Spherical indentation hardness of shape memory alloys

Using dimensional analysis and the finite element method, the spherical indentation hardness of shape memory alloys (SMAs) is investigated. The scaling relationship between the hardness and the mechanical properties of a SMA, such as the forward transformation stress, the maximum transformation strain magnitude, has been derived. Numerical results demonstrated that the hardness increases with the indentation depth but there is no three-fold relationship between the hardness and the forward transformation stress. Increasing the maximum transformation strain magnitude would reduce the hardness of the material. These research results enhance our understanding of the hardness from the spherical indentation of SMAs.

Spherical harmonics descriptor for 2D-image retrieval

In this paper, spherical harmonics are proposed as shape descriptors for 2D images. We introduce the concept of connectivity; 2D images are decomposed using connectivity, which is followed by 3D model construction. Spherical harmonics are obtained for 3D models and used as descriptors for the underlying 2D shapes. Difference between two images is computed as the Euclidean distance between their spherical harmonics descriptors. Experiments are performed to test the effectiveness of spherical harmonics for retrieval of 2D images. Item S8 within the MPEG-7 still images content set is used for performing experiments; this dataset consists of 3621 still images. Experimental results show that the proposed descriptors for 2D images are effective

Spherical indentation of superelastic shape memory alloys

Spherical indentation of superelastic shape memory alloys (SMAs) has been theoretically analyzed. Two characteristic points on the superelastic indentation curve have been discovered. The bifurcation force corresponding to the bifurcation point relies on the forward transformation stress and the return force corresponding to the return point relies on the reverse transformation stress.
Based on these theoretical relationships, an approach to determine the transformation stresses of superelastic SMAs has been proposed. To improve the accuracy of the measurement, a slope method to locate the two characteristic points from the slope curves is further suggested. Additionally, the spherical indentation hardness was also analyzed.

Analysis of spherical indentation of superelastic shape memory alloys

Dimensional analysis and the finite element method are applied in this paper to study spherical indentation of superelastic shape memory alloys. The scaling relationships derived from dimensional analysis bridge the indentation response and the mechanical properties of a superelastic shape memory alloy. Several key variables of a superelastic indentation curve are revealed and examined. We prove that the bifurcation force in a superelastic indentation curve only relies on the forward transformation stress and the elastic properties of the initial austenite; and the return force in a superelastic indentation curve only relies on the reverse transformation stress and the elastic properties of the initial austenite. Furthermore, the dimensionless functions to determine the bifurcation force and the return force are proved to be identical. These results not only enhance our understanding of spherical indentation of superelastic shape memory alloys, but also provide the theoretical basis for developing a practicable method to calibrate the mechanical properties of a superelastic material from the spherical indentation test.

3D haptic needle insertion simulator utilising an agent based spherical voxel model

This paper describes a technique for the real-time modeling of deformable tissue. Specifically geared towards needle insertion simulation, the low computational requirements of the model enable highly accurate haptic feedback to a user without introducing noticeable time delay or buzzing generally associated with haptic surgery simulation. Using a spherical voxel array combined with aspects of computational geometry and agent communication and interaction principals, the model is capable of providing haptic update rates of over 1000Hz with real-time visual feedback. Iterating through over 1000 voxels per millisecond to determine collision and haptic response while making use of Vieta’s Theorem for extraneous force culling.

Determination of plastic yield stress from spherical indentation slope curve

The indentation slope curve from a spherical indentation on elastic-plastic materials is examined. By comparing it with that of an linear elastic material of the same elastic properties, we found that the start point of plastic yielding for an elastic-plastic material can be easily located from the indentation slope curve. Based on this analysis, a simple but effective method is proposed to measure the plastic yield stress of very small samples from a spherical nano-indentation slope curve.

A constructivist approach to the teaching & learning of astronomy

Astronomy is one of the recurrent contemporary issues in the mass media where news related to comets, new stars, satellites, space tests, etc., frequently appear. Through this media presence students develop an interest in learning about aspects of astronomy. However, the information students gain from various sources, both inside and outside the classroom, doesn't often increase their knowledge about the most basic and common aspects of astronomy (Martinez Pena & Gil Quilez, 2001). Studies that have explored students' and teachers' understandings of astronomical concepts (Kalkan et al, 2007; Trumper, 2001) have found many alternative conceptions relating to basic astronomical processes such as day and night, the seasons, gravity and the relative distances between celestial objects.

Year 8 students' understanding of astronomy as a representational issue : insights from a classroom video study

The research described in this paper argues that difficulties of leaming science concepts such as those associated with processes involving the Sun, Moon and Earth, such as day and night, the seasons and phases of the moon, are fundamentally representational in nature. There is a need for learners to use their own representational, cultural and cognitive resources to engage with the subject-specific representational practices of science. From this perspective students need to understand and conceptually integrate different representational modalities or forms in learning science and reasoning in science. The researchers worked with two experienced teachers in planning a teaching sequence in astronomy using a teaching approach that highlight representational issues and options in helping students explore and develop key conceptual understandings. Classroom sequences involving the two teachers were videotaped using a combined focus on the teacher and groups of students. Video analysis software was used to capture the variety of representations used, and sequences of representational negotiation. From a pedagogical perspective the representational approach placed a significant agency in the hands of students which resulted in structured discussions around conceptual problems. Representations were used as tools for reasoning and communication to drive classroom discussions and develop higher levels of understanding in the students. The pre- and post-testing showed significant gains in students thinking from naive to more scientific understandings of astronomy.

Haptically simulating soft tissue using spherical voxel and reactive agents

This thesis describes technology developed by the author enabling trainee surgeons to perform needle insertion procedures with force feedback (haptics) on a virtual patient. Addition of the sense of touch to medical simulation is arguably the most important step forward in the evolution of haptic technology to this day.

Fracture analysis of spherical shells : application to cracking of macadamia nuts

The main consideration in recovering the macadamia kernal is to crack the spherical nutshell without damaging the kernal. Five mechanical cracking tools were tested, and the fracture mechanisms of nutshells, under various cracking loads, were studied. A classical theoretical approach and a numerical method were both used to investigate the influence of crack face closure on the stress intensity factor for a cracked spherical shell subjected to membrane forces and bending moments.

Traces from the astrolabe: art and astronomy

This portfolio represent an ongoing investigation into relationships between art and astronomy with particular reference to photographic imaging of the cosmos and how such imaging has influenced the mapping and modelling of the universe. I am also interested in the subjective interpretation of astronomical observations and the point at which such images fail to represent, ie, the blurred image, which may represent the limits of technology as well and opening the possibility for metaphorical readings and imaginings on the part of the observer.

Spherical harmonics and distance transform for image representation and retrieval

In this paper, we have proposed a method for 2D image retrieval based on object shapes. The method relies on transforming the 2D images into 3D space based on distance transform. Spherical harmonics are obtained for the 3D data and used as descriptors for the underlying 2D images. The proposed method is compared against two existing methods which use spherical harmonics for shape based retrieval of images. MPEG-7 Still Images Content Set is used for performing experiments; this dataset consists of 3621 still images. Experimental results show that the performance of the proposed descriptors is significantly better than other methods in the same category.

Spectral shape descriptor using spherical harmonics

In this paper, we propose a spectral descriptor for shapes of objects. The method relies on transforming the 2D objects into 3D space; distance transform and scale space theory is used to transform objects into 3D space. Spherical harmonics of the voxel grid are used to obtain shape descriptors. The proposed methods are compared against two existing methods which use spherical harmonics for shape based retrieval of images. Comparison is done based on ranking of images which is articulated in recall-precision curves. MPEG-7 Still Images Content Set is used for performing experiments. Experimental results show that the performance of the proposed descriptor is significantly better than other methods in the same category.

Plane wave scattering by a spherical di-electric particle in motion : a relativistic extension of the Mie theory

Light scattering from small spherical particles has applications in a vast number of disciplines including astrophysics, meteorology optics and particle sizing. Mie theory provides an exact analytical characterization of plane wave scattering from spherical dielectric objects. There exist many variants of the Mie theory where fundamental assumptions of the theory has been relaxed to make generalizations. Notable such extensions are generalized Mie theory where plane waves are replaced by optical beams, scattering from lossy particles, scattering from layered particles or shells and scattering of partially coherent (non-classical) light. However, no work has yet been reported in the literature on modifications required to account for scattering when the particle or the source is in motion relative to each other. This is an important problem where many applications can be found in disciplines involving moving particle size characterization. In this paper we propose a novel approach, using special relativity, to address this problem by extending the standard Mie theory for scattering by a particle in motion with a constant speed, which may be very low, moderate or comparable to the speed of light. The proposed technique involves transforming the scattering problem to a reference frame co-moving with the particle, then applying the Mie theory in that frame and transforming the scattered field back to the reference frame of the observer.