2,293 research outputs found
The Greece of the Greeks: By G.A. Perdicaris, A.M. Late Consul of the United Stats at Athens, in two volumes. New-York: Paine and Burgess, 1845.
No full textIntroduction: (introductory) by the authorDedication: by the author to those who are interested in the Fate of GreecePagination: PP21+293P, PP8+300P+1PPVolumes: 2Edition:1stText Genre:Prose / Journa
Activation, Reactivity and Dynamics of Manganese Pincer Complexes in Hydrogenation Catalysis
No full textThe growing demands for sustainable chemical technologies have prompted a wave of searching new catalysts based on earth-abundant metals. In the field of (de)hydrogenation catalysis, however, the huge performance gap is commonly seen between the 3d-metal-based catalysts and their noble metal counterparts, which largely hampers their practical applications. In particular, while the Mn-catalyzed (de)hydrogenation has witnessed significant progress since the pioneering work by Beller and co-workers in 2016, most of the reported systems still require relatively high catalyst loadings. Apart from developing new synthetic methodologies based on the hydrogen transfer reactivity of Mn, searching highly active catalysts for (de)hydrogenation reactions therefore remains one of the central topics in Mn chemistry. The current approach to catalyst development is mainly based on the screening of the ligand backbones that proved to be effective for noble metal-based catalysts. However, the screening assessments with the reaction yields as the sole performance metrics do not probe the intrinsic reactivities of the catalysts and can easily result in the overlook of the potential ones due to suboptimal condition choice. In this thesis, we demonstrate in this thesis that the catalyst performance is defined by a complex reaction network comprised of multiple stages of catalyst operation, that is catalyst activation, deactivation, and catalytic turnover. The reactivity of the catalyst itself and the reaction environment of each process determine synergistically the catalytic performance. As a result, the catalytic transformation should be viewed from the system perspective with the performance being a dynamic and highly condition-dependent characteristic.ChemE/Inorganic Systems Engineerin
Automatic sign language recognition inspired by human sign perception
No full textAutomatic sign language recognition is a relatively new field of research (since ca. 1990). Its objectives are to automatically analyze sign language utterances. There are several issues within the research area that merit investigation: how to capture the utterances (cameras, magnetic sensors, instrumented gloves), how to extract interesting information from the captured data, and how to classify signs or sentences automatically using the extracted information. These issues are of an immediate and basic nature, and must be solved before any automatic recognition of sign language can be achieved. But other issues, pertaining to the nature of sign language and human recognition, are no less interesting: which elements of a sign are important for the meaning of an utterance? How do consecutive signs influence one another? Why are certain types of variation unimportant while others change the meaning of the sign? Automatic sign language recognition has, until recently, mostly focused on the first set of issues. In this thesis, we attempt to integrate knowledge about sign languages and human sign recognition into the automatic sign recognition process. Research on the (psycho)linguistics of sign languages is itself quite young (since ca. 1960), and many questions as yet unanswered. For this reason, we conduct our own studies of human sign language recognition. The knowledge gained from these experiments is applied in an existing automatic sign language recognition system. The thesis is divided into two parts: the first part describes the experiments conducted with human signers, the second part describes experiments investigating the possibilities of integrating such knowledge in the automatic recognizer. This recognizer is meant to be used in an interactive environment for young children to practice sign language vocabulary. For this reason, it is vision-based (which is unobtrusive), and only handles isolated signs. The experiments in part I of the thesis investigate the information content of various sign elements: fragments of a sign in time (chapter 2), and the sign aspects handshape and hand orientation (chapter 3). In time, the central phase of a sign is the most informative one, equally informative to the entire sign. Recognition based on other phases is also possible to a certain extent, and the transition from the preparation phase to the central phase appears to be a salient moment. As for the aspects, the aspect handshape proves more useful for recognition than hand orientation. Chapter 4 gives an overview of the human recognition research and discusses possibilities for application. In part II, the possibilities of utilizing the results of part I in the recognition system are investigated. Chapter 5 describes the addition of the handshape feature to the system (which chapter 3 showed to be the most interesting feature to add). Adding handshape gives a small improvement in the recognition performance. In chapter 6, the salience of the sign fragments used in chapter 2 for the automatic recognizer is investigated. The central phase proves to be the most informative one, as it was for human signers. Chapter 7 describes experiments in which a small set of frames is used to represent a sign. The results show a deterioration in recognition performance. Strict demands on the correctness of the remaining frames are probably partly responsible for the performance decrease. In conclusion, we can say that applying human knowledge in automatic sign language recognition is a complex task. Conclusions about human sign recognition do not necessarily hold for the automatic recognizer as well. The most important obstacles for utilizing information successfully seem to be: 1) data acquisition: computer vision is not as accomplished as human observers in capturing the complex, dynamic hand and face motions that form sign language. This means that information that is present in a sign movement for a human being may not be (correctly) observed by an automatic vision analysis system. Thus, the data that humans work with is not necessarily identical to the data the recognizer works with, and this may cause techniques that are successful for human signers to fail in the automatic system. And 2) differences in basic system architecture. Research into human sign recognition is still ongoing, there is no clear model of human sign recognition yet. This makes it more difficult to translate observations from human sign recognition to the automatic recognizer: human signers may use techniques that are not compatible with the current architecture of the recognizer. For example: human signers may process aspects independently. If the recognition system processes all data as a single stream, then such a technique cannot be implemented. A more thorough understanding of human sign recognition, more sophisticated computer vision techniques, and a close co-operation between the fields of automatic sign language recognition and human sign perception, seems the best way to overcome these obstacles.MediamaticsElectrical Engineering, Mathematics and Computer Scienc
Environmentally Sensitive Luminescence Reveals Spatial Confinement, Dynamics, and Their Molecular Weight Dependence in a Polymer Glass
No full textPolymer glasses have an irregular structure. Among the causes for such complexity are the chemically distinct chain end groups that are the most abundant irregularities in any linear polymer. In this work, we demonstrate that chain end induced defects allow polymer glasses to create confined environments capable of hosting small emissive molecules. Using environmentally sensitive luminescent complexes, we show that the size of these confinements depends on molecular weight and can dramatically affect the photoluminescence of free or covalently bound emissive complexes. We confirm the impact of chain end confinement on the bulk glass transition in poly(methyl acrylate) (pMA) and show that commonly observed Tg changes induced by the chain ends should have a structural origin. Finally, we demonstrate that the size and placement of luminescent molecular probes in pMA can dramatically affect the probe luminescence and its temperature dependence, suggesting that polymer glass is a highly irregular and complex environment, marking its difference with conventional small molecule solvents. Considering the ubiquity of luminescent glassy materials, our work lays down a blueprint for designing them with structural considerations in mind, ones where packing density and chain end size are key factors.ChemE/Advanced Soft MatterChemE/Inorganic Systems Engineerin
Combined Self-Healing Method for Lifetime Extension in Asphalt: A Mechanical and Sustainability Assessment
No full textOver the last 15 years or so, research has revealed the great self-healing prospects possessed by asphaltic mixtures. Researchers have proposed novel methods to harness this capability, aiming to prolong the service life of asphalt pavement, particularly in porous asphalt. To date, the most promising of the healing methods is the combined capsule-induction system. This thesis aims to ascertain whether such a system would show positive results in stone mastic asphalt (SMA). Following that, an optimisation of the composition of self-healing SMA was proposed by assessing the mechanical and healing properties via laboratory testing. Finally, an evaluation of sustainability from an environmental perspective was done using Life Cycle Analysis (LCA) methodology. Results of the healing assessment revealed that each combined healing system was able to recover between 58-63\% of its original fracture strength after 8 healing cycles, while the reference mix (without healing) was only able to regain 10\% fracture strength before failure after 2 cycles. Inclusion of the combined healing system slightly reduced the strength, stiffness and water sensitivity of the SMA mixture compared to the reference. However, improved rutting resistance was observed in each self-healing case. Within the self-healing mixtures, increasing capsule content reduced asphalt density, stiffness and strength and resulted in an increase in asphalt void content.The LCA results show that the self-healing system had environmental benefits in some facets such as a 14\% reduction in fossil fuel resource depletion and a 21\% reduction in land use. However, the present total known environmental costs of other impacts are approximately 15\% lower in the reference system based on a cradle to gate, and use phase analysis. Almost half of this total cost was attributed to maintenance activities. It was concluded that a 32\% increase in maintenance efficiency would ensure environmental viability of a self-healing mixture over a reference mixture within the constraints of the analysis conducted.Materials Science and Engineerin
Color-Based Optical Detection of Glass Transitions on Microsecond Timescales Enabled by Exciplex Dynamics
No full textEvery measurement technique operates on a given timescale and measurements using emissive small molecule sensors are no exception. A family of luminescent sensors providing first optical characterization of dynamic phenomena in polymers at a timescale of several microseconds is described. This performance originates from the dynamics manifested in the excited state of the sensor molecules where diffusioncontrolled events select the emission color while radiative phenomena define the global operation timescale. Since the mechanism responsible for signal generation is confined to the short lived excited state of emissive probe, it is possible observe an unprecedented link between the timescale of sensory action and that of photoluminescence. An application of this new methodology is demonstrated by performing general, short timescale detection of glass transitions in a temperature ranges precluding the informative range of conventional techniques by tens of degrees.ChemE/Catalysis EngineeringChemE/Inorganic Systems Engineerin
Exploring the mechanics of DNA origami nanopores via DNA PAINT imaging
No full textNanopores are narrow channels in cell membranes that control the passage of small molecules. In recent years, they have been repurposed for diverse applications, including single molecule sensing and drug delivery. Due to the small diameters of conventional protein-based, current research efforts are directed to designing nanopores from other materials to achieve larger diameters. DNA origami has emerged as a promising method for the precise fabrication of nanoscale structures. Using advances in structurally-adaptable DNA origami nanotechnology, here we investigate DNA-based nanoactuators with size-adjustable diameters, which can potentially reach diameters of up to 100 nm, that could be used for macromolecules translocation. The focus of this thesis is the study of the mechanical states of these nanoactuators, which can be triggered to change shape in response to a specific molecular trigger. Given the nanoscopic dimensions of our actuators, we select DNA PAINT for imaging, which is a type of super resolution technique, that can achieve a resolution of 10 nm, beating the optical diffraction limit (~200 nm) of conventional light microscopy. DNA PAINT experiments are performed in combination with total internal reflection fluorescence (TIRF) microscopy to characterize the behavior of DNA origami nanopores in physiological conditions. By testing various parameters sample related and imaging software ones we identify optimal conditions suggesting 5mM Mg^(2+) ions in buffer solution and 1nM DNA nanopores. Laser power (40mW), exposure time (400ms), waiting time between frames (300ms), and image duration (50s) are optimized, resulting in the expected fluorescent blinking behavior which enables us to perform single-molecule localization. The individual corners of the nanopores were, however, not resolved with this technique due to limitations in the resolution of the imaging system. We recommend that future work could exploit the even better resolution of a modified DNA PAINT approach i.e. Exchange PAINT, which has been proven to achieve Angstrom level resolution for imaging of DNA nanostructures.Materials Science and Engineerin
Performance of homogeneous catalysts viewed in dynamics
No full textEffective assessment of catalytic performance is the foundation for the rational design and development of new catalysts with superior performance. The ubiquitous screening/optimization studies use reaction yields as the sole performance metric in an approach that often neglects the complexity of the catalytic system and intrinsic reactivities of the catalysts. Using an example of hydrogenation catalysis, we examine the transient behavior of catalysts that are often encountered in activation, deactivation and catalytic turnover processes. Each of these processes and the reaction environment in which they take place are gradually shown to determine the real-time catalyst speciation and the resulting kinetics of the overall catalytic reaction. As a result, the catalyst performance becomes a complex and time-dependent metric defined by multiple descriptors apart from the reaction yield. This behaviour is not limited to hydrogenation catalysis and affects various catalytic transformations. In this feature article, we discuss these catalytically relevant descriptors in an attempt to arrive at a comprehensive depiction of catalytic performance. ChemE/Inorganic Systems EngineeringTeam Georgy Filonenk
Mechanochemistry of Spiropyran under Internal Stresses of a Glassy Polymer
No full textMechanophores are powerful molecular tools used to track bond rupture and characterize mechanical damage in polymers. The majority of mechanophores are known to respond to external stresses, and we report in this study the first precedent of a mechanochemical response to internal, residual stresses that accumulate during polymer vitrification. While internal stress is intrinsic to polymers that can form solids, we demonstrate that it can dramatically affect the mechanochemistry of spiropyran probes and alter their intramolecular isomerization barriers by up to 70 kJ mol-1. This new behavior of spiropyrans (SPs) enables their application for analysis of internal stresses distribution and their mechanochemical characterization on the molecular level. Spectroscopy and imaging based on SP mechanochemistry showed high topological sensitivity and allowed us to discern different levels of internal stress impacting various locations along the polymer chain. The nature of the developed technique allows for wide-field imaging of stress heterogeneities in polymer samples of irregular shapes and dimensions, making it feasible to directly observe molecular-level manifestations of mechanical stresses that accompany the formation of a vast number of solid polymers. BN/BionanoscienceBN/Cees Dekker LabTeam Georgy Filonenk
Alle origini delle discipline aziendali: l’opera di G.A. Tagliente
No full textThe Contribution of G.A. Tagliente to the birth of business disciplines
The paper presents the work of a XVI century Italian Accounting author, G.A. Tagliente, giving a historiographic interpretation under a business economics point of view. The research is placed in a wider project of mapping Early Mod- ern Era contributions on Accounting, where contents, distinctly analyzed, are linked to their respective social and economic contexts. In the paper biograph- ical notes are placed in the Early XVI Century Venice and the whole literary production of the Author is presented before the proper accounting one. He was the second writer on double entry method, after Pacioli’s work. He pub- lished also books on mathematics for business, but his fortune is due mainly to the unique treatise on “simple entry book”, at those times very spread through the small and medium enterprises. Even if “minor” respect to the Great Pacioli, with him a cultural path began that would lead, finally, to the establish- ment of a new stream of thought: Accounting as we recognise it nowadays. In certain respects, furthermore, he underscored not still explored concern as- pects like family’s administration, extraordinary events, fixed assets and other peculiar issues
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