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Abstract: We present a new approach to the simulation of viscous fingering instabilities in incompressible, miscible displacement flows in porous media. In the past, high resolution computational simulations of viscous fingering instabilities have always been performed using high-order finite difference or Fourier-spectral methods which do not posses the flexibility to compute very complex subsurface geometries. Our approach, instead, by means of a fully-coupled nonlinear implementation of the discontinuous Galerkin method, possesses a fundamental differentiating feature, in that it maintains high-order accuracy on fully unstructured meshes. In addition, the proposed method shows very low sensitivity to mesh orientation, in contrast with classical finite volume approximation used in porous media flow simulations. The robustness and accuracy of the method are demonstrated in a number of challenging computational problems. [Copyright &y& Elsevier]

• A longitudinal bar with generic boundary conditions shares the same harmonic response formula as the Fabry-Perot resonator. • The natural frequencies of a longitudinal bar can be determined directly from the phase matching condition of the Fabry-Perot resonators. • The phase shift introduced by a boundary can be derived from the boundary condition. • Concepts and signal processing algorithms developed for optical Fabry-Perot resonator sensors can be directly transferred to the study of a longitudinal bar. • This work lays the theoretical foundation for future developments of mechanical FPR sensors. Fabry-Perot resonator (FPR) is an important concept for the study of optical and microwave systems. But it is a relatively alien concept for mechanical engineers. This paper reveals that a lossless bar (i.e. a bar whose Young's modulus is a real number) undergoing longitudinal vibrations is essentially a Fabry-Perot resonator. First, the harmonic response of a longitudinal bar with generic mass-damper-spring (MDS) boundaries is derived to show that it is identical to the Airy function of an optical FPR. The derivation confirms that the resonance of a longitudinal bar is due to the superposition (i.e. interference) of the longitudinal waves travelling back and forth between the two boundaries. Next, the transmission and phase shifts at the MDS boundaries are derived. Based on which, the resonant frequencies of the longitudinal bar with different boundary conditions are determined directly from the phase matching condition. A perfect agreement with those obtained from conventional approaches was achieved. Finally, the concepts of whitelight interference (WLI) and fringe analysis are applied to determine the bar length from the calculated frequency response function (FRF). The results presented demonstrate that the data processing algorithms developed for optical and microwave FPRs are directly transferable to the study of longitudinal bars. This work lays the theoretical foundation for future developments of mechanical FPR sensors. [ABSTRACT FROM AUTHOR]

Neurotoxic methylmercury (MeHg) accumulates in rice grain from paddy soil, where its concentration is controlled by microbial mercury methylation and demethylation. Both up- and down-regulation of methylation is known to occur in the presence of rice plants in comparison to non-vegetated paddy soils; the influence of rice plant presence/absence on demethylation is unknown. To assess the concurrent influence of rice plant presence/absence on methylation and demethylation, and to determine which process was more dominant in controlling soil MeHg concentrations, we maintained six rhizoboxes of paddy soil with and without rice plants. At the peak of plant growth, we simultaneously measured ambient MeHg, ambient inorganic mercury (IHg), and potential rate constants of methylation and demethylation (K meth and K demeth) in soil using stable isotope tracers and ID-GC-ICPMS. We also measured organic matter content, elemental S, and water-extractable sulfate. We found MeHg concentrations were differentially controlled by MeHg production and degradation processes, depending on whether plants were present. In non-vegetated boxes, MeHg concentration was controlled by K meth , as evidenced by a strong and positive correlation, while K demeth had no relation to MeHg concentration. These results indicate methylation was the dominant driver of MeHg concentration in non-vegetated soil. In vegetated boxes, K demeth strongly and negatively predicted MeHg concentration, indicating that demethylation was the dominant control in soil with plants. MeHg concentration, K meth , and % MeHg all had significantly less variance in vegetated than in non-vegetated soils due to a consistent elimination of greater values. This pattern suggests that reduced MeHg production capacity was a secondary control on MeHg concentrations in vegetated soils. We observed no difference in the magnitude or variance of K demeth between treatments, suggesting that demethylation was robust to soil chemical conditions influenced by the plant, perhaps because of a wider taxonomic diversity of demethylators. Our results suggest that methylation and demethylation processes could both be leveraged to alter MeHg concentrations in rice paddy soil. [Display omitted] • MeHg concentrations are controlled by methylation in soil without plants. • Both methylation and demethylation drive MeHg concentrations in vegetated soil. • IHg bioavailability and C and S dynamics may explain methylation patterns. • Drivers of demethylation should be identified to harness this process as a management strategy. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the integrated optimization of actuator placement and vibration control for piezoelectric adaptive truss is studied. Based on the dynamic finite element (FE) model and a linear-quadratic-Gaussian (LQG) model of vibration control for an adaptive truss, an integrated optimization model is built in which an improved quadratic performance index is adopted as the objective function and the mode closed-loop damping ratio, modal controllability and actuator number are selected as the constraints. A layered optimization strategy is implemented to address this optimization problem with discrete-continuous design variable. To prevent the optimization process from converging to the local optimal solution, the genetic algorithm (GA) for outside-layer optimization is extended with an improved penalty function. Numerical examples and the vibration control experiments for piezoelectric adaptive truss were used to validate the efficiency of the proposed method. The following conclusions were drawn from the results. (1) The improved penalty function can orient the optimization process to the global optimal solution. (2) Although the number of struts on the truss is large, the optimization computation time is short because of the high efficiency of the proposed method. (3) In the experiment, the quadratic performance index, modal response and sensor signals for the present paper''s optimal actuator placement scheme are better than those described in the literature, but the placement requires more energy, which is consistent with the numerical results. [Copyright &y& Elsevier]

The toxic effects of two brominated diphenyl ethers (BDE), BDE-47, and BDE-183, on a benthic oligochaete tubificid, Monopylephorus limosus were studied under laboratory conditions. Investigated responses included survival, growth, and protein expression profiles, at BDE concentrations of 1, 10, 100, and 700ng/g on a dry soil weight basis, with isooctane as the carrier solvent. Body weight losses among treatments were insignificant after 8 weeks of exposure. The 8-wk LC50 of BDE-47 and -183 were 2311 and 169ng/g, respectively. By applying multivariate analysis techniques, protein expression patterns were compared and correlated with stressful sources of long-term culture, carrier solvent, BDE-47 and -183. The treatment of 8-wk 100ng/g BDE-47 was most closely clustered to the 10ng/g BDE-183 treatment, based on the 40 examined protein spots. This indicated that BDE-183 was more potent to M. limosus, than was BDE-47. The 2-wk and 8-wk controls clustered into different groups indicating the occurrence of physiological changes due to long-term laboratory culture. Additionally, solvent effect was shown by grouping the isooctane carrier to different clusters. With further characterization by principle component analysis, it was found that the separation was mainly contributed by the 2nd principal-component. And, the primarily inhibitory variation was at spots 2 (UMP-CMP kinase) and 40 (plasma retinol-binding protein precursor) in the 8-wk groups. On the contrary, protein spots 16 (cell division control protein 2 homolog) and 24 (mitochondrial DNA mismatch repair protein) showed stimulatory variation. In all, the observed proteomic responses suggest that BDEs disrupted metabolic function in M. limosus and multivariate analysis tool offers significant potential for the assessment of various stress sources at biochemical level. [Copyright &y& Elsevier]

Abstract: In this paper, we study constrained multiobjective optimization problems with objectives being closed-graph multifunctions in Banach spaces. In terms of the coderivatives and Clarke''s normal cones, we establish Lagrange multiplier rules for super efficiency as necessary or sufficient optimality conditions of the above problems. [Copyright &y& Elsevier]

Abstract: The need to compute potentials of the form R −ν for ν ⩾1 occur in a variety of areas ranging from electromagnetics to biophysics to molecular dynamics to astrophysics, etc. For instance, Coulomb, London, Lennard-Jones, H-bonds are of the form , 5, 6 (and 12), 10, respectively. For a systems with N source/observation points, the cost of computing these potentials scales proportional to . Methods to overcome this computational bottleneck have been a popular research topic for quite some time. For instance, the fast multipole method (FMM) and their cousins—tree codes—have revolutionized the computation of electrostatic potentials (ν =1). These methods rely on a hierarchical decomposition of the computational domain, i.e, construction of a regular oct-tree decomposition, and exploits the principle of divide and conquer to compute potentials at each observation point. This paper presents two methods, in the vein of FMM, albeit based on Cartesian tensors. The salient features of the first are as follows: (i) it relies on totally symmetric tensors and (ii) the errors are independent of the height of the tree. The second method is presented specifically for ν =1, and relies on traceless totally symmetric Cartesian tensors. Using the relationship between traceless Cartesian tensors and spherical harmonics, it will be shown that this technique has the same computational cost as the classical FMM. Generalization of the second method for ν ≠1 is trivial; however, one needs to use totally symmetric tensors instead. Finally, in the whole computation scheme, only the translation operator (that used to traverse across the tree) depends on ν. Convergence of the proposed method is proven for all . Numerical results that validate the cost and accuracy are presented for several potential functions; these include those typically encountered in the analysis of physical systems (Coulombic, Lennard-Jones, Lattice gas). [Copyright &y& Elsevier]

To characterize the active domain of the simian immunodeficiency virus (SIV) surface unit (SU) enterotoxin, peptides corresponding to the V3 loop of SIVmac239 (SIVmac) and SIVsmmPBj41 (SIVpbj) were synthesized and examined for enterotoxic activity, α-helical structure, and interaction(s) with model membranes. SIVmac and SIVpbj induced a dose-dependent diarrhea in 6–8-day-old mouse pups similar to full-length SU. The peptides mobilized [Ca2+]i in HT-29 cells with distinct oscillations and elevated inositol triphosphate levels. Circular dichroism analyses showed the peptides were predominantly random coil in buffer, but increased in α-helical content when placed in a hydrophobic environment or with cholesterol-containing membrane vesicles that are rich in anionic phospholipids. None of the peptides underwent significant secondary structural changes in the presence of neutral vesicles indicating ionic interactions were important. These data show that the SIV SU enterotoxic domain localizes in part to the V3 loop region and interacts with anionic membrane domains on the host cell surface. [Copyright &y& Elsevier]

Given a convex body K ⊆ R n and p ∈ R , we introduce and study the extremal inner and outer affine surface areas I S p (K) = sup K ′ ⊆ K ⁡ (as p (K ′)) and o s p (K) = inf K ′ ⊇ K ⁡ (as p (K ′)) , where as p (K ′) denotes the L p -affine surface area of K ′ , and the supremum is taken over all convex subsets of K and the infimum over all convex compact subsets containing K. The convex body that realizes I S 1 (K) in dimension 2 was determined in [3] where it was also shown that this body is the limit shape of lattice polytopes in K. In higher dimensions no results are known about the extremal bodies. We use a thin shell estimate of [23] and the Löwner ellipsoid to give asymptotic estimates on the size of I S p (K) and o s p (K). Surprisingly, it turns out that both quantities are proportional to a power of volume. [ABSTRACT FROM AUTHOR]

This paper presents a vibration control strategy for a two-link Flexible Joint Manipulator (FJM) with a Hexapod Active Manipulator (HAM). A dynamic model of the multi-body, rigid–flexible system composed of an FJM, a HAM and a spacecraft was built. A hybrid controller was proposed by combining the Input Shaping (IS) technique with an Adaptive-Parameter Auto Disturbance Rejection Controller (APADRC). The controller was used to suppress the vibration caused by external disturbances and input motions. Parameters of the APADRC were adaptively adjusted to ensure the characteristic of the closed loop system to be a given reference system, even if the configuration of the manipulator significantly changes during motion. Because precise parameters of the flexible manipulator are not required in the IS system, the operation of the controller was sufficiently robust to accommodate uncertainties in system parameters. Simulations results verified the effectiveness of the HAM scheme and controller in the vibration suppression of FJM during operation. [ABSTRACT FROM AUTHOR]

Abstract High resolution simulation of viscous fingering can offer an accurate and detailed prediction for subsurface engineering processes involving fingering phenomena. The fully implicit discontinuous Galerkin (DG) method has been shown to be an accurate and stable method to model viscous fingering with high Peclet number and mobility ratio. In this paper, we present two techniques to speedup large scale simulations of this kind. The first technique relies on a simple p -adaptive scheme in which high order basis functions are employed only in elements near the finger fronts where the concentration has a sharp change. As a result, the number of degrees of freedom is significantly reduced and the simulation yields almost identical results to the more expensive simulation with uniform high order elements throughout the mesh. The second technique for speedup involves improving the solver efficiency. We present an algebraic multigrid (AMG) preconditioner which allows the DG matrix to leverage the robust AMG preconditioner designed for the continuous Galerkin (CG) finite element method. The resulting preconditioner works effectively for fixed order DG as well as p -adaptive DG problems. With the improvements provided by the p -adaptivity and AMG preconditioning, we can perform high resolution three-dimensional viscous fingering simulations required for miscible displacement with high Peclet number and mobility ratio in greater detail than before for well injection problems. Highlights • Two techniques to speedup large scale simulations of viscous fingering using implicit DG are presented. • The first technique relies on a simple p -adaptive scheme and results in significant reduction in the problem size. • In the second technique, we design an algebraic multigrid (AMG) to improve the solver efficiency. • The new techniques enable high resolution 3D viscous fingering simulations in greater detail than before. [ABSTRACT FROM AUTHOR]

The proliferation of four-dimensional imaging technologies, increasing computational speeds, improved simulation algorithms, and the widespread availability of powerful computing platforms is enabling simulations of cardiac hemodynamics with unprecedented speed and fidelity. Since cardiovascular disease is intimately linked to cardiovascular hemodynamics, accurate assessment of the patient's hemodynamic state is critical for the diagnosis and treatment of heart disease. Unfortunately, while a variety of invasive and non-invasive approaches for measuring cardiac hemodynamics are in widespread use, they still only provide an incomplete picture of the hemodynamic state of a patient. In this context, computational modeling of cardiac hemodynamics presents as a powerful non-invasive modality that can fill this information gap, and significantly impact the diagnosis as well as the treatment of cardiac disease. This article reviews the current status of this field as well as the emerging trends and challenges in cardiovascular health, computing, modeling and simulation and that are expected to play a key role in its future development. Some recent advances in modeling and simulations of cardiac flow are described by using examples from our own work as well as the research of other groups. [ABSTRACT FROM AUTHOR]

Background: White matter (WM) integrity declines with normal aging. Physical activity may attenuate age-related WM integrity changes and improve cognitive function. This study examined brain WM integrity in Masters athletes who have engaged in life-long aerobic exercise training. We tested the hypothesis that life-long aerobic training is associated with improved brain WM integrity in older adults. Methods: Ten Masters athletes (3 females, age=72.2±5.3years, endurance training >15years) and 10 sedentary older adults similar in age and educational level (2 females, age=74.5±4.3years) participated. MRI fluid-attenuated-inversion-recovery (FLAIR) images were acquired to assess white matter hyperintensities (WMH) volume. Diffusion tensor imaging (DTI) was performed to evaluate the WM microstructural integrity with a DTI-derived metric, fractional anisotropy (FA) and mean diffusivity (MD). Results: After normalization to whole-brain volume, Masters athletes showed an 83% reduction in deep WMH volume relative to their sedentary counterparts (0.05±0.05% vs. 0.29±0.29%, p<0.05). In addition, we found an inverse relationship between aerobic fitness (VO2max) and deep WMH volume (r=−0.78, p<0.001). Using TBSS, Masters athletes showed higher FA values in the right superior corona radiata (SCR), both sides of superior longitudinal fasciculus (SLF), right inferior fronto-occipital fasciculus (IFO), and left inferior longitudinal fasciculus (ILF). In addition, Masters athletes also showed lower MD values in the left posterior thalamic radiation (PTR) and left cingulum hippocampus. Conclusions: These findings suggest that life-long exercise is associated with reduced WMH and may preserve WM fiber microstructural integrity related to motor control and coordination in older adults. [ABSTRACT FROM AUTHOR]