Showing papers by "Hengyang Normal University published in 2018"

Chirality-Assisted High-Efficiency Metasurfaces with Independent Control of Phase, Amplitude, and Polarization

Abstract: The explosive field of metasurface has intrigued a huge interest from both physics and engineering communities due to its exotic behaviors and promising applications. It, composed of a mass of subwavelength-spaced meta-atoms, has afforded extraordinary capabilities to manipulate electromagnetic (EM) waves.[1–39] The local amplitude, phase, and polarization are three important characteristics for output EM wavefront control, and previous pursuing of light manipulation via metasurfaces could be generally subjected into processing one or two of them. However, the simultaneous modulation of the above three items is rarely reported. In recent years, we have witnessed some progress toward the simultaneous amplitude and phase control.[14–23] Therein, superior performances or completely new functionalities are realized such as higherorder diffractions,[14] quality-enhanced hologram,[16] and radar cross section reduction.[21] However, most attempts are either in reflection geometry,[19–21] or with Simultaneously independent control of phase, amplitude, and polarization is pivotal yet challenging for manipulating electromagnetic waves by transmissive metasurfaces. Huygens’ metasurface affords a high-efficiency recipe primarily by engineering phase-only meta-atoms, restricting itself from realizing unprecedentedly complex functions of the transmission beam. Here, a 3D chirality-assisted metasurface concept relying on integrated magnetoelectric meta-atoms is proposed. It empowers the completely decoupled and arbitrary control of phase and amplitude at large incident angles and arbitrary polarizations. This strategy thus facilitates very sophisticated beam manipulations at close-to-unity cross-polarized efficiency via trilayer integrated resonators with mutual twist. The prescribed phase coverage can be determined by geometrical footprints of the unit cell, while the global azimuthal twist unlocks the capability of tuning amplitudes without affecting the phase. The concept and significance of it are validated to implement several proof-of-prototype demanding functionalities by thin metasurfaces of λo/12, which generate selfaccelerating diffraction-free Airy beams, lateral and axial dual focusing, and even specific multiplexed beam shaping, respectively. This finding opens up an alternative way in very fine control of light with minimalist complexity and advanced performance. It can stimulate novel and high-performance versatile photonic metadevices, thanks to the fully independent control of phase, amplitude, and polarization.

Fabrication of Amine-Modified Magnetite-Electrochemically Reduced Graphene Oxide Nanocomposite Modified Glassy Carbon Electrode for Sensitive Dopamine Determination

Abstract: Amine-modified magnetite (NH2–Fe3O4)/reduced graphene oxide nanocomposite modified glassy carbon electrodes (NH2–Fe3O4/RGO/GCEs) were developed for the sensitive detection of dopamine (DA). The NH2-Fe3O4/RGO/GCEs were fabricated using a drop-casting method followed by an electrochemical reduction process. The surface morphologies, microstructure and chemical compositions of the NH2–Fe3O4 nanoparticles (NPs), reduced graphene oxide (RGO) sheets and NH2–Fe3O4/RGO nanocomposites were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-Ray diffraction (XRD) and Fourier-transform infrared (FTIR) spectroscopy. The electrochemical behaviors of DA on the bare and modified GCEs were investigated in phosphate buffer solution (PBS) by cyclic voltammetry (CV). Compared with bare electrode and RGO/GCE, the oxidation peak current (ipa) on the NH2–Fe3O4/RGO/GCE increase significantly, owing to the synergistic effect between NH2–Fe3O4 NPs and RGO sheets. The oxidation peak currents (ipa) increase linearly with the concentrations of DA in the range of 1 × 10−8 mol/L – 1 × 10−7 mol/L, 1 × 10−7 mol/L – 1 × 10−6 mol/L and 1 × 10−6 mol/L – 1 × 10−5 mol/L. The detection limit is (4.0 ± 0.36) ×10−9 mol/L (S/N = 3). Moreover, the response peak currents of DA were hardly interfered with the coexistence of ascorbic acid (AA) and uric acid (UA). The proposed NH2–Fe3O4/RGO/GCE is successfully applied to the detection of dopamine hydrochloride injections with satisfactory results. Together with low cost, facile operation, good selectivity and high sensitivity, the NH2–Fe3O4/RGO/GCEs have tremendous prospects for the detection of DA in various real samples.

Photonic spin Hall effect enabled refractive index sensor using weak measurements.

Abstract: In this work, we theoretically propose an optical biosensor (consists of a BK7 glass, a metal film, and a graphene sheet) based on photonic spin Hall effect (SHE). We establish a quantitative relationship between the spin-dependent shift in photonic SHE and the refractive index of sensing medium. It is found that, by considering the surface plasmon resonance effect, the refractive index variations owing to the adsorption of biomolecules in sensing medium can effectively change the spin-dependent displacements. Remarkably, using the weak measurement method, this tiny spin-dependent shifts can be detected with a desirable accuracy so that the corresponding biomolecules concentration can be determined.

Facile synthesis of Ag@Cu2O heterogeneous nanocrystals decorated N-doped reduced graphene oxide with enhanced electrocatalytic activity for ultrasensitive detection of H2O2

Abstract: A nanohybrid composed of Ag@Cu2O heterogeneous nanocrystals supported on N-doped reduced graphene oxide (Ag@Cu2O/N-RGO) has been synthesized by a simple wet-chemical method. The resultant composite consists of N-RGO sheets fully and homogeneously coated with a dense layer of Ag@Cu2O nanocrystals. Both Ag and N-RGO are in direct contact with Cu2O, and Ag nanoparticles with sizes of 2–5 nm are mainly deposited on the surface of Cu2O cubes (edge length of 500 nm). The electrochemical studies reveal that the ternary Ag@Cu2O/N-RGO composite exhibit significantly enhanced electrocatalytic activity for H2O2 sensing compared with either the single component (N-RGO) or two component systems (Cu2O/N-RGO and Ag/N-RGO), which is mainly due to the synergetic catalysis of the ternary system. The nonenzymatic sensor based on Ag@Cu2O/N-RGO composite shows overwhelmingly superior comprehensive performance for the H2O2 detection over the documented Ag-based sensors. More specifically, it displays a rapid response (10 s) to H2O2 over a wide linear range of 54–700 nM with a high sensitivity of 1298.3 μA mM−1 cm−2 and a low detection limit of 10 nM. Moreover, the sensor also exhibits the preferable selectivity in the presence of biologically coactive compounds accompanied with long-term stability and good reproducibility.

Frankenstein: Learning Deep Face Representations Using Small Data

Abstract: Deep convolutional neural networks have recently proven extremely effective for difficult face recognition problems in uncontrolled settings. To train such networks, very large training sets are needed with millions of labeled images. For some applications, such as near-infrared (NIR) face recognition, such large training data sets are not publicly available and difficult to collect. In this paper, we propose a method to generate very large training data sets of synthetic images by compositing real face images in a given data set. We show that this method enables to learn models from as few as 10 000 training images, which perform on par with models trained from 500 000 images. Using our approach, we also obtain state-of-the-art results on the CASIA NIR-VIS2.0 heterogeneous face recognition data set.

Deterministic Approach to Achieve Broadband Polarization-Independent Diffusive Scatterings Based on Metasurfaces

Abstract: Diffusive scatterings of electromagnetic (EM) waves by a thin screen are important in many applications, but available approaches cannot ensure uniform angular distributions of low-intensity scatterings without time-consuming optimizations. Here, we propose a robust and deterministic approach to design metasurfaces to achieve polarization-independent diffusive scatterings of EM waves within an ultrabroad frequency band and for wide-range of incident angles. Our key idea is to use high-efficiency Pancharatnam–Berry meta-atoms to form subarrays exhibiting focusing reflection-phase profiles, that can guarantee nearly uniform diffusive scatterings for arbitrarily polarized EM waves. As an illustration, we design and fabricate two metasurfaces and experimentally characterize their wave-diffusion properties in C, X, and Ku bands. Theoretical, numerical and experimental results demonstrate that our approach can diffuse the incident energy much more uniformly than available approaches based on the uniform-phase s...

Preparation of Cu₂O-Reduced Graphene Nanocomposite Modified Electrodes towards Ultrasensitive Dopamine Detection.

Abstract: Cu₂O-reduced graphene oxide nanocomposite (Cu₂O-RGO) was used to modify glassy carbon electrodes (GCE), and applied for the determination of dopamine (DA). The microstructure of Cu₂O-RGO nanocomposite material was characterized by scanning electron microscope. Then the electrochemical reduction condition for preparing Cu₂O-RGO/GCE and experimental conditions for determining DA were further optimized. The electrochemical behaviors of DA on the bare electrode, RGO- and Cu₂O-RGO-modified electrodes were also investigated using cyclic voltammetry in phosphate-buffered saline solution (PBS, pH 3.5). The results show that the oxidation peaks of ascorbic acid (AA), dopamine (DA), and uric acid (UA) could be well separated and the peak-to-peak separations are 204 mV (AA-DA) and 144 mV (DA-UA), respectively. Moreover, the linear response ranges for the determination of 1 × 10-8 mol/L~1 × 10-6 mol/L and 1 × 10-6 mol/L~8 × 10-5 mol/L with the detection limit 6.0 × 10-9 mol/L (S/N = 3). The proposed Cu₂O-RGO/GCE was further applied to the determination of DA in dopamine hydrochloride injections with satisfactory results.

Fluorescent ion-imprinted sensor for selective and sensitive detection of copper (II) ions

Abstract: In the present study, a fluorescent ion-imprinted sensor (FIIS) for rapid and convenient detection of Cu2+ ions was fabricated. A fluorescent polymerizable ligand, i.e., 4-(2-aminomethyl)pyridine-N-allylnaphthalimide, was designed and synthesized. The FIIS was prepared by surface functionalization of PVDF membrane with a thin layer of copper (II) ion-imprinted polymer using the synthesized ligand as the fluorescent functional monomer. The intensity of fluorescence emission of FIIS decreased linearly with the increase of copper (II) ions concentration in the range of 0–70.0 μM. The results of selectivity tests indicated that FIIS has high specific recognition ability for Cu2+ ions. The recoveries for the spiked samples were in the range of 96.4–104.4%, and the relative standard deviations (RSDs) were found to be 2.17–4.75%. The FIIS was successfully applied to the determination of copper (II) ions in real water samples. The Limits of detection (LODs) for Cu2+ ions in real water samples were in the range of 0.11–0.14 uM. The present study provided a feasible strategy for construction of fluorescent ion-imprinted sensor for convenient, sensitive and selective detection of metal ions.

Identification of long-term trends and seasonality in high-frequency water quality data from the Yangtze River basin, China.

Abstract: Comprehensive understanding of the long-term trends and seasonality of water quality is important for controlling water pollution. This study focuses on spatio-temporal distributions, long-term trends, and seasonality of water quality in the Yangtze River basin using a combination of the seasonal Mann-Kendall test and time-series decomposition. The used weekly water quality data were from 17 environmental stations for the period January 2004 to December 2015. Results show gradual improvement in water quality during this period in the Yangtze River basin and greater improvement in the Uppermost Yangtze River basin. The larger cities, with high GDP and population density, experienced relatively higher pollution levels due to discharge of industrial and household wastewater. There are higher pollution levels in Xiang and Gan River basins, as indicated by higher NH4-N and CODMn concentrations measured at the stations within these basins. Significant trends in water quality were identified for the 2004–2015 period. Operations of the three Gorges Reservoir (TGR) enhanced pH fluctuations and possibly attenuated CODMn, and NH4-N transportation. Finally, seasonal cycles of varying strength were detected for time-series of pollutants in river discharge. Seasonal patterns in pH indicate that maxima appear in winter, and minima in summer, with the opposite true for CODMn. Accurate understanding of long-term trends and seasonality are necessary goals of water quality monitoring system efforts and the analysis methods described here provide essential information for effectively controlling water pollution.

A reaction-based, colorimetric and near-infrared fluorescent probe for Cu2+ and its applications

Abstract: A reaction-based near-infrared (NIR) fluorescent probe, (E)-4-(2-(4-(dicyanometh- ylene)-4H-chromen-2-yl)vinyl)phenyl picolinate (DCM-P), was designed and synthesized by employing the dicyanomethylene-4H-pyran chromophore as the fluorophore and the 2-picolinic ester group as the recognition unit. The proposed probe DCM-P showed significant NIR fluorescence “turn-on” response to Cu2+ with distinct colorimetric change from yellow to purple. The recognition mechanism of probe for Cu2+ was confirmed by fluorescence spectroscopy, 1H NMR spectra, HRMS spectrometry and TD-DFT calculations. The probe possesses the advantages of large Stokes shift (116 nm), applicability in physiological conditions, low detection limit (2.3 × 10−8 M), and high selectivity toward Cu2+ in presence of other metal ions. Encouraged by these desirable properties, the probe DCM-P was successfully used for quantitative determination of Cu2+ in real water samples and NIR fluorescence imaging of Cu2+ in living cells with satisfactory results.

Organic-ion-intercalated FeSe-based superconductors

Abstract: Finding a new derivative structure of FeSe-based superconductors with a high superconducting transition temperature (${T}_{c}$) is of great significance. Here, in this work, an organic-ion-[cetyltrimethyl ammonium (${\mathrm{CTA}}^{+}$)]-intercalated FeSe-based superconductor ${(\mathrm{CTA})}_{0.3}\mathrm{FeSe}$ with ${T}_{c}$ as high as 45 K is synthesized by an electrochemical intercalation method. The as-prepared ${(\mathrm{CTA})}_{0.3}\mathrm{FeSe}$ has a hybrid crystal structure consisting of double layers of ${\mathrm{CTA}}^{+}$ and one layer of FeSe, which is consistent with a lateral-bilayer model. The superconductivity of ${(\mathrm{CTA})}_{0.3}\mathrm{FeSe}$ is confirmed by magnetic susceptibility. Furthermore, a negative pressure effect on superconductivity $d{T}_{c}/dP=\ensuremath{-}5$ K/GPa is observed. This is the first pure organic-ion-intercalated FeSe-based superconductor with a high ${T}_{c}$ and high crystallinity. Our work offers a new method to modify the interface interaction between the FeSe layer and the intercalator, and sheds new light on finding new FeSe-based superconductors with higher ${T}_{c}$.

Novel Electrochemical Sensors Based on Cuprous Oxide-Electrochemically Reduced Graphene Oxide Nanocomposites Modified Electrode toward Sensitive Detection of Sunset Yellow

Abstract: Control and detection of sunset yellow is an utmost demanding issue, due to the presence of potential risks for human health if excessively consumed or added. Herein, cuprous oxide-electrochemically reduced graphene nanocomposite modified glassy carbon electrode (Cu₂O-ErGO/GCE) was developed for the determination of sunset yellow. The Cu₂O-ErGO/GCE was fabricated by drop-casting Cu₂O-GO dispersion on the GCE surface following a potentiostatic reduction of graphene oxide (GO). Scanning electron microscope and X-ray powder diffractometer was used to characterize the morphology and microstructure of the modification materials, such as Cu₂O nanoparticles and Cu₂O-ErGO nanocomposites. The electrochemical behavior of sunset yellow on the bare GCE, ErGO/GCE, and Cu₂O-ErGO/GCE were investigated by cyclic voltammetry and second-derivative linear sweep voltammetry, respectively. The analytical parameters (including pH value, sweep rate, and accumulation parameters) were explored systematically. The results show that the anodic peak currents of Cu₂O-ErGO /GCE are 25-fold higher than that of the bare GCE, due to the synergistic enhancement effect between Cu₂O nanoparticles and ErGO sheets. Under the optimum detection conditions, the anodic peak currents are well linear to the concentrations of sunset yellow, ranging from 2.0 × 10-8 mol/L to 2.0 × 10-5 mol/L and from 2.0 × 10-5 mol/L to 1.0 × 10-4 mol/L with a low limit of detection (S/N = 3, 6.0 × 10-9 mol/L). Moreover, Cu₂O-ErGO/GCE was successfully used for the determination of sunset yellow in beverages and food with good recovery. This proposed Cu₂O-ErGO/GCE has an attractive prospect applications on the determination of sunset yellow in diverse real samples.