Aperiodic sunflower like metasurface for diffusive scattering and RCS reduction

This article presents the design of aperiodic sunflower-like metasurface for circularly polarized (CP) wave diffusion and radar cross section (RCS) reduction using Pancharatnam-Berry (PB) meta-atoms. The distribution of the PB meta-atoms across the metasurface aperture is non-uniform and has a sunflower seeds like distribution, i.e., outwardly logarithmic spiral lattice of no transitional periodicity. The proposed metasurface has 600 PB meta-atoms of sub-wavelength size of 5 mm ≈ ${0.33\lambda_{20GHz}}$ and exhibits a randomly chosen diffusive reflection phase between 0o and 360o. Both simulated and experimental results demonstrate that the proposed sunflower-like metasurface can efficiently diffuse the backscattered energy into numerous directions when normally illuminated by a CP-wave with RCS reduction > 7 dB from 16 GHz to 23.8 GHz. Furthermore, the low-level diffuse scattering can be preserved under oblique incidence up to 60o. As a result of using PB concept, the polarization sensitivity of the proposed metasurface is released and this is highly desired in applications when the polarization of the incoming wave is typically unknown

Microstructural Evolution of Au@Pt Core–Shell Nanoparticles under Electrochemical Polarization

Understanding the microstructural evolution of bimetallic Pt nanoparticles under electrochemical polarization is critical to developing durable fuel cell catalysts. In this work, we develop a colloidal synthetic method to generate core–shell Au@Pt nanoparticles of varying surface Pt coverages to understand how as-synthesized bimetallic microstructure influences nanoparticle structural evolution during formic acid oxidation. By comparing the electrochemical and structural properties of our Au@Pt core–shells with bimetallic AuPt alloys at various stages in catalytic cycling, we determine that these two structures evolve in divergent ways. In core–shell nanoparticles, Au atoms from the core migrate outward onto the surface, generating transient “single-atom” Pt active sites with high formic acid oxidation activity. Metal migration continues until Pt is completely encapsulated by Au, and catalytic reactivity ceases. In contrast, AuPt alloys undergo surface dealloying and significant leaching of Pt out of the nanoparticle. Elucidating the dynamic restructuring processes responsible for high electrocatalytic reactivity in Pt bimetallic structures will enable better design and predictive synthesis of nanoparticle catalysts that are both active and stable

Facile Synthesis of Highly Active PdAu Nanowire Networks as Self-Supported Electrocatalyst for Ethanol Electrooxidation

In recent years, direct ethanol fuel cells (DEFCs) are attracting increasing attention owing to their wide applications. However, a significant challenge in the development of DEFC technology is the urgent need for highly active anode catalysts for the ethanol oxidation reaction. In this work, a facile and reproducible method for the high-yield synthesis of PdAu nanowire networks is demonstrated. The whole synthetic process is very simple, just mixing Na2PdCl4, HAuCl4, and KBr in an aqueous solution and using polyvinylpyrrolidone as a protective reagent while sodium borohydride as a reductant. The whole synthetic process can be simply performed at room temperature and completed in 30 min, which can greatly simplify the synthetic process and lower the preparation cost. Electrochemical catalytic measurement results prove that the as-prepared catalysts exhibit dramatically enhanced electrocatalytic activity for ethanol electrooxidation in alkaline solution. The facile synthetic process and excellent catalytic performance of the as-prepared catalysts demonstrate that they can be used as a promising catalyst for DEFCs

Mechanism Study on Mechanical Properties of Physical–Chemical Hybrid Hydrogels by Coarse-Grained Molecular Dynamics Simulations

The toughening mechanism has been a focal point for hydrogel studies. To solve the problems of the pure physical gel’s poor strength and the low toughness of pure chemical gels, hybrid physico-chemical hydrogels are devised. In this paper, we first studied the relationship between the mechanical properties and internal network structure of a physico-chemical hydrogel with hydrophilic–hydrophobic–hydrophilic triblock copolymers by coarse-grained molecular dynamics simulations. The stress and strain curves of the hydrogel system were obtained by tensile simulations, and it was found that the stress and strain curves clearly exhibit two stages with different slopes, which indicate that the aggregation of hydrophobic monomers produces a “hidden length” effect in the physico-chemical hybrid hydrogel. Then, by carrying out the cyclic tensile test and obtaining the loading–unloading curves of the hydrogel system, we found that the hydrophilic chains dominate the energy dissipation. Subsequently, the strain–stress curves at different strain rates revealed an optimal strain rate for the hydrogel’s mechanical property. Finally, we identify an optimal chain-length ratio of 7:1:7 to acquire the best mechanical properties of this hybrid hydrogel. Through this study, we have revealed that the physico-chemical hybrid hydrogel is an excellent candidate to combine the merits of a physical hydrogel and chemical hydrogel, and the length ratio between the hydrophobic and hydrophilic chains is a key for optimizing its mechanical properties

Bifidobacterium protected intestinal barrier function in vitro and in a rat NEC model.

(A) The transepithelial electrical resistance (TEER) was tested at different time points. *P #P P (B) Intestinal permeability was assessed in vitro using the fluorescein permeability (P) test at different time points, *P #P (C) The intestinal barrier function in vivo was evaluated by fluorescent dextran–FITC. *P #P < 0.01 vs the NEC group, n = 6 animals per group.</p

Protective Effects of Bifidobacterium on Intestinal Barrier Function in LPS-Induced Enterocyte Barrier Injury of Caco-2 Monolayers and in a Rat NEC Model

<div><p>Zonulin protein is a newly discovered modulator which modulates the permeability of the intestinal epithelial barrier by disassembling intercellular tight junctions (TJ). Disruption of TJ is associated with neonatal necrotizing enterocolitis (NEC). It has been shown bifidobacterium could protect the intestinal barrier function and prophylactical administration of bifidobacterium has beneficial effects in NEC patients and animals. However, it is still unknown whether the zonulin is involved in the gut barrier dysfunction of NEC, and the protective mechanisms of bifidobacterium on intestinal barrier function are also not well understood. The present study aims to investigate the effects of bifidobacterium on intestinal barrier function, zonulin regulation, and TJ integrity both in LPS-induced enterocyte barrier injury of Caco-2 monolayers and in a rat NEC model. Our results showed bifidobacterium markedly attenuated the decrease in transepithelial electrical resistance and the increase in paracellular permeability in the Caco-2 monolayers treated with LPS (<i>P</i> < 0.01). Compared with the LPS group, bifidobacterium significantly decreased the production of IL-6 and TNF-α (<i>P</i> < 0.01) and suppressed zonulin release (<i>P</i> < 0.05). In addition, bifidobacterium pretreatment up-regulated occludin, claudin-3 and ZO-1 expression (<i>P</i> < 0.01) and also preserved these proteins localization at TJ compared with the LPS group. In the in vivo study, bifidobacterium decreased the incidence of NEC from 88 to 47% (<i>P</i> < 0.05) and reduced the severity in the NEC model. Increased levels of IL-6 and TNF-α in the ileum of NEC rats were normalized in bifidobacterium treated rats (<i>P</i> < 0.05). Moreover, administration of bifidobacterium attenuated the increase in intestinal permeability (<i>P</i> < 0.01), decreased the levels of serum zonulin (<i>P</i> < 0.05), normalized the expression and localization of TJ proteins in the ileum compared with animals with NEC. We concluded that bifidobacterium may protect against intestinal barrier dysfunction both in vitro and in NEC. This protective effect is associated with inhibition of proinflammatory cytokine secretion, suppression of zonulin protein release and improvement of intestinal TJ integrity.</p></div

Aperiodic sunflower like metasurface for diffusive scattering and RCS reduction

This article presents the design of aperiodic sunflower-like metasurface for circularly polarized (CP) wave diffusion and radar cross section (RCS) reduction using Pancharatnam-Berry (PB) meta-atoms. The distribution of the PB meta-atoms across the metasurface aperture is non-uniform and has a sunflower seeds like distribution, i.e., outwardly logarithmic spiral lattice of no transitional periodicity. The proposed metasurface has 600 PB meta-atoms of sub-wavelength size of 5 mm ≈ ${0.33\lambda_{20GHz}}$ and exhibits a randomly chosen diffusive reflection phase between 0o and 360o. Both simulated and experimental results demonstrate that the proposed sunflower-like metasurface can efficiently diffuse the backscattered energy into numerous directions when normally illuminated by a CP-wave with RCS reduction > 7 dB from 16 GHz to 23.8 GHz. Furthermore, the low-level diffuse scattering can be preserved under oblique incidence up to 60o. As a result of using PB concept, the polarization sensitivity of the proposed metasurface is released and this is highly desired in applications when the polarization of the incoming wave is typically unknown

Nature-inspired orbital angular momentum beam generator using aperiodic metasurface

This article presents the design of reflective nature-inspired metasurfaces for generation of wideband and high purity circularly polarized (CP) orbital angular momentum (OAM) waves. It has been shown in this article that the breaking of the transitional periodicity and the combination of aperiodic nature-inspired distribution of sub-wavelength sized meta-atoms based on Pancharatnam–Berry (PB) phase theory can lead to OAM beams of high purity with improved bandwidth. The distribution of the PB anisotropic meta-atoms across the proposed metasurface aperture is non-uniform and distributed along logarithmic spirals similar to sunflower seeds, i.e. outwardly logarithmic spiral lattices of no transitional periodicity. The proposed reflective CP-OAM beam generator metasurface diameter is 140 mm, thickness ≈ 0.11λ17GHz and has 600 anisotropic spatially rotated PB meta-atoms of sub-wavelength size of 5 mm ≈ 0.28λ17GHz. Four OAM metasurface generators have been designed to produce OAM waves of various modes from 1 to 4. Both simulation and experimental results have demonstrated that the proposed metasurfaces can efficiently generate CP-OAM beams from 13.1 GHz to 20.5 GHz (BW = 44%) with high mode purity >90%

Long-Term Preservation of SARS-CoV‑2 RNA in Silk for Downstream RT-PCR Tests

Positive controls made of viral gene components are essential to validate the performance of diagnostic assays for pathogens like severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). However, most of them are target-specific, limiting their application spectrum when validating assays beyond their specified targets. The use of an inactivated whole-virus RNA reference standard could be ideal, but RNA is a labile molecule that needs cold chain storage and transportation to preserve its integrity and activity. The cold chain process stretches the already dwindling storage capacities, incurs huge costs, and limits the distribution of reference materials to low-resource settings. To circumvent these issues, we developed an inactivated whole-virus SARS-CoV-2 RNA reference standard and studied its stability in silk fibroin matrices, i.e., silk solution (SS) and silk film (SF). Compared to preservation in nuclease-free water (ddH2O) and SS, SF was more stable and could preserve the SARS-CoV-2 RNA reference standard at room temperature for over 21 weeks (∼6 months) as determined by reverse transcription polymerase chain reaction (RT-PCR). The preserved RNA reference standard in SF was able to assess the limits of detection of four commercial SARS-CoV-2 RT-PCR assays. In addition, SF is compatible with RT-PCR reactions and can be used to preserve a reaction-ready primer and probe mix for RT-PCR at ambient temperatures without affecting their activity. Taken together, these results offer extensive flexibility and a simpler mechanism of preserving RNA reference materials for a long time at ambient temperatures of ≥25 °C, with the possibility of eliminating cold chains during storage and transportation

Bifidobacterium reduced inflammatory response in vitro and in a rat NEC model.

(A) IL-6 and (B) TNF-α concentrations in the Caco-2 cells were determined by ELISA. three independent experiments were performed in duplicate. *P #P (C) IL-6 and (D) TNF-α concentrations in rat NEC model. *P ##P P < 0.05 vs the NEC group, n = 5 animals per group. Three independent experiments were performed in duplicate.</p