On the Degree Resistance Distance of Unicyclic Graphs

Let Gbe a connected graph with vertex set V(G). Then the degree resistance distance of Gis defined as DR(G)=∑{ u,v }⊆V(G)(d(u)+d(v))R(u,v), where d(u)is the degree of the vertex u, and R(u,v)is the degree resistance distance between uand vin graph G. A unicyclic graph is a connected graph with a unique cycle. In this paper, we characterize the unique graph with the third-maximum degree resistance distance among all unicyclic graphs with nvertices.

Simultaneous Detection and Removal of Formaldehyde at Room Temperature: Janus Au@ZnO@ZIF-8 Nanoparticles

The detection and removal of volatile organic compounds(VOCs) are of great importance to reduce the risk of indoor air quality concerns. This study reports the rational synthesis of a dual-functional Janus nanostructure and its feasibility for simultaneous detection and removal of VOCs.The Janus nanostructure was synthesized via an anisotropic growth method, composed of plasmonic nanoparticles,semiconductors, and metal organic frameworks(e.g.,Au@ZnO@ZIF-8). It exhibits excellent selective detection to formaldehyde(HCHO, as a representative VOC) at room temperature over a wide range of concentrations(from 0.25 to100 ppm), even in the presence of water and toluene molecules as interferences. In addition, HCHO was also found to be partially oxidized into non-toxic formic acid simultaneously with detection. The mechanism underlying this technology was unraveled by both experimental measurements and theoretical calculations: ZnO maintains the conductivity, while ZIF-8 improves the selective gas adsorption; the plasmonic effect of Au nanorods enhances the visible-light-driven photocatalysis of ZnO at room temperature.

STATIONARY DISTRIBUTION OF A STOCHASTIC SIR MODEL WITH SATURATED INCIDENCE AND ITS ASYMPTOTIC STABILITY

In this article, we consider a stochastic SIR model and show that the distributions of the solutions of the system are absolutely continuous. Furthermore, we analyze long-time behaviour of densities of the distributions of the solution. We prove that the densities can converge in L1 to an invariant density.

Numerical simulation and method study of X-ray litho-density logging

To effectively replace the isotope radiation source in litho-density logging,this study presents a method for measuring the formation density and photoelectric absorption index(Pe)using a switchable X-ray tube.First,the gamma-ray litho-density logging(GLD)method for measuring formation density and Pe using chemical sources is introduced.Then,a benchmark verification based on the X-ray litho-density logging tool prototype and data published by Simon(In:Paper presented at the SPWLA 59th annual logging symposium,London,UK,2018)was carried out using Monte Carlo numerical simulations.Second,the impacts of the photoelectric effect and detector statistical error on the GLD method were analyzed.Finally,based on a theoretical analysis,the formation density and Pe measurement algorithm(double energy window(DEW)method)was improved,which was found to be suitable for X-ray litho-density logging.Moreover,the results obtained using this algorithm were compared with those obtained using the GLD method.The results indicate that owing to the impact of photoelectric effect and detector statistical error on the density energy window,the accuracy of formation density and Pe measurement using the GLD method is relatively low,with the uncertainty in formation density and Pe measurement reaching 2.620±0.047 g/cm3 and 4.090±0.580 b/e,respectively.In comparison,the DEW method can improve the accuracy of density and Pe measurement to 0.006 g/cm3 and 0.065 b/e,respectively,as the photoelectric effect in the density window is corrected using the counts in the lithology window of the energy spectrum.This study aims to provide a new theoretical foundation for processing X-ray litho-density logs in the future.

DYNAMICAL BEHAVIOR OF A STOCHASTIC HBV INFECTION MODEL WITH LOGISTIC HEPATOCYTE GROWTH

This paper is concerned with a stochastic HBV infection model with logistic growth. First, by constructing suitable stochastic Lyapunov functions, we establish sufficient conditions for the existence of ergodic stationary distribution of the solution to the HBV infection model. Then we obtain sufficient conditions for extinction of the disease. The stationary distribution shows that the disease can become persistent in vivo.

QUALITATIVE ANALYSIS OF A STOCHASTIC RATIO-DEPENDENT HOLLING-TANNER SYSTEM

This article addresses a stochastic ratio-dependent predator-prey system with Leslie-Gower and Holling type II schemes. Firstly, the existence of the global positive solution is shown by the comparison theorem of stochastic differential equations. Secondly, in the case of persistence, we prove that there exists a ergodic stationary distribution. Finally, numerical simulations for a hypothetical set of parameter values are presented to illustrate the analytical findings.

Adsorption behavior of carbon dioxide and methane in bituminous coal:A molecular simulation study

The adsorption behavior of CO_2, CH_4 and their mixtures in bituminous coal was investigated in this study. First, a bituminous coal model was built through molecular dynamic(MD) simulations, and it was confirmed to be reasonable by comparing the simulated results with the experimental data. Grand Canonical Monte Carlo(GCMC)simulations were then carried out to investigate the single and binary component adsorption of CO_2 and CH_4with the built bituminous coal model. For the single component adsorption, the isosteric heat of CO_2 adsorption is greater than that of CH_4 adsorption. CO_2 also exhibits stronger electrostatic interactions with the heteroatom groups in the bituminous coal model compared with CH_4, which can account for the larger adsorption capacity of CO_2 in the bituminous coal model. In the case of binary adsorption of CO_2 and CH_4mixtures, CO_2 exhibits the preferential adsorption compared with CH_4 under the studied conditions. The adsorption selectivity of CO_2 exhibited obvious change with increasing pressure. At lower pressure, the adsorption selectivity of CO_2 shows a rapid decrease with increasing the temperature, whereas it becomes insensitive to temperature at higher pressure. Additionally, the adsorption selectivity of CO_2 decreases gradually with the increase of the bulk CO_2 mole fraction and the depth of CO_2 injection site.

Impacts of parameter uncertainties on deep chlorophyll maximum simulation revealed by the CNOP-P approach

Parameter uncertainty is a primary source of uncertainty in ocean ecosystem simulations.The deep chlorophyll maximum(DCM)is a ubiquitous ecological phenomenon in the ocean.Using a theoretical nutrients-phytoplankton model and the conditional nonlinear optimal perturbation approach related to parameters,we investigated the eff ects of parameter uncertainties on DCM simulations.First,the sensitivity of single parameter was analyzed.The sensitivity ranking of 10 parameters was obtained by analyzing the top four specifi cally.The most sensitive parameter(background turbidity)aff ects the light supply for DCM formation,whereas the other three parameters(nutrient content of phytoplankton,nutrient recycling coeffi cient,and vertical turbulent diff usivity)control nutrient supply.To explore the interactions among diff erent parameters,the sensitivity of multiple parameters was further studied by examining combinations of four parameters.The results show that background turbidity is replaced by the phytoplankton loss rate in the optimal parameter combination.In addition,we found that interactions among these parameters are responsible for such diff erences.Finally,we found that reducing the uncertainties of sensitive parameters could improve DCM simulations remarkably.Compared with the sensitive parameters identifi ed in the single parameter analysis,reducing parameter uncertainties in the optimal combination produced better model performance.This study shows the importance of nonlinear interactions among various parameters in identifying sensitive parameters.In the future,the conditional nonlinear optimal perturbation approach related to parameters,especially optimal parameter combinations,is expected to greatly improve DCM simulations in complex ecosystem models.

Design and modulation principles of molybdenum carbide-based materials for green hydrogen evolution

The green production of hydrogen from electrocatalytic water splitting is an important base and promising direction for the future of the large-scale application of hydrogen energy.The key of green hydrogen evolution depends on the development of low-cost and highly active electrocatalysts.Molybdenum carbides(MoxC),as a typical of earth-abundant transition-metal material,have accumulated great attention due to their low cost,earth abundance,electrical conductivity,similar d-band state to Pt,and regulated morphology/electronic structures.In this paper,recent researches focusing on MoxC for efficient HER in a wide pH range are summarized from respects of modulation of unique morphology,electronic structure,and electrode interface step by step.Briefly,modulation of morphology influence the apparent activity of catalyst,modulation of electronic structure of active sites by heteroatom doping and designing heterointerface boost intrinsic HER kinetics,and modulation of electrode interface via hybridization of MoxC structures with carbon materials can ensure the fast electron transfer and boost the activity.Besides the above methods discussed,perspective and challenges of designing MoxC as the substitute of Pt-based electrocatalyst for practical hydrogen generation in a wide pH range are pointed out.

Optimization method of fi rst-arrival waveform inversion based on the L-BFGS algorithm

The fi rst arrival waveform inversion(FAWI)has a strong nonlinearity due to the objective function using L2 parametrization.When the initial velocity is not accurate,the inversion can easily fall into local minima.In the full waveform inversion method,adding a cross-correlation function to the objective function can eff ectively reduce the nonlinearity of the inversion process.In this paper,the nonlinearity of this process is reduced by introducing the correlation objective function into the FAWI and by deriving the corresponding gradient formula.We then combine the first-arrival wave travel-time tomography with the FAWI to form a set of inversion processes.This paper uses the limited memory Broyden-Fletcher-Goldfarb-Shanno(L-BFGS)algorithm to improve the computational effi ciency of inversion and solve the problem of the low effi ciency of the FAWI method.The overthrust model and fi eld data test show that the method used in this paper can eff ectively reduce the nonlinearity of inversion and improve the inversion calculation effi ciency at the same time.

Interpenetration of Three 2D In-MOFs with(6,3)Topology:Syntheses,Structures and Fluorescent Properties

Three indium metal-organic frameworks （In-MOFs）, [In（BTB）（2,2＇-bipy）]？NMP （1）, [In（BTB）（2,2＇-bipy）]？NMP？2H2O （2）, and [In（BTB）（NMP）]·0.5NMP （3）, have been constructed by the solvothermal reaction of In（NO3）3·5H2O and 1,3,5-benzenetribenzoic acid （H3BTB） in similar reaction conditions, and characterized by single-crystal X-ray crystallography, power X-ray diffraction （PXRD）, infrared spectroscopy （IR）, elemental analysis （EA） and thermogravimetry analysis （TGA）. Complex 1 bears a two-dimensional （2D） layered structure of 6,3-connected hcb net topology, and complexes 2 and 3 have 2-fold interpenetrating structures based on 6,3-connected layer, which display the same net topologies with the C3-symmetric H3BTB ligands as 3-connected linkers and the In（Ⅲ） ions as 6-connected nodes. Moreover, the fluorescent properties of 1～3 have also been studied.

Symmetry of the Lagrangians of holonomic nonconservative system in event space

This paper analyzes the symmetry of Lagrangians and the conserved quantity for the holonomic non-conservative system in the event space. The criterion and the definition of the symmetry are proposed first, then a quantity caused by the symmetry and its existence condition are given. An example is shown to illustrate the application of the result at the end.

Solvothermal Synthesis,Crystal Structure and Properties of a 3D Organically Amine Templated Lanthanide Sulfate

A new sulfate inorganic framework, {（C2H8N）9[Nds（SO4）12]·2H2O}n （1） templated by organic amine, has been solvothermally synthesized and characterized by TGA, PXRD and single-crystal X-ray diffraction. Compound 1 crystalizes in monoclinic, space group C2/c with a = 20.570（5）, b = 35.815（8）, c = 10.106（2） A, C108H72NgNd5050S12, Mr = 2315.73, V= 6765（3） A3, Z = 4, Dc = 2.274 g·cm-3, μ = 4.253 mm-1, F（000 = 4520, 2.52〈θ〈25°, λ（MoKa） = 0.71073 A, T= 273（2） K, the final R =0.0401, wR = 0.1022 and S = 1.042. X-ray diffraction analysis reveals that complex 1 possesses a 3D inorganic sulfate framework with large 20-membered ring （20 MR） and 10-membered ring （10 MR） channels constructed by two kinds of SBUs. Moreover, the UV-vis and luminescent properties of comolex I were also investigated

Solvothermal Synthesis of a 3D Luminescent Cadmium-organic Framework with msw Topological Net

A new cadmium-organic framework, [Cd2（TBDC）2（DMF）2（H2O）]n （1）, was synthesized by solvothermal reaction of rigid carboxylate ligand 2,3,5,6-tetramethyl-l,4-ben- zenedicarboxylate （H2TBDC） and cadmium nitrate and characterized by elemental analysis, infrared spectrum, thermal analysis, PXRD, single-crystal X-ray diffraction and photoluminescence in the solid state. Compound 1 crystallizes in orthorhombic, space group Pca21 with a = 21.487（6）, b = 7.790（2）, c = 20.666（6） A, C30H40Cd2N2O11, Mr = 829.44, V= 3459.3（16） A3, Z = 4, Dc = 1.593 g.cm-3,μ = 1.29 mm-1, F（000） = 1672, 2.7〈θ〈27.2°, λ（MoKa） = 0.71073 A, T= 293（2） K, the final R = 0.026, wR = 0.0548 and S = 1.027. X-ray diffraction analysis reveals that complex 1 possesses a 3D framework and exhibits rnsw net. Thus, the solid-state luminescent spectrum of 1 displays that the emission of cadmium（lI） complex shows a peak at 317 nm upon 250 nm excitation at room temperature.

The stability of a non-extensive relativistic Fermi system

Based on the statistical theory of non-extensive relativity, and using theoretical analysis and numerical simulation, the non-extensive mechanical stability of ultra-relativistic free Fermi gas is investigated. The expressions of the stability conditions under high and low temperatures are given, and the mechanisms of the influences of temperature, ultra- relativistic effect, and non-extensive parameter q on stability are analysed. Our results show that at high temperature and under the condition of q 〈 1, the stability of a non-extensive system is weaker than that of an extensive system, and the relativistic effect reduces system stability as compared with a non-relativistic system. However, under the condition of q 〉 1, the stability of the non-extensive system is stronger than that of the extensive system, and the relativistic effect strengthens the system stability as compared with the non-relativistic system. In addition, under the condition of low temperature, the variation of the stability of the non-extensive system with temperature has a turning point.

Preparation of Cu-,Zn-,Co-Zeolites and Application for Adsorptive Desulfurization of Saudi Arabian Medium Crude

A series of Cu(II)-, Zn(II)-, Co(II)-loaded zeolites were successfully prepared by liquid phase ion-exchange method and characterized by X-ray diffraction(XRD), N2-adsorption specific surface area measurement(BET), X-ray fluorescence(XRF), and scanning electron microscopy(SEM) techniques. The adsorptive desulfurization performance of different adsorbents for treating Saudi Arabian medium crude oil was investigated, and the results showed that desulfurization efficiency declined in the following order: Zn(II)X > Cu(II)Y > Co(II)X > Cu(II)X > Co(II)Y> Zn(II)Y. The best desulfurization efficiency of 41.01% was achieved by using Zn(II)X as the adsorbent under the optimized conditions.The desulfurization performance of Zn(II)X in different distillates showed that a better performance was obtained in heavy petroleum fractions. Furthermore, the distribution of sulfur compounds in distillates after desulfurization was analyzed and the results showed that the adsorbent Zn(II)X could preferably adsorb aromatic sulfides such as thiophenes,benzothiophenes, and dibenzothiophenes. These results suggested that the π-complexation between zinc ions and sulfides would be crucial to the excellent desulfurization efficiency of Zn(II)X. In addition, the used adsorbent could be regenerated by heating at 700 °C in air, and around 84% of desulfurization capacity was recovered after the first cycle of regeneration.

Response laws of rock electrical property and saturation evaluation method of tight sandstone

To solve the problem that the law of rock electrical response under low and medium water saturation in tight sandstone reservoirs is not clear, an experimental method of high-speed centrifugal displacement rock electricity and nuclear magnetic resonance T2 spectrometry under different water saturation was proposed, which can drive the tight sandstone cores with the permeability less than 0.1×10^-3 μm^2, and provide a reliable experimental means for the study of tight sandstone electrical property. By carrying out supporting experiments such as high-resolution CT scan, MAPS and Qemscan, a multi-mineral component fine three-dimensional digital core based on multi-source information fusion was constructed. The finite element numerical simulation method was used to obtain the electrical response of tight sandstone core with low water saturation which cannot be obtained in laboratory conditions. By combining experiment and numerical simulation, the electrical response laws have been clear of tight sandstone with complex pore structure, and the saturation evaluation method of variable rock electrical parameters based on pore structure has been developed. The processing of logging data of multiple wells in tight sandstone reservoir of Chang 7 Member in the Ordos Basin shows that this method can obtain more accurate oil saturation, and provides a new idea and method for fine logging evaluation of tight sandstone reservoir.

Synthesis, Crystal Structure and Luminescence of a Trinuclear Magnesium Coordination Polymer Based on a Triangle Flexible Carboxylic Ligand

A novel two-dimensional metal organic coordination compound based on flexible 1,3,5-tri（4-carboxyphenoxy）benzene （HaTCPB）, {[Mgl.5（TCPB）（DMF）（H20）]＇（DMF）}n （1）, has been prepared and structurally characterized by single-crystal X-ray diffraction, TGA, and PXRD measurements. Complex 1 crystalizes in triclinic, space group Pi with a = 10.2521（6）, b = 11.0974（7）, c = 16.1113（9） A, C33H31Mg1.5N2012, Mr = 684.06, V= 1669.46（17） A3, Z = 2, Dc = 1.361 g·cm^-3, p = 0.129 mm^-1, F（000） = 714, 3.06≤0≤25°, λ（MoKa） = 0.71073 A, T= 273（2） K, the final R = 0.0386, wR = 0.0892 and S = 1.031. X-ray diffraction analysis reveals that complex 1 possesses a two-dimensional framework constructed by trinuclear Mg SBUs and three-connected TCPB3- linker. In addition, the solid state luminescent property of complex 1 was also investigated at room temperature.

Photophysical Properties of Perylenetetracarboxylic Diimide Dimers with Slipped “Face-to-Face” Stacked Structure and Different Bay Substitutions

A series of perylenetetracarboxylic diimides (PDIs) dimers with slipped “face-to-face” stacked structure and different substituents at the bay positions have been synthesized and the molecular structures are characterized by 1H NMR, MALDI-TOF and elemental analysis. And different substituents at the bay positions of the PDI ring bring about various steric hindrances. These different steric hindrances have caused significant differences on the absorption and emission spectra. The correlation between the photophysical properties and the molecular structure is discussed.

Bifurcation analysis of a diffusive predator-prey model with hyperbolic mortality and prey-taxis

In this paper,we study a diffusive predator-prey model with hyperbolic mortality and prey-taxis under homogeneous Neumann boundary condition.We first analyze the influence of prey-taxis on the local stability of constant equilibria.It turns out that prey-taxis has influence on the stability of the unique positive constant equilibrium,but has no influence on the stability of the trivial equilibrium and the semi-trivial equilibrium.We then derive Hopf bifurcation and steady state bifurcation related to prey-taxis,which imply that the prey-taxis plays an important role in the dynamics.