Experimental demonstration of digital predistortion for orthogonal frequency-division multiplexing-radio over fibre links near laser resonance

Radio over fibre (RoF), an enabling technology for distribution of wireless broadband service signals through analogue optical links, suffers from non-linear distortion. Digital predistortion has been demonstrated as an effective approach to overcome the RoF non-linearity. However, questions remain as to how the approach performs close to laser resonance, a region of significant dynamic non-linearity, and how resilient the approach is to changes in input signal and link operating conditions. In this work, the performance of a digital predistortion approach is studied for directly modulated orthogonal frequency-division multiplexing RoF links operating from 2.47 to 3.7 GHz. It extends previous works to higher frequencies, and to higher quadrature amplitude modulation (QAM) levels. In addition, the resilience of the predistortion approach to changes in modulation level of QAM schemes, and average power levels are investigated, and a novel predistortion training approach is proposed and demonstrated. Both memoryless and memory polynomial predistorter models, and a simple off-line least-squares-based identification method, are used, with excellent performance improvements demonstrated up to 3.0 GHz

On the equivalence of the self-dual and Maxwell-Chern-Simons models coupled to Fermions

We study the exact equivalence between the self-dual model minimally coupled with a Dirac field and the Maxwell-Chern-Simons model with non-minimal magnetic coupling to fermions. We show that the fermion sectors of the models are equivalent only if a Thirring like interaction is included. Using functional methods we verify that, up to renormalizations, the equivalence persists at the quantum level.Comment: 8 pages, revte

Effect of fat content, casing type and smoking procedures on PAHs contents of Portuguese traditional dry fermented sausages

Portuguese dry fermented sausages are traditionally processed through direct drying/smoking, making them susceptible to polycyclic aromatic hydrocarbons (PAHs) contamination. The purpose of this study was to assess the effect of added fat (20% and 40%), casing type (hog and collagen) and smoking procedures (direct and indirect exposure) on the 16 EPA priority PAHs in dry fermented sausages manufactured according traditional processing. The total PAHs content (sum of 16 PAHs) found in whole product (casing included) varied between 150 and 870 lg kg 1, with more than 99% of this content corresponding to harmless low molecular weight compounds. Concerning benzo(a)pyrene (BaP) and PAH4, the respective maximum contents (0.32 and 10.35 lg kg 1, respectively) did not exceed the imposed limits regulated by the European Union. According to our results, casing type was the most influential factor. For hog samples, fat content and smoking regime alone did not influenced the total PAHs amount. However, significantly higher (p < 0.05) contamination levels were detected in hog casing samples combining high fat content and direct smoking procedures. In opposition, irrespective of the fat content and smoking regime, safer products, with significantly lower (p < 0.001) contamination levels, were obtained when collagen casing was used

Biofilm formation under high shear stress increases resilience to chemical and mechanical challenges

The effect that the hydrodynamic conditions under which biofilms are formed has on their persistence is still unknown. This study assessed the behaviour of Pseudomonas fluorescens biofilms, formed on stainless steel under different shear stress (tau w) conditions (1, 2 and 4 Pa), to chemical (benzalkonium chloride - BAC, glutaraldehyde - GLUT and sodium hypochlorite - SHC) and mechanical (20 Pa) treatments (alone and combined). The biofilms formed under different tau w showed different structural characteristics. Those formed under a higher tau w were invariably more tolerant to chemical and mechanical stresses. SHC was the biocide which caused the highest biofilm killing and removal, followed by BAC. The sequential exposure to biocides and mechanical stress was found to be insufficient for effective biofilm control. A basal layer containing biofilm cells mostly in a viable state remained on the surface of the cylinders, particularly for the 2 and 4 Pa-generated biofilms

The Effect of starter Cultures on the Portuguese Traditional Sausage "Paio do Alentejo" in Terms of its Sensory and Textural Characteristics and Polycyclic Aromatic Hydrocarbons Profile

“Paio do Alentejo” is a Portuguese dry-cured sausage, made with meat from the Alentejano pig breed. The main aim of this study is to evaluate the benefits of the use of starter cultures on the quality of the sausage, mainly with regard to its sensory properties, rheological characteristics and PAH profile. Three batches of the product were examined: S1-inoculated with a commercial starter comprising Lactobacillus spp., Micrococcaceae and yeasts; S2-inoculated with a starter comprising Lactobacillus sakei and Staphylococcus xylosus; C-the control batch, was not inoculated. A sensory panel of 12 experts analysed samples in accordance with a descriptive analysis using a structured scale. A Texture Profile Analysis and 16 EPA priority PAHs for dry fermented sausages were performed. Both inoculated batches were well received by the judges, no significant differences being noted between them. The use of S2 led to a slight improvement in terms of cohesiveness. However, the use of starter cultures was not found to influence PAH content

Agroforestry systems can mitigate the impacts of climate change on coffee production: A spatially explicit assessment in Brazil

Climate change may impose severe challenges to farmers to maintain agricultural production levels in the future. In this study we analysed the effect of projected changes in climate on the area suitable for coffee production in 2050, and the potential of agroforestry systems to mitigate these effects in a major coffee production region in southeast Brazil. We conducted a spatially explicit analysis with the bioclimatic model MaxEnt to explore the area that is suitable for coffee production in 2050 when coffee is grown in unshaded plantations and in agroforestry systems. The projected climate in 2050 was assessed using 19 global circulation models, and we accounted for the altered microclimate in agroforestry systems by adjusting the maximum and minimum air temperature. The climate models indicated that the annual mean air temperature is expected to increase 1.7 °C ± 0.3 in the study region, which will lead to almost 60 % reduction in the area suitable for coffee production in unshaded plantations by 2050. However, the adoption of agroforestry systems with 50 % shade cover can reduce the mean temperatures and maintain 75 % of the area suitable for coffee production in 2050, especially between 600 and 800 m altitude. Our study indicates that major shifts in areas suitable for coffee production may take place within three decades, potentially leading to land conflicts for coffee production and nature conservation. Incentives that contribute to the development of coffee agroforestry systems at appropriate locations may be essential to safeguard coffee production in the southeast of Brazil.</p