No abstract

On the basis of theoretical considerations and results from acoustic and perceptual analyses, it is hypothesized that closure duration is the primary cue for gemination in Italian. Results of an acoustic analysis of a large number of single and geminate Italian utterances show two acoustic correlates of gemination: the length of the closure and the length of the vowel preceding the consonant. Other acoustic parameters were not systematically related to gemination. These results were validated perceptually. At the perceptual level, the above cues were used by the listeners in the geminate/nongeminate discrimination; however, closure duration played a major role. Moreover, it was found that the significant lengthening of consonant was only partially compensated by the shortening of the previous vowel and by a small lengthening of the geminate utterance with respect to the nongeminate one. This result suggests that speakers follow a sort of timing (rhythm) which is fixed in duration and depends on the number of syllables in the word: words with equal numbers of syllables do not change in utterance length, an elongated segment being partly compensated by the shortening of another. This process seems to be applied also perceptually suggesting that the timing (rhythm) of a language is also an auditory attitude.

The traditional design of communication networks has rarely been able to focus on the optimization of global network properties. Ultra-wideband (UWB) radio is emerging as an attractive physical layer for wireless communication networks offering new opportunities for the principled design and optimization of network properties. We develop a framework for the principled design of UWB wireless networks based on a flexible cost function that can be tailored and scaled to a wide range of networks and applications, ranging from sensor networks to voice and data wire- less networks. The function comprises cost terms associated with transmission, connection setup, interference, and quality-of-ser- vice. Multihop routing strategies are associated with admissible paths of minimal cost that are computable in linear time. The cost function together with the overall level of requests determine the dynamics of the connections and the equilibrium topology of the network. We report simulation results in the case of simple ring and square lattice networks. Index Terms—Ad hoc networks, cost minimization, routing, sensor networks, small-world networks, UWB (ultra-wideband) radio, wireless networks

The IEEE 802.15.4 standard provides a framework for low data rate communications systems, typically sensor networks. The 802.15.4a revision introduces new options for the physical layer, in order to support higher data rates and accurate ranging capability, enabling new applications based on information on distance and positions of the devices in the network. In this paper the differences among physical layers of 802.15.4 vs. 802.15.4a are briefly reviewed. Next, the MAC layer of 802.15.4 vs. 802.15.4a are reviewed and compared. Device functionalities, network topologies as well as access strategies in both standards are described, and the impact of the new physical layer features on MAC and higher layers are discussed, with particular attention to the ranging scheme adopted in the new revision of the standard

In this paper we propose a new stratem for path selection in a UWB based ad-hoc network which; by minimizing a power-dependent global cost function, can potentially lead to an optimal network organization characterized by low emitted power levels and high network performance.