1,111 research outputs found
Phase Lag and Coherence Function of X-ray emission from Black Hole Candidate XTE J1550-564
We report the results from measuring the phase lag and coherence function of
X-ray emission from black hole candidate (BHC) XTE J1550-564. These X-ray
temporal properties have been recognized to be increasingly important in
providing important diagnostics of the dynamics of accretion flows around black
holes. For XTE J1550-564, we found significant hard lag --- the X-ray
variability in high energy bands {\em lags} behind that in low energy bands ---
associated both with broad-band variability and quasi-periodic oscillation
(QPO). However, the situation is more complicated for the QPO: while hard lag
was measured for the first harmonic of the signal, the fundamental component
showed significant {\em soft} lag. Such behavior is remarkably similar to what
was observed of microquasar GRS 1915+105. The phase lag evolved during the
initial rising phase of the 1998 outburst. The magnitude of both the soft and
hard lags of the QPO increases with X-ray flux, while the Fourier spectrum of
the broad-band lag varies significantly in shape. The coherence function is
relatively high and roughly constant at low frequencies, and begins to drop
almost right after the first harmonic of the QPO. It is near unity at the
beginning and decreases rapidly during the rising phase. Also observed is that
the more widely separated the two energy bands are the less the coherence
function between the two. It is interesting that the coherence function
increases significantly at the frequencies of the QPO and its harmonics. We
discuss the implications of the results on the models proposed for BHCs.Comment: To appear in ApJ Letter
Neutron-Capture Elements in the Double-Enhanced Star HE 1305-0007: a New s- and r-Process Paradigm
The star HE 1305-0007 is a metal-poor double-enhanced star with metallicity
[Fe/H] , which is just at the upper limit of the metallicity for the
observed double-enhanced stars. Using a parametric model, we find that almost
all s-elements were made in a single neutron exposure. This star should be a
member of a post-common-envelope binary. After the s-process material has
experienced only one neutron exposure in the nucleosynthesis region and is
dredged-up to its envelope, the AGB evolution is terminated by the onset of
common-envelope evolution. Based on the high radial-velocity of HE 1305-0007,
we speculate that the star could be a runaway star from a binary system, in
which the AIC event has occurred and produced the r-process elements.Comment: 4 pages, 3 figures, paper accepted for publication in Chinese Physics
letter
Global integrability for solutions to boundary value problems of anisotropic functionals
This paper deals with solutions to boundary value problems of anisotropic integral functionals
I(u) = â«Î© f(x,Du(x))dx,
with the energy f(x,z) has growth pi with respect to zi, like in
â«Î© ((1+âj=1n |Dju|pj )(p1-2)/p1 |D1u|2 + ⯠+ (1+âj=1n |Dju|pj )(pn-2)/pn |Dnu|2) dx.
We show that higher integrability of the boundary datum u* forces minimizers u to be more integrable. A similar result is obtained for obstacle problems
Strong Aperiodic X-ray Variability and Quasi-Periodic Oscillation in X-ray Nova XTE J1550-564
We report the discovery of strong aperiodic X-ray variability and
quasi-periodic oscillation (QPO) in the X-ray light curves of a new X-ray Nova,
XTE J1550-564, and the evolution of the observed temporal properties during the
rise of the recent X-ray outburst. The power spectral analysis of the first
observation reveals strong aperiodic X-ray variability of the source (~28%), as
well as the presence of a QPO at ~82 mHz with fractional rms amplitude ~14%
over the 2-60 keV energy range. Also apparent is the first harmonic of the QPO
with the amplitude ~9%. As the X-ray flux increases, the source tends to become
less variable, and the QPO frequency increases rapidly, from 82 mHz to 4 Hz,
over the flux (2-50 keV) range of 1.73-5.75 x 10^{-8} ergs cm^{-2} s^{-1}. The
amplitude of the fundamental component of the QPO varies little, while that of
the harmonic follows a decreasing trend. The fundamental component strengthens
toward high energies, while its harmonic weakens. Initially, the power spectrum
is roughly flat at low frequencies and turns into a power law at high
frequencies, with the QPO harmonic sitting roughly at the break. In later
observations, however, the high-frequency portion of the continuum can actually
be better described by a broken power law (as opposed to a simple power law).
This effect becomes more apparent at higher energies. The overall amplitude of
the continuum shows a similar energy dependence to that of the fundamental
component of the QPO. Strong rapid X-ray variability, as well as hard energy
spectrum, makes XTE J1550-564 a good black hole candidate. We compare its
temporal properties with those of other black hole candidates.Comment: 12 pages, including 5 figures. To appear in ApJ Letters, vol. 512
(1999
Microstructures and constituents of super-high strength aluminum alloy ingots made through LFEC process
Ingots of a new super-high strength Al-Zn-Mg-Cu-Zr alloy were produced respectively by low frequency electromagnetic casting (LFEC) and by conventional direct chill (DC) casting process. Microstructure and constituents of the ingots were studied. The results indicated that the LFEC process significantly refines microstructure and constituents of the alloy, and to some extent, decreases the area (or volume) fraction of constituents and eutectic structure precipitated at grain boundaries. But, no difference in the type of constituents was observed between LFEC and DC ingots. The results also showed LFEC process can improve the as-cast mechanical properties
Exploring Green Innovation Practices: Content Analysis of the Fortune Global 500 Companies
Green innovation has been attracting increasing attention due to its contributions to the conservation of resources and environmental protection. However, in the process of exploring green innovation, the allocation of resources and the direction of innovation are often inaccurate, which leads to a low efficiency of green innovation. If we can learn the green innovation practices from successful companies, we can certainly provide reference strategies for those companies that are exploring green innovation. Therefore, taking the Fortune Global 500 companies as the analysis object, this research develops the criteria of green innovation practices and conducts a cluster analysis of these companies by using a content analysis method. Finally, this paper summarizes the green innovation practices of the six types of industries and provides corresponding countermeasures and suggestions, which provide a strong reference for relevant companies to carry out green innovation
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