Analytical framework for end-to-end design of optical burst-switched networks

This paper presents an analytical model of TCP throughput in optical burst-switched (OBS) networks. Several parameters characterize this system and influence the network design process, such as the assembly time, the access bandwidth, the burst loss rate, and they are taken into account in the formulation of TCP send rates. Moreover burst loss is considered a consequence of contention in core nodes and it is formulated in relation to a quite general core node architecture. The novelty of the work is represented by the possibility of analytically representing the whole end-to-end connection so that a fast and effective tool to evaluate the relationships between network and access design is provided. An application example is given to prove the practical significance of the approach. Simulation results are provided to validate the model and the related assumptions.     

Packet optical networks for high-speed TCP-IP backbones

This article presents a new proposal for TCP-IP backbone implementation based on optical packet switching technology. The proposed network architecture merges the flexibility in resource management of packet switching with the high capacity offered by full optical technology     

Effectiveness and issues of congestion control in 802.11g wireless LANs

The current paper presents a collection of experimental data portraying the performance achieved in the wireless setting by several TCP-friendly congestion controls recently proposed in literature. This work is partly motivated by the consideration that the majority of the analytical results in this area are validated by simulation, rather than by field tests. Examining these algorithms in real environments can help verify their actual effectiveness over the wireless Internet. To reach such goal, two representative controls among the so-called window-based TCP-friendly schemes have been implemented, namely, the General Additive Increase Multiplicative Decrease (GAIMD) strategy, and the SQuare RooT (SQRT) binomial control; the most representative algorithm among rate-based controls, the TCP Friendly Rate Control (TFRC), has also been considered. Their TCP-fairness and smoothness have been comprehensively evaluated in an IEEE 802.11g Wireless Local Area Network (WLAN). The obtained results show that the GAIMD and SQRT strategies reveal non-negligible scalability and smoothness problems, that markedly limit their performance. It is empirically demonstrated that their “optimal” increase/decrease rules, based on TCP-Reno analytical model, cannot guarantee an adequate performance when GAIMD and SQRT compete with TCP-Sack, a de facto standard for current TCP implementations. TFRC is demonstrated to occasionally behave bewildering: properly tuning one of its congestion control parameters and enhancing the algorithm with a flow-control mechanism result in a definitely fairer share of bandwidth with concurrent TCP flows. Michele Borri received the M.Sc. degree in Computer Engineering from the University of Modena and Reggio Emilia in the academic year 2001–2002 and took a specialisation in Telecommunication Engineering in 2002. His professional activity is currently balanced between researching at the University of Modena and Reggio Emilia, and consulting as a system engineer and network architect. His research interests focus on congestion control and multimedia services in next generation Internet. Michele Borri has been participating to national research projects promoted by the Italian National Research Council (CNR). Maurizio Casoni is Associate Professor in Telecommunications at the University of Modena and Reggio Emilia. He graduated with honors in Electrical Engineering at the University of Bologna in 1991, with a grant by Telecom Italia and received the Ph.D. degree also in Electrical Engineering from the University of Bologna, in 1995. In 1995 he was with the Computer Science Department at Washington University in St. Louis, MO, as a research fellow where he worked on ATM broadband switching architectures. He has studied ATM broadband switching architectures and Clos architectures for the design of large photonic switches in the framework of the European Projects ATMOS and KEOPS. He has also investigated the performance of 3rd generation UMTS systems. His current research interests deal with Optical Networking, mainly focusing on Optical Burst Switching, and Satellite Networks. He currently holds the course of Interconnection Systems for undergraduate students and the course of Switching Systems for graduate students of Telecommunications Engineering. Maria Luisa Merani is currently an associate professor of Telecommunication Networks at the University of Modena and Reggio Emilia, Department of Information Engineering. She is an IEEE Senior member and has served on the Technical Program Committees of several major communication conferences (IEEE ICC, IEEE Globecom, IEEE VTC, APCC). In 2005 she has been technical program cochair of the second IEEE International Symposium in Wireless Communication Systems. In 2007 she will be the Wireless Symposium chair of IEEE Globecom. At present she is involved in research on congestion control for next generation Internet and on multicast video streaming. Her most recent research interests are related to the area of radio communications, with emphasis on performance evaluation of mobile radio systems, 3G data networking and transport solutions for optical networks. Maria Luisa Merani received both her M.Sc. (summa cum laude) and Ph.D. in electrical engineering from the University of Bologna, Italy, in the academic years 1985/86 and 1991/92, respectively. In 1992 she spent one year at the Computer Science Department of the University of California in Los Angeles, CA, USA.     

Laser Melting of Spark Plasma-Sintered Zirconium Carbide: Thermophysical Properties of a Generation IV Very High-Temperature Reactor Material

Melting temperatures of zirconium carbide were investigated in validating a novel thermal analysis technique for refractory materials. Commercial ZrC_0.96 powder was densified by spark plasma sintering to >96% relative density after 6–30 min at 2173–2453 K under 40–100 MPa. Sintered ceramics were heated to >4000 K via pulsed laser heating. Mean values for solidus and liquidus transitions were 3451 and 3608 K, respectively, in fair agreement with the present phase diagram. Postmelting analysis revealed dendritic microstructure and composition consistent with single-phase ZrC. Subsurface gas porosity and ZrC–C eutectic indicate complex processes occurring during melting and freezing.     

Comparison of ultrasonography and magnetic resonance in the postoperative monitoring of complete subcutaneous rupture of the Achilles tendon]

The diagnostic accuracy of US and MRI in the subcutaneous rupture of the Achilles tendon has already been assessed. We used both techniques to study the Achilles tendon during the postoperative repair process after surgery according to Bosworth. The results were compared and discussed in relation to clinical recovery. Ten patients with complete subcutaneous rupture of the Achilles tendon were followed-up with physical examination and submitted to US and MR studies 40, 60 and 90 days postoperatively. Eighty patients recovered in the expected time, while 2 took longer. At 90 days, the US findings in 7 patients and the MR findings in 8 patients who recovered in the expected time could be considered normal. US poorly distinguished the tendon from the reinforcement flap because of gross tendon echostructure. The tendon and the reinforcement flap were not distinguishable at MRI because they were uniformly hypointense. Clinical recovery appeared as a hyperechoic structure and a gross fibrillar pattern at US and as a hypointense structure with some small hyperintense areas at MRI. US and MRI were in disagreement in one patient with a postoperative algodystrophic syndrome, where US showed some alterations which were considered false positives because of clinical recovery and negative MR findings. US and MR patterns were considered abnormal in the 2 patients with delayed recovery. US showed persistent hyperechoic areas within the tendon, while the MR signal was of intermediate intensity in the tendon and reinforcement flap. To conclude, we believe that US is an appropriate technique for the postoperative follow-up of complex subcutaneous ruptures of the Achilles tendon. Additional MRI should be performed in all the cases where US findings are in disagreement with clinics.     

Les défis diagnostiques posés par l'évaluation clinique des allégations de sévices sexuels concernant des enfants.

Knowledge and expertise acquired in clinical and empirical psychology are increasingly requested by social and judicial authorities when confronted with allegations of sexual abuse on children. In view of this increased demand, various evaluation methods and techniques have been developed, some for which the measurement value and conceptual relevance have not been demonstrated. The article brings us up to date on evaluation methods pertaining to allegations of sexual abuse on children and suggests a practical framework that takes into account recognized clinical principles and recent research results in this field. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

On the performance of TCP over a TDD‐TD/CDMA architecture

This paper determines the performance of TCP when it is employed over a TDD‐TD/CDMA architecture which supports different classes of subscribers and adopts an interference‐driven admission control policy. The blocking and the outage probability of the system users are evaluated under various traffic conditions as well as the TCP throughput that data users experience. Call blocking and TCP throughput are determined by means of a semi‐analytical approach. This work shows that when TCP is taken into account, many options come out for the system design in order to optimize radio resources. Resource assignment in the TDD‐TD/CDMA system can then be done as a function of the actual radio link quality with the goal both to serve as many users as possible and to keep the TCP throughput as high as possible. Copyright © 2003 John Wiley & Sons, Ltd.