Frequency mixing in nonlinear interaction of one-way edge-modes of topological photonic crystals

We investigate topological photonic crystals specially designed such that the frequency band gaps appear around ω0, 2ω0, 3ω0 and, more importantly, each band gap contains exactly one unidirectional edge mode. These one-way edge modes are then utilized to implement key nonlinear frequency mixing processes, such as second- and third-harmonic generation

Four-wave mixing of topological edge plasmons in graphene metasurfaces

We study topologically protected four-wave mixing (FWM) interactions in a plasmonic metasurface consisting of a periodic array of nanoholes in a graphene sheet, which exhibits a wide topological bandgap at terahertz frequencies upon the breaking of time reversal symmetry by a static magnetic field. We demonstrate that due to the significant nonlinearity enhancement and large life time of graphene plasmons in specific configurations, a net gain of FWM interaction of plasmonic edge states located in the topological bandgap can be achieved with a pump power of less than 10 nW. In particular, we find that the effective nonlinear edge-waveguide coefficient is about γ ≃ 1.1 × 1013 W−1 m−1, i.e., more than 10 orders of magnitude larger than that of commonly used, highly nonlinear silicon photonic nanowires. These findings could pave a new way for developing ultralow-power-consumption, highly integrated, and robust active photonic systems at deep-subwavelength scale for applications in quantum communications and information processing

Optically and Chemically Controllable Light Flow in Topological Plasmonic Waveguides Based on Graphene Metasurfaces

In this work, topologically-protected plasmon transport is demonstrated in graphene-based plasmonic crystal waveguides, the main ideas being subsequently applied to optically and chemically controllable nanodevices. In two configurations of topological graphene metasurfaces created by breaking their inversion symmetry, symmetry-protected Dirac cones associated to the underlying metasurfaces are gapped out, which leads to the formation of topological valley modes inside the nontrivial bandgap. The propagation of the corresponding topological modes shows unidirectional characteristics in both cases. Based on the proposed plasmonic topological waveguides, an active optical nanoswitch and a gas molecular sensor are designed by optically and chemically tuning the frequency dispersion of graphene metasurfaces via Kerr effect and gas molecular absorption, respectively. Specifically, the variation of the frequency dispersion of graphene can switch the topological mode into the region of leaky bulk modes, resulting in a dramatic variation of the plasmon transmission. Our work may contribute to the development of new ultracompact and ultrafast active photonic nanodevices based on graphene

Lattice topological edge and corner modes of photonic crystal slabs

Surface lattice modes, generated by the evanescent coupling between localized modes of optical resonators arranged in a two-dimensional (2D) array, generally exhibit remarkable optical response beyond the single photonic particle. Here, by employing the lattice mode concept, we demonstrate that lattice topological edge and corner modes can be achieved in properly designed photonic crystal (PhC) slabs. Such slabs consist of an array of finite-sized second-order topological insulators mimicking the 2D Su-Schrieffer-Heeger model. The proposed lattice edge and corner modes emerge within the topological band gap of the PhC slab, which dictates their topological nature. In particular, the band diagram of the lattice corner modes shows that they possess non-degenerate eigenfrequencies and dispersive bands. In addition, we show that the eigenfrequency of the lattice topological modes can be shifted by tuning the intercell and/or intracell optical coupling. Finally, by finely tuning the geometric parameters of the slab, we realize a lattice corner mode possessing flatband dispersion characteristics. Our study can find applications to topological lasing, nonlinearity enhancement, and slow-light effects in topological photonic systems

Reprogrammable plasmonic topological insulators with ultrafast control

Topological photonics has revolutionized our understanding of light propagation, providing a robust way to manipulate light. So far, most of studies in this field are focused on designing a static photonic structure. Developing a dynamic photonic topological platform to switch multiple topological functionalities at ultrafast speed is still a great challenge. Here we theoretically propose and experimentally demonstrate a reprogrammable plasmonic topological insulator, where the topological propagation route can be dynamically changed at nanosecond-level switching time, leading to an experimental demonstration of ultrafast multi-channel optical analog-digital converter. Due to the innovative use of electric switches to implement the programmability of plasmonic topological insulator, each unit cell can be encoded by dynamically controlling its digital plasmonic states while keeping its geometry and material parameters unchanged. Our reprogrammable topological plasmonic platform is fabricated by the printed circuit board technology, making it much more compatible with integrated photoelectric systems. Furthermore, due to its flexible programmability, many photonic topological functionalities can be integrated into this versatile topological platform

Universal Vector-Scalar Potential Framework for Inhomogeneous Electromagnetic System and Its Application in Semiclassical Quantum Electromagnetics

In this work, numerical solution to a general electromagnetic (EM) system is studied using a formalism based on the formulas for the E-B-A-φ formulas with different gauge conditions. The finite-difference time-domain (FDTD) method is employed to discretize these formulas. In addition, the convolutional perfectly matched layer (CPML) technique is successfully applied to absorb outgoing scattered waves described by the proposed formulas. The gauge invariance of EM fields in inhomogeneous environment is demonstrated by numerical examples. Moreover, the proposed EM framework integrated with the Schrödinger equation is introduced to investigate the mesoscopic phenomenon for light-matter interaction, which is useful to design laser pulses for controlling discrete quantum states. The work offers a simple and general numerical EM framework, which is essential to bridge the classical EM and quantum mechanical systems

The effectiveness of a lifestyle-based intervention on physical activity, blood pressure, and health-related quality of life in older adults with hypertension

The purpose of this study was to explore the effects of a 6-month lifestyle intervention in older adults with hypertension. A secondary data analyses was used from Inter-University Consortium for Political and Social Research (ICPSR) to examine the differences between the intervention and the control groups in the changes in physical activity, blood pressure, and health-related quality of life (HRQOL) in older adults with hypertension, from pre-test (baseline) to post-test (6 months), accounting for stress and social support as mediating variables. This study was a randomized controlled trial with pretest-posttest design. A total of 196 participants were randomly assigned to the intervention group (n=103) and the control group (n=93). Descriptive statistics and hierarchical multiple regression were used to analyze characteristics of the sample and hypotheses testing. Most participants were women and low income. The results of hierarchical multiple regression analyses revealed that there were no statistically significant differences between the intervention and the control groups on change in physical activity, blood pressure, and HRQOL, but the final regression models were statistically significant. In the final hierarchical regression model, demographic variables (education, gender, race, age, and monthly income), social support at baseline, and intervention vs. control accounted for 18% of the variance in change in social support (R2=.18, p < .01); demographic variables, stress at baseline, and intervention vs. control accounted for 25% of the variance in change in stress (R2=.25, p < .001). Demographic variables, SF-36 mental component summary (MCS) score at baseline, intervention vs. control, stress at baseline, change in stress, social support at baseline, and change in social support accounted for 39% of the variance in change in the SF-36 MCS (R2=.39, p < .001); demographic variables, SF-36 physical component summary (PCS) score at baseline, intervention vs. control, stress at baseline, change in stress, social support at baseline, and change in social support accounted for 18% of the variance in change in the SF-36 PCS (R2=.18, p < .05). Demographic variables, systolic blood pressure (SBP) at baseline, intervention vs. control, stress at baseline, change in stress, social support at baseline, and change in social support accounted for 36% of the variance in change in SBP (R2=.36, p < .001); demographic variables, diastolic blood pressure (DBP) at baseline, intervention vs. control, stress at baseline, change in stress, social support at baseline, and change in social support accounted for 49% of the variance in change in DBP (R2=.49, p < .001). Also, in the last step, demographic variables, physical activity frequency at baseline, intervention vs. control, stress at baseline, change in stress, social support at baseline, and change in social support accounted for 33% of the variance in change in physical activity frequency (R2=.33, p < .001). As many older adults have hypertension, promoting effective hypertension self-management is crucial for older adults. Lifestyle interventions in combination with physical activity interventions are strongly recommended. Also, stress management and social support resources should be provided for older adults with hypertension. Further research should be considered within individual, interpersonal, societal, and cultural factors when developing lifestyle-based interventions for older adults with hypertension

Biochemical studies of galactokinase from neurospora crassa

Galactokinase (ATP: D-galactose 1-phosphotransferase, EC No. 2.7.1.6) was demonstrated in extracts prepared from the fungus Neurospora crassa. This enzyme was found to have maximal activity at pH 8.5 in Tris-HCl buffer, and optimal concentrations of magnesium chloride and adenosine triphosphate were determined. An important part of the study was comparison of the galactokinase enzyme with the closely related enzyme glucokinase (ATP: Dglucose 6- phosphotransferase, EC No. 2.7.1.2) from Neurospora. Glucokinase was found to be much more thermostabile than galactokinase, and both enzyme activities sedimented at the rate of approximately 4 S on glycerol or sucrose gradients in the preparative ultracentrifuge, Electrophoretic analysis of extracts containing both enzyme activities clearly demonstrated the migration pattern of glucokinase, but galactokinase was inactivated during this separation procedure. This electrophoretic study therefore provided no evidence concerning the separate identity of the proteins associated with the two activities. The process of extraction of protein from the mycelium, however, demonstrated that glucokinase is freely extractable, but a large portion of the total galactokinase activity is associated with some insoluble component of the cell debris. This suggests that separate proteins provide the two enzyme activities, but the evidence on this point is not definitive because of the possibility of activation, inhibition, or steric effects associated with attachment to a cellular organelle

Phenotypic Variation and Bistable Switching in Bacteria

Microbial research generally focuses on clonal populations. However, bacterial cells with identical genotypes frequently display different phenotypes under identical conditions. This microbial cell individuality is receiving increasing attention in the literature because of its impact on cellular differentiation, survival under selective conditions, and the interaction of pathogens with their hosts. It is becoming clear that stochasticity in gene expression in conjunction with the architecture of the gene network that underlies the cellular processes can generate phenotypic variation. An important regulatory mechanism is the so-called positive feedback, in which a system reinforces its own response, for instance by stimulating the production of an activator. Bistability is an interesting and relevant phenomenon, in which two distinct subpopulations of cells showing discrete levels of gene expression coexist in a single culture. In this chapter, we address techniques and approaches used to establish phenotypic variation, and relate three well-characterized examples of bistability to the molecular mechanisms that govern these processes, with a focus on positive feedback.

Interleukin-17 Contributes to the Pathogenesis of Autoimmune Hepatitis through Inducing Hepatic Interleukin-6 Expression

T helper cells that produce IL-17 (Th17 cells) have recently been identified as the third distinct subset of effector T cells. Emerging data suggests that Th17 cells play an important role in the pathogenesis of many liver diseases by regulating innate immunity, adaptive immunity, and autoimmunity. In this study, we examine the role and mechanism of Th17 cells in the pathogenesis of autoimmune hepatitis (AIH). The serum levels of IL-17 and IL-23, as well as the frequency of IL-17+ cells in the liver, were significantly elevated in patients with AIH, compared to other chronic hepatitis and healthy controls. The hepatic expressions of IL-17, IL-23, ROR-γt, IL-6 and IL-1β in patients with AIH were also significantly increased and were associated with increased inflammation and fibrosis. IL-17 induces IL-6 expression via the MAPK signaling pathway in hepatocytes, which, in turn, may further stimulate Th17 cells and forms a positive feedback loop. In conclusion, Th17 cells are key effector T cells that regulate the pathogenesis of AIH, via induction of MAPK dependent hepatic IL-6 expression. Blocking the signaling pathway and interrupting the positive feedback loop are potential therapeutic targets for autoimmune hepatitis