Optoelectronic logic functions based on reconfigurable SiC multilayer devices

WDM multilayered SiC/Si devices based on a-Si:H and a-SiC:H filter design are approached from a reconfigurable point of view. Results show that the devices, under appropriated optical bias, act as reconfigurable active filters that allow optical switching and optoelectronic logic functions development. Under front violet irradiation the magnitude of the red and green channels are amplified and the blue and violet reduced. Violet back irradiation cuts the red channel, slightly influences the magnitude of the green and blue ones and strongly amplifies de violet channel. This nonlinearity provides the possibility for selective removal of useless wavelengths. Particular attention is given to the amplification coefficient weights, which allow taking into account the wavelength background effects when a band needs to be filtered from a wider range of mixed signals, or when optical active filter gates are used to select and filter input signals to specific output ports in WDM communication systems. A truth table of an encoder that performs 8-to-1 multiplexer (MUX) function is presented

Optoelectronic digital capture device based on Si/C multilayer heterostructures

Combined tunable WDM converters based on SiC multilayer photonic active filters are analyzed. The operation combines the properties of active long-pass and short-pass wavelength filter sections into a capacitive active band-pass filter. The sensor element is a multilayered heterostructure produced by PE-CVD. The configuration includes two stacked SiC p-i-n structures sandwiched between two transparent contacts. Transfer function characteristics are studied both theoretically and experimentally. Results show that optical bias activated photonic device combines the demultiplexing operation with the simultaneous photodetection and self amplification of an optical signal acting the device as an integrated photonic filter in the visible range. Depending on the wavelength of the external background and irradiation side, the device acts either as a short- or a long-pass band filter or as a band-stop filter. The output waveform presents a nonlinear amplitude-dependent response to the wavelengths of the input channels. A numerical simulation and two building-blocks active circuit is presented and gives insight into the physics of the device

What drives distinct ploidy phases of isomorphic biphasic life cycles to occur at uneven abundances

Tese de dout., Ciências do Mar, da Terra e do Ambiente (Biologia Populacional), Faculdade de Ciências e Tecnologia, Univ. do Algarve, 2011Throughout the history of eukariotic primary producers, namely the plant and algae, there was an evolution of the life cycles along with their morphological and physiological complexity and role on the ecosystems. The earlier, simpler ones, namely the bryophytes, have haploid life cycles. The most complex and evolved ones, namely the vascular plants, have diploid life cycles. In between there is a whole range of taxa with haploid-diploid life cycles. It most often occurs in brown or red algae. In the former the ploidy phases are heteromorphic whereas in the latter are frequently isomorphic, which raises the question about the reasons for their unbalanced occurrence in their habitats when these are expected to be even as a consequence of isomorphicity. The hypothesis that have been proposed may be resumed to two: (i) ploidy dissimilarities in their fecundities as a consequence of the differential cytological processes of spore production; and (ii) ploidy dissimilarities in growth and survival, of both spores and fronds, as a consequence of a conditional differentiation required to the stability and evolution of their biphasic life cycles. However, there is a gap between the hypotheses proposed and the observed pattern of phase dominance as the link has not been proved so far. The objective of the present thesis is to help filling this gap by establishing how ploidy dissimilarities in the life cycle may generate effective uneven abundances that match the observed in the field. To do that the thesis is divided into six chapters. In the first chapter there is a general introduction to the subject. In the second chapter it was accessed how different types of vital rates may be generally efficient, or inefficient, forcing functions upon the pattern of ploidy phase dominance. In the third chapter it was accessed how efficiently the different types of vital rates may impose a geographical variability of ploidy dominance like the ones reported for a few species. In the forth chapter it was accessed how the life cycle response to time instability is dependent on the ploidy dissimilarities in the vital rates, and how time variability may surge even in stable environments. In the fifth chapter it was accessed how efficiently, or inefficient, the different types of vital rates may impose an intra-population pattern of ploidy dominance with a fine resolution both over space and time, as it has been reported in the literature. In the sixth chapter are the final conclusions. It was found that ploidy phase dissimilarities upon the survival rates of the fronds and/or upon the performance of the spores are the most efficient and likeliest drives for the patterns of ploidy phase dominance observed in the field.Ao longo da história dos eucariotas produtores primários, nomeadamente plantas e algas, deu-se uma evolução dos seus ciclos de vida juntamente com as suas complexidades morfológicas e fisiológicas e papel nos ecossistemas. Os mais ancestrais e simples, como as plantas briófitas, têm ciclos de vida haploides. Os mais complexos e evoluídos, nomeadamente as plantas vasculares, têm ciclos de vida diploides. Pelo meio há todo um manancial de taxa com ciclos de vida haploides-diploides. O mais frequente é ocorrer em algas castanhas ou vermelhas. Nas primeiras, ambas as fases plóidicas são heteromórficas; enquanto nas últimas são frequentemente isomórficas, o que levanta a questão acerca das razões para a sua ocorrência desigual nos seus habitats quando era esperado que ocorressem equilibradamente em consequência da sua isomorficidade. As hipóteses propostas podem ser resumidas em duas: (i) dissimilaridades nas fecundidades em consequência de processos citológicos diferenciados de produção de esporos, e (ii) dissimilaridades no crescimento e sobrevivência dos esporos e talos em consequência da diferenciação condicional necessária para a evolução e estabilidade dos ciclos de vida bifásicos. Contudo, existe um fosso entre as hipóteses propostas e os padrões de dominância plóidica observados porque até agora a sua relação não foi provada. O objectivo desta tese é ajudar a preencher este fosso estabelecendo como as dissimilaridades plóidicas nos diversos momentos do ciclo de vida podem gerar abundâncias desiguais como as observadas no campo. Para tal a tese esta dividida em seis capítulos. No primeiro encontra-se uma introdução geral ao tema. No segundo foi investigado como diferentes tipos de taxas vitais podem ser forçadoras eficientes dos padrões de dominância plóidica. No terceiro foi investigado quão eficientemente os diversos tipos de taxas vitais podem impor uma variabilidade geográfica da dominância, tal como as relatadas para algumas espécies. No quarto capítulo é investigado como as respostas do ciclo de vida à instabilidade temporal estão dependentes das dissimilaridades entre ploidias para as taxas vitais, e como a variabilidade temporal pode surgir mesmo em ambientes estáveis. No quinto capítulo é investigado quão eficientemente os diferentes tipos de taxas vitais podem forçar um padrão intrapopulacional de dominância plóidica com uma resolução fina quer no espaço quer no tempo, conforme relatado na literatura. No sexto capítulo estão as conclusões gerais. As dissimilaridades plóidicas na sobrevivência dos talos e/ou performance dos esporos são as causas mais prováveis para os padrões de dominância observados.Fundação para a Ciência e Tecnologia (FCT

Detection of change in fluorescence between reactive cyan and the yellow fluorophores using a-SiC:H multilayer transducers

The transducer consists of a semiconductor device based on two stacked -i-n heterostructures that were designed to detect the emissions of the fluorescence resonance energy transfer between fluorophores in the cyan (470 nm) and yellow (588 nm) range of the spectrum. This research represents a preliminary study on the use of such wavelength-sensitive devices as photodetectors for this kind of application. The device was characterized through optoelectronic measurements concerning spectral response measurements under different electrical and optical biasing conditions. To simulate the fluorescence resonance energy transfer (FRET) pairs, a chromatic time-dependent combination of cyan and yellow wavelengths was applied to the device. The generated photocurrent was measured under reverse and forward bias to read out the output photocurrent signal. A different wavelength-biasing light was also superimposed. Results show that under reverse bias, the photocurrent signal presents four separate levels, each one assigned to the different wavelength combinations of the FRET pairs. If a blue background is superimposed, the yellow channel is enhanced and the cyan suppressed, while under red irradiation, the opposite behavior occurs. So, under suitable biasing light, the transducer is able to detect separately the cyan and yellow fluorescence pairs. An electrical model, supported by a numerical simulation, supports the transduction mechanism of the device

Logic functions based on optical bias controlled SIC Tandem devices

The purpose of this paper is the design of an optoelectronic circuit based on a-SiC technology, able to act simultaneously as a 4-bit binary encoder or a binary decoder in a 4-to-16 line configurations and show multiplexer-based logical functions. The device consists of a p-i'(a-SiC:H)-n/p-i(a-Si:H)-n multilayered structure produced by PECVD. To analyze it under information-modulated wave (color channels) and uniform irradiation (background) four monochromatic pulsed lights (input channels): red, green, blue and violet shine on the device. Steady state optical bias was superimposed separately from the front and the back sides, and the generated photocurrent was measured. Results show that the devices, under appropriate optical bias, act as reconfigurable active filters that allow optical switching and optoelectronic logic functions development providing the possibility for selective removal of useless wavelengths. The logic functions needed to construct any other complex logic functions are the NOT, and both or either an AND or an OR. Any other complex logic function that might be found can also be used as building blocks to achieve the functions needed for the retrieval of channels within the WDM communication link. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei

Impact of mobile app user acquisition on managerial decisions: Evidence from empirical experiment

In this research we conducted a mixed research, using qualitative and quantitative analysis to study the relationship and impact between mobile advertisement and mobile app user acquisition and the conclusions companies can derive from it. Data was gathered from management of mobile advertisement campaigns of a portfolio of three different mobile apps. We found that a number of implications can be extracted from this intersection, namely to product development, internationalisation and management of marketing budget. We propose further research on alternative app users sources, impact of revenue on apps and exploitation of product segments: wearable technology and Internet of Things

Use of a-SiC:H Semiconductor-Based Transducer for Glucose Sensing through FRET Analysis

Glucose sensing is an issue with great interest in medical and biological applications. One possible approach to glucose detection takes advantage of measuring changes in fluorescence resonance energy transfer (FRET) between a fluorescent donor and an acceptor within a protein which undergoes glucose-induced changes in conformation. This demands the detection of fluorescent signals in the visible spectrum. In this paper we analyzed the emission spectrum obtained from fluorescent labels attached to a protein which changes its conformation in the presence of glucose using a commercial spectrofluorometer. Different glucose nanosensors were used to measure the output spectra with fluorescent signals located at the cyan and yellow bands of the spectrum. A new device is presented based on multilayered a-SiC:H heterostructures to detect identical transient visible signals. The transducer consists of a p-i'(a-SiC:H)-n/p-i(a-Si:H)-n heterostructure optimized for the detection of the fluorescence resonance energy transfer between fluorophores with excitation in the violet (400 nm) and emissions in the cyan (470 nm) and yellow (588 nm) range of the spectrum. Results show that the device photocurrent signal measured under reverse bias and using appropriate steady state optical bias, allows the separate detection of the cyan and yellow fluorescence signals presented

SiC multilayer photonic structures with self optical bias amplification

Characteristics of tunable wavelength pi'n/pin filters based on a-SiC:H multilayered stacked cells are studied both experimental and theoretically. Results show that the device combines the demultiplexing operation with the simultaneous photodetection and self amplification of the signal. An algorithm to decode the multiplex signal is established. A capacitive active band-pass filter model is presented and supported by an electrical simulation of the state variable filter circuit. Experimental and simulated results show that the device acts as a state variable filter. It combines the properties of active high-pass and low-pass filter sections into a capacitive active band-pass filter using a changing photo capacitance to control the power delivered to the load