Estudo de caso aplicando modelo para identificação de potenciais geradores de intangíveis
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Rodney Wernke
2003-12-01
Full Text Available Relata estudo de caso em que foi aplicado o modelo Mapa para Identificação de Potenciais Geradores de Intangíveis. Após mencionar resumidamente a ferramenta utilizada, apresentam-se os procedimentos seguidos para implementar tal modelo numa empresa industrial, evidenciando os passos seguidos, as análises realizadas, os resultados alcançados e as limitações inerentes.This article reports on a case study which applied the model called Map for the Identification of Potential Intangible Asset Generators. After a summarized description of the applied tool, we present the procedures followed to implement such a model in an industrial company, disclosing the steps that were taken, the analyses carried out, obtained results and inherent limitations.
Potenciais benefícios do sistema de rastreabilidade animal dos EUA para o setor de carnes americano
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Moisés de Andrade Resende Filho
2008-12-01
Full Text Available Este artigo investigou os potenciais ganhos do setor de carnes americano advindos da implantação do Sistema Nacional de Identificação Animal (NAIS, dos EUA. Foram analisados os potenciais efeitos do NAIS sobre a percepção de risco dos consumidores americanos em relação aos perigos decorrentes do consumo das carnes bovina, suína e de aves e seus derivados. Sistemas de equações de demanda foram estimados, incorporando-se como "proxies" da percepção de risco do consumidor, séries de índices de segurança do alimento, separadamente construídas para cada tipo de carne. Tais séries foram concebidas, somando-se o número de referências nos principais jornais americanos a problemas de segurança da carne. Foi utilizado o melhor modelo estimado, escolhido com base em uma série de testes de especificação, para se construir três cenários, simulando-se os casos em que o NAIS não está implementado; que está implementado apenas para o gado bovino; e que está implementado para suínos e bovinos. Foram utilizadas as diferenças entre as receitas estimadas para cada cenário e para cada tipo de carne, como uma medida do potencial ganho advindo da implementação do NAIS. Foi concluído que os setores da carne bovina e suína poderiam arcar com os custos do NAIS. Esse resultado, contudo, depende de o quanto desses potenciais ganhos chegarão efetivamente aos produtores agrícolas.This article investigates the potential gains to the U.S. meat sector with the implantation of the U.S. National Animal Identification System (NAIS. The focus is on the effect that the NAIS could have on consumers' risk perception about eating meat. System of demand equations are estimated using time series of food safety indexes variables used as proxies for consumers' reactions to news on meat safety issues. The series of food safety indexes are built on the basis of the number of food safety news reported in top U.S. newspapers. Using the preferred model
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Luzia Maria Pozzobom Ventura
2009-12-01
Full Text Available Os potenciais evocados auditivos de longa latência (PEALLs se referem a uma série de mudanças elétricas, ocorridas no sistema nervoso central, resultante da estimulação da via sensorial auditiva. Muitos estudos abordam o uso destes potenciais, controlando o artefato gerado pelo movimento ocular com a utilização de equipamentos com grande número de canais. Porém, na prática clínica nacional, a realidade é diferente, havendo disponibilidade de equipamentos com número reduzido de canais. OBJETIVO: Comparar dois métodos de controle do artefato gerado pelo movimento ocular durante a captação dos PEALLs usando dois canais de registro. MATERIAL E MÉTODO: Estudo prospectivo pela aplicação de dois métodos de captação dos PEALLs (subtração do artefato ocular e controle do limite de rejeição em 10 adultos ouvintes normais. RESULTADOS: Não foi observada diferença estatisticamente significante entre os valores de latência obtidos com o uso dos dois métodos, apenas entre os valores de amplitude. CONCLUSÃO: Os dois métodos foram eficientes para a captação dos PEALLs e para o controle do artefato do movimento ocular. O método do controle do limite de rejeição promoveu maiores valores de amplitude.Long Latency Auditory Evoked Potentials (LLAEP represents a number of electrical changes occurring in the central nervous system, resulting from stimulation of the auditory sensorial pathways. Many studies approach the use of these potentials controlling the artifact created by eye movement with the use of equipment with a large number of channels. However, what happens is very different in Brazilian clinical practice, where the equipment used has a very limited number of channels. AIM: to compare the two methods used to control the artifacts created by eye movements during LLAEP capture using two recording channels. MATERIALS AND METHODS: this is a prospective study with the application of two LLAEP capturing methods (eye artifact
Espécies potenciais para recuperação de áreas de preservação permanente no Planalto Catarinense
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Paula Iaschitzki Ferreira
Full Text Available Com o objetivo de selecionar espécies para programas de recuperação em Áreas de Preservação Permanente no Planalto Catarinense foi realizado o levantamento da composição florística e da estrutura fitossociológica e, a caracterização dos grupos ecológicos e síndromes de dispersão das espécies ocorrentes nestes locais. A área de estudo, fazenda Campo de Dentro, localiza-se no município de Otacílio Costa (SC, onde foi empregado o método de quadrantes, em 20 transecções compostas por 20 pontos amostrais. As espécies que apresentaram os maiores valores de importância, potenciais para recuperação, foram Sebastiania commersoniana (Baill. L.B.Sm. & Downs; Mimosa scabrella Benth.; Cinnamomum amoenum (Nees & Mart. Kosterm.; Lithraea brasiliensis Marchand, Ocotea pulchella (Nees & Mart. Mez; Ilex paraguariensis A.St.-Hil.; Matayba elaeagnoides Radlk.; Ilex theezans Mart. exReissek e Vernonanthura discolor (Spreng. H.Rob., que representam os diferentes grupos ecológicos, destacando-se a zoocoria como síndrome de dispersão. A alta diversidade de espécies arbóreas evidencia a riqueza desses locais que, muitas vezes, são negligenciados em projetos de recuperação.
Avaliação laboratorial de potenciais doadores de órgãos e tecidos para transplantes
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Quinidia Lúcia Duarte de Almeida Quithé de Vasconcelos
2014-01-01
Full Text Available El objetivo fue describir la evaluación de laboratorio y complementaria en potenciales donantes de órganos y tejidos para trasplantes. Estudio descriptivo, cuantitativo, realizado en seis hospitales de Natal/Rio Grande do Norte, Brasil, entre agosto/2010 y febrero/2011. La muestra compuesta por 65 potenciales donantes y se utilizó como instrumento una lista de verificación. Recolectaron los datos, analizados por estadística descriptiva. Del total, 89,2% realizaron el tiraje de sangre, 80,0% análisis hematológicos y verificación de los electrolitos. Cuanto a las funciones, 70,8% fueron sometidos a exámenes de la función pulmonar y 80,0% de la función renal. De los resultados, 69,2% tenían hiperoxia, 66,2% leucocitosis, 47,7% hipernatremia, 43,1% aumento de la creatina quinasa, 10,0% serología positiva. No se realizaron pruebas pertinentes. Es esencial evaluar los posibles donantes para detectar y tratar los cambios, lo que garantiza la calidad de los órganos y el trasplante.
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L. B. Oliveira
2002-06-01
Full Text Available Funções de pedotransferência são equações usadas para estimar características edáficas de difícil determinação a partir de outras mais facilmente obtidas. Apesar do bom número de equações disponíveis para estimativa da umidade retida a potenciais matriciais específicos, elas não devem ser usadas indiscriminadamente, pois, em sua maioria, foram desenvolvidas com solos de clima temperado e a partir de dados gerados por métodos diversos dos em uso nos laboratórios brasileiros. O presente trabalho teve por objetivos: (a elaborar funções de pedotransferência para estimar o conteúdo de água nos potenciais de -33 e -1.500 kPa e a água disponível, a partir de dados granulométricos e de densidade do solo, para solos do estado de Pernambuco e (b comparar a eficiência de predição das equações propostas em relação a equações similares, disponíveis na literatura. No desenvolvimento das equações, foi utilizada uma base de dados composta por 98 perfis de solos e 467 horizontes. Os perfis foram agrupados, de acordo com Sistema Brasileiro de Classificação de Solos, em 27 classes de terceiro nível categórico (grande grupo. As equações desenvolvidas apresentaram bons coeficientes de determinação e baixo erro de predição. A sistematização dos dados por atividade da fração argila ou grau aproximado de desenvolvimento ou classe textural não produziu melhorias na capacidade preditiva das pedofunções. As equações propostas em outros trabalhos apresentaram elevado erro de predição, o que restringe a sua utilização para solos do estado de Pernambuco.
Conselhos Gestores de Políticas Públicas: Potenciais Espaços para a Coprodução dos Serviços Públicos
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Luciana Francisco de Abreu Ronconi
2011-12-01
Full Text Available A institucionalização dos Conselhos, como espaços públicos de participação, discussão e deliberação, no âmbito das políticas públicas, torna-se relevante nos processos de democratização da gestão das políticas públicas e de controle da sociedade sobre os governos. Esse ensaio teórico pretende argumentar que os Conselhos Gestores de Políticas, apesar de limitações e desafios, podem ser espaços de encontro entre a sociedade e o Estado, ou seja, espaços para a coprodução dos serviços públicos. A coprodução do bem público é um conceito desenvolvido no final da década de setenta. Refere-se à produção de forma conjunta (sociedade, Estado e setor privado de certo bem ou serviço que seja de interesse público. Os componentes principais da coprodução são a descentralização e a interação entre Estado e a sociedade civil em um processo de ressignificação da esfera pública. Assim, os processos de coprodução dentro dos Conselhos podem reafirmar os valores da democracia, da cidadania e do interesse público ao colocar ênfase na participação ativa, ação conjunta e inclusão dos cidadãos na comunidade política. Ao gerar espaços públicos de participação, debate e controle, os Conselhos tornam-se um espaço potencialmente fértil para os processos de coprodução dos serviços públicos.
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Mariana Lopes Fávero
2010-08-01
Full Text Available O Hidrato de cloral é um sedativo usado em procedimentos pediátricos devido à pouca depressão respiratória e cardíaca. OBJETIVO: Avaliar a eficácia da droga para a captação do PEATE e sistematizar o seu emprego. MATERIAL E MÉTODO: Estudo prospectivo transversal com 41 crianças. A dose inicial de HC 10% foi de 50mg/kg com reforço de 6 mg/kg administrado após 30 minutos nos casos onde não houve sedação. A efetividade da droga foi determinada pela indução do sono até 1 hora após a administração da dose inicial. A ocorrência de sono foi correlacionada com as doses (50mg ou 56mg/kg, a idade, o peso e o sexo. RESULTADOS: As 41 crianças que participaram do estudo tomaram 50mg/kg e 23 dormiram em 30 minutos, 2 apresentaram depressão respiratória; 16 crianças tomaram reforço de 6mg/kg e 13 dormiram em mais 30 minutos. A dose total de 56mg/kg apresentou um efeito estatisticamente significante na indução do sono (pChloral Hydrate (CH is a sedative and hypnotic drug used in pediatric procedures owing to the low depressive effect it has on the respiratory and cardiac systems. AIM: To assess the efficacy of the drug in performing ABR and to systematize its use. MATERIALS AND METHODS: A prospective cross-sectional study with 41 children without history of heart or lung disease. The initial dose of CH at 10% was 50mg/Kg, with a boost dose of 6mg/Kg administered 30 minutes later in cases in which there was no sedation. Drug effectiveness was established by sleep induction by 1 hour after the administration of the initial dose. Sleep occurrence was correlated with doses (50mg or 56mg/Kg, age, weight and gender. RESULTS: All the 41 children who participated in the study took 50mg/kgof the agent and 23 of them slept within 30 minutes, 2 had respiratory complications, 16 had the 6mg/Kg boost dose and 13 fell asleep after 30 minutes. The 56 mg/kg dose presented a statistically significant effect on sleep induction (p<0.05 when compared
Repulsive Casimir and Casimir-Polder Forces
Milton, Kimball A; Parashar, Prachi; Pourtolami, Nima; Brevik, Iver; Ellingsen, Simen A
2012-01-01
Casimir and Casimir-Polder repulsion have been known for more than 50 years. The general "Lifshitz" configuration of parallel semi-infinite dielectric slabs permits repulsion if they are separated by a dielectric fluid that has a value of permittivity that is intermediate between those of the dielectric slabs. This was indirectly confirmed in the 1970s, and more directly by Capasso's group recently. It has also been known for many years that electrically and magnetically polarizable bodies can experience a repulsive quantum vacuum force. More amenable to practical application are situations where repulsion could be achieved between ordinary conducting and dielectric bodies in vacuum. The status of the field of Casimir repulsion with emphasis on recent developments will be reviewed. Here, stress will be placed on analytic developments, especially of Casimir-Polder (CP) interactions between anisotropically polarizable atoms, and CP interactions between anisotropic atoms and bodies that also exhibit anisotropy, ...
Gies, H; Gies, Holger; Klingmuller, Klaus
2006-01-01
We compute Casimir forces in open geometries with edges, involving parallel as well as perpendicular semi-infinite plates. We focus on Casimir configurations which are governed by a unique dimensional scaling law with a universal coefficient. With the aid of worldline numerics, we determine this coefficient for various geometries for the case of scalar-field fluctuations with Dirichlet boundary conditions. Our results facilitate an estimate of the systematic error induced by the edges of finite plates, for instance, in a standard parallel-plate experiment. The Casimir edge effects for this case can be reformulated as an increase of the effective area of the configuration.
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Sarah Gabriel Freire
2012-12-01
Full Text Available Objetivou-se descrever as alterações fisiológicas da morte encefálica em potenciais doadores de órgãos e tecidos para transplantes. Estudo exploratório descritivo com dados prospectivos e abordagem quantitativa realizado nas unidades de emergência e terapia intensiva adulto de um hospital de Pernambuco no período de abril a outubro de 2011. A população constou de 32 potenciais doadores de órgãos e tecidos para transplantes. Após aprovação do Comitê de Ética em Pesquisa, os dados foram coletados, tabulados e analisados pela estatística descritiva pelo software SPSS 15.0 e apresentados em forma de tabelas. As alterações fisiológicas foram: hipotensão arterial (100%, hipotermia (75,0%, hipernatremia (62,5%, diabetes insipidus (37,5%, hiperglicemia (32,3%, infecção (25,0%, hipertensão arterial (9,4% e úlcera de córnea (3,1%. Acredita-se que o conhecimento dessas alterações possibilita à equipe de saúde direcionar o cuidado ao potencial doador segundo as suas necessidades e, assim, manter o órgão/tecido viável para transplante.El objetivo del estudio fue describir los cambios fisiológicos de la muerte cerebral en los potenciales donadores de órganos y tejidos para trasplante. Investigación exploratoria, descriptiva, con datos prospectivos y enfoque cuantitativo, hecho en las unidades de emergencia y de cuidados intensivos de adultos de un hospital de Pernambuco en el periodo de abril a octubre de 2011. La población fue formada por 32 potenciales donadores de órganos y tejidos para trasplante. Después de la aprobación en el Comité Ético de Investigación, los datos han sido recogidos, tabulados y analizados mediante estadística descriptiva por el programa informático SPSS 15.0, siendo presentados en forma de tablas. Los cambios fisiológicos fueron: hipotensión (100%, hipotermia (75,0%, hipernatremia (62,5%, diabetes insípida (37,5%, infección (25,0%, hipertensión arterial (9,4% y la úlcera de c
1993-01-01
The release of Casimir energy in filling a dielectric hole is identified as the source of coherent sonoluminescence. Qualitative agreement with recently acquired data is found for the magnitude and shape of the spectrum.
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Edvaldo Leal de Moraes
2009-01-01
Full Text Available OBJETIVO: Conhecer a percepção de familiares de potenciais doadores sobre os motivos de recusa para doação de órgãos e tecidos para transplante. MÉTODOS: Trata-se de uma pesquisa qualitativa, na vertente fenomenológica, modalidade "estrutura do fenômeno situado". Participaram do estudo oito familiares que recusaram a doação dos órgãos e tecidos. RESULTADOS: Após análise das entrevistas, foram revelados dez motivos de recusa, considerados pelos familiares. CONSIDERAÇÕES FINAIS: As proposições que emergiram revelaram que os motivos de recusa familiar para doação de órgãos e tecidos estão relacionados à crença, valores e inadequações no processo de doação e transplante.OBJETIVO: Conocer la percepción de familiares de potenciales donadores sobre los motivos de su negación para la donación de órganos y tejidos para transplante. MÉTODOS: Se trata de una investigación cualitativa, en la vertiente fenomenológica, modalidad "estructura del fenómeno situado". Participaron del estudio ocho familiares que se negaron a la donación de órganos y tejidos. RESULTADOS: Después del análisis de las entrevistas se revelaron diez motivos de negación expuestos por los familiares. CONSIDERACIONES FINALES: Las proposiciones que emergieron revelaron que los motivos de la negativa familiar para la donación de órganos y tejidos están relacionados a la creencia, valores e inadecuaciones en el proceso de donación y transplante.OBJECTIVE: To understand the perception of family members of potential donors in regard to their reasons for refusal to donate organ and tissue for transplant. METHODS: A qualitative phenomenological approach was used to conduct this study. A sample of eight family members who refused to donate organ and tissue for transplant participated in the study. RESULTS: Participants reported ten reasons for refusal to donate organ and tissue for transplant. FINAL CONSIDERATIONS: Reasons for the family members
Interacoes medicamentosas potenciais em pacientes com doenca renal cronica
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Alessandra Batista Marquito
2014-03-01
Full Text Available Introdução: Interações medicamentosas (IMs são frequentes na prática clínica e estão diretamente relacionadas a fatores como polifarmácia, idade avançada e deficiência na metabolização e excreção de fármacos. Indivíduos com doença renal crônica (DRC comumente utilizam diversas classes de medicamentos, constituindo um importante grupo de risco para IMs. Objetivo: Identificar potenciais interações entre medicamentos prescritos a renais crônicos em tratamento conservador, e fatores associados a sua ocorrência. Métodos: Estudo observacional transversal, com análise de 558 prescrições. O potencial interativo dos medicamentos foi traçado tendo como suporte a base de dados MICROMEDEX®, software que disponibiliza farmacopeias conhecidas internacionalmente. Resultados: Houve predomínio de indivíduos do sexo masculino (54,7%, idosos (69,4%, no estágio 3 da DRC (47,5%, com sobrepeso e obesos (66,7%. As comorbidades mais prevalentes foram a hipertensão arterial sistêmica (68,5% e o diabetes mellitus (31,9%. IMs potenciais foram detectadas em 74,9% das prescrições. De um total de 1.364 IMs detectadas, 229 (16,8% foram de gravidade maior e 5 (0,4% contraindicadas, com necessidade de intervenção imediata. Interações de gravidade moderada ou menor foram identificadas respectivamente em 1.049 (76,9% e 81 (5,9% das prescrições. Observou-se que a probabilidade de ocorrência de uma IM aumentou em 2,5 vezes para cada medicamento adicional (IC = 2,18-3,03. Obesidade, diabetes, hipertensão e estágio avançado da DRC foram fatores de risco fortemente associados para ocorrência de IM. Conclusão: A associação de medicamentos em indivíduos com DRC relacionou-se com alta prevalência de IMs potencialmente graves, especialmente nos estágios mais avançados da doença.
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Rodolfo Marques de Brito
2007-10-01
Full Text Available Um experimento foi realizado com o objetivo de avaliar os parâmetros ruminais, a produção de ácidos graxos voláteis e a degradabilidade in situ em tourinhos Santa Gertrudes canulados no rúmen alimentados com dietas compostas de feno de capim-marandu e concentrado. Empregou-se o delineamento em quadrado latino 4 ´ 4, no qual os tratamentos foram compostos dos concentrados, ajustados para ganho de peso corporal (GPC diário de 0,5 e 1 kg/animal e potencial de fermentação microbiana (y de 9,5 e 11 g de proteína bruta microbiana/MJ energia metabolizável fermentável. Não foram encontradas interações significativas nem diferenças entre as dietas para pH, concentração molar dos ácidos acético e butírico e proporção molar dos ácidos acético, propiônico e butírico e relação acético:propiônico. Os teores de amônia diferiram entre os potenciais de fermentação microbiana, 14,67 e 20,83 mg/100 mL para baixo e alto, respectivamente, e a concentração molar de ácido propiônico foi diferente entre os potenciais de ganho de peso, 7,62 e 8,94 mM, respectivamente, para baixo e alto ganho de peso. Não foram detectadas diferenças entre dietas para as degradabilidades das frações do feno de capim-marandu e da soja em grão. Houve diferença no parâmetro "b" e na degradabilidade efetiva a 5%/hora da proteína bruta para os potencias de GPC do milho em grão moído. Para o farelo de soja, ocorreu interação significativa entre os potencias de GPC e de fermentação microbiana para alguns dos parâmetros da MS e PB, o mesmo observado para o farelo de algodão. As diferenças encontradas não justificaram o balanceamento dos concentrados para os diferentes potenciais de produção avaliados.The experiment was carried out with the objective to evaluate the ruminal parameters, volatile fatty acids production and in situ degradability of Santa Gertrudis young bulls, canulated in the rumen, fed diets with palisadegrass hay and
Anos potenciais de vida perdidos e custos hospitalares da leptospirose no Brasil
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Verena Maria Mendes de Souza
2011-12-01
Full Text Available OBJETIVO: Estimar os custos associados à hospitalização e os anos potenciais de vida perdidos devido à leptospirose. MÉTODOS: Foram utilizados os bancos de dados de sistemas de informação em saúde do Ministério da Saúde para o relacionamento probabilístico dos casos e internações que evoluíram a óbito por leptospirose em 2007. No Sistema de Informação de Agravos de Notificação os casos confirmados foram subdivididos em internação e óbito, que foram relacionados às seguintes bases: Sistema de Informações Hospitalares (registros com diagnóstico principal e Sistema de Informações sobre Mortalidade (causa básica do óbito, A27.0, A27.8 e A27.9. Foram estimados os custos parciais de internação, os óbitos pela doença, os anos potenciais de vida e de trabalho perdidos. RESULTADOS: As características da maioria das internações que evoluíram para óbito eram: sexo masculino, entre 18 e 49 anos, raça branca, zona urbana e ensino fundamental incompleto. Foram 6.490 anos potenciais de vida perdidos, sendo 75% da faixa etária de 20 a 49 anos. Quando ajustada pela população, a perda foi de 15 dias de vida/1.000 habitantes. A proporção de anos potenciais de vida perdidos pelo número de óbitos foi em média de 30 anos perdidos para cada óbito. O impacto financeiro estimado foi equivalente a R$ 22,9 milhões em salários não ganhos. Os custos hospitalares foram de R$ 831,5 mil. Considerando os dias de salário perdidos por período de internação (mediana: 6 dias, houve perda de R$ 103,0 mil. CONCLUSÕES: Houve elevado custo social em termo de anos potenciais de vida perdidos e gasto hospitalar parcial com leptospirose quando comparado ao possível tratamento precoce ou não adoecimento, o que poderia ter minimizado o impacto dessa doença na população brasileira.
Hermida, Micely D' El Rei
2013-01-01
A infecção por Leishmania modula a função de integrinas em fagócitos inflamatórios, afetando a migração celular e disseminação do parasito. O conhecimento sobre as populações de fagócitos capazes de transportar Leishmania ou fragmentos de parasitos mortos, e os mecanismos de disseminação da Leishmania do sítio de infecção para os diferentes tecidos ainda está incompleto. Nesse trabalho, nós adaptamos um modelo de migração de células in vivo para estudar o efeito da infecção ...
Os problemas de espalhamento quântico em potenciais elementares
Ribeiro,M. A. Cândido; Franzoni,V.C.; Passos,W.R.; Silva, E.C. [UNESP; Aleixo, A. N. F.
2004-01-01
Neste trabalho estudamos o espalhamento quântico de uma partícula por um potencial generalizado que engloba em si todas as formas de potenciais retangulares unidimensionais. Neste contexto nós calculamos as probabilidades de reflexão e transmissão de uma partícula incidente sobre este potencial generalizado e avaliamos os efeitos de sua assimetria na transmissão dessa partícula através dele para energias abaixo e acima da barreira de potencial. A potential which encompasses all kinds of re...
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Adalberto K. Miura
2011-06-01
Full Text Available A humanidade sempre utilizou a biomassa para fins energéticos, porém com o aumento da demanda, ameaças à segurança energética e os danos para o ambiente e para a saúde decorrentes da utilização dos combustíveis fósseis, a importância desta fonte renovável vem sendo resgatada. Neste cenário, o planejamento agroenergético passa a ser de grande importância para países tropicais como o Brasil, pois permite viabilizar a produção de biomassa para energia onde esta é requerida, de forma sustentável, sem deixar de considerar os aspectos sociais e ambientais. Desta forma, o presente artigo tem por objetivo apresentar importantes questões relacionadas ao planejamento energético regional, como forma de contribuir para soluções e políticas públicas relacionadas à produção de energia de biomassa. Ademais, é apresentada a contribuição das técnicas de Sensoriamento Remoto e Sistemas de Informações Geográficas para avaliações de áreas potenciais ao cultivo de culturas bioenergéticas, além de um modelo conceitual que demonstra como essas técnicas podem constituir-se em ferramentas de apoio à tomada de decisão estratégica nesta área de bioenergia. Adicionalmente, algumas dificuldades e limitações para o planejamento territorial e agroenergético também foram relacionadas.Since early times, the human kind has been using the biomass for energy purposes. However, the current increasing energy demand can endanger the energy security of the nations and, as well, could put in risk the planet's environmental quality and human health. Thus, by the issues concern about the fossil fuels utilization, the importance of renewable energy sources is being rescued. In this scenario, the biomass energy planning becomes very important to tropical countries, like Brazil, because it would allow stimulating the production of biomass for energy where it is required, but in a sustainable way, considering the social and environmental
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Diego Sánchez de Lozada
2006-10-01
desse sistema tradicional incluem a mitigação da geada e altas produtividades. Até recentemente não havia dados para avaliar estes benefícios. Neste contexto, experimentos realizados em campos elevados foram planejados e executados em dois locais dentro do Altiplano boliviano, para obter dados confiáveis em relação à produtividade da batata e das temperaturas reinantes. As produtividades observadas variaram de 2,73 a 10,80 t ha-1 no primeiro local, no qual a salinidade provocou uma variabilidade significante na produtividade (R² = 0,79. No segundo local, as produtividades nas plataformas elevadas variaram de 8,25 a 33,45 t ha-1. Entretanto, produtividades comparáveis foram obtidas nas áreas controle, mesmo na presença de uma geada no meio da estação e de uma diferença de apenas 1ºC entre as parcelas convencionais e as elevadas. Estes resultados sugerem que nas condições dos experimentos, os benefícios dos cultivos elevados, em termos de mitigação de geada ou produtividade aumentada, poderão apenas ser observados em anos excepcionalmente ruins, quando geadas fortes extirpam a totalidade da plantas dos cultivos convencionais. Entretanto, pode-se argumentar que mesmo com estas observações marginais de apoio, a agricultura em campos elevados poderia ser uma opção viável para agricultores se nos canais repletos de água entre os campos elevados fosse adotada a piscicultura e produção de fertilizantes.
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LUCCAS FRANCISCO J.C.
1999-01-01
Full Text Available O EEG digital (DEEG e o quantitativo (QEEG representam métodos recém desenvolvidos na prática clínica que, além da utilidade didática e em pesquisa, também mostram importância clínica. As aplicações clínicas são enumeradas a seguir: 1. O DEEG representa um substituto estabelecido para o EEG convencional, pois acrescenta claros avanços técnicos. 2. Algumas técnicas do QEEG são consideradas estabelecidas para uso clínico como adjunto ao DEEG: 2a detecção automática de possíveis descargas epileptiformes ou crises epilépticas em registros prolongados, facilitando o trabalho subsequente do especialista; 2b monitoração contínua do EEG na sala cirúrgica ou na UTI, visando reduzir complicações. 3. Certas técnicas de QEEG são consideradas possíveis opções práticas como uma adição ao DEEG: 3a análise topográfica e temporal de voltagens e dipolos de espículas na avaliação pré-cirúrgica de alguns tipos de epilepsia; 3b análise de frequências em certos casos com doença cérebro-vascular, em quadros demenciais e em encefalopatias, principalmente quando outros testes, como os exames de imagem e o EEG convencional se mostrarem inconclusivos. 4. O QEEG permanece apenas como instrumento de pesquisa em doenças como síndrome pós-concussional, distúrbios do aprendizado, déficit de atenção, esquizofrenia, depressão, alcoolismo e dependência a drogas. O QEEG deve ser usado sempre em conjunto com o DEEG. Devido aos sérios riscos de erros de interpretação, é inaceitável o uso clínico do QEEG e de técnicas correlatas por médicos sem a adequada especialização em interpretação do EEG convencional e também nessas novas técnicas.
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Nerinéia Dalfollo Ribeiro
2003-06-01
Full Text Available Noventa genótipos de feijão carioca (Phaseolus vulgaris L. foram avaliados, em dois anos agrícolas, em Santa Maria, RS, a fim de definir quais características agromorfológicas constituem-se como melhores descritores, realizar agrupamento em função de dissimilaridade genética e de definir quais combinações híbridas mais promissoras serão obtidas para o desenvolvimento de populações segregantes. Dos 20 caracteres agromorfológicos avaliados, apenas nove (ferrugem nos legumes, acamamento, nota geral, cor do tegumento, rendimento de grãos, massa de 100 sementes, altura de inserção do primeiro legume, altura de inserção do último legume e número de sementes por legume apresentaram maior contribuição para a divergência genética. Os genótipos de feijão carioca foram agrupados pelo método hierárquico de ligação completa. Populações segregantes, com variabilidade genética superior, podem ser obtidas com hibridações entre o genótipo ESAL 550 com genótipos do grupo 2 (LH-6, 17-4-32, R-78, H-4-5 e R-102 e/ou com genótipos do grupo 3 (FT 97-188, Cati-Taquari, CII-328, Carioca Precoce, FT 97-41, LH-11, FT 91-4067, Iapar 31, CI 102, Carioca MG, CII-54 e R-102.Carioca bean genotypes (Phaseolus vulgaris L. were evaluated in two growing seasons in Santa Maria, RS, Brazil. The objectives of this work were to evaluate which morpho-agronomic characteristics were the best descriptors, to group the genotypes in relation to genetic diversity and to determine which hybrid combinations are promissing to obtain higher segregation populations in carioca bean. From the 20 morpho-agronomic characteristics evaluated, only seven (pod rust, lodging, general note, colour of seed tegument, grain yield, 100 seed weight, height of first and final pod insertion and number of seeds per pod showed higher contribution to genetic diversity. The evaluated carioca bean genotypes were clustered by the complete linkage method. The following hybrid
Casimir experiments showing saturation effects
Sernelius, Bo E
2009-01-01
We address several different Casimir experiments where theory and experiment disagree. First out is the classical Casimir force measurement between two metal half spaces; here both in the form of the torsion pendulum experiment by Lamoreaux and in the form of the Casimir pressure measurement between a gold sphere and a gold plate as performed by Decca et al.; theory predicts a large negative thermal correction, absent in the high precision experiments. The third experiment is the measurement of the Casimir force between a metal plate and a laser irradiated semiconductor membrane as performed by Chen et al.; the change in force with laser intensity is larger than predicted by theory. The fourth experiment is the measurement of the Casimir force between an atom and a wall in the form of the measurement by Obrecht et al. of the change in oscillation frequency of a 87 Rb Bose-Einstein condensate trapped to a fused silica wall; the change is smaller than predicted by theory. We show that saturation effects can exp...
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Ana Gabriela dos Reis
2012-04-01
Full Text Available A associação entre medicamentos é uma ferramenta terapêutica amplamente utilizada, devido à existência de comorbidades. Contudo, essa prática eleva o índice de interações medicamentosas (IM, que podem ser benéficas ou acarretar danos à vida do paciente. Nesse contexto, os farmacêuticos de um hospital veterinário do noroeste paulista, implantaram em sua rotina a análise de todas as prescrições por meio de softwares e programas on line quanto à ocorrência de potenciais IM relacionadas à farmacoterapia de animais internados. Foram analisadas 5.376 prescrições, aviadas pelo serviço de farmácia hospitalar no período de 01 de junho de 2009 a 20 de dezembro de 2010. Todas foram elaboradas pelos médicos veterinários da instituição aos animais de pequeno porte que após atendimento ambulatorial permaneceram sob regime de internação. As IM estiveram presentes em 4,92% (n=265 das prescrições, as mais incidentes ocorreram entre ampicilina e heparina com 23,8% (n=63; ranitidina e cetoprofeno 12,9% (n=34; alimento e cefalexina 11,7% (n=31; cetoprofeno e heparina 9,4% (n=25 e metoclopramida e tramadol 8,3% (n=22. Quanto à gravidade, a maioria 52,4% (n=139 foi classificada como de nível menor; 24,9% (n=66 moderadas, 11% (n=29 potencialmente fatais, e 11,7% (n=31 não foram classificadas. As informações sobre estudos de IM e interações alimentares em animais são escassas, embora seja comum a ocorrência de IM na prática clínica. Assim essa avaliação tem o papel principal de alertar o médico veterinário prescritor para as consequências dessas no tratamento medicamentoso do animal e ainda no prognóstico da doença.
Negative Entropies in Casimir and Casimir-Polder Interactions
Milton, Kimball A; Kalauni, Pushpa; Parashar, Prachi; Guérout, Romain; Ingold, Gert-Ludwig; Lambrecht, Astrid; Reynaud, Serge
2016-01-01
It has been increasingly becoming clear that Casimir and Casimir-Polder entropies may be negative in certain regions of temperature and separation. In fact, the occurrence of negative entropy seems to be a nearly ubiquitous phenomenon. This is most highlighted in the quantum vacuum interaction of a nanoparticle with a conducting plate or between two nanoparticles. It has been argued that this phenomenon does not violate physical intuition, since the total entropy, including the self-entropies of the plate and the nanoparticle, should be positive. New calculations, in fact, seem to bear this out at least in certain cases.
Schwinger's Dynamical Casimir Effect Bulk Energy Contribution
Carlson, C E; Pérez-Mercader, J; Visser, M; Carlson, C E; Carlson, Carl E.; Molina-Paris, Carmen; Perez-Mercader, Juan; Visser, Matt
1997-01-01
Schwinger's Dynamical Casimir Effect is one of several candidate explanations for sonoluminescence. Recently, several papers have claimed that Schwinger's estimate of the Casimir energy involved is grossly inaccurate. In this letter, we show that these calculations omit the crucial volume term. When the missing term is correctly included one finds full agreement with Schwinger's result for the Dynamical Casimir Effect. We have nothing new to say about sonoluminescence itself except to affirm that the Casimir effect is energetically adequate as a candidate explanation. Schwinger's Dynamical Casimir Effect is one of several candidate explanations for sonoluminescence. Recently, several papers have claimed that Schwinger's estimate of the Casimir energy involved is grossly inaccurate. In this letter, we show that these calculations omit the crucial volume term. When the missing term is correctly included one finds full agreement with Schwinger's result for the Dynamical Casimir Effect. We have nothing new to say...
Thermodynamics of the Casimir effect
Mitter, H
2000-01-01
A complete thermodynamic treatment of the Casimir effect is presented. Explicit expressions for the free and the internal energy, the entropy and the pressure are discussed. As an example we consider the Casimir effect with different temperatures between the plates ($T$) resp. outside of them ($T'$). For $T'
Fulling, S A; Parashar, P; Romeo, A; Shajesh, K V; Wagner, J; Fulling, Stephen A.; Milton, Kimball A.; Parashar, Prachi; Romeo, August; Wagner, Jef
2007-01-01
Doubt continues to linger over the reality of quantum vacuum energy. It has been suggested that fluctuating fields may not gravitate, or may do so anomalously. Here we show that for the simple case of parallel conducting plates, the associated Casimir energy gravitates just as required by the equivalence principle, and that therefore the inertial and gravitational masses of a system possessing Casimir energy $E_c$ are both $E_c/c^2$. This simple result disproves recent claims in the literature. We clarify some pitfalls in the calculation that can lead to spurious dependences on coordinate system.
Single-interface Casimir torque
Morgado, Tiago A.; Silveirinha, Mário G.
2016-10-01
A different type of Casimir-type interaction is theoretically predicted: a single-interface torque at a junction of an anisotropic material and a vacuum or another material system. The torque acts to reorient the polarizable microscopic units of the involved materials near the interface, and thus to change the internal structure of the materials. The single-interface torque depends on the zero-point energy of the interface localized and extended modes. Our theory demonstrates that the single-interface torque is essential to understand the Casimir physics of material systems with anisotropic elements and may influence the orientation of the director of nematic liquid crystals.
Archimedes Force on Casimir Apparatus
Shevchenko, Vladimir
2016-01-01
We address a problem of Casimir apparatus in dense medium and weak gravitational field. The falling of the apparatus has to be governed by the equivalence principle, with proper account for contributions to the weight of the apparatus from its material part and from distorted quantum fields. We discuss general expression for the corresponding force in metric with cylindrical symmetry. By way of example we compute explicit expression for Archimedes force, acting on the Casimir apparatus of finite size, immersed into thermal bath of free scalar field. It is shown that besides universal term, proportional to the volume of the apparatus, there are non-universal quantum corrections, depending on the boundary conditions.
Advances in the Casimir Effect
Bordag, Michael; Mohideen, Umar; Mostepanenko, Vladimir Mikhaylovich
2009-01-01
The subject of this book is the Casimir effect, a manifestation of zero-point oscillations of the quantum vacuum resulting in forces acting between closely spaced bodies. For the benefit of the reader, the book assembles field-theoretical foundations of this phenomenon, applications of the general theory to real materials, and a comprehensive description of all recently performed measurements of the Casimir force with a comparison between experiment and theory. There is an urgentneed for a book of this type, given the increase of interest in forces originating from the quantum vacuum. Numerous
Interações Medicamentosas Potenciais em Pacientes de Unidades de Terapia Intensiva
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Liliana Batista Vieira
2012-08-01
Full Text Available O objetivo do estudo é determinar a frequência de interações fármaco-fármaco em prescrições de pacientes internados em unidades de terapia intensiva e analisar os fatores associados relativos à farmacoterapia e ao paciente. O estudo descritivo transversal foi realizado em dois hospitais de ensino da região centro oeste do Brasil. As interações medicamentosas potenciais foram identificadas nas prescrições do primeiro dia (24 horas e do quinto dia (120 horas de internação empregando o software Drug Reax. Dos 117 pacientes do estudo, 63,2% apresentaram interações medicamentosas potenciais nas primeiras 24 horas de internação e 68,4% pacientes em 120 horas. Houve associação estatisticamente significativa entre o número de medicamentos prescritos e a ocorrência de interações medicamentosas nos dois momentos de internação. O estudo demonstrou que a prevalência de interações fármaco-fármaco foi elevada nos hospitais investigados e que a chance de interação aumentou com o número de medicamentos prescritos, número de diagnósticos e idade maior que 60 anos. O conhecimento do mecanismo farmacológico e dos fatores de risco para interações medicamentosas potenciais contribuem para aumentar a segurança e efetividade do tratamento. Para ampliar a segurança da farmacoterapia, é essencial implementar estratégias que auxiliem a equipe de saúde a identificar as interações e implementar medidas de prevenção e monitorização de pacientes em riscos de desenvolver interações medicamentosas. A atuação do farmacêutico clínico na unidade de terapia intensiva é uma ferramenta importante para a prevenção, identificação e monitorização das interações medicamentosas.
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Rodolfo Marques de Brito
2007-10-01
Full Text Available Um experimento foi realizado com o objetivo de avaliar o aporte de energia, a composição de bactérias e a eficiência microbiana por tourinhos Santa Gertrudes canulados no rúmen e no duodeno alimentados com dietas compostas de feno de capim-marandu e concentrado. Empregou-se o delineamento em quadrado latino 4 ´ 4, no qual os tratamentos foram concentrados ajustados para ganho de peso corporal (GPC diário de 0,5 e 1 kg/animal e potencial de fermentação microbiana (y de 9,5 e 11 g de PB microbiana/MJ energia metabolizável fermentável. Houve diferença para as concentrações de nutrientes digestíveis totais (NDT e energia metabolizável fermentável (EMFe ingeridos e para a composição em matéria orgânica e mineral das bactérias ruminais para as dietas ajustadas para diferentes GPC. Houve interação significativa GPC ´ y para a ingestão de NDT como porcentagem do peso corporal e a composição em PB e carboidratos totais das bactérias ruminais. Não foram encontradas diferenças para os potenciais de fermentação microbiana. A eficiência de síntese microbiana também não diferiu entre as dietas e apresentou valores de 12,7 g PB microbiana/100 g NDT e 9,2 g PB microbiana/MJ EMFe. As diferenças encontradas não justificaram o balanceamento dos concentrados para os diferentes potenciais de fermentação microbiana avaliados.The experiment was carried out with the objective to evaluate the energy aport, microbial composition and efficiency of Santa Gertrudis young bulls, canulated in the rumen and duodenum, fed diets with palisadegrass hay and concentrates. A 4 x 4 latin square design was used, in which the treatments were composed by the concentrates adjusted for daily body weight gain (BWG of 0.5 and 1 kg/animal and potential microbial fermentation (y of 9.5 and 11 g microbial CP/MJ fermentable metabolizable energy. There were differences for the concentrations of total digestible nutrients (TDN and fermentable metabolizable
Casimir Effect for Dielectric Plates
Institute of Scientific and Technical Information of China (English)
无
2006-01-01
We generalize Kupisewska method to the three-dimensional system and another derivation of the Casimir effect between two dielectric plates is presented based on the explicit quantization of the electromagnetic field in the presence of dielectrics, where the physical meaning of "evanescent mode" is discussed. The Lifshitz's formula is rederived perfect metallic plates will the evanescent modes become unimportant.
Experiment and theory in the Casimir effect
Klimchitskaya, G L
2006-01-01
Casimir effect is the attractive force which acts between two plane parallel, closely spaced, uncharged, metallic plates in vacuum. This phenomenon was predicted theoretically in 1948 and reliably investigated experimentally only in recent years. In fact, the Casimir force is similar to the familiar van der Waals force in the case of relatively large separations when the relativistic effects come into play. We review the most important experiments on measuring the Casimir force by means of torsion pendulum, atomic force microscope and micromechanical torsional oscillator. Special attention is paid to the puzzle of the thermal Casimir force, i.e., to the apparent violation of the third law of thermodynamics when the Lifshitz theory of dispersion forces is applied to real metals. Thereafter we discuss the role of the Casimir force in nanosystems including the stiction phenomenon, actuators, and interaction of hydrogen atoms with carbon nanotubes. The applications of the Casimir effect for constraining predictio...
The Casimir effect: Recent controversies and progress
Milton, K A
2004-01-01
The phenomena implied by the existence of quantum vacuum fluctuations, grouped under the title of the Casimir effect, are reviewed, with emphasis on new results discovered in the past four years. The Casimir force between parallel plates is rederived as the strong-coupling limit of $\\delta$-function potential planes. The role of surface divergences is clarified. A summary of effects relevant to measurements of the Casimir force between real materials is given, starting from a geometrical optics derivation of the Lifshitz formula, and including a rederivation of the Casimir-Polder forces. A great deal of attention is given to the recent controversy concerning temperature corrections to the Casimir force between real metal surfaces. A summary of new improvements to the proximity force approximation is given, followed by a synopsis of the current experimental situation. New results on Casimir self-stress are reported, again based on $\\delta$- function potentials. Progress in understanding divergences in the self...
The electromagnetic Casimir effect of spherical cavity
Institute of Scientific and Technical Information of China (English)
无
2003-01-01
The Casimir effect results from the zero-point energy of vacuum. A spherical cavity can be divided into three regions, and we make an analysis of every region and then give a formal solution of Casimir energy. The zeta-function regularization is also used to dispel the divergence of the summation. At the end, we can see the Casimir effect of a single sphere is included in our results.
Finite Temperature Casimir Effect for Corrugated Plates
Institute of Scientific and Technical Information of China (English)
ZHAO Yan; SHAO Cheng-Gang; LUO Jun
2006-01-01
@@ Using the path-integral method, the corrections to the Casimir energy due to the combined effect of surface roughness and the finite temperature are calculated. For the specific case of two sinusoidally corrugated plates,the lateral Casimir force at finite temperature is obtained. The amplitude of the lateral Casimir force has a maximum at an optimal wavelength of λ≈ 2H with the mean plate distance H. This optimal parameter relation is almost independent of temperature.
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João Batista Silva Junior
2014-05-01
Full Text Available O artigo descreve o método de avaliação de risco potencial em serviços de hemoterapia (MARPSH aplicado pela Vigilância Sanitária (VISA no Brasil. Esse instrumento permite a identificação de riscos potenciais por meio do mapeamento dos multicritérios de controle e modelação das preferências para tomada de decisão, inserindo-o no âmbito da gestão proativa do risco. O MARPSH estrutura-se em 471 itens de controle, sendo 50% relacionados a riscos ao produto, 25% ao paciente, 17% ao doador e 8% ao trabalhador do serviço. Cada risco identificado é categorizado quanto à severidade, sua probabilidade e sua possibilidade de dano. Os sistemas analíticos utilizam a atribuição de duas ponderações, uma na valoração dos itens de controle e outra se refere à complexidade dos procedimentos. A relação entre a pontuação alcançada e a pontuação máxima possível origina o indicador Proporção de Controle (PC, pelo qual o risco potencial é classificado em Baixo (PC ≥ 95%, Médio-Baixo (80% ≤ PC < 95%, Médio (70% ≤ PC < 80%, Médio-Alto (60% ≤ PC < 70% e Alto (PC < 60%. A utilização do MARPSH permite o monitoramento e o controle da redução dos riscos e, consequentemente, o incremento da segurança transfusional. ----------------------------------------------------------------------- This article describes the method for the evaluation of potential risks in hemotherapy services (MARPSH applied by the Brazilian Health Surveillance Agency. It allows the identification of potential risks by mapping them for advanced control and modeling the preferences for decision making as a proactive risk management activity. The MARPSH structure is composed by 471 control items, being 50% related to risks for the product, 25% for the patient, 17% for the donor and 8% for the worker. Each identified inadequacy is categorized by its severity, its probability and relatively of a possibility of a hazard. For its analysis, the system adopted
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Danyllo Fabio Lessa Leao
2014-01-01
Full Text Available As interações medicamentosas são fatores de risco para a ocorrência de reações adversas a medicamentos. Este estudo teve o objetivo de avaliar as interações medicamentosas potenciais em prescrições da atenção primária de Vitória da Conquista (BA, visando preencher a lacuna de conhecimento sobre essa temática no Brasil. Foram coletadas informações sobre diversas variáveis de prescrições oriundas da atenção primária e as interações medicamentosas avaliadas a partir dos bancos de dados do Medscape e Micromedex(r. Verificou-se ainda a frequência de polifarmácia e associação desta com a ocorrência de interações medicamentosas. Os resultados mostraram frequência de 48,9% de interações medicamentosas, 74,9% delas de gravidade moderada ou maior, e 8,6% de prescrições em polifarmácia que, em teste qui-quadrado, mostrou associação positiva com ocorrência de interações medicamentosas potenciais (p < 0,001. As prescrições oriundas da atenção primária de Vitória da Conquista (BA apresentaram uma alta frequência de interações medicamentosas, porém faz-se necessária a análise de outros fatores de risco para ocorrência destas nesse nível de atenção à saúde.
Casimir effect in the presence of metamaterials
Energy Technology Data Exchange (ETDEWEB)
Kort-Kamp, W.J.M.; Pinheiro, F.A.; Maia Neto, P.A.; Farina, C. [Universidade Federal do Rio de Janeiro (UFRJ), RJ (Brazil); Rosa, F.S.S. [Universite Paris-Sud (France). Lab. Charles Fabry
2011-07-01
Full text: The Casimir effect was theoretically predicted in 1948 by H. G. B. Casimir. In its original form, it is the attraction between two parallel plates made of perfectly conductors in vacuum. The novelty in the Casimir result was the method used and not the fact that two neutral bodies attract each other, since the force between two neutral, but polarizable, atoms was previously treated by London in 1930. Casimir demonstrated that the force between the plates could be calculated from the variation in the zero-point energy of the quantized electromagnetic field caused by the presence of the plates. Nowadays there is no doubt about the existence of this effect, which has been observed in the last decade in experiments of great precision. Casimir forces play an important role in nanotechnology, in particular in the study of micro- and nano-electromechanical systems, because these forces become dominant in the nanoscopic scale. Casimir forces are responsible for an attraction of individual parts of these devices, making them eventually to stick together. As a result, attractive Casimir forces constitute a nuisance for practical applications. Therefore the investigation of a repulsive Casimir force is of great current interest. It has been recently argued that Casimir repulsion could be obtained by an adequate choice of artificial materials, the so-called metamaterials, with engineered electromagnetic properties [R. Zhao et al, PRL 103, 103602 (2009)]. In this work we investigate the interaction between an atom and a chiral metamaterial plate. Using realistic parameters, obtained from recent experiments and computer simulations, we show that state-of-the-art chiral metamaterials are not able generate Casimir repulsive forces. We also investigate the possibility of magneto-optical metamaterials to exhibit a repulsive Casimir force. To accomplish this, we discuss the dispersive interaction between a magneto-optical sphere and a chiral surface or a magneto
Casimir torque in weak coupling
Milton, Kimball A; Long, William
2013-01-01
In this paper, dedicated to Johan H{\\o}ye on the occasion of his 70th birthday, we examine manifestations of Casimir torque in the weak-coupling approximation, which allows exact calculations so that comparison with the universally applicable, but generally uncontrolled, proximity force approximation may be made. In particular, we examine Casimir energies between planar objects characterized by $\\delta$-function potentials, and consider the torque that arises when angles between the objects are changed. The results agree very well with the proximity force approximation when the separation distance between the objects is small compared with their sizes. In the opposite limit, where the size of one object is comparable to the separation distance, the shape dependence starts becoming irrelevant. These calculations are illustrative of what to expect for the torques between, for example, conducting planar objects, which eventually should be amenable to both improved theoretical calculation and experimental verific...
The Reality of Casimir Friction
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Kimball A. Milton
2016-04-01
Full Text Available For more than 35 years theorists have studied quantum or Casimir friction, which occurs when two smooth bodies move transversely to each other, experiencing a frictional dissipative force due to quantum electromagnetic fluctuations, which break time-reversal symmetry. These forces are typically very small, unless the bodies are nearly touching, and consequently such effects have never been observed, although lateral Casimir forces have been seen for corrugated surfaces. Partly because of the lack of contact with observations, theoretical predictions for the frictional force between parallel plates, or between a polarizable atom and a metallic plate, have varied widely. Here, we review the history of these calculations, show that theoretical consensus is emerging, and offer some hope that it might be possible to experimentally confirm this phenomenon of dissipative quantum electrodynamics.
Archimedes force on Casimir apparatus
Shevchenko, V.; Shevrin, E.
2016-11-01
The talk addresses a problem of Casimir apparatus in weak gravitational field, surrounded by a dense medium. The falling of the apparatus has to be governed by the equivalence principle, taking into account proper contributions to the weight of the apparatus from its material part and from distorted quantum fields. We discuss general ex pression for the corresponding force in terms of the effective action. By way of example we compute explicit expression for Archimedes force, acting on the Casimir apparatus of finite size, immersed into thermal bath of free scalar field. It is shown that besides universal term, proportional to the volume of the apparatus, there are non-universal quantum corrections, depending on the boundary conditions.
Archimedes force on Casimir apparatus
Directory of Open Access Journals (Sweden)
Shevchenko V.
2016-01-01
Full Text Available The talk addresses a problem of Casimir apparatus in weak gravitational field, surrounded by a dense medium. The falling of the apparatus has to be governed by the equivalence principle, taking into account proper contributions to the weight of the apparatus from its material part and from distorted quantum fields. We discuss general ex pression for the corresponding force in terms of the effective action. By way of example we compute explicit expression for Archimedes force, acting on the Casimir apparatus of finite size, immersed into thermal bath of free scalar field. It is shown that besides universal term, proportional to the volume of the apparatus, there are non-universal quantum corrections, depending on the boundary conditions.
The Reality of Casimir Friction
Milton, K A; Brevik, I
2015-01-01
For more than 35 years theorists have studied quantum or Casimir friction, which occurs when two smooth bodies move transversely to each other, experiencing a frictional dissipative force due to quantum fluctuations. These forces are typically very small, unless the bodies are nearly touching, and consequently such effects have never been observed, although lateral Casimir forces have been seen for corrugated surfaces. Because of the lack of contact with phenomena, theoretical predictions for the frictional force between parallel plates, or between a polarizable atom and a metallic plate, have varied widely. Here we review the history of these calculations, show that theoretical consensus is emerging, and offer some hope that it might be possible to experimentally confirm this phenomenon of dissipative quantum electrodynamics.
A equação de Schrödinger fracionária com potenciais delta
2016-01-01
Neste trabalho, estudaremos o efeito de derivadas fracionárias espaciais na equação de Schrödinger unidimensional independente do tempo, para o caso particular de potenciais do tipo Delta de Dirac. Inicialmente, apresentamos alguns conceitos importantes relacionados ao Cálculo Fracionário e discutimos a formulação da mecânica quântica, obtendo a Equação de Schrödinger, com base em integrais de caminho de Feynman. Em seguida, introduzimos a Equação de Schrödinger Fracionária com derivada fraci...
Mode contributions to the Casimir effect
Intravaia, Francesco
2009-01-01
Applying a sum-over-modes approach to the Casimir interaction between two plates with finite conductivity, we isolate and study the contributions of surface plasmons and Foucault (eddy current) modes. We show in particular that for the TE-polarization eddy currents provide a repulsive force that cancels, at high temperatures, the Casimir free energy calculated with the plasma model.
Critical Casimir forces for colloidal assembly
Nguyen, V.D.; Dang, M.T.; Nguyen, T.A.; Schall, P.
2016-01-01
Critical Casimir forces attract increasing interest due to their opportunities for reversible particle assembly in soft matter and nano science. These forces provide a thermodynamic analogue of the celebrated quantum mechanical Casimir force that arises from the confinement of vacuum fluctuations
Casimir effect for Elko spinor field
Pereira, S H; Santos, Rubia dos
2016-01-01
The Casimir effect for the Elko spinor field in $3+1$ dimension is obtained using Dirichlet boundary conditions. It is shown the existence of a repulsive force four times greater than the case of the scalar field. The precise reason for such differences are highlighted and interpreted, as well as the right parallel of the Casimir effect due to scalar and fermionic fields.
Mode Contributions to the Casimir Effect
Intravaia, F.; Henkel, C.
2010-04-01
Applying a sum-over-modes approach to the Casimir interaction between two plates with finite conductivity, we isolate and study the contributions of surface plasmons and Foucault (eddy current) modes. We show in particular that for the TE-polarization eddy currents provide a repulsive force that cancels, at high temperatures, the Casimir free energy calculated with the plasma model.
Zeta Functions and the Casimir Energy
Blau, Steven K; Wipf, Andreas; 10.1016/0550-3213(88)90059-4
2009-01-01
We use zeta function techniques to give a finite definition for the Casimir energy of an arbitrary ultrastatic spacetime with or without boundaries. We find that the Casimir energy is intimately related to, but not identical to, the one-loop effective energy. We show that in general the Casimir energy depends on a normalization scale. This phenomenon has relevance to applications of the Casimir energy in bag models of QCD. Within the framework of Kaluza-Klein theories we discuss the one-loop corrections to the induced cosmological and Newton constants in terms of a Casimir like effect. We can calculate the dependence of these constants on the radius of the compact dimensions, without having to resort to detailed calculations.
Scalar Casimir effect between two concentric spheres
Ozcan, Mustafa
2012-01-01
The Casimir effect giving rise to an attractive force between the closely spaced two concentric spheres that confine the massless scalar field is calculated by using a direct mode summation with contour integration in the complex plane of eigenfrequencies. We devoleped a new approach appropriate for the calculation of the Casimir energy for spherical boundary conditions. The Casimir energy for a massless scalar field between the closely spaced two concentric spheres coincides with the Casimir energy of the parallel plates for a massless scalar field in the limit when the dimensionless parameter {\\eta}, ({\\eta}=((a-b)/(\\surd(ab))) where a (b) is inner (outer) radius of sphere), goes to zero. The efficiency of new approach is demonstrated by calculation of the Casimir energy for a massless scalar field between the closely spaced two concentric half spheres. PACS number(s): 03.70.+k, 12.20.DS, 11.10.Gh
Optimizing Casimir torque between corrugated metallic plates
Energy Technology Data Exchange (ETDEWEB)
Rodrigues, Robson B. [Universidade Federal Fluminense, Niteroi, RJ (Brazil); Maia Neto, Paulo A. [Instituto de Fisica, Universidade Federal do Rio de Janeiro, RJ (Brazil)
2013-07-01
Full text: The Casimir effect plays a major role in micro- and nano-electromechanical systems (MEMS and NEMS). Besides the normal Casimir force between metallic or dielectric plates, the observation of the lateral Casimir force between corrugated plates opens novel possibilities of micro-mechanical control. The lateral force results from breaking the translational symmetry along directions parallel to the plates by imprinting periodic corrugations on both metallic plates. As the rotational symmetry is broken by this geometry, a Casimir torque arises when the corrugations are not aligned. We calculate the Casimir torque between two parallel metallic plates with surface profiles in the form of 'fans' with arbitrary relative spatial orientation. As compared to the case of anisotropic dielectric plates, the torque per unit area is increased by up to three orders of magnitude for a given separation distance. The experiment proposed here can be performed with torsion pendulum techniques for separation distances as large as 1 μm. From the point of view of fundamental physics, this torque makes possible a precise experimental investigation of the non-trivial geometry dependence of the Casimir effect. We follow the scattering approach and calculate the Casimir energy up to second order in the corrugation amplitudes, taking into account nonspecular reflections, polarization mixing and the finite conductivity of the metals. We investigate the experimental conditions that optimize the effect. (author)
Self-similar plates: Casimir energies
Shajesh, K V; Cavero-Peláez, Inés; Parashar, Prachi
2016-01-01
We construct various self-similar configurations using parallel $\\delta$-function plates and show that it is possible to evaluate the Casimir interaction energy of these configurations using the idea of self-similarity alone. We restrict our analysis to interactions mediated by a scalar field, but the extension to electromagnetic field is immediate. Our work unveils an easy and powerful method that can be easily employed to calculate the Casimir energies of a class of self-similar configurations. As a highlight, in an example, we determine the Casimir interaction energy of a stack of parallel plates constructed by positioning $\\delta$-function plates at the points constituting the Cantor set, a prototype of a fractal. This, to our knowledge, is the first time that the Casimir energy of a fractal configuration has been reported. Remarkably, the Casimir energy of some of the configurations we consider turn out to be positive, and a few even have zero Casimir energy. For the case of positive Casimir energy that ...
The holographic supersymmetric Casimir energy
Genolini, Pietro Benetti; Martelli, Dario; Sparks, James
2016-01-01
We consider a general class of asymptotically locally AdS_5 solutions of minimal gauged supergravity, that are dual to superconformal field theories on curved backgrounds S^1 x M_3 preserving two supercharges. We demonstrate that standard holographic renormalization corresponds to a scheme that breaks supersymmetry. We propose new boundary terms that restore supersymmetry, and show that for smooth solutions with topology S^1 x R^4 the improved on-shell action reproduces both the supersymmetric Casimir energy and the field theory BPS relation between charges.
The holographic supersymmetric Casimir energy
Benetti Genolini, Pietro; Cassani, Davide; Martelli, Dario; Sparks, James
2017-01-01
We consider a general class of asymptotically locally AdS5 solutions of minimal gauged supergravity, which are dual to superconformal field theories on curved backgrounds S1×M3 preserving two supercharges. We demonstrate that standard holographic renormalization corresponds to a scheme that breaks supersymmetry. We propose new boundary terms that restore supersymmetry, and show that for smooth solutions with topology S1×R4 the improved on-shell action reproduces both the supersymmetric Casimir energy and the field theory supersymmetric relation between charges.
Theoretical analysis of Casimir and thermal Casimir effect in stationary space-time
Zhang, Anwei
2017-10-01
We investigate Casimir effect as well as thermal Casimir effect for a pair of parallel perfectly plates placed in general stationary space-time background. It is found that the Casimir energy is influenced by the 00-component of metric and the corresponding quantity in dragging frame. We give a scheme to renormalize thermal correction to free energy in curved space-time. It is shown that the thermal corrections to Casimir thermodynamic quantities not only depend on the proper temperature and proper geometrical parameters of the plates, but also on the determinant of space-time metric.
Repulsive Casimir Force using metamaterials
Pappakrishnan, Venkatesh K.; Mundru, Pattabhiraju C.; Genov, Dentcho A.
We investigate conditions for Casimir Force (CF) reversal between two parallel half-space metamaterial plates separated by air or vacuum at ambient temperatures. Practically, the Casimir effect can lead to stiction in nanoscale devices, degradation and decreased performance. While material realizations of repulsive CF has been proposed for high dielectric host materials, so far the CF reversal with air/vacuum as intermediate medium remain challenging. Here, we propose a two plate design based on artificial electromagnetic materials known as metamaterials. This configuration allows a simple analytical treatment that accurately describes the large and short distance asymptotics of CF and allows extraction of important parameters such as lower and upper cutoff gap distances that define the repulsive force window. A parametric study has been performed in terms of the plate's dielectric and magnetic plasma frequencies, plate separation distance and temperature. The parametric domain for achieving CF reversal is identified. If successfully implemented the proposed design could potentially result in frictionless bio-fluid transport devices, quantum levitation and coating for ultra-clean room environment.
Multiple Scattering Methods in Casimir Calculations
Milton, Kimball A
2007-01-01
Multiple scattering formulations have been recently rediscovered as a method of studying the quantum vacuum or Casimir interactions between distinct bodies. The methods are hardly new, but increased computing power and advances in understanding allow us to extract information efficiently. Here we review the method in the simple context of $\\delta$-function potentials, so-called semitransparent bodies. (In the limit of strong coupling, a semitransparent boundary becomes a Dirichlet one.) After applying the method to rederive the Casimir force between two semitransparent plates and the Casimir self-stress on a semitransparent sphere, we obtain expressions for the Casimir energies between disjoint parallel semitransparent cylinders and between disjoint semitransparent spheres. Simplifications occur for weak and strong coupling. In particular, after performing a power series expansion in the ratio of the radii of the objects to the separation between them, we are able to sum the weak-coupling expansions exactly t...
Casimir effect from macroscopic quantum electrodynamics
Energy Technology Data Exchange (ETDEWEB)
Philbin, T G, E-mail: tgp3@st-andrews.ac.uk [School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, Fife KY16 9SS (United Kingdom)
2011-06-15
The canonical quantization of macroscopic electromagnetism was recently presented in (Philbin 2010 New J. Phys. 12 123008). This theory is used here to derive the Casimir effect, by considering the special case of thermal and zero-point fields. The stress-energy-momentum tensor of the canonical theory follows from Noether's theorem, and its electromagnetic part in thermal equilibrium gives the Casimir energy density and stress tensor. The results hold for arbitrary inhomogeneous magnetodielectrics and are obtained from a rigorous quantization of electromagnetism in dispersive, dissipative media. Continuing doubts about the status of the standard Lifshitz theory as a proper quantum treatment of Casimir forces do not apply to the derivation given here. Moreover, the correct expressions for the Casimir energy density and stress tensor inside media follow automatically from the simple restriction to thermal equilibrium, without the need for complicated thermodynamical or mechanical arguments.
1092-IJBCS-Article-Casimir Anouma KOKO
African Journals Online (AJOL)
KODJIO NORBERT
Quality of fermented cassava flour processed into placali. Casimir ... Fresh roots of one local cassava variety .... an indication of a good stable shelf life if ... content contribute to increase the stability and ... protein (animal and vegetable).
Casimir Force Correction Between Parallel Polysilicon Plates
Institute of Scientific and Technical Information of China (English)
丁建宁; 孟永钢; 温诗铸
2002-01-01
Both the size of the components and the separation between them in some microelectromechanical systems (MEMS) are already in the sub-micrometer regime, where quantum mechanical effects such as the Casimir effect will need to be considered. This paper theoretically analyzes the roughness, electrical conductivity, and temperature corrections due to the Casimir force between two parallel polysilicon plates. The theoretical results show that the combined effects of roughness, conductivity and temperature cause a maximum relative error of the Casimir force per unit area of 26.2% between parallel polysilicon plates separated by 1 μm. Therefore, the surface roughness and finite conductivity corrections should be taken into account when calculating precise Casimir forces with separations on the order of 1 μm.
Casimir Effect, Hawking Radiation and Trace Anomaly
Setare, M R
2001-01-01
The Casimir energy for massless scalar field of two parallel conductor, in two dimensional Schwarzchild black hole background, with Dirichlet boundary conditions is calculated by making use of general properties of renormalized stress tensor. We show that vacuum expectation value of stress tensor can be obtain by Casimir effect, trace anomaly and Hawking radiation. Four-dimensional of this problem, by this method, is under progress by this author.
Stability of suspended graphene under Casimir force
Chudnovsky, E. M.; Zarzuela, R.
2016-08-01
We consider a graphene sheet suspended above a conducting surface. Treating graphene as an elastic membrane subjected to Casimir force, we study its stability against sagging towards the conductor. There exists a critical elevation at the edges below which the central part of the suspended graphene nucleates a trunk that sinks under the action of the Casimir force. The dependence of the critical elevation on temperature, dimensions, and the elastic stress applied to the graphene sheet is computed.
Ultrahigh Casimir interaction torque in nanowire systems.
Morgado, Tiago A; Maslovski, Stanislav I; Silveirinha, Mário G
2013-06-17
We study the Casimir torque arising from the quantum electromagnetic fluctuations due to the interaction of two interfaces in a system formed by a dense array of metallic nanorods embedded in dielectric fluids. It is demonstrated that as a consequence of the ultrahigh density of photonic states in the nanowire array it is possible to channel the quantum fluctuations, and thereby boost the Casimir torque by several orders of magnitude as compared to other known systems (e.g., birefringent parallel plates).
Acoustic Casimir Pressure for Arbitrary Media
Barcenas, J; Esquivel-Sirvent, R
2004-01-01
In this paper we derive a general expression for the acoustic Casimir pressure between two parallel slabs made of arbitrary materials and whose acoustic reflection coefficients are not equal. The formalism is based on the calculation of the local density of modes using a Green's function approach. The results for the Casimir acoustic pressure are generalized to a sphere/plate configuration using the proximity theorem
Potenciais evocados auditivos de tronco encefálico em fumantes
Directory of Open Access Journals (Sweden)
Denise Miranda Terra Martins
2016-02-01
Full Text Available RESUMO Objetivo: comparar os resultados dos exames de potenciais evocados auditivos de tronco encefálico em indivíduos não tabagistas e tabagistas. Métodos: foram estudados 40 indivíduos, sendo 20 não tabagistas e 20 tabagistas, com idades entre 20 e 59 anos. Todos os participantes incluídos na pesquisa deveriam apresentar respostas de limiares tonais dentro dos padrões da normalidade e timpanometria tipo A com presença de reflexos acústicos contralaterais e ipsilaterais. Em ambos os grupos foram realizados os potenciais evocados auditivos de tronco encefálico (PEATE, por meio de cliques. Os parâmetros que foram utilizados na comparação dos dois grupos foram as latências absolutas das ondas I, III e V; as interlatências das ondas I-III, I-V e III-V em ambas as orelhas; a diferença da latência interpico I-V entre as duas orelhas e a diferença interaural da latência absoluta da onda V entre as duas orelhas. Resultados: os resultados encontrados mostraram que o grupo de tabagistas apresentou latência I da Orelha Direita (p=0,036, latência V da Orelha Direita (p=0,007, latência V da Orelha Esquerda (p=0,014, interlatência III-V da Orelha Direita (p=0,015 e Orelha Esquerda (p=0,016 significantemente maior que o grupo de não tabagistas. Não houve diferença significante na latência da onda V entre as duas orelhas. Conclusão: os resultados da pesquisa levaram à conclusão de que o tabaco é um fator de risco para o sistema nervoso auditivo central, que pode interferir nas latências e interlatências das ondas do PEATE no grupo de tabagistas quando comparado com o grupo de não tabagistas.
Casimir effect and quantum field theory in dielectrics
Marachevskij, V N
2002-01-01
The method of continual integration in the coordinate space in accordance with the Casimir effect is set forth. Some examples: the Casimir energy of the rare field dielectric ball by availability of the dispersion; the Casimir energy of the polarized particle in the vicinity of the dielectric ball; the Casimir energy of the polarized particle inside the ideally conducting cavity of the wedge-like form are considered. The equation of the renorm group for the PHI sup 4 -model is obtained in the coordinate space by the new method, underlying the interaction between the background method and the Casimir energy
Oscillating Casimir force between two slabs in a Fermi sea
DEFF Research Database (Denmark)
Li-Wei, Chen; Guo-Zhen, Su; Jin-Can, Chen
2012-01-01
The Casimir effect for two parallel slabs immersed in an ideal Fermi sea is investigated at both zero and nonzero temperatures. It is found that the Casimir effect in a Fermi gas is distinctly different from that in an electromagnetic field or a massive Bose gas. In contrast to the familiar result...... that the Casimir force decreases monotonically with the increase of the separation L between two slabs in an electromagnetic field and a massive Bose gas, the Casimir force in a Fermi gas oscillates as a function of L. The Casimir force can be either attractive or repulsive, depending sensitively on the magnitude...... of L. In addition, it is found that the amplitude of the Casimir force in a Fermi gas decreases with the increase of the temperature, which also is contrary to the case in a Bose gas, since the bosonic Casimir force increases linearly with the increase of the temperature in the region T
Casimir effect in Extended Theories of Gravity
Lambiase, G; Stabile, An
2016-01-01
We study the Casimir vacuum energy density and the Casimir pressure for a massless scalar field confined between two nearby parallel plates in a slightly curved, static spacetime background, employing the weak field approximation in the framework of Extended Theories of Gravity (ETG). Following a perturbative approach upto second order, we find the gravity correction in the ETG to Casimir vacuum energy density and pressure. The corrections to the vacuum energy density in presence of curved spacetime in the framework of General Relativity (GR) are small and today they are still undetected with the current technology. However, future sensitivity improvement in gravitational interferometer experiments will give an useful tool to detect such effect induced by gravity. For these reason we retain interesting from a theoretical point of view generalize the outcomes of GR in the context of ETG. Finally, we find the general relation to constraining the free parameters of the ETG.
Probing the Casimir force with optical tweezers
Ether, D S; Umrath, S; Martinez, D; Ayala, Y; Pontes, B; Araújo, G R de S; Frases, S; Ingold, G -L; Rosa, F S S; Viana, N B; Nussenzveig, H M; Neto, P A Maia
2015-01-01
We propose to use optical tweezers to probe the Casimir interaction between microspheres inside a liquid medium for geometric aspect ratios far beyond the validity of the widely employed proximity force approximation. This setup has the potential for revealing unprecedented features associated to the non-trivial role of the spherical curvatures. For a proof of concept, we measure femtonewton double layer forces between polystyrene microspheres at distances above $400$ nm by employing very soft optical tweezers, with stiffness of the order of fractions of a fN/nm. As a future application, we propose to tune the Casimir interaction between a metallic and a polystyrene microsphere in saline solution from attraction to repulsion by varying the salt concentration. With those materials, the screened Casimir interaction may have a larger magnitude than the unscreened one. This line of investigation has the potential for bringing together different fields including classical and quantum optics, statistical physics an...
Finite temperature Casimir effect for graphene
Fialkovsky, Ignat V; Vassilevich, Dmitri V
2011-01-01
We adopt the Dirac model for quasiparticles in graphene and calculate the finite temperature Casimir interaction between a suspended graphene layer and a parallel conducting surface. We find that at high temperature the Casimir interaction in such system is just one half of that for two ideal conductors separated by the same distance. In this limit single graphene layer behaves exactly as a Drude metal. In particular, the contribution of the TE mode is suppressed, while one of the TM mode saturates the ideal metal value. Behaviour of the Casimir interaction for intermediate temperatures and separations accessible for an experiment is studied in some detail. We also find an interesting interplay between two fundamental constants of graphene physics: the fine structure constant and the Fermi velocity.
POTENCIAIS SEQUÊNCIAS DE APRENDIZAGEM INTERCULTURAL NO TELETANDEM: A IMPORTÂNCIA DA MEDIAÇÃO
Directory of Open Access Journals (Sweden)
Ana Carolina Freschi
2016-12-01
Full Text Available A partir da caracterização do teletandem como Terceiro Espaço, onde o contato intercultural tem território privilegiado (KRAMSCH; URYU, 2014, e dos conceitos de competência intercultural (BELZ, 2003 e paráfrases (ORLANDI, 1987; 2000; PECHÊUX, 1997, discutimos a relevância da identificação de potenciais sequências de aprendizagem intercultural (BORGHETTI et al, 2015 como oportunidades para melhor autocompreensão e autocrítica e desenvolvimento da competência intercultural a partir da mediação realizada no teletandem. Assim, nosso artigo situa-se na interface entre estudos linguísticos, estudos culturais e análise do discurso de linha francesa. Os dados analisados foram coletados em 2011, 2012 e 2014 e tiveram como temas: preconceito linguístico e regional, eleições presidenciais, copa do mundo de futebol no Brasil e generalizações quanto a situação das escolas no Estado de São Paulo. Esses assuntos embasaram parte das interações e suscitaram diversas paráfrases que nos levaram aos questionamentos apresentados. Por meio da análise de quatro sessões de teletandem de pares diferentes, pudemos identificar potenciais sequências de aprendizagem intercultural, o que demonstra o potencial do teletandem como espaço desse tipo de aprendizagem. As sessões de mediação podem contribuir significativamente para o desenvolvimento dessa competência, auxiliando a compreender as identidades e o que entendemos ser a identidade que afirmamos ter.
Nonequilibrium Tuning of the Thermal Casimir Effect
Dean, David S; Maggs, A C; Podgornik, Rudolf
2016-01-01
In net-neutral systems correlations between charge fluctuations generate strong attractive thermal Casimir forces and engineering these forces to optimize nanodevice performance is an important challenge. We show how the normal and lateral thermal Casimir forces between two plates containing Brownian charges can be modulated by decorrelating the system through the application of an electric field, which generates a nonequilibrium steady state with a constant current in one or both plates, reducing the ensuing fluctuation-generated normal force while at the same time generating a lateral drag force. This hypothesis is confirmed by detailed numerical simulations as well as an analytical approach based on stochastic density functional theory.
Casimir Forces between Nanoparticles and Substrates
Román-Velázquez, C E; Villarreal, C; Esquivel-Sirvent, R; Noguez, Cecilia
2002-01-01
We study the Casimir force between a nanoparticle and a substrate. We consider the interaction of metal nanoparticles with different substrates within the dipolar approximation. We study the force as a function of the distance for gold and potassium spheres, which are over a substrate of titanium dioxide, sapphire and a perfect conductor. We show that Casimir force is important in systems at the nanometer scale. We study the force as a function of the material properties, radii of the spheres, and the distance between the sphere and the substrate.
The Casimir Torque on a Cylindrical Gear
Vaidya, Varun
2013-01-01
We utilize Effective Field Theory(EFT) techniques to calculate the casimir torque on a cylindrical gear in the presence of a polarizable but neutral object. We present results for the energy and torque as a function of angle for a gear with multiple cogs, as well as for the case of a concentric cylindrical gear.
Casimir torque on a cylindrical gear
Vaidya, Varun
2014-08-01
I utilize effective field theory(EFT) techniques to calculate the Casimir torque on a cylindrical gear in the presence of a polarizable but neutral object and present results for the energy and torque as a function of angle for a gear with multiple cogs, as well as for the case of a concentric cylindrical gear.
Detecting Chameleons through Casimir Force Measurements
Brax, Philippe; Davis, Anne-Christine; Mota, David F; Shaw, Douglas
2007-01-01
The best laboratory constraints on strongly coupled chameleon fields come not from tests of gravity per se but from precision measurements of the Casimir force. The chameleonic force between two nearby bodies is more akin to a Casimir-like force than a gravitational one: The chameleon force behaves as an inverse power of the distance of separation between the surfaces of two bodies, just as the Casimir force does. Additionally, experimental tests of gravity often employ a thin metallic sheet to shield electrostatic forces, however this sheet mask any detectable signal due to the presence of a strongly coupled chameleon field. As a result of this shielding, experiments that are designed to specifically test the behaviour of gravity are often unable to place any constraint on chameleon fields with a strong coupling to matter. Casimir force measurements do not employ a physical electrostatic shield and as such are able to put tighter constraints on the properties of chameleons fields with a strong matter couplin...
Casimir force measurements from silicon carbide surfaces
Sedighi, M.; Svetovoy, V. B.; Palasantzas, G.
2016-01-01
Using an atomic force microscope we performed measurements of the Casimir force between a gold-coated (Au) microsphere and doped silicon carbide (SiC) samples. The last of these is a promising material for devices operating under severe environments. The roughness of the interacting surfaces was mea
Surface impedance and the Casimir force
Bezerra, V B; Romero, C
2002-01-01
The impedance boundary condition is used to calculate the Casimir force in configurations of two parallel plates and a shpere (spherical lens) above a plate at both zero and nonzero temperature. The impedance approach allows one to find the Casimir force between the realistic test bodies regardless of the electromagnetic fluctuations inside the media. Although this approach is an approximate one, it has wider areas of application than the Lifshitz theory of the Casimir force. The general formulas of the impedance approach to the theory of the Casimir force are given and the formal substitution is found for connecting it with the Lifshitz formula. The range of micrometer separations between the test bodies which is interesting from the experimental point of view is investigated in detail. It is shown that at zero temperature the results obtained on the basis of the surface impedance method are in agreement with those obtained in framework of the Lifshitz theory within a fraction of a percent. The temperature c...
Repulsive Casimir Force in Chiral Metamaterials
Energy Technology Data Exchange (ETDEWEB)
Zhao, R.; Zhou, J.; Koschny, Th.; Economou, E.N.; Soukoulis, C.M.
2009-09-04
We demonstrate theoretically that one can obtain repulsive Casimir forces and stable nanolevitations by using chiral metamaterials. By extending the Lifshitz theory to treat chiral metamaterials, we find that a repulsive force and a minimum of the interaction energy possibly exist for strong chirality, under realistic frequency dependencies and correct limiting values (for zero and infinite frequencies) of the permittivity, permeability, and chiral coefficients.
Repulsive Casimir Force in Chiral Metamaterials
Zhao, R.; J. Zhou; Koschny, Th.; Economou, E. N.; C M Soukoulis
2009-01-01
We demonstrate theoretically that one can obtain repulsive Casimir forces and stable nanolevitations by using chiral metamaterials. By extending the Lifshitz theory to treat chiral metamaterials, we find that a repulsive force and a minimum of the interaction energy exist for strong chirality, under realistic frequency dependencies and correct limiting values (for zero and infinite frequencies) of the permittivity, permeability, and chiral coefficients.
Repulsive Casimir Force in Chiral Metamaterials
Zhao, R.; Zhou, J.; Koschny, Th.; Economou, E. N.; Soukoulis, C. M.
2009-09-01
We demonstrate theoretically that one can obtain repulsive Casimir forces and stable nanolevitations by using chiral metamaterials. By extending the Lifshitz theory to treat chiral metamaterials, we find that a repulsive force and a minimum of the interaction energy possibly exist for strong chirality, under realistic frequency dependencies and correct limiting values (for zero and infinite frequencies) of the permittivity, permeability, and chiral coefficients.
Observation of the thermal Casimir force
Sushkov, A O; Dalvit, D A R; Lamoreaux, S K
2010-01-01
Quantum theory predicts the existence of the Casimir force between macroscopic bodies, due to the zero-point energy of electromagnetic field modes around them. This quantum fluctuation-induced force has been experimentally observed for metallic and semiconducting bodies, although the measurements to date have been unable to clearly settle the question of the correct low-frequency form of the dielectric constant dispersion (the Drude model or the plasma model) to be used for calculating the Casimir forces. At finite temperature a thermal Casimir force, due to thermal, rather than quantum, fluctuations of the electromagnetic field, has been theoretically predicted long ago. Here we report the experimental observation of the thermal Casimir force between two gold plates. We measured the attractive force between a flat and a spherical plate for separations between 0.7 $\\mu$m and 7 $\\mu$m. An electrostatic force caused by potential patches on the plates' surfaces is included in the analysis. The experimental resul...
Casimir stress on lossy magnetodielectric spheres
Raabe, C; Welsch, D G; Raabe, Christian; Knoell, Ludwig; Welsch, Dirk-Gunnar
2003-01-01
An expression for the Casimir stress on arbitrary dispersive and lossy linear magnetodielectric matter at finite temperature, including left-handed material, is derived and applied to spherical systems. To cast the relevant part of the scattering Green tensor for a general magnetodielectric sphere in a convenient form, classical Mie scattering is reformulated.
The Casimir Effect and Thermodynamic Instability
Widom, A.; Sassaroli, E.; Srivastava, Y. N.; Swain, J.
1998-01-01
One loop field theory calculations of free energies quite often yield violations of the stability conditions associated with the thermodynamic second law. Perhaps the best known example involves the equation of state of black holes. Here, it is pointed out that the Casimir force between two parallel conducting plates also violates a thermodynamic stability condition normally associated with the second law of thermodynamics.
Schwinger's Method for the Massive Casimir Effect
1994-01-01
We apply to the massive scalar field a method recently proposed by Schwinger to calculate the Casimir effect. The method is applied with two different regularization schemes: the Schwinger original one by means of Poisson formula and another one by means of analytical continuation.
Casimir light: pieces of the action.
1993-01-01
More realistic dynamics for the collapsing dielectric fluid are introduced in stages by adding contributions to the Lagrangian that forms the action. The elements are kinetic energy, Casimir potential energy, air pressure potential energy, and electromagnetic coupling to the moving dielectric. There are successful tests of partial collapse time and of minimum radius.
Quantum coherence in the dynamical Casimir effect
Samos-Sáenz de Buruaga, D. N.; Sabín, Carlos
2017-02-01
We propose to use quantum coherence as the ultimate proof of the quantum nature of the radiation that appears by means of the dynamical Casimir effect in experiments with superconducting microwave waveguides. We show that, unlike previously considered measurements such as entanglement and discord, quantum coherence does not require a threshold value of the external pump amplitude and is highly robust to thermal noise.
Casimir interactions for anisotropic magnetodielectric metamaterials
Energy Technology Data Exchange (ETDEWEB)
Da Rosa, Felipe S [Los Alamos National Laboratory; Dalvit, Diego A [Los Alamos National Laboratory; Milonni, Peter W [Los Alamos National Laboratory
2008-01-01
We extend our previous work on the generalization of the Casimir-Lifshitz theory to treat anisotropic magnetodielectric media, focusing on the forces between metals and magnetodielectric metamaterials and on the possibility of inferring magnetic effects by measurements of these forces.
Mosquitos vetores potenciais de dirofilariose canina na Região Nordeste do Brasil
Directory of Open Access Journals (Sweden)
Ahid Silvia MM
1999-01-01
Full Text Available INTRODUÇÃO: Em alguns bairros costeiros de São Luís, Maranhão, a prevalência da dirofilariose chega a mais de 40% entre os cães domiciliados. Porém, desconhecem-se os vetores naturais, tanto lá quanto no resto do Nordeste do país. O objetivo do estudo foi identificar os prováveis vetores dessa parasitose. MÉTODOS: Realizaram-se coletas mensais de mosquitos em um bairro costeiro de São Luís, MA, de março de 1996 a maio de 1997, no peridomicílio, tendo cão e homem como iscas. Os mosquitos foram dissecados para a pesquisa de larvas da Dirofilaria immitis. RESULTADOS: Coletaram-se 1.738 mosquitos de 11 espécies. Culex quinquefasciatus, capturada todos os meses, porém menos freqüente na estação chuvosa, correspondeu a 54,5% do total, seguido de Aedes albopictus (20,3%, Aedes taeniorhynchus e Aedes scapularis (ambos 11%. Larvas de D.immitis foram encontradas em 0,1% dos Cx. quinquefasciatus e 0,5% dos Ae. taeniorhynchus. CONCLUSÕES: Ae. taeniorhynchus e Cx. quinquefasciatus foram considerados vetores potenciais da dirofilariose em São Luís. A importância local de Cx. quinquefasciatus como transmissor primário da D. immitis necessita ser melhor avaliada.
Mosquitos vetores potenciais de dirofilariose canina na Região Nordeste do Brasil
Directory of Open Access Journals (Sweden)
Silvia MM Ahid
1999-12-01
Full Text Available INTRODUÇÃO: Em alguns bairros costeiros de São Luís, Maranhão, a prevalência da dirofilariose chega a mais de 40% entre os cães domiciliados. Porém, desconhecem-se os vetores naturais, tanto lá quanto no resto do Nordeste do país. O objetivo do estudo foi identificar os prováveis vetores dessa parasitose. MÉTODOS: Realizaram-se coletas mensais de mosquitos em um bairro costeiro de São Luís, MA, de março de 1996 a maio de 1997, no peridomicílio, tendo cão e homem como iscas. Os mosquitos foram dissecados para a pesquisa de larvas da Dirofilaria immitis. RESULTADOS: Coletaram-se 1.738 mosquitos de 11 espécies. Culex quinquefasciatus, capturada todos os meses, porém menos freqüente na estação chuvosa, correspondeu a 54,5% do total, seguido de Aedes albopictus (20,3%, Aedes taeniorhynchus e Aedes scapularis (ambos 11%. Larvas de D.immitis foram encontradas em 0,1% dos Cx. quinquefasciatus e 0,5% dos Ae. taeniorhynchus. CONCLUSÕES: Ae. taeniorhynchus e Cx. quinquefasciatus foram considerados vetores potenciais da dirofilariose em São Luís. A importância local de Cx. quinquefasciatus como transmissor primário da D. immitis necessita ser melhor avaliada.
Conflitos Potenciais na Relação entre Franqueadores e Franqueados Soteropolitanos
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Marcos Albuquerque
2016-12-01
Full Text Available Este estudo teve como objetivo avaliar conflitos potenciais que ocorrem na relação entre Franqueadores e Franqueados soteropolitanos, atuantes nas áreas de alimentação, vestuário e calçados e acessórios. A seleção dos segmentos investigados deveu-se não somente pela sua participação representativa na produtividade de varejo, mas também por concentrar grande número de empresas, muitas delas associadas à Associação Brasileira de Franchising (ABS. A pesquisa teve caráter exploratório, utilizando técnicas qualitativas do tipo estudos de casos múltiplos, com aplicação de entrevistas semiestruturadas, análise documental e observação participante. Uma vez identificados os pontos de conflitos entre os participantes investigados - perfil do candidato (falta de critérios específicos, previamente, recursos financeiros (nenhum planejamento financeiro anual acompanhado pelo franqueador junto ao seu franqueado, ponto comercial (as franqueadoras não orientam quanto à melhor escolha do ponto ou quanto aos aspectos que podem e devem ser observados e comunicação (ponto de amenização de conflitos, quando constante e bem conduzida – e avaliadas as práticas adotadas, foi possível propor medidas para minimizar o impacto dos conflitos no sistema de franchising.
Casimir Forces due to Matters in Compactified Six Dimensions
Ito, M
2003-01-01
We calculate the Casimir energies due to matters with various boundary conditions along two compact directions in six-dimensional $T^{2}$ compactification. We discuss whether the Casimir forces are attractive or repulsive forces. On the theories with extra dimensions, the Casimir energy plays a crucial role in the mechanism for stabilizing the size of extra dimensions. Finally we argue a procedure of the application to $Z_{2}$ orbifold.
Casimir force in the presence of a magnetodielectric medium
Kheirandish, Fardin; Sarabadani, Jalal
2010-01-01
In this article we investigate the Casimir effect in the presence of a medium by quantizing the Electromagnetic (EM) field in the presence of a magnetodielectric medium by using the path integral formalism. For a given medium with definite electric and magnetic susceptibilities, explicit expressions for the Casimir force are obtained which are in agree with the original Casimir force between two conducting parallel plates immersed in the quantum electromagnetic vacuum.
Ostoma, T; Ostoma, Tom; Trushyk, Mike
1999-01-01
We propose experiments that might be set up to detect the increase in the velocity of light in a vacuum in the laboratory frame for photons travelling between (and perpendicular to) the Casimir plates in a vacuum. The Casimir plates are two closely spaced, conductive plates, where an attractive force is observed to exist between the plates called the 'Casimir Force'. We propose that the velocity of light in a vacuum increases when propagating between two transparent Casimir Plates. We call this effect the 'Light Velocity Casimir Effect' or LVC effect. The LVC effect happens because the vacuum energy density in between the plates is lower than that outside the Casimir plates. The conductive plates disallow certain frequencies of electrically charged virtual particles to exist inside the plates, thus lowering the inside vacuum particle density, compared to the density outside the plates. The reduced (electrically charged) virtual particle density results in fewer photon scattering events inside the plates, whic...
Implications of the Babinet Principle for Casimir Interactions
Maghrebi, Mohammad F; Jaffe, Robert L
2011-01-01
We formulate the Babinet Principle (BP) as a relation between the scattering amplitudes for electromagnetic waves, and combine it with multiple scattering techniques to derive new properties of Casimir forces. We show that the Casimir force exerted by a planar conductor or dielectric on a self- complementary perforated planar mirror is approximately half that on a uniform mirror independent of the distance between them. The BP suggests that Casimir edge effects are anomalously small, supporting results obtained earlier in special cases. Finally, we illustrate how the BP can be used to estimate Casimir forces between perforated planar mirrors.
The role of magnetoplasmons in Casimir force calculations
Esquivel-Sirvent, R; Palomino-Ovando, M A; Cocoletzi, G H
2009-01-01
In this paper we review the role of magneto plasmon polaritons in the Casimir force calculations. By applying an external constant magnetic field a strong optical anisotropy is induced on two parallel slabs reducing the reflectivity and thus the Casimir force. As the external magnetic field increases, the Casimir force decreases. Thus, with an an external magnetic field the Casimir force can be controlled.The calculations are done in the Voigt configuration where the magnetic field is parallel to the slabs. In this configuration the reflection coefficients for TE and TM modes do not show mode conversion.
Casimir force between metal plate and dielectric plate
Institute of Scientific and Technical Information of China (English)
刘中柱; 邵成刚; 罗俊
1999-01-01
The Casimir effect between metal plate and dielectric plate is discussed with 1+1-dimensional potential model without using cut-off method. Calculation shows that the Casimir force between metal plate and dielectric plate is determined not only by the potential V0, the dielectric thickness and the distance α between the metal plate and dielectric plate, but also by the dimension of the vessel. When α is far less than the dimension of the vessel, the Casimir force Fc∝α（-1）; conversely Fc∝α-2. This result is significant for Casimir force experiment.
Potenciais cooperativos do podcast escolar por uma perspectiva freinetiana
National Research Council Canada - National Science Library
FREIRE, EUGÊNIO PACCELLI AGUIAR
2015-01-01
... a hipótese examinada, o referencial freinetiano servirá como alicerce para a elaboração de referenciais educativos para o desenvolvimento de podcasts cooperativos escolares a partir da apropriação, contextualizada à educação formal...
Directory of Open Access Journals (Sweden)
Marcela Pfeiffer
2009-01-01
Full Text Available OBJETIVO: verificar relação existente entre os potenciais auditivos de tronco cerebral e a avaliação comportamental do processamento auditivo. MÉTODOS: foi realizada em um grupo de 60 meninas residentes de Paraíba do Sul na idade de nove a 12 anos com limiares tonais dentro dos padrões de normalidade e timpanometria tipo A com presença dos reflexos acústicos. Os testes utilizados para a avaliação comportamental do processamento auditivo foram: avaliação simplificada do processamento auditivo, teste de fala no ruído, teste de dissílabos alternados e teste dicótico não verbal. Após a avaliação do processamento auditivo, as crianças foram subdivididas em dois grupos, G1 (sem alteração no processamento auditivo e G2 (com alteração no processamento auditivo e submetidas aos potenciais auditivos de tronco cerebral. Os parâmetros utilizados na comparação dos dois grupos foram: latência absoluta das ondas I, III e V; latência interpicos das ondas I-III, I-V, III-V; diferença interaural da latência interpico I-V; e diferença interaural da latência da onda V. RESULTADOS: foram encontradas diferenças estatísticas nos parâmetros de latência interpico das ondas I-V na orelha esquerda (p=0,009, diferença interaural da latência interpico de ondas I-V (p=0,020 e diferença da latência interpico de ondas I e V da orelha direita para a esquerda entre os grupos G1 e G2 (p=0,025. CONCLUSÃO: foi possível encontrar relação dos potenciais evocados auditivos de tronco cerebral com a avaliação comportamental do processamento auditivo nos parâmetros de latência interpico entre as ondas I e V da orelha esquerda e diferença interaural da latência interpico I-V na orelha esquerda.PURPOSE: to investigate the correlation of auditory brainstem response (ABR and behavioral auditory processing evaluation. METHODS: sixty girls, from Paraíba do Sul, ranging from 9 to 12-year-old were evaluated. In order to take part in the study
Matter-screened Casimir force and Casimir-Polder force in planar structures
Raabe, C; Raabe, Christian; Welsch, Dirk-Gunnar
2005-01-01
Using a recently developed theory of the Casimir force (Raabe C and Welsch D-G 2005 Phys. Rev. A 71 013814), we calculate the force that acts on a plate in front of a planar wall and the force that acts on the plate in the case where the plate is part of matter that fills the space in front of the wall. We show that in the limit of a dielectric plate whose permittivity is close to unity, the force obtained in the former case reduces to the ordinary, i.e., unscreened Casimir-Polder force acting on isolated atoms. In the latter case, the theory yields the Casimir-Polder force that is screened by the surrounding matter.
Casimir Torque in Inhomogeneous Dielectric Plates
Long, William
2013-01-01
In this work, we consider a torque caused by the well known quantum mechanical Casimir effect arising from quantized field fluctuations between plates with inhomogeneous, sharply discontinuous, dielectric properties. While the Casimir effect is a relatively well understood phenomenon, systems resulting in lateral or rotational forces are far less developed; to our knowledge, a theoretical study of discontinuous dielectric variants of such systems has not been attempted. We utilize a Proximity Force Approximation in conjunction with the Lifshitz dielectric formula to perform theoretical analyses of resultant torques in systems with bisected and quadrisected dielectric regions. We also develop a high precision Monte Carlo type numerical integrator to approximate our derived expressions. Our calculations of an energy density linear with the alignment angle result in a constant torque and have implications in NEMS (nano electromechanical systems) and MEMS (micro electromechanical systems), including a postulated ...
Thermal diffractive corrections to Casimir energies
Kabat, Daniel
2011-01-01
We study the interplay of thermal and diffractive effects in Casimir energies. We consider plates with edges, oriented either parallel or perpendicular to each other, as well as a single plate with a slit. We compute the Casimir energy at finite temperature using a formalism in which the diffractive effects are encoded in a lower dimensional non-local field theory that lives in the gap between the plates. The formalism allows for a clean separation between direct or geometric effects and diffractive effects, and makes an analytic derivation of the temperature dependence of the free energy possible. At low temperatures, with Dirichlet boundary conditions on the plates, we find that diffractive effects make a correction to the free energy which scales as T^6 for perpendicular plates, as T^4 for slits, and as T^4 log T for parallel plates.
Casimir apparatuses in a weak gravitational field
DEFF Research Database (Denmark)
Bimonte, Giuseppe; Calloni, Enrico; Esposito, Giampiero
2009-01-01
We review and assess a part of the recent work on Casimir apparatuses in the weak gravitational field of the Earth. For a free, real massless scalar field subject to Dirichlet or Neumann boundary conditions on the parallel plates, the resulting regularized and renormalized energy-momentum tensor...... is covariantly conserved, while the trace anomaly vanishes if the massless field is conformally coupled to gravity. Conformal coupling also ensures a finite Casimir energy and finite values of the pressure upon parallel plates. These results have been extended to an electromagnetic field subject to perfect...... conductor (hence idealized) boundary conditions on parallel plates, by various authors. The regularized and renormalized energy-momentum tensor has beene valuated up to second order in the gravity acceleration. In both the scalar and the electromagnetic case, studied to first order in the gravity...
Gravitational and Inertial Mass of Casimir Energy
Milton, Kimball A; Parashar, Prachi; Romeo, August; Shajesh, K V; Wagner, Jeffrey A
2007-01-01
It has been demonstrated, using variational methods, that quantum vacuum energy gravitates according to the equivalence principle, at least for the finite Casimir energies associated with perfectly conducting parallel plates. This conclusion holds independently of the orientation of the plates. We review these arguments and add further support to this conclusion by considering parallel semitransparent plates, that is, $\\delta$-function potentials, acting on a massless scalar field, in a spacetime defined by Rindler coordinates. We calculate the force on systems consisting of one or two such plates undergoing acceleration perpendicular to the plates. In the limit of small acceleration we recover (via the equivalence principle) the situation of weak gravity, and find that the gravitational force on the system is just $M\\mathbf{g}$, where $\\mathbf{g}$ is the gravitational acceleration and $M$ is the total mass of the system, consisting of the mass of the plates renormalized by the Casimir energy of each plate se...
Thermal corrections to the Casimir effect
Brevik, I; Milton, K A; Brevik, Iver; Ellingsen, Simen A.; Milton, Kimball A.
2006-01-01
The Casimir effect, reflecting quantum vacuum fluctuations in the electromagnetic field in a region with material boundaries, has been studied both theoretically and experimentally since 1948. The forces between dielectric and metallic surfaces both plane and curved have been measured at the 10 to 1 percent level in a variety of room-temperature experiments, and remarkable agreement with the zero-temperature theory has been achieved. In fitting the data various corrections due to surface roughness, patch potentials, curvature, and temperature have been incorporated. It is the latter that is the subject of the present article. We point out that, in fact, no temperature dependence has yet been detected, and that the experimental situation is still too fluid to permit conclusions about thermal corrections to the Casimir effect. Theoretically, there are subtle issues concerning thermodynamics and electrodynamics which have resulted in disparate predictions concerning the nature of these corrections. However, a ge...
Casimir pistons with general boundary conditions
Directory of Open Access Journals (Sweden)
Guglielmo Fucci
2015-02-01
Full Text Available In this work we analyze the Casimir energy and force for a scalar field endowed with general self-adjoint boundary conditions propagating in a higher dimensional piston configuration. The piston is constructed as a direct product I×N, with I=[0,L]⊂R and N a smooth, compact Riemannian manifold with or without boundary. The study of the Casimir energy and force for this configuration is performed by employing the spectral zeta function regularization technique. The obtained analytic results depend explicitly on the spectral zeta function associated with the manifold N and the parameters describing the general boundary conditions imposed. These results are then specialized to the case in which the manifold N is a d-dimensional sphere.
Casimir Effects in Renormalizable Quantum Field Theories
Graham, N; Weigel, H; Graham, Noah; Jaffe, Robert L.; Weigel, Herbert
2002-01-01
We review the framework we and our collaborators have developed for the study of one-loop quantum corrections to extended field configurations in renormalizable quantum field theories. We work in the continuum, transforming the standard Casimir sum over modes into a sum over bound states and an integral over scattering states weighted by the density of states. We express the density of states in terms of phase shifts, allowing us to extract divergences by identifying Born approximations to the phase shifts with low order Feynman diagrams. Once isolated in Feynman diagrams, the divergences are canceled against standard counterterms. Thus regulated, the Casimir sum is highly convergent and amenable to numerical computation. Our methods have numerous applications to the theory of solitons, membranes, and quantum field theories in strong external fields or subject to boundary conditions.
Casimir Effects in Renormalizable Quantum Field Theories
Graham, Noah; Jaffe, Robert L.; Weigel, Herbert
We present a framework for the study of one-loop quantum corrections to extended field configurations in renormalizable quantum field theories. We work in the continuum, transforming the standard Casimir sum over modes into a sum over bound states and an integral over scattering states weighted by the density of states. We express the density of states in terms of phase shifts, allowing us to extract divergences by identifying Born approximations to the phase shifts with low order Feynman diagrams. Once isolated in Feynman diagrams, the divergences are canceled against standard counterterms. Thus regulated, the Casimir sum is highly convergent and amenable to numerical computation. Our methods have numerous applications to the theory of solitons, membranes, and quantum field theories in strong external fields or subject to boundary conditions.
Casimir interactions between graphene sheets and metamaterials
Energy Technology Data Exchange (ETDEWEB)
Drosdoff, D.; Woods, Lilia M. [Department of Physics, University of South Florida, Tampa, Florida 33620 (United States)
2011-12-15
The Casimir force between graphene sheets and metamaterials is studied. Theoretical results based on the Lifshitz theory for layered, planar, two-dimensional systems in media are presented. We consider graphene-graphene, graphene-metamaterial, and metal-graphene-metamaterial configurations. We find that quantum effects of the temperature-dependent force are not apparent until the submicron range. In contrast to results with bulk dielectric and bulk metallic materials, no Casimir repulsion is found when graphene is placed on top of a magnetically active metamaterial substrate, regardless of the strength of the low-frequency magnetic response. In the case of the metal-graphene-metamaterial setting, repulsion between the metamaterial and the metal-graphene system is possible only when the dielectric response from the metal contributes significantly.
Casimir apparatuses in a weak gravitational field
DEFF Research Database (Denmark)
Bimonte, Giuseppe; Calloni, Enrico; Esposito, Giampiero;
2009-01-01
We review and assess a part of the recent work on Casimir apparatuses in the weak gravitational field of the Earth. For a free, real massless scalar field subject to Dirichlet or Neumann boundary conditions on the parallel plates, the resulting regularized and renormalized energy-momentum tensor...... is covariantly conserved, while the trace anomaly vanishes if the massless field is conformally coupled to gravity. Conformal coupling also ensures a finite Casimir energy and finite values of the pressure upon parallel plates. These results have been extended to an electromagnetic field subject to perfect...... conductor (hence idealized) boundary conditions on parallel plates, by various authors. The regularized and renormalized energy-momentum tensor has beene valuated up to second order in the gravity acceleration. In both the scalar and the electromagnetic case, studied to first order in the gravity...
Magnetic Anistropy due to the Casimir Effect
Metalidis, G
2009-01-01
We consider the Casimir interaction between a ferromagnetic and a non-magnetic mirror, and show how the Casimir effect gives rise to a magnetic anisotropy in the ferromagnetic layer. The anisotropy is out-of-plane if the non-magnetic plate is optically isotropic. If the non-magnetic plate shows a uniaxial optical anisotropy (with optical axis in the plate plane), we find an in-plane magnetic anisotropy. In both cases, the energetically most favorable magnetization orientation is given by the competition between polar, longitudinal and transverse contributions to the magneto-optical Kerr effect, and will therefore depend on the interplate distance. Numerical results will be presented for a magnetic plate made out of iron, and non-magnetic plates of gold (optically isotropic), quartz, calcite and barium titanate (all uniaxially birefringent).
Extended Analysis of the Casimir Force
Directory of Open Access Journals (Sweden)
Lehnert B.
2014-04-01
Full Text Available There are several arguments for the conventional form of the Zero Point Energy fre- quency spectrum to be put in doubt. It has thus to be revised in to that of a self-consistent system in statistical equilibrium where the total energy de nsity and the equivalent pres- sure become finite. An extended form of the Casimir force is th ereby proposed to be used as a tool for determining the local magnitude of the same pressure. This can be done in terms of measurements on the force between a pair po lished plane plates consisting of different metals, the plates having very small or zero air gaps. T his corre- sponds to the largest possible Casimir force. Even then, the re may arise problems with other adhering forces, possibly to be clarified in further experiments.
Thermodynamics of the Casimir Effect Asymptotic Considerations
Mitter, H
1998-01-01
We study the Casimir effect with different temperatures between the plates ($T$) resp. outside of them ($T'$). If we consider the inner system as the black body radiation for a special geometry, then contrary to common belief the temperature approaches a constant value for vanishing volume during isentropic processes. This means: the reduction of the degrees of freedom can not be compensated by a concentration of the energy during an adiabatic contraction of the two-plate system. Looking at the Casimir pressure, we find one unstable equilibrium point for isothermal processes with $T > T'$. For isentropic processes there is additionally one stable equilibrium point for larger values of the distances between the two plates.}
Maxwell-Chern-Simons Casimir Effect
Milton, K A
1992-01-01
In odd-dimensional spaces, gauge invariance permits a Chern-Simons mass term for the gauge fields in addition to the usual Maxwell-Yang-Mills kinetic energy term. We study the Casimir effect in such a (2+1)-dimensional Abelian theory. For the case of parallel conducting lines the result is the same as for a scalar field. For the case of circular boundary conditions the results are completely different, with even the sign of the effect being opposite for Maxwell-Chern-Simons fields and scalar fields. We further examine the effect of finite temperature. The Casimir stress is found to be attractive at both low and high temperature. Possibilities of observing this effect in the laboratory are discussed.
Directory of Open Access Journals (Sweden)
Claire M. Martel
2009-03-01
Full Text Available Flow cytometry was used to quantify the abundance of mannose-linked glycoconjugates on microalgae precultured using low- or high-nitrate media. Nitrogen-deficient microalgae were richer in cell-surface mannose than nitrogen-sufficient. Findings are discussed in view of recent research which reveals mannose-specific 'feeding receptors' assist prey biorecognition by phagotrophic protozoa that ingest microalgae.Citometria de fluxo foi usada para quantificar a abundância de glicoconjugados com manose em precultivos de microalgas usando meios com baixo e alto teor de nitrato. Microalgas com deficiências de nitrogênio tinham mais manose na superfície celular do que as com nitrogênio suficiente. Resultados são discutidos com base nas pesquisas recentes que revelam receptores específicos para manose que auxiliam no reconhecimento da presa por protozoários fagotróficos que ingerem microalgas.
Finite difference computation of Casimir forces
Pinto, Fabrizio
2016-09-01
In this Invited paper, we begin by a historical introduction to provide a motivation for the classical problems of interatomic force computation and associated challenges. This analysis will lead us from early theoretical and experimental accomplishments to the integration of these fascinating interactions into the operation of realistic, next-generation micro- and nanodevices both for the advanced metrology of fundamental physical processes and in breakthrough industrial applications. Among several powerful strategies enabling vastly enhanced performance and entirely novel technological capabilities, we shall specifically consider Casimir force time-modulation and the adoption of non-trivial geometries. As to the former, the ability to alter the magnitude and sign of the Casimir force will be recognized as a crucial principle to implement thermodynamical nano-engines. As to the latter, we shall first briefly review various reported computational approaches. We shall then discuss the game-changing discovery, in the last decade, that standard methods of numerical classical electromagnetism can be retooled to formulate the problem of Casimir force computation in arbitrary geometries. This remarkable development will be practically illustrated by showing that such an apparently elementary method as standard finite-differencing can be successfully employed to numerically recover results known from the Lifshitz theory of dispersion forces in the case of interacting parallel-plane slabs. Other geometries will be also be explored and consideration given to the potential of non-standard finite-difference methods. Finally, we shall introduce problems at the computational frontier, such as those including membranes deformed by Casimir forces and the effects of anisotropic materials. Conclusions will highlight the dramatic transition from the enduring perception of this field as an exotic application of quantum electrodynamics to the recent demonstration of a human climbing
Inertia from an asymmetric Casimir effect
McCulloch, M E
2013-01-01
The property of inertia has never been fully explained. A model for inertia (MiHsC or quantised inertia) has been suggested that assumes that 1) inertia is due to Unruh radiation and 2) this radiation is subject to a Hubble-scale Casimir effect. This model has no adjustable parameters and predicts the cosmic acceleration, and galaxy rotation without dark matter, suggesting that Unruh radiation indeed causes inertia, but the exact mechanism by which it does this has not been specified. The mechanism suggested here is that when an object accelerates, for example to the right, a dynamical (Rindler) event horizon forms to its left, reducing the Unruh radiation on that side by a Rindler-scale Casimir effect whereas the radiation on the other side is only slightly reduced by a Hubble-scale Casimir effect. This produces an imbalance in the radiation pressure on the object, and a net force that always opposes acceleration, like inertia. A formula for inertia is derived, and an experimental test is suggested.
Quantum spring from the Casimir effect
Feng, Chao-Jun; Li, Xin-Zhou
2010-07-01
The Casimir effect arises not only in the presence of material boundaries but also in space with nontrivial topology. In this Letter, we choose a topology of the flat (D + 1)-dimensional spacetime, which causes the helix boundary condition for a Hermitian massless scalar field. Especially, Casimir effect for a massless scalar field on the helix boundary condition is investigated in two and three dimensions by using the zeta function techniques. The Casimir force parallel to the axis of the helix behaves very much like the force on a spring that obeys the Hooke's law when the ratio r of the pitch to the circumference of the helix is small, but in this case, the force comes from a quantum effect, so we would like to call it quantum spring. When r is large, this force behaves like the Newton's law of universal gravitation in the leading order. On the other hand, the force perpendicular to the axis decreases monotonously with the increasing of the ratio r. Both forces are attractive and their behaviors are the same in two and three dimensions.
Enhancing Casimir repulsion via topological insulator multilayers
Zeng, Ran; Chen, Liang; Nie, Wenjie; Bi, Meihua; Yang, Yaping; Zhu, Shiyao
2016-08-01
We propose to observe the enhanced Casimir repulsion between two parallel multilayer walls made of alternating layers of a topological insulator (TI) and a normal insulator. Based on the transfer matrix method, the Fresnel coefficients matrix is generalized to apply to the TI multilayer structure. The Casimir repulsion under the influence of the magnetization orientation in the magnetic coatings on TI layer surfaces, the layer thicknesses, and the topological magnetoelectric polarizability, is investigated. We show that, for the multilayer structures with parallel magnetization on the TI layer surfaces, it is possible to enhance the repulsion by increasing the TI layer number, which is due to the accumulation of the contribution to the repulsion from the polarization rotation effect occurring on each TI layer surface. Generally, in the distance region where there is Casimir attraction between semi-infinite TIs, the force may turn into repulsion in TI multilayer structure, and in the region of repulsion for semi-infinite TI, the repulsive force can be enhanced in magnitude, the enhancement tends to a maximum while the structure contains sufficiently many layers.
Chiral metamaterials reduce the attractive Casimir force
Zhao, R.; Koschny, Th.; Economou, E. N.; Soukoulis, C. M.
2010-08-01
In our previous work [R. Zhao, J. Zhou, Th. Koschny, E. N. Economou, and C. M. Soukoulis, Phys. Rev. Lett. 103, 103602 (2009)], we demonstrated theoretically that one can obtain repulsive Casimir forces and stable nanolevitations by using chiral metamaterials if the chirality is strong enough. In our recent work [R. Zhao, Th. Koschny, E.N. Economou, and C.M. Soukoulis, Phys. Rev. B 81, 235126 (2010)], we checked some chiral metamaterial designs and found that the artificial chiral metamaterials constructed by passive materials is very difficult to reach the critical chirality to realize repulsive Casimir force. Therefore, in this paper, we give a four-folded rotated Ω-particle chiral metamaterial as an example, use the effective medium approximation to retrieval the constitutive parameters, and take the same procedure as we did before to see how much the chiral metamaterial can reduce the attractive force. It shows that this un-optimized chiral metamaterial can reduce the Casimir attraction by 70%.
Casimir-Polder interaction in second quantization
Energy Technology Data Exchange (ETDEWEB)
Schiefele, Juergen
2011-03-21
The Casimir-Polder interaction between a single neutral atom and a nearby surface, arising from the (quantum and thermal) fluctuations of the electromagnetic field, is a cornerstone of cavity quantum electrodynamics (cQED), and theoretically well established. Recently, Bose-Einstein condensates (BECs) of ultracold atoms have been used to test the predictions of cQED. The purpose of the present thesis is to upgrade single-atom cQED with the many-body theory needed to describe trapped atomic BECs. Tools and methods are developed in a second-quantized picture that treats atom and photon fields on the same footing. We formulate a diagrammatic expansion using correlation functions for both the electromagnetic field and the atomic system. The formalism is applied to investigate, for BECs trapped near surfaces, dispersion interactions of the van der Waals-Casimir-Polder type, and the Bosonic stimulation in spontaneous decay of excited atomic states. We also discuss a phononic Casimir effect, which arises from the quantum fluctuations in an interacting BEC. (orig.)
Sample dependence of the Casimir forces
Pirozhenko, I; Svetovoy, V B
2006-01-01
We have analyzed available optical data for Au in the mid-infrared range which is important for a precise prediction of the Casimir force. Significant variation of the data demonstrates genuine sample dependence of the dielectric function. We demonstrate that the Casimir force is largely determined by the material properties in the low frequency domain and argue that therefore the precise values of the Drude parameters are crucial for an accurate evaluation of the force. These parameters can be estimated by two different methods, either by fitting real and imaginary parts of the dielectric function at low frequencies, or via a Kramers-Kronig analysis based on the imaginary part of the dielectric function in the extended frequency range. Both methods lead to very similar results. We show that the variation of the Casimir force calculated with the use of different optical data can be as large as 5% and at any rate cannot be ignored. To have a reliable prediction of the force with a precision of 1%, one has to m...
Casimir force measurements from silicon carbide surfaces
Sedighi, M.; Svetovoy, V. B.; Palasantzas, G.
2016-02-01
Using an atomic force microscope we performed measurements of the Casimir force between a gold- coated (Au) microsphere and doped silicon carbide (SiC) samples. The last of these is a promising material for devices operating under severe environments. The roughness of the interacting surfaces was measured to obtain information for the minimum separation distance upon contact. Ellipsometry data for both systems were used to extract optical properties needed for the calculation of the Casimir force via the Lifshitz theory and for comparison to the experiment. Special attention is devoted to the separation of the electrostatic contribution to the measured total force. Our measurements demonstrate large contact potential V0(≈0.67 V ) , and a relatively small density of charges trapped in SiC. Knowledge of both Casimir and electrostatic forces between interacting materials is not only important from the fundamental point of view, but also for device applications involving actuating components at separations of less than 200 nm where surface forces play dominant role.
Electromagnetic Casimir piston in higher dimensional spacetimes
Teo, L P
2011-01-01
We consider the Casimir effect of the electromagnetic field in a higher dimensional spacetime of the form $M\\times \\mathcal{N}$, where $M$ is the 4-dimensional Minkowski spacetime and $\\mathcal{N}$ is an $n$-dimensional compact manifold. The Casimir force acting on a planar piston that can move freely inside a closed cylinder with the same cross section is investigated. Different combinations of perfectly conducting boundary conditions and infinitely permeable boundary conditions are imposed on the cylinder and the piston. It is verified that if the piston and the cylinder have the same boundary conditions, the piston is always going to be pulled towards the closer end of the cylinder. However, if the piston and the cylinder have different boundary conditions, the piston is always going to be pushed to the middle of the cylinder. By taking the limit where one end of the cylinder tends to infinity, one obtains the Casimir force acting between two parallel plates inside an infinitely long cylinder. The asymptot...
Casimir effect in de Sitter spacetime
Saharian, A A
2011-01-01
The vacuum expectation value of the energy-momentum tensor and the Casimir forces are investigated for a massive scalar field with an arbitrary curvature coupling parameter in the geometry of two parallel plates, on the background of de Sitter spacetime. The field is prepared in the Bunch--Davies vacuum state and is constrained to satisfy Robin boundary conditions on the plates. The vacuum energy-momentum tensor is non-diagonal, with the off-diagonal component corresponding to the energy flux along the direction normal to the plates. It is shown that the curvature of the background spacetime decisively influences the behavior of the Casimir forces at separations larger than the curvature radius of de Sitter spacetime. In dependence of the curvature coupling parameter and the mass of the field, two different regimes are realized, which exhibit monotonic or oscillatory behavior of the forces. The decay of the Casimir force at large plate separation is shown to be power-law, with independence of the value of the...
Casimir effect in dielectrics Bulk Energy Contribution
Carlson, C E; Pérez-Mercader, J; Visser, M; Visser, Matt
1997-01-01
In a recent series of papers, Schwinger discussed a process that he called the Dynamical Casimir Effect. The key essence of this effect is the change in zero-point energy associated with any change in a dielectric medium. (In particular, if the change in the dielectric medium is taken to be the growth or collapse of a bubble, this effect may have relevance to sonoluminescence.) The kernel of Schwinger's result is that the change in Casimir energy is proportional to the change in volume of the dielectric, plus finite-volume corrections. Other papers have called into question this result, claiming that the volume term should actually be discarded, and that the dominant term remaining is proportional to the surface area of the dielectric. In this communication, which is an expansion of an earlier letter on the same topic, we present a careful and critical review of the relevant analyses. We find that the Casimir energy, defined as the change in zero-point energy due to a change in the medium, has at leading orde...
Casimir effect in dielectrics Surface area contribution
Molina-Paris, C; Molina-Paris, Carmen; Visser, Matt
1997-01-01
In this paper we take a deeper look at the technically elementary but physically robust viewpoint in which the Casimir energy in dielectric media is interpreted as the change in the total zero point energy of the electromagnetic vacuum summed over all states. Extending results presented in previous papers [hep-th/9609195; hep-th/9702007] we approximate the sum over states by an integral over the density of states including finite volume corrections. For an arbitrarily-shaped finite dielectric, the first finite-volume correction to the density of states is shown to be proportional to the surface area of the dielectric interface and is explicitly evaluated as a function of the permeability and permitivity. Since these calculations are founded in an elementary and straightforward way on the underlying physics of the Casimir effect they serve as an important consistency check on field-theoretic calculations. As a concrete example we discuss Schwinger's suggestion that the Casimir effect might be the underlying ph...
Avaliação de teratógenos potenciais na população brasileira
Directory of Open Access Journals (Sweden)
Schüler-Faccini Lavínia
2002-01-01
Full Text Available O fato de agentes ambientais, nomeadamente fármacos, infecções maternas, e agentes químicos ou físicos poderem causar danos ao embrião ou feto em desenvolvimento é um problema reconhecido principalmente a partir do século 20. Nos países em desenvolvimento, existem características especiais que podem tornar esse problema mais agudo. Essas características incluem níveis educacionais e econômicos baixos da população, alta incidência de doenças infecciosas e carenciais, escassos recursos para saúde e pesquisa, prática freqüente e sem controle de automedicação, facilidade de obtenção de medicações que deveriam estar submetidas à prescrição médica e, finalmente, proibição legal de interrupção da gestação. Além disso, pode somar-se uma qualidade ambiental precária ou mesmo condições de trabalho insalubres durante a gravidez. No presente trabalho apresentamos as principais metodologias para detecção e monitorização de potenciais teratógenos, com ênfase especial nos programas desenvolvidos no Brasil e América Latina.
Three dimensional Casimir piston for massive scalar fields
Lim, S C
2008-01-01
We consider Casimir force acting on a three dimensional rectangular piston due to a massive scalar field subject to periodic, Dirichlet and Neumann boundary conditions. Exponential cut-off method is used to derive the Casimir energy in the interior region and the exterior region separated by the piston. It is shown that the divergent term of the Casimir force acting on the piston due to the interior region cancels with that due to the exterior region, thus render a finite well-defined Casimir force acting on the piston. Explicit expressions for the total Casimir force acting on the piston is derived, which show that the Casimir force is always attractive for all the different boundary conditions considered. As a function of a -- the distance from the piston to the opposite wall, it is found that the magnitude of the Casimir force behaves like $1/a^4$ when $a\\to 0^+$ and decays exponentially when $a\\to \\infty$. Moreover, the magnitude of the Casimir force is always a decreasing function of a. On the other hand...
Three-dimensional Casimir piston for massive scalar fields
Lim, S. C.; Teo, L. P.
2009-08-01
We consider Casimir force acting on a three-dimensional rectangular piston due to a massive scalar field subject to periodic, Dirichlet and Neumann boundary conditions. Exponential cut-off method is used to derive the Casimir energy. It is shown that the divergent terms do not contribute to the Casimir force acting on the piston, thus render a finite well-defined Casimir force acting on the piston. Explicit expressions for the total Casimir force acting on the piston is derived, which show that the Casimir force is always attractive for all the different boundary conditions considered. As a function of a - the distance from the piston to the opposite wall, it is found that the magnitude of the Casimir force behaves like 1/a4 when a→0+ and decays exponentially when a→∞. Moreover, the magnitude of the Casimir force is always a decreasing function of a. On the other hand, passing from massless to massive, we find that the effect of the mass is insignificant when a is small, but the magnitude of the force is decreased for large a in the massive case.
Surface Stability of Epitaxial Elastic Films by the Casimir Force
Zhao, Ya-Pu; Li, Wen J.
2002-08-01
We investigate the morphological stability of epitaxial thin elastic films on a substrate by the Casimir force between the film surface and a flat plate. Critical undulation wavelengths are derived for two different limit conditions. Consideration of the Casimir force in both limit cases decreases the critical wavelength of the surface perturbation.
Normal and lateral Casimir force: Advances and prospects
Energy Technology Data Exchange (ETDEWEB)
Klimchitskaya, G L, E-mail: galina.klimchitskaya@itp.uni-leipzig.d [Department of Physics, North-West Technical University, Millionnaya Street 5, St.Petersburg, 191065 (Russian Federation); Institute for Theoretical Physics, Leipzig University, Postfach 100920, D-04009, Leipzig (Germany)
2010-11-01
We discuss recent experimental and theoretical results on the Casimir force between real material bodies made of different materials. Special attention is paid to calculations of the normal Casimir force acting perpendicular to the surface with the help of the Lifshitz theory taking into account the role of free charge carriers. Theoretical results for the thermal Casimir force acting between metallic, dielectric and semiconductor materials are presented and compared with available experimental data. Main attention is concentrated on the possibility to control the magnitude and sign of the Casimir force for applications in nanotechnology. In this respect we consider experiments on the optical modulation of the Casimir force between metal and semiconductor test bodies with laser light. Another option is the use of ferromagnetic materials, specifically, ferromagnetic dielectrics. Under some conditions this allows to get Casimir repulsion. The lateral Casimir force acting between sinusoidally corrugated surfaces can be considered as some kind of noncontact friction caused by zero-point oscillations of the electromagnetic field. Recent experiments and computations using the exact theory have demonstrated the role of diffraction-type effects in this phenomenon and the possibility to get asymmetric force profiles. Conclusion is made that the Casimir force may play important role in the operation of different devices on the nanoscale.
Surface Stability of Epitaxial Elastic Films by the Casimir Force
Institute of Scientific and Technical Information of China (English)
赵亚溥; 李文荣
2002-01-01
We investigate the morphological stability of epitaxial thin elastic films on a substrate by the Casimir force between the film surface and a flat plate. Critical undulation wavelengths are derived for two different limit conditions. Consideration of the Casimir force in both limit cases decreases the critical vavelength of the surface perturbation.
Directory of Open Access Journals (Sweden)
Carlos Alberto Núñez-Colín
2009-09-01
Full Text Available The purposes of this study were to determine the distribution and climatic patterns of current and future physic nut (Jatropha curcas cultivation regions in Mexico, and to identify possible locations for in vivo germplasm banks establishment, using geographic information systems. Current climatic data were processed by Floramap software to obtain distribution maps and climatic patterns of regions where wild physic nuts could be found. DIVA-GIS software analyzed current climatic data (Worldclim model and climatic data generated by CCM3 model to identify current and future physic nut cultivation regions, respectively. The distribution map showed that physic nut was present in most of the tropical and subtropical areas of Mexico, which corresponded to three agroclimatic regions. Climate types were Aw2, Aw1, and Bs1, for regions 1, 2 and 3, respectively. Nontoxic genotypes were associated with region 2, and toxic genotypes were associated with regions 1 and 3. According to the current and future cultivation regions identified, the best suitable ones to establish in vivo germplasm collections were the coast of Michoacán and the Isthmus of Tehuantepec, located among the states of Veracruz, Oaxaca and Chiapas.Os objetivos deste estudo foram determinar a distribuição e os padrões climáticos de regiões de cultivo, atuais e futuras, do pinhão-manso no México, e identificar possíveis locais para o estabelecimento de bancos ativos de germoplasma, com uso de sistemas de informação geográfica. Os dados climáticos atuais foram processados pelo software Floramap, para obter mapas de distribuição e padrões climáticos de regiões onde plantas de pinhão-manso selvagens poderiam ser encontradas. Foi utilizado o software DIVA-GIS para análise dos dados climáticos atuais (modelo Worldclim e dos dados climáticos gerados pelo modelo CCM3, para identificar regiões de cultivo atuais e futuras de pinhão-manso, respectivamente. O pinhão-manso est
Rodrigues, Edmo Montes
2014-01-01
Este estudo teve como objetivos prospectar bactérias capazes de utilizar hidrocarbonetos do petróleo como fonte de carbono e energia, analisar a estrutura e dinâmica da comunidade microbiana que coloniza o petróleo após sua exposição no mar utilizando dados de TRFLP multiplex, assim como simular e analisar a eficiência de diferentes estratégias de biorremediação de petróleo no litoral da Ilha da Trindade Brasil. Para tanto, foi montado um experimento à aproximadamente 100 m da praia das Ta...
Measurement of non-monotonic Casimir forces between silicon nanostructures
Tang, L.; Wang, M.; Ng, C. Y.; Nikolic, M.; Chan, C. T.; Rodriguez, A. W.; Chan, H. B.
2017-01-01
Casimir forces are of fundamental interest because they originate from quantum fluctuations of the electromagnetic field. Apart from controlling this force via the optical properties of materials, a number of novel geometries have been proposed to generate repulsive and/or non-monotonic Casimir forces between bodies separated by vacuum gaps. Experimental realization of these geometries, however, is hindered by the difficulties in alignment when the bodies are brought into close proximity. Here, using an on-chip platform with integrated force sensors and actuators, we circumvent the alignment problem and measure the Casimir force between two surfaces with nanoscale protrusions. We demonstrate that the force depends non-monotonically on the displacement. At some displacements, the Casimir force leads to an effective stiffening of the nanomechanical spring. Our findings pave the way for exploiting the Casimir force in nanomechanical systems using structures of complex and non-conventional shapes.
Repulsive Casimir force at zero and finite temperature
Energy Technology Data Exchange (ETDEWEB)
Lim, S C [Faculty of Engineering, Multimedia University, Jalan Multimedia, Cyberjaya, 63100 Selangor Darul Ehsan (Malaysia); Teo, L P [Faculty of Information Technology, Multimedia University, Jalan Multimedia, Cyberjaya, 63100 Selangor Darul Ehsan (Malaysia)], E-mail: sclim@mmu.edu.my, E-mail: lpteo@mmu.edu.my
2009-01-15
We study the zero and finite temperature Casimir force acting on a perfectly conducting piston with arbitrary cross section moving inside a closed cylinder with infinitely permeable walls. We show that at any temperature, the Casimir force always tends to move the piston away from the walls and toward its equilibrium position. In the case of a rectangular piston, exact expressions for the Casimir force are derived. In the high-temperature regime, we show that the leading term of the Casimir force is linear in temperature and therefore the Casimir force has a classical limit. Due to duality, all these results also hold for an infinitely permeable piston moving inside a closed cylinder with perfectly conducting walls.
Potenciais cooperativos do podcast escolar por uma perspectiva freinetiana
Directory of Open Access Journals (Sweden)
EUGÊNIO PACCELLI AGUIAR FREIRE
2015-01-01
Full Text Available Este artigo investiga se o uso de podcast no Brasil segue a concepção cooperativa de Célestin Freinet (1998, para quem a cooperação é uma ação educativa conjunta, motivada pelo interesse espontâneo e envolta em uma atmosfera livre. Confirmada a hipótese examinada, o referencial freinetiano servirá como alicerce para a elaboração de referenciais educativos para o desenvolvimento de podcasts cooperativos escolares a partir da apropriação, contextualizada à educação formal, das relações produtivas vistas na podosfera brasileira, examinadas por meio de uma observação participante on-line . Esse procedimento será precedido da apresentação da tecnologia tratada, bem como da elucidação dos parâmetros teórico-metodológicos desta pesquisa. Como resultado desses procedimentos, foi elaborado um conjunto de referenciais para projetos que busquem trabalhar a cooperação freinetiana por meio do podcast na educação formal.
Milton, Kimball A; Wagner, Jef; Cavero-Pelaez, Ines
2009-01-01
Various applications of the multiple scattering technique to calculating Casimir energy are described. These include the interaction between dilute bodies of various sizes and shapes, temperature dependence, interactions with multilayered and corrugated bodies, and new examples of exactly solvable separable bodies.
Membrane actuation by Casimir force manipulation
Pinto, Fabrizio
2008-04-01
In our laboratory, we have been developing a practical demonstration of actuation by means of the Casimir force inspired by the capacitive detection approach originally described by Arnold, Hunklinger and Dransfeld (1972 Rev. Sci. Instrum. 43 584-7). In this paper, we first describe the mathematical challenges pertaining to the electrostatic calibration of our measuring device, which has been enhanced by our recently published results regarding the computation of electrostatic fields in axial systems, such as the long-standing classical circular capacitor problem. We also discuss our computational approach to the calculation of the Casimir force in our system, including our adoption of analytical descriptions of the dielectric functions of semiconductors extended to the case of axial geometries. We will illustrate how the original AHD apparatus has been drastically improved upon, for instance by means of modern nanopositioner technology, and we shall discuss our published experimental results on the dynamics of a vibrating membrane with a central disc, which have provided the first direct verification of the mechanical resonances of such a system. The emphasis of our effort is not exclusively directed to fundamental physics research but is focused on, and ultimately motivated by, our goal of identifying viable industrial applications leading to commercially marketable products based on Casimir force actuation. Therefore we conclude this paper by briefly discussing the contribution we believe these results will offer to some current technological problems, in particular in nanotechnology, including some thoughts on the possibility that dispersion forces may enable a new and rapidly expanding industry to develop in the near future.
Casimir energies of self-similar plate configurations
Shajesh, K. V.; Brevik, Iver; Cavero-Peláez, Inés; Parashar, Prachi
2016-09-01
We construct various self-similar configurations using parallel δ -function plates and show that it is possible to evaluate the Casimir interaction energy of these configurations using the idea of self-similarity alone. We restrict our analysis to interactions mediated by a scalar field, but the extension to the electromagnetic field is immediate. Our work unveils an easy and powerful method that can be easily employed to calculate the Casimir energies of a class of self-similar configurations. As a highlight, in an example, we determine the Casimir interaction energy of a stack of parallel plates constructed by positioning δ -function plates at the points constituting the Cantor set, a prototype of a fractal. This, to our knowledge, is the first time that the Casimir energy of a fractal configuration has been reported. Remarkably, the Casimir energy of some of the configurations we consider turn out to be positive, and a few even have zero Casimir energy. For the case of positive Casimir energy that is monotonically decreasing as the stacking parameter increases, the interpretation is that the pressure of vacuum tends to inflate the infinite stack of plates. We further support our results, derived using the idea of self-similarity alone, by rederiving them using the Green's function formalism. These expositions gives us insight into the connections between the regularization methods used in quantum field theories and regularized sums of divergent series in number theory.
Finite temperature Casimir effect in Kaluza-Klein spacetime
Energy Technology Data Exchange (ETDEWEB)
Teo, L.P. [Faculty of Information Technology, Multimedia University, Jalan Multimedia, Cyberjaya, 63100 Selangor Darul Ehsan (Malaysia)], E-mail: lpteo@mmu.edu.my
2009-10-01
In this article, we consider the finite temperature Casimir effect in Kaluza-Klein spacetime due the vacuum fluctuation of massless scalar field with Dirichlet boundary conditions. We consider the general case where the extra dimensions (internal space) can be any compact connected manifold or orbifold without boundaries. Using piston analysis, we show that the Casimir force is always attractive at any temperature, regardless of the geometry of the internal space. Moreover, the magnitude of the Casimir force increases as the size of the internal space increases and it reduces to the Casimir force in (3+1)-dimensional Minkowski spacetime when the size of the internal space shrinks to zero. In the other extreme where the internal space is large, the Casimir force can increase beyond all bound. Asymptotic behaviors of the Casimir force in the low and high temperature regimes are derived and it is observed that the magnitude of the Casimir force grows linearly with temperature in the high temperature regime.
Oscillating Casimir force between two slabs in a Fermi sea
Institute of Scientific and Technical Information of China (English)
Chen Li-Weia; Su Guo-Zhen; Chen Jin-Can; Andresen Bjarne
2012-01-01
The Casimir effect for two parallel slabs immersed in an ideal Fermi sea is investigated at both zero and nonzero temperatures.It is found that the Casimir effect in a Fermi gas is distinctly different from that in an electromagnetic field or a massive Bose gas.In contrast to the familiar result that the Casimir force decreases monotonically with the increase of the separation L between two slabs in an electromagnetic field and a massive Bose gas,the Casimir force in a Fermi gas oscillates as a function of L.The Casimir force can be either attractive or repulsive,depending sensitively on the magnitude of L. In addition,it is found that the amplitude of the Casimir force in a Fermi gas decreases with the increase of the temperature,which also is contrary to the case in a Bose gas,since the bosonic Casimir force increases linearly with the increase of the temperature in the region T ＜ Tc,where Tc is the critical temperature of the Bose-Einstein condensation.
Casimir Energy for a Dielectric Cylinder
Cavero-Pelaez, I; Cavero-Pelaez, Ines; Milton, Kimball A.
2004-01-01
In this paper we calculate the Casimir energy for a dielectric-diamagnetic cylinder with the speed of light differing on the inside and outside. Although the result is in general divergent, special cases are meaningful. The well-known results for a uniform speed of light are reproduced. The self-stress on a purely dielectric cylinder is shown to vanish through second order in the deviation of the permittivity from its vacuum value, in agreement with the result calculated from the sum of van der Waals forces.
EXTENDED CASIMIR APPROACH TO CONTROLLED HAMILTONIAN SYSTEMS
Institute of Scientific and Technical Information of China (English)
Yuqian GUO; Daizhan CHENG
2006-01-01
In this paper, we first propose an extended Casimir method for energy-shaping. Then it is used to solve some control problems of Hamiltonian systems. To solve the H∞ control problem, the energy function of a Hamiltonian system is shaped to such a form that could be a candidate solution of HJI inequality. Next, the energy function is shaped as a candidate of control ISS-Lyapunov function, and then the input-to-state stabilization of port-controlled Hamiltonian systems is achieved. Some easily verifiable sufficient conditions are presented.
Microscopic origin of Casimir-Polder forces
2006-01-01
We establish a general relation between dispersion forces. First, based on QED in causal media, leading-order perturbation theory is used to express both the single-atom Casimir-Polder and the two-atom van der Waals potentials in terms of the atomic polarizabilities and the Green tensor for the body-assisted electromagnetic field. Endowed with this geometry-independent framework, we then employ the Born expansion of the Green tensor together with the Clausius-Mosotti relation to prove that th...
Ultrastrong optomechanics incorporating the dynamical Casimir effect
Nation, P. D.; Suh, J.; Blencowe, M. P.
2016-02-01
We propose a superconducting circuit comprising a dc superconducting quantum interference device with a mechanically compliant arm embedded in a coplanar microwave cavity that realizes an optomechanical system with a degenerate or nondegenerate parametric interaction generated via the dynamical Casimir effect. For experimentally feasible parameters, this setup is capable of reaching the single-photon ultrastrong-coupling regime while simultaneously possessing a parametric coupling strength approaching the renormalized cavity frequency. This opens up the possibility of observing the interplay between these two fundamental nonlinearities at the single-photon level.
Casimir effect in Domain Wall formation
Setare, M R
2003-01-01
The Casimir forces on two parallel plates in conformally flat de Sitter background due to conformally coupled massless scalar field satisfying mixed boundary conditions on the plates is investigated. In the general case of mixed boundary conditions formulae are derived for the vacuum expectation values of the energy-momentum tensor and vacuum forces acting on boundaries. Different cosmological constants are assumed for the space between and outside of the plates to have general results applicable to the case of domain wall formations in the early universe.
Benefícios potenciais do consumo de nozes
Amaral, J.S.; Casal,Susana; Seabra, R.M.; Oliveira, M. B. P. P.
2006-01-01
Os frutos secos, na sua generalidade, apresentam uma composição similar do ponto de vista nutricional sendo, caracteristicamente, alimentos com elevado teor de lípidos. Por este motivo, a generalidade dos consumidores evita o seu consumo, uma vez que associa este tipo de alimentos ao aumento de peso corporal. No entanto, estudos epidemiológicos e clínicos realizados nas últimas décadas sugerem que o consumo frequente de quantidades moderadas de frutos secos pode ter efeitos benéficos para a s...
The covariant electromagnetic Casimir effect for real conducting spherical shells
Razmi, H
2016-01-01
Using the covariant electromagnetic Casimir effect (previously introduced for real conducting cylindrical shells [1]), the Casimir force experienced by a spherical shell, under Dirichlet boundary condition, is calculated. The renormalization procedure is based on the plasma cut-off frequency for real conductors. The real case of a gold (silver) sphere is considered and the corresponding electromagnetic Casimir force is computed. In the covariant approach, there isn't any decomposition of fields to TE and TM modes; thus, we do not need to consider the Neumann boundary condition in parallel to the Dirichlet problem and then add their corresponding results.
Huge Casimir effect at finite temperature in electromagnetic Rindler space
Zhao, Tian-Ming
2011-01-01
We investigate the Casimir effect at finite temperature in electromagnetic Rindler space, and find the Casimir energy is proportional to $\\frac{T^4}{d^2}$ in the high temperature limit, where $T\\approx 27 ^\\circ\\mathrm{C}$ is the temperature and $d\\approx 100nm$ is a small cutoff. We propose to make metamaterials to mimic Rindler space and measure the predicted Casimir effect. Since the parameters of metamaterials we proposed are quite simple, this experiment would be easily implemented in laboratory.
Huge Casimir effect at finite temperature in electromagnetic Rindler space
Zhao, Tian-Ming; Miao, Rong-Xin
2011-12-01
We investigate the Casimir effect at finite temperature in electromagnetic Rindler space, and find the Casimir energy is proportional to $\\frac{T^4}{d^2}$ in the high temperature limit, where $T\\approx 27 ^\\circ\\mathrm{C}$ is the temperature and $d\\approx 100nm$ is a small cutoff. We propose to make metamaterials to mimic Rindler space and measure the predicted Casimir effect. Since the parameters of metamaterials we proposed are quite simple, this experiment would be easily implemented in laboratory.
Huge Casimir effect at finite temperature in electromagnetic Rindler space
Zhao, Tian-Ming; Miao, Rong-Xin
2011-01-01
We investigate the Casimir effect at finite temperature in electromagnetic Rindler space, and find the Casimir energy is proportional to $\\frac{T^4}{d^2}$ in the high temperature limit, where $T\\approx 27 ^\\circ\\mathrm{C}$ is the temperature and $d\\approx 100nm$ is a small cutoff. We propose to make metamaterials to mimic Rindler space and measure the predicted Casimir effect. Since the parameters of metamaterials we proposed are quite simple, this experiment would be easily implemented in la...
Casimir energy for spherical shell in Schwarzchild black hole background
Setare, M R
2004-01-01
In this paper, we consider the Casimir energy of massless scalar field which satisfy Dirichlet boundary condition on a spherical shell. Outside the shell, the spacetime is assumed to be described by the Schwarzschild metric, while inside the shell it is taken to be the flat Minkowski space. Using zeta function regularization and heat kernel coefficients we isolate the divergent contributions of the Casimir energy inside and outside the shell, then using the renormalization procedure of the bag model the divergent parts are cancelled, finally obtaining a renormalized expression for the total Casimir energy.
The Casimir Effect on the Light-Cone
Lenz, F
2003-01-01
The Casimir effect is investigated in light-cone quantization. It is shown that for spacelike separation of the walls enclosing the system the standard result for the pressure exerted on the walls is obtained. For walls separated in light-cone space direction no regularization of the quantum fluctuations exists which would yield a finite pressure. The origin of this failure and its implications for other vacuum properties are discussed by analyzing the Casimir effect as seen from a moving observer approaching the speed of light. The possibility for calculation of thermodynamic quantities in light-cone quantization via the Casimir effect is pointed out.
Excesso de peso em adolescentes: explorando potenciais fatores de risco
Directory of Open Access Journals (Sweden)
Jucemar Benedet
2013-06-01
Full Text Available OBJETIVO: Estimar a prevalência de excesso de peso e identificar associações com fatores sociodemográficos, biológicos e de estilo de vida em adolescentes de Florianópolis, Santa Catarina. MÉTODOS: Estudo transversal, conduzido em 2007, com amostra probabilística de 1.590 escolares de 11 a 14 anos. Estimou-se a prevalência do excesso de peso, com base no índice de massa corpórea, por meio da referência brasileira e da International Obesity Task Force (IOTF. Análises multivariadas expressas como razão de chance foram usadas para identificar associações com fatores sociodemográficos, biológicos e de estilo de vida dos adolescentes. RESULTADOS: A prevalência de excesso de peso foi de 19,3% (24,5% de meninos e 14,5% de meninas, pela referência IOTF, e de 25,8% (31,8% de meninos e 20,5% de meninas, pelo critério brasileiro. Entre os adolescentes do sexo masculino, o excesso de peso associou-se positivamente com a não realização de refeições estruturadas e com o deslocamento não ativo para a escola. Entre as meninas, o excesso de peso materno, a não realização de refeições estruturadas e diferenças interestágios de maturação sexual compuseram o elenco dos fatores associados ao excesso de peso. CONCLUSÕES: A realização de refeições com alimentos de alto valor nutricional apresentou-se como um fator de proteção para o excesso de peso entre os adolescentes. Essa constatação reforça a necessidade de ações com vistas a modificar comportamentos relacionados ao ambiente familiar, incentivando a incorporação de hábitos alimentares saudáveis e o lazer ativo.
Casimir energies: temperature dependence, dispersion, and anomalies.
Brevik, I; Milton, K A
2008-07-01
Assuming the conventional Casimir setting with two thick parallel perfectly conducting plates of large extent with a homogeneous and isotropic medium between them, we discuss the physical meaning of the electromagnetic field energy W disp when the intervening medium is weakly dispersive but nondissipative. The presence of dispersion means that the energy density contains terms of the form d[omega epsilon(omega)]/d omega and d[omega mu(omega)]/d omega . We find that, as W disp refers thermodynamically to a nonclosed physical system, it is not to be identified with the internal thermodynamic energy U following from the free energy F , or the electromagnetic energy W , when the last-mentioned quantities are calculated without such dispersive derivatives. To arrive at this conclusion, we adopt a model in which the system is a capacitor, linked to an external self-inductance L such that stationary oscillations become possible. Therewith the model system becomes a nonclosed one. As an introductory step, we review the meaning of the nondispersive energies, F , U , and W . As a final topic, we consider an anomaly connected with local surface divergences encountered in Casimir energy calculations for higher space-time dimensions, D>4 , and discuss briefly its dispersive generalization. This kind of application is essentially a generalization of the treatment of Alnes [J. Phys. A 40, F315 (2007)] to the case of a medium-filled cavity between two hyperplanes.
Edges and Diffractive Effects in Casimir Energies
Kabat, Daniel; Nair, V P
2010-01-01
The prototypical Casimir effect arises when a scalar field is confined between parallel Dirichlet boundaries. We study corrections to this when the boundaries themselves have apertures and edges. We consider several geometries: a single plate with a slit in it, perpendicular plates separated by a gap, and two parallel plates, one of which has a long slit of large width, related to the case of one plate being semi-infinite. We develop a general formalism for studying such problems, based on the wavefunctional for the field in the gap between the plates. This formalism leads to a lower dimensional theory defined on the open regions of the plates or boundaries. The Casimir energy is then given in terms of the determinant of the nonlocal differential operator which defines the lower dimensional theory. We develop perturbative methods for computing these determinants. Our results are in good agreement with known results based on Monte Carlo simulations. The method is well suited to isolating the diffractive contri...
Casimir forces from conductive silicon carbide surfaces
Sedighi, M.; Svetovoy, V. B.; Broer, W. H.; Palasantzas, G.
2014-05-01
Samples of conductive silicon carbide (SiC), which is a promising material due to its excellent properties for devices operating in severe environments, were characterized with the atomic force microscope for roughness, and the optical properties were measured with ellipsometry in a wide range of frequencies. The samples show significant far-infrared absorption due to concentration of charge carriers and a sharp surface phonon-polariton peak. The Casimir interaction of SiC with different materials is calculated and discussed. As a result of the infrared structure and beyond to low frequencies, the Casimir force for SiC-SiC and SiC-Au approaches very slowly the limit of ideal metals, while it saturates significantly below this limit if interaction with insulators takes place (SiC-SiO2). At short separations (<10 nm) analysis of the van der Waals force yielded Hamaker constants for SiC-SiC interactions lower but comparable to those of metals, which is of significance to adhesion and surface assembly processes. Finally, bifurcation analysis of microelectromechanical system actuation indicated that SiC can enhance the regime of stable equilibria against stiction.
The dynamical Casimir effect generates entanglement
Felicetti, Simone; Sanz, Mikel; Lamata, Lucas; Romero, Guillermo; Johansson, Göran; Delsing, Per; Solano, Enrique
2014-03-01
The existence of vacuum fluctuations, i.e., the presence of virtual particles in empty space, represents one of the most distinctive results of quantum mechanics. It is also known, under the name of dynamical Casimir effect, that fast-oscillating boundary conditions can generate real excitations out of the vacuum fluctuations. Long-awaited, the first experimental demonstration of this phenomenon has been realized only recently, in the framework of superconducting circuits [C. M. Wilson et al. Nature 479, 376-379 (2011)]. In this contribution, we will discuss novel theoretical results, showing that the dynamical Casimir effect can be exploited to generate bipartite and multipartite entanglement among qubits. We will also present a superconducting circuit design which can feasibly implement the model considered with current technology. Our scheme is composed of a SQUID device side-coupled to two transmission line resonators, each one interacting with a superconducting qubit. Such proposal can be straightforwardly generalized to the multipartite case, and it can be scaled up to build strongly correlated cavity lattices for quantum simulation and quantum computation. The authors acknowledge support from Spanish MINECO FIS2012-36673-C03-02; UPV/EHU UFI 11/55;Basque Government IT472-10; SOLID, CCQED, PROMISCE and SCALEQIT EU projects.
Dynamical Casimir effect for surface plasmon polaritons
Energy Technology Data Exchange (ETDEWEB)
Hizhnyakov, V.; Loot, A., E-mail: ardi.loot@ut.ee; Azizabadi, S.Ch.
2015-02-20
The emission of photon pairs by a metal–dielectric interface placed between the mirrors of the resonator and excited by a plane wave is considered. The excitation causes oscillations in time of the optical length of surface plasmon polaritons in the interface. This leads to the dynamical Casimir effect – the generation of pairs of surface plasmon polariton quanta, which transfer to photons outside the interface. In the case of a properly chosen interface, the yield of two-photon emission may exceed that of the usual spontaneous parametric down-conversion. - Highlights: • The theory of dynamical Casimir effect (DCE) in the metal–dielectric interface excited by a monochromatic wave is proposed. • It is shown that the field enhancement associated with surface plasmon polaritons strongly enhances the yield of the DCE. • The numerical calculations of the enhancement factor are made. • The scheme of experimental setup to observe the DCE in the metal–dielectric interface is proposed. • Additional methods to enhance the DCE in the metal–dielectric interface are discussed.
Casimir Effect in Hemisphere Capped Tubes
Bezerra de Mello, E. R.; Saharian, A. A.
2016-02-01
In this paper we investigate the vacuum densities for a massive scalar field with general curvature coupling in background of a (2 + 1)-dimensional spacetime corresponding to a cylindrical tube with a hemispherical cap. A complete set of mode functions is constructed and the positive-frequency Wightman function is evaluated for both the cylindrical and hemispherical subspaces. On the base of this, the vacuum expectation values of the field squared and energy-momentum tensor are investigated. The mean field squared and the normal stress are finite on the boundary separating two subspaces, whereas the energy density and the parallel stress diverge as the inverse power of the distance from the boundary. For a conformally coupled field, the vacuum energy density is negative on the cylindrical part of the space. On the hemisphere, it is negative near the top and positive close to the boundary. In the case of minimal coupling the energy density on the cup is negative. On the tube it is positive near the boundary and negative at large distances. Though the geometries of the subspaces are different, the Casimir pressures on the separate sides of the boundary are equal and the net Casimir force vanishes. The results obtained may be applied to capped carbon nanotubes described by an effective field theory in the long-wavelength approximation.
Casimir-Polder shifts on quantum levitation states
Crépin, P.-P.; Dufour, G.; Guérout, R.; Lambrecht, A.; Reynaud, S.
2017-03-01
An ultracold atom above a horizontal mirror experiences quantum reflection from the attractive Casimir-Polder interaction, which holds it against gravity and leads to quantum levitation states. We analyze this system by using a Liouville transformation of the Schrödinger equation and a Langer coordinate adapted to problems with a classical turning point. Reflection on the Casimir-Polder attractive well is replaced by reflection on a repulsive wall, and the problem is then viewed as an ultracold atom trapped inside a cavity with gravity and Casimir-Polder potentials acting, respectively, as top and bottom mirrors. We calculate numerically Casimir-Polder shifts of the energies of the cavity resonances and propose an approximate treatment which is precise enough to discuss spectroscopy experiments aimed at tests of the weak-equivalence principle on antihydrogen. We also discuss the lifetimes by calculating complex energies associated with cavity resonances.
The complete set of Casimirs in Hall-magnetohydrodynamics
Energy Technology Data Exchange (ETDEWEB)
Kawazura, Yohei [Graduate School of Frontier Sciences, University of Tokyo Kashiwa, Chiba 277-8561 (Japan); Hameiri, Eliezer [Courant Institute of Mathematical Sciences, New York University, New York, New York 10012 (United States)
2012-08-15
A procedure for determining all the Casimir constants of motion in magnetohydrodynamics (MHD) [E. Hameiri, Phys. Plasmas 11, 3423 (2004)] is extended to Hall-MHD. We obtain and solve differential equations for the variational derivatives of all the Casimirs, which must be satisfied for any dynamically accessible motion in Hall-MHD. In an extension of the more commonly considered Hall-MHD model, we also include the electron fluid entropy. The most interesting case for plasma confinement, which is usually true for axisymmetric configurations but desirable in general, is when both the magnetic field and the ion velocity field form the two separate families of nested toroidal surfaces. The Casimirs are then three functionals for each surface, involving the fluxes of certain vector fields and the number of particles contained in each. We also determine a family of independent Casimirs in a general configuration.
Magnetically controllable Casimir force based on a superparamagnetic metametamaterial
Ma, Junming; Zhao, Qian; Meng, Yonggang
2014-02-01
We theoretically investigate the magnetically controllable Casimir force between a parallel metal plate and a superparamagnetic metametamaterial (MMM) plate based on Mie scattering and effective medium theory. A type of MMM composed of superparamagnetic nanoparticles is proposed to fulfill the high frequency magnetic effect to gain Casimir repulsion when interacting with the metal plate. The permeability of such MMM depends on an external magnetic field, which makes it possible to adjust the magnitude of Casimir force. The effects of size, filling ratio, and magnetic property of the superparamagnetic particles on the tuning range are also investigated. Construction of such MMM using the micro/nanofabrication technology is promising to achieve magnetically controllable repulsive Casimir force.
The complete set of Casimirs in Hall-MHD
Kawazura, Yohei; Hameiri, Eliezer
2012-03-01
A procedure to determine all Casimir constants of motion in MHDfootnotetextE. Hameiri, Phy. Plasmas, 11, 3423 (2004). is extended to Hall-MHD. We obtain differential equations for the variational derivatives of all Casimirs which must be satisfied for any dynamically accessible motion of Hall-MHD. In an extension of the more commonly considered model, we also include the electron fluid entropy. The most interesting case, usually true for axisymmetric configurations, is when both the electron and ion entropy functions form families of nested toroidal surfaces. The Casimirs are then three functions of each of the entropies, involving fluxes of certain vector fields and the number of particles contained in each torus. If any of the species loses its nested tori, the number of the associated Casimirs is much larger (but physically less relevant).
The complete set of Casimirs in Hall-magnetohydrodynamics
Kawazura, Yohei; Hameiri, Eliezer
2012-08-01
A procedure for determining all the Casimir constants of motion in magnetohydrodynamics (MHD) [E. Hameiri, Phys. Plasmas 11, 3423 (2004)] is extended to Hall-MHD. We obtain and solve differential equations for the variational derivatives of all the Casimirs, which must be satisfied for any dynamically accessible motion in Hall-MHD. In an extension of the more commonly considered Hall-MHD model, we also include the electron fluid entropy. The most interesting case for plasma confinement, which is usually true for axisymmetric configurations but desirable in general, is when both the magnetic field and the ion velocity field form the two separate families of nested toroidal surfaces. The Casimirs are then three functionals for each surface, involving the fluxes of certain vector fields and the number of particles contained in each. We also determine a family of independent Casimirs in a general configuration.
Classical Casimir interaction of a perfectly conducting sphere and plate
Bimonte, Giuseppe
2017-03-01
We study the Casimir interaction between a perfectly conducting sphere and plate in the classical limit of high temperatures. By taking the small-distance expansion of the exact scattering formula, we compute the leading correction to the Casimir energy beyond the commonly employed proximity force approximation. We find that for a sphere of radius R at a distance d from the plate the correction is of the form ln2(d /R ), in agreement with indications from recent large-scale numerical computations. We develop a fast-converging numerical scheme for computing the Casimir interaction to high precision, based on bispherical partial waves, and we verify that the short-distance formula provides precise values of the Casimir energy also for fairly large distances.
Casimir effect for two lossy dispersive dielectric slabs
Matloob, R.; Keshavarz, A.; Sedighi, D.
1999-11-01
The electromagnetic field is quantized using the Green's-function method for the geometry of a Fabry-Perot cavity, made up of two identical lossy dispersive slabs of finite thickness. The dielectric functions of the slabs are assumed to be an arbitrary complex function of frequency obeying causality requirements. The attractive Casimir force between the two slabs is calculated by the help of the latter field operators, via evaluating the difference between the vacuum pressures on both sides of each slab. Special attention is paid to the limiting case of the Casimir effect for two conducting plates. The Lorentz model of the dielectric function is used to demonstrate the variation of the force in terms of plasma frequency. The Casimir force expression is also related to the imaginary part of the response function. The latter expression is used to introduce the repulsive Casimir force between two conducting plates located inside a Fabry-Perot cavity.
Scalar Casimir effect between two concentric D-dimensional spheres
Özcan, Mustafa
2012-01-01
The Casimir energy for a massless scalar field between the closely spaced two concentric D-dimensional (for D>3) spheres is calculated by using the mode summation with contour integration in the complex plane of eigenfrequencies and the generalized Abel-Plana formula for evenly spaced eigenfrequency at large argument. The sign of the Casimir energy between closely spaced two concentric D-dimensional spheres for a massless scalar field satisfying the Dirichlet boundary conditions is strictly negative. The Casimir energy between D-1 dimensional surfaces close to each other is regarded as interesting both by itself and as the key to describing of stability of the attractive Casimir force. PACS number(s): 03.70.+k, 11.10.Kk, 11.10.Gh, 03.65.Ge
An ``Anatomic approach" to study the Casimir effect
Intravaia, Francesco; Haakh, Harald; Henkel, Carsten
2010-03-01
The Casimir effect, in its simplest definition, is a quantum mechanical force between two objects placed in vacuum. In recent years the Casimir force has been the object of an exponentially growing attention both from theorists and experimentalists. A new generation of experiments paved the way for new challenges and spotted some shadows in the comparison to theory. Here we are going to isolate different contributions to the Casimir interaction and perform a detailed study to shine new light on this phenomenon. As an example, the contributions of Foucault (eddy current) modes will be discussed in different configurations. This ``anatomic approach'' allows to clearly put into evidence special features and to explain unusual behaviors. This brings new physical understanding on the undergoing physical mechanisms and suggests new ways to engineer the Casimir effect.
Gamma ray bursts, neutron star quakes, and the Casimir effect
Carlson, C; Pérez-Mercader, J; Carlson, C; Goldman, T; Perez-Mercader, J
1994-01-01
We propose that the dynamic Casimir effect is a mechanism that converts the energy of neutron starquakes into \\gamma--rays. This mechanism efficiently produces photons from electromagnetic Casimir energy released by the rapid motion of a dielectric medium into a vacuum. Estimates based on the cutoff energy of the gamma ray bursts and the volume involved in a starquake indicate that the total gamma ray energy emission is consonant with observational requirements.
Detecting Casimir Forces through a Tunneling Electromechanical Transducer
Onofrio, Roberto; Carugno, Giovanni
1995-01-01
We propose the use of a tunneling electromechanical transducer to dynamically detect Casimir forces between two conducting surfaces. The maximum distance for which Casimir forces should be detectable with our method is around $1 \\mu$m, while the lower limit is given by the ability to approach the surfaces. This technique should permit to study gravitational forces on the same range of distances, as well as the vacuum friction provided that very low dissipation mechanical resonators are used.
Casimir Energy and Vacua vor Superconducting Ball in Supergravity
Burinskii, A
2002-01-01
Casimir energy for solid conducting ball is considered on the base of some finite models. One model is physical and built of a battery of parallel metallic plates. Two finite models are based on the Higgs model of superconductivity. One of them is supersymmetric and based on the Witten field model for superconducting strings. Treatment shows that contribution of Casimir energy can be very essential for superdence state in the neutron stars and nuclear matter.
The Casimir effect as a candidate of dark energy
Matsumoto, Jiro
2013-01-01
It is known that the simply evaluated value of the zero point energy of quantum fields is extremely deviated from the observed value of dark energy density. In this paper, we consider whether the Casimir energy, which is the zero point energy brought from boundary conditions, can cause the accelerating expansion of the Universe by using proper renormalization method and introducing the fermions of finite temperature living in $3+n+1$ space-time. We show that the zero temperature Casimir energ...
Exact results for Casimir forces using Surface Impedance: Nonlocal Media
Esquivel-Sirvent, R; Mochán, W L
2003-01-01
We show that exact results are obtained for the calculation of Casimir forces between arbitrary materials using the concept of surface impedances, obtaining in a trivial way the force in the limit of perfect conductors and also Lifshitz formula in the limit of semi-infinite media. As an example we present a full and rigorous calculation of the Casimir force between two metallic half-spaces described by a hydrodynamic nonlocal dielectric response.
Dynamical Casimir effect in Circuit QED for Nonuniform Trajectories
Corona-Ugalde, Paulina; Wilson, C M; Mann, Robert B
2015-01-01
We propose a generalization of the superconducting circuit simulation of the dynamical Casimir effect where we consider relativistically moving boundary conditions following different trajectories. We study the feasibility of the setup used in the past to simulate the dynamical Casimir effect to reproduce richer relativistic trajectories differing from purely sinusoidal ones. We show how different relativistic oscillatory trajectories of the boundaries of the same period and similar shape produce a rather different spectrum of particles characteristic of their respective motions.
Bruna Rodrigues Weber; Vanessa Cristina Scherer; Karla Renata Oliveira; Christiane Fátima Colet
2012-01-01
A resistência bacteriana se constitui em preocupação mundial e a prescrição inadequada de antimicrobianos é um dos fatores que pode influenciar nas suas taxas. O objetivo foi avaliar as prescrições contendo antimicrobianos dispensados em uma farmácia comunitária do município de Ijuí/RS, para identificar os antimicrobianos e osfármacos prescritos em associação, bem como interações medicamentosas potenciais. Métodos: A amostra foi constituída por prescrições retidas no local do estudo, de 28 de...
Casimir Force at a Knife's Edge
Graham, Noah; Emig, Thorsten; Rahi, Sahand Jamal; Jaffe, Robert L; Kardar, Mehran
2009-01-01
The Casimir force has been computed exactly for only a few simple geometries, such as infinite plates, cylinders, and spheres. We show that a parabolic cylinder, for which analytic solutions to the Helmholtz equation are available, is another case where such a calculation is possible. We compute the interaction energy of a parabolic cylinder and an infinite plate (both perfect mirrors), as a function of their separation and inclination, $H$ and $\\theta$, and the cylinder's parabolic radius $R$. As $H/R\\to 0$, the proximity force approximation becomes exact. The opposite limit of $R/H\\to 0$ corresponds to the a semi-infinite plate, where the effects of edge and inclination can be probed.
Casimir-Polder Force Reversal with Metamaterials
Pappakrishnan, Venkatesh; Genov, Dentcho
2010-10-01
A promising system design aiming to demonstrate Casimir-Polder force (CPF) reversal is proposed. The constraints when using naturally available materials in designing the system with air as an intermediate medium is resolved by using artificial electromagnetic materials. The parametric space in terms of the plate's magnetic and dielectric plasma frequencies, gap thickness and temperature is investigated. The parametric domain for achieving CPF reversal is obtained. Furthermore, a simple analytical expression for the CPF is derived. The analytical expression accurately describes the large and short distance asymptotics and allows extraction of important parameters such as lower and upper cutoff gap distances that define the repulsive force window. This study could possibly lead us to design of quantum levitation system, frictionless bio-fluid transport devices, etc.
Casimir effect for a Cavity in the Spacetime with an Extra Dimension
Institute of Scientific and Technical Information of China (English)
CHENG Hong-Bo
2005-01-01
@@ We reexamine the Casimir effect for the rectangular cavity with two or three equal edges in the presence of compactified universal extra dimension. We derive the expressions for the Casimir energy and discuss the nature of Casimir force. We show analytically the extra-dimension corrections to the standard Casimir effect to put forward a new method of exploring the existence of extra dimensions of the Universe.
Directory of Open Access Journals (Sweden)
Liliane Aparecida Fagundes Silva
2014-04-01
Full Text Available Introdução: A avaliação de potenciais evocados auditivos de longa latência em crianças usuárias de implante coclear tem se mostrado um método eficaz para avaliar a maturação cortical após estimulação elétrica. Objetivo: Analisar as modificações nos valores de latência do potencial evocado auditivo cortical antes e três meses após o uso do implante coclear. Material e método: Estudo de caso-controle em um grupo de cinco crianças usuárias do implante coclear que aguardavam a ativação dos eletrodos, e um grupo controle constituído por cinco crianças ouvintes. A avaliação eletrofisiológica da audição foi realizada por meio do registro dos potenciais evocados auditivos corticais em duas diferentes etapas: anterior à ativação do implante coclear e após três meses de adaptação. Resultados: Os resultados demonstraram diminuição significativa em relação ao tempo de latência do componente P1 no grupo estudo, cujos valores foram maiores daqueles do grupo controle. Quanto menor a idade na ativação, maior a redução no tempo de latência do componente P1. Conclusão: Modificações nas características dos potenciais evocados auditivos corticais podem ser observadas em crianças que recebem o implante coclear e estas modificações têm uma relação com a idade de intervenção, sugerindo uma rápida maturação das vias auditivas após estimulação elétrica.
Interações Medicamentosas Potenciais em Pacientes de Unidades de Terapia Intensiva
Liliana Batista Vieira; Adriano Max Moreira Reis; Rhanna Emanuela Fontenele Lima de Carvalho; Leila Márcia Pereira de Faria; Silvia Helena de Bortoli Cassiani
2012-01-01
O objetivo do estudo é determinar a frequência de interações fármaco-fármaco em prescrições de pacientes internados em unidades de terapia intensiva e analisar os fatores associados relativos à farmacoterapia e ao paciente. O estudo descritivo transversal foi realizado em dois hospitais de ensino da região centro oeste do Brasil. As interações medicamentosas potenciais foram identificadas nas prescrições do primeiro dia (24 horas) e do quinto dia (120 horas) de interna...
Casimir free energy and pressure for magnetic metal films
Klimchitskaya, G. L.; Mostepanenko, V. M.
2016-07-01
We examine the Casimir free energy and pressure of magnetic metal films, which are free standing in vacuum, sandwiched between two dielectric plates and deposited on either nonmagnetic or magnetic metallic plates. All calculations are performed using both the Drude and plasma model approaches to the Lifshitz theory. According to our results, the Casimir free energies and pressures calculated using both theoretical approaches are significantly different in the magnitude and sign even for thin films of several tens of nanometers thickness. Thus, for the Ni film of 47 nm thickness deposited on a Fe plate the obtained magnitudes of the Casimir free energy differ by the factor of 5866. We show that the Casimir free energy and pressure of a magnetic film calculated using the plasma model approach do not possess the classical limit but exponentially fast drop to zero with increasing film thickness. If the Drude model approach is used, the classical limit is reached for magnetic films of about 150 nm thickness, but the Casimir free energy remains nonzero in the limit of ideal metal, contrary to expectations. For the plasma model approach the Casimir free energy of a film vanishes in this case. Numerical computations are performed for the magnetic films made of Ni, nonmagnetic plates made of Cu and Al, and magnetic plates made of Fe using the tabulated optical data for the complex indexes of refraction of all metals. The obtained results can be used for a discrimination between the plasma and Drude model approaches in the Casimir physics and in the investigation of stability of thin films.
Directory of Open Access Journals (Sweden)
Ana Canen
2008-06-01
Full Text Available O presente artigo argumenta que a compreensão da pesquisa como fenômeno multicultural pode tornar a articulação ensino-pesquisa mais impactante na formação de professores, Desenvolve o argumento, propondo quatro dimensões centrais nessa perspectiva: a compreensão dos futuros professores e professores formadores como identidades culturais plurais de pesquisadores em ação; o incentivo às discussões dos temas educacionais em termos de vozes silenciadas e representadas, analisando tensões entre universalismo e valorização da diversidade; a apresentação dos professores em formação a metodologias plurais de pesquisa; a análise das identidades institucionais ou organizacionais onde se processa a formação docente e sua articulação à perspectiva de pesquisa, problematizando relações desiguais de poder e lutando para que essas instituições se constituam em instituições ou organizações multiculturais.El artículo discute que la comprensión de la investigación como un fenómeno multicultural puede llevar a una articulación entre educación-investigación de más impacto en la formación de profesores. Este trabajo desenvuelve la discusión proponiendo cuatro dimensiones centrales: la comprensión de los futuros profesores y de los profesores formadores como identidades culturales plurales de investigadores en acción; el incentivo a las discusiones de los temas educacionales en término de voces silenciadas y representadas, analizando las tensiones entre universalismo y valorización de la diversidad; la presentación de la metodología plural de investigación a los profesores en formación; el análisis de las identidades institucionales o organizacionales donde se construye la formación del profesor y su articulación a la perspectiva de investigación, colocando como problema las relaciones desiguales de poder y luchando para que esas instituciones se organicen en instituciones o organizaciones multiculturales
Casimir Energies and Pressures for $\\delta$-function Potentials
Milton, K A
2004-01-01
The Casimir energies and pressures for a massless scalar field associated with $\\delta$-function potentials in 1+1 and 3+1 dimensions are calculated. For parallel plane surfaces, the results are finite, coincide with the pressures associated with Dirichlet planes in the limit of strong coupling, and for weak coupling do not possess a power-series expansion in 1+1 dimension. The relation between Casimir energies and Casimir pressures is clarified,and the former are shown to involve surface terms. The Casimir energy for a $\\delta$-function spherical shell in 3+1 dimensions has an expression that reduces to the familiar result for a Dirichlet shell in the strong-coupling limit. However, the Casimir energy for finite coupling possesses a logarithmic divergence first appearing in third order in the weak-coupling expansion, which seems unremovable. The corresponding energies and pressures for a derivative of a $\\delta$-function potential for the same spherical geometry generalizes the TM contributions of electrodyn...
Critical Casimir Interactions: New fluctuation forces in colloidal science
Schall, Peter
2012-02-01
Casimir forces arise from the confinement of fluctuations between two walls. Critical Casimir forces provide thermodynamic analogues of quantum-mechanical Casimir forces and arise from the confinement of concentration fluctuations of a critical solvent. These forces act also between colloidal particles that are suspended in this solvent, giving rise to temperature-dependent attractive interactions between the particles. We use these temperature-dependent forces to control colloidal phase transitions. In this talk, I will present a new index and density-matched model system that allows direct observation of these phase transitions with confocal microscopy. In three dimensions and real time, we follow how a colloidal gas freezes into a colloidal liquid, and the colloidal liquid freezes into a solid, all driven by critical Casimir forces. We measure the critical Casimir particle pair potential directly from the pair correlation function, and use Monte Carlo simulations to map the complete gas-liquid-solid phase diagram. Excellent agreement with the experimental observations is obtained. Our measurements include microgravity experiments on board the International Space Station (ISS) to elucidate non-equilibrium assembly of the particles achieved by controlled temperature quench.
Repulsive Casimir force from fractional Neumann boundary conditions
Energy Technology Data Exchange (ETDEWEB)
Lim, S.C. [Faculty of Engineering, Multimedia University, Jalan Multimedia, 63100 Cyberjaya, Selangor (Malaysia)], E-mail: sclim@mmu.edu.my; Teo, L.P. [Faculty of Information Technology, Multimedia University, Jalan Multimedia, 63100 Cyberjaya, Selangor (Malaysia); Department of Applied Mathematics, Faculty of Engineering, University of Nottingham Malaysia Campus, Jalan Broga, 43500 Semenyih, Selangor Darul Ehsan (Malaysia)], E-mail: lpteo@mmu.edu.my
2009-08-17
This Letter studies the finite temperature Casimir force acting on a rectangular piston associated with a massless fractional Klein-Gordon field at finite temperature. Dirichlet boundary conditions are imposed on the walls of a d-dimensional rectangular cavity, and a fractional Neumann condition is imposed on the piston that moves freely inside the cavity. The fractional Neumann condition gives an interpolation between the Dirichlet and Neumann conditions, where the Casimir force is known to be always attractive and always repulsive respectively. For the fractional Neumann boundary condition, the attractive or repulsive nature of the Casimir force is governed by the fractional order which takes values from zero (Dirichlet) to one (Neumann). When the fractional order is larger than 1/2, the Casimir force is always repulsive. For some fractional orders that are less than but close to 1/2, it is shown that the Casimir force can be either attractive or repulsive depending on the aspect ratio of the cavity and the temperature.
Mariana Macedo Alvim; Lidiane Ayres da Silva; Isabel Cristina Gonçalves Leite; Marcelo Silva Silvério
2015-01-01
RESUMO Objetivo: Avaliar a existência de interações medicamentosas potenciais na unidade de terapia intensiva de um hospital, com foco nos antimicrobianos. Métodos: Estudo transversal, que analisou prescrições eletrônicas de pacientes da unidade de terapia intensiva de um hospital de ensino, avaliando potenciais interações medicamentosas relacionadas aos antimicrobianos, entre 1º de janeiro e 31 de março de 2014. O consumo dos antimicrobianos foi expresso em dose diária definida por 100 pac...
Directory of Open Access Journals (Sweden)
José Batista Cisne Tomaz
Full Text Available Este artigo descreve os principais achados de um inquérito realizado no Estado do Ceará, Brasil, com o objetivo de avaliar a aceitabilidade de um curso baseado em Educação à Distância entre os profissionais que atuam no Programa Saúde da Família - uma nova estratégia para prover Atenção Primária à Saúde para a população brasileira. Foram enviados 255 questionários aos potenciais sujeitos, com uma taxa de resposta de 81,9%. Os achados mostraram que, em geral, os respondentes têm percepções e atitudes positivas em relação à EAD e estão motivados em participar num curso baseado nessa estratégia. Propõe-se uma lista de recomendações para ajudar os planejadores do curso.
Is zero-point energy physical? A toy model for Casimir-like effect
Nikolić, Hrvoje
2017-08-01
Zero-point energy is generally known to be unphysical. Casimir effect, however, is often presented as a counterexample, giving rise to a conceptual confusion. To resolve the confusion we study foundational aspects of Casimir effect at a qualitative level, but also at a quantitative level within a simple toy model with only 3 degrees of freedom. In particular, we point out that Casimir vacuum is not a state without photons, and not a ground state for a Hamiltonian that can describe Casimir force. Instead, Casimir vacuum can be related to the photon vacuum by a non-trivial Bogoliubov transformation, and it is a ground state only for an effective Hamiltonian describing Casimir plates at a fixed distance. At the fundamental microscopic level, Casimir force is best viewed as a manifestation of van der Waals forces.
Pressures and Energies in Magnetized Vacuum and in Casimir effect
Rojas, H P
2004-01-01
We study vacuum pressures and energies for electron-positron vacuum zero point energy in a strong magnetic field $B$ and for photon vacuum in Casimir effect, by a common method. Vacuum becomes magnetized, and due to it, the pressure transversal to $B$ is negative, whereas along $B$ an usual positive pressure arises. Similarly, in addition to the usual negative Casimir pressure perpendicular to the plates, the existence of a positive pressure along the plates is predicted. Both vacua bear the property of leading to a negative energy-momentum tensor trace ${\\cal T}_{\\mu}^{\\mu}<0$, which may lead to a repulsive gravity typical of dark energy. By assuming a space distribution of magnetic and/or Casimir domains, cosmological implications are also discussed.
Casimir Free Energy at High Temperatures: Grounded vs Isolated Conductors
Fosco, C D; Mazzitelli, F D
2016-01-01
We evaluate the difference between the Casimir free energies corresponding to either grounded or isolated perfect conductors, at high temperatures. We show that a general and simple expression for that difference can be given, in terms of the electrostatic capacitance matrix for the system of conductors. For the case of close conductors, we provide approximate expressions for that difference, by evaluating the capacitance matrix using the proximity force approximation. Since the high-temperature limit for the Casimir free energy for a medium described by a frequency-dependent conductivity diverging at zero frequency coincides with that of an isolated conductor, our results may shed light on the corrections to the Casimir force in the presence of real materials.
Finite Casimir Energies in Renormalizable Quantum Field Theory
Milton, K A
2004-01-01
Quantum vacuum energy has been known to have observable consequences since 1948 when Casimir calculated the force of attraction between parallel uncharged plates, a phenomenon confirmed experimentally with ever increasing precision. Casimir himself suggested that a similar attractive self-stress existed for a conducting spherical shell, but Boyer obtained a repulsive stress. Other geometries and higher dimensions have been considered over the years. Local effects, and divergences associated with surfaces and edges have been investigated by several authors. Quite recently, Graham et al. have re-examined such calculations, using conventional techniques of perturbative quantum field theory to remove divergences, and have suggested that previous self-stress results may be suspect. Here we show that most of the examples considered in their work are misleading; in particular, it is well-known that in two dimensions a circular boundary has a divergence in the Casimir energy for massless fields, while for general dim...
Calculating Casimir Energies in Renormalizable Quantum Field Theory
Milton, K A
2003-01-01
Quantum vacuum energy has been known to have observable consequences since 1948 when Casimir calculated the force of attraction between parallel uncharged plates, a phenomenon confirmed experimentally with ever increasing precision. Casimir himself suggested that a similar attractive self-stress existed for a conducting spherical shell, but Boyer obtained a repulsive stress. Other geometries and higher dimensions have been considered over the years. Local effects, and divergences associated with surfaces and edges have been considered by several authors. Quite recently, Graham et al. have re-examined such calculations, using conventional techniques of perturbative quantum field theory to remove divergences, and have suggested that previous self-stress results may be suspect. Here we show that the examples considered in their work are misleading; in particular, it is well-known that in two dimensions a circular boundary has a divergence in the Casimir energy for massless fields, while for general dimension $D$...
Electrodynamic Casimir Effect in a Medium-Filled Wedge II
Ellingsen, Simen Adnoy; Milton, Kimball A
2009-01-01
We consider the Casimir energy in a geometry of an infinite magnetodielectric wedge closed by a circularly cylindrical arc embedded in another magnetodielectric medium, under the condition that the speed of light be the same in both media. An expression for the Casimir energy corresponding to the arc is obtained and it is found that in the limit where the reflectivity of the boundaries tends to unity the finite part of the Casimir energy of a perfectly conducting wedge-shaped sheet closed by a circular cylinder is regained. The energy of the latter geometry possesses divergences due to the presence of sharp corners. We argue how this is a pathology of the assumption of ideal conductor boundaries, and that no analogous term enters in the present geometry.
Geometry-Temperature Interplay in the Casimir Effect
Gies, Holger
2009-01-01
We discuss Casimir phenomena which are dominated by long-range fluctuations. A prime example is given by "geothermal" Casimir phenomena where thermal fluctuations in open Casimir geometries can induce significantly enhanced thermal corrections. We illustrate the underlying mechanism with the aid of the inclined-plates configuration, giving rise to enhanced power-law temperature dependences compared to the parallel-plates case. In limiting cases, we find numerical evidence even for fractional power laws induced by long-range fluctuations. We demonstrate that thermal energy densities for open geometries are typically distributed over length scales of 1/T. As an important consequence, approximation methods for thermal corrections based on local energy-density estimates such as the proximity-force approximation are expected to become unreliable even at small surface separations.
Casimir Effect in the Kerr Spacetime Surrounded by Quintessence
Bezerra, V B; Freitas, L F F; Muniz, C R
2016-01-01
We calculate the Casimir energy of a massless scalar field in a cavity formed by nearby parallel plates orbiting a rotating spherical body surrounded by quintessence, investigating the influence of the gravitational field on that energy, at zero temperature. This influence includes the effects due to the spacetime dragging caused by the source rotation as well as those ones due to the quintessence. We show that the energy depends on all the involved parameters, as source mass, angular momentum and quintessence state parameter, for any radial coordinate and polar angle. We show that at the north pole the Casimir energy is not influenced by the quintessential matter. At the equatorial plane, when the quintessence is canceled, the result obtained in the literature is recovered. Finally, constraints in the quintessence parameters are obtained from the uncertainty in the current measurements of Casimir effect.
Interplay between geometry and temperature for inclined Casimir plates
Weber, Alexej
2009-01-01
We provide further evidence for the nontrivial interplay between geometry and temperature in the Casimir effect. We investigate the temperature dependence of the Casimir force between an inclined semi-infinite plate above an infinite plate in D dimensions using the worldline formalism. Whereas the high-temperature behavior is always found to be linear in T in accordance with dimensional-reduction arguments, different power-law behaviors at small temperatures emerge. Unlike the case of infinite parallel plates, which shows the well-known T^D behavior of the force, we find a T^{D-1} behavior for inclined plates, and a ~T^{D-0.3} behavior for the edge effect in the limit where the plates become parallel. The strongest temperature dependence ~T^{D-2} occurs for the Casimir torque of inclined plates. Numerical as well as analytical worldline results are presented.
Casimir Force Phase Transitions in the Graphene Family
Rodriguez-Lopez, Pablo; Dalvit, Diego A R; Woods, Lilia M
2016-01-01
The Casimir force is a universal interaction induced by electromagnetic quantum fluctuations between any types of objects. The expansion of the graphene family by adding silicene, germanene, and stanene, 2D allotropes of Si, Ge, and Sn, lands itself as a platform to probe Dirac-like physics in honeycomb staggered systems in such a ubiquitous interaction. We discover Casimir force phase transitions between these staggered 2D materials induced by the complex interplay between Dirac physics, spin-orbit coupling, and externally applied fields. In particular, we find that the interaction energy experiences different power law distance decays, magnitudes, and dependences on characteristic physical constants. Furthermore, due to the topological properties of these materials, repulsive and quantized Casimir interactions become possible.
Electromagnetic normal modes and Casimir effects in layered structures
Sernelius, Bo E
2014-01-01
We derive a general procedure for finding the electromagnetic normal modes in layered structures. We apply this procedure to planar, spherical and cylindrical structures. These normal modes are important in a variety of applications. They are the only input needed in calculations of Casimir interactions. We present explicit expression for the condition for modes and Casimir energy for a large number of specific geometries. The layers are allowed to be two-dimensional so graphene and graphene-like sheets as well as two-dimensional electron gases can be handled within the formalism. Also forces on atoms in layered structures are obtained. One side-result is the van der Waals and Casimir-Polder interaction between two atoms.
Casimir attraction in multilayered plane parallel magnetodielectric systems
Ellingsen, S A
2006-01-01
A powerful procedure is presented for calculating the Casimir attraction between plane parallel multilayers made up of homogeneous regions with arbitrary magnetic and dielectric properties by use of the Minkowski energy-momentum tensor. The theory is applied to numerous geometries and shown to reproduce a number of results obtained by other authors. Although the various pieces of theory drawn upon are well known, the relative ease with which the Casimir force density in even complex planar structures may be calculated, appears not to be widely appreciated, and no single paper to the author's knowledge renders explicitly the procedure demonstrated herein. Results may be seen as an important building block in the settling of issues of fundamental interest, such as the long-standing dispute over the thermal behaviour of the Casimir force or the question of what is the correct stress tensor to apply, a discussion re-quickened by the newly suggested alternative theory due to Raabe and Welsch.
Casimir effect in (2+1)dimensional noncommutative theories
Fosco, C D
2008-01-01
We study the Dirichlet Casimir effect for a complex scalar field on two noncommutative spatial coordinates plus a commutative time. To that end, we introduce Dirichlet-like boundary conditions on a curve contained in the spatial plane, in such a way that the correct commutative limit can be reached. We evaluate the resulting Casimir energy for two different curves: (a) Two parallel lines separated by a distance $L$, and (b) a circle of radius $R$. In the first case, the resulting Casimir energy agrees exactly with the one corresponding to the commutative case, regardless of the values of $L$ and of the noncommutativity scale $\\theta$, while for the latter the commutative behaviour is only recovered when $R >> \\sqrt{\\theta}$. Outside of that regime, the dependence of the energy with $R$ is substantially changed due to noncommutative corrections, becoming regular for $R \\to 0$.
Casimir operator dependences of non-perturbative fermionic QCD amplitudes
Fried, H M; Hofmann, R
2015-01-01
In eikonal and quenched approximation, it is argued that the strong coupling fermionic QCD Green's functions and related amplitudes, when based on the newly discovered effective locality property, depart from a sole dependence on the SUc(3) quadratic Casimir operator, evaluated over the fundamental gauge group representation.Though noticed in non-relativistic Quark Models, an additional dependence on the cubic Casimir operator is in contradistinction with perturbation theory, and also with a number of non-perturbative approaches such as the MIT Bag, the Stochastic Vacuum Models and lattice simulations. It accounts for the full algebraic content of the rank-2 Lie algebra of SUc(3). We briefly discuss the orders of magnitude of quadratic and cubic Casimir operator contributions.
Casimir operator dependences of nonperturbative fermionic QCD amplitudes
Fried, H. M.; Grandou, T.; Hofmann, R.
2016-07-01
In eikonal and quenched approximations, it is argued that the strong coupling fermionic QCD Green’s functions and related amplitudes depart from a sole dependence on the SUc(3) quadratic Casimir operator, C2f, evaluated over the fundamental gauge group representation. Noted in nonrelativistic quark models and in a nonperturbative generalization of the Schwinger mechanism, an additional dependence on the cubic Casimir operator shows up, in contradistinction with perturbation theory and other nonperturbative approaches. However, it accounts for the full algebraic content of the rank-2 Lie algebra of SUc(3). Though numerically subleading effects, cubic Casimir dependences, here and elsewhere, appear to be a signature of the nonperturbative fermionic sector of QCD.
Evanescent radiation, quantum mechanics and the Casimir effect
Schatten, Kenneth H.
1989-01-01
An attempt to bridge the gap between classical and quantum mechanics and to explain the Casimir effect is presented. The general nature of chaotic motion is discussed from two points of view: the first uses catastrophe theory and strange attractors to describe the deterministic view of this motion; the underlying framework for chaos in these classical dynamic systems is their extreme sensitivity to initial conditions. The second interpretation refers to randomness associated with probabilistic dynamics, as for Brownian motion. The present approach to understanding evanescent radiation and its relation to the Casimir effect corresponds to the first interpretation, whereas stochastic electrodynamics corresponds to the second viewpoint. The nonlinear behavior of the electromagnetic field is also studied. This well-understood behavior is utilized to examine the motions of two orbiting charges and shows a closeness between the classical behavior and the quantum uncertainty principle. The evanescent radiation is used to help explain the Casimir effect.
Finite Temperature Casimir Effect in Randall-Sundrum Models
Rypestøl, Marianne
2009-01-01
The finite temperature Casimir effect for a scalar field in the bulk region of the two Randall-Sundrum models, RSI and RSII, is studied. We calculate the Casimir energy and the Casimir force for two parallel plates with separation $a$ on the visible brane in the RSI model. High-temperature and low-temperature cases are covered. Attractiveness versus repulsiveness of the temperature correction to the force is discussed in the typical special cases of Dirichlet-Dirichlet, Neumann-Neumann, and Dirichlet-Neumann boundary conditions at low temperature. The Abel-Plana summation formula is made use of, as this turns out to be most convenient. Some comments are made on the related contemporary literature.
Directory of Open Access Journals (Sweden)
Aline Cabral de Oliveira
2008-10-01
Full Text Available O potencial miogênico evocado vestibular (VEMP é um teste clínico que avalia a função vestibular através de um reflexo vestíbulo-cervical inibitório captado nos músculos do corpo em resposta à estimulação acústica de alta intensidade. OBJETIVO: Verificar e analisar os diversos métodos de registro dos potenciais miogênicos evocados vestibulares no homem e em cobaias. MATERIAL E MÉTODO: Realizou-se busca eletrônica nas bases de dados MEDLINE, LILACS, SCIELO e COCHRANE. RESULTADOS: Foram verificadas divergências quanto às formas de registro dos potenciais miogênicos evocados vestibulares, relacionadas com os seguintes fatores: posição do paciente no momento do registro, tipo de estímulo sonoro utilizado (clicks ou tone bursts, parâmetros para a promediação dos estímulos (intensidade, freqüência, tempo de apresentação, filtros, ganho de amplificação das respostas e janelas para captação dos estímulos, tipo de fone utilizado e forma de apresentação dos estímulos (monoaural ou binaural, ipsi ou contralateral. CONCLUSÃO: Não existe consenso na literatura quanto ao melhor método de registro dos potenciais evocados miogênicos vestibulares, havendo necessidade de pesquisas mais específicas para comparação entre estes registros e a definição de um modelo padrão para a utilização na prática clínica.The vestibular evoked myogenic potential (VEMP is a clinical test that assess the vestibular function by means of an inhibitory vestibulo-neck reflex, recorded in body muscles in response to high intensity acoustic stimuli. AIM: To check and analyze the different methods used to record VEMPs in humans and in guinea pigs. MATERIALS AND METHODS: We researched the following databases: MEDLINE, LILACS, SCIELO and COCHRANE. RESULTS: we noticed discrepancies in relation to the ways used to record the vestibular evoked myogenic potentials in relation to the following factors: patient position at the time of recording
Local Casimir Energies for an Annulus
Cavero-Pelaez, I; Wagner, J; Cavero-Pelaez, Ines; Milton, Kimball A.; Wagner, Jeffrey
2005-01-01
The local Casimir energy density for a massless scalar field associated with step-function potentials in a 3+1 dimensional spherical geometry is considered. The potential is chosen to be zero except in an annulus of thickness $\\delta$, where it has height $h$, $h\\delta=1$. In the limit of zero thickness, an ideal $\\delta$-function shell is recovered. The behavior of the energy density as the surface of the annulus is approached is studied in both the strong and weak coupling regimes. The former case corresponds to the well-known Dirichlet shell limit. New results, which shed light on the nature of surface divergences and on the energy contained within the annulus, are obtained in the weak coupling limit. In that case, the energy has a contribution not only from the local energy density, but from an energy term residing entirely on the surface. It is shown that the latter coincides with the integrated local energy density within the annulus. We also study the dependence of local and global quantities on the co...
Casimir-Polder forces: A nonperturbative approach
Buhmann, Stefan Yoshi; Knöll, Ludwig; Welsch, Dirk-Gunnar; Dung, Ho Trung
2004-11-01
Within the frame of macroscopic QED in linear, causal media, we study the radiation force of Casimir-Polder type acting on an atom which is positioned near dispersing and absorbing magnetodielectric bodies and initially prepared in an arbitrary electronic state. It is shown that minimal and multipolar coupling lead to essentially the same lowest-order perturbative result for the force acting on an atom in an energy eigenstate. To go beyond perturbation theory, the calculations are based on the exact center-of-mass equation of motion. For a nondriven atom in the weak-coupling regime, the force as a function of time is a superposition of force components that are related to the electronic density matrix elements at a chosen time. Even the force component associated with the ground state is not derivable from a potential in the ususal way, because of the position dependence of the atomic polarizability. Further, when the atom is initially prepared in a coherent superposition of energy eigenstates, then temporally oscillating force components are observed, which are due to the interaction of the atom with both electric and magnetic fields.
Directory of Open Access Journals (Sweden)
Rafaela de Melo Simões Lima
2014-04-01
Full Text Available Objetivos: o cuidado com a saúde deve ser um ato seguro e livre de eventos adversos. Todavia, na prática diária se observa exposição excessiva a fatores que põem em risco a saúde do profissional. O centro cirúrgico sobressai como um dos locais em que o profissional envolvido está mais vulnerável. O anestesiologista faz desse ambiente o seu local de trabalho e convive com seus agravantes potenciais. Este estudo objetivou avaliar o conhecimento dos anestesiologistas da cidade do Recife acerca das diversas situações de risco do seu ambiente de trabalho. Método: estudo tipo corte transversal, no qual foram aplicados questionários estruturados, preenchidos pelo próprio anestesiologista de forma voluntária e anônima, para avaliar o conhecimento acerca dos riscos potenciais no centro cirúrgico. Os dados foram analisados com o programa software Epi Info versão 7. Resultados: responderam ao questionário 162 anestesiologistas, 38,02% dos cadastrados na Cooperativa de Anestesiologistas de Pernambuco. Desses, 3,7% leram o manual da Comissão de Controle de Infecção Hospitalar (CCIH da sua instituição de trabalho e 40,74% optaram acertadamente pela opção diretor técnico como o responsável por assegurar condições adequadas de trabalho. Do total, 5,56% afirmaram existir monitoração do índice de poluição anestésica nos centros cirúrgicos. Apenas 1,85% da amostra foi submetido à triagem periódica para tuberculose. Ao analisar a situação hipotética de contaminação com paciente portador de hepatite C, apenas 43,83% sabiam não haver profilaxia efetiva após exposição. Conclusão: campanhas educativas devem ser feitas para melhorar o conhecimento dos profissionais de saúde e esclarecer direitos e deveres das instituições e dos profissionais.
One-loop radiative corrections to the QED Casimir energy
Energy Technology Data Exchange (ETDEWEB)
Moazzemi, Reza; Mojavezi, Amirhosein [University of Qom, Department of Physics, Qom (Iran, Islamic Republic of)
2016-05-15
In this paper, we investigate one-loop radiative corrections to the Casimir energy in the presence of two perfectly conducting parallel plates for QED theory within the renormalized perturbation theory. In fact, there are three contributions for radiative corrections to the Casimir energy, up to order α, has been computed by Bordag et. al (Ann. Phys. 165:192, 1985), approximately. Here, up to this order, we consider corrections due to two one-loop terms, i.e., photonic and fermionic loop corrections resulting from renormalized QED Lagrangian, more precisely. Our results show that only the fermionic loop has a very minor correction and the correction of photonic loop vanishes. (orig.)
Theory of Casimir Forces without the Proximity-Force Approximation.
Lapas, Luciano C; Pérez-Madrid, Agustín; Rubí, J Miguel
2016-03-18
We analyze both the attractive and repulsive Casimir-Lifshitz forces recently reported in experimental investigations. By using a kinetic approach, we obtain the Casimir forces from the power absorbed by the materials. We consider collective material excitations through a set of relaxation times distributed in frequency according to a log-normal function. A generalized expression for these forces for arbitrary values of temperature is obtained. We compare our results with experimental measurements and conclude that the model goes beyond the proximity-force approximation.
Casimir Effect in Horava-Lifshitz-like theories
Ulion, I J Morales; Petrov, A Yu
2015-01-01
In this paper we consider a Lorentz-breaking scalar field theory within the Horava-Lifshtz approach. We investigate the changes that a space-time anisotropy produces in the Casimir effect. A massless real quantum scalar field is considered in two distinct situations: between two parallel plates and inside a rectangular two-dimensional box. In both cases we have adopted specific boundary conditions on the field at the boundary. As we shall see, the energy and the Casimir force strongly depends on the parameter associated with the breaking of Lorentz symmetry and also on the boundary conditions.
Comparison of chiral metamaterial designs for repulsive Casimir force
Zhao, R.; Koschny, Th.; Economou, E. N.; Soukoulis, C. M.
2010-06-01
In our previous work [R. Zhao, J. Zhou, Th. Koschny, E. N. Economou, and C. M. Soukoulis, Phys. Rev. Lett. 103, 103602 (2009)], we found that repulsive Casimir forces could be realized by using chiral metamaterials if the chirality is strong enough. In this work, we check four different chiral metamaterial designs (i.e., Twisted-Rosettes, Twisted-Crosswires, Four-U-SRRs, and Conjugate-Swastikas) and find that the designs of Four-U-SRRs and Conjugate-Swastikas are the most promising candidates to realize repulsive Casimir force because of their large chirality and the small ratio of structure length scale to resonance wavelength.
Comparison of Chiral Metamaterial Designs for Repulsive Casimir Force
Zhao, R.; Koschny, Th.; Economou, E. N.; C M Soukoulis
2009-01-01
In our previous work [Phys. Rev. Lett. 103, 103602 (2009)], we found that repulsive Casimir forces could be realized by using chiral metamaterials if the chirality is strong enough. In this work, we check four different chiral metamaterial designs (i.e., Twisted-Rosettes, Twisted-Crosswires, Four-U-SRRs, and Conjugate-Swastikas) and find that the designs of Four-U-SRRs and Conjugate-Swastikas are the most promising candidates to realize repulsive Casimir force because of their large chirality...
Supersymmetric Casimir Energy and $SL(3,\\mathbb{Z})$ Transformations
Brünner, Frederic; Spiridonov, Vyacheslav P
2016-01-01
We provide a recipe to extract the supersymmetric Casimir energy of theories defined on primary Hopf surfaces directly from the superconformal index. It involves an $SL(3,\\mathbb{Z})$ transformation acting on the complex structure moduli of the background geometry. In particular, the known relation between Casimir energy, index and partition function emerges naturally from this framework, allowing rewriting of the latter as a modified elliptic hypergeometric integral. We show this explicitly for $\\mathcal{N}=1$ SQCD and $\\mathcal{N}=4$ supersymmetric Yang-Mills theory for all classical gauge groups, and conjecture that it holds more generally.
Finite temperature Casimir effect in spacetime with extra compactified dimensions
Energy Technology Data Exchange (ETDEWEB)
Teo, L.P. [Faculty of Information Technology, Multimedia University, Jalan Multimedia, Cyberjaya 63100, Selangor Darul Ehsan (Malaysia)], E-mail: lpteo@mmu.edu.my
2009-02-16
In this Letter, we derive the explicit exact formulas for the finite temperature Casimir force acting on a pair of parallel plates in the presence of extra compactified dimensions within the framework of Kaluza-Klein theory. Using the piston analysis, we show that at any temperature, the Casimir force due to massless scalar field with Dirichlet boundary conditions on the plates is always attractive and the effect of extra dimensions becomes stronger when the size or number of the extra dimensions increases. These properties are not affected by the explicit geometry and topology of the Kaluza-Klein space.
Non-local thin films in Casimir force calculations
Esquivel, R
2005-01-01
he Casimir force is calculated between plates with thin metallic coating. Thin films are described with spatially dispersive (nonlocal) dielectric functions. For thin films the nonlocal effects are more relevant than for half-spaces. However, it is shown that even for film thickness smaller than the mean free path for electrons, the difference between local and nonlocal calculations of the Casimir force is of the order of a few tenths of a percent. Thus the local description of thin metallic films is adequate within the current experimental precision and range of separations.
Frequency-dependent Drude damping in Casimir force calculations
Energy Technology Data Exchange (ETDEWEB)
Esquivel-Sirvent, R, E-mail: raul@fisica.unam.m [Instituto de Fisica, Universidad Nacional Autonoma de Mexico, Apdo. Postal 20-364, Mexico D.F. 01000 (Mexico)
2009-04-01
The Casimir force is calculated between Au thin films that are described by a Drude model with a frequency dependent damping function. The model parameters are obtained from available experimental data for Au thin films. Two cases are considered; annealed and nonannealed films that have a different damping function. Compared with the calculations using a Drude model with a constant damping parameter, we observe changes in the Casimir force of a few percent. This behavior is only observed in films of no more than 300 A thick.
The Casimir effect in the sphere-plane geometry
Canaguier-Durand, Antoine; Neto, Paulo A Maia; Lambrecht, Astrid; Reynaud, Serge
2012-01-01
We present calculations of the Casimir interaction between a sphere and a plane, using a multipolar expansion of the scattering formula. This configuration enables us to study the nontrivial dependence of the Casimir force on the geometry, and its correlations with the effects of imperfect reflection and temperature. The accuracy of the Proximity Force Approximation (PFA) is assessed, and is shown to be affected by imperfect reflexion. Our analytical and numerical results at ambient temperature show a rich variety of interplays between the effects of curvature, temperature, finite conductivity, and dissipation.
Casimir switch: steering optical transparency with vacuum forces
Liu, X -f; Jing, H
2016-01-01
The Casimir force, originating from vacuum zero-point energy, is one of the most intriguing purely quantum effects. It has attracted renewed interests in current field of nanomechanics, due to the rapid size decrease of on-chip devices. Here we study the optomechanically-induced transparency (OMIT) with a tunable Casimir force. We find that the optical output rate can be significantly altered by the vacuum force, even terminated and then restored, indicating a highly-controlled optical switch. Our result addresses the possibility of designing exotic optical nano-devices by harnessing the power of vacuum.
Casimir-Polder Potential in Thermal Non-Equilibrium
Ellingsen, Simen Å; Buhmann, Stefan Y; Scheel, Stefan
2009-01-01
Different non-equilibrium situations have recently been considered when studying the thermal Casimir--Polder interaction with a body. We show that the Keldysh Green function method provides a very general common framework for such studies where non-equilibrium of either the atom or the body with the environment can be accounted for. We apply the results to the case of ground state polar molecules out of equilibrium with their environment, observing several striking effects. We consider thermal Casimir--Polder potentials in planar configurations, and new results for a molecule in a cylindrical cavity are reported, showing similar characteristic behaviour as found in planar geometry.
Reavaliação crítica da utilidade dos potenciais evocados em neurologia clínica
Joaquim P. Brasil-Neto
1992-01-01
O autor se propõe a revisar a literatura acerca das indicações clinicas dos potenciais evocados multimodais, com ênfase em sua relação custo-benefício, eficácia diagnóstica e comparação às modernas técnicas de diagnóstico por imagem.
Directory of Open Access Journals (Sweden)
Ricardo Ralisch
2006-06-01
Full Text Available This review discusses the different nature of potential litigation in agricultural and cattle raising activities, which are segmented into rural workers and rural employers. It analyzes lawsuits pending in the Labor Court, as well as in the Common Pleas Court, within the scope of State and Federal Civil Court rules. The objective of this analysis is to promote a better understanding of these legal problems among professionals in the area of Agronomy, who have, traditionally, little information on them. A detailed description of the each litigation, as well as of the pertinent legislation, are provided, to give rise to discussions and reflections on these problems, which are part of these professionals’ everyday life. Litigation involving companies and rural properties, with emphasis on technical inspections carried out and on the type of professional involved will be analyzed, together with the nature of the knowledge necessary for their interdisciplinary education.A presente revisão versa sobre as diferentes naturezas de litígios potenciais na atividade agropecuária, e se encontra segmentada por agrupamentos de empregados e empregadores rurais. Discute as ações judiciais ajuizadas tanto na Justiça Trabalhista como Justiça Comum, entendida no âmbito da Justiça Cível, nas esferas estadual ou federal. Visa oferecer contribuições aos profissionais de agronomia, tradicionalmente pouco familiarizados, possibilitando a melhor compreensão de suas ocorrências. Descrevem-se detalhadamente as características de cada uma das ocorrências, bem como as legislações pertinentes, para que possam ser despertadas as discussões e reflexões sobre a problemática, presente no dia a dia. Serão analisados, também, os litígios atingíveis sobre os empreendimentos e nas propriedades rurais, com a ênfase na realização das perícias técnicas, do tipo de profissional que é direcionado, bem como a natureza dos conhecimentos para a sua forma
Fuerza de Casimir 1D en semiconductores excitónicos
A. D. Hernández de la Luz; M. A. Rodríguez Moreno; J. Olvera Hernández; G. Hernández Cocoletzi
2006-01-01
Se presentan cálculos de la fuerza de Casimir unidimensional entre placas paralelas semiconductoras excitónicas no locales homogéneas y no homogéneas. Los efectos no locales se generan por las transiciones excitónicas An=1 y Bn=1 en CdS. La fuerza se calcula, en el caso homogéneo, como una función de los espesores de las placas d1 = d2 = d y del ancho de la región de vacío L entre ellas. Asimismo, para el caso inhomogéneo se consideran placas construidas por superredes semiinfinitas con celda...
Energy Technology Data Exchange (ETDEWEB)
Ellingsen, Simen Andreas Aadnoey
2011-01-15
The present thesis focuses on several topics within three separate but related branches of the overall field of dispersion forces. The three branches are: temperature corrections to the Casimir force between real materials (Part 1), explicit calculation of Casimir energy in wedge geometries (Part 2), and Casimir-Polder forces on particles out of thermal equilibrium (Part 3). Part 1 deals primarily with analysis of a previously purported thermodynamic inconsistency in the Casimir-Lifshitz free energy of the interaction of two plane mirrors - violation of the third law of thermodynamics - when the latter's dielectric response is described with dissipative models. It is shown analytically and numerically that the Casimir entropy of the interaction between two metallic mirrors described by the Drude model does tend to zero at zero temperature, provided electronic relaxation does not vanish. The leading order terms at low temperature are found. A similar calculation is carried out for the interaction of semiconductors with small but non-zero DC conductivity. In a generalisation, it is shown that a violation of the third law can only occur for permittivities whose low-frequency behaviour is temperature dependent near zero temperature. A calculation using path integral methods shows that the low temperature behaviour of the interaction of fluctuating Foucault currents in two mirrors of Drude metal is identical to that of the full Casimir-Lifshitz free energy, reasserting a previous finding by Intravaia and Henkel that such fluctuating bulk currents are the physical reason for the anomalous entropy behaviour. In a related effort, an analysis of the frequency dependence of the Casimir force by Ford is generalised to imperfectly reflecting mirrors. A paradox is pointed out, in that the effects of a perturbation of the reflecting properties of the mirrors in a finite frequency window can be calculated in two ways giving different results. It is concluded that optimistic
Interplay between geometry and temperature in the Casimir effect
Energy Technology Data Exchange (ETDEWEB)
Weber, Alexej
2010-06-23
In this thesis, we investigate the interplay between geometry and temperature in the Casimir effect for the inclined-plates, sphere-plate and cylinder-plate configurations. We use the worldline approach, which combines the string-inspired quantum field theoretical formalism with Monte Carlo techniques. The approach allows the precise computation of Casimir energies in arbitrary geometries. We analyze the dependence of the Casimir energy, force and torque on the separation parameter and temperature T, and find Casimir phenomena which are dominated by long-range fluctuations. We demonstrate that for open geometries, thermal energy densities are typically distributed on scales of thermal wavelengths. As an important consequence, approximation methods for thermal corrections based on local energy-density estimates, such as the proximity-force approximation, are found to become unreliable even at small surface-separations. Whereas the hightemperature behavior is always found to be linear in T, richer power-law behaviors at small temperatures emerge. In particular, thermal forces can develop a non-monotonic behavior. Many novel numerical as well as analytical results are presented. (orig.)
Self-affine roughness influence on the Casimir effect
Palasantzas, G
2005-01-01
In this work we investigate the influence of self-affine roughness on the Casimir energy for plate-plate geometry. The plate roughness is characterized by the rms roughness amplitude w, the lateral correlation length xi, and the roughness exponent H. It is shown that the latter has a prominent effec
Canonical realization of Bondi-Metzner-Sachs symmetry: Quadratic Casimir
Gomis, Joaquim; Longhi, Giorgio
2016-01-01
We study the canonical realization of Bondi-Metzner-Sacks symmetry for a massive scalar field introduced by Longhi and Materassi [J. Math. Phys. 40, 480 (1999)]. We construct an invariant scalar product for the generalized momenta. As a consequence we introduce a quadratic Casimir with the supertranslations.
Weak Coupling Casimir Energies for Finite Plate Configurations
Wagner, Jef; Parashar, Prachi
2008-01-01
We derive and use an extremely simplified formula for the interaction Casimir energy for two separate bodies in the weak coupling regime for massless scalar fields. We derive closed form solutions for a general arrangement of two $\\delta$-function plates finite in one direction and infinite in another. We examine the situation of two parallel plates finite in both transverse directions.
Materials perspective on Casimir and van der Waals interactions
Woods, L. M.; Dalvit, D. A. R.; Tkatchenko, A.; Rodriguez-Lopez, P.; Rodriguez, A. W.; Podgornik, R.
2016-10-01
Interactions induced by electromagnetic fluctuations, such as van der Waals and Casimir forces, are of universal nature present at any length scale between any types of systems. Such interactions are important not only for the fundamental science of materials behavior, but also for the design and improvement of micro- and nanostructured devices. In the past decade, many new materials have become available, which has stimulated the need for understanding their dispersive interactions. The field of van der Waals and Casimir forces has experienced an impetus in terms of developing novel theoretical and computational methods to provide new insights into related phenomena. The understanding of such forces has far reaching consequences as it bridges concepts in materials, atomic and molecular physics, condensed-matter physics, high-energy physics, chemistry, and biology. This review summarizes major breakthroughs and emphasizes the common origin of van der Waals and Casimir interactions. Progress related to novel ab initio modeling approaches and their application in various systems, interactions in materials with Dirac-like spectra, force manipulations through nontrivial boundary conditions, and applications of van der Waals forces in organic and biological matter are examined. The outlook of the review is to give the scientific community a materials perspective of van der Waals and Casimir phenomena and stimulate the development of experimental techniques and applications.
Dynamical Casimir effect and minimal temperature in quantum thermodynamics
Benenti, G.; Strini, G.
2014-01-01
We study the fundamental limitations of cooling to absolute zero for a qubit, interacting with a single mode of the electromagnetic field. Our results show that the dynamical Casimir effect, which is unavoidable in any finite-time thermodynamic cycle, forbids the attainability of the absolute zero of temperature, even in the limit of an infinite number of cycles.
The Casimir Energy in Curved Space and its Supersymmetric Counterpart
Assel, Benjamin; Di Pietro, Lorenzo; Komargodski, Zohar; Lorenzen, Jakob; Martelli, Dario
2015-01-01
We study $d$-dimensional Conformal Field Theories (CFTs) on the cylinder, $S^{d-1}\\times \\mathbb{R}$, and its deformations. In $d=2$ the Casimir energy (i.e. the vacuum energy) is universal and is related to the central charge $c$. In $d=4$ the vacuum energy depends on the regularization scheme and has no intrinsic value. We show that this property extends to infinitesimally deformed cylinders and support this conclusion with a holographic check. However, for $\\mathcal{N}=1$ supersymmetric CFTs, a natural analog of the Casimir energy turns out to be scheme independent and thus intrinsic. We give two proofs of this result. We compute the Casimir energy for such theories by reducing to a problem in supersymmetric quantum mechanics. For the round cylinder the vacuum energy is proportional to $a+3c$. We also compute the dependence of the Casimir energy on the squashing parameter of the cylinder. Finally, we revisit the problem of supersymmetric regularization of the path integral on Hopf surfaces.
Three-dimensional Casimir force between absorbing multilayer dielectrics
Raabe, C; Welsch, D G; Raabe, Christian; Kn\\"{o}ll, Ludwig; Welsch, Dirk-Gunnar
2003-01-01
Recently the influence of dielectric and geometrical properties on the Casimir force between dispersing and absorbing multilayered plates in the zero-temperature limit has been studied within a 1D quantization scheme for the electromagnetic field in the presence of causal media [R. Esquivel-Sirvent, C. Villarreal, and G.H. Cocoletzi, Phys. Rev. Lett. 64, 052108 (2001)]. In the present paper a rigorous 3D analysis is given, which shows that for complex heterostructures the 1D theory only roughly reflects the dependence of the Casimir force on the plate separation in general. Further, an extension of the very recently derived formula for the Casimir force at zero temperature [M.S. Toma\\v{s}, Phys. Rev. A 66, 052103 (2002)] to finite temperatures is given, and analytical expressions for specific distance laws in the zero-temperature limit are derived. In particular, it is shown that the Casimir force between two single-slab plates behaves asymptotically like $d^{-6}$ in place of $d^{-4}$ ($d$, plate separation).
The Casimir force control in nano and micro electromechanical systems
Sedighi Ghozotkhar, Mehdi
2016-01-01
In this thesis we deal with the analysis and measurement of dispersive surface forces, specifically the Casimir force. Applying Lifshitz theory makes it possible to take into account the material optical property and consequently the obtained results are more realistic. We used contact mode atomic f
Acceleration of the Universe driven by the Casimir force
Szydlowski, Marek
2007-01-01
We investigate an evolutional scenario of the FRW universe with the Casimir energy scaling like $(-)(1+z)^4$. The Casimir effect is used to explain the vacuum energy differences (its value measured from astrophysics is so small compared to value obtained from quantum field theory calculations). The dynamics of the FRW model is represented in terms of a two-dimensional dynamical system to show all evolutional paths of this model in the phase space for all admissible initial conditions. We find also an exact solution for non flat evolutional paths of Universe driven by the Casimir effect. The main difference between the FRW model with the Casimir force and the $\\Lambda$CDM model is that their generic solutions are a set of evolutional paths with a bounce solution and an initial singularity, respectively. The evolutional scenario are tested by using the SNIa data, FRIIb radiogalaxies, baryon oscillation peak and CMB observation. We compare the power of explanation of the model considered and the $\\Lambda$CDM mod...
Nonlocal thin films in calculations of the Casimir force
Esquivel-Sirvent, R.; Svetovoy, V.B.
2005-01-01
The Casimir force is calculated between plates with thin metallic coating. Thin films are described with spatially dispersive (nonlocal) dielectric functions. For thin films the nonlocal effects are more relevant than for half-spaces. However, it is shown that even for film thickness smaller than th
Spatial dispersion in Casimir forces: a brief review
Esquivel-Sirvent, R.; Villarreal, C.; Mochan, W.L.; Contreras-Reyes, A.M.; Svetovoy, V.B.
2006-01-01
We present the basic principles of non-local optics in connection with the calculation of the Casimir force between half-spaces and thin films. At currently accessible distances L, non-local corrections amount to about half a per cent, but they increase roughly as 1/L at smaller separations. Self-co
Casimir densities for parallel plate in the Domain Wall background
Setare, M R
2003-01-01
The Casimir forces on two parallel plates in conformally flat domain wall background due to conformally coupled massless scalar field satisfying mixed boundary conditions on the plates is investigated. In the general case of mixed boundary conditions formulae are derived for the vacuum expectation values of the energy-momentum tensor and vacuum forces acting on boundaries.
Finite temperature Casimir effect in the presence of nonlinear dielectrics
Kheirandish, Fardin; Soltani, Morteza
2010-01-01
Starting from a Lagrangian, electromagnetic field in the presence of a nonlinear dielectric medium is quantized using path-integral techniques and correlation functions of different fields are calculated. The susceptibilities of the nonlinear medium are obtained and their relation to coupling functions are determined. Finally, the Casimir energy and force in the presence of a nonlinear medium at finite temperature is calculated.
Dynamical Casimir Effect for Two Oscillating Mirrors in 3-D
Yuce, Cem
2008-01-01
The generation of photons in a three dimensional rectangular cavity with two moving boundaries is studied by using the Multiple Scale Analysis (MSA). It is shown that number of photons are enhanced for the cavity whose walls oscillate symmetrically with respect to the center of the cavity. The non-stationary Casimir effect is also discussed for the cavity which oscillates as a whole.
Directory of Open Access Journals (Sweden)
Gilberto Antonio Freitas de Moraes
2005-08-01
Full Text Available A hidratação é o fator externo mais importante na germinação de sementes. Para simular as condições complexas do solo, soluções com diferentes potenciais osmóticos têm sido usadas para umedecer os substratos. O objetivo deste trabalho foi avaliar os efeitos do estresse hídrico e salino sobre a germinação e o vigor de sementes de feijão. Sementes da cultivar IAPAR 44 foram colocadas a germinar em papel-toalha embebido em soluções de polietileno glicol (PEG 6000 e cloreto de sódio (NaCl nos potenciais osmóticos zero; -0,05; -0,10; -0,15; -0,20; -0,25 e -0,30 MPa. O desempenho das sementes foi avaliado por meio do teste de germinação, primeira contagem da germinação, comprimento e matéria seca de plântulas. Concluiu-se que a redução do potencial osmótico, induzido por PEG 6000 ou NaCl, reduz o vigor e, a partir de -0,20 MPa, reduz a germinação de sementes de feijão. O PEG 6000 produz efeitos adversos mais drásticos do que o NaCl na qualidade fisiológica das sementes.Hydration is the most important external factor for seed germination. To simulate the complex soil conditions solutions with different osmotic potentials have been used to soak substrata. The objective of this paper was to evaluate the effects of hydric and saline stress to germination and strength of bean seeds. Seeds of the cultivar IAPAR were germinated in towel-paper soaked in PEG 6000 and NaCl solutions in the zero osmotic potentials; -0.05; -0.10; -0.15; -0.20; -0.25 and 0.30 MPa. Seed performance was evaluated through the germination test, first count of germination, length, and dry seedling weight. In conclusion, osmotic potential reduction, induced by Polyethylene glicol (PEG 6000 or Sodium chlorine (NaCl, reduces the strength and, from -0.20 to -0.30 MPa, the germination of bean seeds. The PEG 6000 produces more severe and adverse effects than the NaCl in the physiologic quality of been seeds.
2010-01-01
Trata do problema da integracao economica, tentando estabelecer uma relação dos elementos teóricos com o caso brasileiro. Realiza um survey da teoria da integração economica, ressaltando os novos elementos analiticos que emergem com o desenvol virnento da Nova Teoria do Comercio. Aborda o processo de formação do MERCOSUL e suas atuais tendencias, relacionando o com uma nova, estrategia de desenvolvimento econômico para o país. Analisa as possíveis vatagens para o Brasil ...
Directory of Open Access Journals (Sweden)
Paula Sandrin
2015-12-01
Full Text Available ResumoEste artigo tem como objetivo desafiar a lógica binária que permeia a discussão sobre o impacto da adesão da Turquia na política externa e de segurança comum (PESC da União Europeia (UE. Defende-se que qualquer análise sobre tal impacto precisa levar em consideração as divisões existentes dentro da Europa e dentro da Turquia em termos de culturas de segurança. Com o intuito de ilustrar a pluralidade de culturas de segurança existentes na UE e na Turquia e fornecer indicações sobre as potenciais contribuições do país para a Europa enquanto ator internacional, são analisadas as respostas da União Europeia como um bloco, de alguns países-membros europeus (França, Reino Unido e Alemanha e da Turquia ao conflito na Líbia em 2011. Conclui-se que, com ou sem a Turquia, a União Europeia deverá continuar a atuar como uma potência humanitária no cenário mundial e que, portanto, os potenciais impactos de uma eventual adesão turca não devem ser exagerados.
First-order correction to the Casimir force within an inhomogeneous medium
Bao, Fanglin; He, Sailing
2015-01-01
For the Casimir piston filled with an inhomogeneous medium, the Casimir energy is regularized and expressed with cylinder kernel coefficients by using the first-order perturbation theory. When the refraction index of the medium is smoothly inhomogeneous (i.e., derivatives of all orders exist), logarithmically cutoff-dependent term in Casimir energy is found. We show that in the piston model this term vanishes in the force and thus the Casimir force is always cutoff-independent, but this term will remain in the force in the half-space model and must be removed by additional regularization. We investigate the inhomogeneity of an exponentially decaying profile, and give the first-order corrections to both free Casimir energy and Casimir force. The present method can be extended to other inhomogeneous profiles. Our results should be useful for future relevant calculations and experimental studies.
Finite-temperature Casimir effect in piston geometry and its classical limit
Energy Technology Data Exchange (ETDEWEB)
Lim, S.C. [Multimedia University, Faculty of Engineering, Cyberjaya, Selangor Darul Ehsan (Malaysia); Teo, L.P. [Multimedia University, Faculty of Information Technology, Cyberjaya, Selangor Darul Ehsan (Malaysia)
2009-03-15
We consider the Casimir force acting on a d-dimensional rectangular piston due to a massless scalar field with periodic, Dirichlet and Neumann boundary conditions and an electromagnetic field with perfect electric-conductor and perfect magnetic-conductor boundary conditions. The Casimir energy in a rectangular cavity is derived using the cut-off method. It is shown that the divergent part of the Casimir energy does not contribute to the Casimir force acting on the piston, thus renders an unambiguously defined Casimir force acting on the piston. At any temperature, it is found that the Casimir force acting on the piston increases from -{infinity} to 0 when the separation a between the piston and the opposite wall increases from 0 to {infinity}. This implies that the Casimir force is always an attractive force pulling the piston towards the closer wall, and the magnitude of the force gets larger as the separation a gets smaller. Explicit exact expressions for the Casimir force for small and large plate separations and for low and high temperatures are computed. The limits of the Casimir force acting on the piston when some pairs of transversal plates are large are also derived. An interesting result regarding the influence of temperature is that in contrast to the conventional result that the leading term of the Casimir force acting on a wall of a rectangular cavity at high temperature is the Stefan-Boltzmann (or black-body radiation) term which is of order T {sup d+1}, it is found that the contributions of this term from the two regions separating the piston cancel with each other in the case of piston. The high-temperature leading-order term of the Casimir force acting on the piston is of order T, which shows that the Casimir force has a nontrivial classical {Dirac_h}{yields}0 limit. Explicit formulas for the classical limit are computed. (orig.)
How does Casimir energy fall? III. Inertial forces on vacuum energy
Shajesh, K V; Parashar, Prachi; Wagner, Jeffrey A
2007-01-01
We have recently demonstrated that Casimir energy due to parallel plates, including its divergent parts, falls like conventional mass in a weak gravitational field. The divergent parts were suitably interpreted as renormalizing the bare masses of the plates. Here we corroborate our result regarding the inertial nature of Casimir energy by calculating the centripetal force on a Casimir apparatus rotating with constant angular speed. We show that the centripetal force is independent of the orientation of the Casimir apparatus in a frame whose origin is at the center of inertia of the apparatus.
A diagrammatic expansion of the Casimir energy in multiple reflections: theory and applications
Maghrebi, Mohammad F
2010-01-01
We develop a diagrammatic representation of the Casimir energy of a multibody configuration. The diagrams represent multiple reflections between the objects and can be organized by a few simple rules. The lowest-order diagrams (or reflections) give the main contribution to the Casimir interaction which proves the usefulness of this expansion. Among some applications of this, we find analytical formulae describing the interaction between "edges", i.e. semi-infinite plates, where we also give a first example of blocking in the context of the Casimir energy. We also find the interaction of edges with a needle and describe analytically a recent model of the repulsion due to the Casimir interaction.
Directory of Open Access Journals (Sweden)
LUIZ ANTONIO DE LIMA RESENDE
2000-06-01
Full Text Available There is controversy over how hormonal conditions influence cerebral physiology. We studied pattern-shift visual evoked potentials (PS-VEP, brain stem auditory evoked potentials (BAEP and short-latency somatosensory evoked potentials (SSEV in 20 female volunteers at different phases of the menstrual cycle (estrogen phase, ovulatory day and progesterone phase. Statistical analysis showed decreased latencies for P100 (PS-VEP, N19 and P22 (SSEV waves in the progesterone phase compared with the estrogen phase. There was no significant difference between the estrogen and the ovulation day values. Comparing the three above stages, there were no significant differences in the brainstem auditory evoked potentials. The reduction of the latencies of the potentials generated in multisynaptic circuits provides the first consistent neurophysiological basis for a tentative comprehension of human pre-menstrual syndrome.Há controvérsias sobre como variações hormonais do ciclo menstrual da mulher influenciam a neurofisiologia cerebral. Estudamos potenciais evocados de curta latência, visuais, auditivos e sômato-sensoriais, em 20 mulheres voluntárias normais, nas diferentes fases do ciclo menstrual (fase estrogênica, fase ovulatória, fase progestacional. Comparação entre fase estrogênica e ovulatória mostrou resultados similares. Ondas I, III, V dos potenciais evocados auditivos não apresentaram diferenças estatisticamente significativas entre as três fases do ciclo. Análise estatística dos resultados mostrou diminuição significativa das latências das ondas P100, N19 e P22 obtidas na fase progestacional, comparadas com aquelas obtidas na fase estrogênica. Como estas ondas são geradas em circuitos multissinápticos, tal redução de latências, na fase progestacional, fornece a primeira base neurofisiológica consistente para tentativa de compreensão da síndrome pré-menstrual da mulher.
A Cosmic-box Casimir Theory of Dark Energy
Wreszinski, W F
2006-01-01
It has been recently remarked by Hollands and Wald that the holistic (local) aspects of quantum field theory fully explain the fact that the cosmological constant does not have the absurdly large value which is commonly assumed. There remains the quite different problem of why the cosmological constant leads to an absurdly SMALL dark energy density when applying the field-theoretic Casimir effect to the Universe as a whole. In this paper we propose a LOCAL theory of the Casimir effect, following work of B.S.Kay and a recent paper with L.Manzoni, as well as the "cosmic-box" idea of E.Harrison. Baryons and neutrinos do not explain the numbers, but axions would.
Casimir Energy of a Semi-Circular Infinite Cylinder
Nesterenko, V V; Scarpetta, G
2001-01-01
The Casimir energy of a semi-circular cylindrical shell is calculated by making use of the zeta function technique. This shell is obtained by crossing an infinite circular cylindrical shell by a plane passing through the symmetry axes of the cylinder and by considering only a half of this configuration. All the surfaces, including the cutting plane, are assumed to be perfectly conducting. The zeta functions for scalar massless fields obeying the Dirichlet and Neumann boundary conditions on the semi-circular cylinder are constructed exactly. The sum of these zeta functions gives the zeta function for electromagnetic field in question. The relevant plane problem is considered also. In all the cases the final expressions for the corresponding Casimir energies contain the pole contributions. This implies that further renormalization is needed in order for the finite physical values for vacuum energy to be obtained for given boundary conditions.
Casimir energy of a semi-circular infinite cylinder
Nesterenko, V. V.; Lambiase, G.; Scarpetta, G.
2001-05-01
The Casimir energy of a semi-circular cylindrical shell is calculated by making use of the zeta function technique. This shell is obtained by crossing an infinite circular cylindrical shell by a plane passing through the symmetry axes of the cylinder and by considering only half of this configuration. All the surfaces, including the cutting plane, are assumed to be perfectly conducting. The zeta functions for scalar massless fields obeying the Dirichlet and Neumann boundary conditions on the semi-circular cylinder are constructed exactly. The sum of these zeta functions gives the zeta function for the electromagnetic field in question. The relevant plane problem is considered also. In all the cases the final expressions for the corresponding Casimir energies contain the pole contributions which are the consequence of the edges or corners in the boundaries. This implies that further renormalization is needed in order for the finite physical values for vacuum energy to be obtained for given boundary conditions.
Casimir-Polder repulsion: Polarizable atoms, cylinders, spheres, and ellipsoids
Milton, Kimball A; Pourtolami, Nima; Brevik, Iver
2012-01-01
Recently, the topic of Casimir repulsion has received a great deal of attention, largely because of the possibility of technological application. The general subject has a long history, going back to the self-repulsion of a conducting spherical shell and the repulsion between a perfect electric conductor and a perfect magnetic conductor. Recently it has been observed that repulsion can be achieved between ordinary conducting bodies, provided sufficient anisotropy is present. For example, an anisotropic polarizable atom can be repelled near an aperture in a conducting plate. Here we provide new examples of this effect, including the repulsion on such an atom moving on a trajectory nonintersecting a conducting cylinder; in contrast, such repulsion does not occur outside a sphere. Classically, repulsion does occur between a conducting ellipsoid placed in a uniform electric field and an electric dipole. The Casimir-Polder force between an anisotropic atom and an anisotropic dielectric semispace does not exhibit r...
Casimir Effect for a Semitransparent Wedge and an Annular Piston
Milton, Kimball A; Kirsten, Klaus
2009-01-01
We consider the Casimir energy due to a massless scalar field in a geometry of an infinite wedge closed by a Dirichlet circular cylinder, where the wedge is formed by $\\delta$-function potentials, so-called semitransparent boundaries. A finite expression for the Casimir energy corresponding to the arc and the presence of both semitransparent potentials is obtained, from which the torque on the sidewalls can be derived. The most interesting part of the calculation is the nontrivial nature of the angular mode functions. Numerical results are obtained which are closely analogous to those recently found for a magnetodielectric wedge, with the same speed of light on both sides of the wedge boundaries. Alternative methods are developed for annular regions with radial semitransparent potentials, based on reduced Green's functions for the angular dependence, which allows calculations using the multiple-scattering formalism. Numerical results corresponding to the torque on the radial plates are likewise computed, whic...
Casimir Force on Real Materials - the Slab and Cavity Geometry
Ellingsen, S A; Brevik, Iver; Ellingsen, Simen A.
2006-01-01
We analyse the potential of the geometry of a slab in a planar cavity for the purpose of Casimir force experiments. The force and its dependence on temperature, material properties and finite slab thickness are investigated both analytically and numerically for slab and walls made of aluminium and teflon FEP respectively. We conclude that such a setup is ideal for measurements of the temperature dependence of the Casimir force. By numerical calculation it is shown that temperature effects are dramatically larger for dielectrics, suggesting that a dielectric such as teflon FEP whose properties vary little within a moderate temperature range, should be considered for experimental purposes. We finally discuss the subtle but fundamental matter of the various Green's two-point function approaches present in the literature and show how they are different formulations describing the same phenomenon.
Cosmology in nonlinear multidimensional gravity and the Casimir effect
Bolokhov, S. V.; Bronnikov, K. A.
2017-01-01
We study the possible cosmological models in Kaluza-Klein-type multidimensional gravity with a curvature-nonlinear Lagrangian and a spherical extra space, taking into account the Casimir energy. First, we find a minimum of the effective potential of extra dimensions, leading to a physically reasonable value of the effective cosmological constant in our 4D space-time. In this model, the huge Casimir energy density is compensated by a fine-tuned contribution of the curvature-nonlinear terms in the original action. Second, we present a viable model with slowly evolving extra dimensions and power-law inflation in our space-time. In both models, the results formulated in Einstein and Jordan frames are compared.
Casimir Self-Entropy of an Electromagnetic Thin Sheet
Li, Yang; Kalauni, Pushpa; Parashar, Prachi
2016-01-01
Casimir entropies due to quantum fluctuations in the interaction between electrical bodies can often be negative, either caused by dissipation or by geometry. Although generally such entropies vanish at zero temperature, consistent with the third law of thermodynamics (the Nernst heat theorem), there is a region in the space of temperature and separation between the bodies where negative entropy occurs, while positive interaction entropies arise for large distances or temperatures. Systematic studies on this phenomenon in the Casimir-Polder interaction between a polarizable nanoparticle or atom and a conducting plate in the dipole approximation have been given recently. Since the total entropy should be positive according to the second law of thermodynamics, we expect that the self-entropy of the bodies would be sufficiently positive as to overwhelm the negative interaction entropy. This expectation, however, has not been explicitly verified. Here we compute the self-entropy of an electromagnetic $\\delta$-fun...
On the Casimir Energy of Frequency Dependent Interactions
Graham, N; Weigel, H
2014-01-01
Vacuum polarization (or Casimir) energies can be straightforwardly computed from scattering data for static field configurations whose interactions with the fluctuating field are frequency independent. In effective theories, however,such interactions are typically frequency dependent. As a consequence, the relationship between scattering data and the Green's function is modified, which may or may not induce additional contributions to the vacuum polarization energy. We discuss several examples that naturally include frequency dependent interactions: (i) scalar electrodynamics with a static background potential, (ii) an effective theory that emerges from integrating out a heavy degree of freedom, and (iii) quantum electrodynamics coupled to a frequency dependent dielectric material. In the latter case, we argue that introducing dissipation as required by the Kramers-Kronig relations requires the consideration of the Casimir energy within a statistical mechanics formalism, while in the absence of dissipation we...
Casimir forces in multilayer magnetodielectrics with both gain and loss
DEFF Research Database (Denmark)
Amooghorban, Ehsan; Wubs, Martijn; Mortensen, N. Asger
2011-01-01
and Casimir forces for a multilayer magnetodielectric medium with both gain and loss. We point out the essential differences with a purely passive layered medium. For a single layer, we find different bounds on the Casimir force for fully amplifying and for lossy media. The force is attractive in both cases......, even if the medium exhibits negative refraction. From our Lagrangian we also derive by canonical quantization the postulates of the phenomenological theory of amplifying magnetodielectrics.......A path-integral approach to the quantization of the electromagnetic field in a linearly amplifying magnetodielectric medium is presented. Two continua of inverted harmonic oscillators are used to describe the polarizability and magnetizability of the amplifying medium. The causal susceptibilities...
Non-equilibrium Casimir force between vibrating plates.
Directory of Open Access Journals (Sweden)
Andreas Hanke
Full Text Available We study the fluctuation-induced, time-dependent force between two plates confining a correlated fluid which is driven out of equilibrium mechanically by harmonic vibrations of one of the plates. For a purely relaxational dynamics of the fluid we calculate the fluctuation-induced force generated by the vibrating plate on the plate at rest. The time-dependence of this force is characterized by a positive lag time with respect to the driving. We obtain two distinctive contributions to the force, one generated by diffusion of stress in the fluid and another related to resonant dissipation in the cavity. The relation to the dynamic Casimir effect of the electromagnetic field and possible experiments to measure the time-dependent Casimir force are discussed.
On the static Casimir effect with parity-breaking mirrors
Energy Technology Data Exchange (ETDEWEB)
Fosco, C.D. [Comision Nacional de Energia Atomica, Centro Atomico Bariloche and Instituto Balseiro, Bariloche (Argentina); Remaggi, M.L. [Universidad Nacional de Cuyo, Facultad de Ciencias Exactas y Naturales, Mendoza (Argentina)
2017-03-15
We study the Casimir interaction energy due to the vacuum fluctuations of the electromagnetic (EM) field in the presence of two mirrors, described by 2+1-dimensional, generally nonlocal actions, which may contain both parity-conserving and parity-breaking terms. We compare the results with the ones corresponding to Chern-Simons boundary conditions and evaluate the interaction energy for several particular situations. (orig.)
Tuning the Mass of Chameleon Fields in Casimir Force Experiments
Brax, Ph; Davis, A C; Shaw, D J; Iannuzzi, D
2010-01-01
We have calculated the chameleon pressure between two parallel plates in the presence of an intervening medium that affects the mass of the chameleon field. As intuitively expected, the gas in the gap weakens the chameleon interaction mechanism with a screening effect that increases with the plate separation and with the density of the intervening medium. This phenomenon might open up new directions in the search of chameleon particles with future long range Casimir force experiments.
Symmetries and casimir of an extended classical long wave system
Indian Academy of Sciences (India)
K M Tamizhmani; R Ilangovane; B Dubrovin
2013-04-01
In this paper, we derive Lie point, generalized, master and time-dependent symmetries of a dispersionless equation, which is an extension of a classical long wave system. This equation also admits an infinite-dimensional Lie algebraic structure of Virasoro-type, as in the dispersive integrable systems. We discuss the construction of a sequence of negative ranking symmetries through the property of uniformity in rank. More interestingly, we obtain the conserved quantities directly from the casimir of Poisson pencil.
Sugawara construction and Casimir operators for Krichever-Novikov algebras
Schlichenmaier, M; Schlichenmaier, Martin; Sheinman, Oleg K
1995-01-01
We show how to obtain from highest weight representations of Krichever-Novikov algebras of affine type (also called higher genus affine Kac-Moody algebras) representations of centrally extended Krichever-Novikov vector field algebras via the Sugawara construction. This generalizes classical results where one obtains representations of the Virasoro algebra. Relations between the weights of the corresponding representations are given and Casimir operators are constructed. In an appendix the Sugawara construction for the multi-point situation is done.
Microstructure Effects for Casimir Forces in Chiral Metamaterials
McCauley, Alexander P.; Zhao, Rongkuo; Reid, M. T. Homer; Rodriguez, Alejandro W.; Zhou, Jiangfeng; Rosa, F. S. S.; Joannopoulos, John D; Dalvit, D. A. R.; Soukoulis, Costas M.; Johnson, Steven G.
2010-01-01
We examine a recent prediction for the chirality-dependence of the Casimir force in chiral metamaterials by numerical computation of the forces between the exact microstructures, rather than homogeneous approximations. We compute the exact force for a chiral bent-cross pattern, as well as forces for an idealized "omega"-particle medium in the dilute approximation and identify the effects of structural inhomogeneity (i.e. proximity forces and anisotropy). We find that these microstructure effe...
Proposal for a Casimir-driven parametric amplifier
Imboden, M; Campbell, D K; Bishop, D J
2014-01-01
In this paper, we discuss a design for a MEMS parametric amplifier modulated by the Casimir force. We present the theory for such a device and show that it allows for the implementation of a very sensitive voltage measuring technique, where the amplitude of a high quality factor resonator includes a tenth power dependency on an applied DC voltage. This approach opens up a new and powerful measuring modality, applicable to other measurement types.
Van der Waals and Casimir-Polder interactions between neutrons
Directory of Open Access Journals (Sweden)
Babb James F.
2016-01-01
Full Text Available We investigate the van der Waals interaction between neutrons using the theory of Casimir and Polder, wherein the potential for asymptotically large separations falls off as the inverse seventh power, and compare it to the similar interaction between a neutron and a proton, for which the asymptotic interaction falls off as the inverse fourth power. Modifications of the formalism to extend the validity to smaller separations using dynamic electric and magnetic dipole polarizability data are discussed.
Effective actions, boundaries, and precision calculations of Casimir energies
Aghababaie, Y.; Burgess, C. P.
2004-10-01
We perform the matching required to compute the leading effective boundary contribution to the QED Lagrangian in the presence of a conducting surface, once the electron is integrated out. Our result resolves a confusion in the literature concerning the interpretation of the leading such correction to the Casimir energy. It also provides a useful theoretical laboratory for brane-world calculations in which kinetic terms are generated on the brane, since a lot is known about QED near boundaries.
Spatial dispersion in Casimir forces: A brief review
Esquivel-Sirvent, R; Mochán, W L; Contreras-Reyes, A M; Svetovoy, V B
2005-01-01
We present the basic principles of non-local optics in connection with the calculation of the Casimir force between half-spaces and thin films. At currently accessible distances $L$, non-local corrections amount to about half a percent, but they increase roughly as 1/L at smaller separations. Self consistent models lead to corrections with the opposite sign as models with abrupt surfaces.
On Casimir Forces for Media with Arbitrary Dielectric Properties
Mochán, W L; Esquivel-Sirvent, R
2002-01-01
We derive an expression for the Casimir force between slabs with arbitrary dielectric properties characterized by their reflection coefficients. The formalism presented here is applicable to media with a local or a non-local dielectric response, an infinite or a finite width, inhomogeneous dissipative, etc. Our results reduce to the Lifshitz formula for the force between semi-infinite dielectric slabs by replacing the reflection coefficients by the Fresnel amplitudes.
Casimir rack and pinion as a miniaturized kinetic energy harvester.
Miri, MirFaez; Etesami, Zahra
2016-08-01
We study a nanoscale machine composed of a rack and a pinion with no contact, but intermeshed via the lateral Casimir force. We adopt a simple model for the random velocity of the rack subject to external random forces, namely, a dichotomous noise with zero mean value. We show that the pinion, even when it experiences random thermal torque, can do work against a load. The device thus converts the kinetic energy of the random motions of the rack into useful work.
Casimir operators induced by the Maurer-Cartan equations
Energy Technology Data Exchange (ETDEWEB)
Campoamor-Stursberg, Rutwig [Dpto. GeometrIa y TopologIa, Fac. CC. Matematicas, Universidad Complutense de Madrid, Plaza de Ciencias, 3, E-28040 Madrid (Spain)], E-mail: rutwig@mat.ucm.es
2008-09-12
It is shown that for inhomogeneous Lie algebras with only one Casimir operator, the latter can be explicitly constructed from the Maurer-Cartan equations by means of wedge products. It is further proved that this constraint imposes sharp bounds for the dimension of the representation R defining the semidirect product. The procedure is generalized to compute also the rational invariant of some Lie algebras.
Casimir-Polder intermolecular forces in minimal length theories
Panella, O
2007-01-01
Generalized uncertainty relations are known to provide a minimal length $\\hbar\\sqrt{\\beta}$. The effect of such minimal length in the Casimir-Polder interactions between neutral atoms (molecules) is studied. The first order correction term in the minimal uncertainty parameter is derived and found to describe an attractive potential scaling as $r^{-9}$ as opposed to the well known $r^{-7}$ long range retarded potential.
Nonlocal impedances and the Casimir entropy at low temperatures
Svetovoy, V
2005-01-01
The problem with the temperature dependence of the Casimir force is investigated. Specifically, the entropy behavior in the low temperature limit, which caused debates in the literature, is analyzed. It is stressed that the behavior of the relaxation frequency in the $T\\to0$ limit does not play a physical role since the anomalous skin effect dominates in this range. In contrast with the previous works, where the approximate Leontovich impedance was used for analysis of nonlocal effects, we give description of the problem in terms of exact nonlocal impedances. It is found that the Casimir entropy is going to zero at $T\\to0$ only in the case when $s$ polarization does not contribute to the classical part of the Casimir force. However, the entropy approaching zero from the negative side that, in our opinion, cannot be considered as thermodynamically satisfactory. The resolution of the negative entropy problem proposed in the literature is analyzed and it is shown that it cannot be considered as complete. The cri...
The Casimir effect for fields with arbitrary spin
Energy Technology Data Exchange (ETDEWEB)
Stokes, Adam; Bennett, Robert, E-mail: r.bennett@leeds.ac.uk
2015-09-15
The Casimir force arises when a quantum field is confined between objects that apply boundary conditions to it. In a recent paper we used the two-spinor calculus to derive boundary conditions applicable to fields with arbitrary spin in the presence of perfectly reflecting surfaces. Here we use these general boundary conditions to investigate the Casimir force between two parallel perfectly reflecting plates for fields up to spin-2. We use the two-spinor calculus formalism to present a unified calculation of well-known results for spin-1/2 (Dirac) and spin-1 (Maxwell) fields. We then use our unified framework to derive new results for the spin-3/2 and spin-2 fields, which turn out to be the same as those for spin-1/2 and spin-1. This is part of a broader conclusion that there are only two different Casimir forces for perfectly reflecting plates—one associated with fermions and the other with bosons.
Halving the Casimir force with conductive oxides: experimental details
de Man, Sven; Iannuzzi, Davide
2010-01-01
This work is an extended version of a paper published last year in Physical Review Letters [S. de Man et al., Phys. Rev. Lett. 103, 040402 (2009)], where we presented measurements of the Casimir force between a gold coated sphere and a plate coated with either gold or an indium-tin-oxide (ITO) layer. The experiment, which was performed in air, showed that ITO is sufficiently conducting to prevent charge accumulation, but still transparent enough to halve the Casimir attraction when compared to gold. Here, we report all the experimental details that, due to the limited space available, were omitted in the previous article. We discuss the performance of our setup in terms of stability of the calibration procedure and reproducibility of the Casimir force measurement. We also introduce and demonstrate a new technique to obtain the spring constant of our force sensor. Furthermore, we present a thorough description of the experimental method, a comprehensive explanation of data elaboration and error analysis, and a...
A Generalization of Electromagnetic Fluctuation-Induced Casimir Energy
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Yi Zheng
2015-01-01
Full Text Available Intermolecular forces responsible for adhesion and cohesion can be classified according to their origins; interactions between charges, ions, random dipole—random dipole (Keesom, random dipole—induced dipole (Debye are due to electrostatic effects; covalent bonding, London dispersion forces between fluctuating dipoles, and Lewis acid-base interactions are due to quantum mechanical effects; pressure and osmotic forces are of entropic origin. Of all these interactions, the London dispersion interaction is universal and exists between all types of atoms as well as macroscopic objects. The dispersion force between macroscopic objects is called Casimir/van der Waals force. It results from alteration of the quantum and thermal fluctuations of the electrodynamic field due to the presence of interfaces and plays a significant role in the interaction between macroscopic objects at micrometer and nanometer length scales. This paper discusses how fluctuational electrodynamics can be used to determine the Casimir energy/pressure between planar multilayer objects. Though it is confirmation of the famous work of Dzyaloshinskii, Lifshitz, and Pitaevskii (DLP, we have solved the problem without having to use methods from quantum field theory that DLP resorted to. Because of this new approach, we have been able to clarify the contributions of propagating and evanescent waves to Casimir energy/pressure in dissipative media.
Proof that Casimir force does not originate from vacuum energy
Nikolic, H
2016-01-01
We present a simple general proof that Casimir force cannot originate from the vacuum energy of electromagnetic (EM) field. The full QED Hamiltonian consists of 3 terms: the pure electromagnetic term $H_{\\rm em}$, the pure matter term $H_{\\rm matt}$ and the interaction term $H_{\\rm int}$. The $H_{\\rm em}$-term commutes with all matter fields because it does not have any explicit dependence on matter fields. As a consequence, $H_{\\rm em}$ cannot generate any forces on matter. Since it is precisely this term that generates the vacuum energy of EM field, it follows that the vacuum energy does not generate the forces. The erroneous statements in the literature that vacuum energy generates Casimir force can be boiled down to the fact that $H_{\\rm em}$ attains an implicit dependence on matter fields by the use of the equations of motion and the erroneous treatment of the implicit dependence as if it was explicit. The true origin of the Casimir force is van der Waals force generated by $H_{\\rm int}$.
Proof that Casimir force does not originate from vacuum energy
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Hrvoje Nikolić
2016-10-01
Full Text Available We present a simple general proof that Casimir force cannot originate from the vacuum energy of electromagnetic (EM field. The full QED Hamiltonian consists of 3 terms: the pure electromagnetic term Hem, the pure matter term Hmatt and the interaction term Hint. The Hem-term commutes with all matter fields because it does not have any explicit dependence on matter fields. As a consequence, Hem cannot generate any forces on matter. Since it is precisely this term that generates the vacuum energy of EM field, it follows that the vacuum energy does not generate the forces. The misleading statements in the literature that vacuum energy generates Casimir force can be boiled down to the fact that Hem attains an implicit dependence on matter fields by the use of the equations of motion and to the illegitimate treatment of the implicit dependence as if it was explicit. The true origin of the Casimir force is van der Waals force generated by Hint.
La force de Casimir et les plasmons de surface
Intravaia, F.; Lambrecht, A.; Reynaud, S.
2004-11-01
La présence de fluctuations irréductibles de champ dans le vide est une prédiction importante de la théorie quantique. Ces fluctuations ont de nombreux effets bien connus, dont l'archétype est la force de Casimir apparaîssant entre deux miroirs placés dans le vide par suite de la pression de radiation du vide. Elle a été récemment mesurée avec une précision de l'ordre du %. De nombreux travaux sont consacrés à l'évaluation théorique de cette force en visant une précision du même ordre. Ici nous étudions la force de Casimir dans la configuration de deux miroirs métalliques plans parallèles à température nulle. En supposant les miroirs décrits par un modèle plasma nous interprétons la force de Casimir comme le résultat de l'interaction entre les plasmons de surface des deux miroirs.
Thermodynamic Casimir effect in films: the exchange cluster algorithm.
Hasenbusch, Martin
2015-02-01
We study the thermodynamic Casimir force for films with various types of boundary conditions and the bulk universality class of the three-dimensional Ising model. To this end, we perform Monte Carlo simulations of the improved Blume-Capel model on the simple cubic lattice. In particular, we employ the exchange or geometric cluster cluster algorithm [Heringa and Blöte, Phys. Rev. E 57, 4976 (1998)]. In a previous work, we demonstrated that this algorithm allows us to compute the thermodynamic Casimir force for the plate-sphere geometry efficiently. It turns out that also for the film geometry a substantial reduction of the statistical error can achieved. Concerning physics, we focus on (O,O) boundary conditions, where O denotes the ordinary surface transition. These are implemented by free boundary conditions on both sides of the film. Films with such boundary conditions undergo a phase transition in the universality class of the two-dimensional Ising model. We determine the inverse transition temperature for a large range of thicknesses L(0) of the film and study the scaling of this temperature with L(0). In the neighborhood of the transition, the thermodynamic Casimir force is affected by finite size effects, where finite size refers to a finite transversal extension L of the film. We demonstrate that these finite size effects can be computed by using the universal finite size scaling function of the free energy of the two-dimensional Ising model.
Scattering Theory Calculations of Casimir Energies at High Curvature
Graham, Noah; Emig, Thorsten; Forrow, Aden; Jaffe, Robert; Kardar, Mehran; Maghrebi, Mohammad; Rahi, Jamal; Shpunt, Alex
2013-03-01
Scattering theory provides a powerful tool for capturing the response of an object to electromagnetic charge and field fluctuations. Techniques based on scattering theory have made possible a wide range of new calculations of Casimir energies. In this approach, the Casimir interaction energy for a collection of objects can be expressed in terms of the scattering T-matrices for each object individually, combined with universal translation matrices describing the objects' relative positions and orientations. These translation matrices are derived from an expansion of the free Green's function in an appropriate coordinate system, independent of the details of the objects themselves. This method proves particularly valuable for geometries involving high curvature, such as edges and tips. I will describe this approach in general terms and then give results from several problems to which it has been applied successfully. I will also discuss new developments in scattering theory that have been motivated by these problems. I would like to request that this abstract be part of a session on Casimir physics. Supported by the National Science Foundation, the US Department of Energy, the Defense Advanced Research Projects Agency, and the Deutsche Forschungsgemeinschaft
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Janaina Patricio de Lima
2008-10-01
Full Text Available Os Potenciais Evocados Auditivos de Tronco Encefálico (PEATE são considerados potenciais exógenos, ou seja, as respostas obtidas são altamente dependentes da característica do estímulo utilizado para evocá-los. OBJETIVO: Averiguar a influência da polaridade do estímulo clique na pesquisa dos PEATE em diferentes intensidades, utilizando-se fone de inserção. FORMA DE ESTUDO: Clínico. MATERIAL E MÉTODO: 33 indivíduos, idade entre 18 e 28 anos, sem alteração auditiva foram submetidos à pesquisa dos PEATE, com estímulo clique nas polaridades de rarefação, condensação e alternada, em diferentes intensidades. RESULTADOS: As latências absolutas da onda V mostraram-se menores na polaridade de rarefação quando comparadas às demais e na intensidade de 80 dBnHL houve diferença significante entre a rarefação e as demais polaridades para as latências interpicos III-V e I-V. Houve alta correlação entre as polaridades de condensação e alternada para as latências absolutas e interpicos na intensidade de 80 dBnHL. CONCLUSÃO: A polaridade do estímulo clique influência significativamente nos PEATE. Na rotina em que se utiliza o fone TDH 39, com apresentação de polaridade alternada, sugere-se que o uso da polaridade de condensação seja mais adequado para efeitos de comparação padronizada, devido à maior semelhança das latências encontradas nesse estudo com fone de inserção.Brainstem Auditory Evoked Potentials are considered exogenous potentials, that is, the responses obtained are highly dependent upon the characteristic of the stimulus used to evoke them. AIM: To investigate the influence of the click stimulus polarity in the study of Brainstem Evoked Response Audiometry (BERA at different intensities, using insertion-canal earphones. TYPE OF STUDY: Clinical. MATERIALS AND METHODS: 33 individuals, aged between 18 and 28, with no auditory alteration were submitted to BERA testing, with click stimulus on the
Influence of materials' optical response on actuation dynamics by Casimir forces
Sedighi Ghozotkhar, Mehdi; Broer, W. H.; Van der Veeke, S.; Svetovoy, V. B.; Palasantzas, G.
2015-01-01
The dependence of the Casimir force on the frequency-dependent dielectric functions of interacting materials makes it possible to tailor the actuation dynamics of microactuators. The Casimir force is largest for metallic interacting systems due to the high absorption of conduction electrons in the f
A veriﬁcation of quantum ﬁeld theory – measurement of Casimir force
Indian Academy of Sciences (India)
Anushree Roy; U Mohideen
2001-02-01
Here we review our work on measurement of the Casimir force between a large aluminum coated a sphere and ﬂat plate using an atomic force microscope. The average statistical precision is 1% of the force measured at the closest separation. We have also shown nontrival boundary dependence of the Casimir force.
Casimir Effect at Finite Temperature in the Presence of Compactified Universal Extra Dimensions
Institute of Scientific and Technical Information of China (English)
CHENG Hong-Bo
2005-01-01
@@ We analyse the Casimir effect for parallel plates atfinite temperature in the presence of compactified universal extra dimensions and analytically show the thermal corrections to the effect in detail. The Casimir effect for different sizes of universal extra dimensions is investigated to test the five-dimensional Kaluza-Klein theory.
Liberação de nitrato de hidróxidos duplos lamelares como potenciais fertilizantes de liberação lenta
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Valentim da Silva
2014-06-01
Full Text Available Hidróxidos duplos lamelares (HDL são intercaladores potenciais aniônicos. Com o objetivo de obter fertilizantes de liberação lenta de nitrato, foram sintetizados HDL com a fórmula geral [M2+1-xM3+x(OH2]x-(NO3x.yH2O, em que M2+ = Mg2+ e M3+ = Al3+ e, ou, Fe3+, utilizando-se o método de coprecipitação a pH alcalino constante. Medidas de difração de raios-X evidenciaram que a cristalinidade aumenta com o acréscimo do valor de pH e da razão molar M2+/M3+. As medidas de FTIR apresentaram bandas características de nitrato livre no espaço interlamelar, além de pequena contaminação de íons carbonato. Medidas de TGA/DTA possibilitaram a confirmação das composições e dos teores de íons de nitrato intercalados. As curvas de liberação de nitrato demonstraram dois comportamentos de liberação complementar, um inicial rápido (A e um lento gradativo (D, sendo, este último, relacionado à orientação planar do íon nitrato intercalado. Os materiais sintetizados e investigados neste trabalho apontaram grande potencial para serem utilizados como matrizes para fertilizantes de liberação lenta de nitrato.
Casimir-Foucault interaction: Free energy and entropy at low temperature
Intravaia, F; Henkel, C
2010-01-01
It was recently found that thermodynamic anomalies which arise in the Casimir effect between metals described by the Drude model can be attributed to the interaction of fluctuating Foucault (or eddy) currents [Phys. Rev. Lett. 103, 130405 (2009)]. We show explicitly that the two leading terms of the low-temperature correction to the Casimir free energy of interaction between two plates, are identical to those pertaining to the Foucault current interaction alone, up to a correction which is very small for good metals. Moreover, a mode density along real frequencies is introduced, showing that the Casimir free energy, as given by the Lifshitz theory, separates in a natural manner in contributions from eddy currents and propagating cavity modes, respectively. The latter have long been known to be of little importance to the low-temperature Casimir anomalies. This convincingly demonstrates that eddy current modes are responsible for the large temperature correction to the Casimir effect between Drude metals, pred...
Casimir interaction between spheres in $\\boldsymbol{(D+1)}$-dimensional Minkowski spacetime
Teo, L P
2014-01-01
We consider the Casimir interaction between two spheres in $(D+1)$-dimensional Minkowski spacetime due to the vacuum fluctuations of scalar fields. We consider combinations of Dirichlet and Neumann boundary conditions. The TGTG formula of the Casimir interaction energy is derived. The computations of the T matrices of the two spheres are straightforward. To compute the two G matrices, known as translation matrices, which relate the hyper-spherical waves in two spherical coordinate frames differ by a translation, we generalize the operator approach employed in [IEEE Trans. Antennas Propag. \\textbf{36}, 1078 (1988)]. The result is expressed in terms of an integral over Gegenbauer polynomials. Using our expression for the Casimir interaction energy, we derive the large separation and small separation asymptotic expansions of the Casimir interaction energy. In the large separation regime, we find that the Casimir interaction energy is of order $L^{-2D+3}$, $L^{-2D+1}$ and $L^{-2D-1}$ respectively for Dirichlet-Di...
Hide It to See It Better: A Robust Setup to Probe the Thermal Casimir Effect
Bimonte, Giuseppe
2014-06-01
We describe a Casimir setup consisting of two aligned sinusoidally corrugated Ni surfaces, one of which is "hidden" by a thin opaque layer of gold with a flat exposed surface. The gold layer acts as a low-pass filter that allows for a clean observation of the controversial thermal Casimir force between the corrugations, with currently available Casimir apparatuses. The proposed scheme of measurement, based on the phase-dependent modulation of the Casimir force, requires no electrostatic calibrations of the apparatus, and is unaffected by uncertainties in the knowledge of the optical properties of the surfaces. This scheme should allow for an unambiguous discrimination between alternative theoretical prescriptions that have been proposed in the literature for the thermal Casimir effect.
PREFACE: International Workshop '60 Years of the Casimir Effect'
Barton, Gabriel; Carugno, Giovanni; Dodonov, Victor; Man'ko, Margarita
2009-07-01
In 1948 Hendrick Casimir published a short article predicting that (neutral) ideal metallic plates attract each other. This attraction is widely ascribed to the quantum vacuum fluctuations of the electromagnetic field (even though away from the limit of ideal metals it depends demonstrably on the physics of the charge carriers vanishing when they cease to carry). Casimir's remarkable discovery, nowadays called the Casimir effect, has charmed several generations of physicists. In the last decade alone, more than a thousand publications have addressed its many consequences, generalizations, and possible applications in different areas from particle physics to cosmology. Interest in the field is still growing driven by impressive progress in experimental skills and its importance for the recently opened-up area of micro- and nano-electromechanical systems: according to the Thompson ISI Web of Science database, in 2005 the number of papers related to the Casimir effect or to Casimir forces jumped to over 125, compared to approximately 60 in 2000 and 30 in 1995. The increase continues, with more than 170 papers in 2008. The International Workshop '60 Years of the Casimir Effect' took place on 23-27June 2008, in Brasilia (Brazil) organized by the International Center for Condensed Matter Physics (ICCMP). The purpose was to celebrate this anniversary of Casimir's pioneering paper by inviting the leading specialists in the area, both theorists and experimentalists, together with young researchers and post-graduate students interested in hearing about the most recent achievements in the field. The Workshop was attended by 65 participants from 14 countries, who presented 41 talks and 12 posters. These Proceedings contain extended versions of almost all the talks and some posters, plus several papers by authors who had planned to attend but for various reasons could not. The contributions are divided (with some inevitable arbitrariness) into four groups. The largest one
Geometrical investigations of the Casimir effect: Thickness and corrugation dependencies
Parashar, Prachi
2011-12-01
In the quantum theory the vacuum is not empty space. It is considered as a state of infinite energy arising due to zero point fluctuations of the vacuum. Calculation of any physically relevant process requires subtracting this infinite energy using a procedure called normalization. As such the vacuum energy is treated as an infinite constant. However, it has been established beyond doubt that mere subtraction of this infinite constant does not remove the effect of vacuum fluctuations and it cannot be treated just as a mathematical artifact. The presence of boundaries, which restricts the vacuum field, causes vacuum polarization. Any non-trivial space-time topology can cause similar effects. This is manifested as the Casimir effect, whereby the boundaries experience a force due to a change in the energy of the vacuum. To calculate the vacuum energy we treat the boundaries or other restrictive conditions as classical backgrounds, which impose boundary conditions on the solution of the vacuum field equations. Alternatively, we can incorporate the classical background in the Lagrangian of the system as classical potentials, which automatically include the boundary conditions in the field equations. Any change in the boundary conditions changes the vacuum energy and consequently the Casimir force is experienced by the boundaries. In this dissertation we study the geometric aspect of the Casimir effect. We consider both the scalar field and the physically relevant electromagnetic field. After a brief survey of the field in Chapter 1, we derive the energy expression using the Schwinger's quantum action principle in Chapter 2. We present the multiple scattering formalism for calculating the vacuum energy, which allows us to calculate the interaction energy between disjoint bodies and subtract out the divergent terms from the beginning. We then solve the Green's dyadic equation for the electromagnetic field interacting with the planar background surfaces, where we can
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Mariana Macedo Alvim
2015-12-01
Full Text Available RESUMO Objetivo: Avaliar a existência de interações medicamentosas potenciais na unidade de terapia intensiva de um hospital, com foco nos antimicrobianos. Métodos: Estudo transversal, que analisou prescrições eletrônicas de pacientes da unidade de terapia intensiva de um hospital de ensino, avaliando potenciais interações medicamentosas relacionadas aos antimicrobianos, entre 1º de janeiro e 31 de março de 2014. O consumo dos antimicrobianos foi expresso em dose diária definida por 100 pacientes-dia. A busca e a classificação das interações foram realizadas com base no sistema Micromedex®. Resultados: Foram analisadas prescrições diárias de 82 pacientes, totalizando 656 prescrições. Do total de medicamentos prescritos, 25% eram antimicrobianos, sendo meropenem, vancomicina e ceftriaxona os mais prescritos. Os antimicrobianos mais consumidos, segundo a metodologia de dose diária definida por 100 pacientes-dia, foram cefepime, meropenem, sulfametoxazol + trimetoprima e ciprofloxacino. A média de interações por paciente foi de 2,6. Entre as interações, 51% foram classificadas como contraindicadas ou de gravidade importante. Destacaram-se as interações altamente significativas (valor clínico 1 e 2, com prevalência de 98%. Conclusão: Com o presente trabalho verifica-se que os antimicrobianos são uma classe frequentemente prescrita na unidade de terapia intensiva, apresentando elevada quantidade de interações medicamentosas potenciais, sendo a maior parte das interações considerada altamente significativa.
Energy Technology Data Exchange (ETDEWEB)
Seyedzahedi, A. [Department of Science, University of Kurdistan, Sanandaj (Iran, Islamic Republic of); Moradian, A., E-mail: a.moradian@uok.ac.ir [Department of Science, Campus of Bijar, University of Kurdistan, Bijar (Iran, Islamic Republic of); Setare, M.R., E-mail: rezakord@ipm.ir [Department of Science, University of Kurdistan, Sanandaj (Iran, Islamic Republic of)
2016-04-01
We investigate the Casimir force for a system composed of two thick slabs as substrates within three different homogeneous layers. We use the scattering approach along with the Matsubara formalism in order to calculate the Casimir force at finite temperature. First, we focus on constructing the reflection matrices and then we calculate the Casimir force for a water–lipid system. According to the conventional use of silicon as a substrate, we apply the formalism to calculate the Casimir force for layers of Au, VO{sub 2}, mica, KCl and foam rubber on the thick slabs of silicon. Afterwards, introducing an increasing factor, we compare our results with Lifshitz force in the vacuum between two semispaces of silicon in order to illustrate the influence of the layers on intensifying the Casimir force. We also calculate the Casimir force between two slabs of the forementioned materials with finite thicknesses to indicate the substrate's role in increasing the obtained Casimir force. Our simple calculation is interesting since one can extend it along with the Rigorous Coupled Wave Analysis to systems containing inhomogeneous layers as good candidates for designing nanomechanical devices.
Positive Casimir and Central Characters of Split Real Quantum Groups
Ip, Ivan C. H.
2016-06-01
We describe the generalized Casimir operators and their actions on the positive representations {mathcal{P}_λ} of the modular double of split real quantum groups {mathcal{U}_{qtilde{q}}(mathfrak{g}_mathbb{R})}. We introduce the notion of virtual highest and lowest weights, and show that the central characters admit positive values for all parameters {λ}. We show that their image defines a semi-algebraic region bounded by real points of the discriminant variety independent of q, and we discuss explicit examples in the lower rank cases.
Repulsive Casimir force between silicon dioxide and superconductor
Energy Technology Data Exchange (ETDEWEB)
Phan, Anh D. [Department of Physics, University of South Florida, Tampa, Florida (United States); Viet, N.A. [Institute of Physics, Badinh, Hanoi (Viet Nam)
2012-06-15
We present a detailed investigation of the Casimir interaction between the superconductor Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} (BSCCO) and silicon dioxide with bromobenzene present in between. We found that the dispersion force is repulsive and the magnitude of the force can be changed by varying the thickness of the object and the temperature. The repulsive force would provide a method to deal with stiction problems and provide much significant from the practical point of view. (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Generalized Bogoliubov Transformation for Confined Fields Applications in Casimir Effect
Silva, J C; Neto, A M; Santana, A E
2002-01-01
The Bogoliubov transformation in thermofield dynamics, an operator formalism for the finite-temperature quantum-field theory, is generalized to describe a field in arbitrary confined regions of space and time. Starting with the scalar field, the approach is extended to the electromagnetic field and the energy-momentum tensor is written via the Bogoliubov transformation. In this context, the Casimir effect is calculated for zero and non-zero temperature, and therefore it can be considered as a vacuum condensation effect of the electromagnetic field. This aspect opens an interesting perspective for using this procedure as an effective scheme for calculations in the studies of confined fields, including the interacting fields.
Nonlinear behavior for nanoscale electrostatic actuators with Casimir force
Energy Technology Data Exchange (ETDEWEB)
Lin Wenhui [College of Science, China Agricultural University, Beijing 100083 (China); Zhao Yapu [State Key Laboratory of Nonlinear Mechanics (LNM), Institute of Mechanics, Chinese Academy of Sciences, Beijing 100080 (China)]. E-mail: yzhao@lnm.imech.ac.cn
2005-03-01
The influence of Casimir force on the nonlinear behavior of nanoscale electrostatic actuators is studied in this paper. A one degree of freedom mass-spring model is adopted and the bifurcation properties of the actuators are obtained. With the change of the geometrical dimensions, the number of equilibrium point varies from zero to two. Stability analysis shows that one equilibrium point is Hopf point and the other is unstable saddle point when there are two equilibrium points. We also obtain the phase portraits, in which the periodic orbits exist around the Hopf point, and a homoclinic orbit passes through the unstable saddle point.
Repulsive Casimir forces with finite-thickness slabs
Zhao, R.; Koschny, Th.; Economou, E. N.; C M Soukoulis
2010-01-01
We use the extended Lifshitz theory to study the behaviors of the Casimir forces between finite-thickness effective medium slabs. We first study the interaction between a semi-infinite Drude metal and a finite-thickness magnetic slab with or without substrate. For no substrate, the large distance $d$ dependence of the force is repulsive and goes as $1/d^5$; for the Drude metal substrate, a stable equilibrium point appears at an intermediate distance which can be tuned by the thickness of the ...
Casimir force between δ -δ' mirrors transparent at high frequencies
Braga, Alessandra N.; Silva, Jeferson Danilo L.; Alves, Danilo T.
2016-12-01
We investigate, in the context of a real massless scalar field in 1 +1 dimensions, models of partially reflecting mirrors simulated by Dirac δ -δ' point interactions. In the literature, these models do not exhibit full transparency at high frequencies. In order to provide a more realistic feature for these models, we propose a modified δ -δ' point interaction that enables full transparency in the limit of high frequencies. Taking this modified δ -δ' model into account, we investigate the Casimir force, comparing our results with those found in the literature.
Casimir effect on nontrivial topology spaces in Krein space quantization
Naseri, M; Takook, M V
2007-01-01
Casimir effect of a topologically nontrivial two-dimensional space-time, through Krein space quantization [1,2], has been calculated. In other words, auxiliary negative norm states have been utilized here. Presence of negative norm states play the role of an automatic renormalization device for the theory. The negative norm states (which do not interact with the physical world) could be chosen in two perspective. In the first case our method results in zero or vanishing values for energy. In the second case, however, the result are the same as the renormalization procedure.
Mixing rules and the Casimir force between composite systems
Esquivel-Sirvent, R
2011-01-01
The Casimir-Lifshitz force is calculated between two inhomogeneous composite slabs, each made of a homogeneous matrix with spherical metallic inclusions. The effective dielectric function of the slabs is calculated using several effective medium approximations and we compare the resulting forces as a function of slab separation and filling fraction. We show that the choice of effective medium approximation is critical in making precise comparisons between theory and experiment. The role that the spectral representation of the effective medium plays in making a Wick rotation to the complex frequency axis is also discussed.
Mixing rules and the Casimir force between composite systems
Energy Technology Data Exchange (ETDEWEB)
Esquivel-Sirvent, R.; Schatz, George C.
2011-04-20
The Casimir-Lifshitz force is calculated between two inhomogeneous composite slabs, each made of a homogeneous matrix with spherical metallic inclusions. The effective dielectric function of the slabs is calculated using several effective medium approximations and we compare the resulting forces as a function of slab separation and filling fraction. We show that the choice of effective medium approximation is critical in making precise comparisons between theory and experiment. The role that the spectral representation of the effective medium plays in making a Wick rotation to the complex frequency axis is also discussed.
Determinantal formulae for the Casimir operators of inhomogeneous Lie algebras
Energy Technology Data Exchange (ETDEWEB)
Campoamor-Stursberg, Rutwig [Dpto. Geometria y Topologia, Fac CC Matematicas, Universidad Complutense de Madrid, Plaza de Ciencias, 3, E-28040 Madrid (Spain)
2006-03-10
Contractions of Lie algebras are combined with the classical matrix method of Gel'fand to obtain matrix formulae for the Casimir operators of inhomogeneous Lie algebras. The method is presented for the inhomogeneous pseudo-unitary Lie algebras Iu(p,q). This procedure is extended to contractions of Iu(p,q) isomorphic to an extension by a derivation of the inhomogeneous special pseudo-unitary Lie algebras Isu(p-1,q), providing an additional analytical method to obtain their invariants. Further, matrix formulae for the invariants of other inhomogeneous Lie algebras are presented.
The Casimir effect physical manifestations of zero-point energy
Milton, K A
2001-01-01
In its simplest manifestation, the Casimir effect is a quantum force of attraction between two parallel uncharged conducting plates. More generally, it refers to the interaction - which may be either attractive or repulsive - between material bodies due to quantum fluctuations in whatever fields are relevant. It is a local version of the van der Waals force between molecules. Its sweep ranges from perhaps its being the origin of the cosmological constant to its being responsible for the confinement of quarks. This monograph develops the theory of such forces, based primarily on physically tran
Using boundary methods to compute the Casimir energy
Lombardo, F C; Villar, P I
2010-01-01
We discuss new approaches to compute numerically the Casimir interaction energy for waveguides of arbitrary section, based on the boundary methods traditionally used to compute eigenvalues of the 2D Helmholtz equation. These methods are combined with the Cauchy's theorem in order to perform the sum over modes. As an illustration, we describe a point-matching technique to compute the vacuum energy for waveguides containing media with different permittivities. We present explicit numerical evaluations for perfect conducting surfaces in the case of concentric corrugated cylinders and a circular cylinder inside an elliptic one.
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Luciene Burlandy
2016-06-01
Full Text Available Resumo O estudo analisou os potenciais conflitos de interesses (CDI que envolvem o setor privado comercial no âmbito das políticas de promoção da saúde (PS, especialmente em sua interface com o campo da alimentação e nutrição no Brasil. Consideraram-se as influências do ideário internacional nesse processo e, para tal, foram analisadas as duas edições da Política Nacional de Promoção da Saúde (2006 e 2014 e os pactos internacionais que as subsidiaram. O estudo pautou-se em método de análise documental, considerando as seguintes dimensões e categorias de análise: na dimensão do ideário da PS foram identificados os enfoques, os princípios e as estratégias propostos; na dimensão dos CDI foram identificadas a abordagem do tema nos documentos, as relações com o setor privado comercial, e as propostas denominadas “parcerias público-privado”. Concluiu-se que a abordagem de CDI ainda é frágil nessas políticas. O debate é despolitizado quando não são explicitadas as assimetrias de poder entre os setores envolvidos nas relações público-privado, ou quando são desconsideradas as práticas do setor privado comercial que ferem objetivos, princípios e valores das políticas de PS.
Scalar Casimir effect in the presence of extra dimensions with helix boundary conditions
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GE Feifei
2012-12-01
Full Text Available In this paper,we consider the scalar Casimir effect for parallel plates in the presence of extra dimensions with helix boundary conditions.Using zeta function regularization technique,we get the Casimir pressure explicitly expressed by the modified Bessel function of the second kind.We find the Casimir force is always attractive but for the same magnitude of the helix parameter as the parallel separation,the magnitude of the force between the parallel plates decreases by one order of magnitude.The smaller the helix parameter compared to the plate separation,the more magnitudes the force decreases.
Casimir energy calculations within the formalism of the noncompact lattice QED
Pavlovsky, Oleg
2009-01-01
A new method based on the Monte-Carlo calculation on the lattice is proposed to study the Casimir effect in the noncompact lattice QED. We have studied the standard Casimir problem with two parallel plane surfaces (mirrors) and oblique boundary conditions on those as a test of our method. Physically, this boundary conditions may appear in the problem of modelling of the thin material films interaction and are generated by additional Chern-Simons boundary term. This approach for the boundary condition generation is very suitable for the lattice formulation of the Casimir problem due to gauge invariance.
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Amanda Martins Viel
2014-09-01
Full Text Available A prática de associações medicamentosas é comum em pacientes hospitalizados, Esta prática é muitas vezes necessária, principalmente em pacientes psiquiátricos, uma vez que, juntamente com as doenças neuropsiquiátricas, podem ocorrer outras comorbidades, Entretanto, esta prática pode favorecer a ocorrência de interações medicamentosas com consequente potencialização de diferentes efeitos adversos, Diante deste quadro, o presente trabalho teve como objetivo avaliar a ocorrência de potenciais interações medicamentosas com os benzodiazepínicos, prescritos aos pacientes internados na Clínica Psiquiátrica do Hospital Regional de Assis – SP, a fim de gerar informações que contribuam para a eficácia do tratamento estabelecido ao paciente, Para isso, foi realizada uma análise de 100 prescrições médicas, nas quais foram avaliadas as possibilidades de ocorrência de interações medicamentosas entre os diferentes fármacos da classe dos benzodiazepínicos administrados concomitantemente, bem como com outras classes de fármacos, Por meio deste estudo, verificou-se que das 100 prescrições médicas analisadas 93 apresentaram a possibilidade de ocorrência de interações farmacológicas entre benzodiazepínicos e com outras classes de fármacos, totalizando 356 possíveis interações, Desse total, destacam-se as associações dos benzodiazepínicos com os antipsicóticos, anti-histamínicos, antiepilépticos e antidepressivos, as quais podem potencializar a manifestação de inúmeros efeitos adversos, em destaque, a exacerbação do efeito depressor do sistema nervoso central, com repercussões que podem variar desde a manifestação clínica leve até risco de êxito letal, Neste contexto, busca-se com este trabalho contribuir para uma melhor compreensão, reconhecimento e intervenção precoce ou profilática em situações clínicas decorrentes de interações farmacológicas entre diferentes classes de fármacos com os
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Ruberval Azevedo
2015-04-01
Abstract. The citrus industry in Brazil plays a role of great economic, social, generating jobs, income and development. Brazil is the largest producer of citrus, the State of Sergipe stands out in 5th place in national production. Among the many pest problems faced by Brazilian citrus is Citrus Variegated Chlorosis (CVC, known as the yellowing caused by the bacterium Xylella fastidiosa Wells et al. The CVC was officially identified in Brazil in 1987, in orchards of “Triângulo Mineiro” and North and northwest of the state of São Paulo. In the Northeast Region of Brazil, was found in 1996 in the municipality of Boquim Sergipe, and Bahia in 1997, the municipalities of Rio Real and Itapicuru. The aim was to review the literature on the species of leafhoppers vectors of CVC, and verify that occur in the state of Sergipe. The first symptoms are seen in the leaves, then go for the fruits and end up affecting the entire plant, and to be perceived can take between five months and two years. The main vectors of X. fastidiosa in citrus are the sharpshooters of the family Cicadellidae. In Brazil 12 sharpshooters species have already been confirmed. For the state of Sergipe, is scarce information about the Cicadellidae vectors, the data are limited to the northern coast of Bahia, except for vague quote about four genus (Oncometropia, Acrogonia, Dilobopterus and Homolodisca and three species (Homolodisca ignorata Melichar, Acrogonia sp. and Homolodisca spottii Takiya, Cavichioli & McKamey.
Local and Global Casimir Energies for a Semitransparent Cylindrical Shell
Cavero-Pelaez, I; Milton, K A; Cavero-Pelaez, Ines; Kirsten, Klaus; Milton, Kimball A.
2006-01-01
The local Casimir energy density and the global Casimir energy for a massless scalar field associated with a $\\lambda\\delta$-function potential in a 3+1 dimensional circular cylindrical geometry are considered. The global energy is examined for both weak and strong coupling, the latter being the well-studied Dirichlet cylinder case. For weak-coupling,in $\\mathcal{O}(\\lambda^2)$, the total energy is shown to vanish by both analytic and numerical arguments, based both on Green's-function and zeta-function techniques. Divergences occurring in the calculation are shown to be absorbable by renormalization of physical parameters of the model. The global energy may be obtained by integrating the local energy density only when the latter is supplemented by an energy term residing precisely on the surface of the cylinder. The latter is identified as the integrated local energy density of the cylindrical shell when the latter is physically expanded to have finite thickness. Inside and outside the shell, the local energ...
Casimir self-entropy of an electromagnetic thin sheet
Li, Yang; Milton, Kimball A.; Kalauni, Pushpa; Parashar, Prachi
2016-10-01
Casimir entropies due to quantum fluctuations in the interaction between electrical bodies can often be negative, caused either by dissipation or by geometry. Although generally such entropies vanish at zero temperature, consistent with the third law of thermodynamics (the Nernst heat theorem), there is a region in the space of temperature and separation between the bodies where negative entropy occurs, while positive interaction entropies arise for large distances or temperatures. Systematic studies on this phenomenon in the Casimir-Polder interaction between a polarizable nanoparticle or atom and a conducting plate in the dipole approximation have been given recently. Since the total entropy should be positive according to the second law of thermodynamics, we expect that the self-entropy of the bodies would be sufficiently positive as to overwhelm the negative interaction entropy. This expectation, however, has not been explicitly verified. Here we compute the self-entropy of an electromagnetic δ -function plate, which corresponds to a perfectly conducting sheet in the strong coupling limit. The transverse electric contribution to the self-entropy is negative, while the transverse magnetic contribution is larger and positive, so the total self-entropy is positive. However, this self-entropy vanishes in the strong-coupling limit. In that case, it is the self-entropy of the nanoparticle, which we recalculate in the perfect conducting limit, that is just sufficient to result in a non-negative total entropy.
Observation of the dynamical Casimir effect in a superconducting circuit.
Wilson, C M; Johansson, G; Pourkabirian, A; Simoen, M; Johansson, J R; Duty, T; Nori, F; Delsing, P
2011-11-16
One of the most surprising predictions of modern quantum theory is that the vacuum of space is not empty. In fact, quantum theory predicts that it teems with virtual particles flitting in and out of existence. Although initially a curiosity, it was quickly realized that these vacuum fluctuations had measurable consequences--for instance, producing the Lamb shift of atomic spectra and modifying the magnetic moment of the electron. This type of renormalization due to vacuum fluctuations is now central to our understanding of nature. However, these effects provide indirect evidence for the existence of vacuum fluctuations. From early on, it was discussed whether it might be possible to more directly observe the virtual particles that compose the quantum vacuum. Forty years ago, it was suggested that a mirror undergoing relativistic motion could convert virtual photons into directly observable real photons. The phenomenon, later termed the dynamical Casimir effect, has not been demonstrated previously. Here we observe the dynamical Casimir effect in a superconducting circuit consisting of a coplanar transmission line with a tunable electrical length. The rate of change of the electrical length can be made very fast (a substantial fraction of the speed of light) by modulating the inductance of a superconducting quantum interference device at high frequencies (>10 gigahertz). In addition to observing the creation of real photons, we detect two-mode squeezing in the emitted radiation, which is a signature of the quantum character of the generation process.
Determination of the Contact Angle Based on the Casimir Effect
Mazuruk, K.; Volz, M. P.
2015-01-01
In several crystal growth processed based on capillarity, a melt comes into contact with a crucible wall at an angle defined as the contact angle. For molten metals and semiconductors, this contact angle is dependent upon both the crucible and melt material and typical values fall in the range 80-170deg. However, on a microscopic scale, there does not exist a precise and sharp contact angle but rather the melt and solid surfaces merge smoothly and continuously over a distance of up to several micrometers. Accurate modeling requires a more advanced treatment of this interaction. The interaction between the melt and solid surfaces can be calculated by considering two forces: a short-range repulsive force and a longer range (up to a few micrometers) Casimir force. The Casimir force between the two bodies of complex geometry is calculated using a retarded temperature Green's function (Matsubara type) for the photon in the medium. The governing equations are cast in the form of a set of boundary integral equations which are then solved numerically for the case of molten Ge on SiO2. The shape of the molten surface approaching the flat solid body is determined, and the contact angle is defined as the angle between the two surfaces at the microscopically asymptotic distance of 1-2 micrometers. The formulation of this model and the results of the numerical calculations will be presented and discussed.
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Paulo Sergio A. Henriques Filho
2006-09-01
malformações de Arnold-Chiari de tipo I e 48 (64% apresentavam malformações de tipo II. Em 53 (71% do total de pacientes os potenciais evocados auditivos mostraram algum grau de anormalidade. Os testes foram normais nos restantes 22 (29%. CONCLUSÃO: O potencial evocado auditivo pode ser considerado valioso instrumento para o diagnóstico e avaliação da gravidade das anormalidades funcionais de tronco cerebral em pacientes portadores de malformações de Arnold-Chiari de tipo I e II. Esta avaliação pode contribuir de maneira significativa não somente no diagnóstico como também na prevenção de ulteriores lesões, pela adoção de medidas preventivas, tanto por meio de fisioterapia como por intervenção cirúrgica precoce.
Energy Technology Data Exchange (ETDEWEB)
Mohideen, Umar [Univ. of California, Riverside, CA (United States)
2015-04-14
Duration of award was from 4/15/10-4/14/15. In this grant period our contributions to the field of VdW/Casimir forces are 24 refereed publications in journals such as Physical Review Letters (4) [1-4], Physical Review B (10) [5-14], Physical Review D (2) [15,16], Applied Physics Letters (1) [17], Review of Scientific Instruments (1) [18] and the International Journal of Modern Physics A (5) [19-23] and B(1) (invited review article [24]). We presented 2 plenary conference talks, 3 lectures at the Pan American School on Frontiers in Casimir Physics, 2 conferences, 1 colloquium and 11 APS talks. If publications are restricted to only those with direct connection to the aims proposed in the prior grant period, then it will be a total of 12: Physical Review Letters (3) [2-4], Physical Review B (6) [6-8,12,13,25], Review of Scientific Instruments (1) [18], International Journal of Modern Physics A (1) [19] and B(1) [169]. A brief aggregated description of the directly connected accomplishments is below. The following topics are detailed: dispersion force measurements with graphene, dispersion force from ferromagnetic metals, conclusion on role of electrostatic patches, UV radiation induced modification of the Casimir force, low temperature measurement of the Casimir force, and Casimir force from thin fluctuating membranes.
Casimir Energy for a Purely Dielectric Cylinder by the Mode Summation Method
Romeo, A; Romeo, August; Milton, Kimball A.
2005-01-01
We use the mode summation method together with zeta-function regularization to compute the Casimir energy of a dilute dielectric cylinder. The method is very transparent, and sheds light on the reason the resulting energy vanishes.
Critical Casimir forces from the equation of state of quantum critical systems
Rançon, Adam; Henry, Louis-Paul; Rose, Félix; Cardozo, David Lopes; Dupuis, Nicolas; Holdsworth, Peter C. W.; Roscilde, Tommaso
2016-10-01
The mapping between a classical length and inverse temperature as imaginary time provides a direct equivalence between the Casimir force of a classical system in D dimensions and internal energy of a quantum system in d =D -1 dimensions. The scaling functions of the critical Casimir force of the classical system with periodic boundaries thus emerge from the analysis of the symmetry related quantum critical point. We show that both nonperturbative renormalization group and quantum Monte Carlo analysis of quantum critical points provide quantitative estimates for the critical Casimir force in the corresponding classical model, giving access to widely different aspect ratios for the geometry of confined systems. In light of these results, we propose protocols for the realization of critical Casimir forces for periodic boundaries through state-of-the-art cold-atom and solid-state experiments.
Casimir Effect Near the Future Singularity in Kaluza Klein Viscous Cosmology
Khadekar, G. S.
2016-02-01
In this paper we investigate the analytical properties of the scalar expansion θ in the cosmic fluid close to the future singularity, when the fluid possesses a constant bulk viscosity ζ in the framework of Kaluza-Klein theory of gravitation. In addition, we assume the viscous cosmology theories in the sense that the Casimir contributions to the energy density and pressure are both proportional to 1/ a 4, where a being scale factor. We also worked out the series expansion for the scalar expansion θ under the condition that the Casimir influence is small. However, near to the big rip singularity the Casimir term has to fade away and we obtain the same singularity behavior for the scalar expansion θ, energy density ρ, the scale factor a as in the Casimir-free viscous case.
Role of surface states in the Casimir force between semiconducting films
Govoni, Marco; Benassi, Andrea
2010-01-01
We present results of first principle calculations of the Casimir force between Si films of nanometric size, which show that it depends significantly upon the configuration of the surface atoms, and give evidence of the importance of surface states.
Sedighi, M.; Broer, W. H.; Palasantzas, G.; Kooi, B. J.
2013-10-01
Amorphous to crystalline phase transitions in phase change materials (PCM) can have strong influence on the actuation of microelectromechanical systems under the influence of Casimir forces. Indeed, the bifurcation curves of the stationary equilibrium points and the corresponding phase portraits of the actuation dynamics between gold and AIST (Ag5In5Sb60Te30) PCM, where an increase of the Casimir force of up ˜25% has been measured upon crystallization, show strong sensitivity to changes of the Casimir force as the stiffness of the actuating component decreases and/or the effective interaction area of the Casimir force increases, which can also lead to stiction. However, introduction of intrinsic energy dissipation (associated with a finite quality factor of the actuating system) can prevent stiction by driving the system to attenuated motion towards stable equilibrium depending on the PCM state and the system quality factor.
Scattering potentials with LS-terms from first-order Casimir operators
Energy Technology Data Exchange (ETDEWEB)
Levay, P. [Inst. of Phys., Tech. Univ. Budapest (Hungary)
1995-10-21
Using a first-order Casimir operator calculated in a non-standard realization for the so(3,1) algebra, we obtain a one-dimensional scattering problem with LS-type interaction terms. It is shown that for this realization the square of this operator can be expressed in terms of the usual quadratic Casimir. Due to this constraint the scattering states are completely specified by restricting the possible set of eigenvalues accordingly. The results show that the use of extra Casimir operators can provide additional insight into the group theoretical structure of the scattering problem. A generalization for the so(2n-1,1), n>2 case is also given. The underlying supersymmetry of the resulting Schrodinger equations is pointed out. The supersymmetric charge operators are related to our first-order Casimir operators. (author)
Energy Technology Data Exchange (ETDEWEB)
Teo, L P [Faculty of Information Technology, Multimedia University, Jalan Multimedia, Cyberjaya, 63100, Selangor Darul Ehsan (Malaysia)], E-mail: lpteo@mmu.edu.my
2009-03-13
In this paper, the finite-temperature Casimir force acting on a two-dimensional Casimir piston due to an electromagnetic field is computed. It was found that if mixed boundary conditions are assumed on the piston and its opposite wall, then the Casimir force always tends to restore the piston toward the equilibrium position, regardless of the boundary conditions assumed on the walls transverse to the piston. In contrast, if pure boundary conditions are assumed on the piston and the opposite wall, then the Casimir force always tends to pull the piston toward the closer wall and away from the equilibrium position. The nature of the force is not affected by temperature. However, in the high-temperature regime, the magnitude of the Casimir force grows linearly with respect to temperature. This shows that the Casimir effect has a classical limit as has been observed in other literature.
An experimental apparatus for measuring the Casimir effect at large distances
Energy Technology Data Exchange (ETDEWEB)
Antonini, P; Carugno, G; Messineo, G [INFN sez di Padova, via Marzolo 8, 35131 Padova (Italy); Bimonte, G [Dipartimento di Scienze Fisiche Universita di Napoli Federico II Complesso Universitario MSA, Via Cintia, 80126 Napoli, Italy and INFN, Sezione di Napoli, Napoli (Italy); Bressi, G [INFN sez. di Pavia, via Bassi 6, 27100 Pavia (Italy); Galeazzi, G [Dipartimento di Fisica, Universita di Padova, via Marzolo 8, 35131 Padova (Italy); Ruoso, G, E-mail: Giuseppe.Ruoso@lnl.infn.i [INFN Lab. Naz. Legnaro, viale dell' Universita 2, 35020 Legnaro (Italy)
2009-04-01
An experimental set-up for the measurement of the Casimir effect at separations larger than a few microns is presented. The apparatus is based on a mechanical resonator and uses a homodyne detection technique to sense the Casimir force in the plane-parallel configuration. First measurements in the 3-10 micrometer range show an unexpected large force probably due to patch effects.
Demonstration of the difference Casimir force for samples with different charge carrier densities
Chen, F; Mohideen, U; Mostepanenko, V M
2006-01-01
A measurement of the Casimir force between a gold coated sphere and two Si plates of different carrier densities is performed using a high vacuum based atomic force microscope. The results are compared with the Lifshitz theory and good agreement is found. Our experiment demonstrates that by changing the carrier density of the semiconductor plate by several orders of magnitude it is possible to modify the Casimir interaction. This result may find applications in nanotechnology.
Investigation of the Casimir force between metal and semiconductor test bodies
Chen, F; Klimchitskaya, G L; Mostepanenko, V M
2005-01-01
The measurement of the Casimir force between a large gold coated sphere and single crystal silicon plate is performed with an atomic force microscope. A rigorous statistical comparison of data with theory is done, without use of the concept of root-mean-square deviation, and excellent agreement is obtained. The Casimir force between metal and semiconductor is demonstrated to be significantly different than between two similar or dissimilar metals.
Spectral representation of the Casimir Force Between a Sphere and a Substrate
Román-Velázquez, C E; Villarreal, C; Esquivel-Sirvent, R; Noguez, Cecilia
2003-01-01
We calculate the Casimir force in the non-retarded limit between a spherical nanoparticle and a substrate, and we found that high-multipolar contributions are very important when the sphere is very close to the substrate. We show that the highly inhomegenous electromagnetic field induced by the presence of the substrate, can enhance the Casimir force by orders of magnitude, compared with the classical dipolar approximation.
Casimir effects for classical and quantum liquids in slab geometry: A brief review
Energy Technology Data Exchange (ETDEWEB)
Biswas, Shyamal, E-mail: sbsp@uohyd.ac.in [School of Physics, University of Hyderabad, C.R. Rao Road, Gachibowli, Hyderabad-500046 (India)
2015-05-15
We analytically explore Casimir effects for confinement of classical and quantum fluctuations in slab (film) geometry (i) for classical (critical) fluctuations over {sup 4}He liquid around the λ point, and (ii) for quantum (phonon) fluctuations of Bogoliubov excitations over an interacting Bose-Einstein condensate. We also briefly review Casimir effects for confinement of quantum vacuum fluctuations confined to two plates of different geometries.
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Bruna Rodrigues Weber
2012-01-01
Full Text Available A resistência bacteriana se constitui em preocupação mundial e a prescrição inadequada de antimicrobianos é um dos fatores que pode influenciar nas suas taxas. O objetivo foi avaliar as prescrições contendo antimicrobianos dispensados em uma farmácia comunitária do município de Ijuí/RS, para identificar os antimicrobianos e osfármacos prescritos em associação, bem como interações medicamentosas potenciais. Métodos: A amostra foi constituída por prescrições retidas no local do estudo, de 28 de novembro de 2010 a 31 de março de 2011, que continham ao menos um antimicrobiano listado no Anexo I da RDC 44/2010. Resultados: Foram analisadas 268 prescrições, contendo 283 antimicrobianos, em 15 prescrições foram prescritos dois produtos. A classe das penicilinas, presente em 30,04% das prescrições, e as quinolonas (23,67% foram os mais prescritos. Em 45,9% das prescrições, pelo menos mais um medicamento foi associado aoantimicrobiano, totalizando 167 medicamentos, sendo principalmente a classe dos analgésicos e antipiréticos (43,11% e dos antiinflamatórios e antirreumáticos não-esteróides (29,94%. Os antiinflamatórios e antirreumáticos não-esteróides estavampresentes em 82,05% das 39 interações medicamentosas potenciais encontradas, sendo que a principal classe de antimicrobianosenvolvida foi a das penicilinas (64,1%. Conclusão: é necessário que os profissionais responsáveis pela prescrição e pela dispensação estejam capacitados para identificar e evitar a presença de interações medicamentosas, proporcionando mais segurança para o usuário e efetividade no tratamento. Entende-se que seja necessário rever e padronizar os critérios de prescrição, dispensação e administração, a fim de racionalizar o uso dos antimicrobianos.
Repulsive and Restoring Casimir Forces Based on Magneto-Optical Effect
Institute of Scientific and Technical Information of China (English)
ZENG Ran; YANG Ya-Ping
2011-01-01
The Casimir force direction tuned by the external magnetic field due to the magneto-optical Voigt effect is investigated. The magneto-optical effect gives rise to the modified frequency-dependent electric permittivity and thus the electromagnetic properties of the materials can be adjusted to satisfy the condition of the formation of repulsive Casimir force. It is found that between the ordinary dielectric slab and magneto-optical material slab, a repulsive force may exist by adjusting the applied magnetic field. The restoring Casimir force can also be obtained if suitable parameter values are taken. For realistic materials, the repulsive and the restoring force is shown to possibly take place at typical distances in microelectromechanical systems.%@@ The Casimir force direction tuned by the external magnetic field due to the magneto-optical Voigt effect is investigated.The magneto-optical effect gives rise to the modified frequency-dependent electric permittivity and thus the electromagnetic properties of the materials can be adjusted to satisfy the condition of the formation of repulsive Casimir force.It is found that between the ordinary dielectric slab and magneto-optical material slab,a repulsive force may exist by adjusting the applied magnetic field.The restoring Casimir force can also be obtained if suitable parameter values are taken.For realistic materials,the repulsive and the restoring force is shown to possibly take place at typical distances in microelectromechanical systems.
Casimir Function on Leibniz Manifolds%Leibniz流形上Casimir函数
Institute of Scientific and Technical Information of China (English)
曾辉; 张福娥
2012-01-01
The effects of diffeomorphism and Leibniz mapping on Casimir function of Leibniz manifolds are investigated,which finds the following conclusions：（1） Casimir function C（x） on Leibniz manifolds（M,M）,can be induced by diffeomorphism φ∶M→N to a Casimir function（φ-1）＊C on N;（2） with invertible Leibniz mapping Ψ∶M→N,the linear combination of No＇s Casimir functions ∑s i=1λiCion N,can be pulled back into a Casimir function on M.Finally,several formulas concerning Leibniz vector field and Casimir function are presented.%通过研究微分同胚及Leibniz映射对Leibniz流形上Casimir函数的作用,得出了：（1）Leibniz流形（M,[.,.]M）上的Casimir函数C（x）,可以由微分同胚φ：M→N诱导为N上的Casimir函数（φ-1）＊C;（2）可逆的Leibniz映射ψ：M→N,可以把N上的Casimir函数的线性组合sum （λiCi） from i=1 to s拉回为M上的Casimir函数.最后给出了Leibniz向量场和Casimir函数间的几个公式.
Nernst heat theorem for the thermal Casimir interaction between two graphene sheets
Bezerra, V. B.; Klimchitskaya, G. L.; Mostepanenko, V. M.; Romero, C.
2016-10-01
We find analytic asymptotic expressions at low temperature for the Casimir free energy, entropy, and pressure of two parallel graphene sheets in the framework of the Lifshitz theory. The reflection coefficients of electromagnetic waves on graphene are described on the basis of first principles of quantum electrodynamics at nonzero temperature using the polarization tensor in (2+1)-dimensional space-time. The leading contributions to the Casimir entropy and to the thermal corrections to the Casimir energy and pressure are given by the thermal correction to the polarization tensor at nonzero Matsubara frequencies. It is shown that the Casimir entropy for two graphene sheets goes to zero when the temperature vanishes, i.e., the third law of thermodynamics (the Nernst heat theorem) is satisfied. At low temperature, the magnitude of the thermal correction to the Casimir pressure between two graphene sheets is shown to vary inversely proportional to the separation. The Nernst heat theorem for graphene is discussed in the context of problems occurring in Casimir physics for both metallic and dielectric plates.
Mackrory, Jonathan B.; Bhattacharya, Tanmoy; Steck, Daniel A.
2016-10-01
We present a worldline method for the calculation of Casimir energies for scalar fields coupled to magnetodielectric media. The scalar model we consider may be applied in arbitrary geometries, and it corresponds exactly to one polarization of the electromagnetic field in planar layered media. Starting from the field theory for electromagnetism, we work with the two decoupled polarizations in planar media and develop worldline path integrals, which represent the two polarizations separately, for computing both Casimir and Casimir-Polder potentials. We then show analytically that the path integrals for the transverse-electric polarization coupled to a dielectric medium converge to the proper solutions in certain special cases, including the Casimir-Polder potential of an atom near a planar interface, and the Casimir energy due to two planar interfaces. We also evaluate the path integrals numerically via Monte Carlo path-averaging for these cases, studying the convergence and performance of the resulting computational techniques. While these scalar methods are only exact in particular geometries, they may serve as an approximation for Casimir energies for the vector electromagnetic field in other geometries.
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MÁRCIA WADDINGTON CRUZ
1998-12-01
Full Text Available Tivemos como objetivo investigar por eletroneuromiografia (ENMG e potenciais evocados somatossensitivos a possibilidade de acometimento do nervo periférico na mielopatia pelo HTLV-I (HAM, correlacionando os achados com os parâmetos clínicos e com a síntese intratecal de anticorpos anti HTLV-I. Os pacientes tinham sorologia negativa para HIV e apresentaram VDRL negativo. Outras causas para mielopatia ou neuropatia periférica foram excluídas. De 32 pacientes que realizaram ENMG, em 34,3% ela foi considerada sugestiva de neuropatia periférica. Esta foi sobretudo assimétrica (82%, sensitivo-motora (90%,com padrão axonal (54,5% ou misto (45,4%. Em 63,6% dos casos de neuropatia periférica, havia sintomas correlatos. O potencial evocado auditivo foi anormal em apenas um caso. O potencial evocado visual foi anormal em 28,5% dos casos. Não havia sinais ou sintomas auditivos ou visuais. Em 85,5% dos casos obteve-se potencial evocado sensitivo alterado. Desses, 50% tinham manifestação clínica compatível. Em 28% dos pacientes com potencial evocado sensitivo anormal houve concomitância de ENMG sugestiva de neuropatia periférica.The objective of the present study was to correlate electroneuromyography (ENMG and evoked potentials findings with clinical aspects and intrathecal synthesis of HTLV-I antibodies production on HTLV-I myelopathy (HAM. Patients were seropositive for HTLV-I by different assays and seronegative for HIV and VDRL. They had no other causes of myelopathy and peripheral neuropathy. Peripheral neuropathy was stablished in 34.3% of the cases by ENMG. Peripheral neuropathy was mostly asymmetric (82%, sensory motor (90%, axonal (54,5% or of a mixed type (45,4%. In 63.6% of these cases related symptoms were observed. ABR was abnormal in one patient and the PRVEP in 28.5% ,who were symptom-free. The SEP was abnormal in 85.7% of the cases, half of them presenting clinical complaints. In only 14% of the individuals with clinical
The Casimir effect in light-front quantization
Hiller, J R
2014-01-01
We show that the standard result for the Casimir force between conducting plates at rest in an inertial frame can be computed in light-front quantization. This is not the same as light-front analyses where the plates are at "rest" in an infinite momentum frame. In that case, Lenz and Steinbacher have shown that the result does not agree with the standard result for plates at rest. The two important ingredients in the present analysis are a careful treatment of the boundary conditions, inspired by the work of Almeida et al. on oblique light-front coordinates, and computation of the ordinary energy density, rather than the light-front energy density.
Sympathetic laser cooling of graphene with Casimir-Polder forces
Ribeiro, Sofia; Terças, Hugo
2016-10-01
We propose a scheme to actively cool the fundamental flexural (out-of-plane) mode of a graphene sheet via vacuum forces. Our setup consists of a cold-atom cloud placed close to a graphene sheet at distances of a few micrometers. The atoms couple to the graphene membrane via Casimir-Polder forces. By deriving a self-consistent set of equations governing the dynamics of the atomic gas and the flexural modes of the graphene, we show it is possible to cool graphene from room temperatures by actively (laser) cooling an atomic gas. By choosing the right set of experimental parameters we are able to cool a graphene sheet down to ˜60 μ K .
Exact Casimir Interaction Between Semitransparent Spheres and Cylinders
Milton, Kimball A
2007-01-01
A multiple scattering formulation is used to calculate the force, arising from fluctuating scalar fields, between distinct bodies described by $\\delta$-function potentials, so-called semitransparent bodies. (In the limit of strong coupling, a semitransparent boundary becomes a Dirichlet one.) We obtain expressions for the Casimir energies between disjoint parallel semitransparent cylinders and between disjoint semitransparent spheres. In the limit of weak coupling, we derive power series expansions for the energy, which can be exactly summed, so that explicit, very simple, closed-form expressions are obtained in both cases. The proximity force theorem holds when the objects are almost touching, but is subject to large corrections as the bodies are moved further apart.
Casimir effect at nonzero temperature for wedges and cylinders
Ellingsen, Simen Å; Milton, Kimball A
2010-01-01
We consider the Casimir-Helmholtz free energy at nonzero temperature $T$ for a circular cylinder and perfectly conducting wedge closed by a cylindrical arc, either perfectly conducting or isorefractive. The energy expression at nonzero temperature may be regularized to obtain a finite value, except for a singular corner term in the case of the wedge which is present also at zero temperature. Assuming the medium in the interior of the cylinder or wedge be nondispersive with refractive index $n$, the temperature dependence enters only through the non-dimensional parameter $2\\pi naT$, $a$ being the radius of the cylinder or cylindrical arc. We show explicitly that the known zero temperature result is regained in the limit $aT\\to 0$ and that previously derived high temperature asymptotics for the cylindrical shell are reproduced exactly.
Electrodynamic Casimir effect in a medium-filled wedge.
Brevik, Iver; Ellingsen, Simen A; Milton, Kimball A
2009-04-01
We re-examine the electrodynamic Casimir effect in a wedge defined by two perfect conductors making dihedral angle alpha=pi/p. This system is analogous to the system defined by a cosmic string. We consider the wedge region as filled with an azimuthally symmetric material, with permittivity and permeability epsilon1, micro1 for distance from the axis ra. The results are closely related to those for a circular-cylindrical geometry, but with noninteger azimuthal quantum number mp. Apart from a zero-mode divergence, which may be removed by choosing periodic boundary conditions on the wedge, and may be made finite if dispersion is included, we obtain finite results for the free energy corresponding to changes in a for the case when the speed of light is the same inside and outside the radius a , and for weak coupling, |epsilon1-epsilon2|cosmic string, situated along the cusp line of the pre-existing wedge.
Microstructure effects for Casimir forces in chiral metamaterials
McCauley, Alexander P.; Zhao, Rongkuo; Reid, M. T. Homer; Rodriguez, Alejandro W.; Zhou, Jiangfeng; Rosa, F. S. S.; Joannopoulos, John D.; Dalvit, D. A. R.; Soukoulis, Costas M.; Johnson, Steven G.
2010-10-01
We examine a recent prediction for the chirality dependence of the Casimir force in chiral metamaterials by numerical computation of the forces between the exact microstructures, rather than homogeneous approximations. Although repulsion in the metamaterial regime is rigorously impossible, it is unknown whether a reduction in the attractive force can be achieved through suitable material engineering. We compute the exact force for a chiral bent-cross pattern, as well as forces for an idealized “omega”-particle medium in the dilute approximation and identify the effects of structural inhomogeneity (i.e., proximity forces and anisotropy). We find that these microstructure effects dominate the force for separations where chirality was predicted to have a strong influence. At separations where the homogeneous approximation is valid, in even the most ideal circumstances the effects of chirality are less than 10-4 of the total force, making them virtually undetectable in experiments.
Microstructure Effects for Casimir Forces in Chiral Metamaterials
McCauley, Alexander P; Reid, M T Homer; Rodriguez, Alejandro W; Zhou, Jiangfeng; Rosa, F S S; Joannopoulos, John D; Dalvit, D A R; Soukoulis, Costas M; Johnson, Steven G
2010-01-01
We examine a recent prediction for the chirality-dependence of the Casimir force in chiral metamaterials by numerical computation of the forces between the exact microstructures, rather than homogeneous approximations. We compute the exact force for a chiral bent-cross pattern, as well as forces for an idealized "omega"-particle medium in the dilute approximation and identify the effects of structural inhomogeneity (i.e. proximity forces and anisotropy). We find that these microstructure effects dominate the force for separations where chirality was predicted to have a strong influence. To get observations of chirality free from microstructure effects, one must go to large separations where the effect of chirality is at most $\\sim10^{-4}$ of the total force.
On the Temperature Dependence of the Casimir Effect
Brevik, I; Høye, J S; Milton, K A
2004-01-01
The temperature dependence of the Casimir force between a real metallic plate and a metallic sphere is analyzed on the basis of optical data concerning the dispersion relation of metals such as gold and copper. Realistic permittivities imply, in accordance with basic thermodynamic considerations, that the transverse electric zero mode does not contribute. This results in observable differences with the conventional prediction, which does not take this physical requirement into account. The results are shown to be consistent with the third law of thermodynamics, as well as with current experiments. However, the predicted temperature dependence should be detectable in future experiments. The inadequacies of approaches based on {\\it ad hoc} assumptions, such as the plasma dispersion relation and the use of surface impedance without transverse momentum dependence, are discussed.
Zeta-function approach to Casimir energy with singular potentials
Khusnutdinov, N R
2006-01-01
In the framework of zeta-function approach the Casimir energy for three simple model system: single delta potential, step function potential and three delta potentials is analyzed. It is shown that the energy contains contributions which are peculiar to the potentials. It is suggested to renormalize the energy using the condition that the energy of infinitely separated potentials is zero which corresponds to subtraction all terms of asymptotic expansion of zeta-function. The energy obtained in this way obeys all physically reasonable conditions. It is finite in the Dirichlet limit and it may be attractive or repulsive depending on the strength of potential. The effective action is calculated and it is shown that the surface contribution appears. The renormalization of the effective action is discussed.
Strongly Interacting Fermions and Phases of the Casimir Effect
Flachi, Antonino
2013-01-01
With the intent of exploring how the interplay between boundary effects and chiral symmetry breaking may alter the thermodynamical behavior of a system of strongly interacting fermions, we study the Casimir effect for the set-up of two parallel layers using a four-fermion effective field theory at zero density. This system reveals a number of interesting features. While for infinitely large separation (no boundaries), chiral symmetry is broken/restored via a second order phase transition, in the opposite case of small (and, in general, finite) separation the transition becomes first order, rendering effects of finite size, for the present set-up, similar to those of a chemical potential. Appropriately moving on the separation--temperature plane, it is possible to generate a peculiar behavior in the temperature dependence of the thermodynamic potential and of the condensate, compensating thermal with geometrical variations. A behavior similar to what we find here has been predicted to occur in bilayer graphene...
Observation of the Dynamical Casimir Effect in a Superconducting Circuit
Wilson, C M; Pourkabirian, A; Johansson, J R; Duty, T; Nori, F; Delsing, P
2011-01-01
One of the most surprising predictions of modern quantum theory is that the vacuum of space is not empty. In fact, quantum theory predicts that it teems with virtual particles flitting in and out of existence. While initially a curiosity, it was quickly realized that these vacuum fluctuations had measurable consequences, for instance producing the Lamb shift of atomic spectra and modifying the magnetic moment for the electron. This type of renormalization due to vacuum fluctuations is now central to our understanding of nature. However, these effects provide indirect evidence for the existence of vacuum fluctuations. From early on, it was discussed if it might instead be possible to more directly observe the virtual particles that compose the quantum vacuum. 40 years ago, Moore suggested that a mirror undergoing relativistic motion could convert virtual photons into directly observable real photons. This effect was later named the dynamical Casimir effect (DCE). Using a superconducting circuit, we have observ...
Bubble-wall Casimir interaction in fermionic environments
Flachi, Antonino
2015-01-01
We consider the Casimir interaction, mediated by massless fermions, between a spherical defect and a flat potential barrier, assuming hard (bag-type) boundary conditions at both the barrier and the surface of the sphere. The computation of the quantum interaction energy is carried out using the multiple scattering approach, adapted here to the setup in question. We find an exact integral formula for the energy, from which we extract both the large and short distance asymptotic behaviour. At large distance the fermionic contribution is found to scale as $L^{-3}$, in contrast to that of electromagnetic vacuum fluctuations that, assuming perfectly conducting boundaries, scales as $L^{-4}$. At short distance, we compute the leading and sub-leading contribution to the vacuum energy. The leading one coincides with what it is expected from the proximity force approximation, while the sub-leading term gives, contrary to the electromagnetic case, a positive correction to the proximity force result.
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Gabriela Ribeiro Ivo Rodrigues
2010-02-01
Full Text Available Os Potenciais Evocados Auditivos de Estado Estável (PEAEE têm sido apontados como uma técnica promissora na avaliação audiológica infantil. OBJETIVO: Investigar o nível de concordância entre os resultados dos PEAEE e dos Potenciais Evocados Auditivos de Tronco Encefálico (PEATE-clique em um grupo de crianças com perda auditiva sensorioneural, averiguando assim a aplicabilidade clínica desta técnica na avaliação audiológica infantil. FORMA DE ESTUDO: Clínico prospectivo de coorte transversal. MATERIAL E MÉTODO: 15 crianças com idade entre dois e 36 meses e diagnóstico de perda auditiva sensorioneural. A concordância entre as respostas dos dois testes foi avaliada por meio do coeficiente de correlação intraclasse e o teste de McNemar comparou os dois testes quanto à probabilidade de ocorrência de resposta. RESULTADOS: Os coeficientes de correlação encontrados foram 0,70; 0,64; 0,49; 0,69; 0,63 e 0,68 respectivamente para as frequências de 1, 2, 4, 1-2, 2-4 e 1-2-4kHz. No teste de McNemar foi obtido p=0.000, indicando que a probabilidade de se obter resposta presente nos dois testes não é igual, sendo maior nos PEAEE. CONCLUSÃO: A boa concordância observada entre as técnicas sugere que um exame pode ser complementar ao outro. Os PEAEE, entretanto, promoveram informações adicionais nos casos de perdas severas e profundas, acrescentando dados importantes para a reabilitação destas crianças e proporcionando maior precisão no diagnóstico audiológico.Auditory Steady-State Responses (ASSR are being recognized as a promising technique in the assessment of hearing in children. AIM: To investigate the agreement level between results obtained from ASSR and click-ABR in a group of children with sensorineural hearing loss, in order to study the clinical applicability of this technique to evaluate the hearing status in young children. STUDY DESIGN: clinical prospective with a cross-sectional cohort. MATERIALS AND METHODS
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Fernanda Ludmilla Rossi Rocha
2004-06-01
Full Text Available Constituíram objetivos deste estudo: identificar as informações que os trabalhadores de enfermagem possuem sobre os riscos a que estão expostos quando da manipulação de antineoplásicos, identificar quais as precauções de segurança utilizadas. Trata-se de pesquisa descritiva, com análise quantitativa dos dados, realizada num hospital privado do Estado de São Paulo. A amostra foi constituída por 30 trabalhadores de enfermagem. Utilizou-se um questionário e observação das práticas de trabalho para coleta dos dados. Os resultados revelaram que a maioria dos trabalhadores consideram que a manipulação de quimioterápicos antineoplásicos oferece riscos à sua saúde, não sendo capazes, porém, de identificar claramente esses riscos.Fueron objetivos de este estudio: identificar las informaciones que los trabajadores de enfermería tienen sobre los riesgos a que están expuestos cuando manipulan antineoplásicos; identificar las precauciones de seguridad utilizadas por los trabajadores de enfermería. Se trata de una investigación descriptiva con análisis cuantitativo de los datos, realizada en un hospital privado del interior del estado de São Paulo. La muestra fue constituida por 30 trabajadores de enfermería. Se utilizó un cuestionario y observación de las prácticas de trabajo para recopilar los datos. Los resultados revelaron que la mayoría de los trabajadores consideran que la manipulación de quimioterápicos antineoplásicos ofrece riesgos a su salud, no siendo capaces, todavía, de identificar claramente estos riesgos.This research aimed to identify which information nursing workers have on the risks they are exposed to when handling cytotoxic drugs and which security precautions are used. This is a descriptive research with quantitative data analysis, carried out at a private hospital in Sao Paulo State, Brazil. The sample consisted of 30 nursing workers. A questionnaire and work practice observation were used for
Casimir-Foucault interaction: Free energy and entropy at low temperature
Intravaia, Francesco; Ellingsen, Simen Å.; Henkel, Carsten
2010-09-01
It was recently found that thermodynamic anomalies which arise in the Casimir effect between metals described by the Drude model can be attributed to the interaction of fluctuating Foucault (or eddy) currents [F. Intravaia and C. Henkel, Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.103.130405 103, 130405 (2009).] We focus on the transverse electric (TE) polarization, where the anomalies occur, and show explicitly that the two leading terms of the low-temperature correction to the Casimir free energy of interaction between two plates are identical to those pertaining to the Foucault current interaction alone, up to a correction which is very small for good metals. Moreover, a mode density along real frequencies is introduced, showing that the TE contribution to the Casimir free energy, as given by the Lifshitz theory, separates in a natural manner into contributions from eddy currents and propagating cavity modes, respectively. The latter have long been known to be of little importance to the low-temperature Casimir anomalies. This convincingly demonstrates that eddy current modes are responsible for the large temperature correction to the Casimir effect between Drude metals, predicted by the Lifshitz theory, but not observed in experiments.
Characteristic properties of the Casimir free energy for metal films deposited on metallic plates
Klimchitskaya, G. L.; Mostepanenko, V. M.
2016-04-01
The Casimir free energy and pressure of thin metal films deposited on metallic plates are considered using the Lifshitz theory and the Drude and plasma model approaches to the role of conduction electrons. The bound electrons are taken into account by using the complete optical data of film and plate metals. It is shown that for films of several tens of nanometers thickness the Casimir free energy and pressure calculated using these approaches differ by hundreds and thousands percent and can be easily discriminated experimentally. According to our results, the free energy of a metal film does not vanish in the limiting case of ideal metal if the Drude model approach is used in contradiction with the fact that the fluctuating field cannot penetrate in its interior. Numerical computations of the Casimir free energy and pressure of Ag and Au films deposited on Cu and Al plates have been performed using both theoretical approaches. It is shown that the free energy of a film can be both negative and positive depending on the metals used. For a Au film on a Ag plate and vice versa the Casimir energy of a film changes its sign with increasing film thickness. Applications of the obtained results for resolving the Casimir puzzle and the problem of stability of thin films are discussed.
Casimir force on a piston at finite temperature in Randall-Sundrum models
Institute of Scientific and Technical Information of China (English)
CHENG Hong-Bo
2011-01-01
The Casimir effect for a three-parallel-plate system at finite temperature within the framework of five-dimensional Randall-Sundrum models is studied.In the case of the Randall-Sundrum model involving two branes we find that the Casimir force depends on the plate distance and temperature after one outer plate has been moved to a distant place.Further we discover that the sign of the reduced force is negative if the plate and piston are located close together,but the nature of reduced force becomes repulsive when the plate distance is not very small and finally the repulsive force vanishes with extremely large plate separation.A higher temperature causes a greater repulsive Casimir force.Within the framework of a one-brane scenario the reduced Casimir force between the piston and one plate remains attractive no matter how high the temperature is.It is interesting that a stronger thermal effect leads to a greater attractive Casimir force instead of changing the nature of the force.
Energy Technology Data Exchange (ETDEWEB)
Grueneberg, Daniel
2008-02-15
To study how the behavior of the thermodynamic Casimir force changes qualitatively and quantitatively due to the presence of such interactions - compared to systems with purely short-range interactions - is the aim of this work. Considering d-dimensional models belonging to the universality class of the O(n)-symmetrical systems, the thermodynamic Casimir force and its leading corrections are derived for temperatures at and above the transition temperature (T{>=}T{sub c,{infinity}}). The underlying pair potential is assumed to be isotropic and long-ranged, decaying asymptotically proportional to x{sup -(d+{sigma}}{sup )} for large separations x, where the value of the parameter {sigma} is restricted to the interval 2<{sigma}<4. By solving an appropriate spherical model in 2
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Gabriela Ribeiro Ivo Rodrigues
2009-01-01
Full Text Available Preconiza-se o diagnóstico até os três meses de idade em crianças com deficiência auditiva congênita. Após a etapa inicial de confirmação do diagnóstico, é necessário que se obtenha limiares precisos nas diferentes frequências, para que seja possível uma adequada seleção, indicação e regulagem de aparelhos de amplificação sonora. Nesse contexto, inserem-se os Potenciais Evocados Auditivos de Tronco Encefálico por Frequência Específica (PEATE-FE e, mais recentemente, os Potenciais Evocados Auditivos de Estado Estável (PEAEE. O objetivo deste estudo de caso foi apresentar os achados das duas técnicas para estimar os limiares auditivos em uma criança de três meses de idade, com perda auditiva neurossensorial bilateral, diagnosticada utilizando-se como primeiro método de avaliação os Potenciais Evocados Auditivos de Tronco Encefálico com estímulo clique, tanto por via aérea como por via óssea. As duas técnicas mostraram-se eficientes para estimar os limiares auditivos, com uma vantagem dos PEAEE com relação ao tempo de duração de exame.It is recommended that congenital hearing loss is identified as early as three months old. After the initial step of confirming the diagnosis, it is necessary to obtain accurate hearing thresholds, allowing an adequate selection, indication and regulation of hearing aids for these children. It is inserted, in this context, the Frequency-Specific Auditory Brainstem Responses (FSABR and, more recently, the Auditory Steady-State Responses (ASSR. The aim of the present study was to describe the findings of the use of both techniques to estimate the auditory thresholds of a three-month-old infant with bilateral sensorineural hearing loss diagnosed using, as primary evaluation method, the click-evoked Auditory Brainstem Responses, with both air and bone stimuli conduction. Both techniques provided reliable findings for estimating auditory thresholds. The ASSR had an advantage regarding
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Fabíola Bagatini
2011-02-01
Full Text Available INTRODUÇÃO: O termo polifarmácia, ou seja, a utilização concomitante de múltiplos fármacos pelo mesmo indivíduo vem sendo amplamente associado a pacientes institucionalizados e idosos, no entanto pode ocorrer em grupos de pacientes portadores de doenças crônicas como artrite reumatoide (AR. OBJETIVO: Quantificar a polifarmácia em um grupo de pacientes com AR e realizar um levantamento sobre o risco de potenciais interações indesejáveis entre os medicamentos utilizados no manejo dessa doença e os fármacos utilizados em enfermidades não crônicas. MÉTODOS: Realizou-se um estudo de coorte com 103 pacientes portadores de AR, atendidos no Componente Especializado da Assistência Farmacêutica/MS, Florianópolis/SC. Os pacientes foram acompanhados mensalmente, por meio de fichas. As interações medicamentosas foram identificadas pelo Drugdex System - Thomson Micromedex® - Interactions. RESULTADOS: Observou-se a presença de polifarmácia em 95,1% dos pacientes e de 19 potenciais interações indesejáveis entre os medicamentos utilizados por 74 pacientes, em média 3,0 ± 1,2 interações/paciente. Todas as potenciais interações estavam relacionadas a metotrexato. Omeprazol foi o principal representante, correspondendo a 29,3% delas, seguido por diclofenaco sódico (17,6% e dipirona sódica (13,2%. CONCLUSÃO: Considerando que este estudo confirma que a polifarmácia é uma prática comum na terapêutica dos pacientes portadores de AR, deve haver maior vigilância acerca de efeitos adversos ou de redução da efetividade de determinados fármacos devido às suas interações farmacológicasINTRODUCTION: The term polypharmacy, meaning the concomitant use of multiple medications by one individual, has been widely reported in institutionalized or elderly patients. It can, however, occur in patients with chronic diseases, such as rheumatoid arthritis (RA. OBJECTIVE: To quantify polypharmacy in a group of RA patients and to assess the
Mode Summation Approach to Casimir Effect Between Two Objects
Teo, L. P.
2012-10-01
In the last few years, several approaches have been developed to compute the exact Casimir interaction energy between two nonplanar objects, all lead to the same functional form, which is called the TGTG formula. In this paper, we explore the TGTG formula from the perspective of mode summation approach. Both scalar fields and electromagnetic fields are considered. In this approach, one has to first solve the equation of motion to find a wave basis for each object. The two T's in the TGTG formula are T-matrices representing the Lippmann-Schwinger T-operators, one for each of the objects. Each T-matrix can be found by matching the boundary conditions imposed on the object, and it is independent of the other object. However, it depends on whether the object is interacting with an object outside it, or an object inside it. The two G's in the TGTG formula are the translation matrices, relating the wave basis of an object to the wave basis of the other object. These translation matrices only depend on the wave basis chosen for each object, and they are independent of the boundary conditions on the objects. After discussing the general theory, we apply the prescription to derive the explicit formulas for the Casimir energies for the sphere-sphere, sphere-plane, cylinder-cylinder and cylinder-plane interactions. First the T-matrices for a plane, a sphere and a cylinder are derived for the following cases: the object is imposed with Dirichlet, Neumann or general Robin boundary conditions; the object is semitransparent; and the object is a magnetodielectric object immersed in a magnetodielectric media. Then the operator approach developed by R. C. Wittman [IEEE Trans. Antennas Propag.36, 1078 (1988)] is used to derive the translation matrices. From these, the explicit TGTG formula for each of the scenarios can be written down. On the one hand, we have summarized all the TGTG formulas that have been derived so far for the sphere-sphere, cylinder-cylinder, sphere-plane and
Identificação de potenciais plantas hospedeiras alternativas de Xanthomonas campestris pv. Viticola.
2014-01-01
Este estudo teve como objetivo identificar possíveis hospedeiras alternativas de Xanthomonas campestris pv. viticola (Xcv), visando a fornecer subsídios para o manejo do cancro bacteriano da videira. Vinte e seis espécies vegetais foram inoculadas artificialmente com o isolado Xcv3 e mantidas em condições de casa de vegetação, sendo avaliada a evolução sintomatológica da doença, como manchas necróticas angulares e lesões nas nervuras. O Xcv3 foi reisolado a partir de cada hospedeiro alternati...
Non-contact gears: II. Casimir torque between concentric corrugated cylinders for the scalar case
Cavero-Pelaez, Ines; Parashar, Prachi; Shajesh, K V
2008-01-01
The Casimir interaction between two concentric corrugated cylinders provides the mechanism for non-contact gears. To this end, we calculate the Casimir torque between two such cylinders, described by $\\delta$-potentials, which interact through a scalar field. We derive analytic expressions for the Casimir torque for the case when the corrugation amplitudes are small in comparison to the corrugation wavelengths. We derive explicit results for the Dirichlet case, and exact results for the weak coupling limit, in the leading order. The results for the corrugated cylinders approach the corresponding expressions for the case of corrugated parallel plates in the limit of large radii of cylinders (relative to the difference in their radii) while keeping the corrugation wavelength fixed.
Inhomogeneity-related cutoff dependence of the Casimir energy and stress
Bao, F; Fang, M; He, S
2015-01-01
The cutoff dependence of the Casimir energy and stress is studied using the Green's function method for a system that is piecewise-smoothly inhomogeneous along one dimension. The asymptotic cylinder kernel expansions of the energy and stress are obtained, with some extra cutoff terms that are induced by the inhomogeneity. Introducing interfaces to the system one by one shows how those cutoff terms emerge and illuminates their physical interpretations. Based on that, we propose a subtraction scheme to address the problem of the remaining cutoff dependence in the Casimir stress in an inhomogeneous medium, and show that the nontouching Casimir force between two separated bodies is cutoff independent. The cancellation of the electric and magnetic contributions to the surface divergence near a perfectly conducting wall is found to be incomplete in the case of inhomogeneity.
Constraints on axion and corrections to Newtonian gravity from the Casimir effect
Klimchitskaya, G L
2015-01-01
Axion is a light pseudoscalar particle of much interest for physics of elementary particles and for astrophysics. We review the recently obtained constraints on axion to nucleon coupling constants following from different experiments on measuring the Casimir interaction. These constraints are compared with those following from other laboratory experiments within the wide range of masses of axion-like particles from 10^{-10} to 20 eV. We also collect the most strong constraints on the Yukawa-type and power-type corrections to the Newton law of gravitation which follow from measurements of the Casimir interaction, Eotvos- and Cavendish-type experiments. The possibility to obtain stronger constraints on an axion from the Casimir effect is proposed.
Modifying the Casimir force between indium tin oxide film and Au sphere
Banishev, A A; Castillo-Garza, R; Klimchitskaya, G L; Mostepanenko, V M; Mohideen, U; 10.1103/PhysRevB.85.045436
2012-01-01
We present complete results of the experiment on measuring the Casimir force between an Au-coated sphere and an untreated or, alternatively, UV-treated indium tin oxide film deposited on a quartz substrate. Measurements were performed using an atomic force microscope in a high vacuum chamber. The measurement system was calibrated electrostatically. Special analysis of the systematic deviations is performed, and respective corrections in the calibration parameters are introduced. The corrected parameters are free from anomalies discussed in the literature. The experimental data for the Casimir force from two measurement sets for both untreated and UV-treated samples are presented. The experimental errors are determined at a 95% confidence level. It is demonstrated that the UV treatment of an I TO plate results in a significant decrease in the magnitude of the Casimir force (from 21% to 35% depending on separation). However, ellipsometry measurements of the imaginary parts of dielectric permittivities of the un...
Geothermal Casimir phenomena for the sphere-plate and cylinder-plate configurations
Weber, Alexej
2010-01-01
We investigate the nontrivial interplay between geometry and temperature in the Casimir effect for the sphere-plate and cylinder-plate configurations. At low temperature, the thermal contribution to the Casimir force is dominated by this interplay, implying that standard approximation techniques such as the PFA are inapplicable even in the limit of small surface separation. Thermal fluctuations on scales of the thermal wavelength lead to a delocalization of the thermal force density at low temperatures. As a consequence, the temperature dependence strongly differs from naive expectations. Most prominently, thermal forces can develop non-monotonic behavior below a critical temperature. We perform a comprehensive study of such geothermal phenomena in these Casimir geometries, using analytical and numerical worldline techniques for Dirichlet scalar fluctuations.
Decca, R S; Fischbach, E; Klimchitskaya, G L; Krause, D E; Mostepanenko, V M
2007-01-01
We present supplementary information on the recent indirect measurement of the Casimir pressure between two parallel plates using a micromachined oscillator. The equivalent pressure between the plates is obtained by means of the proximity force approximation after measuring the force gradient between a gold coated sphere and a gold coated plate. The data are compared with a new theoretical approach to the thermal Casimir force based on the use of the Lifshitz formula, combined with a generalized plasma-like dielectric permittivity which takes into account interband transitions of core electrons. The theoretical Casimir pressures calculated using the new approach are compared with those computed in the framework of the previously used impedance approach and also with the Drude model approach. The latter is shown to be excluded by the data at a 99.9% confidence level within a wide separation range from 210 to 620 nm. The level of agreement between the data and theoretical approaches based on the generalized pla...
Measurement of the Casimir force with a ferrule-top sensor
Zuurbier, P; Gruca, G; Heeck, K; Iannuzzi, D
2011-01-01
We present a Casimir force setup based on an all-optical ferrule-top sensor. We demonstrate that the instrument can be used to measure the gradient of the Casimir force between a gold coated sphere and a gold coated plate with results that are comparable to those achieved by similar atomic force microscope experiments. Thanks to the monolithic design of the force sensor (which does not require any optical triangulation readout) and to the absence of electronics on the sensing head, the instrument represents a significant step ahead for future studies of the Casimir effect under engineered conditions, where the intervening medium or the environmental conditions might be unsuitable for the use of more standard setups.
Casimir Effect as a Test for Thermal Corrections and Hypothetical Long-Range Interactions
Klimchitskaya, G L; Fischbach, E; Krause, D E; López, D; Mostepanenko, V M
2005-01-01
We have performed a precise experimental determination of the Casimir pressure between two gold-coated parallel plates by means of a micromachined oscillator. In contrast to all previous experiments on the Casimir effect, where a small relative error (varying from 1% to 15%) was achieved only at the shortest separation, our smallest experimental error ($\\sim 0.5$%) is achieved over a wide separation range from 170 nm to 300 nm at 95% confidence. We have formulated a rigorous metrological procedure for the comparison of experiment and theory without resorting to the previously used root-mean-square deviation, which has been criticized in the literature. This enables us to discriminate among different competing theories of the thermal Casimir force, and to resolve a thermodynamic puzzle arising from the application of Lifshitz theory to real metals. Our results lead to a more rigorous approach for obtaining constraints on hypothetical long-range interactions predicted by extra-dimensional physics and other exte...
How to observe the giant thermal effect in the Casimir force for graphene systems
Bimonte, G.; Klimchitskaya, G. L.; Mostepanenko, V. M.
2017-07-01
A differential measurement scheme is proposed which allows for clear observation of the giant thermal effect for the Casimir force, which was recently predicted to occur in graphene systems at short separation distances. The difference among the Casimir forces acting between a metal-coated sphere and the two halves of a dielectric plate, one uncoated and the other coated with graphene, is calculated in the framework of the Dirac model using the rigorous formalism of the polarization tensor. It is shown that in the proposed configuration both the difference among the Casimir forces and its thermal contribution can be easily measured using existing experimental setups. An observation of the giant thermal effect should open opportunities for modulation and control of dispersion forces in micromechanical systems based on graphene and other novel two-dimensional (2D) materials.
Many-body effects in the van der Waals-Casimir interaction between graphene layers
Sarabadani, Jalal; Naji, Ali; Asgari, Reza; Podgornik, Rudolf
2011-10-01
Van der Waals-Casimir dispersion interactions between two apposed graphene layers, a graphene layer and a substrate, and in a multilamellar graphene system are analyzed within the framework of the Lifshitz theory. This formulation hinges on a known form of the dielectric response function of an undoped or doped graphene sheet, assumed to be of a random-phase-approximation form. In the geometry of two apposed layers, the separation dependence of the van der Waals-Casimir interaction for both types of graphene sheets is determined and critically compared with some well-known limiting cases. In a multilamellar array, the many-body effects are quantified and shown to increase the magnitude of the van der Waals-Casimir interactions.
On the Casimir energy for a 2N-piece relativistic string
Brevik, I
1997-01-01
The Casimir energy for the transverse oscillations of a piecewise uniform closed string is calculated. The string consists of 2N pieces of equal length, of alternating type I and type II material, and is taken to be relativistic in the sense that the velocity of sound always equals the velocity of light. By means of a new recursion formula we manage to calculate the Casimir energy for arbitrary integers N. Agreement with results obtained in earlier works on the string is found in all special cases. As basic regularization method we use the contour integration method. As a check, agreement is found with results obtained from the \\zeta function method (the Hurwitz function) in the case of low N (N = 1-4). The Casimir energy is generally negative, and the more so the larger is the value of N. We illustrate the results graphically in some cases. The generalization to finite temperature theory is also given.
L'effet Casimir : théorie et expériences
Lambrecht, A.; Genet, C.; Intravaia, F.; Reynaud, S.
2004-11-01
L'existence de fluctuations irréductibles de champ dans le vide est une prédiction importante de la théorie quantique. Ces fluctuations ont de nombreuses conséquences observables comme l'effet Casimir, qui est maintenant mesuré avec une bonne précision et un bon accord avec la théorie, pourvu que celle-ci tienne compte des différences entre les expériences rélles et la situation idéale considérée par H.G.B. Casimir. Nous présenterons quelqu'unes des expériences récentes et discuterons les principales corrections à la force de Casimir liées à la situation expérimentale.
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Verena Maria Mendes de Souza
2011-12-01
Full Text Available OBJETIVO: Estimar os custos associados à hospitalização e os anos potenciais de vida perdidos devido à leptospirose. MÉTODOS: Foram utilizados os bancos de dados de sistemas de informação em saúde do Ministério da Saúde para o relacionamento probabilístico dos casos e internações que evoluíram a óbito por leptospirose em 2007. No Sistema de Informação de Agravos de Notificação os casos confirmados foram subdivididos em internação e óbito, que foram relacionados às seguintes bases: Sistema de Informações Hospitalares (registros com diagnóstico principal e Sistema de Informações sobre Mortalidade (causa básica do óbito, A27.0, A27.8 e A27.9. Foram estimados os custos parciais de internação, os óbitos pela doença, os anos potenciais de vida e de trabalho perdidos. RESULTADOS: As características da maioria das internações que evoluíram para óbito eram: sexo masculino, entre 18 e 49 anos, raça branca, zona urbana e ensino fundamental incompleto. Foram 6.490 anos potenciais de vida perdidos, sendo 75% da faixa etária de 20 a 49 anos. Quando ajustada pela população, a perda foi de 15 dias de vida/1.000 habitantes. A proporção de anos potenciais de vida perdidos pelo número de óbitos foi em média de 30 anos perdidos para cada óbito. O impacto financeiro estimado foi equivalente a R$ 22,9 milhões em salários não ganhos. Os custos hospitalares foram de R$ 831,5 mil. Considerando os dias de salário perdidos por período de internação (mediana: 6 dias, houve perda de R$ 103,0 mil. CONCLUSÕES: Houve elevado custo social em termo de anos potenciais de vida perdidos e gasto hospitalar parcial com leptospirose quando comparado ao possível tratamento precoce ou não adoecimento, o que poderia ter minimizado o impacto dessa doença na população brasileira.OBJETIVO: Estimar los costos asociados a la hospitalización y los años potenciales de vida perdidos debido a la leptospirosis. MÉTODOS: Se utilizaron
PERFIL DE POTENCIAIS DOADORES DE ÓRGÃOS EM HOSPITAL DE REFERÊNCIA
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Thamy Braga Rodrigues
2013-01-01
Full Text Available El objetivo fue caracterizar el perfil de potenciales donadores de órganos en hospital de la zona norte del Ceará, Brasil. Estudio cuantitativo, retrospectivo, documental, realizado en hospital del Ceará, a partir de informaciones contenidas en registros médicos de donadores potenciales, de mayo a septiembre de 2009. Los datos fueron tabulados, centrándose en el proceso de identificación y logística. Los diagnósticos más prevalentes fueron traumatismo craneoencefálico (51,4% y accidentes cerebrovasculares (31,4% y 57,1% completaron el proceso en el tiempo adecuado para captación de los órganos. Se espera, por lo tanto, que la evaluación de la política y de los datos de donación contribuya al aumento de las tasas de donación, a favor del reconocimiento de las debilidades del proceso y aplicación de medidas para promover su éxito.
Desreguladores Endócrinos no Meio Ambiente e o Uso de Potenciais Bioindicadores
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Joyce de Araújo Schiavini
2015-07-01
Full Text Available Os disruptores endócrinos são substâncias que interferem no funcionamento natural do sistema endócrino de homens e animais, estes por sua vez podem ser utilizados como bioindicadores, já que interagem direta ou indiretamente com estas substâncias. O presente trabalho apresenta o estado da arte sobre os desreguladores endócrinos no meio ambiente e o uso potencial de bioindicadores na detecção destas substâncias. A partir dos dados levantados na literatura científica, verifica-se um crescimento no uso de desreguladores endócrinos ao longo do tempo e que os processos de tratamentos dos efluentes contaminados com estas substâncias são incipientes e pouco aplicáveis. Apesar da ampla utilização dos bioindicadores para detecção de substância xenobióticas verifica-se que pouco deles tem resposta direta e precisa dos disruptores endócrinos, permitindo estudos mais aprofundados para aperfeiçoar e selecionar espécies mais eficientes no processo de indicação de alterações de qualidade ambiental.
Light-front analysis of the Casimir effect
Chabysheva, Sophia S
2013-01-01
The Casimir force between conducting plates at rest in an inertial frame is usually computed in equal-time quantization, the natural choice for the given boundary conditions. We show that the well-known result obtained in this way can also be obtained in light-front quantization. This differs from a light-front analysis where the plates are at "rest" in an infinite momentum frame, rather than an inertial frame; in that case, as shown by Lenz and Steinbacher, the result does not agree with the standard result. As is usually done, the analysis is simplified by working with a scalar field and periodic boundary conditions, in place of the complexity of quantum electrodynamics. The two key ingredients are a careful implementation of the boundary conditions, following the work of Almeida et al. on oblique light-front coordinates, and computation of the ordinary energy density, rather than the light-front energy density. The analysis demonstrates that the physics of the effect is independent of the coordinate choice...
Determination of the Contact Angle Based on the Casimir Effect
Mazuruk, Konstantin; Volz, Martin P.
2015-01-01
On a macroscopic scale, a nonreactive liquid partially covering a homogeneous solid surface will intersect the solid at an angle called the contact angle. For molten metals and semiconductors, the contact angle is materially dependent upon both the solid and liquid and typical values fall in the range 80-170 deg, depending on the crucible material. On a microscopic scale, there does not exist a precise and sharp contact angle but rather the liquid and solid surfaces merge smoothly and continuously. Consider the example of the so called detached Bridgman crystal growth process. In this technique, a small gap is formed between the growing crystal and the crucible. At the crystal/melt interface, a meniscus ring is formed. Its width can be in the range of a few micrometers, approaching a microscopic scale. It then becomes questionable to describe the shape of this meniscus by the contact angle. A more advanced treatment of the interface is needed and here we propose such a refined model. The interaction of the liquid surface with the solid can be calculated by considering two forces: a short-range repulsive force and a longer range (up to a few micrometers) Casimir or van der Waals force.
A Toy Cosmology Using a Hubble-Scale Casimir Effect
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Michael E. McCulloch
2014-02-01
Full Text Available The visible mass of the observable universe agrees with that needed for a flat cosmos, and the reason for this is not known. It is shown that this can be explained by modelling the Hubble volume as a black hole that emits Hawking radiation inwards, disallowing wavelengths that do not fit exactly into the Hubble diameter, since partial waves would allow an inference of what lies outside the horizon. This model of “horizon wave censorship” is equivalent to a Hubble-scale Casimir effect. This incomplete toy model is presented to stimulate discussion. It predicts a minimum mass and acceleration for the observable universe which are in agreement with the observed mass and acceleration, and predicts that the observable universe gains mass as it expands and was hotter in the past. It also predicts a suppression of variation on the largest cosmic scales that agrees with the low-l cosmic microwave background anomaly seen by the Planck satellite.
Repulsive Casimir forces with finite-thickness slabs
Zhao, R.; Koschny, Th.; Economou, E. N.; Soukoulis, C. M.
2011-02-01
We use the extended Lifshitz theory to study the behaviors of the Casimir forces between finite-thickness effective medium slabs. We first study the interaction between a semi-infinite Drude metal and a finite-thickness magnetic slab with or without substrate. For no substrate, the large distance d dependence of the force is repulsive and goes as 1/d5; for the Drude metal substrate, a stable equilibrium point appears at an intermediate distance that can be tuned by the thickness of the slab. We then study the interaction between two identical chiral metamaterial slabs, with and without substrate. For no substrate, the finite thickness of the slabs D does not significantly influence the repulsive character of the force at short distances, while the attractive character at large distances becomes weaker and behaves as 1/d6; for the Drude metal substrate, the finite thickness of the slabs D does not influence the repulsive force too much at short distances until D=0.05λ0.
Electromagnetic Casimir effect for conducting plates in de Sitter spacetime
Kotanjyan, A S; Nersisyan, H A
2015-01-01
Two-point functions, the mean field squared and the vacuum expectation value (VEV) of the energy-momentum tensor are investigated for the electromagnetic field in the geometry of parallel plates on background of $(D+1)$% -dimensional dS spacetime. We assume that the field is prepared in the Bunch-Davies vacuum state and on the plates a boundary condition is imposed that is a generalization of the perfectly conducting boundary condition for an arbitrary number of spatial dimensions. It is shown that for $D\\geq 4$ the background gravitational field essentially changes the behavior of the VEVs at separations between the plates larger than the curvature radius of dS spacetime. At large separations, the Casimir forces are proportional to the inverse fourth power of the distance for all values of spatial dimension $D\\geq 3$. For $D\\geq 4$ this behavior is in sharp contrast with the case of plates in Minkowski bulk where the force decays as the inverse $(D+1)$th power of the distance.
Casimir-Polder repulsion: Three-body effects
Milton, Kimball A; Parashar, Prachi; Pourtolami, Nima; Brevik, Iver; Ellingsen, Simen A; Buhmann, Stefan Yoshi; Scheel, Stefan
2015-01-01
In this paper we study an archetypical scenario in which repulsive Casimir-Polder forces between an atom or molecule and two macroscopic bodies can be achieved. This is an extension of previous studies of the interaction between a polarizable atom and a wedge, in which repulsion occurs if the atom is sufficiently anisotropic and close enough to the symmetry plane of the wedge. A similar repulsion occurs if such an atom passes a thin cylinder or a wire. An obvious extension is to compute the interaction between such an atom and two facing wedges, which includes as a special case the interaction of an atom with a conducting screen possessing a slit, or between two parallel wires. To this end we further extend the electromagnetic multiple-scattering formalism for three-body interactions. To test this machinery we reinvestigate the interaction of a polarizable atom between two parallel conducting plates. In that case, three-body effects are shown to be small, and are dominated by three- and four-scattering terms....
Observation of the dynamical Casimir effect in a superconducting circuit
Wilson, Christopher
2012-02-01
Modern quantum theory predicts that the vacuum of space is not empty, but instead teeming with virtual particles flitting in and out of existence. While initially a curiosity, it was quickly realized that these vacuum fluctuations had measurable consequences, for instance producing the Lamb shift of atomic spectra and modifying the magnetic moment for the electron. This type of renormalization due to vacuum fluctuations is now central to our understanding of nature. 40 years ago, Moore suggested that a mirror undergoing relativistic motion could convert virtual photons into directly observable real photons. This effect was later named the dynamical Casimir effect (DCE). Using a superconducting circuit, we have observed the DCE for the first time. The circuit consists of a coplanar transmission line with an electrical length that can be changed at a substantial fraction of the speed of light. The length is changed by modulating the inductance of a superconducting quantum interference device (SQUID) at high frequencies (> 10 GHz). In addition to observing the creation of real photons, we observe two-mode squeezing of the emitted radiation, which is a signature of the quantum character of the generation process.
Casimir-Polder forces -- a non-perturbative approach
Buhmann, S Y; Knöll, L; Welsch, D G; Buhmann, Stefan Yoshi; Dung, Ho Trung; Kn\\"{o}ll, Ludwig; Welsch, Dirk-Gunnar
2004-01-01
Within the frame of macroscopic quantum electrodynamics in linear, causal media, the problem of radiation forces acting on excited atomic systems near dispersing and absorbing magnetodielectric bodies is studied. It is shown that minimal and multipolar coupling lead to essentially the same lowest-order perturbative result for the Casimir-Polder force. To go beyond perturbation theory, the exact Heisenberg equation of motion for the center-of-mass gross motion is used to derive a very general expression for the force. For a non-driven atomic system in the weak coupling regime the total force as a function of time is a superposition of force components that are related to the intra-atomic density matrix elements at chosen time. It is shown that even the force component associated with the atomic ground state is not exactly derivable from a potential, because of the position dependence of the atomic polarizability. Further, it is found that when the atomic system is initially prepared in a coherent superposition...
Quantum backreaction (Casimir) effect. II. Scalar and electromagnetic fields
Herdegen, A
2005-01-01
Casimir effect in most general terms may be understood as a backreaction of a quantum system causing an adiabatic change of the external conditions under which it is placed. This paper is the second installment of a work scrutinizing this effect with the use of algebraic methods in quantum theory. The general scheme worked out in the first part is applied here to the discussion of particular models. We consider models of the quantum scalar field subject to external interaction with ``softened'' Dirichlet or Neumann boundary conditions on two parallel planes. We show that the case of electromagnetic field with softened perfect conductor conditions on the planes may be reduced to the other two. The ``softening'' is implemented on the level of the dynamics, and is not imposed ad hoc, as is usual in most treatments, on the level of observables. We calculate formulas for the backreaction energy in these models. We find that the common belief that for electromagnetic field the backreaction force tends to the strict...
Milton, Kimball A; Wagner, Jef; Shajesh, K V
2009-01-01
In this paper, dedicated to the career of Tom Erber, we consider the Casimir interaction between weakly coupled bodies at nonzero temperature. For the case of semitransparent bodies, that is, ones described by delta-function potentials, we first examine the interaction between an infinite plane and an arbitrary curved surface. In weak coupling, such an interaction energy coincides with the exact form of the proximity force approximation obtained by summing the interaction between opposite surface elements at arbitrary temperature. This result generalizes a theorem proved recently by Decca et al. We also obtain exact closed-form results for the Casimir energy at arbitrary temperature for weakly coupled semitransparent spheres.
Bao, Y; Lussange, J; Lambrecht, A; Cirelli, R A; Klemens, F; Mansfield, W M; Pai, C S; Chan, H B
2010-01-01
We measure the Casimir force between a gold sphere and a silicon plate with nanoscale, rectangular corrugations with depth comparable to the separation between the surfaces. In the proximity force approximation (PFA), both the top and bottom surfaces of the corrugations contribute to the force, leading to a distance dependence that is distinct from a flat surface. The measured Casimir force is found to deviate from the PFA by up to 15%, in good agreement with calculations based on scattering theory that includes both geometry effects and the optical properties of the material.
A novel experimental approach for the detection of the dynamical Casimir effect
Energy Technology Data Exchange (ETDEWEB)
Braggio, C. [Ferrara Univ. (Italy). Dipt. di Fisica; Bressi, G. [Istituto Nazionale di Fisica Nucleare, Pavia (Italy); Carugno, G.; Del Noce, C. [Istituto Nazionale di Fisica Nucleare, Padova (Italy); Galeazzi, G.; Lombardi, A.; Palmieri, A.; Ruoso, G. [Istituto Nazionale di Fisica Nucleare, LNL, Legnaro (Italy); Zanello, D. [Istituto Nazionale di Fisica Nucleare, Rome (Italy)
2005-06-01
In order to observe the Casimir radiation we propose a new experimental scheme with no mechanically moving mirror. In fact we estimate that the power required for a sustained mechanical vibration would be beyond present experimental possibilities. Our apparatus consists of a superconducting electromagnetic resonant cavity with a wall covered by a semiconductor layer whose reflectivity is driven by a laser at giga-hertz frequencies. The semiconductor thus acts as a moving mirror. Preliminary laboratory tests showed that a semiconductor can indeed reflect microwaves as efficiently as a conductor. In this paper we present the complete scheme that we intend to set up for the detection of the Casimir radiation. (authors)
Influence of materials' optical response on actuation dynamics by Casimir forces
Sedighi, M.; Broer, W. H.; Van der Veeke, S.; Svetovoy, V. B.; Palasantzas, G.
2015-06-01
The dependence of the Casimir force on the frequency-dependent dielectric functions of interacting materials makes it possible to tailor the actuation dynamics of microactuators. The Casimir force is largest for metallic interacting systems due to the high absorption of conduction electrons in the far-infrared range. For less conductive systems, such as phase change materials or conductive silicon carbide, the reduced force offers the advantage of increased stable operation of MEMS devices against pull-in instabilities that lead to unwanted stiction. Bifurcation analysis with phase portraits has been used to compare the sensitivity of a model actuator when the optical properties are altered.
Sedighi, Mehdi; Palasantzas, George
2015-04-01
The role of the Casimir force on the analysis of microactuators is strongly influenced by the optical properties of interacting materials. Bifurcation and phase portrait analysis were used to compare the sensitivity of actuators when the optical properties at low optical frequencies were modeled using the Drude and Plasma models. Indeed, for metallic systems, which have strong Casimir attraction, the details of the modeling of the low optical frequency regime can be dramatic, leading to predictions of either stable motion or stiction instability. However, this difference is strongly minimized for weakly conductive systems as are the doped insulators making actuation modeling more certain to predict.
Sedighi, Mehdi; Palasantzas, George
2014-02-01
Casimir and hydrodynamic dissipation forces can strongly influence the actuation of microelectromechanical systems in ambient conditions. The dissipative and stiction dynamics of an actuating system is shown to depend on surface physical processes related to fluid slip and the size of the actuating components. Using phase change materials the Casimir force magnitude can be modulated via amorphous-crystalline phase transitions. The dissipative motion between amorphous coated phase change material components can be changed towards stiction upon crystallization and suitable choice of restoring spring constants. By contrast, amorphization can augment switching from stiction to dissipative dynamics.
Energy Technology Data Exchange (ETDEWEB)
Dalvit, Diego A1 [Los Alamos National Laboratory; Rodriguez, Alejandro W [MASS INST OF TECH; Munday, J N [HARVARD UNIV; Joannopoulos, J D [MASS INST OF TECH
2008-01-01
Using accurate numerical methods for finite-size nonplanar objects, we demonstrate a stable mechanical suspension of a silica cylinder within a metallic cylinder separated by ethanol, via a repulsive Casimir force between the silica and the metal. We investigate cylinders with both circular and square cross sections, and show that the latter exhibit a stable orientation as well as a stable position, employing a new method to accurately compute Casimir torques for finite objects. Furthermore, the stable orientation of the square cylinder is shown to undergo an unusual 45 transition as a function of the separation lengthscale, and this transition is explained as a consequence of material dispersion.
Casimir Effect at finite temperature for the CPT-even extension of QED
Silva, L M; Helayël-Neto, J A
2016-01-01
By the thermofield dynamics (TFD) formalism we obtain the energy-momentum tensor for the Electromagnetism with Lorentz Breaking Even term of the Standard Model Extended (SME) Sector in a topology $S^{1}\\times S^{1}\\times R^{2}$. We carry out the compactification by a generalized TFD-Bogoliubov transformation that is used to define a renormalized energy-momentum tensor, and the Casimir energy and pressure at finite temperature are then derived. A comparative analysis with the electromagnetic case is developed, and we remark the influence of the background in the traditional Casimir effect.
Standard Model Extension and Casimir effect for fermions at finite temperature
Santos, A. F.; Khanna, Faqir C.
2016-11-01
Lorentz and CPT symmetries are foundations for important processes in particle physics. Recent studies in Standard Model Extension (SME) at high energy indicate that these symmetries may be violated. Modifications in the lagrangian are necessary to achieve a hermitian hamiltonian. The fermion sector of the standard model extension is used to calculate the effects of the Lorentz and CPT violation on the Casimir effect at zero and finite temperature. The Casimir effect and Stefan-Boltzmann law at finite temperature are calculated using the thermo field dynamics formalism.
Pull-in control due to Casimir forces using external magnetic fields
Esquivel-Sirvent, R; Cocoletzi, G H
2009-01-01
We present a theoretical calculation of the pull-in control in capacitive micro switches actuated by Casimir forces, using external magnetic fields. The external magnetic fields induces an optical anisotropy due to the excitation of magneto plasmons, that reduces the Casimir force. The calculations are performed in the Voigt configuration, and the results show that as the magnetic field increases the system becomes more stable. The detachment length for a cantilever is also calculated for a cantilever, showing that it increases with increasing magnetic field. At the pull-in separation, the stiffness of the system decreases with increasing magnetic field.
Casimir effect on the lattice: U(1) gauge theory in two spatial dimensions
Chernodub, M N; Molochkov, A V
2016-01-01
We propose a general numerical method to study the Casimir effect in lattice gauge theories. We illustrate the method by calculating the energy density of zero-point fluctuations around two parallel wires of finite static permittivity in Abelian gauge theory in two spatial dimensions. We discuss various subtle issues related to the lattice formulation of the problem and show how they can successfully be resolved. Finally, we calculate the Casimir potential between the wires of a fixed permittivity, extrapolate our results to the limit of ideally conducting wires and demonstrate excellent agreement with a known theoretical result.
Casimir effect on the lattice: U(1) gauge theory in two spatial dimensions
Chernodub, M. N.; Goy, V. A.; Molochkov, A. V.
2016-11-01
We propose a general numerical method to study the Casimir effect in lattice gauge theories. We illustrate the method by calculating the energy density of zero-point fluctuations around two parallel wires of finite static permittivity in Abelian gauge theory in two spatial dimensions. We discuss various subtle issues related to the lattice formulation of the problem and show how they can successfully be resolved. Finally, we calculate the Casimir potential between the wires of a fixed permittivity, extrapolate our results to the limit of ideally conducting wires and demonstrate excellent agreement with a known theoretical result.
Síntese de 2-aril e 2,5-diarilfuranos funcionalizados: potenciais sondas fluorescentes
Giancarlo di Vaccari Botteselle
2009-01-01
A utilização de sondas fluorescentes para marcação ou detecção de biomoléculas de interesse em processos biológicos distintos, vem recebendo grande atenção em pesquisas biomédicas, de análises clínicas e biologia celular. Em geral, estas sondas fluorescentes são constituídas por moléculas orgânicas pequenas, as quais apresentam características fluorescentes e capacidade de conjugar-se com estas biomoléculas. Desta forma, esta dissertação descreve inicialmente a síntese de compostos 2-aril ou ...
Identificação de potenciais plantas hospedeiras alternativas de Xanthomonas campestris pv. viticola
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Morgana Mateus Santos
2014-04-01
Full Text Available Este estudo teve como objetivo identificar possíveis hospedeiras alternativas de Xanthomonas campestris pv. viticola (Xcv, visando a fornecer subsídios para o manejo do cancro bacteriano da videira. Vinte e seis espécies vegetais foram inoculadas artificialmente com o isolado Xcv3 e mantidas em condições de casa de vegetação, sendo avaliada a evolução sintomatológica da doença, como manchas necróticas angulares e lesões nas nervuras. O Xcv3 foi reisolado a partir de cada hospedeiro alternativo com sintomas, sendo identificado por PCR (Polymerase Chain Reaction, com iniciadores específicos. As espécies inoculadas que apresentaram os sintomas típicos da doença foram Glycine sp., Senna obtusifolia, Desmodium discolor, Amaranthus deflexus, Azadirachta indica, Solanum lycopersicum e Vigna unguiculata. As espécies da família Poaceae, Bidens pilosa, Emilia fosbergii, Praxelis pauciflora, Macroptilium lathyroides e Portulaca oleracea não apresentaram sintomas durante o período da avaliação.
Institute of Scientific and Technical Information of China (English)
郑茂盛; 周根树; 赵文轸; 顾海澄
2002-01-01
Casimir force and residual stresses actually appear in over-layers or films simultaneously. The study of the behaviour of micro- and nano-electromechanical systems in the presence of Casimir force and residual stress is of significance to the design of the relevant devices. We derive analytical expressions of the deflection of a bridge-shaped device under the mutual actions of Casimir force and residual stress in films. It is shown that the tensile residual stress enhances wavy behaviour of the deflection, while the compressive residual stress increases the deflection value and reduces the wavy behaviour.
Zheng, Mao-Sheng; Gen, -Shu, Zhou; Zhao, Wen-Zhen; Gu, Hai-Cheng
2002-06-01
Casimir force and residual stresses actually appear in over-layers or films simultaneously. The study of the behaviour of micro- and nano-electromechanical systems in the presence of Casimir force and residual stress is of significance to the design of the relevant devices. We derive analytical expressions of the deflection of a bridge-shaped device under the mutual actions of Casimir force and residual stress in films. It is shown that the tensile residual stress enhances wavy behaviour of the deflection, while the compressive residual stress increases the deflection value and reduces the wavy behaviour.
Petrov, V M
2016-01-01
The objective of the meeting is to promote contacts between scientists working in the field of Relativity, Gravitation and Cosmology and related fields. It is well known that the important role in Gravitation and Cosmology is played by the Casimir effect. To underline this, special Satellite Symposia devoted to this effect have been included in the Programs of the 7th and 8th Friedmann Seminars. The Casimir effect is a multidisciplinary subject. Its applications extend from gravitation and cosmology to the van der Waals forces, materials properties and nanotechnology. All these subjects are traditionally touched at the Satellite Simposia on the Casimir effect.
Uma introdução aos métodos de cálculo da energia de Casimir
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Passos Sobrinho J.J.
2001-01-01
Full Text Available O efeito Casimir é um dos aspectos mais intrigantes da física moderna. A previsão da existência de uma força macroscópica de origem quântica entre condutores neutros e sua posterior comprovação experimental é sem dúvida um dos triunfos da teoria quântica dos campos. Complementando uma introdução conceitual publicada recentemente nesta revista, apresentamos alguns métodos de cálculo da energia de Casimir, que é a grandeza fundamental que origina o efeito Casimir.
The Casimir effect in rugby-ball type flux compactifications
Minamitsuji, M.
2008-04-01
We discuss volume stabilization in a 6D braneworld model based on 6D supergravity theory. The internal space is compactified by magnetic flux and contains codimension two 3-branes (conical singularities) as its boundaries. In general the external 4D spacetime is warped and in the unwrapped limit the shape of the internal space looks like a 'rugby ball'. The size of the internal space is not fixed due to the scale invariance of the supergravity theory. We discuss the possibility of volume stabilization by the Casimir effect for a massless, minimally coupled bulk scalar field. The main obstacle in studying this case is that the brane (conical) part of the relevant heat kernel coefficient (a6) has not been formulated. Thus as a first step, we consider the 4D analog model with boundary codimension two 1-branes. The spacetime structure of the 4D model is very similar to that of the original 6D model, where now the relevant heat kernel coefficient is well known. We derive the one-loop effective potential induced by a scalar field in the bulk by employing zeta function regularization with heat kernel analysis. As a result, the volume is stabilized for most possible choices of the parameters. Especially, for a larger degree of warping, our results imply that a large hierarchy between the mass scales and a tiny amount of effective cosmological constant can be realized on the brane. In the non-warped limit the ratio tends to converge to the same value, independently of the bulk gauge coupling constant. Finally, we will analyze volume stabilization in the original model 6D by employing the same mode-sum technique.
MIR status report: an experiment for the measurement of the dynamical Casimir effect
Energy Technology Data Exchange (ETDEWEB)
Agnesi, A; Pirzio, F; Reali, G [Dipartimento di Elettronica, Universita di Pavia, Via Ferrata 1, 27100 Pavia (Italy); Braggio, C; Carugno, G [INFN-Sezione di Padova, Via Marzolo 8, 35131 Padova (Italy); Bressi, G [INFN-Sezione di Pavia, Via U. Bassi 6, 27100 Pavia (Italy); Galeazzi, G; Ruoso, G [INFN-Laboratori Nazionali di Legnaro, Viale dell' Universita 2, 35020 Legnaro (Italy); Zanello, D [INFN-Sezione di Roma, P.le A. Moro 2, 00185 Roma (Italy)], E-mail: Giuseppe.Ruoso@lnl.infn.it
2008-04-25
In this paper, the status of the experiment MIR (motion induced radiation) is reported. This experiment aims at measuring for the first time the dynamical Casimir effect by using an effective motion of a wall of a superconducting microwave resonant cavity. Effective motion is produced by periodic illumination of a semiconductor slab by means of an ultra-high-frequency amplitude modulated laser.
Casimir effect as a source of chiral symmetry breaking in QCD
Energy Technology Data Exchange (ETDEWEB)
Floratos, E. (Crete Univ., Iraklion (Greece). Physics Dept.; European Organization for Nuclear Research, Geneva (Switzerland)); Papantonopoulos, E. (Ethnikon Metsovion Polytechneion, Athens (Greece). Physics Dept.); Zoupanos, G. (European Organization for Nuclear Research, Geneva (Switzerland))
1985-02-21
The vacuum of QCD, defined on a space-time topology T/sup 3/ x R, breaks chiral symmetry. The physical mechanism responsible is the formation of fermionic condensates due to Casimir forces. Representations of coloured fermions, which possess asymptotic freedom, stabilize the formation of these condensates through their gauge interactions. Estimates of ratios of the order parameters are given for various representations.
Edge effects in electrostatic calibrations for the measurement of the Casimir force
Wei, Qun
2011-01-01
We have performed numerical simulations to evaluate the effect on the capacitance of finite size boundaries realistically present in the parallel plane, sphere-plane, and cylinder-plane geometries. The potential impact of edge effects in assessing the accuracy of the parameters obtained in the electrostatic calibrations of Casimir force experiments is then discussed.
Kinetic Roughening and Material Optical Properties Influence on Van der Waals/Casimir Forces
van Zwol, P. J.; Palasantzas, G.
Atomic force microscopy measurements and force theory calculations using the Lifshitz theory show that van der Waals/Casimir dispersive forces have a strong dependence on surface roughness and material optical properties. It is found that at separations below 100 nm the roughness effect is
Influence of dielectric properties on van der Waals/Casimir forces in solid-liquid systems
van Zwol, P. J.; Palasantzas, G.; De Hosson, J. Th. M.
In this paper, we present calculations of van der Waals/Casimir forces, described by Lifshitz theory, for the solid-liquid-solid system using measured dielectric functions of all involved materials for the wavelength range from millimeters down to subnanometers. It is shown that even if the
Kramers-Kronig relations for plasma-like permittivities and the Casimir force
Klimchitskaya, G L; Mostepanenko, V M
2007-01-01
The Kramers-Kronig relations are derived for the permittivity of the usual plasma model which neglects dissipation and of a generalized model which takes into account the interband transitions. The generalized plasma model is shown to be consistent with all precision experiments on the measurement of the Casimir force.
Sedighi Ghozotkhar, Mehdi; Broer, W. H.; Palasantzas, G.; Kooi, B. J.
2013-01-01
Amorphous to crystalline phase transitions in phase change materials (PCM) can have strong influence on the actuation of microelectromechanical systems under the influence of Casimir forces. Indeed, the bifurcation curves of the stationary equilibrium points and the corresponding phase portraits of
Sedighi Ghozotkhar, Mehdi; Palasantzas, Georgios
2015-01-01
The role of the Casimir force on the analysis of microactuators is strongly influenced by the optical properties of interacting materials. Bifurcation and phase portrait analysis were used to compare the sensitivity of actuators when the optical properties at low optical frequencies were modeled usi
Sedighi Ghozotkhar, Mehdi; Palasantzas, Georgios
2014-01-01
Casimir and hydrodynamic dissipation forces can strongly influence the actuation of microelectromechanical systems in ambient conditions. The dissipative and stiction dynamics of an actuating system is shown to depend on surface physical processes related to fluid slip and the size of the actuating
Dirichlet Casimir Energy for a Scalar Field in a Sphere: An Alternative Method
Valuyan, M A
2009-01-01
In this paper we compute the leading order of the Casimir energy for a free massless scalar field confined in a sphere in three spatial dimensions, with the Dirichlet boundary condition. When one tabulates all of the reported values of the Casimir energies for two closed geometries, cubical and spherical, in different space-time dimensions and with different boundary conditions, one observes a complicated pattern of signs. This pattern shows that the Casimir energy depends crucially on the details of the geometry, the number of the spatial dimensions, and the boundary conditions. The dependence of the \\emph{sign} of the Casimir energy on the details of the geometry, for a fixed spatial dimensions and boundary conditions has been a surprise to us and this is our main motivation for doing the calculations presented in this paper. Moreover, all of the calculations for spherical geometries include the use of numerical methods combined with intricate analytic continuations to handle many different sorts of diverge...
Influence of ultrathin water layer on the van der Waals/Casimir force between gold surfaces
Palasantzas, G.; Svetovoy, V. B.; van Zwol, P. J.
In this paper we investigate the influence of ultrathin water layer (similar to 1-1.5 nm) on the van der Waals/Casimir force between gold surfaces. Adsorbed water is inevitably present on gold surfaces at ambient conditions as jump-up-to contact during adhesion experiments demonstrate. Calculations
Weak localization as a definitive test of diffusive models in the Casimir effect
Allocca, Andrew; Wilson, Justin; Galitski, Victor
2015-03-01
Results from many measurements of the Casimir effect suggest that the metallic plates in these experiments should be modeled with the plasma model of free electrons as opposed to the naive diffusive Drude model, while other experiments seem to indicate the exact opposite, with results more in line with a diffusive model. We study the Casimir effect at low temperatures between a thick disordered plate and purely two-dimensional disordered system where the Drude conductivity decreases logarithmically at low temperatures due to weak localization. This effect can be tuned with either temperature or applied magnetic field leading to a measurable change in the Casimir force. On the other hand, a ballistic model cannot experience such an effect and is only weakly dependent on temperature and magnetic field. As a result, we propose that an experiment would unambiguously differentiate between diffusive and ballistic models by measuring the effect at low temperatures with an applied magnetic field. Additionally, we calculate the impact that fluctuations in the disorder distribution have on the Casimir effect. Assuming the validity of a diffusive model, we find that the Drude model is a good approximation of a more exact treatment of disorder. This work was supported by the DOE-BES (Grant No. DESC0001911) (A.A. and V.G.), the JQI-PFC (J.W.), and the Simons Foundation.
Gross, Markus; Gambassi, Andrea; Dietrich, S
2017-08-01
The effect of imposing a constraint on a fluctuating scalar order parameter field in a system of finite volume is studied within statistical field theory. The canonical ensemble, corresponding to a fixed total integrated order parameter (e.g., the total number of particles), is obtained as a special case of the theory. A perturbative expansion is developed which allows one to systematically determine the constraint-induced finite-volume corrections to the free energy and to correlation functions. In particular, we focus on the Landau-Ginzburg model in a film geometry (i.e., in a rectangular parallelepiped with a small aspect ratio) with periodic, Dirichlet, or Neumann boundary conditions in the transverse direction and periodic boundary conditions in the remaining, lateral directions. Within the expansion in terms of ε=4-d, where d is the spatial dimension of the bulk, the finite-size contribution to the free energy of the confined system and the associated critical Casimir force are calculated to leading order in ε and are compared to the corresponding expressions for an unconstrained (grand canonical) system. The constraint restricts the fluctuations within the system and it accordingly modifies the residual finite-size free energy. The resulting critical Casimir force is shown to depend on whether it is defined by assuming a fixed transverse area or a fixed total volume. In the former case, the constraint is typically found to significantly enhance the attractive character of the force as compared to the grand canonical case. In contrast to the grand canonical Casimir force, which, for supercritical temperatures, vanishes in the limit of thick films, in the canonical case with fixed transverse area the critical Casimir force attains for thick films a negative value for all boundary conditions studied here. Typically, the dependence of the critical Casimir force both on the temperaturelike and on the fieldlike scaling variables is different in the two ensembles.
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Ana Claudia F. Frizzo
2001-09-01
Full Text Available Introdução: A partir dos primeiros registros de atividades elétricas cerebrais (EEG em resposta à apresentação de estímulos auditivos em seres humanos, durante a década de 30, pôde-se observar os potenciais evocados auditivos de longa latência - PEALLs (Mendel, 1989. Desde então, muitas pesquisas têm sido realizadas enfatizando o estudo do sistema auditivo em sua totalidade (periférico e central. Considerando a diferenciação funcional entre os hemisférios cerebrais, o presente estudo procurou identificar evidências eletrofisiológicas que constatem diferenciações interhemisféricas. Forma de estudo: Prospectivo clínico randomizado. Objetivo: O objetivo principal foi verificar a ocorrência de possíveis diferenciações entre os PEALLs dos hemisférios direito (Cz/A2 e esquerdo (Cz/A1 em um grupo de normoouvintes entre 8 e 18 anos de idade, por meio da análise comparativa dos registros dos PEALLs, quanto à latência e amplitude. Resultados: Não foram observadas diferenças estatisticamente significantes entre as medidas, exceto para o componente P2, na população masculina. Porém, não se pode negar a diferenciação funcional entre os hemisférios e deve-se considerar essa variável durante a realização da pesquisa dos PEALLs. Conclusão: Contudo, futuros trabalhos ainda serão necessários, com amostras maiores ou até mesmo com diferentes posicionamentos de eletrodos, a fim de verificarmos a existência ou não de evidências eletrofisiológicas que constatam essas diferenciações, garantindo a aplicação mais segura e efetiva deste método.Introduction: Since of the first registration of cerebral electric activities (EEG in response to the presentation hearing stimulus in human, decade 30‘s, can be observed the late components or long latency auditory evoked potentials - LLAEP (Mendel, 1989. Ever since, a lot of number of researches have been performed emphasizing the study of the hearing system (the ear and
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Tainara Milbradt Weich
2012-10-01
Full Text Available As drogas ilícitas são conhecidas pelos seus efeitos deletérios no sistema nervoso central; no entanto, elas também podem atingir o sistema auditivo, provocando alterações. OBJETIVOS: Analisar e comparar os resultados dos potenciais evocados auditivos de tronco encefálico (PEATE de frequentadores de grupos de apoio a ex-usuários de drogas. MÉTODO: Estudo transversal, não experimental, descritivo e quantitativo. A amostra foi composta por 17 indivíduos divididos conforme o tipo de droga mais consumida: 10 indivíduos no grupo maconha (G1 e sete no grupo crack/cocaína (G2. Eles foram subdivididos pelo tempo de uso de drogas: um a cinco anos, seis a 10 anos e mais que 15 anos. A avaliação foi feita por meio de anamnese, audiometria tonal liminar, medidas de imitância acústica e PEATE. RESULTADOS: Ao comparar os resultados de G1 e G2, independente do tempo de uso de drogas, não se observou diferença estatisticamente significante nas latências absolutas e nos intervalos interpicos. No entanto, apenas cinco dos 17 indivíduos tiveram PEATE com resultados adequados para a faixa etária. CONCLUSÃO: Independentemente do tempo de utilização das drogas, o uso de maconha e crack/cocaína pode provocar alterações difusas no tronco encefálico, comprometendo a transmissão do estímulo auditivo.Illicit drugs are known for their deleterious effects upon the central nervous system and more specifically for how they adversely affect hearing. OBJECTIVE: This study aims to analyze and compare the hearing complaints and the results of brainstem evoked response audiometry (BERA of former drug user support group goers. METHODS: This is a cross-sectional non-experimental descriptive quantitative study. The sample consisted of 17 subjects divided by their preferred drug of use. Ten individuals were placed in the marijuana group (G1 and seven in the crack/cocaine group (G2. The subjects were further divided based on how long they had been using
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Silvia MM Ahid
1999-12-01
Full Text Available INTRODUÇÃO: Em alguns bairros costeiros de São Luís, Maranhão, a prevalência da dirofilariose chega a mais de 40% entre os cães domiciliados. Porém, desconhecem-se os vetores naturais, tanto lá quanto no resto do Nordeste do país. O objetivo do estudo foi identificar os prováveis vetores dessa parasitose. MÉTODOS: Realizaram-se coletas mensais de mosquitos em um bairro costeiro de São Luís, MA, de março de 1996 a maio de 1997, no peridomicílio, tendo cão e homem como iscas. Os mosquitos foram dissecados para a pesquisa de larvas da Dirofilaria immitis. RESULTADOS: Coletaram-se 1.738 mosquitos de 11 espécies. Culex quinquefasciatus, capturada todos os meses, porém menos freqüente na estação chuvosa, correspondeu a 54,5% do total, seguido de Aedes albopictus (20,3%, Aedes taeniorhynchus e Aedes scapularis (ambos 11%. Larvas de D.immitis foram encontradas em 0,1% dos Cx. quinquefasciatus e 0,5% dos Ae. taeniorhynchus. CONCLUSÕES: Ae. taeniorhynchus e Cx. quinquefasciatus foram considerados vetores potenciais da dirofilariose em São Luís. A importância local de Cx. quinquefasciatus como transmissor primário da D. immitis necessita ser melhor avaliada.INTRODUCTION: In some coastal districts of São Luís, capital of the state of Maranhão, Brazil, the prevalence of Dirofilaria immitis is more than 40% in house dogs. Natural potential vectors, as found in other areas of Northeastern Brazil, are unknown. The aim of this study was to identify probable vectors of the disease. METHODS: Mosquito catches were performed at a coastal, district Olho d'Água, in S. Luís, to look for local potential vectors. Captures were carried out monthly, from March 1996 to May 1997, outdoors, having a man and a dog as baits. Mosquitoes were dissected for D. immitis larvae. RESULTS: A total of 1,738 mosquitoes belonging to 11 species were collected. Culex quinquefasciatus, the only species collected every month, was more frequently in the dry
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Edvaldo Leal de Moraes
2009-10-01
doadores, segundo o sexo, faixa etária, causa de morte encefálica, quantificar os doadores que apresentaram hipernatremia, hiperpotassemia e hipopotassemia e conhecer quais os órgãos mais utilizados para transplante. Trata-se de estudo de caráter quantitativo, descritivo, exploratório e retrospectivo. A pesquisa foi realizada na Organização de Procura de Órgãos do Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo. Foram analisados os dados dos prontuários de 187 potenciais doadores. O acidente vascular cerebral representou 53,48% de todas as causas de morte encefálica, os distúrbios de sódio e potássio ocorreram em 82,36% dos casos e 45,46% dos potenciais doadores tinham de 41 a 60 anos. Os resultados obtidos evidenciaram que as causas naturais de morte superaram as mortes traumáticas e a maioria dos doadores apresentou alterações de sódio e potássio provavelmente relacionadas à manutenção inadequada.
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Glauco Henrique Reggiani Mello
2010-10-01
Full Text Available OBJETIVO: Quantificar os potenciais doadores de córnea nas diferentes unidades hospitalares do Hospital de Clínicas da Universidade Federal do Paraná - UFPR. MÉTODOS: Foram analisados 369 prontuários de pacientes que foram a óbito nos meses de abril a julho de 2005 no HC-UFPR. No prontuário de cada paciente foram avaliados: evolução clínica, CID-10 e unidade hospitalar do óbito. Para ser considerado potencial doador (PD utilizou-se como critérios de exclusão os tópicos citados no Manual de Transplantes (2ª edição - 2004 da Secretaria Estadual da Saúde do Estado do Paraná. Os PD foram agrupados em: data do óbito, tipo de internamento e unidade hospitalar. Analisamos a quantidade de PD e total de óbitos. RESULTADOS: Dos 369 prontuários analisados, foram considerados potenciais doadores (PD 70 pacientes (18,97% do total de prontuários analisados As unidades: Centro de Terapia Intensiva, Centro de Terapia Semi e Pronto Atendimento Adulto foram responsáveis por 62,8% dos PD. Já a Neurocirurgia, Emergência Cárdio e UTI Cirurgia Cardíaca apresentaram uma relação de PD por óbito superior a 60%. CONCLUSÃO: Nesse estudo constatou-se que tanto as unidades com grande número de PD como aquelas com uma grande relação PD por óbito são locais de escolha para uma intervenção com o intuito de aumentar o número de doações em nosso meio.PURPOSE: To quantify the potential cornea donor from the different units of Clinical Hospital of the UFPR. METHODS: 369 records of patients who died from april until july of 2005 in the HC-UFPR were analyzed. The medical records of each patient had been evaluated: the clinical evolution, CID-10 and hospital unit of the death. To be considered potential donor (PD it was used as exclusion criteria the topics cited in the Manual of Transplants (2ª edition-2004 of the State Secretariat of the Health of the State of the Paraná. The PD had been grouped in: date of the death, type of internment
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Lenita da Silva Quevedo
2012-12-01
Full Text Available A ototoxidade dos solventes orgânicos pode atingir o sistema auditivo a nível coclear e retrococlear. OBJETIVO: Avaliar a integridade neurofisiológica do sistema auditivo até tronco cerebral por meio do PEATE. MÉTODO: Estudo prospectivo. Estudados frentistas de três postos de gasolina da cidade de Santa Maria/RS. A amostra ficou composta por 21 sujeitos, que foram avaliados por meio de potenciais evocados auditivos de tronco encefálico. RESULTADOS: Alteração nas latências absolutas das ondas I e III e em todas as latências interpicos, na orelha direita. Na orelha esquerda houve alteração na latência absoluta de todas as ondas, e em todos os intervalos interpicos. Alteração na diferença interaural da onda V foi verificada em 19% dos sujeitos. No grupo exposto há mais de cinco anos, foram estatisticamente significantes o número de sujeitos com alteração: no intervalo interpico I-V da orelha direita; na latência absoluta da onda I e no intervalo interpico III-V da orelha esquerda. CONCLUSÃO: A exposição a combustíveis pode causar alterações no sistema auditivo central.Ototoxicity of organic solvents can affect the hearing system up to the cochlea level and the central structures of hearing. OBJECTIVE: To evaluate the neurophysiological integrity of the hearing system in subjects exposed to fuels using ABR. METHOD: Prospective study. We evaluated attendants from three gas stations in Santa Maria/RS. The sample had 21 subjects, who were evaluated by auditory brainstem response. RESULTS: We found an alteration in the absolute latencies of Waves I and III and in all the interpeak latencies, in the right ear. In the left ear there was a change in the absolute latencies of all Waves, and in all the interpeak intervals. A change in the interaural difference of Wave V was found in 19% of the individuals. In the group exposed for more than five years, there were subjects with a statistically significant changes: in the I
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Erlon Barbosa Valdetaro
2011-03-01
Full Text Available
As espécies florestais possuem grande importância, oferecendo diversos produtos madeireiros e não madeireiros fundamentais para a sociedade. Neste contexto, a busca de novas tecnologias capazes de promover incremento na produtividade das florestas comerciais tem merecido grande atenção, sendo que a biotecnologia tem contribuído substancialmente para isso. Este ramo da ciência pode promover a modificação direta do genoma de um organismo alvo, por meio da análise e manipulação do DNA ou pela inserção de fragmentos do mesmo com função conhecida e, deste modo, alcançar características previamente desejadas, tais como resistência a doenças e ataques de pragas, redução do teor de lignina na madeira e geração de plantas tolerantes a diferentes tipos de estresse. Esta revisão objetiva relatar técnicas para a geração de árvores geneticamente modificadas, aplicações da transformação genética em essências florestais, riscos do uso desta tecnologia e seus potenciais impactos ambientais.
doi: 10.4336/2011.pfb.31.65.51
Forest species have great economic and social importance, offering various products as wood and non-timber fundamental to society. In this context, the search for new technologies that promote increase in productivity of commercial forests has received special attention and biotechnology has contributed substantially to this. This branch of science can promote direct modification of the genome of a target organism, through the analysis and manipulation of DNA genome or by insertion of fragments of the same with known function and thus to achieve desired characteristics, such as resistance to diseases and pests, lignin reduction in wood and generation of plants tolerant to different kinds of stresses. This review aims at reporting techniques for the generation of genetically modified trees, applications of genetic transformation in forest species, risks of using this technology and its potential
Casimir-Polder interaction of neutrons with metal or dielectric surfaces
Gebhart, Valentin; Buhmann, Stefan Yoshi
2016-01-01
We predict a repulsive Casimir-Polder-type dispersion interaction between a single neutron and a metal or dielectric surface. Our model scenario assumes a single neutron subject to an external magnetic field. Due to its intrinsic magnetic moment, the neutron then forms a magnetisable two-level system which can exchange virtual photons with a nearby surface. The resulting dispersion interaction between a purely magnetic object (neutron) and a purely electric one (surface) is found to be repulsive. Its magnitude is considerably smaller than than the standard atom-surface Casimir-Polder force due to the magnetic nature of the interaction and the smallness of the electron-to-neutron mass ratio. Nevertheless, we show that it can be comparable to the gravitational potential of the same surface.
Corrections to the Casimir Force Due to Interactions of Plasmons and Electromagnetic Field
Institute of Scientific and Technical Information of China (English)
无
2005-01-01
Considering the interaction between the electromagnetic field and matter field, a concise method is used to calculate the ground-state energy of the interacting system. With the assumption of squeezed-like state, a new vacuum state is obtained for the interacting system. The energy of the new vacuum state is obviously lower than that of unperturbed vacuum state. Based on the new vacuum state, the correction to the Casimir force is obtained.The result shows that the contribution of the interaction is a repulsive one and the Casimir effect is attributed to both electromagnetic field and matter field. On the basis of the obtained results, the recent experimental data can be explained reasonably.
On the Difference Between the Vacuum Casimir Energies for Grounded and Isolated Conductors
Fosco, C D; Mazzitelli, F D
2016-01-01
We study the vacuum (i.e., zero-temperature) Casimir energy for a system of neutral conductors which are isolated, as opposed to grounded. The former is meant to describe a situation where the total charge on each conductor, as well as all of its fluctuations, vanishes, while the latter describes a situation where the conductors are connected to a charge reservoir. We compute the difference between the vacuum energies for a given system of conductors, but subjected to the two different conditions stated above. The results can be written in terms of a generalized, frequency-dependent capacitance matrix of the system. Using a multipolar expansion, we show that the grounded Casimir energy includes a monopole-monopole interaction term that is absent in the isolated case in the large distance limit
Casimir-Polder repulsion near edges: wedge apex and a screen with an aperture
Milton, Kimball A; Parashar, Prachi; Pourtolami, Nima; Brevik, Iver; Ellingsen, Simen A
2011-01-01
Although repulsive effects have been predicted for quantum vacuum forces between bodies with nontrivial electromagnetic properties, such as between a perfect electric conductor and a perfect magnetic conductor, realistic repulsion seems difficult to achieve. Repulsion is possible if the medium between the bodies has a permittivity in value intermediate to those of the two bodies, but this may not be a useful configuration. Here, inspired by recent numerical work, we initiate analytic calculations of the Casimir-Polder interaction between an atom with anisotropic polarizability and a plate with an aperture. In particular, for a semi-infinite plate, and, more generally, for a wedge, the problem is exactly solvable, and for sufficiently large anisotropy, Casimir-Polder repulsion is indeed possible, in agreement with the previous numerical studies. In order to achieve repulsion, what is needed is a sufficiently sharp edge (not so very sharp, in fact) so that the directions of polarizability of the conductor and t...
Finite temperature Casimir effect for massive scalars in a magnetic field
Erdas, Andrea
2013-01-01
The finite temperature Casimir effect for a charged, massive scalar field confined between very large, perfectly conducting parallel plates is studied using the zeta function regularization technique. The scalar field satisfies Dirichlet boundary conditions at the plates and a magnetic field perpendicular to the plates is present. Four equivalent expressions for the zeta function are obtained, which are exact to all orders in the magnetic field strength, temperature, scalar field mass, and plate distance. The zeta function is used to calculate the Helmholtz free energy of the scalar field and the Casimir pressure on the plates, in the case of high temperature, small plate distance, strong magnetic field and large scalar mass. In all cases, simple analytic expressions of the zeta function, free energy and pressure are obtained, which are very accurate and valid for practically all values of temperature, plate distance, magnetic field and mass.
Temperature correction to the Casimir force in cryogenic range and anomalous skin effect
Svetovoy, V B
2003-01-01
Temperature correction to the Casimir force is considered for real metals at low temperatures. With the temperature decrease the mean free path for electrons becomes larger than the field penetration depth. In this condition description of metals with the impedance of anomalous skin effect is shown to be more appropriate than with the permittivity. The effect is crucial for the temperature correction. It is demonstrated that in the zero frequency limit the reflection coefficients should coincide with those of ideal metal if we demand the entropy to be zero at T=0. All the other prescriptions discussed in the literature for the $n=0$ term in the Lifshitz formula give negative entropy. It is shown that the temperature correction in the region of anomalous skin effect is not suppressed as it happens in the plasma model. This correction will be important in the future cryogenic measurements of the Casimir force.
Chen, F; Mohideen, U; Mostepanenko, V M
2004-01-01
We compare theory and experiment in the Casimir force measurement between gold surfaces performed with the atomic force microscope. Both random and systematic experimental errors are found leading to a total absolute error equal to 8.5 pN at 95% confidence. In terms of the relative errors, experimental precision of 1.75% is obtained at the shortest separation of 62 nm at 95% confidence level (at 60% confidence the experimental precision of 1% is confirmed at the shortest separation). An independent determination of the accuracy of the theoretical calculations of the Casimir force and its application to the experimental configuration is carefully made. Special attention is paid to the sample-dependent variations of the optical tabulated data due to the presence of grains, contribution of surface plasmons, and errors introduced by the use of the proximity force theorem. Nonmultiplicative and diffraction-type contributions to the surface roughness corrections are examined. The electric forces due to patch potent...
Enhanced near-field thermal radiation and reduced Casimir stiction between doped-Si gratings
Liu, Xianglei; Zhao, Bo; Zhang, Zhuomin M.
2015-06-01
Based on the scattering theory, simultaneously enhanced energy transport and suppressed momentum exchange are demonstrated by patterning doped-silicon surfaces in the near field. The radiative heat flux between doped-silicon gratings exceeds that between planar surfaces and can be one or even two orders of magnitude higher than what is predicted by the geometry-based Derjaguin proximity approximation (PA). The underlying mechanism is interpreted as due to the excitation of broadband hyperbolic modes that facilitate photon tunneling, especially when the period is small. This is confirmed by a comparison of the results from the scattering theory with those from the effective-medium theory. The Casimir force, which may cause stiction and even failure of mesoscopic devices, is reduced with the grating structures as predicted by both the scattering theory and PA. However, depending on the separation distance, the PA may over- or underpredict the Casimir force.
Surface-impedance approach solves problems with the thermal Casimir force between real metals
Geyer, B; Mostepanenko, V M
2003-01-01
The surface impedance approach to the description of the thermal Casimir effect in the case of real metals is elaborated starting from the free energy of oscillators. The Lifshitz formula expressed in terms of the dielectric permittivity depending only on frequency is shown to be inapplicable in the frequency region where a real current may arise leading to Joule heating of the metal. The standard concept of a fluctuating electromagnetic field on such frequencies meets difficulties when used as a model for the zero-point oscillations or thermal photons in the thermal equilibrium inside metals. Instead, the surface impedance permits not to consider the electromagnetic oscillations inside the metal but taking the realistic material properties into account by means of the effective boundary condition. An independent derivation of the Lifshitz-type formulas for the Casimir free energy and force between two metal plates is presented within the impedance approach. It is shown that they are free of the contradiction...
Temperature control of colloidal phases by Critical Casimir forces -- a simulation study
Triet Dang, Minh; Nguyen, Van Duc; Vila Verde, Ana; Bolhuis, Peter; Schall, Peter
2012-02-01
Critical Casimir forces arising from the confinement of critical solvent fluctuations between the surfaces of colloidal particles have recently been shown a promising route to control colloidal assembly. Such forces are strongly temperature dependent, and thus allow for direct temperature control of colloidal interactions. However, colloidal phase transitions controlled by this highly temperature-dependent potential are still poorly understood. Here, we report Monte Carlo simulations of critical Casimir-driven colloidal phase behavior using input potentials directly measured in experiments. We map the gas-liquid coexistence region using Gibbs ensemble simulations and the solid-fluid coexistence boundaries using Gibbs-Duhem integration, and determine the gas-liquid critical point by applying scaling theory. The constructed gas-liquid-solid phase diagram agrees quantitatively with that observed in experiments. Remarkably, the simulated gas-liquid coexistence curve exhibits 3D Ising scaling despite the strong temperature dependence of the pair potentials.
Casimir Dark Energy, Stabilization of the Extra Dimensions and Gauss-Bonnet Term
Wongjun, Pitayuth
2013-01-01
Casimir dark energy model in five-dimensional and six-dimensional spacetime including non-relativistic matter and Gauss-Bonnet term is investigated. The Casimir energy can play the role of dark energy to drive the late-time acceleration of the universe while the radius of the extra dimensions can be stabilized. The qualitative analysis in radion picture in four-dimensional spacetime shows that the contribution from Gauss-Bonnet term will effectively slows down the radion field at the beginning time. Therefore, the radion field does not pass minimum point of the effective potential before the minimum the potential exists. This leads to the stabilizing mechanism of the extra dimensions eventually.
Casimir energy in a small volume multiply connected static hyperbolic pre-inflationary Universe
Müller, D; Opher, R; Muller, Daniel; Fagundes, Helio V.; Opher, Reuven
2001-01-01
A few years ago, Cornish, Spergel and Starkman (CSS), suggested that a multiply connected ``small'' Universe could allow for classical chaotic mixing as a pre-inflationary homogenization process. The smaller the volume, the more important the process. Also, a smaller Universe has a greater probability of being spontaneously created. Previously DeWitt, Hart and Isham (DHI) calculated the Casimir energy for static multiply connected flat space-times. Due to the interest in small volume hyperbolic Universes (e.g. CSS), we generalize the DHI calculation by making a a numerical investigation of the Casimir energy for a conformally coupled, massive scalar field in a static Universe, whose spatial sections are the Weeks manifold, the smallest Universe of negative curvature known. In spite of being a numerical calculation, our result is in fact exact. It is shown that there is spontaneous vacuum excitation of low multipolar components.
Casimir scaling and renormalization of Polyakov loops in large-N gauge theories
Mykkanen, Anne; Rummukainen, Kari
2012-01-01
We study Casimir scaling and renormalization properties of Polyakov loops in different irreducible representations in SU(N) gauge theories; in particular, we investigate the approach to the large-N limit, by performing lattice simulations of Yang-Mills theories with an increasing number of colors, from 2 to 6. We consider the twelve lowest irreducible representations for each gauge group, and find strong numerical evidence for nearly perfect Casimir scaling of the bare Polyakov loops in the deconfined phase. Then we discuss the temperature dependence of renormalized loops, which is found to be qualitatively and quantitatively very similar for the various gauge groups. In particular, close to the deconfinement transition, the renormalized Polyakov loop increases with the temperature, and its logarithm reveals a characteristic dependence on the inverse of the square of the temperature. At higher temperatures, the renormalized Polyakov loop overshoots one, reaches a maximum, and then starts decreasing, in agreem...
Critical Casimir forces between defects in the 2D Ising model
Nowakowski, P.; Maciołek, A.; Dietrich, S.
2016-12-01
An exact statistical mechanical derivation is given of the critical Casimir interactions between two defects in a planar lattice-gas Ising model. Each defect is a finite group of nearest-neighbor spins with modified coupling constants. Such a system can be regarded as a model of a binary liquid mixture with the molecules confined to a membrane and the defects mimicking protein inclusions embedded into the membrane. As suggested by recent experiments, certain cellular membranes appear to be tuned to the proximity of a critical demixing point belonging to the two-dimensional Ising universality class. Therefore one can expect the emergence of critical Casimir forces between membrane inclusions. These forces are governed by universal scaling functions, which we derive for simple defects. We prove that the scaling law appearing at criticality is the same for all types of defects considered here.
Energy Technology Data Exchange (ETDEWEB)
Campoamor-Stursberg, R [Dpto. GeometrIa y TopologIa, Fac. CC. Matematicas, Universidad Complutense de Madrid, Plaza de Ciencias, 3, E-28040 Madrid (Spain); Low, S G [Austin, TX (United States)], E-mail: rutwig@mat.ucm.es, E-mail: Stephen.Low@alumni.utexas.net
2009-02-13
Given a semidirect product g=s oplus{sup {yields}} r of semisimple Lie algebras s and solvable algebras r, we construct polynomial operators in the enveloping algebra U(g) of g that commute with r and transform like the generators of s, up to a functional factor that turns out to be a Casimir operator of r. Such operators are said to generate a virtual copy of s in U(g), and allow us to compute the Casimir operators of g in a closed form, using the classical formulae for the invariants of s. The behavior of virtual copies with respect to contractions of Lie algebras is analyzed. Applications to the class of Hamilton algebras and their inhomogeneous extensions are given.
Van der Waals and Casimir interactions between atoms and carbon nanotubes
Klimchitskaya, G. L.(Central Astronomical Observatory at Pulkovo of the Russian Academy of Sciences, 196140, St. Petersburg, Russia); Blagov, E. V.; Mostepanenko, V. M.
2008-01-01
The van der Waals and Casimir interactions of a hydrogen atom (molecule) with a single-walled and a multiwalled carbon nanotubes are compared. It is shown that the macroscopic concept of graphite dielectric permittivity is already applicable for nanotubes with only two or three walls. The absorption of hydrogen atoms by a nanotube at separations below one nanometer is considered. The lateral force due to exchange repulsion moves the atom to a position above the cell center, where it is absorb...
Casimir Effect of Massive Scalar Field with Hybrid Boundary Condition in (1+1)-Dimensional Spacetime
Institute of Scientific and Technical Information of China (English)
HE Xiao-Kai; LIU Wen-Biao; QIU Wei-Gang
2009-01-01
The Casimir energy of maesive scalar field with hybrid (Dirichlet-Neumann) boundary condition is calcu-lated. In order to regularize the model, the typical methods named as mode summation method and Green's function method are used respectively. It is found that the regularized zero-point energy density depends on the scalar field's mass. When the field is massless, the result is consistent with previous literatures.
Casimir force between two parallel semiconductor slabs: Magnetic field effects in the Voigt geometry
Energy Technology Data Exchange (ETDEWEB)
Garcia-Serrano, R.; Palomino-Ovando, M. [Facultad de Ciencias Fisico-Matematicas, Universidad Autonoma de Puebla, Puebla (Mexico); Martinez, G.; Hernandez, P.H.; Cocoletzi, Gregorio H. [Instituto de Fisica, Universidad Autonoma de Puebla, Puebla (Mexico)
2009-06-15
We investigate the Casimir force F between two parallel semiconductor slabs taking into account magnetoplasmon effects. For our calculations we consider an external magnetic field applied in the Voigt geometry. Studies are carried out using the formula of F, which is written in terms of the reflectivities of the incident electromagnetic (EM) waves onto the surfaces of the semiconductor slabs, in the vacuum gap between slabs. Results show that the Casimir force depends strongly on the slab thickness as well as on the magnetic-field strength (or equivalently on the cyclotron frequency). At a constant cyclotron frequency and for small slab thickness F/F{sub 0} (F{sub 0} is the ideal force) displays a dip at small separation distances L between slabs. F/F{sub 0} increases with L up to saturation as the slab thickness increases. The curve with the strongest value of F/F{sub 0} corresponds to the semi-infinite medium geometry. For a constant slab thickness and small cyclotron frequency, F/F{sub 0} as a function of L shows a monotonic increase as L increases, and eventually reaches saturation. At high cyclotron frequency F/F{sub 0} displays a dip. The curve of F/F{sub 0} with no applied external field corresponds to the one with the strongest Casimir force. Therefore, magnetoplasmon effects, with an applied magnetic field in the Voigt geometry may inhibit the Casimir force. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Casimir-Polder interaction of neutrons with metal or dielectric surfaces
Gebhart, Valentin; Klatt, Juliane; Buhmann, Stefan Yoshi
2016-01-01
We predict a repulsive Casimir-Polder-type dispersion interaction between a single neutron and a metal or dielectric surface. Our model scenario assumes a single neutron subject to an external magnetic field. Due to its intrinsic magnetic moment, the neutron then forms a magnetisable two-level system which can exchange virtual photons with a nearby surface. The resulting dispersion interaction between a purely magnetic object (neutron) and a purely electric one (surface) is found to be repuls...
Algebraic approach to multiple defects on the line and application to Casimir force
Mintchev, M
2007-01-01
An algebraic framework for quantization in presence of arbitrary number of point-like defects on the line is developed. We consider a scalar field which interacts with the defects and freely propagates away of them. As an application we compute the Casimir force both at zero and finite temperature. We derive also the charge density in the Gibbs state of a complex scalar field with defects. The example of two delta-defects is treated in detail.
Casimir energies and special dimensions in a toy model for branes
Cohen, Isaac
1988-12-01
We consider a generalization to branes of the old action for the strings without reparamentrization invariance. These actions admit natural supplementary mass-shell conditions. By regularizing the Casimir energies we calculate the special dimensions at which these toy branes show vector massless states in its spectrum. They all turn out to be non-integers. On sabbatical leave from Departamento de Física, Facultad de Ciencias, Universidad Central de Venezuela, Apartado Postal 66961, Caracas 1061A, Venezuela.
Institute of Scientific and Technical Information of China (English)
Lou Zhi-Mei; Chen Zi-Dong; Wang Wen-Long
2005-01-01
In this paper, we express the differential equations of a noncentral dynamical system in Ermakov formalism to obtain the Ermakov invariant. In term of Hamiltonian theories and using the Ermakov invariant as the Hamiltonian,the Poisson structure of a noncentral dynamical system in four-dimensional phase space are constructed. The result indicates that the Poisson structure is degenerate and the noncentral dynamical system possesses four invariants: the Hamiltonian, the Ermakov invariant and two Casimir functions.
High-multipolar effects on the Casimir force: the non-retarded limit
Noguez, C; Esquivel-Sirvent, R; Villarreal, C; Noguez, Cecilia; Roman-Velazquez, Carlos E.; Esquivel-Sirvent, Raul; Villarreal, Carlos
2003-01-01
We calculate exactly the Casimir force or dispersive force, in the non-retarded limit, between a spherical nanoparticle and a substrate beyond the London's or dipolar approximation. We find that the force is a non-monotonic function of the distance between the sphere and the substrate, such that, it is enhanced by several orders of magnitude as the sphere approaches the substrate. Our results do not agree with previous predictions like the Proximity theorem approach.
Casimir energy of massive MIT fermions in a Bohm-Aharonov background
Beneventano, C G; Kirsten, K; Santangelo, E M
2000-01-01
We study the effect of a background flux string on the vacuum energy of massive Dirac fermions in 2+1 dimensions confined to a finite spatial region through MIT boundary conditions. We treat two admissible self-adjoint extensions of the Hamiltonian and compare the results. In particular, for one of these extensions, the Casimir energy turns out to be discontinuous at integer values of the flux.
Guérout, R.; Lambrecht, A.; Milton, K. A.; Reynaud, S.
2014-10-01
We carefully reexamine the conditions of validity for the consistent derivation of the Lifshitz-Matsubara sum formula for the Casimir pressure between metallic plane mirrors. We recover the usual expression for the lossy Drude model but not for the lossless plasma model. We give an interpretation of this new result in terms of the modes associated with the Foucault currents, which play a role in the limit of vanishing losses, in contrast to common expectations.
Do the precise measurements of the Casimir force agree with the expectations?
Svetovoy, V B
2000-01-01
An upper limit on the Casimir force is found using the dielectric functions of perfect crystalline materials which depend only on well defined material constants. The force measured with the atomic force microscope is larger than this limit at small separations between bodies and the discrepancy is significant. The simplest modification of the experiment is proposed allowing to make its results more reliable and answer the question if the discrepancy has any relation with the existence of a new force.
Dubail, J.; Santachiara, R.; Emig, T.
2017-03-01
Systems as diverse as binary mixtures and inclusions in biological membranes, and many more, can be described effectively by interacting spins. When the critical fluctuations in these systems are constrained by boundary conditions, critical Casimir forces (CCF) emerge. Here we analyze CCF between boundaries with alternating boundary conditions in two dimensions, employing conformal field theory (CFT). After presenting the concept of boundary changing operators, we specifically consider two different boundary configurations for a strip of critical Ising spins: (I) alternating equi-sized domains of up and down spins on both sides of the strip, with a possible lateral shift, and (II) alternating domains of up and down spins of different size on one side and homogeneously fixed spins on the other side of the strip. Asymptotic results for the CCF at small and large distances are derived. We introduce a novel modified Szegö formula for determinants of real antisymmetric block Toeplitz matrices to obtain the exact CCF and the corresponding scaling functions at all distances. We demonstrate the existence of a surface renormalization group flow between universal force amplitudes of different magnitude and sign. The Casimir force can vanish at a stable equilibrium position that can be controlled by parameters of the boundary conditions. Lateral Casimir forces assume a universal simple cosine form at large separations.
How does Casimir energy fall? II. Gravitational acceleration of quantum vacuum energy
Milton, Kimball A; Shajesh, K V; Wagner, Jef
2007-01-01
It has been demonstrated that quantum vacuum energy gravitates according to the equivalence principle, at least for the finite Casimir energies associated with perfectly conducting parallel plates. We here add further support to this conclusion by considering parallel semitransparent plates, that is, delta-function potentials, acting on a massless scalar field, in a spacetime defined by Rindler coordinates (tau,x,y,xi). Fixed xi in such a spacetime represents uniform acceleration. We calculate the force on systems consisting of one or two such plates at fixed values of xi. In the limit of large Rindler coordinate xi (small acceleration), we recover (via the equivalence principle) the situation of weak gravity, and find that the gravitational force on the system is just Mg, where g is the gravitational acceleration and M is the total mass of the system, consisting of the mass of the plates renormalized by the Casimir energy of each plate separately, plus the energy of the Casimir interaction between the plates...
Invariance of bipartite separability and PPT-probabilities over Casimir invariants of reduced states
Slater, Paul B.
2016-09-01
Milz and Strunz (J Phys A 48:035306, 2015) recently studied the probabilities that two-qubit and qubit-qutrit states, randomly generated with respect to Hilbert-Schmidt (Euclidean/flat) measure, are separable. They concluded that in both cases, the separability probabilities (apparently exactly 8/33 in the two-qubit scenario) hold constant over the Bloch radii ( r) of the single-qubit subsystems, jumping to 1 at the pure state boundaries (r=1). Here, firstly, we present evidence that in the qubit-qutrit case, the separability probability is uniformly distributed, as well, over the generalized Bloch radius ( R) of the qutrit subsystem. While the qubit (standard) Bloch vector is positioned in three-dimensional space, the qutrit generalized Bloch vector lives in eight-dimensional space. The radii variables r and R themselves are the lengths/norms (being square roots of quadratic Casimir invariants) of these ("coherence") vectors. Additionally, we find that not only are the qubit-qutrit separability probabilities invariant over the quadratic Casimir invariant of the qutrit subsystem, but apparently also over the cubic one—and similarly the case, more generally, with the use of random induced measure. We also investigate two-qutrit (3 × 3) and qubit- qudit (2 × 4) systems—with seemingly analogous positive partial transpose-probability invariances holding over what has been termed by Altafini the partial Casimir invariants of these systems.
Critical Casimir force and its fluctuations in lattice spin models: exact and Monte Carlo results.
Dantchev, Daniel; Krech, Michael
2004-04-01
We present general arguments and construct a stress tensor operator for finite lattice spin models. The average value of this operator gives the Casimir force of the system close to the bulk critical temperature T(c). We verify our arguments via exact results for the force in the two-dimensional Ising model, d -dimensional Gaussian, and mean spherical model with 2Monte Carlo simulations for three-dimensional Ising, XY, and Heisenberg models we demonstrate that the standard deviation of the Casimir force F(C) in a slab geometry confining a critical substance in-between is k(b) TD(T) (A/ a(d-1) )(1/2), where A is the surface area of the plates, a is the lattice spacing, and D(T) is a slowly varying nonuniversal function of the temperature T. The numerical calculations demonstrate that at the critical temperature T(c) the force possesses a Gaussian distribution centered at the mean value of the force = k(b) T(c) (d-1)Delta/ (L/a)(d), where L is the distance between the plates and Delta is the (universal) Casimir amplitude.
Kelvin probe force microscopy of metallic surfaces used in Casimir force measurements
Behunin, R. O.; Dalvit, D. A. R.; Decca, R. S.; Genet, C.; Jung, I. W.; Lambrecht, A.; Liscio, A.; López, D.; Reynaud, S.; Schnoering, G.; Voisin, G.; Zeng, Y.
2014-12-01
Kelvin probe force microscopy at normal pressure was performed by two different groups on the same Au-coated planar sample used to measure the Casimir interaction in a sphere-plane geometry. The obtained voltage distribution was used to calculate the separation dependence of the electrostatic pressure Pres(D ) in the configuration of the Casimir experiments. In the calculation it was assumed that the potential distribution in the sphere has the same statistical properties as the measured one, and that there are no correlation effects on the potential distributions due to the presence of the other surface. The result of this calculation, using the currently available knowledge, is that Pres(D ) does not explain the magnitude or the separation dependence of the difference Δ P (D ) between the measured Casimir pressure and the one calculated using a Drude model for the electromagnetic response of Au. We discuss in the conclusions the points which have to be checked out by future work, including the influence of pressure and a more accurate determination of the patch distribution, in order to confirm these results.
Scalar cylinder-plate and cylinder-cylinder Casimir interaction in higher dimensional spacetime
Teo, L P
2015-01-01
We study the cylinder-plate and the cylinder-cylinder Casimir interaction in the $(D+1)$-dimensional Minkowski spacetime due to the vacuum fluctuations of massless scalar fields. Different combinations of Dirichlet (D) and Neumann (N) boundary conditions are imposed on the two interacting objects. For the cylinder-cylinder interaction, we consider the case where one cylinder is inside the other, and the case where the two cylinders are outside each other. By computing the transition matrices of the objects and the translation matrices that relate different coordinate systems, the explicit formulas for the Casimir interaction energies are derived. Using perturbation technique, we compute the small separation asymptotic expansions of the Casimir interaction energies up to the next-to-leading order terms. The leading terms coincide with the respective results obtained using proximity force approximation, which is of order $d^{-D+1/2}$, where $d$ is the distance between the two objects. The results on the next-to...
Casimir type effects as a source of Dark Energy. Deformed QCD as a toy model
Thomas, Evan
2011-01-01
We study a Casimir-like behaviour in the so-called "deformed QCD". We demonstrate that for the system defined on a manifold size \\mathbb L the \\theta- dependent portion of the energy shows the Casimir-like scaling E = - A\\cdot [1 + \\frac{B}{\\mathbb L} +{\\cal O}(\\frac{1}{\\mathbb L^2})] despite the presence of a mass gap in the system, in contrast with naive expectation E = - A\\cdot [1 + {B}\\exp(-m{\\mathbb L})] which would normally originate from any physical massive propagating degrees of freedom consequent to conventional dispersion relations. The Casimir-like behaviour in our system comes instead from non-dispersive ("contact") term which is not related to any physical propagating degrees of freedom, such that the naive argument is simply not applicable. These ideas can be explicitly tested as the "deformations" bring QCD into weakly coupled regime, such that all computations are under complete theoretical control, while retaining the essential properties of real strongly coupled QCD. We speculate that the p...
Casimir friction and near-field radiative heat transfer in graphene structures
Energy Technology Data Exchange (ETDEWEB)
Volokitin, A.I. [Forschungszentrum Juelich (Germany). Peter Gruenberg Inst.; Samara State Technical Univ. (Russian Federation). Physical Dept.
2017-05-01
The dependence of the Casimir friction force between a graphene sheet and a (amorphous) SiO{sub 2} substrate on the drift velocity of the electrons in the graphene sheet is studied. It is shown that the Casimir friction is strongly enhanced for the drift velocity above the threshold velocity when the friction is determined by the resonant excitation of the surface phonon-polaritons in the SiO{sub 2} substrate and the electron-hole pairs in graphene. The theory agrees well with the experimental data for the current-voltage dependence for unsuspended graphene on the SiO{sub 2} substrate. The theories of the Casimir friction and the near-field radiative energy transfer are used to study the heat generation and dissipation in graphene due to the interaction with phonon-polaritons in the (amorphous) SiO{sub 2} substrate and acoustic phonons in graphene. For suspended graphene, the energy transfer coefficient at nanoscale gap is ∝ three orders of magnitude larger than the radiative heat transfer coefficient of the blackbody radiation limit.
Radiative correction to the Casimir energy for massive scalar field on a spherical surface
Valuyan, M. A.
2017-08-01
In this paper, the first-order radiative correction to the Casimir energy for a massive scalar field in the ϕ4 theory on a spherical surface with S2 topology was calculated. In common methods for calculating the radiative correction to the Casimir energy, the counter-terms related to free theory are used. However, in this study, by using a systematic perturbation expansion, the obtained counter-terms in renormalization program were automatically position-dependent. We maintained that this dependency was permitted, reflecting the effects of the boundary conditions imposed or background space in the problem. Additionally, along with the renormalization program, a supplementary regularization technique that we named Box Subtraction Scheme (BSS) was performed. This scheme presents a useful method for the regularization of divergences, providing a situation that the infinities would be removed spontaneously without any ambiguity. Analysis of the necessary limits of the obtained results for the Casimir energy of the massive and massless scalar field confirmed the appropriate and reasonable consistency of the answers.
Casimir interaction between normal or superfluid grains in the Fermi sea
Wirzba, A; Magierski, P; Wirzba, Andreas; Bulgac, Aurel; Magierski, Piotr
2005-01-01
We report on a new force that acts on cavities (literally empty regions of space) when they are immersed in a background of non-interacting fermionic matter fields. The interaction follows from the obstructions to the (quantum mechanical) motions of the fermions caused by the presence of bubbles or other (heavy) particles in the Fermi sea, as, for example, nuclei in the neutron sea in the inner crust of a neutron star or superfluid grains in a normal Fermi liquid. The effect resembles the traditional Casimir interaction between metallic mirrors in the vacuum. However, the fluctuating electromagnetic fields are replaced by fermionic matter fields. We show that the fermionic Casimir problem for a system of spherical cavities can be solved exactly, since the calculation can be mapped onto a quantum mechanical billiard problem of a point-particle scattered off a finite number of non-overlapping spheres or disks. Finally we generalize the map method to other Casimir systems, especially to the case of a fluctuating...
Casimir Friction and Near-field Radiative Heat Transfer in Graphene Structures
Volokitin, A. I.
2017-02-01
The dependence of the Casimir friction force between a graphene sheet and a (amorphous) SiO2 substrate on the drift velocity of the electrons in the graphene sheet is studied. It is shown that the Casimir friction is strongly enhanced for the drift velocity above the threshold velocity when the friction is determined by the resonant excitation of the surface phonon-polaritons in the SiO2 substrate and the electron-hole pairs in graphene. The theory agrees well with the experimental data for the current-voltage dependence for unsuspended graphene on the SiO2 substrate. The theories of the Casimir friction and the near-field radiative energy transfer are used to study the heat generation and dissipation in graphene due to the interaction with phonon-polaritons in the (amorphous) SiO2 substrate and acoustic phonons in graphene. For suspended graphene, the energy transfer coefficient at nanoscale gap is three orders of magnitude larger than the radiative heat transfer coefficient of the blackbody radiation limit.
Energy Technology Data Exchange (ETDEWEB)
Campoamor-Stursberg, Rutwig [Depto. Geometria y Topologia, Fac. cc. Matematicas UCM, E-28040 Madrid (Spain)
2004-10-08
We show that the Casimir operators of the semidirect products G{sub 2} {rvec {circle_plus}}{sub 2{gamma}{sub (a,b){circle_plus}{Lambda}{sub (0,0)}}}h of the exceptional Lie algebra G{sub 2} and a Heisenberg algebra h can be constructed explicitly from the Casimir operators of G{sub 2}.
Directory of Open Access Journals (Sweden)
LIN Ruihui
2014-02-01
Full Text Available We reconsider the thermal scalar Casimir effect for p-dimensional hypercubic cavity inside D+1-dimensional Minkowski space-time.The thermal Casimir free energy can be divided into the divergent zero-temperature part and the automatically finite temperature-dependent part through standard quantum field theory treatments.Due to the finiteness,the regularization of the temperature-dependent part,which is also required for the convergency of the Casimir energy and the vanishing of the Casimir force with the separation increasing to infinity,is neglected in some literatures.We derive rigorously the regularization of the zero temperature part as well as the temperature-dependent part of the free energy by making use of the zeta function technique and the Abel-Plana formula.In the cases of D=3,p=1 and D=3,p=3,we precisely recover the results of parallel plates and three-dimensional box in the literature.And explicit expressions of the Casimir free energy in both low temperature (small separations and high temperature (large separations regimes are given,through which we find that after the regularization of both parts,with the side length going to infinity the force always tends to zero for different boundary conditions.Our study may be helpful in providing a comprehensive and complete understanding of this old problem.
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Pablo Mibielli
2014-09-01
Full Text Available O objetivo deste estudo foi estimar a prevalência de interações medicamentosas potenciais entre anti-hipertensivos e outros fármacos. Foi realizado um inquérito domiciliar com pessoas de 60 anos ou mais de idade, residentes no Rio de Janeiro, Brasil. Foram identificadas as interações medicamentosas potenciais entre os anti- hipertensivos com evidência estabelecida, provável ou suspeita e com gravidade moderada ou elevada. Foram entrevistados 577 idosos (média de idade = 72 anos, 45,2% dos quais em uso de anti-hipertensivos, sendo 31,0% deles sujeitos a interações medicamentosas potenciais. A maioria das interações foi moderadamente grave. Comparados aos demais, os sujeitos às interações medicamentosas potenciais têm chance acima de 4 vezes de usar 5 ou mais medicamentos e acima de duas vezes de ter sido hospitalizado no ano anterior. Entre os pares de interações mais frequentes, 75% produzem redução do efeito hipotensivo (65/87, o que pode resultar em baixa efetividade no controle da pressão arterial, prescrição de mais medicamentos e risco de outros efeitos adversos e de interações.
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Marianne Weber Arnold
2007-11-01
Full Text Available OBJETIVOS: determinar a freqüência dos óbitos de mulheres em idade fértil segundo os quatro principais grupos de causas básicas de óbito, calcular os Anos Potenciais de Vida Perdidos (APVP para homicídio, comparando-o com as outras causas de morte mais freqüentes e os coeficientes de APVP destas quatro causas de óbito. MÉTODOS: estudo descritivo, tipo corte transversal, incluindo as declarações de óbito de mulheres com idade entre 10 e 49 anos, na cidade de Recife, Pernambuco, nos anos de 2001 a 2002. A causa básica de óbito foi classificada de acordo com a CID-10, os APVP foram analisados segundo critérios do Ministério da Saúde e de Romeder e McWhinnie, utilizando-se o Epi-Info 2000. RESULTADOS: o grupo das neoplasias foi a causa de óbito mais freqüente (25,7%, seguida das doenças do aparelho circulatório (21,2%, causas externas (17,6 e doença infecciosa e parasitária (9,6%. Os homicídios foram responsáveis por 49% (4380 do total de anos potenciais de vida perdidos, com um coeficiente de APVP de 8,82. O coeficiente de APVP para câncer de mama correspondeu a 4,14 e 3,77 para o infarto agudo do miocárdio. CONCLUSÕES: o risco das mulheres perderem anos potenciais de vida por homicídio foi 2,1 vezes maior do que por câncer de mama e 2,3 do que por infarto agudo do miocárdio.OBJECTIVES: to determine the frequency of death among women of child-bearing age, according to the main groups of basic causes of death; to calculate the Years of Potential Life Lost (YPLL for homicide, comparing this index to the other most frequent causes of death; and to determine the YPLL coefficient for all four causes of death. METHODS: a descriptive, cross-sectional cohort study was carried out using the death certificates of women aged between 10 and 49 years in the city of Recife, State of Pernambuco, Brazil, in 2001 and 2002. The basic cause of death was classified according to the ICD-10; the YPLL was analyzed according to the criteria
Marques,Otavio Augusto Vuolo; NOGUEIRA, Cristiano; Martins, Marcio; Sawaya, Ricardo Jannini [UNIFESP
2010-01-01
Avaliamos os impactos potenciais sobre a fauna brasileira de répteis (721 espécies descritas até o momento), caso sejam adotadas mudanças propostas por um substitutivo do atual Código Florestal Brasileiro. A possibilidade de compensação ambiental (obrigação legal no caso de degradação de habitats naturais) em bacias ou microbacias distintas daquelas degradadas seria uma das modificações do código vigente que prejudicaria a manutenção da diversidade de répteis. Alguns gêneros de répteis são co...
Bimonte, Giuseppe
2010-01-01
The possibility of making precise predictions for the Casimir force is essential for addressing the striking contradiction that has arisen between the a new large distance Casimir experiment with gold plates, that has been interpreted as being consistent with the so-called Drude prescription and to rule out the plasma prescription, and a series of older precise short distance experiments, which were instead interpreted as being consistent with the plasma prescription and to rule out the Drude one. In a previous paper by the author [Phys. Rev. A {\\bf 81}, 062501 (2010)] it was shown that a precise prediction of the Casimir force is possible in principle by a simple modification of the standard Kramers-Kronig relations, involving suitable analytic window functions, solely on the basis of experimental optical data in the frequency interval where they are available, without using uncontrolled data extrapolations towards zero frequency that are necessary with standard Kramers-Kronig relations. In the present paper...
Borjan, Z.
2016-09-01
We consider critical Casimir force in the Ising strips with boundary conditions defined by standard normal and ordinary surface universality classes containing also the internal grain boundary. Using exact variational approach of Mikheev and Fisher we have elaborated on behaviors of Casimir amplitudes Δ++(g) , ΔOO(g) and Δ+O(g) , corresponding to normal-normal, ordinary-ordinary and mixed normal-ordinary boundary conditions, respectively, with g as a strength of the grain boundary. Closed analytic results describe Casimir amplitudes Δ++(g) and ΔOO(g) as continuous functions of the grain boundary's strength g, changing the character of the Casimir force from repulsive to attractive and vice versa for certain domains of g. Present results reveal a new type of symmetry between Casimir amplitudes Δ++(g) and ΔOO(g) . Unexpectedly simple constant result for the Casimir amplitude Δ+O(g) = π/12 we have comprehensively interpreted in terms of equilibrium states of the present Ising strip as a complex interacting system comprising two sub-systems. Short-distance expansions of energy density profiles in the vicinity of the grain boundary reveal new distant-wall correction amplitudes that we examined in detail. Analogy of present considerations with earlier more usual short-distance expansions near one of the (N), (O) and (SB) boundaries, as well as close to surfaces with variable boundary conditions refers to the set of scaling dimensions appearing in the present calculations but also to the discovery of the de Gennes-Fisher distant wall correction amplitudes.
Energy Technology Data Exchange (ETDEWEB)
Klimchitskaya, G.L.; Mostepanenko, V.M. [Central Astronomical Observatory at Pulkovo of the Russian Academy of Sciences, St. Petersburg (Russian Federation); St. Petersburg State Polytechnical University, Institute of Physics, Nanotechnology and Telecommunications, St. Petersburg (Russian Federation)
2015-04-01
We obtain improved constraints on the coupling constants of axion-like particles to nucleons from a recently performed Casimir-less experiment. For this purpose, the differential force between a Au-coated sphere and either the Au or the Si sector of a rotating disc, arising due to two-axion exchange, is calculated. Over a wide region of axion masses, from 1.7 x 10{sup -3} eV to 0.9 eV, the obtained constraints are up to a factor of 60 stronger than the previously known ones following from the Cavendish-type experiment and measurements of the effective Casimir pressure. (orig.)
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Renata Filippini
2009-06-01
Full Text Available Although the clinical use of click stimuli to assess auditory function at the brainstem is already established, and numerous research projects use such stimuli to study human hearing, little is known about the auditory processing of a complex stimulus like speech. AIM: This study aimed at validating the speech stimulus as an effective method to evaluate speech auditory processing, to help us better understand its disorders. MATERIALS AND METHODS:This prospective clinical study tested 20 subjects with Auditory Processing Disorders (APD and 20 subjects with normal development (ND - control group using the Brainstem Auditory Evoked Potentials with clicks and speech stimuli. The latter is based on first 40ms of the spoken syllable /da/. RESULTS: No differences were observed between the groups regarding the click stimulus. However, with the speech stimulus the APD group presented latency delay and lower amplitudes when compared to the ND group. CONCLUSION: Speech stimulus proved to be more sensitive for the evaluation of Auditory Processing Disorders, showing possible alterations in synchronicity and speech processing neural input speed, especially as to the linguistic information of the latter.Embora o uso clínico do estímulo clique na avaliação da função auditiva no tronco encefálico já esteja bastante difundido e uma variedade de pesquisas use tal estímulo no estudo da audição humana, pouco se sabe a respeito do processamento auditivo de estímulos complexos como a fala. OBJETIVO: O presente estudo buscou validar o estímulo de fala como método efetivo de avaliação do processamento auditivo da fala. CASUÍSTICA E MÉTODO: Neste estudo clínico prospectivo, 20 sujeitos portadores de transtorno do processamento auditivo (TPA - grupo estudo e 20 sujeitos com desenvolvimento típico (DT - grupo controle foram testados quanto aos Potenciais Evocados Auditivos de Tronco Encefálico para estímulo clique e para estímulo de fala, o qual
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Dzedzej, Maira; Correa, Fabio; Malta, Joao [IX Consultoria e Representacoes Ltda, Itajuba, MG (Brazil); Flauzino, Barbara Karoline [IX Consultoria e Representacoes Ltda, Itajuba, MG (Brazil); Universidade Federal de Itajuba (UNIFEI), MG (Brazil); Santos, Afonso Henriques Moreira [MS Consultoria Ltda, Itajuba, MG (Brazil); Universidade Federal de Itajuba (UNIFEI), MG (Brazil)
2010-07-01
The hydropower plants are responsible for much of the energy generated in the country, there is also a large hydro potential in Brazilian rivers. This form of power generation is considered renewable and fits into the concept of sustainable development, however, social and environmental impacts from the implementation of hydropower projects are known and widely discussed, especially when it comes to large plants. In this context, study the environmental analysis of potential hydropower was incorporated at various stages of the studies implementation, in order to, identify environmental factors and that will restrict or impede construction, to obtain the best option for the environment, evaluate the role and of social and environmental impacts, contribute to improving the design and functionality of the enterprises in order to reduce overall costs, minimize conflicts and assist in preserving the environment. To fulfill these functions to a satisfactory and reliable level, it the study has increasingly used the techniques, tools and applications of Geographic Information Systems in the process of environmental assessment, since they provide procurement, integration, visualization and data analysis of natural resources, its uses and protection, offering greater security and speed in decision making. This paper presents some applications of GIS in environmental assessment processes, developed mainly in the steps of estimating hydropower potential, hydropower inventory, basic design and environmental licensing. (author)
ESPÉCIES ARBÓREAS POTENCIAIS PARA A REVEGETAÇÃO DE REJEITO SALINO CONTAMINADO COM ARSÊNIO
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Lorena Abdalla de Oliveira Prata Guimarães
2017-01-01
Full Text Available The processing of gold ores exploited in Paracatu, MG, generates tailings with chemical and physical characteristics adverse to plants growth, mainly by high concentration of arsenic (As and salinity. The revegetation of this material requeres identify species capable of grow under these conditions. This study aimed to evaluate the potential of four tree species for revegetation of saline tailing contaminated with As. The planting substrate consisted of tailings from processing of ore called B1. The species Tibouchina granulosa (quaresmeira, Schizolobium amazonicum Huber ex Ducke (paricá, Euterpe edulis Mart. (juçara and Cassia grandis (cássia-rósea were planted by seedlings and, after four months, the atributes of the substrate and plants were evaluated. Several plants showed symptoms possibly caused by As-toxicity. These symptoms were more evident and intense in quaresmeira and juçara. However, only the plants of quaresmeira died, probably due to the high rate of As-translocation (51 % and absence of tolerance mechanisms of the specie. The potential use of species for revegetation of tailings follows the order paricá > cássia-rósea. Paricá is the one with the greatest potential for initial deployment of vegetation, demonstrating the greater ability to adapt to tailing characteristics. The juçara and quaresmeira species are not recommended for the revegetation of tailings. Probably arsenic and/or salinity affect the development of plants, being lethal to quaresmeira.
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Henrique Machado Dias
2014-01-01
Full Text Available In Caravelas, located in southern Bahia state, the main vegetation formations are the mangrove forests and ‘restingas’ (sandbanks presenting, the latter, a high degree of degradation. The aim of this paper is to describe the main forest species of these ‘restingas’ and their direct uses associated with the recovery and management of degraded areas and creation of jobs and income, making thus an important tool for integrated coastal zone. For this, elaborate floral listings and field visits were necessary for recognizing the environment. In the selection of species, a literature about the use, management and value of each species were used, and from there, four species with potential for generating jobs and income along of this proposal were recognized: Mangaba ( Hancornia speciosa , Pitanga ( Eugenia uniflora , Mangaba ( Anacardium occidentale and Aroeira ( Schinus terebinthifolius . The first three are associated with the use of its fruit food, serving these ‘aroeiras’ as pepper trees, with a high value on the world market, and cashew, because of its fertile structure. The identification of products provided sustainable use of species and environment and the Non-Timber Forest Products can be strategic in coastal management, making it an instrument to subsidize social inclusion through the creation of jobs and income, under the movement of Social Technology, contributing to reduce the social vulnerability of traditional coastal communities.
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NONE
2009-10-15
The evaluation of the potential areas for the expansion of the sugar cane cultivation was based on the estimation of the agricultural productivity aptitude as function of the soil and climate characteristics using maps with geo referred in scales of 1/5,000,000. Areas had been discarded which integrate of three large biomass of the country: Amazonia, Pantanal and Mata Atlantica, and all the areas with some type of restriction, such as environmental reservations, national parks, indigenous, military and urban areas. Were not considered areas with crop mechanization essential for the environmental and social sustainability with declivity more than 12%.
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Petraconi, G.; Maciel, H.S.; Borges, C. [Centro Tecnico Aeroespacial, Sao Jose dos Campos, SP (Brazil). Inst. Tecnologico de Aeronautica. Lab. de Plasmas e Processos
1999-12-01
In this paper two circuits for plasma potential measurement are presented. The first one is an emissive probe control circuit for fast probe characteristics reading. The second one is a differential emissive probe control circuit that adjusts the bias voltage automatically and allows a direct potential measurement. These circuits present inconveniences if the characteristic of the probe does not exhibit an ideal saturation of the current as show the results obtained in continuous current discharge and RF discharge. (author)
Phillips, Nicholas G.; Hu, B. L.
2000-10-01
We present calculations of the variance of fluctuations and of the mean of the energy momentum tensor of a massless scalar field for the Minkowski and Casimir vacua as a function of an intrinsic scale defined by a smeared field or by point separation. We point out that, contrary to prior claims, the ratio of variance to mean-squared being of the order unity is not necessarily a good criterion for measuring the invalidity of semiclassical gravity. For the Casimir topology we obtain expressions for the variance to mean-squared ratio as a function of the intrinsic scale (defined by a smeared field) compared to the extrinsic scale (defined by the separation of the plates, or the periodicity of space). Our results make it possible to identify the spatial extent where negative energy density prevails which could be useful for studying quantum field effects in worm holes and baby universes, and for examining the design feasibility of real-life ``time machines.'' For the Minkowski vacuum we find that the ratio of the variance to the mean-squared, calculated from the coincidence limit, is identical to the value of the Casimir case at the same limit for spatial point separation while identical to the value of a hot flat space result with a temporal point separation. We analyze the origin of divergences in the fluctuations of the energy density and discuss choices in formulating a procedure for their removal, thus raising new questions about the uniqueness and even the very meaning of regularization of the energy momentum tensor for quantum fields in curved or even flat spacetimes when spacetime is viewed as having an extended structure.
Tratamento eletroquímico e físico-químico para efluente de lavanderia industrial têxtil
Gonçalves, Leandro Vicente
2015-01-01
A lavanderia industrial têxtil é caracterizada pela variedade dos processos aplicados, pelo alto volume de efluentes gerados e pela carga poluidora. A caracterização física e química destes efluentes é de suma importância para determinação do tratamento apropriado, bem como para avaliação dos agentes poluentes e seus impactos potenciais. Desta forma, o desenvolvimento do presente estudo permite o aperfeiçoamento do conhecimento acerca dos processos eletroquímicos e físico-químico para a remoç...
Self-adjointness and the Casimir effect with confined quantized spinor matter
Sitenko, Yurii A
2015-01-01
A generalization of the MIT bag boundary condition for spinor matter is proposed basing on the requirement that the Dirac hamiltonian operator be self-adjoint. An influence of a background magnetic field on the vacuum of charged spinor matter confined between two parallel material plates is studied. Employing the most general set of boundary conditions at the plates in the case of the uniform magnetic field directed orthogonally to the plates, we find the pressure from the vacuum onto the plates. In physically plausible situations, the Casimir effect is shown to be repulsive, independently of a choice of boundary conditions and of a distance between the plates.
MIR: An experiment for the measurement of the dynamical Casimir effect
Energy Technology Data Exchange (ETDEWEB)
Agnesi, A; Pirzio, F; Reali, G; Scarpa, D [Dipartimento di Elettronica, Universita di Pavia, Via Ferrata 1, 27100 Pavia (Italy); Braggio, C; Galeazzi, G [Dipartimento di Fisica, Universita di Padova, via Marzolo 8, 35131 Padova (Italy); Bressi, G [INFN sez. di Pavia, via Bassi 6, 27100 Pavia (Italy); Carugno, G [INFN sez. di Padova, via Marzolo 8, 35131 Padova (Italy); Valle, F Della; Messineo, G [INFN sez. di Trieste and Dipartimento di Fisica, Universita di Trieste, Via Valerio 2, 34127 Trieste (Italy); Ruoso, G [INFN lab. naz. Legnaro, viale dell' Universita 2, 35020 Legnaro (Pd) (Italy); Zanello, D, E-mail: Caterina.Braggio@pd.infn.i [INFN sez. di Roma, P.le A. Moro 2, 00185 Roma (Italy)
2009-04-01
In this paper we report the status of the experiment MIR (Motion Induced Radiation), aimed at the experimental verification of the dynamical Casimir effect. The stringent theoretical requirements to observe the effect are satisfied in a scheme in which the conductivity of a semiconductor inside a superconducting microwave resonant cavity is varied in time. Free carriers in the semiconductor are periodically excited and recombine at 5 GHz. In this process vacuum and thermal photons are parametrically amplified in a time interval of 200-500 ns.
Aether field in extra dimensions: Stefan-Boltzmann law and Casimir effect at finite temperature
Santos, A. F.; Khanna, Faqir C.
2017-01-01
The Lorentz and C P T symmetries are not violated at the highest laboratory energies available. However these symmetries may be violated at Planck scale. A particular development is to investigate the breakdown of Lorentz and C P T symmetries by introducing an aether field that exhibits nonzero vacuum expectation value along the fifth dimension. The interactions of the aether field with scalar, electromagnetic, and fermions fields are analyzed. The Stefan-Boltzmann law and Casimir effect at finite temperature are calculated using the Thermo Field Dynamics formalism.
Casimir effect at finite temperature for pure-photon sector of the minimal Standard Model Extension
Energy Technology Data Exchange (ETDEWEB)
Santos, A.F., E-mail: alesandroferreira@fisica.ufmt.br [Instituto de Física, Universidade Federal de Mato Grosso, 78060-900, Cuiabá, Mato Grosso (Brazil); Department of Physics and Astronomy, University of Victoria, 3800 Finnerty Road Victoria, BC (Canada); Khanna, Faqir C., E-mail: khannaf@uvic.ca [Department of Physics and Astronomy, University of Victoria, 3800 Finnerty Road Victoria, BC (Canada)
2016-12-15
Dynamics between particles is governed by Lorentz and CPT symmetry. There is a violation of Parity (P) and CP symmetry at low levels. The unified theory, that includes particle physics and quantum gravity, may be expected to be covariant with Lorentz and CPT symmetry. At high enough energies, will the unified theory display violation of any symmetry? The Standard Model Extension (SME), with Lorentz and CPT violating terms, has been suggested to include particle dynamics. The minimal SME in the pure photon sector is considered in order to calculate the Casimir effect at finite temperature.
Lifshitz-Matsubara sum formula for the Casimir pressure between magnetic metallic mirrors
Guérout, R.; Lambrecht, A.; Milton, K. A.; Reynaud, S.
2016-02-01
We examine the conditions of validity for the Lifshitz-Matsubara sum formula for the Casimir pressure between magnetic metallic plane mirrors. As in the previously studied case of nonmagnetic materials [Guérout et al., Phys. Rev. E 90, 042125 (2014), 10.1103/PhysRevE.90.042125], we recover the usual expression for the lossy model of optical response, but not for the lossless plasma model. We also show that the modes associated with the Foucault currents play a crucial role in the limit of vanishing losses, in contrast to expectations.
Casimir force between $\\delta-\\delta^{\\prime}$ mirrors transparent at high frequencies
Braga, Alessandra N; Alves, Danilo T
2016-01-01
We investigate, in the context of a real massless scalar field in $1+1$ dimensions, models of partially reflecting mirrors simulated by Dirac $\\delta-\\delta^{\\prime}$ point interactions. In the literature, these models do not exhibit full transparency at high frequencies. In order to provide a more realistic feature for these models, we propose a modified $\\delta-\\delta^{\\prime}$ point interaction that enables to achieve full transparency in the limit of high frequencies. Taking this modified $\\delta-\\delta^{\\prime}$ model into account, we investigate the Casimir force, comparing our results with those found in the literature.
Precision Measurement of the Casimir Force for Au Using a Dynamic Afm
Chang, C.-C.; Banishev, A. A.; Castillo-Garza, R.; Klimchitskaya, G. L.; Mostepanenko, V. M.; Mohideen, U.
2012-07-01
The gradient of the Casimir force between carefully cleaned Au surfaces of a sphere and a plate is measured using a dynamic atomic force microscope in the frequency modulation regime in high vacuum. The electrostatic calibration of the setup did not reveal any effect of patches or surface contaminants. The experimental data for the force gradient are found to be consistent with theory using the plasma model approach over the entire measurement range. The Drude model approach is excluded by the data at separations from 235 to 400 nm at a 67% confidence level.
Xiong, Jie L; Atkins, Phillip; Chew, Weng Cho
2010-01-01
In this paper, we generalized the surface integral equation method for the evaluation of Casimir force in arbitrary three-dimensional geometries. Similar to the two-dimensional case, the evaluation of the mean Maxwell stress tensor is cast into solving a series of three-dimensional scattering problems. The formulation and solution of the three-dimensional scattering problem is well-studied in classical computational electromagnetics. This paper demonstrates that this quantum electrodynamic phenomena can be studied using the knowledge and techniques of classical electrodynamics.
Experiments on Sphere Cylinder Geometry Dependence in the Electromagnetic Casimir Effect
Mukhopadhyay, Shomeek; Noruzifar, Ehsan; Wagner, Jeffrey; Zandi, Roya; Mohideen, Umar
2013-03-01
We report on ongoing experimental investigations on the geometry dependence of the electromagnetic Casimir force in the sphere-cylinder configuration. A gold coated hollow glass sphere which forms one surface is attached to a Silicon AFM cantilever. The cylinder, which is constructed from tapered optical fiber is also gold coated. The resonance frequency shift of the cantilever is measured as a function of the sphere-cylinder surface separation. The sphere-cylinder electrostatic force is used for alignment of the sphere and the cylinder and also for calibrating the system. The results are compared to numerical simulations in the framework of the Proximity Force Approximation (PFA).
Nori, Franco
2012-02-01
This talk will present an overview of some of our recent results on atomic physics and quantum optics using superconducting circuits. Particular emphasis will be given to photons interacting with qubits, interferometry, the Dynamical Casimir effect, and also studying Majorana fermions using superconducting circuits.[4pt] References available online at our web site:[0pt] J.Q. You, Z.D. Wang, W. Zhang, F. Nori, Manipulating and probing Majorana fermions using superconducting circuits, (2011). Arxiv. J.R. Johansson, G. Johansson, C.M. Wilson, F. Nori, Dynamical Casimir effect in a superconducting coplanar waveguide, Phys. Rev. Lett. 103, 147003 (2009). [0pt] J.R. Johansson, G. Johansson, C.M. Wilson, F. Nori, Dynamical Casimir effect in superconducting microwave circuits, Phys. Rev. A 82, 052509 (2010). [0pt] C.M. Wilson, G. Johansson, A. Pourkabirian, J.R. Johansson, T. Duty, F. Nori, P. Delsing, Observation of the Dynamical Casimir Effect in a superconducting circuit. Nature, in press (Nov. 2011). P.D. Nation, J.R. Johansson, M.P. Blencowe, F. Nori, Stimulating uncertainty: Amplifying the quantum vacuum with superconducting circuits, Rev. Mod. Phys., in press (2011). [0pt] J.Q. You, F. Nori, Atomic physics and quantum optics using superconducting circuits, Nature 474, 589 (2011). [0pt] S.N. Shevchenko, S. Ashhab, F. Nori, Landau-Zener-Stuckelberg interferometry, Phys. Reports 492, 1 (2010). [0pt] I. Buluta, S. Ashhab, F. Nori. Natural and artificial atoms for quantum computation, Reports on Progress in Physics 74, 104401 (2011). [0pt] I.Buluta, F. Nori, Quantum Simulators, Science 326, 108 (2009). [0pt] L.F. Wei, K. Maruyama, X.B. Wang, J.Q. You, F. Nori, Testing quantum contextuality with macroscopic superconducting circuits, Phys. Rev. B 81, 174513 (2010). [0pt] J.Q. You, X.-F. Shi, X. Hu, F. Nori, Quantum emulation of a spin system with topologically protected ground states using superconducting quantum circuit, Phys. Rev. A 81, 063823 (2010).
Zeta Function Regularization in Casimir Effect Calculations and J. S. Dowker's Contribution
Elizalde, Emilio
2012-07-01
A summary of relevant contributions, ordered in time, to the subject of operator zeta functions and their application to physical issues is provided. The description ends with the seminal contributions of Stephen Hawking and Stuart Dowker and collaborators, considered by many authors as the actual starting point of the introduction of zeta function regularization methods in theoretical physics, in particular, for quantum vacuum fluctuation and Casimir effect calculations. After recalling a number of the strengths of this powerful and elegant method, some of its limitations are discussed. Finally, recent results of the so called operator regularization procedure are presented.
Casimir effect at finite temperature for pure-photon sector of the minimal Standard Model Extension
Santos, A. F.; Khanna, Faqir C.
2016-12-01
Dynamics between particles is governed by Lorentz and CPT symmetry. There is a violation of Parity (P) and CP symmetry at low levels. The unified theory, that includes particle physics and quantum gravity, may be expected to be covariant with Lorentz and CPT symmetry. At high enough energies, will the unified theory display violation of any symmetry? The Standard Model Extension (SME), with Lorentz and CPT violating terms, has been suggested to include particle dynamics. The minimal SME in the pure photon sector is considered in order to calculate the Casimir effect at finite temperature.
NC plane waves, Casimir effect and flux tube potential with L\\"uscher terms
Kováčik, Samuel
2016-01-01
We analyze plane waves in a model of quantum mechanics in a three dimensional noncommutative (NC) space $R^3_{\\lambda}$. Signature features of NC models are impossibility of probing distances smaller than a certain length scale {\\lambda} and a presence of natural energetic cut-off at energy scale of order $1/{\\lambda}^2$ (in convenient units). We analyze consequences of such restrictions on a 1 dimensional Casimir effect. The result shows resemblance to flux tube potential for quark-antiquark pairs and to effective bosonic string theories with L\\"uscher terms. Such behavior might effect the radius of possible compact (fuzzy) dimensions.
The Spectrum of the Thermal Correction to the Casimir Force between Metallic Films
Torgerson, J R
2003-01-01
The frequency spectrum of the finite temperature correction to the Casimir force is determined by use of the Lifshitz formalism for metallic plates of finite conductivity. We show that the correction for the $TE$ electromagnetic modes is dominated by low frequencies, where low is defined by the transverse dimensions of the plates. Through a heuristic argument, we apply our result to the much more complicated case where one "plate" has a spherical surface. Our result brings the thermal correction into agreement with experimental results that were previously obtained. We also address issues relating to the behavior of electromagnetic fields at the surfaces and within metallic conductors.
Particle creation by a black hole as a consequence of the Casimir effect
Energy Technology Data Exchange (ETDEWEB)
Nugayev, R.M.
1987-08-01
Particle creation by a blackhole is investigated in terms of temperature corrections to the Casimir effect. The reduction of the Hawking effect to more familiar effects observed in the laboratory enables us to reveal the mechanism of particle creation. The blackbody nature of the Hawking radiation is due to the interaction of virtual particles with the surface of a ''cavity'' formed by the Schwarzschild gravitational field potential barrier. These particles are ''squeezed out'' by the contraction of the potential barrier and appear to an observer at J/sup +/ as the real blackbody ones.
Tuning Casimir-Polder interactions in atom-metamaterial hybrid devices
Chan, Eng Aik; Adamo, Giorgio; Laliotis, Athanasios; Ducloy, Martial; Wilkowski, David
2016-01-01
We report on the coupling of a surface plasmonic mode with a thermal vapor of cesium atoms. The plasmonic resonance is created using a nano-structured metallic surface. By changing the geometrical properties of the metamaterial, we tune the plasmonic resonance wavelength with respect to the D2 line of cesium. When the two resonances are close, we observe a strong modification of the Casimir-Polder interaction accompanied by a change of the atomic lifetime. A proper tuning leads to an almost suppression of the frequency shift of the cesium transition. This result paves the way for precision atomic spectroscopy in the vicinity of a material surface.
Thermal corrections to the Casimir energy in a general weak gravitational field
Nazari, Borzoo
2016-12-01
We calculate finite temperature corrections to the energy of the Casimir effect of a two conducting parallel plates in a general weak gravitational field. After solving the Klein-Gordon equation inside the apparatus, mode frequencies inside the apparatus are obtained in terms of the parameters of the weak background. Using Matsubara’s approach to quantum statistical mechanics gravity-induced thermal corrections of the energy density are obtained. Well-known weak static and stationary gravitational fields are analyzed and it is found that in the low temperature limit the energy of the system increases compared to that in the zero temperature case.
Directory of Open Access Journals (Sweden)
Tania Mara Assis Lima
2009-04-01
Full Text Available A presença de alterações nos potenciais evocados auditivos do tronco encefálico (PEATE em indivíduos com doenças desmielinizantes sugere lesão do tronco encefálico. OBJETIVOS: O objetivo do presente estudo foi avaliar a incidência de alterações auditivas e dos PEATE em indivíduos com esclerose múltipla (EM. MATERIAL E MÉTODO: Participaram do estudo 16 pacientes do sexo feminino e 9 do sexo masculino com diagnóstico definido de EM. Testes audiométricos e pesquisa dos PEATE foram realizados em todos os indivíduos. Para a classificação dos PEATE utilizou-se a classificação proposta por Jerger (1986 na análise da morfologia das ondas. FORMA DE ESTUDO: Estudo de coorte contemporânea com corte transversal. RESULTADOS: Dos 50 PEATE realizados, 70% foram classificados como tipo I (resposta normal pela classificação de Jerger. Considerando-se como alterados os PEATE dos tipos II, III, IV ou V da classificação de Jerger em pelo menos um dos lados, encontrou-se 31,25% de alterações no sexo feminino e 44,44% no masculino, totalizando 36%. CONCLUSÕES: Estes achados enfatizam a relevância do estudo dos PEATE em casos de suspeita clínica de doenças desmielinizantes e naqueles com diagnóstico definido de EM.Alterations in early auditory evoked potentials (EAEP in individuals with demyelinating disease are suggestive of lesions in the brainstem. AIM: this study aims to evaluate the prevalence of hearing disorders and altered EAEP in multiple sclerosis (MS patients. MATERIALS AND METHOD: sixteen female and nine male patients with a defined diagnosis of multiple sclerosis took part in this study. All individuals underwent hearing and EAEP tests. The wave forms were categorized according to Jerger (1986. RESULTS: fifty EAEP tests were carried out; 70% were classified as type I (normal response according to Jerger's criteria. Altered EAEP results in at least one ear were classified into types II, III, IV or V according to Jerger
Comunicação aumentativa e alternativa para o desenvolvimento da oralidade de pessoas com autismo
Bárbara Gorziza Avila
2011-01-01
A pesquisa de mestrado relatada ao longo desta dissertação contemplou o desenvolvimento de um sistema de comunicação altenativa em alta tecnologia voltado para a comunicação de crianças com autismo não oralizadas. O processo de construção do Sistema de Comunicação Alternativa para o Letramento de pessoas com Autismo, SCALA, desdobrou-se em três etapas, abrangendo o seu desenvolvimento e avaliação do mesmo com potenciais usuários da ferramenta. Na primeira etapa deste trabalho, foram estabelec...
Diagnóstico organizacional participativo: potenciais e limites na análise de organizações
Naves,Flávia Luciana; Mafra,Luiz Antonio Staub; Gomes, Marcos Affonso Ortiz; Amâncio,Robson
2000-01-01
A crescente complexidade que envolve as organizações e o ambiente em que se inserem tem levado seus membros e os pesquisadores da área de administração a contínuas buscas de novas e mais adequadas abordagens para análises que contribuam para o desenvolvimento organizacional. Entretanto, observa-se que a maior parte desses esforços teóricos ou práticos não tem alcançado os resultados desejados, pois a gama de métodos disponíveis, com as mais distintas características, não tem conseguido apreen...
Abraham, John Bishoy Sam
Saturated thick films of 4Helium adsorbed on a copper substrate are studied experimentally. The film thickness is measured with an ultra-sensitive capacitance bridge capable of resolving sub-Angstrom changes in film thickness. Through the use of this capacitance bridge, the critical Casimir effect in the films is studied in the vicinity of the lambda transition. Additionally, the copper substrate assembly is used to generate and detect third sound in the film. Measurements are made of the third sound speed and attenuation in thick film from 1.6 K to the Kosterlitz-Thouless transition in the films. The position of the Kosterlitz-Thouless transition relative to the critical Casimir effect in the films is identifieded. It is discovered that the Kosterlitz-Thouless transition occurs at the beginning of the dip in film thickness due to the critical Casimir effect. When the temperature of the system is swept extremely slowly across the lambda transition, a step in film thickness is observed. This step is possibly a non-universal critical Casimir effect. A model of thermal second sound excitations is developed to describe this new observation.
Cavero-Pelaez, Ines; Parashar, Prachi; Shajesh, K V
2008-01-01
We calculate the lateral Casimir force between corrugated parallel plates, described by $\\delta$-function potentials, interacting through a scalar field, using the multiple scattering formalism. The contributions to the Casimir energy due to uncorrugated parallel plates is treated as a background from the outset. We derive the leading- and next-to-leading-order contribution to the lateral Casimir force for the case when the corrugation amplitudes are small in comparison to corrugation wavelengths. We present explicit results in terms of finite integrals for the case of the Dirichlet limit, and exact results for the weak-coupling limit, for the leading- and next-to-leading-orders. The correction due to the next-to-leading contribution is significant. In the weak coupling limit we calculate the lateral Casimir force exactly in terms of a single integral which we evaluate numerically. Exact results for the case of the weak limit allows us to estimate the error in the perturbative results. We show that the error ...
Palasantzas, George
2007-01-01
In this work, we investigate the combined influence of electromagnetic and acoustic Casimir forces on the pull-in voltage of microswitches with self-affine rough plates. It is shown that for plate separations within the micron range the acoustic term arising from pressure fluctuations can influence