Buckling and vibration of periodic lattice structures

Lattice booms and platforms composed of flexible members or large diameter rings which may be stiffened by cables in order to support membrane-like antennas or reflector surfaces are the main components of some large space structures. The nature of these structures, repetitive geometry with few different members, makes possible relatively simple solutions for buckling and vibration of a certain class of these structures. Each member is represented by a stiffness matrix derived from the exact solution of the beam column equation. This transcendental matrix gives the current member stiffness at any end load or frequency. Using conventional finite element techniques, equilibrium equations can be written involving displacements and rotations of a typical node and its neighbors. The assumptions of a simple trigonometric mode shape is found to satisfy these equations exactly; thus the entire problem is governed by just one 6 x 6 matrix equation involving the amplitude of the displacement and rotation mode shapes. The boundary conditions implied by this solution are simple supported ends for the column type configurations

Application of transport techniques to the analysis of NERVA shadow shields

A radiation shield internal to the NERVA nuclear rocket reactor required to limit the neutron and photon radiation levels at critical components located external to the reactor was evaluated. Two significantly different shield mockups were analyzed: BATH, a composite mixture of boron carbide, aluminum and titanium hydride, and a borated steel-liquid hydrogen system. Based on the comparisons between experimental and calculated neutron and photon radiation levels, the following conclusions were noted: (1) The ability of two-dimensional discrete ordinates code to predict the radiation levels internal to and at the surface of the shield mockups was clearly demonstrated. (2) Internal to the BATH shield mockups, the one-dimensional technique predicted the axial variation of neutron fluxes and photon dose rates; however, the magnitude of the neutron fluxes was about a factor of 1.8 lower than the two-dimensional analysis and the photon dose rate was a factor of 1.3 lower

New Symbolic Tools for Differential Geometry, Gravitation, and Field Theory

DifferentialGeometry is a Maple software package which symbolically performs fundamental operations of calculus on manifolds, differential geometry, tensor calculus, Lie algebras, Lie groups, transformation groups, jet spaces, and the variational calculus. These capabilities, combined with dramatic recent improvements in symbolic approaches to solving algebraic and differential equations, have allowed for development of powerful new tools for solving research problems in gravitation and field theory. The purpose of this paper is to describe some of these new tools and present some advanced applications involving: Killing vector fields and isometry groups, Killing tensors and other tensorial invariants, algebraic classification of curvature, and symmetry reduction of field equations.Comment: 42 page

The curatorial consequences of being moved, moveable or portable: the case of carved stones

It matters whether a carved stone is moved, moveable or portable. This influences perceptions of significance and of form and nature – is it a monument or an artefact? This duality may in turn affect understanding and appreciation of the resource. It has implications for how and if carved stones can be legally protected, who owns them, where and how they are administered, and by whom. The complexities of the legislation mean that all too often this is also a grey area. This paper explores these curatorial issues and their impact

Computer program for structural analysis of layered orthotropic ring-stiffened shells of revolution (SALORS): Linear stress analysis option

Program handles segmented, laminar, orthotropic shells with discrete rings. Meridional variations are handled in material properties, temperatures, and wall thickness. Allows for linear variations of temperature through each layer of shell wall

Schema Independent Relational Learning

Learning novel concepts and relations from relational databases is an important problem with many applications in database systems and machine learning. Relational learning algorithms learn the definition of a new relation in terms of existing relations in the database. Nevertheless, the same data set may be represented under different schemas for various reasons, such as efficiency, data quality, and usability. Unfortunately, the output of current relational learning algorithms tends to vary quite substantially over the choice of schema, both in terms of learning accuracy and efficiency. This variation complicates their off-the-shelf application. In this paper, we introduce and formalize the property of schema independence of relational learning algorithms, and study both the theoretical and empirical dependence of existing algorithms on the common class of (de) composition schema transformations. We study both sample-based learning algorithms, which learn from sets of labeled examples, and query-based algorithms, which learn by asking queries to an oracle. We prove that current relational learning algorithms are generally not schema independent. For query-based learning algorithms we show that the (de) composition transformations influence their query complexity. We propose Castor, a sample-based relational learning algorithm that achieves schema independence by leveraging data dependencies. We support the theoretical results with an empirical study that demonstrates the schema dependence/independence of several algorithms on existing benchmark and real-world datasets under (de) compositions