2,458 research outputs found

    Modified gravity as a common cause for cosmic acceleration and flat galaxy rotation curves

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    Flat galaxy rotation curves and the accelerating Universe both imply the existence of a critical acceleration, which is of the same order of magnitude in both the cases, in spite of the galactic and cosmic length scales being vastly different. Yet, it is customary to explain galactic acceleration by invoking gravitationally bound dark matter, and cosmic acceleration by invoking a `repulsive` dark energy. Instead, might it not be the case that the flatness of rotation curves and the acceleration of the Universe have a common cause? In this essay we propose a modified theory of gravity. By applying the theory on galactic scales we demonstrate flat rotation curves without dark matter, and by applying it on cosmological scales we demonstrate cosmic acceleration without dark energy.Comment: 7 pages, 1 fgure. Honorable Mention in Gravity Research Foundation Essay Contest 2012. v2: Two minor typos correcte

    Approximate MAP Decoding on Tail-Biting Trellises

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    We propose two approximate algorithms for MAP decoding on tail-biting trellises. The algorithms work on a subset of nodes of the tail-biting trellis, judiciously selected. We report the results of simulations on an AWGN channel using the approximate algorithms on tail-biting trellises for the (24,12)(24,12) Extended Golay Code and a rate 1/2 convolutional code with memory 6.Comment: 5 pages, 2 figures, ISIT 200

    Towards an Undetectable Computer Virus

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    Metamorphic viruses modify their own code to produce viral copies which are syntactically different from their parents. The viral copies have the same functionality as the parent but may have different signatures. This makes signature-based virus scanners unreliable for detecting metamorphic viruses. But statistical pattern analysis tool such as Hidden Markov Models (HMMs) can detect metamorphic viruses. Virus writers use many different code obfuscation techniques to generate metamorphic viruses. In this project we develop a metamorphic engine using code obfuscation techniques. Our metamorphic engine is designed to produce highly diverse morphed copies of the base virus. We show that commercial virus scanners cannot detect metamorphic viruses produced by our engine. We then proceed to determine whether HMMs can detect metamorphic viruses generated by our engine
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