Four years tracking unrevealed topological changes in the african interdomain

Despite extensive studies on the Internet topology, little is still known about the AS level topology of the African Internet, especially when it comes to its IXP substrate. The main reason for this is the lack of vantage points that are needed to obtain the proper information. From 2013 to 2016, we enhanced the RIPE Atlas measurement infrastructure in the region to shed light on both IPv4 and IPv6 topologies interconnecting local ISPs. We increased the number of vantage points in Africa by 278.3% and carried out measurements between them at random periods. To infer results that depict the behavior of ISPs in the region, we propose reproducible traceroute data analysis techniques suitable for the treatment of any set of similar measurements. We first reveal a large variety of ISP transit habits and their dependence on socio-economic factors. We then compare QoS within African countries, European countries, and the US to find that West African networks in particular need to promote investments in fiber networks and to implement traffic engineering techniques. Our results indicate the remaining dominance of ISPs based outside Africa for the provision of intra-continental paths, but also shed light on traffic localization efforts. We map, in our traceroute data, 62.2% of the IXPs in Africa and infer their respective peers. Finally, we highlight the launch of new IXPs and quantify their impacts on end-to-end connectivity. The study clearly demonstrates that to better assess interdomain routing in a continent, it is necessary to perform measurements from a diversified range of vantage points.The work done by Rodérick Fanou was funded by IMDEA Networks Institute as part of the project “Mapping and Measuring the African Internet”. Francisco Valera has been partially funded by the European Commission under FP7 project LEONE (FP7-317647).Publicad

Methods for revealing and reshaping the African Internet Ecosystem as a case study for developing regions: from isolated networks to a connected continent

Mención Internacional en el título de doctorWhile connecting end-users worldwide, the Internet increasingly promotes local development by making challenges much simpler to overcome, regardless of the field in which it is used: governance, economy, education, health, etc. However, African Network Information Centre (AfriNIC), the Regional Internet Registry (RIR) of Africa, is characterized by the lowest Internet penetration: 28.6% as of March 2017 compared to an average of 49.7% worldwide according to the International Telecommunication Union (ITU) estimates [139]. Moreover, end-users experience a poor Quality of Service (QoS) provided at high costs. It is thus of interest to enlarge the Internet footprint in such under-connected regions and determine where the situation can be improved. Along these lines, this doctoral thesis thoroughly inspects, using both active and passive data analysis, the critical aspects of the African Internet ecosystem and outlines the milestones of a methodology that could be adopted for achieving similar purposes in other developing regions. The thesis first presents our efforts to help build measurements infrastructures for alleviating the shortage of a diversified range of Vantage Points (VPs) in the region, as we cannot improve what we can not measure. It then unveils our timely and longitudinal inspection of the African interdomain routing using the enhanced RIPE Atlas measurements infrastructure for filling the lack of knowledge of both IPv4 and IPv6 topologies interconnecting local Internet Service Providers (ISPs). It notably proposes reproducible data analysis techniques suitable for the treatment of any set of similar measurements to infer the behavior of ISPs in the region. The results show a large variety of transit habits, which depend on socio-economic factors such as the language, the currency area, or the geographic location of the country in which the ISP operates. They indicate the prevailing dominance of ISPs based outside Africa for the provision of intracontinental paths, but also shed light on the efforts of stakeholders for traffic localization. Next, the thesis investigates the causes and impacts of congestion in the African IXP substrate, as the prevalence of this endemic phenomenon in local Internet markets may hinder their growth. Towards this end, Ark monitors were deployed at six strategically selected local Internet eXchange Points (IXPs) and used for collecting Time-Sequence Latency Probes (TSLP) measurements during a whole year. The analysis of these datasets reveals no evidence of widespread congestion: only 2.2% of the monitored links experienced noticeable indication of congestion, thus promoting peering. The causes of these events were identified during IXP operator interviews, showing how essential collaboration with stakeholders is to understanding the causes of performance degradations. As part of the Internet Society (ISOC) strategy to allow the Internet community to profile the IXPs of a particular region and monitor their evolution, a route-collector data analyzer was then developed and afterward, it was deployed and tested in AfriNIC. This open source web platform titled the “African” Route-collectors Data Analyzer (ARDA) provides metrics, which picture in real-time the status of interconnection at different levels, using public routing information available at local route-collectors with a peering viewpoint of the Internet. The results highlight that a small proportion of Autonomous System Numbers (ASNs) assigned by AfriNIC (17 %) are peering in the region, a fraction that remained static from April to September 2017 despite the significant growth of IXPs in some countries. They show how ARDA can help detect the impact of a policy on the IXP substrate and help ISPs worldwide identify new interconnection opportunities in Africa, the targeted region. Since broadening the underlying network is not useful without appropriately provisioned services to exploit it, the thesis then delves into the availability and utilization of the web infrastructure serving the continent. Towards this end, a comprehensive measurement methodology is applied to collect data from various sources. A focus on Google reveals that its content infrastructure in Africa is, indeed, expanding; nevertheless, much of its web content is still served from the United States (US) and Europe, although being the most popular content source in many African countries. Further, the same analysis is repeated across top global and regional websites, showing that even top African websites prefer to host their content abroad. Following that, the primary bottlenecks faced by Content Providers (CPs) in the region such as the lack of peering between the networks hosting our probes and poorly configured DNS resolvers are explored to outline proposals for further ISP and CP deployments. Considering the above, an option to enrich connectivity and incentivize CPs to establish a presence in the region is to interconnect ISPs present at isolated IXPs by creating a distributed IXP layout spanning the continent. In this respect, the thesis finally provides a four-step interconnection scheme, which parameterizes socio-economic, geographical, and political factors using public datasets. It demonstrates that this constrained solution doubles the percentage of continental intra-African paths, reduces their length, and drastically decreases the median of their Round Trip Times (RTTs) as well as RTTs to ASes hosting the top 10 global and top 10 regional Alexa websites. We hope that quantitatively demonstrating the benefits of this framework will incentivize ISPs to intensify peering and CPs to increase their presence, for enabling fast, affordable, and available access at the Internet frontier.Programa Oficial de Doctorado en Ingeniería TelemáticaPresidente: David Fernández Cambronero.- Secretario: Alberto García Martínez.- Vocal: Cristel Pelsse

Identification And Molecular Analysis Of DNA In Exosomes

Exosomes are heterogeneous nanoparticles 50-150nm in diameter. Exosomes contain many functional cargo components, such as protein, DNA, and RNA. While protein and RNA exosome content has been extensively studied, very little work has been done to characterize exosomal DNA. Here, we demonstrate that exosomal DNA is heterogeneous and its packaging into exosomes is dependent on the cell of origin. Furthermore, through a rigorous assessment of various isolation methods, we identify Size Exclusion Chromatography (SEC) as the best method for the isolation of exosomal DNA for downstream applications. Additionally, we evaluate the methylation status of exosomal DNA and demonstrate that exosomal DNA is both methylated and fully recapitulates the methylation patterns observed in the cells of origin. We also propose a potential mechanism for DNA packaging into exosomes by disruption of the nuclear membrane. Finally, we investigated the ability of exosomes to induce paracrine DNA damage responses (DDR) in treatment-naïve cells. We explore the specificity of exosome-induced DDR to exosomes released by damaged cancer cells, and provide a potential molecular mechanism of action via the shuttling of activated DDR pathway proteins

Effects of selected nitrogen-containing aromatic compounds (NCACs) on physiological properties in Escherichia coli

This research examined the effects of quinoline and 4-azafluorene on respiratory electron transport rate (ET), outer membrane permeability and topology, oxygen consumption, and viable cell density in Escherichia coli cell suspensions. ET was estimated spectrophotometrically using INT (2-(p-iodophenyl)-3-(p-nitrophenyl)-5-(phenyl)-2H-tetrazolium chloride, which is reduced in vivo to a red colored formazan (INTF). Both test compounds caused anomalous dose-response behavior in INT assays: in a defined window of doses, ET rates near or above the controls were observed. These doses showed altered INT reduction kinetics, decreased cellular oxygen demand, and decreased viable cell densities. Experiments with E. coli spheroplast preparations, gram(+) cells, and deep rough mutants suggested that the toxicants increased outer membrane permeability and inhibited normal respiratory function. Results of cell-free ET assays and transmission electron microscopy further indicated altered outer membrane structure and inhibition of respiratory ET via, (1) secondary topological effects on the periplasm and inner membrane, (2) redox cycling of electrons in the respiratory chain, or (3) both 1 and 2 together. Quantitative studies of INT chemical structure and aqueous electrochemistry at Hg, C, and Pt electrodes were conducted to address analytical shortcomings in the literature. Data include nuclear magnetic resonance spectra, results from normal and differential pulse polarography, cyclic voltammetry, ring disc electrode, and spectroelectrochemical experiments. The route of INT reduction involves a slow one electron reduction to a tetrazolinyl radical followed by a fast one electron reduction and addition of one proton to yield formazan. Results on C and Pt electrodes indicated interfering reactions involving adsorbed hydrogen species and the possibility of underpotential generation of hydrogen gas

Stress-mediated reaction pathways for dislocation nucleation in copper

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007.Includes bibliographical references (p. 111-119).The ductile behavior of metals requires dislocation nucleation, from either homogeneous or heterogeneous sources, in order to produce the large number of dislocations necessary for extensive plastic deformation. As with the majority of the defect processes that comprise deformation and failure of materials, dislocation nucleation is well described in the framework of transition state theory as a stress-mediated, thermally activated process. We have used reaction pathway sampling methods and well-fit empirical potentials to determine the stress-dependent behavior of and atomistic mechanisms for dislocation nucleation at stresses much lower than typically accessible to atomistic techniques. We have shown that a significant range of stresses exist for which homogeneous dislocation loop nucleation is feasible because the critical nucleate transitions to an in-plane shear perturbation where the shear displacement of most particles is significantly less than the Burger's vector. We have also revealed that the common structural conception of activation volume for dislocation nucleation does not apply for all stresses and in general over-predicts the stress-dependence of activation by considering only the shear displacement of the critical defect.(cont.) Furthermore, by considering the full reaction pathway for dislocation nucleation in perfect crystals and at a vacancy, we have provided a fully atomistic description of shear localization via an expanded one-dimensional chain analysis of the wave-steepening behavior. Lastly, both breaking the local atomic symmetry and increasing the extent of heterogeneous nucleation sites are shown to lower the activation energy for dislocation nucleation. In general we have applied reaction pathway sampling to the problem of dislocation nucleation in Cu not only for a perfect crystal, but also in the presence of point defects, vacancy clusters and nanowire surfaces. As a result the strength of a variety of nucleation sites in mediating activation as well as specific atomistic mechanisms for dislocation nucleation have been discussed from both structural and energetic perspectives.by Robert D. Boyer.Ph.D

A multi-physics simulation approach to Investigating the underlying mechanisms of Low-Speed Pre-Ignition

As part of the effort to improve thermal efficiency, engines are being significantly downsized. A common issue in gasoline engines which limits thermal efficiency and is further exacerbated by downsizing, is low speed pre ignition (LSPI). This thesis uses a Multiphysics approach, initially using a validated 1D engine performance model of a GTDI engine, to define realistic boundary conditions. A strong emphasis on validating each simulation methodology as much as possible is maintained at each stage. A hydrodynamic model of the ring-liner and Lagrangian CFD model are used to investigate the impact of engine oil fluid properties on the mass of oil transported from the crevice volume to the combustion chamber. A heat transfer and evaporation model of a single droplet inside an engine environment was developed for alkanes of chain lengths representing the extremes of the chain lengths present in engine oil. It was found the droplet generally evaporates at a crank angle which is close to the point where LSPI is observed. The hydrocarbon study ends with a CFD constant volume simulation to understand why engine oil like hydrocarbons ignite in rig tests but not in an engine. This research then proceeds to develop a single particle detergent model in an engine environment, to initially understand why ignition occurs when a calcium Ca based detergent is present but not in the case of a magnesium Mg detergent. It was found from simulation that the common theory of calcium oxide CaO resulting from thermal degradation from the previous cycle then reacting with Carbon dioxide CO2 late in the compression stroke is unlikely. There is a stronger case for the CaO particle causing ignition as it is present in fresh engine oil sprayed onto the liner. As predicted by the hydrocarbon evaporation model the oil will cover and protect the CaO particle until late in the compression stroke when the oil will evaporate, exposing the CaO particle to CO2

The Portrayal of Women in Selected Short Stories by Eudora Welty. (Volumes I and II).

Although Eudora Welty is a literary artist noted for her feminine approach, she is not a feminist. In writing fiction, she says, I think imagination comes ahead of sex. Most of the selections in her short-story volumes portray women characters, however, usually from points of view which focus upon the experiences of women from their particular angles of vision. Her women range from the young girl in A Visit of Charity to the aged Phoenix in A Worn Path. This study examines Miss Welty\u27s portrayal of women, their roles and conflicts, an aspect of her fiction that has received comparatively little critical treatment. Twenty-one stories are analyzed in detail, twenty from A Curtain of Green, The Wide Net, The Golden Apples, and The Bride of the Innisfallen, and an additional story, A Sketching Trip, from The Atlantic Monthly (June 1945). Three of the several patterns of characterization of women in Miss Welty\u27s short stories have been selected for analysis: initiates, isolated spinsters, and mother-women. The initiates include seven girls or women who under­ go or are ber,inning to undergo a heightened awareness cf themselves in relation to other people and to the world. A Visit of Charity is analyzed as an example of tentative initiation; A Memory, The Winds, and At the Landing as examples of uncompleted initiation; and Livvie, A Sketching Trip, and A Curtain of Green as examples of decisive initiation. The analyses are set within the context of American literary treatments of initiation and of psychological theories about initiation. The isolated spinsters, those whose singleness causes spiritual, psychological, or economic isolation, include ten women in six stories. These characters are studied against the background of Erich Fromm\u27s beliefs about isolation and life-fulfillment and against the stereotype of the single woman in American fiction. Why I Live at the P.O. depicts a spinster in a public posi­ tion. Asphodel presents three women as feminine, helpless spinsters. Clytie and The Burning contain aristocratic spinster sisters. June Recital and The Wanderers depict a teacher and her student as isolated spinsters. The mother-women, Kate Chopin\u27s term for women devoted to home and family, include characters in seven stories. Death of a Traveling Salesman, Flowers for Marjorie, and The Wide Net present expectant mothers. Ladies in Spring, Shower of Gold, Going to Naples, and A Worn Path depict women with already-established families. An eighth story, Petrified Man, portrays women whose views toward marriage and childbirtt make them anti-mother-women. This study concludes that Miss Welty\u27s portrayal of women is neither simple nor sentimental and that she uses realism of homely details to force her reader\u27s attention upon conditions of the human spirit which transcend the world of things. By carefully individualizing her characters, she avoids re-creating stereotypes found in much popular fiction about women. Miss Welty\u27s women are not only human, but their experiences also cross the sexual divide and provide iLsight into the common human situation. Her women seek, but do not always find, ful­ fillment through relationships with others. Sometimes, as in The Bride of the Innisfallen, her women discover freedom outside the marriage-bonds. Finally, patterns of characterization in her short stories point the ay toward portrayal of women in her major novels

Computational imaging and automated identification for aqueous environments

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 2011Sampling the vast volumes of the ocean requires tools capable of observing from a distance while retaining detail necessary for biology and ecology, ideal for optical methods. Algorithms that work with existing SeaBED AUV imagery are developed, including habitat classi fication with bag-of-words models and multi-stage boosting for rock sh detection. Methods for extracting images of sh from videos of longline operations are demonstrated. A prototype digital holographic imaging device is designed and tested for quantitative in situ microscale imaging. Theory to support the device is developed, including particle noise and the effects of motion. A Wigner-domain model provides optimal settings and optical limits for spherical and planar holographic references. Algorithms to extract the information from real-world digital holograms are created. Focus metrics are discussed, including a novel focus detector using local Zernike moments. Two methods for estimating lateral positions of objects in holograms without reconstruction are presented by extending a summation kernel to spherical references and using a local frequency signature from a Riesz transform. A new metric for quickly estimating object depths without reconstruction is proposed and tested. An example application, quantifying oil droplet size distributions in an underwater plume, demonstrates the efficacy of the prototype and algorithms.Funding was provided by NOAA Grant #5710002014, NOAA NMFS Grant #NA17RJ1223, NSF Grant #OCE-0925284, and NOAA Grant #NA10OAR417008

Frankenstein: a monstrous romanticism

Includes bibliographical references.The purpose of this thesis is to examine the relationship between Mary Shelley's first novel Frankenstein and her own understanding of Romanticism. The overarching theme is to illustrate how Mary Shelley navigates her criticism of Romanticism through the medium of Victor Frankenstein as a character. With the inspection of Victor Frankenstein some autobiographical similarities are drawn between the protagonist and Percy Bysshe Shelley. Another aim and extension of this autobiographical project is to examine how Percy Shelley's editing of the original manuscript of Frankenstein added or detracted from the plot. Finally, the genre implications of Frankenstein are examined in this thesis. In the first chapter, Romanticism is examined in relation to how the Romantics themselves envisioned their ideology so as to ascertain which aspects Mary Shelley draws particular attention to. The Romantic theorists used in this section specifically, Abercrombie and Schueller, are used to highlight the fact that Romanticism can be defined as a unified system of belief. Certain tenets of this ideology are then shown to be the main points that Mary Shelley criticises. In the second chapter, the autobiographical element of Mary Shelley's relationship with Percy Shelley is examined. The parallels between Victor Frankenstein and Percy Shelley are made apparent through the use of biographers Hoobler and Seymour. From that, the precise changes that Percy Shelley made to the original manuscript of Frankenstein are scrutinised with Mellor's insightful explication of the original that exists in the Bodleian Library. The conclusion of this chapter solidifies the argument of the first chapter, and as close attention is paid throughout both chapters to the novel as a primary source of confirmation, the complex navigations and articulations of Romanticism throughout Frankenstein are made apparent. In the third chapter, attention is given specifically to the genre implications of Frankenstein, and the relationship and consistent oscillation between Romanticism and the Gothic is traced. The theorists used in this part of the thesis vary widely and include Botting, Golinski and Alwes. It is argued that in her destabilisation of Romanticism, Mary Shelley invariably incorporates the Gothic into her text. It is this complex weaving of genres which is particularly interesting in relation to how Mary Shelley's disillusionment with Romanticism produces a text that has such a vast array of genre possibilities. Finally, this thesis looks at the negative interpretation of Romanticism specifically in relation to Mary Shelley's critical expressions of its ideology in Frankenstein. As a cautionary tale, the consequences of Romantic principles unchecked by a societal conscience, Mary Shelley seems to have used Frankenstein as a way of expressing her disillusionment. The repercussions of what ultimately is an original story of a scientist who unleashes his creation without concern for its welfare are still present in the common consciousness of modern society