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In this paper, a model of stochastic competition between plasmid-bearing and plasmid-free organisms in a chemostat is investigated. First, we show that there is a unique global positive solution for the stochastic system. Second, by employing stochastic Lyapunov functions, Itô formula, strong law of large number and some other important inequalities, stochastic characteristics of the stochastic competition chemostat model are studied such as the stochastic asymptotic behaviors of the system. Finally, some numerical simulations are given.

Vectorial optical fields (VOFs) exhibiting arbitrarily designed wavefronts and polarization distributions are highly desired in photonics. However, current methods to generate them either require complicated setups or exhibit limited functionalities, which is unfavorable for integration-optics applications. Here, we propose a generic approach to efficiently generate arbitrary VOFs based on metasurfaces exhibiting full-matrix yet inhomogeneous Jones-matrix distributions. We illustrate our strategy with analytical calculations on a model system and an experimental demonstration of a meta-device that can simultaneously deflect light and manipulate its polarization. Based on these benchmark results, we next experimentally demonstrate the generation of a far-field VOF exhibiting both a vortex wavefront and an inhomogeneous polarization distribution. Finally, we design/fabricate a meta-device and experimentally demonstrate that it can generate a complex near-field VOF—a cylindrically polarized surface plasmon wave possessing orbital angular momentum—with an efficiency of ~34%. Our results establish an efficient and ultracompact platform for generating arbitrary predesigned VOFs in both the near- and far-fields, which may find many applications in optical manipulation and communications.

Hydrogel-based flexible strain sensors for personal health monitoring and human-machine interaction have attracted wide interest among researchers. In this paper, hydrophobic association and nanocomposite conductive hydrogels were successfully prepared by introducing polyaniline coated silica (SiO2@PANI) core-shell particles into an acrylamide-lauryl methacrylate (P(AM/LMA)) copolymer matrix. The hydrophobic interaction between the SiO2@PANI core-shell particles and the hydrophobic LMA in the P(AM/LMA) chains induced the hydrogels with outstanding mechanical properties. Furthermore, the polyaniline on the SiO2 surface and the inorganic salt formed a conductive network, which synergistically enhanced the conductivity of the hydrogels. The obtained hydrogels integrate high tensile strength (1398 kPa), ultra-stretchability (>1000%), wonderful strain sensitivity (gauge factor = 10.407 at 100-1100% strain), quick response (300 ms), and excellent durability (>300 cycles) due to the hydrophobic association and nanocomposite effect. The prepared SiO2@PANI-P(AM/LMA) hydrogel shows high stress sensitivity to detect human movements and displays a broad application prospect in flexible strain-sensor field.

Vectorial optical fields (VOFs) exhibiting tailored wave fronts and spatially inhomogeneous polarization distributions are particularly useful in photonic applications. However, devices to generate them, made by natural materials or recently proposed metasurfaces, are either bulky in size or less efficient, or exhibit restricted performances. Here, we propose a general approach to design metadevices that can efficiently generate two distinct VOFs under illuminations of circularly polarized lights with different helicity. After illustrating our scheme via both Jones matrix analyses and analytical model calculations, we experimentally demonstrate two metadevices in the near-infrared regime, which can generate vortex beams carrying different orbital angular momenta yet with distinct inhomogeneous polarization distributions. Our results provide an ultracompact platform for bifunctional generations of VOFs, which may stimulate future works on VOF-related applications in integration photonics.

Although many approaches have been proposed to manipulate propagating waves (PWs) and surface waves (SWs), usually each operation needs a separate meta-device, being unfavorable for optical integrations. Here, we propose a scheme to design a single meta-device that can efficiently generate SWs and/or PWs with pre-designed wavefronts, under the excitations of circularly polarized (CP) PWs with different helicity. As a proof of concept, we design and fabricate a microwave meta-device and experimentally demonstrate that it can convert incident CP waves of opposite helicity to SWs possessing different wavefronts and traveling to opposite directions, both exhibiting very high efficiencies. We further generalize our scheme to design a meta-device and numerically demonstrate that it can either excite a SW beam with tailored wavefront or generate a far-field PW with pre-designed wavefront, as shined by CP waves with different helicity. Our work opens the door to achieving simultaneous controls on far- and near-field electromagnetic environments based on a single ultra-compact platform.

Hydrogeological active zones found in mine waste (tailings) dumping sites are a major source of concern that threatens the safety of the environment and groundwater, especially in karstic areas. Therefore, detecting and identifying these regions correctly will help in selecting the appropriate sites for tailings disposal and avoid consequential environmental problems. In this study, electrical resistivity imaging (ERI) surveys with high-resolution data were carried out to detect hydrogeological active zones in an area proposed as a settling pond for mining tailings accumulated from El Mochito mine property, located in the north-western section of Honduras. Two-dimensional (2-D) inversion results of thirty-four survey lines revealed several zones of low resistivity. These zones indicate water-/clay-bearing regions that are structurally weak. However, some survey lines, the limestone beneath the surface is entirely compacted; as such, it is considered to be an ideal site for tailings pond construction. In addition, on the eastern side of the valley, there is a large chunk limestone layer that is compacted and can be considered for tailings pond construction. The ERI method provided insight and developed an informative subsurface map to detect the hydrogeological active zones, thus proving it as a beneficial tool used for selecting disposal sites for mining tailings in karstic areas.

Plasmons, as emerging optical diffraction-unlimited information carriers, promise the high-capacity, high-speed, and integrated photonic chips. The on-chip precise manipulations of plasmon in an arbitrary platform, whether two-dimensional (2D) or one-dimensional (1D), appears demanding but non-trivial. Here, we proposed a meta-wall, consisting of specifically designed meta-atoms, that allows the high-efficiency transformation of propagating plasmon polaritons from 2D platforms to 1D plasmonic waveguides, forming the trans-dimensional plasmonic routers. The mechanism to compensate the momentum transformation in the router can be traced via a local dynamic phase gradient of the meta-atom and reciprocal lattice vector. To demonstrate such a scheme, a directional router based on phase-gradient meta-wall is designed to couple 2D SPP to a 1D plasmonic waveguide, while a unidirectional router based on grating metawall is designed to route 2D SPP to the arbitrarily desired direction along the 1D plasmonic waveguide by changing the incident angle of 2D SPP. The on-chip routers of trans-dimensional SPP demonstrated here provide a flexible tool to manipulate propagation of surface plasmon polaritons (SPPs) and may pave the way for designing integrated plasmonic network and devices.

Ionic liquids (ILs) hydrogels as an appropriate candidate for the absorption of nanoparticles, had gained immense interests due to its friendly environment, low cost, high efficiency, and insensiti...

In this paper, we consider a stochastic delayed two-species competition chemostat model with the Monod growth response function. First, we verify that there is a unique global positive solution for any given initial conditions for this stochastic delayed system. Second, we give the dynamical behavior of the solution of stochastic delay system around the washout equilibrium of deterministic system; moreover, we discuss the competition exclusion and coexistence of microorganisms $$x_1$$ and $$x_2$$ . Finally, computer simulations are carried out to illustrate the obtained results; in addition, results show that time delay has critical effects on the survival of the microorganisms.

Metamaterial-based electromagnetic absorbers have attracted much attention recently, but most previous realizations suffer from issues of narrow bandwidth, time-consuming and high-cost fabrication methods, and/or fixed functionalities, and so are unfavorable for practical applications. Here, we demonstrate experimentally a large-scale, broadband, polarization-independent, and tunable metamaterial absorber, which works for both visible and near-infrared light. A lithography-free and low-cost method was utilized to fabricate a centimeter-sized metamaterial sample in a metal-insulator-metal (MIM) configuration with nano-scale precision, in which a phase-change material, Ge2Sb2Te5 (GST), was adopted as the insulating spacer of the MIM structure. With two different resonance mechanisms working together, the proposed device was shown to exhibit high absorptivity (>80%) within a broad wavelength band (480-1020 nm). By thermally tuning the phase state of the GST layer, we can dramatically enlarge the working bandwidth of the metamaterial absorber by shifting one absorption peak by about 470 nm. These findings may stimulate many potential applications in, for example, solar cells, energy harvesting, smart sensing/imaging, and color printing.

A reactive core–shell modifier with the polybutadiene (PB) as core and styrene/acrylonitrile/glycidyl methacrylate terpolymer as shell (PB-g-SAG) was prepared to toughen the polylactide (PLA). Simultaneously, the epoxy-based multifunctional chain extender (CE) was used to further improve the modification ability of PB-g-SAG on the PLA properties. For the PLA/PB-g-SAG/CE blends, the compatibilization reaction between PLA and PB-g-SAG formed the PLA-g-SAG-g-PB copolymer, which improved the interfacial strength between the PLA and PB-g-SAG. At the same time, the branching reaction among the chain extender and the PLA formed the long chain branching structure which enhanced the molecular weight and entanglement density of the PLA. The aid of the epoxy-based chain extender further increased the melt strength, toughness and stiffness of PB-g-SAG toughened PLA blends. When PB-g-SAG content was 20 wt%, 0.5 wt% CE induced the melt strength, impact strength and Young’s modulus of PLA/PB-g-SAG blend increase from 9.2 × 104 Pa·s, 428 J/m and 1634 MPa to 1.27 × 105 Pa·s, 530 J/m and 1845 MPa for the PLA/PB-g-SAG/CE blend. Compared with the pure PLA, the melt strength and impact strength were increased by 1150% and 1666%. Deformation results indicated the massive shearing yielding of the PLA matrix, the cavitation of the polybutadiene and interfacial debonding between the PB-g-SAG and the PLA were the major toughening mechanisms. This research provided a simple and practical strategy to overcome the shortcomings of the PLA and could promote its application in the industrial fields.

Spoof surface plasmons (SSPs) play crucial roles in terahertz (THz) near‐field photonics. However, both high‐efficiency excitation and wavefront engineering of SSPs remain great challenges, which hinder their wide applications in practice. Here, a scheme is proposed to simultaneously achieve these two goals efficiently using a single ultracompact device. First, it is shown that a gradient meta‐coupler constructed by high‐efficiency Pancharatnam–Berry (PB) meta‐atoms can convert circularly polarized (CP) THz beams into SSPs with absolute efficiency up to 60%. Encoding a parabolic phase profile into the meta‐coupler based on the PB mechanism, it is demonstrated that the device can covert CP beams into SSPs with focusing or defocusing wavefronts, dictated by the chirality of the incident wave. Finally, two distinct chirality‐dependent phase distributions are encoded into the meta‐coupler design by combining the PB and resonance phase mechanisms, and it is demonstrated that the resulting meta‐device can achieve SSP excitations with chirality‐delinked bifunctional wavefront engineering. THz near‐field experiments are performed to characterize all three devices, in excellent agreement with full‐wave simulations. The results pave the road to realize ultracompact devices integrating different functionalities on near‐field manipulations, which can find many applications (e.g., optical sensing, imaging, on‐chip photonics, etc.) in different frequency domains., High‐efficiency bifunctional manipulations on surface‐plasmon wavefronts are enabled by a single ultracompact meta‐device. Constructed with meta‐atoms possessing both geometric and resonant phases, the meta‐device exhibits distinct phase profiles for impinging lights with different spins, thus generating independent surface‐plasmon profiles. These findings may find many applications in integration photonics, such as coupling on‐chip optical devices and enhancing light–matter interactions.

The Epoxy-based Ionic Liquid/carboxylated multi-walled carbon nanotubes/polybutylene terephthalate nanocomposites (EPIL/c-MWCNTs/PBT) were prepared through melt-blending method. Due to πcation-π interactions between EPIL and c-MWCNTs, and the reaction of a carboxyl group of PBT matrices with an epoxy group of EPIL, the c-MWCNTs displayed a homogeneous dispersion in the EPIL/c-MWCNTs/PBT, which could present better electrical properties than that of c-MWCNTs/PBT composites. SEM results presented that the compatibility between of c-MWCNTs and PBT had been improved due to the excellent dispersibility of c-MWCNTs in PBT matrix Meanwhile, the crystallization temperature of EPIL/c-MWCNTs/PBT also increased to 213.4 °C, higher than that of c-MWCNTs/PBT and pure PBT. Furthermore, the EPIL/c-MWCNTs/PBT nanocomposites showed excellent 3D conducting network and exhibited a low conductivity of percolation threshold when the loading of c-MWCNTs was only 0.7 wt%. The addition of EPIL and c-MWCNTs to PBT could effectively increase the dielectric constant and the uniformly dispersed c-MWCNT in low dielectric loss, which opened a new direction for the fabrication of EPIL/c-MWCNTs/polymer nanocomposites.

The researches on how to prepare the polymer composites with high dielectric constant (high-k) and low dielectric loss were important for the rapid development of electronic industry. In this paper, by using silane coupling agent, the multi-wall carbon nanotubes (MWCNTs) could graft the thiol groups with high chain transfer constant on the surface, which made the polystyrene (PS) chain coat more efficiently on the surface of MWCNTs to form the core-shell structure. 1H NMR, TGA and TEM results, showed polystyrene were grafted on the surface of MWCNTs. The grafted PS could reduce the dielectric loss of composite materials and promote the dispersion of the coating MWCNTs in the matrix. In addition, the insulating layer effectively improved the interaction between the MWCNTs and PS matrix, which strengthened the binding force between the filler and matrix, resulting in the increase of the thermal stability of the PS composites. In terms of AC conductivity, the insulating layer could effectively prevent the contact between adjacent MWCNTs from forming a complete conducting network, which inhibited the generation of leakage current. Therefore, compared with untreated multi-wall carbon nanotubes/polystyrene composites, the above composites had excellent dielectric properties with high dielectric constant (214) and low dielectric loss (2.23) at low CNTs mass fraction (4 wt%).

Although metasurfaces have shown great potential for manipulating light, most previously realized meta-devices suffer from uncontrolled angular dispersions, making them unfavorable for many applications. Here, we propose a general strategy to realize optical metasurfaces with desired angular dispersions based on carefully controlling both the near-field couplings between meta-atoms and the radiation pattern of a single meta-atom. Utilizing such a strategy, we experimentally demonstrate a series of optical meta-devices with predesigned angular dispersions, including two incident-angle-insensitive absorbers, one incident-angle-selective absorber, and one multifunctional meta-polarizer whose functionality changes from a perfect mirror to a half-waveplate as the excitation angle varies. Finally, we design a gradient meta-device using meta-atom arrays with purposely controlled angular dispersions and numerically demonstrate that it can exhibit distinct wavefront-control functionalities when illuminated at different incident angles. Our findings establish a new platform for achieving angle-multiplexed functional meta-devices, significantly expanding the wave-manipulation capabilities of optical metasurfaces., Metasurfaces: Controlling interactions with angular light Scientists can control how optical meta-surfaces interact with different angles of incident light by making changes to their individual building blocks. The finding, by Lei Zhou and colleagues at China’s Fudan University, could lead to the realization of angle-multiplexed meta-devices. The researchers measured how light was reflected by a typical optical meta-surface depending on its incident angle. Their observations led them to theorize that reflected light was controlled by the interactions between meta-atoms and by radiation from individual ones. Changes to the meta-atom arrays allowed them to fabricate devices that altered light’s polarization, selectively absorbed light based on the incident angle, or absorbed light regardless of it. Finally, they were able to simulate a device with specific meta-atom arrangements that could both focus light or act as a mirror depending on the incident angle.

The unrestricted control of circularly polarized (CP) terahertz (THz) waves is important in science and applications, but conventional THz devices suffer from issues of bulky size and low efficiency. Although Pancharatnam–Berry (PB) metasurfaces have shown strong capabilities to control CP waves, transmission-mode PB devices realized in the THz regime are less efficient, limiting their applications in practice. Here, based on Jones matrix analysis, we design a tri-layer structure (thickness of ~λ/5) and experimentally demonstrate that the structure can serve as a highly efficient transmissive meta-atom (relative efficiency of ~90%) to build PB metadevices for manipulating CP THz waves. Two ultrathin THz metadevices are fabricated and experimentally characterized with a z-scan THz imaging system. The first device can realize a photonic spin Hall effect with an experimentally demonstrated relative efficiency of ~90%, whereas the second device can generate a high-quality background-free CP Bessel beam with measured longitudinal and transverse field patterns that exhibit the nondiffracting characteristics of a Bessel beam. All the experimental results are in excellent agreement with full-wave simulations. Our results pave the way to freely manipulate CP THz beams, laying a solid basis for future applications such as biomolecular control and THz signal transportation., Metasurfaces: efficient terahertz control Ultrathin metasurfaces that can efficiently manipulate circularly polarized terahertz waves in transmission rather reflection have been demonstrated by scientists in China. The devices were fabricated by Min Jia and colleagues from Fudan University and Capital Normal University. The tri-layer structures operate at frequencies of around 0.6 THz and suit future on-chip applications for terahertz photonics. Various designs were tested resulting in a circularly polarized terahertz Bessel beam generator and a device exhibiting the photonic spin Hall effect. The metasurfaces consist of a periodic array of meta-atoms, each composed of three thin layers of metal in a U-shape that are separated and surrounded by polyimide. Changing the angular orientation of the meta-atoms allows different phase gradients to be programmed into the metasurfaces bringing the desired functionality.

In this paper, a stochastic delay differential equations chemostat model with nonmonotone uptake function is considered, and the nutrient conversion process involves time delay. First, we verify that there is a unique global positive solution of the stochastic system. Second, we find that the solutions of stochastic system will oscillate around the equilibria of the corresponding deterministic model, moreover, results show that time delay has critical effects on the extinction and persistence of the microorganism, that is to say, under small noise, when the time delay is small, microorganism is persistent; when the time delay is large, microorganism will be extinct. In addition, we can find by the computer simulation that large noise may lead to microorganism become extinct, although microorganism is persistent in the deterministic systems when the time delay is small. Finally, computer simulations are carried out to illustrate the obtained results and the existence of bistability is observed.

In this work, graphene oxide sheets (GO) filled polyvinylidene fluoride (PVDF) nanodielectric composites with methyl methacrylate-co-glycidyl methacrylate copolymer (MG) as compatibilizer were fabricated by solution blend process. MG improved the dispersion of GO and enhanced the interface strength between GO and PVDF matrix. The strong dipolar interaction between MG on the surface of GO and PVDF resulted in the crystal transformation of PVDF from α-phase to β/γ-phase and nearly 81% β/γ-phase PVDF formed for PVDF/MG@GO7.0 composite. The thermal stability, mechanical property, melting and crystallization behaviors of PVDF/MG@GO composites were improved obviously due to the enhanced interface strength between GO and PVDF matrix with the aid of MG. MG copolymers not only contributed to the uniform dispersion of GO in PVDF, but also prevented the direct connection of GO and effectively inhibited the occurrence of leakage current in composites. Therefore, the dielectric properties of PVDF/MG@GO composites were also enhanced significantly with the addition of MG compared with the PVDF/GO composites, which supported the fact that the dielectric properties of resulted composites could be tailored by using MG copolymer as compatibilizer.

Ba(1−x)CaxTi0.92Zr0.08O3 (BTZ-xCa; x = 0–0.20) lead-free ceramics were prepared at a low temperature of 1210°C using as-synthesized nanoparticles through a modified Pechini method. The structure, permittivity, ferroelectricity, piezoelectricity, and thermal expansion characteristics of the ceramics that were influenced by varying calcium contents were studied in detail. X-ray powder diffraction and Raman results suggested that calcium could not induce the rhombohedral phase transition, and impurity phases were detected with excessive x. The electrical properties were basically elevated firstly in the room temperature direction of the temperature of phase transitions for orthorhombic-to-tetragonal with weaker internal stress, and then they apparently deteriorated with the shrunk octahedron size and strongly distorted structure with an increase of calcium content. The optimum electrical properties, i.e., d33, kp, and Qm of the BTZ-xCa ceramics were 261 pC/N, 24.9%, and 98 were obtained when the calcium content was 0.05, respectively. Additionally, the thermal expansion coefficient was studied for providing guidance on the ceramic materials production and usage.

In this paper, a stochastic delayed chemostat model with nutrient storage is proposed and investigated. First, we state that there is a unique global positive solution for this stochastic system. Second, using the classical approach of Lyapunov function analysis, this stochastic delayed chemostat model is discussed in detail. We establish some sufficient conditions for the extinction of the microorganism, furthermore, we prove that the microorganism will become persistent in the mean in the chemostat under some conditions. Finally, the obtained results are illustrated by computer simulations, and simulation results reveal the effects of time delay on the persistence and extinction of the microorganism.

Optical microcavities with whispering-gallery modes (WGMs) have been indispensable in both photonic researches and applications. Besides, metasurfaces, have attracted much attention recently due to their strong abilities to manipulate electromagnetic waves. Here, combining these two optical elements together, we show a tubular cavity can convert input propagating cylindrical waves into directed localized surface waves (SWs), enabling the circulating like WGMs along the wall surface of the designed tubular cavity. Finite element method (FEM) simulations demonstrate that such near-field WGM shows both large chirality and high local field. This work may stimulate interesting potential applications in e.g. directional emission, sensing, and lasing.

This article presents new zircon U–Pb geochronology, Hf isotopic, and whole-rock major- and trace-element geochemical data that provide insights into the petrogenesis and tectonic history of the Ri...

In this paper, a stochastic chemostat model with an inhibitor is considered, here the inhibitor is input from an external source and two organisms in chemostat compete for a nutrient. Firstly, we show that the system has a unique global positive solution. Secondly, by constructing some suitable Lyapunov functions, we investigate that the average in time of the second moment of the solutions of the stochastic model is bounded for a relatively small noise. That is, the asymptotic behaviors of the stochastic system around the equilibrium points of the deterministic system are studied. However, the sufficient large noise can make the microorganisms become extinct with probability one, although the solutions to the original deterministic model may be persistent. Finally, the obtained analytical results are illustrated by computer simulations.

An electrochemical platform was designed using biocompatible quaternary ammonium salts containing alkyl groups with different chain lengths as electrode materials for visible protein immobilization on a glassy carbon (GC) electrode. The electrode was constructed using a simple self-assembly method relying on the electrostatic interaction between negatively charged hemoglobin (Hb) and positively charged quaternary ammonium materials. The Hb/quaternary ammonium salts/GC assembly exhibited excellent catalytic and electrochemical activities. Additionally, the structure-function properties of the quaternary ammonium salts on the electrochemical behavior of Hb was systematically investigated for various alkyl chain lengths between monomer and polymeric structures. Meanwhile, the corresponding bactericidal activities of the monomers and related polymers were evaluated by determining the minimum bactericidal concentration (MBC), minimum inhibitory concentration (MIC), and inhibitory zone diameters against bacteria. The results of these studies demonstrated that the quaternary ammonium monomers not only immobilized more proteins, but also displayed better antibacterial activity as alkyl chain length increased. Moreover, polymers possessed higher antimicrobial activities than their monomeric counterparts. However, the efficiency of the direct electron transfer process and the antibacterial properties of long-chain polymers were limited because they were prone to aggregation and blistering. In summary, the present results provide convenient access to direct electrochemistry using an immobilized redox protein. Furthermore, the potential to use the obtained materials in the construction of third-generation electrochemical biosensors was evaluated.

Sodium saccharin (SS) is a commonly used synthetic sweetener in carbonated soft drinks and beverages. Long-term consumption of SS could result in health problems. Here, a sensitive surface-enhanced Raman spectroscopy (SERS) method with silver nanorod (AgNR) array substrates was explored for quantification of SS in soft drinks. The AgNR array substrates fabricated by an oblique angle deposition technique exhibited an excellent SERS activity with an enhancement factor of ∼108. A good linear relationship was demonstrated between SERS peak intensity and SS concentration in the concentration range of 0.5–100 mg/L, and a limit of detection was determined to be 0.3 mg/L. The detection of SS in different soft drinks was further explored by combining SERS spectra with the partial least squares discriminant analysis. The results showed that the LODs of SS from Sprite, Cola, Fanta and Schweppes detected by SERS were 20, 5, 20 and 10 mg/L, respectively, which was far below the national standard. This SERS-based method enables the rapid and highly sensitive detection of SS with minimal sample pretreatment, and holds great promise in this food safety application.

1-Butyl-3-vinylimdazolium tetrafluoroborate ([BVIM][BF4]) was used as ionic liquid to in situ copolymerized with methyl methacrylate (MMA) in poly(vinylidene fluoride) (PVDF) solution by the free radical polymerization method. The content of [BVIM][BF4] in the copolymerized monomers ranges from 0 to 50%. Soxhlet extraction results showed that more than 60% P(MMA-co-[BVIM][BF4]) were grafted onto the PVDF chains and the grafting degree was higher than 15%. 1H NMR tests proved the occurrence of grafting reaction. SEM morphology indicated that phase separation took place for the in situ PVDF/P(MMA-co-[BVIM][BF4]) composites when the [BVIM][BF4] content was more than 40 wt%. FTIR and XRD measurements indicated the crystal transformation of PVDF from α-phase to s/γ phase due to the ion-dipole interaction between PVDF and [BVIM][BF4]. Furthermore, the introduction of [BVIM][BF4] into the in situ PVDF/P(MMA-co-[BVIM][BF4]) composites enhanced the electrical conductivity and dielectric constant of PVDF. The present method improved the stability of ionic liquid in the PVDF composites and the in situ PVDF/P(MMA-co-[BVIM][BF4]) composites show potential applications in sensor, actuator and battery fields.

In this paper, a chemostat model with general monotone response functions and two discrete time delays is proposed to describe the dynamical behavior about predator–prey system. First, by analyzing the characteristic equation associated with the model, we obtain the conditions of the existence and stability of extinction equilibrium and positive equilibrium. Choosing delays as bifurcation parameters, the existence of Hopf bifurcations is investigated in detail. Second, by virtue of the Poincare normal form method and center manifold theorem, explicit formulas are derived to determine the direction of Hopf bifurcation and the stability of the bifurcating periodic solutions. Finally, some numerical simulations are carried out to illustrate the theoretical results and the biological significance.

Colloid silica nanoparticles were hydrophobic modified by γ-methacryloxypropyl trimethoxysilane (MPS) for the encapsulation into polymer. The alkoxysilane-functionalized core-shell latexes were successfully synthesized via miniemulsion copolymerization of the butyl acrylate, styrene with MPS as the functional monomer in the presence of the modified silica. When these latexes dried at room-temperature, the post-cross-linking occurred due to the alkoxysilane groups on the particle surface and lead to the formation of the films. The morphology of the nanocomposite latexes and the mechanical properties, thermal properties, fire-resistant, optical properties and micro-structure of the resulted films were characterized and discussed. Scanning electron microscope result showed most of the nanoparticles dispersed homogeneously in the polymer matrix when the content of MPS-silica was 10%. However, when the content of MPS-silica nanoparticles was beyond 10%, the aggregation of the nanoparticles became obvious. The tensile test showed that the stress at break increased a lot with the increase of silica content. The thermal and fire-resistant behaviors of the nanocomposite films were improved greatly by the incorporation of silica particles. The optical test showed that the hybrid film was comparable to the pure polymer film at around 84% transmittance.

This paper studies a stochastic two-species Monod competition chemostat model which is subject to environment noises. Such noises are described by independent standard Brownian motions. It proves that the initial value problem of the model has a unique positive global solution. However, unlike the corresponding deterministic model, the stochastic model no longer has positive equilibrium points. The asymptotic behaviors and the steady state distributions are established by using Ito's formula, Lyaponov method and Gronwall inequality. In addition, numerical simulations are given to illustrate the theoretical results.

Mineral exploration in the Canadian shield is a major challenge nowadays. This is because of the thick overburden cover and complex geology. Borehole tomography using resistivity and induced polarization (BHDCIP) method has a big advantage here due to that the data is acquired underneath the cover and data quality, in general, is superior to that acquired at the surface. BHDCIP provides good resistivity and chargeability data, which can identify mineralization easily. In this study, the BHDCIP survey with high-resolution data was carried out to identify mineralization zones in the McCreedy West zone, north-western Sudbury, Ontario, Canada. Two and three-dimensional (2-D and 3-D) inversion results of three boreholes clearly revealed the mineralization zones and that harmonised with previous geological studies in the study area. The BHDCIP method provided insight and developed an informative subsurface map to identify the mineralization zones, thus proving it as a beneficial tool used for mineral exploration in complex geology with a minimal data survey and an irregular geometrical distribution.

In this paper, a stochastic chemostat model with variable yield and Contois growth function is investigated. The yield coefficient depends on the limiting nutrient, and the environmental noises are given by independent standard Brownian motions. First, the existence and uniqueness of global positive solution are proved. Second, by using stochastic Lyapunov function, Itô’s formula, and some important inequalities, stochastic characteristics for the stochastic model are studied, including the extinction of micro-organism, the strong persistence in the mean of micro-organism and, the existence of a unique stationary distribution of the stochastic model. Third, the necessary condition of an optimal stochastic control for the stochastic model is established by Hamiltonian function. In addition, some numerical simulations are carried out to illustrate the theoretical results and the influence of the variable yield on the microorganism.

Poly(lactic acid) (PLA) was toughened by the thermoplastic poly(propylene carbonate) polyurethane (PPCU), and the mechanical properties, crystallization behaviour and enzymatic degradation of the PLA/PPCU blends were investigated. The mechanical testing results showed that the impact strength and elongation at break of PLA/PPCU blends were remarkably higher than those of pure PLA. The impact strength was enhanced from 4.8 kJ m−2 for pure PLA to 102.8 kJ m−2 for the 50/50 PLA/PPCU blend. The impact testing showed obvious ductile fracture after PLA was blended with PPCU. It was found that the PLA matrix showed large plastic deformation (shear yielding) in the blend subjected to impact tests, which is an important energy-dissipation process and led to a toughened polymer blend. PPCU could act as an impact modifier for PLA. The maximum improvement in the cold crystallization temperature (Tcc) value was observed for PLA/PPCU blends where Tcc was increased from 113 °C to 128 °C. PPCU enhanced the crystallization degree of PLA, but the positive function of crystallization was weakened when the content of PPCU was increased from 10 to 50 wt%. Isothermal crystallization kinetics showed that PPCU improved the crystallinity of the PLA and reduced the crystallization rate of blends. And the incorporation of PPCU did not alter the crystal structure of the PLA matrix. The PLA/PPCU blends were high strength and high toughness, entirely biodegradable materials, which is important for manufacture and application.

Metalens have been recently introduced to overcome shortcomings of traditional lenses and optical systems, such as large volume and complicated assembly. As a proof-of-principle demonstration, we design an all-dielectric converging cylindrical metalens (CML) for working in long-wave infrared regions around 9 µm, which is made up of silicon-pillar on MgF2 dielectric layer. We further demonstrate the focusing effect of an orthogonal doublet cylindrical metalens (ODCM). Two CMLs are combined orthogonally and a circular focusing spot was demonstrated. This proves that within a certain size range, the focusing effect achieved by the ODCM is similar to that of a traditional circular metalens.

Manipulating circularly polarized (CP) light waves at will are highly important for photonic researches and applications. Recently, while Pancharatnam-Berry (PB) metasurfaces have shown unprecedented capabilities to control CP light, meta-devices constructed so far always suffer from the limitations of low-efficiency and narrow bandwidth. Here, we propose a scheme to construct PB metasurfaces with these two issues well addressed. To verify our idea, two PB meta-devices are designed and fabricated for achieving high-efficiency and broadband photonic spin Hall effect and focusing effect, respectively. Experimental results, in good agreement with full wave simulations, demonstrate the desired functionalities with efficiencies reaching 80% within an ultra-wide frequency band (8.2-17.3GHz). The proposed design scheme is generic and can be extended to high-frequency regimes. Our work can stimulate the realizations of high-performance and broadband PB meta-devices with diversified functionalities.

Metasurfaces, ultrathin metamaterials constructed by planar meta-atoms with tailored electromagnetic (EM) responses, have attracted tremendous attention due to their exotic abilities to freely control EM waves. With active elements incorporated into metasurface designs, one can realize tunable and/or reconfigurable metadevices with functionalities controlled by external stimuli, opening a new platform to dynamically manipulate EM waves. In this article, we briefly review recent progress on tunable/reconfigurable metasurfaces, focusing on their working mechanisms and practical applications. We first describe available approaches, categorized into different classes based on external stimuli applied, to realize homogeneous tunable/reconfigurable metasurfaces, which can offer uniform manipulations on EM waves. We next summarize recent achievements on inhomogeneous tunable/reconfigurable metasurfaces with constitutional meta-atoms locally tuned by external knobs, which can dynamically control the wave-fronts of EM waves. We conclude this review by presenting our own perspectives on possible future directions and existing challenges in this fast developing field.

Transparent dielectric composites with high electroactive, low dielectric loss and high energy density are highly desirable due to the potential applications in electronic and electric industry. In this work, simultaneously achieving excellent electroactive, high dielectric and energy storage performance in a transparent dielectric composite is proposed by compounding nano-montmorillonite (Na+ MMT) and ionic liquid (IL) with poly (vinylidene fluoride) (PVDF) through one-step melt blending technique. The microstructure, crystal forms, transparency, mechanical, dielectric and energy storage performances of PVDF/MMT/IL nanocomposites were systematically investigated. The existence of IL and shearing force contributes to the effective exfoliation of MMT in the PVDF matrix. Based on the synergy of Na+ MMT and IL, the PVDF/IL/MMT composites not only exhibited almost 100% polar phase PVDF but also the optical transmittance was significantly enhanced. The improved dielectric constant and reduced dielectric loss were successfully achieved in the PVDF/IL/MMT nanocomposites due to the inhibition of ion migration by exfoliated silicate layers. Moreover, the PVDF/IL/MMT nanocomposite exhibited improved energy storage performance compared with the nanocomposites containing IL or Na+ MMT independently. Therefore, the PVDF/IL/MMT nanocomposite with high electroactive, excellent transparency, high dielectric and energy storage performance shows potential applications in microelectronic device.

The invisibility cloak, a long-standing fantastic dream for humans, has become more tangible with the development of metamaterials. Recently, metasurface-based invisibility cloaks have been proposed and realized with significantly reduced thickness and complexity of the cloaking shell. However, the previous scheme is based on reflection-type metasurfaces and is thus limited to reflection geometry. In this work, by integrating the wavefront tailoring functionality of transparent metasurfaces and the wave tunneling functionality of zero-index materials, we have realized a unique type of hybrid invisibility cloak that functions in transmission geometry. The principle is general and applicable to arbitrary shapes. For experimental demonstration, we constructed a rhombic double-layer cloaking shell composed of a highly transparent metasurface and a double-zero medium consisting of dielectric photonic crystals with Dirac cone dispersions. The cloaking effect is verified by both full-wave simulations and microwave experimental results. The principle also reveals exciting possibilities for realizing skin-thick ultrathin cloaking shells in transmission geometry, which can eliminate the need for spatially varying extreme parameters. Our work paves a path for novel optical and electromagnetic devices based on the integration of metasurfaces and metamaterials., Optics: Another step closer to an invisibility cloak Chinese scientists have developed an innovative technique for making an invisibility cloak that could pave the way for new optical and electromagnetic devices. Although invisibility cloaks by bending light around an object have been around for some time, they are bulky and complex devices with spatially gradient parameters, limiting their uses. Now, Yun Lai and his colleagues from Nanjing University and Soochow University, in collaboration with researchers from Fudan University, have developed a new technique that combines the properties of metamaterials and metasurfaces to produce an invisibility cloak that is significantly thinner and less complex than currently available. The hybrid device integrates the wavefront tailoring functionality of transparent metasurfaces with the wave tunneling functionality of materials with near-zero-refractive index, and enables a new approach of cloaking by creating the illusion of free space.

Methyl methacrylate (MMA), butyl acrylate (BA) and 1-butyl-3-vinylimdazolium tetrafluoroborate ([BVIM][BF4]) copolymer (MMA-BA-IL) was prepared and used to enhance the electroactive phase content, toughness and dielectric properties of poly(vinylidene fluoride) (PVDF). Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and differential scanning calorimetry (DSC) tests indicated that crystal transformation of PVDF from α-phase to β/γ-phase occurred due to ion-dipole interaction between PVDF and [BVIM][BF4]. Scanning electron microscope (SEM) results showed MMA-BA-IL copolymer dispersed in the PVDF uniformly and the partial replacement of MMA components by [BVIM][BF4] decreased the miscibility between PVDF and MMA-BA copolymer. MMA-BA-IL copolymer improved the tensile ductility and impact toughness of PVDF. When the content of MMA-BA-IL was beyond 10 wt%, the elongation at break was higher than 400% and the impact strength was higher than 600 J/m. Deformation mechanism researches proved that shear yielding of the PVDF matrix and debonding/cavitation of the MMA-BA-IL copolymer particles were the major toughening mechanisms. The addition of MMA-BA-IL copolymer enhanced the dielectric properties of PVDF significantly. When the MMA-BA-IL content was 15 wt%, the dielectric constant of the PVDF/MMA-BA-IL blend increased to 54.3 at the 100 Hz frequency, which improved by 246% relative to that of the pure PVDF.

Angular dispersion is an intrinsic property of metasurfaces, but its physical origin remains obscure, hindering metasurface design. This work establishes a theory to quantitatively describe such intriguing effects, and verifies it for a typical terahertz metasurface by means of experiments and numerical simulations. With this understanding, the authors propose a design strategy for meta-devices exhibiting incidence-angle-dependent multifunctionalities. As an illustration, they describe a polarization-control device that can behave as a half- or quarter-wave plate under different excitation angles.

Electromagnetic (EM) wave absorption plays a vital role in photonics. While metasurfaces are proposed to absorb EM waves efficiently, most of them exhibit limited bandwidth and fixed functionalities. Here, we propose a broadband and tunable terahertz (THz) absorber based on a graphene-based metasurface, which is constructed by a single layer of closely patterned graphene concentric double rings and a metallic mirror separated by an ultrathin SiO2 layer. Plasmonic hybridization between two graphene rings significantly enlarges the absorption bandwidth, which can be further tuned by gating the graphene. Moreover, the specific design also makes our device insensitive to the incident angle and polarization state of impinging EM waves. Our results may inspire certain wave-modulation-related applications, such as THz imaging, smart absorber, tunable sensor, etc.

The objective of this article is to fabricate poly(lactic acid) (PLA) and nano silica (SiO2) composites and investigate effect of SiO2 on the properties of PLA composites. Surface-grafting modification was used in this study by grafting 3-Glycidoxypropyltrimethoxysilane (KH-560) onto the surface of silica nanoparticles. The surface-grafting reaction was confirmed by Fourier transform infrared spectroscopy and thermogravimetric analysis. Then the hydrophilic silica nanoparticles became hydrophobic and dispersed homogeneously in PLA matrix. Scanning electron microscope and Dynamic thermomechanical analysis (DMA) results revealed that the compatibility between PLA and SiO2 was improved. Differential scanning calorimetry and polarized optical microscope tests showed that nano-silica had a good effect on crystallization of PLA. The transparency analysis showed an increase in transparency of PLA, which had great benefit for the application of PLA. The thermal stability, fire resistance, and mechanical properties were also enhanced because of the addition of nano silica particles. Copyright © 2016 John Wiley & Sons, Ltd.

Acrylic impact modifier (ACR), one kind of methyl methacrylate–butyl acrylate copolymer with a core–shell structure, was prepared by seed emulsion polymerization. The weight ratio of core–shell ranges from 85.5/14.5 to 71.9/28.1. Then PLA/ACR blends were prepared with a constant ratio of 80/20. The effect of core–shell ratio of ACR on toughening PLA was investigated. Torque analysis revealed that the torque values of PLA/ACR blends increased with increasing shell content of ACR. The impact strength of PLA/ACR blends reached the highest value of 77.1 kJ m−2 when the core–shell ratio of ACR was 79.2/20.8. Transmission electron microscope (TEM) photographs revealed that ACR was dispersed uniformly in the PLA matrix. Scanning electron microscopy (SEM) suggested that the plastic deformation and cavitations were the major toughening mechanism for the PLA/ACR blends. The shell partition PMMA of ACR was partially miscible with PLA from dynamic mechanical analysis.

A distinct “split and recoalescence” growth mechanism of tubular ZnO micro/nanostructures is observed for the first time. On the basis of experimental growth studies and first-principles calculations, it is proposed that H2/H2O vapor, added to the traditional carbothermal reduction process, changes the intrinsic surface energy of ZnO crystal, which affects the ZnO crystal growth mode and subsequently controls the geometry of ZnO micro/nanotubes. It is shown that these tubular ZnO micro/nanostructures exhibit regular hexagonal cross sections and smooth outer and inner surfaces. Optical studies of ZnO micro/nanotubes reveal characteristic coherent intensity modulations of their emission spectra which reflect the excitation of either whispering gallery modes or wave-guided modes. The specific type of mode can be selected by controlling the microtube geometry, specifically by its wall thickness to diameter ratio, as demonstrated both experimentally by photoluminescence spectroscopy, and theoretically by finite-element-method simulations.

A facile strategy is adopted to prepare carboxylic functionalized multiwalled carbon nanotube (c-MWCNT) modified high dielectric constant (high-k) poly(vinylidene fluoride) (PVDF) composites with the aid of methyl methacrylate-co-glycidyl methacrylate copolymer (MG). The MG is miscible with PVDF and the epoxy groups of the copolymer can react with the carboxylic groups of c-MWCNT, which induce the uniform dispersion of c-MWCNT and a form insulator layer on the surface of c-MWCNT. The c-MWCNTs/MG/PVDF composites with 8 vol % c-MWCNT present excellent dielectric properties with high dielectric constant (~448) and low dielectric loss (~2.36) at the frequency of 1 KHz, the dielectric loss is much lower than the c-MWCNT/PVDF composites without MG. The obvious improvement in dielectric properties ascribes to the existence of MG, which impede the direct contact of c-MWCNTs and PVDF and avoid the formation of conductive network. Therefore, we propose a practical and simple strategy for preparing composites with excellent dielectric properties, which are promising for applications in electronics devices.

Free control of electromagnetic wave fronts remains a key issue in photonics. Traditional wave-shaping elements, used for centuries, suffer from limited functionalities and excessive size. Now metasurfaces offer exotic abilities to reshape the wave front of light, but are mainly used to manipulate propagating waves. Extending the idea of metasurfaces for propagating waves to surface waves (SWs), the authors create a gradient metawall that yields focusing effects and high-efficiency reflection per a generalized Snell's Law for SWs. This development may inspire applications such as SW holograms, superresolution imaging, and enhanced nonlinear optical effects.

We present a novel colloidal quantum dot (CQD)/ZnO whispering gallery mode microcavity composite. The whispering gallery mode emission of the CQDs induced by the ZnO microcavity is realized. The resonant properties of the composite optical cavities are systematically investigated, and the obtained results are supported by finite element method simulations. The work presents a new research platform to study light–matter interactions in such a composite microcavity.

In order to overcome the brittleness of polylactide (PLA), reactive core-shell particles (RCS) with polybutadiene as core and methyl methacrylate-co-styrene-co-glycidyl methacrylate as shell were prepared to toughen PLA. Tert-dodecyl mercaptan (TDDM) was used as chain transfer agent to modify the grafting properties (such as grafting degree, shell thickness, internal and external grafting) of the core-shell particles. The introduction of TDDM decreased the grafting degree, shell thickness and the Tg of the core phase. When the content of TDDM was lower than 1.15%, the RCS particles dispersed in the PLA matrix uniformly—otherwise, agglomeration took place. The addition of RCS particles induced a higher cold crystallization temperature and a lower melting temperature of PLA which indicated the decreased crystallization ability of PLA. Dynamic mechanical analysis (DMA) results proved the good miscibility between PLA and the RCS particles and the increase of TDDM in RCS induced higher storage modulus of PLA/RCS blends. Suitable TDDM addition improved the toughening ability of RCS particles for PLA. In the present research, PLA/RCS-T4 (RCS-T4: the reactive core-shell particles with 0.76 wt % TDDM addition) blends displayed much better impact strength than other blends due to the easier cavitation/debonding ability and good dispersion morphology of the RCS-T4 particles. When the RCS-T4 content was 25 wt %, the impact strength of PLA/RCS-T4 blend reached 768 J/m, which was more than 25 times that of the pure PLA.

Metasurfaces offered great opportunities to control electromagnetic (EM) waves, but currently available meta-devices typically work either in pure reflection or pure transmission mode, leaving half of EM space completely unexplored. Here, we propose a new type of metasurface, composed by specifically designed meta-atoms with polarization-dependent transmission and reflection properties, to efficiently manipulate EM waves in the full space. As a proof of concept, three microwave meta-devices are designed, fabricated and experimentally characterized. The first two can bend or focus EM waves at different sides (i.e., transmission/reflection sides) of the metasurfaces depending on the incident polarization, while the third one changes from a wave bender for reflected wave to a focusing lens for transmitted wave as the excitation polarization is rotated, with all these functionalities exhibiting very high efficiencies (in the range of 85%-91%). Our findings significantly expand the capabilities of metasurfaces in controlling EM waves, and can stimulate high-performance multi-functional meta-devices facing more challenging and diversified application demands., 25 pages and 7 figures in the main text

Glycidyl methacrylate (GMA) functionalized methyl methacrylate-butadiene-styrene core-shell particles (PB-g-MSG) were prepared to toughen poly (butylene terephthalate) (PBT) and polycarbonate (PC) blends. T-dodecyl mercaptan (TDDM) was used to modify the grafting character of the core-shell particles. The addition of TDDM decreased the grafting degree, particles size and crosslinking degree of PB-g-MSG particles. At the same time, the free methyl methacrylate-co-styrene-co-glyceryl methacrylate copolymer (f-MSG) increased. The f-MSG reacted with PBT and suppressed the transesterification between PBT and PC. On the other hand, f-MSG promoted the crystallization of PBT by heterogeneous nucleation. When the TDDM content was lower than 0.76%, PB-g-MSG particles dispersed in the matrix uniformly, otherwise, agglomeration took place. The change of TDDM content in the PB-g-MSG particles influenced the toughening ability and tensile properties. When the TDDM content was 0.76%, the PBT/PC/PB-g-MSG blend showed the optimum impact toughness and yield strength, which are 908 J/m and 49.4Mpa. Fracture mechanism results indicated that cavitation induced shear yielding occurred in the PBT/PC/PB-g-MSG blend when no TDDM addition for the core-shell particles. With the addition of TDDM, the interfacial strength decreased between the PB-g-MSG core-shell particles and the matrix. So voids appeared due to debonding, which also could promote the shear yielding process.