41. Orbital selective dynamics in Fe-pnictides triggered by polarized pump pulse excitationsGanesh Adhikary, Tanusree Saha, Primož Rebernik Ribič, Matija Stupar, Barbara Ressel, Jurij Urbančič, Giovanni De Ninno, A. Thamizhavel, Kalobaran Maiti, 2021, original scientific article Abstract: Quantum materials display exotic behaviours related to the interplay between temperature-driven phase transitions. Here, we study the electron dynamics in one such material, CaFe$_2$As$_2$, a parent Fe-based superconductor, employing time and angle-resolved photoemission spectroscopy. CaFe$_2$As$_2$ exhibits concomitant transition to spin density wave state and tetragonal to orthorhombic structure below 170 K. The Fermi surface of this material consists of three hole pockets ($\alpha$, $\beta$ and $\gamma$) around $\Gamma$-point and two electron pockets around $X$-point. The hole pockets have $d_{xy}$, $d_{yz}$ and $d_{zx}$ orbital symmetries. The $\beta$ band constituted by $d_{xz}$/$d_{yz}$ orbitals exhibit a gap across the magnetic phase transition. We discover that polarized pump pulses can induce excitations of electrons of a selected symmetry. More specifically, while $s$-polarized light (polarization vector perpendicular to the $xz$-plane) excites electrons corresponding to all the three hole bands, $p$-polarized light excites electrons essentially from ($\alpha$,$\beta$) bands which are responsible for magnetic order. Interestingly, within the magnetically ordered phase, the excitation due to the $p$-polarized pump pulses occur at a time scale of 50 fs, which is significantly faster than the excitation induced by $s$-polarized light ($\sim$ 200 fs). These results suggest that the relaxation of different ordered phases occurs at different time scales and this method can be used to achieve selective excitations to disentangle complexity in the study of quantum materials.
Keywords: Electronic structure, Pnictides and chalcogenides, Time-resolved spectroscopy
Published in RUNG: 13.10.2021; Views: 2954; Downloads: 9
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42. Comparative analysis of epidemiological models for COVID-19 pandemic predictionsRajan Gupta, Gaurav Pandey, Saibal K. Pal, 2021, original scientific article Abstract: Epidemiological modeling is an important problem around the world. This research presents COVID-19 analysis to understand which model works better for different regions. A comparative analysis of three growth curve fitting models (Gompertz, Logistic, and Exponential), two mathematical models (SEIR and IDEA), two forecasting models (Holt’s exponential and ARIMA), and four machine/deep learning models (Neural Network, LSTM Networks, GANs, and Random Forest) using three evaluation criteria on ten prominent regions around the world from North America, South America, Europe, and Asia has been presented. The minimum and median values for RMSE were 1.8 and 5372.9; the values for the mean absolute percentage error were 0.005
and 6.63; and the values for AIC were 87.07 and 613.3, respectively, from a total of 125 experiments across 10 regions. The growth curve fitting models worked well where flattening of the cases has started. Based on region’s growth curve, a relevant model from the list can be used for predicting the number of infected cases for COVID-19. Some other models used in forecasting the number of cases have been added in the future work section, which can help researchers to forecast the number of cases in different regions of the world.
Keywords: epidemic modeling, machine learning, neural networks, pandemic forecasting, time-series forecasting
Published in RUNG: 15.07.2021; Views: 3374; Downloads: 34
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43. Dissecting Mott and charge-density wave dynamics in the photoinduced phase of 1T-TaS[sub]2Alberto Simoncig, Matija Stupar, Barbara Ressel, Tanusree Saha, Primož Rebernik Ribič, Giovanni De Ninno, 2021, original scientific article Abstract: The two-dimensional transition-metal dichalcogenide 1T−TaS2 is a complex material standing out for its puzzling low temperature phase marked by signatures amenable to both Mott-insulating and charge-density wave states. Electronic Mott states, coupled to a lattice, respond to coherent optical excitations via a modulation of the lower (valence) Hubbard band. Such dynamics is driven by strong electron-phonon coupling and typically lasts for tens of picoseconds, mimicking coherent structural distortions. Instead, the response occurring at the much faster timescale, mainly dominated by electronic many-body effects, is still a matter of intense research. By performing time- and angle-resolved photoemission spectroscopy, we investigated the photoinduced phase of 1T−TaS2 and found out that its lower Hubbard band promptly reacts to coherent optical excitations by shifting its binding energy towards a slightly larger value. This process lasts for a time comparable to the optical pump pulse length, mirroring a transient change of the onsite Coulomb repulsion energy (U). Such an observation suggests that the correction to the bare value of U, ascribed to the phonon-mediated screening which slightly opposes the Hubbard repulsion, is lost within an interval of a few tens of femtoseconds and can be understood as a fingerprint of electronic states largely decoupled from the lattice. Additionally, these results enforce the hypothesis, envisaged in the current literature, that the transient photoinduced states belong to a sort of crossover phase instead of an equilibrium metallic one.
Keywords: ultrafast phenomena, time resolved photoemission, strongly correlated systems, transition metal dichalcogenide
Published in RUNG: 13.04.2021; Views: 3668; Downloads: 0
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45. Multiresponsive nonvolatile memories based on optically switchable ferroelectric organic field-effect transistorsMarco Carroli, Alex Dixon, Martin Herder, Egon Pavlica, Stefan Hecht, Gvido Bratina, Emanuele Orgiu, Paolo Samorì, 2021, original scientific article Abstract: Organic transistors are key elements for flexible, wearable, and biocompatible logic applications. Multiresponsivity is highly sought‐after in organic electronics to enable sophisticated operations and functions. Such a challenge can be pursued by integrating more components in a single device, each one responding to a specific external stimulus. Here, the first multiresponsive organic device based on a photochromic–ferroelectric organic field‐effect transistor, which is capable of operating as nonvolatile memory with 11 bit memory storage capacity in a single device, is reported. The memory elements can be written and erased independently by means of light or an electric field, with accurate control over the readout signal, excellent repeatability, fast response, and high retention time. Such a proof of concept paves the way toward enhanced functional complexity in optoelectronics via the interfacing of multiple components in a single device, in a fully integrated low‐cost technology compatible with flexible substrates.
Keywords: organic transistors, memory, time-dependent
Published in RUNG: 11.03.2021; Views: 3558; Downloads: 0
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46. MULTIPLE TEMPORALITIES OF THE PARTISAN STRUGGLEGal Kirn, 2014, independent scientific component part or a chapter in a monograph Keywords: multistability, parallax view, multiple temporality, revolutionary time, partisan poetry, WW2, partisan art, determination, alternative world
Published in RUNG: 21.08.2020; Views: 3468; Downloads: 0
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48. The role of charge transfer at reduced graphene oxide/organic semiconductor interface on the charge transport propertiesGvido Bratina, Egon Pavlica, 2019, original scientific article Abstract: The effect of 1-pyrenesulfonicacid sodium salt (1-PSA), tetracyanoethylene (TCNE) and tetrafluoro- tetracyanoquinodimethane (F4-TCNQ) on charge transport properties of reduced graphene oxide (RGO) is examined by measuring the transfer characteristics of field-effect transistors and co-planar time-of-flight photocurrent technique. Evidence of p-type doping and a reduction of mobility of electrons in RGO upon deposition of these materials is observed. Time-resolved photocurrent measurements show a reduction in elec- tron mobility even at submonolayer coverage of these materials. The variation of transit time with different coverages reveals that electron mobility decreases with increasing the surface coverage of 1-PSA, TCNE and F4- TCNQ to a certain extent, while at higher coverage the electron mobility is slightly recovered. All three molecules show the same trend in charge carrier mobility variation with coverage, but with different magnitude. Among all three molecules, 1-PSA acts as weak electron acceptor compared to TCNE and F4-TCNQ. The additional fluorine moieties in F4-TCNQ provides excellent electron withdrawing capability compared to TCNE. The experimental results are consistent with the density functional theory calculations.
Keywords: organic semiconductors, reduced graphene oxide, time-resolved photocurrent measurements, organic thin film transistors
Published in RUNG: 28.10.2019; Views: 5071; Downloads: 1
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49. On the Cost of Scalar Implicatures : An Eye-Tracking StudyGreta Mazzaggio, Anne Reboul, Chiara Caretta, Mélody Darblade, Jean-Baptiste van der Henst, Anne Cheylus, Penka Stateva, 2019, published scientific conference contribution abstract Keywords: scalar implicature, reaction time, eye-tracking, sentence evaluation task
Published in RUNG: 02.09.2019; Views: 4225; Downloads: 0
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50. Evaluation and Improvement of Lidar Performance Based on Temporal and Spatial Variance CalculationFei Gao, Xinxin Xu, Qingsong Zhu, Li Wang, Tingyao He, Longlong Wang, Samo Stanič, Dengxin Hua, 2019, original scientific article Keywords: spatial variance, temporal variance, analog data, photon-counting data, dead time, threshold voltage, linear working range, data gluing
Published in RUNG: 06.05.2019; Views: 4389; Downloads: 0
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