Enhancing the Activity of Carboxymethyl Cellulase Enzyme Using Highly Stable Selenium Nanoparticles Biosynthesized by Bacillus paralicheniformis Y4.

The inorganic selenium is absorbed and utilized inefficiently, and the range between toxicity and demand is narrow, so the application is strictly limited. Selenium nanoparticles have higher bioactivity and biosafety properties, including increased antioxidant and anticancer properties. Thus, producing and applying eco-friendly, non-toxic selenium nanoparticles in feed additives is crucial. Bacillus paralicheniformis Y4 was investigated for its potential ability to produce selenium nanoparticles and the activity of carboxymethyl cellulases. The selenium nanoparticles were characterized using zeta potential analyses, Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM). Additionally, evaluations of the anti-α-glucosidase activity and the antioxidant activity of the selenium nanoparticles and the ethyl acetate extracts of Y4 were conducted. B. paralicheniformis Y4 exhibited high selenite tolerance of 400 mM and the selenium nanoparticles had an average particle size of 80 nm with a zeta potential value of -35.8 mV at a pH of 7.0, suggesting that the particles are relatively stable against aggregation. After 72 h of incubation with 5 mM selenite, B. paralicheniformis Y4 was able to reduce it by 76.4%, yielding red spherical bio-derived selenium nanoparticles and increasing the carboxymethyl cellulase activity by 1.49 times to 8.96 U/mL. For the first time, this study reports that the carboxymethyl cellulase activity of Bacillus paralicheniforis was greatly enhanced by selenite. The results also indicated that B. paralicheniformis Y4 could be capable of ecologically removing selenite from contaminated sites and has great potential for producing selenium nanoparticles as feed additives to enhance the added value of agricultural products.

Real-time observation of the thermo-optical and heat dissipation processes in microsphere resonators.

This work reports the real-time observation of the thermo-optical dynamics in silica microsphere resonators based on the dispersive time stretch technique. In general, the thermo-optical dynamics of silica microsphere resonators, including the thermal refraction and thermal expansion, can be characterized by the resonance wavelength shift, whose duration is at the millisecond timescale. However, this fast wavelength shift process cannot be directly captured by conventional spectroscopy, and only its transmission feature can be characterized by a fast-scanning laser and an intensity detector. With the advance of the time-stretch spectroscopy, whose temporal resolution is up to tens of nanoseconds, the thermo-optical dynamics can be observed in a more straight-forward way, by utilizing the pump-probe technology and mapping the resonance wavelength to the time domain. Here, the thermo-optical dynamics are explored as a function of the power and the scanning rate of the pump laser. Theoretical simulations reproduce the experimental results, revealing that the thermo-optical dynamics of silica microsphere resonators is dominated by the fast thermo-optical effect and the slow heat dissipation process to the surroundings, which leads to gradual regression of the resonance wavelength. This work provides an alternative solution for studying the thermo-optical dynamics in whispering gallery mode microresonators, which would be crucial for future applications of microresonator photonic systems.

First-principles exploration of oxygen vacancy impact on electronic and optical properties of ABO3-δ (A = La, Sr; B = Cr, Mn) perovskites.

ABO3-δ perovskites are utilized in many applications including optical gas sensing for energy systems. Understanding the opto-electronic properties allows rational selection of the perovskite-based sensors from a diverse family of ABO3-δ perovskites, associated with the choices of A and B cations and range of oxygen concentrations. Herein, we assess the impact of oxygen vacancies on the electronic structure and optical response of pristine and oxygen-vacant ABO3-δ (A = La, Sr; B = Cr, Mn) perovskites via first-principles calculations. The endothermic formation energy for oxygen vacancies shows that the generation of ABO3-δ defect structures is thermodynamically possible. LaCrO3 and LaMnO3 have direct and indirect ground-state band gaps, respectively, whereas SrCrO3 and SrMnO3 are metallic. In the presence of an oxygen mono-vacancy, however, the band gap decreases in LaCrO3-δ and vanishes in LaMnO3-δ. In contrast to the decrease in the band gaps, the oxygen vacancies in ABO3-δ are found to increase optical absorption in the visible to near-infrared wavelength regime, and thus lower the onset energy of absorption compared with the pristine materials. Our assessments emphasize the role of the oxygen vacancy, or other possible oxygen non-stoichiometry defects, in perovskite oxides with respect to the opto-electronic performance parameters that are of interest for optical gas sensors for energy generation process environments.

The optimal co-doping of SrFe1-xCoxO3-δ oxygen carriers in redox applications.

Although the oxygen carrier SrCoO3 has higher redox activity than SrFeO3, cobalt is both more expensive and scarcer than iron, which would hinder the wide implementation of SrCoO3. For these reasons, doping SrFeO3 with Co is a potential compromise, benefitting the redox properties of SrFeO3, while still limiting the overall amount of cobalt being used. To find the optimal level of Co-doping, density functional theory calculations were performed to investigate the Co-doping effect on the oxygen vacancy formation and oxygen migration in SrFe1-xCoxO3-δ (x = 0, 0.125, 0.25, 0.375, 0.5). Our findings show that the oxygen vacancy formation energies (Ef) decrease with the increase of Co content resulting from the increased composition of the O-2p band at the Fermi level upon Co doping. In particular, the Ef decreases nearly 0.5 eV between the x = 0 and x = 0.25 samples while Ef only decreases 0.1 eV further as Co content is increased to x = 0.5. We obtain that x = 0.25 is an optimal cost/benefit ratio for Co doping, which is preserved at both low oxygen vacancy concentrations (δ = 0.0625 values listed above) and at high concentrations of δ = 0.1875 and 0.375. Kinetically, the oxygen migration barrier has slight change upon Co doping due to the similar size of Co and Fe. Therefore, considering both redox activity and economics in reversible oxygen storage applications, x = 0.25 is suggested as the optimal Co-doping value in SrFe1-xCoxO3-δ.

Ultrafast discrete swept source based on dual chirped combs for microscopic imaging.

An inertial-free, ultrafast frequency comb source based on two chirped optical frequency combs (OFCs) is proposed and experimentally demonstrated. The high linearity frequency sweeping is realized by the Vernier effect between the two OFCs rather than any mechanical motion component, so that good stability and reliability are ensured and no recalibration or resampling process is required. Swept rate up to 1 MHz is realized while keeping a narrow instantaneous linewidth of 0.03 nm, thanks to the extra-cavity frequency sweeping method. The wavelength step is proportional to the swept rate (3.8 pm at 10 kHz), and can be tuned by changing the repetition rate difference between the two OFCs. This swept source is applied for high-speed wavelength encoded imaging and achieves 4.4-µm spatial resolution at a 329-kHz frame rate. Compared with the traditional time-stretch microscopy, the signal acquisition bandwidth decreased from 3.8 GHz to below 90 MHz to achieve the same spatial resolution. Furthermore, the exposure time for a specific wavelength is much longer due to the discrete sweeping feature, which is a benefit for higher sensitivity. This discrete swept source provided a promising low-cost option for high-speed biomedical imaging systems and high-accuracy spectroscopy.

Temporally structured illumination for ultrafast time-stretch microscopy.

This work developed a temporally structured illumination scheme to conquer the detector bandwidth limitation that is increasingly becoming a stumbling block of ultrafast single-pixel measurement. Inspired by structured illumination microscopy and space-time duality, an electro-optic modulator resembling the temporal counterpart of a spatial grating is used to impart a sinusoidal pattern onto the time-stretch signal before detection. Consequently, the detector bandwidth is equivalently doubled based on three measurements and a subsequent reconstruction, thereby capturing the high-frequency components originally beyond the detector bandwidth. As a proof of concept, this method is applied to an ultrafast single-pixel imaging modality, the time-stretch microscopy, to verify its capability to surpass the resolution limit imposed by the detector bandwidth. High-quality images with ∼4.0 µm spatial resolution are acquired at ∼30 MHz frame rates by merely half of the detector bandwidth, compared to the traditional system. This Letter provides a simple and economical solution for high-speed signal acquisition, which is demanded in a variety of applications, ranging from ultrafast imaging to single-shot spectroscopy.

Calibration-free time-stretch optical coherence tomography with large imaging depth.

We demonstrate a calibration-free time-stretch optical coherence tomography (TS-OCT), based on an optical higher order dispersion compensation scheme, which substitutes the digital calibration with optical dispersion compensation. As a result, the acquired raw data can directly perform the Fourier transform, and data processing time is greatly reduced by 82%, compared with the digital calibration. Moreover, because of the high-sensitivity and calibration-free characteristics, the high-order dispersion compensation-based TS-OCT can increase sensitivity roll-off by 2.6 times to 6.91 mm/dB and effective imaging depth by 14.2% to 16 mm. The in vivo biological tissue imaging has been demonstrated, with the single-shot A-scan rate approaching 19 MHz. This higher order dispersion compensation scheme could provide a promising solution for the TS-OCT system to realize 3D imaging in real time and enhanced imaging quality.

Theoretical study of the optical and thermodynamic properties of LaxSr1-xCo1-yFeyO3-δ (x/y = 0.25, 0.5, 0.75) perovskites.

The performance of LaxSr1-xCo1-yFeyO3-δ perovskite systems in applications such as solid oxide fuel cells and catalysis is related to the proportion of substitution atoms. Using a density functional theory method, we investigate the doping effect on the electronic, optical, and thermodynamic properties of LaxSr1-xCo1-yFeyO3-δ (x/y = 0.25, 0.5, 0.75). Our results show that La doping introduces an empty state and pushes the Fermi level upwards. The doping Fe derived states locate away from the Fermi level as compared with Co states. From the results of optical absorption, the peak at 200-300 nm is enhanced and experiences a blue-shift with increasing La concentration. The corresponding peak at 400-700 nm also shows a blue-shift induced by both La and Fe doping, and it could be enhanced by Fe doping while being suppressed by La doping. And the peak above 1500 nm is enhanced by the cooperation of La and Fe doping. From thermodynamic calculations via an Ellingham diagram, it is found that the parent SrCoO3 is the most favorable composition for releasing O2, with both La and Fe doping hampering the reduction reaction. Therefore, the optical and thermodynamic properties of LaxSr1-xCo1-yFeyO3-δ could be adjusted by special doping values.

The influence of oxygen vacancy on the electronic and optical properties of ABO3-δ (A = La, Sr, B = Fe, Co) perovskites.

ABO3-δ (A = La, Sr, B = Fe, Co) perovskites are useful in a wide range of applications, including their recent exploration for application in high-temperature optical oxygen sensing for energy conversion devices such as solid oxide fuel cells. To elucidate the dependence of functional properties and oxygen vacancy formation on defect chemistry and composition, first principles calculations are presented. The obtained results show that oxygen vacancy (VO) formation energies are in the order of LaFeO3 > LaCoO3 > SrFeO3 > SrCoO3. Furthermore, the influence of VO on the electronic and optical properties is investigated for the high temperature stable phases (T = 1100 K). For the LaFeO3 insulator, the VO donated electrons are all localized on the down-spin d3z2-r2 orbitals of the nearest Fe ions. These defect states located in the band gap induce a drop in the energy onset of absorption as pristine bulk → V2+O → V1+O → V0O, and especially, an extra absorption peak appears between 0.5 and 1.5 eV due to V0O and V1+O formation. In the rest of the crystals that expressed a metallic feature, the VO donated electrons partially localize on the down-spin d3z2-r2 orbital and partially delocalize through the lattice, by which the absorption peaks (0.5-2.0 eV for LaCoO3, 0.0-0.5 eV for SrFeO3 and SrCoO3) from the electronic excitation near the Fermi level are enhanced. A high VO concentration of oxygen divacancy in SrFeO3 and SrCoO3 could enhance charge localization on down-spin d3z2-r2 orbitals, resulting in a remarkable increase of optical absorption at 1.5-3.0 eV.

Temporal radio-frequency spectrum analyzer, based on asynchronous optical sampling assisted temporal convolution.

We propose and experimentally demonstrated an all-optical radio-frequency (RF) spectrum analyzer, based on asynchronous optical sampling (ASOPS) assisted temporal convolution. The RF spectrum is mapped onto the time axis with the help of the temporal convolution system. In combination with the bandwidth compression capability of the ASOPS scheme, up to 28-GHz RF spectrum can be directly read out by an acquisition system with bandwidth as low as 20 MHz. The experimental results demonstrated about 100-MHz resolution and 28-GHz observation bandwidth. The resolution can be improved by increasing the amount of temporal dispersion or optical spectral bandwidth, and the bandwidth can be further extended by compensating the higher-order dispersion, although it is currently mainly limited by that of the electro-optic modulator. The frame rate is flexibly tunable by changing the repetition rate difference between the two mode-locked fiber lasers. Moreover, nearly 25-dB dynamic range indicates this system has a promising application prospect.

Ultrafast electrical spectrum analyzer based on all-optical Fourier transform and temporal magnification.

Real-time electrical spectrum analysis is of great significance for applications involving radio astronomy and electronic warfare, e.g. the dynamic spectrum monitoring of outer space signal, and the instantaneous capture of frequency from other electronic systems. However, conventional electrical spectrum analyzer (ESA) has limited operation speed and observation bandwidth due to the electronic bottleneck. Therefore, a variety of photonics-assisted methods have been extensively explored due to the bandwidth advantage of the optical domain. Alternatively, we proposed and experimentally demonstrated an ultrafast ESA based on all-optical Fourier transform and temporal magnification in this paper. The radio-frequency (RF) signal under test is temporally multiplexed to the spectrum of an ultrashort pulse, thus the frequency information is converted to the time axis. Moreover, since the bandwidth of this ultrashort pulse is far beyond that of the state-of-the-art photo-detector, a temporal magnification system is applied to stretch the time axis, and capture the RF spectrum with 1-GHz resolution. The observation bandwidth of this ultrafast ESA is over 20 GHz, limited by that of the electro-optic modulator. Since all the signal processing is in the optical domain, the acquisition frame rate can be as high as 50 MHz. This ultrafast ESA scheme can be further improved with better dispersive engineering, and is promising for some ultrafast spectral information acquisition applications.

Real-time broadband radio frequency spectrum analyzer based on parametric spectro-temporal analyzer (PASTA).

A real-time broadband radio frequency (RF) spectrum analyzer is proposed and experimentally demonstrated to rapidly measure the RF spectrum of broadband optical signal. Cross phase modulation in the highly-nonlinear fiber is used to convert the RF spectrum carried by the pump to the optical spectrum of the probe signal, then the optical spectrum is real-time analyzed with the parametric spectro-temporal analyzer (PASTA) technology. The system performances are investigated in detail, including bandwidth, resolution, frame rate, and dynamic range. It achieves large RF bandwidth of over 800 GHz, as well as 91-MHz frame rate without sacrificing the resolution. It is noted that 91-MHz frame rate is several orders of magnitude improvement over those previous reported all-optical RF spectrum analyzers. As a proof-of-concept demonstration, this real-time broadband RF spectrum analyzer successfully characterizes the ultra-short pulse trains with repetition rate of 160GHz, which is far beyond capability of the conventional electrical spectrum analyzer. It presents a new way to implement rapid and broadband RF spectrum measurement, and would be of great interests for some ultrafast scenarios, where the real-time RF spectrum analysis can be applied.

Frequency-domain light intensity spectrum analyzer based on temporal convolution.

We propose and experimentally demonstrate a new type of all-optical radio frequency (RF) spectrum analyzer based on temporal convolution and cross-phase modulation (XPM) that can be regarded as the frequency-domain counterpart of a conventional light intensity spectrum analyzer (LISA). The XPM effect converts the intensity envelope of an optical signal to the phase of the probe signal, while the temporal convolution helps to enable the RF spectrum to be temporally resolved with a high frame rate. This frequency-domain LISA (f-LISA) has experimentally demonstrated an 800-GHz observation bandwidth with 1.25-GHz resolution (1 GHz for a single frequency) and a 94-MHz frame rate. To showcase its potential applications, this analyzer has successfully characterized the dynamic RF spectrum of an ultrafast wavelength-switching signal with a 10-ns switching interval. We believe that it is promising for some ultrafast dynamic RF spectrum acquisition applications, e.g., fast tuning lasers and real-time channel monitoring.

Regeneration mechanisms of high-lithium content zirconates as CO2 capture sorbents: experimental measurements and theoretical investigations.

By combining TGA and XRD measurements with theoretical calculations of the capture of CO2 by lithium-rich zirconates (Li8ZrO6 and Li6Zr2O7), it has been demonstrated that the primary regeneration product during absorption/desorption cycling is in the form of Li2ZrO3. During absorption/desorption cycles, lithium-rich zirconates will be consumed and will not be regenerated. This result indicates that among known lithium zirconates, Li2ZrO3 is the best sorbent for CO2 capture.

Strong lithium polysulfide chemisorption on electroactive sites of nitrogen-doped carbon composites for high-performance lithium-sulfur battery cathodes.

Despite the high theoretical capacity of lithium-sulfur batteries, their practical applications are severely hindered by a fast capacity decay, stemming from the dissolution and diffusion of lithium polysulfides in the electrolyte. A novel functional carbon composite (carbon-nanotube-interpenetrated mesoporous nitrogen-doped carbon spheres, MNCS/CNT), which can strongly adsorb lithium polysulfides, is now reported to act as a sulfur host. The nitrogen functional groups of this composite enable the effective trapping of lithium polysulfides on electroactive sites within the cathode, leading to a much improved electrochemical performance (1200 mAh g(-1) after 200 cycles). The enhancement in adsorption can be attributed to the chemical bonding of lithium ions by nitrogen functional groups in the MNCS/CNT framework. Furthermore, the micrometer-sized spherical structure of the material yields a high areal capacity (ca. 6 mAh cm(-2)) with a high sulfur loading of approximately 5 mg cm(-2), which is ideal for practical applications of the lithium-sulfur batteries.

Effect of Zwitterionic Additives on Solvation and Transport of Sodium and Potassium Cations in (Ethylene Oxide)10: A Molecular Dynamics Simulation Study.

Sodium- (Na+) and potassium- (K+) ion batteries are cost-effective alternatives to lithium-ion (Li+) batteries due to the abundant sodium and potassium resources. Solid polymer electrolytes (SPEs) are essential for safer and more efficient Na+ and K+ batteries because they often exhibit low ionic conductivity at room temperature. While zwitterionic (ZW) materials enhance Li+ battery conductivity, their potential for Na+ and K+ transport in batteries remains unexplored. In this study, we investigated the effect of three ZW molecules (ChoPO4, i.e., 2-methacryloyloxyethyl phosphorylcholine, ImSO3, i.e., sulfobetaine ethylimidazole, and ImCO2, i.e., carboxybetaine ethylimidazole) on the dissociation of Na+ and K+ coordination with ethylene oxide (EO) chains in EO-based electrolytes through molecular dynamics simulations. Our results showed that ChoPO4 possessed the highest cation-EO10 dissociation ability, while ImSO3 exhibited the lowest. Such dissociation ability correlated with the cation-ZW molecule coordination strength: ChoPO4 and ImSO3 showed the strongest and the weakest coordination with cations. However, the cation-ZW molecule coordination could slow the cationic diffusion. The competition of these effects resulted in accelerating or decelerating cationic diffusion. Our simulated results showed that ImCO2 enhanced Na+ diffusion by 20%, while ChoPO4 and ImSO3 led to a 10% reduction. For K+, ChoPO4 reduced its diffusion by 40%, while ImCO2 and ImSO3 caused a similar decrease of 15%. These findings suggest that the ZW structure and the cationic size play an important role in the ionic dissociation effect of ZW materials.

How Well Can Quantum Embedding Method Predict the Reaction Profiles for Hydrogenation of Small Li Clusters?

Quantum computing leverages the principles of quantum mechanics in novel ways to tackle complex chemistry problems that cannot be accurately addressed using traditional quantum chemistry methods. However, the high computational cost and available number of physical qubits with high fidelity limit its application to small chemical systems. This work employed a quantum-classical framework which features a quantum active space-embedding approach to perform simulations of chemical reactions that require up to 14 qubits. This framework was applied to prototypical example metal hydrogenation reactions: the coupling between hydrogen and Li2, Li3, and Li4 clusters. Particular attention was paid to the computation of barriers and reaction energies. The predicted reaction profiles compare well with advanced classical quantum chemistry methods, demonstrating the potential of the quantum embedding algorithm to map out reaction profiles of realistic gas-phase chemical reactions to ascertain qualitative energetic trends. Additionally, the predicted potential energy curves provide a benchmark to compare against both current and future quantum embedding approaches.

Sensing at the Nanoscale Using Nitrogen-Vacancy Centers in Diamond: A Model for a Quantum Pressure Sensor.

The sensing of stress under harsh environmental conditions with high resolution has critical importance for a range of applications including earth's subsurface scanning, geological CO2 storage monitoring, and mineral and resource recovery. Using a first-principles density functional theory (DFT) approach combined with the theoretical modelling of the low-energy Hamiltonian, here, we investigate a novel approach to detect unprecedented levels of pressure by taking advantage of the solid-state electronic spin of nitrogen-vacancy (NV) centers in diamond. We computationally explore the effect of strain on the defect band edges and band gaps by varying the lattice parameters of a diamond supercell hosting a single NV center. A low-energy Hamiltonian is developed that includes the effect of stress on the energy level of a ±1 spin manifold at the ground state. By quantifying the energy level shift and split, we predict pressure sensing of up to 0.3 MPa/Hz using the experimentally measured spin dephasing time. We show the superiority of the quantum sensing approach over traditional optical sensing techniques by discussing our results from DFT and theoretical modelling for the frequency shift per unit pressure. Importantly, we propose a quantum manometer that could be useful to measure earth's subsurface vibrations as well as for pressure detection and monitoring in high-temperature superconductivity studies and in material sciences. Our results open avenues for the development of a sensing technology with high sensitivity and resolution under extreme pressure limits that potentially has a wider applicability than the existing pressure sensing technologies.

Exploration of Streptomyces fradiae J1-021 as a Potential Host for the Heterologous Production of Spinosad.

Spinosad is a potent insecticide produced by Saccharopolyspora spinosa. However, it harbors certain limitations of a low growing rate and unfeasible genetic manipulation that can be overcome by adopting a superior platform, such as Streptomyces. Herein, we exploited the industrial tylosin-producing Streptomyces fradiae J1-021 for the heterologous production of spinosad. An engineered strain (HW01) with deletion of the tylosin biosynthetic gene cluster (BGC) was constructed and then transformed with the natural spinosad BGC. The distribution and expression levels of the tylosin BGC operons were assessed to construct a natural promoter library. The rate-limiting steps of spinosad biosynthesis were identified by analyzing the transcriptional expression of the spinosad biosynthetic genes. The stepwise engineering work involved the overexpression of the biosynthetic genes participating in rate-limiting pathways using strong promoters, affording an increase in spinosad production to 112.4 µg/L. These results demonstrate that strain HW01 has the potential to be used as a chassis for the heterologous production of polyketides.

Structural and electronic properties of Li8ZrO6 and its CO2 capture capabilities: an ab initio thermodynamic approach.

The structural, electronic, and phonon properties of Li8ZrO6 are investigated with the application of density functional theory and lattice phonon dynamics. Based on the calculated data, the thermodynamics of CO2 absorption-desorption for Li8ZrO6 is analyzed and compared with those of Li2ZrO3 and Li6Zr2O7. The band gap of Li8ZrO6 is indirect along Γ-L with a value of 4.74 eV. From the calculated thermodynamic properties of Li8ZrO6 reacting with CO2, we found that Li8ZrO6 could be regenerated at high temperatures (>1100 K). Our results indicated that the lithium zirconate with a lower Li2O/ZrO2 ratio has a lower turnover temperature. Hence, by mixing or doping two or more materials to form a new material, it is possible to find or synthesize CO2 sorbents that can fit the industrial needs for optimal performance. Although the CO2 capture capacity of Li8ZrO6 is much higher than that of Li2ZrO3, the high energy required for regeneration, the capacity loss during long absorption-desorption cycles, solid sintering at high temperature, and the material cost may affect its overall capture performance. Our results also provided some general guidelines for designing new CO2 sorbents.