121 research outputs found
Dynamique du pin blanc (Pinus strobus Linnaeus) dans les tourbières ombrotrophes du sud du Québec
No full textPlusieurs tourbières du Québec sont aujourd'hui caractérisées par un processus de boisement qui est souvent une conséquence des activités anthropiques in ou ex situ ayant affecté leurs conditions hydrologiques. Bien que le pin blanc (Pinus strobus) soit une espèce arborescente que l'on rencontre plutôt rarement dans les tourbières ombrotrophes, les individus qui y poussent semblent afficher dans plusieurs cas une bonne croissance, autant en hauteur qu'en diamètre. Les objectifs de la présente étude étaient (1) de déterminer l'époque d'établissement de l'espèce dans quelques tourbières de la région écologique de la Plaine du Saint-Laurent et les facteurs ayant favorisé cet établissement, (2) de caractériser leur croissance radiale et (3) de déterminer les facteurs qui ont régi la croissance. Cinq tourbières ont été étudiées. Des analyses dendrochronologiques ont été réalisées pour des individus sur tourbe et sur sol minéral à proximité afin de comparer la croissance entre les deux types de milieu. Des fonctions de réponse et de corrélation ont été effectuées sur les séries dendrochronologiques afin de déterminer l'influence du climat sur la croissance. Enfin, des monolithes de tourbe de surface furent l'objet d'une analyse macrofossile afin de trouver des restes de pin blanc. La présence du pin blanc en milieu tourbeux semble être un phénomène relativement récent, la colonisation ayant débuté au plus tôt un peu avant la moitié du XIXe siècle. Cette installation récente concorde avec la présence de macrorestes de l'espèce dans les seuls premiers centimètres de la tourbe en surface. Bien qu'elle soit majoritairement inférieure à celle des individus sur sol minéral, la croissance radiale des individus sur tourbe s'avère très bonne. Le climat ne semble pas avoir influencé la croissance des individus et ce, autant sur tourbe que sur sol minéral ce qui suggère que d'autres facteurs régissent la croissance. Les précipitations moins abondantes durant certaines périodes du XXe siècle et le feu sont, selon les sites, des facteurs ayant fort probablement favorisé l'établissement du pin blanc sur les tourbières
On-line wear monitoring of polymer matrix composites
No full textThe Laboratory Soete developed a new test setup, based on the well-known pin-on-disc test rig. Instead of the standard composite specimen and steel disc, a rotating composite disc and a steel pin is presently used to have a visible wear track. Other measurement techniques (Acoustic Emission, vibrations, temperature) can be used on the test rig. Continuous monitoring of the wear track combined with standard wear and friction measurements, give results of the current state of the wear track. Fourier frequency analysis (FFT) of these signals gives an indication of the change in condition and contact geometry of the resulting pin-disc combination. A high-speed camera will be used to acquire digital images of the worn composite surface. These online measurements yield to the gradual evolution in damage of the composite specimens
Numerical modelling of composite laminates with through-thickness-reinforcements
No full textThe main objective of the present research study was to develop numerical models to investigate the mechanical properties and effectiveness of z-fibre reinforced laminates. A survey of relevant literature on through-thickness reinforcements (TTR) was undertaken and z-fibre pinning was chosen as the main topic of study. The development of numerical tools was mainly based on the finite element (FE) method and was carried out at different model scale levels.
At a micro-mechanical level of analysis, two models were presented. Firstly a unit cell FE model based on the actual geometric configuration of a z-pinned composite was used. Calculations were performed to understand how the through-thickness reinforcement modified the engineering elastic constants and local stress distributions.
Secondly the study of an analytical micro-mechanical model was undertaken. The model simulated a z-fibre bridging a delamination crack tinder mixed-mode loads. A constitutive law relating the z-pin bridging forces with the crack displacements was defined as the "bridging law". Numerical examples for z-fibre bridging laws under Mode I and Mode II loads were computed along with design evaluations of the effect of several micro-mechanical parameters on the bridging laws. This analytical model was then implemented into a MATLAB code specifically written by the author. The code generated constitutive relationship for interface elements simulating the bridging laws of a single z-pin to be used in a FE analysis.
A detailed numerical study of the mode I interlaminar fracture of composite laminates with z-pins was then carried out. AFL• model of a double cantilever beam (DCB) was developed. The numerical analysis focused on the large scale bridging (LSB) caused by z-pins mechanics, which increased the laminate resistance against delamination growth. The numerical results were validated against experimental data. Computational curves for the energy balance and energy rates were also determined showing that the LSB process consumed a significant amount of irreversible energy. The assumption made by the linear elastic fracture mechanics (LEFM) that all energy dissipations were included in the fracture energy and confined within the damage front, was not valid for z-pinned laminates.
The FE analysis was then extended to study a curved single-lap shear joint, to prove the effectiveness of TTR against debond failure of the joint. The presence of TTR was shown to delay the propagation of the debonding and generally to enhance the load carrying capability of the joint. TTR is proved to be more effective in reducing the Mode I component of debonding driving force than that of the Mode II.
Finally a global-local approach was proposed to implement the TTR elements into large composite stnictural FE models. Possible future studies for TTR numerical modelling were also addressed
Structural performance of spacecraft honeycomb panels
No full textHoneycomb sandwich structures (commonly referred to as honeycomb sandwich panels) have found wide spread application in the aerospace industry thanks to their excellent properties, in particular their high strength-to-weight and high stiffness-to-weight ratios. Surrey Satellite Technology Ltd. (SSTL), like many other space companies, often use honeycomb sandwich panels as part of the primary and secondary structures of the small satellites they develop.Although honeycomb panels have been used for the past 50 years gaining a better understanding of these sandwich structures, and the methods and solutions used to producestructural assemblies from them is still a major concern in the aerospace industry. Whether directly or indirectly, there are still significant research efforts ongoing that affect these areas. This work focuses on some of these issues and covers several research fields including material science, tribology and adhesive bonding technology.The first area of focus of this work deals with the structural performance of honeycomb panels alone and mainly concentrates on hexagonal honeycomb cores. An experimentalinvestigation using the rail shear test was conducted to study the shear behaviour of hexagonal honeycomb cores. This involved both static and fatigue tests using numerous honeycomb panel test samples with the loading direction at various angles to the core ribbon. From these tests it was found that core shear strength did not have a linear relationship with loading orientation and that contrary to what is commonly assumed the transverse direction (to the ribbon) is not always necessarily the weakest orientation.The optimal design and performance of the load introduction points was the second area of focus for this work which covers equipment inserts and bolted joints. Two types of inserts where investigated in this work: hot bonded inserts and cold bonded inserts. A study on hot bonded and cold bonded inserts was conducted to assess their performance and effectively compare the two insert systems. A large portion of the study was experimental and involvedcarrying out numerous insert pull-out tests to measure static pull strength capability. From the study it was found that contrary to what was expected cold bonded potted inserts outperformed the hot bonded inserts in terms of static strength capability. Using finite element it was found that this was due to the different filler materials used for the two insert systems.The last area covered in this work concerns friction grip bolted joint between honeycomb panels. Here a simple method to analyze the efficiency of shear joint units is proposed. An extensive test campaign was also carried out to determine the influence of various parameters on the friction coefficient. Surface abrasion was found to be a reliable way of achieving high values of friction coefficient
Unprecedented porosity transformation of hierarchically porous TiO2 derived from Ti-Oxo clusters
No full textAlthough attaining a high porosity in TiO2 is critical to enhancing its photocatalytic and photoelectric activities, its synthesis has been challenging owing to the high reactivity of conventional Ti precursors and the laborious template removal process. Thus, we herein report a versatile method for preparing hierarchically porous organic-functionalized TiO2 (HiPOTs) using Ti-oxo clusters consisting of a rigid reactive ligand, para-aminobenzoate (p-ABA). The presence of p-ABA as a structure-directing template is crucial to obtain microporous structures with sufficiently high yields. The HiPOTs gradually transform from hierarchically micro/mesoporous structures into mesoporous structures during a sol–gel process. The Brunauer–Emmett–Teller surface areas of the HiPOTs range from 242 to 739 m2/g, which are among the highest reported for porous TiO2 materials. The presence of p-ABA on the HiPOT surface decreases the band gap of TiO2 to 2.7 eV, and prolonging the sol–gel process releases greater quantities of p-ABA, thereby increasing the band gap and the crystallinity of the anatase phase. Interestingly, unlike conventional TiO2, which experiences rapid charge recombination, the Ti3+ oxidation states of HiPOTs are successfully isolated during UV irradiation and can be applied as a proof of concept to generate reactive oxygen species such as 1O2 and •O2 −. © 2020FALS
Applied and fundamental aspects of BABY BOOM-mediated regeneration
No full textKeywords: Somatic embryogenesis, Transcription factor, AINTEGUMENTA-LIKE, BABY BOOM, BBM, Sweet Pepper Transformation Title: Applied and Fundamental Aspects of BBM-mediated Regeneration Author: Iris Heidmann Catergories: Plant regeneration, Plant transformation, transcription factor, somatic embryogenesis Plant regeneration from tissues or single cells is essential for plant propagation. Efficient regeneration can be archieved through somatic embryogenesis using the plant growth regulator auxin or overexpression of specific transcription factors, but the underlying mechanisms are poorly understood. The potency of the BABY BOOM (BBM) AINTEGUMENTA-LIKE transcription factor to induce somatic embryogenesis in crop (sweet pepper) and model species (tobacco) was investigated. It was found that the introduction of BBM into sweet pepper, which is recalcitrant for transformation, enhanced the regeneration of transgenic plants. Exogenous cytokinin was necessary to induce somatic embryogenesis in both tobacco and sweet pepper. The mechanism underlying BBM-mediated somatic embryogenesis was studied in Arabidopsis by identifying BBM target genes (ChIPSeq). Genes controlling zygotic embryo identity and maturation (LAFL), as well as auxin biosynthesis (TAA1, YUCCA) and transport (PIN) are BBM targets. Mutant analysis and chemical inhibition studies showed that these genes play positive roles in BBM-induced somatic embryogenesis. </p
Comprehensive phenotypic assessment of nonsense mutations in mitochondrial ND5 in mice
No full textAbstract Mitochondrial dysfunction induced by mitochondrial DNA (mtDNA) mutations has been implicated in various human diseases. A comprehensive analysis of mitochondrial genetic disorders requires suitable animal models for human disease studies. While gene knockout via premature stop codons is a powerful method for investigating the unique functions of target genes, achieving knockout of mtDNA has been rare. Here, we report the genotypes and phenotypes of heteroplasmic MT-ND5 gene-knockout mice. These mutant mice presented damaged mitochondrial cristae in the cerebral cortex, hippocampal atrophy, and asymmetry, leading to learning and memory abnormalities. Moreover, mutant mice are susceptible to obesity and thermogenetic disorders. We propose that these mtDNA gene-knockdown mice could serve as valuable animal models for studying the MT-ND5 gene and developing therapies for human mitochondrial disorders in the future
An innovative approach using CRISPR-ribonucleoprotein packaged in virus-like particles to generate genetically engineered mouse models
No full textGenetically engineered mouse models (GEMMs) are crucial for investigating disease mechanisms, developing therapeutic strategies, and advancing fundamental biological research. While CRISPR gene editing has greatly facilitated the creation of these models, existing techniques still present technical challenges and efficiency limitations. Here, we establish a CRISPR-VLP-induced targeted mutagenesis (CRISPR-VIM) strategy, enabling precise genome editing by co-culturing zygotes with virus-like particle (VLP)-delivered gene editing ribonucleoproteins (RNPs) without requiring physical manipulation or causing cellular damage. We generate Plin1- and Tyr-knockout mice through VLP-based SpCas9 or adenine base editor (ABE)/sgRNA RNPs and characterize their phenotype and germline transmission. Additionally, we demonstrate cytosine base editor (CBE)/sgRNA-based C-to-T substitution or SpCas9/sgRNA-based knock-in using VLPs. This method further simplifies and accelerates GEMM generation without specialized techniques or equipment. Consequently, the CRISPR-VIM method can facilitate mouse modeling and be applied in various research fields.Y
The selection and application of design methodologies for the design of bone tissue scaffolds
No full textResearch motivation: Bone tissue scaffolds offer a way forward in a strategy to change from tissue replacement to tissue regeneration. Bone tissue scaffolds are a combination of a physical construct, with clearly defined three-dimensional spatial properties, and biological cells. The microstructure of this construct is the bridge between the physicochemical properties of the scaffold and the cellular processes responsible for tissue regeneration.
Gap statement: A formal design methodology has yet to be applied for the design of bone tissue scaffolds
Aims and objectives:
The aim of this research thesis is to select and apply design methods to the design of bone tissue scaffolds.
The objectives are:
1. Review the current state of the art in design theory and methodologies for successful applications of design methods
2. Identify which design techniques are currently implemented in bone tissue scaffold design
3. To apply appropriate design methods to the design of bone tissue scaffolds
4. To validate the design outputs via a survey of expert opinion
Methodologies: The following design methodologies were applied; Quality Function Deployment (QFD) and Theory of Inventive Problem Solving (TRIZ), an expanded house of quality, three-dimensional relationship technology chart (3DRTC) and Axiomatic Design (AD).Results: The multi-tiered literature review for design methodologies, firstly, identified the above design methods and, secondly, found no reason to exclude them for consideration as design methods for bone tissue scaffolds. The second literature review identified extensive computer-image-based-design as the current most advanced design method in the domain for bone tissue scaffolds. No formal design methods were in use.
The first Quality Function Deployment method identified conflicts in the design which were used as inputs into TRIZ to generate potential solutions. The second QFD approach identified an extensive list of design requirements along with target engineering metrics. The three-dimensional relationship technology chart proposed how to organise design requirements into a scaffold design based upon differing scaffold design strategies. In Axiomatic Design, two approaches were followed: the first based upon percolation theory and the second based upon time-dependent behaviour. These models proposed designs at a higher level of abstraction for scaffold designers, rather than the providing the more practical solutions achieved by the QFD and 3DRTC approaches.
Validation: The output of the design methodologies were validated by a survey of expert opinion. The responses indicated that both Axiomatic Design and an expanded house of quality tool offered innovation, and enhancement to, the field of bone tissue scaffold design.
Conclusion: Formal design methodologies such as Axiomatic Design and Quality Function Deployment provide design solutions which offer innovation, and enhancement to, the field of bone tissue scaffold design
Interplay between network configurations and network governance mechanisms in supply networks a systematic literature review
No full textPurpose: This work systematically reviews the extant academic management literature on supply networks. It specifically examines how network configurations and network governance mechanisms influence each other in supply networks.
Design: 125 analytical and empirical studies were identified using an evidence-based approach to review the literature mainly published between 1985 and 2012.
Synthesis: Drawing on a multi-disciplinary theoretical foundation, this work develops an integrative framework to identify three distinct yet interdependent themes that characterize the study of supply networks: a) Network Configurations (structures and relationships); b) Network Governance Mechanisms (formal and informal); and c) The Interplay between Network Configurations and Network Governance Mechanisms.
Findings: Network configurations and network governance mechanisms mutually influence each other and cannot be considered in isolation. Formal and informal governance mechanisms provide better control when used as complements rather than as substitutes. The choice of governance mechanism depends on the nature of exchange; role of management; desired level of control; level of flexibility in formal contracts; and complementary role of formal and informal governance mechanism.
Research implications: This nascent field has thematic and methodological research opportunities for academics. Comparative network analysis using longitudinal case studies offers a rich area for further study.
Practical Implications: The complexity surrounding the conflicting roles of managers at the organisation and network levels poses a significant challenge during the development and implementation stage of strategic network policies.
Originality/value: This review reveals that formal and informal governance mechanisms provide better control when used as complements rather than as substitutes
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