Beyond developable: computational design and fabrication with auxetic materials

We present a computational method for interactive 3D design and rationalization of surfaces via auxetic materials, i.e., flat flexible material that can stretch uniformly up to a certain extent. A key motivation for studying such material is that one can approximate doubly-curved surfaces (such as the sphere) using only flat pieces, making it attractive for fabrication. We physically realize surfaces by introducing cuts into approximately inextensible material such as sheet metal, plastic, or leather. The cutting pattern is modeled as a regular triangular linkage that yields hexagonal openings of spatially-varying radius when stretched. In the same way that isometry is fundamental to modeling developable surfaces, we leverage conformal geometry to understand auxetic design. In particular, we compute a global conformal map with bounded scale factor to initialize an otherwise intractable non-linear optimization. We demonstrate that this global approach can handle non-trivial topology and non-local dependencies inherent in auxetic material. Design studies and physical prototypes are used to illustrate a wide range of possible applications

Interactive real-time physics: An intuitive approach to form-finding and structural analysis for design and education

Real-time physics simulation has been extensively used in computer games, but its potential has yet to be fully realized in design and education. We present an interactive 3D physics engine with a wide variety of applications. In common with traditional FEM, the use of a local element stiffness matrix is retained. However, unlike typical non-linear FEM routines elements forces, moments and inertia are appropriately lumped at nodes following the dynamic relaxation method. A semi-implicit time integration scheme updates linear and angular momentum, and subsequently the local coordinate frames of the nodes. A co-rotational approach is used to compute the resultant field of displacements in global coordinates including the effect of large deformations. The results obtained compare well against established commercial software. We demonstrate that the method presented allows the making of interactive structural models that can be used in teaching to develop an intuitive understanding of structural behaviour. We also show that the same interactive physics framework allows real-time optimization that can be used for geometric and structural design applications

Learning lessons from Earth and Space towards Sustainable Multi-planetary Design

Off-Earth structural design has been a subject of fascination and research for decades. Given that the vision of permanent lunar and Martian human presence is materialising, it is an opportune moment to reflect on the future applicability and challenges of off-Earth design. This article investigates contemporary thinking about off-Earth structural design – specifically focused on large-scale infrastructure such as habitats – and assesses it in terms of its sustainability. We suggest that the extra-terrestrial setting, which is characterised by resource, construction, and labour constraints, is to be analysed as an extreme case of the built environment on Earth. Subsequently, we propose that structural design methodologies originating on Earth can benefit both the off-Earth context, through their inherent material efficiency and use of local materials, and the on-Earth context, where unsustainable growth and material inefficiency dominate our built environment. As our planet rapidly heads towards a scarcity of construction materials and disruptive environmental change, what sustainability lessons can we learn from our past, and how can we apply these to extra-terrestrial construction? Finally, how can we use these lessons to futureproof our built environment

Modelling curved-layered printing paths for fabricating large-scale construction components

In this paper, a non-conventional way of additive manufacturing, curved-layered printing, has been applied to large-scale construction process. Despite the number of research works on Curved Layered Fused Deposition Modelling (CLFDM) over the last decade, few practical applications have been reported. An alternative method adopting the CLFDM principle, that generates a curved-layered printing path, was developed using a single scripting environment called Grasshopper – a plugin of Rhinoceros® . The method was evaluated with the 3D Concrete Printing process developed at Loughborough University. The evaluation of the method including the results of simulation and printing revealed three principal benefits compared with existing flat-layered printing paths, which are particularly beneficial to large-scale AM techniques: (i) better surface quality, (ii) shorter printing time and (iii) higher surface strengths

Evaluation of lung MDCT nodule annotation across radiologists and methods

RATIONALE AND OBJECTIVES: Integral to the mission of the National Institutes of Health–sponsored Lung Imaging Database Consortium is the accurate definition of the spatial location of pulmonary nodules. Because the majority of small lung nodules are not resected, a reference standard from histopathology is generally unavailable. Thus assessing the source of variability in defining the spatial location of lung nodules by expert radiologists using different software tools as an alternative form of truth is necessary. MATERIALS AND METHODS: The relative differences in performance of six radiologists each applying three annotation methods to the task of defining the spatial extent of 23 different lung nodules were evaluated. The variability of radiologists’ spatial definitions for a nodule was measured using both volumes and probability maps (p-map). Results were analyzed using a linear mixed-effects model that included nested random effects. RESULTS: Across the combination of all nodules, volume and p-map model parameters were found to be significant at P < .05 for all methods, all radiologists, and all second-order interactions except one. The radiologist and methods variables accounted for 15% and 3.5% of the total p-map variance, respectively, and 40.4% and 31.1% of the total volume variance, respectively. CONCLUSION: Radiologists represent the major source of variance as compared with drawing tools independent of drawing metric used. Although the random noise component is larger for the p-map analysis than for volume estimation, the p-map analysis appears to have more power to detect differences in radiologist-method combinations. The standard deviation of the volume measurement task appears to be proportional to nodule volume

Role of age and middle ear transmission characteristics in the frequency tuning of cVEMP and oVEMP

Project Description Ageing causes a decline in the functioning of most sensory systems, including the vestibular system. Decrements in vestibular function are an independent risk factor for falling. Therefore, there is a need for efficient vestibular diagnostic tests that identify clinically meaningful vestibular impairments in older patients. Background: Age related degenerative changes of the vestibular system occur in the vestibular end organs as well as the central vestibular structures. The vestibular end organs: saccule and utricle can be assessed using cervical evoked myogenic potential (cVEMP) and ocular vestibular evoked myogenic potential (oVEMP) respectively. The cVEMP and oVEMP are some of the most widely used vestibular diagnostic assessments; however previous works have showed that both responses, when elicited using a conventional and widely used stimulus of 500 Hz, are often bilaterally absent in older adults yielding results that are difficult to interpret. Therefore, there is a need to identify a stimulus that could best assess the older adult’s saccular and utricular functioning. Objective and methods: The purpose of this study was: 1) to assess age-related changes on various stimuli that can be used to assess cVEMP and oVEMP, and 2) to determine the optimal stimulus frequency in the young adult, middle age, and older adult populations. Additionally, we performed middle ear evaluation, to delineate age related changes in the middle ear from changes occurring in the inner ear of balance. A total of 107 participants consented to be in the study. Participants were divided in three groups: young adults (18-30 years), middle aged adults (41-59 years) and older adults (60-80 years). All of the participants underwent cVEMP and oVEMP testing using 500 Hz, 750 Hz and 1000 Hz air conducted stimuli. Middle ear functioning was also calculated for each of the participants. Results and Conclusion: It was found that age did not cause any change in measures of middle ear functioning. However, age did alter the saccular (cVEMP) and utricular (oVEMP) responses and this age effect was dependent on the stimulus frequency. The strength/amplitude of the cVEMP decreased with increasing age for the more conventional frequency (500 Hz), but the age effect was not observed at the higher frequency of 1000 Hz. Further, for the older adults, cVEMP was largest in amplitude and more often present at 1000 Hz. This differed from the young adult group where 500 Hz was the best frequency to elicit a cVEMP. For the oVEMP, the strength/amplitude decreased with increasing age for all the three stimuli/frequencies and the best stimulus frequency in all the three age groups was 1000 Hz. We also found that middle ear did not contribute towards shaping the response of cVEMP and oVEMP for various stimuli. Thus, the changes in the cVEMP and oVEMP frequency tuning observed in the older adults may not be stemming from middle ear but could be due to age related changes in the vestibular system

The Clinical Significance of the Failure to Perceive Vertigo in the Postcaloric Period Despite a Robust Caloric Response

Purpose The purpose of this project was to explore the association between the perception of motion during caloric testing and two tasks associated with central vestibular processing: postural stability and visuospatial memory. Method This was a prospective study of 25 patients who were found to have nonvestibular etiologies of their symptoms and normal vestibular function test results and who underwent caloric testing with a mean maximum slow phase eye velocity for each irrigation of 15° or greater. Following each caloric irrigation, patients were asked whether they had any sensation of movement. Patients were grouped based on the presence or absence of motion during the caloric exam (motion perception vs. absent perception). Postural stability was assessed using computerized dynamic posturography, and visuospatial memory was assessed using a memory match card game application. Results There were no significant differences between groups on any measures of peripheral vestibular function. However, the Absent Perception Group showed greater postural instability during Condition 5 of posturography and performed significantly worse on a task of visuospatial working memory. Both age and absence of motion perception predicted abnormal performance on measures of postural stability and visuospatial working memory. Conclusions There appears to be clinical implications to a lack of motion perception during the caloric exam in patients with an otherwise normal peripheral vestibular system. Based on the current findings, we are unable to determine whether differences in postural stability and visuospatial memory were due to age or a central vestibular processing deficit

Magnitude estimates of angular motion: Perception of speed and displacement across vestibular and visual modalities

Both the vestibular system (e.g. VOR) and optokinetic system (e.g. OKN) generate conjugate eye movements in response to either movement of the head or movement of the visual surround. Both systems help to maintain gaze stability. While the VOR is most sensitive to input frequencies above .2 Hz, the oculomotor system helps maintain gaze stability at lower frequencies. Psychophysics is the study of the relationship between perception and a physical stimulus. Previous research on perceptual thresholds across the two sensory modalities shows that there are frequency-dependent differences between vestibular and visual perception. The purpose of this study is to extend previous vestibular psychophysics work by measuring magnitude estimates of speed and angular displacement in response to suprathreshold stimulation from either vestibular or visual stimuli. Participants were exposed to 12 experimental conditions of angular rotation of varying frequencies, peak velocities, and acceleration rates across both sensory modalities. Vestibular stimulation was provided with a rotary chair and visual stimulation with equivalent conditions but under a virtual reality headset. Participants provided magnitude estimates of their speed and angle of displacement. Results reveal that vestibular and visual perception of suprathreshold motion stimuli differ as a function of frequency and agree with perceptual threshold data