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Rubin Observatory's Survey Strategy Performance for Tidal Disruption Events
Katja Bučar Bricman, Sjoert van Velzen, Matt Nicholl, Andreja Gomboc, 2023, original scientific article

Keywords: Rubin observatory, Legacy survey of space and time, tidal disruption event
Published in RUNG: 29.08.2023; Views: 188; Downloads: 5
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Modulation of charge transfer exciton dynamics in organic semiconductors using different structural arrangements : none
Cristian Soncini, Abhishek Kumar, Federica Bondino, Elena Magnano, Matija Stupar, Barbara Ressel, Giovanni De Ninno, Antonis Papadopoulos, Efthymis Serpetzoglou, Emmanuel Stratakis, Maddalena Pedio, 2023, original scientific article

Abstract: In devices based on organic semiconductors, aggregation and inter-molecular interactions play a key role in affecting the photo-physical and dynamical carrier properties of the material, potentially becoming a limiting factor to achieving high efficiency. As a consequence, a detailed understanding of the interplay between the film molecular structure and the material properties is essential to properly design devices with optimized performance. Here we demonstrate how different molecular structural arrangements modulate the charge transfer (CT) dynamics in cobalt phthalocyanine (CoPc) thin films. By transient absorption spectroscopy and time-resolved photoemission spectroscopy, we study the influence of different CoPc structures on the dynamical electronic properties, the CoPc intra and inter- molecular de-excitation pathways up to 7 ns. We rationalize the ultrafast formation of triplet states in the CoPc through an electron exchange process between the single-occupied Co3dz2 orbital and p orbitals of the macrocycle, which obviate for an energetically unfavourable spin-flip. We found enhanced CT exciton lifetime in the case of the herringbone structure with respect to the brickwork one, possibly explainable by a more efficient CT exciton delocalization along the stacking axis.
Keywords: Charge transfer, organic molecules, time resolved spectroscopies
Published in RUNG: 30.06.2023; Views: 367; Downloads: 2
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Amina Uglješa, 2023, master's thesis

Abstract: Hydrogen is playing an important role in many sectors of modern economy (green vehicles, energy conversion and storage in electrical grids, processing industry). Solid oxide electrolysis cell (SOEC) is an emerging technology for the production of hydrogen from steam and electrical energy as well as for renewable energies storage. Unfortunately, operating at high current and electrical transients cause degradation that leads to premature end of life. A remedy is to implement a hardware module capable to perform online condition monitoring and optimization of SOEC systems resulting in improved overall performance and extended lifetime. That is expected to significantly expand their deployment on the market. However, very little has been done so far. The H2020 project REACTT seems to be one of the first attempts to build an embedded system for monitoring, diagnosis, prognostics, and control (MDPC) for SOEC system. The underlying master's thesis contributes to the REACTT project in the segment related to the supervision of different modules of the MDPC system. The supervisor module is aimed to orchestrate the operation of various functional modules (agents) such as data acquisition, system optimization, diagnosis, prognostics, and mitigation. The thesis focuses on the design of the supervisor module and its implementation on a control platform based on Raspberry Pi 4. The main contributions of the thesis are twofold. First, the dynamic operation of the supervisor modelled by using the state transition diagram (STD). Second, the code for implementation of the supervisor on the target platform done in Python in a way that complies with the requirements imposed in the project.
Keywords: supervisor, module, agent, method, solid oxide electrolysis cell system, diagnosis, prognostics, real-time optimization, Python programming, state transition diagram
Published in RUNG: 20.06.2023; Views: 416; Downloads: 8
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Tanusree Saha, 2023, doctoral dissertation

Abstract: Complex systems in condensed matter are characterized by strong coupling between different degrees of freedom constituting a solid. In materials described by many-body physics, these interactions may lead to the formation of new ground states such as excitonic insulators, Mott insulators, and charge and spin density waves. However, the inherent complexity in such materials poses a challenge to identifying the dominant interactions governing these phases using equilibrium studies. Owing to the distinct timescales associated with the elementary interactions, such complexities can be readily addressed in the non-equilibrium regime. Additionally, these materials might also show the emergence of new, metastable “hidden“ phases under non-equilibrium. The thesis investigates the ultrafast timescales of fundamental interactions in candidate systems by employing time-and angle-resolved photoemission spectroscopy in the femtosecond time domain. In the (supposed) excitonic insulator model system Ta2NiSe5, the timescale of band gap closure and the dependence of rise time (of the photoemission signal) on the photoexcitation strength point to a predominantly electronic origin of the band gap at the Fermi level. The charge density wave (CDW) - Mott insulator 1T-TaS2 undergoes photoinduced phase transition to two different phases. The initial one is a transient phase which resembles the systems’s high temperature equilibrium phase, followed by a long-lived “hidden“ phase with a different CDW amplitude and is primarily driven by the CDW lattice order. For the spin density wave system CaFe2As2 where multiple bands contribute in the formation of Fermi surfaces, selective photoexcitation was used to disentangle the role played by different electron orbitals. By varying the polarization of photoexcitation pulses, it is observed that dxz/dyz orbitals primarily contribute to the magnetic ordering while the dxy orbitals have dominant role in the structural order. The findings of the present study provide deeper perspectives on the underlying interactions in complex ground phases of matter, therefore, initiating further experimental and theoretical studies on such materials.
Keywords: complex systems, charge density wave, excitonic insulator, metastable phase, Mott insulator, non-equilibrium, spin density wave, timescales, time- and angle-resolved photoemission, ultrafast dynamics
Published in RUNG: 01.06.2023; Views: 494; Downloads: 14
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A New Variant of Dynamic Pickup and Delivery Problem with Time Windows
Petr Valenta, Hana Rudová, Soumen Atta, 2020, published scientific conference contribution

Abstract: Motivated by the challenges faced by a logistics company, we present a new variant of the dynamic capacitated pickup and delivery problem with time windows (PDPTW) where excessive changes of unaffected routes are undesirable. In real-life scenarios, different dynamism sources such as canceled requests, change of demands, change of pickup, or delivery time windows often disrupt the existing planning of routes. The static PDPTW is solved with the current information about the problem well before executing the routes, such as the previous night. We present an algorithmic idea of a dynamic solver quickly addressing changes that occur due to the dynamism while avoiding excessive modifications to the previous solution. Since the company has not yet the dynamic data, new dynamic instances are generated from the existing static PDPTW instances in the literature. Preliminary results demonstrate that we can quickly incorporate the required changes. Future perspectives of this ongoing work are discussed in the end.
Keywords: Dynamic Pickup and Delivery Problem, Time Windows, Heuristic
Published in RUNG: 17.04.2023; Views: 436; Downloads: 0
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Time-of-flight photoconductivity investigation of high charge carrier mobility in Ti3C2Tx MXenes thin-film
Jurij Urbančič, Erika Tomsič, Manisha Chhikara, Nadiia Pastukhova, Vadym Tkachuk, Andraž Mavrič, Gvido Bratina, Egon Pavlica, 2023, original scientific article

Abstract: Charge transport through a randomly oriented multilayered network of two-dimensional (2D) Ti3C2Tx (where Tx is the surface termination and corresponds to O, OH and F) was studied using time-of-flight photoconductivity (TOFP) method, which is highly sensitive to the distribution of charge carrier velocities. We prepared samples comprising Ti3C2Tx with thickness of 12 nm or 6-monolayers. MXene flakes of size up to 16 μm were randomly deposited on the surface by spin-coating from water solution. Using TOFP, we have measured electron mobility that reached values up to 279 cm2/Vs and increase with electric-field in a Poole-Frenkel manner. These values are approximately 50 times higher than previously reported field-effect mobility. Interestingly, our zero-electric-field extrapolate approaches electron mobility measured using terahertz absorption method, which represents intra-flake transport. Our data suggest that macroscopic charge transport is governed by two distinct mechanisms. The high mobility values are characteristic for the intra-flake charge transport via the manifold of delocalized states. On the other hand, the observed Poole-Frenkel dependence of charge carrier mobility on the electric field is typical for the disordered materials and suggest the existence of an important contribution of inter-flake hopping to the overall charge transport.
Keywords: Charge transport in multilayered network of flakes, Time-of-flight photoconductivity, MXene exfoliation, High-mobility solution-cast thin-film, Semiconducting mxene
Published in RUNG: 31.03.2023; Views: 454; Downloads: 0
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Photoexcited charge mobility in quasi two-dimensional polyacetylene
Nadiia Pastukhova, Kejun Liu, Renhao Dong, Gvido Bratina, Xinliang Feng, Egon Pavlica, 2022, published scientific conference contribution abstract

Abstract: Two-dimensional conjugated polymers (2DCPs) have been described and recognised as crystalline, one- to two-layer polymer nanosheets prepared by 2D covalent polymerization exhibiting strong in-plane π-electron delocalization with two orthogonal directions and weak out-of-plane π-π stacking.[1,2] The extension of polymer dimensionality into two dimensions improves the alignment of individual polymer sheets and overcomes the limitations associated with charge carrier hopping between polymer chains in one-dimensional and crosslinked polymers.[3] Compared to other two-dimensional materials such as graphene or transition metal dichalcogenides, 2DCPs offer a high degree of flexibility in chemical design and are compatible with liquid-based processing methods. Various 2DCPs have been synthesised by surfactant monolayer-assisted interfacial synthesis (SMAIS).[5] Of particular interest is the photoresponse of these materials due to their tunable properties, such as bandgap and associated wavelength-dependent photoexcitation, which enables a wide range of applications in optoelectronic devices. Using time-of-flight photoconductivity (TOF-PC) measurements [4], we investigate the charge transport properties of 2D polyacetylene prepared by SMAIS method. We preform TOF-PC measurement of 2D polyacetylene using a focused nanosecond pulse laser at 325 nm and electrode separation of 250 µm. From the bias polarity and time duration of the photocurrent, we can determine the polarity, velocity and mobility of photoexcited charge carriers as a function of applied bias voltage and excitation wavelength. Using excitation at 325 m, we observed an electron mobility in the range of 150 cm2 V-1 s-1, which is in the realm of most advances small-molecule single-crystal organic semiconductors and almost an order of magnitude higher than linear polymeric semiconductors.
Keywords: Two-dimensional conjugated polymers, 2DCPs, 2Dpolymers, charge mobility, time-of-flight photoconductivity
Published in RUNG: 29.11.2022; Views: 543; Downloads: 0
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