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Electromagnetic induction (EMI) is a popular technique to detect and discriminate buried unexploded ordnance (UXO). However, modeling of the EMI response from many types of UXO is difficult due to the small skin depth of the interior fields. In grid-based numerical methods, meshing the target volume or surface to resolve the skin depth is often highly impractical, yet a failure to do so yields inaccurate results. This paper addresses the problem with a time-domain hybrid technique based on thin-skin approximation (TSA) that is very accurate for small skin depths. The TSA method is applied to axisymmetric problems and is shown to be both fast and accurate when the skin depth is small. The method is compared with analytical results, and excellent agreement is obtained. For magnetic materials (such as steel), the TSA method is accurate for the complete time-domain EMI response. In such cases, the TSA method provides an improved accuracy along with an order-of-magnitude reduction in CPU time compared to a dense-mesh finite-element method (FEM). For nonmagnetic materials, the TSA loses accuracy as time progresses and must be combined with a coarse-mesh FEM. In such cases, the combined method still provides greater accuracy with comparable CPU time. Index Terms--Buried object detection, electromagnetic induction (EMI), finite-element method (FEM), method of moments (MoM).

A fast method of moments is presented to calculate electromagnetic wave scattering from layered one-dimensional rough surfaces. The formulation is provided for M stratified homogeneous regions, separated by M - 1 rough surfaces, and solved using point matching and pulse basis functions. Compared to the single surface case, the solution of scattering from M - 1 surfaces requires significantly more memory and computational time. To facilitate the solution, the forward-backward method with spectral acceleration is applied. As an example, a dielectric layer on a perfect electric conductor surface is studied. The numerical results are compared with the analytical solution for layered flat surfaces to partly validate the formulation. The accuracy, efficiency, and convergence of the method are then studied for various rough surfaces and layer permittivities. Index Terms--Forward-backward (FB) method, layered surfaces, method of moments, novel spectral acceleration (SA), rough surfaces, stratified surfaces.

Four properties related to left-handed metamaterials are studied numerically: transmission within a stop-band, backward phase, negative refraction, and partial focusing. The unit cell of the metamaterial under study is composed of a rod and a ring originally proposed at infrared frequencies and redesigned here at microwave frequencies. We show that this ring, because of its symmetry, exhibits a better transmission in a parallel-plate waveguide than the original concentric split-ring resonator. Negative refraction is studied from a prism-shaped metamaterial, while all of the other properties are studied from a slab-shaped metamaterial. In particular, transmission and backward phase are studied on a slab where rings naturally couple with the incident wave, while partial focusing is studied on a slab of rings perpendicular to the direction of propagation. The numerical simulations are based on a two-dimensional periodic method of moments, whose Green's function is computed via Ewald's method, and a three-dimensional finite-difference time-domain technique. Index Terms--Focusing, left-handed (LH) metamaterial, method of moments (MoM), negative index of refraction, phase measurements, prism measurements.

A mode-expansion method that needs less than 6% the number of unknowns required by conventional method of moments is introduced in calculating two-dimensional electromagnetic wave scattering from perfectly conducting objects on rough ocean surfaces. Modes are selected for dominant propagation waves so that the number of unknowns in the matrix equation are minimized. In the numerical examples, ocean surfaces are modeled as perfectly conducting rough surfaces described by the Pierson--Moskowitz power spectrum. Bistatic radar cross-sections (RCS) of various objects, such as ship-like and low-observable targets, are calculated for a 1-GHz incident plane wave and are validated for accuracy against an iterative MoM solution. Index Terms--Electromagnetic wave scattering, method of moments (MoM), mode-expansion method (MEM), rough surface.

In this paper, we present three-dimensional finite-difference time-domain (FDTD) algorithms for transient simulation of electromagnetic-wave propagation in arbitrary inhomogeneous media, which incorporate the perfectly matched layer (PML) absorbing boundary condition. We discuss the choice of constitutive parameters inside the PML layers to match the interior inhomogeneous media for planar interfaces and corner regions. We illustrate the method using both a split-field PML-FDTD formulation in Cartesian coordinates and an anisotropic medium (unsplit) PML-FDTD formulation in cylindrical coordinates. Index Terms--Absorbing boundary condition, finite-difference time domain, inhomogeneous media, perfectly matched layer.

This study analyzes the biofilm growth and long‐term current production of mixed‐culture, electrochemically active biofilms (EABs) on macrostructured electrodes under low‐shear‐force conditions. The channel dimensions were altered systematically in the range 400 μm to 2 mm, and the channel heights were varied between 1 and 4 mm to simulate macrostructures of different scales. Electrodes with finer‐structured surfaces produced higher current densities in the short term owing to their large surface area but were outperformed in the long term because the accumulation of biomass led to limitations of mass transfer into the structures. The best long‐term performance was observed for electrodes with channel dimensions of 1×4 mm, which showed no significant decrease in performance in the long term. Channels with a diameter of 400 μm were overgrown by the biofilm, which led to a transition from 3 D to 2 D behavior, indicating that structures of this scale might not be suitable for long‐term operation under low‐shear‐stress conditions. [ABSTRACT FROM AUTHOR]

In spite of its success in molecular dynamics and the advantage of being a first order propagation technique, the Car–Parrinello method and its variations have not been successful in self-consistent-field (SCF) wave function optimization due to slow convergence. In this article, we introduce a first principles fictitious mass scheme to weigh each individual density element differently and instantaneously. As an alternative to diagonalization in SCF, the Car–Parrinello scheme is implemented as a density matrix search method. Not only does the fictitious mass scheme developed herein allow a very fast SCF convergence, but also the Car–Parrinello density matrix search (CP-DMS) exhibits linear scaling with respect to the system size for alanine helical chain test molecules. The excellent performance of CP-DMS holds even for very challenging compact three-dimensional quantum particles. While the conventional diagonalization based SCF method has difficulties optimizing electronic wave functions for CdSe quantum dots, CP-DMS shows both smooth and faster convergence. [ABSTRACT FROM AUTHOR]

We present a very efficient simultaneous optimization method for both molecular geometry and electronic wave function. We introduce a simultaneous least squares scheme to minimize errors in a full local quadratic space of both geometric and wave function vectors. Several self-consistent-field iterations are taken until a uniform search direction is achieved in every geometry optimization step. Not only does this new simultaneous optimization method significantly reduce the number of self-consistent-field iterations to reach convergence, it is able to overcome shallow potential wells to find a better stationary point. This new method exhibits up to ∼60% savings in computational cost compared to conventional geometry optimization methods. [ABSTRACT FROM AUTHOR]

Electron-transfer and -capture dissociations of doubly protonated peptides have provided different product ions for a series of histidine-containing pentapeptides of both non-tryptic and tryptic type. The differences found in the dissociation are explained by different electronic states being accessed upon electron transfer and capture.

Current approaches in human embryonic stem cell (hESC) to pancreatic beta cell differentiation have largely been based on knowledge gained from developmental studies of the epithelial pancreas, while the potential roles of other supporting tissue compartments have not been fully explored. One such tissue is the pancreatic mesenchyme that supports epithelial organogenesis throughout embryogenesis. We hypothesized that detailed characterization of the pancreatic mesenchyme might result in the identification of novel factors not used in current differentiation protocols. Supplementing existing hESC differentiation conditions with such factors might create a more comprehensive simulation of normal development in cell culture. To validate our hypothesis, we took advantage of a novel transgenic mouse model to isolate the pancreatic mesenchyme at distinct embryonic and postnatal stages for subsequent proteomic analysis. Refined sample preparation and analysis conditions across four embryonic and prenatal time points resulted in the identification of 21,498 peptides with high-confidence mapping to 1,502 proteins. Expression analysis of pancreata confirmed the presence of three potentially important factors in cell differentiation: Galectin-1 (LGALS1), Neuroplastin (NPTN), and the Laminin α-2 subunit (LAMA2). Two of the three factors (LGALS1 and LAMA2) increased expression of pancreatic progenitor transcript levels in a published hESC to beta cell differentiation protocol. In addition, LAMA2 partially blocks cell culture induced beta cell dedifferentiation. Summarily, we provide evidence that proteomic analysis of supporting tissues such as the pancreatic mesenchyme allows for the identification of potentially important factors guiding hESC to pancreas differentiation. [ABSTRACT FROM AUTHOR]