An easy synthetic approach to 1,2,3-triazole-fused heterocycles

A convenient synthesis of 1,2,3-triazole-fused isoindolines and dihydroisoquinolines in good to excellent yield is reported, starting from easily available terminal alkynes and (2-haloaryl)alkylazides. The method is based upon a cycloaddition reaction, via click chemistry, followed by a transition metal-catalyzed functionalization of a C-H bond.     

Distortions compensation in linear optical links adopting wavelength converters based on FWM in semiconductor amplifiers

Wavelength conversion by four-wave mixing in high-speed, long-distance optical links compensates for fiber dispersion and source chirping. Wavelength converters based on four-wave mixing in semiconductor amplifiers could be key components in wavelength-switched networks. The link performances are estimated by simulation using a physical model of all devices; the bit error rate is evaluated by a semianalytical model.     

Theoretical analysis of optical pulse position modulation communication systems using semiconductor lasers

In this paper the performance of a pulse position modulation (PPM) optical system is analysed both for direct and coherent detection schemes taking into account time jitter of the semiconductor laser. This phenomenon can introduce a large sensitivity penalty if the system parameters are not accurately selected. In particular, the optimum value of the PPM order is strongly influenced by the laser time jitter, and the modulation index cannot be chosen below a threshold value that, with the assumed laser parameters, is about 0.7.     

Toward an optimum use of the optical channel capacity

Abstract

In recent decades, in addition to long-haul, high-capacity links, research activity in optical fiber communication systems has addressed possible advantageous applications in distribution networks, local and metropolitan area networks, CATV backbones and distribution, and high-speed computer networks. As a consequence, new possibilities in optical transmission systems have been explored to face the new requirements in terms of capacity, spectral efficiency, and receiver sensitivity. Among the possible solutions capable to exploit effectively the potentials offered by the optical channel, novel multilevel modulation formats have been proposed for future communication environment. This paper reviews multilevel modulation techniques for optical transmission: a comparative analysis is performed between conventional modulations, such as N-PSK and N-QAM, and new modulation/demodulation techniques, such as N-4QSK, N-SPSK, and PM-DD, taking into account both system performance and technological constraints.     

WDM-PON Architecture for FTTx Networks

Abstract

Broadband services for residential users in European countries have until now largely relied on xDSL technologies, while FTTx technologies have been mainly exploited in Asia and North America. The increasing bandwidth demand and the growing penetration of new services are pushing the deployment of optical access networks, and major European operators are now announcing FTTx projects. While FTTH is recognized as the target solution to bring broadband services to residential users, the identification of an FTTx evolutionary path able to seamlessly migrate to FTTH is key to enabling a massive deployment, easing the huge investments needed. WDM-PON architecture is an interesting solution that is able to accommodate the strategic need of building a new fiber-based access infrastructure with the possibility of adapting investments to actual demands and evolving to FTTH without requiring further interventions on fiber infrastructures.     

Polarization modulated coherent optical communication systems

Abstract

Polarization modulated coherent optical communication systems are interesting for low-phase noise-induced penalty and insensitivity to the fluctuations of the field state of polarization if a suitable tracking is adopted. In this paper, sever kinds of binary and multilevel polarization modulated systems are presented based c Stokes parameters detection. Quantum limit performance is determined and phase noise-induced penalty is evaluated both in the presence of a sample and hold decision device and in case of postdetection filtering.     

Theoretical analysis of a PSK coherent heterodyne optical receiver using external cavity semiconductor lasers

The performance of a PSK heterodyne optical transmission system using external cavity semiconductor lasers as remote and local oscillators in evaluated theoretically. The actual shape of the instantaneous frequency fluctuations power spectral density of the optical oscillators is taken into account, obtaining indications for optimum design of the external optical feedback.     

Nitroxides as metabolic and EPR imaging probes in biological model systems

Nitroxides are unusually stable free radicals and sensitive “reporters” of the chemico-physical environment which surround them. The term “reporter group” was used to indicate this property, later the term spin label or spin probe was preferred. The facile synthesis and the multiplicity of compounds which have been coupled to the nitroxide moiety has allowed the development of a number of applications. Nitroxides have been used to study molecular mobility of proteins and lipids in membranes, enzyme active sites, DNA synthesis, and measure of electrical potential, pH, temperature as well as oxygen gradients across membranes; more recently, as contrast agents in magnetic resonance imaging and electron paramagnetic resonance imaging (EPRI). Aim of this work is to review and comment on the use of various nitroxides as metabolic probes, and in EPRI in studies of biomedical interest.     

Generation of N-tert-butyl-α-phenylnitrone radical adducts in iron breakdown of tert-butyl-hydroperoxide

ESR spectroscopy coupled to the spin trapping technique was used to evaluate the generation of radical species arising from the ferrous ion induced decomposition of tert-butyl hydroperoxide (’BuOOH) in methylene chloride. We report here that N-tert-butyl-α-phenylinitrone (PBN) can trap peroxyl radicals generated in the ferrous ion induced breakdown of high concentration of ’BuOOH (IM) at room temperature, the radical adduct being stable under the light. The peroxyl radical formation was demonstrated by direct ESR measurements at 77K. In contrast, alkoxyl and methyl radicals were trapped only in the presence of low hydroperoxide concentration (ImM). In order to measure the hyperfine splitting constants (hfsc) of the PBN-methyl adduct spectra were obtained in the presence of diphenylamine (DPA) or 2,6-di-tert-butyl-4-methylphenol (BHT), which quenched the alkoxyl radical. For this latter radical, the hfsc were calculated by computer simulation. A mechanism for a direct interaction between DPA and the alkoxyl radical is presented. DPA quenched the peroxyl radical in the reaction of high hydroperoxide concentrations, with the concomitant generation of a DPA nitrogen-based radical.     

NMR study of water exchange across the hepatocyte membrane

An understanding of the cellular permeability for water is needed to evaluate MR images of complex tissues, such as liver, and to interpret the effects of contrast agents. To obtain data essential for such an understanding we measured water exchange across the isolated rodent hepatocyte membrane by proton NMR relaxation with dextranmagnetite as a relaxation agent. The results are treated as water exchange in a two-compartment system, and possible reasons for deviations from that behavior are analyzed. The mean residence time of intracellular water was approximately 40 ms at 37 degrees C. We found the lower limit for the diffusional permeability of the hepatocyte membrane to be 8 x 10(-3) cm s-1. These results, combined with consideration of hepatic anatomy indicate that the failure to observe effects on the T1 of liver from particulate contrast agents such as magnetite, Gd-starch, and liposome encapsulated Mn2+ is due to the localization of these agents in the Kupffer cells. Also, the nonexponential T1 decay observed in normal liver is unlikely to be due to slow exchange of water between compartments.