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de, Bettignies A. S. "Wnt/Fz interactions in the developing central nervous system." Thesis, University College London (University of London), 2007. http://discovery.ucl.ac.uk/1444543/.
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Wnt signalling is central to many early developmental processes including embryonic patterning, programmed cell death and cell migration. Recent studies have implicated Wnt signalling in the formation of neuronal connections in the nervous system. Wntl a regulates synapse formation in the cerebellum by inducing presynaptic differentiation characterized by axonal remodelling and presynaptic assembly. A very similar gene, Wnt7b regulates dendritic development in hippocampal neurons, but can also trigger axonal remodelling. These different responses are due to the activation of different signalling pathways. We aim to identify the receptors triggering these processes in neurons. Intracellular signalling by Wnts is initiated by the activation of their seven transmembrane receptors Frizzled (Fz). Three known Wnt signalling pathways may be activated: the canonical, the planar cell polarity and Calcium pathways. Ten Fz receptors and 19 Wnts have been identified in the mouse genome. To begin to address what Fz receptors are used by Wnts, we examined the pattern of expression of Wnt 7a and Wnt 7b together with several Fz receptors during postnatal brain development. We found that Wnt7a,fz7, and fz3 are expressed in the postnatal and adult cerebellum. Wnt7b and fz3 are highly expressed in the postnatal hippocampus. These overlapping patterns of expression led us to investigate the ability of Wnt7a and Wnt7b to bind to the cell surface of HEK293 cells expressing the ligand-binding domain of Fz receptors. Binding of Wnt7a an -7b to Fz-3, -5, -7 and -8 was tested. Wnt7b binds Fz3 and Fz5, whilst Wnt7a binds Fz7 and Fz3. Signalling activity was then assessed by measuring TCF/LEF mediated transcription (Top-Flash assay) and by the increased levels of 6-catenin. Wnt-7a is able to activate the canonical pathway in Fz7 and Fz3/LRP6 transfected HEK293 cells. These studies highlight the idea that activation of the canonical / p-catenin pathway by Wnt7a can be mediated by Fz7 and the LRP6/Fz3 complex.
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Martin, Jennifer. "Wnt regulated transcription factor networks mediate vertebrate cardiogenesis." Thesis, Available from the University of Aberdeen Library and Historic Collections Digital Resources. Online version available for University members only until Feb. 15, 2012, 2009. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?application=DIGITOOL-3&owner=resourcediscovery&custom_att_2=simple_viewer&pid=25801.
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Stevens, Mariana L. "Genomic integration of Wnt/β-catenin and BMP/Smad1 signaling coordinates digestive system development." University of Cincinnati / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1490352976010044.
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Iyengar, Sharanya. "Insights into Melanocyte Regeneration and Melanoma Initiation Using the Zebrafish Model System: A Dissertation." eScholarship@UMMS, 2015. https://escholarship.umassmed.edu/gsbs_diss/796.
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During regeneration, cells must coordinate proliferation and differentiation to rebuild tissues that are lost. Understanding how source cells execute the regeneration process has been a longstanding goal in regenerative biology with implications in wound healing and cell replacement therapies. Melanocytes are pigment-producing cells in the skin of vertebrates that can be lost during hair graying, injury and disease-related depigmentation. Melanoma is an aggressive skin cancer that develops from melanocytes, and it is hypothesized that melanoma cells have properties that are similar to melanocyte stem cells.
To gain insight into melanocyte regeneration we set out to identify the source of regeneration melanocytes in adult zebrafish and the path through which progenitor cells reconstitute the pigment pattern. Using targeted cell ablation and single cell lineage-tracing analyses we identified that a majority of regeneration melanocytes arise through direct differentiation of mitfa-expressing progenitor cells. Concurrently, other mitfa-expressing cells divide symmetrically to generate additional mitfa-positive progenitors, thus maintaining regeneration capability. Using reporter assays and drug studies, we found that Wnt signaling gets turned on in progenitor cells during regeneration and Wnt inhibition after melanocyte ablation blocks regeneration. Based on our finding that Wnt signaling is active in differentiated melanocytes but not in the progenitor cells, we explored the role of Wnt signaling in tumor initiation. We found that approximately half of the melanomas are Wnt silent, and overexpression of dkk1b, a negative regulator of canonical Wnt signaling, accelerates melanoma onset.
This work defines an unappreciated contribution by direct differentiation in melanocyte regeneration and suggests a broader role for this process in the maintenance of epithelial sheets. This study also identifies a shared pathway between melanocyte progenitors and melanoma cells, which could be applicable to other cancers.
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Iyengar, Sharanya. "Insights into Melanocyte Regeneration and Melanoma Initiation Using the Zebrafish Model System: A Dissertation." eScholarship@UMMS, 2010. http://escholarship.umassmed.edu/gsbs_diss/796.
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During regeneration, cells must coordinate proliferation and differentiation to rebuild tissues that are lost. Understanding how source cells execute the regeneration process has been a longstanding goal in regenerative biology with implications in wound healing and cell replacement therapies. Melanocytes are pigment-producing cells in the skin of vertebrates that can be lost during hair graying, injury and disease-related depigmentation. Melanoma is an aggressive skin cancer that develops from melanocytes, and it is hypothesized that melanoma cells have properties that are similar to melanocyte stem cells.
To gain insight into melanocyte regeneration we set out to identify the source of regeneration melanocytes in adult zebrafish and the path through which progenitor cells reconstitute the pigment pattern. Using targeted cell ablation and single cell lineage-tracing analyses we identified that a majority of regeneration melanocytes arise through direct differentiation of mitfa-expressing progenitor cells. Concurrently, other mitfa-expressing cells divide symmetrically to generate additional mitfa-positive progenitors, thus maintaining regeneration capability. Using reporter assays and drug studies, we found that Wnt signaling gets turned on in progenitor cells during regeneration and Wnt inhibition after melanocyte ablation blocks regeneration. Based on our finding that Wnt signaling is active in differentiated melanocytes but not in the progenitor cells, we explored the role of Wnt signaling in tumor initiation. We found that approximately half of the melanomas are Wnt silent, and overexpression of dkk1b, a negative regulator of canonical Wnt signaling, accelerates melanoma onset.
This work defines an unappreciated contribution by direct differentiation in melanocyte regeneration and suggests a broader role for this process in the maintenance of epithelial sheets. This study also identifies a shared pathway between melanocyte progenitors and melanoma cells, which could be applicable to other cancers.
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Patthey, Cédric. "Induction of the isthmic organizer and specification of the neural plate border /." Umeå : Univ, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-1811.
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Bertalot, Thomas. "Microenviroment modulation on plasticity of Enteric Nervous System derived cells." Doctoral thesis, Università degli studi di Padova, 2014. http://hdl.handle.net/11577/3423755.
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Growth factors such as EGF, bFGF and GDNF play an essential role in the ENS development and homeostasis. In vivo conditions which provide a reduction or absence of these factors promote the development of diseases such as intestinal agangliosis. Thus two models of in vitro culture that simulate the physiological condition (SM) and that of agangliosis (BM) was evaluated. ENS-derived cells (ENSc) were isolated from the myenteric plexus of the Sprague Dawley rats [Schaefer et al., 1997]. Particular attention was given to the regulation mechanisms mediated by TLR4 and Wnt signalling. At time of isolation, immunophenotypical characterization by flow cytometry showed the expression of stem cell (SOX2, NANOG, and CD34), neuronal and glial (p75, Nestin, GFAP) markers. Culturing in SM and BM showed a specific modulation of neuronal and glial differentiation and a greater responsiveness mediated by Frizzled 9 (SM) and TLR4 (BM) was observed. Moreover, a neuronal subpopulation co-expressed the receptors TLR4 and Frizzled-9 suggesting that this cell population may be involved in the maintenance of homeostasis and in the regulation of inflammatory processes. Furthermore, only SM cultures formed neurosphere-like structures. Wnt3a stimulation activated the canonical Wnt pathway through Frizzled-9 and qRT-PCR analysis demonstrated anti-inflammatory activity. In addition, a cross-talk between LPS/TLR4 and Wnt pathway was demonstrated by western blotting. Differentiation processes are also influenced by the extracellular matrix (ECM). In this study, the modulatory effect induced by ECM was evaluated assessing an in vitro model: ENS-derived cells cultured on a decellularized ECM of adult rat jejunum. Acellular matrixes (AMs) were provided using a modified enzyme detergent decellularization protocol [Meezan et al., 1975]. Histological study, SEM and quantification of residual DNA verified the complete decellularization. Immunofluorescence and western blotting demonstrated that the structural proteins such as collagen I, III , IV and laminin were preserved. After culturing ENSc on AMs for 7 and 14 days, the ECM demonstrated to influence the ENSc spatial organization, exerting a synergic effect with the factors present in the culture medium. In fact, only the AM cultures with SM, showed ganglion-like structures partially interconnected and positive for βIII tubulin. ENSc cultured on acellular matrix may represent a useful in vitro model for toxicological and pharmacological studies as well as a possible tissue scaffold in regenerative medicine.E’ noto che i fattori di crescita quali EGF, bFGF e GDNF giocano un ruolo essenziale nello sviluppo e nell’omeostasi del sistema nervoso enterico (SNE). Condizioni in vivo che prevedono un calo o un’assenza del loro apporto, favoriscono lo sviluppo di patologie quali agangliosi intestinale. In questo lavoro di tesi, allestendo due modelli di coltura in vitro che simulano la condizione fisiologica (SM) e quella di agangliosi (BM) mediante coltura in presenza (SM) o meno di fattori di crescita (BM) è stata oggetto di studio la risposta differenziativa di cellule isolate da plesso mienterico di ratto Sprague Dawley (ENSc) [Schaefer et al., 1997]. In particolare, veniva prestata attenzione ai meccanismi di regolazione della risposta cellulare mediata dal segnale TLR4 e Wnt. Lo studio di caratterizzazione dell’immunofenotipo mediante citofluorimetria evidenziava nelle popolazioni estratte l’espressione di marcatori di staminalità (SOX2, Nanog e CD34) e di linea neuronale e gliale (p75, Nestina, GFAP). Inoltre, si evidenziava la presenza di una sottopolazione con caratteristiche neuronali che co-esprimeva i recettori TLR4 e Frizzled-9, suggerendo un ruolo nella regolazione del processo infiammatorio. La coltura in terreno SM e BM dimostrava di modulare in maniera specifica il differenziamento neuronale e gliale delle ENSc e di conferire una maggiore reattività mediata dal Frizzled 9 (coltura SM) e dal TLR4 (coltura BM). Inoltre, l’analisi di microscopia ottica evidenziava la formazione di strutture del tipo neurosfere solo nelle colture trattate con terreno standard. Lo stimolo indotto dal Wnt3a risultava efficace nell’attivare la via di segnale canonica di Wnt attraverso il recettore Frizzled 9 e, all’analisi di espressione genica mediante qRT-PCR, dimostrava un’attività di tipo anti-infiammatorio. Inoltre, mediante uno studio di western blotting, si dimostrava che la via pro-infiammatoria del TLR4 cross-reagiva con il segnale Wnt attivandolo. E’ noto che il processo differenziativo è fortemente condizionato dalla matrice extracellulare. In questo studio l’effetto modulatorio indotto dalla matrice sulla risposta differenziativa delle cellule ENSc è stato valutato utilizzando matrice acellularizzata (AM) di tessuto intestinale di ratto. La preparazione dello scaffold ha previsto 5 cicli ripetuti di decellularizzazione del trattamento modificato detergente enzimatico di Meezan [1975]. La completa decellularizzazione del tessuto veniva verificata mediante studio istologico, analisi di microscopia elettronica a scansione (SEM) e quantificazione del contenuto di DNA residuo. All’analisi di immunofluorescenza e western blotting, le proteine strutturali quali collagene I, III, IV e laminina risultavano preservate al termine della decellularizzazione. Dopo coltura per 7, 14 giorni delle cellule ENSc sulla matrice, AM dimostrava di condizionare l’organizzazione spaziale delle cellule ENSc esercitando un effetto specifico differenziativo in sinergia con i fattori di crescita. Infatti, solo le matrici mantenute in terreno SM mostravano una caratteristica organizzazione delle cellule ENSc in strutture interconnesse di tipo simil-gangliare esprimenti il marcatore neuronale βIII tubulina. Le colture di ENSc su matrice acellulare possono rappresentare un valido modello in vitro per studi tossicologici ed un possibile sostituto tessutale nella medicina rigenerativa.
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Dias, Neto Domingos Pedro Manuel. "The wnt/b-catenin signalling pathway and anterior posterior patterning in the vertebrate central nervous system." Thesis, University College London (University of London), 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368691.
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Hanson, Miranda Leah. "Prenatal cadmium exposure dysregulates sonic hedgehog and Wnt/beta-catenin signaling in the thymus resulting in immunomodulatory effects." Morgantown, W. Va. : [West Virginia University Libraries], 2009. http://hdl.handle.net/10450/10625.
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Thesis (Ph. D.)--West Virginia University, 2009.Title from document title page. Document formatted into pages; contains vii, 250 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references.
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Matzelle, Melissa M. "Inflammation Inhibits Osteoblast-Mediated Bone Formation in Rheumatoid Arthritis and Regulates the Wnt and BMP Signaling Pathways: A Dissertation." eScholarship@UMMS, 2012. https://escholarship.umassmed.edu/gsbs_diss/596.
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Osteoclast-mediated focal articular bone erosion is a hallmark of rheumatoid arthritis, a disease of inflammation-induced bone loss. Inflammation in the bone microenvironment enhances osteoclast differentiation leading to bone erosion. Simultaneously, inflammation also inhibits osteoblast-mediated bone formation, further contributing to the net loss of bone. Previous studies have shown a paucity of mature osteoblasts at eroded bone surfaces correlating with suppression of bone formation and upregulation of antagonists of the Wnt pathway, a signaling cascade essential for osteoblast lineage commitment. Despite these observations, the exact pathogenesis of impaired bone formation in the setting of inflammation is not clearly understood.
This dissertation aims to delineate the mechanisms by which inflammation suppresses osteoblast differentiation and activity in inflammatory arthritis. Specifically, this research elucidates how inflammation-induced alterations in the Wnt and bone morphogenetic protein (BMP) osteogenic signaling pathways contribute to bone loss and formation at distinct inflammatory microenvironments within the bone. Secondly, the means by which cellular mediators, including lymphocytes and macrophages, facilitate bone erosion and formation was addressed.
Taken together, the research in this dissertation underscores the relationship between inflammation-induced bone loss and alterations in osteogenic signaling. Using an innovative murine inflammatory arthritis model, this study definitively demonstrates that resolving inflammation promotes osteoblast-mediated bone formation. Repair of erosions correlates with upregulation of synovial expression of Wnt10b, a Wnt agonist, and downregulation of sFRP1 and sFRP2, Wnt antagonists. This work also directly evaluates the contribution of sFRP1 to inflammation-induced bone destruction. Furthermore, this research demonstrates that expression of BMP3, a negative regulator of BMP signaling, is upregulated in osteoblasts by IL-17, a pro-inflammatory cytokine. BMP3-expressing osteoblasts are also observed at erosion sites in murine arthritis. Lastly, evaluation of the mediators of inflammation-induced periosteal bone formation implicates BMP2 as a means by which inflammation may positively regulate osteoblast function.
This dissertation further elucidates the role of T cells and macrophages in the erosion and formation processes, respectively. In the absence of lymphocytes, bone erosion occurred normally, demonstrating that RANKL-expressing lymphocytes are not absolutely required for the bone erosion. Preliminary studies also suggest that M2 macrophages are potential mediators of bone formation via the expression of BMP2.
In conclusion, this dissertation explores the ability of inflammation to act as a rheostat, which controls the fate of bone by modulating not only osteoclast differentiation, but also osteogenic signaling pathways and cellular mediators in the bone microenvironment. The soluble mediators and cell types identified in this research highlight novel mechanisms by which inflammation may regulate osteoblast activity within the bone microenvironment. Collectively, these data imply that strict control of inflammation may be necessary in order to create an anabolic environment that preserves bone architecture in diseases of inflammation-induced bone loss.
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Sjödal, My. "Specification of the lens and olfactory placodes and dorsoventral patterning of the telencephalon." Doctoral thesis, Umeå universitet, Umeå centrum för molekylär medicin (UCMM), 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-1347.
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The vertebrate nervous system is a highly complex and intriguing structure with diverse functions. To understand the functional nervous system, we first have to be aware of how it is assembled during development. In this thesis the mechanism of early diversification and regionalisation necessary for subsequent formation of part of the nervous system, namely the telencephalon and the placodes, will be addressed. We have identified signalling molecules involved in the dorsoventral patterning of the telencephalon and we propose a mechanism for the induction and differential specification of the olfactory and lens placodes. The telencephalon is regionalised along the dorsoventral axis during development. The cells situated dorsally will give rise to the cerebral cortex while the ventral and intermediate cells are mainly progenitors for the basal ganglia. The cerebral cortex is associated with higher cognitive functions whereas the basal ganglia control movements. We provide evidence that dorsal and intermediate telencephalic cells are re-specified from cells with an intrinsic ventral character. Dorsal telencephalic cells are specified at stage 10 in chick, while the intermediate cells are specified a few hours later, at stage 14. The expression of Wnt and Fibroblast growth factors (Fgfs) coincides with the time point when the dorsal cells are specified, and we provide evidence that Wnt and FGF signals act in a sequential way to specify dorsal telencephalic cells. The retinoic acid (RA) synthesising enzyme Raldh3 is expressed in proximity to the telencephalon, and our result suggests that RA is both required and sufficient to induce intermediate telencephalic cell types. Additionally, Fgf8 is expressed in the anterior neural ridge and the ventral telencephalic cells require FGF signals that oppose RA to maintain their character. The olfactory and lens placodes contribute to the special sense organs associated with olfaction and vision, respectively. Olfactory and lens placodes are specified at gastrula stage in chick, and become spatially separated at the neural fold stage. We provide evidence that Bone morphogenetic protein (BMP) signalling is required for the induction of a pool of placodal progenitor cells. Furthermore, time of exposure to BMP signals plays a key role in the differential specification of the olfactory and lens placodes, where continued exposure to BMP signals promotes lens character at the expense of olfactory placodal cells.
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Merenda, Alessandra. "Development of a new screening system for the identification of RNF43-related genes and characterisation of other PA-RING family members." Thesis, University of Cambridge, 2017. https://www.repository.cam.ac.uk/handle/1810/267982.
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The E3 ubiquitin ligase RNF43 (RING finger protein 43) is an important negative modulator of the WNT signalling pathway that acts at the plasma membrane by targeting Frizzled and its co-receptor LRP for degradation. In the small intestine, this prevents uncontrolled expansion of the stem cell compartment and so it is essential to the maintenance of normal tissue homeostasis. However, despite its crucial role in fine-tuning the WNT pathway and its role as a tumour suppressor, it is unclear whether RNF43 has further binding partners and what their functional relevance is to the modulation of WNT signalling. Here, I describe the development of a new screening strategy which combines CRISPR/Cas9 technology with 3D-intestinal organoid culture for the identification of novel molecular interactors of RNF43. Overall, this study and the technology developed provide a tool to enable the detailed description of the mechanism of action of RNF43, which is important not only in order to increase our understanding of WNT pathway regulation but also to gain potential new insights into RNF43 paralogs, by analogy. The investigation of paralogs is crucial as RNF43 belongs to a newly identified family of E3 ubiquitin ligases, named the PA-RING family, whose members are still poorly characterised. The majority of PA-RING family members have not been linked to any signalling pathway, most of their targets are still unknown and in many cases their in vivo function has not been addressed. In this context, my work has specifically focused on the investigation of the potential involvement of additional PA-RING family members in WNT pathway modulation and also on target identification for selected members. The results summarised in this dissertation show that no other PA-RING family member plays a prominent role in WNT pathway modulation aside from Rnf43 and its homologue Znrf3, however, different classes of adhesion molecules are likely to be regulated by certain of these E3 ligases. In conclusion, my work has contributed to unravelling previously unexplored aspects of this protein family, with particular regard to RNF43 and its mechanism of action. Thanks to this original approach, it was possible to identify potential new players involved either in membrane clearance of Frizzled or in RNF43 maturation. In particular, my thesis focuses on the characterisation of the role of DAAM in RNF43-mediated Frizzled internalisation.
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Ripp, Caroline [Verfasser], Andreas [Akademischer Betreuer] Wodarz, and Sigrid [Akademischer Betreuer] Hoyer-Fender. "Analysis of the Wnt receptors Ror, Otk and Otk2 during nervous system development in Drosophila melanogaster / Caroline Ripp. Betreuer: Andreas Wodarz. Gutachter: Andreas Wodarz ; Sigrid Hoyer-Fender." Göttingen : Niedersächsische Staats- und Universitätsbibliothek Göttingen, 2016. http://d-nb.info/1081543582/34.
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Fischer, Thomas Verfasser], Wolfgang [Akademischer Betreuer] Wurst, de Angelis Martin [Akademischer Betreuer] [Hrabé, and Kay H. [Akademischer Betreuer] Schneitz. "Fibroblast growth factor and Wnt signaling in the development of the vertebrate central nervous system / Thomas Fischer. Gutachter: Martin Hrabé de Angelis ; Kay H. Schneitz. Betreuer: Wolfgang Wurst." München : Universitätsbibliothek der TU München, 2006. http://d-nb.info/1058866435/34.
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Manenti, R. "DEVELOPMENT OF THE LARVAL PERIPHERAL NERVOUS SYSTEM IN THE ASCIDIAN CIONA INTESTINALIS: ROLE OF THE RETINOIC ACID AND FGF/WNT SIGNALLING PATHWAYS AND OF THE POU TRANSCRIPTION FACTORS." Doctoral thesis, Università degli Studi di Milano, 2010. http://hdl.handle.net/2434/150061.
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The research presented in this document focuses on the development of the larval peripheral nervous system of the Tunicate Ciona intestinalis with two main aims: a) to understand how the interactions between Retinoic Acid (RA) and the FGF/WNT pathways control its development; b) to study the role played by transcription factors of the POU family in its differentiation. Within chordates, tunicates represent the sister group of vertebrates and their larvae have a typical chordate body plan. Notably, larval nervous system is formed by few cells whose organization mirrors that of vertebrates. For these reasons the species C. intestinalis, whose genome is completely sequenced, is a good animal model often used to understand the basic mechanisms of Chordate development. POU genes are an important family of transcription factors with several members that regulate the neural patterning and differentiation in both vertebrate and invertebrate embryos. C. intestinalis has only three genes coding for POU transcription factors: Ci-POU-2 Ci-POU-IV and Ci-POU-like. The gene Ci-POU-IV is specifically expressed in all peripheral nervous system (PNS) territories and in some cells of the central nervous system (CNS) during development. Since the expression of the two other genes was not previously studied in detail, a part of this research consisted in their characterization. Several experiments of in situ hybridization showed that the transcripts of Ci-POU-2 are present early during cleavage stages while Ci-POU-like gene expression is restricted to the lateral mesenchime cells of the larva and to their precursors during embryonic development. Thus the research was focused on the Ci-POU-IV gene. Its expression had been formerly studied by the research team of Prof. De Bernardi that discovered the existence of two alternative transcripts. In order to study the role that they play in neural differentiation Morpholino oligos were designed to perform gene knock-down experiments for the two different isoforms. The results from these experiments revealed that the expression of the serotonin rate-limiting synthesis enzyme, tryptophane hydroxylase (TPH), and glutamate transporter (vGlut) in the PNS neurons could be regulated by the product of the long transcript. To verify if the alternative transcripts were expressed in different PNS neuron populations in situ hybridizations were performed with a probe selective for the short isoform. These in situ hybridizations, compared to the whole expression profile of Ci-POU-IV, showed a lack of expression of the short form in the sensory epidermal neurons of the trunk. Moreover experiments were performed to understand the relationship between Ci-POU-IV and the Delta/Notch pathway. The latter has an important role in determining the cell to cell interactions in a number of taxa and to affect the neural or the epidermal fate of the PNS precursors. The Delta/Notch pathway was inhibited both using DAPT that inhibits the –secretase, responsible of the correct functioning of the pathway and electroporing the pFOG::VeSu(H)DBM construct that blocks the pathway activity. Embryos treated showed an abnormal development of epidermic sensorial neurons and the following in situ hybridizations for Ci-POU-IV pointed out an ectopic expression of the gene. Furthermore the study looked for the Ci-POU-IV targets in order to identify the genes regulated by Ci-POU-IV during the PNS differentiation. A bioinformatic approach was used. The possible consensus sequences were obtained by bibliographic research of those known for the POU IV family in both invertebrates and vertebrates. These sequences have been used to build a matrix that was employed to perform a bioinformatic research in the whole C. intestinalis genome with a software elaborated by the Lemaire team of the IBDML of Marseille. The search identified 19 possible targets of Ci-POU-IV; 8 regions, corresponding to 6 genes including TPH, have been preliminary selected. The activity of the selected regions is being evaluated.
The second part of the thesis has been developed during a period of research with Dr. A. Pasini at the Institut de Biologie du Développent of Marseille. The aim was to identify the mechanisms with which RA and the FGF/WNT pathways act on antero-posterior differentiation of PNS during C. intestinalis embryonic development. In vertebrates it was already known that during the antero-posterior extension of the body axis these pathways antagonize each other to coordinate mesoderm and nervous system differentiation. For this reason the hypothesis that an analogous mechanism could occur in other Chordates, including tunicates was tested. Thus in C. intestinalis I performed in situ hybridizations for different genes potentially involved in this mechanism. I employed also the electroporation technique with specific constructs. In particular results showed that the expression of the gene Ci-Raldh that codes for Retinaldehyde dehydrogenase, the enzyme responsible of RA synthesis, is confined to the anterior part of the tail in tailbud stage embryos. To this region is limited also the expression of some gene responsive to RA such as Ci-Hox-1 and Ci-Cyp26. On the contrary, at the posterior extremity of the tail it is predictable the existence of a source of FGF and WNT signals as shown by the expression of Ci-FGF-8 and Ci-WNT-5. Moreover, embryos treated with RA showed Ci-Hox-1 up-regulation at throughout tail epidermis and the inhibition of the posterior Ci-Hox-12 expression. On the contrary, embryos treated with FGF showed an opposite situation with Ci-Hox-12 activation and Ci-Hox-1 inhibition. Moreover, quantifications of differentiated caudal epidermal neurons and meticulous analysis of their position along the tail have been performed in late stage embryos treated with RA, FGF, their respective inhibitors and an inhibitor of the enzyme Ci-Cyp26, responsible for RA catabolism. This showed significant alterations in both the number of neurons and their position. In particular RA treatment increased the oveall number of caudal epidermal neurones but causes the loss of the most posterior ones; on the contrary FGF treatment induced a decrease in the number of neurons but maintained the posterior ones. Treatment with FGF and Ci-Cyp26 inhibitors mimicks the effects of RA while treatment with RA synthesis inhibitor mimicks the effect of FGF. On the whole a complex picture of antagonistic interactions, both direct and indirect has been revealed posing interesting questions from an evolutionary point of view.
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Subedi, Ashok. "Roles of Primary Cilia in the Oligodendrocyte Lineage." Thesis, University of North Texas, 2018. https://digital.library.unt.edu/ark:/67531/metadc1404594/.
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Primary cilia are nonmotile, hair-shaped organelles that extend from the basal body in the centrosome. The present study is the first investigation of this organelle in the oligodendrocyte lineage in vivo. I used immunohistochemical approaches in normal and cilia-deficient mutant mice to study cilia in relation to oligodendrogenesis and myelination. Primary cilia immunoreactive for Arl13b and ACIII were commonly present in NG2+ oligodendrocyte progenitor cells (OPCs), in which cilia-associated pathways control proliferation, differentiation, and migration. The loss of primary cilia is generally associated with enhanced Wnt/β-catenin signaling, and Wnt/β-catenin signaling has been shown to promote myelin gene expression. I examined whether the lack of cilia in the oligodendrocyte lineage is associated with elevated Wnt/β-catenin activity. I found that absence of a primary cilium was associated with with higher levels of TCF3, and with β-galactosidase in Axin2-lacZ Wnt reporter mice. This evidence supports the proposal that cilia loss in oligodendrocytes leads to enhanced Wnt/β-catenin activity, which promotes myelination. Cilia are dependent on the centrosome, which assembles microtubules for the cilium, the cytoskeleton, and the mitotic spindle. Centrosomes are the organizing center for microtubule assembly in OPCs, but this function is decentralized in oligodendrocytes. I found that the intensity of centrosomal pericentrin was reduced in oligodendrocytes relative to OPCs, and γ-tubulin was evident in centrosomes of OPCs but not in mature oligodendrocytes. These decreases in centrosomal proteins might contribute to functional differences between OPCs and oligodendrocytes. The importance of cilia in the oligodendrocyte lineage was examined in Tg737orpk mice, which have a hypomorphic IFT88 mutation resulting in decreased cilia numbers and lengths. These mice showed marked, differential decreases in numbers of oligodendrocytes and myelin, yet little or no change in OPC populations. It appears that sufficient cells were available for maturation, but lineage progression was stalled. There were no evident effects of the mutation on Wnt/β-catenin. Factors that might contribute to the abnormalities in the oligodendrocyte lineage of Tg737orpk mice include decreased cilia-dependent Shh mitogenic signaling and dysregulation in cilia-associated pathways such as Notch and Wnt/β-catenin.
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Hehn, Sina [Verfasser]. "Beta-Catenin : Studien zur onkogenen Stabilisierung in der akuten myeloischen Leukämie und zu WNT Signalweg unabhängigen Funktionen im hämatopoetischen System / Sina Hehn. Biochemie I -- Fakultät für Chemie. Zentrum der innere Medizin, med. Klinik II (Universitätsklinikum Frankfurt/Main)." Bielefeld : Universitätsbibliothek Bielefeld, Hochschulschriften, 2011. http://d-nb.info/1013227220/34.
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Marklund, Matthew. "Specification of Dorsal and Intermediate Telencephalic Character." Doctoral thesis, Umeå : Molekylärbiologi, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-502.
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Berglund, Kim. "Sustainable performance of wet clutch systems." Licentiate thesis, Luleå tekniska universitet, Maskinelement, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-18008.
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In industry today there are increasing demands not only on product performance, but also on environmental performance. In striving to develop high performance environmentally adapted products, optimization of product life is a central issue. The success of design optimization relies on an understanding of the degradation process and of the associated degradation mechanisms. A high level of costs is often associated with downtime of machinery caused by service and by replacement of machine components. Knowledge of ageing mechanisms facilitates evaluation of the remaining useful life, thus optimizing performance during the entire service life of components. In this study the ageing process of wet clutches has been investigated. Wet clutches are used in automatic transmissions and limited slip differentials in private vehicles and are designed to transfer torque. A wet clutch consists of a clutch pack submerged in lubricant. Separator and friction discs are alternately positioned in the clutch pack. The separator discs are connected to the input shaft and the friction discs are connected to the output shaft. When the clutch pack is pushed together friction is generated between the friction and separator discs. Torque transfer is thus created in the interface between contacting surfaces and torque transfer characteristics are determined by the interaction between lubricant and contacting surfaces. The investigations performed in this thesis have been designed to increase the understanding of wet clutch ageing and failure. Tests have been performed from full scale to model tests. Full scale testing describes the actual system which means that all significant degradation mechanisms are present. The disadvantage with full scale testing is that it is difficult to separate and isolate degradation mechanisms. In small scale model tests it is possible to isolate the degradation mechanisms and hence also what effects they have. Correlation of results from full scale to small scale can in turn increase the understanding of which degradation mechanisms are important for the system and how they influence the wet clutch system. The wet clutch lubricant and the contacting surfaces provide the friction characteristics of the clutch. Therefore, this work has focused on how lubricant degradation affects friction characteristics and hence wet clutch performance. Results in this study show that friction levels increase as lubricant degradation proceeds. In accelerated wet clutch test rig ageing, results in this study indicate that high temperatures in the interface between contacting surfaces greatly influence wet clutch degradation.Godkänd; 2010; 20100503 (kimber); LICENTIATSEMINARIUM Ämnesområde: Maskinelement/Machine Elements Examinator: Professor Roland Larsson, Luleå tekniska universitet Diskutant: Doktor Rikard Mäki, Volvo Construction Equipment, Eskilstuna Tid: Torsdag den 3 juni 2010 kl 10.00 Plats: E131, Luleå tekniska universitet
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Graham, W. J. "Adaptive control of wet heating systems." Thesis, University of Oxford, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370317.
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Shackleford, Ghjuvan'Ghjacumu. "Impacts des oxystérols par le biais des LXRs et du AhR dans la myélinisation." Thesis, Paris 5, 2014. http://www.theses.fr/2014PA05P638/document.
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La formation de la gaine de myéline est un processus complexe et finement régulé. Une altération de l’expression des gènes codant pour les protéines structurales de cette gaine entraine de graves neuropathies démyélinisantes. Notre objectif est d’identifier de nouvelles voies de signalisation capables de moduler l’expression de ces gènes. Les cellules de Schwann et les oligodendrocytes contiennent et synthétisent de grande quantité de dérivés oxydés du cholestérol : les oxystérols. Ces molécules sont connues pour leurs rôles dans le maintien de l’homéostasie du cholestérol et dans la progression des maladies neurodégénératives. Les oxystérols peuvent être classés en deux groupes : ceux dont l’oxydation a lieu sur la chaine carbonée latérale (25OH) et ceux qui portent une oxydation sur l’un des cycles du cholestérol (7KC). Nous nous sommes tout d’abord intéressés à la première catégorie d’oxystérols. Nous avons montré que le 25OH, réprimait l’expression des gènes de la myéline périphérique P0 et PMP22. Cette activité répressive était le fruit d’un mécanisme direct conduisant à une augmentation de la quantité des LXRs liés à leurs éléments de réponse sur les promoteurs des gènes de la myéline, et d’un mécanisme indirect provoquant une diminution de l’activité de la voie Wnt/β-caténine. En revanche, dans le SNC, nos résultats indiquent que le 25OH active l’expression des gènes de la myéline PLP et MBP. Le traitement, par ces oxystérols, de cultures organotypiques de cervelet démyélinisées par la lysolécithine permet une remyélinisation des axones des cellules de Purkinje. Nous nous sommes ensuite penchés sur le rôle du corégulateur transcriptionnel RIP140. Ce dernier peut soit agir comme un corépresseur soit comme un coactivateur. Il peut interagir avec le LXR. L’invalidation de RIP140 dans le poisson zèbre altère les gaines de myéline. Nous avons montré que RIP140 possédait des rôles bivalents dans la régulation de la myélinisation. En effet, il est capable d’activer mais aussi de réprimer l’activité transcriptionnelle de P0 et de PMP22. Enfin, nous nous sommes intéressés à la seconde catégorie d’oxystérols. Le 7KC est l’oxystérol majoritairement présent dans le SNP et la CS. Il est connu pour moduler l’action du récepteur aux dioxines : le AhR. Ce récepteur a été très largement étudié dans un cadre toxicologique. Cependant ses rôles et ses ligands endogènes restent à ce jour encore assez méconnus. Nos résultats indiquent que le AhR est impliqué dans le contrôle de l’expression des gènes de la myéline périphérique. L’invalidation du AhR, chez la souris, provoque des anomalies structurales de la gaine de myéline conduisant à des déficits moteurs. Cette étude a permis de mieux comprendre les dialogues entre les voies de signalisation gouvernant le processus de myélinisation. Ce travail apporte également de nouvelles perspectives thérapeutiques des maladies neurodégénératives comme la CMT1A ou la sclérose en plaquesThe myelination of axons is a complex process performed by Schwann cells (SC) and by oligodendrocytes (OL) respectively in the peripheral nervous system (PNS) and in the central nervous system (CNS). A slight change in expression of myelin structural proteins has a deep impact on the development and preservation of nerve fibers and their myelin sheaths, as observed for example in Charcot-Marie-Tooth disease or in Pelizaeus-Merzbacher disease. Our aim is to identify new signaling pathways able to control the expression of these structural proteins. SC and OL contain and synthesize high amount of reactive molecules generated from the oxidation of cholesterol: the oxysterols. Their implication in cholesterol homeostasis and in the progression of neurodegenerative disorders is well known but few data are available for their functions in myelination of PNS and CNS. Firstly, we demonstrate that oxysterols inhibit peripheral myelin gene expression: MPZ and PMP22. This downregulation is mediated by two mechanisms: by increasing the binding of LXRs to myelin genes promoters and by inhibiting the Wnt/β-catenin pathway leading to a decrease of b-catenin recruitment at the levels of the MPZ and PMP22 promoters. However, in the CNS, our data demonstrate that activation of LXRS by oxysterols stimulate myelin genes expression (PLP and MBP). Interestingly, by using demyelinated organotipc culture of cerebellum, we show that oxysterols enhance OL differentiation and promote remyelination, via LXRs. Then, we studied the role of the transcriptional coregulatory, RIP140, in myelination. RIP140 is able to act as a corepressor or as a coactivator and can interact with LXRs. In Zebrafish, the knocked down of the orthologue of RIP140 led to a decrease of peripheral and central myelin gene expression and to a defect in myelin sheath ultrastructure. Finally, we focused on impact of AhR in myelination process. AhR is a ligand activated transcription factor mostly known to interact with environmental pollutant like dioxins to mediate their toxic and carcinogenic effect. However, its detoxifying activity is posterior to the apparition of the gene and its physiological roles and endogenous ligands remain elusive. We show that the main oxysterol in the nervous system is 7-ketocholesterol which is an endogenous modulator of AhR. We report that the constitutive absence of AhR in mice leads to defects in locomotion behaviors. We studied the impact of this invalidation on the myelin of sciatic nerve. We observed a severe demyelinating phenotype and deregulation of myelin genes expression. Moreover, we demonstrated a cross-talk between AhR and Wnt/β-catenin pathways. Our data reveal a new endogenous role of AhR in myelination process
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Heebl, Jason Daniel. "Development and Characterization of a Tunable Resonant Shielded Loop Wireless Non-Radiative Power Transfer System." University of Dayton / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1304426560.
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Clukey, David Alan. "Evaluation and Analysis of Underwater "Wet" Welding Process." The Ohio State University, 1999. http://rave.ohiolink.edu/etdc/view?acc_num=osu1391793136.
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Heyns, Johan Adam. "Performance characteristics of an air-cooled steam condenser incorporating a hybrid (dry/wet) dephlegmator." Thesis, Stellenbosch : Stellenbosch University, 2008. http://hdl.handle.net/10019.1/350.
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Thesis (MScEng (Mechanical and Mechatronic Engineering))--Stellenbosch University, 2008.This study evaluates the performance characteristics of a power plant incorporating a steam turbine and a direct air-cooled dry/wet condenser operating at different ambient temperatures. The proposed cooling system uses existing A-frame air-cooled condenser (ACC) technology and through the introduction of a hybrid (dry/wet) dephiegmator achieves measurable enhancement in cooling performance when temperatures are high. In order to determine the thermal-flow performance characteristics of the wet section of the dephlegmator, tests are conducted on an evaporative cooler. From the experimental results, correlations for the water film heat transfer coefficient, air-water mass transfer coefficient and the air-side pressure drop over a deluged tube bundle are developed. During periods of high ambient temperatures the hybrid (dry/wet) condenser operating in a wet mode can achieve the same increased turbine performance as an oversized air-cooled condenser or an air-cooled condenser rith adiabatic cooling (spray cooling) of the inlet air at a considerably lower cost. For the same turbine power output the water consumed by an air-cooled condenser incorporating a hybrid (dry/wet) dephlegmator is at least 20% less than an air- cooled condenser with adiabatic cooling of the inlet air.
Sponsored by the Centre for Renewable and Sustainable Energy Studies, Stellenbosch University
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Tinoco, Lucio Cunha. "Online Evaluation in WWW-Based Courseware: The Quizit System." Thesis, Virginia Tech, 1996. http://hdl.handle.net/10919/36881.
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The QUIZIT system has been developed to support adaptive and standard testing, along with automatic grading, record keeping, and test administration using the WWW as a delivery vehicle. We have applied QUIZIT in connection with our NSF-supported Education Infrastructure project on Interactive Learning with a Digital Library in Computer Science to help with evaluation in a master's level course as well as a large freshmen level service course. Preliminary testing in these courses has shown us that QUIZIT is a promising supplement to other forms of evaluation in self-paced education.
We also conjecture QUIZIT might be a valuable tool in distance learning environment.Master of Science
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Jasti, Nagapadma. "Attached growth fungal system for corn wet milling wastewater treatment." [Ames, Iowa : Iowa State University], 2006.
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Colandro, Michelle Elizabeth. "Baculovirus stability in serum-free lyophilized and wet storage conditions." Thesis, Virginia Tech, 2013. http://hdl.handle.net/10919/51596.
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The baculovirus expression vector system (BEVS) is an effective way to produce recombinant proteins for biopharmaceuticals. However baculovirus stocks are stored in subzero temperatures to maintain virus stability, and fetal bovine serum is commonly used in the storage solution. In an effort to lower transportation and storage costs, a storage formulation that can effectively store the baculovirus in above frozen temperatures without the use of FBS would be beneficial. In this study, DMSO, ethylene glycol, glycerol, sucrose, sorbitol, sucrose-phosphate, and sucrose-phosphate-glutamate were added to baculovirus stock at various concentrations to determine the most effective stabilizer for virus storage at 4°C. Of the seven additives studied, 1 M sorbitol most effectively preserved baculovirus stock over a period of 47 weeks stored in 4°C. Formulations that include sucrose, L-arginine, and Pluronic F68 were created to determine their effectiveness on virus stability in a freeze-dried state stored at room temperature. In a lyophilized state, 0.5 M sucrose maintained baculovirus stock stability after 5 weeks of storage. Lyophilized stocks not containing sucrose were no longer infective after 5 weeks.Master of Science
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Dey, Michael John. "Optimisation of wet massing and related processes for extruision-spheronisation." Thesis, Open University, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.236300.
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Fatima, Nowshir. "Wet clutch friction reliability : influence of water contamination and system design." Licentiate thesis, Luleå tekniska universitet, Maskinelement, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-26351.
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Wet clutches are machine components using friction to transfer torque and providing interruptible connection between rotating shafts in different automobile applications including automatic transmissions. Like any friction generating machine components, wet clutches are susceptible to continuous wear and degradation during sliding. This regular deterioration process as well as the choice of operating conditions, ultimately change the overall system performance during operation due to resultant change in the system parameters. The first part of this thesis summarizes some of the notable studies on the wet clutch tribological performance and clarifies goals of the investigation.Previously, plenty of experimental studies on wet clutches have been reported but still some effects regarding the water contamination problem and the influence of mechanical design factors are not covered thoroughly. The thesis aims to experimentally analyse these two different aspects for improving wet clutch performance regarding frictional characteristics and reliability. These two investigations are focused on wet clutches in automatic transmission applications. For evaluating friction behaviour during a long clutch engagement period, suitable test equipment is designed where standard paper based friction plates and steel separator plates are tested with commercially available ATF. To investigate a clutch operated in a controlled environment is one of main the research objectives. The vital concern while designing the test rig is to monitor the clutch parameters for achieving the desired operating conditions for individual tests. Instead of using a multiple clutch plate configuration, as in real applications, a single friction and reaction plate arrangement is considered to simplify the analyses.An experimental study on wet clutch frictional behaviour under water contaminated lubrication condition reveals the change in the friction level for a water contaminated lubricant. It was shown that the friction level increased for the addition of water in the system. This is not a desirable clutch frictional behaviour for maintaining frictional stability. The increase of friction for added water was influenced by the water amount but not by the water exposure time. The test results also showed a higher change in the separator plate's roughness parameter (Ra) for water contaminated systems compared to an uncontaminated wet clutch. In the second part of this thesis, the influence of the clutch’s output shaft’s stiffness and inertia on the clutch system‘s friction reliability is experimentally evaluated. Test results show that the choice of these design factors can provide different outcome concerning clutch frictional performance and shudder sensitivity. Shudder tendency is seen to be increased for decreased torsion shaft stiffness. High frictional losses and clutch degradation are observed for systems with less inertia.Godkänd; 2012; 20120813 (nowfat); LICENTIATSEMINARIUM Examinator: Professor Roland Larsson, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet Diskutant: Donald McCarthy, Volvo Tid: Fredag den 14 september 2012 kl 10.00 Plats: D770, Luleå tekniska universitet
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Khayi, Noureddine. "Deammonification efficiency in combined UASB and IFAS system for mainstream WWT." Thesis, KTH, Mark- och vattenteknik (flyttat 20130630), 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-210809.
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The study is about Nitrogen removal from the low concentrated mainstream wastewater after Upflow Anaerobic Sludge Blanket reactor process (UASB) by single-stage Partial Nitritation/Anammox process in a pilot scale reactor at Hammarby Sjöstad in Stockholm. A mixture of various concentrations of dissolved oxygen and different aeration methods have been tested in the pilot scale reactor in five months divided into five periods where the temperature was set at 15° C throughout the study. The best result was in period 4, the average nitrogen removal efficiency was 52% varying between 40 and 60 % with aeration method of the ratio R = 1/3 (R = 20 minutes with aeration to 40 minutes without aeration) and a dissolved oxygen concentration of 1.3 mg/L. Partial nitritation/Anammox is considered more environmentally friendly due to reduced energy requirements for aeration, no need for an external carbon source. The process also allows for a more cost-effective nitrogen removal from wastewater.Vatten är nödvändigt för existensen av allt liv på jorden och spelar en avgörande roll i alla mänskliga aktiviteter. Antropogena aktiviteter förorenar denna viktiga resurs och medför stor risk för människors och djurs hälsa samt växter. Kvävebelastning från jordbruket och avloppsvatten i mark- eller vattenmiljön har resulterat till övergödning, vilket är ett miljö- och ekonomiskt problem på grund av en obalans mellan ekosystemtillförseln och den naturliga näringsförbrukningen. I denna studie behandlades avloppsvatten i en pilotskala reaktor med en integrerad fastfilm aktiverat slam (IFAS) som drivs med ett enstegs partial nitritation/Anammox-process. Kväverening från den lågkoncentrerade huvudström avloppsvatten efter Uppflöde Anaerob Slam Blankett reaktor process (UASB) undersöktes. En blandning av olika koncentrationer av upplöst syre och olika luftningsmetoder har testats i pilotskala reaktorn i fem månader uppdelad i fem perioder där temperaturen sattes vid 15° C under hela studien. De bästa resultaten i kväve reningseffektivitet var 52 % i genomsnitt i period 4 varierande mellan 40 och 60 %, luftningsmetod med ett förhållande av R = 1/3 (R = 20 minuter med luftning till 40 minuter utan luftning) och ett upplöst syre Koncentration av 1,3 mg/l. Jämförelsen tog hänsyn till alla former av utsläpp av kväve- och energikostnader för luftning. Under de senaste decennierna har vattenbehandlingsprocesserna haft många positiva utvecklingar, vilket har lett till en kvalitetsförbättring av vatten samtidigt som kostnaden för kväveavlägsnande från avloppsvatten har minskat. För närvarande flyttar kvävereningsteknik från konventionell nitrifikations/denitrifikationsprocessen till partiell nitritation/Anammox (PN/A) -processen kallad deammonification. Det verkar som om den största svårigheten är att upprätthålla en stabil ackumulation av nitrit medan man försöker delvis med nitritation av ammonium. Partiell nitritation/Anammox (PN/A) anses vara mer kostnadseffektivt avlägsnande av kväve från avloppsvatten, mer miljövänligt än konventionella nitrifikations-denitrifikationsprocesser på grund av minskat energibehov för luftning och inget behov av en yttre källa av kol.
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Kors, Deborah Joy. "Does social support reduce cardiovascular stress reactivity only if you want support: a test of a match/mismatch hypothesis." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape10/PQDD_0032/NQ38917.pdf.
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Ziehm, Ulrike. "Intensity adaptation in the cricket auditory system." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2013. http://dx.doi.org/10.18452/16947.
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Die Intensität verhaltensrelevanter Signale variiert oft über viele Größenordnungen. Gleichzeitig müssen sensorische Systeme in der Lage sein, über den gesamten relevanten Bereich feine Intensitätsunterschiede aufzulösen. Auf neuronaler Ebene ergibt sich bei Nutzung eines Feuerratencodes aus diesen Anforderungen ein grundsätzlicher Konflikt, da neuronale Antwortbereiche beschränkt sind. Eine Lösung, die in vielen Sinnessystemen beschrieben wurde, ist die Verschiebung von Intensität-Kennlinien, so dass der gesamte Antwortbereich des Neurons zur Verfügung steht, um schnelle Abweichungen vom Mittelwert zu kodieren. Diese Arbeit versucht anhand mathematischer Modelle zu beantworten, wie die Verschiebung von Kennlinien in einem neuronalen Netzwerk entstehen könnte. Ausgangspunkt ist eine Rezeptorpopulation mit Intensitätsbereichsaufteilung und einem begrenzten Verschiebungsbereich der Kennlinien von Einzelrezeptoren, die auf ein Output-Neuron konvergieren. Diese Organisation wurde vom auditorischen System der Grille inspiriert. Modelle, die auf einer Kombination aus einer sättigenden Nichtlinearität und Spike-Frequenz-Adaptation basieren, reproduzieren die Verschiebung der Kennlinien entlang der Intensitäts-Achse. Diese Modelle sind in der Intensitätsdiskriminierung dem Rezeptormodell und der Summe von Rezeptorantworten über große Intensitätsbereiche deutlich überlegen. Die Kennlinien dieser Modelle besitzen zudem weitere Eigenschaften, die in ihrer Kombination übereinstimmend in verschiedenen sensorischen Systemen beschrieben wurden: Insbesondere erklären sie eine zusätzliche scheinbare Verschiebung entlang der Antwortachse, unterschiedliche Steigungen der verschobenen Kennlinien, sowie Steigungsänderungen innerhalb einzelner Kennlinien. Die einfachen, abstrakt formulierten Modelle ermöglichen ein tieferes Verständnis adaptiver Mechanismen über das Modellsystem Grille hinaus.Intensities of behaviourally relevant signals often vary over many orders of magnitude. At the same time, sensory systems need to ensure high sensitivity to minute intensity differences across the full intensity range. These demands conflict on the neuronal level due to the boundedness of neuronal response ranges. To solve this dilemma, intensity response curves in many sensory system were found to shift towards the actual mean intensity so that the full response range can be used to encode fast fluctuations around the slowly varying mean. Using mathematical models, this study approaches the question how shifts of intensity response curves might arise in small neural networks. The starting point is a population of receptors with stacked response thresholds and limited capacity of adaptive shift that converge onto one output neuron. This organization was inspired by the auditory system of the cricket. A combination of a static saturating non-linearity and spike-frequency adaptation reproduced the desired shift of response curves along the intensity axis. With respect to intensity discrimination, these models are superior to the receptor model and the sum of receptor responses over a wide range of absolute intensities. The response curves generated by these model also displayed details of response curve behaviour consistently observed in numerous experimental studies. In particular, they explain an apparent shift along the response axis, different slopes of the shifted response curves, and changes in the slope within individual response curves. The simple, abstract models allow for a deeper understanding of adaptive mechanisms beyond the auditory system of the cricket.
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Alharbi, Abdulrahman. "Investigation of sub-wet bulb temperature evaporative cooling system for cooling in buildings." Thesis, University of Nottingham, 2014. http://eprints.nottingham.ac.uk/27806/.
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The work presented in this thesis investigates design, computer modelling and testing a sub-wet bulb temperature evaporative cooling system for space air conditioning in buildings. The context of this evaporative cooling technology design is specifically targeted at locations with a hot and dry climate such as that prevailing in most regions of Middle East countries. The focus of this technology is to address the ever-escalating energy consumption in buildings for space cooling using mechanical vapour compression air conditioning systems. In this work, two evaporative cooling configurations both based on sub-wet bulb temperature principle have been studied. Furthermore, in these designs, it was sought to adopt porous ceramic materials as wet media for the evaporative cooler and as building element and use of heat pipes as heat transfer devices. In the first test rig, the prototype system uses porous ceramic materials as part of a functioning building wall element. Experimental and modelling results were obtained for ambient inlet air dry bulb temperature of 30 and 35oC, relative humidity ranging from 35% to 55% and intake air velocity less than 2 (m/s). It was found that the design achieved sub-wet bulb air temperature conditions and a maximum cooling capacity approaching 242 W/m2 of exposed ceramic material wet surface area. The wet bulb effectiveness of the system was higher than unity. The second design exploits the high thermal conductivity of heat pipes to be integrated as an effective heat transfer device with wet porous ceramic flat panels for evaporative cooling. The thermal performance of the prototype was presented and the computer model was validated using laboratory tests at temperatures of 30 and 35oC and relative humidity ranging from 35% to 55%. It was found that at airflow rates of 0.0031kg/s, inlet dry-bulb temperature of 35oC and relative humidity of 35%, the supply air could be cooled to below the inlet air wet bulb temperature and achieve a maximum cooling capacity of about 206 W/m2 of wet ceramic surface area. It was shown that the computer model and experimental tests are largely in good agreement. Finally, a brief case study on direct evaporative cooling thermal performance and environmental impact was conducted as part of a field trip study conducted on an existing large scale installation in Mina Valley, Saudi Arabia. It was found that the evaporative cooling systems used for space cooling in pilgrims’ accommodations and in train stations could reduce energy consumption by as much as 75% and cut carbon dioxide emission by 78% compared to traditional vapour compression systems. This demonstrates strongly that in a region with a hot and dry climate such as Mina Valley, evaporative cooling systems can be an environmentally friendly and energy-efficient cooling system compared to conventional vapour compression systems.
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Hulays, Rafeh Ahmad. "The analysis of wet snow effects on earth-space transmission systems." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0011/NQ34555.pdf.
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Javaheri, Hoda. "Wet granulated liquisolid drug delivery systems with hydrophobic and hydrophilic drugs." Thesis, University of Sunderland, 2017. http://sure.sunderland.ac.uk/8549/.
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The formulation of hydrophobic drugs into appropriate dosage forms is challenging due to the problems associated with those drugs such as low solubility and poor dissolution. Using a liquisolid system is a promising method to improve the dissolution of hydrophobic drugs and in sustaining the release of hydrophilic drugs, in which solid drugs are dispersed in non-volatile liquid vehicles. The aim of this research was to use the liquisolid technique to enhance the dissolution rate of glibenclamide, a model hydrophobic drug, and to sustain the release of metformin-HCl, as a model hydrophilic drug. The wet granulation process was applied to liquisolid powders with the aim of overcoming issues of poor powder flowability and compressibility, especially using high viscosity liquid vehicles. This process was performed with liquisolid powders prior to compaction into tablets. Different liquisolid formulations were prepared using three liquid vehicles (polyethylene glycol400 (PEG® 400), Synperonic® PE/L44 and Cremophor® ELP), at 10 and 30 % w/w drug concentrations for glibenclamide; and 30% and 60% w/w drug concentrations for metformin-HCl. Avicel®PH102 was used as a carrier, whilst colloidal silicon dioxide was employed as a coating material to convert the wet mixtures into dry powders. Potato starch, 5% w/w, as a disintegrant was blended with the mixtures manually for 10 minutes and then 0.75% of magnesium stearate as a lubricant was added and mixed for 5 minutes. The final powder (depending on its flowability and compactability) was then compacted automatically using a single-punch tableting machine to give tablets with 4 mg for glibenclamide and 40 mg for metformin-HCl. Prepared liquisolid compacts were characterized by using British Pharmacopeia quality control tests: uniformity of weight, friability, disintegration, hardness and drug dissolution. iii It was found, for both drugs, that by application of wet granulation to liquisolid powder admixtures, the large-scale production of liquisolid compacts is feasible, which can be easily adapted to the pharmaceutical industry. In addition to enhancing the flowability and compressibility of the powders, the glibenclamide dissolution was also improved due to the enhanced binding of particles and because of the wetting effect of liquid vehicles on the hydrophobic drug, which make the drug more available for dissolution. For the sustained release preparations of liquisolid metformin-HCl, hydroxyl propyl cellulose (HPC) was used as a novel carrier in liquisolid compacts. The results showed 92% drug release after 12 hours using Cremophor®ELP (with 30% w/w drug concentration) which was the best sustained drug release formulation. Additionally, Eudragit® RL30D and Eudragit® RLPO have been used to study their effects on drug release from liquisolid formulations, examining if they can sustain or give more rapid drug release. Both types of Eudragit revealed immediate release with metformin-HCl rather than sustained drug release, with the tablets disintegrating within seconds. This suggests formulating orodispersible metformin-HCl tablets using Eudragit® RL30D as a liquid vehicle. In summary, liquisolid technology has led to promising results, not only in enhancing the drug dissolution of hydrophobic drugs, but also in sustaining and promoting the release of hydrophilic drugs.
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Martin, Gregory Dean. "Microbial Community Composition and Activities in Wet Flue Gas Desulfurization Systems." University of Akron / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron1493919370366314.
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Chettaoui, Chadha. "Towards the systems biology of tissues : interface between intracellular and multicellular modeling." Paris 7, 2012. http://www.theses.fr/2012PA077266.
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La biologie des systèmes est un domaine de recherche en plein développement, qui s'appuie sur les progrès rapides des techniques d'investigation biologique et sur des approches multidisciplinaires, afin de construire de nouveaux modèles quantitatifs permettant de comprendre l'organisation et le fonctionnement du vivant. L'objectif de cette thèse est de construire un modèle multi-échelle qui intègre les aspects génétiques, moléculaires et cellulaires tout en se basant sur les données des expériences biologiques. Un tel modèle permet d'analyser les éléments individuels d'un système et leurs interactions. Nous avons modélisé deux applications biologiques en utilisant le modèle à base d'agent pour décrire la cellule comme un objet individuel, ayant des propriétés physiques, capable d'interagir avec les cellules voisines et l'environnement. Ces deux applications concernent des problématiques liées la morphogenèse des tissus embryonnaires chez les ruminants et le développement de la tumeur dans le foieSystems biology is a highly interdisciplinary field that requires the understanding of complex biological systems at different levels. Based on experimental data, we are concerned in this thesis, with building a multi-scale integrative model that takes into account genetic, molecular and cellular aspects. Such a model allows the analysis of individual components and their interactions. We use the agent-based model to describe the biological cell by an individual object able to interact with its cells neighbors and the environment. This model is then studied through computer simulations to test its validity. The biological phenomena we are interested in concern the study of liver development and the early stages of embryo development. In the application to liver development, we built a mathematical model for two intracellular pathways: the P-catenin and Ras signaling pathways, which play a crucial role in liver cancer. The established model is studied in a cross-section of the liver lobule to analyze hepatocyte proliferation and apoptosis. According to the application to early stages of embryo development, we built a biophysical model to study two main stages in the development of ruminants embryo: the blastocyst formation followed by the rapid elongation of its surrounding epithelium named trophoblast. We are particularly interested in mimicking the development of the blastocyst which consists in a hollow sphere of cells that retains a spherical shape while cell division. Moreover, we are interested in understanding the mechanisms governing the trophoblast tissue elongation
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De, Wet Sarel Joubert. "Development of a system for tracking objects in a confined space / S.J. de Wet." Thesis, North-West University, 2009. http://hdl.handle.net/10394/4010.
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Velez, Rodriguez Kenneth Xavier. "Systemic Network-Level Approaches for Identifying Locations with High Potential for Wet and Hydroplaning Crashes." Diss., Virginia Tech, 2021. http://hdl.handle.net/10919/104926.
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Crashes on wet pavements are responsible for 25% of all crashes and 13.5% of fatal crashes in the US (Harwood et al. 1988). This number represents a significant portion of all crashes. Current methods used by the Department of Transportations (DOTs) are based on wet over dry ratios and simplified approaches to estimate hydroplaning speeds. A fraction of all wet crashes is hydroplaning; although they are related, the difference between a "wet crash" and "hydroplaning" is a wet-crash hydrodynamic-based severity scale is less compared to hydroplaning where the driver loses control. This dissertation presents a new conceptual framework design to reduce wet- and hydroplaning-related crashes by identifying locations with a high risk of crashes using systemic, data-driven, risk-based approaches and available data.
The first method is a robust systemic approach to identify areas with a high risk of wet crashes using a negative binomial regression to quantify the relationship between wet to dry ratio (WDR), traffic, and road characteristics. Results indicate that the estimates are more reliable than current methods of WDR used by DOTs. Two significant parameters are grade difference and its absolute value.
The second method is a simplified approach to identify areas with a high risk of wet crashes with only crash counts by applying a spatial multiresolution analysis (SMA). Results indicate that SMA performs better than current hazardous-road segments identification (HRSI) methods based on crash counts by consistently identifying sites during several years for selected 0.1 km sections.
A third method is a novel systemic approach to identify locations with a high risk of hydroplaning through a new risk-measuring parameter named performance margin, which considers road geometry, environmental condition, vehicle characteristics, and operational conditions. The performance margin can replace the traditional parameter of interest of hydroplaning speed. The hydroplaning risk depends on more factors than those identified in previous research that focuses solely on tire inflation pressure, tire footprint area, or wheel load. The braking and tire-tread parameters significantly affected the performance margin. Highway engineers now incorporate an enhanced tool for hydroplaning risk estimation that allows systemic analysis.
Finally, a critical review was conducted to identify existing solutions to reduce the high potential of skidding or hydroplaning on wet pavement. The recommended strategies to help mitigate skidding and hydroplaning are presented to help in the decision process and resource allocation. Geometric design optimization provides a permanent impact on pavement runoff characteristics that reduces the water accumulation and water thickness on the lanes. Road surface modification provides a temporary impact on practical performance and non-engineering measures.Doctor of Philosophy
Crashes on wet pavements are responsible for 25% of all crashes and 13.5% of fatal crashes in the US (Harwood et al. 1988). This number represents a significant portion of all crashes. Current procedures used by DOTs to identify locations with a high number of wet crashes and hydroplaning are too simple and might not represent actual risk. A fraction of all wet crashes is hydroplaning, although they are related to the difference between a "wet crash" and "hydroplaning" is a wet crash water-vehicle interaction is less compared to hydroplaning where the driver loses control. This dissertation presents a new procedure to evaluate the road network to identify locations with a high risk of wet crashes and hydroplaning. The risk estimation process uses data collected in the field to determine the risk at a particular location and, depending on the available data a transportation agency uses, will be the approach to apply. The first statistical method estimates the frequency of wet crashes at a location. This estimate is developed by using a statistical model, negative binomial regression. This model measures the frequency of dry crashes, wet crashes, traffic, and road characteristics to determine the total number of wet crashes at a location. Results indicate that this option is more reliable than the current methods used by DOTs. They divide the number of wet crashes by the number of dry crashes. Two elements identified to influence the results are the difference in road grade and its absolute value. The second statistical method to estimate wet crashes considers crash counts by applying a statistical process, spatial multiresolution analysis (SMA). Results indicate that SMA performs better than current processes based only on the crash counts. This option can identify the high-risk location for different years, called consistency. The more consistent the method is, the more accurate is the results. A third statistical method is a novel way to estimate hydroplaning risk. Hydroplaning risk is currently based on finding the maximum speed before hydroplaning occurs. A vehicle's performance related to the water-film thickness provides an estimation method developed by (Gallaway et al. 1971), which includes rainfall intensities, road characteristics, vehicle characteristics, and operating conditions. The hydroplaning risk depends on more aspects than tire inflation pressure, tire footprint area, or vehicle load on the wheel. The braking and tire tread affect the performance margin. Highway engineers can use this improved hydroplaning risk-estimation tool to analyze the road network. Finally, a critical review showed the available solutions to reduce the probability of having a wet crash or hydroplaning on wet pavement. The recommended strategies to mitigate wet crashes and hydroplaning provide information to allocate resources based on proven, practical strategies. Road geometry design can be optimized to remove water from the road. This geometry is a permanent modification of pavement characteristics to reduce water accumulation and water thickness on the road. Road surface treatments and non-engineering measures provide temporary measures to improve vehicle performance or driver operation.
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Fsadni, Andrew M. "The fundamentals of two-phase flow in wet domestic central heating systems." Thesis, Brunel University, 2012. http://bura.brunel.ac.uk/handle/2438/6953.
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An emerging trend in the building services industry is the installation of passive deaerators on the flow line of domestic wet central heating systems. To date, no data and theoretical models predicting the two-phase flow characteristics in domestic wet central heating systems are available in the open literature. This gap in literature has prevented essential design improvements to passive deaerators thus impeding the efficiency enhancement of such devices. Hence, the current study is aimed at assisting designers of deaeration devices by providing fundamental data and model correlations with respect to the two-phase flow characteristics typical in a wet domestic central heating system. For this purpose an experimental research project was adopted and several studies were carried out, including; (1) a comprehensive review to understand the background of the phenomena, (2) the design and construction of an experimental test rig to conduct the necessary investigations into the phenomenon of two-phase flow in domestic wet central heating systems, (3) the development of a reliable image capture and analysis technique, (4) the completion of a number of experiments to investigate typical bubble sizes, volumetric void fractions, bubble distributions and nucleation and dissolution rates and (5) the correlation of the data gathered as part of the present study with existing bubble size, nucleation and dissolution prediction models. This research has, for the first time, provided an in depth analysis into two-phase flow characteristics in wet domestic central heating systems through the use of a high speed camera and image analysis techniques. The two-phase phenomenon finds its origins in high dissolved gas concentrations present in the water flowing through the closed loop system, thus resulting in super saturation conditions at the primary heat exchange wall conditions. Bubble sizes at the boiler flow line were found to be dependent on the bulk fluid velocity, heat flux and pressure, with a measured mean diameter in the range of 0.13 mm to 0.39 mm. The Winterton (1972a) force balance model for bubble size prediction was in reasonable agreement with the experimental results. This model was further improved through the correlation of our data with the inclusion of dimensionless groups. Bubble nucleation rates have been calculated in the range of 0.3 to 4 bubbles / cm2 s with total system bubble production rates measured in the range of 784 to 6920 bubbles per second. Bubble nucleation rates have been calculated through the consideration of the heat exchanger surface under super saturation conditions. A correlation for the model by Hepworth et al. (2003) for nonclassical heterogeneous nucleation is proposed based on the experimental data gathered during the present study. Experimental results have shown dissolution rates for the bubble size ratio in the range of 0.4 to 12 % per second with system conditions. A modification of the model developed by Epstein and Plesset (1950) for stationary bubble dissolution is proposed with the inclusion of the Sherwood number to capture the effects of turbulent diffusion. The volumetric void fraction distribution in vertical pipes was found to be quasi-homogenous across the pipe section while being strongly dependent on gravitational and turbulence effects in horizontal pipe bubbly flow. A CFD simulation predicted the volumetric void fraction distribution with reasonable accuracy.
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McGillen, J. G. "Studies on the wet spinning of cellulose fibres from novel solvent systems." Thesis, University of Strathclyde, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372448.
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VILLELA, MARCOS JOSE REI. "TEMPERATURE BEHAVIOR ANALYSIS OF OIL PRODUCTION SYSTEMS: DRY AND WET COMPLETION COMPARISON." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2004. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=6084@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCerca de 50 por cento das reservas brasileiras de hidrocarbonetos estão localizadas na plataforma continental em lâminas de água superiores a mil metros. As temperaturas congelantes do fundo do mar tornam os problemas inerentes ao escoamento da produção de petróleo, ainda mais críticos. Entretanto, os desafios da garantia de escoamento, não são os únicos obstáculos para a produção de petróleo em águas ultra-profundas. Além dos aspectos relacionados à geologia e fatores econômicos, a decisão de desenvolvimento de um campo de petróleo no mar, adotando completação submarina ou seca, precisa ser respaldada por uma análise criteriosa dos problemas relacionados com a garantia de escoamento, principalmente em locações de águas profundas e ultra- profundas. Nestes cenários, a maior variação da energia potencial e conseqüente intensificação do efeito Joule-Thomson, contribuem de uma forma bem mais significativa para a queda de temperatura e pressão. Este trabalho objetiva promover a comparação entre um sistema de produção usando poços direcionais de grande afastamento, produzindo para uma unidade de completação seca e um sistema adotando poços com completação submarina, a 850, 1.550 e 2.300m de lâmina de água, avaliando os efeitos das perdas de carga e calor em um fluxo multifásico. Com o uso de completação molhada, é avaliada a máxima distância viável entre a zona produtora e a plataforma de produção, de forma a permitir o fluxo de hidrocarbonetos sem formação de cristais de parafina. Com base nos resultados alcançados, podemos tirar algumas conclusões importantes quanto à tendência dos sistemas de produção em águas profundas e ultra- profundas, que nortearão no futuro próximo o desenvolvimento de campos de petróleo na plataforma continental brasileira.
Around 50 percent of the Brazilian reserves of hydrocarbons are located in the continental platform in water depths with more than one thousand meters. The freezing temperatures of the sea bottom make problems related to oil production, even more critical. However, the flow assurance challenges are not the only obstacles for the oil production in ultra-deep waters. Besides the aspects related to the geology and economical factors, the decision of development of an offshore oil field adopting a system with wet completion or with dry completion, needs to be supported by discerning analyses of the problems related to flow assurance aspects, mainly in deep and ultra-deep water locations. In these scenarios, a larger variation of the potential energy and consequent intensification of the Joule-Thomson effect, contribute in a much more significant way to the temperature and pressure drops. This work aims to promote the comparison between an oil production system using extended reach wells with a dry completion unit and another system with wet completion, at 850, 1.550 and 2.300m of water depth, evaluating the effects of pressure drop and heat loss in a multiphase flow. Using wet completion, it is evaluated the maximum feasible distances between the producing zone of the formation and the floating production unit, allowing the flow of hydrocarbons without interruption by the formation of paraffin crystals. Based on the reached results, we can reach some important conclusions regarding trend of production systems in deep and ultra-deep water, that will guide the development of oil fields in the near future in the Brazilian continental platform.
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Ryazanov, Andrey. "Pore scale network modelling of residual oil saturation in mixed-wet systems." Thesis, Heriot-Watt University, 2012. http://hdl.handle.net/10399/2546.
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The prediction of residual oil saturation (Sor) and relative permeabilities after waterflooding in mixed-wet systems is a very challenging task. These are important parameters which must be estimated for a full field simulation of waterflooding. The Sor also defines the target oil for any proposed EOR process after an initial waterflood. Pore-scale network modelling can be used to estimate relative permeabilities, and the amount and nature of the trapped residual oil if the correct physics of oil displacement are properly included. During the waterflooding of mixed-wet systems, oil may drain down to relatively low residual saturations. Such Sor levels can only be calculated correctly when oil layers in pore corners are included in the pore-scale modelling. van Dijke and Sorbie (J. Coll. Int. Sci. 293 (2006) 455) obtained an accurate thermodynamically derived criterion for oil layers’ existence in pores with non-uniform wettability caused by ageing, which is more restrictive than the previously used geometrical layer existence criterion. This thermodynamic criterion has been included in a newly developed two-phase pore network model to calculate realistic Sor values for mixed-wet sandstones. A new ncornered star pore shape characterization technique has also been implemented in this model since the precise description of the pore shape was found to be important. Two unstructured networks, derived from Berea sandstone have been used for a number of sensitivities of the Sor and relative permeabilities with respect to wettability conditions. It is shown that Sor is lower for the more strongly oil-wet cases, while the water relative permeability curves increase gradually with oil-wetness at the higher water saturations. It has also been shown that pore shape approximations and oil layers collapse criterion have a significant impact on the Sor and the relative permeabilities. In particular, the thermodynamic oil layer existence criterion gives higher and more realistic Sor compared to previously used geometrical criterion. The network modelling has been used to match experimental data for water-wet and mixed-wet systems. In particular, the good agreement with mixed-wet systems strongly indicates that using the correct oil layer existence criteria is a significant step forward in the reliable prediction of Sor.
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Pawtowski, E. C. "Development of the second-generation IMTS (Intelligent Monitoring and Trending System) and WOT (Wizard of Tech) expert system for rotating machinery." Thesis, This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-10022008-063235/.
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Badr, Lamya. "A Comparative Study of Cooling System Parameters in U.S. Thermoelectric Power Plants." Thesis, Virginia Tech, 2010. http://hdl.handle.net/10919/72990.
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As the importance of water use in the power generation sector increases across the nation, the ability to obtain and analyze real power plant data is pivotal in understanding the water energy nexus. The Navajo Generating Station in Arizona and the Browns Ferry Nuclear Plant in Alabama are examples of where water shortages have threatened the operation of power generators. The availability of freshwater in the United States is beginning to dictate how and where new power plants are constructed. The purpose of this study is to provide and analyze cooling system parameters using 2008 data provided by the Energy Information Administration. Additionally, the cost of water saved among different categories of power plants is calculated. In general, the conditions which cause cooling systems to withdraw less water are not necessarily the more expensive conditions, and vice versa. While not all the variability in the cost of cooling systems is being accounted for, the results from this study prove that nameplate capacity, capacity factor, age of power plant, and region affect the costs of installed cooling systems. This study also indicates that it would be most cost effective for once-through cooling systems to be replaced with recirculating- pond instead of recirculating- tower systems. The implications of this study are that as power plant owner's struggle in balancing cost with water dependence, several parameters must first be considered in the decision-making process.Master of Science
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Renga, Simonetta. "Unemployment, social security system, new working patterns : the capitalist answer to the 'giant' of want." Thesis, University of Bristol, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328067.
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Liljegren, Marcus, and Edin Ljeskovica. "Predicting drag losses & oil flow characteristics in a wet clutch system using numerical analysis." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-60374.
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This report presents the Master Thesis done by two students at the Mechanical Engineering program, Design Engineering at Luleå University of Technology. The thesis was performed at Luleå University of Technology in collaboration with BorgWarner PDS located in Landskrona. The objective for the thesis was to study the potential for predicting and optimizing drag losses and oil flow characteristics in a wet clutch system using numerical simulations in LS-DYNA. BorgWarner PDS manufactures and distributes the Haldex coupling, which is an electro-hydraulic coupling used in an active four-wheel drive system. BorgWarner PDS strives to make the Haldex coupling more efficient by minimizing energy losses in order to lower fuel consumption for the vehicle and a smaller impact on the environment. As testing on prototypes are costly and time consuming it is therefore desirable to use numerical simulations instead. To determine the potential for numerical simulations to predict and optimize both drag losses and oil flow characteristics a numerical model was set up using LS-DYNA. A test rig was designed in order to achieve a controlled testing environment in order to validate the numerical models, both qualitatively and quantitatively. The numerical model uses the built in Fluid Structure Interaction method in LS-DYNA, which is a combination of a structural model and an incompressible fluid model. The test rig measures torque on the clutch housing induced by the dragging of oil as the clutch drum rotates. The tests were performed using different rotational speeds, varying from 250-1500 rpm, and different clutch housing geometries. The results were gathered from an average of ten measurements of the drag torque. A high- speed camera was also used to capture the oil flow characteristics. The numerical simulations were done using the same parameters used for the tests i.e. different rotational speeds and clutch housing geometries. In addition, each simulation was performed using different mesh sizes; 0.5 mm, 1 mm and 2 mm in order to analyze mesh dependence. The numerical model was set to measure the drag torque on the clutch drum and was then compared to the experimental results in order to validate the numerical model quantitatively. The oil flow characteristics from the numerical simulation were compared to the high-speed movies to validate the numerical model qualitatively. The numerical model shows promising results when it comes to predicting drag torque and oil flow characteristics. The results also show that using a numerical model for optimization purposes are possible as the experimentally measured drag torque at different clutch house geometries corresponds to the numerically simulated drag torque. The conclusions from this Master Thesis is that numerical simulations do have a potential for predicting drag losses and oil flow characteristics in a wet clutch system. The numerical model created in this project can also be used to obtain valuable information about geometry changes when it comes to optimizing the wet clutch system. However, the numerical model is still at an early stage and can be seen as a second generation model where further work needs to be done in order to include more of the complex geometries of a wet clutch system have. Although LS-DYNA is state-of-the-art when it comes to these kinds of complex simulations it still needs to be developed further to handle such complex simulations.
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Melichar, Heather J. "SOX13, A γδ T Cell-Specific Gene, Is a WNT-Signaling Antagonist Regulating T Cell Development: A Dissertation." eScholarship@UMMS, 2006. https://escholarship.umassmed.edu/gsbs_diss/251.
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Mature αβ and γδ T cells arise from a common precursor population in the thymus. Much debate has focused on the mechanism of T cell lineage choice made by these multi-potential precursor cells. It is widely believed that the decision of these precursor cells to commit to the γδ or αβ T cell lineages is regulated primarily by a specific instructive signal relayed through the appropriate T cell receptor. Contrary to this model, we present evidence for a TCR-independent lineage commitment process. Comparison of global gene expression profiles from immature αβ and γδ lineage thymocytes identified Sox13, an HMG-box transcription factor, as a γδ T cell-specific gene. Unlike other HMG-box transcription factors such as TCF1, LEF1 and SOX4, that are critical for proper αβ T cell development, Sox13 expression is restricted to early precursor subsets and γδ lineage cells. Importantly, SOX13 appears to influence the developmental fate of T cell precursors prior to T cell receptor expression on the cell surface. Transgenic over-expression of Sox13 in early T cell precursors strongly inhibits αβ lineage development, in part, by inhibiting precursor cell proliferation and concomitantly, leading to increased cell death among αβ lineage subsets. Steady-state γδ T cell numbers, however, appear unaffected. Strikingly, the DP αβ lineage cells that do develop in Sox13 transgenic mice are imprinted with a γδ- or precursor-like molecular profile, suggesting that SOX13 plays an active role in the lineage fate decision process or maintenance. Sox13-deficient mice, on the other hand, have selectively reduced numbers of γδ thymocytes, indicating that SOX13 is essential for proper development of γδ T cells. We present additional data demonstrating that SOX13 is a canonical WNT signaling antagonist modulating TCF1 activity, raising a strong possibility that WNT signals, and their modulators, are at the nexus of γδ versus αβ T cell lineage commitment.
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Foster, Michelle Tranace. "Central Nervous System Regulation of Fat Cell Lipid Mobilization: The Role of the Sympathetic Nervous System." Digital Archive @ GSU, 2006. http://digitalarchive.gsu.edu/biology_diss/2.
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Obesity is a growing disorder in the United States, affecting over 60% of the population. We previously defined sympathetic nervous system (SNS) outflow from brain to white adipose tissue (WAT) using a viral transneuronal tract tracer. SNS innervation of WAT is the principle initiator of lipolysis, whereas decreases in sympathetic drive promote lipid accumulation. Which of the many origins of SNS outflow from brain to WAT results in SNS-mediated changes in lipid mobilization (increases in drive) or accumulation (decrease in drive) is unknown. Previous research indicates that sympathetic denervation blocks lipid mobilization; thus, rostral sites in the neuroaxis connected to WAT via the SNS may promote WAT lipid mobilization. The hypothalamic paraventricular nucleus (PVN) may play a role via its descending projections to the intermediolateral horn of the spinal cord. Therefore, the consequences of PVN lesions (PVNx) on WAT mobilization or accumulation were tested. PVNx resulted in increased lipid accumulation, indicated by increases in retroperitoneal (RWAT) , epididymal (EWAT) , and inguinal WAT (IWAT) pad masses, in fed hamsters, but PVNx did not block fasting (56 h)-induced lipid mobilization. Because adrenal medullary catecholamines, especially epinephrine, also play a minor role in lipid mobilization, we tested the contribution of catecholamine release on lipid mobilization through adrenal demedullation (ADMEDx), with and without PVNx, and found fastinginduced lipid mobilization was not blocked. There was, however, a suggestion that distal denervation of IWAT, with and without ADMEDx, partially blocked lipid mobilization. In addition, evidence suggests SNS also may be an important controller of fat cell proliferation. Surgical denervation of WAT triggers increases in fat cell number (FCN), but have not determined if this FCN increase is due to preadipocyte proliferation or differentiation of preadipocytes into mature fat cells. We also have not demonstrated what role sensory innervation may have in regulating white adipocyte proliferation. Therefore, the role of WAT sympathetic or sensory innervation on adipocyte proliferation was tested. The SNS but not sensory denervation triggered bona fide proliferation as indicated by bromodeoxyuridine plus AD3, a specific adipocyte membrane protein, colabeling. These and previous data suggest that the SNS plays a role in regulating adiposity.
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Wat, Chi Ling Elaine. "Dietary milk phospholipids and their effects on cardiovascular risk factors / Chi Ling Elaine Wat." Thesis, The University of Sydney, 2009. https://hdl.handle.net/2123/28853.
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Cardiovascular disease is responsible for a significant portion of morbidity and mortality in Australia. The metabolic syndrome, which is the clustering of cardiometabolic risk factors, is well known to be associated with increased risk of CVD. There is thus great interest in treating and preventing this metabolic disease. Pharmaceutical approaches
to the treatment of the metabolic syndrome to this date have been inadequate. Increasing evidence suggests that dietary PLs may be potentially cardioprotective. The aim of this thesis is therefore to investigate the possibility that PLs can be extracted from dairy milk, and to identify and characterise the potent ability of dairy milk PLs to
be used to treat and/or prevent CVD.