2,786 research outputs found

    ‘Twiddling’ of the pacemaker resulting in lead dislodgement

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    Twiddler’s syndrome is a rare condition in which patient manipulation of the pulse generator within its pocket may result in coiling of the lead and lead dislodgement, thereby causing pacemaker malfunction. Retraction of the electrode may cause phrenic nerve stimulation resulting in diaphragmatic stimulation and a sensation of abdominal pulsations. As the leads are further wrapped around the generator, rhythmic arm twitching may occur as a result of pacing of the brachial plexus.1 Twiddler’s syndrome was first described by Bayliss et al in 1968 as a complication of pacemaker implantation.2 It has also been reported with implantable cardioverter-defibrillators (ICDs)3 and cardiac resynchronisation therapy (CRT).4 This is a case report of an elderly lady with Twiddler’s syndrome resulting in pacemaker malfunction secondary to lead retraction, who emphatically denied any manipulation of her device. She subsequently underwent lead repositioning and appropriate counselling.peer-reviewe

    Trees and the dynamics of polynomials

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    The basin of infinity of a polynomial map f : {\bf C} \arrow {\bf C} carries a natural foliation and a flat metric with singularities, making it into a metrized Riemann surface X(f)X(f). As ff diverges in the moduli space of polynomials, the surface X(f)X(f) collapses along its foliation to yield a metrized simplicial tree (T,η)(T,\eta), with limiting dynamics F : T \arrow T. In this paper we characterize the trees that arise as limits, and show they provide a natural boundary \PT_d compactifying the moduli space of polynomials of degree dd. We show that (T,η,F)(T,\eta,F) records the limiting behavior of multipliers at periodic points, and that any divergent meromorphic family of polynomials \{f_t(z) : t \mem \Delta^* \} can be completed by a unique tree at its central fiber. Finally we show that in the cubic case, the boundary of moduli space \PT_3 is itself a tree. The metrized trees (T,η,F)(T,\eta,F) provide a counterpart, in the setting of iterated rational maps, to the R{\bf R}-trees that arise as limits of hyperbolic manifolds.Comment: 60 page

    Limits to Sympathetic Evaporative Cooling of a Two-Component Fermi Gas

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    We find a limit cycle in a quasi-equilibrium model of evaporative cooling of a two-component fermion gas. The existence of such a limit cycle represents an obstruction to reaching the quantum ground state evaporatively. We show that evaporatively the \beta\mu ~ 1. We speculate that one may be able to cool an atomic fermi gas further by photoassociating dimers near the bottom of the fermi sea.Comment: Submitted to Phys. Rev

    Two-species magneto-optical trap with 40K and 87Rb

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    We trap and cool a gas composed of 40K and 87Rb, using a two-species magneto-optical trap (MOT). This trap represents the first step towards cooling the Bose-Fermi mixture to quantum degeneracy. Laser light for the MOT is derived from laser diodes and amplified with a single high power semiconductor amplifier chip. The four-color laser system is described, and the single-species and two-species MOTs are characterized. Atom numbers of 1x10^7 40K and 2x10^9 87Rb are trapped in the two-species MOT. Observation of trap loss due to collisions between species is presented and future prospects for the experiment are discussed.Comment: 4 pages, 4 figures; accepted for publication in Physical Review

    Brain natriuretic peptide decreases pulmonary artery pressure in rats with pulmonary hypertension

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    Abstract only availableINTRODUCTION: B-type or Brain natriuretic peptide (BNP) was first isolated from the porcine brain, but it is primarily secreted from the cardiac ventricles in humans. As a cardiac hormone it has a physiologic regulatory function in the cardiovascular system. Along with atrial, and C-type natriuretic peptides, BNP aids in the natriuretic, diuretic, and vasorelaxant responses intended to reduce blood pressure and fluid volume homeostasis. Its vasodilator properties are known to be present in the pulmonary circulation; therefore, we hypothesized that BNP can be used as a therapy to lower the pulmonary artery pressure in an animal model of pulmonary hypertension. METHODS: Male Sprague-Dawley rats were given a one-time subcutaneous injection of 60 mg/kg monocrotaline to induce PH over a five week period. After establishment of PH, rats were anesthetized and ventilated. A catheter was placed in the right jugular vein and passed into the right ventricle to record right ventricular pressure (RVSP), an estimate of pulmonary artery pressure. A second catheter was placed in the right carotid artery to measure mean arterial pressure (MAP). RVSP and MAP were recorded before, during, and after infusions of BNP. RESULTS: One hour infusions of 5, 25, 50 or 150 ng/kg min BNP caused 24, 31 38, or 36% decreases in RVSP, respectively. There was no evidence of systemic hypotension at these doses of BNP. CONCLUSION: These preliminary findings suggest that BNP causes dose dependent decreases in pulmonary artery pressure in rats with pulmonary hypertension. Further study is needed to confirm these preliminary results.Louis Stokes Missouri Alliance for Minority Participatio

    Cooper pairing and single particle properties of trapped Fermi gases

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    We calculate the elementary excitations and pairing of a trapped atomic Fermi gas in the superfluid phase. The level spectra and pairing gaps undergo several transitions as the strength of the interactions between and the number of atoms are varied. For weak interactions, the Cooper pairs are formed between particles residing in the same harmonic oscillator shell. In this regime, the nature of the paired state is shown to depend critically on the position of the chemical potential relative to the harmonic oscillator shells and on the size of the mean field. For stronger interactions, we find a region where pairing occur between time-reversed harmonic oscillator states in different shells also.Comment: Slightly revised version: Mistakes in equation references in figures corrected. Accepted for Phys. Rev.

    Spin Excitations in a Fermi Gas of Atoms

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    We have experimentally investigated a spin excitation in a quantum degenerate Fermi gas of atoms. In the hydrodynamic regime the damping time of the collective excitation is used to probe the quantum behavior of the gas. At temperatures below the Fermi temperature we measure up to a factor of 2 reduction in the excitation damping time. In addition we observe a strong excitation energy dependence for this quantum statistical effect.Comment: 4 pages, 3 figure

    Superfluidity in the interior-gap states

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    We investigate superfluidity in the interior-gap states proposed by Liu and Wilczek. At weak coupling, we find the {\em gapless} interior-gap state unstable in physically accessible regimes of the parameter space, where the superfluid density is shown to be always negative. We therefore conclude that the spatially-uniform interior-gap phase is extremely unstable unless it is fully gapped; in this case, however, the state is rather similar to conventional BCS states.Comment: To appear in Physical Review

    Low energy collective excitations in a superfluid trapped Fermi gas

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    We study low energy collective excitations in a trapped superfluid Fermi gas, that describe slow variations of the phase of the superfluid order parameter. Well below the critical temperature the corresponding eigenfrequencies turn out to be of the order of the trap frequency, and these modes manifest themselves as the eigenmodes of the density fluctuations of the gas sample. The latter could provide an experimental evidence of the presence of the superfluid phase.Comment: 5 pages, REVTeX, referencies correcte
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