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In this paper, we present an efficient and effective method to predict the pressure dependence and temperature dependence of second-order elastic constants (SOECs) by introducing third-order elastic constants (TOECs) in the monocarbide ultrahigh temperature ceramics. The method is validated by comparing with experiments and previous calculations in four TMCs (TM = Nb, Ti, V, Zr). Using this method, we investigate the derivatives of SOECs against pressure and temperature as well as the anisotropic properties of polycrystalline modulus. In addition, we fit the SOECs with pressure and temperature under the framework of CALPHAD for practice usage.

This study investigates how firms’ social capital affects their access to informal finance. We argue that social capital helps reduce information asymmetry, increase trust between related parties and enforce lending contracts, so it has positive effects on firms’ access to informal finance. Using novel survey data of Chinese private firms, we find that firms with more social capital have more access to informal finance with lower costs. Further tests show that the effect of social capital is more significant when firms are located in regions with less developed market and lower community’s social capital and during the 2008 financial crisis.

Dilute magnetic semiconductors (DMSs), such as (In, Mn)As and (Ga, Mn)As prototypes, are limited to III–V semiconductors with Curie temperatures ( T c ) far from room temperature, thereby hindering their wide application. Here, one kind of DMS based on perovskite niobates is reported. BaM x Nb (1− x ) O 3− δ ( M = Fe, Co) powders are prepared by the composite-hydroxide-mediated method. The addition of M elements endows BaM x Nb (1− x ) O 3− δ with local ferromagnetism. The tetragonal BaCo x Nb (1− x ) O 3− δ nanocrystals can be obtained by Co doping, which shows strong saturation magnetization ( M sat ) of 2.22 emu g −1 , a remnant magnetization ( M r ) of 0.084 emu g −1 and a small coercive field ( H c ) of 167.02 Oe at room temperature. The ab initio calculations indicate that Co doping could lead to a 64% local spin polarization at the Fermi level ( E F ) with net spin DOS of 0.89 electrons eV −1 , this result shows the possibility of maintaining strong ferromagnetism at room temperature. In addition, the trade-off effect between the defect band absorption and ferromagnetic properties of BaM x Nb (1− x ) O 3− δ is verified experimentally and theoretically.

Melting temperature has great influence on the high temperature properties and working temperature limits of ultra-high temperature ceramics (UHTCs) In order to bypass the challenge in the measurement of ultra-high melting points, this paper proposed a novel method to predict UHTCs melting temperature via machine learning. A dataset including more than ten thousand melting temperature data has been established, which covers 8 elements and most of the known non-oxide UHTCs. We built up an element to ceramic system framework by back propagation artificial neural network (BPANN) with the accuracy approaching to 90% and the correlation coefficients approaching to 0.95. Our work provides a probability to get the high accuracy melting temperature of UHTCs, and a more convenient way to develop novel materials with higher working temperature. The given case of melting temperature prediction of Hf-C-N ceramics proves the generality of the artificial neural network (ANN). An inter-validation of melting temperature prediction using our network with materials thermodynamics and density functional theory (DFT) has been demonstrated, indicating that our network is of powerful prediction ability.

What types of entrepreneurs are more likely to ‘stay tuned’ to government policies and does it pay? Integrating work on opportunity recognition and the institution-based view, this study examines t...

In this work, numerical modeling and simulation method was firstly used to obtain the hot-pressing sintering parameter of high entropy alloy (HEA). The finite element model was built to describe the consolidation process. Constitutive relation of powder material was applied assuming that metal powder is a kind of elasto-plastic material with an elliptical yield criterion. The change law of relative density for sintered bulk varying with pressure, time and temperature were obtained. Besides, the flow stress as well as relative density distributions were acknowledged with different sintering time. The simulation results indicate that the HEA would achieve a relative density of more than 95 % if the pressure above 45 MPa at 1150 ℃. The relative density from experiment is well agreement with that of simulation results when the sintering parameter are within the predicted range. This work is of great importance to the study of hot-press sintering of HEA.

The influence of alloying elements on phase stability, elastic and thermodynamic properties of random Nb-Ti-V-Zr high entropy alloys was investigated by virtual crystal approximation (VCA) based on first principles calculation. The lattice constant, elastic constant and thermal expansion coefficient of equimolar NbTiVZr agree well with other calculations and experiments, which indicates that VCA scheme is suitable for random Nb-Ti-V-Zr system. The stable crystal structure was judged by energy criterion, which shows that BCC is the most stable structure except NbxTiVZr(x ≦ 0.4) and NbTiVZrx(x ≧ 1.6). Based on BCC structure, the dependence of elastic stiffness on composition was built using CALPHAD model, which fits well with the value calculated by first principles. Furthermore, the polycrystalline elastic modulus and anisotropy were estimated. In addition, the thermodynamic properties, such as thermal expansion coefficient, as a function of component and temperature were calculated using quasi-harmonic Debyeg-Gruneisen model.

To increase the understanding of entrepreneurship in China and contribute to the view that deregulation facilitates the rapid development of the private sector in transitional economies, we examine the positive relationship between entrepreneurial attention to deregulation (formal institution at the country level) and reinvestment by Chinese private firms. We supplement this main aim by identifying two moderating factors: the entrepreneurs’ political connections (informal institution) and the regional institution development (formal institution at the regional level). We also explore how the interaction of political connections and regional institution development moderate the “entrepreneurial attention to deregulation-reinvestment” link. We find support for our hypotheses from survey data on 3,284 private firms in China. This paper contributes to the research on the relationship between institution and entrepreneurship in general and the association of deregulation and reinvestment in particular by considering two categories of institutional arrangements (formal and informal institutions; national and regional institutions) simultaneously and by exploring the antecedent of reinvestment from a fresh perspective—the attention-based view, highlighting the importance of “noticed” or “perceived” deregulation that influences entrepreneurial decision-making.

The Polar discontinuity at heterointerface and the bare surface reconstructs the electronic phase of perovskite oxides. This gives rise to confined free electrons which intrinsically transit material from band insulator to metal. However, the insulator–metal transition induced by free holes has not been investigated so far due to the challenge in obtaining free hole state in oxides. Here, we propose a simple method whereby free holes can be obtained via polar facet reorientation. In the high polarity case, free holes can be supported by the lift up of O 2p subbands, which split into three independent subbands (one heavy hole subband and two light hole subbands) due to strong quantum confinement. Results show that both of the free electron and hole states are confined in a two dimensional quantum well, subjecting to the confined energy (E − EF) and occupied density of states around the Fermi level, indicating a finite thickness for preserving the metal states.

In this work, we present a software package in Python for high-throughput first-principles calculations of thermodynamic properties at finite temperatures, which we refer to as DFTTK (Density Functional Theory Tool Kit). DFTTK is based on the atomate package and integrates our experiences in the last decades on the development of theoretical methods and computational software. It includes task submissions on all major operating systems and task execution on high-performance computing environments. The distribution of the DFTTK package comes with examples of calculations of phonon density of states, heat capacity, entropy, enthalpy, and free energy under the quasi-harmonic phonon scheme for the stoichiometric phases of Al, Ni, Al3Ni, AlNi, AlNi3, Al3Ni4, and Al3Ni5, and the fcc solution phases treated using the special quasirandom structures at the compositions of Al3Ni, AlNi, and AlNi3., 50 pages, 18 figures

The effect of fabrication methods on microstructures, mechanical properties, and strengthening mechanisms of high-entropy alloys has been systematically studied. In this work, a non-equiatomic Fe0.25CrNiAl medium-entropy alloy (MEA) was selected and fabricated by arc-melting, spark plasma sintering (SPS), and hot-press sintering (HPS). The results indicate that the fabrication method has little effect on the main phase compositions of Fe0.25CrNiAl MEA while marked impacts on microstructures, mechanical properties, and strengthening mechanisms. All alloys mainly consist of a disordered body-centered cubic (BCC) phase and an ordered body-centered cubic (B2) phase. However, the arc-melted alloy possesses a typical dendritic structure, while a speckle-like microstructure for the SPS-ed and HPS-ed alloys. Particularly the grain is refined dramatically by powder metallurgical methods of SPS and HPS. The yield strength of powder metallurgical alloys is over 400 MPa higher than that of arc-melted alloy, and without sacrificing the ductility (~30%). The strengthening mechanism analysis demonstrates that precipitate strengthening plays a significant role for arc-melted alloy while grain boundary strengthening is the dominant strengthening mechanism for powder metallurgical alloys. The Fe0.25CrNiAl MEAs by powder metallurgy achieve a trade-off between high strength and strain-to-failure, which suggests that the method is available for improving the mechanical properties of high-entropy alloys.

In this letter, we study the higher-order effect on the third-order elastic constants (TOECs) of diamond using longitudinal stress-uniaxial strain (LSUS) approach based on density functional theory. The result shows that the higher-order effect on TOECs is not negligible in the shock wave experiments and similar calculations. By taking the higher-order elastic response (up to fifth order) into consideration, the convergence of TOECs against maximum stain gets improved significantly and resolves the discrepancy of several different theoretical methods and experiments., 9 pages, 3 figures, 2 tables

The interfacial properties of graphene/Al composites are of critical important for exploring its high mechanical performance. To improve the mechanical properties, many experimental works have been done in past decades, however, the understanding of their physical mechanisms are limited. Here, the electronic structures and interfacial adhesion properties of pristine/virous deficient graphene(0 0 1)/Al(1 1 1) interfaces are calculated by first-principles method. Results show that single vacancy defective graphene (SVG)/Al interface has larger work of adhesion (Wad) of 5.62 J/m2 than the pristine (Wad of 1.03 J/m2) and other defective graphene/Al interfaces (Wad of 5.12 J/m2 for boron doped single vacancy defective graphene (BVG)/Al and Wad of 5.12 J/m2 for double vacancy defective graphene (DVG)/Al, respectively) due to the strong hybridization of Al-2p and C-2p orbits, which giving rise to the formation of polar covalent bonds with the bond populations of 0.62–0.72 at the deficient site The corresponding interface spacing decreasing from 2.72 A (Pristine Gra/Al) to 2.17 A (SVG/Al). And the defective graphene doped by B atoms could inhibit the interaction between Al and C atoms in the BVG/Al interface. Comparing with the SVG and BVG cases, the interface interaction strength of DVG/Al interface decreases due to the formation of octatomic ring, which could cape the carbon dangling bond and lead to a small structure deformation of graphene. However, it maintains a high Wad of 3.98 J/m2, indicating a better interface bonding strength than idea Gra/Al.

A grain refined FeCrNiAlTi0.2 high entropy alloy (HEA) was firstly produced by powder metallurgy, and the alloy combines well with high strength, good ductility and low cost. The sintered HEA exhibits a major body-centered cubic (BCC) matrix and a minor ordered BCC (B2) phase. The alloy possesses an excellent properties, reaching the yield strength of 1877 MPa and plastic strain of 26.6% at room temperature. Compared with the current FeCrNi-based HEAs, the compressive strength is improved distinctly without sacrificing plastic strain. The analysis of strengthening mechanism suggests that the main strengthening contribution is the grain boundary strengthening.

Bridging both the edges and the center of multicomponent space, which have been widely investigated in traditional alloys and high entropy alloys respectively, is significant but difficult in the design of alloys. In this paper, the single-crystal elastic constant model of the quaternary BCC Nb-Ti-V-Zr system across full composition space was established using first principles combined with the CALPHAD model. The accuracy of the model was confirmed by comparing with previous calculations and experiments. Using the fitted model, the alloying effect on stability and polycrystalline elastic properties of the current research system was analyzed. We find that there exists an area where BCC becomes unstable, and all the instability is caused by breaking C11-C12 > 0. And all of the stable Nb-Ti-V-Zr is ductile. In addition, there lies a surface on which the alloys are completely isotropic in elasticity. Furthermore, some alloys promising in some special aspects are predicted, such as gum metal, directional auxetic properties and biomedical application materials.

Murderers sometimes dispose of bodies in zipped suitcases in an attempt to conceal their crimes. In these cases, the species of insects found and their succession patterns are typically different from those found on exposed corpses due to hindrances or delays in colonization. Here we report a case in which an unidentified female corpse was found in a soft-shell suitcase in a wetland area among some reeds in Guangdong, China on 13 May 2018. The suitcase was unbroken and zippers were well-sealed. The victim was a young woman, naked, and curled up in the suitcase. The insect evidence we collected include (i) pupae and empty puparia of Chrysomya nigripes (Aubertin) (Diptera: Calliphoridae) and Fannia canicularis (Linnaeus) (Diptera, Muscidae), (ii) larvae, pupae and empty puparia of Megaselia scalaris (Loew) (Diptera: Phoridae) and Hermetia illucens (Linnaeus) (Diptera: Stratiomyidae). According to this insect evidence, we estimated the PMImin as 56 days. Bhadra et al. (2014) show that larvae of Calliphora vomitoria (Linnaeus) (Diptera: Calliphoridae) and Calliphora vicina (Robineau-Desvoidy) (Diptera, Calliphoridae) can colonize carcasses concealed in zipped suitcases. Although the size of the zipper (7mm) in this case is larger than that described in Bhadra et al. (4mm), we did not find Chrysomya megacephala (Fabricius) (Diptera: Calliphoridae), Chrysomya rufifacies (Macquart) (Diptera: Calliphoridae), or Lucilia sericata (Meigen) (Diptera: Calliphoridae) which usually colonize fresh corpses in this area. Therefore, we deduced that the victim may have been killed in winter. After the crime was solved, the murderer confessed that he killed the victim on 5 January.