NASA Tech Briefs, October 1990

Topics: New Product Ideas; NASA TU Services; Electronic Components and Circuits; Electronic Systems; Physical' Sciences; Materials; Computer Programs; Mechanics; Machinery; Fabrication Technology; Mathematics and Information Sciences; Life Sciences

Level set and PDE methods for visualization

Notes from IEEE Visualization 2005 Course #6, Minneapolis, MN, October 25, 2005. Retrieved 3/16/2006 from http://www.cs.drexel.edu/~david/Papers/Viz05_Course6_Notes.pdf.Level set methods, an important class of partial differential equation (PDE) methods, define dynamic surfaces implicitly as the level set (isosurface) of a sampled, evolving nD function. This course is targeted for researchers interested in learning about level set and other PDE-based methods, and their application to visualization. The course material will be presented by several of the recognized experts in the field, and will include introductory concepts, practical considerations and extensive details on a variety of level set/PDE applications. The course will begin with preparatory material that introduces the concept of using partial differential equations to solve problems in visualization. This will include the structure and behavior of several different types of differential equations, e.g. the level set, heat and reaction-diffusion equations, as well as a general approach to developing PDE-based applications. The second stage of the course will describe the numerical methods and algorithms needed to implement the mathematics and methods presented in the first stage, including information on implementing the algorithms on GPUs. Throughout the course the technical material will be tied to applications, e.g. image processing, geometric modeling, dataset segmentation, model processing, surface reconstruction, anisotropic geometric diffusion, flow field post-processing and vector visualization. Prerequisites: Knowledge of calculus, linear algebra, computer graphics, visualization, geometric modeling and computer vision. Some familiarity with differential geometry, differential equations, numerical computing and image processing is strongly recommended, but not required

Advanced Characterization and On-Line Process Monitoring of Additively Manufactured Materials and Components

This reprint is concerned with the microstructural characterization and the defect analysis of metallic additively manufactured (AM) materials and parts. Special attention is paid to the determination of residual stress in such parts and to online monitoring techniques devised to predict the appearance of defects. Finally, several non-destructive testing techniques are employed to assess the quality of AM materials and parts

Index to 1986 NASA Tech Briefs, volume 11, numbers 1-4

Short announcements of new technology derived from the R&D activities of NASA are presented. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This index for 1986 Tech Briefs contains abstracts and four indexes: subject, personal author, originating center, and Tech Brief Number. The following areas are covered: electronic components and circuits, electronic systems, physical sciences, materials, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences

Molecular Imaging

The present book gives an exceptional overview of molecular imaging. Practical approach represents the red thread through the whole book, covering at the same time detailed background information that goes very deep into molecular as well as cellular level. Ideas how molecular imaging will develop in the near future present a special delicacy. This should be of special interest as the contributors are members of leading research groups from all over the world

The Generation and Control of Ultrasonic Waves in Nonlinear Media

The objective of this thesis is to utilise modern open-design ultrasound research platforms to develop new and advance several existing techniques that incorporate nonlinear phenomena. Acoustically, nonlinearity refers to changes in speed of sound, attenuation or elasticity that vary with frequency, temperature or pressure. These effects cannot be linearised by the wave equation and require fluid dynamics and elasticity equations to be fully understood. While this is a hindrance and source of error in many areas of ultrasound such as high-intensity focused ultrasound (HIFU) and medical imaging, nonlinearities do have uses in non-destructive guided wave (GW) testing. These effects are influenced greatly by the transducer surface pressure, and so precise control of the excitation is necessary to achieve the desired nonlinear effect, if any, in the medium. In this thesis, aided by the use of two new research platforms, several new ultrasound techniques were developed. It was shown the frequency content in the electrical waveform is pertinent and so distortion must be minimised. This requirement conflicts with several hardware limitations, however. Accordingly, a genetic algorithm was applied to find novel switched waveform designs. It was found to achieve a 2% granularity in amplitude control with harmonic reduction, where existing waveform designs could not produce any. This fine amplitude control is a requirement for array applications. Following this, a technique to control the direction of GWs without knowledge of the waveguide was devised. Recordings of a propagating GW, induced by the first element of an array transducer, were re-transmitted in a recursive fashion. The effect was that the transducer's transmissions constructively interfered with the transverse wave, causing most of the guided wave energy to travel in the direction of the transducer's spatial influence. Experimental results show a 34 dB enhancement in one direction compared with the other. GWs were then applied to bone for two purposes: for assessment of osteoporosis and for measurement of skull properties to assist transcranial therapy. It was shown that existing methods for obtaining dispersion curves are ineffectual due to limitations in the available sampling area. A signal processing scheme was devised to temporally align transverse dispersive waves so that beamforming style techniques could be applied to prove or disprove the existence of certain modes. The technique in combination with multiplication was applied to numerical, ex vivo and in vivo experiments. It was found to improve the contrast of the higher order modes. The technique could improve the reliability of osteoporosis diagnosis with ultrasound, but may also prove useful for acquiring dispersion images in NDT. Numerically the technique was shown to improve the S3 and A3 mode intensity by 6 dB and 13 dB respectively compared with an existing Fourier method. In skull, a relationship was found between the curved therapeutic array geometry and the delay profile necessary to form GWs in skull. Several numerical models were tested and it was shown that the thickness could be obtained from the group velocity. The estimated maximum error using this technique was 0.2 mm. Since the data is co-registered with the therapeutic elements, this method could be used to improve the accuracy of thermal treatments in the brain. Finally, the application of switched excitation for HIFU was considered. To improve on cost, efficiency and size, alternative excitation methods have the potential to replace the linear amplifier circuitry currently used in HIFU. In this final study, harmonic reduction pulse width modulation (HRPWM) was proposed as an algorithmic solution to the design of switched waveforms. Its appropriateness for HIFU was assessed by design of a high power 5 level unfiltered amplifier and subsequent thermal-only lesioning of ex vivo chicken breast. HRPWM produced symmetric, thermal-only lesions that were the same size as their linear amplifier equivalents (p > 0.05). These results demonstrate that HRPWM can minimise HIFU drive circuity size without the need for filters to remove harmonics or adjustable power supplies to achieve array apodisation. Overall it has been shown in this thesis that precise control of the nonlinear wave phenomena can be afforded when using open-platform ultrasound research hardware. The methods described within may reduce the cost and increase the efficacy of future commercial systems

NASA Tech Briefs, April 1997

Topics covered include: Video and Imaging; Electronic Components and Circuits; Electronic Systems; Physical Sciences; Materials; Computer Programs; Mechanics; Machinery/Automation; Manufacturing/Fabrication; Mathematics and Information Sciences; Life Sciences; Books and Reports