Onsager coefficients of a Brownian Carnot cycle

We study a Brownian Carnot cycle introduced by T. Schmiedl and U. Seifert [Europhys. Lett. \textbf{81}, 20003 (2008)] from a viewpoint of the linear irreversible thermodynamics. By considering the entropy production rate of this cycle, we can determine thermodynamic forces and fluxes of the cycle and calculate the Onsager coefficients for general protocols, that is, arbitrary schedules to change the potential confining the Brownian particle. We show that these Onsager coefficients contain the information of the protocol shape and they satisfy the tight-coupling condition irrespective of whatever protocol shape we choose. These properties may give an explanation why the Curzon-Ahlborn efficiency often appears in the finite-time heat engines

Quantum thermodynamic processes: A control theory for machine cycles

The minimal set of thermodynamic control parameters consists of a statistical (thermal) and a mechanical one. These suffice to introduce all the pertinent thermodynamic variables; thermodynamic processes can then be defined as paths on this 2-dimensional control plane. Putting aside coherence we show that for a large class of quantum objects with discrete spectra and for the cycles considered the Carnot efficiency applies as a universal upper bound. In the dynamic (finite time) regime renormalized thermodynamic variables allow to include non-equilibrium phenomena in a systematic way. The machine function ceases to exist in the large speed limit; the way, in which this limit is reached, depends on the type of cycle considered.Comment: 14 pages, 12 figures, Replaced by version accepted for publication in European Physical Journal

Finite-time quantum thermodynamic processes

We study a single quantum object subject to a parametrized distortion of its discrete spectrum and to a parametrized change of its state, which remains diagonal in its invariant energy eigenbasis. The Carnot and the Otto cycle are investigated in the quasistatic as well as in the dynamic (finite time) regime. The second law is found to be valid as a result of this control, irrespective of the type of attractor states chosen. For specific control functions analytical results are obtained for the work, heat, and efficiency. The influence of dissipation is discussed

Influ?ncia do laser de alta pot?ncia na inibi??o de processos desmineralizadores do esmalte dental

Made available in DSpace on 2015-04-14T13:29:14Z (GMT). No. of bitstreams: 1 399354.pdf: 7916796 bytes, checksum: 52f9942a655db745c4d2a97dff7dead8 (MD5) Previous issue date: 2007-12-12Artigo 1 - Aim: The aim of this in vitro study was to investigate the effect of Nd:YAG and argon laser irradiations on the enamel acid demineralization by two different chemical laboratory models (pH cycling).Summary background data: The use of lasers to prevent enamel caries has been shown good results, but there are few comparative studies about the effect of different lasers in different pH models cycling.Methods and materials: Twenty one extracted human third molars were sectioned into tooth quarters. The quarters were distributed in three groups: GROUP I (control), non-treated; GROUP II received the Nd:YAG laser irradiation with the following protocol: 60 mJ, 15 pps, 0.9 W e 47.77 J/cm2, 30 seconds; and GROUP III received the argon laser irradiation with the following protocol: 250 mW, 12 J/cm2, 48 seconds. The surfaces were covered with an acid resistent varnish to be immersed in standard acidfied buffer solutions. The tooth quarters were submitted to a two different pH cycling: cycle 1: a 14-day remineralization (6 hours) and demineralization (18 hours) solutions, 37?C; cycle 2 with 48 hours in demineralization solution. The samples were prepared in slices (60 to 100 &#956;m) to be evaluated by polarized light microscopy. The demineralizations areas were measured (mm2) (n=11). Results: Means followed by different letters are significantly different to ANOVA and Tukey s test (p<0,05): 0.2509 A (control cycle 2); 0.1836 AB (control cycle 1); 0.1782 AB (Nd:YAG cycle 1); 0.1391 BC (argon cycle 2); 0.0927 BC (Nd:YAG cycle 2) e 0.0682 C (argon cycle 1). Conclusion:The results suggest that the treatment with argon laser was more effective, showing the smaller demineralization area by two different pH model cycling. Artigo 2 - Aim: The aim of this in vitro study was to investigate the effect of Nd:YAG and argon laser irradiations on the enamel acid demineralization by a chemical laboratory model to simulate acid erosion lesions.Summary background data: Erosive lesions in enamel are frequently found in patients with gastric-alimentary disturbs. There are no studies examining the use of lasers to prevent enamel erosions.Methods and materials: Third extracted human third molars were sectioned into tooth quarters. The quarters were distributed in three groups: GROUP I (control), non-treated; GROUP II received the Nd:YAG laser irradiation with the following protocol: 60 mJ, 15 pps, 0.9 W e 47.77 J/cm2, 30 seconds; and GROUP III received the argon laser irradiation with the following protocol: 250 mW, 12 J/cm2, 48 seconds. The surfaces were covered with an acid resistent varnish to be immersed in standard acidfied buffer solutions. The tooth quarters were submitted to a pH cycling: 14-day remineralization (6 hours) and demineralization (pH 2,5 - 18 hours) solutions, 37?C. The samples were prepared in slices (60 to 100 &#956;m) to be evaluated by polarized light microscopy. The demineralizations depths were mesured in mm (n=21). Results: Means followed by different letters are significantly different to ANOVA and Tukey s test (p<0,05): 0.1881 A (control occlusal); 0.1867 A (control cervical); 0.1610 B (argon occlusal); 0.1576 B (argon cervical); 0.1529 B (Nd:YAG occlusal); 0.1481 B (Nd:YAG cervical). Conclusions: The results suggest that the treatment with lasers increased the enamel acid demineralization resistance, so it can be indicated to prevent gastric-alimentary disturbs.Artigo 1 - Objetivo: O objetivo deste trabalho foi avaliar a ?rea de desmineraliza??o do esmalte irradiado com os lasers de Nd:YAG ou arg?nio, al?m de investigar dois m?todos de ciclagem de pH que simulam o desenvolvimento da doen?a c?rie.Problema: O uso dos lasers na preven??o de c?rie em esmalte tem sido pesquisado, mostrando bons resultados principalmente quando associados ao fl?or. Todavia, poucos estudos comparativos acerca do uso de lasers sobre o esmalte em diferentes ciclos de pH est?o dispon?veis.Materiais e m?todos: Vinte e um terceiros molares humanos inclusos extra?dos tiveram a por??o coron?ria seccionada em duas faces, vestibular e lingual; que, posteriormente, foram seccionadas em duas hemifaces. Os fragmentos foram distribu?dos aleatoriamente em tr?s grupos: o GRUPO I, de controle, n?o recebeu qualquer tratamento; o GRUPO II foi tratado com laser de Nd:YAG com 60 mJ, 15 pps, 0,9 W e 47,77 J/cm2, por 30 segundos; e, enfim, o GRUPO III tratado com laser de arg?nio com 250 mW, 12 J/cm2, por 48 segundos. Ap?s, as hemifaces de cada grupo tiveram a superf?cie de esmalte coberta com verniz, restando uma ?rea central de 3 mm x 3 mm, a qual foi exposta a um dos seguintes ciclos de pH: ciclo 1, compreendendo 14 dias de imers?o em solu??o desmineralizante por 6 horas/dia e solu??o remineralizante por 18 horas/dia a 37?C; ciclo 2, com 48 horas de imers?o em solu??o desmineralizante. As hemifaces foram cortadas em fatias com espessura de 60 a 100 &#956;m para obten??o das l?minas histol?gicas. Em seguida, foram observadas em microscopia de luz polarizada para medi??o das ?reas de desmineraliza??o (mm2) (n=11 por grupo). As m?dias obtidas foram: 0,2509 A (controle ciclo 2); 0,1836 AB (controle ciclo 1); 0,1782 AB (Nd:YAG ciclo 1); 0,1391 BC (arg?nio ciclo 2); 0,0927 BC (Nd:YAG ciclo 2) e 0,0682 C (arg?nio ciclo 1). M?dias seguidas de letras distintas apresentam diferen?a estat?stica para ANOVA e Tukey (p<0,05). Foi poss?vel concluir que o tratamento com o laser de arg?nio foi mais efetivo, apresentando uma menor ?rea de desmineraliza??o, sob a ciclagem de pH de 14 dias. Artigo 2 - Objetivo: O objetivo deste trabalho consistiu em avaliar a profundidade de desmineraliza??o do esmalte, nas paredes cervical e oclusal, ap?s a aplica??o dos lasers de Nd:YAG e arg?nio.Problema: Les?es erosivas s?o comuns em indiv?duos com dist?rbios gastro-alimentares e podem levar ? perda do esmalte dental. N?o h? relatos na literatura do uso de lasers como um tratamento preventivo desta situa??o cl?nica.Materiais e m?todos: Trinta terceiros molares extra?dos tiveram as coroas seccionadas em duas partes, vestibular e lingual; sendo cada face vestibular e cada face lingual seccionada no sentido oclusocervical, no centro da face, obtendo-se 4 hemifaces, as quais foram distribu?das em tr?s grupos: o, GRUPO I, de controle, que n?o recebeu qualquer tratamento; o GRUPO II, tratado com o laser de Nd:YAG com 60 mJ, 15 pps, 0,9 W e 47,77 J/cm2, por 30 segundos; e, enfim, o GRUPO III, tratado com o laser de arg?nio com 250 mW, 12 J/cm2, por 48 segundos. Ap?s a aplica??o dos lasers, os fragmentos foram submetidos ? ciclagem de pH 2,5 por 14 dias. Em seguida, foram obtidas l?minas histol?gicas de 60 a 100 &#956;m para serem observadas em microsc?pio ?ptico de luz polarizada (n=21 por grupo). A profundidade de desmineraliza??o foi mensurada (mm) e os resultados m?dios obtidos foram: 0,1881 A (controle oclusal); 0,1867 A (controle cervical); 0,1610 B (arg?nio oclusal); 0,1576 B (arg?nio cervical); 0,1529 B (Nd:YAG oclusal); 0,1481 B (Nd:YAG cervical). M?dias seguidas de letras distintas apresentam diferen?a estat?stica para ANOVA e Tukey (p<0,05). Foi poss?vel concluir que o tratamento com os lasers aumentou a resist?ncia do esmalte ao ?cido, podendo ser empregado como m?todo preventivo frente a dist?rbios gastro-alimentares. Al?m disso, n?o houve diferen?a na profundidade de desmineraliza??o do esmalte nas paredes cervical e oclusal

Limitations of the quantum Jarzynski estimator: boundary switching processes

The Jarzynski relation aims at an estimate of the free energy change along a finite isotherm. Its application in the quantum domain requires a proper choice of substitute processes combined with quantum mechanical (projective) measurements at the beginning and in the end. The Jarzynski relation can be violated by non-unitary processes like those generated by instantaneous constraint switching (boundary switching). For a complementary model space with a moving barrier of arbitrary, but finite height, the Jarzynski relation is fulfilled. However, its application may be limited due to bad statistics