325,583 research outputs found
A 2 h periodic variation in the low-mass X-ray binary Ser X-1
No full textSpectroscopy of the low-mass X-ray binary Ser X-1 using the Gran Telescopio Canarias have revealed a ?2 h periodic variability that is present in the three strongest emission lines. We tentatively interpret this variability as due to orbital motion, making it the first indication of the orbital period of Ser X-1. Together with the fact that the emission lines are remarkably narrow, but still resolved, we show that a main-sequence K dwarf together with a canonical 1.4 M? neutron star gives a good description of the system. In this scenario, the most likely place for the emission lines to arise is the accretion disc, instead of a localized region in the binary (such as the irradiated surface or the stream-impact point), and their narrowness is due instead to the low inclination (?10°) of Ser X-1
Relations between x-ray timing features and spectral parameters of galactic black hole x-ray binaries
No full textWe present a study of correlations between spectral and timing parameters for a sample of black hole X-ray binary candidates. Data are taken from GX
339-4, H 1743-322, and XTE J1650-500, as the Rossi X-ray Timing Explorer
(RXTE) observed complete outbursts of these sources. In our study we investigate outbursts that happened before the end of 2009 to make use of the high-energy coverage of the HEXTE detector and select observations that
show a certain type of quasi-periodic oscillations (type-C QPOs). The spectral parameters are derived using the empirical convolution model simpl to model the Comptonized component of the emission together with a disc blackbody for the emission of the accretion disc. Additional spectral features, namely a reflection component, a high-energy cut-off, and excess emission at 6.4 keV, are taken into account. Our investigations confirm the known positive
correlation between photon index and centroid frequency of the QPOs and reveal an anti-correlation between the fraction of up-scattered photons and the QPO frequency. We show that both correlations behave as expected in the “sombrero”
geometry. Furthermore, we find that during outburst decay the correlation between photon index and QPO frequency follow a general track, independent of individual outbursts
H ? filtering for stochastic singular fuzzy systems with time-varying delay
No full textThis paper considers the H? filtering problem
for stochastic singular fuzzy systems with timevarying
delay. We assume that the state and measurement
are corrupted by stochastic uncertain exogenous
disturbance and that the system dynamic is modeled
by Ito-type stochastic differential equations. Based on
an auxiliary vector and an integral inequality, a set of
delay-dependent sufficient conditions is established,
which ensures that the filtering error system is e?t -
weighted integral input-to-state stable in mean (iISSiM).
A fuzzy filter is designed such that the filtering
error system is impulse-free, e?t -weighted iISSiM and
the H? attenuation level from disturbance to estimation
error is belowa prescribed scalar.Aset of sufficient
conditions for the solvability of the H? filtering problem
is obtained in terms of a new type of Lyapunov
function and a set of linear matrix inequalities. Simulation
examples are provided to illustrate the effectiveness
of the proposed filtering approach developed in
this paper
Magnetocrystalline anisotropic effect in GdCo1-xFexAsO (x=0,0.05)
No full textFrom a systematic study of the electrical resistivity rho(T, H), magnetic susceptibility chi(T, H), isothermal magnetization M(H), and the specific heat C(T, H), a temperature-magnetic field (T - H) phase diagram has been established for GdCo1-xFexAsO (x = 0 and 0.05) polycrystalline compounds. GdCoAsO undergoes two long-range magnetic transitions: ferromagnetic (FM) transition of Co 3d electrons (T-Co(C)) and antiferromagnetic (AFM) transition of Gd 4f electrons (T-N(Gd)). For the Fe-doped sample (x = 0.05), an extra magnetic reorientation transition takes place below T-N(Gd), which is likely associated with Co moments. The two magnetic species of Gd and Co are coupled antiferromagnetically to give rise to ferrimagnetic (FIM) behavior in the magnetic susceptibility. Upon decreasing the temperature (T < T-N(Co)), the magnetocrystalline anisotropy breaks up the FM order of Co by aligning the moments with the local easy axes of the various grains, leading to a spin reorientation transition at T-R(Co). By applying a magnetic field, T-R(Co) monotonically decreases to lower temperatures, while the T-N(Gd) is relatively robust against the external field. On the other hand, the applied magnetic field pulls the magnetization of grains from the local easy direction to the field direction via a first-order reorientation transition, with the transition field (H-M) increasing upon cooling the temperature
X-ray absorption studies on cubic boron nitride thin films
No full textCubic boron nitride (c-BN) films synthesized by various energetic species assisted physical vapor deposition and chemical vapor deposition techniques on Si and diamond-coated Si substrates have been investigated by boron and nitrogen K-edge angle-resolved x-ray absorption near-edge structure in both total electron yield and fluorescence yield modes. X-ray absorption spectrum has been developed to study the film structure, the quantity and distribution of the partially ordered turbostratic (t-BN) and amorphous (a-BN) sp(2)-hybridized BN phases, and the t-BN/a-BN ratios. The preferred direction of the t-BN basal planes at the interface between c-BN and substrate is found to be normal or nearly normal to the substrate. The content of the sp(2)-bonded BN in the c-BN films deposited on diamond-coated Si substrates reduces remarkably. The modifications of the electronic structure of the c-BN films with respect to bulk hexagonal BN and c-BN have been investigated and the crystallinity of c-BN films has also been evaluated from the x-ray absorption near edge structure results. (c) 2007 American Institute of Physics
方程式x^^・(t)=-f(x(t))(g(x(t))+h(x(t-1)))の周期解
No full textThe existence of nontrivial periodic solutions of the scalar equation x^^・(t) = - f(x(t))(g(x(t)) + h(x(t - 1))) is mainly discussed by using a fixed point theorem for a closed convex set. As an application of the main results, we show that a conjecture by G. Seifert is right. Moreover we give a negative answer to a question by G. Seifert
Discovery of an optical counterpart to the hyperluminous X-ray source in ESO 243-49
No full textThe existence of black holes of masses similar to 10(2)-10(5)M(circle dot) has important implications for the formation and evolution of star clusters and supermassive black holes. One of the strongest candidates to date is the hyperluminous X-ray source (HLX1), possibly located in the S0- a galaxy ESO 243-49, but the lack of an identifiable optical counterpart had hampered its interpretation. Using the Magellan telescope, we have discovered an unresolved optical source with R = 23.80 +/- 0.25 mag and V = 24.5 +/- 0.3 mag within HLX1's positional error circle. This implies an average X-ray/optical flux ratio similar to 500. Taking the same distance as ESO 243-49, we obtain an intrinsic brightness M-R = -11.0 +/- 0.3 mag, comparable to that of a massive globular cluster. Alternatively, the optical source is consistent with a main-sequence M star in the Galactic halo (for example an M4.4 star at approximate to 2.5 kpc). We also examined the properties of ESO 243-49 by combining Swift/Ultraviolet/Optical Telescope (UVOT) observations with stellar population modelling. We found that the overall emission is dominated by a similar to 5-Gyr-old stellar population, but the UV emission at approximate to 2000 angstrom is mostly due to ongoing star formation at a rate of similar to 0.03M(circle dot) yr(-1). The UV emission is more intense (at least a 9 sigma enhancement above the mean) north-east of the nucleus, in the same quadrant as HLX1. With the combined optical and X-ray measurements, we put constraints on the nature of HLX1. We rule out a foreground star and a background AGN. Two alternative scenarios are still viable. HLX1 could be an accreting intermediate mass black hole in a star cluster, which may itself be the stripped nucleus of a dwarf galaxy that passed through ESO 243-49, an event which might have caused the current episode of star formation. Or, it could be a neutron star in the Galactic halo, accreting from an M4-M5 donor star
Hardening effects in plastically deformed Pd with the addition of H
No full textWell-annealed Pd and Pd-H alloys were subjected to tensile tests. It is found that the presence of H does not affect the yield strength but enhances the strain hardening of Pd remarkably. This is explained by a negligible solute drag effect of H on the movement of dislocations, and by H-induced enhanced multiplication of dislocations upon plastic deformation, respectively. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved
On the solution of the equation ut+unux+H(x, t, u)=0
No full textWe consider the equation u(t) + u(n)u(x) + H(x, t, u) = 0 and derive a transformation relating it to u(t) + u(n)u(x) = 0. Special cases of the equation appearing in applications are discussed. Initial value problems and asymptotic behaviour of the solution are studied
A sufficient condition for the solvability of the equation T(x)\ni H(x)
No full textSi enuncia un criterio che assicura l'esistenza di soluzioni per equazioni
contingenti del tipo H (x) T (x) con T, in un certo senso,
invertibìle. Seguono alcuni corollari ed applicazioni.We prove a criterion wich guarantees that some contingent equations
like H (x) T (x) have a solutlon. We assume that T is,
in some sense, an invertible map. Some applications are given
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