Electron cyclotron motion excited surface plasmon and radiation with orbital angular momentum on a semiconductor thin film.

In this work, surface plasmons (SPs) on a germanium (Ge) thin film in terahertz (THz) region that are excited by electron cyclotron motion (ECM) and the subsequent SP emission (SPE) by adding Ge gratings on the film are explored by finite-difference time-domain (FDTD) and particle-in-cell FDTD (PIC-FDTD) simulations. The optical properties of ECM-excited SPs are the same as those of SPs that are excited by electron straight motion (ESM). For operating at the flat band of SPs' dispersion curve on the Ge film, changing the electron energy will only change the wavevector of SPs and hence the number of periods of SPs on the circular orbital. When the periodic gratings are deposited on the Ge film along the circular orbital of electrons, the emitted SPE contains the orbital angular momentum (OAM). The number of arms and chirality of the spiral patterns in phase map (i.e. the quantum number of OAM) of SPE are determined by the difference between the number of SPs' periods and the number of gratings. Manipulations of the quantum number of OAM by changing the number of gratings for a fixed electron energy and by changing the electron energy for a fixed number of gratings are also demonstrated. This work provides an active OAM source and it is not required to launch circularly polarized beams or pumping beams into the structure.

Surface plasmons manipulated Smith-Purcell radiation on Yagi-Uda nanoantenna arrays.

An electron bunch (e-bunch) passing through an insulator-metal-insulator (IMI) substrate can excite surface plasmons (SPs) on the substrate. Recent studies demonstrate that Smith-Purcell radiation (SPR) from one-dimensional gratings on an IMI substrate can be manipulated and enhanced by e-bunch excited SPs. However, under this configuration, only the emission along the direction of electron moving can be controlled. To steer both the azimuthal and polar angles of the far-field emission pattern requires other mechanisms. In this work, the SP-manipulated SPR with a Yagi-Uda nanoantenna (YUNA) array on an IMI substrate for generation of light beams with designed far-field patterns is proposed and explored by computer simulations. Emission of SPR along and perpendicular to the direction of electron movement can be manipulated by designing grating period and YUNA structure, respectively. Dependence of the azimuthal and polar angles of emitted light beam on geometry parameters of feed and directors of YUNA are elucidated. Furthermore, emission of multiple beams containing a single wavelength and multiple wavelengths with required far-field angles can be achieved using different groups of YUNA arrays on different IMI substrates. The proposed mechanism may have applications for light sources, optical imaging, optical beam steering, holography, microdisplay and cryptography.

Spiral surface plasmon modes inside metallic nanoholes.

Spiral surface plasmon (SSP) modes that propagate inside a silver (Ag) nanohole are investigated by performing both simulations and theoretical analyses. The SSP modes are formed by a linear combination of two rotating SP eigenmodes of the Ag nanohole in the fast-wave branch. Inside a uniform Ag nanohole, the handedness and the number of strands of the SSP modes are determined by both the component SP eigenmodes and their rotation directions. The spiral pitch of the SSP mode increases with the nanohole radius for a fixed wavelength and is inversely related to the incident wavelength for a fixed nanohole radius. Inside a tapered Ag nanohole, the spiral pitch decreases with the reduction of nanohole radius. However, the azimuth-integrated field energy density increases to a maximum value and then falls. For a tapered Ag-clad fiber capped by a tapered Ag nanorod, the SSP mode reverses its handedness when it passes through the fiber-nanorod interface. Furthermore, using this composite structure, the field energy density of SSP mode that arrives at the tip of the tapered nanorod is largely increased.

Structural analysis of proanthocyanidins isolated from fruit stone of Chinese hawthorn with potent antityrosinase and antioxidant activity.

Proanthocyanidins were isolated from fruit stone of Chinese hawthorn (Crataegus pinnatifida Bge. var. major N.E.Br.). Their structures were analyzed and elucidated by methods of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and high performance liquid chromatography electrospray ionization mass spectrometry (HPLC-ESI-MS). The results demonstrated that these compounds are complicated mixtures of homo- and heteropolymers consisting of procyanidin/procyanidin gallate and prodelphinidin. They possessed structural heterogeneity in monomer units, polymer length, and interflavan linkage (A-type and B-type). Their antityrosinase and antioxidant activity were then investigated. The results revealed that they can inhibit tyrosinase activities, including the monophenolase activity and the diphenolase activity. In addition, proanthocyanidins possessed potent antioxidant activity. Our studies revealed that proanthocyanidins isolated from fruit stone of Chinese hawthorn may be applied in food, agriculture, pharmaceutical, and cosmetic industries.

High-Performance Seizure Detection System Using a Wavelet-Approximate Entropy-fSVM Cascade With Clinical Validation.

The classification of electroencephalography (EEG) signals is one of the most important methods for seizure detection. However, verification of an atypical epileptic seizure often can only be done through long-term EEG monitoring for 24 hours or longer. Hence, automatic EEG signal analysis for clinical screening is necessary for the diagnosis of epilepsy. We propose an EEG analysis system of seizure detection, based on a cascade of wavelet-approximate entropy for feature selection, Fisher scores for adaptive feature selection, and support vector machine for feature classification. Performance of the system was tested on open source data, and the overall accuracy reached 99.97%. We further tested the performance of the system on clinical EEG obtained from a clinical EEG laboratory and bedside EEG recordings. The results showed an overall accuracy of 98.73% for routine EEG, and 94.32% for bedside EEG, which verified the high performance and usefulness of such a cascade system for seizure detection. Also, the prediction model, trained by routine EEG, can be successfully generalized to bedside EEG of independent patients.

Inhibitory kinetics of DABT and DABPT as novel tyrosinase inhibitors.

4-Dimethylaminobenzaldehyde-thiosemicarbazone (DABT) and 4-dimethylaminobenzaldehyde-N-phenyl-thiosemicarbazone (DABPT) were synthesized and established by (1)H and (13)C NMR and mass spectrum. Both compounds were evaluated for their inhibition activities on mushroom tyrosinase and their anti-tyrosinase kinetics was investigated. The results showed that both compounds exhibited significant inhibitory effects on activity of monophenolase and diphenolase; DABT and DABPT decreased the steady-state rate with 1.54 µM and 1.78 µM as their IC50 values respectively. The inhibitory effects of diphenolase activity exhibited sharp in a dose-dependent manner and their IC50 values were estimated as 2.01 µM and 0.80 µM, respectively. Kinetic analysis showed that their inhibition mechanism was reversible. The inhibition type of DABT was mix-type with inhibition constants KI = 1.77 µM and KIS = 6.49 µM, while that of DABPT displays non-competitive with the inhibition constant KI = 0.77 µM.

Long-range surface magnetoplasmon on thin plasmon films in the Voigt configuration.

This study elucidates the characteristics of a long-range surface magnetoplasmon (LRSMP) that propagates on a plasmon film with the Voigt configuration. Particle-in-cell (PIC) simulations and theoretical analyses are performed. Simulation results indicate that LRSMP has non-symmetrical fields. The proposed scheme also verifies the non-reciprocal properties of LRSMP as the direction of an applied external magnetic field is reversed. When surface waves propagate on a plasmon film across an interface on one side of which long-range surface plasmon (LRSP) is allowed while on the other side of which LRSMP is allowed, the interface behaves similar to a defect and transforms the surface waves into radiation modes owing to the mismatch between the field patterns of LRSP and LRSMP. Furthermore, PIC simulation results confirm the presence of a new high-frequency LRSMP whose frequency exceeds the plasma frequency and lacks a LRSP counterpart.