Development of composite auxetic structures for civil engineering applications

Tese de Doutoramento em Engenharia TêxtilAuxetic materials are a class of non-conventional materials having negative Poisson’s ratio. They expand laterally when axially loaded or laterally shrink when compressed. Due to its counterintuitive behaviour, auxetic materials possess enhanced properties that could be beneficial for many specific applications. This thesis aimed to develop such a class of auxetic materials from braided composite rods which can be beneficial for civil engineering applications as a strengthening materials. The developed auxetic structures can be reinforced into either for existing structural elements or for newly built one. Novel macro auxetic structures were developed from core fibre reinforced braided composite rods based on missing rib or lozenge grid and re-entrant hexagon or bow-tie auxetic structural design. The developed structures tested under tensile loading to study their tensile and auxetic behaviour. The auxetic behaviour was studied thorough images taken during tensile loading. Also, the auxetic and tensile behaviour of the developed structures were studied by varying their structural and material parameters. Developed auxetic structures exhibits negative Poisson’s ratio and it is mainly depends up on structural parameters. The Poisson’s ratio of the developed auxetic structures were studied by suitable analytical model either by existing model or by using newly developed model. These analytical models could be useful to predict the Poisson’s ratio of the developed auxetic structures accurately. In addition to analytical model, the FE solver DIANA was used to develop a numerical modelling to predict the tensile and auxetic behaviour. The developed numerical model was accurate to predict the tensile and Poisson’s ratio of the structures. In addition, the auxetic structures were reinforced into the masonry wall specimens, which is built by cement hollow bricks. The reinforced masonry wall specimens were tested under three point flexural loading and the results were compared with plain grid (commercial design) reinforced masonry wall. The auxetic structures strengthened walls performed well under flexural load compared to plain grid reinforced wall, but the crack level was more for auxetic structures reinforced wall due to its lateral expansion. This research works opened novel opportunity to use auxetic materials in the civil engineering field and created huge scope to do more research work in this area.Materiais auxéticas são uma classe de materiais não convencionais que apresentam um Coeficiente de Poisson negativo. Assim, expandem lateralmente quando são carregados longitudialmente e encolhem quando comprimidos. Devido ao seu comportamento fora do comum, os materiais auxéticos possuem propriedades benéficas para muitas aplicações específicas. Este trabalho tem como objetivo o desenvolvimento de materiais compósitos auxéticas a partir de varões entrançados para utilização no reforço em engenharia civil. As estruturas auxéticas desenvolvidas podem ser usadas tanto na reabilitação e reforço de elementos existentes ou na construção de novos elementos estruturais. Estruturas auxéticas inovadoras foram desenvolvidas a partir de varões compósitos entrançados com fibras de alto desempenho no núcleo em modelos teóricos de estruturas “missing rib” ou “lozenge grid” e “re-entrant hexagon” ou “bow-tie”. As estruturas desenvolvidas foram ensaiadas em tração para estudar o seu comportamneto auxético e o seu comportamento e propriedades quando este tipo de cargas são aplicadas. O comportamento auxético foi estudado recorrendo a técnicas de análise imgagem (DIC-Digitally Correlation Image) retiradas durante o ensaio de tração. Para além disso, foi estudada a influência de diversos parãmetros da estrutura e do material correspondente no comportamento auxético, nomeadamente o tipo de fibra utilizada e o ângulo dos elemntos estruturais na estrutura auxética. Os resultados demonstram que as estruturas auxéticas desenvolvidas apresentam um Coeficiente de Poisson negativo devido ao comportamento estrutural da mesma. No âmbito deste trabalho, foi igualmente desenvolvido um modelo recorrendo a Elementos Finitos para previsão do comportamento auxético das estruturas estudadas tendo como base as alterações da sua geometria quando cargas de tração são aplicadas, prevendo igualmente a sua resistência à tração. Além disso, as estruturas auxéticos em material compósito foram utilizadas no reforço de parede de alvenaria. Os provetes de parede de alvenaria reforçados foram testados à flexão em três pontos e os resultados foram comparados com uma parede de alvenaria reforçada convencionalmente recorrendo a uma grellha metálica. As paredes reforçadas por estruturas auxéticas apresentaram um bom desempenho sob carga de flexão quando comparadas com a parede convencional, no entanto, apresentaram maior nível de fissuração devido à expansão lateral do material de reforço. O presente trabalho de investigação abriu novas oportunidades para utilização de materiais auxéticas no campo da engenharia civil servindo como ponto de partida para os trabalhos, nesta área, que se seguirão

Granular cell tumor of the urinary bladder: A case report

Granular cell tumors (GCTs) are the tumors arising from Schwann cells. They should be considered as one of the differential diagnosis in the solid tumors of the bladder. Here, we report the case of a 60-year-old female presented with lower abdominal pain and burning micturition who on evaluation with contrast-enhanced computed tomography was found to have a bladder mass of 4 cm × 3 cm in the left lateral wall. Cystoscopy showed a smooth ovoid mass 4 cm × 3 cm situated above and lateral to the left ureteric orifice covered by normal bladder mucosa. The patient underwent transurethral resection of the bladder tumor, which was diagnosed as a GCT on histopathological examination and immunohistochemistry

The role of statin drugs in combating cardiovascular diseases –A review

Statins clearly confer substantial benefit in people with established cardiovascular (CV) disease. Increased cholesterol levels have been associated with cardiovascular diseases (CVD), and statins are therefore used in the prevention of these diseases. Studies have found that the ability of a particular statin to lower or reduce LDL is proportional to the amount it can increase HDL levels. This review article will focus on the effective role of statin in cardiovascular disease and comparison was made between various classes of statin drugs

Optimizing the Fluorescence Properties of Nanoemulsions for Single Particle Tracking in Live Cells

Nanoemulsions (NEs) are biocompatible lipid nanoparticles composed of an oily core stabilized by a surfactant shell. It is acknowledged that the surface decoration with poly­(ethylene glycol), through the use of nonionic surfactants, confers high stealth in biological medium with reduced nonspecific interactions. Tracking individual NE by fluorescence microscopy techniques would lead to a better understanding of their behavior in cells and thus require the development of bright single particles with enhanced photostability. However, the understanding of the relationship between the physicochemical properties and chemical composition of the NEs, on the one hand, and its fluorescence properties of encapsulated dyes, on the other hand, remains limited. Herein, we synthesized three new dioxaborine barbituryl styryl (DBS) dyes that displayed high molar extinction coefficients (up to 120 000 M–1 cm–1) with relatively low quantum yields in solvents and impressive fluorescence enhancement when dissolved in viscous oils (up to 0.98). The reported screening of nine different oils allowed disclosing a range of efficient “oil/dye” couples and understanding the main parameters that lead to the brightest NEs. We determine vitamin E acetate/DBS-C8 as the representative most efficient couple, combining high dye loading capabilities and low aggregation-induced quenching, leading to <50 nm ultrabright NEs (with brightness as high as 30 × 106 M–1 cm–1) with negligible dye leakage in biological media. Beyond a comprehensive optical and physicochemical characterization of fluorescent NEs, cellular two-photon excitation imaging was performed with polymer-coated cell penetrating NEs. Thanks to their impressive brightness and photostability, NEs displaying different charge surfaces were microinjected in HeLa cells and were individually tracked in the cytosol to study their relative velocity

Development, characterization and analysis of auxetic structures from braided composites and study the influence of material and structural parameters

Auxetic materials are gaining special interest in technical sectors due to their attractive mechanical behaviour. This paper reports a systematic investigation on missing rib design based auxetic structures produced from braided composites for civil engineering applications. The influence of various structural and material parameters on auxetic and mechanical properties was thoroughly investigated. The basic structures were also modified with straight longitudinal rods to enhance their strengthening potential in structural elements. Additionally, a new analytical model was proposed to predict Poisson’s ratio through a semi empirical approach. Auxetic and tensile behaviours were also predicted using finite element analysis. The auxetic and tensile behaviours were observed to be more strongly dependent on their structural parameters than the material parameters. The developed analytical models could well predict the auxetic behaviour of these structures except at very low or high strains. Good agreement was also observed between the experimental results and numerical analysis.University of Minho – UMINHO/BI/146/2012, under the scheme of ‘‘Strategic plan of school of engineering – Agenda 2020: Multidisciplinary projects.

Characterization of the livestock production system and potential for enhancing productivity through improved feeding in Amoni Division, Mweiga District, Central Kenya, May 2010

Lipid droplets (LDs) are intracellular lipid-rich organelles that regulate the storage of neutral lipids and were recently found to be involved in many physiological processes, metabolic disorders, and diseases including obesity, diabetes, and cancers. Herein we present a family of new fluorogenic merocyanine fluorophores based on an indolenine moiety and a dioxaborine barbiturate derivative. These so-called StatoMerocyanines (SMCy) fluoresce from yellow to the near-infrared (NIR) in oil with an impressive fluorescence enhancement compared to aqueous media. Additionally, SMCy display remarkably high molar extinction coefficients (up to 390 000 M^–1 cm^–1) and high quantum yield values (up to 100%). All the members of this new family specifically stain the LDs in live cells with very low background noise. Unlike Nile Red, a well-known lipid droplet marker, SMCy dyes possess narrow absorption and emission bands in the visible, thus allowing multicolor imaging. SMCy proved to be compatible with fixation and led to high-quality 3D images of lipid droplets in cells and tissues. Their high brightness allowed efficient tissue imaging of adipocytes and circulating LDs. Moreover their remarkably high two-photon absorption cross-section, especially SMCy5.5 (up to 13 300 GM), as well as their capacity to efficiently fluoresce in the NIR region led to two-photon multicolor tissue imaging (liver). Taking advantage of the available color palette, lipid droplet exchange between cells was tracked and imaged, thus demonstrating intercellular communication

PEGylated Red-Emitting Calcium Probe with Improved Sensing Properties for Neuroscience.

Monitoring calcium concentration in the cytosol is of main importance as this ion drives many biological cascades within the cell. To this end, molecular calcium probes are widely used. Most of them, especially the red emitting probes, suffer from nonspecific interactions with inner membranes due to the hydrophobic nature of their fluorophore. To circumvent this issue, calcium probes conjugated to dextran can be used to enhance the hydrophilicity and reduce the nonspecific interaction and compartmentalization. However, dextran conjugates also feature important drawbacks including lower affinity, lower dynamic range, and slow diffusion. Herein, we combined the advantage of molecular probes and dextran conjugate without their drawbacks by designing a new red emitting turn-on calcium probe based on PET quenching, Rhod-PEG, in which the rhodamine fluorophore bears four PEG4 units. This modification led to a high affinity calcium probe (Kd = 748 nM) with reduced nonspecific interactions, enhanced photostability, two-photon absorbance, and brightness compared to the commercially available Rhod-2. After spectral characterizations, we showed that Rhod-PEG quickly and efficiently diffused through the dendrites of pyramidal neurons with an enhanced sensitivity (ΔF/F0) at shorter time after patching compared to Rhod-2.journal article2017 Nov 222017 10 24imported"Supporting information" disponible sur le site de l'éditeur à l'adresse suivante : http://pubs.acs.org/doi/suppl/10.1021/acssensors.7b0066

Development and characterization of novel auxetic structures based on re-entrant hexagon design produced from braided composites

This paper reports the first attempt of developing macro-scale auxetic structures based on re-entrant hexagon design from braided composite materials for civil engineering applications. Braided composite rods (BCRs) were produced and arranged as longitudinal and horizontal elements to produce three types of auxetic structures: (1) basic re-entrant hexagon structure, (2) basic structure modified by adding straight longitudinal elements and (3): structure-2 modified by changing structural angle. The influence of various material and structural parameters as well as structure type on Poisson's ratio and tensile properties was thoroughly investigated. The auxetic behaviour was found to strongly depend on the structural angle and straight elements, resulting in lower auxeticity with lower angles and in presence of straight elements. Material parameters influenced the auxetic behaviour to a lesser extent and a decrease in auxetic behaviour was noticed with increase in core fibre linear density and using stiffer fibres such as carbon. The reverse effect was observed in case of tensile strength and work of rupture. Among these structures, structure-3 exhibited good auxetic behaviour, balanced tensile properties, and high energy absorption capacity and their auxetic behaviour could be well predicted with the developed analytical model. Therefore, these novel structures present good potential for strengthening of civil structures.The authors gratefully acknowledge the financial support for carrying out this research work from University of Minho, under the scheme of "Strategic plan of school of engineering - Agenda 2020: Multidisciplinary projects.