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See detailFunctional coatings based on MWCNT-Metal oxide nanocomposite for solar energy harvester application.
Prasadam, Vasu Prasad UL

Doctoral thesis (2021)

Global energy demand propelled humankind in search of clean and renewable energy sources. Among them, solar energy outstands all the available renewable sources. In this context, concentrated solar ... [more ▼]

Global energy demand propelled humankind in search of clean and renewable energy sources. Among them, solar energy outstands all the available renewable sources. In this context, concentrated solar thermal technology (CST) and hydrogen storage via solar water splitting significant feature contributions in global power generation. Nevertheless, the major challenge in CST technology is achieving a high solar absorption selectivity with thermal stability above 923 K. Whereas the limited chemical stability and low performance remain significant challenges in solar water-splitting technology. We address these technologies' critical issues through multiwalled carbon nanotubes (MWCNT)-metal oxide hybrid materials. MWCNTs are known for their high solar absorption, thermal and electrical conductivity. While metal oxides such as VO2, Al-doped ZnO are known for their infrared reflecting properties with high transparency in the visible region. TiO2 and ZnO have appropriate band positions for water splitting reactions. Here, combining CNTs and metal oxides at the nanoscale leads to unique properties not present in individual constituents. We fabricate the MWCNT-metal oxide through the hybrid chemical vapour deposition-atomic layer deposition (CVD-ALD) process. Here the CVD is implemented to grow MWCNTs, while ALD is used to produce conformal metal oxide shells on the 3D porous MWCNT structures. The MWCNT-VO2 nanostructures performed in this study feature a solar selectivity modulation across the semiconductor-metal transition temperature of VO2, i.e., 67˚C. The thermally induced optical modulation was investigated as a function of the morphology of VO2 phase. The grown VO2 nanoparticles on MWCNT illustrate an enhancement in the spectral emissivity across the SMT temperature. A contrasting optical modulation is displayed by the continuous VO2 layer on MWCNT. Aluminium doped zinc oxide (AZO) layer (4.7 at %) illustrated solar absorbance of 0.96 and thermal emittance of 0.6. The limited thermal stability of the engineered MWCNT-AZO was enhanced by the deposition of a thin Al2O3 layer at the MWCNT-AZO interface. A core-double shell structure, i.e., CNT-Al2O3-AZO, withstands thermal treatment at 1000 K for 72 h. Solar water splitting study on MWCNT-TiO2 and MWCNT-ZnO nanostructures revealed a significant performance improvement relative to the respective oxides. For MWCNT-TiO2 core-shell structure, an enhancement of photocurrent by 400 % was observed relative to planar Si-TiO2. While in MWCNT-ZnO core-shell structure, similar results as CNT-TiO2 is observed but with higher photocurrent density because of better electrical properties of ZnO. We observed an increase of 458 % of the photocurrent density relative to Si-ZnO. The difference in performance between Si-ZnO/TiO2 and MWCNT-ZnO/TiO2 was associated with the diminished electron-hole recombination, efficient electron collection and increased relative surface in the core-shell structure. [less ▲]

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See detailHow to catch a space debris
Yalcin, Baris Can UL; Martinez Luna, Carol UL; Delisle, Maxime Hubert et al

Poster (2021, November 18)

The partnership between SpaceR and Spacety Luxembourg aims to develop cutting edge active space debris removal solutions that can be implemented into small cube sats The solution will take the advantage ... [more ▼]

The partnership between SpaceR and Spacety Luxembourg aims to develop cutting edge active space debris removal solutions that can be implemented into small cube sats The solution will take the advantage of latest advancements in many tech domains, such as gecko like sticky adhesives and energy efficient shape memory alloy materials. [less ▲]

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See detailScientific Models, Computer Simulations, and Agent-Based Models. Hermeneutic and Analytic Perspectives.
Durlacher, Thomas UL

Doctoral thesis (2021)

This work is about some of the philosophical problems that arise in the context of agent-based modeling. Agent-based models differ from other modeling techniques primarily in terms of the way they ... [more ▼]

This work is about some of the philosophical problems that arise in the context of agent-based modeling. Agent-based models differ from other modeling techniques primarily in terms of the way they represent their target system. They are a comparatively novel kind of computer simulation and are used to investigate complex systems. In recent decades, agent-based models have been used in disciplines such as economics, archaeology, sociology, and ecology. Typical target systems of agent-based models include markets, foragers, opinion dynamics, and predator-prey interactions. This thesis contributes to the research on agent-based modeling by situating agent-based models in the broader context of scientific modeling and by resolving several important philosophical problems that arise in relation to agent-based modeling research. Those problems mainly concern the character of agent-based models and their capacity to enhance our understanding of social phenomena. The first part of this thesis contributes to ongoing discussions in the philosophy of science about the status of scientific models by providing new perspectives on the function of models, the difference between computer simulations and other modeling techniques, and by analyzing the use of models across several disciplines. The second part of the thesis is concerned with the use of agent-based models in scientific research practice. Several case studies of agent-based modeling projects in archaeology and economics are used to illustrate the role of agent-based models in research practice. These case studies include large-scale projects like the Village Ecodynamics Project and Eurace@Unibi project and smaller models, such as Jeffrey Brantingham’s neutral model. The relationships between agent-based models and complexity science and other social sciences are discussed in order to understand how this modeling type can be used to understand and explain phenomena. Although agent-based models are highly idealized and often do not provide correct explanations, I argue that they can, nonetheless, play a useful role in explanatory research, such as when they are used to identify the difference-makers of phenomena or to rule out potential explanations. [less ▲]

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See detailPresenter: Peripheries at the Centre. Borderland Schooling in Interwar Europe
Venken, Machteld UL

Presentation (2021, November 17)

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See detailA First Look at Security Risks of Android TV Apps
Liu, Yonhui; Li, Li; Kong, Pingfan UL et al

in A First Look at Security Risks of Android TV Apps (2021, November 15)

In this paper, we present to the community the first preliminary study on the security risks of Android TV apps. To the best of our knowledge, despite the fact that various efforts have been put into ... [more ▼]

In this paper, we present to the community the first preliminary study on the security risks of Android TV apps. To the best of our knowledge, despite the fact that various efforts have been put into analyzing Android apps, our community has not explored TV versions of Android apps. There is hence no publicly available dataset containing Android TV apps. To this end, We start by collecting a large set of Android TV apps from the official Google Play store. We then experimentally look at those apps from four security aspects: VirusTotal scans, requested permissions, security flaws, and privacy leaks. Our experimental results reveal that, similar to that of Android smartphone apps, Android TV apps can also come with different security issues. We hence argue that our community should pay more attention to analyze Android TV apps. [less ▲]

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See detailGlobal land dampness characterization using reflectometry by students (GOLDCREST): mission and CubeSat design
Asadi, Niloofar; Gholami-Boroujeni, Farzaneh; Gogoi, Bishwajit et al

in Proceedings of the 12th European CubeSat symposium (2021, November 15)

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See detailImpact of metallic potassium post-deposition treatment on epitaxial Cu(In, Ga)Se2
Martin Lanzoni, Evandro UL; Ramirez Sanchez, Omar UL; Phirke, Himanshu UL et al

in Thin Solid Films (2021)

Alkali post-deposition treatments (PDTs) of Cu(In, Ga)Se2 (CIGSe) absorbers are known to improve the power conversion efficiency of the thin-film solar cell devices. The PDTs are usually carried out via ... [more ▼]

Alkali post-deposition treatments (PDTs) of Cu(In, Ga)Se2 (CIGSe) absorbers are known to improve the power conversion efficiency of the thin-film solar cell devices. The PDTs are usually carried out via evaporation of alkali fluorides in a selenium atmosphere onto a hot substrate. In this work, an alkali metal dispenser was used to evaporate pure metallic potassium onto epitaxial CIGSe absorbers. Subsequently, the absorber layers were heated in-situ to monitor chemical reactions and diffusion into the bulk. Due to the absence of grain boundaries, fluorine, and selenium, the effect of K on CIGSe absorber properties can be directly monitored. We find that potassium effectively diffuses into the bulk of epitaxial CIGSe absorber layers. The diffusion depends on the Cucontent of the CIGSe absorbers, in which Cu-depleted films present higher diffusion rates of K. Photoluminescence (PL) imaging corroborates that K in the bulk of the CIGSe absorber increases the PL yield, suggesting a passivation of defects or an increase in doping. This work highlights that alkali PDTs are not limited by interface and grain boundary modifications but also changes the absorber bulk properties, which needs to be taken into account. [less ▲]

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See detailLiewensgeschichten aus dem Minett
Harnoncourt, Julia UL

Diverse speeches and writings (2021)

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See detailPresenter: Childhood in Times of Political Transformation in the 20th Century
Venken, Machteld UL

Presentation (2021, November 11)

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See detailExploring the Exposomewith HPC
Schymanski, Emma UL

Presentation (2021, November 10)

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See detailElectrospinning Ethanol–Water Solutions of Poly(Acrylic Acid): Nonlinear Viscosity Variations and Dynamic Taylor Cone Behavior
Vats, Shameek UL; Lagerwall, Jan UL

in Macromolecular Materials and Engineering (2021)

Electrospinning of polymer solutions is a multifaceted process that depends on the careful balancing of many parameters to achieve a desired outcome, in many cases including mixtures of multiple solvents ... [more ▼]

Electrospinning of polymer solutions is a multifaceted process that depends on the careful balancing of many parameters to achieve a desired outcome, in many cases including mixtures of multiple solvents. A systematic study of how the solution viscosity 𝜼—a good probe of solvent–polymer interactions—and the electrospinnability change when poly(acrylic acid) (PAA) is dissolved in ethanol–water mixtures at varying mixing ratio is carried out. A pronounced maximum is found in 𝜼 at a water-to-ethanol molar ratio of about 2:1, where the solvent mixture deviates maximally from ideal mixing behavior and partial deprotonation of carboxyl groups by water coincides synergistically with dissolution of the uncharged protonated PAA fraction by ethanol. The PAA concentration is tuned as a function of water–ethanol ratio to obtain a common value of 𝜼 for all solvent mixtures that is suitable for electrospinning. For high PAA content, the Taylor cone grows in volume over time despite minimum solution flow rate, even experiencing surface gelation for ethanol-rich solutions. This is attributed to the hygroscopic nature of PAA, drawing excess water into the Taylor cone from the air during spinning. [less ▲]

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See detailStable Electrospinning of Core-Functionalized Coaxial Fibers Enabled by the Minimum-Energy Interface Given by Partial Core− Sheath Miscibility
Vats, Shameek UL; Lagerwall, Jan UL

in Langmuir (2021), 37(45), 1326513277

Core−sheath electrospinning is a powerful tool for producing composite fibers with one or multiple encapsulated functional materials, but many material combinations are difficult or even impossible to ... [more ▼]

Core−sheath electrospinning is a powerful tool for producing composite fibers with one or multiple encapsulated functional materials, but many material combinations are difficult or even impossible to spin together. We show that the key to success is to ensure a well-defined core−sheath interface while also maintaining a constant and minimal interfacial energy across this interface. Using a thermotropic liquid crystal as a model functional core and polyacrylic acid or styrene-butadiene-styrene block copolymer as a sheath polymer, we study the effects of using water, ethanol, or tetrahydrofuran as polymer solvent. We find that the ideal core and sheath materials are partially miscible, with their phase diagram exhibiting an inner miscibility gap. Complete immiscibility yields a relatively high interfacial tension that causes core breakup, even preventing the core from entering the fiber- producing jet, whereas the lack of a well-defined interface in the case of complete miscibility eliminates the core−sheath morphology, and it turns the core into a coagulation bath for the sheath solution, causing premature gelation in the Taylor cone. Moreover, to minimize Marangoni flows in the Taylor cone due to local interfacial tension variations, a small amount of the sheath solvent should be added to the core prior to spinning. Our findings resolve a long-standing confusion regarding guidelines for selecting core and sheath fluids in core−sheath electrospinning. These discoveries can be applied to many other material combinations than those studied here, enabling new functional composites of large interest and application potential. [less ▲]

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See detailActive matter in infinite dimensions: Fokker–Planck equation and dynamical mean-field theory at low density
Manacorda, Alessandro UL

in Journal of Chemical Physics (2021)

We investigate the behavior of self-propelled particles in infinite space dimensions by comparing two powerful approaches in many-body dynamics: the Fokker-Planck equation and dynamical mean-field theory ... [more ▼]

We investigate the behavior of self-propelled particles in infinite space dimensions by comparing two powerful approaches in many-body dynamics: the Fokker-Planck equation and dynamical mean-field theory. The dynamics of the particles at low densities and infinite persistence time is solved in the steady-state with both methods, thereby proving the consistency of the two approaches in a paradigmatic out-of-equilibrium system. We obtain the analytic expression for the pair distribution function and the effective self-propulsion to first order in the density, confirming the results obtained in a previous paper and extending them to the case of a non-monotonous interaction potential. Furthermore, we obtain the transient behavior of active hard spheres when relaxing from equilibrium to the nonequilibrium steady-state. Our results show how collective dynamics is affected by interactions to first order in the density, and point out future directions for further analytical and numerical solutions of this problem. [less ▲]

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See detailAnisotropic Interlayer Force Field for Transition Metal Dichalcogenides: The Case of Molybdenum Disulfide
Wengen, Ouyang; Reut, Sofer; Xiang, Gao et al

in Journal of Chemical Theory and Computation (2021)

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See detailMoral status and teleofunctional kinds
Hofmann, Frank UL

Presentation (2021, November)

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See detailANCHOR: locating android framework-specific crashing faults
Kong, Pingfan UL; Li, Li; Gao, Jun UL et al

in Automated Software Engineering (2021)

Android framework-specific app crashes are hard to debug. Indeed, the callback-based event-driven mechanism of Android challenges crash localization techniques that are developed for traditional Java ... [more ▼]

Android framework-specific app crashes are hard to debug. Indeed, the callback-based event-driven mechanism of Android challenges crash localization techniques that are developed for traditional Java programs. The key challenge stems from the fact that the buggy code location may not even be listed within the stack trace. For example, our empirical study on 500 framework-specific crashes from an open benchmark has revealed that 37 percent of the crash types are related to bugs that are outside the stack traces. Moreover, Android programs are a mixture of code and extra-code artifacts such as the Manifest file. The fact that any artifact can lead to failures in the app execution creates the need to position the localization target beyond the code realm. In this paper, we propose Anchor, a two-phase suspicious bug location suggestion tool. Anchor specializes in finding crash-inducing bugs outside the stack trace. Anchor is lightweight and source code independent since it only requires the crash message and the apk file to locate the fault. Experimental results, collected via cross-validation and in-the- wild dataset evaluation, show that Anchor is effective in locating Android framework-specific crashing faults. [less ▲]

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See detailIs human face recognition lateralized to the right hemisphere due to neural competition with left‑lateralized visual word recognition? A critical review
Rossion, Bruno; Lochy, Aliette UL

in Brain Structure and Function (2021)

The right hemispheric lateralization of face recognition, which is well documented and appears to be specific to the human species, remains a scientific mystery. According to a long-standing view, the ... [more ▼]

The right hemispheric lateralization of face recognition, which is well documented and appears to be specific to the human species, remains a scientific mystery. According to a long-standing view, the evolution of language, which is typically substantiated in the left hemisphere, competes with the cortical space in that hemisphere available for visuospatial processes, including face recognition. Over the last decade, a specific hypothesis derived from this view according to which neural competition in the left ventral occipito-temporal cortex with selective representations of letter strings causes right hemispheric lateralization of face recognition, has generated considerable interest and research in the scientific community. Here, a systematic review of studies performed in various populations (infants, children, literate and illiterate adults, left-handed adults) and methodologies (behavior, lesion studies, (intra)electroencephalography, neuroimaging) offers little if any support for this reading lateralized neural competition hypothesis. Specifically, right-lateralized face-selective neural activity already emerges at a few months of age, well before reading acquisition. Moreover, consistent evidence of face recognition performance and its right hemispheric lateralization being modulated by literacy level during development or at adulthood is lacking. Given the absence of solid alternative hypotheses and the key role of neural competition in the sensory–motor cortices for selectivity of representations, learning, and plasticity, a revised language-related neural competition hypothesis for the right hemispheric lateralization of face recognition should be further explored in future research, albeit with substantial conceptual clarification and advances in methodological rigor. [less ▲]

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See detailAuf- und ausgezeichnete Lebensgeschichten aus der Minett
Harnoncourt, Julia UL; Krebs, Stefan UL

Article for general public (2021)

Detailed reference viewed: 20 (1 UL)