Understanding Dual-Polar Group Functionalized COFs for Accelerating Li-Ion Transport and Dendrite-Free Deposition in Lithium Metal Anodes

Lithium metal batteries(LMBs)have attracted wide attentions because of their high theoretical specific capacity and low electrochemical potential.However,the growth of lithium dendrites seriously affects the practical application of LMBs.Thus,the lithium-philic carbonyl and carboxy dualgroup-modified covalent organic framework(COF-COOH)is designed to coat the polypropylene(PP)separator(COF-COOH@PP separator),realizing the regulation of ion transport and uniform lithium deposition.The plentiful and negative charge sites in the COF-COOH can suppress the diffusion of the freely movable lithium salt anion by the electrostatic interaction.Density functional theory(DFT)calculations demonstrate that the COF-COOH possesses the function of anchoring anion and desolvation.Consequently,the Li^(+)transference number(0.7),ion conductivity(0.64 mS cm^(-1)),and desolvating of Li^(+)are obviously improved by using the COF-COOH@PP separator.The modified Li-Li symmetric battery delivers stable cycle for more than 1000 h and lower voltage hysteresis(0.02 V).This dendrite-free deposition strategy holds great promise for practical application of Li metal anodes.

Benchmarking of JEFF-3.2, FENDL-3.0 and TENDL-2014 evaluated data for tungsten with 14.8 MeV neutrons

Integral experiments on tungsten slab samples were carried out on the D-T neutron source facility at China Institute of Atomic Energy. Leakage neutron spectra from the irradiated tungsten target were measured by the time-of-flight technique. Accuracy of the nuclear data for tungsten was examined by comparing the measured neutron spectra with the leakage neutron spectra simulated using the MCNP-4C code with evaluated nuclear data of the JEFF-3.2, FENDL-3.0 and TENDL-2014 libraries. The results show that the calculations with JEFF-3.2 agree well with the measurements in the whole energy range and all angles, whereas the spectra calculated with FENDL-3.0 and TENDL-2014 have some discrepancies with the experimental data.

Segregations and desorptions of Ge atoms in nanocomposite Si_(1-x)Ge_x films during high-temperature annealing

Nanocomposite Si1-xGex films are deposited by dual-source jet-type inductively coupled plasma chemical vapor deposition （jet-ICPCVD）. The segregations and desorptions of Ge atoms, which dominate the structural evolutions of the films during high-temperature annealing, are investigated. When the annealing temperature （Ta） is 900℃, the nanocomposite Si1-xGex films are well crystallized, and nanocrystals （NCs） with the core-shell structure form in the films. After being annealed at 1000℃ （above the melting point of bulk Ge）, Ge atoms accumulate on the surfaces of Ge-rich films, whereas pits appear on films with lower Ge content, resulting from desorption. Meanwhile, voids are observed in the films. A cone-like structure involving the percolation of the homogeneous clusters and the crystallization of NCs enhances Ge segregation.

Yield ratio of neutrons to protons in 12C（d,n）13N and 12C（d,p）13C from 0.6 to 3 MeV

The neutron yield in the12C(d,n)13N reaction and the proton yield in the12C(d,p)13C reaction have been measured using deuteron beams of energies 0.6-3 MeV.The deuteron beam is delivered from a 4-MeV electrostatic accelerator and bombarded on a thick carbon target.The neutrons are detected at 0°,24°,and 48°and the protons at135°in the laboratory frame.Further,the ratio of the neutron yield to the proton yield was calculated.This can be used to effectively recognize the resonances.The resonances are found at 1.4 MeV,1.7 MeV,and 2.5 MeV in the12C(d,p)13C reaction,and at 1.6 MeV and 2.7 MeV in the12C(d,n)13N reaction.The proposed method provides a way to reduce systematic uncertainty and helps confirm more resonances in compound nuclei.

GISAXS and ATR-FTIR Studies on Stress-Induced Microstructure Evolution of a-Si:H under H2 Plasma Exposure

Microstructure evolution in the surface layer of hydrogenated amorphous silicon(a-Si:H)film exposed to H2 plasma is investigated using grazing-incidence small-angle x-ray scattering and attenuated total reflection-Fourier transform infrared spectroscopy.Molecular hydrogen generated in the microvoids through H-abstraction reaction drives the evolution of the void shape from spherical to ellipsoidal as well as increases the average void volume and total void volume fraction.High-pressure H_(2) in the microvoid promotes the formation of a strained structure with high compressive stress within the a-Si:H film,which favours the generation of the SiHn complex in the subsurface layer of the a-Si:H film by H insertion into strained Si–Si bonds.

Primary yields of protons measured using CR-39 in laser-induceddeuteron–deuteron fusion reactions

Investigating deuteron–deuteron(DD)fusion reactions in a plasma environment similar to the early stages of the Big Bang is an important topic in nuclear astrophysics.In this study,we experimentally investigated such reactions,using eight laser beams with the third harmonic impacting on a deuterated polyethylene target at the ShenGuang-II Upgrade laser facility.This work focused on the application of range-filter(RF)spectrometers,assembled from a 70 lm aluminum filter and two CR-39 nuclear track detectors,to measure the yields of primary DD-protons.Based on the track diameter calibration results of 3 MeV protons used to diagnose the tracks on the RF spectrometers,an approximate primary DD-proton yield of(8.5±1.7)×10^6 was obtained,consistent with the yields from similar laser facilities worldwide.This indicates that the RF spectrometer is an effective way to measure primary DD-protons.However,due to the low yields of D^3He-protons and its small track diameter,CR-39 detectors were unable to distinguish it from the background spots.Using other accurate detectors may help to measure these rare events.

Extraordinarily stable and wide-temperature range sodium/potassium-ion batteries based on 1D SnSe2-SePAN composite nanofibers

Developing electrodes with long lifespan and wide-temperature adaptability is crucial important to achieve high-performance sodium/potassium-ion batteries(SIBs/PIBs).Herein,the SnSe2-SePAN composite was fabricated for extraordinarily stable and wide-temperature range SIBs/PIBs through a coupling strategy between controllable electrospinning and selenylation,in which SnSe2 nanoparticles were uniformly encapsulated in the SePAN matrix.The unique structure of SnSe2-SePAN not only relieves drastic volume variation but also guarantees the structural integrity of the composite,endowing SnSe2-SePAN with excellent sodium/potassium storage properties.Consequently,SnSe2-SePAN displays a high sodium storage capacity and excellent feasibility in a wide working temperature range(-15 to 60℃:300 mAh g^(-1)/700 cycles/-15℃;352 mAh g^(-1)/100 cycles/60℃at 0.5 A g^(-1)).At room temperature,it delivers a record-ultralong cycling life of 192 mAh g^(-1)that exceeds 66000 cycles even at 15 A g^(-1).It exhibits extremely superb electrochemical performance in PIBs(157 mAh g^(-1)exceeding 15000 cycles at 5 A g^(-1)).The ex situ XRD and TEM results attest the conversion-alloy mechanism of SnSe2-SePAN.Also,computational calculations verify that SePAN takes an important role in intensifying the electrochemical performance of SnSe2-SePAN electrode.Therefore,this study breaks new ground on solving the polyselenide dissolution issue and improving the wide temperature workable performance of sodium/potassium storage.

Optimizing Polynomial-Time Solutions to a Network Weighted Vertex Cover Game

Weighted vertex cover(WVC)is one of the most important combinatorial optimization problems.In this paper,we provide a new game optimization to achieve efficiency and time of solutions for the WVC problem of weighted networks.We first model the WVC problem as a general game on weighted networks.Under the framework of a game,we newly define several cover states to describe the WVC problem.Moreover,we reveal the relationship among these cover states of the weighted network and the strict Nash equilibriums(SNEs)of the game.Then,we propose a game-based asynchronous algorithm(GAA),which can theoretically guarantee that all cover states of vertices converging in an SNE with polynomial time.Subsequently,we improve the GAA by adding 2-hop and 3-hop adjustment mechanisms,termed the improved game-based asynchronous algorithm(IGAA),in which we prove that it can obtain a better solution to the WVC problem than using a the GAA.Finally,numerical simulations demonstrate that the proposed IGAA can obtain a better approximate solution in promising computation time compared with the existing representative algorithms.

MoSe2 nanosheets as a functional host for lithium-sulfur batteries

Lithium-sulfur batteries(LSBs) hold great potential for large-scale electrochemical energy storage applications. Currently, the shuttle of soluble lithium polysulfide(LiPSs) intermediates with sluggish conversion kinetics and random deposition of Li2S have severely degraded the capacity, rate and cycling performances of LSBs, preventing their practical applications. In this work, ultrathin MoSe2 nanosheets with active edge sites were successfully grown on both internal and external surfaces of hollow carbon spheres with mesoporous walls(MCHS). The resulting MoSe2@MCHS composite acted as a novel functional reservoir for Li PSs with high chemical affinity and effectively mediated their fast redox conversion during charge/discharge as elucidated by experimental observations and first-principles density functional theory(DFT) calculations. The as-fabricated Li-S cells delivered high capacity, superior rate and excellent cyclability. The current work presents new insights on the delicate design and fabrication of novel functional composite electrode materials for rechargeable batteries with emerging applications.

An active base designed in high-counting-rate applications for Hamamatsu R1924A photomultiplier tube

Hamamatsu R1924A is one of the most widely used photomultiplier tubes(PMTs) in nuclear physics.Since the active base suitable for R1924A is still not available in market, an active base is designed for Hamamatsu R1924A PMT, and the test results at high counting rates are presented. The active bases with two different sets of resistor chains were tested and compared by a frequency-controlled green straw hat LED light. A stable signal output up to 100 kHz is achieved using frequency-controlled LED pulsed light. The temperature of bases, which reflects the power consumption and is crucial for applications in vacuum, is also monitored with the same LED pulsed light. The temperature of the active base with smaller resistances reaches about twice of that of the active base with larger resistances in the resistor chain. For the applications in vacuum, the active base with resistance between the two sets of resistor chains may be preferable.

Computational exploration and screening of novel Janus MA2Z4 (M = Sc–Zn, Y–Ag, Hf–Au;A=Si, Ge;Z=N, P) monolayers and potential application as a photocatalyst

By high-throughput calculations,13 thermally and environmentally stable Janus MA_(2)Z_(4) monolayers were screened from 104 types of candidates.The 13 stable monolayers have very high charge carrier concentrations(×10^(15) cm^(–2)),which are better than those of the well-known graphene and TaS_(2).Because of their excellent conductivity,the 6 monolayers with band gaps less than 0.5 eV are identified as potential electrode materials for hydrogen evolution reaction applications.For potential applications as photoelectric or photocatalytic materials,bandgaps(Eg-HSE)higher than 0.5 eV remained,which resulted in 7 potential candidates.Based on optical absorption analysis in the visible-light range,H-HfSiGeP_(4) and HMoSiGeP_(4) have higher absorption ability and optical conductivity,which is quite impressive for optoelectronic,solar cell device,and photocatalysis applications.Additionally,the transmittance coefficient of Janus MA_(2)Z_(4) monolayers is approximately 70%–80%in the visible-light range,which implies that these monolayers show good light transmittance.For potential applications as photocatalysts,the redox potential and charge effective mass analysis indicate that H-HfSiGeP_(4),HMoSiGeP_(4),T-ScSiGeN_(4),and T-ZrSiGeN_(4) are suitable photocatalysts for CO_(2) reduction reactions.Using high-throughput identification,13 types of new and stable Janus MA2Z4 monolayers were explored,and the basic properties and potential applications were investigated,which can reduce the time for experiments and provide basic data for the material genome initiative.

Predicted High-Temperature Superconductivity in Rare Earth Hydride ErH2 at Moderate Pressure

Hydrides offer an opportunity to study high critical temperature(high-Tc)superconductivity at experimentally achievable pressures.However,the pressure needed remains extremely high.Using density functional theory calculations,herein we demonstrate that a new rare earth hydride ErH2could be superconducting with Tc~80 K at 14.5 GPa,the lowest reported value for compressed hydrides to date.Intriguingly,due to Kondo destruction,superconductivity was prone to exist at 15 GPa.We also reveal an energy gap at 20 GPa on the background of normal metallic states.At 20 GPa,this compressed system could act as a host of superconductor judged from a sharp jump of spontaneous magnetic susceptibility with an evanescent spin density of state at Fermi level.Finally,electron pairing glue for ErH2at these three typical pressures was attributed to the antiferromagnetic spin fluctuation.

Triple α-particle resonances in the decay of hot nuclear systems

The Efimov(Thomas) trimers in excited 12 C nuclei, for which no observation exists yet, are discussed by means of analyzing the experimental data of 70(64)Zn(64 Ni)+ 70(64)Zn(64 Ni) reactions at the beam energy of E/A = 35 MeV/nucleon. In heavy ion collisions, a-particles interact with each other and can form complex systems such as 8 Be and 12 C. For the 3 a-particle systems,multi-resonance processes give rise to excited levels of 12 C. The interaction between any two of the 3 a-particles provides events with one, two or three 8 Be. Their interfering levels are clearly seen in the minimum relative energy distributions. Events with the three a-particle relative energies consistent with the ground state of 8 Be are observed with the decrease of the instrumental error for the reconstructed 7.458 MeV excitation level in 12 C, which was suggested as the Efimov(Thomas) state.

Symmetry energy and experimentally observed cold fragments in intermediate heavy-ion collisions

An attempt is made to study the symmetry energy at the time of primary fragment formation from the experimentally observed cold fragments for a neutron-rich system of ^64Ni ＋ ^9Be at 140 MeV/nucleon,utilizing the recent finding that the excitation energy becomes lower for more neutron-rich isotopes with a given Z value.The extracted α（sym）/T values from the cold fragments,based on the Modified Fisher Model（MFM）,are compared to those from the primary fragments of the antisymmetrized molecular dynamics（AMD） simulation and become consistent with the simulation when the I = N —Z value becomes larger,indicating that the excitation energy of these neutron-rich isotopes is indeed lower.

Determining the nuclear temperature dependence on source neutron-proton asymmetry in heavy-ion reactions at intermediate energy

In this article,we investigate the dependence of nuclear temperature on emitting source neutron-proton(N/Z)asymmetry with light charged particles(LCPs)and intermediate mass fragments(IMFs)generated from intermediate-velocity sources in thirteen reaction systems with different N/Z asymmetries,^(64)Zn on^(112)Sn,and^(70)Zn,^(64)Ni on^(112,124)Sn,^(58,64)Ni,^(197)Au,and^(232)Th at 40 MeV/nucleon.The apparent temperature values of LCPs and IMFs from different systems are deduced from the measured yields using two helium-related and eight carbon-related double isotope ratio thermometers,respectively.Then,the sequential decay effect on the experimental apparent temperature deduction with the double isotope ratio thermometers is quantitatively corrected explicitly with the aid of the quantum statistical model.The present treatment is an improvement compared to our previous studies in which an indirect method was adopted to qualitatively consider the sequential decay effect.A negligible N/Z asymmetry dependence of the real temperature after the correction is quantitatively addressed in heavy-ion reactions at the present intermediate energy,where a change of o.1 units in source N/Z asymmetry corresponds to an absolute change in temperature of an order of 0.03 to 0.29 MeV on average for LCPs and IMFs.This conclusion is in close agreement with that inferred qualitatively via the indirect method in our previous studies.

通过构筑界面Mo–N–C键提高MoO2/氮掺杂碳复合材料的钠离子存储性能

钠离子电池因具有与锂离子电池接近的工作电压且具有丰富的钠资源优势而受到广泛关注,并有望成为商业化锂离子电池的替代产品.然而,开发合适的钠离子电池负极材料仍存在一些挑战.本文通过一种简单有效的碳化诱导拓扑化学转化法合成了一种MoO2/氮掺杂碳复合材料(MoO2/N-C),其中MoO2纳米晶嵌入在氮掺杂的碳基质里,并与之形成Mo–N–C键.用该MoO2/N-C复合材料组装的钠离子半电池具有很好的倍率性能和循环稳定性,可在5 A g-1的电流密度下循环超5000周.物理化学表征和基于密度泛函理论的第一性原理计算表明,MoO2和氮掺杂碳界面上的化学键合对复合材料电化学性能的提高起了重要作用.更重要的是,该化学键合可有效促进界面上的电荷转移.基于此,用该复合材料和活化碳组装的钠离子电容器在1760 W kg^-1功率密度下可提供15 W h kg^-1的能量密度,同时在10 A g^-1的电流密度下循环1000周后具有92.4%的电容保持率.本文介绍的界面化学键的构筑有望为面向储能器件的高性能电极的设计提供参考.