Efficient computation of hashes

The sequential computation of hashes at the core of many distributed storage systems and found, for example, in grid services can hinder efficiency in service quality and even pose security challenges that can only be addressed by the use of parallel hash tree modes. The main contributions of this paper are, first, the identification of several efficiency and security challenges posed by the use of sequential hash computation based on the Merkle-Damgard engine. In addition, alternatives for the parallel computation of hash trees are discussed, and a prototype for a new parallel implementation of the Keccak function, the SHA-3 winner, is introduced

Effect of quasi-bound states on coherent electron transport in twisted nanowires

Quantum transmission spectra of a twisted electron waveguide expose the coupling between traveling and quasi-bound states. Through a direct numerical solution of the open-boundary Schr\"odinger equation we single out the effects of the twist and show how the presence of a localized state leads to a Breit-Wigner or a Fano resonance in the transmission. We also find that the energy of quasi-bound states is increased by the twist, in spite of the constant section area along the waveguide. While the mixing of different transmission channels is expected to reduce the conductance, the shift of localized levels into the traveling-states energy range can reduce their detrimental effects on coherent transport.Comment: 8 pages, 9 color figures, submitte

Enhanced disengagement of auditory attention and phonological skills in action video gamers

Video games play a major role in the everyday life of children, teenagers, and adults. Several studies show that action video games (AVGs) improve visual attentional efficiency. AVGs also appear to improve reading speed and phonological skills in children with developmental dyslexia. These results have been linked to the intrinsic characteristics of AVGs, in which fast disengagement of multisensory attention allows for efficient extraction of relevant dynamic information, a skill that is crucially also involved in phonological and reading skills. We tested the hypothesis that AVG players demonstrate faster auditory attention disengagement in an auditory spatial cuing task, as well as better phonological and reading performance than non-players. We found that AVG players were faster in spatial localization of auditory targets and showed enhanced attentional disengagement as indexed by a smaller cuing effect. AVG players also showed better phonological decoding and working memory skills. Moreover, the beneficial effects of AVGs, as measured by faster attentional disengagement, were linked to better phonological and reading skills in adult AVG players. We suggest that a more efficient attentional disengagement - controlled by the posterior parietal cortex - induces enhanced multisensory processing in AVG players

Multi-particle states of semiconductor hexagonal rings: Artificial benzene

We present a theoretical and numerical investigation of correlated multi-electron states of hexagonal semiconductor rings. Both single-particle and correlated states show localization patterns in the six corners and energy spectra degeneracies corresponding to a hexagonal benzene ring. Thus, our results can aid the interpretation of energy-loss or near-field experiments that, in turn, shed light on the nature of molecular few-particle orbitals of artificial benzene. Surprisingly, we find that charges get more localized in the corners as the number of electrons increases, up to six, this indicating the deficiency of a picture based on orbitals delocalized on the whole ring. We also expose the presence of several spin-correlated states and the effect of an asymmetry of the syste

Efficient software implementation of AES on 32-bit platforms

Rijndael is the winner algorithm of the AES contest; therefore it should become the most used symmetric-key cryptographic algorithm. One important application of this new standard is cryptography on smart cards. In this paper we present an optimisation of the Rijndael algorithm to speed up execution on 32-bits processors with memory constraints, such as those used in smart cards. First a theoretical analysis of the Rijndael algorithm and of the proposed optimisation is discussed, and then simulation results of the optimised algorithm on different processors are presented and compared with other reference implementations, as known from the technical literature

a single blinded randomized pilot study of botulinum toxin type a combined with non pharmacological treatment for spastic foot

OBJECTIVE: To explore the effect of treatment after botulinum toxin type A combined with treatments for the spastic foot. DESIGN: Single-blind, randomized trial, with 3-month follow-up. SUBJECTS: Twenty-three chronic hemiplegic adult patients with spastic equinus foot. METHODS: Following botulinum toxin type A injection at the medial and lateral gastrocnemius, patients were assigned randomly to 3 groups, and treated with taping, electrical stimulation or stretching. They were evaluated before treatment (t0), and at 10 (t1), 20 (t2) and 90 (t3) days after treatment. Outcome measures were: Modified Ashworth Scale; passive range of motion at the ankle; measurement of muscle action potential at the gastrocnemius medialis; and measurement of maximum ankle dorsiflexion angle in stance using gait analysis. RESULTS: The group treated with electrical stimulation performed better at t1 on the Modified Ashworth Scale. The taping and electrical stimulation groups performed better in all outcome measures at t3. The taping group performed better mainly for maximum ankle dorsiflexion angle in stance. The stretching group showed a less durable result, with some worsening at the t3 evaluation compared with the assessment performed before treatment. CONCLUSIONS: This pilot study indicates that combining botulinum toxin type A administration for the ankle plantar flexors with taping and electrical stimulation might be beneficial