Single-photon source based on FWM with adjustable linear SOP

We present a setup able to generate and detect single photons in optical fibers using the stimulated four-wave mixing (FWM) process. The results show an accurate generation of single photons at four different linear states of polarization (SOPs), with angles 0, 45, 90 and -45 degrees. The detection was performed in back-to-back configuration and after transmission over an optical fiber with a length up to 10 m

O papel do Estado no sistema de media

O objetivo central da nossa investigação é tentar compreender a relação existente entre os sistemas de media e os sistemas políticos, procurando descortinar as dimensões e variáveis associadas à presença do Estado no sistema de media Português. Partimos do pressuposto que o papel do Estado junto daquele sistema deve ser aferido em função da sua intervenção enquanto proprietário, financiador e regulador dos meios de comunicação social. Na análise do papel do Estado enquanto proprietário de media abordamos em profundidade a temática do serviço público de rádio e televisão, agrupando as diversas correntes de pensamento sobre o âmbito da missão de serviço público de acordo com uma tipologia por nós desenvolvida. No que respeita a realidade portuguesa, verificamos que o papel do Estado enquanto proprietário de media é significativo, particularmente pelo esforço financeiro público que suporta com o operador de serviço público RTP, e com o financiamento dos serviços de interesse público prestados pela LUSA. Quanto ao papel do Estado como financiador dos meios de comunicação social, observamos que o Estado português tem tido um papel ativo no apoio à comunicação social regional e local, embora seja de salientar a tendência de redução contínua do esforço financeiro público nos últimos anos. No que concerne a intervenção pública regulatória no sistema dos media, ou por outras palavras, a hetero-regulação da comunicação social, concluímos que a mesma deve atender prioritariamente ao interesse geral e à defesa de direitos e liberdades fundamentais. Entendemos que a regulação dos media tem que ser abrangente, inclusiva, e dirigir-se à totalidade do ecossistema mediático. Reconhecemos que a hetero-regulação não é um sistema completo, e concluímos pela necessidade de coexistirem iniciativas de auto e coregulação.The core objective underpinning this research is to try to understand the relationship between media systems and political systems, and thereby reveal the dimensions and variables associated to the presence of the State in the Portuguese media system. The research is based on the assumption that the State’s role within this system must be gauged in function of its tripartite function as media owner, financer and regulator. In terms of the role of the State as media owner, we provide a thorough analysis of the issue of public radio and television, categorising the various prevailing schools of thought on the appropriate scope of the public service mission, using a specific typology that has been developed within the context of this thesis. Concerning the situation in Portugal, we found that the State's role as a media owner is significant, in particular due to the significant public funding provided to the public broadcaster, RTP, and funding for publicinterest services provided by the state news agency, LUSA. In relation to the role of the State as a financier of the media, we found that the Portuguese State plays an active role in supporting regional and local media, although there is a clear trend towards continuous reduction of public funding in this field over recent years. Regarding the various frameworks of public regulation of the media system, or in other words, hetero-regulation of the media, we conclude that this should primarily serve the public interest and uphold fundamental rights and freedoms. We believe that regulation of media has to be comprehensive, inclusive, and address the entire media ecosystem. We recognize that hetero-regulation is not a complete system, and conclude that it necessary to ensure the co-existence of self-regulatory and co-regulatory initiatives

Fiber-optical communication system using polarization-encoding photons

We present a single-photon source based on the stimulated four-wave mixing process with adjustable linear state of polarization. This source allowed us to generate non-orthogonal states of polarization, that can be used for quantum key distribution experiments. The average number of photon counts as a function of the angle of the analyzer was obtained for two non-orthogonal linear states of polarization. The results show an accurate detection after propagation through a standard single-mode optical fiber with a length equal to 20 km. We also employed a master/slave configuration between two avalanche photodiodes, in order to check the probability of our single-photon source to emit pulses with more than one photon, for an average number of photons per pulse, μ ∼ 0.2, and consequently the probability of a photon to choose one of the paths. Results show that our experimental scheme is suitable for polarization-encoding experiments.QuantTel - Quantum Secure TelecommunicationsQuantPrivTel - Quantum Private Telecommunications - PTDC/EEATEL/ 103402/200

Polarization-entangled photon pairs using spontaneous four-wave mixing in a fiber loop

We generate polarization-entangled photon pairs in the 1550-nm wavelength telecom band, using spontaneous fourwave mixing in a highly nonlinear fiber loop. With accidental coincidences subtracted, we obtain coincidence fringes with visibilities greater than 86%, and thus observe a violation of Clauser, Horne, Shimony and Holt (CHSH) inequality by 2.7 standard deviations. The experimental setup is built using only fiber connections, which contribute to its long time stability.QuantTel - Quantum Secure TelecommunicationsQuantPrivTel - Quantum Private Telecommunications - PTDC/EEATEL/ 103402/200

Time coincidence of entangled photon pairs using spontaneous four-wave mixing in a fiber loop

We obtained a source of entangled photon pairs in the 1550-nm wavelength band using spontaneous four-wave mixing (SpFWM) in a Sagnac fiber loop. Time coincidence of entangled photon pairs was verified for a 300-m dispersion-shifted fiber (DSF), using an avalanche photodiode (APD).QuantTel - Quantum Secure TelecommunicationsQuant- PrivTel - Quantum Private Telecommunications - PTDC/EEATEL/ 103402/200

Sondas de ácido péptido nucleico, estojo e método para detectar espécies do género Lactobacillus spp. e/ou Gardnerella spp. e respectivas aplicações

O presente invento refere-se à concepção de duas sondas de ácido péptido nucleíco (PNA) para detectar as bactérias Lactobacillus e/ou Gardnerella spp.. Estas sondas são aplicadas a um processo baseado em técnicas de biologia molecular, nomeadamente de hibridação fluorescente in situ (FISH), aplicáveis no diagnóstico de vaginose bacteriana ou a detecção e quantificação destes géneros bacterianos em diversos tipos de amostras, incluindo sangue, alimentos, biopsias, fezes, água e outras amostras clínicas, ambientais ou provenientes da indústria agrícola ou alimentar

Correlated photon-pair generation in a highly nonlinear fiber using spontaneous FWM

We generate 1550 nm correlated photon pairs through the spontaneous four-wave mixing (SpFWM) process in a highly nonlinear fiber (HNLF). The pair source quality generation is evaluated by the coincidence-to-accidental ratio (CAR) parameter. It is verified that the spontaneous Raman scattering (SpRS) photons generated inside the fiber contribute to the degradation of the source. Nevertheless, a CAR value of 2.77 is found for a pump power at the input of the fiber of 1.1 mW.QuantPrivTel- Quantum Private Telecommunications - PTDC/EEATEL/ 103402/2008

Development and characterization of a novel hybrid tissue engineering-based scaffold for spinal cord injury repair

Spinal cord injury (SCI) represents a significant health and social problem, and therefore it is vital to develop novel strategies that can specifically target it. In this context, the objective of the present work was to develop a new range of three-dimensional (3D) tubular structures aimed at inducing the regeneration within SCI sites. Up to six different 3D tubular structures were initially developed by rapid prototyping: 3D bioplotting–based on a biodegradable blend of starch. These structures were then further complemented by injecting Gellan Gum, a polysaccharide-based hydrogel, in the central area of structures. The mechanical properties of these structures were assessed using dynamic mechanical analysis, under both dry and wet conditions, and their morphologies= porosities were analyzed using micro-computed tomography and scanning electron microscopy. Biological evaluation was carried out to determine their cytotoxicity, using both minimum essential medium (MEM) extraction and MTS tests, as well as by encapsulation of an oligodendrocyte-like cell (M03-13 cell line) within the hydrogel phase. The histomorphometric analysis showed a fully interconnected network of pores with porosity ranging from 70% to 85%. Scaffolds presented compressive modulus ranging from 17.4 to 62.0MPa and 4.42 to 27.4 MPa under dry and wet conditions, respectively. Cytotoxicity assays revealed that the hybrid starch=poly-ecaprolactone= Gellan Gum scaffolds were noncytotoxic, as they did not cause major alterations on cell morphology, proliferation, and metabolic viability. Moreover, preliminary cell encapsulation assays showed that the hybrid scaffolds could support the in vitro culture of oligodendrocyte-like cells. Finally, preliminary in vivo studies conducted in a hemisection rat SCI model revealed that the above-referred structures were well integrated within the injury and did not trigger chronic inflammatory processes. The results herein presented indicate that these 3D systems might be of use in future SCI regeneration approaches.Portuguese Foundation for Science and Technology through funds from Programa Operacional Ciencia, Tecnologia, Inovacao (POCTI) and/or Fundo Europeu de Desenvolvimento Regional (FEDER) programs (funding to ICVS, 3B's Research Group, predoctoral and postdoctoral fellowships to N. A. Silva, J. T. Oliveira, A. J. Salgado, and R. A. Sousa-SFRH/BD/40684/2007; SFRH/BD/17135/2004; SFRH/BPD/17595/2004; SFRH/BPD/17151/2004)

First-order phase transition in a 2D random-field Ising model with conflicting dynamics

The effects of locally random magnetic fields are considered in a nonequilibrium Ising model defined on a square lattice with nearest-neighbors interactions. In order to generate the random magnetic fields, we have considered random variables $\{h\}$ that change randomly with time according to a double-gaussian probability distribution, which consists of two single gaussian distributions, centered at $+h_{o}$ and $-h_{o}$, with the same width $\sigma$. This distribution is very general, and can recover in appropriate limits the bimodal distribution ($\sigma\to 0$) and the single gaussian one ($ho=0$). We performed Monte Carlo simulations in lattices with linear sizes in the range $L=32 - 512$. The system exhibits ferromagnetic and paramagnetic steady states. Our results suggest the occurence of first-order phase transitions between the above-mentioned phases at low temperatures and large random-field intensities $h_{o}$, for some small values of the width $\sigma$. By means of finite size scaling, we estimate the critical exponents in the low-field region, where we have continuous phase transitions. In addition, we show a sketch of the phase diagram of the model for some values of $\sigma$.Comment: 13 pages, 9 figures, accepted for publication in JSTA