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

Investigation of potential of differential absorption Lidar techniques for remote sensing of atmospheric pollutants

The NASA multipurpose differential absorption lidar (DIAL) system uses two high conversion efficiency dye lasers which are optically pumped by two frequency-doubled Nd:YAG lasers mounted rigidly on a supporting structure that also contains the transmitter, receiver, and data system. The DIAL system hardware design and data acquisition system are described. Timing diagrams, logic diagrams, and schematics, and the theory of operation of the control electronics are presented. Success in obtaining remote measurements of ozone profiles with an airborne systems is reported and results are analyzed

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

A mathematical framework for nerve regeneration in implantable conduits

Matching the performance of autografts with engineered scaffolds remains a challenge in peripheral nerve repair. A combination of 3D biomimetic architecture interspersed with 2D surfaces has been hypothesized to be an ideal environment for neurite regeneration. However, the problem of how best to arrange material within a conduit is an open one. Optimizing material parameters such as density, cross-sectional geometry and spatial distribution would require an extensive programme of experimental testing. By contrast, developing a modelling framework that is capable of testing key parameters may accelerate the design process, and reduce the dependency on animal testing

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

Mechanical response of neural cells to physiologically relevant stiffness gradients

Understanding the influence of the mechanical environment on neurite behavior is crucial in the development of peripheral nerve repair solutions, and could help tissue engineers to direct and guide regeneration. In this study, a new protocol to fabricate physiologically relevant hydrogel substrates with controlled mechanical cues is proposed. These hydrogels allow the analysis of the relative effects of both the absolute stiffness value and the local stiffness gradient on neural cell behavior, particularly for low stiffness values (1–2 kPa). NG108‐15 neural cell behavior is studied using well‐characterized collagen gradient substrates with stiffness values ranging from 1 to 10 kPa and gradient slopes of either 0.84 or 7.9 kPa mm^{-1}. It is found that cell orientation is influenced by specific combinations of stiffness value and stiffness gradient. The results highlight the importance of considering the type of hydrogel as well as both the absolute value of the stiffness and the steepness of its gradient, thus introducing a new framework for the development of tissue engineered scaffolds and the study of substrate stiffness