Gonzalo A Alvarez

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This paper studies the security of a secure communication scheme based on two discrete-time intermittently chaotic systems synchronized via a common random driving signal. Some security defects of the scheme are revealed: 1) The key space can be remarkably reduced; 2) the decryption is insensitive to the mismatch of the secret key; 3) the key-generation(More)
Noninvasive measurements of microstructure in materials, cells, and in biological tissues, constitute a unique capability of gradient-assisted NMR. Diffusion-diffraction MR approaches pioneered by Callaghan demonstrated this ability; Oscillating-Gradient Spin-Echo (OGSE) methodologies tackle the demanding gradient amplitudes required for observing(More)
Since the pioneering works of Carr-Purcell and Meiboom-Gill [Carr HY, Purcell EM (1954) Phys Rev 94:630; Meiboom S, Gill D (1985) Rev Sci Instrum 29:688], trains of π-pulses have featured amongst the main tools of quantum control. Echo trains find widespread use in nuclear magnetic resonance spectroscopy (NMR) and imaging (MRI), thanks to their ability to(More)
We develop the Keldysh formalism for the polarization dynamics of an open spin system. We apply it to a solvable model for a swap operation based in the oscillation between a pair of two qubit states. This model can also be assimilable to an NMR cross-polarization experiment. The role of the environment is assigned to a set of interacting spins. Considering(More)
We have observed an environmentally induced quantum dynamical phase transition in the dynamics of a two spin experimental swapping gate [ and |↓, ↑ gives an oscillation with a Rabi frecuency b/ (the spins coupling). The interaction, /τSE with a spin-bath degrades the oscillation with a characteristic decoherence time. We showed that the swapping regime is(More)
OBJECTIVE To examine the effect of donepezil for the treatment of cognitive and behavioral disorders associated with thalamic lesions in a 45-year-old male who suffered an infarct in the left thalamus. BACKGROUND Recent studies suggest that donepezil may improve executive functions impairments due to subcortical ischemic lesions. METHOD The effects of(More)
The kings of the Spanish Habsburg dynasty (1516-1700) frequently married close relatives in such a way that uncle-niece, first cousins and other consanguineous unions were prevalent in that dynasty. In the historical literature, it has been suggested that inbreeding was a major cause responsible for the extinction of the dynasty when the king Charles II,(More)
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