Destruktive und konstruktive laserbasierte Verfahren zur lokalen Biofunktionalisierung organischer Monoschichten

Die Herstellung von Bio-Arrays erfordert eine Kombination aus Strukturierung und Biofunktionalisierung der Oberfläche, um Biomoleküle, wie DNA oder Proteine, gezielt in einem Muster auf einem Trägermaterial zu immobilisieren. Laserverfahren ermöglichen eine schnelle und einfache Strukturierung im Mikro- und Nanometerbereich. Bei der photothermischen Laserstrukturierung werden nichtlineare Effekte ausgenutzt, um eine hohe laterale Strukturauflösung zu erzielen. Aufgrund der nichtlinearen Abhängigkeit der Kinetik von der Temperatur, können Strukturen erzeugt werden, die deutlich kleiner sind als der zur Strukturierung verwendete Laserspot. Als Ausgangspunkt für die Herstellung strukturierter und funktionalisierter Oberflächen bieten sich selbstorganisierte Monoschichten (SAMs) an. Obwohl sie nur sehr dünn sind, etwa 1-3 nm, eignen sie sich sehr gut, um die Oberflächeneigenschaften, z. B. die Bioaffinität, eines Substrats gezielt zu verändern. Zusammen mit einer lateralen Strukturierung lassen sich die Eigenschaften der Oberfläche lokal maßgeschneidert verändern. Daher können SAMs vielseitig für den Aufbau komplexer Oberflächenstrukturen verwendet werden. In dieser Arbeit wurde die serielle Laserstrukturierung als flexibles Werkzeug zur Strukturierung von SAMs eingesetzt mit dem Ziel, Verfahren zur Biofunktionalisierung in den Nanometerbereich zu übertragen. SAMs wurden hierzu mit Licht der Wellenlänge von 532 nm strukturiert. Die Strukturerzeugung erfolgte sowohl destruktiv, durch Abtrag des SAMs, als auch konstruktiv, durch Modifikation des SAMs. Anschließend wurden Routinen zur Immobilisierung von Proteinen und Oligonukleotiden auf den strukturierten Oberflächen angewendet und so das Potential laserstrukturierter SAMs in der Anwendung als biochemische Template demonstriert

Mechanische Verluste in Materialien für zukünftige kryogene Gravitationswellendetektoren

The aim of this work consisted in the study of the mechanical losses of potential substrate materials for future cryogenic interferometric gravitational wave detectors to reduce the thermal noise of their optical components. Interferometric gravitational wave detectors (IGWDs) are among the instruments with the highest sensitivity ever built. To increase the detection probability and also to gain a deeper look in the universe by establishing a gravitational wave astronomy a further enhancement of sensitivity is inevitable. A main noise source to be reduced is the thermal noise of the optical components like mirrors and beam splitter. A very promising approach for a reduction of thermal noise is to deprive thermal energy by decreasing the operating temperature of the IGWDs from room temperature to cryogenic temperatures. Since thermal noise mainly depends on two physical values - temperature and mechanical loss at that temperature and given frequency - materials showing low mechanical losses at low temperatures are then required for these future detectors. Fused silica, which is the common material of current IGWDs operated at room temperature, and crystalline quartz, crystalline calcium fluoride, and crystalline silicon, which are potential low-loss materials, have been studied in this work.Ziel dieser Arbeit war es, die mechanischen Verluste von potentiellen Substratmaterialien für die Spiegel zukünftiger kryogener interferometrischer Gravitationswellendetektoren (IGWD) zu untersuchen. Da mechanische Verluste mit thermischem Rauschen in diesen äußerst sensitiven Detektoren in Zusammenhang stehen, bietet eine systematische Analyse derselben die Möglichkeit, gezielte Maßnahmen zur Rauschreduzierung zu ergreifen und damit die Detektionswahrscheinlichkeit von Gravitationswellen zu steigern, sowie die technischen Erfordernisse für eine Astronomie basierend auf Gravitationswellen zu schaffen. Ein vielversprechender Weg zur Reduzierung des thermischen Rauschens in den derzeit bei Raumtemperatur betriebenen IGWDs ist der Entzug von thermischer Energie durch Kühlen der Spiegel und Strahlteiler. Da die mechanischen Verluste jedoch im allgemeinen sowohl von der Frequenz als auch von der Temperatur abhängen, werden Materialien für diese optischen Komponenten benötigt, die sehr geringe Verluste bei kryogenen Temperaturen zeigen. Fused silica, als Material der bei Raumtemperatur betriebenen IGWDs, und kristalliner Quarz, kristallines Calciumfluorid und kristallines Silizium, als potentielle verlustarme Materialien, wurden in dieser Arbeit untersucht

The Interplay of Task Characteristics, Linguistic Complexity, and Language Proficiency in High-Stakes English as a Foreign Language Writing

The linguistic characteristics of text productions depend on various factors, including individual language proficiency as well as the tasks used to elicit the production. To date, little attention has been paid to whether some writing tasks are more suitable than others to represent and differentiate students' proficiency levels. This issue is especially relevant in the context of high‐stakes language examinations. In this study, we investigated task effects in English as a foreign language (EFL) Abitur examinations, the high‐stakes test qualifying for higher education admission in Germany. Based on texts produced by 362 students, we examined (a) if and how student writings differ in their linguistic complexity and (b) if the EFL Abitur tasks are equally suited to differentiate the students' proficiency levels. We used a broad operationalization of linguistic complexity, including measures from various linguistic domains in the computational analysis of the texts. The results of our mixed‐effects models show that student texts differ in their linguistic complexity primarily by the functional needs of the task types employed (summary, analysis, and argumentation). Furthermore, writing tasks that demand high independence in language performance are best suited to differentiate between proficiency levels, which becomes especially evident in vocabulary choice and usage.Peer Reviewe

Zukünftige Medienästhetik

Prof. Dr. Jens Schröter, Dr. Pablo Abend und Prof. Dr. Benjamin Beil sind Herausgeber der Reihe. Die Herausgeber*innen der einzelnen Hefte sind renommierte Wissenschaftler*innen aus dem In- und Ausland.Die ab Heft 1/2015 von Prof. Dr. Jens Schröter als Hauptherausgeber zusammen mit dem Graduiertenkolleg Locating Media (Universität Siegen) und Prof. Dr. Benjamin Beil (Universität zu Köln) herausgegebene kultur- und medienwissenschaftliche Zeitschrift Navigationen widmet sich in ihrer aktuellen Ausgabe (2/2021) dem Thema Zukünftige Medienästhetik. Eine zukünftige Medienästhetik ist sowohl eine Medienästhetik der Zukunft, als auch eine Ästhetik zukünftiger Medien. Medienkunst hat schon immer ungedachte und unversuchte Möglichkeiten verschiedenster Medien ausprobiert und damit einen imaginativen Vorschein zukünftiger Medien erzeugt. Medienkunst, eine der zentralen Kunstformen des 20. und 21. Jhds., sah es als eine ihrer Aufgaben an, neue Medien zu erfinden (Rosalind Krauss) – oft gerade im Rückgriff auf obsolet wirkende Technologien und Verfahren. Medienkunst reflektiert also nicht bloß ein zugrundeliegendes Medium, wie es von der (hoch-)modernistischen Ästhetik und problematisch genug, für alle Kunst behauptet wurde. Sie erfindet erst ein Medium. Medien sind dabei von Imaginationen umgeben, die ihrer Erfindung vorhergehen, ihre Durchsetzung begleitet und in ihrem Verschwinden nostalgisch nachklingen. Medienkunst kann deshalb als ein spezieller Fall solcher Imaginationen verstanden werden – eine Imagination, die nicht (nur) diskursiv, sondern materiell, demonstrativ und performativ aufgeführt wird. In dem geplanten Heft sind Beiträge versammelt, die die Praktiken der Erfindung zukünftiger Medien durch die Medienkunst untersuchen. Ein Schwerpunkt liegt dabei auf dem wichtigen medienkünstlerischen Projekt Piazza virtuale von Van Gogh TV, welches auf der documenta IX 1992, genau am Vorabend der Ausbreitung des Internets, das zukünftige Medium eines interaktiven Fernsehens entwarf.A future media aesthetic is both a media aesthetic of the future and an aesthetic of future media. Media art has always explored unimagined and untried possibilities of various media, creating an imaginative glimpse of future media. Media art, one of the central art forms of the 20th and 21st centuries, saw it as one of its tasks to invent new media (Rosalind Krauss) - often precisely by resorting to technologies and processes that seem obsolete. Media art, then, does not merely reflect an underlying medium, as was claimed by (high) modernist aesthetics, and problematically enough, for all art. It first invents a medium. Media are thereby surrounded by imaginaries that precede their invention, accompany their enforcement, and resonate nostalgically in their disappearance. Media art can therefore be understood as a special case of such imaginaries - an imagination that is not (only) discursive, but material, demonstrative and performative. The planned issue gathers contributions that examine the practices of inventing future media through media art. One focus is on the important media art project Piazza virtuale by Van Gogh TV, which conceived the future medium of an interactive television at documenta IX in 1992, precisely on the eve of the spread of the Internet

Neurofilament as a blood marker for diagnosis and monitoring of primary progressive aphasias

Objective: To assess the utility of serum neurofilament for diagnosis and monitoring of primary progressive aphasia (PPA) variants. Methods: We investigated neurofilament light chain (NF-L) levels in blood of 99 patients with PPA (40 with nonfluent variant PPA [nfvPPA], 38 with semantic variant PPA [svPPA], 21 with logopenic variant PPA [lvPPA]) and compared diagnostic performance with that reached by CSF NF-L, phosphorylated neurofilament heavy chain (pNF-H), b-amyloid (Ab(1)-42), tau, and phosphorylated tau. The longitudinal change of blood NF-L levels was measured and analyzed for correlation with functional decline and brain atrophy. Results: Serum NF-L is increased in PPA compared to controls and discriminates between nfvPPA/svPPA and lvPPA with 81% sensitivity and 67% specificity (cutoff 31 pg/mL). CSF NF-L, pNF-H, tau, phosphorylated tau, and Ab1-42 achieved similar performance, and pNF-H was the only marker for discrimination of nfvPPA from svPPA/lvPPA. In most patients with nfvPPA and svPPA, but not lvPPA, serum NF-L increased within follow-up. The increase correlated with functional decline and progression of atrophy of the left frontal lobe of all patients with PPAs and the right middle frontal gyrus of patients with nfvPPA and svPPA. Conclusions: Blood level of NF-L can aid the differential diagnosis of PPA variants, especially in combination with CSF pNF-H. Because serum NF-L correlates with functional decline and atrophy in the disease course, it qualifies as an objective disease status marker. Extended follow-up studies with cases of known neuropathology are imperative

Serum neurofilament light chain in behavioral variant frontotemporal dementia

Objective To determine the association of serum neurofilament light chain (NfL) with functional deterioration and brain atrophy during follow-up of patients with behavioral variant frontotemporal dementia (bvFTD). Methods Blood NfL levels from 74 patients with bvFTD, 26 with Alzheimer disease (AD), 17 with mild cognitive impairment (MCI), and 15 healthy controls (Con) at baseline and follow-up were determined and analyzed for the diagnostic potential in relation to functional assessment (Clinical Dementia Rating Scale Sum of Boxes [CDR-SOB], frontotemporal lobar degeneration-related CDR-SOB, Mini-Mental State Examination [MMSE]) and brain volumetry. Results At baseline, serum NfL level correlated with CSFNfL (bvFTD r = 0.706, p < 0.0001;AD/MCI r = 0.666, p = 0.0003). Highest serum levels were observed in bvFTD (p < 0 0.0001 vs Con and MCI, p = 0.0078 vs AD, respectively). Discrimination of bvFTD from Con/MCI/AD was possible with 91%/74%/74% sensitivity and 79%/74%/58% specificity. At follow-up, serum NfL increased in bvFTD and AD (p = 0.0039 and p = 0.0006, respectively). At baseline and follow-up, NfL correlated with functional scores of patients with bvFTD (e.g., CDR-SOB [baseline] r = 0.4157, p = 0.0006;[follow-up] r = 0.5629, p < 0.0001) and with atrophy in the gray and white matter of many brain regions including frontal and subcortical areas (e.g., frontal lobe: r = -0.5857, p < 0.0001;95% confidence interval -0.7415 to -0.3701). For patients with AD/MCI, NfL correlated with the functional performance as well (e.g., CDR-SOB [baseline] r = 0.6624, p < 0.0001;[follow-up] r = 0.5659, p = 0.0003) but not with regional brain volumes. Conclusions As serum NfL correlates with functional impairment and brain atrophy in bvFTD at different disease stages, we propose it as marker of disease severity, paving the way for its future use as outcome measure for clinical trials. Classification of evidence This study provides Class III evidence that for patients with cognitive problems, serum NfL concentration discriminates bvFTD from other forms of dementia

Modelling carbon overconsumption and the formation of extracellular particulate organic carbon

During phytoplankton growth a fraction of dissolved inorganic carbon (DIC) assimilated by phytoplankton is exuded in the form of dissolved organic carbon (DOC), which can be transformed into extracellular particulate organic carbon (POC). A major fraction of extracellular POC is associated with carbon of transparent exopolymer particles (TEP; carbon content = TEPC) that form from dissolved polysaccharides (PCHO). The exudation of PCHO is linked to an excessive uptake of DIC that is not directly quantifiable from utilisation of dissolved inorganic nitrogen (DIN), called carbon overconsumption. Given these conditions, the concept of assuming a constant stoichiometric carbon-to-nitrogen (C:N) ratio for estimating new production of POC from DIN uptake becomes inappropriate. Here, a model of carbon overconsumption is analysed, combining phytoplankton growth with TEPC formation. The model describes two modes of carbon overconsumption. The first mode is associated with DOC exudation during phytoplankton biomass accumulation. The second mode is decoupled from algal growth, but leads to a continuous rise in POC while particulate organic nitrogen (PON) remains constant. While including PCHO coagulation, the model goes beyond a purely physiological explanation of building up carbon rich particulate organic matter (POM). The model is validated against observations from a mesocosm study. Maximum likelihood estimates of model parameters, such as nitrogen- and carbon loss rates of phytoplankton, are determined. The optimisation yields results with higher rates for carbon exudation than for the loss of organic nitrogen. It also suggests that the PCHO fraction of exuded DOC was 63±20% during the mesocosm experiment. Optimal estimates are obtained for coagulation kernels for PCHO transformation into TEPC. Model state estimates are consistent with observations, where 30% of the POC increase was attributed to TEPC formation. The proposed model is of low complexity and is applicable for large-scale biogeochemical simulations

Pervasive Selection for Cooperative Cross-Feeding in Bacterial Communities

Bacterial communities are taxonomically highly diverse, yet the mechanisms that maintain this diversity remain poorly understood. We hypothesized that an obligate and mutual exchange of metabolites, as is very common among bacterial cells, could stabilize different genotypes within microbial communities. To test this, we developed a cellular automaton to model interactions among six empirically characterized genotypes that differ in their ability and propensity to produce amino acids. By systematically varying intrinsic (i.e. benefit-to-cost ratio) and extrinsic parameters (i.e. metabolite diffusion level, environmental amino acid availability), we show that obligate cross-feeding of essential metabolites is selected for under a broad range of conditions. In spatially structured environments, positive assortment among cross-feeders resulted in the formation of cooperative clusters, which limited exploitation by non-producing auxotrophs, yet allowed them to persist at the clusters’ periphery. Strikingly, cross-feeding helped to maintain genotypic diversity within populations, while amino acid supplementation to the environment decoupled obligate interactions and favored auxotrophic cells that saved amino acid production costs over metabolically autonomous prototrophs. Together, our results suggest that spatially structured environments and limited nutrient availabilities should facilitate the evolution of metabolic interactions, which can help to maintain genotypic diversity within natural microbial populations.ISSN:1553-734XISSN:1553-735