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As a two-dimensional (2D) material, monolayer MoS2 which limits its optical applications has a low absorption efficiency. In this paper, we propose a three-band perfect metamaterial absorber in the visible light range based on monolayer MoS2. The peak absorptivity of the structure at each resonance wavelength is nearly perfect, moreover, the light absorption of monolayer MoS2 is obviously enhanced at the three resonant wavelengths. The dielectric–dielectric–metal structure we designed produces the coupling of Fabry–Perot resonance and high-order diffraction guided-mode resonance at different absorption peaks, which has been proved by the slab waveguide theory. In addition, the multi-modal absorption phenomenon is explained by extracting the equivalent impedance. The results show that we can adjust the absorption peak wavelength by regulating the parameters of the structure. This structure not only provides an idea for enhancing the interaction between light and two-dimensional materials but also has potential applications for optical detection devices.

We present a scheme to control the generated ultrafast magnetic field in H 3 2 + molecules using multi-frequency tricircular pulses composed of co- and counter-rotating bicircular pulses. Simulations show that the field amplitude and the wavelength are two significant factors for magnetic field generation by tricircular pulses. Specifically, the strength of the magnetic field is linearly related to the field amplitude at λ 0 = 50 nm, while at λ 0 = 70 nm, the strength first increases and then decreases with the amplitude, this can be attributed to the resonance between the ground and excited states. Moreover, the phase and helicity of bicircular pulses are shown to have important effects on the magnetic field. The dependence of the magnetic field on the phase arises from the interference effect between multiple ionization pathways. These findings illustrate a guiding principle for controlling the magnetic field in molecular systems for future research in ultrafast magneto-optics.

The generation of electronic currents and magnetic fields by H 6 5 + and H 4 3 + molecules with current-carrying states under circularly polarized (CP) and linearly polarized (LP) laser pulses is investigated. Results show that the electronic currents and magnetic fields induced by CP pulses are higher than those by LP pulses for both molecules in the resonance excitation scheme. This can be attributed to the switchable dipole moment of the laser pulses, inducing selective state-to-state electronic transitions. Moreover, it was found that magnetic fields are sensitive to different initial states of the molecules in the ionization scheme. In particular, the magnetic fields induced by the current-carrying states are much higher than that induced by the ground state, which is because the current-carrying states have a stable electronic ring current and the induced magnetic field is contributed by the current-carrying state itself and the laser field. These findings provide a scheme for generating ring-shaped currents and magnetic fields in molecular systems for future research in ultrafast magneto-optics.

As a microwave generator, spin transfer nano-oscillator (STNO) based on skyrmion promises to become one of the next-generation spintronic devices. However, there still exist a few limitations to the practical applications. In this paper, we propose a new STNO based on synthetic antiferromagnetic (SAF) skyrmion pair assisted by a perpendicular fixed magnetic field. It is found that the oscillation frequency of this kind of STNO can reach up to 5.0 GHz, and the multiple oscillation peak with higher frequency can be realized under a fixed out-of-plane magnetic field. Further investigation shows that the skyrmion stability is improved by bilayer antiferromagnetic coupling, which guarantees the stability process of skyrmion under higher spin-polarized current density. Our results provide the alternative possibilities for designing new skyrmion-based STNO to further improve the oscillation frequency, and realize the output of multiple frequency microwave signal.

The strong-field ionization of dimers is investigated theoretically in counter-rotating circularly polarized laser fields. By numerically solving the two-dimensional (2D) time-dependent Schrödinger equation (TDSE) with the single-electron approximation (SEA) frame, we present the photoelectron momentum distributions (PMDs) and photoelectron angular distribution (PADs) of aligned Ne and Xe dimers. It is found that the PMDs and PADs strongly depend on the time delays by counter-rotating circularly polarized laser pulses. The results can be explained by the ultrafast photoionization model and the evolution of electron wave packets for Ne and Xe dimers. Besides, We make a comparison of PMDs between Ne atom and Ne dimer.

We investigate the ellipticity of the high-order harmonic generation from the oriented H 2 + exposed to a linearly polarized laser field by numerically solving the two-dimensional time-dependent Schrödinger equation (2D TDSE). Numerical simulations show that the harmonic ellipticity is remarkably sensitive to the alignment angle. The harmonic spectrum is highly elliptically polarized at a specific alignment angle θ = 30°, which is insensitive to the variation of the laser parameters. The position of the harmonic intensity minima indicates the high ellipticity, which can be attributed to the two-center interference effect. The high ellipticity can be explained by the phase difference of the harmonics. This result facilitates the synthesis of a highly elliptical isolated attosecond pulse with duration down to 65 as, which can be served as a powerful tool to explore the ultrafast dynamics of molecules and study chiral light–matter interaction.

Coherent electronic dynamics are of great significance in photo-induced processes and molecular magnetism. We theoretically investigate electronic dynamics of triatomic molecule H 3 2 + by circularly polarized pulses, including electron density distributions, induced electronic currents, and ultrafast magnetic field generation. By comparing the results of the coherent resonant excitation and direct ionization, we found that for the coherent resonant excitation, the electron is localized and the coherent electron wave packet moves periodically between three protons, which can be attributed to the coherent superposition of the ground A′ state and excited E+ state. Whereas, for the direct single-photon ionization, the induced electronic currents mainly come from the free electron in the continuum state. It is found that there are differences in the intensity, phase, and frequency of the induced current and the generated magnetic field. The scheme allows one to control the induced electronic current and the ultrafast magnetic field generation.

Valley Photonic Crystals (VPC) have provided a novel topological photonic platform to manipulate light. Here, we construct zigzag and armchair domain walls using two-dimensional silicon VPC, the edges between domains of opposite valley indices link to corresponding topological invariant. We study the light transmission of these edges under defects and sharp bent corners. Based on the Valley-contrasting edges, we design the all-optical logic gates at telecommunication wavelength with XOR/OR function simultaneously. Topologically protected waveguides own high transmission and backscattering-immune features, and coupling of different edge modes result in interference for logic function. Compared with traditional Photonic Crystals logic gates, our device shows outstanding properties including robust transmission, higher contrast ratio and more compact footprint. And it also shows the potential of topological photonics applying in optical logic circuits.

Single atom catalysts (SACs), featured by atomically-level distributed active sites on supports, provide an ideal platform in the fields of energy conversion, and mimic metalloprotease for bridging the gap between natural enzymes and single atom nanozymes by virtue of their maximum atom utilization efficiency, superior selectivity and outstanding catalytic performance. In this review, the recent progress in this field is reported from the perspectives of synthesis routes, which is also a prerequisite for catalytic investigation. Subsequently, we depict their applications in different sensing systems including electrochemical, colorimetric and photoactive sensing, as well as biomedicine such as disease therapy, antibacterial and cytoprotection to demonstrate their nanoenzymatic activity, and their promising applications in electrocatalysis such as water splitting, oxygen and CO2 reduction reaction are highlighted in more details. Finally, the current challenges and future outlooks of higher loading, more activity and stable in SACs are presented.

Terahertz polarization devices are an important part of terahertz optical systems. Traditional terahertz polarization devices rely on birefringent crystals, and their performances are limited by the material structures. In this work, we theoretically demonstrate that the metamaterial consisting of the medium and the periodic metal band embedded in the medium can control broadband polarization effectively. The transmission length of the subwavelength waveguide mode gives rise to a broadband transmission peak. The resonant cavity structure formed by the dielectric layer and the waveguide layer possesses a high transmission efficiency. By optimizing the metamaterial structure parameters, we design a high-efficient (>90%) quarter-wave plate over a frequency range of 0.90 THz–1.10 THz and a high-efficient (>90%) half-wave plate over a frequency range of 0.92 THz–1.02 THz. Besides, due to the anisotropy of the structure, the metamaterials with the same structural parameters can achieve the function of the polarized beam splitting with an efficiency of up to 99% over a frequency range of 0.10 THz–0.55 THz. Therefore, the designed metamaterial has a multifunctional polarization control effect, which has potential applications in the terahertz integrated polarization optical system.

In the present paper a new streamline model for wake development based on a streamline topology is applied and compared with different approaches for modeling the wind turbine wakes. The contribution of the present work is the comparison of the streamline-and straight-wake models as well as the different wake models, e.g., Jensen and Gaussian. The models have been applied to two wind farm cases. The results from the first case are compared against SCADA measurements and computational fluid dynamics simulations (CFD). The CFD simulations are performed using Reynolds-Averaged Navier Stokes (RANS) together with the actuator disc (AD) approach. The mean percent difference in power using the different wake models ranged between 19-20%. Mean percent difference in power for the AD-RANS was approximately 20%. For the second wind farm case only wake models are compared and approximately ±1% difference exists between them. The present work shows that the streamline topology of the wind turbine wake flow as well as the wake models have an effect on the performance prediction of wind farms.

A number of past studies have focused on point and line defects in graphene epitaxially grown on SiC substrates. However, few studies have investigated closed-ring defects formed within grain boundary loops. The present study addresses this issue by applying low-temperature scanning tunneling microscopy/spectroscopy to investigate the atomic structures of closed-ring defects in graphene epitaxially grown on 4H-SiC, and to evaluate their effects on the electron state density. The results indicate that the orientations of the graphene lattice inside and outside of grain boundary loop structures are rotated uniformly by an angle of 30° relative to each other, suggesting that closed-ring defects are highly ordered and are mainly composed of clusters of pentagon-heptagon carbon rings and highly ordered pentagon-heptagon chains. In addition, the spectroscopy results reveal for the first time that the density of electron states inside a closed-ring defect is strongly localized and position-dependent. Moreover, these closed-ring defects can eliminate intervalley scattering while maintaining intravalley scattering. These findings are not only helpful for contributing to a deeper understanding of the effects of closed-ring defects in graphene, but also present a potentially useful valley-filtering mechanism for charge carries that can be applied to the practical development of all-electric valley-based devices.

The performance of type-II superlattice (T2SL) long-wavelength infrared devices is limited by crystalline quality of T2SLs. We optimize the process of growing molecular beam epitaxy deposition T2SL epi-layers on GaSb (100) to improve the material properties. Samples with identical structure but diverse In/Ga beam-equivalent pressure (BEP) ratio are studied by various methods, including high-resolution x-ray diffraction, atomic force microscopy and high-resolution transmission electron microscopy. We find that appropriately increasing the In/Ga BEP ratio contributes to improving the quality of T2SLs, but too large In BEP will much more easily cause a local strain, which can lead to more InSb islands in the InSb interfaces. The InSb islands melt in the InSb interfaces caused by the change of chemical potential of In atoms may result in the “nail” defects covering the whole T2SLs, especially the interfaces of GaSb-on-InAs. When the In/Ga BEP ratio is about 1, the T2SL material possesses a lower full width at half maximum of +1 first-order satellite peak, much smoother surface and excellently larger area uniformity.

We investigated the nonsequential double ionization (NSDI) in Ar by two-color elliptically polarized laser field with a three-dimensional (3D) classical ensemble method. We study the relative phase effect of NSDI and distinguish two particular recollision channels in NSDI, which are recollision–impact ionization (RII) and recollision-induced excitation with subsequent ionization (RESI), according to the delay-time between the recollision and the final double ionization. The numerical results indicate that the ion momentum distribution is changed and the triangle structure is more obvious with the decrease of the relative phase. We also demonstrate that the RESI process always dominates in the whole double ionization process and the ratio of RESI and RII channels can be influenced by the relative phase.

Lithium battery state of charge (SOC) is a core parameter in battery management systems. In order to suppress the influence of noise characteristics on the accuracy of SOC estimation, this paper proposes an adaptive kalman filter (AKF)algorithm with variable noise variance based on the battery equivalent circuit model. In order to improve the accuracy of SOC estimation, the algorithm estimates the noise variance online and applies the noise variance estimation to kalman filter iteration process. Aiming at the modular structure of the battery pack, a segmentation variable weighting coefficient algorithm is proposed to estimate the SOC value of the entire battery pack. Based on the simulation platform of matlab, this paper carries out experimental verification and analysis. The results demonstrate the effectiveness and superiority of the algorithm.

For the lithium battery electrochemical composite equivalent model, the sensitivity of model parameters to the battery state of charge (SOC) estimation is analysed in order to determine the influence of model parameters on SOC estimation and provide optimization basis for SOC estimation algorithm based on battery model. Firstly, the sensitivity analysis method of model parameters is defined, and the sensitivity of model parameters to SOC estimation of lithium ion batteries is quantitatively analysed based on MATLAB software. Then, based on MATLAB /Simulink, the extended Kalman filter algorithm is used to simulate the SOC estimation under variable model parameters and analyse the influence of parameter changes on the SOC value. The experimental results show the correctness and validity of the quantitative analysis results of parameter sensitivity, and provide the corresponding basis for the research of SOC estimation algorithm of lithium-ion battery variable parameter model.

By using classical ensemble method, we investigate the double ionization of C3H6 molecule with different structures (propene and cyclopropane) in intense laser fields. The numerical results show that the non-sequential double ionization occurs in propene molecule rather than cyclopropane molecule in 1200 nm laser field. To further explain this interesting phenomenon, the momentum distribution of double ionized electrons is presented and the result presents the "finger-like" structure at about 30 TW/cm2 of propene molecule, and this structure is more obvious than that in cyclopropane molecule. The above phenomena are also demonstrated by analysing the energy distributions of double-ionized electrons versus time. Moreover, we also investigated the angular distribution at the end of pulse, which is different between propene and cyclopropane.

There is observational evidence that broad-line regions (BLRs) exist in most active galactic nuclei (AGNs), but their origin is still unclear. One scenario is that the BLRs originate from winds accelerated from the hot coronae of the disks, and the winds are suppressed when the black hole is accreting at low rates. This model predicts a relation between ( = /Edd) and the FWHM of broad emission lines. We estimate the central black hole masses for a sample of bright AGNs by using their broad Hβ line-widths and optical luminosities. The dimensionless accretion rates = /Edd are derived from the optical continuum luminosities by using two different models: using an empirical relation between the bolometric luminosity Lbol and the optical luminosity ( = Lbol/LEdd, a fixed radiative efficiency is adopted); and calculating the optical spectra of accretion disks as a function of . We find a significant correlation between the derived and the observed line width of Hβ, FWHM∝−0.37, which almost overlaps the disk-corona model calculations, if the viscosity α≈0.1−0.2 is adopted. Our results provide strong evidence for the physical link between the BLRs and accretion disks in AGNs.

The geometry of broad-line regions (BLRs) in active galactic nuclei (AGNs) is still controversial. We use a sample of BL Lac objects, of which the black hole masses Mbh are estimated from their host galaxy absolute magnitude at R-band, MR, by using the empirical relation between MR and black hole mass Mbh. The sizes of the broad-line regions for MgII are derived from the widths of MgII lines and the black hole masses. Compared with the empirical relation between BLR size RBLR and MgII line luminosity LMgII, it is found the BLR sizes in the BL Lac objects derived in this paper are 2–3 orders of magnitude higher. If the BLR geometry of these sources is disklike, then the viewing angle between the axis and the line of sight is in the range of ~2°−15°, which is consistent with the unification scheme.

We introduce a heterogeneous fractional Fokker–Planck equation (HFFPE) on heterogeneous fractal structure media describing systems involving external force fields. The HFFPE is shown to obey the generalized Einstein relation, and its stationary solution is the Boltzmann distribution. It is proven that the asymptotic shape of its solution is a stretched Gaussian and that its solution can be expressed in the form of a function of a dimensionless similarity variable for constant and generic potentials with polar singularity at origin.

We investigate the molecular beam epitaxy growth of GaSb films on GaAs substrates using compositionally graded GaAs x Sb buffer layers. Optimization of GaAs x Sb growth parameter is aimed at obtaining high GaSb crystal quality and smooth GaSb surface. The optimized growth temperature and thickness of GaAs x Sb layers are found to be 420°C and 0.5 μm, respectively. The smallest full width at half maximum value and the root mean square surface roughness of 0.67 nm over 2 × 2 μm2 area are achieved as a 250 nm GaSb film is grown under optimized conditions.

Type-II InAs/GaSb superlattices made of 13 InAs monolayers (MLs) and 7 GaSb MLs are grown on GaSb substrates by solid source molecular beam epitaxy. To obtain lattice-matched structures, thin InSb layers are inserted between InAs and GaSb layers. We complete a series of experiments to investigate the influence of the InSb deposition time, V/III beam-equivalent pressure ratio and interruption time between each layer, and then characterize the superlattice (SL) structures with high-resolution x-ray diffraction and atomic force microscopy. The optimized growth parameters are applied to grow the 100-period SL structure, resulting in the full-width half-maximum of 29.55 arcsec for the first SL satellite peak and zero lattice-mismatch between the zero-order SL peak and the GaSb substrate peak.

The selective laser melting (SLM) technique is a recent additive manufacturing (AM) technique. Several studies have reported success in the SLM-based production of biocompatible orthopaedic implants and three-dimensional bone defect constructs. In this study, we evaluated the surface properties and biocompatibility of an SLM titanium implant in vitro and compared them with those of a machined (MA) titanium control surface. In addition, we evaluated the osseointegration capability of the SLM implants in vivo and compared it with those of MA and Nobel-speedy (Nobel-S) implants. SLM microtopographical surface analysis revealed porous and high roughness with varied geometry compared with a smooth surface in MA Ti samples but with similar favourable wettability. Osteoblast proliferation and alkaline phosphatase activity were significantly enhanced on the SLM surface. Histological analysis of the bone-implant contact ratio revealed no significant difference among SLM, MA, and Nobel-S implants. Micro-CT assessment indicated that there was no significant difference in bone volume fraction around the implant among SLM implants and other types of surface modification implants. The removal torque value measurement of SLM implants was significantly lower that of than Nobel-S implants P < 0.001 and higher than that of MA implants. The study demonstrates the capability of SLM implants to integrate with living bone. The SLM technique holds promise as a new dental implant manufacturing technique.

We report a theoretical study into the two- and three-mode entanglement inside an atom-like optical cavity. A five-level system is considered and the influence of the multi-dressed parametric amplification four-wave mixing (PA-FWM) process on the quantum correlation of fluctuation spectra is researched. Three-mode entanglement is determined by the coupling of two nonlinear gains; one of enhanced gains via the dressing state plays a dominant role in controlling and optimizing the profile of three-mode entanglement via vacuum Rabi splitting, enhancement/suppression of entanglement as well as two-mode. Specifically, increasing the quantity of dressing fields may result in the single-channel entanglement turning into nonlocal multichannel (multiple anti-crossing behaviors). Moreover, these entanglement channels can be squashed via the lateral squeezing effect of the cavity. Such multichannel entanglement has potential applications in nonlocal quantum imaging and quantum key distribution.

Most of the computational models of drug transport in vascular tumours assume a uniform distribution of blood vessels through which anti-cancer drugs are delivered. However, it is well known that solid tumours are characterized by dilated microvasculature with non-uniform diameters and irregular branching patterns. In this study, the effect of heterogeneous vasculature on drug transport and uptake is investigated by means of mathematical modelling of the key physical and biochemical processes in drug delivery. An anatomically realistic tumour model accounting for heterogeneous distribution of blood vessels is reconstructed based on magnetic resonance images of a liver tumour. Numerical simulations are performed for different drug delivery modes, including direct continuous infusion and thermosensitive liposome-mediated delivery, and the anti-cancer effectiveness is evaluated through changes in tumour cell density based on predicted intracellular concentrations. Comparisons are made between regions of different vascular density, and between the two drug delivery modes. Our numerical results show that both extra- and intra-cellular concentrations in the liver tumour are non-uniform owing to the heterogeneous distribution of tumour vasculature. Drugs accumulate faster in well-vascularized regions, where they are also cleared out more quickly, resulting in less effective tumour cell killing in these regions. Compared with direct continuous infusion, the influence of heterogeneous vasculature on anti-cancer effectiveness is more pronounced for thermosensitive liposome-mediated delivery.

A highly tunable refractive index sensor with excellent performance and good operation angle-polarization-tolerance is proposed and demonstrated numerically by means of the finite element method. The proposed sensor consists of a planar regular array of paired graphene concentric ring resonators sandwiched between a substrate and a sensing medium. Numerical calculation results show that a high sensitivity of 9.59 µm per refractive index unit and figure of merit of 5.82 can be reached for lower sensing medium refractive indices. The introduction of graphene in this sensor can enhance the absorption of biomolecules and make the sensing range actively tunable. Therefore, it can be conveniently used for possible detection of the refractive index variation of gases, liquids or mixed solutions. Also, we predict that a multi-channel sensor can be achieved by introducing several graphene concentric ring resonators into each unit cell of the array.

We demonstrate that the optical absorption is enhanced in small molecule organic solar cells by using a trapezoid grating structure. The enhanced absorption is mainly attributed to both waveguide modes and surface plasmon modes, which is simulated by using finite-difference time-domain method. The simulated results show that the surface plasmon along the semitransparent metallic Ag anode is excited by introducing the periodical trapezoid gratings, which induce the increase of high intensity field in the donor layer. Meanwhile, the waveguide modes result in a high intensity field in acceptor layer. The increase of field improves the absorption of organic solar cells significantly, which is demonstrated by simulating the electrical properties. The simulated results also show that the short-circuit current is increased by 31% in an optimized device, which is supported by the experimental measurement. Experimental result shows that the power conversion efficiency of the grating sample is increased by 7.7%.

A localized plasmon resonance sensor consisting of an asymmetric split-ring resonator array sustaining highly localized field energy with high refractive index sensitivity and good figure of merit is demonstrated and investigated. In the proposed 3-cut split-ring resonator structure with broken symmetry, a highly tunable transmission with a large modulation depth and a narrow resonance linewidth is obtained, which shows polarization-insensitive and angle-independent properties. Numerical calculation results show that a high sensitivity of up to 1006 nm/RIU and a figure of merit of 9.7 can be reached. This plasmonic index sensor is practically obtainable, and is expected to have potential applications for high-sensitivity convenient and efficient detection.

An asymmetric laser heterostructure is developed to improve the beam properties of GaSb-based diode lasers with no degradation in laser parameters. Employing the semivectorial finite difference method, the dependences of beam divergence and optical confinement factor on waveguide width and refractive index step are investigated theoretically. After carefully design, a particular asymmetric laser structure is proposed. Its beam divergence in the fast axis is reduced from 61° to 34° compared with that of the broad-waveguide structure. The optical confinement factor is approximately equal to 0.0362 and comparable to that of the conventional broad-waveguide structure.

A polypropylene nanofibrillar array was successfully fabricated by template-assisted nanofabrication strategy. Adhesion properties of this gecko-inspired structure were studied through two parallel and independent approaches: experiments and finite element simulations. Experimental results show relatively good normal adhesion, but accompanied by high preloads. The interfacial adhesion was modelled by effective spring elements with piecewise-linear constitution. The effective elasticity of the fibre-array system was originally calculated from our measured elasticity of single nanowire. Comparisons of the experimental and simulative results reveal quantitative agreement except for some explainable deviations, which suggests the potential applicability of the present models and applied theories.