770 research outputs found
Approaching the diamond surface: first principles modelling the physics and chemistry of approaching radicals
No full textThe diamond surface plays a central role in much of the diamond research, and as such much of its properties are described and studied in great detail. There is a clear picture of the atomic scale structure of the different facets and their reconstructions. Also terminations with H, O, N and other atomic species as well as the incorporation of these elements has been modelled [1,2]. The electronic structure and the negative electron affinity mechanism is elucidated and so on. In contrast, however, the atomic scale models of diamond growth are much less developed, though progress is being made [3]. In these models the reaction barriers between stable and meta-stable intermediates are being calculated, providing insights into the kinetics of the surface. However, quantum mechanical models can provide much more insights than this. In this work, we simulated the approach of radical atoms and molecules towards the H-terminated diamond 001 surface. By allowing the model to equilibrate at every step, the physics and chemistry of the approach can be followed in minute detail. It allows us to indicate at which distance the surface and radical start interacting, and what that interaction entails. The charge evolution of the radical and the surface is followed by means of Hirshfeld-I charges, providing insights into charge transfer mechanisms. [4] Throughout the approach, the interaction can be followed through different physical and chemical concepts. Different types of bonding are identified as well as H-abstraction events and covalent bonding. In this work, our focus goes to C and P based radicals, showing them to behave very differently near the surface, providing insights into the requirements for improved P incorporation.The author name needs to be updated to include the middle names: Danny E.P. Vanpoucke, and linked to the correct personel account which incorrectly is missing the author middle names
Approaching the diamond surface: first principles modelling the physics and chemistry of approaching radicals
No full textThe diamond surface plays a central role in much of the diamond research, and as such much of its properties are described and studied in great detail. There is a clear picture of the atomic scale structure of the different facets and their reconstructions. Also terminations with H, O, N and other atomic species as well as the incorporation of these elements has been modelled [1,2]. The electronic structure and the negative electron affinity mechanism is elucidated and so on. In contrast, however, the atomic scale models of diamond growth are much less developed, though progress is being made [3]. In these models the reaction barriers between stable and meta-stable intermediates are being calculated, providing insights into the kinetics of the surface. However, quantum mechanical models can provide much more insights than this. In this work, we simulated the approach of radical atoms and molecules towards the H-terminated diamond 001 surface. By allowing the model to equilibrate at every step, the physics and chemistry of the approach can be followed in minute detail. It allows us to indicate at which distance the surface and radical start interacting, and what that interaction entails. The charge evolution of the radical and the surface is followed by means of Hirshfeld-I charges, providing insights into charge transfer mechanisms. [4] Throughout the approach, the interaction can be followed through different physical and chemical concepts. Different types of bonding are identified as well as H-abstraction events and covalent bonding. In this work, our focus goes to C and P based radicals, showing them to behave very differently near the surface, providing insights into the requirements for improved P incorporation.The author name needs to be updated to include the middle names: Danny E.P. Vanpoucke, and linked to the correct personel account which incorrectly is missing the author middle names
DFT-based Vibrational Spectra for THz-Spectroscopy and Defect Fingerprinting in Molecular Crystals and Solids.
No full textSpectroscopic techniques based on atomic vibrations provide a powerful tool for the
atomic scale characterization of solids. Unfortunately, the translation of their spectra into
atomistic structures tends to be an inverse-problem, as a structural model is required to
assign the observed spectral peaks. This is further complicated by the fact that the exact
position of the latter is sensitive to the precise underlying atomic structure. This results
in the need for very accurate models.
With the steady growth of computational resources, the calculation of vibrational spectra
for extended and periodic systems has become more attainable at the level of quantum
mechanical calculations. In this work, we first present the example of the THz vibrational
spectrum of lactose-monohydrate (LM), and use our results to identify the spectral lines
of the observed spectra of different phases, obtained experimentally by heating the LM
sample.1 The accompanying water loss induces two phase transitions. According to our
results, all phases, including the starting high purity commercial sample, are mixtures of
different phases. We discuss the impact of both structural—such as water content and
orientation— and methodological—such as Pulay stresses, periodic boundaries, and
supercell sizes—aspects on the calculated spectra, and show that DFT-based spectra
under periodic boundaries can be matched with experimental data.
The importance of an extended periodic system for obtaining an accurate vibrational
spectrum is also shown in studying defects in diamond. However, here, we show that the
qualitative picture of the defect character of each atom in the system is independent of
the system size, allowing for small periodic cells to determine the relevant defect atoms
at much reduced computational cost.2 Defects tend to be very localized, resulting in
atomic modes.3 Therefore, an often-used strategy for selecting the contributing atoms
considers only their relative position with regard to the defect center. Using the atomprojected
vibrational spectrum, we present a quantitative method for determining the
defect character of each atom in the system, allowing for a rational incremental
improvement of the defect spectrum. This method is then applied on several simple
defects in diamond.Author : Danny E.P. Vanpoucke
Author name needs to be updated to include middle names, and correctly linked to the uhasselt personel databas
DFT-based Vibrational Spectra for THz-Spectroscopy and Defect Fingerprinting in Molecular Crystals and Solids.
No full textSpectroscopic techniques based on atomic vibrations provide a powerful tool for the
atomic scale characterization of solids. Unfortunately, the translation of their spectra into
atomistic structures tends to be an inverse-problem, as a structural model is required to
assign the observed spectral peaks. This is further complicated by the fact that the exact
position of the latter is sensitive to the precise underlying atomic structure. This results
in the need for very accurate models.
With the steady growth of computational resources, the calculation of vibrational spectra
for extended and periodic systems has become more attainable at the level of quantum
mechanical calculations. In this work, we first present the example of the THz vibrational
spectrum of lactose-monohydrate (LM), and use our results to identify the spectral lines
of the observed spectra of different phases, obtained experimentally by heating the LM
sample.1 The accompanying water loss induces two phase transitions. According to our
results, all phases, including the starting high purity commercial sample, are mixtures of
different phases. We discuss the impact of both structural—such as water content and
orientation— and methodological—such as Pulay stresses, periodic boundaries, and
supercell sizes—aspects on the calculated spectra, and show that DFT-based spectra
under periodic boundaries can be matched with experimental data.
The importance of an extended periodic system for obtaining an accurate vibrational
spectrum is also shown in studying defects in diamond. However, here, we show that the
qualitative picture of the defect character of each atom in the system is independent of
the system size, allowing for small periodic cells to determine the relevant defect atoms
at much reduced computational cost.2 Defects tend to be very localized, resulting in
atomic modes.3 Therefore, an often-used strategy for selecting the contributing atoms
considers only their relative position with regard to the defect center. Using the atomprojected
vibrational spectrum, we present a quantitative method for determining the
defect character of each atom in the system, allowing for a rational incremental
improvement of the defect spectrum. This method is then applied on several simple
defects in diamond.Author : Danny E.P. Vanpoucke
Author name needs to be updated to include middle names, and correctly linked to the uhasselt personel databas
Buddhism in Theosophical Interpretation of E.P. Blavatskaya: «Philosophic Invention» Problem
No full textThe subject matter of the paper is a most interesting philosophic phenomenon- theosophy which received a considerable emphasis at the end of the nineteenth and the beginning of the twentieth century and greatly influenced viewpoints of the majority of philosophers, writers, musicians and artists. The key point of the article is the author's approach to the problem of close connection between E.P. Blavatskaya's theory and Buddhism. Diverse viewpoints of both famous Russian religious philosophers and buddhologists of that time as well as modern Russian esoteric investigators and scientific papers of E.P. Blavatskaya have been studied.
The famous Russian neo-Kantian philosopher I.I. Lapshin study «Philosophy of Inventing and Invention in Philosophy: Introduction to the History of Philosophy» being inside the scope of her basic investigations, the author comes to the conclusion that theosophy is the original form of «philosophic invention» based on the specific usage of various philosophic and religious ideas of Neo-Platonism, Christian mysticism, cabbalistic theories' symbols as well as Buddhism from the point of view of their esoteric content
The sword of the spirit /
No full textCopyright date from verso of t.p."By the same author": p. [2] of preliminary p.Mode of access: Internet
Materials design through ensemble learning: When the average model knows best
No full textMachine Learning plays an ever more important role in modern materials-design and-discovery presenting a steady flow of new discoveries. Unfortunately, these achievements are generally rooted in large data sets. Although such big data sets are becoming more common place, they are generally not representative for the day-today work performed by materials researchers, where large numbers of samples are often unfeasible due to production-cost or-time, or availability of raw materials. In this work, we investigate the impact of very small data sets (<25 samples) on model quality and show how even for these data sets high quality models can be constructed. Machine Learning in small data sets Due to the success of Machine Learning within the context of large data sets, there is a natural interest to apply these methods in the context of small data sets. The use of AI and ML is these cases is generally aimed at improved design of experiments for materials optimisation, often in combination with robotic automation. Some work on small datasets (50 to several 100 samples) performed using active learning and small deep neural networks show that, even in the context of small data sets, ML can be successful for materials research. However, the quality of the obtained models is often defined in an ad hoc fashion and their sensitivity on the used data. Though clear, the required human selection steps are generally not discussed. Model quality in small data sets In this work, we present a critical investigation of the role of small (< 25 data samples) data sets in ML based regression analysis. We start from a conceptual analysis of the quality of ML models, using training, validation and test sets. In this discussion the strong dependence of the model quality on the considered datapoints is highlighted as an important limitation of ML. Using both synthetic and experimental data sets, we show that the model instances of an ensemble are distributed around the model average [1,2] This result appears to be independent of the underlying model. More interestingly, we find that this ensemble average presents a model-quality on par with that of the best available model instance in the ensemble for the data set. We therefore propose to construct a model instance that is equivalent to the ensemble average, but presents a much lower computational cost for evaluation and storage. This mitigates the observed limitation of ML for small data sets, and makes it also accessible within the context of day-today small scale materials projects. [2]Author name needs to be updated to include middel names:
Danny Vanpoucke is to be updated to Danny E.P. Vanpoucke, and correctly coupled to the personel ID in the UHasselt database which incorrectly is missing the middle names.
This work is not a duplicate, false possitive as consequence of poor checking on only title of the object
Materials design through ensemble learning: When the average model knows best
No full textMachine Learning plays an ever more important role in modern materials-design and-discovery presenting a steady flow of new discoveries. Unfortunately, these achievements are generally rooted in large data sets. Although such big data sets are becoming more common place, they are generally not representative for the day-today work performed by materials researchers, where large numbers of samples are often unfeasible due to production-cost or-time, or availability of raw materials. In this work, we investigate the impact of very small data sets (<25 samples) on model quality and show how even for these data sets high quality models can be constructed. Machine Learning in small data sets Due to the success of Machine Learning within the context of large data sets, there is a natural interest to apply these methods in the context of small data sets. The use of AI and ML is these cases is generally aimed at improved design of experiments for materials optimisation, often in combination with robotic automation. Some work on small datasets (50 to several 100 samples) performed using active learning and small deep neural networks show that, even in the context of small data sets, ML can be successful for materials research. However, the quality of the obtained models is often defined in an ad hoc fashion and their sensitivity on the used data. Though clear, the required human selection steps are generally not discussed. Model quality in small data sets In this work, we present a critical investigation of the role of small (< 25 data samples) data sets in ML based regression analysis. We start from a conceptual analysis of the quality of ML models, using training, validation and test sets. In this discussion the strong dependence of the model quality on the considered datapoints is highlighted as an important limitation of ML. Using both synthetic and experimental data sets, we show that the model instances of an ensemble are distributed around the model average [1,2] This result appears to be independent of the underlying model. More interestingly, we find that this ensemble average presents a model-quality on par with that of the best available model instance in the ensemble for the data set. We therefore propose to construct a model instance that is equivalent to the ensemble average, but presents a much lower computational cost for evaluation and storage. This mitigates the observed limitation of ML for small data sets, and makes it also accessible within the context of day-today small scale materials projects. [2]Author name needs to be updated to include middel names:
Danny Vanpoucke is to be updated to Danny E.P. Vanpoucke, and correctly coupled to the personel ID in the UHasselt database which incorrectly is missing the middle names.
This work is not a duplicate, false possitive as consequence of poor checking on only title of the object
Double diffusive convection between two parallel plates with different boundary conditions
No full textWe investigate the double diffusive convection between two parallel plates with either no-slip or free-slip boundary conditions. Direct numerical simulations have been conducted systematically for a series of control parameters. Salt fingers can be observed for both boundary conditions and all parameters explored. Compared to the no-slip case, salt fingers are stronger in the free-slip case, which is accompanied by larger salinity flux and flow velocity. For both boundary conditions, thin boundary regions develop adjacent to two plates. The salinity flux and the Reynolds number show similar dependences on the control parameter, namely, the Rayleigh number of the salinity field
Avaliação da influência da ingestão de lixo plástico nos indicadores de estresse oxidativo no sangue de tratarugas verdes (Chelonia mydas)
No full textDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências Biológicas, Programa de Pós-Graduação em Ecologia, Florianópolis, 2012O presente estudo analisou biomarcadores de estresse oxidativo, como as enzimas catalase (CAT), superóxido dismutase (SOD), glutationa peroxidase (GPx), glutationa redutase (GR) e glutationa S-transferase (GST), níveis de glutationa reduzida (GSH), de proteínas carboniladas (PC) e de lipoperoxidação (TBARS), presentes no sangue de tartarugas verdes (Chelonia mydas), vítimas de ingestão de lixo plástico, bem como o peso e volume dos resíduos ingeridos. A obstrução no trato gástrointestinal decorrente promove processos de isquemia-reperfusão associados ao estresse oxidativo sistêmico. Foram amostradas 27 tartarugas, coletadas na região da Ilha de Santa Catarina, Florianópolis, SC. Após a coleta sanguínea realizada durante exame clínico, quando se observou a presença/ausência de alguns sintomas. As tartarugas foram mantidas em tanques individuais e observadas diariamente para a constatação de lixo plástico em suas fezes: os indivíduos que realizaram três evacuações consecutivas livres de lixo plástico e não apresentaram nenhum sintoma formaram o grupo controle (n=7); os indivíduos que apresentaram as mesmas condições do grupo controle, porém em que foi constatado lixo plástico em suas fezes ao menos em uma das evacuações, foram considerados do grupo 2 (n=10); os indivíduos que apresentaram ao menos um dos sintomas avaliados durante o exame clínico e também lixo plástico em ao menos uma das evacuações, foram consideradas do grupo 3 (n=10). Foi verificada a presença de lixo plástico em 74% das tartarugas amostradas e um alto índice de ingestão de resíduos foi verificado em tartarugas sem sintomas (63%). Houve uma diferença significativa, em termos estatísticos, em relação à massa e o volume de resíduos ingeridos entre os grupos 2 e 3 (pAbstract : The aim of this study was to analyze oxidative stress biomarkers such as the enzymes catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione reductase (GR) e glutathione S-transferase (GST), levels of reduced glutathione (GSH), protein carbonyls (PC), lipoperoxidation (TBARS), in the blood of green turtles (Chelonia mydas) victims of plastic debris ingestion, as well as measuring weight and volume of such material. The consequent gastrointestinal obstruction promote an ischemia-reperfusion process associated with systemic oxidative stress, A total of 27 turtles were collected in the region of the Island of Santa Catarina, SC. After blood collection performed during clinical examination, which showed the presence/absence of some symptoms, the turtles were kept in individual tanks and were observed daily for confirmation of plastic debris in their feces: animals that underwent three consecutive evacuations free of plastic debris and that showed no symptoms formed the control group (n=7); those that exhibited similar conditions as in the control group but presented plastic debris in their feces at least in one of the evacuations, were considered group 2 (n=10); and individuals that showed at least one symptom evaluated during clinical examination and also plastic debris in at least one of the evacuations were considered in group 3 (n=10). The presence of plastic debris was detected in 74% of the turtles sampled and a high intake of residues in turtles without symptoms (63%) was also observed. The mean weight and volume of plastic debris ingested by this group were 0.8 g and 3.0 ml, respectively. There was a significant difference regarding mass and volume of waste taken between group 2 and 3 (p<0.0007 and p<0.002, respectively). The volume of waste ingested and the enzyme activities of GPx (R=-0.48) and GR (R=-0.69) were negatively correlated. In group 2, only CAT activity showed a significant decrease (p=0.02), while GR activity showed a significant increase (p=0.04), compared to controls. No statistical variation was detected for the biomarkers studied in animals from group 3 compared to controls, only a tendency of increase in TBARS and PC levels. The means of plastic debris ingested by group 3 were 11.02 g and 19.65 ml, respectively. The results found in this study suggest that the amount of waste ingested by animals in group 2, which presented a survival rate of 100%, was not enough to cause an ischemia-reperfusion of the intestine sufficient to promote a pronounced oxidative stress. The catalase activity was apparently sufficient to detoxify the excess of H2O2. On the other hand, the high mortality of group 3 (100%) seemed to be related to the failure of antioxidant defense system, because the deleterious consequences from the oxidative stress associated with the ischemia-reperfusion injury of the gastrointestinal tract. The development of biomarkers of oxidative stress to assess the health status of marine turtles may provide an important tool in the conservation of these species
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