3,275 research outputs found

    Transient complete heart block following catheter ablation of a left lateral accessory pathway.

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    A 16-year-old female with symptomatic Wolff-Parkinson-White (WPW) syndrome underwent catheter ablation of a left-sided lateral accessory pathway. The accessory pathway was eliminated with the first ablation lesion; however, the patient immediately developed complete heart block (CHB). At first, complete heart block was thought to be due to ablation of left atrial extension of the AV node, and pacemaker therapy was considered. However, careful ECG analysis revealed that the development of CHB was in fact due to bump injury to the AV node during transseptal catheterization. Conservative management allowed resolution of AV nodal conduction without need for a permanent pacemaker

    Two-electron atoms, ions and molecules

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    The quantum mechanics of two-electron systems is reviewed, starting with the ground state of the helium atom and helium-like ions, with central charge Z≄2Z\ge 2. For Z=1, demonstrating the stability of the negative hydrogen ion, H−^-, cannot be achieved using a mere product of individual electron wave functions, and requires instead an explicit account for the anticorrelation among the two electrons. The wave function proposed by Chandrasekhar is revisited, where the permutation symmetry is first broken and then restored by a counter-term. More delicate problems can be studied using the same strategy: the stability of hydrogen-like ions (M+,m−,m−)(M^+,m^-,m^-) for any value of the proton-to-electron mass ratio M/mM/m; the energy of the lowest spin-triplet state of helium and helium-like ions; the stability of the doubly-excited hydrogen ion with unnatural parity. The positronium molecule (e+,e+,e−,e−)(e^+,e^+,e^-,e^-), which has been predicted years ago and discovered recently, can also be shown to be stable against spontaneous dissociation, though the calculation is a little more involved. Emphasis is put on symmetry breaking which can either spoil or improve the stability of systems.Comment: 16 pages, 2 figure

    The QUEST-La Silla AGN Variability Survey

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    We present the characterization and initial results from the QUEST-La Silla AGN variability survey. This is an effort to obtain well sampled optical light curves in extragalactic fields with unique multi-wavelength observations. We present photometry obtained from 2010 to 2012 in the XMM-COSMOS field, which was observed over 150 nights using the QUEST camera on the ESO-Schmidt telescope. The survey uses a broadband filter, the QQ-band, similar to the union of the gg and the rr filters, achieving an intrinsic photometric dispersion of 0.050.05 mag, and a systematic error of 0.050.05 mag in the zero-point. Since some detectors of the camera show significant non-linearity, we use a linear correlation to fit the zero-points as a function of the instrumental magnitudes, thus obtaining a good correction to the non-linear behavior of these detectors. We obtain good photometry to an equivalent limiting magnitude of r∌20.5r\sim 20.5. Studying the optical variability of X-ray detected sources in the XMM-COSMOS field, we find that the survey is ∌75−80\sim75-80% complete to magnitudes r∌20r\sim20, and ∌67\sim67% complete to a magnitude r∌21r\sim21. The determination and parameterization of the structure function (SFnorm(τ)=AÏ„Îł{SF}_{norm}(\tau) = A \tau^{\gamma}) of the variable sources shows that most BL AGN are characterized by A>0.1A > 0.1 and Îł>0.025\gamma > 0.025. It is further shown that variable NL AGN and GAL sources occupying the same parameter space in AA and Îł\gamma are very likely to correspond to obscured or low luminosity AGN. Our samples are, however, small, and we expect to revisit these results using larger samples with longer light curves obtained as part of our ongoing survey.Comment: Accepted for publication in Ap

    Dust in the reionization era: ALMA observations of a zz=8.38 Galaxy

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    We report on the detailed analysis of a gravitationally-lensed Y-band dropout, A2744_YD4, selected from deep Hubble Space Telescope imaging in the Frontier Field cluster Abell 2744. Band 7 observations with the Atacama Large Millimeter Array (ALMA) indicate the proximate detection of a significant 1mm continuum flux suggesting the presence of dust for a star-forming galaxy with a photometric redshift of z≃8z\simeq8. Deep X-SHOOTER spectra confirms the high redshift identity of A2744_YD4 via the detection of Lyman α\alpha emission at a redshift zz=8.38. The association with the ALMA detection is confirmed by the presence of [OIII] 88ÎŒ\mum emission at the same redshift. Although both emission features are only significant at the 4 σ\sigma level, we argue their joint detection and the positional coincidence with a high redshift dropout in the HST images confirms the physical association. Analysis of the available photometric data and the modest gravitational magnification (Ό≃2\mu\simeq2) indicates A2744_YD4 has a stellar mass of ∌\sim 2×\times109^9 M⊙_{\odot}, a star formation rate of ∌20\sim20 M⊙_{\odot}/yr and a dust mass of ∌\sim6×\times106^{6} M⊙_{\odot}. We discuss the implications of the formation of such a dust mass only ≃\simeq200 Myr after the onset of cosmic reionisation.Comment: Accepted for publication in ApJ

    Glassy behaviour in an exactly solved spin system with a ferromagnetic transition

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    We show that applying simple dynamical rules to Baxter's eight-vertex model leads to a system which resembles a glass-forming liquid. There are analogies with liquid, supercooled liquid, glassy and crystalline states. The disordered phases exhibit strong dynamical heterogeneity at low temperatures, which may be described in terms of an emergent mobility field. Their dynamics are well-described by a simple model with trivial thermodynamics, but an emergent kinetic constraint. We show that the (second order) thermodynamic transition to the ordered phase may be interpreted in terms of confinement of the excitations in the mobility field. We also describe the aging of disordered states towards the ordered phase, in terms of simple rate equations.Comment: 11 page

    Separation of Test-Free Propositional Dynamic Logics over Context-Free Languages

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    For a class L of languages let PDL[L] be an extension of Propositional Dynamic Logic which allows programs to be in a language of L rather than just to be regular. If L contains a non-regular language, PDL[L] can express non-regular properties, in contrast to pure PDL. For regular, visibly pushdown and deterministic context-free languages, the separation of the respective PDLs can be proven by automata-theoretic techniques. However, these techniques introduce non-determinism on the automata side. As non-determinism is also the difference between DCFL and CFL, these techniques seem to be inappropriate to separate PDL[DCFL] from PDL[CFL]. Nevertheless, this separation is shown but for programs without test operators.Comment: In Proceedings GandALF 2011, arXiv:1106.081

    Eigen model as a quantum spin chain: exact dynamics

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    We map Eigen model of biological evolution [Naturwissenschaften {\bf 58}, 465 (1971)] into a one-dimensional quantum spin model with non-Hermitean Hamiltonian. Based on such a connection, we derive exact relaxation periods for the Eigen model to approach static energy landscape from various initial conditions. We also study a simple case of dynamic fitness function.Comment: 10 pages. Physical Revew E vol. 69, in press (2004

    Observation of Long-Lived Muonic Hydrogen in the 2S State

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    The kinetic energy distribution of ground state muonic hydrogen atoms mu-p(1S) is determined from time-of-flight spectra measured at 4, 16, and 64 hPa H2 room-temperature gas. A 0.9 keV-component is discovered and attributed to radiationless deexcitation of long-lived mu-p(2S) atoms in collisions with H2 molecules. The analysis reveals a relative population of about 1%, and a pressure-dependent lifetime (e.g. (30.4 +21.4 -9.7) ns at 64 hPa) of the long-lived mu-p(2S) population, equivalent to a 2S-quench rate in mu-p(2S) + H2 collisions of (4.4 +2.1 -1.8) 10^11 s^-1 at liquid hydrogen density.Comment: 4 pages, 2 figures, accepted for publication in Physical Review Letter

    Spatiotemporal predictions of soil properties and states in variably saturated landscapes

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    Understanding greenhouse gas (GHG) fluxes from landscapes with variably saturated soil conditions is challenging given the highly dynamic nature of GHG fluxes in both space and time, dubbed hot spots, and hot moments. On one hand, our ability to directly monitor these processes is limited by sparse in situ and surface chamber observational networks. On the other hand, remote sensing approaches provide spatial data sets but are limited by infrequent imaging over time. We use a robust statistical framework to merge sparse sensor network observations with reconnaissance style hydrogeophysical mapping at a well‐characterized site in Ohio. We find that combining time‐lapse electromagnetic induction surveys with empirical orthogonal functions provides additional environmental covariates related to soil properties and states at high spatial resolutions (~5 m). A cross‐validation experiment using eight different spatial interpolation methods versus 120 in situ soil cores indicated an ~30% reduction in root‐mean‐square error for soil properties (clay weight percent and total soil carbon weight percent) using hydrogeophysical derived environmental covariates with regression kriging. In addition, the hydrogeophysical derived environmental covariates were found to be good predictors of soil states (soil temperature, soil water content, and soil oxygen). The presented framework allows for temporal gap filling of individual sensor data sets as well as provides flexible geometric interpolation to complex areas/volumes. We anticipate that the framework, with its flexible temporal and spatial monitoring options, will be useful in designing future monitoring networks as well as support the next generation of hyper‐resolution hydrologic and biogeochemical models
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