Cheminanotechnology: Nanotechnology for Chemistry and Chemical Engineering

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Studies of the microstructure of polymer-modified bitumen emulsions using confocal laser scanning microscopy

Polymer-modified bitumen emulsions present a safer and more environmentally friendly binder for enhancing the properties of roads. Cationic bitumen emulsion binders containing polymer latex were investigated using confocal laser scanning microscopy. The latex was incorporated into the bitumen emulsion by using four different addition methods and all emulsions were processed with a conventional colloid mill. The emulsion binder films were studied after evaporation of the emulsion aqueous phase. We show how the microstructure and distribution of the polymer varies within the bitumen binder depending on latex addition method, and that the microstructure of the binder remains intact when exposed to elevated temperature. It was found that a distinctly fine dispersion of polymer results when the polymer is blended into the bitumen before the emulsifying process (a monophase emulsion). In contrast, bi-phase emulsion binders produced by either post-adding the latex to the bitumen emulsion, or by adding the latex into the emulsifier solution phase before processing, or by comilling the latex with the bitumen, water and emulsifier all resulted in a network formation of bitumen particles surrounded by a continuous polymer film. The use of emulsified binders appears to result in a more evenly distributed polymer network compared to the use of hot polymer-modified binders, and they therefore have greater potential for consistent binder cohesion strength, stone retention and therefore improved pavement performance

Violation of the sphericity assumption and its effect on Type-I error rates in repeated measures ANOVA and multi-level linear models (MLM)

This study aims to investigate the effects of violations of the sphericity assumption on Type I error rates for different methodical approaches of repeated measures analysis using a simulation approach. In contrast to previous simulation studies on this topic, up to nine measurement occasions were considered. Therefore, two populations representing the conditions of a violation vs. a non-violation of the sphericity assumption without any between-group effect or within-subject effect were created and 5,000 random samples of each population were drawn. Finally, the mean Type I error rates for Multilevel linear models (MLM) with an unstructured covariance matrix (MLM-UN), MLM with compound-symmetry (MLM-CS) and for repeated measures analysis of variance (rANOVA) models (without correction, with Greenhouse-Geisser-correction, and Huynh-Feldt-correction) were computed. To examine the effect of both the sample size and the number of measurement occasions, sample sizes of n = 20, 40, 60, 80, and 100 were considered as well as measurement occasions of m = 3, 6 and 9. For MLM-UN, the results illustrate a massive progressive bias for small sample sizes (n =20) and m = 6 or more measurement occasions. This effect could not be found in previous simulation studies with a smaller number of measurement occasions. The mean Type I error rates for rANOVA with Greenhouse-Geisser-correction demonstrate a small conservative bias if sphericity was not violated, sample sizes were small (n = 20), and m = 6 or more measurement occasions were conducted. The results plead for a use of rANOVA with Huynh-Feldt-correction, especially when the sphericity assumption is violated, the sample size is rather small and the number of measurement occasions is large. MLM-UN may be used when the sphericity assumption is violated and when sample sizes are large.Comment: 14 pages, 6 figure

Effect of exercise-induced arterial hypoxemia on quadriceps muscle fatigue in healthy humans

The effect of exercise-induced arterial hypoxemia (EIAH) on quadriceps muscle fatigue was assessed in 11 male endurance-trained subjects [peak O2 uptake (V̇o2 peak) = 56.4 ± 2.8 ml·kg−1·min−1; mean ± SE]. Subjects exercised on a cycle ergometer at ≥90% V̇o2 peak to exhaustion (13.2 ± 0.8 min), during which time arterial O2 saturation (SaO2) fell from 97.7 ± 0.1% at rest to 91.9 ± 0.9% (range 84–94%) at end exercise, primarily because of changes in blood pH (7.183 ± 0.017) and body temperature (38.9 ± 0.2°C). On a separate occasion, subjects repeated the exercise, for the same duration and at the same power output as before, but breathed gas mixtures [inspired O2 fraction (FiO2) = 0.25–0.31] that prevented EIAH (SaO2 = 97–99%). Quadriceps muscle fatigue was assessed via supramaximal paired magnetic stimuli of the femoral nerve (1–100 Hz). Immediately after exercise at FiO2 0.21, the mean force response across 1–100 Hz decreased 33 ± 5% compared with only 15 ± 5% when EIAH was prevented (P < 0.05). In a subgroup of four less fit subjects, who showed minimal EIAH at FiO2 0.21 (SaO2 = 95.3 ± 0.7%), the decrease in evoked force was exacerbated by 35% (P < 0.05) in response to further desaturation induced via FiO2 0.17 (SaO2 = 87.8 ± 0.5%) for the same duration and intensity of exercise. We conclude that the arterial O2 desaturation that occurs in fit subjects during high-intensity exercise in normoxia (−6 ± 1% ΔSaO2 from rest) contributes significantly toward quadriceps muscle fatigue via a peripheral mechanism

Plasmonic Gold Helices for the visible range fabricated by oxygen plasma purification of electron beam induced deposits

Electron beam induced deposition (EBID) currently provides the only direct writing technique for truly three-dimensional nanostructures with geometrical features below 50 nm. Unfortunately, the depositions from metal-organic precursors suffer from a substantial carbon content. This hinders many applications, especially in plasmonics where the metallic nature of the geometric surfaces is mandatory. To overcome this problem a post-deposition treatment with oxygen plasma at room temperature was investigated for the purification of gold containing EBID structures. Upon plasma treatment, the structures experience a shrinkage in diameter of about 18 nm but entirely keep their initial shape. The proposed purification step results in a core-shell structure with the core consisting of mainly unaffected EBID material and a gold shell of about 20 nm in thickness. These purified structures are plasmonically active in the visible wavelength range as shown by dark field optical microscopy on helical nanostructures. Most notably, electromagnetic modeling of the corresponding scattering spectra verified that the thickness and quality of the resulting gold shell ensures an optical response equal to that of pure gold nanostructures

Harp, Harbor and Gray Seal Strandings in the Gulf of Maine: A Retrospective Socio-Ecological Analysis

Over the past several decades, the Gulf of Maine (GOM) has experienced significant socio-ecological change. Extreme climatic variation increases in human population, and visitation of coastal areas have significantly impacted coastal ocean health and redefined multispecies ecologies. While pinniped populations in the Northeast United States have generally grown following federal protection, they have also experienced multiple mortality events over the past two decades. Long-term datasets from marine mammal stranding networks represent a valuable resource for investigating trends in marine mammal health during this period of change. Here, I evaluated potential drivers of marine mammal strandings using data collected from stranded harbor (Phoca vitulina), harp (Pagophilus groenlandicus) and gray (Halichoerus grypus) seals from 2002 to 2017 in Massachusetts, New Hampshire and Maine. I tested for spatio-temporal correlations between stranding density and potential social (e.g., population density) and environmental (e.g., sea surface temperature, North Atlantic Oscillation, snowfall and sea ice extent) factors. Our models reveal significant effects of location and human population density on stranding rates across species—signifying that, even after correcting for reporting effort, pinnipeds are more likely to strand near more densely populated human epicenters in the GOM—as well as speciesspecific relationships with some environmental factors. These analyses increase our understanding of the circumstances that lead pinnipeds to strand in the Gulf of Maine and provide context within which these species may serve as sentinels of coastal ocean health

Where’s the Love? Recentering Indigenous and Feminist Ethics of Care for Engaged Climate Research

Across a range of environmental change and crisis-driven research fields, including conservation, climate change and sustainability studies, the rhetoric of participatory&nbsp;and engaged research has become somewhat of a normative and mainstream mantra. Aligning with cautionary tales of participatory approaches, this article suggests that, all too often, ‘engaged’ research is taken up uncritically and without care, often by pragmatist, post-positivist and neoliberal action-oriented researchers, for whom the radical and relational practice of PAR is paradigmatically (ontologically, epistemologically and/or axiologically) incommensurable. Resisting depoliticised and rationalist interpretations of participatory methodologies, I strive in this article to hold space for the political, relational and ethical dimensions of collaboration and engagement. Drawing on four years of collaborative ethnographic climate research in the Peruvian Andes with campesinos of Quilcayhuanca, I argue that resituating Participatory Action Research (PAR) within a feminist and indigenous ethics of care more fully aligns with the radical participatory praxis for culturally appropriate transformation and the liberation&nbsp;of oppressed groups. Thus, I do not abandon the participatory methodology altogether, rather this article provides a hopeful reworking of the participatory methodology and, specifically, participatory and community-based adaptation (CBA) practices, in terms of&nbsp;a feminist and indigenous praxis of love-care-response. In so doing, I strive to reclaim the more radical feminist and Indigenous elements – the affective, relational and political origins of collaborative knowledge production – and rethink research in the rupture of climate crises, relationally. The ethico-political frictions and tensions inherent in engaged climate scholarship are drawn into sharp relief, and deep reflection on the responsibility researchers take on when asking questions in spaces and times of ecological loss, trauma and grief is offered

Moving with Thought:physical activity and cognitive functions, academic achievement and psychosocial health in adolescents

Physical activity has been linked to strong positive health benefits and better cognitive functioning, however, nowadays more than 80% of adolescents do not adhere to the recommended guidelines for the amount of physical activity. Previous studies on associations between physical activity and fitness with cognitive functioning, academic achievement and psychosocial health in adolescents and showed mixed findings and inconsistent results. The aim of this thesis was to investigate the relations between physical fitness and cognitive functions, academic achievement and psychosocial health in healthy adolescents. In addition, this thesis aimed to investigate the effects of a physical activity intervention on the same outcomes. Data was gathered in the randomized controlled trial study Move to Improve including 453 adolescents and during a literature review. The results of this thesis showed that skill-related physical fitness was related to specific aspects of cognitive functioning and health-related physical fitness was related to better psychosocial health. Furthermore, the results of the literature review demonstrated that there are positive effects of short-term and long-term physical activity interventions on cognition and academic achievement in adolescents and young adults. However, the results of the Move to Improve intervention showed no impact on cognitive functioning and academic achievement. However, a main interaction effect on reduction of symptoms of depression was found. Finally, we found dose-response effects, indicating that spending more time in MVPA during the physical activity intervention in physical education leads to better psychosocial health and that more cognitively challenging exercises lead to better academic achievement

Decay and snapback in superconducting accelerator magnets

This thesis deals with the explanation and compensation of the effects ‘decay’ and ‘snapback’ in superconducting accelerator magnets, in particular in those used in the new Large Hardron Collider at CERN. During periods of constant magnet excitation, as for example during the injection of particles in the storage ring, the magnetic field in superconducting accelerator magnets shows a decay behavior. As soon as the particles are accelerated, the magnets are ramped, and the magnetic field ‘snaps back’ to the original hysteresis curve. Decay and snapback affect the beam in the machine and have to be compensated precisely in order to avoid losses of particles