Rotational Doppler effect in left-handed materials

We explain the rotational Doppler effect associated with light beams carrying with orbital angular momentum in left-handed materials (LHMs). We demonstrate that the rotational Doppler effect in LHMs is unreversed, which is significantly different from the linear Doppler effect. The physics underlying this intriguing effect is the combined contributions of negative phase velocity and inverse screw of wave-front. In the normal dispersion region, the rotational Doppler effect induces a upstream energy flow but a downstream momentum flow. In the anomalous dispersion region, however, the rotational Doppler effect produces a downstream energy flow but a upstream momentum flow. We theoretically predict that the rotational Doppler effect can induce a transfer of angular momentum of the LHM to orbital angular momentum of the beam.Comment: 6 pages, 3 figure

Effects of a traditional Chinese medicine, Longdanxiegan formula granule, on Toll-like receptor pathway in female guinea pigs with recurrent genital herpes

AbstractObjectiveThe aim of the present study was to investigate the effects of Longdanxiegan formula granule (LDXGFG), a Chinese traditional medicine on Toll-like receptor (TLR) pathway in recurrent genital herpes.Materials and MethodsAn experimental recurrent genital herpes model was constructed using herpes guinea pig model. The effect of LDXGFG on expression levels of TLR pathway genes were detected using real-time polymerase chain reaction. Furthermore, the dendritic cells and Langerhans cells were isolated and the TLR pathway genes of these cells were assayed after LDXGFG treatment.ResultsThe result suggested two different expression patterns of TLR pathway genes in genital herpes and recurrent genital herpes, including upregulated genes and downregulated genes. TLR1, TLR4, TLR6, TLR7, TLR8, TLR9, and TLR10 showed a significant decrease while, TLR2, TLR3, and TLR5 increased in genital herpes and recurrent genital herpes guinea pigs. Meanwhile, the downregulated genes in genital herpes and recurrent genital herpes were stimulated by LDXGFG. By contrast, the upregulated genes decreased significantly after LDXGFG treatment. In both dendritic cells and Langerhans cells, the TLR pathway genes exhibited same pattern: the LDXGFG corrected the abnormal expression of TLR pathway genes.ConclusionThe present results suggest that LDXGFG is an alternative, inexpensive, and lasting-effect medicine for herpes simplex virus 2 infection

Robustness Analysis of Voltage Control Strategies of Smart Transformer

The increasing penetration of Distributed Generators (DG) in the modern electric distribution network poses high priority on the problem of the stability. In this article the Harmonic Stability of a Smart Transformer-fed microgrid is investigated under different control strategies. The considered microgrid is composed by a Smart Transformer and three Distributed Generators, considering the bandwidth of the DGs unknown. The robustness is evaluated analysing the eigenvalues as a consequence of a variation of the DGs bandwidth. The system is modelled as a Multi Input Multi Output System (MIMO); the eigenvalue based analysis is carried out to assess the stability and compare the robustness of the traditional double-loop PI and a state-feedback (SF) integral controller. The results show that the SF controller ensures a higher robustness than the traditional PI controller with respect to increasing bandwidths of the DGs

Interactions Between Two Phase-locked Loop Synchronized Grid Converters

Grid converters synchronized by phase-locked loops (PLLs) could suffer from stability problems, especially being connected to a weak grid or high penetration of converters. The existing literature assesses the stability of the paralleled PLL-synchronized converters at the same point of common coupling (PCC) using identical control and system parameters. However, in an actual grid, the parameters of grid converters are normally different due to different manufacturers. In this regard, this paper aims to study the stability indices and margins of two PLL-synchronized converters with different parameters, particularly with different PLL bandwidths and power injections. The main purpose of this paper is to provide a general design guidelines of PLL bandwidths of two converters (can be extended to two wind/solar farms) for stable operation in practical grids. State-space model of the PLL-synchronized converter based on the component connection method (CCM) is developed and eigenvalue-based analysis is used to investigate the interactions between the two converters. Moreover, the stability borders of two PLL-synchronized converters using different PLL bandwidths and power setpoints are studies. Monte-Carlo simulations and experimental results are provided to validate the effectiveness of the developed model and theoretical analysis

Control and stabilization of grid-connected converters operating as constant power load in a smart transformer grid scenario

The development of power electronics and control technology provides improved performance of the electrical appliances, making them robust to changes in the supply voltage or frequency. However, power electronic converters behave as constant power loads (CPLs), which have negative impedance characteristics, and this non-linear behavior is challenging the stability of the grid. This paper investigates the input impedance of a three-phase low-voltage grid connected ac-dc converter that operating as a CPL when interfaced to a single DC bus and a changeable load. The possibility of adopting a Smart Transformer (ST), a power electronics converter which feeds a low-voltage grid, for the CPL stabilization is also addressed. To analyze the behavior of CPLs, a strategy of impedance modelling is employed. Gain Margin Phase Margin (GMPM) Criterion is referred to judge the stability of the system and verify the stabilization operation for CPLs. Simulation results are presented to be as a support