83 research outputs found
Algorithms for small spanning trees
No full textIn this paper we consider the well known NP-hard problem k-MST. We aregiven a weighted complete graph and we want to find a minimum weightspanning tree which spans only k vertices (with fixed k) of the graph.We consider the special case in which the edge weights correspond toEuclidean distances. This case is relevant for the applications inreal-time situations like fault-tolerant networks or oil rigslocation.Here, we propose two application algorithms, which are less effective(from the theoretical approximation point of view) that those presentin literature, but are more efficient. The efficiency of the algorithmis extremely important for the applications.We tested the performance of the proposed algorithms by comparing thesolutions found and the computation times with other known algorithms
Impact of channel-state information on coded transmission over fading channels with diversity reception
No full textBrowse Journals & Magazines > Communications, IEEE Transact ...> Volume:47 Issue:9 Prev | Back to Results | Next » Impact of channel-state information on coded transmission over fading channels with diversity reception .This paper appears in: Communications, IEEE Transactions on Date of Publication: Sep 1999 Author(s): Taricco, Giorgio Dipt. di Elettronica, Politecnico di Torino, Italy Biglieri, Ezio M.; Caire, Giuseppe Volume: 47 , Issue: 9 Page(s): 1284 - 1287 Product Type: Journals & Magazines 1 1 789660 searchabstract .Abstract We study the synergy between coded modulation and antenna-diversity reception on channels affected by slow Rician fading. Specifically, we assess the impact of channel-state information (CSI) on error probability. We show that with a good coding and constant envelope modulations (for example, phase-shift keying) scheme the loss in performance when CSI is not available is moderate (around 1.5 dB). Moreover, as the diversity order grows, the channel tends to become Gaussia
Local Restoration for Trees and Arborescences
No full textProtocols belonging to the Spanning Tree Protocol (STP) route traffic demands on tree topologies that are evaluated through shortest path procedures. In this paper we deal with the problem of assigning costs to the arcs of a network in order to guarantee that SPT protocols efficiently re-route traffic demands in failure situations: namely, without redirecting traffic demands that are not affected by the failure. We say that a communication network has the local tree-restoration property if there exists a set of costs for its arcs such that the above property holds. We show that an undirected network has the local tree-restoration property if and only if it is 2-connected. In particular, we provide a quite simple procedure for assigning costs to the arcs of a 2-connected network so that the property holds. For the directed case, we show that deciding whether a network has the local tree-restoration property is NP-hard, even in some “simple” cases.DISOP
Combinatorial structures for communication networks
No full textThis thesis deals with a class of theoretical problems arising in applications
in communication networks. The dissertation is mainly divided in two parts.
In the first part, we attempt to solve a set of survivability network design
problems. Network survivability refers to the guarantees that a communication
network provides in the event that one or more failures occur. An attack or
failure can significantly reduce the capability of the communication network to
efficiently deliver basic services to users. In several cases, when a failure occurs,
the network operators are interested in restoring traffic by re-routing it through
different links. Since re-routing traffic can be rather expensive and may cause
delays in transmissions, a key property is that of requiring that traffic which is
not affected by the failure is not redirected in failure situations.
We study the problem of determining whether a given network, where the traffic
is commonly routed on the edges of a shortest path tree (e.g. Ethernet networks
with the Spanning Tree Protocol), may satisfy the above mentioned property.
We provide computational complexity results for directed and undirected net-
works. In particular, for the directed case, we prove that such problem is in
general NP-hard and that it remains NP-hard also in some special cases. More-
over, we show how to assign weights to the links of the network in order to
configure a routing topology with the above mentioned property.
In the second part of the thesis, we deal with a problem regarding broadcast-
ing in telecommunication networks. We investigate a new version of the well
known Minimum Broadcast Time problem which has been deeply studied in
the past, since broadcasting is a basic primitive in the communication networks
area. Fundamental requirements for a broadcast process are that it completes in
the quickest way and that, at the end of the procedure, all the peers in the net-
work are informed. In this thesis we deal with an objective function that takes
into account the quality of the service associated with the broadcast, namely
the minimization of the average broadcast time of the peers.
We show that the considered version of the broadcast problem is an NP-hard
problem. Indeed, the problem becomes polynomially solvable, if the instance
graph is a tree. We also provide a distributed approximation algorithm for our
version of the broadcast problem, in which every network node does not know
the network topology
Ezio Mauro e il suo scrittore senza nome Mauro Ezio, Lo scrittore senza nome. Mosca 1966: processo alla letteratura, Milano, Feltrinelli, 2021, 333 p.
No full textThis review deals with the most recent novel written by Italian journalist and former editor-in-chief of la Repubblica Ezio Mauro, Lo scrittore senza nome: processo alla letteratura (2021). The plot revolves around the events that precede and follow the arrest and trial of Russian authors Andrei Sinyavsky and Yuli Daniel. However, from the very beginning, the reader is made aware of the character around whom the story is centered: Yuli
Daniel. To tell this story, the author writes a journalistic novel, which is a variation of the traditional literary genres combining fictional and non-fictional elements
From Tyrol to Venice: the papers of Giovanni Arduino (1714-1795) as valuable sources for the history of mining and geology
No full textThe Italian scientist and mining expert Giovanni Arduino holds a significant place in the history of geology, in spite of a prolonged historiographical ‘impasse’ which has reduced the knowledge of his studies and research. His relevant mining background, achieved in mountain areas such as Tyrol and the Venetian pre-Alps (but also the Tuscan Apennines), was at the base of a new geological expertise which led to the lithostratigraphical theory presented by Arduino in 1760 and which is widely regarded by historians as one of the main contributions to the origin of modern geology. Several documents supporting this interpretation may be found in the collection of manuscripts “Fondo Giovanni Arduino” in the Public Library of Verona, which today represents a significant case of recovery and reorganization of unpublished important sources for the history of the geological sciences. The catalogue of this precious collection, published in 1994, marked the conclusion of a long work started by the author in 1987. The existence of Giovanni Arduino’s collection of manuscripts was known by geologists and historians since the early 20th century. Unfortunately Arduino's papers were not of much use in the past because of the lack of organization within the collection contained in six boxes (about one thousand handwritten papers), now newly divided in thematic folders under various subject headings: geology, mineralogy, chemistry, metallurgy, mining, hydraulic and agriculture. The majority of the collection consists of Arduino’s correspondence, his notes, rough copies of his writings, his geological sketches and drawings. It is a significant example of the papers of an 18th century European scientist and an impressive collection of manuscript sources that constitute an interesting case of valuable cultural heritage in the history of geosciences and mining
The Control Paradox:from AI to Populism
No full textIs technological innovation spinning out of control? Within one week in 2018, social media was revealed to have had huge undue influence on the 2016 presidential elections in the United States; while the first fatality from self-driving cars was recorded. What’s paradoxical about these understandable fears of machines taking over control through software, robots and AI, is that often new technology is introduced for the very purpose of improving our control over a certain task. This is what Ezio Di Nucci calls the ‘control paradox’.Di Nucci also brings this notion to bear on politics: we delegate power and control to political representatives in order to improve democratic governance. However, recent populist uprisings have shown that voters can feel disempowered and neglected by this system. Through the notion of the control paradox, the author shows how this lack of direct control within representative democracies could be motivating populism and argues that a better understanding of delegation is a possible solution
Human papillomavirus in cervical adenocarcinoma. An in situ hybridization study.
No full textTwenty cervical adenocarcinomas (CACs) in women aged 22 to 71 were investigated by in situ hybridization (ISH) with 6, 11, 16, 18, 31, 35 and 51 HPV biotinylated probes. Two cases, one adenocarcinoma and one adenosquamous carcinoma (in women aged 28 and 40 respectively) showed focal nuclear positivity to 16 HPV Probe in some neoplastic glands. We used ISH, rather than other hybridization techniques, in order to exclude a positivity to viral DNA, due to adjacent squamous epithelium, either normal or metaplastic, and in squamous foci within adenosquamous tumors. Reviewing the literature, we found 33 out of 98 CACs positive to viral DNA by ISH (33.6%). In spite of the differences found from author to author, a relationship between adenocarcinomas of the uterine cervix and HPV infection seems to be possible, as was demonstrated for CIN and invasive cervical carcinomas. These data could explain why the incidence of this neoplasia has tended to increase over the last few years, mainly in younger patients
- …
