Structural factoring approach for analyzing stochastic networks

The problem of finding the distribution of the shortest path length through a stochastic network is investigated. A general algorithm for determining the exact distribution of the shortest path length is developed based on the concept of conditional factoring, in which a directed, stochastic network is decomposed into an equivalent set of smaller, generally less complex subnetworks. Several network constructs are identified and exploited to reduce significantly the computational effort required to solve a network problem relative to complete enumeration. This algorithm can be applied to two important classes of stochastic path problems: determining the critical path distribution for acyclic networks and the exact two-terminal reliability for probabilistic networks. Computational experience with the algorithm was encouraging and allowed the exact solution of networks that have been previously analyzed only by approximation techniques

Device for testing continuity and/or short circuits in a cable

A device for testing current paths is attachable to a conductor. The device automatically checks the current paths of the conductor for continuity of a center conductor, continuity of a shield and a short circuit between the shield and the center conductor. The device includes a pair of connectors and a circuit to provide for testing of the conductive paths of the cable. The pair of connectors electrically connects the conductive paths of a cable to be tested with the circuit paths of the circuit. The circuit paths in the circuit include indicators to simultaneously indicate the results of the testing

Expanding the Envelope of UAS Certification: What it Takes to Type Certify a UAS for Precision Agricultural Spraying

One of the key challenges to the development of a commercial Unmanned Air-craft System (UAS) market is the lack of explicit consideration of UAS in the current regulatory framework. Despite recent progress, additional steps are needed to enable broad UAS types and operational models. This paper discusses recent research that examines how a risk-based approach for safety might change the process and substance of airworthiness requirements for UAS. The project proposed risk-centric airworthiness requirements for a midsize un-manned rotorcraft used for agricultural spraying and also identified factors that may contribute to distinguishing safety risk among different UAS types and operational concepts. Lessons learned regarding how a risk-based approach can expand the envelope of UAS certification are discussed

Spectroscopic signature of phosphate crystallization in Erbium-doped optical fibre preforms

In rare-earth-doped silica optical fibres, the homogeneous distribution of amplifying ions and part of their spectroscopic properties are usually improved by adding selected elements, such as phosphorus or aluminum, as structural modifier. In erbium ion (Er3+) doped fibres, phosphorus preferentially coordinates to Er3+ ions to form regular cages around it. However, the crystalline structures described in literature never gave particular spectroscopic signature. In this article, we report emission and excitation spectra of Er3+ in a transparent phosphorus-doped silica fibre preform. The observed line features observed at room and low temperature are attributed to ErPO4 crystallites

Kinetic Characterisation of a Single Chain Antibody against the Hormone Abscisic Acid: Comparison with Its Parental Monoclonal

A single-chain Fv fragment antibody (scFv) specific for the plant hormone abscisic acid (ABA) has been expressed in the bacterium Escherichia coli as a fusion protein. The kinetics of ABA binding have been measured using surface plasmon resonance spectrometry (BIAcore 2000) using surface and solution assays. Care was taken to calculate the concentration of active protein in each sample using initial rate measurements under conditions of partial mass transport limitation. The fusion product, parental monoclonal antibody and the free scFv all have low nanomolar affinity constants, but there is a lower dissociation rate constant for the parental monoclonal resulting in a three-fold greater affinity. Analogue specificity was tested and structure-activity binding preferences measured. The biologically-active (+)-ABA enantiomer is recognised with an affinity three orders of magnitude higher than the inactive (-)-ABA. Metabolites of ABA including phaseic acid, dihydrophaseic acid and deoxy-ABA have affinities over 100-fold lower than that for (+)-ABA. These properties of the scFv make it suitable as a sensor domain in bioreporters specific for the naturally occurring form of ABA

Numerical analysis of the coupling between mechanical strain and thermal conductivity of ceramic matrix composites

The paper addresses the numerical modeling of the coupling between mechanical strain and thermal conductivity in Ceramic Matrix Composites {CMCs} when subjected to uni-axial mechanical straining. A computationally economic finite element-based multi-linear elastic orthotropic mechanical materials description combined with a multi-linear discretisation of thermal conductivity-strain response has been developed to predict the stress-strain, fracture, and thermal conductivity-strain behaviour of a ceramic matrix composites with strain-induced damage. The finite element analysis utilises a solid element to represent an homogenised orthotropic medium of a heterogeneous uni-directional tow. The discretised non-linear multiaxial stress-strain curves and non-linear multi-axial strain dependent thermal behaviour have been implemented by a user defined subroutine in the commercial finite element package ABAQUS. The model has been used to study the performance of a carbon fibre/carbon matrix-SiC matrix (C/C-SiC) plain weave laminate DLR-XT. With the effects of fibre waviness included, the global stress-strain curves, with catastrophic fracture behaviour, and the thermal conductivity-strain response have been predicted. Excellent comparisons have been made between predictions and experimental data, with fibre waviness included

Thickness and multi-axial stress creep rupture criteria of the Type IV component of a ferritic steel weld

The paper summarises previously derived constitutive parameters for the temperatures 575, 590, 600, 620 and 640oC. Values of the multi-axial stress rupture parameter are reviewed and recorded. This constitutive parameter set is used to determine the thickness of the Type IV material zone to be 0.7mm. Next, values of Type IV multi-axial stress rupture parameter are determined for a wide range of butt-welded pipe and crosswelded uni-axial specimens, and an interpolation equation has been derived in terms of temperatures and stress level. Finally, CDM analyses have been performed for pipes and crosswelded testpieces, which include a CG-HAZ zone; and it has been shown that the constitutive parameter set, which corresponds to a minimum creep rate ratio of 1/2.5, with respect to the parent material, gives accurate predictions of lifetimes and damage distributions

Thickness and multi-axial stress creep rupture criteria of the Type IV component of a ferritic steel weld

The paper summarises previously derived constitutive parameters for the temperatures 575, 590, 600, 620 and 640oC. Values of the multi-axial stress rupture parameter are reviewed and recorded. This constitutive parameter set is used to determine the thickness of the Type IV material zone to be 0.7mm. Next, values of Type IV multi-axial stress rupture parameter are determined for a wide range of butt-welded pipe and crosswelded uni-axial specimens, and an interpolation equation has been derived in terms of temperatures and stress level. Finally, CDM analyses have been performed for pipes and crosswelded testpieces, which include a CG-HAZ zone; and it has been shown that the constitutive parameter set, which corresponds to a minimum creep rate ratio of 1/2.5, with respect to the parent material, gives accurate predictions of lifetimes and damage distributions