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See detailOptimal equilibrium stabilization for a nonlinear infinite-dimensional plug-flow reactor model
Hastir, Anthony; Lamoline, François UL

in Automatica (2021), 130

This paper studies the stabilization of optimal equilibrium profiles in nonisothermal plug-flow tubular reactors actuated by a heat exchanger that acts as a distributed control input. As a first result ... [more ▼]

This paper studies the stabilization of optimal equilibrium profiles in nonisothermal plug-flow tubular reactors actuated by a heat exchanger that acts as a distributed control input. As a first result, we show that the heat exchanger temperature that achieves the minimal value of the steady-state reactant concentration at the outlet is the maximal allowed one. Then, a control strategy is proposed to reach these optimal equilibrium profiles. As main results, we prove that the control law stabilizes exponentially the nonlinear dynamics around the optimal equilibrium while it converges to the optimal heat exchanger temperature. In addition we show that the control law is optimal for some cost criterion of infinite-horizon integral type. Finally, the main results are illustrated with some numerical simulations. [less ▲]

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See detailStädtebau ökologisch, ökonomisch und sozial gestalten
Hertweck, Florian UL

in IzR Informationen zur Raumentwicklung (2021), 4

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See detailIssue 6
During, Marten UL; Beck, Clemens; Rollinger, Christian et al

in Journal of Historical Network Research (2021), 6(1), 262

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See detailExciton band structure of molybdenum disulfide: from monolayer to bulk
Fugallo, Giorgia; Cudazzo, Pier Luigi UL; Gatti, Matteo et al

in Electronic Structure (2021), 3

Exciton band structures analysis provides a powerful tool to identify the exciton character of materials, from bulk to isolated systems, and goes beyond the mere analysis of the optical spectra. In this ... [more ▼]

Exciton band structures analysis provides a powerful tool to identify the exciton character of materials, from bulk to isolated systems, and goes beyond the mere analysis of the optical spectra. In this work, we focus on the exciton properties of molybdenum sisulfide (MoS 2 ) by solving the ab initio many-body Bethe–Salpeter equation, as a function of momentum, to obtain the excitation spectra of both monolayer and bulk MoS 2 . We analyse the spectrum and the exciton dispersion on the basis of a model excitonic Hamiltonian capable of providing an efficient description of the excitations in the bulk crystal, starting from the knowledge of the excitons of a single layer. In this way, we obtain a general characterization of both bright and darks excitons in terms of the interplay between the electronic band dispersion (i.e. interlayer hopping) and the electron–hole exchange interaction. We identify for both the 2D and the 3D limiting cases the character of the lowest-energy excitons in MoS 2 , we explain the effects and relative weights of both band dispersion and electron–hole exchange interaction and finally we interpret the differences observed when changing the dimensionality of the system. [less ▲]

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See detailTime-Dependent Screening Explains the Ultrafast Excitonic Signal Rise in 2D Semiconductors
Smejkal, Valerie; Libisch, Florian; Molina-Sanchez, Alejandro et al

in ACS Nano (2021), 15(1), 1179--1185

We calculate the time evolution of the transient reflection signal in an MoS2 monolayer on a SiO2/Si substrate using first-principles out-of-equilibrium real-time methods. Our simulations provide a simple ... [more ▼]

We calculate the time evolution of the transient reflection signal in an MoS2 monolayer on a SiO2/Si substrate using first-principles out-of-equilibrium real-time methods. Our simulations provide a simple and intuitive physical picture for the delayed, yet ultrafast, evolution of the signal whose rise time depends on the excess energy of the pump laser: at laser energies above the A- and B-exciton, the pump pulse excites electrons and holes far away from the K valleys in the first Brillouin zone. Electron–phonon and hole–phonon scattering lead to a gradual relaxation of the carriers toward small Active Excitonic Regions around K, enhancing the dielectric screening. The accompanying time-dependent band gap renormalization dominates over Pauli blocking and the excitonic binding energy renormalization. This explains the delayed buildup of the transient reflection signal of the probe pulse, in excellent agreement with recent experimental data. Our results show that the observed delay is not a unique signature of an exciton formation process but rather caused by coordinated carrier dynamics and its influence on the screening. [less ▲]

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See detailEDYPOLU Recruiter Survey. Scientific Use File. Data Documentation.
Gutfleisch, Tamara; Samuel, Robin UL

Report (2021)

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See detailEDYPOLU Recruiter Survey. Scientific Use File [Data]
Gutfleisch, Tamara; Samuel, Robin UL

Textual, factual or bibliographical database (2021)

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See detailBrexit and the free movement of goods: a bitter goodbye to Cassis?
Gerardy, Marie UL

in European Law blog (2021)

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See detailSkills assessment in education
Greiff, Samuel UL; Dörendahl, Jan UL

in AI and the future of skills. Volume 1, capabilities and assessments (2021)

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See detailThe future of intelligence and the intelligence of the future
Demetriou, Andreas; Golino, H; Spanoudis, George et al

in Intelligence (2021), 87

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See detailElectronic structure of TiSe2 from a quasi-self-consistent G0W0 approach
Hellgren, Maria; Baguet, Lucas; Calandra, Matteo et al

in Physical Review. B (2021), 103

n a previous work, it was shown that the inclusion of exact exchange is essential for a first-principles description of both the electronic and the vibrational properties of TiSe2, M. Hellgren et al ... [more ▼]

n a previous work, it was shown that the inclusion of exact exchange is essential for a first-principles description of both the electronic and the vibrational properties of TiSe2, M. Hellgren et al. [Phys. Rev. Lett. 119, 176401 (2017)]. The GW approximation provides a parameter-free description of screened exchange but is usually employed perturbatively (G0W0), making results more or less dependent on the starting point. In this work, we develop a quasi-self-consistent extension of G0W0 based on the random phase approximation (RPA) and the optimized effective potential of hybrid density functional theory. This approach generates an optimal G0W0 starting point and a hybrid exchange parameter consistent with the RPA. While self-consistency plays a minor role for systems such as Ar, BN, and ScN, it is shown to be crucial for TiS2 and TiSe2. We find the high-temperature phase of TiSe2 to be a semimetal with a band structure in good agreement with experiment. Furthermore, the optimized hybrid functional agrees well with our previous estimate and therefore accurately reproduces the low-temperature charge-density-wave phase. [less ▲]

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See detailCollective electronic excitations in charge density wave systems: The case of CuTe
Cudazzo, Pier Luigi UL; Wirtz, Ludger UL

in Physical Review. B (2021), 104(12), 125101

The study of neutral electronic excitations directly probed by electron energy loss spectroscopy experiments allows obtaining important insight about the physical origin of the charge density wave (CDW ... [more ▼]

The study of neutral electronic excitations directly probed by electron energy loss spectroscopy experiments allows obtaining important insight about the physical origin of the charge density wave (CDW) transition in solids. In particular it allows us to disentangle purely phononic mechanisms from the excitonic insulator scenario which is associated to a purely electronic mechanism. As a matter of fact, while the the loss function of the excitonic insulators should display negative dispersive features associated to the softening of neutral electronic excitations at the CDW wave vector above the critical temperature, no softening is expected when the driving force is purely phononic. Here we perform a microscopic analysis of the dynamical charge response of CuTe, a material that displays a low-temperature Peierls-like CDW instability. By means of first-principles time-dependent density functional calculations of the loss function, we characterize the plasmon dispersion along the different directions, highlighting the role of the intrinsic structural anisotropy and the effects of the crystal local fields that are responsible for the periodic reappearance of the spectra of the first Brillouin zone as well as the formation of an acousticlike plasmon. Finally, we demonstrate that also in this system, in analogy with other materials displaying excitonic insulator instability, the low energy region of the loss function presents negative dispersive structures at momentum transfer close to the CDW wave vector. This is a feature common to both excitonic insulator transition and Peierls distortion that further highlights how the difference between the two mechanisms is at most quantitative. [less ▲]

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See detailField monitoring data on a residential exhaust air heat pump system (air-to-air heat pump)
Shirani, Arsalan UL; Merzkirch, Alexander; Roesler, Jennifer et al

in Data in Brief (2021)

This data article presents the raw data used in the article “Experimental and analytical evaluation of exhaust air heat pumps in ventilation-based heating systems” (in review). The data set contains ... [more ▼]

This data article presents the raw data used in the article “Experimental and analytical evaluation of exhaust air heat pumps in ventilation-based heating systems” (in review). The data set contains measurement results of a field monitoring on a residential exhaust air heat pump system (air-to-air heat pump) in Germany. This data could be used to investigate the dynamic behaviour and performance of the exhaust air heat pump systems. The data set contains air temperature and humidity of all four sides of the heat pump unit. Moreover, the electrical consumption of the unit and the dynamic pressure difference on the exhaust side (as indication of the air volume rate) could be also found in the data set. [less ▲]

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See detailAdversarial Robustness in Multi-Task Learning: Promises and Illusions
Ghamizi, Salah UL; Cordy, Maxime UL; Papadakis, Mike UL et al

E-print/Working paper (2021)

Vulnerability to adversarial attacks is a well-known weakness of Deep Neural networks. While most of the studies focus on single-task neural networks with computer vision datasets, very little research ... [more ▼]

Vulnerability to adversarial attacks is a well-known weakness of Deep Neural networks. While most of the studies focus on single-task neural networks with computer vision datasets, very little research has considered complex multi-task models that are common in real applications. In this paper, we evaluate the design choices that impact the robustness of multi-task deep learning networks. We provide evidence that blindly adding auxiliary tasks, or weighing the tasks provides a false sense of robustness. Thereby, we tone down the claim made by previous research and study the different factors which may affect robustness. In particular, we show that the choice of the task to incorporate in the loss function are important factors that can be leveraged to yield more robust models. [less ▲]

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See detailExperimental and analytical evaluation of exhaust air heat pumps in ventilation-based heating systems
Shirani, Arsalan UL; Merzkirch, Alexander UL; Roesler, Jennifer et al

in Journal of Building Engineering (2021)

Due to the significant energy loss in the building sector, energy efficiency of the buildings and their heating systems is gaining interest especially in the last decades. Application of exhaust air heat ... [more ▼]

Due to the significant energy loss in the building sector, energy efficiency of the buildings and their heating systems is gaining interest especially in the last decades. Application of exhaust air heat pumps as an energy efficient heating technology to cover the heating and venting demand of the building is becoming conventional. The exhaust air heat pumps are attracting considerable interest due to their normally reasonable price and small footprint. This heat pump type is often installed as part of an air based heating system together with electrical heaters. These electrical heaters are installed to cover the residual heating demand and/or to insure thermal comfort. The technology of exhaust air heat pumps has been investigated in several studies. Available studies on exhaust air heat pumps have tended mostly to focus on comparison between different technologies utilized in efficient buildings. Almost all of the existing studies have ignored the actual application of this technology in air based heating systems together with electrical heaters. In this sense, there is still a need for discussion on the influence of different buildings’ standards and control strategies on the heating system performance. The present paper aims to call into question the energy efficiency of exhaust air heat pumps under different boundary conditions. In this study, the results of a long time field monitoring are utilized in order to model the dynamic behavior of an exhaust air heat pump in MATLAB/Simulink. The impact of different boundary conditions on the heat pump’s efficiency is studied and additionally compared to previous studies. The developed model is used for annual simulations of air based hybrid heating systems in three different building standards. Finally, the influence of control strategy on the system performance is investigated. It is shown that under certain boundary conditions and control strategy, the studied system could provide an efficient heating system with acceptable user comfort. Nevertheless, applying conventional heating control methods or installing the system in buildings with high heating energy demand could lead to high electrical energy consumption and/or undesirable thermal comfort. [less ▲]

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See detailLa libertas, vecteur idéel de l’expansion territoriale de la commune de Florence au XIVe siècle
Abeles, Solal UL

in Zorzi, Andrea (Ed.) La libertà nelle città comunali e signorili italiane (2021)

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