Mechanically-Induced Transport Switching Effect in Graphene-based Nanojunctions

We report a theoretical study suggesting a novel type of electronic switching effect, driven by the geometrical reconstruction of nanoscale graphene-based junctions. We considered junction struc- tures which have alternative metastable configurations transformed by rotations of local carbon dimers. The use of external mechanical strain allows a control of the energy barrier heights of the potential profiles and also changes the reaction character from endothermic to exothermic or vice-versa. The reshaping of the atomic details of the junction encode binary electronic ON or OFF states, with ON/OFF transmission ratio that can reach up to 10^4-10^5. Our results suggest the possibility to design modern logical switching devices or mechanophore sensors, monitored by mechanical strain and structural rearrangements.Comment: 10 pages, 4 figure

Comparative Numerical Study on Focusing Wave Interaction with FPSO-like Structure

Evaluating the interactions between offshore structures and extreme waves plays an essential role for securing the surviv-ability of the structures. For this purpose, various numerical tools—for example, the fully nonlinear potential theory (FNPT),the Navier–Stokes (NS) models, and hybrid approaches combining different numerical models—have been developed andemployed. However, there is still great uncertainty over the required level of model fidelity when being applied to a widerange of wave-structure interaction problems. This paper aims to shed some light on this issue with a specific focus on theoverall error sourced from wave generation/absorbing techniques and resolving the viscous and turbulent effects, by com-paring the performances of three different models, including the quasi-arbitrary Lagrangian Eulerian finite element method(QALE-FEM) based on the FNPT, an in-house two-phase NS model with large-eddy simulation and a hybrid model couplingthe QALE-FEM with the OpenFOAM/InterDymFoam, in the cases with a fixed FPSO-like structure under extreme focus-ing waves. The relative errors of numerical models are defined against the experimental data, which are released after thenumerical works have been completed (i.e., a blind test), in terms of the pressure and wave elevations. This paper providesa practical reference for not only choosing an appropriate model in practices but also on developing/optimizing numericaltools for more reliable and robust predications

Generalized Haldane Equation and Fluctuation Theorem in the Steady State Cycle Kinetics of Single Enzymes

Enyzme kinetics are cyclic. We study a Markov renewal process model of single-enzyme turnover in nonequilibrium steady-state (NESS) with sustained concentrations for substrates and products. We show that the forward and backward cycle times have idential non-exponential distributions: \QQ_+(t)=\QQ_-(t). This equation generalizes the Haldane relation in reversible enzyme kinetics. In terms of the probabilities for the forward ($p_+$) and backward ($p_-$) cycles, $k_BT\ln(p_+/p_-)$ is shown to be the chemical driving force of the NESS, $\Delta\mu$. More interestingly, the moment generating function of the stochastic number of substrate cycle $\nu(t)$, follows the fluctuation theorem in the form of Kurchan-Lebowitz-Spohn-type symmetry. When $\lambda$ = $\Delta\mu/k_BT$, we obtain the Jarzynski-Hatano-Sasa-type equality: $\equiv$ 1 for all $t$, where $\nu\Delta\mu$ is the fluctuating chemical work done for sustaining the NESS. This theory suggests possible methods to experimentally determine the nonequilibrium driving force {\it in situ} from turnover data via single-molecule enzymology.Comment: 4 pages, 3 figure

Some estimates of Wang-Yau quasilocal energy

Given a spacelike 2-surface $\Sigma$ in a spacetime $N$ and a constant future timelike unit vector $T_0$ in $\R^{3,1}$, we derive upper and lower estimates of Wang-Yau quasilocal energy $E(\Sigma, X, T_0)$ for a given isometric embedding $X$ of $\Sigma$ into a flat 3-slice in $\R^{3,1}$. The quantity $E(\Sigma, X, T_0)$ itself depends on the choice of $X$, however the infimum of $E(\Sigma, X, T_0)$ over $T_0$ does not. In particular, when $\Sigma$ lies in a time symmetric 3-slice in $N$ and has nonnegative Brown-York quasilocal mass \mby(\Sigma), our estimates show that $\inf\limits_{T_0}E(\Sigma, X, T_0)$ equals \mby (\Sigma). We also study the spatial limit of $\inf\limits_{T_0}E(S_r,X_r,T_0)$, where $S_r$ is a large coordinate sphere in a fixed end of an asymptotically flat initial data set $(M, g, p)$ and $X_r$ is an isometric embeddings of $S_r$ into $\mathbb{R}^3 \subset \mathbb{R}^{3,1}$. We show that if $(M, g, p)$ has future timelike ADM energy-momentum, then $\lim\limits_{r\to\infty}\inf\limits_{T_0}E(S_r,X_r,T_0)$ equals the ADM mass of $(M, g, p)$.Comment: 17 page

Algebraic-matrix calculation of vibrational levels of triatomic molecules

We introduce an accurate and efficient algebraic technique for the computation of the vibrational spectra of triatomic molecules, of both linear and bent equilibrium geometry. The full three-dimensional potential energy surface (PES), which can be based on entirely {\it ab initio} data, is parameterized as a product Morse-cosine expansion, expressed in bond-angle internal coordinates, and includes explicit interactions among the local modes. We describe the stretching degrees of freedom in the framework of a Morse-type expansion on a suitable algebraic basis, which provides exact analytical expressions for the elements of a sparse Hamiltonian matrix. Likewise, we use a cosine power expansion on a spherical harmonics basis for the bending degree of freedom. The resulting matrix representation in the product space is very sparse and vibrational levels and eigenfunctions can be obtained by efficient diagonalization techniques. We apply this method to carbonyl sulfide OCS, hydrogen cyanide HCN, water H$_2$O, and nitrogen dioxide NO$_2$. When we base our calculations on high-quality PESs tuned to the experimental data, the computed spectra are in very good agreement with the observed band origins.Comment: 11 pages, 2 figures, containg additional supporting information in epaps.ps (results in tables, which are useful but not too important for the paper

A Cartesian cut-cell based multiphase flow model for large-eddy simulation of three-dimensional wave-structure interaction

A multiphase flow numerical approach for performing large-eddy simulations of three-dimensional (3D) wave-structure interaction is presented in this study. The approach combines a volume-of-fluid method to capture the air-water interface and a Cartesian cut-cell method to deal with complex geometries. The filtered Navier–Stokes equations are discretised by the finite volume method with the PISO algorithm for velocity-pressure coupling and the dynamic Smagorinsky subgrid-scale model is used to compute the unresolved (subgrid) scales of turbulence. The versatility and robustness of the presented numerical approach are illustrated by applying it to solve various three-dimensional wave-structure interaction problems featuring complex geometries, such as a 3D travelling wave in a closed channel, a 3D solitary wave interacting with a vertical circular cylinder, a 3D solitary wave interacting with a horizontal thin plate, and a 3D focusing wave impacting on an FPSO-like structure. For all cases, convincing agreement between the numerical predictions and the corresponding experimental data and/or analytical or numerical solutions is obtained. In addition, for all cases, water surface profiles and turbulent vortical structures are presented and discussed

A Cartesian cut-cell based multiphase flow model for large-eddy simulation of three-dimensional wave-structure interaction

A multiphase flow numerical approach for performing large-eddy simulations of three-dimensional (3D) wave-structure interaction is presented in this study. The approach combines a volume-of-fluid method to capture the air-water interface and a Cartesian cut-cell method to deal with complex geometries. The filtered Navier–Stokes equations are discretised by the finite volume method with the PISO algorithm for velocity-pressure coupling and the dynamic Smagorinsky subgrid-scale model is used to compute the unresolved (subgrid) scales of turbulence. The versatility and robustness of the presented numerical approach are illustrated by applying it to solve various three-dimensional wave-structure interaction problems featuring complex geometries, such as a 3D travelling wave in a closed channel, a 3D solitary wave interacting with a vertical circular cylinder, a 3D solitary wave interacting with a horizontal thin plate, and a 3D focusing wave impacting on an FPSO-like structure. For all cases, convincing agreement between the numerical predictions and the corresponding experimental data and/or analytical or numerical solutions is obtained. In addition, for all cases, water surface profiles and turbulent vortical structures are presented and discussed