The Influence of Preparation Temperature on the Different Facets of Bulk MgB2 Superconductors.

Two MgB2 samples were prepared using the spark plasma sintering (SPS) technique at different temperatures-950 °C (S1) and 975 °C (S2)-for 2 h under 50 MPa pressure to study the influence of preparation temperature on different facets, namely those perpendicular (PeF) and parallel (PaF) to the compression direction of uniaxial pressure during the SPS of MgB2 samples. We analyzed the superconducting properties of the PeF and PaF of two MgB2 samples prepared at different temperatures from the curves of the critical temperature (TC), the curves of critical current density (JC), the microstructures of MgB2 samples, and the crystal size from SEM. The values of the onset of the critical transition temperature, Tc,onset, were around 37.5 K and the transition widths were about 1 K, which indicates that the two samples exhibit good crystallinity and homogeneity. The PeF of the SPSed samples exhibited slightly higher JC compared with that of the PaF of the SPSed samples over the whole magnetic field. The values of the pinning force related to parameters h0 and Kn of the PeF were lower than those of the PaF, except for Kn of the PeF of S1, which means that the PeF has a stronger GBP than the PaF. In low field, the most outstanding performance was S1-PeF, whose critical current density (JC) was 503 kA/cm2 self-field at 10 K, and its crystal size was the smallest (0.24 µm) among all the tested samples, which is consistent with the theory that a smaller crystal size can improve the JC of MgB2. However, in high field, S2-PeF had the highest JC value, which is related to the pinning mechanism and can be explained by grain boundary pinning (GBP). With an increase in preparation temperature, S2 showed a slightly stronger anisotropy of properties. In addition, with an increase in temperature, point pinning becomes stronger to form effective pinning centers, leading to a higher JC.

Comparative Study on the Densification, Microstructure and Properties of WC-10(Ni, Ni/Co) Cemented Carbides Using Electroless Plated and Coprecipitated Powders.

More and more attention is being paid to the influence of powder mixing on the mechanical properties and corrosion resistance of WC-based cemented carbides. In this study, WC was mixed with Ni and Ni/Co, respectively, by chemical plating and co-precipitated-hydrogen reduction, which are labelled as WC-NiEP, WC-Ni/CoEP, WC-NiCP and WC-Ni/CoCP, respectively. After being densified in a vacuum, the density and grain size of CP were denser and finer than those of EP were. Simultaneously, the better mechanical properties of flexural strength (1110 MPa) and impact toughness (33 kJ/m2) were obtained by WC-Ni/CoCP due to the uniform distribution of WC and binding phase and solid solution enhancement of the Ni-Co alloy. In addition, the lowest self-corrosion current density of 8.17 × 10-7 A·cm-2, a self-corrosion potential of -0.25 V and the biggest corrosion resistance of 1.26 × 105 Ω in 3.5 wt % NaCl solution were obtained by WC-NiEP because of the presence of the Ni-Co-P alloy.

A causal test of the strength of weak ties.

The authors analyzed data from multiple large-scale randomized experiments on LinkedIn's People You May Know algorithm, which recommends new connections to LinkedIn members, to test the extent to which weak ties increased job mobility in the world's largest professional social network. The experiments randomly varied the prevalence of weak ties in the networks of over 20 million people over a 5-year period, during which 2 billion new ties and 600,000 new jobs were created. The results provided experimental causal evidence supporting the strength of weak ties and suggested three revisions to the theory. First, the strength of weak ties was nonlinear. Statistical analysis found an inverted U-shaped relationship between tie strength and job transmission such that weaker ties increased job transmission but only to a point, after which there were diminishing marginal returns to tie weakness. Second, weak ties measured by interaction intensity and the number of mutual connections displayed varying effects. Moderately weak ties (measured by mutual connections) and the weakest ties (measured by interaction intensity) created the most job mobility. Third, the strength of weak ties varied by industry. Whereas weak ties increased job mobility in more digital industries, strong ties increased job mobility in less digital industries.

Phonon Engineering for Thermoelectric Enhancement of p-Type Bismuth Telluride by a Hot-Pressing Texture Method.

Phonon engineering is a core stratagem to improve the thermoelectric performance, and multi-scale defects are expected to scatter a broad range of phonons and compress the lattice thermal conductivity. Here, we demonstrate obviously enhanced thermoelectric properties in Bi0.48Sb1.52Te3 alloy by a hot-pressing texture method along the axial direction of a zone-melted ingot. It is found that a plastic deformation of grain refinement and rearrangement occurs during the textured pressing process. Although the obtained power factor is slightly decreased, a large amount of grain boundaries emerges in the textured samples and dense dislocations are observed around the boundaries and inside the grains. These additional phonon scattering centers can effectively scatter the low- and mid-frequency phonons, and the corresponding lattice thermal conductivity is significantly reduced to only 50% of that of zone-melted samples. Consequently, the maximum figure of merit (ZT) reaches 1.44 at 330 K and the average ZT (300-380 K) reaches 1.38. This study suggests that the simple hot-pressing texture technique is a promising method to significantly optimize the cooling capacity of Bi0.48Sb1.52Te3-based thermoelectric refrigeration.

Dated language phylogenies shed light on the ancestry of Sino-Tibetan.

The Sino-Tibetan language family is one of the world's largest and most prominent families, spoken by nearly 1.4 billion people. Despite the importance of the Sino-Tibetan languages, their prehistory remains controversial, with ongoing debate about when and where they originated. To shed light on this debate we develop a database of comparative linguistic data, and apply the linguistic comparative method to identify sound correspondences and establish cognates. We then use phylogenetic methods to infer the relationships among these languages and estimate the age of their origin and homeland. Our findings point to Sino-Tibetan originating with north Chinese millet farmers around 7200 B.P. and suggest a link to the late Cishan and the early Yangshao cultures.

Anisotropy of Transport Properties Correlated to Grain Boundary Density and Quantified Texture in Thick Oriented Ca3Co4O9 Ceramics.

The misfit-layered Ca3Co4O9 oxide is being seen as a potential thermoelectric (TE) candidate for high-temperature power generation in air. Given the very small size and low strength exhibited by single crystals, grain-oriented Ca3Co4O9 ceramics are worth elaborating to capitalize on their anisotropy. However, the usual textured pellets are too thin to probe the TE properties along their principal crystallographic directions. In this paper, we report on the anisotropy of TE properties in the 350⁻860 K range within thick textured Ca3Co4O9 ceramics fabricated by moderately pressing at 1173 K stacks of pellets primarily textured using spark plasma sintering (SPS), spark plasma texturing (SPT), and hot pressing (HP). The texture was quantitatively assessed, and the influent microstructural parameters were identified, particularly the grain boundary density parallel (GBDc) and perpendicular (GBDab) to the mean c*-axis. We found that the edge-free processing fostered material texturing and (a,b) plane grain growth, thereby dropping GBDab and increasing GBDc. This resulted in a resistivity ρab reduction, leading to a marked enhancement in power factor PFab, which reached 520 µW·m-1·K-2 at 800 K for the HP sample. The anisotropy ρc/ρab was substantially promoted as the texture was reinforced and the GBDc/GBDab ratio increased, with ρc/ρab (HP) > ρc/ρab (SPT) > ρc/ρab (SPS). The Seebeck coefficient S also revealed an anisotropic behavior, with a ratio Sc/Sab >1 for the SPS-processed materials. This behavior was reversed (Sc/Sab <1) for the more textured SPT and HP specimens. It therefore resulted in a PF anisotropy PFc/PFab (HP) < PFc/PFab (SPT) < PFc/PFab (SPS). The PFab/PFc ratio attained 13.6 at 800 K for the thick HP sample, which is the largest ratio recorded thus far on undoped Ca3Co4O9 ceramics.

Wild food plants and fungi used in the mycophilous Tibetan community of Zhagana (Tewo County, Gansu, China).

BACKGROUND: The aim of the study was to investigate knowledge and use of wild food plants and fungi in a highland valley in the Gannan Tibetan Autonomous Region on the north-eastern edges of the Tibetan Plateau. METHODS: Field research was carried out in four neighbouring villages in a mountain valley of the Diebu (Tewo) county, surrounded by spruce forests. The study consisted of 30 interviews with single informants, or group interviews (altogether 63 informants). Apart from collecting voucher specimens, we also identified fungi using DNA barcoding. RESULTS: We recorded the use of 54 species of vascular plants. We also recorded the use of 22 mushroom taxa, which made up the largest category of wild foods. Fruits formed the largest category of food plants, with 21 species, larger than the wild greens category, which consisted of 20 species eaten after boiling or frying and 7 as raw snacks. We also recorded the alimentary use of 10 species of edible flowers and 3 species with underground edible organs. On average, 20.8 edible taxa were listed per interview (median - 21). The most listed category of wild foods was green vegetables (mean - 7.5 species, median - 8 species), but fruits and mushrooms were listed nearly as frequently (mean - 6.3, median - 6 and mean - 5.8, - median 6 respectively). Other category lists were very short, e.g., flowers (mean - 1.3, median - 1) and underground edible parts (mean - 0.7, median - 1). Wild vegetables are usually boiled and/or fried and served as side-dishes, or their green parts are eaten as snacks during mountain treks (e.g., peeled rhubarb shoots). Wild fruits are mainly collected by children and eaten raw, they are not stored for further use. The most widely used wild staple foods are Potetilla anserina roots, an important ceremonial food served on such occasions as New Year or at funerals. They are boiled and served with sugar and butter. The most important famine plants remembered by people are the aerial bulbils of Persicaria vivipara. Flowers are used as children's snacks - their nectar is sucked. CONCLUSIONS: The number of wild taxa eaten in the studied valley is similar to that of other Tibetan areas. The structure of wild food plant taxa is also very typical for Tibetan speaking areas (e.g., the use of rhubarb shoots, Potentilla anserina, Persicaria vivipara). The studied community show a high level of mycophilia.