4,057 research outputs found
A correction on Shiloach's algorithm for minimum linear arrangement of trees
More than 30 years ago, Shiloach published an algorithm to solve the minimum
linear arrangement problem for undirected trees. Here we fix a small error in
the original version of the algorithm and discuss its effect on subsequent
literature. We also improve some aspects of the notation.Comment: A new introductory paragraph has been added; error solutions and
notation improvements are discussed with more dept
Performance analysis of a second order delay-lock loop with application to a CDMA system with multipath propagation
CDMA systems require synchronization between the received sequence and the locally generated sequence. This is done by means of a delay-lock loop (DLL). The differential equation of an incoherent second-order DLL has been programmed. The mean time to lose lock (MTLL) of the DLL is a very important design parameter. The authors have obtained this parameter by computer simulation and are able to plot the MTLL as a function of the signal to noise ratio in the data bandwidth. In a narrow-band system, the simulation shows that the effect of the fast Rayleigh fading is a performance degradation even with high mean signal to noise ratio. Assuming a wide-band system, so that the receiver has enough bandwidth to resolve the different propagation paths, the authors propose a modified DLL scheme. The MTLL of the proposed DLL is evaluated using a dynamic simulation of the multipath channel. The results show an improvement with respect to the conventional DLL.Peer ReviewedPostprint (published version
Algorithms and structures for source separation based on the constant modulus property
We propose two structures and theirs associated algorithms designed to solve the blind source separation problem in the presence of noise and interferences. Both structures exploit the non convexity of the Constant Modulus cost function, finding its multiple local minima. A convergence analysis shows that both schemes achieve the desired solution, separately extracting the sources of interest while rejecting noise and interferences, provided that they do not share the constant modulus property.Peer ReviewedPostprint (published version
Creatable Universes
We consider the question of properly defining energy and momenta for non
asymptotic Minkowskian spaces in general relativity. Only spaces of this type,
whose energy, linear 3-momentum, and intrinsic angular momentum vanish, would
be candidates for creatable universes, that is, for universes which could have
arisen from a vacuum quantum fluctuation. Given a universe, we completely
characterize the family of coordinate systems for which one could sensibly say
that this universe is a creatable universe.Comment: 19 pages; v2: we have added an Appendix to make explicit the proof of
the quasi-uniqueness of the defined energy and momenta of the Universe, for
every space-like 3-surfac
Inside-outside money competition
We study how competition from privately supplied currency substitutes affects monetary equilibria. Whenever currency is inefficiently provided, inside money competition plays a disciplinary role by providing an upper bound on equilibrium inflation rates. Furthermore, if "inside monies" can be produced at a sufficiently low cost, outside money is driven out of circulation. Whenever a 'benevolent' government can commit to its fiscal policy, sequential monetary policy is efficient and inside money competition plays no role.Money ; Payment systems
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