Excitonic Instability in Ta_(2)Pd_(3)Te_(5) Monolayer

By systematic theoretical calculations,we reveal an excitonic insulator(EI)in the Ta_(2)Pd_(3)Te_(5)monolayer.The bulk Ta_(2)Pd_(3)Te_(5)is a van der Waals(vdW)layered compound,whereas the vdW layer can be obtained through exfoliation or molecular-beam epitaxy.First-principles calculations show that the monolayer is a nearly zero-gap semiconductor with the modified Becke–Johnson functional.Due to the same symmetry of the band-edge states,the two-dimensional polarization 2D would be finite as the band gap goes to zero,allowing for an EI state in the compound.Using the first-principles many-body perturbation theory,the GW plus Bethe–Salpeter equation calculation reveals that the exciton binding energy is larger than the single-particle band gap,indicating the excitonic instability.The computed phonon spectrum suggests that the monolayer is dynamically stable without lattice distortion.Our findings suggest that the Ta_(2)Pd_(3)Te_(5) monolayer is an excitonic insulator without structural distortion.

Simulation study of hydrogen sulfide removal in underground gas storage converted from the multilayered sour gas field

A simulation study was carried out to investigate the temporal evolution of H_(2)S in the Huangcaoxia underground gas storage (UGS), which is converted from a depleted sulfur-containing gas field. Based on the rock and fluid properties of the Huangcaoxia gas field, a multilayered model was built. The upper layer Jia-2 contains a high concentration of H_(2)S (27.2 g/m^(3)), and the lower layer Jia-1 contains a low concentration of H_(2)S (14.0 mg/m^(3)). There is also a low-permeability interlayer between Jia-1 and Jia-2. The multi-component fluid characterizations for Jia-1 and Jia-2 were implemented separately using the Peng-Robinson equation of state in order to perform the compositional simulation. The H_(2)S concentration gradually increased in a single cycle and peaked at the end of the production season. The peak H_(2)S concentration in each cycle showed a decreasing trend when the recovery factor (RF) of the gas field was lower than 70%. When the RF was above 70%, the peak H_(2)S concentration increased first and then decreased. A higher reservoir RF, a higher maximum working pressure, and a higher working gas ratio will lead to a higher H_(2)S removal efficiency. Similar to developing multi-layered petroleum fields, the operation of multilayered gas storage can also be divided into multi-layer commingled operation and independent operation for different layers. When the two layers are combined to build the storage, the sweet gas produced from Jia-1 can spontaneously mix with the sour gas produced from Jia-2 within the wellbore, which can significantly reduce the overall H_(2)S concentration in the wellstream. When the working gas volume is set constant, the allocation ratio between the two layers has little effect on the H_(2)S removal. After nine cycles, the produced gas’s H_(2)S concentration can be lowered to 20 mg/m^(3). Our study recommends combining the Jia-2 and Jia-1 layers to build the Huangcaoxia underground gas storage. This plan can quickly reduce the H_(2)S concentration of the produced gas to 20 mg/m^(3), thus meeting the gas export standards as well as the HSE (Health, Safety, and Environment) requirements in the field. This study helps the engineers understand the H_(2)S removal for sulfur-containing UGS as well as provides technical guidelines for converting other multilayered sour gas fields into underground storage sites.

Simulation of the Production Performances of Horizontal Wells with a Fractured Shale Gas Reservoir

The production performances of a well with a shale gas reservoir displaying a complex fracture network are simulated.In particular,a micro-seismic cloud diagram is used to describe the fracture network,and accordingly,a production model is introduced based on a multi-scale flow mechanism.A finite volume method is then exploited for the integration of the model equations.The effects of apparent permeability,conductivity,Langmuir volume,and bottom hole pressure on gas well production are studied accordingly.The simulation results show that ignoring the micro-scale flow mechanism of the shale gas leads to underestimating the well gas production.It is shown that after ten years of production,the cumulative gas production difference between the two scenarios with and without considering the micro-scale flow mechanisms is 19.5%.The greater the fracture conductivity,the higher the initial gas production of the gas well and the cumulative gas production.The larger the Langmuir volume,the higher the gas production rate and the cumulative gas production.With the reduction of the bottom hole pressure,the cumulative gas production increases,but the growth rate gradually decreases.

A Li-S battery with ultrahigh cycling stability and enhanced rate capability based on novel ZnO yolk-shell sulfur host

Currently,lithium-sulfur(Li-S)batteries still suffer from fast capacity decay,poor coulombic efficiency(CE)and short cycling lifespan,which result from the severe shuttle effect issue caused by high solubility and rapid diffusion of lithium polysulfides(Li PSs)in organic electrolytes.Here,yolk-shell zinc oxide(YSZn O)spheres are synthesized and for the first time,applied as a host for Li-S batteries to tackle this challenge.The polar Zn O exhibits high chemical anchoring ability toward Li PSs while the unique yolk-shell structure not only provides an additional physical barrier to Li PSs but also enables much more uniform sulfur distribution,thus significantly suppressing Li PSs shuttling effect meanwhile promoting sulfur conversion reactions.As a result,the YS-Zn O enables the Li-S battery to display an initial specific capacity of1355 m Ah g^(-1) and an outstanding capacity retention capability(~89.44%retention rate)even after 500 cycles with the average CE of~99.46%at the current of 0.5 C.By contrast,the capacity of conventional-Zn O-nanoparticles based battery severely decays to 472 m Ah g^(-1) after cycling for 500 times.More impressively,the S/YS-Zn O based Li-S battery can maintain a low decay rate of 0.040%every cycle and high average CE of 98.82%over 1000 cycles at 3 C.

ADDITIVE MAPPINGS PRESERVING FREDHOLM OPERATORS WITH FIXED NULLITY OR DEFECT

Let X be an infinite-dimensional real or complex Banach space,and B(X)the Banach algebra of all bounded linear operators on X.In this paper,given any non-negative integer n,we characterize the surjective additive maps on B(X)preserving Fredholm operators with fixed nullity or defect equal to n in both directions,and describe completely the structure of these maps.

Constituents from leaves of Macaranga hemsleyana

Objective:To study constituents of the leaves of Macaranga hemsleyana,and evaluate their inhibitory effects against NOD-like receptor thermal protein domain associated protein 3(NLRP3)inflammasome activation,and antiproliferative activity.Methods:The constituents were isolated and purified by column chromatography on MCI gel CHP20P/P120,silica gel,Sephadex LH-20,and HPLC.The structures of compounds were determined by 1D,2D NMR,and HR-ESI-MS data.The inhibitory effect of compounds on inflammasome activation was determined by lactate dehydrogenase(LDH)procedure.The antiproliferative activity was evaluated using MTT assay.Results:The study led to the isolation of 23 compounds,including one new compound,identified as(2Z)-3-[4-(β-D-glucopyranosyloxy)-2′-hydroxy-5′-methoxyphenyl]-2-propenoic acid(1),together with 22 known compounds recognized as 1,4-dihydro-4-oxo-3-pyridinecarbonitrile(2),methyl 4-methoxynicotinate(3),4-methoxynicotinonitrile(4),1-(3-O-β-D-glucopyranosyl-4,5-dihydroxyphenyl)-ethanone(5),neoisoastilbin(6),isoastilbin(7),aromadendrin(8),neoastilbin(9),astilbin(10),quercitrin(11),neoschaftoside(12),apigenin 6,8-bis-C-α-L-arabinoside(13),vitexin(14),bergenin(15),scopoletin(16),glucopyranoside salicyl(17),koaburside(18),benzylβ-D-glucoside(19),icariside B5(20),roseoside(21),loliolide(22),and adenosine(23).The tested compounds did not show LDH inhibition nor antiproliferative activity.Conclusion:Compound 1 was a new glycoside.Compounds 2 and 3 were obtained for the first time from natural source.The 22 known compounds constituted of alkaloids(2–4,23),phenolics(5,15,17,18),flavonoids(6–14),coumarin(16),benzyl glycoside(19),and norsesquiterpenes(20–22).All the compounds,1–23,were revealed from M.hemsleyana for the first time.This is the initial uncovering of molecules 1–10,12,13,17–19,and 23 from the genus Macaranga.The isolated compounds,11,14–16,and 20–22 established taxonomic classification of M.hemsleyana in Euphorbiaceae family.Flavonoids were outstanding as chemosystematic markers of Macaranga genus.

Unconventional phonon spectra and obstructed edge phonon modes

Based on the elementary band representations(EBR),many topologically trivial materials are classified as unconventional ones(obstructed atomic limit),where the EBR decomposition for a set of electronic states is not consistent with atomic valenceelectron band representations.In the work,we identify that the unconventional nature can also exist in phonon spectra,where the EBR decomposition for a set of well-separated phonon modes is not consistent with atomic vibration band representations(ABR).The unconventionality has two types:typeⅠis on an empty site;and typeⅡis on an atom site with non-atomic vibration orbitals.The unconventionality is described by the nonzero real-space invariant at the site.Our detailed calculations show that the black phosphorus(BP)has the typeⅠunconventional phonon spectrum,while 1H-Mo Se_(2)has the typeⅡone,although their electronic structures are also unconventional.Accordingly,the obstructed phonon modes are obtained for two types of unconventional phonon spectra.

Large Spin Hall Conductivity and Excellent Hydrogen Evolution Reaction Activity in Unconventional PtTe1.75 Monolayer

Two-dimensional(2D)materials have gained lots of attention due to the potential applications.In this work,we propose that based on first-principles calculations,the(2×2)patterned PtTe_(2)monolayer with kagome lattice formed by the well-ordered Te vacancy(PtTe_(1.75))hosts large and tunable spin Hall conductivity(SHC)and excellent hydrogen evolution reaction(HER)activity.The unconventional nature relies on the A1@1b band representation of the highest valence band without spin–orbit coupling(SOC).The large SHC comes from the Rashba SOC in the noncentrosymmetric structure induced by the Te vacancy.Even though it has a metallic SOC band structure,theℤ_(2)invariant is well defined because of the existence of the direct bandgap and is computed to be nontrivial.The calculated SHC is as large as 1.25×10^(3)h/e(Ωcm)^(−1)at the Fermi level(EF).By tuning the chemical potential from EF−0.3 to EF+0.3 eV,it varies rapidly and monotonically from−1.2×10^(3)to 3.1×10^(3)h/e(Ωcm)^(−1)In addition,we also find that the Te vacancy in the patterned monolayer can induce excellent HER activity.Our results not only offer a new idea to search 2D materials with large SHC,i.e.,by introducing inversion–symmetry breaking vacancies in large SOC systems,but also provide a feasible system with tunable SHC(by applying gate voltage)and excellent HER activity.

Improvement of thermal conductivities and simulation model for glass fabrics reinforced epoxy laminated composites via introducing hetero-structured BNN-30@BNNS fillers

Hetero-structured thermally conductive spherical boron nitride and boron nitride nanosheets(BNN-30@BNNS)fillers were prepared via electro static self-assembly method.And the corresponding thermally conductive&electrically insulating BNN-30@BNNS/Si-GFs/E-44 laminated composites were then fabricated via hot compression.BNN-30@BNNS-Ⅲ(fBNN-30/fBNNS,1/2,wt/wt)fillers presented the optimal synergistic improvement effects on the thermal conductivities of epoxy composites.When the mass fraction of BNN-30@BNNS-Ⅲwas 15 wt%,λvalue of the BNN-30@BNNS-Ⅲ/E-44 composites was up to0.61 W m^(-1)K^(-1),increased by 2.8 times compared with pure E-44(λ=0.22 W m^(-1)K^(-1)),also higher than that of the 15 wt%BNN-30/E-44(0.56 W m^(-1)K^(-1)),15 wt%BNNS/E-44(0.42 W m^(-1)K^(-1)),and 15 wt%(BNN-30/BNNS)/E-44(direct blending BNN-30/BNNS hybrid fillers,1/2,wt/wt,0.49 W m^(-1)K^(-1))composites.Theλin-plane(λ//)andλcross-plane(λ_(⊥))of 15 wt%BNN-30@BNNS-Ⅲ/Si-GFs/E-44 laminated composites significantly reached 2.75 W m^(-1)K^(-1)and 1.32 W m^(-1)K^(-1),186.5%and 187.0%higher than those of Si-GFs/E-44 laminated composites(λ//=0.96 W m^(-1)K^(-1)andλ_(⊥)=0.46 W m^(-1)K^(-1)).Established models can well simulate heat transfer efficiency in the BNN-30@BNNS-Ⅲ/Si-GFs/E-44 laminated composites.Under the condition of point heat source,the introduction of BNN-30@BNNS-Ⅲfillers were conducive to accelerating heat flow trans fe r.BNN-30@BNNS-Ⅲ/Si-GFs/E-44 laminated composites also demonstrated outstanding electrical insulating properties(cross-plane withstanding voltage,breakdown strength,surface&volume resistivity of 51.3 kV,23.8 kV mm^(-1),3.7×10^(14)Ω&3.4×10^(14)Ω·cm,favorable mechanical properties(flexural strength of 401.0 MPa and ILSS of 22.3 MPa),excellent dielectric properties(εof 4.92 and tanδof 0.008)and terrific thermal properties(T_(g )of 167.3℃and T_(HRI) of 199.2℃).

Ab initio prediction and characterization of phosphorene-like SiS and SiSe as anode materials for sodium-ion batteries

In this work, a density functional theory （DFT） based first-principles study is carried out to investigate tile potential of phosphorene-like SiS and SiSe monolayers as anode materials for sodium-ion （Na-ion） bat- teries. Results show that both SiS and SiSe have large adsorption energies towards single Na atom of 0.94 and -0.43 eV, owing to the charge transfers from Na to SiS or SiSe. In addition, it is found that the highest Na concentration for both SiS and SiSe is x = 1 with the chemical formulas of NaSiS and NaSiSe, corresponding to the high theoretical specific capacities for Na storages of 445.6 and 250.4 mAh g 1, respectively. Moreover, Na diffusions are very fast and show strong directional behaviors on SiS and SiSe monolayers, with the energy barriers of only 0.135 and 0.158 eV, lower than those of con- ventional anode materials for Na-ion batteries such as Na2Ti3O7 （0.19 eV） and Na3Sb （0.21 eV）. Finally, although SiS and SiSe show semiconducting behaviors, they transform to metallic states after adsorbing Na atoms, indicating enhanced electrical conductivity during battery cycling. Given these advantages, it is expected that both SiS and SiSe monolayers are promising anode materials for Na-ion batteries, and in principle, other Na-based batteries as well.

Anti-NLRP3 inflammasome abietane diterpenoids from Callicarpa bodinieri and their structure elucidation

Callica rpabodinieri is a Chinese traditional medicine herb with anti-inflammatory activity in clinic.Herein,we report two new 9,10-seco and etherified abietane diterpenoids bodinieric acids J and K(1 and 2) and one known compound(3) isolated from the leaves and twigs of this plant.Their chemical structures were elucidated by detailed spectrometry data analysis and DP4+NMR calculation methods.Hypothetical biosynthetic pathways of 1-3 were preliminarily speculated.Compound 3 inhibited inflammasome activation and exhibited blockage of NLRP3 inflammasome activation at non-cytotoxic concentrations in vitro.

A Poriferous Nanoflake-Assembled Flower-Like Ni_(5)P_(4) Anode forHigh-Performance Sodium-Ion Batteries

Sodium-ion batteries(SIBs)have been regarded as one of the most competitive alternatives for lithium-ion batteries(LIBs)due to the abundance of sodium and comparable electrochemical characteristics of sodium to that of lithium.However,while highly desired,developing stable anode materials remains a critical challenge.In this work,the development of a stable anode for SIBs is reported,a poriferous nanoflake-assembled flower-like nickel tetraphosphide(PNAF-NP)with high surface area and typical mesoporous property.Due to the unique structure,the PANF-NP anode exhibits excellent reversible capacity of 648.34mAhg^(-1) at 0.2Ag^(-1) with a Coulombic efficiency of 98.67%,and superior cycling stability at 0.2Ag^(-1) with high retention capacity of 456.34 mAhg^(-1) and average Coulombic efficiency of 99.19%after 300 cycles.Moreover,the high reversible capacity of 614.43,589.49,512.66,and 432.23mAhg^(-1) is achieved at 0.5,1,2,and 5Ag^(-1),respectively,indicating the superior rate capability of the PNAF-NP anode.This work represents a great advancement in the field of SIBs by reporting a high-performance anode material.