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Dissimilar weld joints of QP980 and TRIP800 were fabricated by a fibre laser. The microstructure and mechanical properties of dissimilar weld joints were studied. The tensile properties of weld joi...

The practical use of a point-of-care (POC) device is of particular interest in performing liquid biopsies related to cancer. Herein, taking advantage of the practical convenience of a commercially available personal glucose meter (PGM), we report a convenient, low-cost and sensitive detection strategy for circulating microRNA-155 (miRNA155) in human serum. First, miRNA155 in serum triggers the catalyzed hairpin assembly (CHA) reaction, and then the CHA product is specifically captured by the peptide nucleic acid (PNA) probes attached to the surface of a 96-well plate, which in turn triggers the hybridization chain reaction (HCR), resulting in the local enrichment of invertase. Next, introduction of a substrate (sucrose) for the invertase results in the generation of glucose, which can be detected by a PGM. In this sensor, neutrally charged PNA (12 nt) is more likely to hybridize with the CHA products than with the negatively charged DNA in kinetics, which improves the detection sensitivity and specificity. Due to the synergistic isothermal amplification reaction between CHA and HCR, the sensor is able to achieve a broad dynamic range (from 1 fM to 10 nM) with a detection limit down to 0.36 fM (3 orders of magnitude lower than that without HCR) and is capable of distinguishing single-base mismatched sequences. Thus the convenient, sensitive, robust and low-cost PGM sensor makes on-site nucleic acids detection possible, suggesting its great application prospect as a promising POC device in cancer diagnostics.

The modification of welding current waveform according to practical conditions and requirements, is an important way to improve the welding quality of various metals, especially the application of high-frequency pulsed current in arc welding. In this paper, the research activities and progress to date in the application of high-frequency (usually more than 5 kHz) pulsed current in arc welding are reviewed in detail, mainly including four significant categories of output current waveforms and their performance characteristics and weld quality: high-frequency pulsed current waveform, high-frequency pulsed variable polarity current waveform, double-pulsed current waveform and inter-pulse GTAW welding adopting SiC-based power devices. In conclusion, in the fusion welding process, the introduction of high-frequency pulsed current is beneficial to the constriction of welding arc, the increase of weld penetration depth, the reduction of weld porosity, the refinement of the microstructure in weld zone and the enhancement of weld mechanical properties. And in the future, the advanced SiC-based power devices is going to replace the present Si-based power devices and bring about a profound change to the welding processes.

A thermoplastic ABS and an aluminium alloy 6061-T6 were joined using friction lap welding (FLW). The joint characteristics were evaluated to investigate the effects of 6061-T6 surface and the weldi...

With the help of peptide nucleic acid (PNA) and single-stranded (ss) DNA-specific nucleases, a simple, rapid, and label-free nanosensor is demonstrated for the sensitive and accurate detection of s...

Here, taking the advantage of single-stranded (ss) DNA specific nuclease (S1) and peptide nucleic acid (PNA), we demonstrated a novel, rapid, and label-free colorimetric nanosensor for the sensitive and accurate detection of SNPs based on the intrinsic peroxidase-like activity of hemin-functionalized single-walled carbon nanotubes (hemin-SWCNTs). PNA, a man-made mimic of DNA with extraordinary stability toward enzymatic degradation, can effectively protect DNA in the fully matched DNA/PNA duplexes from nuclease digestion. While the DNA in DNA/PNA duplexes containing a mismatch can be cleaved into small fragments. This difference can be visually monitored from the specific color change of TMB/H2O2 system by employing the peroxidase activity of hemin-SWCNTs because of its different aggregation states responding to ssPNA or DNA/PNA duplex. Under optimized conditions, the SNPs in the human tumor suppressor gene TP53 have been successfully genotyped in a linear range of 50–1000 nM with a detection limit of 0.11 nM. Moreover, this platform can effectively discriminate a series of single-base mismatches. This assay avoids the assistance of sophisticated instruments and complicated modifications of probes or nanomaterials, and function well for both cell lysate samples and PCR amplicons from standard cell lines, implying its potential practical applications for bioanalysis and biosensors.

A convenient fluorometric method was developed for specific determination of DNA based on peptide nuclei acid (PNA)-regulated fluorescence resonance energy transfer (FRET) between carbon dots (CDs) and gold nanoparticles (AuNPs). In this system, CDs that display lake blue fluorescence with excitation/emission maxima at 345/445 nm were used as fluorometric reporter, while AuNPs were used as fluorescence nanoquencher. A neutral PNA probe, which is designed to recognize the target DNA, was used as a coagulant to control the dispersion and aggregation of AuNPs. Without DNA, PNA can induce immediate AuNP aggregation, thus leading to the recovery of the FRET-quenched fluorescence emission of CDs. However, the addition of the complementary target DNA can protect AuNPs from being aggregated due to the formation of DNA/PNA complexes, which subsequently produces a high fluorescence quenching efficiency of CDs by dispersed AuNPs. Under optimized conditions, quantitative evaluation of DNA was achieved in a linear range of 5-100 nM with a detection limit of 0.21 nM. This method exhibited an excellent specificity towards fully matched DNA. In addition, the application of this assay for sensitive determination of DNA in cell lysate demonstrates its potential for bioanalysis and biodetection. Graphical abstract A simple fluorometric biosensor for specific detection of DNA was developed based on peptide nuclei acid (PNA)-regulated fluorescence resonance energy transfer (FRET) between carbon dots (CDs) and gold nanoparticles (AuNPs).

In this paper, two filler metals of alloy 690 were evaluated on their hot cracking resistance based on the fractal analysis of random high-angle grain boundary (RHGB) morphologies. A grain reference orientation deviation (GROD) map based on EBSD technique was conducted to investigate the polycrystalline strain distribution on different RHGB network. It was found that for the 52M weld metal, specimen from the cross section with straight dendritic GBs exhibited lower fractal dimension, showing higher DDC susceptibility than the specimen from the surface section with higher fractal dimension due to equiaxed grains with tortuous GBs. With Mo and more Nb adding to the filler metal 52MSS, smaller grains nucleated and fractal dimension of the RHGB network increased, thus the cracking resistance was greatly improved. The GROD results revealed that local strain commonly concentrated around RHGB at high temperatures, especially near long and straight RHGB. The dense and tortuous RHGB network, resulting in the higher fractal dimension, could bear a more uniform strain distribution and balance the deformation between GB and grains, leading to better performance on cracking resistance. Moreover, dynamic recrystallized grains were observed beside GBs and their amount increases where there was cracking at 1050 °C, especially for the 52MSS. As a result, crack propagation path was blocked and fractal dimension increased as well.

Economical, fast and sensitive detection of proteins is essential to biomedical research as well as clinical diagnosis. Here, we demonstrated a label-free colorimetric aptasensor that uses PNA/DNA hybrids and a cyanine dye (DiSC2(5)) for highly sensitive and selective detection of proteins in aqueous solution. This protocol, based on the difference in the binding interactions of DiSC2(5) with PNA and the PNA/DNA hybrid causing different colors, can be applied for the detection of proteins. This sensing platform can specifically detect thrombin, our example analyte, with a detection limit of 0.4 nM. Moreover, the assay does not involve any chemical modification and enzyme amplification, and hence it is convenient, fast and low-cost. In principle, this approach can be used to detect proteins with specific aptamers by simply changing the sequences of the probe DNA for specific targets. Furthermore, this sensing platform provides a promising approach for the analysis of target proteins at point-of-care in resource-limited settings.

The metal-thermoplastic hybrid structure has been widely employed in the aviation and aerospace industry. In this work, we developed a feasible way of laser surface texturing to address the poor adhesion between PEEK and 6061-T6 aluminum alloy. With the laser surface modification on 6061-T6 aluminum alloy, the PEEK/6061-T6 friction lap joining strength was improved significantly. The experimental results showed that the tensile shear strength between PEEK and 6061-T6 with laser textured surfaces achieved the maximum of 48.14 MPa. The enhanced bonding strength was attributed to the mechanical interlocking at the interface between PEEK and 6061-T6 caused by periodic micro-pores and nano-particles. After the progress of laser surface texturing, the double-scale hierarchical structures were produced on the surface of modified 6061-T6 alloy, leading to the formation of superhydrophobic or hydrophobic surfaces. Besides, quantitative fractal analysis of 6061-T6 surfaces was performed to study the relation between the morphology of 6061-T6 surface and the adhesion property of PEEK and 6061-T6. The results indicated that the superhydrophobic surface of 6061-T6 exhibited higher adhesion property with PEEK than the hydrophobic surface. A flawless interface was observed in the joint of PEEK and 6061-T6 with the superhydrophobic surface, compared to the voids observed at the interface of PEEK and 6061-T6 with the hydrophobic surface.

The unmixed zone (UMZ) was found in 439 tube/308L tube-sheet weld, which was jointed with 316L filler metal. The effect of microstructure of UMZ on hardness and corrosion behavior was investigated. The mechanism of macrosegregation combined with fluid flow was applied to account for the formation of UMZ, based on that the liquidus temperature of the bulk weld metal was relatively lower than that of the base metal. The microstructure of UMZ predominantly consisted of ferrite, Widmanstatten austenite (WA) and a few martensite. Martensite fraction in UMZ varied from weldment side to 439 side. It is found that the sample with UMZ was more vulnerable to corrosion and pitting. Difference in liquidus temperature and cooling rate contributed to the different microstructure in UMZ, and resulting in poor corrosion resistance of this dissimilar metal welded joint.

Screening epidermal growth factor receptor (EGFR) mutations, especially deletions, is essential for diagnosis of non-small cell lung cancer (NSCLC) and also critical to inform treatment decisions for NSCLC patients. Here, we demonstrated a facile peptide nucleic acid (PNA) microarray-based fluorometric method for sensitive and specific detection of EGFR mutation, using rolling circle amplification (RCA), graphene oxide (GO), and a fluorescently-labeled detection probe (F-DP). First, the EGFR gene sequence was efficiently captured by the label-free PNA probe which was attached on the surface of a 96-well plate. And then, the EGFR mutation sequence was specifically amplified by RCA using the circular DNA, which was formed by the ligation of the padlock probe when hybridizing with the EGFR mutation, as a template. The single-stranded RCA product (RCAP) was then sensitively detected with the F-DP and GO system. This method has a detection limit of 0.3 pM for EGFR mutation and a high discrimination capability to target EGFR mutation against EGFR wildtype. The use of a PNA microarray and a fluorescence quenching platform make this system quite suitable for high-throughput analysis of EGFR mutations in resource-limited settings without the need of costly and cumbersome equipment. Furthermore, this detection system provides a novel way for the diagnosis of other diseases that are caused by gene deletion mutations.

The multi-pass ERNiCrFe-7A overlay depositions, produced by cold wire feed (CWF) or hot wire feed (HWF) gas tungsten arc welding (GTAW) process with typical parameters, were employed to investigate the effects of different micro-characteristics on ductility-dip cracking (DDC) susceptibility. The results show that, the HWF-produced deposit exhibited the texture with larger quantity of 〈001〉 oriented grains in the pass region (away from the fusion line), while the CWF-produced deposit was weakly textured with increased crystallographic misorientation for the higher heat input per unit volume. Crystal misorientation also increased in the interpass region (near the fusion line) of both the overlays. Results of strain-to-fracture (STF) tests indicated that the overall DDC resistance in the deposit CWF was lower than that in the deposit HWF. And the interpass region exhibited higher DDC susceptibility than the pass region. The intergranular cracking is found to be triggered by the strain accumulation between differently oriented grains. Meanwhile, both the over 30° misorientation angle and melting of Cr-rich M23C6 carbides reduced the grain boundary (GB) strength and promoted the cracking. Therefore, the DDC resistance would be increased by decreasing the GBs those have misorientation angles over 30°, as well as the carbides distributed on the GBs. Keywords: Local texture, Nickel-based alloy, Ductility dip cracking, Grain boundary misorientation, M23C6

Effect of residual stresses on creep behavior was investigated using designed compact tension specimens in 2.25Cr-1.6W steel before and after heat treatment. The heat treatment was carried out to obtain partial austenitization microstructure and to cause zigzag configuration of grain boundaries. Residual stresses were generated ahead of crack root by loading in compression beyond yield and then unloading. A three-dimensional finite element model was developed to predict the evolution of creep damage and residual stress within the specimens during creep time. The extent of creep crack has also been assessed through destructive examination, providing validation for the creep damage prediction model. Fractal analysis was applied to quantitative determinate the correlation between the grain boundary configuration and creep behavior.

Multi-scale simulation of nanoindentation on cast Inconel 718 superalloy and its NbC precipitate were performed with combined first principle study and crystal plasticity finite element method (CPFEM). The concerned parameters were calibrated through a representative volume element (RVE) model compared with the stress–strain curves obtained from tensile tests. Nanoindentation was carried out on the matrix. First principle calculations were applied to estimate the mechanical properties of precipitate NbC, including elastic modulus and hardness. The simulated force–displacement curves match well with the experimental results. The simulated results indicate that the local pile-up pattern in the indentation zone depends significantly on the crystallographic orientations. In addition, large precipitate NbC inserted in the matrix was also indented and simulated. The elastic modulus calculated by first principle is quite accurate while the yield stress is determined using inversion calculations. It appears that the proposed CPFE analysis approach combined with first principle calculation do help estimate the mechanical behavior of large precipitates on the Ni-based superalloy.

Herein we demonstrated a facile electrochemical method for simultaneous detection of miRNA21 and miRNA155 using a peptide nucleic acids (PNAs)-modified gold electrode coupled with the target-catalyzed hairpin assembly (CHA) strategy. In the presence of the target miRNA, the CHA was triggered selectively between two hairpins with one ferrocene (Fc) or methylene blue (MB) labelled. The resulting redox-active group modified CHA products (Fc-CHA21 or MB-CHA155) were then specifically captured by the PNA probes (PNA21 or PNA155) attached on the surface of a gold electrode, which bring the Fc and MB labels into close proximity to generate apparently enhanced electrochemical signals for sensitive and simultaneous detecting of low amount miRNA21 and miRNA155 in cancer cells. This assay was highly selective for discriminating miRNAs with similar sequences and has detection limits of 2.49 fM and 11.63 fM for miRNA21 and miRNA155, respectively. The feasibility of the method for sensitive determination of miRNA21 and miRNA155 from human cancer cells was also demonstrated. This method thus has great potential to be applied for simultaneous detecting of a variety of miRNA biomarkers for clinic applications due to its simple, sensitive and accurate features.

The effect of bonding temperature on the microstructure and mechanical properties of transient liquid phase (TLP) joints of GH4169 superalloy was investigated. Joining processes were carried out at 1040&ndash, 1100 &deg, C for 30 min using BNi-2 solder paste. The results showed that three distinct microstructural zones were formed in the joint region: an athermal solidification zone (ASZ), consisting of eutectic compounds, an isothermal solidification zone (ISZ), consisting of &gamma, solid solution, and a diffusion affected zone (DAZ), consisting of Ni-Cr rich boride and Cr-Nb-Mo-rich boride compounds. With increasing bonding temperature, the amounts of eutectic compounds in ASZ first decreased and then increased. A eutectic-free joint centerline was obtained at 1080 &deg, C. The maximum bonding shear strength reached 728.03 MPa due to the completion of isothermal solidification. Fractographic studies revealed that the boride compounds in ASZ and the intermetallic compounds in DAZ were the main causes for the failure of joints. The fracture mode of the sample bonded at 1040 &deg, C was brittle, and the fracture path was along the ASZ. However, the fracture mode of the sample bonded at 1080 &deg, C was ductile, and the fracture occurred along the DAZ.

(Cr, Fe)7C3/[Formula: see text]-Fe composite layer has been in situ synthesized on a low carbon steel surface by vacuum electron beam VEB irradiation. The synthesized samples were then subdued to different heat treatments to improve their impaired impact toughness. The microstructure, impact toughness and wear resistance of the heat-treated samples were studied by means of optical microscope (OM), X-ray diffraction (XRD), scanning electron microscope (SEM), microhardness tester, impact test machine and tribological tester. After heat treatment, the primary and eutectic carbides remained in their original shape and size, and a large number of secondary carbides precipitated in the iron matrix. Since the Widmanstatten ferrite in the heat affected zone (HAZ) transformed to fine ferrite completely, the impact toughness of the heat-treated samples increased significantly. The microhardness of the heat-treated samples decreased slightly due to the decreased chromium content in the iron matrix. The wear resistance of 1000[Formula: see text]C and 900[Formula: see text]C heat-treated samples was almost same with the as-synthesized sample. While the wear resistance of the 800[Formula: see text]C heat-treated one decreased slightly because part of the austenite matrix had transformed to ferrite matrix, which reduced the bonding of carbides particulates.

The Ni-based coatings were deposited on the 1Cr10Mo1NiWVNbN steel by using laser cladding process. The microstructure and properties of the coatings interface area were investigated by OM (Optical Microscopy), SEM (Scanning Electron Microscope), XRD (X-Ray Diffraction) microhardness test and EDS (Energy Spectrum Analysis) analysis. The results show that the bonding condition of the coatings interface is different in the monolayer and the trilayer. The monolayer coatings have a small dilution area. The dilution rate in a coating layer increases by layers. The scale of ferrite (α) phase increases with the layer increases. The surface cladding quality of a monolayer is better than that of the trilayer coatings. The width of the interface increases with the increase of the layer. The width of the interface region in the trilayer coatings increases significantly. The microhardness of the interface zone is much higher than that in the coatings zone and the substrate zone. The microhardness of trilayer coatings is higher than that of the monolayer.