1,721,016 research outputs found
Functional adaptation of the infant craniofacial system to mechanical loadings arising from masticatory forces
No full text: The morphology and biomechanics of infant crania undergo significant changes between the pre- and post-weaning phases due to increasing loading of the masticatory system. The aims of this study were to characterize the changes in muscle forces, bite forces and the pattern of mechanical strain and stress arising from the aforementioned forces across crania in the first 48 months of life using imaging and finite element methods. A total of 51 head computed tomography scans of normal individuals were collected and analysed from a larger database of 217 individuals. The estimated mean muscle forces of temporalis, masseter and medial pterygoid increase from 30.9 to 87.0 N, 25.6 to 69.6 N and 23.1 to 58.9 N, respectively (0-48 months). Maximum bite force increases from 90.5 to 184.2 N (3-48 months). There is a change in the pattern of strain and stress from the calvaria to the face during postnatal development. Overall, this study highlights the changes in the mechanics of the craniofacial system during normal development. It further raises questions as to how and what level of changes in the mechanical forces during the development can alter the morphology of the craniofacial system
Craniofacial system under external loads: Wild type and Crouzon mice
No full textCranial sutures permit postnatal craniofacial growth and absorb external forces. Craniosynostosis, the premature fusion of these joints, can cause craniofacial abnormalities including dysmorphology and increased intracranial pressure, typically requiring multiple invasive surgeries. Our previous research suggested that external cyclic loading of the frontal bone in Crouzon mouse models might improve suture patency and skull shape.
This study aimed to investigate the biomechanical responses during external loading and evaluate morphological effects following treatment regimes.
Biomechanical investigations demonstrated that static loading adequately represented cyclic loading for mechanical suture deformation analysis. Substantial strains (~0.6 to ~0.8) were observed in coronal sutures during frontal bone loading, along with post-loading plastic deformation. The development of BounTI allowed the investigations to be expanded. The interparietal and lambdoid sutures and additional loading locations were included. These investigations revealed that skull deformation is highly location-dependent, with posterior loading producing greater deformation. BounTI facilitated rapid finite element model development for comparison with experimental data.
Morphological investigations revealed significantly higher inter-litter variation compared to intra-litter variation, suggesting that litter-based treatment groups may introduce statistical artefacts and false positive results. Our findings indicated that each litter should be randomly divided into equal control and treatment groups, reducing erroneous statistical significance to the expected 5%. Further in vivo experiments, including the original treatment regime and five variations, showed no clear loading effects on skull morphology or suture patency. Importantly, effects that appeared statistically significant when comparing individual treatment groups to all controls disappeared when treatment groups were compared to littermate controls.
While our biomechanical investigations established the groundwork for treatment translation to larger animal models, the morphological investigations demonstrated milder therapeutic benefits than previously reported. Further experimental work with robust morphological and statistical study design is essential to definitively establish the efficacy of the original treatment regime
: Advances in the automatic extraction and volume calculation of cranial cavities
No full textThe use of non-destructive approaches for digital acquisition (e.g. computerised tomography-CT) allows detailed qualitative and quantitative study of internal structures of skeletal material. Here, we present a new R-based software tool, Icex, applicable to the study of the sizes and shapes of skeletal cavities and fossae in 3D digital images. Traditional methods of volume extraction involve the manual labelling (i.e. segmentation) of the areas of interest on each section of the image stack. This is time-consuming, error-prone and challenging to apply to complex cavities. Icex facilitates rapid quantification of such structures. We describe and detail its application to the isolation and calculation of volumes of various cranial cavities. The R tool is used here to automatically extract the orbital volumes, the paranasal sinuses, the nasal cavity and the upper oral volumes, based on the coordinates of 18 cranial anatomical points used to define their limits, from 3D cranial surface meshes obtained by segmenting CT scans. Icex includes an algorithm (Icv) for the calculation of volumes by defining a 3D convex hull of the extracted cavity. We demonstrate the use of Icex on an ontogenetic sample (0-19 years) of modern humans and on the fossil hominin crania Kabwe (Broken Hill) 1, Gibraltar (Forbes' Quarry) and Guattari 1. We also test the tool on three species of non-human primates. In the modern human subsample, Icex allowed us to perform a preliminary analysis on the absolute and relative expansion of cranial sinuses and pneumatisations during growth. The performance of Icex, applied to diverse crania, shows the potential for an extensive evaluation of the developmental and/or evolutionary significance of hollow cranial structures. Furthermore, being open source, Icex is a fully customisable tool, easily applicable to other taxa and skeletal regions
Normal human craniofacial growth and development from 0 to 4 years
Get PDFKnowledge of human craniofacial growth (increase in size) and development (change in shape) is important in the clinical treatment of a range of conditions that affects it. This study uses an extensive collection of clinical CT scans to investigate craniofacial growth and development over the first 48 months of life, detail how the cranium changes in form (size and shape) in each sex and how these changes are associated with the growth and development of various soft tissues such as the brain, eyes and tongue and the expansion of the nasal cavity. This is achieved through multivariate analyses of cranial form based on 3D landmarks and semi-landmarks and by analyses of linear dimensions, and cranial volumes. The results highlight accelerations and decelerations in cranial form changes throughout early childhood. They show that from 0 to 12 months, the cranium undergoes greater changes in form than from 12 to 48 months. However, in terms of the development of overall cranial shape, there is no significant sexual dimorphism in the age range considered in this study. In consequence a single model of human craniofacial growth and development is presented for future studies to examine the physio-mechanical interactions of the craniofacial growth
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Investigating the biomechanics of a lizard skull using advanced computer modelling techniques with experimental validation
Get PDFLizard skulls vary greatly in shape and construction, and radical changes in skull form during evolution have made this an intriguing subject of research. The mechanics of feeding have surely been affected by this change in skull form, but whether this change in feeding is the driving force behind the change in skull shape is the underlying question being addressed throughout this project.Here the skull of 'Uromastyx hardwickii', an akinetic herbivorous lizard has been analysed using advanced computer modelling techniques. This study aimed to perform a multibody dynamics analysis (MDA) on a biting lizard skull so that bite forces, joint forces, ligament forces and muscle forces could be accurately predicted. Then, using this MDA load data stresses and strains within the skull were assessed using finite element analysis (FEA). These FE analyses were used to assess biting performance and to test hypotheses that consider biomechanical optimization of bone as the main reason behind the modification of skull shape during its evolution. Sutures were modelled and their effect on skull strains was assessed through a series of investigative studies. Finally, representative basal skull forms were examined to highlight potential implications of specific skull variations. To assist in validation of the computational modelling experimental strain gauging was conducted.The MDA provided detailed information on cranial biomechanics and associated cranial forces in this animal. It is believed that this technique will play a pivotal role in the analysis of skulls in the future and this study has demonstrated its definite potential. Cranial kinesis was seen to be mechanically significant in reducing joint reaction forces acting upon the skull, and specific groups of sutures (i.e. the frontal-parietal suture) in the Uromastyx skull played a substantial role in relieving strain compared to the other sutures, raising the questions about the original role of mesokinesis in squamate evolution
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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