Search for chaos in neutron star systems: Is Cyg X-3 a black hole?

The accretion disk around a compact object is a nonlinear general relativistic system involving magnetohydrodynamics. Naturally the question arises whether such a system is chaotic (deterministic) or stochastic (random) which might be related to the associated transport properties whose origin is still not confirmed. Earlier, the black hole system GRS 1915+105 was shown to be low dimensional chaos in certain temporal classes. However, so far such nonlinear phenomena have not been studied fairly well for neutron stars which are unique for their magnetosphere and kHz quasi-periodic oscillation (QPO). On the other hand, it was argued that the QPO is a result of nonlinear magnetohydrodynamic effects in accretion disks. If a neutron star exhibits chaotic signature, then what is the chaotic/correlation dimension? We analyze RXTE/PCA data of neutron stars Sco X-1 and Cyg X-2, along with the black hole Cyg X-1 and the unknown source Cyg X-3, and show that while Sco X-1 and Cyg X-2 are low dimensional chaotic systems, Cyg X-1 and Cyg X-3 are stochastic sources. Based on our analysis, we argue that Cyg X-3 may be a black hole.Comment: 9 pages including 6 figures; to appear in The Astrophysical Journa

Functional roles of the two cyclic AMP-dependent forms of cyclic AMP receptor protein from Escherichia coli

AbstractThe cyclic AMP receptor protein activates transcription in Escherichia coli, only when complexed with cyclic AMP. The cyclic AMP receptor protein-cyclic AMP complex formed at low concentrations of cyclic AMP has a different conformation from either cyclic AMP receptor protein alone or its complex with cyclic AMP formed at high cyclic AMP concentrations. Various biophysical data suggest that the latter complex resembles free cyclic AMP receptor protein. We have examined the conformational and biological properties of cyclic AMP receptor protein as a function of cyclic AMP concentrations, using the gal operon of E. coli. A biphasic behavior is observed. It is shown that only the complex formed at lower concentrations of cyclic AMP is the transcriptionally active form. This difference between the complexes at different levels of cyclic AMP arises from a decreased ability of the cyclic AMP receptor protein-cyclic AMP complex at high cyclic AMP concentrations to bind to DNA at specific sites

A JPEG-Like Algorithm for Compression of Single-Sensor Camera Image

International audienceThis paper presents a JPEG-like coder for image compression of single-sensor camera images using a Bayer Color Filter Array (CFA). The originality of the method is a joint scheme of compression.demosaicking in the DCT domain. In this method, the captured CFA raw data is first separated in four distinct components and then converted to YCbCr. A JPEG compression scheme is then applied. At the decoding level, the bitstream is decompressed until reaching the DCT coefficients. These latter are used for the interpolation stage. The obtained results are better than those obtained by the conventional JPEG in terms of CPSNR, DeltaE2000 and SSIM. The obtained JPEG-like scheme is also less complex

An efficient source localization method in presence of multipath using smart antenna system

In this paper, a MATLAB based smart antenna testbed that efficiently localizes the line-of-sight (LOS) source in the presence of multipath signals is developed. By exploiting the consistent amplitude nature of the LOS signal, a variant of Constant Modulus Algorithm, namely Multitarget-Least Square Constant Modulus Algorithm is employed to adapt and update the weights of the smart antenna for estimation of the direction-of-arrival (DOA) of the of the LOS and multipath interference signals. Performance is compared with the conventional and recently proposed algorithms in the same testbed with alike considerations. Simulation result shows that the proposed method of DOA estimation performs better in terms of probability of resolution and root mean square error

An Efficient Source Localization Method in Presence of Multipath using Smart Antenna System

1069-1073In this paper, a MATLAB based smart antenna testbed that efficiently localizes the line-of-sight (LOS) source in the presence of multipath signals is developed. By exploiting the consistent amplitude nature of the LOS signal, a variant of Constant Modulus Algorithm, namely Multitarget-Least Square Constant Modulus Algorithm is employed to adapt and update the weights of the smart antenna for estimation of the direction-of-arrival (DOA) of the of the LOS and multipath interference signals. Performance is compared with the conventional and recently proposed algorithms in the same testbed with alike considerations. Simulation result shows that the proposed method of DOA estimation performs better in terms of probability of resolution and root mean square error