Effective governing equations for poroelastic growing media

A new mathematical model is developed for the macroscopic behaviour of a porous, linear elastic solid, saturated with a slowly flowing incompressible, viscous fluid, with surface accretion of the solid phase. The derivation uses a formal two-scale asymptotic expansion to exploit the well-separated length scales of the material: the pores are small compared to the macroscale, with a spatially periodic microstructure. Surface accretion occurs at the interface between the solid and fluid phases, resulting in growth of the solid phase through mass exchange from the fluid at a prescribed rate (and vice versa). The averaging derives a new poroelastic model, which reduces to the classical result of Burridge and Keller in the limit of no growth. The new model is of relevance to a large range of applications including packed snow, tissue growth, biofilms and subsurface rocks or soils

Acoustic spectral analysis and testing techniques

Subjects covered in four reports are described including: (1) mathematical techniques for combining decibel levels of octaves or constant bandwidth: (2) techniques for determining equation for power spectral density function; (3) computer program to analyze acoustical test data; and (4) computer simulation of horn responses utilizing hyperbolic horn theory

Introduction: From Autocracy to Democracy: The Effort to Establish Market Democracies in Iraq and Afghanistan

These remarks were made at the Georgia Journal of international and Comparative Law\u27s conference of April 16, 2004, From Autocracy to Democracy: The Effort to Establish Market Democracies in Iraq and Afghanistan

The Ariel II (UK-2) International Satellite Environmental Test Program

An important new aspect of the space sciences is the associated field of reliability. The largest part of this effort on a space flight project is environmental testing. This paper presents, as an example, the successful environmental test program of the International Satellite Ariel II. Several specialized tests and unique techniques were employed to assure the quality necessary to accomplish the spacecraft mission. Valuable background information is provided on the mission, technical description, and launch of Ariel II. United Kingdom scientists have received data from more than 5000 orbits on: (a) galactic noise in the 0.75 to 3.0 Me region, (b) the vertical distribution of ozone in the earth\u27s atmosphere, and (c) micrometeoroid density

Fluoroscopically guided extraforaminal cervical nerve root blocks: Analysis of epidural flow of the injectate with respect to needle tip position

Study Design Retrospective evaluation of consecutively performed fluoroscopically guided cervical nerve root blocks. Objective To describe the incidence of injectate central epidural flow with respect to needle tip position during fluoroscopically guided extraforaminal cervical nerve root blocks (ECNRBs). Methods Between February 19, 2003 and June 11, 2003, 132 consecutive fluoroscopically guided ECNRBs performed with contrast media in the final injected material (injectate) were reviewed on 95 patients with average of 1.3 injections per patient. Fluoroscopic spot images documenting the procedure were obtained as part of standard quality assurance. An independent observer not directly involved in the procedures retrospectively reviewed the images, and the data were placed into a database. Image review was performed to determine optimal needle tip positioning for injectate epidural flow. Results Central epidural injectate flow was obtained in only 28.9% of injections with the needle tip lateral to midline of the lateral mass (zone 2). 83.8% of injectate went into epidural space when the needle tip was medial to midline of the lateral mass (zone 3). 100% of injectate flowed epidurally when the needle tip was medial to or at the medial cortex of the lateral mass (zone 4). There was no statistically significant difference with regards to central epidural flow and the needle tip position on lateral view. Conclusion To ensure central epidural flow with ECNRBs one must be prepared to pass the needle tip medial to midplane of the lateral mass or to medial cortex of the lateral mass. Approximately 16% of ECNRBs with needle tip medial to midline of the lateral mass did not flow into epidural space. One cannot claim a nerve block is an epidural block unless epidural flow of injectate is observed

A combined experimental and computational framework to evaluate the behavior of therapeutic cells for peripheral nerve regeneration

Recent studies have explored the potential of tissue-mimetic scaffolds in encouraging nerve regeneration. One of the major determinants of the regenerative success of cellular nerve repair constructs is the local microenvironment, particularly native low oxygen conditions which can affect implanted cell survival and functional performance. In vivo, cells reside in a range of environmental conditions due to the spatial gradients of nutrient concentrations that are established. Here we evaluate in vitro the differences in cellular behaviour that such conditions induce, including key biological features such as oxygen metabolism, glucose consumption, cell death, and VEGF secretion. Experimental measurements are used to devise and parameterise a mathematical model that describes the behaviour of the cells. The proposed model effectively describes the interactions between cells and their microenvironment and could in the future be extended, allowing researchers to compare the behaviour of different therapeutic cells. Such a combinatorial approach could be used to accelerate the clinical translation of nerve repair constructs by identifying which critical design features should be optimised when fabricating engineered nerve repair conduits. This article is protected by copyright. All rights reserved

Comparison of measured and calculated dynamic loads for the Mod-2 2.5 mW wind turbine system

The Boeing Company, under contract to the Electric Power Research Institute (EPRI), has completed a test program on the Mod-2 wind turbines at Goodnoe Hills, Washington. The objectives were to update fatigue load spectra, discern site and machine differences, measure vortex generator effects, and to evaluate rotational sampling techniques. This paper shows the test setup and loads instrumentation, loads data comparisons and test/analysis correlations. Test data are correlated with DYLOSAT predictions using both the NASA interim turbulence model and rotationally sampled winds as inputs. The latter is demonstrated to have the potential to improve the test/analysis correlations. The paper concludes with an assessment of the importance of vortex generators, site dependence, and machine differences on fatigue loads. The adequacy of prediction techniques used are evaluated and recommendations are made for improvements to the methodology