The development of a physiologically-based pharmacokinetic model using the distribution of 2,3,7,8-tetrachlorodibenzo-p-dioxin in the tissues of the eastern oyster (Crassostrea virginica)

A physiologically-based pharmacokinetic model (PBPK) was developed to describe the kinetics of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the eastern oyster (Crassostrea virginica). The estimated t(1/2) of elimination for a bolus dose of TCDD in C. virginica is approximately 14-24 days based on both the experimental data and the PBPK model. The highest dioxin concentration reached during 28-days was in the digestive gland followed by the mantle, gonad, hemolymph, gill, adductor muscle, and the kidney/heart. A binding protein for 2,3,7,8-TCDD had been reported in the literature for both the digestive gland and gonad. Incorporating a binding component in the model resulted in a better fit for the data. The PBPK model predicted the distribution and the elimination concentrations for 2,3,7,8-TCDD within each of the tissue compartments. This model will serve as a useful tool for predicting the kinetics of other persistent organic pollutants as well as, allow for a more refined ecological risk assessment by estimating dioxin concentrations in sensitive tissues such as the gonad.     

Seismic shear vibration of embankment dams in semi-cylindrical valleys

A rigorous analytical solution is developed for the lateral linear shear response of embankment dams in semi-cylindrical valleys. Closed-form algebraic expressions are presented pertaining to both free and base-induced oscillations, and extensive parametric and comparative studies elucidate the prominent effects of canyon geometry (shape and aspect ratio) on dynamic response. Harmonic steady-state as well as earthquake-induced accelerations, displacements and shear strains in the dam are studied and compared with those obtained from 3-Dimensional analyses for other canyon geometries, as well as from 2-Dimensional (2-D) analyses of the dam mid-section. It is shown that such 2-D analyses may provide significantly lower values of near-crest accelerations, but slightly higher values of shear strains and stresses than the 3-D analyses. The proposed method of analysis is at least three orders of magnitude less expensive than other presently available numerical procedures.     

Local-soil and source-mechanism effects in the 1986 kalamata (Greece) earthquake

An M_s ～ 6 earthquake, originating at a normal fault directly underneath the town of Kalamata, caused substantial structural damage to reinforced-concrete and masonry buildings, to contemporary as well as centuries-old churches, and to a major harbour quaywall. Two accelerograms were recorded on stiff alluvial deposits. The seismologic and engineering facts of the earthquake are presented in the first half of the paper. Particular attention is paid to the non-uniform pattern of damage distribution, at both regional and local scale. The second half of the paper investigates the possible role of the ‘local soil conditions’ and of the ‘mechanics of the source’ in the observed pattern of damage and in the amplitude and frequency composition of the two records. To this end, numerical modelling of site-specific motions is attempted using state-of-practice methods, and utilizing the results of an extensive geotechnical exploration programme. It is concluded that substantial evidence does exist indicating that both soil and source effects have contributed to the non-uniform spatial distribution of damage. The effect of through-soil ‘filtering’ of the seismic waves appears most evident in the coastal neighbourhoods of the town, where the underlying loose saturated silty sands in the over-50 m-deep soil deposit may have played a beneficial role in weakening the ground-surface shaking; the structural damage in these areas was insignificant. Qualitative arguments are also put forward for explaining some aspects of the observed pattern of damage in terms of fault orientation and ‘directivity’ effects.     

Nonlinear dynamic analysis of multi-base seismically isolated structures with uplift potential I： formulation

The complexity of modern seismically isolated structures requires the analysis of the structural system and the isolation system in its entirety and the ability to capture potential discontinuous phenomena such as isolator uplift and their effects on the superstructures and the isolation hardware. In this paper, an analytical model is developed and a computational algorithm is formulated to analyze complex seismically isolated superstructures even when undergoing highly-nonlinear phenomena such as uplift. The computational model has the capability of modeling various types of isolation devices with strong nonlinearities, analyzing multiple superstructures (up to five separate superstructures) on multiple bases (up to five bases), and capturing the effects of lateral loads on bearing axial forces, including bearing uplift. The model developed herein has been utilized to form the software platform 3D-BASIS-ME-MB, which provides the practicing engineering community with a versatile tool for analysis and design of complex structures with modern isolation systems.     

Nonlinear dynamic analysis of multi-base seismically isolated structures with uplift potential II： verification examples

The work presented in this paper serves as numerical verification of the analytical model developed in the companion paper for nonlinear dynamic analysis of multi-base seismically isolated structures. To this end, two numerical examples have been analyzed using the computational algorithm incorporated into program 3D-BASIS-ME-MB, developed on the basis of the newly-formulated analytical model. The first example concerns a seven-story model structure that was tested on the earthquake simulator at the University at Buffalo and was also used as a verification example for program SAP2000. The second example concerns a two-tower, multi-story structure with a split-level seismic-isolation system. For purposes of verification, key results produced by 3D-BASIS-ME-MB are compared to experimental results, or results obtained from other structural/finite element programs. In both examples, the analyzed structure is excited under conditions of bearing uplift, thus yielding a case of much interest in verifying the capabilities of the developed analysis tool.     

Galaxies and Star Clusters – From the Computer to the Real World

G01 New evidence for a connection between massive black holes and ULX G02 Long‐Term Evolution of Massive Black Hole Binaries G03 NBODY Meets Stellar Population Synthesis G04 N‐body modelling of real globular star clusters G05 Fokker‐Planck rotating models of globular clusters with black hole G06 Observational Manifestation of chaos in spiral galaxies: quantitative analysis and qualitative explanation G07 GRAPE Clusters: Beyond the Million‐Body Problem G08 Orbital decay of star clusters and Massive Black Holes in cuspy galactic nuclei G09 An Edge‐on Disk Galaxy Catalog G10 Complexes of open clusters in the Solar neighborhood G11 Search for and investigation of new stellar clusters using the data from huge stellar catalogues G12 Computing 2D images of 3D galactic disk models G13 Outer Pseudoring in the Galaxy G14 Where are tidal‐dwarf galaxies? G15 Ultra compact dwarf galaxies in nearby clusters G16 Impact of an Accretion Disk on the Structure of a stellar cluster in active galactic nuclei G17 Order and Chaos in the edge‐on profiles of disk galaxies G18 On the stability of OB‐star configurations in the Orion Nebula cluster G19 Older stars captured in young star clusters by cloud collapse G20 General features of the population of open clusters within 1 kpc from the Sun G21 Unstable modes in thin stellar disks G22 From Newton to Einstein – Dynamics of N‐body systems G23 On the relation between the maximum stellar mass and the star cluster mass     

Behavior of cemented sands—I. Testing

This paper is accompanied by a study on constitutive modelling issues of cemented sands. The concentration here is on experimental issues related to the triaxial testing of cemented sands. A preliminary investigation is performed aiming to identify potential effects of specimen size and slenderness on the stress–strain–strength characteristics of cemented sands. A comprehensive experimental study follows where clean sand specimens, as well as specimens with 2, 4 and 6 per cent cement content, are tested. The aim of the study is to examine the effects of cement content and confinement on the shear strength, stiffness, softening and dilation characteristics of cemented sand. © 1997 John Wiley & Sons, Ltd.     

ELASTOPLASTIC ANALYSIS OF CYLINDRICAL CAVITY PROBLEMS IN GEOMATERIALS

A large-strain elastoplastic analysis is presented for a cylindrical cavity embedded in an infinite medium under uniform radial pressure. The investigation employs invariant, non-associated deformation-type theories for Mohr–Coulomb (M–C) and Drucker–Prager (D–P) solids, accounting for arbitrary hardening, with the equivalent stress as the independent variable. The M–C model results in a single first-order differential equation, whereas for the D–P solid an algebraic constraint supplements the governing differential equation. Material parameters and response characteristics were determined by calibrating the models with data from triaxial compression tests on Castlegate sandstone and on Jurassic shale. A comparison is presented between predictions obtained from the two models and experimental data from hollow cylinder tests under external loading. A sensitivity of the results to material parameters, like friction and dilation angles, is provided for the case of a cavity subjected to internal pressure in terms of limit pressure predictions. In all cases it has been found that the results of the D–P inner cone model are in close agreement with those obtained from the M–C model. © 1997 by John Wiley & Sons, Ltd.