Fast computation of a rational point of a variety over a finite field

We exhibit a probabilistic algorithm which computes a rational point of an absolutely irreducible variety over a finite field defined by a reduced regular sequence. Its time-space complexity is roughly quadratic in the logarithm of the cardinality of the field and a geometric invariant of the input system. This invariant, called the degree, is bounded by the Bézout number of the system. Our algorithm works for fields of any characteristic, but requires the cardinality of the field to be greater than a quantity which is roughly the fourth power of the degree of the input variety.

     

One-dimensional order in atactic polyacrylates containing aromatic side groups

To help in the understanding of the relations between chemical structure and morphological order in polymers of the type of poly(p-biphenyl acrylate) (PPBA), some polymers of similar structure have been synthesized and some of their physical properties studied. These polymers are: poly(p-biphenyl methacrylate), poly(vinyl p-phenyl benzoate), poly(p-phenyl benzyl acrylate), poly(p-benzyl phenyl acrylate) and poly(p-cyclohexyl phenyl acrylate) (PPCPA). Only PPCPA has been shown to possess a one-dimensional order in the solid state for reasons which are briefly discussed.The effect of copolymerization on the structural order of PPBA has also been given preliminary study. Copolymers of p-biphenyl acrylate (PBA) with p-biphenyl methacrylate (PBMA), N-vinyl carbazole (NVC) and p-cyclohexyl phenyl acrylate (PCPA) have been prepared and their properties have been studied by DSC and X-ray techniques. Small concentrations of PBMA or NVC units are sufficient to cancel the order of PPBA. On the contrary, copolymers of PBA and PCPA of any composition display morphological order in the solid state.     

Experiments on 40 Gb/s Transmission with Wavelength Conversion: Results from the IST ATLAS Project

In this article we report the main experimental results obtained in the framework of the IST ATLAS project regarding the transmission at 40 Gb/s over long terrestrial links, including the frequency conversion of a signal. We report the single-channel 40 Gb/s transmission over a link 500 km long with an amplifier spacing of 100 km, both with G.652 fibers and G.653 fibers by periodically compensating the chromatic dispersion with dispersion-compensating fibers. We report the single-channel transmission at 40 Gb/s, also, after the wavelength conversion of a channel with both PPLN and semiconductor optical amplifier devices. In particular, 500 km distances are obtained with PPLN wavelength conversion and 300 km distances with semiconductor optical amplifiers. Some results have been reported for electronic devices operating at 40 Gb/s.     

Semiclassical approach to surface plasmons in spheroidal clusters

The linearized Vlasov equation gives a semiclassical version of the random phase approximation. The solution of this equation is studied for electrons moving in a deformed equilibrium mean field which is approximated by a cavity of a spheroidal shape (both prolate and oblate). Contrary to spherical systems, there is a coupling between excitations of different multipolarity induced by the interaction between constituents. The dipole response presents a typical double-peaked profile with a strong dependence on the deformation. Presented by A. Dellafiore at the International Conference on “Atomic Nuclei and Metallic Clusters”, Prague, September 1–5, 1997.     

Adlayer inhomogeneity without lateral interactions: rationalizing correlation effects in CO oxidation at RuO2(110) with first-principles kinetic Monte Carlo

Microkinetic modeling of surface chemical reactions still relies heavily on the mean-field based rate equation approach. This approach is expected to be most accurate for systems without appreciable lateral interactions among the adsorbed chemicals, and there in particular for the uniform adlayers resulting in poisoned regimes with predominant coverage of one species. Using first-principles kinetic Monte Carlo simulations and the CO oxidation at RuO(2)(110) as a showcase, we demonstrate that even in this limit mean-field rate equations fail to predict the catalytic activity by orders of magnitude. This deficiency is traced back to the inability to account for the vacancy pair formation that is kinetically driven by the ongoing reactions.     

Exploitation of the Fiber Capacity in Optical Networks Using Time, Frequency, and Space Division Multiple Accesses

In this work we investigate how to obtain very high capacity transmissions in optical networks taking into account the limitations due to the physical channel. We consider both the case in which all the users are connected by a star coupler and the case in which the users are directly connected by the network topology. As a reference, we consider a ring network and a Shuffle Multihop Network (SMN). The use of optical systems to implement high-capacity networks is numerically investi gated by means of numerical simulations taking into consideration the channel limitations due to the chromatic dispersion, the Kerr effect, and the amplified spontaneous emission (ASE) noise of the optical amplifiers. In our model, we consider that the signal, during the routing process that is performed at the user position, undergoes only an attenuation. We suppose the use of intensity modulated signals and receivers with direct detection. Packet switching and digital transmission are assumed with soliton and conventional nonreturn to zero signals. Both wave length and time division multiple accesses are considered. The results show that, in the case of the Time Division Multiple Access (TDMA) technique, the use of a star coupler to connect the users reduces the capacity of a network with respect to the case in which a direct connection of the users is used. This is due to the strong power fluctuations that are present during the signal propagation and to the large quantity of accumulated ASE noise. On the other hand, the use of a star coupler shows the advantage to being easily reconfigurable. The Wavelength Divison Multiple Access (WDMA) technique permits us to achieve higher capacities with respect to the TDMA. This is due to the fact that in the propagation conditions, due to the presence of a star coupler, high bit rate signals are strongly degraded. On the other hand, several low bit rate signals operating at different wavelengths can propagate with a low power level, avoiding strong degradation due to the Four Wave Mixing (FWM) effect. Among the topologies considered in this work, the SMN is the one that generally permits us to reach the highest throughput because in the SMN the signal hops in a limited number of Network Interface Units (NIUs) before reaching the final destination.     

High repetition rate effects in XeCl tea lasers

The high repetition rate capability of a discharge pumped XeCl laser with static fill has been studied by double pulse experiments. By suitably selecting the laser parameters (energy deposition, gas mixture composition, filling pressure), following an analytical model of the discharge induced thermal effects, laser action from the second pulse for delays as short as 5 ms with an energy of 12.5 mJ has been achieved.     

Analysis of Transmission Performance in SUPERPONs

In this work we study how optical amplifiers can deeply improve the performance of the passive optical networks (PONs), permitting a large number of optical network units (ONUs), transmitting at high bit rate. These high-capacity networks are called SUPERPONs, and we show how to achieve a network with 8,192 ONUs with a transmission in the downstream direction up to 10 Gbit/s.