117 research outputs found
Eight-Pointed Star quilt, by Sylvia Delight Collings Musig
No full textImage of Eight-Pointed Star quilt created in 1913 by Sylvia Delight Collings Musig. Also includes questionnaires describing the quilt completed by Merial Musig Hawkins as part of the Utah Quilt Guild\u27s documentation days held from 1988-1994. Quilter father was a wool grower, so she got the raw wool from their sheep; she washed and dried the wool; then she and her aunt corded the wool to form the batt; this is the only quilt she ever made; Merial inherited it from her mother upon her leaving her home in 197
234. Coat owned by Mrs. Sylvia Musig of Monroe, Utah
No full textPhotographs of and document for a coat owned by Mrs. Sylvia Musig of Monroe, Utah. Belonged to owner\u27s mother, AUgusta Bohman Collings (born 1860 in Sweden), who came to Utah in 1863. Bought coat in Utah in late 1880
MuSig-DN: Schnorr Multi-Signatures with Verifiably Deterministic Nonces
No full textMuSig is a multi-signature scheme for Schnorr signatures, which supports key aggregation and is secure in the plain public key model. Standard derandomization techniques for discrete logarithm-based signatures such as RFC 6979, which make the signing procedure immune to catastrophic failures in the randomness generation, are not applicable to multi-signatures as an attacker could trick an honest user into producing two different partial signatures with the same randomness, which would reveal the user\u27s secret key.
In this paper, we propose a variant of MuSig in which signers generate their nonce deterministically as a pseudorandom function of the message and all signers\u27 public keys and prove that they did so by providing a non-interactive zero-knowledge proof to their cosigners. The resulting scheme, which we call MuSig-DN, is the first Schnorr multi-signature scheme with deterministic signing. Therefore its signing protocol is robust against failures in the randomness generation as well as attacks trying to exploit the statefulness of the signing procedure, e.g., virtual machine rewinding attacks. As an additional benefit, a signing session in MuSig-DN requires only two rounds instead of three as required by all previous Schnorr multi-signatures including MuSig. To instantiate our construction, we identify a suitable algebraic pseudorandom function and provide an efficient implementation of this function as an arithmetic circuit. This makes it possible to realize MuSig-DN efficiently using zero-knowledge proof frameworks for arithmetic circuits which support inputs given in Pedersen commitments, e.g., Bulletproofs. We demonstrate the practicality of our technique by implementing it for the secp256k1 elliptic curve used in Bitcoin
Catalyseurs nanostructurés pour la méthanisation du CO2 assistée par plasma
No full textWork presented for the double degree of: Doctor por la Universidad de Zaragoza in the framework of the program of Ingeniería Química y del Medio Ambiente Diplôme naDonal de Doctorat de Sorbonne Université, specialité EnergéDque génie des procédés.-- It was read 20/10/2023, Sobresaliente Cum Laude.[EN] Among the different processes for carbon capture and utilisation, CO2 methanation is experiencing a renaissance as a promising technology for the development of Power-to-gas as an energy storage solution and carbon circular economy. The field of plasma catalysis, which considers the association of a catalyst with non-thermal plasma, has been recently developed for boosting CO2 methanation. The challenges of plasma catalysis focus on taking advantage of the activated species and electrons created by the plasma to achieve more favourable reaction pathways and interaction with the active sites of the catalyst and on plasma-catalyst synergy, meaning the enhancement of the catalyst properties by contact with plasma and vice versa. The goal of this work is to explore the effect of morphology and physicochemical properties of nanostructured Ni/CeO2 catalysts on plasma-catalyst synergy and to highlight the key characteristics of the catalysis that control an efficient plasma-assisted CO2 methanation in order to advance in the rational design of materials tailored for applications in plasma catalysis. For the plasma-assisted CO2 methanation tests, a suitable non-thermal plasma type is the dielectric barrier discharge due to mild temperature conditions, which allow the catalyst to be in direct contact with the plasma in a packed bed configuration, and operation at atmospheric pressure, promising for industrial applications. Nickel catalysts supported on Ce-based metal oxides have been proposed in recent publications for plasma-assisted CO2 methanation. Ni is a reliable solution as it is active for CO2 methanation as well as cost-effective. Cerium oxide (CeO2) is an interesting material to be used as support thanks to its redox properties related to the tendency to form oxygen vacancies. Such property can be tuned by enhancing the non-stoichiometric nature of the CeO2 surface, either by doping or, as in this case, by morphology modification, which has been reported for cerium oxide to be controllable via synthesis method. The parameters of the hydrothermal synthesis were varied and CeO2 nanomaterials with different morphology (polyhedra, nanorods, nanocubes), crystallite size, and surface area were produced. The Ni catalysts synthesised with these supports were further characterised by state-of-the-art techniques to examine the most relevant physicochemical properties, e.g., surface area, reducibility and metal-support interaction, surface basicity, and formation of oxygen vacancies. In addition, the electrical behaviour of the catalysts was assessed with focus on how the materials affect the plasma discharge, charge transfer, and the dielectric property of the packed bed. FTIR operando technique was utilised to suggest a possible reaction pathway of the plasma-assisted CO2 methanation on Ni/CeO2. In conclusion, it was found that the physicochemical properties which are relevant in conventional thermal methanation, such as surface area and basicity, are applicable to plasma catalysis but the importance of low dielectric permittivity of the catalyst and charge transfer mechanism was also highlighted for an energy efficient plasma-assisted methanation process. Furthermore, a rod or needle-like CeO2 support allows enhancing the surface defects, the interaction with Ni, and macroposority, which seem to facilitate the methanation reaction in plasma via formate route.[ES] Entre los diferentes procesos de captura y utilización del carbono, la metanización del CO2 experimenta últimamente un renacimiento como tecnología prometedora para el desarrollo de la conversión de electricidad en gas, del almacenamiento de energía y de la economía circular del carbono. El campo de la catálisis asistida por plasma, que considera la asociación de un catalizador con plasma no térmico, se ha desarrollado recientemente para impulsar la metanización de CO2. Los retos de esta tecnología se centran en aprovechar las especies activadas y los electrones para conseguir vías de reacción e interacción más favorables con los sitios activos del catalizador y en la sinergia plasma-catalizador, es decir, la mejora de las propiedades del catalizador por contacto con el plasma y viceversa. El objetivo de este trabajo es explorar el efecto de la morfología y las propiedades físicoquímicas de los catalizadores de Ni/CeO2 nanoestructurados en la sinergia plasma-catalizador y resaltar las características clave del catalizador que controlan una eficiente metanación de CO2 asistida por plasma con el fin de avanzar en el diseño de materiales para aplicaciones en plasma catálisis. Para los experimentos de metanación de CO2 asistida por plasma, un tipo de plasma no térmico adecuado es la descarga de barrera dieléctrica debido a las condiciones de temperatura suaves, que permiten que el catalizador esté en contacto directo con el plasma en una configuración de lecho fijo, y el funcionamiento a presión atmosférica, prometedor para aplicaciones industriales. En publicaciones recientes se han propuesto catalizadores de níquel soportados sobre óxidos metálicos basados en Ce para la metanación de CO2 asistida por plasma. El niquel es un metal adecuado ya que es activo para la metanación de CO2, además relativamente de bajo costo. El óxido de cerio (CeO2) es un material interesante para ser utilizado como soporte gracias a sus propiedades de redox relacionadas con la tendencia a formar vacantes de oxígeno. Dicha propiedad puede ajustarse potenciando la no estequiometria de la superficie del CeO2, ya sea por dopaje o, como en este caso, por modificación de la morfología, que se ha descrito para el óxido de cerio como controlable a través del método de síntesis. Se variaron los parámetros de la síntesis hidrotermal y se produjeron nanomateriales de CeO2 con diferente morfología (poliedros, nanorods, nanocubos), tamaño de cristalito y área superficial. Los catalizadores de Ni sintetizados con estos soportes se caracterizaron además mediante técnicas avanzadas para examinar las propiedades fisicoquímicas más relevantes, por ejemplo, el área superficial, la reducibilidad y la interacción metal-soporte, la basicidad superficial y la formación de vacantes de oxígeno. Además, se evaluó el comportamiento eléctrico de los catalizadores centrándose en cómo afectan los materiales a la descarga de plasma, la transferencia de carga y la propiedad dieléctrica del lecho fijo. Se utilizó la técnica operando FTIR para sugerir una posible vía de reacción de la metanización de CO2 con Ni/CeO2 asistida por plasma. En conclusión, se encontró que las propiedades fisicoquímicas que son relevantes en la metanación térmica convencional, como el área superficial y la basicidad, no son aplicables a la plasma catálisis, pero también se enfatiza la importancia de la baja permitividad dieléctrica del catalizador y el mecanismo de transferencia de carga para un proceso energéticamente eficiente. Además, un soporte de CeO2 en forma de barra o de aguja permite potenciar los defectos superficiales, la interacción con el Ni y la macroposoridad, que parecen facilitar la reacción de metanación en plasma por vía del formiato.[FR] Parmi les différents procédés de capture et d'utilisation du carbone, la méthanisation du CO2 connaît une renaissance comme une technologie prometteuse pour le développement du Power-to-gas et en tant que solution de stockage de l'énergie et de l'économie circulaire du carbone. Le domaine de la catalyse plasma, qui considère l'association d'un catalyseur avec un plasma non thermique, a été récemment développé pour stimuler la méthanation du CO2. Les défis de la catalyse assistée par plasma consistent à tirer profit des espèces activées et des électrons créés par le plasma pour obtenir des voies de réaction et des interactions plus favorables avec les sites actifs du catalyseur, ainsi que de la synergie plasma-catalyseur, c'est-à-dire de la modification des propriétés du catalyseur par contact avec le plasma et vice-versa. L'objectif de cette thèse est d'explorer l'effet de la morphologie et des propriétés physicochimiques des catalyseurs Ni/CeO2 nanostructurés sur la synergie plasma-catalyseur et de mettre en évidence les caractéristiques clés du catalyseur qui permettent une méthanisation efficace du CO2 assistée par plasma, afin de progresser dans la conception rationnelle de matériaux adaptés aux applications de la plasma-catalyse. Pour les essais de méthanation du CO2 assistée par plasma, les plasmas froids à décharge de barrière diélectrique (DBD) permettent des températures douces, ainsi qu’un contact direct entre le plasma et le catalyseur dans une configuration de lit fixe. Au même temps ils permettent l’opération sous pression atmosphérique, conditions idéales pour des applications industrielles. Des catalyseurs à base de nickel supportés par des oxydes métalliques à base de Ce ont été proposés dans des publications récentes pour la méthanisation du CO2 assistée par plasma. Le nickel est une solution fiable, car il est actif dans la méthanisation du CO2 et au même temps économiquement rentable. L'oxyde de cérium (CeO2) est un matériau intéressant à utiliser comme support grâce à ses propriétés d'oxydoréduction liées à sa capacité d’échange d'oxygène. Ces propriétés peuvent être ajustées en améliorant la nature non stœchiométrique de la surface de CeO2, soit par dopage, soit, comme dans le cas présent, par modification de la morphologie, ce qui a été rapporté pour l'oxyde de cérium comme pouvant être contrôlé par la méthode de synthèse. Ainsi, les paramètres de la synthèse hydrothermale ont été modifiés, ce qui a permis d’obtenir des nanomatériaux de CeO2 présentant différentes morphologies (polyèdres, nanorods, nanocubes), tailles de cristallites et surfaces actives. Les catalyseurs Ni synthétisés avec ces supports ont été caractérisés par des techniques de pointe afin d'examiner les propriétés physicochimiques les plus pertinentes, par exemple la surface, la réductibilité et l'interaction métal-support, la basicité de la surface et la formation de lacunes dans l'oxygène. En outre, le comportement électrique des catalyseurs a été évalué en mettant l'accent sur la manière dont les matériaux affectent la décharge du plasma, le transfert de charge et le comportement diélectrique du lit fixe. La technique FTIR operando a été utilisée pour suggérer une voie de réaction possible de la méthanisation du CO2 assistée par plasma sur Ni/CeO2. En conclusion, il a été constaté que les propriétés physicochimiques qui sont pertinentes dans la méthanisation thermique conventionnelle ne sont pas entièrement applicables à la catalyse par plasma, car l'importance d'une faible permittivité diélectrique du catalyseur et d'un mécanisme de transfert de charge est mise en évidence pour un processus de méthanisation efficace sur le plan énergétique. Finalement, un support CeO2 contenant des nanostructures en forme de tige ou d'aiguille permet d'améliorer les défauts de surface, l'interaction avec le Ni et la macroposorité, ce qui semble faciliter la réaction de méthanisation dans le plasma par la voie du formiate.This project has received funding from the European Union’s Horizon H2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement n.º 813393.Peer reviewe
Uma implementação do esquema de multi-assinaturas MuSig no cenário m-de-n com árvores de Merkle e suas aplicações ao bitcoin
No full textNeste trabalho é proposto uma implementação prova de conceito do esquema de multi-
assinatura MuSig no cenário m-de-n com validação de chaves públicas agregadas através
de árvores de Merkle, expandindo a descrição original do MuSig neste cenário. Foi uti-
lizado a linguagem de programação Python e curvas elípticas (com destaque para a curva
secp256k1) para a construção da implementação. As multi-assinaturas produzidas man-
têm o tamanho de uma assinatura individual de Schnorr e podem ser verificadas utilizando
uma única chave pública agregada calculada a partir das chaves públicas dos signatarios,
tal situação traz expectativas positivas quanto a melhorias no desempenho e privacidade
do Bitcoin. Melhorias futuras incluem a implementação de uma prova de conceito que
integre o MuSig diretamente ao protocolo Bitcoin e a utilização do MuSig para construção
de um esquema de assinatura agregada interativa (IAS).This work presents a proof-of-concept implementation of the multi-signature scheme MuSig
in the m-of-n scenario with aggregated key validation using Merkle trees, expanding the
original MuSig description in this scenario. Python was the programming language of
choice and elliptic curves (mainly secp256k1) were used as the basis of the implementa-
tion. The multi-signatures generated by the scheme can keep the same size as a single
Schnorr signature and can be verified with a single aggregated public key computed from
the individual public keys of the signers, this scenario brings positive expectations for per-
formance and privacy improvements in Bitcoin. Future works includes a proof-of-concept
implementation that integrates the MuSig scheme directly into the Bitcoin protocol and
the implementation of an interactive signature scheme (IAS) with the MuSig scheme as
its basis
Inhomogeneous MUSIG Model -a Population Balance Approach for Polydispersed Bubbly Flows
No full textAbstract A generalized inhomogeneous Multiple Size Group (MUSIG) Model based on the Eulerian modeling framework was developed in close cooperation of ANSYS-CFX and Forschungszentrum Dresden-Rossendorf and implemented into CFX-10. Simulating a poly-dispersed gaseous liquid two phase flow along with the mass exchanged between bubble size classes by bubble coalescence and bubble break-up and the momentum exchange of bubble size dependent bubble forces have to be considered. Particularly the lift force has been proved to play an important role establishing a certain flow regime. The paper describes the main concepts of the model approach and presents a model validation case. Further application test cases are presented b
Validation of the multiple velocity multiple size group (CFX10.0 N x M MUSIG) model for polydispersed multiphase flows
No full textTo simulate dispersed two-phase flows CFD tools for predicting the local particle number density and the size distribution are required. These quantities do not only have a significant effect on rates of mixing, heterogeneous chemical reaction rates or interfacial heat and mass transfers, but also a direct relevance to the hydrodynamics of the total system, such as the flow pattern and flow regime. The Multiple Size Group (MUSIG) model available in the commercial codes CFX-4 and CFX-5 was developed for this purpose. Mathematically, this model is based on the population balance method and the two-fluid modeling approach. The dispersed phase is divided into N size classes. In order to reduce the computational cost, all size groups are assumed to share the same velocity field. This model allows to use a sufficient number of particle size groups required for the coalescence and breakup calculation. Nevertheless, the assumption also restricts its applicability to homogeneous dispersed flows. We refer to the CFX MUSIG model mentioned above as the homogeneous model, which fails to predict the correct phase distribution when heterogeneous particle motion becomes important. In many flows the non-drag forces play an essential role with respect to the bubble motion. Especially, the lift force acting on large deformed bubbles, which is dominated by the asymmetrical wake, has a direction opposite to the shear induced lift force on a small bubble. This bubble separation cannot be predicted by the homogeneous MUSIG model. In order to overcome this shortcoming we developed an efficient inhomogeneous MUSIG model in cooperation with ANSYS CFX. A novel multiple velocity multiple size group model, which incorporates the population balance equation into the multi-fluid modeling framework, was proposed. The validation of this new model is discussed in this report
Tissue plasminogen activator in treatment of acute fibrinous reaction of anterior chamber in acute iridocyclitis
No full textAbstract boo
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