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The desire for lightweight, carbon-negative materials has been increasing in recent years, particularly as the transportation sector reduces its global carbon footprint. Natural fibers, such as flax fiber and their composites, offer a compelling combination of properties including low density, high specific strength, and carbon negativity. However, because of the low modulus and high variability in performance, natural fibers can't compete with glass fibers as structural reinforcements in polymer composites. In this study, flax technical fibers were treated in supercritical CO2 (scCO2), and the effects of this treatment on the morphology and properties of flax fibers are reported. Treatment in scCO2 successfully resulted in higher fiber modulus and strength by 33% and 40%, respectively. Fiber porosity was reduced by 50% and morphological changes to the fibers were observed. Specifically, fiber lumen collapsed during treatment and micro/mesoporosity was reduced by 27%. Treated flax fibers were used to create 30 vol% unidirectional flax-epoxy composites. ScCO2 treatment raised composite modulus and strength by 33% and 25%, respectively. Because of the dependence between technical fiber size and mechanical properties, the relationship between fiber modulus and fiber size were created and applied to the rule-of-mixtures. This relationship were found to be viable representations of the fiber performance within each composite. Overall, the treatment developed in this study has the potential to significantly improve natural fiber properties, enabling their consideration for use in lightweight, semi-structural composites. [ABSTRACT FROM AUTHOR]

Resonator-based optical frequency comb generation is an enabling technology for a myriad of applications ranging from communications to precision spectroscopy. These frequency combs can be generated in nonlinear resonators driven using either continuous-wave (CW) light, which requires alignment of the pump frequency with the cavity resonance, or pulsed light, which also mandates that the pulse repetition rate and cavity free spectral range (FSR) are carefully matched. Advancements in nanophotonics have ignited interest in chip-scale optical frequency combs. However, realizing pulse-driven on-chip Kerr combs remains challenging, as microresonator cavities have limited tuning range in their FSR and resonance frequency. Here, we take steps to overcome this limitation and demonstrate broadband frequency comb generation using a χ(3) resonator synchronously pumped by a tunable femtosecond pulse generator with on-chip amplitude and phase modulators. Notably, employing pulsed pumping overcomes limitations in Kerr comb generation typically seen in crystalline resonators from stimulated Raman scattering. Here the authors use on-chip amplitude and phase modulation to synchronously pump a resonator on thin-film lithium niobate for frequency comb generation. They find that pulsed pumping significantly mitigates stimulated Raman scattering and improves the overall efficiency of the device. [ABSTRACT FROM AUTHOR]

Background and Aims: Critical peatland functions are intricately linked to biogeochemical processes mediated by soil microbes. The belowground microbial activities are associated and interacted with aboveground vegetation types. Vegetation shifts from Sphagnum mosses to vascular plants in peatlands may alter soil microbial community, leading to changes in ecological functions. However, our knowledge in this area is still limited. Methods: We selected four sites (two core areas and two marginal areas) in the Sphagnum-dominated wetland in Zhejiang Hynobius amjiensis National Nature Reserve. At each site, peat soils under three common peatland vegetation communities (OW: only Sphagnum; HW: herbaceous plants with Sphagnum carpet; SW: shrubs with Sphagnum carpet) were collected at two depths. A high-throughput sequencing method was adopted to investigate the alteration in soil bacterial and fungal communities. Results: Vascular plant did not significantly alter soil properties and microbial α-diversity, given that mosses are still the dominant plants and have higher resistance levels to multiple environmental-changes than vascular plants. The features of bacterial co-occurrence network in HW revealed higher stability than that in OW and SW, indicating that herbaceous plants may contribute to the stable coexistence with Sphagnum. The microbial diversity, community structure and putative functions differed between core and marginal areas of the peatland. Conclusion: The results demonstrated that the spatial heterogeneity of environmental factors may play a more important role in microbial activities than vegetation types at the early successional stages. These insights provide a novel perspective for development of management practices to preserve subtropical peatlands. [ABSTRACT FROM AUTHOR]

Dual-comb interferometry harnesses the interference of two laser frequency combs to provide unprecedented capability in spectroscopy applications. In the past decade, the state-of-the-art systems have reached a point where the signal-to-noise ratio per unit acquisition time is fundamentally limited by shot noise from vacuum fluctuations. To address the issue, we propose an entanglement-enhanced dual-comb spectroscopy protocol that leverages quantum resources to significantly improve the signal-to-noise ratio performance. To analyze the performance of real systems, we develop a quantum model of dual-comb spectroscopy that takes practical noises into consideration. Based on this model, we propose quantum combs with side-band entanglement around each comb lines to suppress the shot noise in heterodyne detection. Our results show significant quantum advantages in the uW to mW power range, making this technique particularly attractive for biological and chemical sensing applications. Furthermore, the quantum comb can be engineered using nonlinear optics and promises near-term experimentation. [ABSTRACT FROM AUTHOR]

Optical isolators are indispensable components of almost any optical system and are used to protect a laser from unwanted reflections for phase-stable coherent operation. The emergence of chip-scale optical systems, powered by semiconductor lasers that are integrated on the same chip, has generated a demand for a fully integrated optical isolator. Conventional approaches, which rely on the use of magneto-optic materials to break Lorentz reciprocity, present substantial challenges in terms of material integration. Although alternative magnetic-free approaches have been explored, an integrated isolator with a low insertion loss, high isolation ratio, broad bandwidth and low power consumption on a monolithic material platform is yet to be achieved. Here we realize a non-reciprocal travelling-wave-based electro-optic isolator on thin-film lithium niobate. The isolator enables a maximum optical isolation of 48.0 dB with an on-chip insertion loss of 0.5 dB and uses a single-frequency microwave drive power of 21 dBm. The isolation ratio remains larger than 37 dB across a tunable optical wavelength range from 1,510 to 1,630 nm. We realize a hybrid distributed feedback laser–lithium niobate isolator module that successfully protects the single-mode operation and linewidth of the laser from reflection. Our result represents an important step towards a practical high-performance optical isolator on chip. An integrated electro-optic isolator on thin-film lithium niobate enables non-reciprocal isolation by microwave-driven travelling-wave phase modulation. The isolator exhibits a maximum optical isolation of 48.0 dB at around 1,553 nm and an on-chip insertion loss of 0.5 dB. [ABSTRACT FROM AUTHOR]

Integrated femtosecond pulse and frequency comb sources are critical components for a wide range of applications, including optical atomic clocks1, microwave photonics2, spectroscopy3, optical wave synthesis4, frequency conversion5, communications6, lidar7, optical computing8 and astronomy9. The leading approaches for on-chip pulse generation rely on mode-locking inside microresonators with either third-order nonlinearity10 or with semiconductor gain11,12. These approaches, however, are limited in noise performance, wavelength and repetition rate tunability 10,13. Alternatively, subpicosecond pulses can be synthesized without mode-locking, by modulating a continuous-wave single-frequency laser using electro-optic modulators1,14–17. Here we demonstrate a chip-scale femtosecond pulse source implemented on an integrated lithium niobate photonic platform18, using cascaded low-loss electro-optic amplitude and phase modulators and chirped Bragg grating, forming a time-lens system19. The device is driven by a continuous-wave distributed feedback laser chip and controlled by a single continuous-wave microwave source without the need for any stabilization or locking. We measure femtosecond pulse trains (520-femtosecond duration) with a 30-gigahertz repetition rate, flat-top optical spectra with a 10-decibel optical bandwidth of 12.6 nanometres, individual comb-line powers above 0.1 milliwatts, and pulse energies of 0.54 picojoules. Our results represent a tunable, robust and low-cost integrated pulsed light source with continuous-wave-to-pulse conversion efficiencies an order of magnitude higher than those achieved with previous integrated sources. Our pulse generator may find applications in fields such as ultrafast optical measurement19,20 or networks of distributed quantum computers21,22.A femtosecond pulse generator is realized using an electro-optic time-lens system integrated on a lithium niobate photonic chip, capable of tunable repetition rates and wavelengths. [ABSTRACT FROM AUTHOR]

Mirrors are ubiquitous in optics and are used to control the propagation of optical signals in space. Here we propose and demonstrate frequency domain mirrors that provide reflections of the optical energy in a frequency synthetic dimension, using electro-optic modulation. First, we theoretically explore the concept of frequency mirrors with the investigation of propagation loss, and reflectivity in the frequency domain. Next, we explore the mirror formed through polarization mode-splitting in a thin-film lithium niobate micro-resonator. By exciting the Bloch waves of the synthetic frequency crystal with different wave vectors, we show various states formed by the interference between forward propagating and reflected waves. Finally, we expand on this idea, and generate tunable frequency mirrors as well as demonstrate trapped states formed by these mirrors using coupled lithium niobate micro-resonators. The ability to control the flow of light in the frequency domain could enable a wide range of applications, including the study of random walks, boson sampling, frequency comb sources, optical computation, and topological photonics. Furthermore, demonstration of optical elements such as cavities, lasers, and photonic crystals in the frequency domain, may be possible. We show frequency domain mirrors that provide reflections of optical mode propagation in the frequency domain. We theoretically investigated the mirror properties and experimentally demonstrate it using polarization and coupled-resonator-based coupling on thin film Lithium Niobate. [ABSTRACT FROM AUTHOR]

Developments in integrated photonics have led to stable, compact and broadband comb generators that support a wide range of applications including communications1, ranging2, spectroscopy3, frequency metrology4, optical computing5,6 and quantum information7,8. Broadband optical frequency combs can be generated in electro-optical cavities, where light passes through a phase modulator multiple times while circulating in an optical resonator9–12. However, broadband electro-optic frequency combs are currently limited by low conversion efficiencies. Here we demonstrate an integrated electro-optic frequency comb with a conversion efficiency of 30% and an optical span of 132 nm, based on a coupled-resonator platform on thin-film lithium niobate13. We further show that, enabled by the high efficiency, the device acts as an on-chip femtosecond pulse source (336 fs pulse duration), which is important for applications in nonlinear optics, sensing and computing. As an example, in the ultrafast and high-power regime, we demonstrate a frequency comb with simultaneous electro-optic and third-order nonlinearity effects. Our device paves the way for practical optical frequency comb generators and provides a platform to investigate new regimes of optical physics that simultaneously involve multiple nonlinearities. A double-ring-resonator device on thin-film lithium niobate enables the generation of electro-optic frequency combs with a 30% power efficiency and an optical span of 132 nm. [ABSTRACT FROM AUTHOR]

The small-scale whelk (Rapana venosa) and Asian paddle crab (Charybdis japonica) pot fishery are of great socio-economic importance to coastal communities of the Yellow Sea, China. However, the conventional pot with a regulated mesh size of 25 mm is unfavorable to the sustainability of these two species due to its poor selectivity. In this study, we intend to improve the size selectivity of pots by configuring escape vents. Three different escape vent sizes (diameter of 45 mm, 50 mm, and 55 mm) were tested using a catch comparison method. Our results demonstrated that escape vents significantly improved the size selectivity of pots for whelk and crab. The escape vent with a diameter of 55 mm released the maximum number of undersized whelk and meanwhile maintained the catch efficiency of individuals above the Market Reference Size (MRS; 45 mm) compared with the conventional (control) pots. The escape vent with a diameter of 50 mm significantly reduced the retention of undersized crab to 21% and increased the catch rates of individuals above the Minimum Landing Size (MLS; 50 mm) to 112%. Although hard to achieve "perfect selectivity" for morphologically different species in mixed fisheries, we recommend a compromise escape vent size of 52 mm in comprehensive consideration of resources' sustainability and fishermen's profits. The promising results of this study can provide feasibility and insight to develop management strategies for small-scale pot fishery. [ABSTRACT FROM AUTHOR]

Heterogeneous catalytic hydrogenation reactions are of great significance in chemical industry. In this work, ultrasmall Pd nanoparticles (NPs) supported on porous g-C3N4 nanosheets (Pd/CN) have been prepared for efficient hydrogenation reactions. The special structure of the catalytic metal–semiconductor heterojunction not only stabilize the Pd NPs but also improve their electronic activation. In addition, the high surface area of Pd/CN provides a large numbers of adsorption sites for styrene and H2. As a result, the optimized Pd/CN-0.5 nanocomposites achieved 100% conversion of styrene in 60 min under mild conditions. [ABSTRACT FROM AUTHOR]

Laser frequency comb generators on photonic chips open up the exciting prospect of integrated dual-comb microspectrometers. Amongst all nanophotonic platforms, the technology of low-loss thin-film lithium-niobate-on-insulator shows distinguishing features, such as the possibility to combine various optoelectronic and nonlinear optical functionalities that harness second- and third-order nonlinearities, and thus promises the fabrication of a fully on-chip instrument. Here, a critical step towards such achievement is demonstrated with an electro-optic microring-based dual-comb interferometer. Spectra centered at 191.5 THz and spanning 1.6 THz (53 cm−1) at a resolution of 10 GHz (0.33 cm−1) are obtained in a single measurement without requiring frequency scanning or moving parts. The frequency agility of the system enables spectrally-tailored multiplexed sensing, which allows for interrogation of non-adjacent spectral regions, here separated by 6.6 THz (220 cm−1), without compromising the signal-to-noise ratio. Our studies show that electro-optic-based nanophotonic technology holds much promise for new strategies of molecular sensing over broad spectral bandwidths. Thin-film lithium niobate is a promising photonic platform owing to its strong optical nonlinearity and low losses. Here, the utility of this platform is demonstrated as a tunable dual frequency comb spectrometer based on second-order nonlinearities in a proof-of-principle experiment. [ABSTRACT FROM AUTHOR]

Purpose: It is unknown how the Cd-mediated changes in the rhizospheric nitrifier community affect plant growth under different water management practices. This study examined the effect of Cd on microbial N transformation and its association with rice growth in two water regimes, continuous flooding (CF) and alternate wetting and drying (AWD), in a paddy soil. Methods: The 16S rRNA, amoA genes in the rhizosphere and endosphere, and OsNTRs were determined using qPCR. Nitrifier community analysis was performed by sequencing the amoA genes. Concentrations of N and Cd in shoots and roots, and IAA in the roots were determined by flow injection analyzer, ICP-MS and enzyme-linked immunosorbent (ELISA), respectively. Results: The direct and indirect negative effects of Cd bioavailability in the rhizosphere on plant growth and ultra-structure of roots and leaves were greater under AWD than CF after 56-day growth. Nitrifier community was changed by water and Cd treatments. Crenarchaeota, Nitrosopumilus, Nitrosopira, and Nitrosovibrio tenuis related species were the dominant nitrifier players. Increasing Cd level decreased plant N uptake, root-IAA concentration, and the abundance of 16S rRNA gene in the rhizosphere and endosphere to a greater extent under AWD than under CF. This in turn decreased the colonization of endophytes and the surface area of the roots, leading to decreased N uptake from the soil. Conclusion: The results imply that appropriate water management and rhizospheric engineering in Cd-contaminated paddy fields may be important approaches to decreasing plant Cd uptake and rhizospheric nitrification. [ABSTRACT FROM AUTHOR]

Purpose: Elevated CO2 contributes greatly to global warming, playing a pivotal role in terrestrial ecosystem processes, in particular microbially regulated C and N cycling. However, the responses of microbial C and N anabolic and metabolic processes to elevated CO2 are unclear. Methods: This study used a meta-analysis based on a global dataset (i.e., 312 observations from 66 studies) to calculate the effect size (i.e., natural log response ratio) of soil microbial C and N metabolic processes and relevant soil C and N concentrations under elevated CO2. Results: Results showed that elevated CO2 increased soil total C concentrations by 5.3% and total N concentrations by 4.8%, and decreased soil dissolved organic N and NO3− concentrations by 4.4% and 9.4%, respectively, but did not affect dissolved organic C or C:N ratios across global terrestrial ecosystems. Elevated CO2 significantly increased soil CO2 emissions and microbial biomass C by 19.3% and 13.3%, respectively, indicating that elevated CO2 increased both microbial anabolic and catabolic processes in soil. Similarly, elevated CO2 significantly increased soil N2O emissions and microbial biomass N by 18.7% and 9.0%, respectively. Microbial C cycling processes were associated with microbial N cycling processes under elevated CO2. Specifically, CO2 and N2O emissions were highest in soils with moisture contents of 40–60% and 60–80%, respectively, and microbial biomass C was largest in soils with pH values of 6.5–7.5. Conclusion: Our findings demonstrated the profound impacts of elevated CO2 on microbially regulated C and N metabolic processes and the close linkage between soil microbial C and N cycling under global warming. [ABSTRACT FROM AUTHOR]

Efficient frequency shifting and beam splitting are important for a wide range of applications, including atomic physics1,2, microwave photonics3–6, optical communication7,8 and photonic quantum computing9–14. However, realizing gigahertz-scale frequency shifts with high efficiency, low loss and tunability—in particular using a miniature and scalable device—is challenging because it requires efficient and controllable nonlinear processes. Existing approaches based on acousto-optics6,15–17, all-optical wave mixing10,13,18–22 and electro-optics23–27 are either limited to low efficiencies or frequencies, or are bulky. Furthermore, most approaches are not bi-directional, which renders them unsuitable for frequency beam splitters. Here we demonstrate electro-optic frequency shifters that are controlled using only continuous and single-tone microwaves. This is accomplished by engineering the density of states of, and coupling between, optical modes in ultralow-loss waveguides and resonators in lithium niobate nanophotonics28. Our devices, consisting of two coupled ring-resonators, provide frequency shifts as high as 28 gigahertz with an on-chip conversion efficiency of approximately 90 per cent. Importantly, the devices can be reconfigured as tunable frequency-domain beam splitters. We also demonstrate a non-blocking and efficient swap of information between two frequency channels with one of the devices. Finally, we propose and demonstrate a scheme for cascaded frequency shifting that allows shifts of 119.2 gigahertz using a 29.8 gigahertz continuous and single-tone microwave signal. Our devices could become building blocks for future high-speed and large-scale classical information processors7,29 as well as emerging frequency-domain photonic quantum computers9,11,14.Engineering of the coupling between optical modes in a lithium niobate chip enables the realization of tunable, bi-directional and low-loss electro-optic frequency shifters controlled using only continuous and single-tone microwaves. [ABSTRACT FROM AUTHOR]

The development of a spectroscopy device on a chip that could realize real-time fingerprinting with label-free and high-throughput detection of trace molecules represents one of the big challenges in sensing. Dual-comb spectroscopy (DCS) in the mid-infrared is a powerful technique offering high acquisition rates and signal-to-noise ratios through use of only a single detector with no moving parts. Here, we present a nanophotonic silicon-oninsulator platform designed for mid-infrared (mid-IR) DCS. A single continuous-wave lowpower pump source generates two mutually coherent mode-locked frequency combs spanning from 2.6 to 4.1 μm in two silicon microresonators. A proof-of-principle experiment of vibrational absorption DCS in the liquid phase is achieved acquiring spectra of acetone spanning from 2900 to 3100 nm at 127-GHz (4.2-cm-1) resolution. These results represent a significant step towards a broadband, mid-IR spectroscopy instrument on a chip for liquid/ condensed matter phase studies. [ABSTRACT FROM AUTHOR]

Minimal information is available on the oral bioavailability and liver-targeting properties of sorafenib solid lipid nanoparticles (SRF-SLNs) in rats. In this study, SRF-SLNs were prepared via the combined methods of high-speed shearing and ultrasonic treatment. SRF-SLN formulations were also optimized. Particle size, zeta potential, entrapment efficiency (EE), and drug loading (DL) were used as indices for the evaluation of the as-prepared SRF-SLNs. SRF concentration was determined by the high-performance liquid chromatography method. Results showed that the average EE and DL of SRF-SLNs were 89.87 and 5.39%. The average particle size, polydispersity index, and zeta potential of SRF-SLNs were 77.16 nm, 0.28, and − 18.1 mV, respectively. The results of the stability test showed that SRF-SLNs remained stable for more than 1 month at room temperature. After oral administration to rats (7.5 mg/kg), the liver-targeting evaluation results showed that the average drug selectivity index value of SRF-SLNs was 2.20 times higher, than that of the SRF-suspension. Furthermore, the area under the concentration–time curve of SRF increased by 66.7% in the SRF-SLN group comparing with that in the SRF-suspension. Our results suggested that SLNs were a promising approach for the oral delivery of SRF. [ABSTRACT FROM AUTHOR]

Diatoms are the largest group of heterokont algae with more than 100,000 species. As one of the single-celled photosynthetic organisms that inhabit marine, aquatic and terrestrial ecosystems, diatoms contribute ~ 45% of global primary production. Despite their ubiquity and environmental significance, very few diatom plastid genomes (plastomes) have been sequenced and studied. This study explored patterns of nucleotide substitution rates of diatom plastids across the entire suite of plastome protein-coding genes for 40 taxa representing the major clades. The highest substitution rate was lineage-specific within the araphid 2 taxon Astrosyne radiata and radial 2 taxon Proboscia sp. Rate heterogeneity was also evident in different functional classes and individual genes. Similar to land plants, proteins genes involved in photosynthetic metabolism have lower synonymous and nonsynonymous substitutions rates than those involved in transcription and translation. Significant positive correlations were identified between substitution rates and measures of genomic rearrangements, including indels and inversions, which is a similar result to what was found in legume plants. This work advances the understanding of the molecular evolution of diatom plastomes and provides a foundation for future studies. [ABSTRACT FROM AUTHOR]

The need for solving optimization problems is prevalent in various physical applications, including neuroscience, network design, biological systems, socio-economics, and chemical reactions. Many of these are classified as non-deterministic polynomial-time hard and thus become intractable to solve as the system scales to a large number of elements. Recent research advances in photonics have sparked interest in using a network of coupled degenerate optical parametric oscillators (DOPOs) to effectively find the ground state of the Ising Hamiltonian, which can be used to solve other combinatorial optimization problems through polynomial-time mapping. Here, using the nanophotonic silicon-nitride platform, we demonstrate a spatial-multiplexed DOPO system using continuous-wave pumping. We experimentally demonstrate the generation and coupling of two microresonator-based DOPOs on a single chip. Through a reconfigurable phase link, we achieve both in-phase and out-of-phase operation, which can be deterministically achieved at a fast regeneration speed of 400 kHz with a large phase tolerance. The use of a photonic network of coupled degenerate optical parametric oscillators for solving complex optimisation problems would require scalable integration capabilities. Here, the authors exploit χ (3) nonlinearity in SiN to demonstrate on-chip phase-tunable coupling between two DOPO based Ising nodes. [ABSTRACT FROM AUTHOR]

Microresonator Kerr frequency combs could provide miniaturised solutions for a wide range of applications. Many of these applications however require further manipulation of the generated frequency comb signal using photonic elements with strong second-order nonlinearity (χ(2)). To date these functionalities have largely been implemented as discrete components due to material limitations, which comes at the expense of extra system complexity and increased optical losses. Here we demonstrate the generation, filtering and electro-optic modulation of a frequency comb on a single monolithic integrated chip, using a nanophotonic lithium-niobate platform that simultaneously possesses large electro-optic (χ(2)) and Kerr (χ(3)) nonlinearities, and low optical losses. We generate broadband Kerr frequency combs using a dispersion-engineered high-Q lithium-niobate microresonator, select a single comb line using an electrically programmable add-drop filter, and modulate the intensity of the selected line. Our results pave the way towards monolithic integrated frequency comb solutions for spectroscopy, data communication, ranging and quantum photonics. Kerr microcombs promise the miniaturization of frequency comb sources, but many applications require additional second-order nonlinearities. Here, Wang et al. demonstrate that comb generation and second-order functionalities can be monolithically integrated on a single lithium niobate chip. [ABSTRACT FROM AUTHOR]