Polytechnic University of Turin

About: Polytechnic University of Turin is a education organization based out in Turin, Piemonte, Italy. It is known for research contribution in the topics: Finite element method & Computer science. The organization has 11553 authors who have published 41395 publications receiving 789320 citations. The organization is also known as: POLITO & Politecnico di Torino.

Gauging of Flat Groups in Four Dimensional Supergravity

Abstract: We show that N = 8 spontaneously broken supergravity in four dimensions obtained by Scherk-Schwarz generalized dimensional reduction can be obtained from a pure four dimensional perspective by gauging a suitable electric subgroup of E7,7. Owing to the fact that there are non isomorphic choices of maximal electric subgroups of the U-duality group their gaugings give rise to inequivalent theories. This in particular shows that the Scherk-Schwarz gaugings do not fall in previous classifications of possible gauged N = 8 supergravities. Gauging of flat groups appear in many examples of string compactifications in presence of brane fluxes.

Iterative decoding of serially concatenated convolutional codes

Abstract: Serial concatenation of convolutional codes separated by an interleaver has recently been shown, through the use of upper bounds to the maximum likelihood performance, to be competitive with parallel concatenated coding schemes known in the literature as ‘turbo codes’. The most important feature of turbo codes consists in their relatively simple, yet high performance, iterative decoding algorithm. The authors propose a new iterative decoding algorithm for serial concatenation, and show that the new coding scheme can yield a significant advantage with respect to turbo codes.

End-to-end delay analysis of videoconferencing over packet-switched networks

Abstract: Videoconferencing is an important global application-it enables people around the globe to interact when distance separates them. In order for the participants in a videoconference call to interact naturally, the end-to-end delay should be below human perception; even though an objective and unique figure cannot be set, 100 ms is widely recognized as the desired one-way delay requirement for interaction. Since the global propagation delay can be about 100 ms, the actual end-to-end delay budget available to the system designer (excluding propagation delay) can be no more than 10 ms. We identify the components of the end-to-end delay in various configurations with the objective of understanding how it can be kept below the desired 10-ms bound. We analyze these components step-by-step through six system configurations obtained by combining three generic network architectures with two video encoding schemes. We study the transmission of raw video and variable bit rate (VBR) MPEG video encoding over (1) circuit switching; (2) synchronous packet switching; and (3) asynchronous packet switching. In addition, we show that constant bit rate (CBR) MPEG encoding delivers unacceptable delay-on the order of the group of pictures (GOP) time interval-when maximizing the quality for static scenes. This study aims at showing that having a global common time reference, together with time-driven priority (TDP) and VBR MPEG video encoding, provides adequate end-to-end delay, which is (1) below 10 ms; (2) independent of the network instant load; and (3) independent of the connection rate. The resulting end-to-end delay (excluding propagation delay) can be smaller than the video frame period, which is better than what can be obtained with circuit switching.

Coupled Dynamics of Photosynthesis, Transpiration, and Soil Water Balance. Part I: Upscaling from Hourly to Daily Level

Abstract: The governing equations of soil moisture dynamics, photosynthesis, and transpiration are reviewed and coupled to study the dependence of plant carbon assimilation on soil moisture. The model follows the scheme of the soil‐plant‐atmosphere continuum (SPAC) and uses a simplified model of the atmospheric boundary layer to arrive at an upscaled, parsimonious representation at the daily time scale. The analysis of soil moisture, transpiration, and carbon assimilation dynamics provides an assessment of the role of soil, plant, and boundary layer characteristics on the diurnal courses of photosynthesis and transpiration rates, while the subsequent upscaling at the daily level provides a functional dependence of stomatal conductance on soil moisture that is in good agreement with field experiments. The upscaled dependence of transpiration and carbon assimilation on soil moisture is used in Part II of this paper to explore the impact of soil moisture dynamics on plant conditions when rainfall variability is explicitly considered.