29,384 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
Periodic solutions of Duffing's equations with superquadratic potential
No full textAbstractThis paper is devoted to the study of harmonic and subharmonic solutions for the second order scalar nonlinear Duffing's equation x″ + g(x) = p(t, x, x′), where g and p are continuous functions with p bounded and periodic in the first variable and g satisfying the assumption g(x)sign(x) → + ∞, as ¦x¦ → + ∞. Among other results, we prove the existence of infinitely many harmonic and subharmonic solutions (of any order) p = p(t) and if the potential G(x) of g(x) satisfies certain conditions of superquadratic growth at ∞. The new existence results can be applied to situations in which the more classical superlinear growth condition g(x)x → + ∞, as ¦x¦ → + ∞, is not satisfied. In this manner, various preceding theorems are improved and sharpened (see the “Introduction” for more details). Proofs are based on a generalized version of the Poincaré-Birkhoff “twist” theorem due to W. Ding
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
Automorphic forms and fermion masses
No full textWe extend the framework of modular invariant supersymmetric theories to encompass invariance under more general discrete groups Γ, that allow the presence of several moduli and make connection with the theory of automorphic forms. Moduli span a coset space G/K, where G is a Lie group and K is a compact subgroup of G, modded out by Γ. For a general choice of G, K, Γ and a generic matter content, we explicitly construct a minimal Kähler potential and a general superpotential, for both rigid and local N = 1 supersymmetric theories. We also specialize our construction to the case G = Sp(2g, R), K = U(g) and Γ = Sp(2g, Z), whose automorphic forms are Siegel modular forms. We show how our general theory can be consistently restricted to multi-dimensional regions of the moduli space enjoying residual symmetries. After choosing g = 2, we present several examples of models for lepton and quark masses where Yukawa couplings are Siegel modular forms of level 2
A General Method for Designing ESPAR Antenna with Planar Beam Scanning Capabilities
No full textWe propose a general computational method for guiding the design of an electronically steerable parasitic array radiator (ESPAR) antenna. The radiation field of the 2-element unit cell is calculated to ascertain the port characteristics of the parasitic element, followed by the retrieval of reactive load values as the beam steers. So, DC bias and diode operating parameters have been considered thoroughly. A 9-element ESPAR antenna is proposed to verify the method, with the observed congruence between calculated and measured results validating the method and highlighting its value for designing ESPAR antennas
Design of in-phase and quadrature two paths space-time-modulated metasurfaces
No full textSpace-time-modulated metasurfaces can manipulate electromagnetic waves in space and frequency domain simultaneously. In this paper, an analytical design of space-time-modulated metasurfaces with modulation elements composed of two paths, In-phase (I) and Quadrature (Q), is proposed. The model is derived analytically, the space/frequency domain manipulations are achieved by designing the dimension and time sequence of I and Q paths. In the specular reflection direction, an objective frequency shift of the reflected first order harmonic can be obtained. While, in other directions, the opposite first order harmonic can be easily controlled by changing the dimension of I/Q paths and the objective first order harmonic remains unchanged. Furthermore, with a small dimension of I/Q paths, the first order harmonic can be used for beam scanning by pre-designing the start time of the modulation element. To realize the space-time-modulated metasurface with the required periodically time-varying responses, 2-bit unit-cells loaded with dynamically switchable pin diodes are employed as I/Q modulation. Both analytical and numerical results demonstrate that space and frequency domain manipulations of the reflected fields by the first order harmonics can be simultaneously obtained. The proposed designs have potential applications in wireless communications, radar camouflaging, and cloaking
Investigation of the interaction of evaporated aluminum with vapor deposited Teflon AF films via X-ray photoelectron spectroscopy
No full textThe interfacial bonding and mixing between evaporated aluminum and a vapor deposited Teflon AF (abbreviated to AF) film have been investigated with X-ray photoelectron spectroscopy. Graphite carbon (C–C), and aluminum carbide (Al–C), oxide (Al–O–C) and fluoride (Al–F) are formed when aluminum atoms are deposited on to the AF film. With increasing deposition of aluminum, the concentrations of these newly formed components increase gradually. Moreover, in situ annealing results in remarkable increases in the C–C, Al–C, Al–O–C and Al–F configurations and a decrease in metallic aluminum. No significant diffusion of aluminum into the AF film was observed during the annealing. The Al compounds form a layer at the Al/AF interface that acts as an adhesion promoter and diffusion barrier. <br/
Syntheses, structures and properties of [{HC(CMeNAr)(2)}Ge(E)X] (Ar=2,6-iPr(2)C(6)H(3); E = S, Se; X = F, Cl)
No full textFor the first time the structurally characterized heavier chalcogen analogues of alkanoyl halides,[{HC(CMeNAr)(2)}Ge(S)X] (Ar = 2,6-iPr(2)C(6)H(3); X = Cl (1), F (2)) and [{HC(CMeNAr)(2)}Ge(Se)X] (X = Cl (4), F (5)) have been prepared from the starting material [{HC(CMeNAr)(2)}GeCl] (3). The nature of the germanium-chalcogen bond is best described as between the two resonance structures, Ge+-E- Ge=E. The investigation of the reactivity of the germanium-halogen bond with RLi reagents (R = Me, nBu) led to the formation of [{HC(CMeNAr)(2)}Ge(E)R] (E = S, R = Me (6); E = Se, R = Me (7), nBu (8)). The solid-state structures of 1, 2, 4, 5, 6, and 8 are reported
A General Analytical Arrangement for Large-Spacing Planar Scanning Array Grating Lobe Suppression Based on Energy Homogenization Theory
No full textThis communication introduces a general analytical method for suppressing the grating lobes (GL) of planar scanning arrays with spacing exceeding half a wavelength from an array configuration perspective. First, the positions of GLs are analyzed, followed to derive an analytic relationship between the positions of these GLs and the spacings of the element. On this basis, a general array arrangement expression with arbitrary-order GL suppression capabilities is derived. With this arrangement approach, an analytical method for suppressing GLs is proposed without limiting the spacing, bandwidth, and element pattern. Afterward, a series of numerical results are presented, and a prototype with a relative bandwidth of 22.3% is fabricated and measured to validate the proposed method. The measured results show that the prototype array with spacing at least greater than one wavelength can steer its main lobe from -50° to 50° both in E- and H-planes, and maintain the sidelobe levels less than -6.2 dB and -5.1 dB and scan-loss less than 5.4 dB. The SLLs improve further with the exponential increase in the number of elements
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