Multibuffer delay line architectures for efficient contentionresolution in optical switching nodes

This paper proposes an efficient contention resolution switching architecture which can serve as the basis for all-optical switching nodes. The presented solution builds on fiber delay lines used as temporary optical storage and 2×2 space photonic switches, a solution principle also known as Quadro or switched delay lines (SDLs). The efficiency of SDLs is fundamentally linked to its storage capacity, i.e., the length of the fiber delay lines, while its cost depends on the number of 2×2 photonic switches, i.e., the number of stages in the switch. This work presents a solution that makes use of multibuffer fiber delay lines which allow multiple packets to be concurrently stored (propagated) on each line. With a novel switch control, it is shown that this solution increases the total storage capacity and significantly improves switch and network performance, without increasing the number of the 2×2 switches in the system, i.e., its cost     

Local and Global Handovers Based on In-Band Signaling in Wireless ATM Networks

This paper presents a handover protocol for wireless ATM networks, which makes use of in-band signaling, i.e., of ATM resource management cells, to process network handovers and guarantee the in-sequence and loss-free delivery of the ATM cells containing user data. The goal of the proposed approach is to minimize the modifications of the ATM signaling standard required to overlay user mobility onto the fixed network infrastructure, and provide for a gradual upgrade of the fixed network to handle mobility. The proposed protocol handles both local handovers, in which the connection access point needs not migrate to a new ATM local exchange, and global handovers, in which the connection access point must migrate to a new local exchange. The handover scheme is devised so as to grant in-sequence delivery of cells. The performance of the network during handover is analyzed in case of connections requiring loss-free operation. The considered performance figures are the cell transmission delay introduced by the handover and the cell buffering requirements posed to the network. The behavior of the proposed protocol in presence of multiple handovers is studied via simulation, while a simple analytical method is derived for the performance evaluation of a single handover in isolation.     

Implementing Stochastic Preplanned Restoration with Proportional Weighted Path Choice in IP/GMPLS/WDM Networks

IP over WDM networking and related GMPLS standards, appear to be attractive solutions for today's and future Internet applications due to their ability to handle multiple traffic flows independently of one another, and reserve wavelengths to carry a large number of aggregated flows. Another advantage of these solutions is the simplified IP over WDM stack, that provides all the vital network functionalities, including network reliability. The paper investigates the use of the stochastic preplanned restoration scheme with proportional weighted path choice (SPR-PW) to design reliable and efficient IP/GMPLS/WDM networks. Upon the disruption of a primary flow determined by a link failure, one of the associated preplanned secondary paths is readily selected by the SPR-PW scheme to continue the flow transmission. The selection of the secondary path is performed on a probabilistic base, without requiring time-consuming coordination among the restoration attempts of the disrupted flows. As a result of this stochastic selection, the SPR-PW scheme has the potential to yield short recovery times. In addition, the SPR-PW required signaling, upon and before the failure occurrence, is limited, which makes SPR-PW a scheme suitable for highly dynamic traffic scenarios, in which flows are subject to frequent changes. The paper describes the SPR-PW scheme as it is applied to cope with physical link failures, depicts a possible implementation of such a scheme using standard IP/GMPLS signaling capabilities, and numerically demonstrates two properties of the SPR-PW scheme, i.e., low blocking probability and short restoration times.     

Magnetic properties of textured CoPd nanocrystalline thin films

CoPd is an important nanomaterial for magnetic and magneto-optic storage of information. In this work, CoPd alloyed thin films are grown via radio frequency magnetron sputtering on silicon, glass and polyimide substrates in a vacuum chamber with base pressure of 5 x 10(-8) mbar. The films are nanocrystalline with grain size between 4 and 80 nm. The magnetic properties of thoroughly textured CoPd alloyed thin films are compared to random polycrystalline ones. Magnetization hysteresis loops recorded under fields up to 12 kOe via a home-made magneto-optic Kerr-effect magnetometer reveal strong tendency for perpendicular magnetic anisotropy for the textured film. This anisotropy leads to the formation of well-defined stripe or labyrinthine ferromagnetic domains with the local spins oriented perpendicular to the film plane. The domain patterns and the hysteresis loops are simulated with micromagnetic calculations. Finally, an induced magnetic moment of 0.44 microB/atom is measured for Pd via X-ray magnetic circular dichroism and it is separated into spin and orbital magnetic moment contributions.     

VPO catalyst for n-butane oxidation to maleic anhydride: A goal achieved, or a still open challenge?

This review describes recent findings in the oxidation of n-butane to maleic anhydride. The process is commercial since the 80’s, but yet the yield is far from being optimised. Therefore, it represents an emblematic example of how several scientific disciplines, from solid-state science to reactor technology, can contribute to the improvement of the process performance.     

The catalytic performance of Cs-doped V/Ti/O catalysts in the oxidation of o-xylene to phthalic anhydride: a TPR/TPO and reactivity study

Titania-supported vanadia (V/Ti/O) systems were modified by addition of cesium oxide for application as catalysts in the selective oxidation of o-xylene to phthalic anhydride (PA). Catalytic tests demonstrated that cesium is a strong promoter of the activity and selectivity to PA, but this effect is evident only under well-defined reaction conditions. Samples with a Cs content lower than 0.35 wt.% Cs₂O exhibited a considerable increase in conversion as compared with the undoped V/Ti/O system. Catalytic tests made with varying o-xylene and oxygen concentrations in the feed demonstrated that in Cs-doped V/Ti/O catalysts the rate-determining step is the re-oxidation of vanadium by molecular oxygen. Thermal-programmed reduction (TPR) and thermal-programmed re-oxidation (TPO) tests evidenced that the addition of Cs decreases the vanadium reducibility and increases the re-oxidizability of the reduced vanadium sites. The positive effect of Cs on selectivity to PA was evident only for o-xylene concentrations in feed lower than 1.5 mol%.