4242 research outputs found
Sort by
Synthesis and characterization of fluorescent iron oxide nanoparticles to study uptake and intracellular trafficking of nanoparticles in neural cells
Get PDFIron oxide nanoparticles (IONPs) have promising features for biomedical applications and are already used for some therapeutic and diagnostic approaches. As IONPs can reach the brain it is important to study the potential consequences of an exposure to IONPs on brain cells. In the presented thesis, fluorescent IONPs were synthesized by functionalizing the coating material dimercaptosuccinate (DMSA) of the IONPs with either the green dye Oregon Green (OG) or the red dye tetramethylrhodamine (TMR). Comparison to previously used BODIPY-labeled DMSA-coated IONPs, OG- and TMR-IONPs revealed higher fluorescence signal intensities and improved stability, while these fluorescent IONPs had almost identical physicochemical properties and colloidal stability as the corresponding non-fluorescent DMSA-coated IONPs. To investigate the accumulation of IONPs in brain cells, C6 glioma cells were used as model system. IONPs exposure studies revealed that these cells accumulate fluorescent and non-fluorescent IONPs in a time-, concentration- and temperature-dependent manner. Due to the strong fluorescence observed in cells that had been exposed to OG- or TMR-IONPs and due to the slow bleaching of cellular fluorescence, these fluorescent IONPs were considered as suitable tools for further studies of cellular uptake and intracellular trafficking of internalized IONPs. To monitor the intracellular trafficking of fluorescent nanoparticles with improved temporal and spatial resolution, single and double nanoparticle pulse-chase experiments were established for OG- and TMR-IONPs. As IONPs efficiently adsorb to the cell membrane but are not internalized at 4AdegreeC, the fluorescent IONPs were bound to the cells by a 10 min pulse at 4AdegreeC. Subsequently, unbound nanoparticles were removed by washing before an increase of the incubation temperature to 37AdegreeC started a synchronized internalization of the IONPs by the cells. Double nanoparticle pulse-chase experiment with the two types of fluorescent IONPs allowed to even monitor the sequential uptake of OG- and TMR-IONPs. The usage of nanoparticle pulse-chase experiments in the presence of inhibitors of the cytoskeleton integrity revealed an actin-dependent formation of IONPs-containing vesicles and a microtubules-dependent transport of these vesicles to the perinuclear area. Additionally, the separation of the fluorescent DMSA coat and the iron oxide core during the intracellular trafficking was observed in nanoparticle pulse-chase experiments. Finally, limitations, requirements and special challenges of studies on the exposure of in cultured neural cells with fluorescent IONPs were investigated, and are described and discussed. In conclusion, the data presented in this thesis revealed that the synthesized fluorescent IONPs are suitable tools to study the uptake and intracellular fate of DMSA-coated IONPs by microscopical approaches and that the established nanoparticles pulse-chase setup allows to study internalization and mechanisms involved in intracellular IONPs trafficking with improved resolution
Disentangling the effects of thermal stress on symbiont-bearing coral reef foraminifera : from populations to proteins
Get PDFPhotosymbiosis is of central importance for the wellbeing and proliferation of many tropical marine organisms, but the balance within this relationship can react delicately to changes in environmental conditions. Many of such reef-building calcifiers, e.g. corals and large benthic foraminifera (LBF), construct ecologically important habitats along the oceans tropical coasts and contribute considerably to global carbonate sediment production. Ocean warming is among the most damaging factors to coral reef ecosystems, often leading to the disruption of the photosymbiotic associations. Seen as bleaching, it may ultimately lead to mass mortality of reef-calcifiers. Understanding the characteristics that influence adaptive mechanisms of these photosymbiotic holobionts is hence crucial to project their future fate. To disentangle the drivers of holobiont resilience, characteristics influencing the stress responses of both, host and photosynthesizing symbiont, need to be considered, including differences in species-specific adaptations and in local environmental conditions that may result in different acclimatization. This thesis aims to extend the understanding of adaptive mechanisms in photosymbiotic calcifiers in modern times of ocean warming by focusing on various levels of organismal responses of the common reef-associated diatom-bearing foraminifera Amphistegina, from populations to the proteomes of host and symbiont. To test for inter-species and intra-species variations in thermal stress responses and symbiont assemblages, the widespread Indo-Pacific species A. lessonii, and its Atlantic counterpart A. gibbosa, were exposed to different ocean warming scenarios. Three thermal-stress treatments were simulated over one month in an experiment: a single thermal peak, followed by lower control temperature; episodic stress, simulated by four thermal peaks that alternated with periods at control temperature; and chronic stress. In addition to determining various parameters indicating holobiont and photosymbiont performance, the photosymbionts were characterized by genetic fingerprinting. Although test populations of A. gibbosa were collected from habitats with different temperature ranges, their responses were similar, with only marginally higher tolerance to thermal peaks in specimens from a shallower-water site as compared to a deeper-water site in the direct vicinity. In contrast, differences between species bring evidence for higher tolerance of A. lessonii as compared to A. gibbosa, as episodic stress had no and chronic stress less pronounced impact, especially with regard to photosymbionts. These inter-species variations were consistent with the presence of different and more diverse symbiont assemblages in A. lessonii, which demonstrates the importance of considering symbiont diversity in the assessment of stress response and adaptive capacity of LBF. Monitoring performance of the deeper-dwelling group of A. gibbosa over the experimental period revealed that after three to twelve days, chronic stress led to bleaching, however, without inducing mortality, which may be a result of the steep increase in total antioxidant capacity in this treatment. Single and episodic stress induced both the same minor responses. As this population experiences fluctuating temperatures in its natural habitat, it is likely adapted to thermal peaks. This highlights the potential of such variable marine environments to support resilient physiological mechanisms among photosymbiotic organisms. Nonetheless, reproduction seemed to be suppressed by episodic and chronic stress. Such possible trade-offs may have far-reaching implications for LBF communities. To reveal underlying molecular mechanisms, changes in the proteome were analyzed. A quantitative bottom-up proteomics approach was employed to link the cellular mechanisms to the observed stress responses in A. gibbosa. This offered the opportunity to separate the effect of the LBF host and its photosymbiont. High congruency to physiological parameters validated the presented novel workflow and showed major changes in the abundance of manifold proteins, induced by the different thermal-stress treatments. The proteome regulations going along with bleaching included the impairment of symbiont carbon concentrating mechanisms, and led to cell death and degradation. In the host, efficient repair mechanisms and enhanced protein synthesis maintained homeostasis. Metabolic pathways were adjusted to the symbiont loss, which demonstrates the importance of shifting feeding modes as resilience mechanism. This thesis contributes to disentangling the underlying drivers of photosymbiotic reef organisms, including the flexibility in symbiotic associations, interactions between host and symbionts, and the role of environmental factors shaping the range of their ecological constraints
Tailored aerosol synthesis of nanosized multicomponent catalysts
Get PDFNanoparticles consisting of multiple components play a key role in the development of new materials and heterogeneous catalysts for novel types of energy conversion processes. This thesis demonstrates the flexibility of the Double Flame Spray Pyrolysis for the production of tailored multicomponent catalysts from almost all metals and transition metals by gas-to-particle conversion. Two experimental studies determine the optimal geometric process parameters of the two flames for the synthesis of highly active binary Fischer-Tropsch (FT) catalysts and ternary catalysts for the preferential oxidation of CO (CO-PrOx). Further investigates the thesis for the first time the main underlying process conditions during the double flame synthesis process e.g. the temperature profile of the intersecting flames and the mixing characteristic of the two components in the reaction zone. For the last one, two novel image based methods for the determination of the degree of mixing in deposited systems (active component on support: platinum (Pt) on titania (TiO2)) and in aggregated systems (two types of support: tungsten-oxide (WO3) and titania (TiO2)) are developed
PDE-restringierte Optimierung in Anwendungen der spanenden Trockenbearbeitung
Get PDFNowadays industrial manufacturing is highly widespread while the demand of high-precision manufacturing is increasing constantly. In such processes, it is common to apply coolants to reduce the thermal stress of workpieces and tools as well as to guarantee the functional performance of the final parts. Nonetheless, there are several reasons like cost reduction and ecological benefits for omitting coolants or to use minimum quantity lubrication (MQL). In order to satisfy the quality standards in dry machining, compensation strategies of shape deviations are necessary. Due to the increasing digitalization of process chains (Industry 4.0), modern sensors and the usage of high-performance computing, nonlinear optimization is more convenient than ever before. In this context, a prediction model is required by which the machining can be optimized. In this work a hybrid approach is used to model thermo-elastic effects as well as geometrical deviations caused by a change of the residual stress state. Physical correlations of the modeling which are not investigated yet can be synthesized by empirical regression with a wide variety of data. The first part of this elaboration is the determination of heat fluxes in milling and drilling which cana t be measured directly. One goal is to utilize nonlinear optimization to solve parameter identification problems. The second part is the minimization of shape deviations in dry milling processes by means of the hybrid model. To achieve this, different milling strategies are compared and machining parameters are optimized with nonlinear optimization techniques, while an efficient machining process is sought at the same time. The mathematical majority of this work covers the PDE-constrained optimization. Still a challenging topic in this field is the treatment of complex problems involving high computational costs. It is still advisable to increase the efficiency of the optimization methods whereby the accuracy of the underlying model can be improved. One promising approach is the Simultaneous Analysis and Design (SAND) where a discretized PDE act as constraints of the optimization. This approach gives importance to exploiting the system structure of the optimization problem. Another common method is the Nested Analysis and Design (NAND). Theoretical considerations suggest that the SAND approach favored in this work has computational benefits for treating nonlinear PDEs. Beside the successful application of the SAND approach in dry machining one goal is to provide evidence of its computational efficiency
Objective assessment and feedback generation in dental surgical simulation : a framework based on correlating procedure and outcome
Get PDFFine motor skill is indispensable for a dentist. As in many other medical fields of study, the traditional surgical master-apprentice model is widely adopted in dental education. Recently, virtual reality (VR) simulators have been employed as supplementary components to the traditional skill-training curriculum, and numerous dental VR systems have been developed academically and commercially. However, the full promise of such systems has yet to be realized due to the lack of sufficient support for formative feedback. Without such a mechanism, evaluation still demands dedicated time of experts in scarce supply. With the aim to fill the gap of formative assessment using VR simulators in skill training in dentistry, this thesis presents a framework to objectively assess the surgical skill and generate formative feedback automatically. VR simulators enable collecting detailed data on relevant metrics throughout a procedure. Our approach to formative feedback is to correlate procedure metrics with the procedure outcome in order to identify the portions of a procedure that need to be improved. Prior to the correlation, the procedure outcome needs to be evaluated. The scoring algorithm designed in this thesis provides an overall score and identifies specific errors and their severity. Building upon this, we developed techniques to identify the portion of the procedure responsible for the errors. Specifically, for the errors in the outcome the responsible portions of the procedure are identified based on correlation of location of the error. For some types of feedback one mode may be more suitable than another. Tutoring formative feedback are provided using the video- and haptic- modalities. The effectiveness of the feedback systems have been evaluated with the dental students with randomized controlled trials and the findings show the feedback mechanisms to be effective and have potentials to use as valuable supplemental training resources
Environmental and Physical Factors Affecting the Diversity and Distribution of the Ichthyoplankton in an Inverse Estuary , the Sine Saloum (Senegal)
Get PDFEstuarine mangrove ecosystems are considered essential nursery grounds and feeding areas for the early life stages of many fish species, often including commercially important ones. Particularly, climate change is expected to affect and have a substantial impact on mangrove estuaries, through processes including changes in precipitation, increased temperature, and changing patterns of ocean and estuarine circulation. As a result, the inversion of the salinity gradient in several estuaries throughout the dry tropics is either underway or can be expected in the near future. Such modifications of these important estuarine environments are cause of concern because spawning and nursery grounds of fishes have requisite environmental and physical attributes. Thus, there is a strong scientific consensus that related pressing contemporary research questions regarding the early life history of fishes in these transformed estuaries should be addressed. Located in Senegal, West Africa, the Sine Saloum system is representative of estuaries where the salinity gradient has been inverted due to climatic changes in the region. Given the high overall salinity and the resulting mangrove degradation that is taking place there, its potential role (compared to a classic estuarya ) as a recruitment and nursery area for fish larvae is far to be clear. Thus, the Sine Saloum estuary is a natural and excellent choice to study how these climatic environmental transformations are affecting the ichthyoplankton community. The aim of this thesis is to gain knowledge on the environmental and physical factors affecting the Sine Saloum ichthyoplankton diversity and distribution. The survival of fish larvae is known to be influenced by complex interactions between environmental changes and tropho- and hydrodynamic processes. Consequently, I first analysed the spatial and seasonal distribution of the fish larval assemblages related to environmental parameters. Second, a field experiment measuring simultaneously vertical current profiles and larval transport were conducted to investigate the effectiveness of larval fishes in regulating transport in and out of the estuary. Lastly, stable isotope analysis was used to evaluate the contribution of the sea surface microlayer (SML) to the diet of larval and juvenile African halfbeaks (Hyporamphus picarti), one of the dominant species in the system. The summarised key findings of the thesis are: A total of 41 taxa representing 24 families and 34 genera were sampled in the estuary, which is lower than that of other tropical estuaries, providing evidences that high salinity environment may harbour a less diverse ichthyoplankton fauna. Additionally, the distributional pattern of fish larvae revealed that the total abundance and the richness in the estuary decreased from the lower to the upstream areas with salinity and water temperature as the variables that best explained the spatial and temporal differences observed. Larval fish assemblages also showed a clear vertical structure corresponding to three distinct water strata.The circulation at the entrance of the Sine Saloum estuary was characterized by the existence of a longitudinal gravitational circulation with vertical shear and net near-surface inflow into the estuarine system. This is of critical importance in the context of fish recruitment because it offers a natural path into (resp. out of) the estuarine system for organisms that would be able to maintain themselves in the upper (resp. lower) part of the water column. The distribution of the fish larvae taxa that were examined revealed depth range preferences that did not change in time, independent from tide conditions, and were consistent with the use of these pathways. From a behavioural perspective, this mechanism can be viewed as simpler than selective tidal stream transport in that it does not require the organisms to synchronise their vertical migrations with the phase of the tidal currents. By obtaining statistically distinct A 13C and A 15N isotopic signatures for the SML, its presence at the entrance of the Sine Saloum estuary was confirmed. The organisms contained in the SML presented an important food source for H. picarti larvae and juveniles, contributing to more than 70 % of their diets. These results underline the importance of the SML and the role of this estuary as a spawning and nursery habitat for H. picarti
Natural and artificial radionuclides as tracers in fluvial systems
No full textThe environmental pathways of medical 131I have been the subject of several studies presenting its ability as a tracer in lakes, rivers and estuarine systems. In this study 131I, originating from the local wastewater treatment plant (WWTP), is used as a readily available tracer with the aim of obtaining a better understanding on the distribution of radioisotopes in the tidal influenced Weser River. In order to detect low concentration of 131I on Weser River water, a well-defined chemical extraction method needs to be applied. Focused on this aspect, upon investigating 12 different methods, a procedure with a high extraction yield (86 A /- 15)% which targets inorganic and organically bound iodine at the same time was developed, tested and used for bulk water samples. Large amount of water and sediment samples were collected and measured by gamma spectroscopy, for the period autumn 2014 a autumn 2015, during 17 different sampling campaigns. The 131I activity concentration in the river water is strongly dependent on the tidal cycle. Its profile is similar to the one in bank sediments with maximum values directly in the WWTP outflow and lowest in the opposite river bank and upstream direction. A model which computes the 131I behavior in Weser River for routine releases was developed. For assessing the model, water and sediment samples taken from the river are required as well as information on hydrological and morphological data of the river. The model provides realistic radionuclide distributions in water and bank sediments. The simulated currents and 131I activity concentration in the system are, in general, in agreement with observations. Despite the simplifications considered, the assessment of the model indicates its capability of predicting the dispersion of medically derived iodine, originating from the WWTP, in the water body and banks of Weser River. With minor adjustments, one could possibly use the model for the prediction of dispersion for different radionuclides, in different area and in emergency situations
Critical Practice Study of Nursing Evaluated by Teachers
Get PDFPurpose: Competent nursing care is essential to positive patient outcomes and quality patient care. Graduate nurses begin practice as novices in knowledge and experience often entering an environment where patients have several disease processes complicating their care. A strong foundation of educational competencies prior to entering practice is vital for the development and growth of graduate nurses into the role of RN. The purpose of this study was to examine the use of the Nurse Competence Scale among nursing faculty. Method: Nursing faculty were surveyed to determine which competencies were a priority in nursing practice. The Nurse Competence Scale was used to identify and categorize nurse competences. Brenner s novice to expert theoretical framework was used to apply findings to curricular programs. IRB approval was granted from each educational institution. SPSS statistical analysis was used to analyze survey results. Results: Among the categories of the Nurse Competence Scale, nursing faculty identified Acting appropriately in life-threatening situations in the Managing Situations section as most important to practice. In the category of Helping, Planning patient care according to individual needs was identified as most important. Additionally the nursing faculty surveyed rated Contributing to further development of multidisciplinary clinical paths in the Therapeutic Interventions category as the lowest. Conclusion: This study contributes to the discussion on nursing competence. Priorities for nursing faculty aligned with register nurses in practice. This study helps pair nursing education with practice in several ways including aligning current practice with education. Nurse Educators may use these findings to help join curricular outcomes with practice. Evaluating each item on the Nurse Competence Scale using the critical to practice scale provides insight to the necessary skills and knowledge needed to be competent in nursing. In addition the results may be compared to current practice guidelines to ensure best practice. Further research linking education and practice using nursing competence is needed
Ground-based Remote Sensing of Carbon Dioxide, Carbon Monoxide and Methane on Ascension Island Using Fourier Transform Infrared Spectroscopy
Get PDFIn May, 2012, a remote sensing observatory for performing ground-based total column measurements was established on Ascension Island (7.93AAdegreeS, 14.39AAdegreeW) in the South Atlantic Ocean. Since then measurements of greenhouse gases such as CO2 and CH4 and other gases are conducted in the framework of the Total Carbon Column Observing Network (TCCON). The time series of the measurements of CO2, CH4 and CO (denoted as XCO2, XCH4 and XCO, respectively) now comprise more than five years. A detailed analysis for all time series is shown here. Other data sets like aircraft profiles and in situ data are also used for interpreting the results. The time series of XCO2 is influenced by fluxes from both hemispheres. For CH4, the main finding is an atypical positive gradient with increasing altiude which can be attributed to transport from the continents and the trade wind inversion occuring around Ascension. The time series of XCO allows the detection of the two biomass burning seasons of the Africa
Öffentlichkeitsarbeit und Nachwuchsförderung im Sonderforschungsbereich SFB 747
Get PDFmikromal ist das Öffentlichkeits- und Nachwuchsförderungsprojekt des Sonderforschungsbereichs (SFB) 747 Mikrokaltumformen der Universität Bremen. Von 2008 bis 2018 förderten die Wissenschaftler innen im Rahmen von mikromal Jugendliche durch Konstruktionsworkshops, Laborführungen sowie Vorträge und bereiteten ihre Forschung lai innengerecht im Rahmen von Formaten wie Facebook, Science Cafes, Ausstellungen und Bürgerfesten auf. Der Grundgedanke des Projekts ist, dass Wissenschaftler innen ihre Forschungsthemen selber Lai innen vermitteln. Dabei unterstützt sie der SFB unter anderem im Rahmen der Graduiertenförderung. Dieser Erfahrungsbericht stellt die vielfältigen Aktionen des Projekts mikromal vor