General Dynamics

Abstract: The COordinate Rotation DIgital Computer(CORDIC) is a special-purpose digital computer for real-time airborne computation. In this computer, a unique computing technique is employed which is especially suitable for solving the trigonometric relationships involved in plane coordinate rotation and conversion from rectangular to polar coordinates. CORDIC is an entire-transfer computer; it contains a special serial arithmetic unit consisting of three shift registers, three adder-subtractors, and special interconnections. By use of a prescribed sequence of conditional additions or subtractions, the CORDIC arithmetic unit can be controlled to solve either set of the following equations: Y' = K(Y cos? + X sin?) X' = K(X cos? - Y sin?), or R = K?X2 + Y2 ? = tan-1 Y/X, where K is an invariable constant. This special arithmetic unit is also suitable for other computations such as multiplication, division, and the conversion between binary and mixed radix number systems. However, only the trigonometric algorithms used in this computer and the instrumentation of these algorithms are discussed in this paper.

Abstract: Two refractory high entropy alloys with compositions near Nb25Mo25Ta25W25 and V20Nb20Mo20Ta20W20, were produced by vacuum arc-melting. Despite containing many constituents, both alloys had a single-phase body-centered cubic (BCC) structure that remained not only stable after exposure to 1400 °C, but also disordered, as confirmed by the absence of superlattice reflections in neutron diffraction data. Compressive flow properties and microstructure development of these alloys were determined from room temperature up to 1600 °C. Limited compressive plasticity and quasi-cleavage fracture at room temperature suggest that the ductile-to-brittle transition for these alloys occurs above room temperature. At 600 °C and above, both alloys showed extensive compressive plastic strain. The yield stress of both alloys dropped by 30–40% between room temperature and 600 °C, but was relatively insensitive to temperature above 600 °C, comparing favorably with conventional superalloys.

Abstract: Two refractory high-entropy alloys with near-equiatomic concentrations, W–Nb–Mo–Ta and W–Nb–Mo–Ta–V, were produced by vacuum arc melting. Despite containing many constituents both alloys have a single-phase body-centered cubic (BCC) structure. The lattice parameters a = 3.2134(3) A for the quaternary alloy and a = 3.1832(2) A for the quinternary alloy were determined with high-energy X-ray diffraction using a scattering vector length range from 0.7 to 20 A−1. The alloy density and Vickers microhardness were ρ = 13.75 g/cm3 and Hv = 4455 MPa for the W–Nb–Mo–Ta alloy and ρ = 12.36 g/cm3 and Hv = 5250 MPa for the W–Nb–Mo–Ta–V alloy. The exceptional microhardness in these alloys is greater than any individual constituent, suggesting the operation of a solid-solution-like strengthening mechanism.

Abstract: Dynamic Time Warping (DTW) has a quadratic time and space complexity that limits its use to small time series. In this paper we introduce FastDTW, an approximation of DTW that has a linear time and space complexity. FastDTW uses a multilevel approach that recursively projects a solution from a coarser resolution and refines the projected solution. We prove the linear time and space complexity of FastDTW both theoretically and empirically. We also analyze the accuracy of FastDTW by comparing it to two other types of existing approximate DTW algorithms: constraints (such as Sakoe-Chiba Bands) and abstraction. Our results show a large improvement in accuracy over existing methods.

Abstract: The response of a finite-width composite laminate under uniform axial strain is treated through the application of classical elasticity theory. Finite-difference solution techniques are employed to obtain solutions for stresses and displacements throughout the region. Results for material properties typical of a high modulus graphite-epoxy composite material system are presented which explain the mechanism of shear transfer within a symmetric laminate. In addition, results of this work are compared to those given in a recent approximate formulation.