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The reactor is an extreme environment of high temperature, high pressure, and high radiation dose. Damage accumulates in structural materials over service time. It will eventually lead to material failure, such as hardening, embrittlement, and swelling. The radiation damage accumulation is an inherent, complex, and multiscale process, which has been studied extensively with multiscale modeling and simulation methods. The rapid development of high-performance computing makes it possible to accurately operate multiscale simulation for the microstructure evolution of irradiated reactor materials. The European Union, the USA, and China have put great effort into this, and many related works have been carried out. This paper first outlines the basic application of multiscale modeling and simulation technology in understanding the effects of radiation on reactor structural materials. Then, some relevant projects carried out by the USA, the European Union, and China in recent years are summarized. Next, the paper focuses on three widely used simulation techniques at different scales: molecular dynamics, kinetic Monte Carlo, and cluster dynamics. For each method, some key developments in algorithms and computer implementations are reviewed. Finally, the comparison between them is discussed. [ABSTRACT FROM AUTHOR]

Addressing the low conductivity and porosity of ZIF-67-based oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts is a top priority. Noble metal-free highly active bifunctional catalysts F-N/FeCoNC 900 with three-dimensional interconnected porous structure and high electrical conductivity were successfully prepared by co-doping Fe, F, and N on the precursor ZIF-67. In terms of ORR performance, F-N/FeCoNC 900 has a high onset potential (E onset) of 0.97 V (vs. RHE), a half-wave potential (E 1/2) of 0.87 V (vs. RHE), and an ultimate current density (J L) of 5.7 mA cm−2, superior to commercially available Pt/C (0.95 V, 0.85 V, 5.3 mA cm−2). In addition, F-N/FeCoNC 900 provides high ORR activity with constant 4 electron transfer (n = 3.91–3.99) for methanol resistance and long-lasting stability (initial current retention of 96.32% after 21600 s). In terms of OER performance, F-N/FeCoNC 900 exhibits ultra-low overpotential (273 mV) and ultra-high Faraday efficiency (93%) at constant 4 (n = 3.91–3.99) electron transfer mode. This work provides a new pathway of doped ZIFs-derived composites as efficient bifunctional non-precious metal catalysts. [Display omitted] • Exquisite structure: The F-N/FeCoNC 900 catalyst has the following structural advantages:(a) A unique three-dimensional interconnected hierarchical porous structure is formed, which promotes the diffusion of oxygen and electrolytes and improves the utilization of internal active sites. (b) High specific surface area and high electrochemical active surface area enable highly exposed active centers, while abundant pyridinic nitrogen and graphitic nitrogen content overcome reaction barriers. • The highly efficient synergistic effect between composition and structure: The F-N/FeCoNC 900 catalyst has the following structure-activity relationship: (a) In view of the positive deep synergies among Co, Fe, F, N, and C atoms in the graphite lattice of F-N/FeCoNC 900 catalyst, reflecting F-N/FeCoNC 900 contains higher charge density to have smaller electrochemical impedance. (b) Abundant M-N x species serve as active sites with high structural stability and electrochemical activity. • This work not only delivers a low-cost and high-efficient ORR and OER catalyst, but also offers a new insight to develop a well-organized carbon hybrid electrocatalyst for various energy-related applications. [ABSTRACT FROM AUTHOR]

Radiation-induced defects are the significant cause of radiation damage in austenitic stainless steels. In this work, the interactions between a screw dislocation and stacking fault tetrahedrons (SFTs) are studied in Fe–10Ni–20Cr (a model alloy of austenitic stainless steel) and Ni, using molecular dynamics simulations. Four interaction processes were primarily found, including (1) partial absorption, (2) sheared, (3) bypassing, and (4) restored through double cross-slip. In Fe–10Ni–20Cr alloys, there is almost no correlation between the critical resolved shear stress (CRSS) value and SFT size, but the intersection position largely impacts the results. And the CRSS value decreases with temperature increasing in Fe–10Ni–20Cr. The occurrence of cross-slip has a significant effect on the interactions, and there exist greater CRSS value in the interactions of cross-slipping. Besides, the occurrence of the cross-slip is linked to the stacking fault energy and the distribution of solute atoms of the alloys. [ABSTRACT FROM AUTHOR]

With the increasing fault rate on high-end supercomputers, the topic of fault tolerance has been gathering attention. To cope with this situation, various fault-tolerance techniques are under investigation; these include user-level, algorithm-based fault-tolerance techniques and parallel execution environments that enable jobs to continue following node failure. Even with these techniques, some programs with static load balancing, such as stencil computation, may underperform after a failure recovery. Even when spare nodes are present, they are not always substituted for failed nodes in an effective way. This article considers the questions of how spare nodes should be allocated, how to substitute them for faulty nodes, and how much the communication performance is affected by such a substitution. The third question stems from the modification of the rank mapping by node substitutions, which can incur additional message collisions. In a stencil computation, rank mapping is done in a straightforward way on a Cartesian network without incurring any message collisions. However, once a substitution has occurred, the optimal node-rank mapping may be destroyed. Therefore, these questions must be answered in a way that minimizes the degradation of communication performance. In this article, several spare node allocation and failed node substitution methods will be proposed, analyzed, and compared in terms of communication performance following the substitution. The proposed substitution methods are named sliding methods. The sliding methods are analyzed by using our developed simulation program and evaluated by using the K computer, Blue Gene/Q (BG/Q), and TSUBAME 2.5. It will be shown that when failures occur, the stencil communication performance on the K and BG/Q can be slowed around 10 times depending on the number of node failures. The barrier performance on the K can be cut in half. On BG/Q, barrier performance can be slowed by a factor of 10. Further, it will also be shown that almost no such communication performance degradation can be seen on TSUBAME 2.5. This is because TSUBAME 2.5 has an Infiniband network connected with a FatTree topology, while the K computer and BG/Q have dedicated Cartesian networks. Thus, the communication performance degradation depends on network characteristics. [ABSTRACT FROM AUTHOR]

The matrix–matrix products for matrices of small size have continued to play an important part in a range of scientific applications. The heterogeneous architecture, which is predicted to be a trend in the exascale supercomputing era, gives rises to the challenges of porting and optimizing small matrix products. We present a method to accelerating and tune small matrix multiplications on Sunway TaihuLight supercomputer, which has been titled as the most powerful supercomputer four times in the Top5000 list. Sunway TaihuLight is equipped with Shen-Wei hybrid manycore processors. We use Nek5000 as a case study to demonstrate our methods. Nek5000 is an open-source computational fluid dynamics (CFD) solver based on the spectral element method (SEM) for incompressible flow. The high-order SEM method, of which the computation kernel is small dense matrix products, is regarded to have the potential to overcome constraints of standard CFD software. By optimizing using vectorization, we gained about 30% performance improvement on management processing element. We accelerated Nek5000 using computing processing elements (CPEs). The experiments results suggest that employing 32 CPEs delivers the best performance enhancements. We scaled Nek5000 to 16,384 core groups with 540,672 cores, reaching about 30% performance improvements. [ABSTRACT FROM AUTHOR]

In this article, we study the I/O performance of the Santos Dumont supercomputer, since the gap between processing and data access speeds causes many applications to spend a large portion of their execution on I/O operations. For a large-scale expensive supercomputer, it is essential to ensure applications achieve the best I/O performance to promote efficient usage. We monitor a week of the machine's activity and present a detailed study on the obtained metrics, aiming at providing an understanding of its workload. From experiences with one numerical simulation, we identified large I/O performance differences between the MPI implementations available to users. We investigated the phenomenon and narrowed it down to collective I/O operations with small request sizes. For these, we concluded that the customized MPI implementation by the machine's vendor (used by more than 20% of the jobs) presents the worst performance. By investigating the issue, we provide information to help improve future MPI-IO collective write implementations and practical guidelines to help users and steer future system upgrades. Finally, we discuss the challenge of describing applications I/O behavior without depending on information from users. That allows for identifying the application's I/O bottlenecks and proposing ways of improving its I/O performance. We propose a methodology to do so, and use GROMACS, the application with the largest number of jobs in 2017, as a case study. [ABSTRACT FROM AUTHOR]

This article discusses scheduling strategies for the problem of maximizing the expected number of tasks that can be executed on a cloud platform within a given budget and under a deadline constraint. The execution times of tasks follow independent and identically distributed probability laws. The main questions are how many processors to enroll and whether and when to interrupt tasks that have been executing for some time. We provide complexity results and an asymptotically optimal strategy for the problem instance with discrete probability distributions and without deadline. We extend the latter strategy for the general case with continuous distributions and a deadline and we design an efficient heuristic which is shown to outperform standard approaches when running simulations for a variety of useful distribution laws. [ABSTRACT FROM AUTHOR]

Hybrid density-functional calculation is one of the most commonly adopted electronic structure theories in computational chemistry and materials science because of its balance between accuracy and computational cost. Recently, we have developed a novel scheme called NAO2GTO to achieve linear scaling (Order-N) calculations for hybrid density-functionals. In our scheme, the most time-consuming step is the calculation of the electron repulsion integrals (ERIs) part, so creating an even distribution of these ERIs in parallel implementation is an issue of particular importance. Here, we present two static scalable distributed algorithms for the ERIs computation. Firstly, the ERIs are distributed over ERIs shell pairs. Secondly, the ERIs are distributed over ERIs shell quartets. In both algorithms, the calculation of ERIs is independent of each other, so the communication time is minimized. We show our speedup results to demonstrate the performance of these static parallel distributed algorithms in the Hefei Order-N packages for ab initio simulations. [ABSTRACT FROM AUTHOR]

The chimera grid methods have been widely used in the simulation of flow over complex configurations and unsteady moving boundary process. Lee and Baeder presented the implicit hole cutting (IHC) method, which improves the practicability and robustness of chimera grid method. But the excessive time consumption of this method restricts the scalability of parallelism. In this article, based on the parallel implementation of IHC method with structured multi-block grid, the factors which restrict the performance and efficiency are analyzed. Cartesian auxiliary grid is introduced to reduce the communication and computing cost. Finally, test cases are presented to demonstrate the effectiveness of this algorithm, and the calculation and data communication are reduced on the premise of maintaining accuracy. [ABSTRACT FROM AUTHOR]

Power draw is a complex physical response to the workload of a given application on the hardware, which is difficult to model, in part, due to its variability. The empirical mode decomposition and Hilbert–Huang transform (EMD/HHT) is a method commonly applied to physical systems varying with time to analyze their complex behavior. In authors' work, the EMD/HHT is considered for the first time to study power usage of high-performance applications. Here, this method is applied to the power measurement sequences (called here power traces) collected on three different computing platforms featuring two generations of Intel Xeon Phi, which are an attractive solution under the power budget constraints. The high-performance applications explored in this work are codesign molecular synamics and general atomic and molecular electronic structure system—which exhibit different power draw characteristics—to showcase strengths and limitations of the EMD/HHT analysis. Specifically, EMD/HHT measures intensity of an execution, which shows the concentration of power draw with respect to execution time and provides insights into performance bottlenecks. This article compares intensity among executions, noting on a relationship between intensity and execution characteristics, such as computation amount and data movement. In general, this article concludes that the EMD/HHT method is a viable tool to compare application power usage and performance over the entire execution and that it has much potential in selecting most appropriate execution configurations. [ABSTRACT FROM AUTHOR]

The ever-increasing computational requirements of HPC and service provider applications are becoming a great challenge for hardware and software designers. These requirements are reaching levels where the isolated development on either computational field is not enough to deal with such challenge. A holistic view of the computational thinking is therefore the only way to success in real scenarios. However, this is not a trivial task as it requires, among others, of hardware–software codesign. In the hardware side, most high-throughput computers are designed aiming for heterogeneity, where accelerators (e.g. Graphics Processing Units (GPUs), Field-Programmable Gate Arrays (FPGAs), etc.) are connected through high-bandwidth bus, such as PCI-Express, to the host CPUs. Applications, either via programmers, compilers, or runtime, should orchestrate data movement, synchronization, and so on among devices with different compute and memory capabilities. This increases the programming complexity and it may reduce the overall application performance. This article evaluates different offloading strategies to leverage heterogeneous systems, based on several cards with the first-generation Xeon Phi coprocessors (Knights Corner). We use a 11-point 3-D Stencil kernel that models heat dissipation as a case study. Our results reveal substantial performance improvements when using several accelerator cards. Additionally, we show that computing of an approximate result by reducing the communication overhead can yield 23% performance gains for double-precision data sets. [ABSTRACT FROM AUTHOR]

Irradiation induced dislocation loops in Fe-based alloys can cause material hardening by impeding the mobility of dislocation. Using molecular dynamics (MD), the interaction between 1 / 2 < 1 1 1 > { 1 1 ¯ 0 } edge dislocation (ED) and 1/2<1 1 1> interstitial dislocation loops with Burgers vector (BV) along different directions in BCC (body centered cubic)-Fe were investigated, and the influence of interaction geometry (means the relative position between dislocation glide plane (GP) and loop equator plane) on the CRSS (critical resolved shear stress) for dislocation to move again induced by loops was analyzed. It was found that the pinning strength of 1/2<1 1 1> loop was estimated to be 0.2–0.8, varying with the BVs direction of loops and the interaction geometries. The present study clearly showed that when parameterizing the dislocation dynamics, more interaction geometries should be considered in order to get a more quantitative pinning strength. [ABSTRACT FROM AUTHOR]

Reactor pressure vessel (RPV) of pressurized water reactor undergoes severe neutron irradiation during normal operation and life-extension phase, thus leading to the formation of numerous nanometric irradiation-accelerated and irradiation-induced solute-enriched clusters among the ferritic matrix, including so-called late blooming phases (LBP), which was believed as Mn-Ni-Si enriched stable precipitates to emerge lately and grow rapidly and show great threat to the mechanical performance of RPV steels. However, the mechanism of nucleation and growing for LBP remains not in light, especially the effect of inherent defects such as dislocation and grain boundary on that. We investigated the atomic configurations of Fe-Cu, Fe-Mn, Fe-Ni, Fe-Mn-Ni, Fe-Mn-Cu, Fe-Ni-Cu and Fe-Mn-Ni-Cu as RPV model alloys at 600 K, implemented firstly by constructing an enough big simulation box containing edge dislocation and random-distributed alloy atoms and secondly evolving to equilibrium status after essential simulation steps with Metropolis Monte Carlo (MMC) method. The number of clusters, average solute numbers contained in each cluster and the volume atomic fraction of all clusters were characterized, as well as the structure of typical big clusters among simulation analyzed. [ABSTRACT FROM AUTHOR]

A kind of Co-N-C catalysts with hollow core-shell structures with large amount of carbon nano tubes (CNTs) growing on the surface were prepared, using polystyrene (PS) spheres as sacrificial templates, ZIF-8 @ZIF-67 as Co-N-C source and PVP as binder, and their performances in oxygen reduction reaction (ORR) were further explored. The electrochemical test results show that the prepared electrocatalyst Co/NHCNT-160 has good catalytic activity for ORR process and a nearly four-electron reaction path. Co/NHCNT-160 has long-term stability at high onset potential (0.955 V), half-wave potential (0.88 V) and limiting current density (6.3 mA cm−2), with a current retention rate of 99.7 % after 7 h. The ORR performance of Co/NHCNT-160 has surpassed that of commercially available Pt/C catalyst and most of the non-precious metal catalysts reported to date. Its excellent ORR catalytic performance is mainly due to its unique hollow core-shell structure and the abundance of CNTs spawned, the high degree of graphitization facilitating electron migration, the graded pores facilitating mass migration, and the functionalization of the Co-Nx active site with a highly dispersed carbon backbone. This catalyst preparation strategy will provide some ideas for the development of other ZIF-based ORR catalysts for energy storage and electrochemical devices. [Display omitted] [ABSTRACT FROM AUTHOR]

The integrated processes of Shenmu subbituminous coal pyrolysis and CO2reforming of methane over catalyst (Ni/SiO2) with and without using dielectric barrier discharge plasma (ICCP and ICCC) were carried out to check the effectiveness of the integrated process on improving the tar yield of coal pyrolysis. The effects of the pyrolysis temperature and time on product yields were investigated. The results indicate that both the ICCC and ICCP have an effect on increasing the tar yield compared with coal pyrolysis under N2or H2. The tar yield increases with the increase of pyrolysis temperature and time in the ICCC, while relatively lower pyrolysis temperature and shorter pyrolysis time is preferable in the ICCP. The highest tar yield is 24.8 wt% at 600°C for 22 min in the ICCC and that is 23.7 wt% at 500°C for 7 min in the ICCP. [ABSTRACT FROM PUBLISHER]

A modified model based on kinetic rate theory is presented to simulate the dose dependence of defects nucleation and growth in reduced-activation ferritic/martensitic (RAFM) steel under helium ion irradiation by considering the motion of dislocation loops. The modeling results are compared with the transmission electron microscopy (TEM) experiments. The TEM analysis shows that the mean size of dislocation loops increases with the increasing atomic displacement damage dose, while the density of the observed loops exhibits minor change. To investigate the evolution of dislocation loops, we compare two cases incorporating mobile and immobile interstitial clusters in our modified model, respectively. The calculated results reveal a good agreement with experiments in the case of considering mobile interstitial clusters. It is included the motion of interstitial clusters plays an important role in the evolution of dislocation loops in RAFM steel. [ABSTRACT FROM AUTHOR]

Abstract: In present work, the irradiation damage in nickel-base alloy C-276 irradiated with Ar-ions was studied. Specimens of C-276 alloy were subjected to an irradiation of Ar-ions (with 120keV) to dose levels of 6 and 10dpa at 300 and 550°C, respectively. The size distributions and densities of dislocation loops caused by irradiation were investigated with transmission electron microscopy. Irradiation hardening due to the formation of the loops was calculated using the dispersed barrier-hardening model, showing that irradiation hardening was greatest at 300°C/6dpa. The microstructure evolution induced by Ar-ion irradiation (0–10dpa) in nickel-base alloy C-276 has been studied using a multi-scale modeling code Radieff constructed based on rate theory, and the size of dislocation loops simulated by Radieff was in good agreement with the experiment. [Copyright &y& Elsevier]

Abstract: A LiD assembly was proposed to produce fusion neutrons from thermal neutrons in D2O region of the China Advanced Research Reactor (CARR). The transportation of produced fusion neutrons in the LiD assembly can obtain the fusion neutron flux in its central hole. The neutron flux and the distribution of 6Li(n,α) reaction rate in the LiD assembly were calculated by a computer simulation method with MCNP code. The calculation results show that the fusion neutron flux in the central hole of LiD assembly, , is dependent on the size and structure of assembly, 6Li enrichment, tritium concentration in LiD rods and the physical state of LiD. In the case of LiD rods containing 5% tritium and 6Li enrichment 20%, value reaches to 5.4×1013 cm−2 s−1, when the assembly was placed at the thermal neutron flux about 8.0×1014 cm−2 s−1 in CARR. [Copyright &y& Elsevier]

Computer-based simulation has been playing an indispensable role in the engineering fields, such as materials, thermal fluids, energy systems, mechanics, and aerodynamics. Supported by the continuously grown high-performance computing resources, simulation nowadays leverages high-order accuracy numerical methods, accurate models, and mesh technologies. In "A Parallel Algorithm for Chimera Grid with Implicit Hole Cutting Method", Xiaodong Hu et al. introduce the concept of a Cartesian Auxiliary Grid to parallelize and enhance the efficiency of the implicit hole cutting method in Chimera computational fluid dynamics (CFD) calculations. [Extracted from the article]

• The interaction between 27 transition metals, O and vacancy in Mo are implemented by first-principles calculations. • The interaction between solute and O can be accurately separated into elastic and chemical contribution. • Simonovic's model indicates dilute TMS atoms can capture O and inhibit the enrichment of O in Mo. • Solute Sc, Ti, Zr, Hf, and Ta can be the top priority to inhibit O segregation and embrittlement in Mo alloys. The trapping effect of solute on oxygen (O) can be benefit for inhibiting its segregation and embrittlement at the GBs in Mo alloys. In this work, the interaction between solutes (including 27 transition metals), interstitial O and vacancy in Mo are implemented by first-principles calculations, and their trapping effects on O are evaluated by Simonovic's model. Single transition metal solute (TMS) has a strong attraction for O, and it is strengthened by the second solute for all 3 d , oversized 4 d and 5 d series. Furthermore, there is a significant synergistic effect between solute, vacancy, and oxygen for oversized solutes, i.e., the binding energy between solute atom (vacancy) and oxygen atoms is enhanced by the presence of vacancy (solute). The distribution of oxygen indicates that oxygen can be captured by dilute TMS atoms, and more oxygen atoms will be trapped as the solute concentration increases in Mo. Based on our extensive calculations, Sc, Ti, Zr, Hf, and Ta can be the top priority for suppressing the segregation and embrittlement of O in Mo alloys. It is interesting that the interaction between solute and O can be accurately separated into elastic and chemical contributions though delicate calculation, and the counterintuitive strong binding effect of fifth-nearest solute-O pairs for undersized 4 d and 5 d elements is owning to the chemical contribution driven by Coulomb interaction. [ABSTRACT FROM AUTHOR]

Development of low-cost and high-efficient oxygen reduction reaction (ORR) catalyst is a crucial challenge in fuel cell technology. Herein, we proposed a simple and scalable strategy to fabricate an interconnected 3D Fe 3 O 4 /rGO composite, in which Fe 3 O 4 nanoparticles mechanically anchor in reduced graphene oxide (rGO). Benefiting from its 3D layered structure with loose skeleton and rich porosity, and strong synergetic coupling between Fe 3 O 4 nanoparticles and rGO, the prepared composite, Fe 3 O 4 /rGO, provides better catalytic performance for ORR compared with commercial Pt/C catalyst, featuring high limiting current density (4.6 mA cm−2) close to that of Pt/C (4.7 mA cm−2), low H 2 O 2 yield (1%–6%), high electron transfer number (∼4), and outstanding long-term durability and methanol resistance in alkaline electrolytes. These encouraging results manifest that the Fe 3 O 4 /rGO composite holds great promise as a low-cost and high-performance alternative catalyst for ORR. • Simple and effective method to prepare 3D structured Fe 3 O 4 /rGO as ORR catalyst. • Fe 3 O 4 /rGO has a 3D layered structure with loose skeleton and rich porosity. • Fe 3 O 4 with an average particle size of about 20 nm uniformly anchored on graphene. • Fe 3 O 4 /rGO shows similar catalytic activity and better stability compared with Pt/C. [ABSTRACT FROM AUTHOR]

Insulating interlayer between nanoparticles and polymer matrix is crucial for suppressing the dielectric loss of polymer composites. In this study, titanium carbide (TiC) particles were surface modified by polydopamine (PDA), and the obtained PDA@TiC powders were used to reinforce thermoplastic polyurethane (TPU). The results indicate that the PDA@TiC were homogenously dispersed in the matrix compared with the pristine TiC, and that the PDA@TiC/TPU composites show improved dielectric and mechanical properties, i.e., much lower dissipation factors and obviously enhanced dielectric breakdown strength, as well as higher tensile strength and elongation at break as compared to the raw TiC/TPU. The nanoscale PDA interlayer contributes to the dielectric and mechanical enhancements because it not only serves as an insulating shell that prevents TiC particles from direct contacting and suppresses the loss and leakage current to very low levels, but also enhances the interfacial interactions thereby leading to improved mechanical strength and toughness. The prepared flexible PDA@TiC/TPU with high permittivity but low loss will find potential applications in electronic and electrical applications. [ABSTRACT FROM AUTHOR]

17-4PH martensitic steel is usually used as valve stems in nuclear power plants and it suffers from thermal aging embrittlement due to long-time service in a high-temperature and high-pressure environment. Here, we characterized the evolution of microstructures at the nano-scale in 17-4PH steel by in situ small-angle neutron scattering (SANS) with a thermo-mechanically coupled loading device. The device could set different temperatures and tensile so that an in situ SANS experiment could dynamically characterize the process of nanoscale structural changes. The results showed that with increasing thermal aging time, the ε-Cu phase precipitates and grows as the temperature is 475 °C and 590 °C, and the ε-Cu phase is spherical at 475 °C but became elongated cylinders at 590 °C. Moreover, the loading stress could aid in the growth of the ε-Cu phase at 475 °C. [ABSTRACT FROM AUTHOR]

Uranium is an important strategic metal widely applied in the nuclear industry. Using first-principles calculations, we investigated the plane slip properties, anisotropy, and bonding characteristics between atoms of α -uranium. We found that the DFT+ U has limited effect on elastic constants and the generalized stacking fault energy of α -uranium, although it includes 5 f electrons. Then we calculated the elastic constants and shear deformation properties using standard DFT, and found that the energy barrier of plane slip of α -uranium is arranged from high to low as: (010)[001] > (100) [ 010 ] > (100)[001] > (001) [ 010 ] > (001) [ 100 ] > (010)[100], which perfectly supports the assumption of wrinkled quasi-atomic planes. At last, electronic structure calculations reveal that the wrinkled strong quasi-atomic planes are composed of metallic bonds with partial covalent character. [ABSTRACT FROM AUTHOR]

Rate theory (RT) is a commonly used method to simulate the evolution of material defects. A promising numerical method, exponential time difference (ETD), can reduce the stiff RT equations to explicit ordinary differential equations (ODEs). Previous implementations of ETD on the "Sunway TaihuLight" supercomputer suffer from high computation cost and poor parallel efficiency while solving a large amount of ODEs. This paper improves the algorithm with hybrid MPI+SIMD and additional instruction-level optimizations by taking advantage of the architecture of "Sunway TaihuLight". The execution time of a single iteration is reduced by about 40%. Scaling from 64 to 4096 processes, the parallel efficiency of the new algorithm achieves 33.5% and 50.6% in strong and weak scalability, which corresponds to 21.4 and 32.4 in speedup, respectively. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a new process to integrate methane aromatization over Mo/HZSM-5 catalyst with coal pyrolysis was put forward for improving tar yield. Shenmu coal was used to confirm the validity of the process. The effects of pyrolysis temperature, CH4 flow rate, Mo loading on the tar, water and char yields were investigated in an atmospheric fixed-bed reactor containing upper catalyst layer and lower coal layer. The results show that the tar yield can be improved by integrating the coal pyrolysis with methane aromatization. The tar yield is 21.5wt.% (daf) under the optimum conditions of 700°C pyrolysis temperature, 25ml/min CH4 flow rate, 4wt.% Mo loading and 30min holding time, obviously higher than 14.6% in N2 atmosphere and 15.3% in H2 atmosphere. Further studies confirm the synergistic effect between the coal pyrolysis and methane aromatization. [Copyright &y& Elsevier]

This research revealed the irradiation hardening mechanism in two novel NbZrTiV and VNbMoTaWTi refractory high entropy alloys (RHEAs). The RHEA sample irradiated by a dual-beam of 0.5 MeV protons and 2 MeV He ions at 300 K. Irradiation-induced defects were characterized by transmission electron microscope (TEM). It was discovered that the defect clusters were mostly consisted of nano-sized dislocation loops and bubbles. The density of defects was higher in the peak region than in the plateau region for both irradiated samples. The effects of irradiation-induced defects on hardening were evaluated by the nanoindentation test and dispersed barrier hardening (DBH) model. The results show that the peak region contributes more to the hardening than the plateau region in both irradiated alloys. The DBH hardness increments agree well with those measured by nanoindentation. Dual-beam irradiation led to ∼14% hardening for NbZrTiV and ∼ 18% for VNbMoTaWTi. The effects of the chemical disorder and lattice distortion induced by compositional complexity on defect formation and hardening were discussed. The excellent irradiation resistance makes RHEAs to be potential candidate materials used as core component in advanced nuclear reactors. • The irradiation effects of two novel BCC RHEAs were studied. • The relationship between irradiation hardening and irradiation-induced defects was established. • The mechanism of compositional complexity on irradiation tolerance of BCC RHEAs was discussed. [ABSTRACT FROM AUTHOR]

U-10Zr metallic fuel (alloys of U with 10 wt% Zr) is considered as a potential candidate for fast reactors due to its excellent performance. However, the fission gas swelling has a significant impact on its properties and prevents it from reaching higher burnup. To gain a deeper understanding of the fission gas swelling mechanism, molecular dynamics simulations based on interatomic potentials are underway to fill the key knowledge gaps. In this work, two modified embedded-atom method (MEAM) potentials are developed for the U-Zr system with Xe, one for α-U-Zr and δ-UZr 2 , and the other for γ-U-Zr. The parameters of the potentials are determined by fitting the material properties from experiments or density functional theory (DFT) calculations. It is verified that the potentials can reproduce well the lattice constants, elastic constants, point defects, surface energy, and the melting point of U. In addition, the lattice constants, elastic constants, cohesive energy, and point defect formation energy of Zr are in good agreement with the experimental and DFT results. For the alloy system, the typical defect properties of Zr and Xe in U, as well as the formation energy and elastic constant of δ-UZr 2 are close to the DFT. The lattice constant, linear thermal expansion, and mixing enthalpy of γ-U-Zr alloy are following the experimental values. The results show that the obtained potentials are suitable for simulating the defect evolution and Xe behaviors in the U-Zr system. [ABSTRACT FROM AUTHOR]

Abstract: Activated carbons (ACs) are of good potential to be the catalysts for methane decomposition to produce hydrogen without CO and CO2. Coal liquefaction residue (CLR) seems to be a promising precursor for ACs. In this work, several types of ACs were prepared by KOH activation from Shenhua CLR with addition of SiO2 or SBA-15. The catalytic activity and stability for methane decomposition were investigated and compared with commercial coal-based AC and carbon black (BP2000). The results show that the prepared ACs have larger surface area, narrower pore distribution, and higher catalytic activity than those directly prepared by KOH activation, and are superior to the commercial carbons. The increased microporosity resulting from the soluble salts formed by the reaction between the additive and KOH is responsible for the high catalytic activity. [Copyright &y& Elsevier]

Abstract: A novel plasma-treated Ni/MgO catalyst was prepared by treating coprecipitated NiCO3–MgCO3 with dielectric-barrier discharge plasma. The results by XRD, TEM and N2 adsorption analyses showed that the plasma-prepared Ni/MgO catalyst possessed smaller particle size, enhanced nickel dispersion, and higher specific surface area than a conventionally reduced Ni/MgO catalyst. The plasma-prepared Ni/MgO catalyst also exhibited better catalytic activity for carbon dioxide reforming of methane. More than 20% higher conversions of methane and carbon dioxide were obtained than those over the conventional Ni/MgO catalyst at 700°C and a space velocity of 96,000mL/(h∙gcat). [Copyright &y& Elsevier]

The vacuum electron beam welding (EBW) properties of Mo-14Re alloys were studied in this work. The weld morphology and microstructure were observed by optical microscope (OM) and scanning electron microscope (SEM). By using 3D Measuring Laser Microscope, energy dispersive spectroscopy (EDS), electronic probe micro analysis (EPMA) and transmission electron microscope (TEM), the weld pore was further characterized. In addition, its formation mechanism was analyzed. The results showed that the grains in fusion zone (FZ) of the powder metallurgy (PM) alloy weld obviously grew up to about 226.6 ± 75.7 μm and there were a large number of 12∼80 μm spherical pores. The element oxygen was enriched in the pores and a layer of MoO 2 was formed on the surface. The formation of pores may be closely related to the micropores and high oxygen content in the materials. Under the strong stirring of the molten pool, the generated carbon monoxide (CO) and molybdenum monoxide (MoO) bubbles couldn't escape and remained in the weld to form pores. However, no pores were found in the melted alloy weld. It was difficult to generate bubbles by homogeneous nucleation for the melted alloy. Due to the grain coarsening, the microhardness value of the weld significantly decreased. • Some pores with a size of 12∼80 μm were found in the powder metallurgy alloy weld. • A layer of MoO 2 was formed on the weld pore surface. • It is deduced that the CO and MoO bubbles were generated in the weld pool. • The grains in the weld were coarsened and the microhardness was obviously reduced. [ABSTRACT FROM AUTHOR]

The main problem hindering the application of uranium-zirconium (U-Zr) fuel is the swelling caused by the generation of fission gas. In this study, investigating the behavior of fission gas xenon (Xe) in δ-UZr 2 using the first-principles method is the focus. The formation energies of substitutional and interstitial Xe atoms are significantly dependent on the local atomic environment. According to the present study, the Xe formation energy increases as the number of coordinated U atoms increases. δ-UZr 2 exhibits a more remarkable ability to capture Xe than α-U due to the lower Xe formation energies. In addition, the interstitial Xe energetically prefers to occupy octahedral sites or form a dumbbell with a metallic atom at the 2d site along the 〈0001〉 direction. The diffusion of interstitial Xe also relies on the local environment, while Zr-rich conditions can enhance it. Compared with α-U, Xe atoms energetically preferers to form clusters in δ -UZr2 [ABSTRACT FROM AUTHOR]

The first-principles calculation and the evaluation of transport kinetics indicate that solutes Si and P can both welcome vacancies and self-interstitial atoms, promote vacancy diffusion at low temperature. Therefore, their addition to austenitic steels should be potentially beneficial to enhance recombination rates of vacancy and self-interstitial atoms, drop of net defect concentrations and result in a reduction of the rates of void growth under irradiation. [Display omitted] • In this work, the solute properties of Si and P, their interaction with point defect, vacancy-mediated migration energies were obtained through first-principles calculations, and the diffusion behavior of solutes and vacancies are evaluated by both methods by solving the Onsager matrix. • The solution energies of Si and P in the antiferromagnetic (0 0 1) double-layer with face-centered tetragonal structure (fct_afmD) Fe imply their relative high solubility. • Vacancies can be attracted by Si and P at 1NN sites with the binding energies of 0.12 ∼ 0.19 eV, and 0.30 ∼ 0.42 eV, respectively. • The vacancy wind and the ratio of tracer diffusion coefficient demonstrate that Si and P will be dragged by vacancy, diffuse faster than that of Fe, and strongly promote vacancy diffusion at low temperature while they have weak inhibition at high temperature. • Simultaneously, as a function of temperature, compared to the phenomenological Manning method, the results of the Green-function method generally exhibit a left shift. The addition of silicon (Si) and phosphorus (P) to austenitic stainless steel is observed to reduce swelling, but the inhibition mechanism has not been well understood. In this work, the solute properties of Si and P, their interaction with point defect, vacancy-mediated migration energies were obtained through first-principles calculations, and the diffusion behavior of solutes and vacancies are evaluated by both methods by solving the Onsager matrix. The solution energies of Si and P in the antiferromagnetic (0 0 1) double-layer with face-centered tetragonal structure (fct_afmD) Fe imply their relative high solubility. Vacancies can be attracted by Si and P at 1NN sites with the binding energies of 0.12 ∼ 0.19 eV, and 0.30 ∼ 0.42 eV, respectively. The vacancy wind and the ratio of tracer diffusion coefficient demonstrate that Si and P will be dragged by vacancy, diffuse faster than that of Fe, and strongly promote vacancy diffusion at low temperature while they have weak inhibition at high temperature. Simultaneously, as a function of temperature, compared to the phenomenological Manning method, the results of the Green-function method generally exhibit a left shift. Furthermore, Si and P are also found to attract the self-interstitial atoms (SIAs). Our results indicate that solutes Si and P can both welcome vacancies and SIAs, promote vacancy diffusion at low temperature, in which the effect of P is much stronger than that of Si. Therefore, their addition to austenitic steels may be beneficial to enhance recombination rates of vacancy and SIAs, drop of net defect concentrations and result in a reduction of the rates of void growth under irradiation. [ABSTRACT FROM AUTHOR]

A relative contribution to irradiation hardening caused by dislocation loops and solute-rich precipitates is established for RPV steels of WWER-440 and WWER-1000 reactors, based on TEM measurements and mechanical testing at reactor operating temperature of 563 K. The pinning strength factors evaluated for loops and precipitates are shown to be much lower than those obtained for model alloys based on the room temperature testing as well as those evaluated by means of atomistic simulations in the temperature range of 300–600 K. This discrepancy is explained in the framework of a model of thermally activated dislocation motion, which takes into account the difference in temperature and strain rate employed in atomistic simulations and in mechanical testing. [ABSTRACT FROM AUTHOR]

The uranium zirconium (U-Zr) metallic nuclear fuel has long been considered as a promising candidate fuel type for fast breeder reactors. One of the key performance issues of the U-10Zr metallic fuel is its rather strong swelling, which would lead to significant fuel cladding mechanical interaction (FCMI) at relatively high fuel burn-ups. It is therefore imperative to understand the fuel swelling behaviors and the underlying physics mechanisms. Recently published experimental results of U-10Zr fuel swelling behaviors in a low temperature regime (400-600K) showed perceivable swelling of the in-pile irradiated fuel. However, the underlying physics mechanism behind this swelling is not clear. In this work, we performed in-depth analyses on the microstructural features of the irradiated fuel with metallography and conducted a finite-element based simulation on a computational platform, COMSOL, to determine the hydrostatic stress in the irradiated fuel. The spherical objects in the metallography result have been identified as cavities with relatively low fission gas pressure instead of equilibrium gas bubbles. A rate theory code based on the cavitational void swelling model has been developed and the fuel swelling behaviors of U-10Zr fuel in the low temperature regime have been assessed. The simulation results suggest a much lower migration energy for vacancy diffusion in the metallic fuel compared to what is currently used, and a new set of key parameters for the rate theory model were determined. [ABSTRACT FROM AUTHOR]

• A core-shell ZIF-8@ZIF-67 derived route was synthesized by CoNHPC ORR electrocatalysts. • The carbonation temperature affected the performance of CoNHPC-920. • The CoNHPC-920 could catalyze ORR via a direct 4e- pathway. • Unique hollow polyhedral structure gives CoNHPC-920 excellent ORR activity. [Display omitted] The rational design and construction of non-precious metal-based electrocatalysts with high activity and stability toward oxygen reduction reactions (ORR) are essential but challenging. In this work, a novel hybrid nanoporous structure of Co nanoparticles uniformly embedded in hollow porous carbon doped with nitrogen (CoNHPC) was constructed by a melt-evaporation-pyrolysis method, in which NaCl is utilized as an auxiliary template. The introduction to NaCl in this process served as the confining template to prevent nitrogen loss and promote graphitization, and the intercalating agent to form a mesoporous product. Due to the composite hierarchical porous structure, higher graphitization degree, and desirable nitrogen bonding type, the as-prepared CoNHPC-920 presents outstanding ORR electrocatalytic activity in terms of a half-wave potential of 0.87 V (vs. RHE) and onset potential of 0.97 V (vs. RHE). The composite material also shows higher selectivity and outstanding durability with most transition metal porous carbon materials reported. The strategy proposed in this study may provide ideas about metal nitrogen-carbon type catalysts enriched with carbon nanotubes and bare leaky hollow structures of the construction of advanced ORR electrocatalysts, opening up a new pathway. [ABSTRACT FROM AUTHOR]

• A facile epitaxial growth-pyrolysis tactic is proposed. • Highly porous and hollow non-noble metal carbon nanoarchitecture has been constructed. • The N-rich carbon protective layers embedded with cobalt nanoparticles boost the stability of the catalyst. • The Co@N-CNT-HC shows superior electrocatalytic activity for ORR. Fuel cells have emerged as a charming candidate for next-generation energy conversion devices. However, it is highly desired but challenging to engineer advanced non-precious oxygen reduction catalysts with highly actives and stability due to the sluggish kinetics of oxygen reduction reaction (ORR) on fuel cell cathode. Herein, a novel hybrid architecture with Co nanoparticles embedded in N-doped carbon nanotubes and hollow nanocarbon polyhedron (Co@N-CNT-HC) was constructed from core-shell ZIF-67@ZIF-8 via a facile epitaxial growth-pyrolysis process. With the Co@N-CNT-HC as the catalyst, a remarkable ORR performance is achieved in terms of a high half-wave potential of 0.84 V, a large limiting current density of 4.70 mA/cm2, and excellent long-term durability (97.8% current retention after 8 h) in alkaline medium, which outperform commercial Pt/C catalyst. Further dynamic calculations indicated that ORR follows a four-electron reaction mechanism. The enhancement activity of Co@N-CNT-HC is mainly due to the effective integration of 0D Co nanoparticles, 1D carbon nanotubes and 3D hollow nanocarbon, which synergistically strengthen the interfacial reaction kinetics of oxygen and accelerate mass/charge transfer. The strategy reported in this work provides a new insight to synthesis of low-cost and well-designed carbon hybrid electrocatalyst for ORR. [ABSTRACT FROM AUTHOR]

[Display omitted] The point defect properties of body-centered cubic medium-entropy alloy NbZrTi were studied by first-principles calculations. Due to severe lattice distortion, a significant portion of conventional vacancy and interstitial structures are unstable and require large structural relaxation, indicating an irregular energy landscape with large site-to-site variations. The average vacancy and interstitial formation energy are 0.95 eV ± 0.34 eV and 1.92 eV ± 0.39 eV, respectively, much lower than that of Nb (2.77 eV and 4.38 eV). The vacancy migration energy exhibits a wide distribution extending to 0 eV, resulting in preferential vacancy migration through low barrier sites. The interstitial diffusion is slower than that of pure Nb due to the reduction of long <111> diffusion induced by the site-to-site variations in stable interstitial orientations. Ti atoms diffuse much faster than Nb and Zr atoms due to the preferential interstitial binding with Ti. The effect of atomic composition and short-range order on elemental and total interstitial diffusion was also investigated. The obtained first-principles results are important for the development of interatomic potentials for radiation damage studies. When irradiated with 3-MeV Fe ions at 675 ∘ C to a peak dose of ∼ 100 dpa, NbZrTi reduced the void formation at high temperature compared to Nb owing to its higher equilibrium vacancy concentration and closer mobility between vacancies and interstitial atoms. [ABSTRACT FROM AUTHOR]

• Interatomic potential for V-Ti-Ta ternary system based on F-S formalism has been developed. • The Ti potential well reproduce the point-defect properties of vacancy and self-interstitial atoms and the pressure-volume relation. • The typical defect energies of solute atoms Ti and Ta in the V matrix and Ti and V in the Ta matrix predicted by the present potential were in good agreement with DFT results. Vanadium (V)-based alloys are potential candidates for structural materials of fusion reactors because of their excellent properties; recently, the V–Ti–Ta alloy has received considerable attention. The irradiation-resistant performance is significant for the development and application of fusion reactor materials. In this study, combining with our previously developed potentials of V and Ta, we developed the V-Ti-Ta interatomic potential based on the Finnis–Sinclair (FS) formalism, which is an important step towards an atomic-scale investigation of V-based alloys. The potential parameters were determined by fitting to a large database of experimental data and density functional theory (DFT) calculations. The formation energies of vacancy and self-interstitial atoms, as well as the pressure-volume relation obtained from the present Ti potential, were well reproduced. The typical defect energies of solute atoms Ti and Ta in the V matrix and Ti and V in the Ta matrix, such as the formation energies of substitutional solute atoms, binding energies between solute atoms and point defects, agree well with DFT results. Thus, the developed potentials are expected to be suitable for atomistic simulations of point defects evolution in the V-Ti-Ta ternary system. [ABSTRACT FROM AUTHOR]

• Ti-V-Cr-Al light-weight medium entropy alloys are developed with outstanding tensile properties at the as-cast state. • The tensile ductility is much improved when Cr and Al are added equiatomically in the Ti 44 V 44 Cr x Al (12−x) alloys. • As-cast (TiV) 91 Cr 4.5 Al 4.5 alloy has a specific tensile yield stress of 160 MPa/(g/cm3) and a fracture elongation of 32%. [Display omitted] Light-weight (LW) high/medium entropy alloys have gained much attention due to the high specific strength, but they usually suffer from poor ductility, especially in the tensile tests at the as-cast state. In this study, the mechanical properties of a series of Ti-V-Cr-Al medium entropy alloys, with Ti and V maintaining equiatomic ratio, are investigated. An outstanding strength-ductility relationship is achieved in a (TiV) 91 Cr 4.5 Al 4.5 alloy, with a relatively low density of 5.1 g/cm3, a high specific yield strength of 160 MPa/(g/cm3), and a high tensile fracture elongation over 30%, even at its as-cast state. The tensile deformation is dominantly through the typical nucleation, planar migration, and entanglement of dislocations. Secondary phase formation and chemical inhomogeneity in this alloy are both insignificant. The frustration of dislocation motions are mainly attributed to the solid solution strengthening, which also enhances the work-hardening, delays the occurrence of necking, and benefits the overall ductility. The outstanding specific strength-ductility combination of this LW-alloy at the as-cast state makes it promising for potential engineering applications. [ABSTRACT FROM AUTHOR]

Abstract: The pyrolysis behaviors of vitrinite and inertinite from Chinese Pingshuo coal were investigated by using the thermogravimetry coupled with mass spectrometry (TG–MS) and in a fixed bed reactor, respectively. The results showed that inertinite has lower pyrolysis reactivity, lower tar and gas yields, but higher water yield than vitrinite. At 650°C, the tar and gas yield of vitrinite is 22.4% and 14.4%, respectively, obviously higher than 13.4% and 10.2% of inertinite. The TG–MS analysis also showed much difference of vitrinite and inertinite in gas evolution profile. The ultimate and XRD analyses of chars indicated that the difference in element composition of vitrinite char and inertinite char decreases with the increase of temperature, and have similar element composition and structure characteristic at 650°C. The total sulfur removal of both vitrinite and inertinite increases with the pyrolysis temperature, and reaches to 60% at 650°C, but the organic sulfur in inertinite seems more stable than that in vitrinite. [Copyright &y& Elsevier]

• Highly ordered hexgonal mesoporous TiO 2 -Al 2 O 3 have been synthesized. • TiO 2 content affects the morphology of both TiO 2 -Al 2 O 3 crystals and the mesopores. • The MSI has been modulated by the incorporated TiO 2 species. • TiO 2 promotes the formation of "Type II" NiMoS phases. • The enhanced HDS activity mainly contributed by the enhanced HYDS activity. Highly ordered mesoporous TiO 2 -Al 2 O 3 composites with different TiO 2 mass contents (MA-xTi) were successfully synthesized via an improved solvent evaporation-induced self-assembly method and the corresponding NiMo supported hydrodesulfurization (HDS) catalysts were prepared via wetness incipient co-impregnation method. The materials were characterized by means of XRD, ICP-OES, N 2 physical adsorption-desorption, SEM, TEM, Py-FTIR, H 2 -TPR, HRTEM and XPS and the catalytic activities for 4,6-dimethyldibenzothiophene (4,6-DMDBT) HDS over the prepared NiMo/MA-xTi series catalysts were investigated. The results show that the crystal forms, crystal morphologies, pore structures, pore arrangements and acidity properties of the MA-xTi samples varied with the incorporation and increase of TiO 2 species; the interaction between the active metals and the support materials (MSI) can be modulated by the incorporation of TiO 2 species, and TiO 2 incorporation also can promote the formation of the so-called "Type II" NiMoS active phase via changing the morphology of Ni promoted MoS 2 slabs, promoting the sulfidation of both Ni and Mo species and enhancing the proportion of NiMoS phase. The catalytic evaluation results show that the enhancement in the overall HDS activity of the NiMo/MA-xTi series catalysts were mainly contributed by the enhancement in the hydrogenation desulfurization (HYDS) activity. Catalyst NiMo/MA-20Ti exhibited the superior catalytic performance due to its highly ordered mesopore arrangement, proper acidity, moderate MSI, moderate stacking and high proportion of NiMoS phase which leads to more highly active "Type II" active sites. [ABSTRACT FROM AUTHOR]