561 research outputs found
Modelling Skin-Stringer Separation in a Post-Buckled Composite Stiffened Panel through Single Stringer Specimens
No full textThe collapse of composite stiffened panels in compression is complex and involves the interactions of many different failure modes. However, when the panel is allowed to enter the post-buckling regime, skin-stringer separation due to the interaction of the post-buckling deformations with the skin-stringer interface is often the critical failure mode. The accurate prediction of skin-stringer separation in these types of panels is therefore crucial for their design. Due to the high computational costs associated with modelling damage in a large multistringer panel and the manufacturing and testing costs associated with testing such a panel, single stringer specimens that accurately represent the behaviour of critical regions in these panels have been proposed in literature. In this thesis, transversely loaded single stringer specimens are designed and verified and are used to predict skin-stringer separation in the critical regions of a specific multistringer panel. A specific composite stiffened panel is considered that contains a skin of a tape material and four co-cured stringers of a fabric material. At the intersections of the skin and stringers, resin-rich noodle regions are created. A buckling analysis is first performed on the panel to obtain its post-buckling deformations. Based on these, two types of regions where skin-stringer separation may occur are identified; a mode I dominated skin-stringer separation at the minima of the buckling waves and a combined mode II and mode III skin-stringer separation at the inflection points of the buckling waves. A seven point bending specimen is designed based on the panel deformations near the former critical region, while a four point twisting specimen is designed based on the deformations near the latter region. Finally, detailed damage models are set up for the single stringer specimens to predict skin-stringer separation and the models are verified with the multistringer panel. The analyses showed that a mode I dominated skin-stringer separation is critical for this panel. The detailed analysis of the four point twisting specimen showed that no damage occurred at the inflection point. To predict the skin-stringer separation at the minimum, a verified seven point bending specimen has successfully been obtained. To do so, it was important to accurately simulate the deformation of the skin at the stringer flange edge, since this proved to be driving for the initiation and propagation of skin-stringer separation. Next to that, a trilinear cohesive law was used to capture the R-curve effect in the tape/fabric interfaces. Finally, a first assessment of the noodle region behaviour showed that damage in this region will probably happen at the location of maximum bending. Recommendations for future research have been provided.Aerospace Engineerin
Orientation dependence of THz scattering from cylindrical strands
No full text© Copyright 2009 IEEE – All Rights ReservedScattering of terahertz radiation from cylindrical strands is explored as a means of studying the effects of hair on the results of bio-tissue analysis. Strands of fiberglass are aligned either parallel or perpendicular to the polarization vector of the incoming terahertz beam. Spectroscopic results reveal that the material's intrinsic THz transmission properties are highly dependent on fiber orientation. ©IEEE.Gretel M. Png, Mark R. Stringer, Brian W.-H. Ng, Derek Abbott and Robert E. Mileshttp://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=466551
Terahertz scattering by subwavelength cylindrical arrays
No full textWe demonstrate the use of a full-wave electromagnetic field simulator to verify terahertz (THz) transmission-mode spectroscopic measurements of periodic arrays containing subwavelength cylindrical scatterers. Many existing THz scattering studies utilize analytical solutions, which were developed for a single scatterer. For multiple scatterers, a scaling factor equal to the number of scatterers is applied, accounting for interference between far-field radiative contributions from those scatterers but not their near-field mutual coupling. Consequently, analytical solutions do not accurately verify measurements. Conversely, results from the full-wave electromagnetic field simulator elucidate our measurements well, and provide an important insight into how the scattering behavior of cylindrical scatterers is influenced by test conditions.Gretel M. Png, Christophe Fumeaux, Mark R. Stringer, Robert E. Miles and Derek Abbot
Enigmatic *-nt-Stems : an investigation of the secondary -t- of the Greek neuter nouns in *-men- and *-r/n-
Get PDFRésumé
Cette étude vise l’explication de l’origine du -t- secondaire qui s’insère en grec ancien au thème oblique des neutres du type πρᾶγμα, πράγματος et ἧπαρ, ἥπατος. Après une courte exposition des données grecques, et du contexte indo-européen, les hypothèses déjà proposées sont évaluées, démarche qui nécessite une exposition de l’éventuel suffixe *-mentom, des thèmes animés en -n- dotés d’un élargissement ou d’un suffixe -t-, du suffixe ablatif en -tos, du -t- final de certains neutres *r/n-sanscrits, de l’« ergatif » hittite et de l’apophonie des participes en -nt. Certaines questions phonologiques font également l’objet de développements. La plupart des hypothèses déjà formulées pour expliquer les données grecques datent du dix-neuvième siècle; celles-ci sont réévaluées à la lumière de travaux plus récents, notamment sur les classes apophoniques du proto-indo-européen. Sont également prises en compte certaines hypothèses du vingt-et-unième siècle, selon lesquelles les données grecques relèvent d’un problème plus large du proto-indo-européen.
Le présent mémoire ne cherche pas à expliquer l’origine de la flexion *-r/n- ni du suffixe *-nt- du proto-indo-européen. L’auteure se contente de démontrer que la plupart des phénomènes dans d’autres langues, y compris le proto-indo-européen, ne peuvent être directement liés à la situation grecque. Elle conclut que la meilleure explication de la flexion grecque suppose une refonte analogique. Ont servi de modèle les formes neutres du participe actif athématique ainsi que les adjectifs en *-nt- (surtout ceux en *-went-).This paper aims to provide an explanation of the secondary -t- found in the oblique stem of ancient Greek neuters such as πρᾶγμα, πράγματος and ἧπαρ, ἥπατος. After a brief overview of the Greek data, and a survey of the relevant nominal classes in Greek and Indo- European, previous hypotheses are evaluated. To this end, several problems of nominal morphology are discussed, including the existence of a PIE suffix *-m(e)ntom, the secondary -t-s of certain animate nouns, the ablatival suffix *-tos, the Hittite ergative; and the ablaut of neuter active participles. Certain phonological issues are also addressed. Since the majority of hypotheses formulated to explain the secondary -nt- inflection of Greek neuters date from the nineteenth century, attempts are made to re-evaluate their conclusions in the light of more recent research, particularly that related to ablaut classes. Also considered are a number of twenty-first century works which purport to explain the Greek data as part of a larger Indo- European phenomenon. This paper makes no attempt, however, to explain the PIE origins of either the *r/n-, or of the *nt- stems. It concludes that the best explanation of the Greek declensional pattern is to be found in the analogy between stems in -nt- and those in *-mn- or *-r/n-
Creeping decay: cult soundtracks, residual media, and digital technologies
No full textThis paper explores the recent resurgence in the collecting of cult film soundtracks, in particular films stemming from the late 1960s to the early 1980s and often linked to horror and other modes of exploitation cinema. I consider this phenomenon as an important component of cult film fandom, but one which has largely been overlooked in cult cinema research because it is often considered as belonging to popular music, as opposed to film, research. As films can become cultified in many different ways and across different media, I look into how areas of music culture can both be inspired by, as well as influence, aspects of film culture. The paper also addresses the importance of ‘residual’ technologies within cult film/music cultures, noting in particular the preference for vinyl records as well as VHS tapes in certain cult fan communities, and explores the appeal that such ‘old media’ retain within an increasingly digital mediascape
Relationship of the cricothyroid space with vocal range in female singers
No full textIt is well documented that the cricothyroid (CT) space opens and closes with changes in pitch, narrowing with rising pitch and widening with falling pitch. Indeed, cricothyroid approximation surgery, a procedure where the CT space is deliberately made smaller, is used in male to female transgender subjects to successfully elevate vocal pitch.
The present study focuses on investigating the relationship between the anterior CT space at rest and vocal range in female singers. Laryngeal dimensions (anterior CT space and heights of the thyroid and cricoid cartilages) were measured using ultrasound in 43 healthy, classically trained, female singers. Potential associations with and between age, ethnicity, anthropometric indices (height, weight, body mass index), neck dimensions (circumference and length), vocal data (practice and performance vocal range, lowest and highest practice and performance notes) along with usual speaking fundamental frequency were also explored.
The main finding was that mezzo-sopranos have a significantly wider resting CT space than sopranos (11.6 mm versus 10.4 mm; P=0.007). Mezzo-sopranos also had significantly lower ‘lowest and highest’ performance notes and speaking fundamental frequencies than sopranos. Furthermore, there was a weak but significant negative correlation between the magnitude of the anterior CT space and the lowest performance note (r=-0.448; P=0.003) but there was no significant correlation with either the highest performance note or vocal range.
These results suggest there is a relationship between the CT space and the lowest note a female can sing. This was evident in the correlation of a small CT space with a higher ‘lowest performance note’. It appears that the CT space influences how low female singers can sing, but not how high they can sing
Constraints and subsequent limitations to parental involvement in primary schools in Abu Dhabi: stakeholders' perspective
No full textThe United Arab Emirates (UAE) is developing its public schools by initiating reform agendas for school improvement. High on the list of reforms is the call to increase parental involvement in schools. For this reform to work successfully, it is important to identify and examine the constraints and subsequent limitations that exist. Seven primary Public, Private Partnership schools (PPP) in Abu Dhabi were the focus of this qualitative case study. Participants were school stakeholders: school administrators, social workers, teachers and parents. The findings will assist in developing continuing policies and practices which take these limitations into account and work to mitigate them. Recommendations are made based within the context of the findings
Constraints and subsequent limitations to parental involvement in primary schools in Abu Dhabi: stakeholders' perspective
No full textThe United Arab Emirates (UAE) is developing its public schools by initiating reform agendas for school improvement. High on the list of reforms is the call to increase parental involvement in schools. For this reform to work successfully, it is important to identify and examine the constraints and subsequent limitations that exist. Seven primary Public, Private Partnership schools (PPP) in Abu Dhabi were the focus of this qualitative case study. Participants were school stakeholders: school administrators, social workers, teachers and parents. The findings will assist in developing continuing policies and practices which take these limitations into account and work to mitigate them. Recommendations are made based within the context of the findings
Mitogenomes from Two Uncommon Haplogroups Mark Late Glacial/Postglacial Expansions from the Near East and Neolithic Dispersals within Europe
No full textThe current human mitochondrial (mtDNA) phylogeny does not equally represent all human populations but is biased in favour of representatives originally from north and central Europe. This especially affects the phylogeny of some uncommon West Eurasian haplogroups, including I and W, whose southern European and Near Eastern components are very poorly represented, suggesting that extensive hidden phylogenetic substructure remains to be uncovered. This study expanded and re-analysed the available datasets of I and W complete mtDNA genomes, reaching a comprehensive 419 mitogenomes, and searched for precise correlations between the ages and geographical distributions of their numerous newly identified subclades with events of human dispersal which contributed to the genetic formation of modern Europeans. Our results showed that haplogroups I (within N1a1b) and W originated in the Near East during the Last Glacial Maximum or pre-warming period (the period of gradual warming between the end of the LGM, ~19 ky ago, and the beginning of the first main warming phase, ~15 ky ago) and, like the much more common haplogroups J and T, may have been involved in Late Glacial expansions starting from the Near East. Thus our data contribute to a better definition of the Late and postglacial re-peopling of Europe, providing further evidence for the scenario that major population expansions started after the Last Glacial Maximum but before Neolithic times, but also evidencing traces of diffusion events in several I and W subclades dating to the European Neolithic and restricted to Europe
Experimental determination of fracture toughness for delamination analysis in structural components
No full textDelamination is an important damage mechanism in composite materials. A correct prediction of its behaviour is of great importance in the design of aerospace composite structures. Nevertheless, when using simple numerical models which do not account for the delamination migrating to other interfaces or other intralaminar damage mechanisms, the accuracy of the numerical analyses is restricted by the inadequacy of the standardised experimental determination of the fracture toughness. This interlaminar property is usually measured using unidirectional specimens, which ignores the effect of the lay-up. Furthermore, the changing fracture toughness as the crack propagates, the so-called R-curve effect, is generally ignored as well by only employing the initiation values from the experiments. This leads to highly conservative results as the resistance to delamination is not correctly accounted for. The aim of this MSc Thesis was to contribute to the improvement of the blind simulation of delamination in co-cured composite aerospace structures. In particular, the experimental determination of the fracture toughness in coupons without a 0/0 interface to then be used as parameters in the simulation of one structural component: a single-stringer compression (SSC) specimen.Based on the lay-up formed by the skin and the stringer of the SSC specimen, various layups were defined for DCB and MMB testing. After evaluating them numerically, the fracture toughness was measured experimentally in unidirectional [012//012] and multidirectional [011, 45//-5, 011] coupons, in DCB and MMB for mode mixtures 20% and 50%. The R-curve effect of the multidirectional specimens was far greater than for the unidirectional ones, the steady-state fracture toughness was around three times higher, due to the crack migrating to other interfaces or propagating simultaneously in between different plies.The experimental results were used to improve the numerical analyses of the tests performed. A new approach was presented to model the measured R-curve effect by varying the fracture toughness values according to the distance to the crack tip. The improvements achieved were especially relevant for the multidirectional specimens. This approach and the R-curve from the multidirectional specimen were employed in the analysis of the SSC specimen. The results obtained emphasise the importance of accounting for the effect of the lay-up and the crack growth length on the fracture toughness. Furthermore, it was shown the potential and shortcomings of using an experimentally determined material law, accounting for delamination migration and other damage mechanisms, to improve delamination modelling.Aerospace Engineerin
- …
