1,721,038 research outputs found
Light optimization and management technologies for increasing algal bioreactors efficiency
No full textIllumination in microalgae cultivation is a key factor for the achievement of target biomass productivity, and it is strongly influenced by operating variables of the plant. Traditionally, autotrophic microalgae cultivation at mid to large scale is carried out in outdoor open ponds, exploiting sun radiation. This approach often suffers from low photosynthetic efficiencies and low productivities limiting the spread of the microalgae market, which struggle to develop and to ensure the productivity required by an increasing bio-based industrial demand. This chapter is focused on strategies for managing light utilization and improving efficiency under both natural and artificial light. Outdoor cultivation technologies such as sunlight concentrators, spectral converters, and photovoltaics are discussed, among others. The aim is to avoid excessive stress and culture damages due to peak radiation and simultaneously produce electricity to increase the overall process efficiency. For what concerns the artificial light, the improvement in solid-state lighting technologies, represents an alternative to produce high amount of algae biomass, even though artificial lighting increases both capital and operating costs. The minimization of energy losses is then required to curtail the running costs of the system and can be obtained with two main approaches: focusing on spectral matching between the light source and the microalgae absorption; careful management of the reactor operation. The main outcome is that a low light intensity should be used to increase the energy conversion efficiency, carefully assessing the light compensation point. The use of flashing light also represents a viable approach to be considered
Complementary chromatic adaptation as a strategy to increase energy conversion efficiency of microalgae-cyanobacteria consortia in continuous LED photobioreactors
No full textPhototrophic cultivation of microalgae represents a potential sustainable process to obtain valuable commercial products, but the industrial cultivation is still hampered by low energy-to-biomass conversion efficiency. However, a number of cyanobacteria species evolved the ability to adapt to the prevailing light spectrum exploiting phycobiliproteins and Complementary Chromatic Adaptation (CCA). Spectral properties of such accessory pigments can be, hence, used to cover the green gap and possibly use light energy more efficiently. In this work, the green microalgae Tetradesmus obliquus and the chromatically adapting cyanobacterium Tolypothrix tenuis were cultivated as an alga-alga consortium in chemostat, aimed at increasing the light utilization efficiency in LEDs illuminated photobioreactors. When grown in co-culture, the advantage of consortium, with respect to monocultures, was maintained under different spectra, achieving an areal productivity up to 38 g m−2 d−1 under low red light. A remarkable photosynthetic conversion efficiency was reached under cocultivation, as a result of a wider absorption of photons with different wavelengths by the two species. Red light also resulted the most suitable one from the overall energy balance when artificial light is used. In this condition, by also considering the lamp efficiency, an overall conversion efficiency equal to 21% was reached (on Photosynthetically Active Radiations of RED light and calculated for the biomass of the two species together). The consortium performances were preliminary evaluated in continuous photobioreactors at pilot scale in 16 L and 160 L reactors, confirming the results obtained at lab scale. Hence, we found that is possible to efficiently convert light energy supplied to photobioreactors through a rationale use of light and widening wavelengths absorption spectrum thanks to co-existing species. Such results indicate that innovative consortia establishment can be advantageous for future research and industrial microalgae cultivation
Effect of blue light at 410 and 455 nm on Pseudomonas aeruginosa biofilm
No full textPseudomonas aeruginosa is an opportunistic pathogen resistant to many antibiotics, able to form biofilm and causes serious nosocomial infections. Among anti-Pseudomonas light-based approaches, the recent antimicrobial Blue Light (aBL) treatment seems very promising. The aim of this study was to evaluate the efficiency of blue light in inhibiting and/or eradicating P. aeruginosa biofilm. Light at 410 nm has been identified as successful in inhibiting biofilm formation not only of the model strain PAO1, but also of CAUTI (catheter-associated urinary tract infection) isolates characterized by their ability to form biofilm. Results of this work on 410 nm light also demonstrated that: i) at the lowest tested radiant exposure (75 J cm−2) prevents matrix formation; ii) higher radiant exposures (225 and 450 J cm−2) light impairs the cellular components of biofilm, adherent and planktonic ones; iii) light eradicates with a good rate young and older biofilms in a light dose dependent manner; iv) it is also efficient in inactivating catalase A, a virulence factor playing an important role in pathogenic mechanisms. Light at 455 nm, even if at a lower extent than 410 nm, showed a certain anti-Pseudomonas activity. Furthermore, light at 410 nm caused detrimental effects on enzyme activity of β-galactosidase and catalase A, and changes on plasmid DNA conformation and ortho-nitrophenyl-β-D-galactopyranoside structure. This study supports the potential of blue light for anti-infective and disinfection applications
Modeling Approach to Capture the Effect of High Frequency Flashing Light in Steady-State Microalgae Cultures
Full text linkWith the advent of efficient artificial light systems, the possibility of exploiting pulsed light (PL) in microalgal cultivation is gaining renewed attention. In this work, a model was developed to describeArthrospira maxima production in continuous cultivation systems, under both continuous and high-frequency pulsed light regimes. The model is based on the one originally developed by Camacho-Rubio, modified to link photosynthetic units activation to biomass growth, accounting also for maintenance. The modified model, calibrated in continuous light regime, was found to properly predict steady-state microalgal growth at different light intensities and residence times. The model was then validated on experimental data carried out under extreme PL conditions (high frequencies up to 3700 Hz and duty cycles as low as 0.01). Remarkably, it was able to account for the flashing light effect (FLE, i.e., increased biomass production with respect to continuous light supply) measured under such conditions and can therefore be a valuable tool to optimize the energetic efficiency of algal cultivation
Optoelectronic technologies to boost photobioreactors for algae production: from pulsed light sources to PV integrated net zero system
No full textMicro-Algae production has seen growth of interest as a renewable source of food, nutraceutical, and biofuels. In this work we studied the integration of light emitting diodes (LED) in photobioreactors (PBRs) to increase the algal production efficiency. A multiwavelength LED light source with selectable intensity able to operate under continuous wave irradiation (CW) or with high intensity, short pulses, has been developed. The efficiency of biomass production has been examined both for CW and pulsed operations. The efficiency obtained with the Photovoltaic (PV) + LED light source is then compared to that of the solar radiation to analyze the performances of an indoor and outdoor system
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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