872,720 research outputs found
Energy dependence of jet transport parameter and parton saturation in quark-gluon plasma
We study the evolution and saturation of the gluon distribution function in
the quark-gluon plasma as probed by a propagating parton and its effect on the
computation of jet quenching or transport parameter . For thermal
partons, the saturation scale is found to be proportional to the Debye
screening mass . For hard probes, evolution at small
leads to jet energy dependence of . We study this dependence for both
a conformal gauge theory in weak and strong coupling limit and for (pure gluon)
QCD. The energy dependence can be used to extract the shear viscosity of
the medium since can be related to the transport parameter for thermal
partons in a transport description. We also derive upper bounds on the
transport parameter for both energetic and thermal partons. The later leads to
a lower bound on shear viscosity-to-entropy density ratio which is consistent
with the conjectured lower bound . We also discuss the
implications on the study of jet quenching at the BNL Relativistic Heavy Ion
Collider and the CERN Large Hadron Collider and the bulk properties of the
dense matter.Comment: 15 pages in RevTex with 9 figures (v4 final published version
A Robust Image Hashing Algorithm Resistant Against Geometrical Attacks
This paper proposes a robust image hashing method which is robust against common image processing attacks and geometric distortion attacks. In order to resist against geometric attacks, the log-polar mapping (LPM) and contourlet transform are employed to obtain the low frequency sub-band image. Then the sub-band image is divided into some non-overlapping blocks, and low and middle frequency coefficients are selected from each block after discrete cosine transform. The singular value decomposition (SVD) is applied in each block to obtain the first digit of the maximum singular value. Finally, the features are scrambled and quantized as the safe hash bits. Experimental results show that the algorithm is not only resistant against common image processing attacks and geometric distortion attacks, but also discriminative to content changes
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