Multisurface Chemoplasticity. I: Material Model for Shotcrete

Employing a thermodynamic framework, chemomechanical couplings for shotcrete are treated in this paper. A new material model based on multisurface chemoplasticity is presented. It accounts for hydration kinetics and chemomechanical couplings related to the strength growth and the evolution of stiffness properties as well as for autogeneous shrinkage in early-age shotcrete. The underlying intrinsic material functions, which are independent of field and boundary conditions, are determined from standard material tests. As for the numerical treatment of the constitutive equations of the material model, an extended form of the return mapping algorithm is proposed. The constitutive equations are applied to a two-surface chemoplastic model, consisting of a Drucker-Prager loading surface and a tension cut-off. In a companion paper, the proposed material model is employed for 2D structural analyses of tunnels driven according to the New Austrian Tunneling Method.     

On an alleged philosophers' stone concerning variational principles with subsidiary conditions

In general, the Lagrange multiplier method (LMM) is used to incorporate subsidiary conditions into variational principles. The Lagrange multipliers represent an additional field of independent variables. The attempt to satisfy subsidiary conditions without employing additional independent unknowns has led to the development of simplified variational principles (SVP). They are characterized by expressing Lagrange multipliers in terms of original field variables by means of the Euler-Lagrange equations for the multipliers, providing their physical interpretation. In the first part of the theoretical investigation, systems with infinitely many degrees-of-freedom are studied. It is shown that the Euler-Lagrange equations of a LMM based on a modification of the principle of minimum of potential energy (PMIPE) do not hold unconditionally, that is, for arbitrary subsidiary conditions, for the corresponding SVP. The second part of the theoretical investigation is concerned with systems with a finite number of degrees-of-freedom. The finite element method (FEM) is employed to discuss and compare the characteristics of the LMM and of the corresponding SVP. Contrary to the former, the latter are found to be problem-dependent. Several shortcomings of the SVP are listed, including the possibility of obtaining an infinite sequence of singular coefficient matrices in the process of a systematic mesh refinement. Consequently, convergence of finite element solutions to the true solution in the limit of finite element representations is not guaranteed. The theoretical findings are corroborated by the results of a detailed numerical study.     

Morphology and conductivity of polyaniline sub-micron fibers prepared by electrospinning

Sub-micron fibers of pure polyaniline (PANI) doped with sulfuric acid or hydrochloric acid were prepared by electrospinning PANI with suitable molecular weight dissolved in hot sulfuric acid. A modified electrospinning setup was employed with a coagulation bath as a collector, where dilute sulfuric acid was used as coagulation bath. The factors influencing the morphology and conductivity of the synthesized PANI fibers were investigated, including the concentration of dilute H₂SO₄ solution in the coagulation bath, the doped PANI concentration in H₂SO₄ solution, the type of doping acid and the voltage applied to the solution. The morphologies of doped PANI fibers were characterized by scanning electron microscope (SEM). The structure of the resulting fibers was analyzed by Fourier transform infrared spectroscopy and UV–vis spectrometer. The conductivity of PANI fibers were characterized by I–V characteristics. Homogeneous PANI fibers with a diameter of 370 nm and a high conductivity of 52.9 S/cm were prepared. The possible mechanisms of different morphology formation and conductivity of PANI fibers were also discussed.     

Maxwellian circuit models for analysis of printed spiral antennas

In this letter, it is the first time to implement the theory of Maxwellian circuits (TMC) to the printed spiral antennas. First, the Maxwellian circuit models (MCM) for the printed spiral antennas are established through two independent sets of full-wave solutions of current and scalar potential distributions. In this stage, a relationship between the scalar potential and voltage is proposed to satisfy Ohm's law at the terminals of the antennas. Second, broadband MCM are developed to predict the characteristics of the antennas over a quite wide band by using the information at only three sampling frequencies. Numerical results indicate that solutions of the MCM (sparse matrix system) are much more efficient than those of the conventional integral equation solutions (full matrix system) without any accuracy sacrifice.     

Preparation and characterization of a layered perovskite-type organic–inorganic hybrid compound based on (C6H4)2N (CH2)6NH3Cl

The organic–inorganic hybrid compound ((C₆H₄)₂N(CH₂)₆NH₃)₂PbCl₄ (N6AHMC–PbCl₄) and ((C₆H₄)₂N(CH₂)₆NH₃)₂PbCl₂I₂ (N6AHMC–PbCl₂I₂) were synthesized by treating N-6-aminohexamethylcarbazole chloride (N6AHMC–HCl) with stoichiometric amount of PbX₂ (X = Cl, I) at room temperature using dimethylformamide (DMF) as solution. High order diffraction peaks corresponding to (0 0 l) (l = 2, 4, 6, …) were observed in the X-ray diffraction profile of N6AHMC–PbCl₄ and N6AHMC–PbCl₂I₂, indicating the formation of hybrid crystal with layered perovskite structure. N6AHMC–PbCl₄ presented characteristic absorptions of PbCl-based layered perovskite centered at about 329 nm. Similar to the PL spectrum of N6AHMC–HCl, the film of N6AHMC–PbCl₄ showed three strong emission peaks, indicating that the exciton emission of the N6AHMC–PbCl₄ film comes from the organic layer of the hybrids. Owing to the partially replacement of Cl^? with I^?, the fluorescence quenched N6AHMC–PbCl₂I₂ showed broad absorption at about 400 nm, which is assigned to the transition from the hybrid orbital hybridized by Cl 3p and I 5p valence states to Pb 6p conduction bands. For the reason of the variation of the energy band structure, from type I quantum well structure to type II heterojunction, the photoconductivity of N6AHMC–PbCl₂I₂ is higher than that of N6AHMC–PbCl₄.     

Conjugated polymers based on benzodithiophene and arylene imides: Extended absorptions and tunable electrochemical properties

Three novel conjugated polymers have been designed and synthesized via the alternative copolymerization of the electron-donating monomer benzodithiophene (BDT) and three different electron-accepting monomers: perylene diimide (PDI), naphthalene diimide (NDI), and phthalimide (PhI). All obtained copolymers show good solubility in common organic solvents as well as broader absorptions in visible region and narrower optical band gaps compared to homopolymers from BDT units. It is found that the absorptions of the copolymers are red-shifted with increasing the electron-withdrawing ability of the co-monomer. In particular, the absorption edge of P(BDT-NDI) film extends to 760 nm, whereas that of P(BDT-PhI) film is only at 577 nm. Cyclic voltammograms of the three polymers disclose that P(BDT-PDI) and P(BDT-NDI) are typical n-type materials because PDI and NDI are strong electron-accepting groups, while P(BDT-PhI) is a stable p-type material where the weak electron-withdrawing monomer (PhI) is introduced. The results suggest that the absorption range and the electrochemical properties of the conjugated polymers can be tuned by appropriate molecule-tailoring, which will help exploring ideal conducting polymers for potential applications in polymer optoelectronics, especially in polymer solar cells.     

菲在Fenton体系中的氧化特性研究

为考察Fenton反应氧化菲的影响因素,以三角瓶批处理的方式,研究了土样中的菲在不同浓度的H2O2和铁盐时的氧化反应效率,并用GC/MS对菲的氧化产物进行了检测。结果发现,开始的0.5 h反应速率很快,大部分菲氧化是在这期间完成的,之后氧化速率相对缓慢。高浓度的H2O2可获得更高的氧化效率。相同浓度的H2O2下,铁盐浓度为5 mmol.L-1时的氧化效率要小于铁盐浓度为1 mmol.L-1时的。GC/MS检测出3种氧化产物。菲经Fenton试剂氧化芳环被打开,可产生多种含氧化合物,这些物质可进一步被转化。     

油气田硫化氢形成机理与安全防治研究

油气田开采过程中常伴生硫化氢剧毒气体,其对人和设备都具有高危害性。硫化氢的有效防治对于油气田的安全开采至关重要。本文对油气田中硫化氢的形成机理进行了探讨,对硫化氢在开采过程的危害进行了分析,并提出了相应的安全防治措施。为进一步加强油气田安全开采提供参考。     

Enhanced photoelectrochemical performance of anatase TiO2 by metal-assisted S–O coupling for water splitting

In this study, hybrid density functional theory calculations have been used to investigate the electronic structures of (Mg, S), (2Al, S), (Ca, S), and (2Ga, S) codoped anatase TiO₂, aiming at improving their photoelectochemical performance for water splitting. It is found that the acceptor metals (Mg, Al, Ca, and Ga), assisting the coupling of the incorporated S with the neighboring O in TiO₂, lead to the fully occupied energy levels in the forbidden band of TiO₂, which is driven by the antibonding state π* of the S–O bond. It is also found that the metal-assisted S–O coupling can prevent the recombination of the photo-generated electron–hole pairs and effectively reduce the band gap of TiO₂. Among these systems, the (Mg, S) codoped anatase TiO₂ has the narrowest band gap of 2.206 eV, and its band edges match well with the redox potentials of water. We propose that this metal-assisted S–O coupling could improve the visible light photoelectrochemical activity of anatase TiO₂.     

Modeling of Early-Age Creep of Shotcrete. II: Application to Tunneling

This paper presents the application of the material model presented in the companion paper to the structural analysis of tunnels driven according to the new Austrian tunneling method (NATM). On the one hand, two-dimensional simulations of the excavation of a tunnel driven according to the NATM are presented. They show the significance of shotcrete creep for the soil-shotcrete compound structure. These simulations constitute the main part of the paper. On the other hand, as an outlook, a hybrid method is addressed that combines, (in the framework of nonlinear finite-element analyses) the aforementioned material law with three-dimensional in situ displacement measurements performed continuously during the construction process of NATM tunnels. This method enables continuous safety assessment of tunnels and, hence, contributes essentially to online monitoring of tunnels.