Diffusion Research in BCC Ti-Al-Zr Ternary Alloys

Diffusion behavior in the BCC Ti-Al-Zr ternary alloys was experimentally investigated at 1273 K (1000 °C) and 1473 K (1200 °C) by means of the diffusion-couple technique. Upon the Whittle-Green and generalized Hall methods, the inter- and impurity diffusion coefficients were respectively extracted from the composition profiles acquired by the electron microprobe analysis (EPMA) and subsequently represented by the error function expansion. The extracted main interdiffusion coefficient D~AlAlTi increases with increasing the content of either Al or Zr, and the increase is appearing more considerably at the higher temperature. However, D~ZrZrTi was noticed to decrease with the increase of Al and Zr contents at 1273 K (1000 °C) while there is an upward trend at 1473 K (1200 °C). The impurity diffusion coefficients of Al in Ti-Zr binary alloys, DAl(Ti - Zr)*, and of Zr in Ti-Al binary alloys, DZr(Ti - Al)*, increase with increasing the Zr and Al contents respectively. A comparison of average main interdiffusion coefficient D~XXTi¯ made among ten Ti-Al-X ternary systems suggests that the Zr diffusion is most comparable to Cr and could operate via a vacancy-controlled mechanism

Improved fracture toughness by microalloying of Fe in Ti-6Al-4V

The widely used Ti–6Al–4V (TC4) titanium alloy has been modified through the micro-alloying of Fe. The microstructural features and mechanical properties of the designed alloy, TC4F, are compared with other alloys in Ti–6Al–4V class by combining experimental characterizations and thermodynamic calculations. TC4F alloy not only maintains strength, hardness, and elongation similar to baseline TC4 but also exhibits improved fracture toughness comparable to TC4_ELI and even superior to TC4_DT under the heat-treated condition. It opens up a new cost-reducing way to enhance fracture toughness in place of controlling interstitial contents, showing potential in engineering applications. The discerned mechanisms indicate that the trace addition of Fe gives rise to composition redistribution between V and Fe in the ß phase, boosts the lattice distortion and vibration, thereafter enhances Young''s modulus and fracture toughness. It has been validated and verified by experiments, thermodynamic calculations, and Hahn-Rosenfield empirical research. The enhanced fracture toughness also benefits from the kinked ß+a lamellar microstructure at crack tip as well as the improved fracture surface due to the Fe addition. The enlarged plastic zone, redirected crack propagation, and more dimples with even-distributed size additionally contribute to the improvement of fracture toughness

Identifying potential RNAi targets in grain aphid (Sitobion avenae F.) based on transcriptome profiling of its alimentary canal after feeding on wheat plants

BACKGROUND: The grain aphid (Sitobion avenae F.) is a major agricultural pest which causes significant yield losses of wheat in China, Europe and North America annually. Transcriptome profiling of the grain aphid alimentary canal after feeding on wheat plants could provide comprehensive gene expression information involved in feeding, ingestion and digestion. Furthermore, selection of aphid-specific RNAi target genes would be essential for utilizing a plant-mediated RNAi strategy to control aphids via a non-toxic mode of action. However, due to the tiny size of the alimentary canal and lack of genomic information on grain aphid as a whole, selection of the RNAi targets is a challenging task that as far as we are aware, has never been documented previously. RESULTS: In this study, we performed de novo transcriptome assembly and gene expression analyses of the alimentary canals of grain aphids before and after feeding on wheat plants using Illumina RNA sequencing. The transcriptome profiling generated 30,427 unigenes with an average length of 664 bp. Furthermore, comparison of the transcriptomes of alimentary canals of pre- and post feeding grain aphids indicated that 5490 unigenes were differentially expressed, among which, diverse genes and/or pathways were identified and annotated. Based on the RPKM values of these unigenes, 16 of them that were significantly up or down-regulated upon feeding were selected for dsRNA artificial feeding assay. Of these, 5 unigenes led to higher mortality and developmental stunting in an artificial feeding assay due to the down-regulation of the target gene expression. Finally, by adding fluorescently labelled dsRNA into the artificial diet, the spread of fluorescence signal in the whole body tissues of grain aphid was observed. CONCLUSIONS: Comparison of the transcriptome profiles of the alimentary canals of pre- and post-feeding grain aphids on wheat plants provided comprehensive gene expression information that could facilitate our understanding of the molecular mechanisms underlying feeding, ingestion and digestion. Furthermore, five novel and effective potential RNAi target genes were identified in grain aphid for the first time. This finding would provide a fundamental basis for aphid control in wheat through plant mediated RNAi strategy

Catalytic Hydrolysis of Ammonia Borane by Cobalt Nickel Nanoparticles Supported on Reduced Graphene Oxide for Hydrogen Generation

Well dispersed magnetically recyclable bimetallic CoNi nanoparticles (NPs) supported on the reduced graphene oxide (RGO) were synthesized by one-step in situ coreduction of aqueous solution of cobalt(II) chloride, nickel (II) chloride, and graphite oxide (GO) with ammonia borane (AB) as the reducing agent under ambient condition. The CoNi/RGO NPs exhibits excellent catalytic activity with a total turnover frequency (TOF) value of 19.54 mol H2 mol catalyst−1 min−1 and a low activation energy value of 39.89 kJ mol−1 at room temperature. Additionally, the RGO supported CoNi NPs exhibit much higher catalytic activity than the monometallic and RGO-free CoNi counterparts. Moreover, the as-prepared catalysts exert satisfying durable stability and magnetically recyclability for the hydrolytic dehydrogenation of AB, which make the practical reusing application of the catalysts more convenient. The usage of the low-cost, easy-getting catalyst to realize the production of hydrogen under mild condition gives more confidence for the application of ammonia borane as a hydrogen storage material. Hence, this general method indicates that AB can be used as both a potential hydrogen storage material and an efficient reducing agent, and can be easily extended to facile preparation of other RGO-based metallic systems

Segmentation of local youths' leisure motivations towards local tourist attractions.

Singapore tourism industry has been growing robustly in past few years. Singapore Tourism Statistics has shown that Singaporean’s contribution to the Total Tourism Receipts was falling constantly over the years. This can be an indication that Singapore tourist attractions may not appeal to the locals. Given the locals is a lucrative segment to the tourism industry, thus it is important for tourism marketer to understand the leisure motivations and psychographic characteristics of Singaporeans. The purpose of this study is to examine locals’ leisure motivations by adopting the push and pull motivation theory. From this study, five different psychographic profiles were identified through the segmentation of 100 local youths’ leisure motivations. This was derived from factor analysis followed by cluster analysis to segment the leisure motivations of our respondents. Subsequently, clusters identified were then matched with their rankings of attractions. Based on the distinct characteristics and travel preferences of each cluster, several packages, promotional concepts and suitable communication medium were recommended. The findings of the study will provide important marketing implications for the vendors in the tourism sector to develop effective marketing strategies, as well as the basis for the future developments of tourism in Singapore.BUSINES

Optimization of Low-Cost Ti-35421 Titanium Alloy: Phase Transformation, Bimodal Microstructure, and Combinatorial Mechanical Properties

A sophisticated understanding of phase transformations and microstructure evolution is crucial in mechanical property optimization for the newly developed low-cost Ti-35421 (Ti-3Al-5Mo-4Cr-2Zr-1Fe wt.%) titanium alloy. The phase transformations in dual-phase Ti-35421 were studied by experiments and thermo-kinetic modeling. The phase transformation reactions and temperature ranges were determined as β→αlamellar [410–660 °C], αlamellar→β [660–740 °C], αlath→β [740–825 °C]. The Gibbs-Thomson effect and multicomponent diffusivities were proven to be responsible for the distinguishing behaviors of growth and dissolution between two α phases. The aging temperature of 540 °C was optimized based on calculations. It introduced a bimodal microstructure containing stubby α lamellae and β matrix. The mechanical properties of bimodal Ti-35421 were tested and compared with baseline alloy Ti-B19 and other near-β titanium alloys. The 540 °C aged alloy exhibits an optimal combination of mechanical properties with tensile strength of 1313 MPa, yield strength of 1240 MPa, elongation of 8.62%, and fracture toughness of 75.8 MPa·m1/2. The bimodal Ti-35421 shows comparable performance to Ti-B19 but has lower cost in raw materials and processing. The results also demonstrate that thermo-kinetic modeling can effectively be utilized in tailoring microstructure and enhancing mechanical properties

One step synthesis of graphene oxide under low-temperature and its microwave reduction

The graphene oxide was prepared via one step under low-temperature with natural flake graphite as raw material. Factors affecting oxidation degree and layer spacing of graphene oxide were discussed in the process of low-temperature oxidation, such as the dosage of oxidant and oxidation time in system. The results indicate that high C-O bond and low defect structure (ID:IG=0.63) graphene oxide with the carbon and oxygen atom ratio of 1.98 can be prepared in the condition of the potassium permanganate with natural flake graphite mass ratio of 1:3, oxidation temperature of 0℃, oxidation time of 48h.This way avoids the increase of graphene oxide defects in the process of Hummers preparation due to the formation of CO2, which leads to the hexagon fracture and the absence of carbon atoms. After microwave reduction, the reduced graphene oxide with low defect is obtained, which the distance between defects(LD)is 12nm,the defect density(nD) is 2.21×1011cm-2 and the ratio of ID:IG is only 0.85 (ΓG=32.1cm-1)

Effects of Trace Erbium Addition on Microstructure and Mechanical Properties of Ti6Al4V-<i>x</i>Er Alloys

In order to discern the effect of rare earth element Er addition on grain refinement of the most widely used titanium alloy Ti6Al4V, new erbium modified Ti6Al4V alloys with compositions of Ti6Al4V-xEr (x = 0, 0.2, 0.4, 0.6 wt %) were developed and investigated for their microstructural characteristics and mechanical properties in comparison with their unmodified baseline alloy. Microstructural examinations revealed that, by adding Er, (1) the microstructure primarily retained a two-phase structure consisting of &#945; and &#946;, (2) remarkable grain refining occurred, and (3) some Er2O3 and Al2Er disperses were formed largely around the &#946; phase and near the grain boundaries. Mechanical property measurements evidenced an overall enhancement under tension and hardness tests. An increase in both strength and plasticity with increasing Er content was obtained but followed by a drop, while a gradual monotonous improvement in hardness was achieved. The Ti6Al4V-0.2Er alloy exhibits optimal mechanical properties

Research progress on deep learning algorithms to assist 3D tooth segmentation of digital dental models

Three-dimensional tooth segmentation is the segmentation of single-tooth models from a digital dental model. It is an important foundation for diagnosis, planning, treatment and customized appliance manufacturing in digital orthodontics. With the deep integration of artificial intelligence technology and big data from stomatology, the use of deep learning algorithms to assist 3D tooth segmentation has gradually become mainstream. This review summarizes the current situation of deep learning algorithms that assist 3D tooth segmentation from the aspects of dataset establishment, algorithm architecture, algorithm performance, innovation and advantages, deficiencies of current research and prospects. The results of the literature review showed that deep learning tooth segmentation methods could obtain an accuracy of more than 95% and had good robustness. However, the segmentation of complex dental models, operation time and richness of the training database still need to be improved. Research and development of the "consumption reduction and strong core" algorithm, establishment of an authoritative data sample base with multiple centers, and expansion of data application depth and breadth will lead to further development in this field

The first complete chloroplast genome sequence of Lanxangia tsaoko and phylogenetic analysis

Lanxangia tsaoko is a famous Chinese traditional medicine with long history. In this study, the complete chloroplast (cp) genome of L. tsaoko was characterized and assembled using a high-throughput sequencing method. The complete cp genome is 164,008 bp in length, including a large single copy (LSC) region of 89,134 bp and a small single copy (SSC) region of 15,372 bp separated by two inverted repeat (IR) regions of 29,751 bp. A total of 137 genes were identified, including 88 protein-coding genes (PCG), 38 transfer RNA genes, 8 ribosomal RNA genes, and 3 pseudogenes. The phylogenetic analysis revealed that L. tsaoko is located in Zingiberaceace, closely related to Amomum and Alpinia with a 100% bootstrap support