Degree of polarization degradation due to cross-phase modulation and its impact on polarization-mode dispersion compensators

A novel analytical model is proposed to predict the cross-phase modulation (XPM)-induced depolarization in a two-channel transmission system, in which the Stokes' vector of each channel rotates around a space-invariant pivot by a time-varying angle which depends on the total instantaneous optical power in the fiber, on the angle between pump and probe input Stokes' vectors, and on the walk-off between channels. The model leads to a simple formula of the probe degree of polarization (DOP) which is validated both by simulation and experiment. The model helps identify the key physical factors that determine the XPM-induced performance degradation of DOP-based first-order polarization-mode dispersion compensators, and experiments that quantify such degradation are presented.     

Influence of age on enzyme activities of pyrimidine metabolism in the chicken heart

We and others found that cardioprotection is acquired not only soon after, but also 24 h after ischemic preconditioning in canine and rabbit myocardial infarction models (second window of protection). However, a second window phenomenon against myocardial infarction was dependent on species limitations and has not been observed in porcine hearts. In this study, we examined whether the "second window of protection" against myocardial infarction is observed in the rat heart. In the ischemic preconditioning (IP) group, the left main coronary artery (LCA) of rats was occluded four times for 3 min. each separated by reperfusion for 10 min. After 0, 3, and 24 h, the rats were subjected to a 20-min LCA occlusion followed by 48-h reperfusion. At 0 and 24 h after IP, infarct size and the incidence of ventricular fibrillation (VF) during ischemia were significantly reduced compared with corresponding sham-operated groups without preconditioning. After 3 h of IP, there were no differences either in the incidence of VF during ischemia or in infarct size. Manganese superoxide dismutase (Mn-SOD) content in ischemic (LCA) region of myocardium significantly increased as compared with that of sham-operated rats 24 h after IP. Treatment with N-2-mercaptopropionyl glycine, an antioxidant and a hydroxyl radical scavenger, during IP abolished the early-phase (0 h after IP) and late-phase (24 h after IP) cardioprotection and the corresponding late increase in Mn-SOD content. These results indicate that a "second window of protection" against myocardial infarction also exists in rat hearts and the induction of an intrinsic scavenger, Mn-SOD, via free radical production during IP may be important in the second window of protection.     

Geographical characterisation of honeys according to their mineral content and antioxidant activity using a chemometric approach

In this article, discrimination models are presented, relating the origin of honey samples to several variables, being the concentrations of different cations and anions in the honey samples measured by ion chromatography, and parameters that measure/reflect the antioxidant activity of the honey samples. The unsupervised method, principal component analysis, and supervised discrimination methods, such as linear and quadratic discriminant analysis, and classification and regression trees (CART), were applied to evaluate the existence of data patterns and the relationship between geographical origin and the measured parameters. The model with the best predictive ability (%CCR_TEST = 66.67%), the best overall % specificity (80%) and the best overall % sensitivity (67%) was found to be CART. It was proven that the mineral content and parameters analysed can provide enough information for the geographical characterisation and discrimination of honey.     

Energy crops for biofuel production: Analysis of the potential in Tuscany

The possibility of using biomass as a source of energy in reducing green-house gas emissions is a matter of great interest. In particular, biomasse from agriculture represent one of the largest and most diversified sources to be exploited and more specifically, ethanol and diesel deriving from biomass have the potential to be a sustainable means of replacing fossil fuels for transportation. Nevertheless, the cultivation of dedicated energy crops does meet with some criticism (competitiveness with food crop cultivation, water requirements, use of fertilizers, etc.) and the economical and environmental advantages of this activity depend on accurate evaluations of the total efficiency of the production system. This paper illustrates the production potential of two energy crops, sunflower (Helianthus annuus) and maize (Zea mais), cultivated with different water and fertilization supplies in the region of Tuscany, in central Italy. A 50-year climatic series of 19 weather stations scattered around Tuscany was used to run the crop model CropSyst for obtaining crop biomass predictions. The effect of climate change and variability was analyzed and the potential production of bioenergy was investigated in terms of pure vegetable oil (sunflower) and bioethanol (maize). The results demonstrated that despite a reduction in crop yields and an increase of their variability due to climate change, the cultivation of maize in the regional set-aside areas would be capable of supplying approximately 50% of the energy requirements in terms of biofuel for transportation obtained, while the cultivation of a sunflower crops would supply less than 10%.     

Parametric-gain approach to the analysis of single-channel DPSK/DQPSK systems with nonlinear phase noise

This paper presents a novel method based on a parametric gain (PG) approach to study the impact of nonlinear phase noise in single-channel dispersion-managed differentially phase-modulated systems. This paper first shows through Monte Carlo simulations that the received amplified spontaneous emission (ASE) noise statistics, before photodetection, can be reasonably assumed to be Gaussian, provided a sufficiently large chromatic dispersion is present in the transmission fiber. This paper then evaluates in a closed form the ASE power spectral density by linearizing the interaction between a signal and a noise in the limit of a distributed system. Even if the received ASE is nonstationary in time due to pulse shape and modulation, this paper shows that it can be approximated by an equivalent stationary process, as if the signal were continuous wave (CW). This paper then applies the CW-equivalent ASE model to bit-error-rate evaluation by using an extension of a known Karhunen-Loe/spl acute/ve method for quadratic detectors in colored Gaussian noise. Such a method avoids calculation of the nonlinear phase statistics and accounts for intersymbol interference due to a nonlinear waveform distortion and optical and electrical postdetection filtering. This paper compares binary and quaternary schemes with both nonreturn- and return-to-zero (RZ) pulses for various values of nonlinear phases and bit rates. The results confirm that PG deeply affects the system performance, especially with RZ pulses and with quaternary schemes. This paper also compares ON-OFF keying (OOK) differential phase-shifted keying (DPSK) systems, showing that the initial 3-dB advantage of DPSK is lost for increasing nonlinear phases because DPSK is less robust to PG than OOK.     

Synthesis and antimicrobial activity of 7 beta-[N-(arylmethyloxyimino) acetamido]cephalosporanic acid derivatives

Some cephalosporanic acid derivatives substituted on the C(7) amino nitrogen with (arylmethyloxyimino)acetyl moieties were synthesized and tested in vitro for their antimicrobial activity against Gram positive and Gram negative bacteria. The new compounds showed a modest activity directed only against Gram positive microorganisms.