We study the scattering properties, field divergence, and field enhancement near an Au wedge bounded by SiO2 upon illumination by TM-polarized light using hypersingular integral equations, as a function of wavelength, wedge angle, and angle of incidence. The transverse scattered field components show a convergent behavior at wavelengths approaching the surface plasmon energy asymptote (on the corresponding flat Au-SiO2 interface), and become strongly divergent at longer wavelengths. The computed divergence is compared with Meixner's theory and is found to be in good agreement over a restricted range of parameters.     

银吸收边附近X射线衰减系数测量

在北京同步辐射装置的4B7A中能X光束线上,光源能区为2.1~6.0keV,能量分辨大于5000,高次谐波小于0.1%,光源强度大于109光子/s。通过全能区多能点的透过率精确测量Ag样品质量厚度,然后采用Ag薄膜对单能X光子的透过率进行测量,给出了Ag薄膜在吸收边(3.4~3.9keV)的衰减系数。建立了Ag样品吸收边附近衰减系数同步辐射测量方法。通过不确定度分析给出衰减系数测量不确定度小于1%,填补了在该区间衰减系数的空白。     

银吸收边附近X射线衰减系数测量

在北京同步辐射装置的4B7A中能X光束线上,光源能区为2.1~6.0 keV,能量分辨大于5000,高次谐波小于0.1%,光源强度大于109光子/s。通过全能区多能点的透过率精确测量Ag样品质量厚度,然后采用Ag薄膜对单能X光子的透过率进行测量,给出了Ag薄膜在吸收边（3.4~3.9 keV）的衰减系数 。建立了Ag样品吸收边附近衰减系数同步辐射测量方法。通过不确定度分析给出衰减系数测量不确定度小于1％,填补了在该区间衰减系数的空白。     

Disorder-induced localization of light near edges of nonlinear photonic lattices

We investigated the influence of edges and corners on the Anderson localization of light in disordered two-dimensional photonic lattices that are optically induced in nonlinear saturable photorefractive media. A systematic quantitative study of gradual transition from corner to bulk Anderson localization in truncated two-dimensional photonic lattices was carried out. We analyzed numerically the localization at several corners and edges of the square and triangular photonic lattices and compared them with the localization in bulk medium. We found that, for strong disorder, corners and edges effectively suppress Anderson localization, as compared to the bulk, but to a varying degree.     

Long-wavelength local density of states oscillations near graphene step edges

Using scanning tunneling microscopy and spectroscopy, we have studied the local density of states (LDOS) of graphene over step edges in boron nitride. Long-wavelength oscillations in the LDOS are observed with maxima parallel to the step edge. Their wavelength and amplitude are controlled by the energy of the quasiparticles allowing a direct probe of the graphene dispersion relation. We also observe a faster decay of the LDOS oscillations away from the step edge than in conventional metals. This is due to the chiral nature of the Dirac fermions in graphene.     

Calculation of strayfields near grain edges in permanent magnet material

The internal strayfields near the edges of permanent magnetic grains are calculated. A numerical algorithm has been developed to consider the modification of the strayfield resulting from the rotation of the magnetization from the easy axis in external and internal fields. Anisotropy constants of higher order are considered. The results are applied to Nd₂Fe₁₄B. The ratio between strayfield strength and saturation magnetization defines a theoretical local demagnetizing factor which is comparable with the effective demagnetizing factor used to describe the temperature dependence of coercivity. The effect of strayfields on the coercive field and its angular dependence is discussed.     

Experim ental investigation of sound propagation from an impulsive source near rigid wedges

The acoustic signal from an impulsive source near an ideal rigidwedge consists of the reflected waves from the inclined plane andthe diffracted waves from the apex of the wedge.There are two theoreti-cal solutions of the problem.The first was obtained by Biot-Tolstoyusing normal coordinates.The second was Trorey's Helmholtz-Kirchhoffsolution.So far the experimental measurements have concentrated on thediffracted wave from the wedge apex and ignored the rest of the solution.The Biot-Tolstoy exact wedge solution is used in this paper to study thesound transmission in wedges of angle 12°and 52°approximately.Thetheory and the experiments are consistent.Also studied is the behaviourof the reflected and diffracted waves from a 270°wedge.Both theoriespredicted the existence a specular"image"reflection when a coincidentsource and receiver are over a half plane.The experimental results showedthat the Biot-Tolstoy theory was accurate and the Trorey solution pro-duced quite large errors.     

近壁面气泡运动特性的数值计算

采用体积加速度模型确定水下爆炸气泡运动的初始条件,基于MSC.DYTRAN有限元软件开发了定义流场初始条件和边界条件的子程序,对气泡在水平刚性壁面附近的运动特性进行了数值模拟,通过对比发现数值计算结果与实验结果具有较好的一致性,证明了初始条件定义、子程序开发和有限元模型建立的正确性和数值计算的准确性。以此为基础,研究了水深、泡心与刚性底面之间的距离对气泡动态特性和射流速度的影响,通过数值计算得到了一些有规律的曲线。计算模型、方法及结果对相关的工程研究和计算具有一定的参考价值。     

Enhanced optical nonlinearity near the photonic bandgap edges of a cholesteric liquid crystal

The third-order Kerr nonlinear optical effect of a one-dimensional photonic bandgap structure of a cholesteric liquid crystal is investigated. In a femtosecond nonlinear transmission measurement, nonlinear optical changes in the bandgap edges are observed. From analysis of the dispersion relation, Kerr nonlinear coefficients of nematics, forming the cholesteric liquid crystal, are found to be enhanced by 1-2 orders of magnitude through the photonic bandgap structure.     

Raman spectra of IVB and VIB transition metal disulfides using laser energies near the absorption edges

In this paper, we present Raman spectra of ZrS₂, HfS₂, MoS₂ and WS₂ using laser energies near the energies of the absorption edges. The Raman spectra probe the properties of the first-excited electronic state and the nature of the electron-phonon coupling. The spectra of the IVB disulfides are independent of the laser excitation energy, suggesting weak electron-phonon interaction. In contrast, additional Raman bands appear in the spectra of the VIB disulfides as the laser energy approaches the band gap energy. The new modes in the spectra of MoS₂ and WS₂ cannot be assigned as first-order processes nor as combination bands of the phonons with zero momentum. The resonance Raman scattering of MoS₂ is analyzed in terms of second-order scattering due to the coupling of phonon modes of nonzero momentum with an electronic transition associated with excitonic states.     

Line tension and the shape of nanodroplets

Various factors are discussed which might influence the equilibrium contact angle of nanodroplets placed on a solid substrate. Special emphasis is put on the possible role of the dependence of the solid-liquid interface tension g^SL \gamma^{{{\rm SL}}}_{} on the pressure in the liquid, which in nanodrops considerably exceeds the saturation pressure. We show that certain published data regarding that dependence are meaningless because these have been deduced based on an inconsistent data analysis.     

接地导体球附近点电荷运动的讨论

在应用镜像法讨论了点电荷和接地导体球之间相互作用力的基础上,从牛顿力学和相对论力学两个角度分别讨论分析了接地导体球附近点电荷运动情形,并进行了比较.     

Motion and collision of particles near Plebanski-Demianski black hole: Shadow and gravitational lensing

Here we consider accelerating and rotating charged Plebanski-Demianski (PD) class of black hole metric as a particle accelerator. We obtain the geodesic motions (timelike, null and spacelike) of particles in a non-equatorial plane around the PD black hole. We find the effective potential, energy, angular momentum, impact parameters, and discuss the circular orbit. We study the center of mass energy of two neutral particles falling from infinity to near the non-extremal horizons (event and Cauchy horizons), extremal horizon, accelerating horizons, and near the center of the PD black hole. Also, we study the collision of a particle and a massless photon. Then we find the center of mass energy due to the collision of two massless photons in the PD black hole background. We compute the redshift and blueshift of the emitted photons by massive particles while light signal travels along null geodesics towards the observer located far away from the source. We study the Penrose process, which occurs within the ergosphere, and examines the particle’s motion with its implications. Here, we analyze the PD black hole shadow’s apparent shape, which forms far away from the black hole. We study the possible visibility of the PD black hole through photon’s shadow and energy emission rate. We also investigate the effect on the shadow of the PD black hole in plasma for a distant observer. We study the strong gravitational lensing by PD black hole. Finally, we analyze the deflection angle, lens equation, position, magnification, Einstein ring and observables by taking the supermassive PD black hole in the Galaxy’s center.     

Photoelectron spectroscopy of doped helium nanodroplets

The photoionization dynamics of aniline doped helium droplets has been investigated by photoelectron spectroscopy. The photoelectron spectra resemble closely that of gas phase aniline, except for a droplet-size-dependent shift. This shift is caused by lowering of the ionization threshold upon solvation and can be readily estimated. The individual peaks in the photoelectron spectrum are broadened towards lower kinetic energy which is attributed to the relaxation of the photoelectrons as they pass through the helium droplet.     

Characterization of organic thin films with resonant soft X-ray scattering and reflectivity near the carbon and fluorine absorption edges

The use of soft X-rays near the carbon absorption edge (∼270–300 eV) for small angle X-ray scattering and X-ray reflectivity experiments has significantly expanded the scientific capabilities to investigate thin films of soft matter that are primarily composed of carbon and low Z heteroatoms. In this perspective, we will delineate the basic operating principles and underlying physics of these methods and exemplify their impact by discussing a few recent applications. An extension of these methods to the fluorine edge is also included, demonstrating that the general concepts are also applicable to absorption edges of hetero atoms in soft matter. A short perspective of some future developments is provided.     

Characterising the chemical and physical properties of phase-change nanodroplets

Phase-change nanodroplets have attracted increasing interest in recent years as ultrasound theranostic nanoparticles. They are smaller compared to microbubbles and they may distribute better in tissues (e.g. in tumours). They are composed of a stabilising shell and a perfluorocarbon core. Nanodroplets can vaporise into echogenic microbubbles forming cavitation nuclei when exposed to ultrasound. Their perfluorocarbon core phase-change is responsible for the acoustic droplet vaporisation. However, methods to quantify the perfluorocarbon core in nanodroplets are lacking. This is an important feature that can help explain nanodroplet phase change characteristics. In this study, we fabricated nanodroplets using lipids shell and perfluorocarbons. To assess the amount of perfluorocarbon in the core we used two methods, ¹⁹F NMR and FTIR. To assess the cavitation after vaporisation we used an ultrasound transducer (1.1 MHz) and a high-speed camera. The ¹⁹F NMR based method showed that the fluorine signal correlated accurately with the perfluorocarbon concentration. Using this correlation, we were able to quantify the perfluorocarbon core of nanodroplets. This method was used to assess the content of the perfluorocarbon of the nanodroplets in solutions over time. It was found that perfluoropentane nanodroplets lost their content faster and at higher ratio compared to perfluorohexane nanodroplets. The high-speed imaging indicates that the nanodroplets generate cavitation comparable to that from commercial contrast agent microbubbles. Nanodroplet characterisation should include perfluorocarbon concentration assessment as critical information for their development.