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Magnetic skyrmions and hopfions are topological solitons1, well-localized field configurations that have gained significant attention over the past decade due to their unique particle-like properties, making them promising objects for spintronic applications. Skyrmions2,3 are two-dimensional solitons resembling vortex-like string structures that can penetrate an entire sample. Hopfions4-9 are three-dimensional solitons confined within a magnetic sample volume and can be considered as closed twisted skyrmion strings that take the shape of a ring in the simplest case. Despite extensive research on magnetic skyrmions, the direct observation of magnetic hopfions has remained challenging. Here, we present the first direct observations of coupled states of hopfions and skyrmion strings in FeGe plates using transmission electron microscopy. Furthermore, we provide a protocol for nucleating hopfion rings around skyrmion strings in confined samples, which we verify using Lorentz imaging and electron holography. Our results are highly reproducible, in full agreement with micromagnetic simulations, and offer new insight into the diversity of topological solitons in three-dimensional chiral magnets and their potential for practical applications.

Using a combination of insitu bulk and surface characterization techniques, we provide atomic-scale insight into the complex surface and bulk dynamics of a LaNiO3 perovskite material during heating in vacuo. Driven by the outstanding activity LaNiO3 in the methane dry reforming reaction (DRM), attributable to the decomposition of LaNiO3 during DRM operation into a Ni//La2O3 composite, we reveal the Ni exsolution dynamics both on a local and global scale by insitu electron microscopy, insitu X-ray diffraction and insitu X-ray photoelectron spectroscopy. To reduce the complexity and disentangle thermal from self-activation and reaction-induced effects, we embarked on a heating experiment in vacuo under comparable experimental conditions in all methods. Associated with the Ni exsolution, the remaining perovskite grains suffer a drastic shrinkage of the grain volume and compression of the structure. Ni particles mainly evolve at grain boundaries and stacking faults. Sophisticated structure analysis of the elemental composition by electron-energy loss mapping allows us to disentangle the distribution of the different structures resulting from LaNiO3 decomposition on a local scale. Important for explaining the DRM activity, our results indicate that most of the Ni moieties are oxidized and that the formation of NiO occurs preferentially at grain edges, resulting from the reaction of the exsolved Ni particles with oxygen released from the perovskite lattice during decomposition via a spillover process from the perovskite to the Ni particles. Correlating electron microscopy and X-ray diffraction data allows us to establish a sequential two-step process in the decomposition of LaNiO3 via a Ruddlesden–Popper La2NiO4 intermediate structure. Exemplified for the archetypical LaNiO3 perovskite material, our results underscore the importance of focusing on both surface and bulk characterization for a thorough understanding of the catalyst dynamics and set the stage for a generalized concept in the understanding of state-of-the art catalyst materials on an atomic level.

Single crystal Ni-based superalloys are the typical structural materials for high-pressure turbine blades, and their microstructure is critical in determining their mechanical properties. The withdrawal rate is a key parameter affecting the microstructure during the single crystal growth process. In the present work the effect of the withdrawal rate on the microstructure of a third-generation single crystal superalloy containing 6.8 ​wt% Re has been investigated, and the creep resistance of the alloy determined. The results showed that increased withdrawal rate refined the dendritic structure, reduced dendritic arm spacing, promoted the growth of secondary tertiary dendrites and decreased solidification segregation with a reduced size of γ′ phase. The porosity density of the as-cast alloy first decreased and then increased with the withdrawal rate, while the minimum porosity densityoccurred when the alloy was under the solidification condition of withdrawal rate of 4.5 ​mm/min. The maximum creep rupture life of 326.4 ​h of the heat-treated alloys under the test condition of 1100 ​°C/140 ​MPa also appeared at the alloys under the withdrawal rates of 4.5 ​mm/min. It is believed that the minimum porosity density and reduced size of the γ′ phase may be the main reasons for the enhanced creep rupture life of the alloys with withdrawal rates of 4.5 ​mm/min. This investigation provides theoretical support and a practical basis for the development of third-generation single crystal superalloys.

Twin crystal structured Al-10 wt.% Mg alloys that were grown over a broad solidification velocity range were prepared and studied for the first time. The high thermal gradient (G) and growth velocity (V) of directional solidification resulted in the dominant solidification of twins: the twinned dendrite trunks at constant high Vs curved in the G direction with large angles in 7 mm diameter crucibles and invaded regular columnar grains because of a distinct kinetics growth advantage. Transitive deceleration experiments were designed to produce twin crystals that evolved with lower values of V (100, 10, and 0.5 μm/s) and had a structural coarsening trend. Twin cell growth in the absence of arms occurred at a growth velocity of 10 μm/s. A coherency loss was observed at a growth velocity of 0.5 μm/s with straight coherent twin boundaries turning into curved incoherent boundaries. Linear theoretical analyses were performed to understand the structural evolution of the twins. These results demonstrate the possibility of producing dense and controlled twin crystals in the Al-Mg system under most industrial production conditions; thus, this approach can be a new structural choice for designing Al-Mg-based alloys that have widespread commercial applications.

Chinese older immigrants who live in senior housing communities are at high risks of experiencing discrimination and social isolation during the COVID-19 pandemic. This study examines how and to what extent the pandemic has affected this population’s social network and mental health. Participants reported a decrease in social contact with their family and friends. Before the pandemic, many paid regular visits back to the home country and could not do so in the past two years. The loss of connection left some feeling despaired and expressed uncertainty on whether they could ever go back “home” before death. Participants also reported being in a low mood and feeling bored constantly. Participants reported resilience generated from their religious beliefs, having neighbors as role models, and wisdom learned from past life experiences. Knowledge produced in this project can inform the planning for responding to future crises in affordable senior housing.

Mesoporphyrin IX (MPIX) contains a planar macrocycle center that can interact with various divalent metal ions through the exposed binding sites, leading to the metalation of MPIX. The DNA aptamers for porphyrin molecules usually display different catalytic functions (termed deoxyribozymes or DNAzymes), which can accelerate such chemical reactions. Inspired by this, an affinity chromatography selection approach was designed for identifying a porphyrin metalation DNAzyme. In our experiment, N-methyl mesoporphyrin IX (NMM), an analog of MPIX, is used as the target molecule, owing to its stable and high fluorescence enhancement after combining with specific oligonucleotides. Our results showed that the selected aptamer Nm1 is capable of binding to NMM with a low micromolar dissociation constant (0.75 ± 0.08 μM) and displays a catalytic activity for MPIX metalation with 3.3-fold rate enhancement. The protocol for isolation of such a porphyrin metalation DNAzyme is described in detail here.

A fundamental property of particles and antiparticles (such as electrons and positrons, respectively) is their ability to annihilate one another. A similar behaviour is predicted for magnetic solitons1—localized spin textures that can be distinguished by their topological index Q. Theoretically, magnetic topological solitons with opposite values of Q, such as skyrmions2 and their antiparticles (namely, antiskyrmions), are expected to be able to continuously merge and annihilate3. However, experimental verification of such particle–antiparticle pair production and annihilation processes has been lacking. Here we report the creation and annihilation of skyrmion–antiskyrmion pairs in an exceptionally thin film of the cubic chiral magnet of B20-type FeGe observed using transmission electron microscopy. Our observations are highly reproducible and are fully consistent with micromagnetic simulations. Our findings provide a new platform for the fundamental studies of particles and antiparticles based on magnetic solids and open new perspectives for practical applications of thin films of isotropic chiral magnets.

It is generally acknowledged that G-quadruplexes (G4s) acquire peroxidase activity upon interaction with hemin. Hemin has been demonstrated to bind selectively to the 3′-terminal G-tetrad of parallel G4s via end-stacking; however, the relationships between different terminal G-tetrads and the catalytic functions of G4/hemin DNAzymes are not fully understood. Herein, the oligonucleotide d(AGGGGA) and its three analogues, d(AGBrGBrGGA), d(AGBrGGGBrA) and d(AGBrGGBrGA) (GBr indicates 8-bromo-2′-deoxyguanosine), were designed. These oligonucleotides form three parallel G4s and one antiparallel G4 without loop regions. The scaffolds had terminal G-tetrads that were either anti-deoxyguanosines (anti-dGs) or syn-deoxyguanosines (syn-dGs) at different proportions. The results showed that the parallel G4 DNAzymes exhibited 2 to 5-fold higher peroxidase activities than the antiparallel G4 DNAzyme, which is due to the absence of the 3′-terminal G-tetrad in the antiparallel G4. Furthermore, the 3′-terminal G-tetrad consisting of four anti-dGs in parallel G4s was more energetically favorable and thus more preferable for hemin stacking compared with that consisting of four syn-dGs. We further investigated the influence of 3′ and 5′ deoxyadenosine (dA) caps on the enzymatic performance by adding 3′-3′ or 5′-5′ phosphodiester bonds to AG4A. Our data demonstrated that 3′ dA caps are versatile residues in promoting the interaction of G4s with hemin. Thus, by increasing the number of 3′ dA caps, the DNAzyme of 3′A5′-5′GG3′-3′GG5′-5′A3′ with two 5′-terminal G-tetrads can exhibit significantly high catalytic activity, which is comparable to that of 5′A3′-3′GG5′-5′GG3′-3′A5′ with two 3′-terminal G-tetrads. This study may provide insights into the catalytic mechanism of G4-based DNAzymes and strategies for promoting their catalytic activities., Investigation of the peroxidase activities of G4/hemin DNAzymes using designed terminal G-tetrads by eliminating the steric effect of loop regions.

A fundamental property of particles and antiparticles, such as electrons and positrons, is their ability to annihilate one another. Similar behavior is predicted for magnetic solitons~\cite{Kovalev_90}-- localized spin textures that can be distinguished by their topological index Q.Theoretically, magnetic topological solitons with opposite values of Q, such as skyrmions~\cite{Bogdanov_89} and their antiparticles -- antiskyrmions -- are expected to be able to merge continuously and to annihilate~\cite{Kuchkin_20i}. However, experimental verification of such particle-antiparticle pair production and annihilation processes has been lacking. Here, we report the creation and annihilation of skyrmion-antiskyrmion pairs in an exceptionally thin film of the cubic chiral magnet B20-type FeGe observed using transmission electron microscopy. Our observations are highly reproducible and are fully consistent with micromagnetic simulations. Our findings provide a new platform for fundamental studies of particles and antiparticles based on magnetic solids and open new perspectives for practical applications of thin films of isotropic chiral magnets.

A quadruplex-integrated assembly method is proposed for the organization and regulation of various nanoscale architectures. In this method, two types of one-dimensional DNA nanostructures formed by two well-designed GC-rich single strands assemble into two-dimensional (2D) DNA nanostructures based on the self-assembly of dimeric G-quadruplex and I-motif structures. Subsequently, a C-rich strand and two biotin-modified G-rich strands primordially form a notched double helix in LiCl solution (pH 8). However, a linear "DNA-protein" nanostructure linked by I-motif structures and biotin-streptavidin interaction can be formed when hydrogen ions and streptavidin are sequentially titrated. Furthermore, the linear "DNA-protein" nanostructure is assembled into 2D nanomaterials connected by K+-stabilized G-quadruplexes formed from terminal G-rich repeats of the two G-rich strands. Interestingly, the 2D nanohybrids form two-lined "DNA-protein" nanostructures if the terminal G-rich repeats in one of the biotin-modified G-rich strands are removed. Our results indicate that quadruplex DNAs are promising building blocks in the fabrication of nanomaterials and that the assembly of quadruplex DNAs has potential applications in the directional arrangement of macromolecules.

In order to develop a simple, convenient and economic method to detect and quantify the level of sarcosine in human urine samples, we have selected DNA aptamers for sarcosine through a modified affinity chromatography SELEX (Systematic Evolution of Ligands by Exponential Enrichment), which is based on the aptamer sequences bound by the target molecules would be released from the DNA hybridizations coupled on streptavidin-agarose beads. 4 aptamer candidates were obtained after 12 rounds of selection, and their affinities were preliminarily checked by SYBR green I staining. The best of them is Sar11, which with the dissociation constant (Kd) of 134.8 nM was further modified and used to design a fluorescence sensor to quantify sarcosine. The detection limit of sarcosine by this sensor is 55 nM, while its quantitative range is 100 to 2000 nM. Also, the aptamer Sar11 shows good selectivity for sarcosine to its analogues. Moreover, the fluorescent aptasensor obtains a satisfying result for the detection of sarcosine in human urine samples.

Several studies suggest strong correlation between different types of cancer and the relative concentration of short circulating RNA sequences (miRNA). Because of short length and low concentration, miRNA detection is not easy. Standard methods such as RT-PCR require both the standard PCR amplification step and a preliminary additional step of reverse transcription. In this paper, we investigate the use of DNA nanopores as a tool to detect short oligonucleotide sequences at the single molecule level. These nanostructures show two different conformations depending on the presence of DNA analogues of miRNA sequences. By monitoring current across a lipid bilayer, we show that this change of conformation translates to different levels of conductivity.

Nucleic acid aptamers are single-stranded oligonucleotides that may be evolved for affinity and specificity for their targets and can be easily produced, regenerated, and stabilized. In this study, we adapted Ni-NTA (nickle-charged nitrilotriacetic acid) affinity-chromatography in the development of single-stranded DNA aptamers against N-cadherin protein by systematic evolution of ligands by exponential enrichment (SELEX). After ten rounds of selection, two aptamers, designated NS13 and NC23, were selected, which showed low dissociation constants of 93 and 174 nM, respectively. The 5'-carboxyfluorescein-labeled NS13 was used for the sensitive detection of N-cadherin protein by the enzyme-linked oligonucleotide assay (ELONA) method.

The structure of defects and their elemental distributions is the decisive factor to metal&rsquo, s mechanical properties. The &gamma, /&gamma, &prime, structure Co-Al-W-based superalloy is a potential replicable alloy to Ni-based superalloys that have been used for a long time. Revealing the microstructure of a defect induced by high-temperature crept provides direct clues for the alloy development. Our work revealed the high-resolution, high-angle annular dark field images and corresponding elemental distributions on crept defects. Defects in the &gamma, phase mainly contain dislocation networks, while the &gamma, ' phase contains lots of stacking faults and anti-phase boundaries. The results indicate that dislocation networks and stacking faults contain more weight elements than the base &gamma, phase, while anti-phase boundaries contain more light elements. Disclosing atomic structure and its elemental distributions gives direct evidence for alloy design and further high-temperature mechanical improvement.

Novel Al2O3 nanoparticle-reinforced heterogeneous CrCoNi-matrix composites (CrCoNi–Al2O3P) with 10–30 wt% of coarse grain (CG) matrix were prepared by multi-step mechanical milling plus hot pressing sintering. The relationships between microstructure and mechanical properties of the composites were studied in detail. The results reveal that the heterogeneous structure in CrCoNi–Al2O3P composites is composed of CG region and ultrafine grain (UFG) region with uniform distribution of Al2O3 nanoparticles. With increasing content of CG matrix in the nanocomposite, the hardness first decreases but then increases, and the increase of hardness may be due to the formation of carbides. Compared with homogeneous CrCoNi–Al2O3P composite, the compressive fracture strain of heterogenous composite increases by 53.2% at most, while sacrificing a small amount of strength, among which the 20 wt% CG heterogeneous composite exhibits an excellent strength-ductility synergy. For the mechanisms of strengthening and toughening, hetero-deformation induced (HDI) hardening makes the heterogeneous composites almost as strong as the homogeneous composite. Meanwhile, the CrCoNi matrix with low stacking fault energy can be deformed by dislocation slipping and twinning at room temperature, which improves the plasticity of the composite. Furthermore, the heterogeneous structure with soft and hard domains increases the work hardening ability of the composite.

G-Quadruplexes (G4s) assembled from tandem G-rich repeat sequences exhibit significant biological functions and applications, which may well depend on their structural features, such as the planar arrangement of G-tetrads and flexibility of loop regions. It has been found that cytosine-intercalated G-repeat sequences also assemble to be quadruplex structures, involving the formation of nonplanar GCGC-tetrads. Herein, to investigate the effect of GCGC-tetrads on structural properties of G4s, some previously studied quadruplexes with or without GCGC-tetrads were selected, and were used to interact with various developed G4 ligands. Our data show that stacked G-tetrads in quadruplexes are important for the π-π stacking interactions, thus promoting the combination with end-stacking ligands, such as porphyrins or planar small molecules. This is confirmed by the observation that the quadruplex formed by d(GGGCT4 GGGC) with two internal G-tetrads and two external GCGC-tetrads can bind to planar ligands in the presence of specific G4-stabilizing cations, including K+ and Pb2+ , and can realize the sensitive detection of Pb2+ . However, the quadruplex composed of two external G-tetrads and two internal GCGC-tetrads formed by d(GCGGT3 GCGG) facilitates the binding of nonplanar ligands, such as triphenylmethane (TPM) dyes, owing to the structural flexibility induced by internal GCGC-tetrads. This work provides new insights into the interaction between DNA quadruplexes and specific ligands, which is beneficial to the development of quadruplex-based biosensors and the design of anticancer drugs.

Twinned dendrites and regular dendrites have been respectively produced in A356 alloy by Bridgman solidification. The primary trunks of twinned dendrites grew along direction and were split by a coherent (111) twin plane were characterized by electron backscattered diffraction (EBSD), which is different from the regular dendrites. The growth of twinned dendrites was found to have a rotation relationship around a common direction. With respect to the specimens with regular dendrites, the mean tensile strength, elongation and toughness of the specimens with twinned dendrites were increased from 230 MPa to 239 MPa, 16.69–18.99%, 34.45 J/m3 to 40.88 J/m3, respectively. Meanwhile, the coefficient of thermal expansion (CTE) of the specimen with twinned dendrites increase monotonically up to 2.28 × 10 − 5 K − 1 at temperature of 473 K. This CTE was successfully lowered than that of specimen with regular dendrites at the temperature above 323 K, and reaches the maximum decrease around 4.2% at 473 K. The fractures of two types of specimens were both originated from the Si-rich regions where dimples formed. In addition, detailed analyses on coherent twin boundary (CTB) of twinned dendrites by transmission electron microscope (TEM) and high-resolution TEM (HRTEM) indicate that the mechanisms of twin and dislocation-CTB interactions can enhance the strength and ductility of the A356 alloy with twinned dendrites.

Feathery crystals are an ensemble of twinned dendrites, and are characterized by a unique twin boundary (TB) structure in the solidification pattern of aluminum alloys. In this work, the high-density twinned dendrites of Al-4.5 wt% Cu alloys, produced during the Bridgman solidification, have been studied using electron backscattered diffraction (EBSD) and high-resolution transmission electron microscopy (HRTEM). The experimental results showed that, after systematically decreasing the growth rate from 3000 μm/s to 1 μm/s, the TBs remained stable, while the solute field around the TBs changed significantly. According to the HRTEM results, successive stacking faults were occurred near the TBs at 1 μm/s, while slight distortion was observed around the TBs at 3000 μm/s. The composition analysis revealed an obvious solute enrichment near the TBs. Furthermore, the solute gradient profile within the TBs became smoother with the decrease in the growth speed. This is due to the more sufficient solid-state back diffusion occurring perpendicular to the twin plane after the solidification.

By using the electron backscattered diffraction (EBSD) technique, pattern selection of twinned growth in Al-4.5 wt% Cu alloy has been studied in Bridgman solidification experiments. Based on the original twin planes formed at 3000 μm/s, the twinned growth was produced till the end of solidification after abruptly decreasing the growth rate to 100, 50, 20, 10, 5, 3, 1 and 0.3 μm/s. The stable twinned growth could be achieved during a wide range of solidification process. For the first time, the so-called twinned cell pattern was observed and prevailed in the solidified structure at 3 and less than 3 μm/s. The twinned growth in aluminum alloy was not limited to dendrite pattern as has previously been reported. The twinned pattern selection map was also revealed. Meanwhile, an interesting orientation rotation phenomenon was elucidated using EBSD technique on both sides of the coherent twin boundary during twinned cell growth. At a lower rate of 0.3 μm/s, the orientation rotation deflection concerning the original Σ3 60° twinning relation was confirmed. Some coincidence site lattice boundaries with higher Σ values served as the preferred states for this orientation deflection during growth.

Based on the twin planes formed at 3000 μm/s, the growth stability of twinned dendrites in Al-4.5 wt% Cu alloy was studied in detail at a low growth rate during Bridgman solidification. Experimental results show that the twinned dendrite growth could still keep stable even after decreasing the rate to 20 μm/s. This is far below the usual rate threshold for the formation of twinned dendrites (∼1000 μm/s). The dominated twinned structures at 20 μm/s have their (1 1 1) twin plane and 〈1 1 0〉 dendritic trunk closest to thermal gradient direction. Importantly, distinct stacking fault (SF) structures directly connecting two adjacent twin boundaries provide a direct experimental evidence for the close correlation between the SFs and the twinned dendrite growth in aluminum alloys.

Rhenium is the key element for improving the mechanical properties in γ/γ'-structured single-crystal Ni-based superalloys, but its oxidation-induced evaporation results in a detrimental decrease in corrosion resistance. The in situ Re evaporation process of a single lamella of a high Re-containing Ni-based superalloy is recorded with an environmental transmission electron microscope, and volatilization is observed. The local aggregation of Re in the inner border of the γ phase and subsequent evaporation forms channels for the accelerated oxidation of the base and other elements. The real oxidation process of Re evaporation provides detailed and essential information on corrosive gas resistance properties at the nanoscale.

Understanding the high-temperature initial oxidation mechanism and its dynamic processes is generally important because a small amount of initial oxidation can induce rapid corrosion and cause catastrophic failure. We reveal the mechanism of initial oxidation in a third-generation Ni-based superalloy by in situ visualizations and investigations of the nano- and atomic-scale dynamic processes from room temperature to 900 °C with a Cs-corrected environmental transmission electron microscope. The initial oxidation starts from the γ/γ′ interface at low temperatures. The high-temperature oxidation process with deficient oxygen prefers oxidation sites at the cross-junctions of the γ/γ′ interfaces. The growth rate of the oxide nanoparticles depends on the oxidation temperatures, with a low rate below 600 °C and a rapid-growth speed at temperatures higher than 700 °C. Mass transfer from the γ′ and γ phases to the γ/γ′ interface, particularly at the cross-junctions of these interfaces, is observed to cause oxide accumulation. This study provides a direct observation of the interphase, interface-junction-initiated outward oxidization including Al and Cr elements. These results shed light on the initial oxidation mechanisms of materials containing a second phase with interphase interfaces and the materials at deficient oxygen conditions as well as those with protection coating layers.

With the advent of the information age, the university library reader service work has gradually developed toward informatization, networking and facilitation. In a certain extent, the service level of libraries can be improved by the study of libraries’ development rules and trends in a scientific way. The study mainly analyzes the current situation of the development of university libraries in China. The University Library in the new era is bound to be a complex library of traditional libraries, digital libraries and mobile libraries. It will be the development direction of university library in the future to pay equal attention to high-tech hardware equipment and high quality extension service without losing its own characteristics.

In this study, a new strategy for the selection of aptamers against small-molecule target was established using gold nanoparticles (AuNPs) as the separation matrix and Zinc(II)-Protoporphyrin IX (ZnPPIX) as the target molecule without the immobilization step due to the absorption of ssDNA on AuNPs. The progress of the selection process was monitored by the recovery rate and the fluorescence enhancement of N-methyl mesoporphyrin IX (NMM) after reacting with each selected pool. After 11 rounds of selection, a truncated aptamer ZnP1.2 with a low-micromolar dissociation constant was obtained, and it also showed good fluorescence enhancement for NMM and the enhanced peroxidase activity after binding with hemin, indicating this functional aptamer has potential to be a light-up fluorescent probe and a DNAzyme which could be used as an alternative to peroxidases for many colorimetric or chemiluminescent detections in biosensing events. The experimental results show that the simple and convenient AuNP-based SELEX is very conducive to the selection of aptamers for small-molecule targets.

To develop a novel light-up probe and DNAzyme, we selected aptamers for N-methyl mesoporphyrin IX (NMM), a common fluorogenic analogue of coenzyme hemin, by a modified affinity chromatography-based systematic evolution of ligands by exponential enrichment (SELEX). Two truncated aptamers Nm1 and Nm2 with low micromolar dissociation constants (0.75 and 13.27 μM) were obtained after 11 rounds of selection and the final minimized 39-mer aptamer Nm2.1 showed 24-fold fluorescence enhancement for NMM at saturated concentration. Study of the interactions between aptamers and other porphyrin compounds by circular dichroism (CD) and absorption spectroscopy showed that Nm1 mainly assembled as a stem-loop structure, which exhibited a catalytic activity for the metal insertion reaction of mesoporphyrin IX with 3.3-fold rate enhancement. In contrast, the G-rich Nm2 and Nm2.1 were likely to form G-quadruplexes in the presence of alkali metal cations (K+ and Na+), which displayed excellent peroxidase activity exhibiting 19-fold higher catalytic efficiency than hemin alone. The selected aptamers could therefore be used as novel light-up fluorescent probes and DNAzymes by pairing with porphyrin compounds that have potential to construct sensors for various applications.

Spallation of thermal oxidation-induced cavities is the main failure mode in CoAl-based alloys, and the γ/γ′ phase structure in Co–Al–W–Ti–Ta alloys has a propensity to form oxide cavities. Multidimensional investigations were carried out herein on irregular oxide cavities by analytical microscopy, including electron tomography and energy dispersive X-ray spectroscopy techniques, to disclose the time-resolved three-dimensional morphological structure and elemental distributions. The alloy nanotip was exposed isothermally in air at 350 °C, and its oxidation evolution was characterized and analysed. The size and quantities of cavities in the γ phase were larger than those in the γ′ phase, which was attributed to the higher content of cobalt in the γ phase than in the γ′ phase. Different migration rates between cobalt outward and aluminium inward prompted the formation of cavities between the outer and inner layers.

It is known that Ni-based superalloys experience microstructural rafting during high temperature straining. This paper presents a comparative study of the different rafting models by means of finite element modeling and experimentation investigation. It was found that uniaxial elastic loading does not alter the misfit or misfit isotropy of the structure, but causes repartitioning of the misfit into elastic strains in the γ and γ' phases. This causes an elastic strain energy anisotropy and hydrostatic stress anisotropy among the vertical and horizontal γ phase channels. Both anisotropies predict a raft structure that is contrary to the experimental observation. Through a carefully designed pre-treatment at 750 °C and under a uniaxial stress of 750 MPa, an anisotropic dislocation structure was created on the {001} γ'/γ interfaces without altering the cuboidal morphology of the γ' phase. This allows the evaluation of the influence of dislocations on the rafting behavior of the alloy. It was found that rafting occurred in the pre-treated samples containing anisotropic dislocation structures during thermal exposure without applied stress, instead of isotropic corsening, and that the raft structures conform to the expectations base don the anistropic dislocation strucutres. This demonstrates that an anisotropic dislocation structure on the {001} γ'/γ interfaces is a direct cause of rafting. This is attributted to the fact that dislocations on γ'/γ interfaces help to relax the local misfit strains, causing some to expand at the expense of others. At the same time, the formation of the anisotropic dislocation structure is a direct result of the anisotropy of elastic strains induced by the applied bia stess in during the pre-treatment. These explain the complex interplay of the elastic and plastic models reported the literature.

Modern in situ oxidation processes can be observed down to the nanoscale using environmental transmission electron microscope (TEM), and this technology has been applied to conventional corrosion science to provide more detailed intrinsic information on the oxidation properties of materials. The influence of chromium (0–10 at.%) addition on the microstructure and oxidation properties of a γ/γ′ two-phase Co82Al9W9-based superalloy was systematically investigated. The in situ oxidation behaviour of Cr-containing alloys was studied using environmental TEM, and the addition of moderate Cr amounts is suggested for the alloy design.

In this paper, a methodology based on Bayesian Network (BN) was proposed to deal with the difficulty of risk analysis in RoPax transport. Based on data collection and expert survey, BN model for RoPax sailing risk analysis was constructed first. Then the Expectation Maximization (EM) algorithm for parameter learning and Evidence Prepropagation Importance Sampling (EPIS) algorithm for reasoning were designed. Finally, a sensitivity analysis was conducted. To validate the model algorithms, a case study on the RoPax system of Bohai gulf in China was provided. Results indicate that the BN model can effectively address the problem of data deficiency and mutual dependency of incidents in risk analysis. It can also model the development process of unexpected hazards and provide decision support for risk mitigation. First published online:10 Sep 2014

Twinned dendrites were successfully produced with high reproducibility in Al–4.5 wt.% Cu alloys at various growth speeds ( V ) of 100, 200, 500, 1000, 1500 and 2000 μm s −1 during Bridgman solidification. Under a relatively high thermal gradient ( G , around 200 K cm −1 ), the growth speed condition necessary for the twinned dendrite growth has been broadened. Experimental results indicate that the increase in growth speed has substantially changed the twinned morphologies. Importantly, the isolated twinned dendrite growth was observed at the growth speeds less than 1 mm s −1 (100, 200, and 500 μm s −1 ). At higher growth speeds, the finer twinned dendrites developed the usual appearance of an ordered sequence of alternating twinned and untwinned lamellae. The G / V value is considered as the critical factor for the isolated or usual twinned dendrite growth. A detailed analysis of the melt flow confirms that the slight convection during Bridgman solidification is large enough for the twinned dendrite growth. Furthermore, a visualized way to evaluate the velocity of the in-plane twinned extension was provided and the extension velocity was typically one third of the growth speed (500 μm s −1 ). Based on frequent “penetration” growth phenomena among secondary arms, a possible lateral propagation mechanism of the twinned dendrites has been hypothesized.

Nano-noble metal materials loaded metal oxide greatly reduce application costs, improve catalytic performance and sensing efficiency compared with oxide substrates. A simple and efficient load method plays an important role in promoting its commercialization. Nano-tungsten oxide is a kind of excellent gas sensing materials and it had been widely used. Noble metal loading can form abundant active centers on the surface of tungsten oxide and become an effective way to improve its gas detecting performance. The complexity and high cost of the loading methods hinder the its application and commercialization on supported catalysts. In this paper, Au/WO2.6 composites with high loading rate were prepared on layered tungsten oxide nano-flakes by a simple and low-cost method. The gas sensitivity of WO2.6 to ethanol and formaldehyde without Au and with Au were tested. The results show that the loading rate is the highest after reaction for 24 hours. The gas sensitivity of Au loaded WO2.6 is significantly improved. The sensitive mechanism on Au/WO2.6 composite were discussed in our work.

The morphology, composition, structure and formation mechanisms of precipitates in three Ni-base single crystal superalloys containing 3.2 at. % Ru by adding Cr (0 to 6.5 at. %) were investigated. The precipitation speed in the Low-Cr alloy was low at a temperature of 1100 °C. The ReRu-rich δ phase, with a hexagonal structure, was the primary phase. A high quantity of precipitates appeared in the high Cr alloy after 50 h of heat treatment. The quantity increased rapidly from that time. The σ phases dominated the precipitate after a short period of heating at 1100 °C, with the orientation relationship corresponding to [111] γ/γ′ // [111] σ and (110) γ/γ′ // (110) σ . The σ phase transformed into the intergrowth of the σ and the P phases discontinuously through the σ needle as the exposure time increased. The large elemental γ/γ′ partitioning ratio of Re in 6.5 at. % Cr was the key factor that promoted nucleation in the σ phase.