Decoherence and entropy of primordial fluctuations II. The entropy budget

We calculate the entropy of adiabatic perturbations associated with a truncation of the hierarchy of Green functions at the first non trivial level, i.e. in a self-consistent Gaussian approximation. We give the equation governing the entropy growth and discuss its phenomenology. It is parameterized by two model-dependent kernels. We then examine two particular inflationary models, one with isocurvature perturbations, the other with corrections due to loops of matter fields. In the first model the entropy grows rapidely, while in the second the state remains pure (at one loop).Comment: 28 page

Downregulation of major histocompatibility complex class I in bovine papillomas

Bovine papillomavirus (BPV) induces papillomas in cattle; in the great majority of cases, these regress due to the host immune response, but they can persist and progress to malignancy. Even in the absence of malignant transformation, BPV infection persists for a significant period of time before activation of the host immune system, suggesting that the host immune system is unaware of, or disabled by, BPV. E5 is the major oncoprotein of BPV, which, in addition to its transforming properties, downregulates the expression and transport to the cell surface of major histocompatibility complex class I (MHC I). Here, it is shown that co-expression of MHC I and E5 in papillomas caused by BPV-4 infection is mutually exclusive, in agreement with the inhibition of surface MHC I expression by E5 that is observed in vitro. The inhibition of MHC expression in E5-expressing papilloma cells could explain the long period that is required for activation of the immune response and has implications for the progression of papillomas to the malignant stage; absence of peptide presentation by MHC I to cytotoxic T lymphocytes would allow the infected cells to evade the host cellular immune response and allow the lesions to persist

Atom laser dynamics in a tight-waveguide

We study the transient dynamics that arise during the formation of an atom laser beam in a tight waveguide. During the time evolution the density profile develops a series of wiggles which are related to the diffraction in time phenomenon. The apodization of matter waves, which relies on the use of smooth aperture functions, allows to suppress such oscillations in a time interval, after which there is a revival of the diffraction in time. The revival time scale is directly related to the inverse of the harmonic trap frequency for the atom reservoir.Comment: 6 pages, 5 figures, to be published in the Proceedings of the 395th WE-Heraeus Seminar on "Time Dependent Phenomena in Quantum Mechanics ", organized by T. Kramer and M. Kleber (Blaubeuren, Germany, September 2007

Raman transitions between hyperfine clock states in a magnetic trap

We present our experimental investigation of an optical Raman transition between the magnetic clock states of $^{87}$Rb in an atom chip magnetic trap. The transfer of atomic population is induced by a pair of diode lasers which couple the two clock states off-resonantly to an intermediate state manifold. This transition is subject to destructive interference of two excitation paths, which leads to a reduction of the effective two-photon Rabi-frequency. Furthermore, we find that the transition frequency is highly sensitive to the intensity ratio of the diode lasers. Our results are well described in terms of light shifts in the multi-level structure of $^{87}$Rb. The differential light shifts vanish at an optimal intensity ratio, which we observe as a narrowing of the transition linewidth. We also observe the temporal dynamics of the population transfer and find good agreement with a model based on the system's master equation and a Gaussian laser beam profile. Finally, we identify several sources of decoherence in our system, and discuss possible improvements.Comment: 10 pages, 7 figure

Resistência constitutiva e induzida em plantas a insetos e a metabolômica.

As plantas desenvolveram ao longo dos séculos um sofisticado mecanismo de defesa a estresses bióticos e abióticos. Além do mecanismo de defesa intrínseco, denominado constitutivo, característico de cada genótipo, as plantas apresentam defesa induzida cuja reação inicia apenas quando são submetidas a estresses causos por agentes bióticos (insetos, fungos, nematoides), ou abióticos (temperatura, CO2, estresse hídrico, etc.). Vários metabólitos secundários sao envolvidos nas interações de plantas com esses agentes. Metabolômica é o estudo científico que visa identificar e quantificar o conjunto de metabólitos produzidos e/ou modificados nas plantas pela ação de um organismo. Assim, estudos amplos e precisos dos metabólitos produzidos na interação insetos-planta representam uma possibilidade inovadora na busca de alternativas de controle através da identificação de genes ou rotas metabólicas importantes que podem diminuir o tempo para a obtenção de genótipos resistentes a pragas, sem afetar a produtividade e outras características agronômicas, tanto através de melhoramento tradicional, como das modernas técnicas de biotecnologia. As folhas de soja apresentam constitutivamente uma variedade de isoflavonas e flavonóis glicosídicos e, alguns deles como genistina e rutina, respectivamente, interferem negativamente na biologia de lagartas desfolhadoras, como Anticarsia gemmatalis, Trichoplusia ni e Heliothis virescens. Ainda, após sofrer dano de percevejos sugadores de sementes, como Euschistus heros, Nezara viridula e Piezodorus guildini, e da mosca branca (Bemisia tabaci), a soja aumenta a concentração de isoflavonas glicosídicas (constitutivas), como genistina, daidzina e glicitina, nas formas malonil e acetil, e/ou induz a produção de agliconas e de fitoalexinas (coumestrol e gliceolinas) que, em geral, são mais toxicas aos organismos. Além dessas informações, potenciais aplicações práticas da interação inseto-planta e da metabolômica serão examinadas nesta palestra.Palestra

Resistência induzida como ferramenta para o desenvolvimento de genótipos de soja resistentes a fitopatógenos.

Poster

Structural defects in ion crystals by quenching the external potential: the inhomogeneous Kibble-Zurek mechanism

The non-equilibrium dynamics of an ion chain in a highly anisotropic trap is studied when the transverse trap frequency is quenched across the value at which the chain undergoes a continuous phase transition from a linear to a zigzag structure. Within Landau theory, an equation for the order parameter, corresponding to the transverse size of the zigzag structure, is determined when the vibrational motion is damped via laser cooling. The number of structural defects produced during a linear quench of the transverse trapping frequency is predicted and verified numerically. It is shown to obey the scaling predicted by the Kibble-Zurek mechanism, when extended to take into account the spatial inhomogeneities of the ion chain in a linear Paul trap.Comment: 5 pages, 3 figure