870 research outputs found
Space and Time Redundancy in Microcomputer Bus Communication
No full textElsevier Science B.V., Amsterda
A precision baseline offset and drift corrector for low frequency applications
No full textAn analog technique for correcting baseline offset and drift in low-frequencv systems is analyzed. The described method applies to periodic and nearly periodic signals, characterized by a time interval in which they may be considered at rest (electrocardiogram (ECG) signals, for instance), and is limited to linear drifts. Two different circuits have been developed and are discussed here. Signal conditioning performed on suitable input waveforms is presented. Noise effects have been theoreticallv considered and experimentally evaluated
Cohomology of D-complex manifolds
No full textIn order to look for a well-behaved counterpart to Dolbeault cohomology in D-complex geometry, we study the de Rham cohomology of an almost D-complex manifold and its subgroups made up of the classes admitting invariant, respectively anti-invariant, representatives with respect to the almost D-complex structure, miming the theory introduced by Li and Zhang (2009) in [20] for almost complex manifolds. In particular, we prove that, on a 4-dimensional D-complex nilmanifold, such subgroups provide a decomposition at the level of the real second de Rham cohomology group. Moreover, we study deformations of D-complex structures, showing in particular that admitting D-Kähler structures is not a stable property under small deformations
Black hole nonmodal linear stability : odd perturbations of Reissner-Nordström
No full textArtículo finalmente publicado en: Fernández Tío, J. M. y Dotti, G. D. (2017). Black hole nonmodal linear stability under odd perturbations: the Reissner-Nordström case. Physical Review D, 95 (12), 124041. https://doi.org/10.1103/PhysRevD.95.124041Fil: Fernández Tío, Julián María. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía, Física y Computación; Argentina.Fil: Fernández Tío, Julián María. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina.Fil: Fernández Tío, Julián María. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Física Enrique Gaviola; Argentina.Fil: Dotti, Gustavo Daniel. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía, Física y Computación; Argentina.Fil: Dotti, Gustavo Daniel. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina.Fil: Dotti, Gustavo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Física Enrique Gaviola; Argentina.Following a program on black hole nonmodal linear stability initiated in Phys. Rev. Lett. 112 (2014) 191101, we study odd linear perturbations of the Einstein-Maxwell equations around a Reissner-Nordström (A)dS black hole. We show that all the gauge invariant information in the metric and Maxwell field perturbations is encoded in the spacetime scalars F = δ(F∗ αβ F αβ ) and Q = δ( 1/ 48 C∗ αβγδ Cαβγδ ), where Cαβγδ is the Weyl tensor, Fαβ the Maxwell field, a star denotes Hodge dual and δ means first order variation, and that the linearized Einstein-Maxwell equations are equivalent to a coupled system of wave equations for F and Q. For nonnegative cosmological constant we prove that F and Q are pointwise bounded on the outer static region. The fields are shown to diverge as the Cauchy horizon is approached from the inner dynamical region, providing evidence supporting strong cosmic censorship. In the asymptotically AdS case the dynamics depends on the boundary condition at the conformal timelike boundary and there are instabilities if Robin boundary conditions are chosen.http://link.aps.org/doi/10.1103/PhysRevD.95.124041info:eu-repo/semantics/submittedVersionFil: Fernández Tío, Julián María. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía, Física y Computación; Argentina.Fil: Fernández Tío, Julián María. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina.Fil: Fernández Tío, Julián María. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Física Enrique Gaviola; Argentina.Fil: Dotti, Gustavo Daniel. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía, Física y Computación; Argentina.Fil: Dotti, Gustavo Daniel. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina.Fil: Dotti, Gustavo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Física Enrique Gaviola; Argentina.Física de Partículas y Campo
Dentro e fuori la corte: note sulla pittura a Padova e sulla committenza della famiglia Dotti nel Trecento
No full textIl saggio considera un caso di committenza artistica legata alla corte padovana dei da Carrara, quella della famiglia Dotti. E' una testimonianza utile per capire come l'arte della corte avesse un valore esemplare e fosse di riferimento per l'entourage del signore
Bar formation as driver of gas inflows in isolated disc galaxies
No full textStellar bars are a common feature in massive disc galaxies. On a theoretical ground, the response of gas to a bar is generally thought to cause nuclear starbursts and, possibly, AGN activity once the perturbed gas reaches the central supermassive black hole. By means of high-resolution numerical simulations, we detail the purely dynamical effects that a forming bar exerts on the gas of an isolated disc galaxy. The galaxy is initially unstable to the formation of non-axisymmetric structures, and within ˜1 Gyr it develops spiral arms that eventually evolve into a central stellar bar on kpc scale. A first major episode of gas inflow occurs during the formation of the spiral arms while at later times, when the stellar bar is establishing, a low-density region is carved between the bar corotational and inner Lindblad resonance radii. The development of such `dead zone' inhibits further massive gas inflows. Indeed, the gas inflow reaches its maximum during the relatively fast bar-formation phase and not, as often assumed, when the bar is fully formed. We conclude that the low efficiency of long-lived, evolved bars in driving gas towards galactic nuclei is the reason why observational studies have failed to establish an indisputable link between bars and AGNs. On the other hand, the high efficiency in driving strong gas inflows of the intrinsically transient process of bar formation suggests that the importance of bars as drivers of AGN activity in disc galaxies has been overlooked so far. We finally prove that our conclusions are robust against different numerical implementations of the hydrodynamics routinely used in galaxy evolution studies
Multiexciton complex from extrinsic centers in AlGaAs epilayers on Ge and Si substrates
No full textThe multiexciton properties of extrinsic centers from AlGaAs layers on Ge and Si substrates are addressed. The two photon cascade is found both in steady state and in time resolved experiments. Polarization analysis of the photoluminescence provides clearcut attribution to neutral biexciton complexes. Our findings demonstrate the prospect of exploiting extrinsic centers for generating entangled photon pairs on a Si based device.Sarti, F.; Muñoz Matutano, G.; Bauer, D.; Dotti, N.; Bietti, S.; Isella, G.; Vinattieri, A.... (2013). Multiexciton complex from extrinsic centers in AlGaAs epilayers on Ge and Si substrates. Journal of Applied Physics. 114(22):2243141-2243143. doi:10.1063/1.4844375S2243141224314311422Kimble, H. J. (2008). The quantum internet. Nature, 453(7198), 1023-1030. doi:10.1038/nature07127Bouwmeester, D., Pan, J.-W., Mattle, K., Eibl, M., Weinfurter, H., & Zeilinger, A. (1997). Experimental quantum teleportation. Nature, 390(6660), 575-579. doi:10.1038/37539Shields, A. J. (2007). Semiconductor quantum light sources. Nature Photonics, 1(4), 215-223. doi:10.1038/nphoton.2007.46Akopian, N., Lindner, N. H., Poem, E., Berlatzky, Y., Avron, J., Gershoni, D., … Petroff, P. M. (2006). Entangled Photon Pairs from Semiconductor Quantum Dots. Physical Review Letters, 96(13). doi:10.1103/physrevlett.96.130501Dousse, A., Suffczyński, J., Beveratos, A., Krebs, O., Lemaître, A., Sagnes, I., … Senellart, P. (2010). Ultrabright source of entangled photon pairs. Nature, 466(7303), 217-220. doi:10.1038/nature09148Cavigli, L., Bietti, S., Accanto, N., Minari, S., Abbarchi, M., Isella, G., … Sanguinetti, S. (2012). High temperature single photon emitter monolithically integrated on silicon. Applied Physics Letters, 100(23), 231112. doi:10.1063/1.4726189Accanto, N., Minari, S., Cavigli, L., Bietti, S., Isella, G., Vinattieri, A., … Gurioli, M. (2013). Kinetics of multiexciton complex in GaAs quantum dots on Si. Applied Physics Letters, 102(5), 053109. doi:10.1063/1.4790148Kurtsiefer, C., Mayer, S., Zarda, P., & Weinfurter, H. (2000). Stable Solid-State Source of Single Photons. Physical Review Letters, 85(2), 290-293. doi:10.1103/physrevlett.85.290Brouri, R., Beveratos, A., Poizat, J.-P., & Grangier, P. (2000). Photon antibunching in the fluorescence of individual color centers in diamond. Optics Letters, 25(17), 1294. doi:10.1364/ol.25.001294Strauf, S., Michler, P., Klude, M., Hommel, D., Bacher, G., & Forchel, A. (2002). Quantum Optical Studies on Individual Acceptor Bound Excitons in a Semiconductor. Physical Review Letters, 89(17). doi:10.1103/physrevlett.89.177403Muller, A., Bianucci, P., Piermarocchi, C., Fornari, M., Robin, I. C., André, R., & Shih, C. K. (2006). Time-resolved photoluminescence spectroscopy of individual Te impurity centers inZnSe. Physical Review B, 73(8). doi:10.1103/physrevb.73.081306Sanaka, K., Pawlis, A., Ladd, T. D., Sleiter, D. J., Lischka, K., & Yamamoto, Y. (2012). Entangling Single Photons from Independently Tuned Semiconductor Nanoemitters. Nano Letters, 12(9), 4611-4616. doi:10.1021/nl301911tIkezawa, M., Sakuma, Y., Zhang, L., Sone, Y., Mori, T., Hamano, T., … Masumoto, Y. (2012). Single-photon generation from a nitrogen impurity center in GaAs. Applied Physics Letters, 100(4), 042106. doi:10.1063/1.3679181Minari, S., Cavigli, L., Sarti, F., Abbarchi, M., Accanto, N., Muñoz Matutano, G., … Gurioli, M. (2012). Single photon emission from impurity centers in AlGaAs epilayers on Ge and Si substrates. Applied Physics Letters, 101(17), 172105. doi:10.1063/1.4761939Marcet, S., Ouellet-Plamondon, C., Éthier-Majcher, G., Saint-Jean, P., André, R., Klem, J. F., & Francoeur, S. (2010). Charged excitons and biexcitons bound to isoelectronic centers. Physical Review B, 82(23). doi:10.1103/physrevb.82.235311Jo, M., Mano, T., Kuroda, T., Sakuma, Y., & Sakoda, K. (2013). Visible single-photon emission from a nitrogen impurity center in AlAs. Applied Physics Letters, 102(6), 062107. doi:10.1063/1.4792315Abbarchi, M., Mastrandrea, C., Kuroda, T., Mano, T., Vinattieri, A., Sakoda, K., & Gurioli, M. (2009). Poissonian statistics of excitonic complexes in quantum dots. Journal of Applied Physics, 106(5), 053504. doi:10.1063/1.3197848Kuroda, T., Sanguinetti, S., Gurioli, M., Watanabe, K., Minami, F., & Koguchi, N. (2002). Picosecond nonlinear relaxation of photoinjected carriers in a singleGaAs/Al0.3Ga0.7Asquantum dot. Physical Review B, 66(12). doi:10.1103/physrevb.66.121302Gammon, D., Snow, E. S., Shanabrook, B. V., Katzer, D. S., & Park, D. (1996). Fine Structure Splitting in the Optical Spectra of Single GaAs Quantum Dots. Physical Review Letters, 76(16), 3005-3008. doi:10.1103/physrevlett.76.3005Abbarchi, M., Mastrandrea, C. A., Kuroda, T., Mano, T., Sakoda, K., Koguchi, N., … Gurioli, M. (2008). Exciton fine structure in strain-freeGaAs/Al0.3Ga0.7Asquantum dots: Extrinsic effects. Physical Review B, 78(12). doi:10.1103/physrevb.78.125321Heiss, M., Fontana, Y., Gustafsson, A., Wüst, G., Magen, C., O’Regan, D. D., … Fontcuberta i Morral, A. (2013). Self-assembled quantum dots in a nanowire system for quantum photonics. Nature Materials, 12(5), 439-444. doi:10.1038/nmat355
Instability of asymptotically anti de Sitter black holes under Robin conditions at the timelike boundary
No full textArtículo finalmente publicado en: Araneda, B. G. y Dotti, G. D. (2017). Instability of asymptotically anti de Sitter black holes under Robin conditions at the timelike boundary. Physical Review D, 96(10), 104020. https://doi.org/10.1103/PhysRevD.96.104020Fil: Araneda, Bernardo Gabriel. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía, Física y Computación; Argentina.Fil: Araneda, Bernardo Gabriel. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina.Fil: Araneda, Bernardo Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Física Enrique Gaviola; Argentina.Fil: Dotti, Gustavo Daniel. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía, Física y Computación; Argentina.Fil: Dotti, Gustavo Daniel. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina.Fil: Dotti, Gustavo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Física Enrique Gaviola; Argentina.The static region outside the event horizon of an asymptotically anti de Sitter black hole has a conformal timelike boundary I on which boundary conditions have to be imposed for the evolution of linear fields from initial data to be a well posed problem. Only homogeneous Dirichlet, Neumann or Robin conditions preserve the action of the background isometry group on the solution space. We study the case in which the modal decomposition of the linear field leads to potentials not diverging at the conformal timelike boundary. We prove that there is always an instability if Robin boundary conditions with large enough γ (the quotient between the values of the derivative of the field and the field at the boundary) are allowed. We explain the origin of this instability, show that for modes with nonnegative potentials there is a single unstable state and prove a number of properties of this state. Although our results apply in general to 1+1 wave equations on a half infinite domain with a potential that is not singular at the boundary, our motivation is to analyze the gravitational stability of the four dimensional Schwarzschild anti de Sitter black holes (SAdS 4 ) in the context of the black hole non modal linear stability program initiated in Phys. Rev. Lett. 112, 191101 (2014), and the related supersymmetric type of duality exchanging odd and even modes. We prove that this symmetry is broken except when a combination of Dirichlet conditions in the even sector and a particular Robin condition in the odd sector is enforced, or viceversa, and that only the first of these two choices leads to a stable dynamics.https://link.aps.org/doi/10.1103/PhysRevD.96.104020info:eu-repo/semantics/submittedVersionFil: Araneda, Bernardo Gabriel. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía, Física y Computación; Argentina.Fil: Araneda, Bernardo Gabriel. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina.Fil: Araneda, Bernardo Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Física Enrique Gaviola; Argentina.Fil: Dotti, Gustavo Daniel. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía, Física y Computación; Argentina.Fil: Dotti, Gustavo Daniel. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina.Fil: Dotti, Gustavo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Física Enrique Gaviola; Argentina.Física de Partículas y Campo
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