Shock-induced energy localization and reaction growth considering chemical-inclusions effects for crystalline explosives

Chemical inclusions significantly alter shock responses of crystalline explosives in macroscale gap experiments but their microscale dynamics origin remains unclear.Herein shock-induced energy localization,overall physical responses,and reactions in a-1,3,5-trinitro-1,3,5-triazinane(a-RDX)crystal entrained various chemical inclusions were investigated by the multi-scale shock technique implemented in the reactive molecular dynamics method.Results indicated that energy localization and shock reaction were affected by the intrinsic factors within chemical inclusions,i.e.,phase states,chemical compositions,and concentrations.The atomic origin of chemical-inclusions effects on energy localization is dependent on the dynamics mechanism of interfacial molecules with free space volume,which includes homogeneous intermolecular compression,interfacial impact and shear,and void collapse and jet.As introducing various chemical inclusions,the initiation of those dynamics mechanisms triggers diverse decay rates of bulk RDX molecules and hereby impacts on growth speeds of final reactions.Adding chemical inclusions can reduce the effectiveness of the void during the shock impacting.Under the shockwave velocity of 9 km/s,the parent RDX decay rate in RDX entrained amorphous carbon decreases the most and is about one fourth of that in RDX with a vacuum void,and solid HMX and TATB inclusions are more reactive than amorphous carbon but less reactive than dry air or acetone inclusions.The lessdense shocking system denotes the greater increases in local temperature and stress,the faster energy liberation,and the earlier final reaction into equilibrium,revealing more pronounced responses to the present intense shockwave.The quantitative models associated with the relative system density(RD_(sys))were proposed for indicating energy-localization mechanisms and evaluating initiation safety in the shocked crystalline explosive.RD_(sys)is defined by the density ratio of defective RDX to perfect crystal after dynamics relaxation and reveals the global density characteristic in shocked systems filled with chemical inclusions.When RD_(sys)is below 0.9,local hydrodynamic jet initiated by void collapse dominates upon energy localization instead of interfacial impact.This study sheds light on novel insights for understanding the shock chemistry and physical-based atomic origin in crystalline explosives considering chemical-inclusions effects.

Effect of different machinery and rolling times on the microbial activity of reclamation soil in coal area

Mechanical construction will put influence on the biological characters of reclaimed soils,as well as the soil quality.In order to explore the changing rule of soil microbial quantity and respiratory capacity under different construction machineries and rolling times,and find the optimal processing conditions,an experiment was set up and a simulation experimental area was chosen,in which we simulated the main types of reclamation in coal mine area.After 2 years’natural aging,we collected surface soil samples(0-20 cm)that can be used for experimental analysis.The result shows that changing rules of soil biological factors are different with different construction machineries,and soil properties are closest to the normal soil when adopting the combination of“crawler dozer×5 compaction times”and“dump truck×3 compaction times”,which shows that the soil quality is better under this condition.

Thermal and mechanical characterization of under-2-μm-thick AlCrNbSiTi high-entropy thin film

High-entropy alloys(HEAs)exhibit extraordinary physical properties such as superior strength-to-weight ratios and enhanced corrosion and oxidation resistance,making them potentially useful in energy storage and gener-ation industries.However,thermal and mechanical properties of HEAs with various compositions vary signifi-cantly.Furthermore,these properties have rarely been investigated simultaneously owing to material or instru-mentation limitations.Herein,we synthesize an HEA(AlCrNbSiTi)coating with a thickness of less than 2μm.We customize a frequency-domain photothermal testing system to characterize the thermal and mechanical proper-ties of the proposed coating with high accuracy.Owing to the large mixing enthalpy of the Al-Ti,Nb-Si,and Ti-Si pairs in the coating,its hardness and elastic modulus are 15.2 and 254.7 GPa,respectively,which are higher than those of previously reported HEAs.The thermal conductivity of the AlCrNbSiTi coating is characterized to be 2.90 W·m^(−1)·K^(−1),within the expected range and well explained by the free-electron consistency diversity and phonon scattering from the amorphous structure.Additionally,the coating exhibits adequate wear performance,with a wear rate of 5.4×10^(−8) mm^(3)·N^(−1)·m^(−1).This relatively low thermal conductivity,combined with extraordi-nary mechanical properties,makes the proposed material an excellent candidate as a protective coating material for nuclear reactor components which require high strength,irradiation resistance,and thermal protection.

Grain boundaries induce significant decrease in lattice thermal conductivity of CdTe

Semiconductors are promising in photoelectric and thermoelectric devices, for which the thermal transport properties are of particular interest. However, they have not been fully understood, especially when crystalline imperfections are present. Here, using cadmium telluride (CdTe) as an example, we illustrate how grain boundaries (GBs) affect the thermal transport properties of semiconductors. We develop a machine-learning force field from density functional theory calculations for predicting the lattice thermal conductivity (LTC) via equilibrium molecular dynamics simulations. The LTC of crystalline CdTe decreases with the relationship of κL~1/T in the simulation temperature range of 300 – 900 K, in which the isotropic LTC decreases from 3.34 to 0.23 W/ (m⋅K) due to the enhanced anharmonicity. More important, after introducing GBs, the LTC is suppressed in all directions, especially in the direction normal to the GB planes. More severe LTC suppression occurs in CdTe with Σ9 GB than that with Σ3 GB at 300 K, decreasing by 92.8% and 61.4% along the direction normal to the GB planes compared to the isotropic LTC of the crystalline CdTe, respectively. The decreased LTC is consistent with the weaker bonding near GB planes and lower shear modulus of the defective material. The analyses of the phonon dispersion curves, vibrational density of states, and phonon participation ratio indicate that the decreased LTC mainly arises from phonon scattering at GBs. Overall, our work highlights that GBs can greatly influence the LTC of semiconductors, thus providing a promising approach for thermal property design.

In-situ formed NiS/Ni coupled interface for efficient oxygen evolution and hydrogen evolution

High-performance electrocatalysts for water splitting are desired due to the urgent requirement of clean and sustainable hydrogen production.To reduce the energy barrier,herein,we adopt a facile in-situ surface modification strategy to develop a low-cost and efficient electrocatalyst for water splitting.The synthesized mulberry-like NiS/Ni nanoparticles exhibit excellent catalytic performance for water splitting.Small overpotentials of 301 and 161 mV are needed to drive the current density of 10 mA cm^-2 accompanying with remarkably low Tafel slopes of 46 and 74 mV dec^-1 for oxygen evolution reaction(OER)and hydrogen evolution reaction(HER),respectively.Meanwhile,a robust electrochemical stability is demonstrated.Further high-resolution X-ray photoelectron spectroscopy analyses reveal that the intrinsic HER activity improvement is attributed to the electron-enriched S on the strongly coupled NiS and Ni interface,which simultaneously facilitates the important electron transfer,consistent with the electrochemical impedance results.The post characterizations demonstrate that surface reconstructed oxyhydroxide contributes to the OER activity and NiS/Ni is an OER precatalyst.This structure construction with in-situ formation of active interface provides an effective way to design efficient electrocatalysts for energy conversion.

PCGF6 regulates stem cell pluripotency as a transcription activator via super-enhancer dependent chromatin interactions

Polycomb group(PcG)ring finger protein 6(PCGF6),though known as a member of the transcription-re-pressing complexes,PcG,also has activation function in regulating pluripotency gene expression.However,the mechanism underlying the activation function of PCGF6 is poorly understood.Here,we found that PCGF6 co-localizes to gene activation regions along with pluripotency factors such as OCT4.In addition,PCGF6 was recruited to a subset of the super-enhancer(SE)regions upstream of cell cycle-associated genes by OCT4,and increased their expression.By combining with promoter capture Hi-C data,we found that PCGF6 activates cell cycle genes by regulating SE-promoter interactions via 3D chromatin.Our fin dings highlight a novel mechanism of PcG protein in regulating pluripotency,and provide a research basis for the therapeutic application of pluripotent stem cells.

Analysis of Early Essential Newborn Care Capacities of Rural Health Facilities--Four Provinces in Western China, 2016

What is already known about this topic?The Early Essential Newborn Care(EENC)intervention package recommended by World Health Organization(WHO)is shown to prevent and treat the leading causes of newborn illness and death.China has begun widespread implementation of the EENC.What is added by this report?Among the 14 core interventions,including using antibiotics for mothers with premature rupture of membranes,immediate skin-to-skin contact of mother and baby,delayed umbilical cord clamping,kangaroo mother care for preterm newborn,and neonatal sepsis and pneumonia management,were not sufficiently implemented in health facilities in western China.What are the implications for public health practice?There are gaps between the implementation situation and WHO recommendations in terms of EENC capacities in western China.Targeted interventions developed accordingly can ensure quality child health care and decrease newborn mortality in China.

Nanotwinning induced decreased lattice thermal conductivity of high temperature thermoelectric boron subphosphide (B12P2) from deep learning potential simulations

Boron subphosphide(B_(12)P_(2))is a promising high temperature thermoelectric material due to its good thermal stability,and chemical inertness.However,the thermal properties of B_(12)P_(2) have not been well revealed so far.Here,we first develop a deep learning potential for B_(12)P_(2) based on quantum mechanical calculations.Then the isotropic lattice thermal conductivity(LTC)of crystalline B_(12)P_(2) is predicted to be 39.70±4.38 W/m⋅K from molecular dynamics simulations using this deep learning potential.The LTC exhibits the relationship ofκL~1/T in the temperature range of 300~1500 K.More important,a twin boundary strategy is proposed to reduce the LTC of B_(12)P_(2).In nanotwinned B_(12)P_(2),the phonon transport in all directions is significantly suppressed by twin boundaries(TBs)with the isotropic LTC of 15.85±2.70 W/m⋅K,especially in the direction normal to the TB plane.The decrease of vibrational density of states and phonon participation ratio due to TBs’phonon scattering is the main reason of the low LTC in nanotwinned B_(12)P_(2).In addition,the elastic moduli(B and G)of B_(12)P_(2) crystal decrease by less than 7%after inducing TBs,which suggests that the mechanical properties are not significantly affected by TBs.Overall,this work enriches our understanding of the thermal properties of B_(12)P_(2) and offers a promising approach,i.e.,introducing TBs,to design high-performance thermoelectric materials.