34 research outputs found
Regulation of the mammalian-brain V-ATPase through ultraslow mode-switching
No full textVacuolar-type adenosine triphosphatases (V-ATPases)1–3 are electrogenic rotary mechanoenzymes structurally related to F-type ATP synthases4,5. They hydrolyse ATP to establish electrochemical proton gradients for a plethora of cellular processes1,3. In neurons, the loading of all neurotransmitters into synaptic vesicles is energized by about one V-ATPase molecule per synaptic vesicle6,7. To shed light on this bona fide single-molecule biological process, we investigated electrogenic proton-pumping by single mammalian-brain V-ATPases in single synaptic vesicles. Here we show that V-ATPases do not pump continuously in time, as suggested by observing the rotation of bacterial homologues8 and assuming strict ATP–proton coupling. Instead, they stochastically switch between three ultralong-lived modes: proton-pumping, inactive and proton-leaky. Notably, direct observation of pumping revealed that physiologically relevant concentrations of ATP do not regulate the intrinsic pumping rate. ATP regulates V-ATPase activity through the switching probability of the proton-pumping mode. By contrast, electrochemical proton gradients regulate the pumping rate and the switching of the pumping and inactive modes. A direct consequence of mode-switching is all-or-none stochastic fluctuations in the electrochemical gradient of synaptic vesicles that would be expected to introduce stochasticity in proton-driven secondary active loading of neurotransmitters and may thus have important implications for neurotransmission. This work reveals and emphasizes the mechanistic and biological importance of ultraslow mode-switching.</p
Solar tracking of perovskite-silicon tandem PV modules under real-world conditions
No full textIncreasing the energy yield per unit area of Photovoltaic (PV) modules is one of the main challenges the PV technology is currently facing. In search of ways to address this issue, solar tracking systems are a favorable solution, which according to literature can enhance the energy yield by up to 45%. Another way is to opt for high-efficiency solar cells. Tandem cells have emerged as a promising technology, achieving efficiencies of over 30%. The integration of these tandem cells with sun-tracking techniques suggests high-performing solar modules. The present work develops a solar tracking model to simulate the performance of tracking PV systems equipped with tandem modules. The model will be incorporated into the PVMD toolbox, a PV modeling software developed within the PVMD group. This software can predict the energy yield of PV systems using self-consistent models for each aspect of the energy conversion.The current version of the toolbox makes it impractical to include solar tracking due to the time-consuming nature of ray tracing used to compute the irradiance. Ray tracing generates sensitivity values that illustrate how sensitive is the module to incoming irradiance from any direction in the skydome. Initially, this work focuses on substituting ray tracing with an alternative faster approach to express sensitivity based on view factors. The view factor and ray tracing method are compared with respect to computational time and extent of agreement. It was found that the view factor can significantly reduce the computational time from over 12 minutes, as required in ray tracing, to a few milliseconds for a single module orientation. Additionally, the view factor method generates sensitivity values closely matching those from ray tracing. For instance, a mean RMSE of 1.2% between the two methods is achieved, for an albedo of 0.2 and module tilt of 30 degrees. Sun tracking aims to locate the module orientation that maximizes the in-plane irradiance. Directly calculating the irradiance for every orientation to identify the optimal, is not a viable option, as it requires substantialtime. Thus, sun tracking was expressed as an optimization problem and algorithms were employed to address it. Based on the prevailing sky conditions three optimization case studies were defined on an hourly basis: sunny, cloudy, and intermediate hours. Multiple algorithms were compared across the three cases with selected criteria the convergence to the optimum and runtime. Matlab’s surrogate solver and an author-developed algorithm were selected, as a satisfying solution, compromising those two criteria.Finally, energy yield simulations were performed on perovskite-silicon tandem modules mounted on a dual-axis tracking system. Four locations were selected, representing different real-world conditions: Stockholm, Athens, Bombay and Bogota. Results show the module’s tilt dynamic adaptability to sky conditions: increas- ing nearly to the sun’s zenith when direct light dominates, and lowering when diffuse light is prevalent. Furthermore, the seasonal fluctuations of the energy gain of tracking systems are explored, with locations further from the equator such as Stockholm exhibiting the highest variability of 19% in winter to 36.9% in summer. In addition, the annual energy gained among the locations was found to span between 24.8% (Bogota) and 34.1% (Bombay). An important finding is the direct proportionality in gains from absorbed irradiance to DC and AC yields, illustrating a 1:1:1 ratio. Then, the effect of tracking technology on mismatch losses of tandem modules was examined. Results indicated that tracking has little impact on both the current and power mismatch. For example, the power mismatch losses slightly increased from 1.10-1.46% in static PV systems to 1.29-1.77% for tracking topologies in the locations examined. Moreover, the tandem’s annual energy gain is compared to silicon heterojunction modules. The analysis showed similar gains across locations for both cell technologies.Electrical Engineering | Sustainable Energy Technolog
"Ecce Mycenaea scaena" : stage directions and pantomimic effects in the "Orestis tragoedia"
No full textDracontius’s Orestis tragoedia, despite its disputable title, is a poem clearly defined by the author himself as epic, as the appeal to Melpomene to step down from her tragic cothurns since the iambics are to be replaced by the dactylic meter (ll. 13-14) is unambiguous enough. At the same time, however, it is true that the OT is composed with an eye on tragedy. Even, upon a closer look one can notice that the poet’s inspirations are not only in tragedy understood as a literary (i.e. ‘textual’) genre and repository of motifs but also in the most important and popular mythological spectacle known to the Roman public, i.e. the tragic pantomime. It is hardly surprising considering that pantomimic references are noticeable also in other epyllions and in the Medea they are openly declared. In fact, Dracontius’s approach to the tragoedia saltata turns out to be emulative as he apparently aims at making his readers believe that through the verbal description and the speaking ego’s directions they can see the image not worse (possibly better) than in the theater.L’Orestis tragoedia de Dracontius, malgré son titre contestable, appartient sans nul doute au genre épique, selon l’auteur lui-même : s’adressant à Melpomène, le poète lui demande d’ôter ses cothurnes tragiques, puisqu’il faut à présent remplacer les iambes par l’hexamètre dactylique (vv. 13-14). Il n’en est pas moins vrai que l’Orestis tragoedia se réfère nettement à la tragédie. Une analyse attentive révèle en outre que le poète s’inspire non seulement de la tragédie en tant que genre littéraire, mais aussi des spectacles mythologiques (ou pantomime tragique), si appréciés du public romain. On ne s’étonnera donc pas de trouver dans ses autres épyllions des renvois à la pantomime ; dans Médée, ils sont même explicitement désignés. En fait, on peut dire que Dracontius rivalise avec la tragoedia saltata ; il veut, semble-t-il, persuader ses lecteurs que, grâce aux descriptions verbales et aux indications (de mise en scène) du sujet parlant, ils parviendront à se représenter la scène aussi bien, ou même mieux, que s’ils l’avaient vue au théâtre
Automatically Testing a Conversational Crowd Computing Platform
No full textThe rise in the use of crowd computing platforms led to the birth of Dandelion, a conversational crowd computing platform developed at TU Delft with the main goals being to connect students with researchers and to allow students to report on their well-being by using a friendly interface. Dandelion was tested manually up to the time of drafting this paper; thus, the primary motivation behind this paper is to ensure the robustness and measure the responsiveness of Dandelion.Robustness was exercised by utilizing a simulated user behaving unexpectedly. The testing framework then classifies the behaviour of Dandelion according to the C.R.A.S.H. scale. The testing framework is validated by altering Dandelion's behaviour and ensuring that the test results reflect the change. Furthermore, a lower bound to the run time of a task will be estimated using a Multi-Agent System (M.A.S.) simulation on Dandelion.Upon verifying the correctness of the robustness test, a faulty assumption was uncovered on which the user's input validation was based. Furthermore, the M.A.S. simulation run estimated a lower bound of seconds, while revealing a lack of user's input validation before posting them in the database.CSE3000 Research ProjectComputer Science and Engineerin
Comparative enviro-economic impact assessment of Dutch chlorine production systems: Investigating different methods for monetizing environmental externalities
No full textTo fend off the probable adverse effects of climate change as well as the subsequent economic and social impacts as a consequence of humans’ industrial activities, drastic changes are required in the way of processing, managing and exploiting natural resources. Based on a case study, the present report combines life-cycle assessment and life-cycle costing techniques on the basis of environmental externalities monetization with a view to conducting a multi-perspective comparative assessment of different chlorine manufacturing systems so that to identify which alternative can lead to the lowest environmental footprint and cost-intensity. Our findings suggest that the most cost-effective and less environmentally-intensive technical solution concerns the modification of the electrolysis cell’s configuration type from gap to zero-gap one when the heat is supplied by an on-site CHP facility. This modification is accompanied by 39% reduction of CO2 emissions in the membrane electrolysis stage and 24% reduction in the total CO2 emissions per ton of chlorine produced. Moreover, annual savings and profits increase while chain-related environmental costs substantially decline.Management of Technology (MoT
Free spirit
No full textTitle: ’Eλεύθερο Πνεῦμα (Free spirit) Originally Published: ’Aθήνα, ’Eκδότης Α I. Ράλλης, 1929 Language: Greek The excerpts used are from the annotated edition by Konstantinos Th. Dimaras, (Athens: Ερμής, 1973), pp. 10, 61–64. About the author Giorgos Theotokas, known also by the penname Orestis Digenis [1905, Istanbul – 1966, Athens]: novelist and critic. He completed his secondary education in a French lyceum in Istanbul. He wrote his first essays on literature during his high school years...
Author Correction: QUAREP-LiMi: a community endeavor to advance quality assessment and reproducibility in light microscopy
No full textThe App Store Model for Enterprise Application Software
No full textKumulative Dissertation, Otto-Friedrich-Universität Bamberg, 2018App stores in the consumer software market are omnipresent and have significantly changed the way how software is being produced, marketed, and consumed. Enterprise software customers also demand higher flexibility in buying and adopting standardized enterprise application software - and new technologies such as cloud computing and highly efficient development platforms provide new options for software vendors and the entire software value chain. This application-oriented work researches the challenge of establishing the app store model for enterprise application software as a technology-driven business model in a two-sided platform ecosystem. The author analyzes the topic comprehensively from the software buyer’s, the software provider’s and the platform provider’s perspective and uncovers detailed insights on barriers, drivers, and constraints. Moreover he proposes solutions on the level business processes and detailed requirements. His research is highly interdisciplinary and utilizes both empirical qualitative and design-oriented methods
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Campaign finance law ::a comparative constitutional analysis between the US, the UK and Greece /
No full textThis book provides a detailed analysis of the different principles that shape the constitutional background of campaign finance law. Through three indicative country specific examples, the author examines legislation and jurisprudence that reflect such principles and demonstrate the common and different approaches in this upcoming field of law as driven by different constitutional traditions. This is the first time in legal scholarship that such an analytical effort is made to draw universal conclusions on campaign finance law principles. The US, the UK and Greece represent different jurisdictional examples of regulatory evolution in the effort to control the effect of money in politics. The author achieves to set the foundations of a practical and academic debate on global campaign finance reform. The book is a useful tool for public law scholars, political scientists as well as politicians and legal practitioners who are faced with campaign finance regulation and enforcement questions in the three jurisdictions and globally
Le roi d’Hélène de Christos Choménidis : L’histoire d’Hélène racontée par Ménélas
No full textIn April of 2020, Christos Chomenidis (Athens, 1966) published his eleventh novel, a book of over 400 pages by the title Her king. The main character is Menelaus and the starting point is Helen’s run away with Paris. Menelaus decides to tell his truth about this well-known story. In Her king all great heroes of the legend of Troy participate, but they are presented through a distorting mirror: e.g. Menelaus is the bravest son of Atreus and not Agamemnon; Leda’s story is a lie; the Dioscuri are a couple of imbeciles. My paper is mostly a review on Chomenidis’ book, where I highlight the deviations from the “official” story about the beginning of the Trojan war and find the possible ancient sources that the author chose to follow or not.In April of 2020, Christos Chomenidis (Athens, 1966) published his eleventh novel, a book of over 400 pages by the title Her king. The main character is Menelaus and the starting point is Helen’s run away with Paris. Menelaus decides to tell his truth about this well-known story. In Her king all great heroes of the legend of Troy participate, but they are presented through a distorting mirror: e.g. Menelaus is the bravest son of Atreus and not Agamemnon; Leda’s story is a lie; the Dioscuri are a couple of imbeciles. My paper is mostly a review on Chomenidis’ book, where I highlight the deviations from the “official” story about the beginning of the Trojan war and find the possible ancient sources that the author chose to follow or not
