2,798 research outputs found
Novel structure for large area image sensing
This work presents preliminary results in the study of a novel structure for a laser scanned photodiode (LSP) type of image sensor. In order to increase the signal output, a stacked p-i-n-p-i-n structure with an intermediate light-blocking layer is used. The image and the scanning beam are incident through opposite sides of the sensor and their absorption is kept in separate junctions by an intermediate light-blocking layer. As in the usual LSP structure the scanning beam-induced photocurrent is dependent on the local illumination conditions of the image. The main difference between the two structures arises from the fact that in this new structure the image and the scanner have different optical paths leading to an increase in the photocurrent when the scanning beam is incident on a region illuminated on the image side of the sensor, while a decreasing in the photocurrent was observed in the single junction LSP. The results show that the structure can be successfully used as an image sensor even though some optimization is needed to enhance the performance of the device
Modelling radiation emission in the transition from the classical to the quantum regime
An emissivity formula is derived using the generalised
Fermi-Weizacker-Williams method of virtual photons which accounts for the
recoil the charged particle experiences as it emits radiation. It is found that
through this derivation the formula obtained by Sokolov et al using QED
perturbation theory is recovered. The corrected emissivity formula is applied
to nonlinear Thomson scattering scenarios in the transition from the classical
to the quantum regime, for small values of the nonlinear quantum parameter
\chi. Good agreement is found between this method and a QED probabilistic
approach for scenarios where both are valid. In addition, signatures of the
quantum corrections are identified and explored.Comment: 11 pages, 4 figures, submitted for publicatio
Astrometry of mutual approximations between natural satellites. Application to the Galilean moons
Typically we can deliver astrometric positions of natural satellites with
errors in the 50-150 mas range. Apparent distances from mutual phenomena, have
much smaller errors, less than 10 mas. However, this method can only be applied
during the equinox of the planets. We developed a method that can provide
accurate astrometric data for natural satellites -- the mutual approximations.
The method can be applied when any two satellites pass close by each other in
the apparent sky plane. The fundamental parameter is the central instant
of the passage when the distances reach a minimum.
We applied the method for the Galilean moons. All observations were made with
a 0.6 m telescope with a narrow-band filter centred at 889 nm with width of 15
nm which attenuated Jupiter's scattered light. We obtained central instants for
14 mutual approximations observed in 2014-2015. We determined with an
average precision of 3.42 mas (10.43 km). For comparison, we also applied the
method for 5 occultations in the 2009 mutual phenomena campaign and for 22
occultations in the 2014-2015 campaign. The comparisons of determined by
our method with the results from mutual phenomena show an agreement by less
than 1-sigma error in , typically less than 10 mas. This new method is
particularly suitable for observations by small telescopes.Comment: 13 pages, 11 figures and 8 tables. Based on observations made at the
Laborat\'orio Nacional de Astrof\'isica (LNA), Itajub\'a-MG, Brazi
Magnetically assisted self-injection and radiation generation for plasma based acceleration
It is shown through analytical modeling and numerical simulations that
external magnetic fields can relax the self-trapping thresholds in plasma based
accelerators. In addition, the transverse location where self-trapping occurs
can be selected by adequate choice of the spatial profile of the external
magnetic field. We also find that magnetic-field assisted self-injection can
lead to the emission of betatron radiation at well defined frequencies. This
controlled injection technique could be explored using state-of-the-art
magnetic fields in current/next generation plasma/laser wakefield accelerator
experiments.Comment: 7 pages, 4 figures, accepted for publication in Plasma Physics and
Controlled Fusio
Podcasts in portuguese journalism – The case P24
A existência de um podcast diário trouxe à redação do jornal Público um espaço complementar onde os jornalistas podem aprofundar as suas histórias através do áudio. Entre 9 de Abril de 2019 e 17 de Julho de 2020, o jornal produziu 300 episó- dios do podcast intitulado P24, destacando-se os temas ligados às secções de in- ternacional (conhecida no jornal como “mundo”), política e sociedade. Neste artigo analisamos os conteúdos produzidos neste universo temporal e a evolução da sua audiência, temáticas e protagonistas.
Este podcast, lançado inicialmente com financiamento do fundo Digital News Innovation Fund da Google, abriu também espaço para a criação de uma estratégia de podcasting no jornal. Ainda assim, os dados sugerem que o áudio continua a ser um parente pobre dentro do espaço dos jornais online (Reis, 2018).info:eu-repo/semantics/publishedVersio
New media producers? The profile of the portuguese podcast producer
Com a massificação do formato de podcast (Morgan, 2015), surgiram em Portugal conteúdos áudio criados fora dos circuitos tradicionais das rádios. A acessibilidade desta tecnologia fez com que os produtores de conteúdo a usassem para chegar a uma audiência (Berry, 2006).
A digitalização da rádio e o surgimento da tecnologia de podcasting levou à existência de novos produtores de conteúdos em áudio exclusivamente para a internet. A democratização do meio (Balzen, 2017), possibilitada através da existência de software de baixo custo ou de código aberto, da massificação dos reprodutores portáteis, e das plataformas de online blogging (Berry, 2018) tem levado ao aumento e diversificação dos conteúdos disponíveis.
Para perceber quem são os produtores de podcasts (podcasters) em Portugal foi aplicado um inquérito online (com uma amostra de 92) através do qual foi possível identificar o perfil-tipo do produtor português: homem, com formação superior, sem experiência anterior em rádio, que lança em média um episódio novo do seu formato a cada semana e com uma idade média de 31 anos.
Este artigo apresenta ainda a caracterização do mercado português de podcasts independentes no momento imediatamente anterior à realização do inquérito (Setembro de 2018), tendo sido registado a existência de uma centena de formatos, 77 dos quais ativos aquando do levantamento. Eram as categorias de “Comédia”, “TV e Cinema” e “Desporto e lazer” que apresentavam mais episódios disponíveis.info:eu-repo/semantics/publishedVersio
Large area image sensing structures based on a-SiC : H: a dynamic characterization
In recent works large area hydrogenated amorphous silicon p-i-n structures with low conductivity doped layers were proposed as single element image sensors. The working principle of this type of sensor is based on the modulation, by the local illumination conditions, of the photocurrent generated by a light beam scanning the active area of the device. In order to evaluate the sensor capabilities is necessary to perform a response time characterization. This work focuses on the transient response of such sensor and on the influence of the carbon contents of the doped layers. In order to evaluate the response time a set of devices with different percentage of carbon incorporation in the doped layers is analyzed by measuring the scanner-induced photocurrent under different bias conditions
Contribuição da Microscopia Confocal In Vivo para o Diagnóstico e Follow-Up de Neoplasias Conjuntivais Intraepiteliais
Objectivo: Analisar o contributo da microscopia confocal in vivo para o diagnóstico efollow-up de neoplasias conjuntivais intraepiteliais.
Métodos: Avaliámos 5 doentes com neoplasia conjuntival intraepitelial unilateral com o Heidelberg Retina Tomograph II, Rostock Cornea Module. Três doentes foram submetidos a excisão com crioterapia adjuvante, um doente a excisão com crioterapia adjuvante e ciclos de IFN-a2b e um doente a excisão simples e ciclos de IFN-a2b. As imagens de microscopia confocal foram comparadas com a histologia das mesmas lesões. 0 follow-up clínico, através de fotografias do segmento anterior, foi comparado com os achados da microscopia confocal.
Resultados: Três dos doentes foram identificados histologicamente como neoplasia intraepitelial de alto grau e dois como carcinoma in situ. As características histológicas descritas correlacionam-
se bem com as visíveis à microscopia confocal: alteração da estrutura do epitélio com acantose, disqueratose, pleomorfismo celular, aumento da refletibilidade celular e nuclear, com relação núcleo/citoplasma aumentada e por vezes binucleação. A lesão é bem delimitada e os plexos nervosos sob a lesão não são visíveis. A microscopia confocal identificou uma recidiva e
demonstrou-se útil na monitorização da resposta ao tratamento.
Conclusão: A microscopia confocal ill vivo pode ter um papel importante não só no diagnóstico
inicial como também na deteção de recidivas e na avaliação da resposta ao tratamento, de uma forma minimamente invasiva
Magnetic control of particle-injection in plasma based accelerators
The use of an external transverse magnetic field to trigger and to control
electron self-injection in laser- and particle-beam driven wakefield
accelerators is examined analytically and through full-scale particle-in-cell
simulations. A magnetic field can relax the injection threshold and can be used
to control main output beam features such as charge, energy, and transverse
dynamics in the ion channel associated with the plasma blowout. It is shown
that this mechanism could be studied using state-of-the-art magnetic fields in
next generation plasma accelerator experiments.Comment: 10 pages, 3 figure
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