(UWB)<Superscript>2</Superscript>: Uncoordinated,Wireless, Baseborn Medium Access for UWB Communication Networks

A MAC protocol for Ultra Wide Band (UWB) radio networks named (UWB)² is proposed. The algorithm exploits typical features of impulse radio such as large processing gain, and is conceived in conjunction with a synchronization strategy which foresees the presence of a synchronization sequence in each transmitted packet. (UWB)² adopts a pure Aloha approach; Performance analysis of the synchronization tracking mechanism showed in fact that under the preliminary simplistic hypothesis of an AWGN channel, and for a sufficient number of pulses in the synchronization sequence, a fairly high probability of successful synchronization can be achieved, even in the presence of several users and Multi User Interference (MUI). The multiple access scheme is based on the combination of a common control channel provided by a common Time Hopping (TH) code with dedicated data channels associated to transmitter specific TH codes.Results obtained by simulation indicate that (UWB)² can be successfully applied when the number of users spans from a few tens to about one hundred, for data rates ranging from a few thousands to a few hundreds of bits per second. Network throughput was above 99.8% in all considered simulation settings. Such achievement confirms that (UWB)² is a suitable and straightforward solution for large networks of terminals using impulse radio for transmission at low bit rates.On leave from the Institut für Elektro- und Informationstechnik, College of Engineering, University of Duisburg-Essen, Duisburg, Germany.Maria-Gabriella Di Benedetto obtained her Ph.D. in Telecommunications in 1987 from the University of Rome La Sapienza, Italy. In 1991, she joined the Faculty of Engineering of University of Rome La Sapienza, where currently she is a Full Professor of Telecommunications at the Infocom Department. She has held visiting positions at the Massachusetts Institute of Technology, the University of California, Berkeley, and the University of Paris XI, France. In 1994, she received the Mac Kay Professorship award from the University of California, Berkeley. Her research interests include speech analysis and synthesis, and digital communication systems. From 1995 to 2000, she directed four European projects for the design of UMTS. Since 2000 she has been active in fostering the development of Ultra Wide Band (UWB) radio communications in Europe. Within the 5th framework, she directs for the Infocom Dept. two European projects (whyless.com and UCAN) aimed at the design and implementation of UWB ad-hoc networks. Within the 6th EU Framework her “Networking with UWB” research group participates in the PULSERS Integrated Project which will integrate UWB research and development in Europe for the next years, and in the LIAISON Integrated Project as regards the application of UWB to location-based services. She currently also participates in the HYCON network of excellence. Dr. Di Benedetto is co-editor for the IEEE JSAC Special Issue on UWB Radio in Multi-Access Wireless Communications (December 2002)and for the Journal of Communications and Networks Special Issue on Ultra-Wideband Communications (December 2003). Dr. Di Benedetto recently co-authored with Guerino Giancola a book on Ultra Wide Band from radio to the network, titled “Understanding Ultra Wide Band Radio Fundamentals” and published by Prentice Hall in May 2004.Luca De Nardis received his “Laurea” degree in telecommunications engineering from the University of Rome La Sapienza in 2001 with a thesis on wireless network topologies in the framework of the European project whyless.com. He is now pursuing a Ph.D. in Information and Communication Theory in the INFOCOM Department of the University of Rome. Since 2002, he has been participating in the European IST project UCAN, dealing with application of UWB radio to ad-hoc networking. Currently, he is involved in the 6th Framework European projects PULSERS and LIAISON. His research focuses on UWB technology, ad-hoc communication networks organization, Medium Access Control and routing protocols for wireless networks.Matthias Junk was born in Oberhausen, Germany, in 1978. From 1997 to 2004 he studied electrical engineering with main subject communications at the University of Duisburg-Essen, Germany. In 2004 he received his diploma. During his diploma thesis at the University “La Sapienza” in Rome, Italy, he focused on synchronization problems in Ultrawideband Communication Networks.Guerino Giancola received the Laurea degree (magna cum laude) in Telecommunications Engineering from the University of Rome La Sapienza, Italy, 2001, with a thesis on the analysis and the modelling of electromagnetic propagation in outdoor urban scenarios for mobile radio communications systems. Currently, he is working toward the Ph.D. degree in Information and Communication Theory in the INFOCOM Department of the University of Rome La Sapienza. His research interests include Ultra Wide Band radio technology, multi-carrier transmission techniques, and Medium Access Control protocols. From 2001 to 2002, he participated in a national research project financed by the Italian Ministry for University and Scientific-Technological Research (MURST), project PRIN2000: “OFDM Systems for Applications in the Wireless LANs.” Since 2002, he participates in two European Union research projects within the International Society Technologies program (IST): project No. IST-2001-32710: “Ultra-wideband Concepts for Ad-hoc Networks (UCAN)”, and project No. IST-2000-25197: “Whyless.com-The Open Mobile Access Networks.” From 2003, he also participates in the national research project financed by the Italian Ministry for University and Research (MIUR), project FIRB: VICOM-Virtual Immersive COMmunications.     

Standardized evaluation of techniques for measuring the spectralcompression of the myoelectric signal

A digital algorithm was designed to produce band-limited noise with adjustable median frequency and amplitude. This algorithm produces test signals with spectral characteristics typical of those of the surface myoelectric signals encountered in muscle fatigue studies. These synthesized signals provide the basis for standardized evaluation of the performance of various techniques which monitor the spectral compression of the myoelectric signal during muscle fatigue.     

On the centers of a language

The center of a language has been defined in [7, 8, 9] as the set of all words which have infinite right completions in the language. In this paper we extend this notion by taking into account also left and two-sided completions. Thus, for any language X, we consider the left center C_l(X), the right center C_r(X) and two different bilateral centers C₁(X) and C₂(X). Some properties of these centers are derived. In particular the main results of the paper give some general conditions under which C₁(X)=C₂(X)and C_r(C_l(X))=C_l(C_r(X)). These conditions deal with ‘strong’ and ‘weak’ iteration properties and ‘periodicity’ of a language.     

A revised mono-dimensional particle bed model for fluidized beds

The formulation of the equations of change proposed by Foscolo and Gibilaro in their original mono-dimensional particle bed model (PBM) for the prediction of the fluid-bed stability of Geldart's group A powders has been revisited along with the relevant closure relationships. The buoyancy has been expressed in accordance with its “classical” definition, which regards it as being equal to the weight of the fluidizing fluid displaced by the particle phase. A new constitutive equation has been developed for the drag force; this proves more accurate than the expression used in the original PMB particularly in the intermediate flow regimes comprised between the viscous and inertial ones. The “elastic” force has been estimated by employing a rigorous approach which needs not resort to equilibrium-based relations. The result, enhanced in accuracy and breadth of validity, considers “elastic” force and drag force proportional. The equations of change themselves have been partly revised. The pressure gradient is no longer shared by the two phases in proportion to their volume fractions, but has been accounted for only in the continuous one. Conversely, the “elastic” force has been included, with opposite signs, in the linear momentum equations pertaining to both phases, so that the principle of action and reaction, to which the force is subjected, is fulfilled. The revised model has been validated by performing a fluid-bed stability analysis on a wide range of Geldart's group A powders at different operating temperatures. Predicted values for the minimum bubbling voidage estimated by means of the revised model have been compared with experimental values and with predictions from both the original Foscolo and Gibilaro model and that previously revised by Jean and Fan. The latter has been found to be always in good agreement with the model proposed here, whereas the former has seemed to somewhat underestimate the bed minimum bubbling voidage thus anticipating the transition between homogeneous and bubbling fluidization. All of the models have proved to yield predictions whose validity is strongly dependent on the particular powder in hand and on the operating conditions considered.     

Closure operations on measures of computational complexity

In this paper, after a suitable characterization of computational complexity measures, we analyze some closure operations defined on the class of all measures with respect to a given acceptable Gödel numebering. Such a class is a distributive lattice without universal bounds. The problem of the invariance of the class of measures changing the Gödel numbering is finally considered.     

Detection of Escherichia coli O157 in bovine meat products in northern Italy

Tests for Escherichia coli and E. coli O157 were carried out on meat samples collected from randomly chosen stores throughout the city of Bologna and suburban areas. The samples consisted of 25 g of loose minced beef, sometimes already shaped into meatballs or hamburgers, some of which were mixed with vegetables. The meat was purchased from retail outlets, open market stalls, and supermarket chains during 25 sampling visits from October 2000 to December 2001. For E. coli detection, Tryptone soya broth (TSB) supplemented with novobiocin and C-EC agar were used. Immunomagnetic separation with SMAC-BCIG-CT agar and chromogenic E. coli O 157 agar, API 20E system and agglutination latex test were used to detect E. coli O157; Vero cell assay and polymerase chain reaction (PCR) were used to assess toxin production and the presence of virulence genes.

E. coli were detected in 45 (30.2%) of the 149 samples examined, mainly in the hamburger samples mixed with vegetables and in the loose minced beef. E. coli O157 was found in one sample of hamburger and two samples of hamburger mixed with vegetables (2%) collected from three different butcher's stores between July and October. All the strains of E. coli O157 and most cases of E. coli were found in meat from small retailers.

The three strains of E. coli O157 were positive for verocytotoxin production. PCR analysis revealed genes coding for vt2 and one strain possessed the gene for eae A. Chromogenic E. coli O157 agar was found to be more selective and differential, allowing easier identification of suspected colonies with mixed flora and producing less false-positive colonies.     

Three-dimensional acquisition of large and detailed cultural heritage objects

Cultural heritage digitization is becoming more common every day, but the applications discussed in the literature address mainly the digitization of objects at a resolution proportional to the object size, using low resolution for large artifacts such as buildings or large statues, and high resolution for small detailed objects. The case studied in this paper concerns a huge physical model of imperial Rome (16 × 17.5 m) whose extremely small details forced the use of high resolution and low noise scanning, in contrast with the long range needed. This paper gives an account of the procedures and the technologies used for solving this “contradiction”.