2,434 research outputs found
Dynamics of long bubbles propagating through cylindrical micro-pin fin arrays
The dynamics of two-phase flows confined within complex and non-straight geometries is of interest for a variety of applications such as micro-pin fin evaporators and flow in unsaturated porous media. Despite the propagation of bubbles in straight channels of circular and noncircular cross-sections has been studied extensively, very little is known about the fluid dynamics features of bubbles and liquid films deposited upon the inner walls of complex geometries. In this work, we investigate the dynamics of long gas bubbles and thin films as bubbles propagate through arrays of in-line cylindrical pins of circular shape in cross-flow, for a range of capillary and Reynolds numbers relevant to heat transfer applications and flow in porous media, different pitch of the cylinders and bubble lengths. Three-dimensional numerical simulations of the two-phase flow are performed using the open-source finite-volume library OpenFOAM v.1812, using a geometric Volume of Fluid (VOF) method to capture the interface dynamics. Systematic analyses are conducted for a range of capillary numbers Ca = 0. 04 --2R, Reynolds numbers Re = 1 -- 1000, streamwise pitch of the cylinders sx = 0. 125R, with R being the radius of the pin fins, and initial bubble length Lb = 2. 5R --12R. The simulations reveal that when bubbles propagate through pin fin arrays, they tend to partially coat the cylinders with a thin liquid film and to expand in the cross-stream direction within the gap left between adjacent cylinders. The liquid film deposited on the cylinders is significantly thinner than that reported for straight channels and similar geometrical constraints. As the streamwise distance between the cylinders is decreased, the flow configuration tends towards that for a straight channel, whereas larger distances cause the bubble to expand excessively in the cross-stream direction, and to eventually arrest when sx > 2R. Inertial effects have a strong impact on the bubble shape and dynamics when Re > 500, triggering time-dependent patterns that lead to bubble fragmentation and much thicker liquid films
Cell lineage-specific mitochondrial resilience during mammalian organogenesis
Mitochondrial activity differs markedly between organs, but it is not known how and when this arises. Here we show that cell lineage-specific expression profiles involving essential mitochondrial genes emerge at an early stage in mouse development, including tissue-specific isoforms present before organ formation. However, the nuclear transcriptional signatures were not independent of organelle function. Genetically disrupting intra-mitochondrial protein synthesis with two different mtDNA mutations induced cell lineage-specific compensatory responses, including molecular pathways not previously implicated in organellar maintenance. We saw downregulation of genes whose expression is known to exacerbate the effects of exogenous mitochondrial toxins, indicating a transcriptional adaptation to mitochondrial dysfunction during embryonic development. The compensatory pathways were both tissue and mutation specific and under the control of transcription factors which promote organelle resilience. These are likely to contribute to the tissue specificity which characterizes human mitochondrial diseases and are potential targets for organ-directed treatments
Mean-shift exploration in shape assembly of robot swarms
The fascinating collective behaviors of biological systems have inspired extensive studies on shape assembly of robot swarms. Here, we propose a strategy for shape assembly of robot swarms based on the idea of mean-shift exploration: when a robot is surrounded by neighboring robots and unoccupied locations, it would actively give up its current location by exploring the highest density of nearby unoccupied locations in the desired shape. This idea is realized by adapting the mean-shift algorithm, which is an optimization technique widely used in machine learning for locating the maxima of a density function. The proposed strategy empowers robot swarms to assemble highly complex shapes with strong adaptability, as verified by experiments with swarms of 50 ground robots. The comparison between the proposed strategy and the state-of-the-art demonstrates its high efficiency especially for large-scale swarms. The proposed strategy can also be adapted to generate interesting behaviors including shape regeneration, cooperative cargo transportation, and complex environment exploration
2023-2024 Graduate School Catalog
You and your peers represent more than 67 countries and your shared scholarship spans 140 programs - from business administration and biomedical engineering to history, horticulture, musical performance, marine science, and more. Your ideas and interests will inform public health, create opportunities for art and innovation, contribute to the greater good, and positively impact economic development in Maine and beyond
Use of omic tools for environmental risk assessment of emerging contaminants in marine species of commercial interest
La presente tesis doctoral busca evaluar los posibles efectos toxicológicos que pueden
tener los contaminantes ‘emergentes’ (CE) en los organismos marinos expuestos a
ellos. En concreto, se han evaluado dos filtros solares, un repelente de insectos y un
biocida, todos ellos presentes en productos de cuidado personal (PCP). Estas
sustancias llegan a los sistemas marinos a través de los vertidos de aguas residuales,
así como las entradas directas procedentes de actividades recreativas, tales como la
natación y el baño. La exposición a estos contaminantes se hace a muy bajas
concentraciones y de forma crónica, por tanto, evaluar sus posibles efectos a nivel
molecular resulta un paso clave para determinar su toxicidad. Las tecnologías “ómicas”
permiten el estudio global de los diferentes niveles biológicos (transcriptoma, proteoma,
metaboloma…) desde un punto de vista holístico e integrado. La integración de datos
ómicos, junto con la fusión de datos de bioconcentración y toxicocinética, es un método
extremadamente útil para dilucidar el modo de acción (MoA) de los contaminantes. De
este modo, en la presente tesis doctoral se ha implementado el uso y la integración de
herramientas ómicas (metabolómica y transcriptómica) para evaluar el efecto
toxicológico de dos filtros solares (4-metilbencilideno alcanfor (4-MBC) y sulisobenzona
(BP-4)), un repelente de insectos (N,N-Dietil-meta-toluamida (DEET)) y un biocida
(triclosán (TCS)) en dos especies marinas de interés comercial, la dorada (Sparus
aurata) y la almeja japonesa (Ruditapes philippinarum). Adicionalmente se realizaron
estudios de bioconcentración y toxicocinética.
Primero, se realizaron siete experimentos de exposición con los contaminantes y
organismos anteriormente mencionados usando un flujo continuo para reproducir
escenarios de exposición ambiental bajo condiciones controladas de laboratorio. Tras la
aplicación de técnicas analíticas y de alto rendimiento, se observó que la
bioacumulación de los contaminantes es superior en la almeja que en los peces. Esto
evidencia la importancia de tener en cuenta organismos de distintos niveles tróficos para
evaluar el potencial de bioacumulación de los contaminantes ambientales. Además, se observó que el filtro solar 4-MBC presentó el factor de bioacumulación (BCF) más alto
(368 565 L Kg -1) y la tasa de eliminación más baja (61.65%) que, junto con la
persistencia de este compuesto en el medio, son probablemente indicativos de un riesgo
potencial para el medio acuático marino que puede llegar a magnificarse a través de la
red alimentaria. También se observó que este compuesto sufría varias
biotransformaciones (reducción, oxidación, hidroxilación…) con el fin de ser excretado,
afectando al metabolismo de las drogas y xenobióticos y al del glutatión, llegando a
producir estrés oxidativo. Por otro lado, se observó que, aunque el TCS y BP-4 tenían
altos BCF en la almeja (1309 y 850 L Kg -1 respectivamente), sus tasas de eliminación
también eran altas (97.12 y 99.99%). Sin embargo, la exposición a estos contaminantes
produjo, entre otros, alteraciones en el metabolismo de los lípidos lo que puede deberse
a su capacidad como disruptores endocrinos. El DEET presentó el BCF más bajo en la
almeja (9.9 L Kg -1) y una alta tasa de eliminación (98.85%). El principal impacto de la
exposición de este compuesto a nivel transcriptómico se observó en el metabolismo de
biodegradación de xenobióticos y en el de los carbohidratos, lo que sugiere que se
estaba realizando un gran consumo energético para poder llevar a cabo la excreción del
compuesto.
En el músculo de la dorada se observó que tanto el DEET como la BP-4 presentaban
bajos BCF (2.6 y 0.7 L Kg -1 respectivamente) mientras que el TCS presentaba un BCF
de 113 L Kg -1. Sin embargo, los análisis transcriptómicos en el hígado de las doradas
revelaron que tras la exposición a DEET y BP-4, se expresaron 250 y 371 genes
diferencialmente, mientras que no se encontraron genes diferencialmente expresados
en la dorada tras la exposición a TCS. Tras la integración con los datos metabolómicos
realizados en las mismas muestras, se determinó que el DEET causaba en la dorada
agotamiento energético a través de la alteración de los metabolismos de carbohidratos
y aminoácidos, estrés oxidativo que daba lugar a daños en el ADN, peroxidación lipídica
y daños en la membrana celular y apoptosis. También se observó la activación del
metabolismo de los xenobióticos, así como una reacción inmune-inflamatoria. Finalmente, la integración de datos multiómicos reveló que la BP-4 causaba en la dorada
impacto en el metabolismo energético y oxidación lipídica, así como, impacto en la
biosíntesis de las hormonas esteroideas y tiroideas y en el metabolismo de los
nucleótidos. En conclusión, esta tesis muestra la utilidad de integrar datos a distintos
niveles biológicos y demuestra que el enfoque multiómico desarrollado y aplicado
supone una gran ventaja para dilucidar modos de acción de los compuestos estudiados
que, con enfoques diferentes, como el uso de una sola herramienta ómica, podrían
haberse pasado por alto
Contextualising Title Pages by Material Culture: Typography & List of Rarities A Case Study Don Saltero’s Coffeehouse Catalogues, 1729 – 1795.
Using A Catalogue of the Rarities to Be Seen at Don Saltero’s Coffeehouse in Chelsea. To Which Is Added, a Compleat List of the Donors Thereof - published in London, England between 1729 and 1795, this case study contextualises the catalogue’s title pages through a change over time examination of the typography and then listed of rarities through strategies from material culture to understand better the intersecting identities floating around the public sphere. What was reflected were characteristics of religion, nationhood, and gender. Don Saltero’s rarities catalogues were a topic of discussion for patrons of Don Saltero’s coffeehouse in London. Catalogues analysed in this research existed in the coffee house environment, private homes, and wherever these catalogues ended up. The catalogues added legitimacy to the collections they accompanied and did so by placing objects within various Enlightenment discussions and tying the listed objects to contemporary cultural knowledge. Additionally, the object’s descriptions allowed spectators and readers to interact with the ‘science’ of the emerging field of natural history. They presented catalogues in a way that emulated emerging scientific works within the academic sphere of the natural world. The sources used here gained further fame and legitimacy through the connection to well-known naturalist Sir Hans Sloane, a physician to the royal family, president of the Royal Society, and founder of the British Museum. Owning rarity collections was often an elite enterprise, but a collection’s stories were deliberately pitched to a much broader audience offering access to the collections and the ideas they represented. Thus, these catalogues add significance to their collections by expanding public discourse on objects known as rarities
Cell lineage-specific mitochondrial resilience during mammalian organogenesis
Mitochondrial activity differs markedly between organs, but it is not known how and when this arises. Here we show that cell lineage-specific expression profiles involving essential mitochondrial genes emerge at an early stage in mouse development, including tissue-specific isoforms present before organ formation. However, the nuclear transcriptional signatures were not independent of organelle function. Genetically disrupting intra-mitochondrial protein synthesis with two different mtDNA mutations induced cell lineage-specific compensatory responses, including molecular pathways not previously implicated in organellar maintenance. We saw downregulation of genes whose expression is known to exacerbate the effects of exogenous mitochondrial toxins, indicating a transcriptional adaptation to mitochondrial dysfunction during embryonic development. The compensatory pathways were both tissue and mutation specific and under the control of transcription factors which promote organelle resilience. These are likely to contribute to the tissue specificity which characterizes human mitochondrial diseases and are potential targets for organ-directed treatments
A novel hybrid methodology to secure GOOSE messages against cyberattacks in smart grids
: IEC 61850 is emerging as a popular communication standard for smart grids. Standardized communication in smart grids has an unwanted consequence of higher vulnerability to cyber-attacks. Attackers exploit the standardized semantics of the communication protocols to launch different types of attacks such as false data injection (FDI) attacks. Hence, there is a need to develop a cybersecurity testbed and novel mitigation strategies to study the impact of attacks and mitigate them. This paper presents a testbed and methodology to simulate FDI attacks on IEC 61850 standard compliant Generic Object-Oriented Substation Events (GOOSE) protocol using real time digital simulator (RTDS) together with open-source tools such as Snort and Wireshark. Furthermore, a novel hybrid cybersecurity solution by the name of sequence content resolver is proposed to counter such attacks on the GOOSE protocol in smart grids. Utilizing the developed testbed FDI attacks in the form of replay and masquerade attacks on are launched and the impact of attacks on electrical side is studied. Finally, the proposed hybrid cybersecurity solution is implemented with the developed testbed and its effectiveness is demonstrated
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Sonic heritage: listening to the past
History is so often told through objects, images and photographs, but the potential of sounds to reveal place and space is often neglected. Our research project ‘Sonic Palimpsest’1 explores the potential of sound to evoke impressions and new understandings of the past, to embrace the sonic as a tool to understand what was, in a way that can complement and add to our predominant visual understandings. Our work includes the expansion of the Oral History archives held at Chatham Dockyard to include women’s voices and experiences, and the creation of sonic works to engage the public with their heritage. Our research highlights the social and cultural value of oral history and field recordings in the transmission of knowledge to both researchers and the public. Together these recordings document how buildings and spaces within the dockyard were used and experienced by those who worked there. We can begin to understand the social and cultural roles of these buildings within the community, both past and present
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