Feature-based reverse engineering of mechanical parts

Journal ArticleReverse engineering of mechanical parts requires extraction of information about an instance of a particular part sufficient to replicate the part using appropriate manufacturing techniques. This is important in a wide variety of situations, since functioning CAD models are often unavailable or unusable for parts which must be duplicated or modified. Computer vision techniques applied to 3-D data acquired using non-contact, three-dimensional position digitizers have the potential for significantly aiding the process. Serious challenges must be overcome, however, if sufficient accuracy is to be obtained and if models produced from sensed data are truly useful for manufacturing operations. This paper describes a prototype of a reverse engineering system which uses geometric representations natural to the manufacturing process. The system is interactive, which improves performance and allows for human entry of information that cannot be acquired from sensed data alone

Calculation of the Response of Angle Beam EMATs to Flaws in the Far Field

In the design of a system for NDE, it is necessary to quantify the relationship of flaw size and orientation to transducer signal levels. This is particularly true for automated systems, in which the transducer coordinates cannot be adjusted by an operator to maximize the signal. This paper presents the result of a model calculation for the case of angle beam inspection using EMATs, which appear likely to find extensive use in such systems. Included in the model are calculations of the elastic wave radiation pattern in three dimensions for plates, calculations of the elastic wave scattering from cracks using existent approximate models, and calculation of the electrical response to the scattered wave. Transducer apodization is used to reduce spurious side lobe signals and blind areas where flaws are weakly detected. Emphasis is placed on the case of SH wave generation

Geometric reasoning for map-based localization

Journal ArticleAn essential aspect of map-based navigation is the determination of an agent's current location based on sensed data from the environment. Formally, this amounts to specifying the current viewpoint in some world model coordinate system. This localization process has two distinct components: one involving the establishment of correspondences between aspects of the sensed data and the map or model, and the other involving derivation of constraints on the viewpoint based on the correspondences that have been determined

Wall Street Scandals: The Curative Effects of Law and Finance

This Article studies three scandals that embroiled U.S. financial markets during the past decade or so, including the Nasdaq market-makers\u27 use only of odd-eighths quotes, the abuse of specialist power on the New York Stock Exchange, and the mutual fund scandal. We attempt to attribute the resolution of these situations to the curative effects of markets versus regulation. We argue that the intervention of the legal system through regulation and/or litigation is often necessary to help resolve the misalignment of incentives needed for markets to accomplish their goal of maximizing value. The Article suggests that there exists an important synergy between financial markets and law that is often overlooked

Evaluating the accuracy of size perception in real and virtual environments

ManuscriptAccurate perception of the size of 3D objects depicted on 2D desktop displays is important for many applications. Whether users perceive objects depicted on a display to be the same size as comparable real world objects is not well understood. We propose using affordances judgments as a way of measuring the perceived size of objects depicted in desktop virtual environments and the real world. The methodology involves indicating whether or not a particular action can be performed in a given environment, making it a flexible measure that can be used across different display technologies. In two studies, we test users' perceptions of size by asking them to make affordance judgments in both the real world and a geometrically matched desktop virtual environment. In the first study, users judge whether they can grasp an object and in the second study, they judge whether they can fit their hand through an opening. In both experiments we show that users perceive the size of objects in the desktop virtual environment to be smaller than in the real world

Half-Space Radiation by EMAT\u27s

A Green\u27s function calculation of the far field radiation patterns of EMAT\u27s is presented. The approach is based upon (a) closed form expressions for the eddy current and static magnetic field distributions, established by the EMAT, which react to produce the driving Lorentz forces and (b) a Green\u27s function derived from the steepest descent approximation to the far field response of an arbitary surface point force on a half space. Numerical results are presented, illustrating the radiation patterns of the three common EMAT designs. Included are vertically polarized shear waves as radiated by both meander coil and periodic magnet EMAT\u27s and horizontally polarized shear waves as radiated by the latter

Temperature Dependence of Blue Phosphorescent Cyclometalated Ir(III) Complexes

The photophysical properties for a series of facial (fac) cyclometalated Ir(III) complexes (fac-Ir(C^N)_3 (C^N = 2-phenylpyridyl (ppy), 2-(4,6-difluorophenyl)pyridyl (F2ppy), 1-phenylpyrazolyl (ppz), 1-(2,4-difluorophenyl)pyrazolyl) (F2ppz), and 1-(2-(9,9′-dimethylfluorenyl))pyrazolyl (flz)), fac-Ir(C^N)_2(C^N′) (C^N = ppz or F2ppz and C^N′ = ppy or F2ppy), and fac-Ir(CC′)_3 (C^C′ = 1-phenyl-3-methylbenzimidazolyl (pmb)) have been studied in dilute 2-methyltetrahydrofuran (2-MeTHF) solution in a temperature range of 77−378 K. Photoluminescent quantum yields (Φ) for the 10 compounds at room temperature vary between near zero and unity, whereas all emit with high efficiency at low temperature (77 K). The quantum yield for fac-Ir(ppy)_3 (Φ = 0.97) is temperature-independent. For the other complexes, the temperature-dependent data indicates that the luminescent efficiency is primarily determined by thermal deactivation to a nonradiative state. Activation energies and rate constants for both radiative and nonradiative processes were obtained using a Boltzmann analysis of the temperature-dependent luminescent decay data. Activation energies to the nonradiative state are found to range between 1600 and 4800 cm^−1. The pre-exponential factors for deactivation are large for complexes with C^N ligands (1011−1013 s^−1) and significantly smaller for fac-Ir(pmb)_3 (109 s^−1). The kinetic parameters for decay and results from density functional theory (DFT) calculations of the triplet state are consistent with a nonradiative process involving Ir−N (Ir−C for fac-Ir(pmb)_3) bond rupture leading to a five-coordinate species that has triplet metal-centered (^3MC) character. Linear correlations are observed between the activation energy and the energy difference calculated for the emissive and ^3MC states. The energy level for the ^3MC state is estimated to lie between 21700 and 24000 cm^−1 for the fac-Ir(C^N)_3 complexes and at 28000 cm^−1 for fac-Ir(pmb)_3

Entrepreneurship-as-practice:grounding contemporary theories of practice into entrepreneurship studies

In this article, we contend that entrepreneurship studies would greatly benefit from engagement with contemporary theorizations of practice. The practice tradition conceives of the process of entrepreneuring as the enactment and entanglement of multiple practices. Appreciating entrepreneurial phenomena as the enactment and entanglement of practices orients researchers to an ontological understanding of entrepreneuring as relational, material and processual. Therefore, practice theories direct scholars towards observing and explaining the real-time practices of entrepreneuring practitioners. Articles in this special issue on ‘entrepreneurship-as-practice’ are discussed and suggestions for future research and scholarship that utilize contemporary theorizations of practice are offered