Estimating the Performance of Direct-Detection DPSK in Optical Networking Environments Using Eigenfunction Expansion Techniques

WOS:000281971100002 (Nº de Acesso Web of Science)“Prémio Científico ISCTE-IUL 2011”In-band crosstalk, due to multiple interferers, has been identified as one of the most severe impairments in optical transparent networks, especially in the ones with a large number of nodes and a high wavelength density. Due to its robustness to in-band crosstalk differential phase-shift keying (DPSK) emerges as an attractive modulation scheme to be used in such environments. This paper proposes a rigorous formulation to estimate the performance of direct-detection DPSK receivers using an eigenfunction expansion technique in the time domain. The method takes into account both the in-band crosstalk, due to an arbitrary number of interfering terms, and the amplified spontaneous emission noise and is able to deal with any combination of optical and electrical filter shapes. Using this method the accuracy of an approximation based on the wideband optical filtering assumption was evaluated and shown that the approximation, although not providing reliable results for the error probabilities, can be used with confidence to compute power penalties due to in-band crosstalk. Furthermore, the crosstalk tolerance of DPSK over on-off keying was quantified and shown that this tolerance is reduced when the number of interferers increases

Applying the skew-normal distribution to model coherent MPI and to evaluate its impact on PAM signals

We statistically model the coherent multipath interference (MPI) using an extended skewnormal distribution, with the results showing a good agreement with published experimental data. This distribution is very flexible and permits to model data with large skewness values, which is a typical feature in coherent MPI histograms. Furthermore, the developed model was applied to estimate the impact of coherent MPI on PAM-4 systems, with the results showing a 1-dB Q-penalty for an MPI level of -24 dB and a bit error ratio of 10^-3.info:eu-repo/semantics/acceptedVersio

The Portuguese Radical Left Parties Supporting Government: From Policy-Takers to Policymakers?

How do parties that have long been confined to opposition behave once they take the decision to support government? This article analyses the case of the three Portuguese radical left parties that took such a move in the wake of the post-bailout 2015 election. Leveraging the concept of contract parliamentarism and the analysis of different data sources through different methods, we show that the three parties adopted a similar strategy after agreeing deals with the centre-left socialists. Specifically, while keeping close scrutiny on the executive action, the parties have voted consensually on most of the legislation proposed by the government. In exchange, the majority of policy pledges agreed with the socialists were implemented by the beginning of the legislature. Based on these findings, the article underlines the importance for supporting parties of conducting a thorough negotiation of policy goals and the timing of their implementation before joining the government, and of pursuing an autonomous discursive agenda

Fish models of induced osteoporosis

Osteopenia and osteoporosis are bone disorders characterized by reduced bone mineral density (BMD), altered bone microarchitecture and increased bone fragility. Because of global aging, their incidence is rapidly increasing worldwide and novel treatments that would be more efficient at preventing disease progression and at reducing the risk of bone fractures are needed. Preclinical studies are today a major bottleneck to the collection of new data and the discovery of new drugs, since they are commonly based on rodent in vivo systems that are time consuming and expensive, or in vitro systems that do not exactly recapitulate the complexity of low BMD disorders. In this regard, teleost fish, in particular zebrafish and medaka, have recently emerged as suitable alternatives to study bone formation and mineralization and to model human bone disorders. In addition to the many technical advantages that allow faster and larger studies, the availability of several fish models that efficiently mimic human osteopenia and osteoporosis phenotypes has stimulated the interest of the academia and industry toward a better understanding of the mechanisms of pathogenesis but also toward the discovery of new bone anabolic or antiresorptive compounds. This mini review recapitulates the in vivo teleost fish systems available to study low BMD disorders and highlights their applications and the recent advances in the field.UIDB/04326/2020, EAPA_151/2016/BLUEHUMANinfo:eu-repo/semantics/publishedVersio

Fast volumetric registration method for tumor follow-up in pulmonary CT exams

An oncological patient may go through several tomographic acquisitions during a period of time, needing an appropriate registration. We propose an automatic volumetric intrapatient registration method for tumor follow-up in pulmonary CT exams. The performance of our method is evaluated and compared with other registration methods based on optimization techniques. We also compared the metrics behavior to inspect which metric is more sensitive to changes due to the presence of lung tumors

Exploring the tabu search algorithm as a graph coloring technique for wavelength assignment in optical networks

The aim of this work is to study the Tabu Search algorithm as a graph coloring technique for wavelength assignment in optical networks, a crucial function in optical network planning. The performance of the Tabu Search is assessed in terms of the number of wavelengths and computation time and is compared with the one of the most common Greedy algorithm. It is concluded that for real networks with a large number of nodes and a higher variance node degree of the path graph relatively to its average node degree value, the Greedy algorithm is preferable to the Tabu Search algorithm since it returns the same number of colors of Tabu Search, but in a shorter computation time.info:eu-repo/semantics/acceptedVersio

Beta cells preferentially exchange cationic molecules via connexin 36 gap junction channels

Aims/hypothesis: Pancreatic beta cells are connected by gap junction channels made of connexin 36 (Cx36), which permit intercellular exchanges of current-carrying ions (ionic coupling) and other molecules (metabolic coupling). Previous studies have suggested that ionic coupling may extend to larger regions of pancreatic islets than metabolic coupling. The aim of the present study was to investigate whether this apparent discrepancy reflects a difference in the sensitivity of the techniques used to evaluate beta cell communication or a specific characteristic of the Cx36 channels themselves. Methods: We microinjected several gap junction tracers, differing in size and charge, into individual insulin-producing cells and evaluated their intercellular exchange either within intact islets of control, knockout and transgenic mice featuring beta cells with various levels of Cx36, or in cultures of wild-type and Cx36-transfected MIN6 cells. Results: We found that (1) Cx36 channels favour the exchange of cations and larger positively charged molecules between beta cells at the expense of anionic molecules; (2) this exchange occurs across sizable portions of pancreatic islets; and (3) during glibenclamide (known as glyburide in the USA and Canada) stimulation beta cell coupling increases to an extent that varies for different gap junction-permeant molecules. Conclusions/interpretation: The data show that beta cells are extensively coupled within pancreatic islets via exchanges of mostly positively charged molecules across Cx36 channels. These exchanges selectively increase during stimulation of insulin secretion. The identification of this permselectivity is expected to facilitate the identification of endogenous permeant molecules and of the mechanism whereby Cx36 signalling significantly contributes to the modulation of insulin secretio

Impact of traffic load and spectral occupancy on Gaussian noise models performance for multiband networks

In a network scenario, wavelength division multiplexing channels are added and dropped leading to fluctuations on the network traffic loads along the optical path. In this work, a comparison between the optical signal-to-noise ratio (OSNR) predictions of the recently proposed closed-form generalized Gaussian noise (GGN) model and a closed-form Gaussian noise (GN) model that does not take into account the stimulated Raman scattering (SRS) is performed, for different network traffic loads and spectral occupancy over the entire C+L band. In all results obtained, the maximum difference between the OSNR predictions of GN (without SRS) and GGN models closed forms is below 0.7 dB at optimum OSNR and maximum C+L band occupancy, indicating that the GN-model can also be used in C+L band transmission. For channel launch powers higher than the optimum, the OSNR differences increase up to 3 dB, being the GN-model (without SRS) unsuitable to assess the network performance in such situations.info:eu-repo/semantics/acceptedVersio

Graph coloring heuristics for optical networks planning

This work focuses on the study of wavelength assignment algorithms based on Graph Coloring techniques. We analyze the performance of the Greedy heuristic, a well-known Graph Coloring heuristic, as well as the Degree of Saturation (DSATUR) and the Recursive Largest First (RLF) heuristics, for planning optical networks. These last two heuristics, to the best of our knowledge, have not yet been applied in the context of optical networks. Extensive simulations have been performed, using real network topologies under a static traffic scenario and we have concluded that the DSATUR and RLF heuristics can outperform the Greedy heuristic in network scenarios where there are several network clusters interconnected by only one or two links. In these cases, the RLF and DSATUR heuristics can provide less 9 and 5 wavelengths, respectively, than the Greedy heuristic, in networks with 34 nodes.info:eu-repo/semantics/acceptedVersio

Assessing the quality of transmission of lightpaths in multiband C+L networks through Gaussian noise models

In an optical network scenario, wavelength division-multiplexing (WDM) channels are constantly being added and dropped, leading to dynamic traffic variations in the lightpaths. In this work, the impact of the network traffic load and spectral occupancy on the quality of transmission, namely on the normalized nonlinear interference (NLI) power, power transfer due to stimulated Raman scattering (SRS) and optical signal-to-noise ratio (OSNR) of the lightpaths in a C+L multiband optical network is assessed using the recently proposed closed-form interchannel SRS Gaussian noise model (ISRS GN-model). We show that, due to the dynamic traffic behavior, the normalized NLI power can oscillate up to 2 dB in the highest frequency channels due to NLI variations when the tested channels have unequal spacing along the spectrum. For the optimum channel launch power and by increasing the network traffic load, the power transfer between the outer channels can increase up to 5.1 dB due to the SRS effect. With 201 WDM channels, high traffic load and for the optimum channel power, we obtained a maximum OSNR variation along the channel frequencies of only about 0.7 dB. A comparison between the OSNR predictions of the closed-form ISRS GN-model and a closed-form Gaussian noise (GN) model that does not take into account the SRS effect is also performed. In all results obtained, the maximum difference between the OSNR predictions of GN (without SRS) and ISRS GN models is below 0.7 dB at optimum OSNR and maximum C+L band occupancy. For channel launch powers higher than the optimum, the OSNR differences increase up to 3 dB.info:eu-repo/semantics/publishedVersio