1,720,986 research outputs found
Centimeter-long electrical transport in cable bacteria - structural and electro-optical properties
No full textThis thesis is the result of the first PhD research project within the research group X-LAB, which has the main objective of performing interdisciplinaryand exploratory research with the aim on a creative and sustainable future. The interdisciplinary research of this PhD project explores the boundary between microelectrobiology and bio- and organic electronics by bridging the gap between different disciplines (biology, physics, chemistry, electronics, ...). Bioelectronics is an upcoming interdisciplinary research field, where biological or biomimetic materials are used as building blocks in microelectronics or electro-optical applications, sensors and bio-energetic systems (e.g. microbial fuel cell).
In this thesis, which is the result of a collaboration with the group of prof. dr. ir. Filip Meysman, we study a recently discovered species of bacteria with exceptional electrical properties - the so called cable bacteria. Cable bacteria are intriguing microorganisms; they grow in marine or freshwater sediment and one bacterium (a ”filament”) can reach a length of up to 7 cm. One cable bacterium filament is a single chain of sometimes more than 10.000 cells, growing vertically between oxygen-rich seawater and into sulfide-rich sediment. The uptake of oxygen and sulfide is separated by centimeters distances, although these processes have to be able to exchange electrons to produce energy for the bacterium. It was therefore proposed that conductive fibers reside in the bacteria which transport the electrons over the whole length of the filament. For comparison, electron transport in photosynthesis or in other electrogenic bacteria (bacteria capable of extracellular electron transport) achieves distances in the range of a few nanometers to micrometers.
The overall goal of this thesis is to gain insight in the ’Terra Incognita’ of electrical transport in cable bacteria by an exploratory study of the morphological and intrinsic electro-optical properties. An interdisciplinary approach is used with methodologies also used in the study of organic and inorganic semiconductors. This PhD thesis consists of a bundle of manuscripts preceded by a number of introductory chapters.
The first chapter describes what cable bacteria are, and how they are able to survive in marine sediment. Electrogenic bacteria - bacteria that are able to conduct electrons over long distances - are used as modelorganisms to better understand electron transport in cable bacteria. Cable bacteria also have a direct effect on their environment. For example, it was discovered that they promote the formation a ’firewall’ which prevents the release of toxic sulfides into the seawater. The introduction ends with some applications of electrogenic bacteria, including power generation and biofuel production. Possibly, cable bacteria could also be used for these and other applications in the future (microbial fuel cells, sensors, ...).
Since the discovery of cable bacteria in 2012, only a few articles have further explored their architecture. In paper A of this thesis we measured the overall dimensions of differently sized cable bacteria, and built a quantitative structural model. A unique feature of cable bacteria is that the outer membrane is deformed; the full contour of a cell has ridges which run continuously over the whole length of the filament. The conductive fibers are believed to be embedded in these ridges. By making cross-sections at several locations in a filament, it became clear that fiber-like structures are indeed located in the periplasm (the space between the outer and inner cell membrane), and that they cross the gap between adjacent cells. Between two cells the outer membrane folds inwards, surrounding the radial connections in a cartwheel-like structure. Our colleagues from UAntwerp and TU Delft developed a procedure to remove the membranes and cytoplasm from cable bacteria. This way, they were able to retain the fibers which remained connected to an underlying sheath and at the junctions. This extracted fiber sheath, when proven to be electrically conductive, might be very interesting for future use in bioelectronic applications.
Although record-breaking electron transport distances have been attributed to cable bacteria, it has proven difficult to directly measure a current flow through a filament. Normally, it is sufficient to connect an electrogenic bacterium between two conductive electrodes, and subsequently measure a current with an applied voltage. Up to now this has never succeeded for cable bacteria, and it was presumed that their outer membrane was electrically insulating. Paper B in this thesis describes how we were able to measure for the first time the electrical properties, which is a significant breakthrough in electrobiology. The conductivity of the bacteria was observed to decay upon contact with oxygen; after a few hours the bacteria were again electrically insulating. Electrical measurements on single filaments yielded the conductivity of a single fiber (~11.5 S cm -1), which is of the same order of magnitude as some organic semiconductors. Furthermore, we measured a current through a filament of a length of 10.1 mm, which make cable bacteria the biological record holders for long-distance electron transport. We determined that the extracted fiber sheath from the first article is also electrically conductive, making them the primary conductive structures responsible for long-distance electron transport in cable bacteria. Further study of the electrical properties is required to gain insight in the potential of applying these structures in e.g. bio-electronics.
The use of cable bacteria in photovoltaics or as (transparent) electrodes depends among other things on the optical properties, such as emission and absorbance spectra. Paper C in this thesis is an exploration of the optical properties of cable bacteria. One result of this study is that cable bacteria fluoresce when removed from their natural environment. The autofluorescence originates from the cell envelope and from the junctions, indicating a relation with the metabolic cycles. We also used a technique which is rarely used in biology, photothermal deflection spectroscopy. It measures the emission of heat after illumination with varying photon energy, yielding a measure for the absorbance of cable bacteria. These investigations yielded the photon emission and photothermal spectra of cable bacteria. Further research is needed to gain insight into the autofluorescence behavior and the possible relation with the electrical properties.
This thesis ends with the conclusions and outlook with some future research ideas.UHasselt, FW
Centimeter-long electrical transport in cable bacteria - structural and electro-optical properties
No full textThis thesis is the result of the first PhD research project within the research group X-LAB, which has the main objective of performing interdisciplinaryand exploratory research with the aim on a creative and sustainable future. The interdisciplinary research of this PhD project explores the boundary between microelectrobiology and bio- and organic electronics by bridging the gap between different disciplines (biology, physics, chemistry, electronics, ...). Bioelectronics is an upcoming interdisciplinary research field, where biological or biomimetic materials are used as building blocks in microelectronics or electro-optical applications, sensors and bio-energetic systems (e.g. microbial fuel cell).
In this thesis, which is the result of a collaboration with the group of prof. dr. ir. Filip Meysman, we study a recently discovered species of bacteria with exceptional electrical properties - the so called cable bacteria. Cable bacteria are intriguing microorganisms; they grow in marine or freshwater sediment and one bacterium (a ”filament”) can reach a length of up to 7 cm. One cable bacterium filament is a single chain of sometimes more than 10.000 cells, growing vertically between oxygen-rich seawater and into sulfide-rich sediment. The uptake of oxygen and sulfide is separated by centimeters distances, although these processes have to be able to exchange electrons to produce energy for the bacterium. It was therefore proposed that conductive fibers reside in the bacteria which transport the electrons over the whole length of the filament. For comparison, electron transport in photosynthesis or in other electrogenic bacteria (bacteria capable of extracellular electron transport) achieves distances in the range of a few nanometers to micrometers.
The overall goal of this thesis is to gain insight in the ’Terra Incognita’ of electrical transport in cable bacteria by an exploratory study of the morphological and intrinsic electro-optical properties. An interdisciplinary approach is used with methodologies also used in the study of organic and inorganic semiconductors. This PhD thesis consists of a bundle of manuscripts preceded by a number of introductory chapters.
The first chapter describes what cable bacteria are, and how they are able to survive in marine sediment. Electrogenic bacteria - bacteria that are able to conduct electrons over long distances - are used as modelorganisms to better understand electron transport in cable bacteria. Cable bacteria also have a direct effect on their environment. For example, it was discovered that they promote the formation a ’firewall’ which prevents the release of toxic sulfides into the seawater. The introduction ends with some applications of electrogenic bacteria, including power generation and biofuel production. Possibly, cable bacteria could also be used for these and other applications in the future (microbial fuel cells, sensors, ...).
Since the discovery of cable bacteria in 2012, only a few articles have further explored their architecture. In paper A of this thesis we measured the overall dimensions of differently sized cable bacteria, and built a quantitative structural model. A unique feature of cable bacteria is that the outer membrane is deformed; the full contour of a cell has ridges which run continuously over the whole length of the filament. The conductive fibers are believed to be embedded in these ridges. By making cross-sections at several locations in a filament, it became clear that fiber-like structures are indeed located in the periplasm (the space between the outer and inner cell membrane), and that they cross the gap between adjacent cells. Between two cells the outer membrane folds inwards, surrounding the radial connections in a cartwheel-like structure. Our colleagues from UAntwerp and TU Delft developed a procedure to remove the membranes and cytoplasm from cable bacteria. This way, they were able to retain the fibers which remained connected to an underlying sheath and at the junctions. This extracted fiber sheath, when proven to be electrically conductive, might be very interesting for future use in bioelectronic applications.
Although record-breaking electron transport distances have been attributed to cable bacteria, it has proven difficult to directly measure a current flow through a filament. Normally, it is sufficient to connect an electrogenic bacterium between two conductive electrodes, and subsequently measure a current with an applied voltage. Up to now this has never succeeded for cable bacteria, and it was presumed that their outer membrane was electrically insulating. Paper B in this thesis describes how we were able to measure for the first time the electrical properties, which is a significant breakthrough in electrobiology. The conductivity of the bacteria was observed to decay upon contact with oxygen; after a few hours the bacteria were again electrically insulating. Electrical measurements on single filaments yielded the conductivity of a single fiber (~11.5 S cm -1), which is of the same order of magnitude as some organic semiconductors. Furthermore, we measured a current through a filament of a length of 10.1 mm, which make cable bacteria the biological record holders for long-distance electron transport. We determined that the extracted fiber sheath from the first article is also electrically conductive, making them the primary conductive structures responsible for long-distance electron transport in cable bacteria. Further study of the electrical properties is required to gain insight in the potential of applying these structures in e.g. bio-electronics.
The use of cable bacteria in photovoltaics or as (transparent) electrodes depends among other things on the optical properties, such as emission and absorbance spectra. Paper C in this thesis is an exploration of the optical properties of cable bacteria. One result of this study is that cable bacteria fluoresce when removed from their natural environment. The autofluorescence originates from the cell envelope and from the junctions, indicating a relation with the metabolic cycles. We also used a technique which is rarely used in biology, photothermal deflection spectroscopy. It measures the emission of heat after illumination with varying photon energy, yielding a measure for the absorbance of cable bacteria. These investigations yielded the photon emission and photothermal spectra of cable bacteria. Further research is needed to gain insight into the autofluorescence behavior and the possible relation with the electrical properties.
This thesis ends with the conclusions and outlook with some future research ideas.UHasselt, FW
Charge-transfer states in photosynthesis and organic solar cells
No full textLight-induced charge-transfer mechanisms are at the heart of both photosynthesis and photovoltaics. The underlying photophysical mechanisms occurring within photosynthesis and organic photovoltaics in particular show striking similarities. However, they are studied by distinct research communities, often using different terminology. This contribution aims to provide an introductory review and comparison of the light-induced charge-transfer mechanisms occurring in natural photosynthesis and synthetic organic photovoltaics, with a particular focus on the role of so-called charge-transfer complexes characterized by an excited state in which there is charge-transfer from an electron-donating to an electron-accepting molecular entity. From light absorption to fully separated charges, it is important to understand how a charge-transfer complex is excited, forming a charge-transfer state, which can decay to the ground state or provide free charge carries in the case of photovoltaics, or radicals for photochemistry in photosynthetic complexes. Our motivation originates from an ambiguity in the interpretation of charge-transfer states. This review attempts to standardize terminology between both research fields with the general aim of initiating a cross-fertilization between the insights and methodologies of these two worlds regarding the role of charge-transfer complexes, inspiring the cross-disciplinary development of next-generation solar cells. Likewise, we hope to encourage photosynthesis researchers to collaborate with the photovoltaics field, thereby gaining further knowledge of the charge-transfer process in natural light-harvesting systems.Funding
This research was supported by the Research Foundation—Flanders (FWO) with research project G089918N (JH and JM).
Acknowledgments
The authors thank the colleagues from X-LAB from UHasselt for discussions and feedback
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
ESA–BEXUS project: OSCAR - Zonne-Energie Voor De Planeet Aarde En Verder
No full textZonne–energie is ontegensprekelijk één van de belangrijkste en duurzaamste oplossingen voor de globale energie– en klimaatuitdagingen waar onze planeet voor staat. Nieuwe generatie printbare, plooibare en ultra–dunnen zonnecellen kunnen bovendien leiden tot tal van nieuwe toepassingen, gaande van energie–bevoorrading voor draag bare elektronica (smartphones, tablets, …) tot grensverleggende toepassingen voor toekomstige ruimtereizen. Printbare organische en perovskiet–zonnecellen zijn namelijk de wereldkampioenen qua verhouding energie–opbrengst versus gewicht. Voor toekomstige ruimtevaartmissies hebben deze zonnecellen dus de bijzondere voordelen dat ze een ultra–licht gewicht hebben, plooibaar en uitvouwbaar zijn en bovendien ter plaatse (in ruimteschepen of in ruimtestations op bijvoorbeeld de Maan of op Mars) kunnen geprint worden.
Door deelname aan het BEXUS–programma (Balloon Experiments for University Students) van de Europese ruimtevaartorganisatie ESA, hebben een team van negen UHasselt–doctoraatstudenten en studenten Fysica (Miguel–Angel Beynaerts, Ilaria Cardinaletti, Rob Cornelissen, Jaroslav Hruby, Steven Nagels, Dieter Schreurs, Jelle Vodnik, Tim Vangerven & Koen Wouters) een wereldrecord gebroken qua gebruik van printbare zonnecellen op grote hoogte. Met het OSCAR–project (Optical Sensors based on CARbon Materials) hebben ze voor het eerste de prestaties van printbare zonnecellen en van een nieuwe magnetische–veldsensor bestudeerd in echte ruimtevaartcondities. Vanuit het lanceerstation Kiruna in Zweden werd een onderzoeksballon in de stratosfeer gebracht — op 32 kilometer hoogte (3x hoogte van vliegtuigtrajecten) — waarbij extreme condities heersen zoals lage luchtdruk, lage temperaturen (tot wel –60 graden Celsius) en een pak meer straling van de zon
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
BEXUS 23 OSCAR: Solar Cell I-V Monitoring System for Space Environments
No full textNovel thin film solar cells exhibit unprecedented specific power, which is a key figure of merit for space applications. To get a first indication of their possible degradation in space environments, the OSCAR (‘Optical Sensors based on CARbon materials’) team has built a solar cell performance monitoring system and deployed it on the BEXUS 23 flight. This paper reports the design, testing and performance of said system. Our system
performed impeccably over its 4h mission course, maintaining communication and reliably reporting solar cell I-V curves. It forms a guideline for anyone who needs to measure millivolts and microamperes in similar conditions, monitor solar cells on remote locations or wants to follow up on degradation of thin film solar cells in space
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