ESTIMATION OF AVERAGE DIFFERENTIAL ENTROPY FOR A STATIONARY ERGODIC SPACE-TIME RANDOM FIELD ON A BOUNDED AREA

In this paper,we mainly discuss a discrete estimation of the average differential entropy for a continuous time-stationary ergodic space-time random field.By estimating the probability value of a time-stationary random field in a small range,we give an entropy estimation and obtain the average entropy estimation formula in a certain bounded space region.It can be proven that the estimation of the average differential entropy converges to the theoretical value with a probability of 1.In addition,we also conducted numerical experiments for different parameters to verify the convergence result obtained in the theoretical proofs.

Separation of salidroside from the fermentation broth of engineered Escherichia coli using macroporous adsorbent resins

Salidroside(8-O-β-D-glucoside of tyrosol),a plant-derived natural product,is used for treatment of hypoxia,fatigue and aging diseases.The availability of salidroside is restricted since it is extracted from3-5 years old Rhodiola roots,which grow very slowly in the cold region of northern hemisphere of Earth.Our laboratory has constructed an engineered Escherichia coli and established a fermentation process to produce salidroside from glucose.In this article,nine macroporous resins from polarity to non-polarity,including NKA-9,S-8,AB-8,SP825,D101,LSA-8,LX-12,LX-18 and LX-68 resins,were tested to separate salidroside from fermentation broth.After static and dynamic experiments,the weakly polar SP825 resin had a better separation efficiency among nine resins.The adsorption kinetic and isotherm of salidroside on the SP825 resin were determined,and the pseudo-second-order kinetic model and Langmuir model could be fitted well.The effects of the pH on adsorption and ethanol concentration on desorption were investigated,and an optimal separation process was established.The adsorption for salidroside in the SP825 resin column was conducted with loading 150 ml at pH 7,and desorpted by washing 50 ml of80%ethanol solution.Under the best process conditions,the purity and yield of salidroside in the final product were 91.6%and 74.0%,respectively.The results showed that the macroporous SP825 resin would be feasible and effective to prepare salidroside and has promising application in the downstream process of microbial fermentation.

Interactions of phenol and benzaldehyde in electrocatalytic upgrading process

Biomass pyrolysis oil can be improved effectively by electrocatalytic hydrogenation(ECH).However,the unclear interactions among different components lead to low bio-oil upgrading efficiency in the conversion process.Herein,benzaldehyde and phenol,as common compounds in bio-oil,were chosen as model compounds.The interactions between the two components were explored in the ECH process by combining experiments and theoretical calculations.Results showed that phenol could accelerate the conversion of benzaldehyde in the ECH.The selectivity of benzyl alcohol was increased from 60.9%of unadded phenol to 99.1%with 30 mmol/L phenol concentration at 5 h.Benzaldehyde inhibited the ECH of phenol.In the presence of benzaldehyde,the conversion rate of phenol was below 10.0%with no cyclohexanone and cyclohexanol formation at 5 h.The density functional theory(DFT)calculations revealed that the phenol could promote the adsorption of benzaldehyde and facilitate the targeted conversion of benzaldehyde on the active site by lowering the reaction energy barrier.The research on the interaction between phenol and benzaldehyde in the ECH provides a theoretical basis for the application of ECH in practical bio-oil upgrading.

Rational construction of genome-minimized Streptomyces host for the expression of secondary metabolite gene clusters

Streptomyces offer a wealth of naturally occurring compounds with diverse structures,many of which possess significant pharmaceutical values.However,new product exploration and increased yield of specific compounds in Streptomyces have been technically challenging due to their slow growth rate,complex culture conditions and intricate genetic backgrounds.In this study,we screened dozens of Streptomyces strains inhabiting in a plant rhizosphere for fast-growing candidates,and further employed CRISPR/Cas-based engineering techniques for stepwise refinement of a particular strain,Streptomyces sp.A-14 that harbors a 7.47 Mb genome.After strategic removal of nonessential genomic regions and most gene clusters,we reduced its genome size to 6.13 Mb,while preserving its growth rate to the greatest extent.We further demonstrated that cleaner metabolic background of this engineered strain was well suited for the expression and characterization of heterologous gene clusters,including the biosynthetic pathways of actinorhodin and polycyclic tetramate macrolactams.Moreover,this streamlined genome is anticipated to facilitate directing the metabolic flux towards the production of desired compounds and increasing their yields.

Preparation and characterization of M_(1)-N_(x)-C_(y)based single atom catalysts for environmental applications

Single atom catalysts(SACs)have become the frontier research fields in catalysis.The M_(1)-N_(x)-C_(y)based SACs,wherein single metal atoms(M1)are stabilized by N-doped carbonaceous materials,have provided new opportunities for catalysis due to their high reactivity,maximized atomic utilization,and high selectivity.In this review,the fabrication methods of M_(1)-N_(x)-C_(y)based SACs via support anchoring strategy and coordination design strategy are summarized to help the readers understand the interaction mechanism of single atoms and support.Then,characterization technologies for identifying single metal atoms are presented.Besides,the environmental applications including management of harmful gases,water purification are discussed.Finally,future opportunities and challenges for preparation strategies,mechanisms and applications are concluded.We conclude this review by emphasizing the fact that M_(1)-N_(x)-C_(y)based SACs has the potential to become an important candidate for solving current and future environmental pollution problems.

New insight into the synergy of nitrogen-related sites on biochar surface for sulfamethoxazole adsorption from water

In-depth exploration of the relationship among different adsorption sites is conducive to design of efficient adsorbents for target pollutants removal from water.In this study,the experiments,multivariate non-linear regression and density functional theory calculations are applied to explore the possible synergistic effects of three nitrogen(N)-containing sites on cow dung biochar surface for sulfamethoxazole(SMX)adsorption.Notably,a strong synergistic effect between pyridinic N and pyrrolic N sites was found for sulfamethoxazole adsorption.The adsorption energies of SMX on four pyrrolic N-coupled pyridinic N structures were-1.02,-0.41,-0.49 and-0.72 e V,much higher than the sum of adsorption energies(-0.31 e V)on pyrrolic N and pyridinic N.Besides,the alteration of Mulliken charge revealed that the simultaneous presence of pyridinic N and pyrrolic N improved the electron transfer remarkably from-0.459 e and 0.094 e to-0.649 e and 0.186 e,benefiting for SMX adsorption.This work firstly explored the possible synergies of adsorption sites on biochar surface for organic contaminants removal from water,which shed new lights on the adsorption mechanism and provided valuable information to design efficient adsorbents in the field of water treatment.

Reconfigurable and nonvolatile terahertz lithography-free photonic devices based on phase change films

High-performance terahertz(THz)devices with reconfigurable features are highly desirable in many promising THz applications.However,most of the existing reconfigurable THz elements are still limited to volatile responses,single functionality,and time-consuming multistep manufacturing procedures.In this paper,we report a lithography-free approach to create reconfigurable and nonvolatile THz components by exploring the reversible,nonvolatile,and continuous THz modulation capability of the phase change material Ge_(2)Sb_(2)Te_(5).As a proof of concept,THz gratings with significant Rayleigh anomalies and diffraction as well as ultrathin THz flat lenses with subwavelength and ultra-broadband focusing capabilities are designed and fabricated on ultrathin Ge_(2)Sb_(2)Te_(5)films using the presented photo-imprint strategy.Moreover,such a method can also be adopted to create more complex THz devices,such as Pancharatnam–Berry phase metasurfaces and grayscale holographic plates.With these findings,the proposed method will provide a promising solution to realize reconfigurable and nonvolatile THz elements.

Improvement of betanin biosynthesis in Saccharomyces cerevisiae by metabolic engineering

Betanin is a member of natural pigment betacyanins family and has extensive application in the food industry as an important natural red food colorant.Its relatively inefficient production in nature however hampers access to this phytochemicals through traditional crop-based manufacturing.Microbial bioproduction therefore represents an attractive alternative.Here,we present the construction of a Saccharomyces cerevisiae strain for betanin production.Through minimizing metabolic crosstalk,screening and modifying biosynthetic enzymes,enhancing pathway flux and optimizing fermentation conditions,a final titer of betanin of 28.7 mg/L was achieved from glucose at 25℃ in baffled shake-flask,which is the highest reported titer produced by yeast to our knowledge.This work provides a promising step towards developing synthetic yeast cell factories for de novo biosynthesis of value-added betanin and other betacyanins.

Sideband-free dispersion-managed Yb-doped mode-locked fiber laser with Gires–Tournois interferometer mirrors

High-order dispersion introduced by Gires–Tournois interferometer mirrors usually causes spectral sidebands in the nearzero dispersion region of mode-locked fiber lasers.Here,we demonstrate a sideband-free Yb-doped mode-locked fiber laser with dispersion-compensating Gires–Tournois interferometer mirrors.Both the simulation and the experiment demonstrate that the wavelength and energy of the sidebands can be tuned by changing the transmission coefficient of the output mirror,the pump power,and the ratio of the net cavity dispersion to the net third-order dispersion in the cavity.By optimizing these three parameters,the laser can generate a sideband-free,Gaussian-shaped spectrum with a 13.56-nm bandwidth at-0.0232 ps^(2)net cavity dispersion,which corresponds to a 153-fs pulse duration.

Nonvolatile reconfigurable dynamic Janus metasurfaces in the terahertz regime

Metasurfaces,especially tunable ones,have played a major role in controlling the amplitude,phase,and polarization of electromagnetic waves and attracted growing interest,with a view toward a new generation of miniaturized devices.However,to date,most existing reconfigurable devices are bounded in volatile nature with sustained external energy to maintain and single functionality,which restrict their further applications.Here,we demonstrate for the first time,to our knowledge,nonvolatile,reconfigurable,and dynamic Janus metasurfaces by incorporating phase-change material Ge_(2)Se_(2)Te_(5)(GST)in the terahertz(THz)regime.First,we experimentally show the reversible switching characteristic of GST on large areas by applying a single nanosecond laser pulse,which exhibits excellent contrast of THz properties in both states.Then,we present a multiplex metasurface scheme.In each metasurface,three sets of structures are adopted,in which two sets integrate GST.The effective structures can be reversely modulated by the amorphization and crystallization of GST.As a proof of concept,the dynamic beam splitter,bifocal metalens,dual-mode focusing optical vortex generators,and switchable metalens/focusing optical vortex generators are designed,fabricated,and experimentally characterized,and can be switched reversibly and repeatedly with the help of optical and thermal stimuli.Our scheme will pave the way toward the development of multifunctional and compact THz devices and may find use for applications in THz imaging,sensing,and communications.

Modular engineering of E. coli coculture for efficient production of resveratrol from glucose and arabinose mixture

Resveratrol,a valuable plant-derived polyphenolic compound with various bioactivities,has been widely used in nutraceutical industries.Microbial production of resveratrol suffers from metabolic burden and low malonyl-CoA availability,which is a big challenge for synthetic biology.Herein,we took advantage of coculture engineering and divided the biosynthetic pathway of resveratrol into the upstream and downstream strains.By enhancing the supply of malonyl-CoA via CRISPRi system and fine-tuning the expression intensity of the synthetic pathway genes,we significantly improved the resveratrol productivity of the downstream strain.Furthermore,we developed a resveratrol addiction circuit that coupled the growth of the upstream strain and the resveratrol production of the downstream strain.The bidirectional interaction stabilized the coculture system and increased the production of resveratrol by 74%.Moreover,co-utilization of glucose and arabinose by the coculture system maintained the growth advantage of the downstream strain for production of resveratrol throughout the fermentation process.Under optimized conditions,the engineered E.coli coculture system produced 204.80 mg/L of resveratrol,12.8-fold improvement over monoculture system.This study demonstrates the promising potential of coculture engineering for efficient production of natural products from biomass.

Generation of sub-three-cycle pulses at 53 MHz repetition rate via nonlinear compression in optical parametric oscillator

We report an experimental generation of few-cycle pulses at 53 MHz repetition rate. Femtosecond pulses with pulse duration of 181 fs are firstly generated from an optical parametric oscillator(OPO). Then, the pulses are compressed to subthree-cycle with a hybrid compressor composed of a commercial single-mode fiber and a pair of prisms, taking advantage of the tunability of the OPO and the numerical simulating of the nonlinear compression system. Our compressed optical pulses possess an ultrabroadband spectrum covering over 470 nm bandwidth(at-10 dB), and the output intensity fluctuation of our system is less than 0.8%. These results show that our system can effectively generate few-cycle pulses at a repetition rate of tens of megahertz with excellent long-term stability, which could benefit future possible applications.