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The power spectral densities (PSDs) for a sample of active galactic nuclei (AGNs) are analyzed in both the frequency domain
and the time domain. We find for each object that for broadband noise a character timescale-bifurcation timescale of Fourier
and time-domain PSD exists in the 103–106 s range, below which the time-domain power spectrum is systematically higher than the corresponding Fourier spectrum. The
relationship between bifurcation timescale, AGN mass and luminosity is studied. Compared with the fact that similar phenomena
have been found for Galactic black hole candidates (GBHs) with bifurcation timescale ∼0.1 s but not for accreting neutron
stars, our finding indicates that AGNs and GBHs have common intrinsic nature in rapid X-ray variability with a character time
parameter scaled with their masses
Supported by the Special Funds for Major State Basic Research Projects (Grant No. 2009CB824800) and the National Natural Science
Foundation of China (Grant No. 10533020) 相似文献
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For black hole binaries (BHBs) and active galactic nuclei (AGNs), bifurcation timescales (BTs) Δt b exist, below which time-domain power is significantly higher than the corresponding Fourier power. Quasi-periodic oscillations (QPOs) are removed from the Fourier spectra of BHBs. A relationship between BT, black hole mass and bolometric luminosity is derived. Strong anti-correlation between BT and luminosity of Cyg X-1 is found. After removing the QPOs, BTs are also obtained for two ultraluminous X-ray sources (ULXs), M82 X-1 and NGC5408 X-1. The results support that they harbor intermediate mass black holes (IMBHs).
相似文献4.
Hexia Gan Quanzeng Zhang Han Zhang Yue Chen Jianzhong Lin TaiShan Kang Jiaxing Zhang Frederic A. Troy II Bing Wang 《Magnetic resonance imaging》2014
Propose
To design a set of brain templates for postnatal piglet brains based on high-resolution T1-weighted imaging for voxel-based morphometric analysis.Materials and methods
Using a 3.0 T magnetic resonance (MR) scanner, a population-based whole brain template was developed by averaging forty T1 images in the brains of postnatal piglets at 38 days of age. The templates for gray and white matter, and cerebrospinal fluid were designed based on the corresponding probability maps by adapting individual data sets using statistical parametric mapping. Anatomical labeling maps were generated from labeling propagation derived from the established Pig Brain Atlas. Differences in the coordinates from four significant structural landmarks in the template, plus an additional 12 normalized images and anatomical labeling maps were measured to validate the accuracy of the registration of the template.Results
A whole brain template, a set of tissue-specific probability and anatomical labeling maps were developed. The location deviation of the four significant structural landmarks, including the anterior and posterior regions in the corpus callosum, and the left and right caudate nucleus, was found to be < 0.25 cm, validating the sensitivity and resolution of the template.Conclusion
A whole brain template map and a set of tissue-specific probability and anatomical labeling maps were developed to analyze the morphometric imaging of the postnatal piglet brain, an animal model of the human infant. 相似文献5.
CdTe nanocrystals (CdTe NCs) were achieved by reaction of CdCl2 with KHTe solution and were capped with sodium mercaptoacetate. The product was detected by transmission electron microscopy
(TEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive spectroscopy (EDS), fluorescence spectra,
ultraviolet-visible spectra and X-ray diffraction (XRD). The CdTe NCs are of cubic structure and the average size is about
5 nm. The fluorescence quantum yield of CdTe NCs aqueous solution increased from 37% to 97% after 20 d under room light. The
maximum λ
em of fluorescence changed from 543 nm to 510 nm and the blue shift was 33 nm. CdTe NCs aqueous solution can be steady for at
least 10 months at 4 in° a refrigerator. The resonance Rayleigh scattering (RRS) of CdTe NCs in the aqueous solution was investigated.
The maximum scattering peak was located at about 554 nm. The interactions of CdTe NCs with amikacin sulfate (AS) and micronomicin
sulfate (MS) were investigated respectively. The effects of AS and MS on fluorescence and RRS of CdTe NCs were analyzed. It
was found that AS and MS quenched the photoluminescence of CdTe NCs and enhanced RRS of CdTe NCs. Under optimum conditions,
there are linear relationships between quenching intensity (F
0-F), intensity of RRS (I-I
0) and concentration of AS and MS. The detection limits (3б) of AS and MS are respectively 3.4 ng·mL−1 and 2.6 ng·mL−1 by the fluorescence quenching method, and 15.2 ng·mL−1 and 14.0 ng·mL−1 by the RRS method. The methods have high sensitivity, thus CdTe NCs may be used as fluorescence probes and RRS probes for
the detection of aminoglycoside antibiotics.
Supported by the National Natural Science Foundation of China (Grant No. 20475045) 相似文献
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