Dynamics in fermentation quality, bacterial community, and metabolic profile during silage fermentation of late-harvested elephant grass.

The present study aimed to evaluate the effects of delayed harvest and storage length on fermentation products, bacterial community, and metabolic shifts of elephant grass silage. The late-harvested elephant grass (LG) was naturally fermented (NLG) for 1, 3, 7, 15, 30, and 60 days, respectively. After 60-day ensiling, NLG displayed homolactic fermentation with low pH value, butyric acid, and ammonia nitrogen concentrations, and high lactic acid concentration, and ratio of lactic acid to acetic acid. Pseudomonas, Sphingomonas, and Pantoea dominated the bacterial community in LG, but Lactobacillus, Lactococcus, and Pediococcus were the advantageous genera in a 3-day and 60-day NLG. The correlation heatmap revealed that Acetobacter was positively related to acetic acid, ethanol, ammonia nitrogen, and butyric acid concentrations. There were distinct differences in the KEGG (Kyoto Encyclopedia of Genes and Genomes) metabolic profiles of fresh and ensiled LG. Ensiling suppressed the metabolism of amino acid, vitamins, and energy, while promoted the metabolism of carbohydrate. The LG can be well-fermented without additives, but its low crude protein content should not be ignored when applied in agricultural practice. The ensiling process remarkably affected the fermentation quality, bacterial community, and metabolic profiles of NLG.

A filtering reconfigurable intelligent surface for interference-free wireless communications.

The powerful capability of reconfigurable intelligent surfaces (RISs) in tailoring electromagnetic waves and fields has put them under the spotlight in wireless communications. However, the current designs are criticized due to their poor frequency selectivity, which hinders their applications in real-world scenarios where the spectrum is becoming increasingly congested. Here we propose a filtering RIS to feature sharp frequency-selecting and 2-bit phase-shifting properties. It permits the signals in a narrow bandwidth to transmit but rejects the out-of-band ones; meanwhile, the phase of the transmitted signals can be digitally controlled, enabling flexible manipulations of signal propagations. A prototype is designed, fabricated, and measured, and its high quality factor and phase-shifting characteristics are validated by scattering parameters and beam-steering phenomena. Further, we conduct a wireless communication experiment to illustrate the intriguing functions of the RIS. The filtering behavior enables the RIS to perform wireless signal manipulations with anti-interference ability, thus showing big potential to advance the development of next-generation wireless communications.

Radar Micro-Doppler Signature Generation Based on Time-Domain Digital Coding Metasurface.

Micro-Doppler effect is a vital feature of a target that reflects its oscillatory motions apart from bulk motion and provides an important evidence for target recognition with radars. However, establishing the micro-Doppler database poses a great challenge, since plenty of experiments are required to get the micro-Doppler signatures of different targets for the purpose of analyses and interpretations with radars, which are dramatically limited by high cost and time-consuming. Aiming to overcome these limits, a low-cost and powerful simulation platform of the micro-Doppler effects is proposed based on time-domain digital coding metasurface (TDCM). Owing to the outstanding capabilities of TDCM in generating and manipulating nonlinear harmonics during wave-matter interactions, it enables to supply rich and high-precision electromagnetic signals with multiple micro-Doppler frequencies to describe the micro-motions of different objects, which are especially favored for the training of artificial intelligence algorithms in automatic target recognition and benefit a host of applications like imaging and biosensing.

Manipulations of multi-frequency waves and signals via multi-partition asynchronous space-time-coding digital metasurface.

Manipulations of multiple carrier frequencies are especially important in a variety of fields like radar detection and wireless communications. In conventional radio-frequency architecture, the multi-frequency control is implemented by microwave circuits, which are hard to integrate with antenna apertures, thus bringing the problems of expensive system and high power consumption. Previous studies demonstrate the possibility to jointly control the multiple harmonics using space-time-coding digital metasurface, but suffer from the drawback of inherent harmonic entanglement. To overcome the difficulties, we propose a multi-partition asynchronous space-time-coding digital metasurface (ASTCM) to generate and manipulate multiple frequencies with more flexibility. We further establish an ASTCM-based transmitter to realize wireless communications with frequency-division multiplexing, where the metasurface is responsible for carrier-wave generations and signal modulations. The direct multi-frequency controls with ASTCM provides a new avenue to simplify the traditional wireless systems with reduced costs and low power consumption.

Dynamics of Phyllosphere Microbiota and Chemical Parameters at Various Growth Stages and Their Contribution to Anaerobic Fermentation of Pennisetum giganteum.

This work evaluated the dynamic changes of phyllosphere microbiota and chemical parameters at various growth stages of Pennisetum giganteum and their effects on the bacterial community, cooccurrence networks, and functional properties during anaerobic fermentation. P. giganteum was collected at two growth stages (early vegetative stage [PA] and late vegetative stage [PB]) and was naturally fermented (NPA and NPB) for 1, 3, 7, 15, 30, and 60 days, respectively. At each time point, NPA or NPB was randomly sampled for the analysis of chemical composition, fermentation parameter, and microbial number. In addition, the fresh, 3-day, and 60-day NPA and NPB were subjected to high-throughput sequencing and Kyoto Encyclopedia of Genes and Genomes (KEGG) functional prediction analyses. Growth stage obviously affected the phyllosphere microbiota and chemical parameters of P. giganteum. After 60 days of fermentation, NPB had a higher lactic acid concentration and ratio of lactic acid to acetic acid but a lower pH value and ammonia nitrogen concentration than NPA. Weissella and Enterobacter were dominant in 3-day NPA and Weissella was dominant in 3-day NPB, while Lactobacillus was the most abundant genus in both 60-day NPA and NPB. The complexity of bacterial cooccurrence networks in the phyllosphere decreased with P. giganteum growth. The ensiling process further decreased the complexity of bacterial networks, with the simplest bacterial correlation structures in NPB. There were great differences in the KEGG functional profiles of PA and PB. Ensiling promoted the metabolism of lipid, cofactors, vitamins, energy, and amino acids but suppressed the metabolism of carbohydrates and nucleotides. Storage time had a greater influence than growth stage on bacterial community diversity, cooccurrence networks, and functional profiles of P. giganteum silage. Differences in bacterial diversity and functionality of P. giganteum silage caused by growth stage appear to be offset by long-term storage. IMPORTANCE The phyllosphere microbiota consists of various and complex microbes, including bacteria with crucial relevance to the quality and safety of fermented food and feed. It initially derives from soil and becomes specific to its host after interaction with plants and climate. Bacteria associated with the phyllosphere are highly abundant and diverse, but we know little about their succession. Here, the phyllospheric microbiota structure was analyzed within the growth of P. giganteum. We also evaluated the effects of phyllosphere microbiota and chemical parameter changes on the anaerobic fermentation of P. giganteum. We observed remarkable differences in bacterial diversity, cooccurrence, and functionality of P. giganteum at various growth stages and storage times. The obtained results are important for understanding the fermentation mechanism and may contribute to high-efficient production without additional cost.

Sustainable utilization of residual grass: effect of anaerobic storage days on chemical composition, fermentation performance, microbial community, and functional profiles of Pennisetum giganteum.

The seasonal surplus and putrefactive property of moist forages inevitably increase the pressure on environmental protection and residual grass disposal. In the current work, the anaerobic fermentation approach was adopted to assist the sustainable recycling of leftover Pennisetum giganteum (LP), and its chemical composition, fermentation performance, bacterial community and functional profiles during anaerobic fermentation were studied. Fresh LP was spontaneously fermented for up to 60 d. At the end of anaerobic fermentation, fermented LP (FLP) displayed homolactic fermentation with low pH value, ethanol, and ammonia nitrogen concentrations but high lactic acid concentration. Weissella was dominant in 3-day FLP, yet Lactobacillus was the overwhelming genus (92.6%) in 60-day FLP. The anaerobic fermentation process promoted (P < 0.05) the metabolism of carbohydrate and nucleotide while suppressing (P < 0.05) that of lipid, cofactors, vitamins, energy, and amino acid. The results showed that the residual grass with LP as an example could be successfully fermented even if no additives were added, without signs of clostridial and fungal contamination.

Asynchronous Space-Time-Coding Digital Metasurface.

Recent progress in space-time-coding digital metasurface (STCM) manifests itself a powerful tool to engineer the properties of electromagnetic (EM) waves in both space and time domains, and greatly expands its capabilities from the physical manipulation to information processing. However, the current studies on STCM are focused under the synchrony frame, namely, all meta-atoms follow the same variation frequency. Here, an asynchronous STCM is proposed, where the meta-atoms are modulated by different time-coding periods. In the proposed asynchronous STCM, the phase discontinuities on traditional metasurface are replaced with the frequency discontinuities. It is shown that dynamic wavefronts can be automatically realized for both fundamental and high-order harmonics by elaborately arranging the spatial distribution of meta-atoms with various time-coding periods. The physics insight is due to the accumulated rapidly changing phase difference with time, which offers an additional degree of freedom during the wave-matter interactions. As a proof-of-principle example, an asynchronous STCM for automatic spatial scanning and dynamic scattering control is investigated. From the theory, numerical simulations, and experiments, it can be found that the proposed STCM exhibits significant potentials for applications in radars and wireless communications.

Changes in the fermentation products, taxonomic and functional profiles of microbiota during high-moisture sweet sorghum silage fermentation.

The purpose of this study was to evaluate the fermentation quality, microbial community, and functional shifts of sweet sorghum during ensiling. The high-moisture sweet sorghum (SS) was naturally ensiled for 1, 3, 7, 15, 30, and 60 days. After 60 days of ensiling, sweet sorghum silage (SSS) showed homolactic fermentation with absent butyric acid, low pH value, acceptable concentrations of propionic acid, ethanol, and ammonia nitrogen and high lactic acid concentration. Acinetobacter, Sphingomonas, and Pseudomonas were the advantage genera in SS. While, Lactococcus, Weissella, and Pediococcus were dominant in 3-day SSS and subsequently replaced by Lactobacillus in 60-day SSS. Spearman's correlation heatmap showed that Pediococcus and Leuconostoc were negatively related to the pH value of SSS. There were great differences in the Kyoto Encyclopedia of Genes and Genomes (KEGG) functional profiles of SS and SSS. Ensiling process downregulated the metabolism of amino acid, energy, cofactors, and vitamins, but upregulated the metabolism of nucleotides and carbohydrates. Overall, next-generation sequencing in conjunction with KEGG functional prediction revealed the distinct differences in the initial and late phases of ensiling in terms of both community succession and functional shifts. The knowledge regarding bacterial community dynamics and functional shifts of SS during ensiling is important for understanding the fermentation mechanism and may contribute to the production of high-quality sweet sorghum silage.