Phase structure evolution and its effect on magnetic and mechanical properties of B-doped Sm_(2)Co_(17)-type magnets with high Fe content

The unique cellular microstructure of Fe-rich Sm_(2)Co_(17)-type permanent magnets is closely associated with the structure of the solid solution precursor.We investigate the phase structure,magnetic properties,and mechanical behavior of B-doped Sm_(2)Co_(17)-type magnets with high Fe content.The doped B atoms can diffuse into the interstitial vacancy,resulting in lattice expansion and promote the homogenization of the phase organizational structure during the solid solution treatment in theory.However,the resulting second phase plays a dominant role to result in more microtwin structures and highly ordered 2:17R phases in the solid solution stage,which inhibits the ordering transformation of 1:7H phase during aging and affects the generation of the cellular structure,and to result in a decrease in magnetic properties,yet the interface formed between it and the matrix phase hinders the movement of dislocations and enhances the mechanical properties.Hence,the precipitation of high flexural strain grain boundary phase induced by B element doping is also a new and effective way to improve the flexural strain of Sm_(2)Co_(17)-type magnets.Our study provides a new understanding of the phase structure evolution and its effect on the magnetic and mechanical properties of Sm_(2)Co_(17)-type magnets with high Fe content.

Atomic scale structural characterization of {10 12} twin boundaries in zinc

The structure and the migration mechanisms of {10 12} twin boundaries（TBs） of pure zinc deformed by rolling were studied using high-resolution transmission electron microscopy（HRTEM） at atomic scale. We found the presence of basal/prismatic（BP/PB） planes serrations on {10 12} TBs and the coexistence of two kinds of TBs with different structures in the same {10 12} twin： TBs composed of {10 12} coherent twin boundaries（CTBs） plus short BP/PB serrations, and TBs composed of successive BP/PB segments without {10 12} CTBs. The formation of BP/PB serrations has no relation to the c/a ratio of hexagonal-closepacked（HCP） metals because the BP/PB serrations are energetically preferred and geometrically favored. Based on dislocation theory, we proposed the migration mechanisms of the TBs to be the glide of twinning dislocations（TDs） on the CTBs and the climb of interface dislocations（IDs） on the BP/PB segments.

Magnetic properties and resistivity of a 2:17-type SmCo magnet doped with ZrO_(2)

In order to counteract the demagnetization caused by eddy current loss,widespread attention has been devoted to increasing the resistivity of permanent magnets.We prepared 2:17-type Sm Co magnets doped with different ZrO_(2)contents and investigated the influence of the ZrO_(2)content on the magnetic properties and resistive anisotropism.The results showed that not only was the resistivity of the magnet improved,but,in addition,the coercivity of the magnet was significantly increased.The microstructure was studied with TEM,which showed that ZrO_(2)doping was able to cause a decrease in the lamellar phase density and the growth of cellular structures.The increased grain boundaries and Sm_(2)O_(3)phases were favorable to the improvement of resistivity.The decrease of the lamellar phases caused a narrowing of the resistive anisotropism.The additional Cu in the center of the cellular boundaries was the main reason for the enhancement of Hcj.However,an excessive amount caused an increase of the Zr_6(Fe Co)_(23)phase and a deterioration of the cellular structure,thereby leading to a decrease in coercivity.

Significant effect of ordered micro-domain on cell boundary phase distribution and demagnetization curve squareness of Sm_(2)Co_(17)-type magnet

Cu-rich cell boundary phase is difficult to precipitate evenly,resulting in a generally poor demagnetization curve squareness for Fe-rich Sm_(2)Co_(17)-type magnet,which is a key factor limiting the further improvement of magnetic energy product.In this study,we report that nanoscale strip-like ordered micro-domains distributed in1:7H disordered matrix phase of the solid solution precursor is a new factor significantly affecting the precipitation and distribution of the cell boundary phase.Long strip-like and continuous micro-twin structure with twin boundaries neatly perpendicular to the C-axis is observed after sintering treatment.After solution treatment,sequential and long strip-like micro-twins gradually transform into disordered state along the basal plane,forming narrow disordered 1:7H(TbCu_(7)-type structure)phase between the separated strip-like ordered micro-domains.This disordering transformation takes place via broken down of the long strip-like ordered micro-domains,which is accomplished by narrowing along the width direction followed by reduction of the length.Furthermore,a new model revealing the effect of the ordered micro-domains on the formation of the cell boundary phase is proposed.Antiphase boundaries enriched in Cu have already existed in the precursor with long strip-like ordered micro-domains.Therefore,the Cu-rich cell boundary phase acting as strong pinning centers cannot be precipitated homogeneously and distributed continuously after aging,resulting in a poor demagnetization curve squareness of Sm_(2)Co_(17)-type magnet.Our results indicate that significant broken down of the nanoscale ordered micro-domains in solution precursor is the key factor improving the distribution of cell boundary phase in Sm_(2)Co_(17)-type magnets.

Application of Biological Nanopore Sequencing Technology in the Detection of Microorganisms

Environmental pollution and the spread of pathogenic microorganisms pose a significant threat to the health of humans and the planet.Thus,understanding and detecting microorganisms is crucial for maintaining a healthy living environment.Nanopore sequencing is a single-molecule detection method developed in the 1990s that has revolutionized various research fields.It offers several advantages over traditional sequencing methods,including low cost,label-free,time-saving detection speed,long sequencing reading,real-time monitoring,convenient carrying,and other significant advantages.In this review,we summarize the technical principles and characteristics of nanopore sequencing and discuss its applications in amplicon sequencing,metagenome sequencing,and whole-genome sequencing of environmental microorganisms,as well as its in situ application under some special circumstances.We also analyze the advantages and challenges of nanopore sequencing in microbiology research.Overall,nanopore sequencing has the potential to greatly enhance the detection and understanding of microorganisms in environmental research,but further developments are needed to overcome the current challenges.

Selective detection of mercury(II) and methylmercury(II) via coordinationinduced emission of a small-molecule probe

Mercury is one of the major toxic pollutants and has many adverse effects on human health. The main mercury species in the environment or in living organisms are inorganic mercuric ion （Hg2＋） and organic methylmercury （CH3Hg＋）. Detection of the two mercury ions is a particularly active topic in the molecular sensing field during the past decade. However, efficient sensors that can sensitively detect and discriminate the two species are rare. In this work, we adopt the concept of restriction of intramolecular rotations which is the basis of aggregation induced emission, and design a molecular probe with pyridyl group as the chelating unit and 1,8-naphthalimide as the fluorescent unit for the detection of both Hg2＋ and CH3Hg＋. When the probe is free in solution, it exhibits weak fluorescence because free intramolecular rotations of the 1,8-naphthalimide moieties non-radiatively annihilate its excited state. However, upon coordination with Hg2＋ or CH3Hg＋, the rotation of 1,8-naphthalimide moieties would be restricted due to the chelation between 1,8-naphthalimide and Hg2＋ or CH3Hg＋, leading to significantly enhanced fluorescent emission. The response induced by Hg2＋ is much stronger than CH3Hg＋; but for specific detection of CH3Hg＋, we introduced a T-rich DNA fragment which could completely mask Hg2＋ in solution. Furthermore, we have employed the sensor for confocal imaging of rig2＋ and CH3Hg＋in immobilized cells. We expect the probe design tactics can be generally useful for sensing many other analytes.

Characterization of thermal-induced distorted face-centered cubic structure in pure titanium

After 900 ℃ high-vacuum annealing and air cooling, a special band was observed in pure titanium. Energy-dispersive spectrum showed that the composition of the band and the matrix is the same. By tilting the band to different zone axes and taking selected-area electron diffraction (SAED) patterns, we found that the structure of the band is distorted face-centered cubic (fcc) with the lattice constants a, b, and c deviating slightly from each other on the basis of the analyses of the SAED patterns together with the tilting angles. The lattice constants a, b, and c are calculated based on the measurement of interplanar spacing according to high-resolution transmission electron microscopy (HRTEM) images. The orientation relation between the hexagonal-close-packed (hcp) matrix and the distorted fcc band is [11(2)0]hcp//[110]fcc and (0001)hcp//(1(1)1)fcc according to SAED analysis. The phase boundary between the matrix and the band was observed to demonstrate serrated configuration composed of two kinds of micro-steps: ((1)11)//(0002) and ((1)11)//(10(1)1) on the basis of Cs-corrected HRTEM characterization. The distorted fcc band is deduced to be a thermal-induced metastable phase transformed from the high-temperature body-centered cubic (bcc) structure during the allotropic transformation from bcc to hcp based on orientation relation analysis.

The effect of secondary structures on the generation of characteristic events during the translocation of DNA hybrid through ?-hemolysin

Nanopore has been developed to be a powerful,single-molecule analytical tool for sensing ions,small organic molecules and biomacromolecules such as proteins and DNAs.Generally,the identity of the analyte can be revealed by current amplitude changes and mean dwell time of the analyte binding events.In some cases,generation of highly characteristic current events affords an alternative way of analyte determination with high confidence level.However,we found that secondary structures in DNA/RNA hybrids might severely hinder the generation of signature events during their translocation through?-hemolysin nanopore.In this report,we propose a strategy to add a certain concentration of urea in the buffer solution for single channel recordings and validate that low concentration of urea can effectively denature the secondary structures in DNA hybrids and recover the generation of signature events.This finding might be useful in other secondary structure-related nanopore sensing activities.