Thèses : « Regulation of the mode of division »

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Mida, Baptiste. « Un nouveau rôle de CDKN1C dans le contrôle de la transition des modes de division au cours de la neurogenèse des vertébrés ». Electronic Thesis or Diss., Sorbonne université, 2023. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2023SORUS371.pdf.

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Le système nerveux central des vertébrés est constitué d’un assemblage complexe de nombreux types cellulaires, qui se développent à partir d’un réservoir limité de cellules souches neuroépithéliales. Pendant la neurogenèse, la transition progressive du mode de division des cellules progénitrices de symétrique prolifératif (SYM - produisant deux progéniteurs) vers asymétrique neurogénique (ASYM - produisant un neurone et un progéniteur) contrôle l’équilibre entre croissance et différenciation. Certains travaux pionniers ont montré que les progéniteurs SYM et ASYM diffèrent au niveau transcriptomique, suggérant que cette transition de SYM vers ASYM est placée sous un contrôle génétique spécifique. Par exemple, l’expression du facteur de transcription Tis21 est initiée dans les progéniteurs neuraux lors de la transition d’un mode de division SYM vers ASYM. Mon projet de thèse a eu pour objectif d’identifier de nouveaux acteurs et régulateurs de la transition SYM vers ASYM, et de valider fonctionnellement le rôle de ces candidats dans la régulation de cette transition. A travers l’analyse de données de RNA-seq à l’échelle cellule-unique provenant de tubes neuraux d’embryons de poulet et souris en développement, j’ai identifié en partenariat avec une équipe de bio-informaticiens (Morgane Thomas-Chollier, Nathalie Lehmann, IBENS) plusieurs gènes candidats à la régulation de la transition du mode de division, selon 2 critères : 1) l’expression différentielle du gène entre progéniteurs Tis21-positifs et négatifs et 2) un profil d’expression pseudo-temporel similaire à celui de Tis21 au cours de la neurogenèse. Parmi ces gènes, je me suis focalisé sur l’étude de CDKN1C (p57Kip2) qui jusqu’à présent avait été décrit principalement comme un régulateur négatif du cycle cellulaire. Mes travaux ont montré l’expression progressive de l’ARNm de CDKN1C dans la région ventrale du tube neural embryonnaire de poulet en développement, suggérant fortement une expression de CDKN1C dans les progéniteurs. J’ai également montré que la perte de fonction in vivo de CDKN1C (via shRNA) diminue la neurogenèse à l’échelle tissulaire, et favorise la prolifération des progéniteurs neuraux. L’exploration de ce phénotype a montré que les progéniteurs présentant une expression diminuée de CDKN1C ont une durée moyenne de cycle cellulaire plus courte, notamment due à une réduction de la durée de la phase G1, comparée à celle des progéniteurs sauvages. A travers une analyse clonale de la descendance de progéniteurs, j’ai ensuite montré que la diminution de l’expression de CDKN1C dans ces progéniteurs favorisait le mode de division SYM. Enfin, dans le but de déterminer si l’effet de CDKN1C sur le mode de division dépendait de son rôle régulateur du cycle cellulaire, et en particulier de la durée de G1, j’ai combiné une diminution d’expression de CDKN1C à une diminution de l’expression de la Cycline D1, qui devrait quant à elle allonger la durée de G1. Cette perte de fonction combinée permet de restaurer le phénotype observé après la diminution seule de CDKN1C, à l’échelle tissulaire et cellulaire, indiquant que le rôle de CDKN1C dans le contrôle du mode de division semble s’effectuer principalement à travers son rôle de régulateur négatif du cycle cellulaire. Dans l'ensemble, mon projet suggère un nouveau rôle de CDKN1C dans la régulation de la transition SYM-ASYM, et contribue à élucider les mécanismes fondamentaux qui régulent cette transition et donc l'équilibre entre prolifération et différenciation dans les progéniteurs neuraux au cours de la neurogenèse
The vertebrate central nervous system (CNS) is produced from a limited reservoir of neuroepithelial stem cells, which initially amplify through symmetric proliferative divisions (SYM) in which one progenitor produces two progenitors. Progressively, progenitors engage in an asymmetric neurogenic mode of division (ASYM), producing one progenitor and one neuron. Finally, symmetric terminal divisions (TERM) produce two neurons. The fine regulation of these division patterns is crucial for proper brain development, and alteration of these processes can lead to excessive proliferation or, conversely, generate early differentiation into neurons. In the developing CNS, SYM, ASYM and TERM modes of division appear in a sequential order within cell clones, indicating that transitions between modes of division are definitive, and correspond to compartmentalized cell states. Moreover, some pioneering works have shown that SYM and ASYM progenitors differ at the molecular level, notably at the transcriptomic level, suggesting that this transition from SYM to ASYM is under a specific genetic control. For example, the expression of the transcription factor Tis21 begins in neural progenitors during the transition from a proliferative to a neurogenic mode of division. My thesis project aimed at identifying new actors and regulators of the SYM to ASYM transition, at the border between proliferation and differentiation, and to functionally validate the role of these candidates in the regulation of this transition. Through the analysis of single-cell RNA-seq data from neural tubes of developing chick and mouse embryos, I identified in partnership with a team of bioinformaticians (Morgane Thomas-Chollier, Nathalie Lehmann, IBENS) several candidate genes in the regulation of the transition of the mode of division, according to 2 criteria: 1) a differential gene expression between Tis21-positive and negative progenitors and 2) a pseudo-temporal expression profile similar to the one of Tis21 during neurogenesis. Among these genes, I focused on the study of CDKN1C (p57Kip2) which until now had been described mainly as a negative regulator of the cell cycle. My work showed the progressive expression of CDKN1C mRNA in the ventral region of the developing chick embryonic neural tube, strongly suggesting the expression of CDKN1C in progenitors. I also showed that in vivo loss of function of CDKN1C (via shRNA) unfavors neurogenesis at the tissue level, and promotes neural progenitor proliferation. Exploration of this phenotype showed that progenitors with decreased CDKN1C expression have a shorter cell cycle duration on average, notably due to a reduction in the duration of the G1 phase, compared to wild-type progenitors. Through clonal analysis of the progenitors’ progeny, I then showed that decreased CDKN1C expression in progenitors favoured the SYM mode of division. Finally, in order to determine whether the effect of CDKN1C on the mode of division was dependent on its role in the cell cycle, I sought to counterbalance the decrease in G1 duration observed upon CDKN1C loss-of-function. To do so, I decreased the expression of Cyclin D1 in order to lengthen the duration of G1. The combined loss of function of CDKN1C and Cyclin D1 shows an almost complete rescue of the phenotype generated by the decrease in CDKN1C alone, at both the tissue and cellular levels, indicating that the role of CDKN1C in controlling the division mode seems to be directed mainly through its role as a negative regulator of the cell cycle. Overall, my project suggests a novel role for CDKN1C in the regulation of the SYM-ASYM transition, and contributes to elucidate the fundamental mechanisms that regulate this transition and thus the balance between proliferation and differentiation in neural progenitors during neurogenesis

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Šćepanović, Danilo (Danilo R. ). « A model of sinoatrial node cell regulation by the autonomic nervous system ». Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/68457.

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Thesis (Ph. D.)--Harvard-MIT Division of Health Sciences and Technology, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 243-260).
The primary function of the heart is to pump blood at a sufficient rate to ensure perfusion of all the organs. This vital task is achieved in large part by controlling the rate of cardiac contractions, which are initiated by cells in the sinoatrial node, the "pacemaker" of the heart. The oscillation rate of these spontaneously active cells is tightly regulated by the sympathetic and parasympathetic branches of the autonomic nervous system. Our understanding of sinoatrial node cell function has been greatly advanced by experimental and modeling efforts that quantitatively describe the numerous ionic currents responsible for the cell's spontaneous depolarization and generation of the action potential. Several models have also explored the effect of sympathetic and parasympathetic activity on specific ion channels and have reproduced the classic slowing and acceleration phenomena. However, a complete model of this interaction does not exist: current models lack the ability to simulate simultaneous sympathetic and parasympathetic activation or to reproduce heart rate dynamics in response to time-varying autonomic inputs. We addressed this need by constructing a bottom-up model of sinoatrial node cell regulation by the autonomic nervous system, with a focus on reproducing the full range of heart rates observed under simultaneous sympathetic and parasympathetic nerve stimulation, as well as the dynamic heart rate response to steps in sympathetic or parasympathetic stimulation rate. In constructing our model, we consolidate a large body of experimental data in a consistent mathematical framework. The model comprises 57 nonlinear coupled ordinary differential equations based on first principles and the current mechanistic understanding of the component reactions, fits well all the experimental data used to build the model, and reproduces high-level features of the system that were not explicitly fit when building the model. The detailed nature of the model also allows numerous conclusions to be drawn about the mechanisms of heart rate control. A better understanding of these mechanisms in health and disease may enable the development of better diagnostics for cardiovascular disease and more targeted drug design. We also identified a number of limitations in the present model that can be refined through further experimental and numerical efforts.
by Danilo Šćepanović.
Ph.D.

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Jenkins, Jesse D. (Jesse David). « Economic regulation of electricity distribution utilities under high penetration of distributed energy resources : applying an incentive compatible menu of contracts, reference network model and uncertainty mechanisms ». Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/90052.

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Thesis: S.M. in Technology and Policy, Massachusetts Institute of Technology, Engineering Systems Division, Technology and Policy Program, 2014.
Cataloged from PDF version of thesis.
Includes bibliographical references.
Ongoing changes in the use and management of electricity distribution systems - including the proliferation of distributed energy resources, smart grid technologies (i.e., advanced power electronics and information and communication technologies) and active system management techniques - present new challenges for the economic regulation of electricity distribution utilities. In particular, regulators are likely to face increased uncertainty regarding the evolution of network uses and the efficient cost of network investments and maintenance, as well as an increased informational disadvantage vis-a-vis the regulated utility. These challenges are especially important for regulatory approaches that establish some share of the utility's allowed revenues ex ante (e.g., incentive regulation, also known as revenue or price cap regulation, RPI-X, performance-based regulation, or output-based regulation). This thesis proposes a novel process for establishing the allowed revenues of an electricity distribution utility and demonstrates its application as a practical solution to the imminent regulatory challenges discussed above. The proposed method is a new combination of three established regulatory tools: an engineering-based reference network model (RNM) for forward-looking benchmarking of efficient network expenditures; an incentive compatible menu of contracts to elicit accurate forecasts from the utility and create incentives for cost saving efficiency efforts; and ex post automatic adjustment mechanisms, or "delta factors," to accommodate uncertainty in the evolution of network use and minimize forecast error. Chapter 1 reviews the theoretical economic foundations of the regulation of network monopolies, identifies emerging challenges in the regulation of electricity distribution companies, and introduces the proposed regulatory method. Chapter 2 describes the simulation of a realistic, large-scale urban distribution network used to demonstrate the novel regulatory process proposed in this thesis. Chapter 3 uses the simulated distribution network to demonstrate, step-by-step, the practical implementation of the novel regulatory process, evaluates its performance, and summarizes the advantages for the economic regulation of electricity distribution utilities under increasing penetration of distributed energy resources.
by Jesse D. Jenkins.
S.M. in Technology and Policy

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Bai, Neng. « Mode-Division Multiplexed Transmission in Few-mode Fibers ». Doctoral diss., University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5761.

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As a promising candidate to break the single-mode fiber capacity limit, mode-division multiplexing (MDM) explores the spatial dimension to increase transmission capacity in fiber-optic communication. Two linear impairments, namely loss and multimode interference, present fundamental challenges to implementing MDM. In this dissertation, techniques to resolve these two issues are presented. To de-multiplex signals subject to multimode interference in MDM, Multiple-Input-Multiple-Output (MIMO) processing using adaptive frequency-domain equalization (FDE) is proposed and investigated. Both simulations and experiments validate that FDE can reduce the algorithmic complexity significantly in comparison with the conventional time-domain equalization (TDE) while achieving similar performance as TDE. To further improve the performance of FDE, two modifications on traditional FDE algorithm are demonstrated. i) normalized adaptive FDE is applied to increase the convergence speed by 5 times; ii) master-slave carrier recovery is proposed to reduce the algorithmic complexity of phase estimation by number of modes. Although FDE can reduce the computational complexity of the MIMO processing, due to large mode group delay (MGD) of FMF link and block processing, the algorithm still requires enormous memory and high hardware complexity. In order to reduce the required tap length (RTL) of the equalizer, differential mode group delay compensated fiber (DMGDC) has been proposed. In this dissertation, the analytical expression for RTL is derived for DMGDC systems under the weak mode coupling assumption. Instead of depending on the overall MGD of the link in DMGD uncompensated (DMGDUC) systems, the RTL of DMGDC systems depend on the MGD of a single DMGDC fiber section. The theoretical and numerical results suggest that by using small compensation step-size, the RTL of DMGDC link can be reduced by 2 orders of magnitude compared to DMGDUC link. To compensate the loss of different modes, multimode EDFAs are presented with re-configurable multimode pumps. By tuning the mode content of the multimode pump, mode-dependent gain (MDG) can be controlled and equalized. A proto-type FM-EDFA which could support 2 LP modes was constructed. The experimental results show that by using high order mode pumps, the modal gain difference can be reduced. By applying both multimode EDFA and equalization techniques, 26.4Tb/s MDM-WDM transmission was successfully demonstrated. A brief summary and several possible future research directions conclude this dissertation.
Ph.D.
Doctorate
Optics and Photonics
Optics and Photonics
Optics

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Carpenter, Joel Anthony. « Holographic mode division multiplexing in optical fibres ». Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610803.

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Spanoudis, Catherine M. « Cell Division Regulation in Staphylococcus aureus ». Scholar Commons, 2017. http://scholarcommons.usf.edu/etd/7090.

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Cell division is a fundamental biological process that occurs in all kingdoms of life. Our understanding of cell division in bacteria stems from studies in the rod-shaped model organisms: Gram-negative Escherichia coli and Gram-positive Bacillus subtilis. The molecular underpinnings of cell division regulation in non-rod-shaped bacteria remain to be studied in detail. Rod-shaped bacteria possess many positive and negative regulatory proteins that are essential to the proper placement of the division septa and ultimately the production of two identical daughter cells, many of which are absent in cocci. Given that essential cell division proteins are attractive antibacterial drug targets, it is imperative for us to identify key cell division factors especially in pathogens, to help counter the emergence of multi-drug resistance. In Staphylococcus aureus, a spherical Gram-positive opportunistic pathogen that causes a range of diseases from minor skin infections to life-threatening sepsis, we have identified the role of an essential protein, GpsB, in the regulation of cell division. We discovered that GpsB preferentially localizes to cell division sites and that overproduction of GpsB results in cell enlargement typical of FtsZ inhibition, while depletion of GpsB results in cell lysis and nucleoid-less minicell formation. The identification of GpsB’s interaction partners will allow us to understand the molecular mechanism by which GpsB regulates cell division.

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Kirby, Melissa Jane. « Regulation of sugar beet cell division ». Thesis, De Montfort University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.391029.

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Dewar, Susan J. « Cell division in Escherichia coli : the expression and regulation of division genes ». Thesis, University of Edinburgh, 1988. http://hdl.handle.net/1842/13636.

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The four essential cell division genes ftsQ, ftsA, ftsZ, and envA are arranged sequentially within a large cluster of genes required for cell envelope growth and form. The bacteriophage λJFL100 carries the 1.8 kilobase EcoR1-HindIII chromosomal restriction fragment which spans the ftsQ and part of ftsA coding sequences. This fragment contains at least two promoters; one within ftsQ is required for the expression of ftsA and one within ftsA is required for expression of ftsZ. The fts fragment is cloned upstream of a lacZ gene so that transcription originating from within the fragment leads to the production of β-galactosidase. Expression from the fts promoters in cells lysogenic for the phage is shown to be derepressed in the absence of FtsA protein. The results presented here suggest that transcription from these promoters is linked to the cell's periodic requirement for FtsA protein during septum formation. The exact positions of the promoters within the group are not yet known although their approximate locations have been determined by promoter assay and sequence analysis. An attempt has been made to define the position of the ftsA promoter more precisely by in-vitro transcription from short, defined templates and by the sequential deletion of ftsQ. Serial deletion through ftsQ has revealed what appears to be a complex upstream regulatory region, reminiscent of a eukaryotic enhancer element, which influences the expression of ftsA. A model is presented for the transcriptional control of ftsA expression.

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Federici, Fernán. « Hormonal regulation of cell division in roots ». Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608578.

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Benyahya, Kaoutar. « Mode group division multiplexing for short reach optical communications ». Thesis, Rennes 1, 2019. http://www.theses.fr/2019REN1S117.

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La demande croissante du trafic de données sera alimentée par des technologies révolutionnaires telles que la réalité virtuelle (VR), la réalité augmentée (AR) et l’Internet des objets (IoT). Par conséquent, les réseaux optiques devraient répondre aux besoins de ces services en termes de débit, faible temps de réponse et grande fiabilité. En effet, les hauts débits représentent un besoin critique pour les systèmes de communication à fibre optique déployés dans les réseaux locaux ainsi que dans les centres de données. Pour ces deux applications, les systèmes basés sur la modulation d'intensité et la détection directe de cette dernière sont très attractifs en raison de leur faible coût et de leur compatibilité avec les applications à courte distance. Dans le cadre de cette thèse, nous répondons à la nécessité d’augmenter les débits pour les systèmes de communication optiques à courte distance basés sur le multiplexage de groupe de modes et la détection directe. Tout d'abord, nous visons à augmenter la capacité des fibres multimodes standard déjà déployées dans les réseaux locaux et à l’intérieur des centres de données où la distance est inférieure à 5 km. Deuxièmement, nous étendons notre solution aux applications avec des distances de déploiement plus longues telles que les connexions entre les centres de données. Dans les deux cas, les architectures des liens optiques, y compris les émetteurs, les récepteurs et les fibres optiques, sont analysées. De plus, les formats de modulation adaptés aux systèmes basés sur la détection directe tels que le format de modulation mono-porteuse 4-PAM et celui multi-porteuse DMT sont comparés dans le contexte de la transmission basée sur le multiplexage spatial. Nous avons démontré les avantages du multiplexage de groupes de modes combiné à la détection directe pour augmenter le débit transmit sur une seule fibre. Premièrement, 5 Tb / s ont été démontré sur 2,2 km de fibre multimode conventionnelle (OM2). Deuxièmement, un record de transmission de 14,5 Tb / s sur fibre OM2 est démontré au moment correspondant à sa réalisation. Enfin, 200 Gb / s sur 20 km de fibre faiblement multimode (FMF) a été démontré, ce qui étend les avantages du multiplexage par groupes de modes aux applications à longue distance par rapport aux réseaux LAN où la distance maximale est limitée à 5 km
The ever-growing demand of data traffic will be fuelled by revolutionary technologies such as virtual reality (VR), augmented reality (AR) and Internet of things (IoT). Therefore, optical networks should support the requirements of these services in terms of high capacity, low latency and high reliability. In fact, large scale capacity is a critical need for fiber optic communication systems deployed in local area networks as well as in datacenters. For both applications, systems relying on intensity modulation and direct detection (IMDD) are highly demanded due to their low cost and compatibility with short range applications. In this thesis, we address the need of increasing the data rates for short reach optical communication systems based on mode group division multiplexing and direct detection schemes. Firstly, we focus on increasing the capacity of already deployed standard multimode fibers in local area networks and intra-datacenters communication where the distance is shorter than 5 km. Secondly, we extend our solution to longer reach applications such as inter-datacenter interconnects. In both cases, optical link architectures, including transmitters, receivers and the optical fibers are analysed. Moreover, modulation formats adapted to IMDD systems such as single carrier 4-PAM and multicarrier DMT are compared in the context of space division multiplexing transmission. In this work we demonstrated the achievable benefit of mode group multiplexing combined with IMDD schemes. First, 5 Tb/s has been achieved over 2.2 km of conventional multimode fiber (OM2). Secondly, transmission record at the corresponding time of its realization of 14.5 Tb/s over OM2 fiber is demonstrated. Finally, 200 Gb/s over 20 km of FMF has been achieved which extend the benefit of mode group multiplexing to longer reach applications compared to LAN and intra-datacenter where the maximum distance is limited to 5 km

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Berry, David (David A. ). « Glycosaminoglycan regulation of cell function ». Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/34153.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Biological Engineering Division, 2005.
Includes bibliographical references (p. 252-285).
Glycosaminoglycans (GAGs) are complex polysaccharides that exist both on the cell surface and free within the extracellular matrix. The intrinsic sequence variety stemming from the large number of building blocks that compose this biopolymer leads to substantial information density as well as to the ability to regulate a wide variety of important biological processes. With the recent and progressive emergence of biochemical and analytical tools to probe GAG structure and function, efforts can be taken to understand the role of GAGs in cell biology and in disease in the various physiological locations where GAGs can exist. As a first step to probe the functions of GAGs, the heparin/heparan sulfate-GAG (HSGAG)-fibroblast growth factor (FGF) system was examined. Understanding the role of HSGAGs in inducing FGF2 dimerization led to the development of a novel engineered protein that was found to be effective at promoting functional recovery in stroke. Subsequently, methods to isolate HSGAGs from the cell surface were optimized and the ability of HSGAGs to support FGF signaling was investigated. Cell surface HSGAGs can define the responsiveness of a given cell to FGF1 and FGF2 through multiple receptor isoforms. Stromal cell derived HSGAGs were also identified as critical regulators of tumor cell growth and metastasis, effecting not only FGF2., but also 1-integrin signaling.
(cont.) Other GAGs, including dermatan sulfates, were characterized as modulators of FGFs and vascular endothelial growth factors. Finally, FGFs and HSGAGs were found to have important roles in maintaining epithelial monolayer integrity, with syndecan-l serving as a critical factor in inflammatory bowel disease. In addition to understanding HSGAGs in their normal physiological settings, techniques to internalize them were developed. Poly(3-amino ester)s were found to condense heparin and enable its endocytosis into cells. Internalized heparin is preferentially taken up by cancer cells, which often have a faster endocytic rate than non-transformed cells, and promotes apoptotic cell death. Internalized heparin can also be used as a tool to probe cell function. In Burkitt's lymphoma, poly(3-amino ester)-heparin conjugates served to identify cell surface HSGAGs as an important modulator of cell growth that can be harnessed to inhibit growth. Finally, studies that sought to broaden the scope of GAG biology were undertaken. Cell surface HSGA(:is were identified as mediators of vascular permeability. Furthermore a novel technique to immobilize GAGs was employed. The interactions between GAG and substrate were via hydrogen bonding. Immobilization of GAGs alters their properties, such that they can affect cells in ways distinct from GAGs free in the ECM.
(cont.) Furthermore, immobilized GAGs can regulate cancer cell adhesion, growth and progression, and may offer a new way to regulate the activity of cancer cells. In addition to directly providing new potential therapeutics and drug targets, these studies represent a foundation to enable additional studies of GAG function. Future work harnessing the techniques presented may open new avenues of research and facilitate the development of novel GAG-based therapeutics.
by David Berry.
Ph.D.

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Geddes, Auste. « Antisense regulation of cell division in Escherichia coli ». Thesis, University of Edinburgh, 2002. http://hdl.handle.net/1842/13882.

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BACKGROUND: FtsZ is an essential cell division protein in bacteria. It is involved in the initiation, timing, and frequency of cell divisions. Consequently it is subject to strict regulation, including transcriptional and post-transcriptional control and protein inhibition. Regulation of ftsZ expression by an antisense RNA has also been proposed. Dewar and Donachie suggested that there is a gene stfZ encoded by the antisense strand of DNA at the ftsA-ftsA gene junction in the mra gene cluster of the Escherichia coli chromosome. Multiple copies of the DNA fragment containing the stfZ gene block cell division. Since an RNA transcribed from stfZ would be complementary to the ribosomal binding site of ftsZ, it has been proposed that the product of stfZ is an antisense RNA that controls translation of ftsZ. RESULTS: To see if there are other antisense genes in the mra gene cluster of the E. coli chromosome, we looked for antisense promoters and terminators in the region. While no promoters have been identified, all the DNA fragments that have been tested had strong termination activity. Northern blotting, RT-PCR, and primer extension experiments confirm that there is an RNA produced from the antisense strand of DNA at the ftsA-ftsZ gene junction of E. coli cells. RT-PCR experiments indicate that the StfZ RNA is at least 423 nt long. Overexpression of an artificial RNA containing a part of the StfZ sequence lowers FtsZ concentration in cells, prevents FtsZ ring formation, and inhibits cell division. Experiments with fusion constructs show that the overexpressed RNA acts on the ribosomal binding site (RBS) of ftsZ. Other experiments using the fusion constructs indicate that the expression from the RBS of ftsZ is strongly dependent on the growth phase of cells. CONCLUSIONS: The antisense RNA StfZ is produced in E. coli cells. It is very likely that StfZ controls translation of ftsZ, and that it does this by binding to the RBS of the ftsZ mRNA.

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Aldridge, Cassie Patricia. « The molecular biology and regulation of plastid division ». Thesis, University of Leicester, 2006. http://hdl.handle.net/2381/29733.

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Min proteins mediate plastid division site selection by controlling the formation of the Z-ring, the initial event of plastid division. The Z-ring is formed by the polymerisation of the FtsZ proteins into a contractile ring at the future division site and acts as a scaffold for the assembly of the rest of the divisions machinery. This study aims to elucidate AtMinD1 function in Arabidopsis thaliana and demonstrates that AtMinD1 has Ca2+-dependent ATPase activity that is stimulated by AtMinE1. Site directed mutagenesis was used to create an active site mutant of AtMinD1, analysis of this mutant revealed loss of interaction with AtMinE1 and mis-localisation. The interaction of the stromal plastid division components was also investigated. Co-localisation and biomolecular fluorescence complementation assays revealed that AtFtsZ1-1 and AtFtsZ2-1 are capable of forming both homopolymeric and heteropolymeric filaments, AtMinD1 and AtMinE1 interact both with themselves and each other and ARC6 interacts specifically with AtFtsZ2-1. Many of the components involved in plastid division have yet to be identified. To identify novel plastid division components, yeast two-hybrid screening and co-immunoprecipitation were used to hunt for novel interacting partners of FtsZ proteins. Although much work has been dedicated to unravelling the machinery of plastid division, very little is known about the regulation of plastid division. DNA microarrays were used to investigate changes in nuclear gene expression upon chloroplast division inhibition. Quantitative PCR experiments demonstrate that the expression of AtFtsZ1-1, AtFtsZ2-1, AtMinD1 and AtMinE1 is light regulated and yeast one-hybrid screening was used to hunt for transcriptional activators/enhancers of AtMinD1 and AtMinE1.

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O'Sullivan, A. M. « The regulation of division of higher plant cells ». Thesis, De Montfort University, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383207.

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Weng, Yi. « Spatial Division Multiplexed Transmission and Sensing in Few-Mode Fibers ». Thesis, University of Louisiana at Lafayette, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10261316.

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Space division multiplexing (SDM) has become a promising approach in the telecom industry to reduce the cost-per-bit of optical fiber transmission and to resolve the approaching bandwidth crunch. Meanwhile, intermodal nonlinear effects in few-mode fibers (FMF) potentially provide some novel applications along with sophisticated optical signal processing functionality. Recently, such spatial channels and modes have been applied in optical sensing applications with the returned echo analyzed for the collection of essential environmental information. The key advantages of implementing SDM techniques in optical measurement systems include the multi-parameter discriminative capability and accuracy improvement. In this dissertation, we conduct theoretical and experimental study on the SDM systems using FMFs for both optical transmission and sensing applications.

We first investigate a fast-convergence single-stage adaptive frequency-domain recursive-least-square algorithm for simultaneously compensating chromatic dispersion and differential mode group delay in a 224 Gbit/s six-mode polarization-division multiplexed 16 quadrature amplitude modulation FMF transmission system, which increases convergence speed by 53.7% over conventional frequency-domain least-mean square method, with 11% hardware complexity reduction over two-stage recursive-least square approach.

We then present an ultrafast all-optical simultaneous wavelength and mode conversion scheme based on intermodal four-wave mixing, with the capability of switching polarization and mode degeneracy orientation in FMFs. The relation among the conversion efficiency, pump power and phase matching conditions is investigated in theory analysis and simulation. The cross-polarization modulation and cross-mode modulation can be achieved, by in the best case up to 50% conversion efficiency.

Finally, a single-end FMF-based distributed sensing system that supports simultaneous temperature and strain monitoring is demonstrated via Brillouin optical time-domain reflectometry and heterodyne detection. Theoretical analysis and experimental assessment of multi-parameter discriminative measurement applied to the distributed sensors are presented, which endows with good sensitivity characteristics and can prevent catastrophic failure in many applications.

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Riesen, Nicolas. « Spatial mode-division multiplexing and advanced distributed fibre sensing techniques ». Phd thesis, Canberra, ACT : The Australian National University, 2014. http://hdl.handle.net/1885/125032.

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Part A: Spatial Mode-Division Multiplexing: As the capacity limits of single-mode optical fibre are being approached, attention has shifted to few-mode fibre. Increasing capacity then amounts to independently exciting and detecting the various spatial modes, in what is known as spatial mode-division multiplexing. In this approach each mode acts as a different data channel. The independent excitation and detection of the individual spatial modes however remains a major technological challenge, and at present experimental demonstrations have relied on lossy bulk free-space optics. In this thesis, simpler and more compact waveguide-based alternatives are proposed and analysed. Firstly, it is shown that asymmetric Y-junctions can be used to adiabatically multiplex/demultiplex the modes of polarization-maintaining or elliptical-core few-mode fibre. Analytical models describing the mode-selective functionality of these devices are developed and it is shown numerically that the performance is largely independent of wavelength, hence permitting wideband wavelength-division multiplexing. Another class of compact waveguide-based devices suitable for mode-division multiplexing are mode-selective couplers. Coupled mode theory is used to develop an analytical model of these devices, and it is shown that specific three-core variants permit demultiplexing of asymmetric higher-order modes irrespective of modal orientation. The wavelength-dependence of these couplers is however shown to limit their use in wavelength-division multiplexed systems. In order to solve the wavelength-dependence issue of these couplers, adiabatic tapers can be introduced into the cores. Such structures are referred to as tapered velocity mode-selective couplers, and unlike standard directional mode-couplers, these novel devices do not require precise phase conditions to be satisfied over an extended length. For this reason they permit ultra-wideband mode-division multiplexing of few-mode fibre. It is again shown that three-core variants of these tapered couplers can permit mode-orientation independent decoupling. These devices are numerically analyzed, and their successful fabrication using the femtosecond-laser direct write technique is also reported. These developments could play a very significant role in future high-capacity telecommunications. Part B: Advanced Distributed Fibre Sensing Techniques: Distributed optical fibre sensing techniques are invariably plagued by trade-offs between the performance metrics of range, spatial resolution and measurement bandwidth. This is especially true for the most well-known frequency domain and time domain fibre sensing techniques of optical frequency domain reflectometry (OFDR) and optical time domain reflectometry (OTDR), respectively. What is needed to lessen the performance trade-offs, is a hybrid technique using both time and frequency domain signal analysis. The merging of the realms of time and frequency domain fibre sensing is demonstrated in this thesis using a range-gated variant of OFDR. The range-gating is achieved by time stamping the optical signal using high-frequency pseudorandom noise phase modulation, also known as digitally enhanced interferometry. The merging of digital interferometry and OFDR is referred to as digitally enhanced OFDR. This technique permits orders of magnitude reduction in the required sampling rates of OFDR, and overcomes the range ambiguity inherent in OFDR when sensing over multiple frequency sweeps. The latter feature means the technique can be used for ultra-high (e.g. acoustic) bandwidth sensing without sacrificing range or spatial resolution.

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Kim, Eun Hie, et Michael Nsiah-Gyimah. « The impact of fuel price volatility on transportation mode choice ». Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/53542.

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Thesis (M. Eng. in Logistics)--Massachusetts Institute of Technology, Engineering Systems Division, 2009.
Includes bibliographical references (leaves 43-45).
In recent years, the price of oil has driven large fluctuations in the price of diesel fuel, which is an important cost component in freight logistics. This thesis explores the impact of fuel price volatility on supply chains by examining the sensitivity of decisions under various scenarios. Specifically, we analyze the transportation mode choice decision between truckload and intermodal (truck combined with rail) transportation using a model to calculate the total relevant cost, consisting of transportation cost and inventory holding cost. We use input from the North American operations for a global retail company regarding annual demand, product characteristics, load size, lead time, transportation rates, fuel surcharges, inventory policies and holding cost to perform sensitivity analysis of the mode choice decision to fuel price and the value density of the product. For several origin-destination pairs we identify the diesel price at which intermodal offers lower total cost than truckload as well as the magnitude of savings that can be achieved by switching modes. We then generalize the insights from this case by providing an equation to calculate the fuel price for this mode choice tradeoff.
by Eun Hie Kim [and] Michael Nsiah-Gyimah.
M.Eng.in Logistics

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Lloyd, S. Julie-Ann (Simone Julie-Ann). « Regulation of apoptosis in human cancer cells ». Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/33873.

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Thesis (S.M.)--Massachusetts Institute of Technology, Biological Engineering Division, 2005.
Includes bibliographical references (leaves 38-44).
Nitric oxide is postulated to protect cancer cells from the death-inducing effects of tumour necrosis factor alpha by S-nitrosating the active site cysteines, inhibiting cleavage of caspase-9. We aimed to test this hypothesis and to determine its validity across cancer cell types. In addition, we hoped to explain the involvement of certain kinases in nitric oxide-induced apoptosis. The experimental setup involved stimulating human colorectal cancer cells, HT-29 and HCT- 116, and human prostate cancer cells, LNCaP, with cytokines in order to induce cell death. Then, we observed the effects of NO inhibitors, kinase inhibitors, and activation of Akt, a kinase up-stream of the caspase cascade, following transfection of a DNA sequence that was proven to protect cells against apoptosis induction. In our series of experiments, inhibition of the nitric oxide synthases removes nitric oxide protection from apoptosis, but inhibition of only the inducible synthase has opposite effects with prostate and colon cancer cells that are considered insignificant, and its effects on the two types of colon cancer cells are in discord. Transformation and transfection of ARK5 into the colorectal cancer cell line, HT-29 did not prove beneficial. Similarly, glucosamine showed no clear pattern of reducing apoptosis in the cells. Therefore, we propose further exploration of the inhibition of constitutive nitric oxide synthases as a potential therapy.
by S. Julie-Ann Lloyd.
S.M.

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Yap, Xiang Ling. « A model-based approach to regulating electricity distribution under new operating conditions ». Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/72905.

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Thesis (S.M. in Technology and Policy)-- Massachusetts Institute of Technology, Engineering Systems Division, Technology and Policy Program, 2012.
Vita. Cataloged from PDF version of thesis.
Includes bibliographical references (p. 147-152).
New technologies such as distributed generation and electric vehicles are connecting to the electricity distribution grid, a regulated natural monopoly. Existing regulatory schemes were not designed for these new technologies and may not provide distribution companies with adequate remuneration to integrate the new technologies. To investigate how regulation should change in the presence of new technologies, current regulatory schemes and possible improvements to make them suitable for new technologies are reviewed. A Reference Network Model capable of calculating the costs of building a distribution network is utilized to compare the costs of accommodating different penetrations and locations of distributed generation. Results for residential generators with a 3 kW/unit power output show that as the penetration of generators among residential customers increases, costs initially decrease but then increase at higher penetration levels. A comparison of results for residential generators with results for distributed generator conurbations located far away from customers shows that residential and far away generators require similar investment costs when total distributed generation power output is lower than effective customer demand. However, when total distributed generation power output exceeds effective demand, residential generators necessitate higher investment costs than far away generators. At all levels of distributed generation power output, residential generators imply lower losses costs than far away generators. A second Reference Network Model capable of calculating the costs of expanding an existing distribution network is utilized to compare the costs of expanding a network to accommodate new technologies under different technology management approaches. Results show that network investment costs are lower for an actively managed network than for a passively managed network, illustrating the potential benefits of active management. Based on an analysis of the modeling results and the regulatory review, an ex ante schedule of charges for distributed generators that incorporates forecast levels of DG penetration is suggested to improve remuneration adequacy for the costs of integrating distributed generation. To promote active management of distribution networks, measures such as funding pots, outputs-focused regulatory schemes, and regulating total expenditure rather than separating the regulation of capital and operating expenditure are selected as proposals.
by Xiang Ling Yap.
S.M.in Technology and Policy

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Cheng, Jade. « Regulation of cell division and cell death by GRASP65 ». Thesis, University of Bristol, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.544414.

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Chung, Jarom Y. « Regulation of Mitochondrial Distribution and Inheritance During Cell Division ». Thesis, Harvard University, 2016. http://nrs.harvard.edu/urn-3:HUL.InstRepos:33493562.

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Mitochondria are crucial to the cell and perform numerous functions including generating cellular ATP, buffering calcium, and creating macromolecules. Mitochondria contain their own DNA and as such, cannot be synthesized de novo. Additionally, both nuclear-encoded and mitochondrial-encoded proteins work in concert in order for mitochondria to function. During cell division, the cell goes through dramatic morphological changes to ensure the appropriate amount of DNA is inherited into daughter cells. Given the importance of mitochondria, our study sought to understand the underlying mechanisms that ensure proper mitochondrial inheritance. Organelles are inherited by two mechanisms: active and passive. Through our studies we found that mitochondria go through phases of both active and passive regulation. Initially, mitochondria undergo a release from microtubules, actin, and the endoplasmic reticulum, which allows mitochondria to passively float throughout the cytoplasm. As the cell enters cytokinesis, an active phase occurs that can compensate for some, but not all, asymmetry prior to cytokinesis. The detachment from microtubules, actin, and ER is regulated during cell division, and we discovered the mechanism behind mitochondrial release from microtubules. Dynein and kinesin motors move mitochondria along microtubules and also attach them to the cytoskeleton. During mitosis, motors shed from the mitochondrial surface, thus releasing mitochondria from microtubules. CDK1 releases dynein through phosphorylation, and Aurora A kinase releases kinesin. When exogenously expressed motors are recruited to mitochondria, it results in asymmetric inheritance of mitochondria, a delay in mitotic progression, and cytokinesis failure. Since mitochondria are initially positioned passively, we were able to manipulate mitochondrial positioning before the onset of mitosis, which persisted into the duration of mitosis. Overall, our study elucidates the mechanism behind mitochondrial inheritance. Undoubtedly, the mechanisms are important for normal inheritance into daughter cells. It remains an open question of whether or not directed inheritance can take place through these same mechanisms.
Medical Sciences

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Andrieu, Nelly, et Lee Weiss. « Transport mode and network architecture : carbon footprint as a new decision metric ». Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/45250.

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Thesis (M. Eng. in Logistics)--Massachusetts Institute of Technology, Engineering Systems Division, 2008.
Includes bibliographical references (leaves 132-133).
This thesis examines the tradeoffs between carbon footprint, cost, time and risk across three case studies of United States' perishable or consumer packaged goods firms and their transportation partners. Building upon previous research, and utilizing an Institute of Management and Administration (IOMA) and MIT Center for Transportation and Logistics (CTL) survey of supply chain professionals, the goal of this thesis is to better understand the decision process and motivations of our case study companies with regard to carbon footprint and implications for transport mode and network architecture, and the tradeoffs involved in making these decisions. We examine: (1) An expedited refrigerated rail service providing coast-to-coast shipment of produce for a major retailer, in lieu of its prior trucking arrangement; (2) A dairy producer which with the help of its trucking partner switched from less-than-truckload (LTL) to full truckload (FTL) and currently explore the possibility to re-organize its distribution network; and (3) A bottled water firm which created an additional container shipping route to reduce the volume of water it ships via truck. Comparisons and contrasts are made between case study firms. Findings from these case studies are used to make forward-looking recommendations for companies interested in altering transport mode and/or network architecture as a means of reducing the carbon footprint of their operations.
by Nelly Andrieu and Lee Weiss.
M.Eng.in Logistics

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Qiu, Tong. « Adaptive Mode Control in Few-Mode and Highly Multimode Fibers ». Thesis, Virginia Tech, 2018. http://hdl.handle.net/10919/82067.

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Few-mode fibers (FMFs) and multimode fibers (MMFs) can provide much higher data-carrying capacities compared with single-mode fibers. But in order to achieve this goal, one must address the challenge of intermodal coupling and dispersion. Therefore the ability to accurately control the optical signal propagation in FMFs/MMFs can play a pivotal role in FMF/MMF applications. This thesis demonstrates the ability to excite, in FMFs and MMFs, the desired linearly polarized (LP) modes as well as their superpositions through adaptive optics (AO). Specifically, in the case of step-index FMFs, a phase-only spatial light modulator (SLM) is employed to manipulate the light at the fiber input end, driven by the feedback signal provided by the correlation between the charge coupled device (CCD) camera captured images at the fiber output end and the target light intensity profile. Through such an adaptive optical system, any arbitrarily selected LP modes can be excited at the distal end of the four-mode and seventeen-mode fibers, respectively. For a graded-index MMF with a uniform Bragg grating, we use a deformable mirror (DM) to perform the wavefront modulation at the fiber input end, where the feedback is based on the ratio of the grating-reflected signal power to the transmitted signal power. At the Bragg grating position of this highly multimode fiber, any desired principal mode groups can be successfully chosen. These experimental results suggest that adaptive control of optical wavefront in FMFs/MMFs is indeed feasible.
Master of Science
Optical fibers, in terms of the number of modes they support, can be generally divided into single-mode fibers (SMFs), and few-mode fibers/multimode fibers (FMFs/MMFs). FMFs/MMFs can provide much higher data-carrying capacities than SMFs. For example, an FMF/MMF that supports M modes can ideally increase the data transmission rate by a factor of M, where each mode can serve as a distinct communication channel. However, in order to achieve good performance, one must accurately control signal propagation in FMFs/MMFs, which are often degraded due to the multiple-mode nature. This thesis demonstrates the ability, using adaptive optics (AO), to control signal propagation in FMFs and a highly MMF, respectively. Specifically, in the case of FMFs, a phase-only spatial light modulator (SLM) is employed to manipulate the light at the fiber input, driven by AO feedback signal provided by the similarity between the real-time fiber output image and the target mode profile. Through such an adaptive optical system, any desired linearly-polarized (LP) modes can be excited at the output of the four-mode and seventeen-mode fibers, respectively. For the highly MMF with uniform Bragg grating, we use a deformable mirror (DM) to perform the wavefront modulation at the fiber input, where AO feedback is provided by the fiber Bragg grating (FBG) reflectivity. At the FBG position, any desired principal mode groups can be successfully chosen. These experimental results suggest that adaptive control of optical wavefront in FMFs/MMFs is indeed feasible, and may find a large number of applications in optical communication, sensing, and imaging.

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Lu, Peng. « Adaptive Control of Waveguide Modes in Two-Mode Fibers ». Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/65006.

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Few mode fibers and multimode fibers (MMFs) are traditionally regarded as unsuitable for important applications such as communications and sensing. A major challenge in using MMFs for aforementioned applications is how to precisely control the waveguide modes propagating within MMFs. In this thesis, we experimentally demonstrate a generic method for controlling the linearly polarized (LP) modes within a two-mode fiber (TMF). Our method is based on adaptive optics (AO), where one utilizes proper feedback signals to shape the wavefront of the input beam in order to achieve the desired LP mode composition. In the first part of this thesis, we demonstrate the feasibility of AO-based mode control by using the correlation between the experimentally measured field distribution and the desired mode profiles as feedback for wavefront optimization. Selectively excitation of pure LP modes or their combinations at the distal end of a TMF are shown. Furthermore, we demonstrate that selective mode excitation in the TMF can be achieved by using only 5×5 independent phase blocks. Afterwards, we extend our AO-based mode control method to more practical scenarios, where feedback signals are provided by all-fiber devices such as a directional fiber coupler or fiber Bragg gratings (FBGs). Using the coupling ratio of a directional coupler as feedback, we demonstrate adaptive control of LP modes at the two output ports of the directional coupler. With feedback determined by the relative magnitude of optical power reflected by a FBG and the transmitted power, selective excitations of the LP01 and the LP11 modes are experimentally shown. As the final component of this thesis, we experimentally combine the AO-based mode control with time-division-multiplexing. By choosing reflected pulses with appropriate arrival time for mode control, we can selectively excite the LP11 mode at different FBG locations within the TMF, based on the ratio of optical signals reflected by FBGs in the TMF and the transmitted signal. Using two lasers set at the two FBG peak reflection wavelengths associated with the LP01 and the LP11 modes, we can accomplish AO-based mode control within a TMF by using only the reflection signals from the FBG. By using the ratio of the reflected signals of two lasers as feedback, we demonstrate selective excitation of almost pure LP01 or LP11 mode at the FBG location within the TMF. The method developed in this thesis is generic and can be extended to many other applications using appropriately chosen feedback signals. It is possible to generalize the AO-based mode control method to MMF as well. This method may find important applications in MMF-based communication, sensing and imaging et. al. in the future.
Ph. D.

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Lindström, Magnus. « Resource allocation for asymmetric traffic in time division duplexing mode cellular networks ». Licentiate thesis, KTH, Signals, Sensors and Systems, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-1576.

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Time Division Duplexing (TDD) mode systems provide greatflexibility that can be used to implement asymmetrical links.Adverse interference conditions easily arise, however.Especially if dicerent asymmetries are required in neighbouringcells.

This thesis examines the feasibility of supportingasymmetric links in a locally centralised system in a Manhattanenvironment. Methods to avoid inter-mobile and inter-basestation interference are studied and possible performance gainsare assessed. Further, the implications of having differentasymmetries in neighbouring cells and the importance of thebase station placement are investigated.

The thesis shows that asymmetric traffic can be provided inTDD mode systems with a locally centralised resource allocationscheme. Capacity is increased noticeably when compared to asystem with a fixed global asymmetry. Careful handling ofinter-mobile station interference is of great importancethough, to keep outage reasonably low. Measuring link-gainsbetween mobile stations is considered infeasible. However, itis shown that outage can be reduced significantly by using somesimple allocation rules and link-gain estimates proposed andevaluated in the thesis. Results also show that it is possibleto have different asymmetry ratios in different parts of thesystem, though large asymmetry differences between neighbouringcells will adversely affect capacity. Where base stations areplaced is important for system capacity, but as long as thebase stations are not placed in the intersections, the exactlocations are not critical.

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Gregory, James Alan. « FtsZ dynamics and the regulation of division site selection by the MinCD division inhibitor in Bacillus subtilis ». Diss., [La Jolla] : University of California, San Diego, 2009. http://wwwlib.umi.com/cr/ucsd/fullcit?p3369211.

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Thesis (Ph. D.)--University of California, San Diego, 2009.
Title from first page of PDF file (viewed September 15, 2009). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 178-205).

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Gamba, Pamela. « The division complex of Bacillus subtilis : assembly dynamics and regulation ». Thesis, University of Newcastle Upon Tyne, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.556090.

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Cell division in Bacillus subtilis is carried out by at least twelve proteins which assemble at midcell and form a complex known as the divisome. The main components of the divisome are known, but their precise function and the order in which they are assembled and organized within the division complex remains largely elusive. To study the dynamics and temporal hierarchy of divisome assembly in B. subtilis, we have examined the in vivo localization pattern of a set of division proteins fused to GFP, in germinating spores and vegetative cells. We have shown that the divisome assembles in two steps: the FtsZ ring assembles early and concomitantly with FtsA, ZapA and EzrA, and only after a time delay of at least 20% of the cell cycle, a second set of division proteins is recruited to midcell. Interestingly, overproduction of FtsZ advances the temporal assembly of EzrA but not of DivIVA, suggesting that a signal different to that of FtsZ polymerization drives the assembly of late divisome proteins. Surprisingly, SepF appeared to belong to the second group of division proteins. From the spore germination analysis, it emerged that FtsW is a late localizing cell division protein: by analysing its recruitment to the division site in different genetic backgrounds, we show that it is interdependent on that of PBP 2B and FtsL. Interestingly, the Z-ring appeared to disassemble upon prolonged depletion of late division proteins, suggesting an additional role for late proteins in the stabilization of the Z-ring. Surprisingly, it was found that the antibiotic tetracycline blocks cell division of an ezrA mutant carrying a functional tetracycline resistance cassette, when the strain is grown on P AB plates in the presence of the antibiotic. Overexpression of FtsL or ZapA could suppress the division defect. A screen for tetracycline insensitive suppressor mutants of ezrA was performed and two suppressor genes were identified. Their possible role in cell division was investigated.

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Van, der Wath Richard Carl. « Computational modelling of hematopoietic stem cell division and regulation dynamics ». Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608642.

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Egan, Alexander John Frederick. « Regulation of peptidoglycan synthesis during cell division in Escherichia coli ». Thesis, University of Newcastle upon Tyne, 2014. http://hdl.handle.net/10443/2531.

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Bacteria surround their cytoplasmic membrane with an essential, stress-bearing macromolecule, the peptidoglycan (PG) layer. During growth and division cells extend this layer through the action of membrane-anchored peptidoglycan synthases. Presumably, sacculus growth is facilitated by dynamic multiprotein complexes which are guided by cytoskeletal elements. These complexes contain all the necessary peptidoglycan synthases and hydrolases for the enlargement of the sacculus, along with their regulators. Biochemical and genetic data gathered in recent years provides evidence for the existence of these complexes, but the molecular mechanisms they employ, and how cell wall synthesis is coordinated with the synthesis of other cell envelope layers, remain largely unknown. In this work we have elucidated key biochemical features of a regulator of PG synthesis, LpoB. Its high resolution structure was solved by NMR spectroscopy and the interaction interface of LpoB with the major peptidoglycan synthase active during cell division in Escherichia coli, PBP1B, was determined. We show that LpoB interacts with the non-catalytic UB2H domain of PBP1B, situated between the glycosyltransferase and transpeptidase domains. Several other proteins have previously been implicated in the regulation of PBP1B. Here we optimised an in vitro glycosyltransferase assay and investigated the effect of interacting proteins on peptidoglycan synthesis. We have shown the first evidence that multiple interaction partners, LpoB and FtsN, exert a simultaneous synergistic regulatory effect on PBP1B GTase. We also identified novel, functional interactions of PBP1B. YbgF and TolA are both members of the Tol-Pal complex which is required for outer membrane stability and its proper invagination during cell division. TolA was shown to interact with PBP1B via its transmembrane region (domain I) and moderately stimulates the GTase activity of the synthase. YbgF also interacts with PBP1B and is the first example of a negative modulator of PG synthetic activity, inhibiting the regulation of PBP1B TPase by Lpo, which is relieved by TolA. We propose that YbgF and TolA function to fine tune the regulation of PBP1B during division which allows for a proper coordination between cell wall synthesis and constriction of the OM during division in E. coli. In summary, this work significantly enhances our understanding of the regulation of the bi-functional PG synthase active during cell division, PBP1B.

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Carrillo, García Julia 1993. « Regulation of Piezo1 channels and its impact on cell division ». Doctoral thesis, TDX (Tesis Doctorals en Xarxa), 2021. http://hdl.handle.net/10803/672669.

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This project has aimed to investigate the regulation of the mechanosensitive ion channel Piezo1 by proteins that sense and modify membrane curvature. Our second objective has been to study this interplay in the context of forces occurring during cytokinetic abscission. In this context, we have discovered that the Piezo1 channel is regulated during cell division to integrate biochemical and physical cues, orchestrating the recruitment of the abscission machinery and mediating vesicle trafficking to the midbody
Este proyecto ha tenido por objetivo investigar la regulación de canales mecanosensibles Piezo1 por proteínas encargadas de sensar y modificar la curvatura de la membrana. Nuestro segundo objetivo ha sido estudiar esta relación en el contexto de las fuerzas que imperan la abscisión de las células hijas durante la citocinesis. En este contexto, hemos descubierto que el canal Piezo1 está regulado durante la división celular para integrar señales físicas y bioquímicas, orquestando el reclutamiento de la maquinaria de abscisión y mediando el tráfico de vesículas al puente intercelular.

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Wang, Xuyang. « Mode division multiplexing optical communications using orbital angular momentum modes in optical fibres ». Thesis, University of Bristol, 2017. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.723511.

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Kang, Qiongyue. « Modelling of Multimode Erbium-Doped Fibre Amplifiers for mode-division multiplexed transmission systems ». Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/386212/.

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This PhD thesis, undertaken within the framework of MODEGAP, covers the design and optimization of high-performance in-line Multimode Erbium-Doped Fiber Amplifiers (MM-EDFAs) or Few-mode (FM) EDFA for next-generation SDM transmission systems based on Mode-Division Multiplexing (MDM). In the MM-EDFAs, minimizing the differential modal gain (DMG) is of paramount importance to prevent system outage. By using an experimentally validated commercial amplifier simulator, I proposed a 2-mode-group EDF design incorporating ring doping that allows accurate modal gain control amongst the two-mode groups using a simple and much more practical LP01 pump mode. Subsequently a 2-mode-group ring-doped EDF according to my design was fabricated in-house and a portable 2-mode-group EDFA with low DMG built and tested, confirming my predictions. My 2-mode-group EDFA design lay at the heart of several successful 2-mode-group fiber based transmission experiments, as listed in this thesis. To investigate the vector modes effects in FM-EDFAs, we developed our own MM-EDFA simulator capable of modelling both the Linear Polarized (LP) modes and the full vector solutions. We have concluded that, in practice, the LP amplifier model is valid and sufficient enough to predict the FM-EDFA performance. I proposed a 4-mode-group EDFA design that offered DMG < 1dB across four-mode groups using a customized pump profile. As the number of guided modes increases, the required pump power also increases which means expensive single-mode pump diodes are needed in the core-pumping approach. Cladding pumping is an alternative way to provide pump radiation with the advantages of reducing the costs. Consequently, I upgraded our in-house amplifier simulator to a cladding-pump-able MM-EDFA design tool incorporating an optimization algorithm (i.e. Genetic Algorithm) that accepts customized criteria and allows a large number of free parameters to be optimized simultaneously. Using this tool, I proposed the designs and optimizations of cladding-pumped 4 and 6-mode-group EDFAs. Apart from the standard step-index MM-EDFAs, I also investigated novel fiber amplifiers with ring-index profiles for SDM applications. The first type of ring-index fiber discussed in this thesis is of solid core and weakly guiding. The solid-core ring core fiber has an advantage of reducing digital signal processing complexity in MDM transmission. I proposed a 6-mode-group ring core multimode erbium doped fiber amplifier (RC-MM-EDFA) capable of providing almost identical gain among the six mode groups within the C band using either core- or cladding-pumped implementations. The second type of ring-index fiber is an air-core fiber that enables the stable transmission of Orbital Angular Momentum (OAM) modes, which can be used as another degree of freedom for information multiplexing. I have created a new variant of my amplifier model targeting OAM modes and have achieved DMG lower than 0.5 dB for 12 OAM modes in an air-core EDF.

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Martínez, Torró Carlos. « Transcriptional Regulation of Cell Division and Metal Uptake in Mycoplasma genitalium ». Doctoral thesis, Universitat Autònoma de Barcelona, 2020. http://hdl.handle.net/10803/671599.

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Mycoplasma genitalium és un patogen humà que es transmet sexualment i causant d’uretritis, cervicitis i inflamació pelviana. Conté el genoma més petit de qualsevol microorganisme capaç d’autoreplicar-se, amb només 580 kb i 500 gens que codifiquen per proteïnes. L’interès en aquest patogen ha anat augmentat durant els darrers anys degut a la seva cada cop major prevalença i l’aparició de soques resistents a múltiples antibiòtics. En aquesta tesi doctoral, analitzem en detall la divisió cel·lular d’aquest microorganisme, així com la seva resposta a l’absència de metalls. Pel que fa a la divisió, M. genitalium conté una versió molt reduïda de l’operó de divisió cel·lular amb només quatre gens: mraZ, mraW, un gen que codifica per una proteïna de funció desconeguda i ftsZ. Els dos primers gens estan molt conservats en el món bacterià, però no hi ha gaire informació sobre el seu rol en la divisió cel·lular. En aquest treball, caracteritzem els mutants de mraZ i mraW i demostrem els defectes de creixement associats a la seva pèrdua. També establim les dinàmiques de FtsZ en aquest microorganisme i observem que hi ha una relació entre la maquinària de motilitat i FtsZ a M. genitalium. Al segon capítol, descrivim la resposta transcripcional d’aquest patogen a la manca de metalls. Caracteritzem un membre de la família de reguladors transcripcionals Ferric Uptake Regulator (Fur) i també detallem els gens que es troben al seu reguló: un gen que codifica per a una lipoproteïna rica en histidines (hrl) i un transportador de metalls de tipus ABC (MG_304, MG_303, MG_302). Definim experimentalment l’operador de Fur: una seqüència palindròmica conservada que es troba a la regió upstream d’aquests gens. A més, detallem una àmplia resposta transcripcional a l’absència de metalls induïda pel quelant 2,2’-Bipyridyl, una resposta que també es produeix al mutant de fur, el que significa que existeixen vies reguladores Fur-independents relacionades amb l’homeòstasi de metalls. Finalment, mostrem a través de ICP-MS que en el mutant defectiu de fur hi ha un increment important de níquel, el que suggereix que aquest regulador pot tenir un rol important en l’adquisició de níquel. En resum, en aquesta tesi doctoral caracteritzem dos vies reguladores importants de M. genitalium associades amb dos processos essencials: la divisió cel·lular i l’adquisició de metalls.
Mycoplasma genitalium es un patógeno humano que se transmite sexualmente y es agente causante de uretritis, cervicitis e inflamación pélvica. Contiene el genoma más pequeño de todos los microorganismos capaces de autoreplicarse, con únicamente 580 kb y 500 genes que codifican para proteínas. El interés en este patógeno ha aumentado recientemente debido a su cada vez más elevada prevalencia y a la aparición de cepas multiresistentes a antibióticos. En esta tesis doctora, analizamos en detalle la división celular de este microorganismo, así como su respuesta a la ausencia de metales. Por lo que respecta a la división, M. genitalium contiene una versión muy reducida del operón de división celular con sólo cuatro genes: mraZ, mraW, un gen que codifica para una proteína de función desconocida y ftsZ. Sobre los dos primeros genes hay poca información disponible sobre su rol en la división, a pesar de que están ampliamente conservados en el mundo bacteriano. En este trabajo, caracterizamos los mutantes de mraZ y mraW y demostramos los defectos en el crecimiento asociados a su pérdida. También establecemos las dinámicas de FtsZ en este microorganismo y observamos que hay una relación entre la maquinaria de motilidad y FtsZ en M. genitalium. En el segundo capítulo, describimos la respuesta transcripcional de este patógeno cuando se enfrenta a la ausencia de metales. Caracterizamos un miembro de la familia de factores de transcripción Ferric Uptake Regulator (Fur) y detallamos los genes que están en su regulón: un gen que codifica para una lipoproteína rica en histidinas (hrl) y un transportador de metales de tipo ABC (MG_304, MG_303, MG_302). También definimos experimentalmente el operador de Fur: una secuencia palindrómica conservada que se encuentra en la región upstream de estos genes. Además, se detalla una amplia respuesta transcripcional a la ausencia de metales inducida por el quelante 2,2'-Bipyridyl, una respuesta que también se produce en el mutante defectivo de fur, con lo cual se evidencia la existencia de vías regulatorias Fur-independientes implicadas en la homeostasis de metales. Finalmente, mostramos a través de ICP-MS que en el mutante de fur hay un incremento importante de níquel, lo que sugiere que este regulador podría tener un rol importante en la adquisición de este metal. En resumen, en esta tesis doctoral caracterizamos dos vías reguladoras importantes de M. genitalium asociadas con dos procesos celular esenciales: la división y la adquisición de metales.
Mycoplasma genitalium is a sexually transmitted human pathogen that causes urethritis, cervicitis and pelvic inflammation. It has the smallest genome of any microorganism capable of self-replication, with only 580 kb and barely 500 protein-coding genes. The interest in this pathogen is rising in recent years due to its increasing prevalence and the appearance of multi-drug resistant strains. In this work, we analyze the cell division of this microorganism as well as its response to a metal depletion stress. Regarding the former, M. genitalium encodes a reduced version of the division and cell wall operon that consists of only four genes: mraZ, mraW, a gene coding for an hypothetical protein and ftsZ. The first two genes are widely conserved among bacteria, but there is little to none information about their role in cell division. In this work, we characterize the mraZ and mraW mutants and we demonstrate the growth defects associated with their deletion. We were also able to establish the FtsZ dynamics in this microorganism and we observed that there is a close relation between the cell motility machinery and FtsZ in M. genitalium. In the second chapter, we assess the transcriptional response of this pathogen to metal starvation. We characterize a member of the Ferric Uptake Regulator (Fur) family of transcription factors in this microorganism and we report the genes in its regulon: a gene coding for a histidine-rich lipoprotein (hrl) and an ABC metal transporter (MG_304-MG_303-MG_302). We are able to describe the Fur operator: a conserved palindromic sequence found in the upstream region of these genes. In addition, we also detail a vast transcriptional response to metal depletion induced by the chelator 2,2'-Bipyridyl even in the mutant that lacks the regulator, demonstrating the existence of Fur-independent regulatory pathways. Finally, we reveal an increased nickel uptake in the fur mutant by ICP-MS, suggesting an important role of this regulator in nickel acquisition. Overall, in this work we are able to characterize two important regulatory networks of the genome-reduced M. genitalium associated with two essential processes: cell division and metal uptake.
Universitat Autònoma de Barcelona. Programa de Doctorat en Bioquímica, Biologia Molecular i Biomedicina

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Vaishnav, Chintan. « The end of core : should disruptive innovation in telecommunication invoke discontinuous regulation ? » Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/62869.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Engineering Systems Division, 2010.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student submitted PDF version of thesis. Page 247 blank.
Includes bibliographical references (p. 239-246).
This research analyzes how a telecommunications regulator can balance regulation with innovation, at a reasonable cost. This question has gained critical importance for telecom regulators as the unregulated Internet technologies such as voice and video over Internet disrupt the regulated traditional technologies such as telephony and television and the historical paradigm of the regulator. The existing U.S. telecommunications regulations were created in the integral age. In that paradigm, functional components that constitute a service compliant with regulation resided inside the network core; each operator was vertically integrated and controlled the total functionality necessary to deliver a service; a few such operators controlled the industry; they faced low competition and were under limited pressure to adopt innovation; and consumers had limited choice. The Internet has introduced a polar opposite paradigm-the modular age. In this paradigm, functional components that constitute a service are dispersed across the network core and edges; each firm controls only a subset of the total functionality necessary to constitute a service; many modular firms interoperate to deliver a service; firms compete fiercely and are under great pressure to innovate; and consumers enjoy far greater choice due to the multi-modal competition among multiple technologies. Although transitioning from an integral to a modular age dramatically flips the environment, the current regulatory response to this dramatic shift has been hesitant to shift its intellectual roots. Consequently, this thesis describes and analyzes the new telecommunications paradigm and explores its implications for an appropriate regulatory paradigm. The research uses the regulation of voice communications in the United States as a representative case. We analyze the new telecommunications paradigm as a dynamic complex system. Our research approach rests upon four principles of systems: two organizational principles (hierarchy and feedback) and two behavioral principles (emergent behavior and strategic and statistical behavior).The telecommunications system is viewed as one of the many subsystems that together fulfill the objectives of a society. The dynamics of the telecommunications system itself are conceptualized as those resulting from the interactions of four subsystems: regulatory dynamics, corporate strategy dynamics, consumer dynamics, and technology dynamics. The regulatory objectives to be fulfilled are conceived as an emergent property of such a system of systems. To carry out this research, we have developed a system-level dynamic feedback model and two case studies. As modular entrants of Internet-based technology disrupt integrated incumbents of traditional technology, bewildering dynamic complexity complicates decision-making by policymakers, managers, consumers, and technologists alike. Our model makes understandable the emergent behavior amidst the uncertainty that surrounds such a disruption phenomenon. The model formulations are behavioral. They are derived from the existing theories of technology and industry disruption, where possible. Alternatively, where theories have a gap, the decision processes of stakeholders, gleaned from unstructured interviews, are mathematised as the basis for the model formulations. The resulting structure is a fully endogenous systems model of regulation, competition, and innovation in telecommunications. In the first case study we analyze the regulatory environment of pre vs. post-Internet periods, both quantitatively and qualitatively. For the analysis, public comments in response to the Telecommunications Act of 1996 Notice for Proposed Rulemaking (NPRM) are compared with those in response to the IP-Enabled Services NPRM published in 2004. The analysis demonstrates how the differences in the integral and modular age are reflected in the regulatory record. The second case study analyzes how market, technology, organizational, and regulatory uncertainties affect technology and industry disruption. For this case, we use a combination of industrial statistics and content analysis of media publications. The analysis demonstrates the limits to technology and industry disruption. The case studies complement the model in two ways: first, they facilitate further refinement of the systems model; second, they empirically validate the arguments deduced from model analysis. Through this research we answer three questions: (1) Can the regulatory structure designed in an integral age-in its objectives, obligations (requirements), and enforcement mechanisms-work for a modular age? (2) How can regulators and managers improve decision making amidst the uncertainty surrounding the disruption of an integrated technology and industry by a modular one? (3) What is the new role of the telecommunications regulator and how can it be fulfilled in the modular age of the Internet? Our analysis shows that the current regulatory structure is inadequate for responding to the challenges the modular age poses. Firstly, the current objectives are appropriate but cannot be met unless regulators discontinue the merely efficiencycentered thinking and begin to address objectives at the societal level. Secondly, the current obligations may attain short-term goals, but have undesirable long-term consequences. Devising obligations that are appropriate in the long-term requires regulators to discontinue myopic measures such as incremental regulation of new technologies. Finally, the current enforcement mechanisms are blunted by the dynamic complexity of the modular age. Enforcing regulations effectively in the modular age necessitates adding to the regulatory quiver new mechanisms that are more versatile than the merely adversarial command-and-control mechanisms. Through model analysis, we demonstrate how a lack of understanding of the various uncertainties, and misperceptions of feedback in a complex system where regulators, firms, consumers, and technologists constantly interact, could lead to decisions that are costly for regulators as well as managers. Yet, as we demonstrate, with better grasp of the dynamic complexity involved, they can significantly improve decision-making to meet the challenges of the modular age. We argue that the most critical role for the telecommunications regulator in the new telecommunications paradigm is to sustain a balance between regulation and innovation, at a reasonable cost. Achieving such a balance in a modular structure is not trivial because of several natural tendencies. First, achieving high compliance at low cost is difficult because in highly modular architectures and industries, coordination costs, such as the time to build consensus, can be inordinately large. Second, keeping the innovationlevel high is difficult because it requires fighting the natural tendency of modular firms to gain and abuse market power. We propose a combination of two policy levers-Limiting Significant Market Power (SMP) Accumulation and Building Broad-based Consensus around Regulatory Issues-that most effectively achieve the desired balance and remain inadequately explored in the United States. We contend that implementing these policy levers will require, first, a more broadly construed antitrust regulation in the United States that will ensure higher modularity, and, second, a telecommunications regulatory agency that is empowered and organized to pursue objectives at the societal level and to build broad-based consensus among divergent interests in a highly modular structure.
by Chintan Vaishnav.
Ph.D.

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Elihu, David Morad. « Regulation of specific connexins differentially alters gap junction permeability and endothelial cell function ». Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/37974.

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Thesis (M. Eng.)--Massachusetts Institute of Technology, Biological Engineering Division, 2006.
Includes bibliographical references (leaves 80-84).
While many have explored how vascular processes alter gap junction communication and composition few have analyzed the role of specific gap junction connexin proteins in regulating cellular communication and wound healing. Using RNA interference or peptide inhibitors to downregulate specific connexins we examined the role of gap junctions in intercellular diffusion, calcium excitation, and in mediating the expression of vascular regulators transforming growth factor-[Beta][ (TGF-[beta]), prostacyclin, and endothelial nitric oxide synthase (eNOS). siRNA inhibition of connexin 43 in porcine aortic endothelial cells (PAEC) significantly decreased the diffusion distance of Lucifer yellow dye and cytoplasmic calcium levels after mechanical wounding. Wound healing experiments suggested that stimulatory signals travel through gap junctions containing connexin 43, while inhibitory signal travel through gap junctions containing connexin 37. Connexin 43 and connexin 37 inhibition, alone or in combination, reduced the levels of secreted latent TGF-[beta] in confluent PAEC monolayers after 24 hours of incubation. Human umbilical vein endothelial cells (HUVEC) behaved in a similar manner. Inhibition of any one of the three connexins resulted in a marked increase in eNOS concentration.
(cont.) Yet, TGF-P was sensitive to simultaneous inhibition of connexins 37, 40, and 43 and prostacyclin was controlled by connexin 37 and/or connexin 40 but not connexin 43. We have demonstrated how selective inhibition of gap junction connexin expression can reveal the potent gap junction mediation of cellular communication, wound healing, and vascular function. We demonstrate for the first time that connexin proteins play distinct roles in vasoregulation with differential effects on TGF- [beta], eNOS and prostacyclin. This technique in general and findings in specific may help explain density-dependent control of vascular signaling and repair.
by David Morad Elihu.
M.Eng.

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Corsi, Alessandro. « Design and characterization of few-mode fibers for space division multiplexing on fiber eigenmodes ». Doctoral thesis, Université Laval, 2020. http://hdl.handle.net/20.500.11794/67890.

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La croissance constante et exponentielle de la demande de trafic de données Internet conduit nos réseaux de télécommunications optiques, principalement composés de liaisons de fibre monomode, à une pénurie imminente de capacité. La limite non linéaire de la fibre monomode, prédite par la théorie de l'information, ne laisse aucune place à l'amélioration de la capacité de communication par fibre optique. Dans ce contexte, la prochaine technologie de rupture dans les transmissions optiques à haute capacité devrait être le multiplexage par répartition spatiale (SDM). La base du SDM consiste à utiliser différents canaux spatiaux d'une seule fibre optique pour transmettre des données indépendantes. Le SDM fournit ainsi une augmentation de la capacité de transport de données d'un facteur qui dépend du nombre de chemins spatiaux qui sont établis. Une façon de réaliser le SDM consiste à utiliser des fibres faiblement multimodes (FMF) spécialisées, conçues pour présenter un couplage faible entre les modes guidés. Un traitement MIMO réduit peut alors être utilisé pour annuler le couplage résiduel des modes. Dans cette thèse, nous donnons tout d'abord un aperçu des progrès récents du multiplexage par répartition de modes (MDM). Les modes à polarisation linéaire (LP), les modes de moment angulaire orbital (OAM) et les modes vectoriels représentent différentes bases de modes orthogonaux possibles dans la fibre. Nous comparons les travaux utilisant ces modes en termes de conception de fibre proposée, nombre de modes, complexité MIMO et résultats expérimentaux de transmission de données. Ensuite, nous introduisons la modélisation de la fibre optique réalisée avec les solveurs numériques de COMSOL Multiphysics, et nous discutons de quelques travaux utilisant cette modélisation de fibre. Nous proposons une nouvelle FMF, composée d'un noyau hautement elliptique et d'une tranchée adjacente ajoutée pour réduire la perte de courbure des modes d'ordre supérieur. La fibre est conçue et optimisée pour prendre en charge cinq modes spatiaux avec une dégénérescence de polarisation double, pour un total de dix canaux. La fibre proposée montre une différence d'indice effectif entre les modes spatiaux supérieure à 1 × 10-3sur la bande C. Ensuite, nous fabriquons la fibre avec un procédé standard de dépôt chimique en phase vapeur modifié (MCVD), et nous caractérisons la fibre en laboratoire. La caractérisation expérimentale a révélé que la fibre présente une propriété de maintien de polarisation. Ceci est obtenu grâce à la combinaison de la structure centrale asymétrique et de la contrainte thermique introduite lors de la fabrication. Nous mesurons la biréfringence avec une technique de réseau de Bragg inscrit dans la fibre (FBG). En incluant la contrainte thermique dans notre modélisation de fibre, un bon accord est obtenu entre la biréfringence simulée et mesurée. Nous avons réussi à effectuer la première transmission de données sur la fibre proposée, en transmettant deux signaux QPSK sur les deux polarisations de chaque mode spatial, sans utiliser de traitement MIMO. Enfin, nous présentons une amélioration d'une technique d'interférométrie hyperfréquence (MICT) précédemment proposée, afin de mesurer expérimentalement la perte en fonction du mode (MDL) des groupes de modes FMF. En conclusion, nous résumons les résultats et présentons les perspectives d'avenir de cette recherche. En résumé, de nouveaux FMF doivent être étudiés si nous voulons résoudre la pénurie imminente de capacité de nos technologies système. Les résultats de cette thèse indique que le FMF à maintien de polarisation proposée dans cette recherche représente une amélioration significative dans le domaine des systèmes de transmission MDM sans MIMO pour des liaisons de communication courtes ; c’est-à-dire distribuant des données sur une longueur inférieure à 10 km. Nous espérons que ce travail conduira au développement de nouveaux composants SD Mutilisant cette fibre, tels que de nouveaux amplificateurs à fibre, ou de nouveaux multiplexeurs/démultiplexeurs, comme par exemple des coupleurs en mode fibre fusionnée ou des dispositifs photoniques au silicium.
The constant and exponential growth of Internet data traffic demand is driving our optical telecommunication networks, mainly composed of single-mode fiber links, to an imminent capacity shortage. The nonlinear limit of the single-mode fiber, predicted by the information theory, leave no room for optical fiber communication capacity improvements. In this direction, the next disruptive technology in high-capacity communication transmissions is expected to be Space Division Multiplexing (SDM). The basic of SDM consists of using different spatial channels of a single optical fiber to transmit information data. SDM thus provides an increase in the data-carrying capacity by a factor that depends on the number of spatial paths that are established. A way to realize SDM is through the use of specialty few-mode fibers (FMFs), designed to have a weak coupling between the guided modes. A reduced MIMO processing can be used to undo the residual mode coupling. In this thesis, we firstly give an overview of the recent progress in mode division multiplexing (MDM). Linearly polarized (LP) modes, orbital angular momentum (OAM) modes and vector modes represent the possible orthogonal modes guided into the fiber. We compare works, making use of those modes, in terms of proposed fiber design, number of modes, MIMO complexity and data transmission experiments. After that, we introduce the optical fiber modelling performed with the numerical solvers of COMSOL Multiphysics, and we discuss some works making use of this fiber modelling. Next, we propose a novel FMF, composed of a highly elliptical core and a surrounding trench added to reduce the bending loss of the higher order modes. The fiber is designed and optimized to support five spatial modes with twofold polarization degeneracy, for a total of ten channels. The proposed fiber shows an effective index difference between the spatial modes higher than 1×10-3 over the C-band. Afterwards, we fabricate the fiber with standard modified chemical vapor deposition (MCVD) process, and we characterize the fiber in the laboratory. The experimental characterization revealed the polarization maintaining properties of the fiber. This is obtained with the combination of the asymmetric core structure and the thermal stress introduced during the fabrication. We measure the birefringence with a fiber Bragg grating (FBG) technique, and we included the thermal stress in our fiber modelling. A good agreement was found between the simulated and measured birefringence. We successfully demonstrate the first data transmission over the proposed fiber, by transmitting two QPSK signals over the two polarizations of each spatial mode, without the use of any MIMO processing. Lastly, we present an improvement of a previously proposed microwave interferometric technique (MICT), in order to experimentally measure the mode dependent loss (MDL) of FMF mode groups. Finally, we present the conclusions and the future perspectives of this research. To conclude, novel FMFs need to be investigated if we want to solve the imminent capacity shortage of our system technologies. We truly believe that the polarization-maintaining FMF proposed in this research represents a significant improvement to the field of MIMO-free MDM transmission systems for short communication links, distributing data over length less than 10 km. We hope that this work will drive the development of new SDM components making use of this fiber, such as new fiber amplifiers, or new mux/demux, as for example fused fiber mode couplers or silicon photonic devices.

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Pérez, Galacho Diego. « High speed optical modulation, advanced modulation formats and mode division multiplexing in Silicon photonics ». Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS194/document.

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La demande en bande passante des systèmes de communication optique ne cesse de croitre. Des débits de données de l’ordre de plusieurs centaines de TBit/s sont attendus dans un futur proche. La photonique silicium est une technologie majeure pour faire face à ces besoins croissants. Sa compatibilité avec les technologies CMOS permet naturellement une co-intégration photonique/électronique sur les mêmes circuits. A court terme, l’augmentation des débits de données dans les générations futures de système de communication optique passe par l’utilisation de formats de modulation avancés, et l’augmentation du nombre de bits par symbole transmis. A plus long terme, de nouvelles techniques de multiplexage sont nécessaires. Le multiplexage de modes est actuellement une solution attractive à l’étude dans ce but.Dans ce travail de thèse, différents moyens pour implémenter ces nouveaux systèmes de communication optiques sont étudiés au niveau de l’émetteur. Ces travaux incluent dans une première partie la modélisation, conception et caractérisation des modulateurs silicium. Dans une seconde partie, de nouveaux composants pour manipuler les modes sur circuits intégrés photoniques sont proposés, conçus et caractérisés, avec pour application le multiplexage de modes.Une nouvelle méthode a été proposée pour la modélisation des modulateurs optiques silicium. Cette méthode permet de réduire le temps de simulation de 2 ordres de grandeur, en maintenant un bon niveau de précision. En utilisant ce modèle, des modulateurs basés sur des diodes PN latérales et interdigitées ont été conçus pour fonctionner en bande O des communications optiques. Les résultats expérimentaux ont permis la mise en évidence de diagrammes de l’œil avec des taux d’extinction de 10 dB pour des modulations de type OOK (ON-OFF Keying) à 10Gbit/s. De plus des modulations de type BPSK (Binary Phase Shift Keying) ont également été démontrées à 10Gbit/s.De nouveaux convertisseurs de modes et multiplexeurs ont été proposés, conçus, fabriqués et caractérisés, pour être utilisés dans des systèmes de multiplexage modal. Les résultats expérimentaux ont permis de mettre en évidence des fonctionnements large bande passante avec de grands taux d’extinction
Bandwidth demand in optical communication systems is continually growing. Data rate values in the order of several hundreds of TBps are expected in the near future. In order to cope with those expectations silicon based technologies are believed to be the best suited. Its naturally compatibility with CMOS easily enables the electronics and photonics co-integration. In the short-term the way increase data rates in next generation optical communication systems goes through using advanced modulation format and increase symbol rates. In the long-term view, new multiplexing techniques will be required. In this sense, mode division multiplexing is nowadays an attractive approach under consideration.In this Thesis work, the way to implement these new optical communication schemes is studied from the transmitter point of view. It includes, on a first part the modeling, design and characterization of silicon modulators. And in a second part, it includes the proposition, design and characterization of novel mode handling devices for mode division multiplexing.A new way of modeling silicon modulators has been developed. This new model permits to reduce the computation time of modulator analysis up to two orders of magnitude, while maintaining a good level of accuracy. Using the model, modulators based on lateral PN junctions and interdigitated PN junctions were designed to work in the O-Band of optical communications. Characterization work has been performed on these modulators with good results. Wide-open OOK (On Off Keying) eye diagrams with 10 dB extinction ratio were obtained at 10GBps. Furthermore, BPSK (Binary Phase Shift Keying) modulation was also demonstrated at 10GBps.New kind of mode converters and multiplexers, intended to work as mode division multiplexing subsystems have been proposed, designed, fabricated and characterized. Measured results show broad bandwidth operation with high extinction ratio

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Piecewicz, Stephanie Marie. « Heparan sulfate glycosaminoglycan regulation of vasculogenesis ». Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/63084.

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Thesis (Ph. D.)--Harvard-MIT Division of Health Sciences and Technology, 2011.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 137-154).
Neovascularization is an essential process to repair ischemic tissues following myocardial infarction, stroke, diabetic complications, or transplant procedures. Blood vessels are generated by distinct vasculogenic and angiogenic processes. Although multiple proangiogenic factors have been identified, limited success has been achieved translating these as clinical therapeutics. Furthermore, recent studies have shown that vasculogenesis contributes to adult neovascularization in multiple settings. Harnessing the vasculogenic potential of embryonic stem cells is an emerging concept to generate neovasculature. The differentiation of embryonic stem cells into endothelium has been well documented, however most studies focus on genetic or chemokine regulation. Limited information exists which implicates the role of the extracellular microenvironment in stem cell differentiation. Heparan sulfate glycosaminoglycans (HSGAG) are a crucial part of the dynamic extracellular matrix and have been shown to regulate multiple signaling cascades, including vasculogenic specific growth factors VEGF and FGF. The goal of this thesis is to elucidate the role of HSGAG in vasculogenesis. An embryonic stem cell embryoid body model was used to establish the necessity of sulfated HSGAG for endothelial differentiation. We identified that the chemical composition of HSGAG sulfation patterns change with differentiation. Perturbation of HSGAG structure by chemical, enzymatic, or genetic modification effectively inhibited vasculogenesis. Genetic silencing of HSGAG modifying enzyme, N-deacetylase/N-sulfotransferase-1, translated to inhibition of HSGAG sulfation and resulted in impaired blood vessel development in zebrafish embryos. Interestingly, vessel formation in both embryonic stem cell and zebrafish models was restored by the addition of exogenous HSGAG, opening the door for engineering glyco-based microenvironments for controlling vascular development. To explore novel mechanisms of vasculogenesis modulated by HSGAG perturbation, we performed a global transcriptome analysis of N-deacetylase/N-sulfotransferase-1 mutant zebrafish embryos. Several novel pathways were identified that regulate vascular differentiation, including Foxo3A and Insulin-Like Growth Factor (IGF) pathways. We explored the role of IGFs in vasculogenesis specifically and determined for the first time that IGF1 and IGF2 promote mesoderm and endothelial differentiation, mediated through HIFl[alpha] stabilization, in embryonic stem cells. In summary, we've identified several mechanisms by which HSGAG regulate neovascularization, laying the groundwork for incorporating HSGAG in strategies for ischemic tissue regeneration.
by Stephanie Marie Piecewicz.
Ph.D.

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Kang, Joanne S. (Joanne Seunghee). « Regulation of jun B gene expression in v-fos tranformed rat-1 fibroblasts and revertants ». Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/38022.

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Doreian, Bryan William. « Molecular Regulation of the Exocytic Mode in Adrenal Chromaffin Cells ». Cleveland, Ohio : Case Western Reserve University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=case1245785721.

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Thesis (Ph.D.)--Case Western Reserve University, 2009
Title from PDF (viewed on 19 August 2009) Department of Physiology and Biophysics Includes abstract Includes bibliographical references Available online via the OhioLINK ETD Center

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Labie, Christophe. « Etude du mode d'action de dicB, inhibiteur de division : produit du gène dicB d'Escherichia coli ». Toulouse 3, 1990. http://www.theses.fr/1990TOU30042.

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Ce travail est une etude du mode d'action du produit du gene dicb, une proteine inhibitrice de la division cellulaire de escherichia coli. Tout d'abord, des mutants resistants a l'inhibition dicb-dependante ont ete isoles et caracterises. Les mutations appartiennent principalement a deux classes affectees dans le controle de la division cellulaire. L'une d'entre-elles regroupe des mutations localisees dans le gene rpob codant pour la sous-unite beta de l'arn polymerase. Ces mutations conduisent a un phenotype de surdivision qui pourrait resulter d'une surexpression relative du gene declencheur de la septation ftsz. L'autre categorie est constituee de mutations situees dans le locus minb. Ce locus, quoique non essentiel pour la cellule, est necessaire pour le positionnement correct des sites de septation. Des donnees genetiques nous ont suggere que ce locus codait pour les fonctions cibles de la proteine dicb. Pour eprouver ce modele, nous avons entrepris d'etablir une correlation fine entre les phenotypes (resistance et taux de divisions polaires) et les sequences des mutations minb#, isolees durant ce travail et par d'autres equipes. Ces resultats nous ont permis de confirmer et d'etendre les donnees deja publiees sur le fonctionnement de l'operon minb, ainsi que d'etablir une modelisation sur les interactions entre dicb et les produits des genes minc, mind et mine de l'operon minb. En outre, un systeme permettant de surproduire la proteine dicb, hautement toxique, a ete developpe dans une optique preparative. Parallelement, l'etude de sa localisation cellulaire a fourni des donnees importantes quant au mode d'action de l'inhibiteur et pour la determination des conditions optimales de sa purification

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Law, Chan How. « Impact of regulation on trucking carrier prices and capacity ». Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/107515.

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Thesis: M. Eng. in Logistics, Massachusetts Institute of Technology, Supply Chain Management Program, 2016.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 42-43).
This thesis analyzes the impact on prices and capacity of trucking industry due to the introduction of ELD mandate. This mandate requires truck drivers to record their working hours in a specified electronic device instead of a pen and paper method. This thesis utilizes the change in average truck driver working hours, cost of ELD equipment and distance from origin to destination of truck loads to determine the potential impact on trucking market. The models used provide an estimation of the impact on capacity and cost and the likelihood of impact on the economics of trucking industry.
by Chan How Law.
M. Eng. in Logistics

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Wang, Yan. « Characterization of the effects of decreased expression of ribosomal proteins on cell transformation and cell cycle regulation ». Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/11190.

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Shipton, Matthew J. « Characterization of Optical Coupling and Back-reflection of Few Mode Fibers ». Thesis, Virginia Tech, 2015. http://hdl.handle.net/10919/56574.

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The continued growth of the communications industry has caused interest in mode-division multiplexing (MDM) techniques to flourish in recent years. These techniques allow individual waveguide modes to be used as distinct channels. However, as with any versatile technique, it should be also useful and beneficial to extend its application to other areas. This work concerns itself with an initial conceptual design of a mode-division multiplexing (MDM) enabled optical sensor network that can use modes to interrogate either specific sensors or sensor subsystems, and specifically with quanitizing and optimizing the injection and detection of the signal of interest. A hypothetical test setup is demonstrated, and the major issue of back reflection burying the intended signal is addressed, analyzed, and improved. Improvements in the signal-to-background contrast ratio (SBCR) of approximately 10dB were achieved depending on fibre type and proximal face. Suggestions for extensions to further improve the SBCR as well as for applications of this system are discussed.
Master of Science

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Bulmer, Richard. « The regulation of the cell division cycle by forkhead proteins in Schizosaccharomyces pombe ». Thesis, University of Newcastle Upon Tyne, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.424014.

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Pic-Taylor, Aline. « The regulation of the cell division cycle by forkhead proteins in Saccharomyces cerevisiae ». Thesis, University of Newcastle Upon Tyne, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341787.

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Bell, G. P. « The roles and regulation of the Drosophila Lgl tumour suppressor in cell division ». Thesis, University College London (University of London), 2014. http://discovery.ucl.ac.uk/1458548/.

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Cell polarity is a fundamental feature of most cells, and is required for a diverse range of cell functions. A conserved set of proteins is involved in the establishment and maintenance of cell polarity. Several of these polarity proteins in Drosophila are recognized as neoplastic tumour suppressors, and loss of cell polarity in general has been linked to cancer malignancy. Although much is known about the general role of the polarity proteins, many questions still remain about the details and extent of their functions. I have focused on the Lgl protein in Drosophila epithelia: a basolaterally-localized tumour suppressor. In mitosis, Lgl undergoes a dramatic relocalisation away from the plasma membrane into the cytoplasm. I have found that this is regulated by direct phosphorylation by the Aurora cell cycle kinases: this is in contrast to the regulation of Lgl in interphase polarity, which is mediated by aPKC. The mitotic relocalisation event appears to play an important role in the correct orientation of the mitotic spindle and cell division in epithelia, which may be necessary for maintaining tissue integrity. Thus in addition to the established role for Lgl in cell polarity, my work suggests a novel function for Lgl during mitosis.

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Baldwin, Austin Thomas. « Wnt signaling and β-catenin regulation during asymmetric cell division in Caenorhabditis elegans ». Diss., University of Iowa, 2015. https://ir.uiowa.edu/etd/2041.

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Wnt/β-catenin signaling and asymmetric cell division are essential to development and homeostasis in metazoans; these two mechanisms join into one in the Wnt/β-catenin Asymmetry (WβA) pathway in the nematode C. elegans. In WβA, nuclear asymmetry of two β-catenins, SYS-1 and WRM-1, is achieved by two parallel pathways that reduce SYS-1 and WRM-1 levels in the anterior daughter and increase their levels in the posterior daughter. While it is known that many conserved regulators of Wnt signaling are involved in WβA, how these components interact to achieve SYS-1 and WRM-1 asymmetry is not well understood. In this thesis, genetics, transgenics, and live-imaging are used to demonstrate how WβA regulates it’s multiple outputs. It is shown that APR-1/APC and PRY-1/Axin control asymmetric localization of both SYS-1 and WRM-1, and that Wnt signaling explicitly controls APR-1 regulation of either β-catenin via the kinase KIN-19/CKIα. Additionally, it is demonstrated that the Dishevelled proteins DSH-2 and MIG-5 are positive regulators of SYS-1, but negative regulators of WRM-1. Additionally, data from a screen designed to identify novel kinase regulators of Wnt signaling/asymmetric cell division is presented. Overall, this thesis takes current knowledge of conserved Wnt signaling component function and provides a compelling model of how those components are adapted to asymmetric cell division.

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Kotwaliwale, Chitra V. « Regulation and functions of the Ipl1/aurora protein kinase / ». Thesis, Connect to this title online ; UW restricted, 2007. http://hdl.handle.net/1773/5081.

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Kim, Ji-Eun 1974. « Regulation of tumor necrosis factor-alpha induced apoptosis via posttranslational modifications in a human colon adenocarcinoma cell line ». Thesis, Massachusetts Institute of Technology, 2004. http://hdl.handle.net/1721.1/28865.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Biological Engineering Division, 2004.
Includes bibliographical references.
(cont.) phosphoproteomics technology, IMAC/LC/MS/MS, [approximately] 200 phosphosites were identified from HT-29 cells, some of which were detected only from insulin-treated cells. Our phosphoproteomics approach also enabled us to detect alteration of both known and unknown phosphorylation states of apoptosis-related proteins at two time points during early apoptosis induced by tumor necrosis factor-α
Apoptosis, a physiologically regulated cell death, plays critical roles in development and immune system by maintaining tissue homeostasis. The thesis project investigates regulations of apoptosis in a human colon adenocarcinoma cell line, HT-29, exposed to diverse cellular stimuli, focusing on a specific protein as well as global level of proteins. The first part of the thesis demonstrated S-nitrosation of procaspase-9. S-nitrosation is a novel protein modification to regulate protein-protein interaction or protein activity. This modification has been implied to inactivate caspases. We could visualize S-nitrosation of an initiator caspase, procaspase-9, by enriching low-abundant procaspase-9 with immunoprecipitation and stabilizing S-nitroso-cysteine with biotin labeling. Nitric oxide synthase inhibitors and tumor necrosis factor-α (TNF-α) reduced the S-nitrosation level of procaspase-9, suggesting that S-nitrosation may be regulated by a nitric oxide synthase and denitrosation is likely a mechanism of apoptosis. The second part of the thesis is to examine survival effects of insulin on cells undergoing TNF-α-induced apoptosis. Insulin decreased the TNF-α-induced cleavage of key apoptotic mediators, caspases, and their substrates as well as apoptosis, in part, depending on phosphatidylinositol-3 kinase (PI-3K)/Akt pathway. One of protective mechanisms by insulin is likely to decrease the TNF-α-induced dissociation of a potent inhibitor of caspases, X-chromosome linked inhibitor of apoptosis protein (XIAP), from procaspase-9 via PI-3K/Akt pathway. Lack of phosphoproteomics data in HT-29 cells led the third part of the thesis to focus on investigating global level regulation of phosphoproteins during apoptosis. With a
by Ji-Eun Kim.
Ph.D.

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