An Equivalent Medium Method for the Vacuum Assisted Resin Transfer Molding Process Simulation

Computer simulation has been an efficient and cost-effective tool for liquid composite molding, including resin transfer molding (RTM), vacuum assisted resin transfer molding (VARTM), and resin infusion, compared to trial and error. The control volume finite element method (CVFEM) has been the predominant method for simulation. When the CVFEM simulation is used for the VARTM process, because of the existence of two distinct flow media: fiber preform and high permeable media (HPM), 3-D models are required. Since the HPM is usually much thinner than the fiber preform, a large number of nodes and elements need to be used in simulation, which significantly increases the computation load and time. In addition, the time-consuming preprocessing process makes simulation not feasible for industry applications. This article presents an equivalent medium method (EMM) for fast and accurate VARTM process simulation. This method increases the thickness of the HPM or both the HPM and the fiber preform and applies the equivalent material properties. This is an improved method over previously presented equivalent permeability method (EPM) by correcting its two shortcomings: (1) The EPM does not account for the influence of the porosity of HPM, thus the resin flow through HPM is changed and (2) The EPM does not consider the change of through-thickness permeability after the equivalence. A new mesh generation algorithm is also discussed, which provides a faster and more convenient way for preprocessing. The approach presented in this article provides the fundamental for developing a universal computer simulation tool for both the RTM and VARTM processes. The effectiveness of this approach has been validated by comparing to the conventional CVFEM simulation and experiments

Axial stretching of extremity artery induces reversible hyperpolarization of smooth muscle cell membrane in vivo

Circumferential stretch due to increases in pressure induces vascular smooth muscle cell depolarization and contraction known as the myogenic response. The aim of this study was to determine the in vivoeffects of axial-longitudinal stretch of the rat saphenous artery (SA) on smooth muscle membrane potential (Em) and on external diameter. Consecutive elongations of the SA were carried out from resting length (L0) in 10% increments up to 140% L0 while changes in membrane potential and diameter were determined in intact and de-endothelized vessels. Axial stretching resulted in a small initial depolarization at 120% of L0 followed by a progressive 20 to 33% hyperpolarizaion of vascular smooth muscle between 130% and 140% of L0. At 140%, an average maximal 10.6 mV reversible hyperpolarization was measured compared to –41.2±0.49 mV Em at 100% L0. De-endothelialization completely eliminated the hyperpolarization to axial stretching and augmented the reduction of diameter beyond 120% L0. These results indicate that arteries have a mechanism to protect them from vasospasm that could otherwise occur with movements of the extremities

Envisioning the future of aquatic animal tracking: Technology, science, and application

Electronic tags are significantly improving our understanding of aquatic animal behavior and are emerging as key sources of information for conservation and management practices. Future aquatic integrative biology and ecology studies will increasingly rely on data from electronic tagging. Continued advances in tracking hardware and software are needed to provide the knowledge required by managers and policymakers to address the challenges posed by the world's changing aquatic ecosystems. We foresee multiplatform tracking systems for simultaneously monitoring the position, activity, and physiology of animals and the environment through which they are moving. Improved data collection will be accompanied by greater data accessibility and analytical tools for processing data, enabled by new infrastructure and cyberinfrastructure. To operationalize advances and facilitate integration into policy, there must be parallel developments in the accessibility of education and training, as well as solutions to key governance and legal issues

Schottky barrier heights at polar metal/semiconductor interfaces

Using a first-principle pseudopotential approach, we have investigated the Schottky barrier heights of abrupt Al/Ge, Al/GaAs, Al/AlAs, and Al/ZnSe (100) junctions, and their dependence on the semiconductor chemical composition and surface termination. A model based on linear-response theory is developed, which provides a simple, yet accurate description of the barrier-height variations with the chemical composition of the semiconductor. The larger barrier values found for the anion- than for the cation-terminated surfaces are explained in terms of the screened charge of the polar semiconductor surface and its image charge at the metal surface. Atomic scale computations show how the classical image charge concept, valid for charges placed at large distances from the metal, extends to distances shorter than the decay length of the metal-induced-gap states.Comment: REVTeX 4, 11 pages, 6 EPS figure

Electron energy loss and induced photon emission in photonic crystals

The interaction of a fast electron with a photonic crystal is investigated by solving the Maxwell equations exactly for the external field provided by the electron in the presence of the crystal. The energy loss is obtained from the retarding force exerted on the electron by the induced electric field. The features of the energy loss spectra are shown to be related to the photonic band structure of the crystal. Two different regimes are discussed: for small lattice constants $a$ relative to the wavelength of the associated electron excitations $\lambda$, an effective medium theory can be used to describe the material; however, for $a\sim\lambda$ the photonic band structure plays an important role. Special attention is paid to the frequency gap regions in the latter case.Comment: 12 pages, 7 figure

Black Hole Spin via Continuum Fitting and the Role of Spin in Powering Transient Jets

The spins of ten stellar black holes have been measured using the continuum-fitting method. These black holes are located in two distinct classes of X-ray binary systems, one that is persistently X-ray bright and another that is transient. Both the persistent and transient black holes remain for long periods in a state where their spectra are dominated by a thermal accretion disk component. The spin of a black hole of known mass and distance can be measured by fitting this thermal continuum spectrum to the thin-disk model of Novikov and Thorne; the key fit parameter is the radius of the inner edge of the black hole's accretion disk. Strong observational and theoretical evidence links the inner-disk radius to the radius of the innermost stable circular orbit, which is trivially related to the dimensionless spin parameter a_* of the black hole (|a_*| < 1). The ten spins that have so far been measured by this continuum-fitting method range widely from a_* \approx 0 to a_* > 0.95. The robustness of the method is demonstrated by the dozens or hundreds of independent and consistent measurements of spin that have been obtained for several black holes, and through careful consideration of many sources of systematic error. Among the results discussed is a dichotomy between the transient and persistent black holes; the latter have higher spins and larger masses. Also discussed is recently discovered evidence in the transient sources for a correlation between the power of ballistic jets and black hole spin.Comment: 30 pages. Accepted for publication in Space Science Reviews. Also to appear in hard cover in the Space Sciences Series of ISSI "The Physics of Accretion onto Black Holes" (Springer Publisher). Changes to Sections 5.2, 6.1 and 7.4. Section 7.4 responds to Russell et al. 2013 (MNRAS, 431, 405) who find no evidence for a correlation between the power of ballistic jets and black hole spi

GWAS for Interleukin-1β levels in gingival crevicular fluid identifies IL37 variants in periodontal inflammation

There is no agnostic GWAS evidence for the genetic control of IL-1β expression in periodontal disease. Here we report a GWAS for “high” gingival crevicular fluid IL-1β expression among 4910 European-American adults and identify association signals in the IL37 locus. rs3811046 at this locus (p = 3.3 × 10−22) is associated with severe chronic periodontitis (OR = 1.50; 95% CI = 1.12–2.00), 10-year incident tooth loss (≥3 teeth: RR = 1.33; 95% CI = 1.09–1.62) and aggressive periodontitis (OR = 1.12; 95% CI = 1.01–1.26) in an independent sample of 4927 German/Dutch adults. The minor allele at rs3811046 is associated with increased expression of IL-1β in periodontal tissue. In RAW macrophages, PBMCs and transgenic mice, the IL37 variant increases expression of IL-1β and IL-6, inducing more severe periodontal disease, while IL-37 protein production is impaired and shows reduced cleavage by caspase-1. A second variant in the IL37 locus (rs2708943, p = 4.2 × 10−7) associates with attenuated IL37 mRNA expression. Overall, we demonstrate that IL37 variants modulate the inflammatory cascade in periodontal disease