1,720,961 research outputs found
La costruzione di un mito: la vera storia del ponte del Risorgimento
No full textThis is the story of a bridge, some courageous men and, above all, about reinforced concrete that, as this story was unfolding, experienced a deep transformation; from a commercial system, protected by patents and restrained by rules governing its use, it developed into a free material at the disposal of any designer capable of fully exploiting its surprising and mysterious structural potential. The main character on this stage was the inventor of reinforced concrete himself, François Hennebique, or rather, the inventor of his most famous patent, filed in 1892, perfected in 1897, and about to expire in 1909 when this story started to unfold. The stage is Italy that more than any other Country was to enhance the properties of this material in all its variants, thanks to the debate that was triggered by the enduring and inexplicable strength of the work at the centre of the story: the Risorgimento Bridge in Rome. There is a rich bibliography on the bridge and many writings that were published at that time. Today’s new reading is made possible because we can compare the documents held in the archives of Giovanni Antonio Porcheddu’s company, Hennebique concessionaire for Northern Italy and builder of the bridge, with the records stored at the Fonds Bétons Armés Hennebique in Paris, and with those found in the Historic Archives of the Campidoglio, in spite of the intricate complexity of this office. The search has once again proven to be fascinating. The daily correspondence, whose sequence was reconstructed thanks to the documents found in the files of the offices in Turin, Rome and Paris, still today, after a hundred years, vividly reflects the audacity, preoccupation, pride, abilities and excitement of the main figure who designed and built the boldest bridge over the River Tiber
High light-load efficiency charge pumps
No full textHere, first, we analyze the undesired charge transfer occurring in charge pumps; afterwards we present a circuit which is less susceptible to this issue, resulting in significant improvements of the light load efficiency in charge pumps which must have a sufficiently high maximum current capability. SPICE simulations confirm the theoretical results
Enhancing transport layer in satellite systems
No full textSatellite networks play a fundamental role in the provision of a broadband and global Internet access. Nonetheless, features of satellite systems imply worse performance of transport protocols, actually more suitable for wired terrestrial networks. In particular, TCP and UDP need enhancements to improve performance in various communication scenarios including both a satellite stand-alone network and satellite- terrestrial integrated networks. This paper addresses three specific study cases where performance of transport layer protocols is degraded. Analysis and performance evaluation have been carried out through two different platforms: a simulator based on Ns-2 and a Linux-based emulator
TCP Noordwijk for high-speed trains
No full textIn a scenario where people need to travel frequently for their business and leisure, spending a lot of time on high-speed trains, airplanes or ships, it is necessary to provide them a broadband Internet connection while moving. Broadband satellite systems, for their characteristics in terms of coverage and flexibility, can be the best solution for this type of scenarios. Nevertheless, although satellite systems allow a global coverage over the railways, the channel related to a high-speed train is characterized by frequent signal outages due to tunnels, steel covered bridges and powerline trellises. In particular, trellises, always and periodically present along the railroad, cause frequent obstructions of the line of sight, which implies packet loss that significantly affects TCP performance. In fact, standard TCP based on classical congestion control mechanisms is required to perform continuous restart of the algorithm. In this paper, the use of a new TCP protocol called TCP Noordwijk is proposed. It is based on burst transmission concept, which matches optimally with channel characteristics. The advantages with respect to the standard TCP will be shown
TCP performance on a railway satellite channel
No full textHigh-speed rail is emerging in the world as an increasingly popular and efficient means of transportation used by a lot of people, who may also need a broadband Internet connection while travelling for their business and leisure. Satellite systems for their intrinsic characteristic, such as global coverage, reduced impact of Doppler effect due to link geometry and flexible bandwidth management, represent an excellent solution to provide broadband services in the identified scenario. Some problems specific of the railway propagation channel such as frequent signal outages due to the periodic electrical trellises, tunnels and steel covered bridges affect TCP/IP performance due to frequent packet losses occurring in bursts. In this paper, performance of TCP-based applications and error recovery mechanisms are investigated and the use of a new transport protocol named TCP-Noordwijk is introduced. TCP-Noordwijk leverages on a burst transmission and is particularly suited for the harsh satellite links. Results show that TCP-Noordwijk outperforms the other analyzed TCP versions
Cross-layer architecture for a satellite-Wi-Fi efficient handover
Full text linkTo achieve fully mobile communications, considering different environments and modern service requirements, a multiple-segment architecture is the most suitable to guarantee service continuity with acceptable performance. Handover (HO) procedures can be invoked either out of necessity (if the current network connection is going off) or to improve performance (if different bandwidth or quality of service is required). In this scenario, to provide uninterrupted communication services, efficient intersegment HO capability must be implemented. The architecture considered includes a satellite segment and a number of Wi-Fi hot spots. A mobile node (MN) can switch from a segment to other exploiting services of mobile Internet protocol (MIP). This architecture introduces great flexibility and ensures capillary coverage; it also strongly affects Transmission Control Protocol (TCP)-based application performance. To efficiently face HO consequences, particularly when the TCP runs as a transport protocol, an innovative protocol architecture based on cross-layer (CL) exchange of information is proposed. Analyses of TCP dynamics during HOs and the performance improvement introduced with the proposed CL architecture, evaluated through the network simulator Ns-2, are presented
Performance evaluation of TCP Noordwijk over satellite systems for fixed and mobile services
No full textTCP Noordwijk has been designed and implemented to optimize short transfers (i.e. HTTP traffic) over satellite links, while assuring good performance for long transfers (i.e. FTP) as well. It was developed in the frame of an European Space Agency (ESA )project [††]. Its target scenario is a controlled communication environment adopting DVB-RCS standard between I-PEPs. A rich test campaign to both validate the protocol and evaluate performance improvements with respect to standard TCP has been performed using the Ns-2 simulator. This paper contributes to the evaluation of TCP-Noordwijk performance showing results of trials over a real DVB-RCS link, simulations to test protocol performance in a mobile satellite system (with a particular focus on high-speed trains) and tests on a satellite Linux-based emulation platform called SNEP
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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