16,422 research outputs found
Isotopic dependence of residual zonal flows
No full textWe identify an isotopic dependence of residual zonal flows from an analytic calculation. While the well-known Rosenbluth-Hinton residual zonal flows with radial scale greater than the magnetically trapped ion radial width rho(bi) have no isotopic dependence (Rosenbluth and Hinton 1998 Phys. Rev. Lett. 80 724), we find that shorter radial scale (shorter than rho(bi), but larger than the magnetically trapped electron radial width rho(be)) residual zonal flows (Wang and Hahm 2009 Phys. Plasmas 16 062309) exhibit isotopic dependence. These finer scale zonal flows in deuterium (D) plasmas can be stronger than those of hydrogen (H) plasmas, and possibly lead to lower turbulence and transport and better confinement in qualitative agreement with experimental results
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
Logarithmic variance profiles and the corresponding f-1 spectra of temperature fluctuations in turbulent Rayleigh-Bénard convection
No full textWe report experimental results for the temperature variance 2(z) and the corresponding frequency spectra P(f) in turbulent Rayleigh-Bénard convection (RBC) in a cylindrical sample of aspect ratioT= D/L = 1:00 (D = 1:12 m is the diameter and L = 1:12 m the height). The measurements were conducted in the Rayleigh-number range 1011 < Ra < 1:35 1014 and Pr ' 0:8. For Ra = 1:35x1014, 2(z) could be described well by a logarithmic dependence on the vertical position z in a range of z 1 < z < z 2 with z 1 ' 70 and z 2 = 0:1L. Here L=(2Nu) is the thickness of a thin thermal sublayer adjacent to the horizontal plate where the heat flux (denoted by the Nusselt number Nu) is carried mostly by thermal diffusion. In the log layer, we found that the temperature spectra had a significant frequency range over which P(f) f with close to 1. As Ra decreased, increased so that the log layer became thinner. At Ra = 2:05 1011, z 2 < z 1 and therefore there was no range for a log layer. Correspondingly, the temperature spectrum near the horizontal plate did not have the f1 scaling form either
On the periodic orbits of the Third-order differential equation x ' ' '- x ' ' x'- x= F(x,x',x ' ')
No full textAgraïments: The second author is partially supported by CAPES/MECD-DGU 222/2010 Brazil and SpainIn this paper we study the periodic orbits of the third-order differential equation x''' − µx'' + x' − µx = εF(x, x', x''), where ε is a small parameter and the function F is of class C2
The generalized Liénard polynomial differential systems x'=y,y'= -g(x) - f (x)y with deg g = deg f 1 are not Liouvillian integrable
No full textAgraïments: The second author was supported by Portuguese National Funds through FCT - Fundação para a Ciência e a Tecnologia within the project PTDC/MAT/117106/2010 and by CAMGSD (PEst-OE/EEI/LA0009/2013)We prove the nonexistence of Liouvillian first integrals for the generalized Li\'enard polynomial differential systems of the form x' = y, y'=-g(x)-f(x)y, where g(x) and f(x) are arbitrary polynomials such that g = f 1
The generalized Liénard polynomial differential systems x'=y,y'= -g(x) - f (x)y with deg g = deg f 1 are not Liouvillian integrable
No full textAgraïments: The second author was supported by Portuguese National Funds through FCT - Fundação para a Ciência e a Tecnologia within the project PTDC/MAT/117106/2010 and by CAMGSD (PEst-OE/EEI/LA0009/2013)We prove the nonexistence of Liouvillian first integrals for the generalized Li\'enard polynomial differential systems of the form x' = y, y'=-g(x)-f(x)y, where g(x) and f(x) are arbitrary polynomials such that g = f 1
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
Also By The Same Author: AKTiveAuthor, a Citation Graph Approach to Name Disambiguation
No full textThe desire for definitive data and the semantic web drive for inference over heterogeneous data sources requires co-reference resolution to be performed on those data. In particular, name disambiguation is required to allow accurate publication lists, citation counts and impact measures to be determined. This paper describes a graph-based approach to author disambiguation on large-scale citation networks. Using self-citation, co-authorship and document source analyses, AKTiveAuthor clusters papers, achieving precision of 0.997 and recall of 0.818 over a test group of eight surname clusters
On The Functional Equation p(x)=h(x, ^[f(x)])
No full textWe shall consider the system of functional equations (1) ^(x) = h^x,^ [f(x)] .... ), i=1,...,m,
where the functions h^ and f of the type Rm+"' —»-R and Rn—*Rn, respectively, are given and are unknown functions. The fundamental theorems regarding the uniqueness and the existence of solutions of the class Cr in the case m=1 are. due to B.Choczewski ( [l] , [2]). This theory has been further extended by J.Matkowski [6]. Our theorem (see §3) generalizes also some result of the author obtained in the case of functions of real variable [4]. On the other hand, the system (1) may be treated as a generalization of Schroeder's
equation. Therefore the results of this paper correspond to others contained in [3], [5] and [8] (Fragment tekstu)
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