3,536 research outputs found

    Characterizing Intermittency of 4-Hz Quasi-periodic Oscillation in XTE J1550-564 using Hilbert-Huang Transform

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    We present the time-frequency analysis results based on the Hilbert-Huang transform (HHT) for the evolution of a 4-Hz low-frequency quasi-periodic oscillation (LFQPO) around the black hole X-ray binary XTE J1550-564. The origin of LFQPOs is still debated. To understand the cause of the peak broadening, we utilized a recently developed time-frequency analysis, HHT, for tracking the evolution of the 4-Hz LFQPO from XTE J1550 564. By adaptively decomposing the ~4-Hz oscillatory component from the light curve and acquiring its instantaneous frequency, the Hilbert spectrum illustrates that the LFQPO is composed of a series of intermittent oscillations appearing occasionally between 3 Hz and 5 Hz. We further characterized this intermittency by computing the confidence limits of the instantaneous amplitudes of the intermittent oscillations, and constructed both the distributions of the QPO's high and low amplitude durations, which are the time intervals with and without significant ~4-Hz oscillations, respectively. The mean high amplitude duration is 1.45 s and 90% of the oscillation segments have lifetimes below 3.1 s. The mean low amplitude duration is 0.42 s and 90% of these segments are shorter than 0.73 s. In addition, these intermittent oscillations exhibit a correlation between the oscillation's rms amplitude and mean count rate. This correlation could be analogous to the linear rms-flux relation found in the 4-Hz LFQPO through Fourier analysis. We conclude that the LFQPO peak in the power spectrum is broadened owing to intermittent oscillations with varying frequencies, which could be explained by using the Lense-Thirring precession model.Comment: 27 pages, 9 figures, accepted for publication in The Astrophysical Journa

    Variation of Mycobacterium tuberculosis antigen-specific IFN-γ and IL-17 responses in healthy tuberculin skin test (TST)-positive human subjects.

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    ObjectiveTo determine the variation of IFN-γ and IL-17 responses to M. tuberculosis antigens in healthy TST+ humans.MethodsWe isolated peripheral blood mononuclear cells from 21 TST+ healthy adults, stimulated them with phytohemagglutinin (PHA), PPD, Ag85B, ESAT-6, and live M. bovis BCG, and assayed IFN-γ and IL-17 secretion by ELISA in supernatants after 24 or 72 hours of incubation respectively.ResultsAs in other studies, we found a wide range of IFN-γ responses to M. tuberculosis antigens; the variation significantly exceeded that observed in the same donors to the polyclonal T cell stimulus, phytohemagglutinin (PHA). In addition, we assayed IL-17 secretion in response to the same stimuli, and found less subject-to-subject variation. Analysis of the ratio of IFN-γ to IL-17 secretion on a subject-to-subject basis also revealed a wide range, with the majority of results distributed in a narrow range, and a minority with extreme results all of which were greater than that in the majority of subjects. The data suggest that study of exceptional responses to M. tuberculosis antigens may reveal immunologic correlates with specific outcomes of M. tuberculosis infection.ConclusionVariation of IFNγ and IFN-γ/IL-17 responses to mycobacterial antigens exceeds that of responses to the polyclonal stimulus, PHA, in TST positive healthy humans. This indicates a quantitative spectrum of human immune responses to infection with M. tuberculosis. Since the outcome of human infection with M. tuberculosis varies greatly, systematic study of multiple immune responses to multiple antigens is likely to reveal correlations between selected immune responses and the outcomes of infection

    An Optimization Approach for Pricing of Sherpa Target Redemption Notes

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    Based on the one-factor CIR interest rate model, the pricing of Sherpa Target Redemption Notes (STARN) with early-excise features is investigated in this paper. Firstly, the characteristics of Sherpa target redemption notes were described and the partial differential equation was proposed. Secondly, both non-arbitrage jump conditions on the coupon date and early-excise policy on the redemption date were provided; furthermore, the boundary conditions of partial differential equations were also discussed. Thirdly, a numerical method for solving the partial differential equation was obtained based on the control volume in the theory of finite volume by making use of the upwind weighting scheme to avoid the numerical oscillation phenomenon. Finally, the sensitivity of the model parameters was analyzed. The results show that the STARN value decreases rapidly with the increase in short-term interest rates, furthermore, when short-term interest rates reached a turning point the rate of decline slowed. As volatility increases, the value of the Notes is increased; increasingly as the proportion redeemed is large, STARN value increases

    Construction of index system for external risk factors of disease on large-scale farm based on the analytic hierarchy process

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    AbstractAnimal health risk analysis technology on large-scale farm is becoming more important, but the assessment of relevant external risk factors of disease spreading into pig farm is an complex multi-dimensional process. The analytic hierarchy process (AHP) has been accepted as a robust and flexible multi-criteria decision-making tool for dealing with complex decision problems. On this study, The index system of external risk factors on large-scale farm is built based on AHP. The result shows that farm management practices, Biosecurity and site are major risk factors and reveals AHP can be used in animal risk analysis for disease control and prevention

    N-[(E)-4-Pyridylmethyl­ene]-4-[(E)-4-(4-pyridylmethyl­eneamino)benz­yl]aniline tetra­hydrate

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    The title compound, C25H20N4·4H2O, crystallizes with the organic mol­ecule lying on a twofold rotation axis through the methyl­ene bridge C atom; there are also two water molecules in the asymmetric unit. The crystal structure is stabilized by C—H⋯O, O—H⋯O and O—H⋯N hydrogen bonds, linking the water mol­ecules to each other and to the pyridine N atom