Electronic band gaps and transport properties in periodically alternating mono- and bi-layer graphene superlattices

We investigate the electronic band structure and transport properties of periodically alternating mono- and bi-layer graphene superlattices (MBLG SLs). In such MBLG SLs, there exists a zero-averaged wave vector (zero-$\overline{k}$) gap that is insensitive to the lattice constant. This zero-$\overline{k}$ gap can be controlled by changing both the ratio of the potential widths and the interlayer coupling coefficient of the bilayer graphene. We also show that there exist extra Dirac points; the conditions for these extra Dirac points are presented analytically. Lastly, we demonstrate that the electronic transport properties and the energy gap of the first two bands in MBLG SLs are tunable through adjustment of the interlayer coupling and the width ratio of the periodic mono- and bi-layer graphene.Comment: More discussion is added and the English is polished. Accepted for publication in EP

New exact traveling wave solutions for the Klein–Gordon–Zakharov equations

AbstractBased on the extended hyperbolic functions method, we obtain the multiple exact explicit solutions of the Klein–Gordon–Zakharov equations. The solutions obtained in this paper include (a) the solitary wave solutions of bell-type for u and n, (b) the solitary wave solutions of kink-type for u and bell-type for n, (c) the solitary wave solutions of a compound of the bell-type and the kink-type for u and n, (d) the singular traveling wave solutions, (e) periodic traveling wave solutions of triangle function types, and solitary wave solutions of rational function types. We not only rederive all known solutions of the Klein–Gordon–Zakharov equations in a systematic way but also obtain several entirely new and more general solutions. The variety of structures of the exact solutions of the Klein–Gordon–Zakharov equations is illustrated

ADI schemes for heat equations with irregular boundaries and interfaces in 3D with applications

In this paper, efficient alternating direction implicit (ADI) schemes are proposed to solve three-dimensional heat equations with irregular boundaries and interfaces. Starting from the well-known Douglas-Gunn ADI scheme, a modified ADI scheme is constructed to mitigate the issue of accuracy loss in solving problems with time-dependent boundary conditions. The unconditional stability of the new ADI scheme is also rigorously proven with the Fourier analysis. Then, by combining the ADI schemes with a 1D kernel-free boundary integral (KFBI) method, KFBI-ADI schemes are developed to solve the heat equation with irregular boundaries. In 1D sub-problems of the KFBI-ADI schemes, the KFBI discretization takes advantage of the Cartesian grid and preserves the structure of the coefficient matrix so that the fast Thomas algorithm can be applied to solve the linear system efficiently. Second-order accuracy and unconditional stability of the KFBI-ADI schemes are verified through several numerical tests for both the heat equation and a reaction-diffusion equation. For the Stefan problem, which is a free boundary problem of the heat equation, a level set method is incorporated into the ADI method to capture the time-dependent interface. Numerical examples for simulating 3D dendritic solidification phenomenons are also presented

A novel fault location method for a cross-bonded hv cable system based on sheath current monitoring

In order to improve the practice in the operation and maintenance of high voltage (HV) cables, this paper proposes a fault location method based on the monitoring of cable sheath currents for use in cross-bonded HV cable systems. This method first analyzes the power–frequency component of the sheath current, which can be acquired at cable terminals and cable link boxes, using a Fast Fourier Transform (FFT). The cable segment where a fault occurs can be localized by the phase difference between the sheath currents at the two ends of the cable segment, because current would flow in the opposite direction towards the two ends of the cable segment with fault. Conversely, in other healthy cable segments of the same circuit, sheath currents would flow in the same direction. The exact fault position can then be located via electromagnetic time reversal (EMTR) analysis of the fault transients of the sheath current. The sheath currents have been simulated and analyzed by assuming a single-phase short-circuit fault to occur in every cable segment of a selected cross-bonded high voltage cable circuit. The sheath current monitoring system has been implemented in a 110 kV cable circuit in China. Results indicate that the proposed method is feasible and effective in location of HV cable short circuit faults

Efficient estimation of binding free energies between peptides and an MHC class II molecule using coarse‐grained molecular dynamics simulations with a weighted histogram analysis method

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137767/1/jcc24845.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137767/2/jcc24845_am.pd

Multi-Scale Modeling of Cellulosic Polymers for Optimal Drug Delivery Properties in Solid Dispersion Formulation

Solid dispersion formulation is a promising method to maintain in vivo drug solubility and to improve drug efficacy. However, the exact drug stabilization and release mechanisms of the solid dispersion formulation are unclear. In this doctoral work, we present a multi-scale modeling approach to study the solvation behavior of cellulosic polymers and their interactions with the model drug phenytoin. We compare a number of atomistic force fields and find they give similar predictions for the stiffness of the cellulose chains. We then develop systematic coarse-grained (CG) force fields for two cellulosic polymers, namely methylcellulose and hydroxylpropyl methylcellulose acetate succinate (HPMCAS), based on the radial distribution functions obtained from atomistic simulations. We use the methylcellulose CG model to simulate the self-assembly of multiple 1000 monomers long polymer chains, and find that they spontaneously form ring or tubular structures with outer diameter of 14nm and void fraction of 26%. These structures appear to be precursors to the methylcellulose fibrils, whose diameter and structure are in good agreement with both theoretical and experimental results, and thus shine light on the methylcellulose gelation mechanism. We also present a simplified continuum analytical model to predict a phase map of the collapse conformations of a single self-attractive semiflexible polymer chain in solution into either folded or ring structures depending on the chains bending energy and self-interaction energy. The predicted phase map is in good qualitative agreement with simulation results for these collapsed structures. We use the HPACAS CG model to study the intermolecular interaction modes between 9 functional groups on HPMCAS and model drug phenytoin. We adopt two criteria to quantify the effectiveness of the polymeric excipients, namely 1) the ability to inhibit drug aggregation and 2) the ability to slow down drug release. We find the size of the functional group is more responsible for the former, while the intermolecular interaction strength is more responsible for the later. Therefore, hydroxypropyl acetyl group, which has both bulky size and strong interaction strength, is the most effective functional group, followed by hydroxypropyl and acetyl group, in good agreement with the results from experimental dissolution tests. In addition, we provide continuum models and predict that the drug release time from a typical solid dispersion particle with 2μm diameter ranges from several seconds to less than 10 minutes depending on the functional group. The systematic coarse-graining approach offer molecular level insights that aid the design of high performance polymeric excipients, and can be extended to cellulosic polymers with novel functional groups and additional drug candidates of interest. Thus, our multi-scale modeling approach is of great interest to the pharmaceutical and material design fields.PHDChemical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/138745/1/wenjunh_1.pd

Construction and Examination of the Chimeric Genes Containing Deletions in the 5'-promoter Region of the L-pk Gene

Biochemistry and Molecular Biolog