164,357 research outputs found

    Slurry infiltration tests for slurry shield tunnelling in saturated sand

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    Tunnelling in saturated sand will cause excess pore pressures in the sand. This was the case during the construction of all tunnels in the Netherlands. This excess pore pressure influences the stability of the tunnel face. Therefore the magnitude of the excess pore pressure is of importance. Furthermore, it requires more information on the penetration process of the bentonite slurry as it will occur at the front of the tunnel face. This paper deals with preliminary infiltration tests to investigate some aspects of the infiltration. Results will be compared with theory

    Electrospinning of poly(ethylene-co-vinyl alcohol) nanofibres encapsulated with Ag nanoparticles for skin wound healing

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    Copyright © 2011 Chao Xu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.Skin wound healing is an urgent problem in clinics and military activities. Although significant advances have been made in its treatment, there are several challenges associated with traditional methods, for example, limited donor skin tissue for transplantation and inflammation during long-term healing time. To address these challenges, in this study we present a method to fabricate Poly(ethylene-co-vinyl alcohol) (EVOH) nanofibres encapsulated with Ag nanoparticle using electrospinning technique. The fibres were fabricated with controlled diameters (59nm-3m) by regulating three main parameters, that is, EVOH solution concentration, the electric voltage, and the distance between the injection needle tip (high-voltage point) and the fibre collector. Ag was added to the nanofibres to offer long-term anti-inflammation effect by slow release of Ag nanoparticles through gradual degradation of EVOH nanofibre. The method developed here could lead to new dressing materials for treatment of skin wounds. © 2011 Chao Xu et al.The work was partially supported by the National Natural Science Foundation of China (nos. 10825210, 10872157, and 31050110125) and the National 111 Project of China (no. B06024)

    Wave Functions of Bosonic Symmetry Protected Topological Phases

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    We study the structure of the ground state wave functions of bosonic Symmetry Protected Topological (SPT) insulators in 3 space dimensions. We demonstrate that the differences with conventional insulators are captured simply in a dual vortex description. As an example we show that a previously studied bosonic topological insulator with both global U(1) and time-reversal symmetry can be described by a rather simple wave function written in terms of dual "vortex ribbons". The wave function is a superposition of all the vortex ribbon configurations of the boson, and a factor (-1) is associated with each self-linking of the vortex ribbons. This wave function can be conveniently derived using an effective field theory of the SPT in the strong coupling limit, and it naturally explains all the phenomena of this SPT phase discussed previously. The ground state structure for other 3d bosonic SPT phases are also discussed similarly in terms of vortex loop gas wave functions. We show that our methods reproduce known results on the ground state structure of some 2d SPT phases.Comment: 10 pages, 4 figure

    Metastability of finite state Markov chains: a recursive procedure to identify slow variables for model reduction

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    Consider a sequence (ηN(t):t≥0)(\eta^N(t) :t\ge 0) of continuous-time, irreducible Markov chains evolving on a fixed finite set EE, indexed by a parameter NN. Denote by RN(η,ξ)R_N(\eta,\xi) the jump rates of the Markov chain ηtN\eta^N_t, and assume that for any pair of bonds (η,ξ)(\eta,\xi), (η′,ξ′)(\eta',\xi') arctan⁡{RN(η,ξ)/RN(η′,ξ′)}\arctan \{R_N(\eta,\xi)/R_N(\eta',\xi')\} converges as N↑∞N\uparrow\infty. Under a hypothesis slightly more restrictive (cf. \eqref{mhyp} below), we present a recursive procedure which provides a sequence of increasing time-scales \theta^1_N, \dots, \theta^{\mf p}_N, θNj≪θNj+1\theta^j_N \ll \theta^{j+1}_N, and of coarsening partitions \{\ms E^j_1, \dots, \ms E^j_{\mf n_j}, \Delta^j\}, 1\le j\le \mf p, of the set EE. Let \phi_j: E \to \{0,1, \dots, \mf n_j\} be the projection defined by \phi_j(\eta) = \sum_{x=1}^{\mf n_j} x \, \mb 1\{\eta \in \ms E^j_x\}. For each 1\le j\le \mf p, we prove that the hidden Markov chain XNj(t)=ϕj(ηN(tθNj))X^j_N(t) = \phi_j(\eta^N(t\theta^j_N)) converges to a Markov chain on \{1, \dots, \mf n_j\}

    Modelling and control of a variable-speed switched reluctance generator based wind turbine

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    This paper studies the system modelling and control aspects of switched reluctance generator (SRG) based variable speed wind turbines. A control system is implemented to provide proper operation of the SRG as well as power tracking capabilities for varying wind speeds. The control system for the grid side inverter that will allow the SRG to properly generate power to the system is also presented. Studies are presented of both the SRG and inverter control systems capabilities during a balanced three-phase fault. The paper will demonstrate that the SRG based wind turbine presents a feasible variable wind speed solution with good fault response capabilities

    Stationary states of boundary driven exclusion processes with nonreversible boundary dynamics

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    We prove a law of large numbers for the empirical density of one-dimensional, boundary driven, symmetric exclusion processes with different types of non-reversible dynamics at the boundary. The proofs rely on duality techniques

    The HIPPO pathway in gynecological malignancies

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