657 research outputs found

    Flexible and Polymer-based CO2 Sensors for Food Packaging and Other Potential Applications

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    CO2 sensing is important in many applications ranging from air-quality monitoring to food packaging. Despite all the advancements in CO2 sensor technology, they are typically qualitative, bulky, expensive, and cross-sensitive to humidity, require high operating temperatures, external power sources, and complicated manufacturing processes making them incompatible with integration into food packaging. In light of this, the present study aims to develop chemiresistive, flexible, miniaturised, low-cost, lowpower, and simple-to-manufacture sensors capable of CO2 measurement at room temperature and high humidity conditions for food packaging and other potential applications. This thesis aims to develop chemiresistive, flexible, miniaturised, low-cost, low-power CO2 sensors for applications such as food packaging. The sensors are based on CO2-responsive polymers that change their electrical properties upon CO2 absorption. The interaction between CO2 and the polymer relies on acid-base chemistry, resulting in protonation of amine groups and altering the resistance. Initially, poly(N-[3-(dimethylamino)propyl] methacrylamide) (pDMAPMAm) is synthesised, but it exhibits irreversible response due to hindered proton hopping. To address this, poly(N-[3- (dimethylamino)propyl]-methacrylamide-co-2-N-morpholinoethyl methacrylate) (p(D-co-M)) with adjusted composition and basicity is developed, showing a reversible response to CO2. However, it has relatively long response and recovery times and cross-sensitivity to ammonia. To improve these shortcomings, a thin layer of Nafion-Na coating is applied to the p(D-co-M) sensor, denoted P-NafionNa sensors, reducing cross-sensitivity, shortening recovery time, and enabling Bluetooth® communication. The developed materials and sensors show promise for creating the next generation of miniaturised, flexible, wireless, and cost-effective CO2 sensors for various applications, including food quality monitoring

    Towards light-driven catalysis in block copolymer micelles

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    Im Rahmen dieser Arbeit wurden die Synthese, Charakterisierung und Untersuchungen polymerbasierter, sogenannter „weicher“ Materie als Matrizen für lichtgetriebene Redoxreaktionen behandelt. Der erste Teil dieser Arbeit umfasste die Präparation von pH-responsiven Mizellen in Wasser auf Grundlage von maßgeschneiderten, amphiphilen Blockcopolymeren, wobei unter anderem die im hydrophilen Teil vorhandenen Liganden zur Anbindung von Übergangsmetallkomplexen genutzt wurden. Auf diese Weise konnten (photo)katalytisch aktive Zentren innerhalb der pH-sensitiven Corona der Mizellen integriert werden. Mit diesem Ansatz war es möglich, mittels Konformationsänderungen der Corona der Mizellen deren Aktivität in verschiedenen, photokatalytischen Systemen experimentell zu kontrollieren und mit theoretischen Modellen zu analysieren. Der zweite Teil dieser Abhandlung widmete sich der Verwendung eines alternativen, polaren und funktionalisierbaren Monomer zum Aufbau analoger Blockcopolymerarchitekturen in methanolischen Lösungen sowie einer Anwendung in photokatalytischen Prozessen. Es ließen sich auf der chemischen Struktur basierende Indizien einer weit über die bloße mechanische Integration hinausreichende Funktion der Matrix feststellen. Dies wurde auch durch eine gesamtheitliche Betrachtung beider Systeme herausgearbeitet. Der dritte Teil dieser Arbeit fokussierte sich auf photokatalytische Modellsysteme, um Fallstudien zur Reproduzierbarkeit in einem modularen Photoreaktor durchzuführen. Ein weiteres Modellsystem wurde für eine didaktische Anwendung zugänglich gemacht. Mit dieser Arbeit war es möglich einen substanziellen Beitrag zur weichen Materie-vermittelten lichtgetriebenen Katalyse zu leisten. Dies geschah sowohl durch die Präsentation von Konzepten zur Integration derartiger Systeme in weicher Materie als auch der resultierenden Möglichkeit stoffliche und energetische Mechanismen in solchen Matrizen nachzuvollziehen

    Comprehensive review of materials, applications, and future innovations in biodegradable esophageal stents

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    Esophageal stricture (ES) results from benign and malignant conditions, such as uncontrolled gastroesophageal reflux disease (GERD) and esophageal neoplasms. Upper gastrointestinal endoscopy is the preferred diagnostic approach for ES and its underlying causes. Stent insertion using an endoscope is a prevalent method for alleviating or treating ES. Nevertheless, the widely used self-expandable metal stents (SEMS) and self-expandable plastic stents (SEPS) can result in complications such as migration and restenosis. Furthermore, they necessitate secondary extraction in cases of benign esophageal stricture (BES), rendering them unsatisfactory for clinical requirements. Over the past 3 decades, significant attention has been devoted to biodegradable materials, including synthetic polyester polymers and magnesium-based alloys, owing to their exceptional biocompatibility and biodegradability while addressing the challenges associated with recurring procedures after BES resolves. Novel esophageal stents have been developed and are undergoing experimental and clinical trials. Drug-eluting stents (DES) with drug-loading and drug-releasing capabilities are currently a research focal point, offering more efficient and precise ES treatments. Functional innovations have been investigated to optimize stent performance, including unidirectional drug-release and anti-migration features. Emerging manufacturing technologies such as three-dimensional (3D) printing and new biodegradable materials such as hydrogels have also contributed to the innovation of esophageal stents. The ultimate objective of the research and development of these materials is their clinical application in the treatment of ES and other benign conditions and the palliative treatment of malignant esophageal stricture (MES). This review aimed to offer a comprehensive overview of current biodegradable esophageal stent materials and their applications, highlight current research limitations and innovations, and offer insights into future development priorities and directions

    Fully epitaxial fcc(111) magnetic tunnel junctions with a Co90Fe10/MgAlO/Co90Fe10 structure

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    Magnetic tunnel junctions (MTJs) with bcc(001)-type structures such as Fe(001)/MgO(001)/Fe(001), have been widely used as the core of various spintronic devices such as magnetoresistive memories; however, the limited material selection of (001)-type MTJs hinders the further development of spintronic devices. Here, as an alternative to the (001)-type MTJs, an fcc(111)-type MTJ using a fully epitaxial CoFe/rock-salt MgAlO (MAO)/CoFe is explored to introduce close-packed lattice systems into MTJs. Using an atomically flat Ru(0001) epitaxial buffer layer, fcc(111) epitaxial growth of the CoFe/MAO/CoFe trilayer is achieved. Sharp CoFe(111)/MAO(111) interfaces are confirmed due to the introduction of periodic dislocations by forming a 5:6 in-plane lattice matching structure. The fabricated (111) MTJ exhibits a tunnel magnetoresistance ratio of 37% at room temperature (47% at 10 K). Symmetric differential conductance curves with respect to bias polarity are observed, indicating the achievement of nearly identical upper and lower MAO interface qualities. Despite the charge-uncompensated (111) orientation for a rock-salt-like MAO barrier, the achievement of flat, stable, and spin-polarized barrier interfaces opens a promising avenue for expanding the design of MTJ structures.Comment: 18 pages, 5 figure

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    School of Energy and Chemical Engineering (Energy Engineering)Solar water splitting is regarded as alternative technology to produce green hydrogen with sustainable solar energy, which enable to reduce massive carbon emissions released from a grey hydrogen production. Water splitting process consist of two half-reactions???hydrogen (HER) and oxygen evolution reaction (OER)???and is conducted by semiconductor photoabsorbers modified with various types of catalysts. For efficient solar water splitting, structural and compositional modification of catalysts have been studied to improve their charge separation and transfer efficiency, and it has focused on the development of inorganic based catalysts so far. However, it has revealed that a main role of inorganic catalysts is increase of charge separation rather than water oxidation kinetics, thereby showing limited PEC performance in solar water splitting. In this regard, we introduced functional molecular multilayers including various types of polyelectrolyte and molecular polyoxometalate (POM) catalyst to enhance charge separation and transfer efficiency together. Polyelectrolytes and POM were deposited by solution-processable method through electrostatic force of each component, and molecular multilayers showed improved solar water splitting efficiency compared to conventional inorganic catalysts. Furthermore, we also confirmed that PEC property of photoelectrodes could be modulated by surface treatment with polyelectrolyte multilayers, providing highly efficient solar water splitting, even without molecular catalysts. Our photoelectrochemical investigation conducted by electrochemical impedance spectroscopy and rate law analysis suggested that functional multilayers enable to achieve efficient charge separation and transfer by surface state passivation and facile charge injection from polyelectrolyte and POM, respectively. To the best of our knowledge, functional molecular multilayers is a first approach to accomplish overall enhancement of water splitting catalysts, and we believe that our study provides new insight for modification of catalysts to elevate the efficiency of solar water splitting as distinct from conventional catalysts.ope

    Organic photosensitizers for light-driven hydrogen evolution: synthesis, characterization and application

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    This work utilizes organic chromophores, namely perylene dyes and BODIPYs, as light-active component in light-driven hydrogen evolution

    Rendering Bodies: The Abattoir in Modern Art and Photography

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    The prevalence of images of the fragmented bodies of nonhuman animals is largely unaccounted for in the history of interwar European art, photography, and cinema, a result of the historical marginalization of the slaughterhouse to the edges of Western culture. But despite, and sometimes because of, the suppression of the visibility of the abattoir, visions of the grisly world of modern animal production form a sizeable and important subset of avant-garde art, photography, film, and literature beginning in the 1920s. No significant studies have placed images of real, disassembled animals into a broader account of avant-garde photography, nor have they made the connection between the great increase in photographic and filmic art and media in the period and the simultaneously rapid growth of animal production leading up to and during it. I argue that the interwar period witnessed a profound interplay between the industrial slaughterhouse, visual culture, and avant-garde art, marked by the dual meaning of Nicole Shukin’s conceptualization of rendering as both the creating of images of and the material processing of nonhuman animal bodies. I assert that through the use of animal-derived gelatin, the industrial processing of animals helped to fuel the explosive growth of photography, cinema, and thus visual culture in the period. I examine a number of examples of artistic and photographic works that picture slaughter animals, ironically through a medium (photography) that is materially tied to the history and conditions of the abattoir, revealing a poignant connection between the content of the images seen and the form of their material substrate. I further read the photographic projects under study in this dissertation as each in their own way turning our attention to the material precarity of the animal body, both human and nonhuman, and a questioning of the human/animal divide that had been accelerating since the nineteenth century

    Sunlight-driven generation of singlet oxygen via porphyrin-coated membranes

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    Self-assembled porous polymer films for improved oxygen sensing

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    Absolute oxygen sensors based on quenching of phosphorescence have been the subject of numerous studies for the monitoring of biological environments. Here, we used simple fabrication techniques with readily available polymers to obtain high performance phosphorescent films. Specifically, evaporation-based phase separation and the breath figure technique were used to induce porosity. The pore sizes ranged from ∼ 37 nm to ∼ 141µm while the maximum average porosity achieved was ∼ 74%. The oxygen sensing properties were evaluated via a standarised calibration procedure with an optoelectronic setup in both transmission and reflection based configurations. When comparing non-porous and porous films, the highest improvements achieved were a factor of ∼ 7.9 in dynamic range and ∼ 7.3 in maximum sensitivity, followed by an improved linearity with a half-sensitivity point at 43% O2 V/V. Also, the recovery time was reduced by an order of magnitude in the high porosity film and all samples prepared were not affected by variations in the humidity of the surrounding environment. Despite the use of common polymers, the fabrication techniques employed led to the significant enhancement of oxygen sensing properties and elucidated the relation between porous film morphologies and sensing performance

    ICT organisations' minimal compliance with affirmative actions regulations: case of the Broad-Based Black Economic Empowerment (B-BBEE) ICT sector code in South Africa

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    Research problem: Broad-Based Black Economic Empowerment (B-BBEE) is a legal framework established by the South African government to eradicate racial and gender exclusionary elements from the apartheid regime. This refers to the process called economic transformation. The B-BBEE Information Communication and Technology (ICT) Sector Code is the primary regulatory instrument for regulating ICT organisations' economic transformation activities. Organisational minimal compliance with the B-BBEE ICT Sector Code is the primary obstacle to including Black people in ICT business. Minimal compliance is a compliance behaviour that looks good on the letter of the law but does not transform the intended systems. While ICT organisations have good B-BBEE certificates, the points earned in the compliance process have not been translating into transformation. In 2020, 17 years after the introduction of the B-BBEE Act, the ICT Sector Council reported that ICT organisations had not made real progress in racial inclusivity in ownership and management structures. Minimal compliance with the B-BBEE ICT Sector Code reveals a policy enforcement dilemma where compliance with regulation makes no social change. Purpose of the research: The study interrogated how contextual factors affect minimal compliance with affirmative action regulations such as the B-BBEE ICT Sector Code. The study is a response to the call for Information Systems researchers to investigate the role of ICTs in achieving social justice and the socio-technical aspects that affect ICT enterprises. Investigating these kinds of regulations in Information Systems research also reveals how ICT business interacts with aspects of the socio-political context in post-colonial contexts such as South Africa. Methodology: This is a qualitative inquiry guided by a critical research paradigm. Data was collected through interviews, observations, and document analysis in various touchpoints of the B-BBEE ICT Sector Code. We employed thematic analysis and content analysis to analyse the research data. We developed a conceptual framework that suggests that minimal compliance stems from the need to protect the achievement of organisational goals. Key findings: Factors that affect minimal compliance with the B-BBEE ICT Sector Code are the organisational perception of the policy implementation context, organisational logic of action, and organisational legitimisation. ICT organisations leverage regulatory loopholes (e.g., pointsystem compliance) in the B-BBEE ICT Sector Code to comply with it in a manner that does not add value for the beneficiaries but allows them to achieve their organisational goals. ICT organisations responded to B-BBEE regulatory requirements through two utilitarian logics (goal prioritisation and maintaining status quo). Businesses are pragmatic institutions! This phrase surfaces every time a question B-BBEE compliance comes up. When they introduced the point-system compliance, B-BBEE policymakers did not consider the granular details concerning the complexity inherent in the South African historical context that would affect Black people's involvement in the digital economy. Quantifying the involvement of Black people in the ICT sector has resulted in the commoditisation of gender and race – making the beneficiaries the means to an end through B-BBEE points. The point-system compliance mechanism is the supreme loophole of the B- BBEE policy implementation context. The point-system enforcement mechanism propels ICT organisations to protect the achievement of their economic goals while neglecting the transformation agenda. Ideological discourses such as “B-BBEE compliance is anti-FDI, BBBEE compliance is costly, and B-BBEE compliance is complex” continue to thrive as legitimisation mechanisms to justify minimal compliance behaviour and its outcome. Research contribution: The study is rich with new knowledge about ICT organisational response to affirmative action policies in post-colonial contexts. The focus on the B-BBEE ICT Sector Code revealed policy discrepancies that future policymakers may consider ensuring that transformation takes place. International actors may benefit from the study's practical contribution to B-BBEE compliance processes, and the stakeholders involved. The study contributes to theory by proposing a conceptual framework for minimal compliance behaviour. The conceptual framework proposes three factors to be considered while analysing compliance behaviour: policy implementation context, organisational logics of action, and organisational legitimisation. Through this conceptual framework, the study shows that minimal compliance behaviour is mostly viewed as a binary behaviour – compliance or noncompliance. The compliance behaviour that looks good in the letter of the law but does not solve the problems that warrant policy introduction is taken for granted. The methodological contribution of the study rests in the use of multiple data sources that provided a heterogeneous perspective on B-BBEE compliance. Moreover, a critical interrogation of compliance behaviour is instrumental in illuminating mechanisms used by dominant powers to maintain hegemony by going around the regulations
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