918 research outputs found
True V or not True V, That is the Question
No full textIn this paper we intend to argue that: (1) the question `True V or not True V' is central to both the philosophical and mathematical investigations of the foundations of mathematics; (2) when posed within a framework in which set theory is seen as a science of objects, the question `True V or not True V' generates a dilemma each horn of which turns out to be unacceptable; (3) a plausible way out of the dilemma mentioned at (2) is provided by an approach to set theory according to which this is considered to be a science of structures
DIENCEFALO: TALAMO-IPOTALAMO. TERMOREGOLAZIONE; REGOLAZIONE DI EQUILIBRIO IDRICO, APPORTO ALIMENTARE E CICLO MESTRUALE
No full textMolecular characterization of skeletal regeneration in the brittle star amphiura filiformis
No full textEchinoderms are well known for their extensive regenerative abilities, but have been neglected in the field due to the lack of available molecular tools and resources [1]. Recently, developmental [2] and adult transcriptomes [3, 4] of the brittle star Amphiura filiformis have been sequenced, which opened up this species for molecular investigations of its rapid arm regeneration process. We use this brittle star as a model to understand the cellular and molecular aspects of skeletogenesis during adult arm regeneration and the potential role of the FGF signalling pathway in this process. Ultimately, we compare the molecular network driving regeneration of the skeleton to that underlying embryonic skeleton development [5].
Following a characterization of the anatomy and development of the skeleton during arm regeneration in A. filiformis [6], we established methods for spatio-temporal expression analysis [7] and pharmacological treatments to characterise genes involved in adult arm regeneration. We found that 18 embryonic skeletogenic mesoderm genes (transcription factors, signaling receptors and downstream differentiation genes) are also expressed in the dermal layer of the adult regenerating arm, where skeletal spicules form. FGF signalling perturbation using the SU5402 inhibitor interferes with skeleton formation during both embryonic development and adult regeneration of this brittle star. A large-scale comparison of genes affected by SU5402 in adult arm regeneration and during embryonic development revealed a conservation of network components downstream of FGF signalling between those two developmental modes.
Acknowledgements: We thank the staff at the Sven Lovén Centre for Marine Sciences in Kristineberg, especially Olga Ortega-Martinez and Sam Dupont, for assistance during animal and sample collection.
References:
1. Dupont S, Thorndyke M (2007) Bridging the regeneration gap: insights from echinoderm models. Nat Rev Genet 8:8–10
2. Delroisse J, Ortega-Martinez O, Dupont S, Mallefet J, Flammang P (2015) De novo transcriptome of the European brittle star Amphiura filiformis pluteus larvae. Mar Genomics. doi: 10.1016/j.margen.2015.05.014
3. Purushothaman S, Saxena S, Meghah V, Swamy CVB, Ortega-Martinez O, Dupont S, Idris M (2014) Transcriptomic and proteomic analyses of Amphiura filiformis arm tissue-undergoing regeneration. J Proteomics 1–12
4. Delroisse J, Mallefet J, Flammang P (2016) De Novo Adult Transcriptomes of Two European Brittle Stars: Spotlight on Opsin-Based Photoreception. PLoS One 11:e0152988
5. Dylus DV, Czarkwiani A, Stångberg J, Ortega-Martinez O, Dupont S, Oliveri P (2016) Large-scale gene expression study in the ophiuroid Amphiura filiformis provides insights into evolution of gene regulatory networks. Evodevo 7:2
6. Czarkwiani A, Ferrario C, Dylus D V., Sugni M, Oliveri P (2016) Skeletal regeneration in the brittle star Amphiura filiformis. Front Zool 13:18
7. Czarkwiani A, Dylus D V., Oliveri P (2013) Expression of skeletogenic genes during arm regeneration in the brittle star Amphiura filiformis. Gene Expr Patterns 13:464–47
Macrophiothrix oliveri Benham 1911
No full textMacrophiothrix oliveri (Benham, 1911) (Fig. 15) Ophiothrix oliveri Benham, 1911: 154 –156, figs. 14–17.—Clark, H.L., 1915: 276.—Clark, A.M., 1967: 647. Ophiothrix (Ophiothrix) oliveri.—Mortensen, 1924: 118–120, fig. 8. Macrophiothrix oliveri.—Hoggett, 1990: 192–194, figs. 3.22 e –i, 3.23 e –g. Material Examined. Bay of Islands. KAH0907/ 194, NIWA 77880 (1). TAN0906/ 2, NIWA 77863 (1). TAN0906/ 60, NIWA 55192 (86). TAN0906/ 81, NIWA 55440 (3). TAN0906/ 96, NIWA 77862 (1). TAN0906/ 99, NIWA 55683 (1). TAN0906/ 102, NIWA 55737 (1). TAN0906/ 170, NIWA 77861 (2). TAN0906/ 240, NIWA 57508 (20). East Coast North Island. TAN 1108 / 197, NIWA 77785 (3). TAN 1108 / 213, NIWA 77800 (3). TAN 1108 / 217, NIWA 77814 (2). TAN 1108 / 239, NIWA 77816 (1). TAN 1108 / 250, NIWA 75543 (1). TAN 1108 / 253, NIWA 75593 (2). TAN 1108 / 268, NIWA 77783 (30). TAN 1108 / 275, NIWA 77812 (3). Far North. TAN0906/ 159, NIWA 56591 (10). TAN 1105 / 60, NIWA 73395 (1). Three Kings Islands. TAN 1105 / 35, NIWA 77846 (8). TAN 1105 / 42, NIWA 77845 (2). TAN 1105 / 53, NIWA 73324 (2). TAN 1105 / 69, NIWA 77831 (18). TAN 1105 / 70, NIWA 77815 (2). Comparative Material. Macrophiothrix oliveri (Benham, 1911): Duncombe Bay, Norfolk Island, 29 ° 0´S, 167 ° 55´E, 15 m, 25 / 9 / 1976, MV F 96553 (1). NZOI/K 797, off L'Esperance Rock, 31 ° 20.82´S, 178 ° 49.2´W, 55 m, 19 / 7 / 1974, NIWA 79573 (20). NZOI/P 968, Raoul Island, Kermadec Chain, 29 ° 14.7´S, 177 ° 52.32´W, 10 m, 11 / 6 / 1980, NIWA 79568 (1). NZOI/T 260, off L'Esperance Rock, 31 ° 20.802´S, 178 ° 49.602´W, 68 m, 28 / 3 / 1982, NIWA 79564 (12). Diagnosis. Disc densely covered in glassy trifid-multifid spinelets, obscuring disc plates and radial shields. Distal edges of white radial shields visible beneath spinelets. Dorsal arm plates twice as wide as long, truncate fan shaped, light pinkish purple interspersed with a darker plate every 2–3 segments, all with variable white blotch on distal border. Ventral disc and arm surface creamy white. Six transparent arm spines, 3–4 arm segments, 4 th spine longest, reducing to less than a segment ventrally, with thorny edges. Description. See Mortensen (1924). Distribution. Kermadec and Norfolk Islands (1–157 m), northern New Zealand (37–205 m) Remarks. This species was transferred to Macrophiothrix by Hoggett (1990) in an unpublished PhD thesis. Examination of the specimens here confirms this decision; the dorsal arm plates are in general twice as wide as long, similar to other Macrophiothrix species. Within Macrophiothrix, Hoggett (1990) distinguished M. oliveri by the length of the fourth-sixth arm spines from the top which are the longest in the series. On other species, the second-third arm spines are longest. This species has a restricted distribution along the north-east coast of New Zealand and around a few islands to the north.Published as part of Mills, V. Sadie & O'Hara, Timothy D., 2013, Ophiuroids (Echinodermata; Ophiuroidea) of biogenic habitats on the continental shelf of New Zealand, pp. 401-444 in Zootaxa 3613 (5) on page 435, DOI: 10.11646/zootaxa.3613.5.1, http://zenodo.org/record/22270
A Rayleigh-Ritz approach for postbuckling analysis of variable angle tow composite stiffened panels
No full textA Rayleigh-Ritz solution approach for generally restrained multilayered variable angle tow stiffened plates in postbuckling regime is presented.
The plate model is based on the first order shear deformation theory and accounts for geometrical nonlinearity through the von K\'arm\'an's assumptions. Stiffened plates are modelled as assembly of plate-like elements and penalty techniques are used to join the elements in the assembled structure and to apply the kinematical boundary conditions.
General symmetric and unsymmetric stacking sequences are considered and Legendre orthogonal polynomials are employed to build the trial functions.A computer code was developed to implement the proposed approach and to establish its applicability and its features for investigating variable angle tow structures.
The proposed solution is validated by comparison with literature and finite elements results. Original results are presented for postbuckling of variable angle tow stiffened plates showing the potentialities of the method
Investigation of buckling characteristics of cracked variable stiffness composite plates by an eXtended Ritz approach
No full textVariable Angle Tow (VAT) composite plates are characterized by in-plane variable stiffness properties, which opens to new concepts of stiffness tailoring and optimization to achieve higher structural performance for advanced lightweight structures where damage tolerance consideration are often mandatory. In this paper, a single-domain eXtended Ritz formulation is proposed to study the buckling behaviour of variable stiffness laminated cracked plates. The plate behaviour is described by the first order shear deformation theory whose generalized displacements, namely reference plane translations and rotations, are expressed via suitable admissible trial functions. These consist of a set of regular terms, built using orthogonal polynomials, augmented with special functions able to describe the crack opening and the singular behaviour at the crack tips; boundary functions are used to ensure the required homogeneous essential boundary conditions. Governing equations are inferred via the stationarity of the energy functional an solved to carry out an extensive study on the buckling behaviour of variable angle tow homogeneous and layered composite plates. The results obtained for homogeneous plates evidence that the crack presence strongly influences the buckling behaviour depending on its length and inclination and plate boundary conditions with a meaningful variability with respect to the fibre paths configuration, which can arrange for better performances with respect to the straight fibre case. Also for cracked laminates the results show that there are several fibre path able to provide higher buckling loads and higher overall axial stiffness with respect to the straight fibre case. In the framework of damage tolerant engineering applications, this allows to select fibre paths that guarantee predefined design levels of buckling load and axial stiffness even in presence of cracks. Finally, this study highlights the potential of the proposed approach for the analysis of the buckling behaviour of cracked composite variable stiffness plates, which provides an efficient analysis tool for the damage tolerant design and optimization of advanced variable stiffness structures
Propellant non-steady burning effects on controllable solid rocket motor internal ballistics
No full textAn analysis of the unsteady non-linear behavior of the controllable solid propellant rocket motor (CSRM) consequent to rapid and relevant nozzle operation is presented. The study includes a development of a non-linear unsteady combustion model able to handle relevant and rapid chamber pressure changes typical of CSRMs. The CSRM nonlinear unsteady model is implemented according to a main solver - sub models architecture and uses different time scales. The formulation of the combustion gas mass flow rate is developed considering the propellant density, the unsteady combustion, the regression of the combustion surface and the outflow through the variable nozzle. The grain surface involved in the combustion is obtained by a regression model of the chamber walls, in reliance on the unsteady burning rate, on the initial grain geometry and integrates the history of performed nozzle operations. The CSRM is described by a system of differential equations that is reduced in sub systems and solved numerically in the main solver sub model frame
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