Linguistic Reflection in Java

Reflective systems allow their own structures to be altered from within. Here we are concerned with a style of reflection, called linguistic reflection, which is the ability of a running program to generate new program fragments and to integrate these into its own execution. In particular we describe how this kind of reflection may be provided in the compiler-based, strongly typed object-oriented programming language Java. The advantages of the programming technique include attaining high levels of genericity and accommodating system evolution. These advantages are illustrated by an example taken from persistent programming which shows how linguistic reflection allows functionality (program code) to be generated on demand (Just-In-Time) from a generic specification and integrated into the evolving running program. The technique is evaluated against alternative implementation approaches with respect to efficiency, safety and ease of use.Comment: 25 pages. Source code for examples at http://www-ppg.dcs.st-and.ac.uk/Java/ReflectionExample/ Dynamic compilation package at http://www-ppg.dcs.st-and.ac.uk/Java/DynamicCompilation

Modelling sound propagation in the ocean: A normal mode approach using finite elements

© 2019 Australian Acoustical Society Annual Conference, AAS 2018. All rights reserved. Modelling the propagation of sound waves in the ocean is challenging because one must account for spatial variation in properties of the fluid and in the ocean geometry, as well as couple the fluid to a seabed that supports both shear and compressional waves. This article presents a f inite element based approach to obtaining the eigenmodes for an axial uniform ocean waveguide. Once these modes have been computed, an orthogonality relation is used to compute the sound pressure field for ranges of up to 5 km. This approach avoids the traditional heavy computational expenditure associated with the finite element method, at least for a uniform waveguide. Furthermore, the numerical approach properly accounts for the depth dependent properties of the ocean, and couples the ocean to a full elastodynamic representation of the seabed, which supports both shear and compressional waves. This permits the implementation of the physically correct transverse boundary conditions, as well as the addition of a perfectly matched layer to enforce the correct boundary conditions at infinite depth in the seabed

Diffusive transport in networks built of containers and tubes

We developed analytical and numerical methods to study a transport of non-interacting particles in large networks consisting of M d-dimensional containers C_1,...,C_M with radii R_i linked together by tubes of length l_{ij} and radii a_{ij} where i,j=1,2,...,M. Tubes may join directly with each other forming junctions. It is possible that some links are absent. Instead of solving the diffusion equation for the full problem we formulated an approach that is computationally more efficient. We derived a set of rate equations that govern the time dependence of the number of particles in each container N_1(t),N_2(t),...,N_M(t). In such a way the complicated transport problem is reduced to a set of M first order integro-differential equations in time, which can be solved efficiently by the algorithm presented here. The workings of the method have been demonstrated on a couple of examples: networks involving three, four and seven containers, and one network with a three-point junction. Already simple networks with relatively few containers exhibit interesting transport behavior. For example, we showed that it is possible to adjust the geometry of the networks so that the particle concentration varies in time in a wave-like manner. Such behavior deviates from simple exponential growth and decay occurring in the two container system.Comment: 21 pages, 18 figures, REVTEX4; new figure added, reduced emphasis on graph theory, additional discussion added (computational cost, one dimensional tubes

A one dimensional numerical approach for computing the eigenmodes of elastic waves in buried pipelines

Ultrasonic guided waves are often used in the detection of defects in oil and gas pipelines. It is common for these pipelines to be buried underground and this may restrict the length of the pipe that can be successfully tested. This is because acoustic energy travelling along the pipe walls may radiate out into the surrounding medium. Accordingly, it is important to develop a better understanding of the way in which elastic waves propagate along the walls of buried pipes, and so in this article a numerical model is developed that is suitable for computing the eigenmodes for uncoated and coated buried pipes. This is achieved by combining a one dimensional eigensolution based on the semi-analytic finite element (SAFE) method, with a perfectly matched layer (PML) for the infinite medium surrounding the pipe. This article also explores an alternative exponential complex coordinate stretching function for the PML in order to improve solution convergence. It is shown for buried pipelines that accurate solutions may be obtained over the entire frequency range typically used in long range ultrasonic testing (LRUT) using a PML layer with a thickness equal to the pipe wall thickness. This delivers a fast and computationally efficient method and it is shown for pipes buried in sand or soil that relevant eigenmodes can be computed and sorted in less than one second using relatively modest computer hardware. The method is also used to find eigenmodes for a buried pipe coated with the viscoelastic material bitumen. It was recently observed in the literature that a viscoelastic coating may effectively isolate particular eigenmodes so that energy does not radiate from these modes into the surrounding [elastic] medium. A similar effect is also observed in this article and it is shown that this occurs even for a relatively thin layer of bitumen, and when the shear impedance of the coating material is larger than that of the surrounding medium

An Assessment of the Impact of Internship Programs in the Agricultural Technical Schools of Egypt as Perceived by Participants Groups

Experiential learning including student internships has been central to instructional programs in agriculture for decades. If the Agricultural Technical Schools of Egypt are to prepare students for successful careers and to enhance the agricultural economy, teachers must be well-prepared to use this teaching technique. Further, all stakeholders, including students, teachers, parents, headmasters and agribusiness owners, must recognize the importance and impact that implementing a student internship program could have. In this study, all groups identified important contributions to student learning and growth as a result of student participation in the internship program. While several suggestions were posited to improve the program, all agreed that the schools, the communities, the agribusinesses and the students received valuable benefits. The program of student internships in Egypt could be adopted in other countries where the agricultural economy could be improved through a better prepared agricultural workforce

Relation of the barberry to stem rust in Iowa

It has been definitely known since 1865 that the European barberry is the alternate host of stem rust (Puccinia graminis); yet the exact relation of this shrub to the annual appearance of stem rust of our grains and grasses is not well understood. Tulasne brothers (18) (1847), de Bary (1) (1865) and others rarely described and figured the morphology of teleutosporic germination. They gave little consideration, however, to the questions as to what environmental conditions influence such germination and the production, dissemination, viability and growth of the sporidia—conditions that have a fundamental bearing on serious attacks of stem rust

Conjugate Generators of Knot and Link Groups

This note shows that if two elements of equal trace (e.g., conjugate elements) generate an arithmetic two-bridge knot or link group, then the elements are parabolic. This includes the figure-eight knot and Whitehead link groups. Similarly, if two conjugate elements generate the trefoil knot group, then the elements are peripheral.Comment: 10 pages, submitted to Journal of Knot Theory and Its Ramification

An active-architecture approach to COTS integration

Commercial off-the-shelf (COTS) software products are increasingly used as standard components within integrated information systems. This creates challenges since both their developers and source code are not usually available, and the ongoing development of COTS cannot be predicted. The ArchWare Framework approach recognises COTS products as part of the ambient environment of an information system and therefore an important part of development is incorporating COTS as effective system components. This integration of COTS components, and the composition of components, is captured by an active architecture model which changes as the system evolves. Indeed the architecture modelling language used enables it to express the monitoring and evolution of a system. This active architecture model is structured using control system principles. By modelling both integration and evolution it can guide the system’s response to both predicted and emergent changes that arise from the use of COTS products.Publisher PDFPeer reviewe

Detecting sound waves generated by leaks in buried water distribution pipes

It is common to use guided sound waves to detect leaks or cracks in pipelines. Applications include the nondestructive testing of oil and gas pipelines, which normally takes places at ultrasonic frequencies, as well as the detection of leaks and ruptures in water filled pipes at much lower audio frequencies. However, if the pipe is buried then sound leaks out of the pipe into the surrounding medium and this lowers the acoustic energy travelling along the pipe wall. This has the potential to limit the applications of this technology, and so it is necessary to develop knowledge of the acoustic properties of the guided waves in order to optimise detection techniques. Accordingly, this work examines the properties of sound waves propagating in an infinitely long fluid-filled buried pipe, with application to leak detection at low audio frequencies. A parametric study is undertaken to examine the sensitivity of sound propagation to the properties of the internal liquid, pipe walls and of the surrounding medium