15,516 research outputs found
Iceberg Scour and Shell Damage in the Antarctic Bivalve Laternula elliptica
No full textWe document differences in shell damage and shell thickness in a bivalve mollusc (Laternula elliptica) from seven sites around Antarctica with differing exposures to ice movement. These range from 60% of the sea bed impacted by ice per year (Hangar Cove, Antarctic Peninsula) to those protected by virtually permanent sea ice cover (McMurdo Sound). Patterns of shell damage consistent with blunt force trauma were observed in populations where ice scour frequently occurs; damage repair frequencies and the thickness of shells correlated positively with the frequency of iceberg scour at the different sites with the highest repair rates and thicker shells at Hangar Cove (74.2% of animals damaged) compared to the other less impacted sites (less than 10% at McMurdo Sound). Genetic analysis of population structure using Amplified Fragment Length Polymorphisms (AFLPs) revealed no genetic differences between the two sites showing the greatest difference in shell morphology and repair rates. Taken together, our results suggest that L. elliptica exhibits considerable phenotypic plasticity in response to geographic variation in physical disturbance
Dynamic expression of ancient and novel molluscan shell genes during ecological transitions
No full textBackground: The Mollusca constitute one of the most morphologically and ecologically diverse metazoan phyla, occupying a wide range of marine, terrestrial and freshwater habitats. The evolutionary success of the molluscs can in part be attributed to the evolvability of the external shell. Typically, the shell first forms during embryonic and larval development, changing dramatically
in shape, colour and mineralogical composition as development and maturation proceeds. Major developmental transitions in shell morphology often correlate with ecological transitions (e.g. from a planktonic to benthic existence at metamorphosis). While the genes involved in molluscan biomineralisation are beginning to be identified, there is little understanding of how these are developmentally regulated, or if the same genes are operational at different stages of the mollusc's life.
Results: Here we relate the developmental expression of nine genes in the tissue responsible for shell production – the mantle – to ecological transitions that occur during the lifetime of the tropical abalone Haliotis asinina (Vetigastropoda). Four of these genes encode evolutionarily ancient proteins, while four others encode secreted proteins with little or no identity to known proteins.
Another gene has been previously described from the mantle of another haliotid vetigastropod. All nine genes display dynamic spatial and temporal expression profiles within the larval shell field and juvenile mantle.
Conclusion: These expression data reflect the regulatory complexity that underlies molluscan shell construction from larval stages to adulthood, and serves to highlight the different ecological demands placed on each stage. The use of both ancient and novel genes in all stages of shell
construction also suggest that a core set of shell-making genes was provided by a shared metazoan ancestor, which has been elaborated upon to produce the range of molluscan shell types we see today
Limit-point buckling analyses using solid, shell and solid–shell elements
No full textIn this paper, the recently-developed solid-shell element SHB8PS is used for the analysis of a representative set of popular limit-point buckling benchmark problems. For this purpose, the element has been implemented in Abaqus/Standard finite element software and the modified Riks method was employed as an efficient path-following strategy. For the. benchmark problems tested, the new element shows better performance compared to solid elements and often performs as well as state-of-the-art shell elements. In contrast to shell elements, it allows for the accurate prescription of boundary conditions as applied to the actual edges of the structure.Agence Nationale de la Recherche, France (ANR-005-RNMP-007
Shell formation and bone strength in laying hens
No full textIn Sweden almost 3.8% of all eggs are ruined due to cracked eggshells as shell quality declines with age during the laying period. This is a concern for food safety as well as an economical problem. Parallel with reduced shell quality the bone strength declines to an extent that the animal's welfare is threatened.
Laying hens of Lohmann Selected Leghorn (LSL) and Lohmann Brown (LB) were monitored during a complete production period. The first sign of declining shell quality was found in mid-production in both hybrids, and even before, in peak production, decreasing bone strength was detected. An imbalance between estrogen receptor alpha (ERα) and estrogen receptor beta (ERβ) in the shell gland and a reduced density of tubular glands are suggested as factors involved in the age-related decline of shell quality. Since the majority of eggshell calcium is absorbed in the duodenum, the dramatic drop in active carbonic anhydrase (CA) seen in duodenum at mid-production, may also contribute. In the shell gland CA is considered a key enzyme in the supply of the carbonate ions needed for shell formation. However, CA in the shell gland did not primarily seem to be involved in declining shell quality, in fact number of capillaries positive for CA activity increased with age. The calcium transporter PMCA was located in shell gland and duodenum but was not altered by age.
Boosting laying hens with a low continuous dose of estradiol at the end of the laying period improved shell quality in both hybrids, while a daidzein supplementation (50mg/kg feed) in the feed did not. Bone strength was unaffected by both treatments. CA activity in the shell gland may be regulated by estrogen and daidzein, possibly by acting via ERβ. However, a difference in sensitivity to daidzein and estradiol was found between the hybrids which complicates the interpretation of results and must be taken into a count when comparing studies from other investigations
On large deformations of thin elasto-plastic shells: Implementation of a finite rotation model for quadrilateral shell element
No full textA large-deformation model for thin shells composed of elasto-plastic material is presented in this work, Formulation of the shell model, equivalent to the two-dimensional Cosserat continuum, is developed from the three-dimensional continuum by employing standard assumptions on the distribution of the displacement held in the shell body, A model for thin shells is obtained by an approximation of terms describing the shell geometry. Finite rotations of the director field are described by a rotation vector formulation. An elasto-plastic constitutive model is developed based on the von Mises yield criterion and isotropic hardening. In this work, attention is restricted to problems where strains remain small allowing for all aspects of material identification and associated computational treatment, developed for small-strain elastoplastic models, to be transferred easily to the present elasto-plastic thin-shell model. A finite element formulation is based on the four-noded isoparametric element. A particular attention is devoted to the consistent linearization of the shell kinematics and elasto-plastic material model, in order to achieve quadratic rate of asymptotic convergence typical for the Newton-Raphson-based solution procedures. To illustrate the main objective of the present approach-namely the simulation of failures of thin elastoplastic shells typically associated with buckling-type instabilities and/or bending-dominated shell problems resulting in formation of plastic hinges-several numerical examples are presented, Numerical results are compared with the available experimental results and representative numerical simulations
Intellec: shell para implementação de sistemas especialistas
No full textDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-graduação em Engenharia ElétricaEste trabalho apresenta o desenvolvimento de uma shell, chamada de Intellec, para a geração automática de Sistemas Especialistas, utilizando lógica fuzzy para tratamento da incerteza. Esta shell utiliza a linguagem Prolog para a implementação da máquina de inferência, por se tratar de uma linguagem de programação lógica. A lógica fuzzy foi escolhida para representar a incerteza a respeito do conhecimento do domínio, permitindo também o uso de variáveis lingüísticas. A interface gráfica com o usuário foi implementada utilizando-se a ferramenta Borland Delphi. A validação do sistema proposto foi feita através de comparação direta entre o Intellec e o Expert SINTA, shell desenvolvida pelo grupo SINTA da Universidade Federal do Ceará, a qual é amplamente utilizada e reconhecida. Dois problemas, de áreas de conhecimento bastante distintas, foram implementados simultaneamente em ambas as shell's e os resultados obtidos foram compatíveis
Qualitative exposure assessment for Salmonella spp. in shell eggs produced on the island of Ireland
No full textA qualitative exposure assessment for Salmonella in eggs produced on the island of Ireland was developed. The assessment was divided into three main modules (production and packing, distribution and storage, and preparation and consumption), and each of these stages into defined steps in the exposure pathway. In the production and packing stage the initial prevalences of Salmonella in the contents and on the shell of eggs were estimated to be negligible and low respectively. Numbers of Salmonella both in and on eggs were estimated to be low. At each subsequent step in the pathway, qualitative assessments were made of the impact of events on the probability and level of Salmonella contamination on the shells and in the contents of eggs. At the end of each module assessments were combined to give an overall probability and level of Salmonella contamination. In the first two modules the assessment focused on the effect of the duration and temperature of storage on yolk membrane integrity and the likelihood of shell penetration. During the final stage the influence of factors such as safe handling procedures, pooling practices, consumption patterns and the effectiveness of cooking, on the prevalence and level of Salmonella contamination in a food item at time of consumption was assessed. The outcome of this assessment was an estimate of a low probability and level of Salmonella contamination of egg containing foods, prepared with eggs produced on the island of Ireland
Shell para criação automática de sistemas especialistas com inferência em Prolog e tratamento de incerteza por fatores de certeza
No full textDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico. Programa de Pós-Graduação em Engenharia Elétrica.Este trabalho apresenta o aprimoramento da ferramenta Shell Intellec System, para a criação automática de Sistemas Especialistas, com a utilização de fatores de certeza para tratamento da incerteza. A máquina de inferência foi desenvolvida em Prolog por se tratar de uma linguagem de programação lógica, utilizando a ferramenta Visual Prolog. A incerteza sobre o conhecimento do domínio é representada por fatores de certeza. Na shell as variáveis podem ser linguísticas, numérica e multimídia, como imagens e vídeos. A interface gráfica com o usuário foi remodelada e transcrita utilizando a ferramenta Borland C++ Builder para melhor integração com o usuário e a máquina de inferência PROLOG. Testes foram realizados para assegurar que os resultados apresentados pela Shell são compatíveis com aqueles da versão anterior. Foi realizada, também, uma avaliação sobre usabilidade da Shell por meio de um questionário chamado QUISS, baseado na norma ISO/IEC 9126, através de aplicação a um grupo de alunos, obtendo-se resultados promissores para interface desenvolvida.This work presents the improvement of shell program Intellec System for the automatic creation of expert systems with the use of certainty factors for the treatment of uncertainty. The inference engine was developed in Prolog because it is a logic programming language, Visual Prolog using the program. Uncertainty about the domain knowledge is represented by certainty factors. In the shell variables can be linguistic, numerical and multimedia such as images and videos. The graphical user interface has been redesigned and transcribed using the tool Borland C++ Builder for better integration with the user and the PROLOG inference engine. Tests were performed to ensure that the results presented by this shell are compatible with those of the previous version. It was also performed an evaluation of usability of the shell through a questionnaire called QUISS, based on the ISO / IEC 9126, by application to a group of students, yielding good results for interfacing developed for this shell
Application of the continuum shell finite element SHB8PS to sheet forming simulation using an extended large strain anisotropic elastic–plastic formulation
No full texthttp://link.springer.com/article/10.1007%2Fs00419-012-0620-xThis paper proposes an extension of the SHB8PS solid–shell finite element to large strain anisotropic elasto-plasticity, with application to several non-linear benchmark tests including sheet metal forming simulations. This hexahedral linear element has an arbitrary number of integration points distributed along a single line, defining the "thickness" direction; and to control the hourglass modes inherent to this reduced integration, a physical stabilization technique is used. In addition, the assumed strain method is adopted for the elimination of locking. The implementation of the element in Abaqus/Standard via the UEL user subroutine has been assessed through a variety of benchmark problems involving geometric non-linearities, anisotropic plasticity, large deformation and contact. Initially designed for the efficient simulation of elastic–plastic thin structures, the SHB8PS exhibits interesting potentialities for sheet metal forming applications – both in terms of efficiency and accuracy. The element shows good performance on the selected tests, including springback and earing predictions for Numisheet benchmark problems
Shell-Restricted Swelling and Core Compression in Poly(<i>N</i>-isopropylacrylamide) Core−Shell Microgels
No full textWe report on an investigation of the structural relationship between the core and shell
components in stimuli-sensitive core/shell microgels. Photon correlation spectroscopy measurements
indicate that the presence of the shell alters the extent of core swelling. Core particles composed of poly(N-isopropylacrylamide-co-acrylic acid) (pNIPAm-co-AAc) undergo volume changes as a function of
temperature and pH, where deprotonation of the acidic sites results in a volume increase (particle swelling).
The addition of a poly(N-isopropylacrylamide) (pNIPAm) shell restricts the core from swelling to its native
volume both above and below the pKa of acrylic acid. Furthermore, the pH responsive core undergoes
only small temperature-induced volume changes above the characteristic lower critical solution temperature (LCST) of pNIPAm (31 °C) at pH values where the acid groups are fully deprotonated. The addition
of a pNIPAm shell results in compression of the core and induces a large volume change at the pNIPAm
LCST. These effects are dependent on the degree of cross-linking in the core and shell. Particles synthesized
with lower concentrations of N,N‘-methylenebis(acrylamide) display greater degrees of shell-restricted
swelling and compression upon the addition of a pNIPAm shell with an identical cross-linker concentration.
These results are interpreted in terms of a previously proposed radial cross-linker density gradient, which
places topological restraints upon the core following shell addition
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