31325 research outputs found
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Monostudiengang - Kern- und Zweitfach im Kombinationsstudiengang mit Lehramtsbezug - Überfachlicher Wahlpflichtbereich für andere Bachelorstudiengänge und -studienfächer
No full textMechanism of Cation Gating and Selectivity in AMPA-Type Glutamate Receptors
No full textIm zentralen Nervensystem von Wirbeltieren formen AMPA-Rezeptoren maßgeblich die Erregungsweiterleitung an den chemischen Synapsen. Sie sind Teil der Familie der ionotropen ligandengesteuerten Glutamatrezeptoren und dienen als unselektive Kationenkanäle in der postsynaptischen Zellmembran. Die Zusammensetzung des Rezeptors aus seinen verschiedenen Untereinheiten spielt hierbei eine wesentliche Rolle. Von den vier möglichen Kernuntereinheiten GluA1-4 ist GluA2 von zentraler Bedeutung. Durch posttranskriptionale RNA-Edierung der GluA2-Untereinheit wird an einer spezifischen Stelle im Bereich des Selektivitätsfilters ein Glutamin (Q) gegen ein Arginin (R) ausgetauscht, was maßgeblich die elektrophysiologischen Eigenschaften des AMPA-Rezeptors beeinflusst und sich unter Anderem auf dessen Calciumpermeabilität auswirkt. Klassische molekulardynamische Simulationen, durchgeführt und analysiert im Rahmen dieser Arbeit, zeigen wie zwei Arginine genügen, um die Permeation von Calciumionen durch den Ionenkanal des AMPA-Rezeptors vollständig zu blockieren. Dabei zeigt sich, dass Kaliumionen in der Lage sind die Blockade der zentralen Permeationsachse im Kanal zu umgehen, indem sie einen Seitenweg hinter den Selektivitätsfilterschleifen passieren können. Eine weitere typische Eigenschaft von AMPA-Rezeptoren ist ihre Fähigkeit, aufgrund ihrer tetrameren Architektur partiell geöffnete Zustände einzunehmen. Die vier Untereinheiten binden unabhängig voneinander Glutamat und werden somit abhängig von der Glutamatkonzentration nacheinander aktiviert. Jede Untereinheit trägt ihren eigenen Anteil zur Öffnung des Ionenkanals bei. Ausgehend von einer Struktur mit einem partiell geöffneten Ionenkanal wird in dieser Arbeit mittels Molekulardynamiksimulationen der Mechanismus dieser sogenannten sub-conductance states untersucht. Die Hydrathülle der Ionen spielt bei der Permeation durch den partiell geöffneten Kanal eine bedeutende Rolle.AMPA receptors play a crucial role in excitatory neurotransmission at chemical synapses in the vertebrate central nervous system. The GluA2 subunit is of central importance for ion selectivity and conductance. Through RNA editing of the GluA2 subunit, a glutamine (Q) is exchanged for an arginine (R) at a specific site in the selectivity filter region, which significantly influences the properties of the AMPA receptor and affects its calcium permeability. To investigate the impact of Q/R editing on ion permeation, classical molecular dynamics simulations were performed. These simulations demonstrate that two arginines are sufficient to completely block calcium ion permeation through the AMPA receptor ion channel, while the channel remains conductive for potassium ions even when all four subunits are edited from Q to R. The simulations further revealed the role of chloride ions in modulating permeation and identified distinct binding sites for potassium and calcium ions within the selectivity filter. The high positive charge density of the four arginines in the pore of the ion channel and hence the resulting electrostatic repulsion of the positively charged cations, as well as the blockade of the central channel pore by chloride ions, which are coordinated by the arginines, play a role. It is shown that potassium ions are able to bypass the blockade of the central permeation axis in the channel by passing a side path behind the selectivity filter loops. Another typical property of AMPA receptors is their ability to assume partially open states due to their tetrameric architecture. Each subunit contributes individually to the opening of the ion channel. Based on a structure with a partially open ion channel, the mechanism of these so-called sub-conductance states is investigated in this work using molecular dynamics simulations. The hydration shell of the ions plays an important role in permeation through the partially open channel
Sustainable Urban Governance and the Digital Divide: Patterns of E-Participation in Istanbul
No full textDigital transformation in public service delivery holds the potential to foster sustainable urban governance by promoting transparency, inclusivity, and citizen engagement. However, unequal access to digital tools and competencies poses challenges to the equitable use of these services. This study examines how different dimensions of the digital divide—socio-demographic characteristics, digital literacy, physical access to technology, and the perceived necessity of the internet—influence citizen engagement with digital public services in Istanbul. Drawing on secondary data from the Istanbul Metropolitan Municipality, a three-step methodology is employed combining logistic regression, thematic analysis, and spatial comparison. The results indicate that factors such as education, gender, age, and perceived necessity significantly affect digital engagement. Notably, digital literacy does not consistently predict e-government service use, suggesting that necessity may override competence. The study also finds that engagement remains limited to passive information-seeking rather than participatory functions. These findings highlight the importance of addressing digital inequalities to promote more inclusive service access. Ultimately, the study contributes to the understanding of how digital inclusion can advance sustainable urban governance and emphasizes the need for policies that ensure digital platforms benefit all segments of the population.This research received no external funding.Peer Reviewe
Mapping previously undetected trees reveals overlooked changes in pan-tropical tree cover
No full textDetecting tree cover is crucial for sustainable land management and climate mitigation. Here we develop an automatic detection algorithm using high-resolution satellite data (<5 m) to map pan-tropical tree cover (2015–2022), enabling identification and change analysis for previously undetected tree cover (PUTC). Our findings reveal that neglecting PUTC represents 17.31 ± 1.78% of the total pan-tropical tree cover. Tree cover net decreased by 61.05 ± 2.36 Mha in both forested areas (63.93%) and non-forested areas (36.07%) between 2015 and 2022. Intense changes in tree cover are primarily observed in regions with PUTC, where the World Cover dataset with a resolution of 10 m often fails to accurately detect tree cover. We also conduct a sensitivity analysis to quantify the contributions f climate factors and anthropogenic impacts (including human activities and land use cover change) to tree cover dynamics. Our findings indicate that 43.98% of tree cover gain is linked to increased precipitation, while 56.03% of tree cover loss is associated with anthropogenic impacts. These findings highlight the need to include undetected tree cover in strategies combating degradation, climate change, and promoting sustainability. Fine-scale mapping can improve biogeochemical cycles modeling and vegetation-climate interactions, improving global change understanding.National Key Research and Development Program of China (Grant No:2021YFE0117900)National Natural Science Foundation of China (National Science Foundation of China)https://doi.org/10.13039/501100001809Postdoctoral Fellowship Program of CPSF (Grant No: GZC20232757); Project funded by China Postdoctoral Science Foundation (Grant No: 2024M763351)Peer Reviewe
Genetic Characterization and Symbiotic Performance of Soybean Rhizobia Under Cold and Water-Deficient Conditions in Poland
No full textSoybeans have been cultivated in Poland for more than 140 years. However, Poland’s cold and water-deficient climatic conditions hinder soybean cultivation. Although the availability of suitable soybean varieties in Poland contributes to meeting the demand for soybean production, it is important to identify rhizobial inoculants in Polish soils suitable for soybean cultivation. In this study, we cultivated soybean varieties (Abelina, Merlin, and Sultana) grown in soils taken from four regions in Poland and isolated 330 strains from soybean root nodules. 16S rRNA gene sequencing identified 49 strains of highly stress-tolerant nodule-associated bacteria, including Bradyrhizobium , Rhizobium , Ensifer , Tardiphaga , and Ralstonia spp. Several isolates exhibited positive effects on soybean growth under cold and water-deficient conditions. In particular, the isolate Bradyrhizobium japonicum PSN49, which is phylogenetically similar to B . japonicum USDA 123, increased plant biomass and nodule formation in the soybean cultivar Abelina under abiotic stress conditions due to its high nitrogen-fixing activity. Whole-genome comparisons between PSN49 and other Bradyrhizobium strains revealed that trehalose biosynthesis genes and cold shock proteins contributed to cold stress tolerance. These findings and the strains identified in this study will enhance soybean production and deepen the understanding of the soybean–rhizobium relationship in Poland.This research was funded by JST-SICORP Concert-Japan [grant number JPMJSC16C2]; JSPS KAKENHI [grant number 20KK0136]; the Cabinet Office, Government of Japan, Moonshot R&D Program for Agriculture, Forestry and Fisheries (JPJ009237, funding agency: Bio-oriented Technology Research Advancement Institution); and SusCrop-ERANET [grant number SUSCROP/I/LegumeGap/01/2019].JST-SICORP Concert-JapanJSPS KAKENHISusCrop-ERANETthe Cabinet Office, Government of Japan, Moonshot R&D Program for Agriculture, Forestry and FisheriesPeer Reviewe
Investigation of defects and transport via cathodoluminescence spectroscopy
No full textIn dieser Arbeit werden die grundlegenden optoelektronischen Eigenschaften von Halbleiter-Nanodrähten (NWs) untersucht. Räumlich aufgelöste Lumineszenzstudien an mehreren NWs innerhalb eines Ensembles liefern wertvolle Einblicke in die Exzitonenbindung an Defekte und den Ladungsträgertransport entlang der NW-Achse. Diese Untersuchungen helfen bei der Etablierung von optimalen Wachstumsbedingungen für verschiedene III-V-NWs mit unterschiedlichen Funktionalitäten. Vier verschiedene Arten von Proben werden in dieser Arbeit diskutiert: (i) (In,Ga) NWs, (ii) Ga(As,Sb) NWs mit lokalisierten (In,Ga)As-Einschlüssen, (iii) phasenreine GaAs NWs und (iv) GaN NWs.
Die homogene Zusammensetzung und die Lumineszenzeigenschaften der untersuchten (In,Ga)As-NWs machen sie zu vielversprechenden Kandidaten für die photonische Integration auf Si-Wellenleitern. Der Einfluss von Zwillingsgrenzen auf den Ladungsträgertransport entlang der Achse von Ga(As,Sb)-NWs, die ebenfalls Potenzial für ihre photonische Integration haben, wird bewertet. Die Existenz und die Auswirkungen von gebundenen Exzitonenzuständen an isolierten Zwillingsgrenzen in GaAs-Nanodrähten werden untersucht, wobei der Schwerpunkt auf dem Ladungsträgertransport liegt. Schließlich werden Punkt- und strukturelle Defekte in GaN-Nanodrähten durch räumlich aufgelöste Kathodolumineszenz und Raman-Spektroskopie untersucht.This thesis studies the fundamental optoelectronic characteristics of semiconductor nanowires (NWs). Spatially-resolved luminescence studies across multiple NWs within an ensemble provide valuable insights into exciton binding to defects and carrier transport along the NW axis. These investigations help establish the optimal growth conditions for various III-V NWs with diverse functionalities. Four different types of samples are discussed throughout this thesis: (i) (In,Ga) NWs, (ii) Ga(As,Sb) NWs with localized (In,Ga)As insertions, (iii) phase-pure GaAs NWs and (iv) GaN NWs.
The homogeneous composition and luminescence properties of the studied (In,Ga)As NWs make them promising candidates for photonic integration on Si waveguides. The influence of twin boundaries on carrier transport along the axis of Ga(As,Sb) NWs, which also hold potential for their photonic integration, is assessed. Shifting the focus to isolated defects, the existence and implications of bound exciton states at isolated twin boundaries within GaAs nanowires are investigated, with a focus on carrier transport. Lastly, point and structural defects in GaN NWs are explored through spatially-resolved cathodoluminescence and Raman spectroscopy
High-Quality GaP(111) Grown by Gas-Source MBE for Photonic Crystals and Advanced Nonlinear Optical Applications
No full textThe precise fabrication of semiconductor-based photonic crystals with tailored optical properties is critical for advancing photonic devices. GaP(111) is a material of particular interest due to its high refractive index, wide optical bandgap, and pronounced optical anisotropy, offering unique opportunities for photonic applications. Its near-lattice matching with silicon substrates further facilitates integration with existing silicon-based technologies. In this study, we present the growth of high-quality GaP(111) thin films using gas-source molecular-beam epitaxy (GSMBE), achieving atomically smooth terraces for the homo-epitaxy of GaP(111). We demonstrate the fabrication of photonic crystal cavities from GaP(111), employing AlGaP(111) as a sacrificial layer, and achieve a quality factor of 1200 for the cavity mode with resonance around 1500 nm. This work highlights the potential of GaP(111) for advanced photonic architectures, particularly in applications requiring strong light confinement and nonlinear optical processes, such as second-harmonic and sum-frequency generation.This research was funded by the European Commission FP7-ICT-2013-613024-GRASP.European CommissionPeer Reviewe
Exploring user experiences of clinicians engaged with the digital healthcare interventions across the referral and university teaching hospitals in Nigeria: a qualitative study
No full textIntroduction: Given that Nigeria and several developing countries are still at the early stage of digital healthcare interventions adoption (like the use of electronic health records systems) there is scarcity of research/empirical reports investigating the overall user experiences of clinicians, the doctors and the nurses who are or who had been practically engaged with the use of these new digital healthcare support implementations that had engendered new culture across their care delivery facilities. The referral and university teaching hospitals in Nigeria numbering over 166 and scattered across over 37 states of the federation and the Federal Capital Territory (FCT) make up a strategic component of Nigeria's healthcare ecosystem. This research was therefore designed and restricted to clinicians who had used these systems so as to explore their experiences with these systems and possibly unveil any challenges/limitations that can bedevil successful and sustainable acquisition of digital healthcare intervention programmes and projects across referral and university teaching hospitals in the Southeastern Region of Nigeria; and could also hamper any future implementations. Method: This study was designed in a manner that allows the clinicians the liberty to conveniently express in writing (via comments) issues, challenges and concerns that they had perceived, encountered or experienced bedevilling electronic health record adoption and use across their care facilities. So a structured interview method was chosen by the research team (after due considerations) as fitting the research context. This (structured interview) was therefore designed and targeted at about 400 clinical participants, including the doctors and the nurses from three select referral and university teaching hospitals in the Southeastern Region of Nigeria (a federal, state, and national specialist referral hospital). Result: Out of the 400 clinicians who were targeted in the survey, 326 of them practically responded to the interview questions. The outcome showed the clinicians willingly exposing several issues and challenges that had stifled electronic health record adoption across the hospitals. Issues identified were categorized into themes including challenges bordering on lack of political will on the part of hospital administration; lack of computer/digital/EHR literacy; poor and often lack of comprehensive training on the workings of EHR; poor maintenance culture; poor EHR system design, poor implementation and use-based struggles and challenges; infrastructure issues, system breakdown and network challenges etc were reported. Conclusion: The outcome of this investigation has profoundly exposed practical issues that had hitherto stifled and often suffocated electronic health record implementation projects across referral and university teaching hospitals in Nigeria. And given the strategic importance of these hospitals in Nigeria healthcare ecosystem, conscious and concerted efforts must be made to address them.Peer Reviewe
effects of pre-treatment on growth and composition
No full textThe article processing charge was funded by the Open Access Publication Fund of Humboldt-Universität zu Berlin.Integrating plant production with insect farming, termed "entomoponics," involves using plant waste as a substrate for insect rearing, while returning insect frass to fertilise the plants. In this study, vegetative wastes from strawberry (Fragaria x ananassa), and common bean (Phaseolus vulgaris), were incorporated into a wheat bran-based substrate for rearing the yellow mealworms (MW; Tenebrio molitor). The wastes were either autoclaved or autoclaved then fermented with the fungus Trichoderma reesei, and mixed in a 50:50 ratio with wheat bran. Replacing 50% of the wheat bran with autoclaved beans waste did not significantly affect MW yield, but the yield was reduced when beans wastes were fermented or left untreated. Incorporating beans waste, whether treated or untreated, increased the Ca, K, and Fe content in the MW. Incorporating strawberry vegetative waste into the substrate compensated the yield regardless of the pre-treatment, but enhanced Mn, Zn, and Fe levels in the produced MW. Plant flavonoids were reduced when the wastes were pre-treated and did not accumulate in the MW biomass. These findings provide insights into using plant vegetative wastes as a partial supplement in MW rearing substrates, and the potential effects on the growth and nutritional composition of the resulting MW biomass.Peer Reviewe
Zirconium fluoride-supported high-entropy fluoride: a catalyst for enhanced oxygen evolution reaction
No full textExtended hydrogen initiatives promote the urgency of research on water splitting technologies and, therein, oxygen evolution reaction catalysts being developed. A route to access a ZrF4 supported high-entropy fluoride catalyst using a facile sol–gel route is presented. The high-entropy character of the catalyst was confirmed by scanning transmission electron microscopy and energy dispersive X-ray spectroscopy (STEM-EDX) as well as inductively coupled plasma-mass spectrometry (ICP-MS). Additional investigations on the local structure were performed using extended X-ray absorption fine structure spectroscopy (EXAFS) and pair distribution function (PDF) analysis. The catalyst shows significant potential for oxygen evolution reaction (OER) in alkaline media with a current density of 100 mA cm−2 at approximately 1.60 V, thus outperforming benchmark materials such as IrO2, despite a significant reduction in electrochemical mass loading. A potential mechanism is suggested based on free energy calculation using DFT calculations.Deutsche Forschungsgemeinschaft 10.13039/501100001659Peer Reviewe