Active polarization-converting metasurface with electrically controlled magnitude amplification.

Recently, reconfigurable polarization-manipulation metasurfaces controlled with active components have gained widespread interest due to their adaptability, compact configuration, and low cost. However, due to the inherent non-negligible ohmic loss, the output energy of these tunable metasurfaces is typically diminished, particularly in the microwave region. To surmount the loss problem, herein, we propose an active polarization-converting metasurface with non-reciprocal polarization responses that is integrated with amplifying transistors. In addition, we provide a design strategy for a polarizer that is insensitive to polarization and has energy amplification capabilities. Experiments are conducted in the microwave region, and amplification of the polarization-converting behaviors is observed around 3.95 GHz. The proposed metasurface is prospective for applications in future wireless communication systems, such as spatial isolation, signal enhancement, and electromagnetic environment shaping.

Direction-Duplex Janus Metasurface for Full-Space Electromagnetic Wave Manipulation and Holography.

Janus metasurfaces, a category of two-faced two-dimensional (2D) materials, are emerging as a promising platform for designing multifunctional metasurfaces by exploring the intrinsic propagation direction (k-direction) of electromagnetic waves. Their out-of-plane asymmetry is utilized for achieving distinct functions selectively excited by choosing the propagation directions, providing an effective strategy to meet the growing demand for the integration of more functionalities into a single optoelectronic device. Here, we propose the concept of direction-duplex Janus metasurface for full-space wave control yielding drastically different transmission and reflection wavefronts for the same polarized incidence with opposite k-directions. A series of Janus metasurface devices that enable asymmetric full-space wave manipulations, such as integrated metalens, beam generators, and fully direction-duplex meta-holography, are experimentally demonstrated. We envision the Janus metasurface platform proposed here to open new possibilities toward a broader exploration of creating sophisticated multifunctional meta-devices ranging from microwaves to optical systems.

Full-space dual-helicity decoupled metasurface for a high-efficiency multi-folded reflective antenna.

The independent tailoring of electromagnetic waves with different circular-polarized (CP) wavefront in both reflection and transmission channels is of broad scientific and technical interest, offering ultimate degrees of freedom in designing advanced devices with the merits of functionality integration and spatial exploitation. However, most metasurfaces only provide dependent wavefront control of dual-helicity in a single channel, restricting their applications to limited practical scenarios. Herein, we propose a full-space dual-helicity decoupled metasurface and apply it to assemble a multi-folded reflective antenna (MFRA) in the microwave regime. A multilayered chiral meta-atom is designed and optimized to reflect a particular helical wave while allowing the orthogonal helical wave to penetrate through, with simultaneous full span of phase modulations in both channels. When a uniform reflection and a hyperbolic transmission phase profile is imposed simultaneously on the metasurface in a polarization-selective manner, it can be engineered to conduct specular reflection for one helical wave and convergent transmission of the other helical wave. Combining the proposed metasurface with a metallic plate as a bottom reflector and an integrated microstrip patch antenna in the center of metasurface as a feed, a MFRA is realized with a low profile, high efficiency, and high polarization purity in a broad frequency band. The proposed design method of the dual-helicity decoupled metasurface and its antenna application provide opportunities for high-performance functional devices, promising more potential in future communication and detection systems.

Switchable metasurface for nearly perfect reflection, transmission, and absorption using PIN diodes.

Active metasurfaces with dynamically switchable functionalities are highly in demands in various practical applications. In this paper, we experimentally present an active metasurface based on PIN diodes which can realize nearly perfect reflection, transmission and absorption in a single design. Such switchable functionalities are accomplished by controlling the PIN diodes integrated in both layers of the metasurface. A transmission line model is employed to further investigate the underlying mechanism of the metasurface. This proposal is confirmed by numerical simulations and experiments. As a novel metasurface with multiple switchable functionalities, our design may find some practical applications such as smart radomes.

Angular-Adaptive Reconfigurable Spin-Locked Metasurface Retroreflector.

Metasurface retroreflectors, which scatter the incident electromagnetic wave back to incoming direction, have received significant attention due to their compelling advantages of low profile and light weight compared with conventional bulky retroreflection devices. However, the current metasurface retroreflectors still have limitations in wide-angle and omnidirectional operations. This work proposes a high-efficiency, wide-angle, reconfigurable, and omnidirectional retroreflector composed of spin-locked phase gradient metasurface with a thickness of only 5.2 mm or 0.07 operating wavelength. The reflection phase of constituent meta-atoms can be controlled dynamically and continuously by altering their orientation states through individually addressing each mechanically rotational meta-atom, whereas the reflection handedness is kept the same as incidence. Therefore, adaptive and arbitrary momentum can be imparted to the incident wave, providing high-efficiency retroreflection over a wide continuous range from -47° to 47°. Moreover, such high-performance retroreflection is extended to omnidirectional level, enabling great degrees of freedom that are unavailable by previous researches. As a proof of concept, a retroreflective metasurface is fabricated and experimentally demonstrated at microwave frequencies. The proposed thin thickness, high efficiency, and reconfigurable metasurface retroreflector can be extended to other frequencies that may offer an untapped platform toward reconfigurable spin-based retroreflection devices for electromagnetic signal processing.

A novel structural class of coumarin-chalcone fibrates as PPARα/γ agonists with potent antioxidant activities: Design, synthesis, biological evaluation and molecular docking studies.

A series of structurally interesting coumarin-chalcone fibrates were synthesized and evaluated for their PPARα/γ agonist activities and antioxidant activities. Among these compounds, compounds 5a, 5d, and 7a were identified as potent PPARα and γ dual agonists, and their PPARα agonist activities were found to be more potent than that of Fenofibrate. Furthermore, the results of antioxidant investigations revealed that compounds 5d and 6a-6d had greater potency than Trolox with IC50 values ranging from 9.40 µM to 18.63 µM. The structure-activity relationship revealed that the electron-withdrawing nitro group substituted at the C6' position of the benzopyran moiety increased the PPARα and γ agonist efficacy. Moreover, the presence of a double bond on the benzopyran moiety was essential for PPARα and γ agonist efficacy. The agonist activity of PPARα exhibited by compound 5d was examined by molecular docking studies. Taken together, the results we obtained showed that compound 5d had the potential to be a lead compound for further research.

Construction of adhesion maps for contacts between a sphere and a half-space: Considering size effects of the sphere.

Previous adhesion maps, such as the JG (Johnson-Greenwood) and YCG (Yao-Ciavarella-Gao) maps, are used to guide the selection of Bradley, DMT, M-D, JKR and Hertz models. However, when the size of the contact sphere decreases to the small scale, the applicability of JG and YCG maps is limited because the assumptions regarding the contact region profile, interaction between contact bodies and sphere shape in the classical models constituting these two maps are no longer valid. To avoid this limitation, in this paper, a new numerical model considering size effects of the sphere is established first and then introduced into the new adhesion maps together with the YGG (Yao-Guduru-Gao) model and Hertz model. Regimes of these models in the new map under a certain sphere radius are demarcated by the criteria related to the relative force differences and the ratio of contact radius to sphere radius. In addition, the approaches at pull-off, jump-in and jump-out for different Tabor parameters and sphere radii are provided in the new maps. Finally, to make the new maps more feasible, the numerical results of approaches, force and contact radius involved in the maps are formularized by using the piecewise fitting.

Roles of a novel Crp/Fnr family transcription factor Lmo0753 in soil survival, biofilm production and surface attachment to fresh produce of Listeria monocytogenes.

Listeria monocytogenes is a foodborne bacterial pathogen and the causative agent of an infectious disease, listeriosis. L. monocytogenes is ubiquitous in nature and has the ability to persist in food processing environments for extended periods of time by forming biofilms and resisting industrial sanitization. Human listeriosis outbreaks are commonly linked to contaminated dairy products, ready-to-eat meats, and in recent years, fresh produce such as lettuce and cantaloupes. We identified a putative Crp/Fnr family transcription factor Lmo0753 that is highly specific to human-associated genetic lineages of L. monocytogenes. Lmo0753 possesses two conserved functional domains similar to the major virulence regulator PrfA in L. monocytogenes. To determine if Lmo0753 is involved in environmental persistence-related mechanisms, we compared lmo0753 deletion mutants with respective wild type and complementation mutants of two fully sequenced L. monocytogenes genetic lineage II strains 10403S and EGDe for the relative ability of growth under different nutrient availability and temperatures, soil survival, biofilm productivity and attachment to select fresh produce surfaces including romaine lettuce leaves and cantaloupe rinds. Our results collectively suggested that Lmo0753 plays an important role in L. monocytogenes biofilm production and attachment to fresh produce, which may contribute to the environmental persistence and recent emergence of this pathogen in human listeriosis outbreaks linked to fresh produce.