Efficient generation of a dual-polarized vortex wave with an ultrathin Huygens' metasurface.

In this paper, an ultrathin Huygens' metasurface is designed for generating an orbital angular momentum (OAM) beam. The Huygens' metasurface is a double-layered metallic structure on a single-layer PCB. Based on induced magnetism, the Huygens' metasurface achieves the abilities of available near-complete transmission phase shift around 28 GHz. According to the principle of vortex wave generation, a Huygens' metasurface is designed, implemented and measured. The simulated and measured results show that the dual-polarized OAM transmitted waves with the mode l = 1 can be efficiently generated on a double-layered Huygens' metasurface around 28 GHz. The measured peak gain is 23.4 dBi at 28 GHz, and the divergence angle is 3.5°. Compared with conventional configurations of OAM transmitted beam generation, this configuration has the advantages of high gain, narrow divergence angle, and low assembly cost. This investigation will provide a new perspective for engineering application of OAM beams.

Ultra-wideband linear-to-circular polarizer realized by bi-layer metasurfaces.

We propose a bi-layer transmissive metasurface to obtain linear-to-circular polarization conversion in a wideband. The unit cell of each metasurface layer, which has identical configuration, consists of a Jerusalem-cross-like resonator and a metal strip. A universal equivalent circuit model is employed to guide the design of the polarizer. By analyzing the circuit parameters of the equivalent circuit, four metal strips are symmetrically inserted in each unit cell to broaden the bandwidth of linear-to-circular polarization conversion. Numerical and experimental results show that the polarizer can convert a linearly polarized wave into a circularly polarized wave in a wideband from 6.1 GHz to 12.6 GHz. Compared to the reported designs, the proposed polarization converter has advantages of ultrathin thickness and ultrawideband, and hence can be used in many applications, such as antennas and remote sensors.

Near-infrared ITO-based photonic hypercrystals with large angle-insensitive bandgaps.

The angle-sensitive photonic bandgap (PBG) is one of the typical features of one-dimensional photonic crystals. Based on the phase-variation compensation effect between the dielectric and hyperbolic metamaterials (HMMs), angle-insensitive PBGs can be realized in photonic hypercrystals. However, since hypercrystals are usually constructed using metal components, these angle-insensitive PBGs are mostly limited to narrow bandwidths in visible range. Here, we replace metal with indium tin oxide (ITO) to construct HMMs in the near-infrared range. In these ITO-based HMMs, we experimentally demonstrate the negative refraction of light in transverse magnetic polarization. With this HMM component, we realize a photonic hypercrystal with an angle-insensitive PBG in the wavelength range of 1.15-2.02 µm. These ITO-based hypercrystals with large angle-insensitive PBGs can find applications in near-infrared reflectors or filters.

RRP9 promotes gemcitabine resistance in pancreatic cancer via activating AKT signaling pathway.

BACKGROUND: Pancreatic cancer (PC) is a highly lethal malignancy regarding digestive system, which is the fourth leading factor of cancer-related mortalities in the globe. Prognosis is poor due to diagnosis at advanced disease stage, low rates of surgical resection, and resistance to traditional radiotherapy and chemotherapy. In order to develop novel therapeutic strategies, further elucidation of the molecular mechanisms underlying PC chemoresistance is required. Ribosomal RNA biogenesis has been implicated in tumorigenesis. Small nucleolar RNAs (snoRNAs) is responsible for post-transcriptional modifications of ribosomal RNAs during biogenesis, which have been identified as potential markers of various cancers. Here, we investigate the U3 snoRNA-associated protein RRP9/U3-55 K along with its role in the development of PC and gemcitabine resistance. METHODS: qRT-PCR, western blot and immunohistochemical staining assays were employed to detect RRP9 expression in human PC tissue samples and cell lines. RRP9-overexpression and siRNA-RRP9 plasmids were constructed to test the effects of RRP9 overexpression and knockdown on cell viability investigated by MTT assay, colony formation, and apoptosis measured by FACS and western blot assays. Immunoprecipitation and immunofluorescence staining were utilized to demonstrate a relationship between RRP9 and IGF2BP1. A subcutaneous xenograft tumor model was elucidated in BALB/c nude mice to examine the RRP9 role in PC in vivo. RESULTS: Significantly elevated RRP9 expression was observed in PC tissues than normal tissues, which was negatively correlated with patient prognosis. We found that RRP9 promoted gemcitabine resistance in PC in vivo and in vitro. Mechanistically, RRP9 activated AKT signaling pathway through interacting with DNA binding region of IGF2BP1 in PC cells, thereby promoting PC progression, and inducing gemcitabine resistance through a reduction in DNA damage and inhibition of apoptosis. Treatment with a combination of the AKT inhibitor MK-2206 and gemcitabine significantly inhibited tumor proliferation induced by overexpression of RRP9 in vitro and in vivo. CONCLUSIONS: Our data reveal that RRP9 has a critical function to induce gemcitabine chemoresistance in PC through the IGF2BP1/AKT signaling pathway activation, which might be a candidate to sensitize PC cells to gemcitabine. Video abstract.

Nonreciprocal Tamm plasmon absorber based on lossy epsilon-near-zero materials.

Contrary to conventional Tamm plasmon (TP) absorbers of which narrow absorptance peaks will shift toward short wavelengths (blueshift) as the incident angle increases for both transverse magnetic (TM) and transverse electric (TE) polarizations, here we theoretically and experimentally achieve nonreciprocal absorption in a planar photonic heterostructure composed of an isotropic epsilon-near-zero (ENZ) slab and a truncated photonic crystal for TM polarization. This exotic phenomenon results from the interplay between ENZ and material loss. And the boundary condition across the ENZ interface and the confinement effect provided by the TP can enhance the absorption in the ENZ slab greatly. As a result, a strong and nonreciprocal absorptance peak is observed experimentally with a maximum absorptance value of 93% in an angle range of 60∼70°. Moreover, this TP absorber shows strong angle-independence and polarization-dependence. As the characteristics above are not at a cost of extra nanopatterning, this structure is promising to offer a practical design in narrowband thermal emitter, highly sensitive biosensing, and nonreciprocal nonlinear optical devices.

Wide-angle ultrasensitive biosensors based on edge states in heterostructures containing hyperbolic metamaterials.

Edge states in photonic heterostructures composed of metal layers and all-dielectric one-dimensional photonic crystals (1DPCs) will shift toward short wavelengths (blueshift) with the increase in the incident angle for both transverses magnetic (TM) and transverse electric (TE) polarizations. However, we achieve redshift edge states for TM polarization and blueshift edge states for TE polarization in heterostructures composed of metal layers and 1DPCs containing layered hyperbolic metamaterials. Owing to the opposite wavelength shift of the edge states for two orthogonal polarizations, the ellipsometric phase will change dramatically around the edge state wavelength in a broad angle range. Based on this wide-angle phase singularity property, we propose a biosensor which can work with high refractive index resolution in a broad angle range.

Perfect optical absorbers in a wide range of incidence by photonic heterostructures containing layered hyperbolic metamaterials.

We theoretically and experimentally investigate the wide-angle perfect absorptance in a photonic heterostructure composed of a metal film and a truncated photonic crystal (PC) with layered hyperbolic metamaterials (HMMs) in the near ultraviolet and visible regions. The wide-angle perfect optical absorption depends on the dispersionless Tamm plasmon polarition (TPP) under TM polarization, which originates from reflection phase compensation condition between the metal and the truncated PC with HMMs. Our experimental results show nearly perfect absorptance over 0.91 in an angle range of 0-45 degree, which facilitates the design of perfect optical absorbers working in a wide angle range.

Topological description for gaps of one-dimensional symmetric all-dielectric photonic crystals.

We propose a topological description for gaps of one-dimensional symmetric all-dielectric photonic crystals (PCs). It is shown that, in the propagating direction, the effective electromagnetic parameters of PCs can be derived from one unit cell with mirror symmetry. Besides, at the frequencies of gaps, these symmetric PCs can be described as photonic insulators with effective negative permittivity or negative permeability. Moreover, based on the mapping of Maxwell's equations to the Dirac equation and the band inversion achieved by tuning the material and structural parameters, we demonstrate that the gaps of PCs with effective negative permittivity or negative permeability possess different topological orders. Lastly, we show that a bound state is robust against the disorder under a zero-average-effective-mass condition in a heterostructure made of two PCs with different topological orders.

Efficient third-harmonic generation based on Tamm plasmon polaritons.

We theoretically investigate efficient third-harmonic generation (THG) in the heterostructure with a one-dimensional photonic crystal (PC) and a thick metal film. There are both the fundamental Tamm plasmon mode and the high-order mode in the heterostructure. Commonly these two Tamm plasmon modes just satisfy single-resonance condition, but the double-resonance condition can be fulfilled by using a binary PC in the heterostructure. Taking advantage of the tunneling effect of Tamm plasmon modes, THG in the single-resonance heterostructure is enhanced over 3 orders of magnitude more than that in the single metal film, and that in the double-resonance one is further enhanced nearly 2 orders of magnitude.

High-efficiency nonlinear platform with usage of metallic nonlinear susceptibility.

A scheme with usage of metallic nonlinearity, especially in generating the surface plasmon polariton (SPP) time-reversal wave (TRW), is investigated. It is composed of a metal film and an attached photonic crystal, in which both a far-field-excitable tunneling mode and an SPP guided mode could exist. Two modes are degenerated, deeply penetrated into metal, well overlapped, and localized. Therefore, the tunneling mode acts as the pumping field, while the SPP mode acts as the signal field. Because of the large metallic nonlinear susceptibility, the TRW efficiency could increase thousand times. This scheme can be widely used as a high-efficiency platform for other nonlinear devices.

A Double-Layer Dual-Polarized Huygens Metasurface and Its Meta-Lens Antenna Applications.

In this paper, a dual-polarized Huygens unit is proposed, which has a double-layer metallic pattern etched on both sides of one dielectric substrate. Induced magnetism enables the structure to support Huygens' resonance, thus obtaining nearly complete available transmission phase coverage. By optimizing the structural parameters, a better transmission performance can be achieved. When the Huygens metasurface was used for the design of a meta-lens, good radiation performance was exhibited, with a maximum gain of 31.15 dBi at 28 GHz, an aperture efficiency of 42.7% and a 3 dB gain bandwidth of 26.4 GHz to 30 GHz (12.86%). Due to its excellent radiation performance and very simple fabrication, this Huygens meta-lens has important applications in millimeter-wave communication systems.

Subwavelength electromagnetic switch: bistable wave transmission of side-coupling nonlinear meta-atom.

We propose a scheme for subwavelength electromagnetic switch by employing nonlinear meta-atom. Bistable response is conceptually demonstrated on a microwave transmission line, which is side-coupled to a varactor-loaded split ring resonator acting as a nonlinear meta-atom. Calculations and experiments show that by applying conductive coupling instead of near-field interaction between the transmission line and the nonlinear meta-atom, switch performances are improved. The switch threshold of low to -5.8 dBm and the transmission contrast of up to 4.0 dB between the two bistable states were achieved. Subwavelength size of our switch should be useful for miniaturization of integrated optical nanocircuits.

Nonlinear resonance-enhanced excitation of surface plasmon polaritons.

We theoretically investigate nonlinear resonance-enhanced excitation of surface plasmon polaritons in a metal coated by a one-dimensional photonic crystal. Tunneling modes above the air-light line can be directly excited in this structure. Then, with suitable parameters, photon energy and momentum conservation between the tunneling mode and the surface plasmon polaritons can be realized by means of nonlinear four-wave mixing. Compared with the nonlinear excitation of surface plasmon polaritons in a bulk metal [Phys. Rev. Lett. 103, 266802 (2009)], the conversion efficiency in our structure is noticeably enhanced.

The Effect of Brain-Computer Interface Training on Rehabilitation of Upper Limb Dysfunction After Stroke: A Meta-Analysis of Randomized Controlled Trials.

BACKGROUND: Upper limb motor dysfunction caused by stroke greatly affects the daily life of patients, significantly reduces their quality of life, and places serious burdens on society. As an emerging rehabilitation training method, brain-computer interface (BCI)-based training can provide closed-loop rehabilitation and is currently being applied to the restoration of upper limb function following stroke. However, because of the differences in the type of experimental clinical research, the quality of the literature varies greatly, and debate around the efficacy of BCI for the rehabilitation of upper limb dysfunction after stroke has continued. OBJECTIVE: We aimed to provide medical evidence-based support for BCI in the treatment of upper limb dysfunction after stroke by conducting a meta-analysis of relevant clinical studies. METHODS: The search terms used to retrieve related articles included "brain-computer interface," "stroke," and "upper extremity." A total of 13 randomized controlled trials involving 258 participants were retrieved from five databases (PubMed, Cochrane Library, Science Direct, MEDLINE, and Web of Science), and RevMan 5.3 was used for data analysis. RESULTS: The total effect size for BCI training on upper limb motor function of post-stroke patients was 0.56 (95% CI: 0.29-0.83). Subgroup analysis indicated that the standard mean differences of BCI training on upper limb motor function of subacute stroke patients and chronic stroke patients were 1.10 (95% CI: 0.20-2.01) and 0.51 (95% CI: 0.09-0.92), respectively (p = 0.24). CONCLUSION: Brain-computer interface training was shown to be effective in promoting upper limb motor function recovery in post-stroke patients, and the effect size was moderate.

AKT1/FOXP3 axis-mediated expression of CerS6 promotes p53 mutant pancreatic tumorigenesis.

Ceramide synthases (CerSs) catalyze the formation of ceramides from sphingoid bases and acyl-CoA substrates. Increasing evidence suggests that cancer cells generally exhibit altered sphingolipid metabolism in the tumorigenesis of multiple cancers. However, there is no evidence that CerSs are associated with pancreatic ductal carcinoma (PDAC). In the present study, we examined CerS expression in clinical tissue and conducted data mining to investigate the clinical significance of CerSs in the TCGA-PAAD database. We found that high CerS6 expression positively correlated with progression and predicted worse prognosis in PDAC patients, establishing CerS6 as a potential biomarker for PDAC. Furthermore, CerS6 promoted cell proliferation, colony formation and invasion by producing C16-ceramide and was required for tumor formation. Mechanistically, AKT1 interacted with and phosphorylated FOXP3 at S418, which decreased the binding of FOXP3 to the CERS6 promoter and in turn induced CerS6 expression by reconstituting an activated state on the CERS6 promoter. The AKT1/FOXP3 axis mediated the CerS6 expression and promoted p53 mutant pancreatic tumorigenesis by producing excessive C16-ceramide, which induced the accumulation of mutant p53. Thus, our study explores the relationship between PI3K/AKT signaling and sphingolipid metabolism, revealing an oncogenic role for CerS6, which may represent a potential target for PDAC treatment.

Highly efficient all-optical diode action based on light-tunneling heterostructures.

We theoretically investigate the feasibility of constructing compact and highly efficient all-optical diodes (AODs) based on light tunneling mechanism in heterostructures. Due to light tunneling behaviors in heterostructures with one-dimensional photonic crystals (1D PC) and lossy metallic film, not only very large nonlinear permittivity of metal can be utilized sufficiently but also the structures with strongly nonreciprocal electric field distributions can be constructed. Finally we design a composite structure consisting of 1D PC-metal heterostructures to achieve the optimal unidirectional light transmission with 0.984 transmission contrasts, 42% transmission and 0.93 GW/cm(2) operating light power at working wavelength 557.2nm.

Author Correction: Photonic Spin Hall Effect in Waveguides Composed of Two Types of Single-Negative Metamaterials.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Different discrete soliton states in periodic optical induced waveguide lattice.

Different discrete soliton states in optical waveguide lattices are studied theoretically for the different external conditions such as the biased field, lattice spacing and the position of the input pulse. It is demonstrated that the discrete solitons can be formed in an appropriate biased field and exhibit different discrete properties in different biased field. The results also indicate that lattice spacing and the position of input pulse can affect apparently the discreteness of discrete solitons. If changing the ratio of the waist width of input beam to lattice period, the discrete solitons will be excited in more or less channels. In addition, the increase of lattice intensity almost does not affect the propagation behavior of soliton.

Photonic Spin Hall Effect in Waveguides Composed of Two Types of Single-Negative Metamaterials.

The polarization controlled optical signal routing has many important applications in photonics such as polarization beam splitter. By using two-dimensional transmission lines with lumped elements, we experimentally demonstrate the selective excitation of guided modes in waveguides composed of two kinds of single-negative metamaterials. A localized, circularly polarized emitter placed near the interface of the two kinds of single-negative metamaterials only couples with one guided mode with a specific propagating direction determined by the polarization handedness of the source. Moreover, this optical spin-orbit locking phenomenon, also called the photonic spin Hall effect, is robust against interface fluctuations, which may be very useful in the manipulation of electromagnetic signals.

Wide-angle Spectrally Selective Perfect Absorber by Utilizing Dispersionless Tamm Plasmon Polaritons.

We theoretically investigate wide-angle spectrally selective absorber by utilizing dispersionless Tamm plasmon polaritons (TPPs) under TM polarization. TPPs are resonant tunneling effects occurring on the interface between one-dimensional photonic crystals (1DPCs) and metal slab, and their dispersion properties are essentially determined by that of 1DPCs. Our investigations show that dispersionless TPPs can be excited in 1DPCs containing hyperbolic metamaterials (HMMs) on metal substrate. Based on dispersionless TPPs, electromagnetic waves penetrate into metal substrate and are absorbed entirely by lossy metal, exhibiting a narrow-band and wide-angle perfect absorption for TM polarization. Our results exhibit nearly perfect absorption with a value over 98% in the angle of incidence region of 0-80 degree.