Self-sealing of thermal fatigue and mechanical damage in fiber-reinforced composite materials

Fiber reinforced composite tanks provide a promising method of storage for liquid oxygen and hydrogen for aerospace applications. The inherent thermal fatigue of these vessels leads to the formation of microcracks, which allow gas phase leakage across the tank walls. In this dissertation, self-healing functionality is imparted to a structural composite to effectively seal microcracks induced by both mechanical and thermal loading cycles. Two different microencapsulated healing chemistries are investigated in woven glass fiber/epoxy and uni-weave carbon fiber/epoxy composites. Self-healing of mechanically induced damage was first studied in a room temperature cured plain weave E-glass/epoxy composite with encapsulated dicyclopentadiene (DCPD) monomer and wax protected Grubbs' catalyst healing components. A controlled amount of microcracking was introduced through cyclic indentation of opposing surfaces of the composite. The resulting damage zone was proportional to the indentation load. Healing was assessed through the use of a pressure cell apparatus to detect nitrogen flow through the thickness direction of the damaged composite. Successful healing resulted in a perfect seal, with no measurable gas flow. The effect of DCPD microcapsule size (51 um and 18 um) and concentration (0 - 12.2 wt%) on the self-sealing ability was investigated. Composite specimens with 6.5 wt% 51 um capsules sealed 67% of the time, compared to 13% for the control panels without healing components. A thermally stable, dual microcapsule healing chemistry comprised of silanol terminated poly(dimethyl siloxane) plus a crosslinking agent and a tin catalyst was employed to allow higher composite processing temperatures. The microcapsules were incorporated into a satin weave E-glass fiber/epoxy composite processed at 120C to yield a glass transition temperature of 127C. Self-sealing ability after mechanical damage was assessed for different microcapsule sizes (25 um and 42 um) and concentrations (0 - 11 vol%). Incorporating 9 vol% 42 um capsules or 11 vol% 25 um capsules into the composite matrix leads to 100% of the samples sealing. The effect of microcapsule concentration on the short beam strength, storage modulus, and glass transition temperature of the composite specimens was also investigated. The thermally stable tin catalyzed poly(dimethyl siloxane) healing chemistry was then integrated into a [0/90]s uniweave carbon fiber/epoxy composite. Thermal cycling (-196C to 35C) of these specimens lead to the formation of microcracks, over time, formed a percolating crack network from one side of the composite to the other, resulting in a gas permeable specimen. Crack damage accumulation and sample permeability was monitored with number of cycles for both self-healing and traditional non-healing composites. Crack accumulation occurred at a similar rate for all sample types tested. A 63% increase in lifetime extension was achieved for the self-healing specimens over traditional non-healing composites.

Utilização de diferentes fontes de carbono no cultivo do camarão litopenaeus vannamei em sistemas com bioflocos

A tecnologia do sistema de cultivo com bioflocos (BFT) permite a intensificação da densidade de estocagem, bem como o aumento da produtividade no qual exige esforços no manejo para a manutenção de qualidade de água. No entanto, um dos problemas é a liberação de nitrogênio através de alimento não consumidos, juntamente com as excretas dos organismos cultivados, principalmente na forma de amônia total. A adição de fontes de carbono orgânico é uma alternativa na redução de amônia tornando possível a conversão deste composto em proteína bacteriana, sendo disponível como alimento suplementar no ambiente de cultivo. Portanto foram testadas fontes de carbono como o melaço de cana-de-açúcar, dextrose e farelo de arroz no cultivo do camarão L. vannamei em sistemas BFT, avaliando a redução da concentração do nitrogênio amoniacal total em experimentos nas fases de berçário e engorda, bem como a análise de desempenho zootécnico dos animais. Os experimentos foram realizados utilizando caixas com volume útil de 800 L. O experimento berçário teve a duração de 35 dias, com densidade de estocagem de 1200 camarões m- ² e peso médio de 0,024±0,01 g. As fontes de carbono melaço de cana-de-açúcar (M) e farelo de arroz (F) foram combinadas em diferentes percentuais. No experimento engorda foi utilizada densidade de estocagem de 300 camarões m- ², peso médio de 4,09±0,51 g, durante 70 dias. Os tratamentos foram distinguidos pelas fontes de carbono dextrose e farelo de arroz. No experimento berçário a concentração da amônia foi significativamente menor (p<0,05) com o uso do melaço. O nitrito acumulou até o final do experimento, mas devido ao curto período experimental não interferiu nos índices de desempenho zootécnico, nos quais não apresentaram diferenças pelo uso das fontes de carbono. No experimento engorda, com o uso da dextrose, a concentração de amônia foi significativamente menor (p<0,05). Apesar de elevadas concentrações de nitrito, as sobrevivências foram similares e acima de 80%. Dados zootécnicos como peso final, ganho de peso semanal, conversão alimentar aparente e produtividade foram significativamente melhores (p<0,05) no tratamento farelo de arroz. Em ambos os experimentos as fontes de carbono de degradação rápida, como o melaço e a dextrose foram mais eficientes na redução de amônia. A degradação rápida destas fontes podem ter disponibilizado maiores teores de carbono como substrato para as bactérias heterotróficas metabolizarem a amônia, melhorando a qualidade da água.

Estratégia alimentar com ciclos de restrição e realimentação no desempenho produtivo de juvenis de tilápia do Nilo da linhagem GIFT

O objetivo deste estudo foi avaliar a ocorrência de resposta compensatória no desempenho produtivo de juvenis de tilápia do Nilo Oreochromis niloticus, linhagem GIFT, submetidos a diferentes estratégias alimentares. Foram utilizados 135 juvenis de tilápia, distribuídos em nove tanques de polietileno de 100L cada. As estratégias testadas foram: grupo controle (alimentado todo dia), grupo alimentado por cinco dias seguidos de dois dias de restrição de alimento (5A/2R) e grupo alimentado por quatro dias seguidos de três dias de restrição de alimento (4A/3R). Foram avaliados parâmetros físico-químicos da água e de desempenho produtivo. Os resultados foram submetidos à análise de variância, e as médias foram comparadas pelo teste Tukey, a 5% de probabilidade. A qualidade de água, o fator de condição e a conversão alimentar não foram influenciados pela estratégia alimentar. O grupo alimentado com a estratégia 5A/2R apresentou peso final, ganho de peso e taxa de crescimento específico semelhantes ao grupo continuamente alimentado (7,8 e 9,2g; 6,4 e 7,8g e 2,7 e 3,0% dia-1, para peso final, ganho de peso e taxa de crescimento especifico, respectivamente). A estratégia 4A/3R apresentou os piores resultados de desempenho produtivo, e a estratégia 5A/2R pode ser usada na alimentação de juvenis de tilápia do Nilo sem prejuízo ao desempenho produtivo, possibilitando inclusive redução de até 22,5% na quantidade de alimento ofertada.

Diseño y evaluación de una red de sensores para analizar entornos acuáticos

En la acuicultura, la producción de camarón depende de parámetros ambientales, y químicos en el agua. Usualmente, la medición y compilación de datos acerca de estos parámetros se realiza manualmente. En este trabajo se propone y evalúa una red de sensores cuyos nodos se interconectan inalámbricamente para recolectar datos automáticamente. El diseño de la red explota la topología de malla, misma que permite incrementar la fiabilidad en la transmisión de datos. Adicionalmente, los módulos de hardware utilizados se configuran para reducir el consumo de energía. Se realizaron pruebas en entornos reales (tanques y piscinas) con varios nodos colocados en plataformas flotantes para capturar, transmitir y acumular datos relativos a temperatura del agua. Los resultados obtenidos son alentadores y demuestran las posibilidades que existen para explotar componentes electrónicos de bajo costo en aplicaciones de acuicultura inteligente.

UST news

The Underground Storage Tank program at the South Carolina Department of Health and Environmental Control publishes a biannual publication of compliance, technical, and financial information to supply outreach to tank owners, contractors, and the general public.

The Origins and Legacy of a Currency Board in Argentina

This is a qualitative case study of the adoption of a currency board in Argentina in 1991. It presents a discursive analysis and intellectual history of four overlaying and mutually influencing stories of Convertibility’s adoption. It is (1) the story of how Menem aligned himself to the Washington Consensus as a means to win a Presidential election. This ideological alignment influences and is influenced by a (2) reconstitution of the Peronist Party’s historically entrenched identity. This in turn re-fashion the whole system of interest articulation and relative power of interest groups in Argentina. The adoption of a currency board also marks the pace of (3) the entrenchment neoliberal interests across a domestic network of neoliberal think-tanks, technocrats, politicians, and “technopoles” articulating neoliberal interests outside of the Washington Consensus, within an International Neoliberal Network. Argentina’s adoption of a currency board falls in line with the Corner Solutions, a neoliberal doctrine promoted to influence developing countries to adopt two forms of exchange rate regimes that allow for less government involvement, including a currency board. Argentina starts as a test country and then becomes (4) an ideological stepping stone to help promote the creation of currency boards across more “developing” countries. These stories are not sequential but concurrent, and they help advance an alternative critique of neoliberalism that focuses on specifics to induce case-specific lessons versus a theory claiming to provide any universal truth.

The SUPERB Advisory Committee Annual Report

The State Underground Petroleum Environmental Response Bank (SUPERB) Act requires the SUPERB Advisory Committee to submit an annual report that addresses the financial status and viability of the SUPERB Account and the SUPERB Financial Responsibility Fund, the number of sites successfully remediated, the number of sites remaining to be remediated, and any statutory or regulatory changes the committee recommends.

SUPERB Advisory Committee Annual report

The State Underground Petroleum Environmental Response Bank (SUPERB) Act requires the SUPERB Advisory Committee to submit an annual report that addresses the financial status and viability of the SUPERB Account and the SUPERB Financial Responsibility Fund, the number of sites successfully remediated, the number of sites remaining to be remediated, and any statutory or regulatory changes the committee recommends.

The SUPERB Advisory Committee Annual Report

The State Underground Petroleum Environmental Response Bank (SUPERB) Act requires the SUPERB Advisory Committee to submit an annual report that addresses the financial status and viability of the SUPERB Account and the SUPERB Financial Responsibility Fund, the number of sites successfully remediated, the number of sites remaining to be remediated, and any statutory or regulatory changes the committee recommends.

The SUPERB Advisory Committee 2008 Annual Report

The State Underground Petroleum Environmental Response Bank (SUPERB) Act requires the SUPERB Advisory Committee to submit an annual report that addresses the financial status and viability of the SUPERB Account and the SUPERB Financial Responsibility Fund, the number of sites successfully remediated, the number of sites remaining to be remediated, and any statutory or regulatory changes the committee recommends.

The SUPERB Advisory Committee 2009 Annual Report

The State Underground Petroleum Environmental Response Bank (SUPERB) Act requires the SUPERB Advisory Committee to submit an annual report that addresses the financial status and viability of the SUPERB Account and the SUPERB Financial Responsibility Fund, the number of sites successfully remediated, the number of sites remaining to be remediated, and any statutory or regulatory changes the committee recommends.

The SUPERB Advisory Committee 2010 Annual Report

The State Underground Petroleum Environmental Response Bank (SUPERB) Act requires the SUPERB Advisory Committee to submit an annual report that addresses the financial status and viability of the SUPERB Account and the SUPERB Financial Responsibility Fund, the number of sites successfully remediated, the number of sites remaining to be remediated, and any statutory or regulatory changes the committee recommends.

The SUPERB Advisory Committee 2011 Annual Report

The State Underground Petroleum Environmental Response Bank (SUPERB) Act requires the SUPERB Advisory Committee to submit an annual report that addresses the financial status and viability of the SUPERB Account and the SUPERB Financial Responsibility Fund, the number of sites successfully remediated, the number of sites remaining to be remediated, and any statutory or regulatory changes the committee recommends.

The SUPERB Advisory Committee 2013 Annual Report

The State Underground Petroleum Environmental Response Bank (SUPERB) Act requires the SUPERB Advisory Committee to submit an annual report that addresses the financial status and viability of the SUPERB Account and the SUPERB Financial Responsibility Fund, the number of sites successfully remediated, the number of sites remaining to be remediated, and any statutory or regulatory changes the committee recommends.

The SUPERB Advisory Committee 2014 Annual Report

The State Underground Petroleum Environmental Response Bank (SUPERB) Act requires the SUPERB Advisory Committee to submit an annual report that addresses the financial status and viability of the SUPERB Account and the SUPERB Financial Responsibility Fund, the number of sites successfully remediated, the number of sites remaining to be remediated, and any statutory or regulatory changes the committee recommends.