Simultaneously Sparse Solutions to Linear Inverse Problems with Multiple System Matrices and a Single Observation Vector

A linear inverse problem is proposed that requires the determination of multiple unknown signal vectors. Each unknown vector passes through a different system matrix and the results are added to yield a single observation vector. Given the matrices and lone observation, the objective is to find a simultaneously sparse set of unknown vectors that solves the system. We will refer to this as the multiple-system single-output (MSSO) simultaneous sparsity problem. This manuscript contrasts the MSSO problem with other simultaneous sparsity problems and conducts a thorough initial exploration of algorithms with which to solve it. Seven algorithms are formulated that approximately solve this NP-Hard problem. Three greedy techniques are developed (matching pursuit, orthogonal matching pursuit, and least squares matching pursuit) along with four methods based on a convex relaxation (iteratively reweighted least squares, two forms of iterative shrinkage, and formulation as a second-order cone program). The algorithms are evaluated across three experiments: the first and second involve sparsity profile recovery in noiseless and noisy scenarios, respectively, while the third deals with magnetic resonance imaging radio-frequency excitation pulse design.Comment: 36 pages; manuscript unchanged from July 21, 2008, except for updated references; content appears in September 2008 PhD thesi

Graded cellular structures for enhanced performance of additively manufactured orthopaedic implants

Hip implants face a significant challenge due to their limited lifespan, a concern amplified by the rising human life expectancy. Lattice structures have demonstrated the ability to provide precise control over geometry, thereby significantly enhancing implant performance. This paper introduces the development of graded additively manufactured Ti6Al4V lattice structures for orthopaedic implants. The objective focuses on developing a graded lattice unit cell design mirroring human bone properties, emphasising high surface curvature and design versatility to improve mechanical and biomedical properties, specifically osseointegration and stress shielding. The study involves modelling and grading simple cubic (SC) and body-centred cubic (BCC) lattice structures with various geometries and graded conditions and conducting compressive tests to identify the optimal configuration. The results showed that filleting was found to be the mechanical strength. On the other hand, BCC lattice structures demonstrated superior performance compared to SC structures. The optimised structure with a pore size of 400 µm provided an elastic modulus of 15.7 GPa, yield strength of 296 MPa and compressive strength of 530 MPa. This graded lattice design approach provides a promising technique for enhancing hip implant performance, offering potential improvements

Designing lightweight 3D-printable bioinspired structures for enhanced compression and energy absorption properties

Recent progress in additive manufacturing, also known as 3D printing, has offered several benefits, including high geometrical freedom and the ability to create bioinspired structures with intricate details. Mantis shrimp can scrape the shells of prey molluscs with its hammer-shaped stick, while beetles have highly adapted forewings that are lightweight, tough, and strong. This paper introduces a design approach for bioinspired lattice structures by mimicking the internal microstructures of a beetle’s forewing, a mantis shrimp’s shell, and a mantis shrimp’s dactyl club, with improved mechanical properties. Finite element analysis (FEA) and experimental characterisation of 3D printed polylactic acid (PLA) samples with bioinspired structures were performed to determine their compression and impact properties. The results showed that designing a bioinspired lattice with unit cells parallel to the load direction improved quasi-static compressive performance, among other lattice structures. The gyroid honeycomb lattice design of the insect forewings and mantis shrimp dactyl clubs outperformed the gyroid honeycomb design of the mantis shrimp shell, with improvements in ultimate mechanical strength, Young’s modulus, and drop weight impact. On the other hand, hybrid designs created by merging two different designs reduced bending deformation to control collapse during drop weight impact. This work holds promise for the development of bioinspired lattices employing designs with improved properties, which can have potential implications for lightweight high-performance applications

Designing Lightweight 3D-Printable Bioinspired Structures for Enhanced Compression and Energy Absorption Properties

Recent progress in additive manufacturing, also known as 3D printing, has offered several bene-fits, including high geometrical freedom and the ability to create bioinspired structures with intri-cate details. Mantis shrimp can scrape the shells of prey molluscs with its hammer-shaped stick, while beetles have highly adapted forewings that are lightweight, tough, and strong. This paper introduces a design approach for bioinspired lattice structures by mimicking the internal micro-structures of a beetle’s forewing, a mantis shrimp’s shell, and a mantis shrimp’s dactyl club, with improved mechanical properties. Finite element analysis (FEA) and experimental characterisation of 3D printed polylactic acid (PLA) samples with bioinspired structures were performed to deter-mine their compression and impact properties. The results showed that designing a bioinspired lattice with unit cells parallel to the load direction improved quasi-static compressive perfor-mance, among other lattice structures. The gyroid honeycomb lattice design of the insect forewings and mantis shrimp dactyl clubs outperformed the gyroid honeycomb design of the mantis shrimp shell, with improvements in ultimate mechanical strength, Young’s modulus, and drop weight impact. On the other hand, hybrid designs created by merging two different designs reduced bend-ing deformation to control collapse during drop weight impact. This work holds promise for the development of bioinspired lattices employing designs with improved properties, which can have potential implications for lightweight high-performance applications

Designing Lightweight 3D-Printable Bioinspired Structures for Enhanced Compression and Energy Absorption Properties

Recent progress in additive manufacturing, also known as 3D printing, has offered several bene-fits, including high geometrical freedom and the ability to create bioinspired structures with intri-cate details. Mantis shrimp can scrape the shells of prey molluscs with its hammer-shaped stick, while beetles have highly adapted forewings that are lightweight, tough, and strong. This paper introduces a design approach for bioinspired lattice structures by mimicking the internal micro-structures of a beetle’s forewing, a mantis shrimp’s shell, and a mantis shrimp’s dactyl club, with improved mechanical properties. Finite element analysis (FEA) and experimental characterisation of 3D printed polylactic acid (PLA) samples with bioinspired structures were performed to deter-mine their compression and impact properties. The results showed that designing a bioinspired lattice with unit cells parallel to the load direction improved quasi-static compressive perfor-mance, among other lattice structures. The gyroid honeycomb lattice design of the insect forewings and mantis shrimp dactyl clubs outperformed the gyroid honeycomb design of the mantis shrimp shell, with improvements in ultimate mechanical strength, Young’s modulus, and drop weight impact. On the other hand, hybrid designs created by merging two different designs reduced bend-ing deformation to control collapse during drop weight impact. This work holds promise for the development of bioinspired lattices employing designs with improved properties, which can have potential implications for lightweight high-performance applications

Fast pseudo-CT synthesis from MRI T1-weighted images using a patch-based approach

MRI-based bone segmentation is a challenging task because bone tissue and air both present low signal intensity on MR images, making it difficult to accurately delimit the bone boundaries. However, estimating bone from MRI images may allow decreasing patient ionization by removing the need of patient-specific CT acquisition in several applications. In this work, we propose a fast GPU-based pseudo-CT generation from a patient-specific MRI T1-weighted image using a group-wise patch-based approach and a limited MRI and CT atlas dictionary. For every voxel in the input MR image, we compute the similarity of the patch containing that voxel with the patches of all MR images in the database, which lie in a certain anatomical neighborhood. The pseudo-CT is obtained as a local weighted linear combination of the CT values of the corresponding patches. The algorithm was implemented in a GPU. The use of patch-based techniques allows a fast and accurate estimation of the pseudo-CT from MR T1-weighted images, with a similar accuracy as the patient-specific CT. The experimental normalized cross correlation reaches 0.9324±0.0048 for an atlas with 10 datasets. The high NCC values indicate how our method can accurately approximate the patient-specific CT. The GPU implementation led to a substantial decrease in computational time making the approach suitable for real applications

Recovery of the vomiting reflex following area postrema ablation in squirrel monkeys

The role of the area postrema (AP) in motion-induced emesis was re-assessed recently in several different species. In a few of these studies, the role of the AP in motion-induced conditioned taste aversion (CTA) was also addressed. The purpose was to extend this comparative study to the squirrel monkey, to evaluate further the role of AP in vomiting, and to investigate the dynamics of the recovery process. The AP was ablated bilaterally in 7 motion-susceptible squirrel monkeys which previously had been characterized in terms of their responses to various motion sickness-inducing stimuli. After recovery from surgery all animals were tested at 30-day intervals for a period of 11 months to determine the effects of AP ablations on susceptibility to the same sickness-inducing conditions. In addition, the effectiveness of motion in preducing CTA was evaluated. All pre-ablation motion tests involved stimulation for 30 min., while post-lesion tests were 60 min., in duration. All animals showed significant increases in latencies to vomiting after AP ablations. However, the latencies tended to decrease with time after ablation. All but one animal vomited on at least one of the 10 motion tests occurring after ablation of AP. In addition, CTA was produced by motion used in the conditioning sessions. These results suggest that structures other than AP, and processes other that those mediated through AP, may play an important role in motion-induced emesis

The prevalence of cubital tunnel syndrome: A cross-sectional study in a U.S. metropolitan cohort

BACKGROUND: Although cubital tunnel syndrome is the second most common peripheral mononeuropathy (after carpal tunnel syndrome) encountered in clinical practice, its prevalence in the population is unknown. The objective of this study was to evaluate the prevalence of cubital tunnel syndrome in the general population. METHODS: We surveyed a cohort of adult residents of the St. Louis metropolitan area to assess for the severity and localization of hand symptoms using the Boston Carpal Tunnel Questionnaire Symptom Severity Scale (BCTQ-SSS) and the Katz hand diagram. We identified subjects who met our case definitions for cubital tunnel syndrome and carpal tunnel syndrome: self-reported hand symptoms associated with a BCTQ-SSS score of >2 and localization of symptoms to the ulnar nerve or median nerve distributions. RESULTS: Of 1,001 individuals who participated in the cross-sectional survey, 75% were women and 79% of the cohort was white; the mean age (and standard deviation) was 46 ± 15.7 years. Using a more sensitive case definition (lax criteria), we identified 59 subjects (5.9%) with cubital tunnel syndrome and 68 subjects (6.8%) with carpal tunnel syndrome. Using a more specific case definition (strict criteria), we identified 18 subjects (1.8%) with cubital tunnel syndrome and 27 subjects (2.7%) with carpal tunnel syndrome. CONCLUSIONS: The prevalence of cubital tunnel syndrome in the general population may be higher than that reported previously. When compared with previous estimates of disease burden, the active surveillance technique used in this study may account for the higher reported prevalence. This finding suggests that a proportion of symptomatic subjects may not self-identify and may not seek medical treatment. CLINICAL RELEVANCE: This baseline estimate of prevalence for cubital tunnel syndrome provides a valuable reference for future diagnostic and prognostic study research and for the development of clinical practice guidelines