Selective laser melting (SLM) in situ alloying is an effective way to design and fabricate novel materials in which the elemental powder is adopted as the raw material and micro-areas of elemental ...powder blend are alloyed synchronously in the forming process of selective laser melting (SLM). The pre-alloying process of preparation of raw material powder can be left out, and a batch of bulk samples can be prepared via the technology combined with quantitative powder mixing and feeding. The technique can be applied to high-throughput sample preparation to efficiently obtain a microstructure and performance data for material design. In the present work, bulk equiatomic FeCoCrNi high-entropy alloys with different processing parameters were fabricated via laser in situ alloying. Finite element simulation and CALPHAD calculation were used to determine the appropriate SLM and post-heating parameters. SEM (scanning electron microscope), EDS (energy dispersive spectroscopy), XRD (X-ray diffraction), and mechanical testing were used to characterize the composition, microstructure, and mechanical properties of as-printed and post-heat-treated samples. The experimental results show that the composition deviation of laser in situ alloying samples could be controlled within 20 wt %. The crystal structure of as-printed samples is a single-phase face-centered cubic (FCC), which is the same as those prepared by the traditional method. The mechanical properties of the samples prepared by laser in situ alloying with elemental powder blend are comparable to those prepared by pre-alloying powder and much higher than those prepared by the traditional method (arc melting). As-printed samples can get a homogeneous microstructure under the optimal laser in situ alloying process combined with post-heat treatment at 1200 °C for 20 h.
The construction of multifunctional sensors has attracted considerable attention due to their multifunctional properties, such as high sensitivity and rapid detection. Herein, near-infrared ...multifunctional fluorescent sensing materials based on core-shell upconversion nanoparticle@magnetic nanoparticle and molecularly imprinted polymers were synthesized for rapid detection of deltamethrin. The difunctional core-shell upconversion nanoparticle@magnetic nanoparticle was introduced as the optical signal and rapid separator. Firstly, the difunctional core-shell materials were prepared through solvothermal method. Then, molecularly imprinted polymers (MIPs) as recognition elements for deltamethrin were coated on the surface of upconversion nanoparticle@magnetic nanoparticle through polymerization. The structure and recognition characterizations of multifunctional fluorescent sensing materials were evaluated. Under optimal condition, the imprinting factor of sensing materials was 3.63, and the fluorescence intensity of sensing materials decreased linearly with increasing concentration of deltamethrin from 0.001 to 1 mg L
−1
with a detection limit of 0.749 μg L
−1
, and a relative standard deviation of 3.10% was obtained with 5 mg L
−1
deltamethrin. The sensing materials showed a high selectivity and were successfully utilized for the detection of deltamethrin in grapes and cabbages; the results showed that the recoveries for two samples obtained were 95.6–102% and 91.8–105%.
Graphical abstract
Sentinel lymph node (LN) biopsy is currently the standard procedure for clinical LN‐negative breast cancer (BC) patients but it is prone to false‐negative results and complications. Thus, an accurate ...noninvasive approach for LN staging is urgently needed in clinical practice. Here, circulating exosomal microRNA (miRNA) expression profiles in peripheral blood from BC patients and age‐matched healthy women were obtained and analyzed. We identified an exosomal miRNA, miR‐363‐5p, that was significantly downregulated in exosomes from plasma of BC patients with LN metastasis which exhibited a consistent decreasing trend in tissue samples from multiple independent datasets. Plasma exosomal miR‐363‐5p achieved high diagnostic performance in distinguishing LN‐positive patients from LN‐negative patients. The high miR‐363‐5p expression level was significantly correlated with improved overall survival. Functional assays demonstrated that exosomal miR‐363‐5p modulates platelet‐derived growth factor (PDGF) signaling activity by targeting PDGFB to inhibit cell proliferation and migration. Our study revealed, for the first time, plasma exosomal miR‐363‐5p plays a tumor suppressor role in BC and has the potential for noninvasive LN staging and prognosis prediction of BC.
This study identified downregulated circulating exosomal miR‐363‐5p in breast cancer (BC) patients with lymph node (LN) metastasis. The miR‐363‐5p achieved high performance as a noninvasive predictor of LN metastasis and prognosis. The exosomal miR‐363‐5p inhibits metastatic properties and suppresses platelet‐derived growth factor B expression by targeting the 3′‐UTR. Our study provides a potential biomarker for LN staging and prognosis prediction of BC.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The physics and mechanism of sheet/cloud cavitation in a convergent–divergent channel are investigated using synchronized dynamic surface pressure measurement and high-speed imaging in a water tunnel ...to probe the cavity shedding mechanism. Experiments are conducted at a fixed Reynolds number of
Re
= 7.8 × 10
5
for different values of the cavitation number
σ
between 1.20 and 0.65, ranging from intermittent inception cavitation, sheet cavitation to quasi-periodic cloud cavitation. Two distinct cloud cavitation regimes, i.e. the re-entrant jet and shockwave shedding mechanism, are observed, accompanied by complex flow phenomenon and dynamics, and are examined in detail. An increase in pressure fluctuation intensity at the numbers 3 and 4 transducer locations are captured during the transition from re-entrant jet to shockwave shedding mechanism. The spectral content analysis shows that, in cloud cavitation, several frequency peaks are identified with the dominant frequency caused by the large-scale cavity shedding process and the secondary frequency related to re-entrant jet/shockwave dynamics. Statistical analysis based on defined grey level profiles reveals that, in cloud cavitation, the double-peak behaviours of the probability density functions with negative skewness values are found to be owing to the interactions of the re-entrant jet/shockwave with cavities in the region of 0.25 ~ 0.65 mean cavity length (
L
c
). In addition, multi-scale proper orthogonal decomposition analysis with an emphasis on the flow structures in the region of 0.25 ~ 0.65
L
c
reveals that, under the shockwave shedding mechanism, both the re-entrant jet and shockwave are captured and their interactions are responsible for the dynamics and statistics of cloud shedding process.
As a result of ongoing global warming, approximately 30% of the world's population lives in areas where the temperature reaches the death risk threshold at least 20 days a year. The distribution of ...heat and vulnerability, however, varies in a city; where mitigation actions should begin is a simple question that must be answered. Therefore, it is important to identify hotspots and provide a concrete foundation for the following decision-making process that can be used to integrate urban risk management systems. This paper critically reviewed previous studies from 2006 to 2018 on this subject with the following three main research objectives: (1) What are the definitions and connotations regarding the current discussions on "hotspots"? (2) What are the emerging approaches used to define the threshold, intensity and other properties of hotspots according to their different connotations? (3) Where are the gaps between hotspot recognition and urban heat-related risk management? The results indicate that the concepts, especially related to threshold detection methods, are overcomplicated and vague, suggesting the need for further communication among disciplines.
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BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
Although many studies have reported the behaviors of thermal cycling of Sn-based solder joints, the corresponding mechanism is difficult to describe universally due to the complexity of different ...cases. In the present study, microstructural evolution and failure of Sn–Bi57–Ag0.7 solder joints caused by thermal cycling between − 40 and 85 °C from 0 to 1000 cycles were systematically investigated. The results indicated that the Sn–Bi–Ag solder joint was composed of Sn-rich phase, Bi-rich phase, large numbers of Bi dispersed-particles, and Ag
3
Sn precipitate. With the extension of time during thermal cycling, the microstructure of Sn–Bi–Ag solder joint gradually coarsened and the IMC layer became thicker (from 0.82 to 2.38 μm). However, Sn–Bi–Ag solder joints failed after 3000 thermal cycles. Two different stages of failure were found and the mechanism, related to the increment of thermal mismatch stress, was illuminated. Furthermore, Electron Backscattered Diffraction was used to detailedly elucidate the grain characteristics of the failed Sn–Bi–Ag solder joints, and the effect of thermal stress on orientations of Sn and Bi grains was also revealed. Being different from the orientation change observed in traditional Sn–Bi eutectic solder joints in previous studies, the present results demonstrated that both Sn and Bi grains did not present any preferred orientations after thermal cycling. And the reason of this phenomenon might be attributed to the Ag
3
Sn, which could be regarded as second-phase particles. Our present work would provide theoretical guidance for the development of new Sn–Bi-X solders with high reliabilities.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The synergy of cavitation and sediment erosion is the most severe destruction in hydraulic machinery in sediment-laden rivers, and currently the physics and mechanism are still lack of understanding. ...The synergy effects of cavitation and sediment erosion not only reduce the efficiency and life of hydraulic machinery but also cause costs in operation and maintenance. With the rapid development of renewable clean energy and the transformation of water resources, an increasing number of new hydropower stations and water diversion projects are currently planned or under construction, where most of them are in sediment-laden rivers. In the present paper, the research work, including theory, experiment, and simulation, in this field carried out by various investigators are presented and discussed. Physical mechanisms involved in the synergy of cavitation and sediment erosion which is responsible for material damage as investigated by researchers have also been discussed, and would help to identify gaps for future studies.
•Unsteady sheet/cloud cavitating flows are studied using the compressible cavitation solver developed on OpenFOAM.•Cavitation fluid compressibility effects on transient flow structures and dynamics ...are illustrated.•Effects of density variance on velocity divergence are proposed.•The physics for the compressibility effects on cavitation vortex dynamics are investigated based on VTE budget analysis.
The objective of the paper is to investigate the physics involved in the compressible cavitating flows, with emphasis on the compressibility effects. 3-D numerical simulations were conducted on the open source software platform OpenFOAM, using both the native incompressible cavitation solver interPhaseChangeFOAM and implemented compressible cavitation solver, where the cavitation model and turbulence model are kept the same and differences of the two approaches mainly root in the density variances of pure liquid and pure vapor. Results are presented for the transient sheet/cloud cavitating flows around a Clark-Y hydrofoil fixed at attack of angle α=8° at inlet velocity U=10m/s and cavitation number σ=0.8, where both ensemble averaged statistics and transient characteristics are analyzed. Good agreement can be obtained using both the incompressible and compressible approaches when compared with the experiment data. While it is found that compared with the incompressible approach, the compressible approach can predict the unsteady cavitation evolution and cavity shedding frequency better. With the compressibility effects considered, the time averaged void fraction distribution decreases, and the cavity size (i.e. cavitation area) becomes smaller. The re-entrant flow thickness normalized by local cavity thickness predicted by the compressible approach is larger than that by the incompressible approach, indicating that the compressible approach can predict the re-entrant jet dynamics well. The velocity divergence analysis show that compared with that in incompressible approach, where velocity divergence mainly comes from the mass transfer between phases, in compressible approach, the velocity divergence originates from both the cavitation two-phase fluid compressibility and mass transfer, and the fluid density variance dominates in compressible results. Following, the budget analysis of vorticity transport equation (VTE) show that the vortex stretching term dominates the cavitation vortex dynamics. Compressibility effects will significantly increase the dilatation term and decrease baroclinic term by decreasing the misalignment between density gradient and pressure gradient. Finally, the temperature and density variance in different cavitation structures are presented.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•A simultaneous sampling technique is applied to investigate cavitation shedding dynamics.•Two shedding mechanisms in a convergent-divergent channel are observed.•Unsteady pressure fluctuation ...characteristics for two shedding behaviors are clarified.
The objective of this paper is to investigate the unsteady pressure fluctuation characteristics in the process of breakup and shedding of unsteady sheet/cloud cavitating flows via combined experimental and computational methods. Experiments are conducted in the divergent section of a convergent-divergent channel using a simultaneous sampling technique to synchronize the transient cavitation behaviors and wall-pressure signals. In the numerical simulations, the Zwart cavitation model and the modified RNG k-ε turbulence model are solved, with the compressibility effects of both water and vapor considered. In addition, one-dimensional bubbly shock wave relationship is applied to analyze the process of the vapor fraction discontinuity propagation. Two different types of cavity breakup and shedding existing in the unsteady sheet/cloud cavitating flows are observed, which is induced by re-entrant flow and vapor fraction discontinuity propagation mechanism, respectively. The re-entrant flow generates at the rear of the cavity, moving forward along the wall. When it arrives at the throat, it breaks up the attached cavity, resulting in the cloud cavity shedding. During the process, the wall pressure fluctuation is relatively small. The vapor fraction discontinuity propagation is resulted from the bubbly shock in water/vapor mixture of the sheet/cloud cavity. There is a significant difference of vapor fraction between the pre- and post of the discontinuity. The pre-discontinuity area is almost pure vapor, and the post-discontinuity area consists of water/vapor mixtures with relatively low vapor fraction. During the discontinuity propagation, the pressure peak exists at shock wave front. When the discontinuity arrives at the throat, the void fraction will suddenly decrease, which indicates the low vapor generation rate. Under the convection of the main flow, the attached cavity will be separated from the newly generated vapor, resulting in the attached cavity breaking up and the cavity cloud shedding.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
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