Technische Universität Dresden: Qucosa
Not a member yet
16344 research outputs found
Sort by
Modulare Synthese von strukturell diversen polyzyklischen aromatischen Kohlenwasserstoffen mit eingebetteten Azulenen durch Knoevenagelartige Kondensation
No full textDas Forschungsinteresse an in polyzyklische aromatische Kohlenwasserstoffe (PAKs) eingebettete Azulene hat sich in den letzten Jahren signifikant erhöht, aber der Mangel an effizienten Synthesestrategien hemmt die Studien der Struktur-Eigenschaftsbeziehungen sowie weiterer opto-elektronischer Anwendungen. Wir berichten hier von einer neuen modularen Synthesestrategie für diverse Azulen-eingebettete PAKs durch eine Tandem Suzuki Kupplung und basenvermittelte Kondensation des knoevenagel Typs in guten Ausbeuten und exzellenter struktureller Vielfalt. Die Substrate beinhalten nicht-alternierende thiophenreiche PAKs, schmetterlings- und z-förmige PAKs mit zwei Azuleneinheiten sowie das erste Beispiel zweier eingebetteter Azuleneinheiten, welche ein doppel-[5]Helicen bilden. Die strukturelle Topologie, Aromatizität und die photophysischen Eigenschaften wurden per NMR Spektroskopie, Einkristallstrukturanalyse, UV/Vis Absorptionsspektroskopie sowie durch DFT Simulationen untersucht. Diese Strategie stellt eine neue Herangehensweise für die zügige Synthese bisher nicht erforschter, nicht-alternierender PAKs oder Graphennanostreifen mit mehreren Azuleneinheiten dar
Pushing Up the Size Limit of Boron-doped peri-Acenes: Modular Synthesis and Characterizations
No full textHeteroatom-doped peri-acenes (PAs) have recently attracted considerable attention considering their fascinating physical properties and chemical stability. However, the precise sole addition of boron atoms along the zigzag edges of PAs remains challenging, primarily due to the limited synthetic approach. Herein, we present a novel one-pot modular synthetic strategy toward unprecedented boron-doped PAs (B-PAs), including B-[4,2]PA (1 a-2), B-[4,3]PA (1 b-2) and B-[7,2]PA (1 c-3) derivatives, through efficient intramolecular electrophilic borylation. Their chemical structures are unequivocally confirmed with a combination of mass spectrometry, NMR, and single-crystal X-ray diffraction analysis. Notably, 1 b-2 exhibits an almost planar geometry, whereas 1 a-2 displays a distinctive bowl-like distortion. Furthermore, the optoelectronic properties of this series of B-PAs are thoroughly investigated by UV/Vis absorption and fluorescence spectroscopy combined with DFT calculation. Compared with their parent all-carbon analogs, the obtained B-PAs exhibit high stability, wide energy gaps, and high photoluminescence quantum yields of up to 84 %. This study reveals the exceptional ability of boron doping to finely tune the physicochemical properties of PAs, showcasing their potential applications in optoelectronics
Volatile Memory Motifs: Minimal Spiking Neural Networks
No full textHow spiking neuronal networks encode memories in their different time and spatial scales constitute a fundamental topic in neuroscience and neuro-inspired engineering. Much attention has been paid to large networks and long-term memory, for example in models of associative memory. Smaller circuit motifs may play an important complementary role on shorter time scales, where broader network effects may be of less relevance. Yet, compact computational models of spiking neural networks that exhibit short-term volatile memory and actively hold information until their energy source is switched off, seem not fully understood. Here we propose that small spiking neural circuit motifs may act as volatile memory components. A minimal motif consists of only two interconnected neurons – one self-connected excitatory neuron and one inhibitory neuron – and realizes a single-bit volatile memory. An excitatory, delayed self-connection promotes a bistable circuit in which a self-sustained periodic orbit generating spike trains co-exists with the quiescent state of no neuron spiking. Transient external inputs may straightforwardly induce switching between those states. Moreover, the inhibitory neuron may act as an autonomous turn-off switch. It integrates incoming excitatory pulses until a threshold is reached after which the inhibitory neuron emits a spike that then inhibits further spikes in the excitatory neuron, terminating the memory. Our results show how external bits of information (excitatory signal), can be actively held in memory for a pre-defined amount of time. We show that such memory operations are robust against parameter variations and exemplify how sequences of multidimensional input signals may control the dynamics of a many-bits memory circuit in a desired way
Word Recognition with a Cochlear Implant in Relation to Prediction and Electrode Position
No full textBackground: the word recognition score (WRS) achieved with cochlear implants (CIs) varies widely. To account for this, a predictive model was developed based on patients’ age and their pre-operative WRS. This retrospective study aimed to find out whether the insertion depth of the nucleus lateral-wall electrode arrays contributes to the deviation of the CI-achieved WRS from the predicted WRS. Materials and methods: patients with a pre-operative maximum WRS > 0 or a pure-tone audiogram ≥80 dB were included. The insertion depth was determined via digital volume tomography. Results: fifty-three patients met the inclusion criteria. The median WRS achieved with the CI was 70%. The comparison of pre- and post-operative scores achieved with a hearing aid and a CI respectively in the aided condition showed a median improvement of 65 percentage points (pp). A total of 90% of the patients improved by at least 20 pp. The majority of patients reached or exceeded the prediction, with a median absolute error of 11 pp. No significant correlation was found between the deviation from the predicted WRS and the insertion depth. Conclusions: our data support a previously published model for the prediction of the WRS after cochlear implantation. For the lateral-wall electrode arrays evaluated, the insertion depth did not influence the WRS with a CI
Thyroid hormone receptor Thra and Thrb knockout differentially affects osteoblast biology and thyroid hormone responsiveness in vitro
No full textThyroid hormones (TH) are important modulators of bone remodeling and thus, thyroid diseases, in particular hyperthyroidism, are able to compromise bone quality and fracture resistance. TH actions on bone are mediated by the thyroid hormone receptors (TR) TRα1 and TRβ1, encoded by Thra and Thrb, respectively. Skeletal phenotypes of mice lacking Thra (Thra⁰⸍⁰) and Thrb (Thrb⁻⸍⁻) are well-described and suggest that TRα1 is the predominant mediator of TH actions in bone. Considering that bone cells might be affected by systemic TH changes seen in these mutant mice, here we investigated the effects of TR knockout on osteoblasts exclusively at the cellular level. Primary osteoblasts obtained from Thra⁰⸍⁰, Thrb⁻⸍⁻, and respective wildtype (WT) mice were analyzed regarding their differentiation potential, activity and TH responsiveness in vitro. Thra, but not Thrb knockout promoted differentiation and activity of early, mature and late osteoblasts as compared to respective WT cells. Interestingly, while mineralization capacity and expression of osteoblast marker genes and TH target gene Klf9 was increased by TH in WT and Thra-deficient osteoblasts, Thrb knockout mitigated the responsiveness of osteoblasts to short (48 h) and long term (10 d) TH treatment. Further, we found a low ratio of Rankl, a potent osteoclast stimulator, over osteoprotegerin, an osteoclast inhibitor, in Thrb-deficient osteoblasts and in line, supernatants obtained from Thrb⁻⸍⁻ osteoblasts reduced numbers of primary osteoclasts in vitro. In accordance to the increased Rankl/Opg ratio in TH-treated WT osteoblasts only, supernatants from these cells, but not from TH-treated Thrb⁻⸍⁻ osteoblasts increased the expression of Trap and Ctsk in osteoclasts, suggesting that osteoclasts are indirectly stimulated by TH via TRβ1 in osteoblasts. In conclusion, our study shows that both Thra and Thrb differentially affect activity, differentiation and TH response of osteoblasts in vitro and emphasizes the importance of TRβ1 to mediate TH actions in bone
Isometric Freehand Quadrature of Urban Sights: The “Squares‑are‑the‑Key Method”
No full textIn this paper, I propose the “squares-are-the-key method” as an update of the outdoor freehand-drawing class for architectural design. Let’s generate simplified 2D grids of site and floor plans, transform them to isometric grids, and insert essential height edges, taken from simplified elevations and sections, into it, on site
Interaction between habits as action sequences and goal-directed behavior under time pressure
No full textHuman behavior consists in large parts of action sequences that are often repeated in mostly the same way. Through extensive repetition, sequential responses become automatic or habitual, but our environment often confronts us with events to which we have to react flexibly and in a goal-directed manner. To assess how implicitly learned action sequences interfere with goal-directed control, we developed a novel behavioral paradigm in which we combined action sequence learning through repetition with a goal-directed task component. So-called dual-target trials require the goal-directed selection of the response with the highest reward probability in a fast succession of trials with short response deadlines. Importantly, the response primed by the learned action sequence is sometimes different from that required by the goal-directed task. As expected, we found that participants learned the action sequence through repetition, as evidenced by reduced reaction times (RT) and error rates (ER), while still acting in a goal-directed manner in dual-target trials. Specifically, we found that the learned action sequence biased choices in the goal-directed task toward the sequential response, and this effect was more pronounced the better individuals had learned the sequence. Our novel task may help shed light on the acquisition of automatic behavioral patterns and habits through extensive repetition, allows to assess positive features of habitual behavior (e.g., increased response speed and reduced error rates), and importantly also the interaction of habitual and goal-directed behaviors under time pressure
Berlin Pankow: a 15-min city for everyone?: A case study combining accessibility, trafc noise, air pollution, and socio-structural data
No full textCars are dominating urban traffic in cities around the world, even though daily trips in many cities are often realized with active modes of transportation or public transport. Urban transport planning processes need to adapt to this reality and the necessity of climate change mitigation. Against this background, the research project “Mobility Reporting”, a joint undertaking of the district Pankow in Berlin and researchers from TU Berlin and TU Dresden, established a new, goal-driven, and participative planning process. The process identified local mobility as one of the central planning goals. The 15-min city (FMC) was thus adduced as a benchmark to analyze the district’s current mobility system and development potential. We conducted extensive accessibility analyses to examine the status quo concerning the FMC. We calculated travel times to essential destinations in daily life by foot, public transport, and car. This analysis was accompanied by a mixed online and paper–pencil survey conducted to evaluate the perceived accessibility of people in Pankow. The survey results shed light on the question of which walking time thresholds constitute a “very good” or “good” accessibility. Further analyses included environmental and social variables, allowing us to check whether areas with different accessibility levels also differ regarding the socio-economic characteristics of their inhabitants. For example, do socially advantaged neighborhoods have better local accessibility? Is there a trade-off between exposure to environmental pollution and good accessibility? With this contribution, we shed light on what an FMC is and ought to be. Results from the survey support the normative and political vision of the FMC. Pankow generally offers the merits of a walkable city, showing the expected travel time differences between the dense inner city and the outskirts. Socially disadvantaged neighborhoods are not consistently less accessible. However, there seems to be a trade-off between good accessibility (especially PT accessibility) and correlated externalities of transport, namely air pollution and noise
The relationship of organizational culture with management control systems and environmental management control systems
No full textThis paper expands upon examinations of the flexibility–stability continuum of organizational culture in the extant literature by identifying how the four culture types of the competing values framework are associated with the emphasis on management control systems (MCS) and environmental management control systems (EMCS). By analyzing data drawn from a dyadic survey addressing both heads of management accounting and heads of sustainability or environmental management, this paper provides empirical evidence for multiple direct associations of different culture types, specifically, adhocracy, bureaucracy, clan, and market cultures, with a set of environmental and general management controls, specifically, action, cultural, personnel, and results controls. For instance, bureaucracy cultures are positively associated with action, personnel, and results controls for MCS and cultural controls for EMCS, while clan cultures are positively associated with cultural and personnel controls for MCS but negatively associated with action and results controls for EMCS. According to our findings, firms cannot transfer their emphasis on general MCS to specific EMCS because different organizational cultures are associated with MCS and EMCS in different ways. This disentanglement of organizational culture facilitates a deeper understanding of environmental controls at the organizational level
Swelling of beech wood (Fagus sylvatica L.) during gaseous ammonia treatment as a function of pressure
No full textThis paper deals with the optical observation and evaluation of the swelling of beech wood samples (Fagus sylvatica L.) during gaseous ammonia treatment. The pressure level was varied in several experiments from ambient pressure to almost saturated steam pressure at isothermal conditions at 20 °C. The initial moisture content of the wood was oven dried and also conditioned (65% RH/20 °C). All experiments were carried out in a self-developed experimental setup. It consisted of three parts: a pressure vessel with a glass pane at the top, a camera with additional lighting above it and an algorithm for the semi-automatic evaluation of the data. Parallel investigation of the maximum swelling in water of specimens of the same origin showed that ammonia leads to a higher swelling in tangential direction (up to 23%). The swell-inhibiting influence by the wood rays can be observed on the basis of the comparison to the water swelling in radial direction. Furthermore, the results visualise the change in crystal structure from cellulose I to ammonia-cellulose I