Carbon dots derived from Poria cocos polysaccharide as an effective“on-off”fluorescence sensor for chromium(Ⅵ)detection

Chromium is a harmful contaminant showing mutagenicity and carcinogenicity.Therefore,detection of chromium requires the development of low-cost and high-sensitivity sensors.Herein,blue-fluorescent carbon quantum dots were synthesized by one-step hydrothermal method from alkali-soluble Poria cocos polysaccharide,which is green source,cheap and easy to obtain,and has no pharmacological activity due to low water solubility.These carbon quantum dots exhibit good fluorescence stability,water solubility,anti-interference and low cytotoxicity,and can be specifically combined with the detection of Cr(Ⅵ)to form a non-fluorescent complex that causes fluorescence quenching,so they can be used as a label-free nanosensor.High-sensitivity detection of Cr(Ⅵ)was achieved through internal filtering and static quenching effects.The fluorescence quenching degree of carbon dots fluorescent probe showed a good linear relationship with Cr(Ⅵ)concentration in the range of 1-100μM.The linear equation was F;/F=0.9942+0.01472[Cr(Ⅵ)](R;=0.9922),and the detection limit can be as low as 0.25μM(S/N=3),which has been successfully applied to Cr(Ⅵ)detection in actual water samples herein.

Study on eliminating noises in short-period data of geomagnetic intensity by using nu-merical multichannel predictive filtering

The effectiveness of eliminating the noises in short-period data of geomagnetic intensity recorded in a little seismo-geomagnetic array by using numerical multichannel predictive filtering has been studied. The result shows that this technique is effective to fit external magnetic disturbance to inner electromagnetic induced difference field and reduce the noise level of difference data successfully. The filter quality factor Q of two examples in this work are 0. 86 and 0.68 respectively. The spectral analysis shows that during geomagnetic-calm days the fourfold-frequency harmonics of S q in difference data are main components. The length of the optimum filter depends on not only the frequency of predicable energy in difference data but also maybe the phase difference between input and expected output data. It is difficult to obtain the filter fitting both the data during magnetic-disturbed days and calm days. The result shows that the conductivity in Yanqing-Huailai basin west to Beijing may be much non-uniform.

Effects of Dispex A40 on Rheology and Filter Pressing Behaviours of Concentrated Alumina Suspensions

Variation of plastic viscosity and extrapolated shear yield stress with the concentration of Dispex A40 for the concentrated Alcoa A16 α-Al2O3 suspensions at 0.27 powder volume fraction was investigated at 294 K. An optimum level of Dispex A40 for full deflocculation is found to be at 0.18% mass fraction of the powder, at which the rheological behaviour shows little different to that of adjusting the pH to 4 to obtain full deflocculation. It is demonstrated that the shear stress drop can roughly work as an index for the thixotropy in particular fixed conditions, and consequently an index for the deflocculation as the shear stress drop becomes larger when the level of the flocculation increases, and vice versa. It is also found that the addition of Dispex A40 can prevent the filter cakes from cracking, whereas the cakes at various pH values with polyvinyl alcohol as a sole polymer normally develop cracking during drying.

Effects of Forest Filtering and Cold Trapping on Polycyclic Aromatic Hydrocarbons Distribution in Southeast Tibet

New pollutants in remote regions have become a global issue of concern.This study collected soil,lichen,moss,and air samples from the high mountain area of southeastern Tibet to analyze the altitude pollution distribution of 16 polycyclic aromatic hydrocarbons(PAHs)and the related influencing factors.The results revealed that the average levels ofΣ6PAH in soil,moss,lichen,and air samples were 46.8 ng/g dry weight(dw),140.6 ng/g dw,712.0 ng/g dw,and 60.1 ng/m^(3),respectively.Naphthalene and phenanthrene were the most abundant individual isomers,and 2–4 rings PAHs accounted for approximately 90%of the totalΣPAH concentration in the samples.Source apportionment analysis highlighted the impact of atmospheric PAH inputs on this region.Octanol/air distribution factor(K_(oa)),altitude,plant coverage,and soil organic matter were the key determinants of PAH concentration along the altitudinal gradient.Across all the soil sampling sites,the average contribution of the forest filter effect(FFE)was greater than that of the mountain cold trapping effect based on the principal component analysis and multiple linear regression.The findings of this study strengthened the reasons for the preferential accumulation of organic pollutants in the high-altitude mountainous area,and provided important insights for effective environmental strategies of new pollutants.

Spin and valley filter in strain engineered silicene

The realization of a perfect spin or valley filtering effect in two-dimensional graphene-like materials is one of the fundamental objectives in spintronics and valleytronics. For this purpose, we study spin- and valley-dependent transport in a silicene system with spatially alternative strains. It is found that due to the valley-opposite gauge field induced by the strain, the strained silicene with a superlattice structure exhibits an angle-resolved valley and spin filtering effect when the spin–orbit interaction is considered. When the interaction that breaks the time reversal symmetry is introduced, such as the spin or valley dependent staggered magnetization, the system is shown to be a perfect spin and valley half metal in which only one spin and valley species is allowed to transport. Our findings are helpful to design both spintronic and valleytronic devices based on silicene.

Spin transport properties for B-doped zigzag silicene nanoribbons with different edge hydrogenations

Exploring silicon-based spin modulating junction is one of the most promising areas of spintronics.Using nonequilibrium Green's function combined with density functional theory,a set of spin filters of hydrogenated zigzag silicene nanoribbons is designed by substituting a silicon atom with a boron one and the spin-correlated transport properties are studied.The results show that the spin polarization can be realized by structural symmetry breaking induced by boron doping.Remarkably,by tuning the edge hydrogenation,it is found that the spin filter efficiency can be varied from 30%to 58%.Moreover,it is also found and explained that the asymmetric hydrogenation can give rise to an obvious negative differential resistance which usually appears at weakly coupled junction.These findings indicate that the boron-doped ZSiNR is a promising material for spintronic applications.

Electrically-manipulable electron-momentum filter based on antiparallel asymmetric doubleδ-magnetic-barrier semiconductor microstructure

We theoretically investigate the wave-vector filtering(WVF)effect for electrons in an antiparallel asymmetric doubleδ-magnetic-barrier microstructure under a bias,which can be fabricated experimentally by patterning two asymmetric ferromagnetic(FM)stripes on the top and the bottom of GaAs/AlxGa1−xAs heterostructure,respectively.It is found that an appreciable WVF effect appears because of an essentially two-dimensional(2D)process for electrons across this microstructure.WVF effect is found to be sensitive to the applied bias.WVF efficiency can be tuned by changing bias,which may lead to an electrically-controllable momentum filter for nanoelectronics device applications.

Improved preprocessed Yaroslavsky filter based on shearlet features

An improved preprocessed Yaroslavsky filter（IPYF）is proposed to avoid the nick effects and obtain a better denoising result when the noise variance is unknown.Different from its predecessors,the similarity between two pixels is calculated by shearlet features.The feature vector consists of initial denoised results by the non-subsampled shearlet transform hard thresholding（NSST-HT）and NSST coefficients,which can help allocate the averaging weights more reasonably.With the correct estimated noise variance,the NSST-HT can provide good denoised results as the initial estimation and high-frequency coefficients contribute large weights to preserve textures.In case of the incorrect estimated noise variance,the low-frequency coefficients will mitigate the nick effect in cartoon regions greatly,making the IPYF more robust than the original PYF.Detailed experimental results show that the IPYF is a very competitive method based on a comprehensive consideration involving peak signal to noise ratio（PSNR）,computing time,visual quality and method noise.

Ratiometric fluorescence immunoassay of SARS-CoV-2 nucleocapsid protein via Si-FITC nanoprobe-based inner filter effect

The global pandemic caused by severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)virus has necessitated rapid,easy-to-use,and accurate diagnostic methods to monitor the virus infection.Herein,a ratiometric fluorescence enzyme-linked immunosorbent assay(ELISA)was developed using Si-fluorescein isothiocyanate nanoparticles(FITC NPs)for detecting SARSCoV-2 nucleocapsid(N)protein.Si-FITC NPs were prepared by a one-pot hydrothermal method using 3-aminopropyl triethoxysilane(APTES)-FITC as the Si source.This method did not need post-modification and avoided the reduction in quantum yield and stability.The p-nitrophenyl(pNP)produced by the alkaline phosphatase(ALP)-mediated hydrolysis of pnitrophenyl phosphate(pNPP)could quench Si fluorescence in Si-FITC NPs via the inner filter effect.In ELISA,an immunocomplex was formed by the recognition of capture antibody/N protein/reporter antibody.ALP-linked secondary antibody bound to the reporter antibody and induced pNPP hydrolysis to specifically quench Si fluorescence in Si-FITC NPs.The change in fluorescence intensity ratio could be used for detecting N protein,with a wide linearity range(0.01-10.0 and 50-300 ng/mL)and low detection limit(0.002 ng/mL).The concentration of spiked SARS-CoV-2 N protein could be determined accurately in human serum.Moreover,this proposed method can accurately distinguish coronavirus disease 2019(COVID-19)and non-COVID-19 patient samples.Therefore,this simple,sensitive,and accurate method can be applied for the early diagnosis of SARS-CoV-2 virus infection.

Achieving high thermoelectric performance through carrier concentration optimization and energy filtering in Cu_(3)SbSe_(4)-based materials

The previous works commonly adjust the carrier concentration through acceptor doping,but at the same time,the decrease of the Seebeck coefficient limits the further improvement of electrical properties in Cu_(3)SbSe_(4)-based materials.In this work,a microwave-assisted hydrothermal synthesis method was used to synthesize Cu_(3)SbSe_(4)/TiO_(2) hollow microspheres.Part of TiO_(2) participates in the reaction,replaces the Sb site of Cu_(3)SbSe_(4) to form holes,and the rest is dispersed in the matrix in the form of the second phase.The first-principles calculations reveal that the doping of Ti significantly changes the band structure and phonon spectrum,thereby regulating carrier concentration while increasing phonon scattering.In addition,experimental results show that the energy filtering effect generated by the extra-mixed TiO_(2) nano particles,which suppresses the decrease of Seebeck coefficient by acceptor doping.Consequently,the highest average power factor 897.5 mW m^(-1) K^(-2) and the zT peak value of 0.70 can be obtained in Cu_(3)SbSe_(4)/6%TiO_(2) sample at 298e623 K.This work provides a new sight to improve the thermoelectric properties in Cu_(3)SbSe_(4) through carrier concentration regulation and nano-phase composition.

9.4 nm Tunable Vertically Coupled Microring Resonator Filter by Thermo-Optic Effect

A wide range (9.4nm) tuning of vertically coupled microring resonator filter was demonstrated utilizing a large TO coefficient of polymer. The power consumption was about 60m W and no degradation of filter response was observed.

Development of an active-site titrant for SARS-CoV-2 main protease as an indispensable tool for evaluating enzyme kinetics

A titrant for the SARS-CoV-2 main protease(M^(pro))was developed that enables,for the first time,the exact determination of the concentration of the enzymatically active M^(pro) by active-site titration.The covalent binding mode of the tetrapeptidic titrant was elucidated by the determination of the crystal structure of the enzyme–titrant complex.Four fluorogenic substrates of M^(pro),including a prototypical,internally quenched Dabcyl-EDANS peptide,were compared in terms of solubility under typical assay conditions.By exploiting the new titrant,key kinetic parameters for the M^(pro)-catalyzed cleavage of these substrates were determined.

纳米结构和能带工程提高Bi-Sb-Te合金的热电性能

碲化铋由于其优异的性能,已成为商业上广泛使用的热电材料.然而,通过熔化方法获得的p型Bi-Sb-Te热电材料的性能仍有进一步改进的空间.在这项工作中,CsBr化合物被用来提高Bi_(0.42)Sb_(1.58)Te_(3)(BST)材料的热电性能.采用熔化法和放电等离子体烧结相结合的方法制备了BST+x wt%CsBr(x=0,0.10,0.20,0.30)的块状材料.Cs和Br共掺杂可以显著提高BST合金的电导率,同时降低其热导率,使其在323 K下的最大ZT值为1.2.对于x=0.20的样品,在400 K以下具有1.1的平均ZT.密度泛函理论和透射电子显微镜分析表明,Cs掺杂有效地减小了带隙,增加了费米能级附近的态密度,并使能带变平缓,从而使电输运特性得到了明显增强(最大功率因子接近3500μW mK^(-2)).此外,Cs掺杂可以使得Sb从晶格中脱离出来并与晶格中的游离氧结合形成纳米级Sb_(2)O_(3),使其能够有效地散射中频声子并降低热导率,同时保持相对较高的塞贝克系数.这项研究提出了一种新的方法,可以仅单独通过CsBr掺杂来解决热电材料中电导率和热导率之间的矛盾.

IFE based nanosensor composed of UCNPs and Fe(Ⅱ)-phenanthroline for detection of hypochlorous acid and periodic acid

Oxidizing CIO^(-)and IO_(4)^(-)exist widely in environment and are closely related to the health of organisms.Accordingly,fast,sensitive,and direct detection of the two species is significant.Using IFE in UCNPs@PAA and Fe(Ⅱ)-phenanthroline system,an elegant ratiometric fluorescent nanosensor,without noble metal nanoparticle,was designed for the detection of CIO-and IO4-.Fe(Ⅱ)-phenanthroline complex is used as fluorescent absorber,which can quench green light of UCNPs with gradually varied extent depending on the concentration of Fe(Ⅱ).The linear zone extends to 800 and 120μmol/L while the detection limit is 1.30 and 0.58μmol/L for NaCIO and NaIO_(4),respectively.Finally,the nanosensor was successfully applied to detect NaCIO and NaIO4spiked in milk,spring water,and tap water with good recoveries.

Site-specific fabrication of gold nanocluster-based fluorescence photoswitch enabled by the dual roles of albumin proteins

Fluorescence photoswitch is becoming increasingly desirable for many applications,but its controllable fabrication still remains challenging yet.In this paper,a new strategy is proposed to fabricate fluorescence photoswitch by harnessing dual roles of albumin proteins as both photochrome carriers and biotemplates of fluorophore.As an example,we demonstrated the successful fabrication of a fluorescence photoswitch by incorporating both the photochromic diarylethene dye(CMTE)and red-emitting fluorescent gold nanoclusters(AuNCs)into the specific domains of bovine serum albumin(BSA)in a highly controllable manner.Detailed spectral and photophysical characterisation showed that CMTE well-retains the photochromic properties within the CMTE–BSA–AuNC construct,although its photoconversion rate is slightly retarded.Different from previously reported photoswitches,the fluorescence of the present system is mainly modulated via the inner filter effect(IFE)mechanism,which exhibits high switching efficiency with an on-off ratio up to 90%,reversible fluorescence response and good antifatigue performance.This work provides a new,generable albumin protein-assisted strategy of fabricating advanced fluorescence photoswitch,which can find wide applications in biological,optical and information fields.

Low lattice thermal conductivity and enhanced thermoelectric performance of SnTe via chemical electroless plating of Ag

Interface engineering has been regarded as an effective strategy to manipulate the thermoelectric performance of materials.Here,we use a facile chemical electroless plating and a spark plasma sintering process to fabricate Ag-plated SnTe bulk.After sintering,a small amount of plated Ag can be doped into SnTe to suppress the Sn vacancies and the others form Ag precipitates with a size distribution from nanoscale to microscale,which introduces Ag/SnTe interfaces to enhance the Seebeck coefficient via energy filtering effect.Simultaneously,these structures result in strong scattering to reach a low lattice thermal conductivity of-0.62 W·m^(–1)·K^(–1).Consequently,a maximum figure of merit(zT)of-0.67 at 823 K is achieved in 2 wt%Ag-plated SnTe,which is-60%higher than that of pristine SnTe.Moreover,the microhardness indentation test results show that the mean microhardness of 2 wt%Ag-plated SnTe is HV 64.26,which is much higher than that of pristine SnTe,indicating that Ag electroless plating can improve the mechanical properties of SnTe.This work has provided a facile and eco-friendly method to realize the interface engineering for manipulating the thermoelectric and mechanical properties of SnTe.

Investigations into sensing characteristics of circular thin-plate electrostatic sensors for gas path monitoring

Circular thin-plate electrostatic sensors are promising in gas path monitoring due to their advantages of non-intrusiveness and easy installation. The spatial sensitivity and filtering effect are two important performance parameters. In this paper, an analytically mathematical model of induced charge on a circular thin-plate electrode is first derived. Then the spatial sensitivity and filtering effect of the circular electrostatic sensor are investigated by numerical calculations. Finally,experimental studies are performed to testify the theoretical results. Both theoretical and experimental results demonstrate that circular thin-plate electrostatic sensors act as a low-pass filter in the spatial frequency domain, and both the spatial filtering effect and the temporal frequency response characteristics depend strongly on the spatial position and velocity of the charged particle. These conclusions can provide guidelines for the optimal design of circular thin-plate electrostatic sensors.

N,P Co-Doped Carbon Dots as Multifunctional Fluorescence Nano-Sensor for Sensitive and Selective Detection of Cr(Ⅵ) and Ascorbic Acid

It is particularly important to monitor Cr(Ⅵ)for its high toxicity.In this paper,a novel,simple,low-cost and"on-off-on"fluorescence sensor of carbon dots doped with nitrogen and phosphorus(N,P-CDs)was developed via one-step hydrothermal method for highly sensitive and good selective detection of Cr(Ⅵ)and ascorbic acid(AA).The prepared N,P-CDs exhibited the ability for detection of Cr(Ⅵ)based on the inner filter effect(IFE)and static quenching.Under optimized conditions,the fluorescence quenching efficiency of N,P-CDs showed a good linear correlation with Cr(Ⅵ)concentration ranged from0.68 to 87.38μmol/L(R^(2)=0.9946).The limit of detection(LOD)was 0.18μmol/L,which was acceptable compared with the maximum Cr(Ⅵ)concentration of 0.96μmol/L in drinking water prescribed by WHO.In addition,the N,P-CDs/Cr(Ⅵ)hybrid were also used as"turn-on"fluorescent transducers for detecting AA with a wide linear region ranged from 0.02 to933.33μmol/L(R^(2)=0.9972).Furthermore,the N,P-CDs fluorescence sensor had admissible applicability for Cr(Ⅵ)and AA detection in actual water samples with acceptable recovery rate,indicating that the fluorescence sensor had great application potential in environmental monitoring and food field.

A new fluorescence probing strategy for the detection of parathion-methyl based on N-doped carbon dots and methyl parathion hydrolase

A new facile fluorescence probing strategy, which was based on N-doped carbon dots（NCDs） and methyl parathion hydrolase（MPH）, was developed for the determination of parathion-methyl（PM）. The fluorescence intensity of NCDs-MPH system was proportional to PM concentration in the range of 2.38–73.78 mmol/L, with a detection limit of 0.338 mmol/L. Moreover, the present simple and facile method could be used to determine methyl parathion in environmental and agricultural samples successfully.Furthermore, the detection mechanism of this system is inner filter effect and molecular interactions between NCDs and p-nitrophenol, which is the hydrolysis product of PM catalyzed by methyl parathion hydrolase.