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1.
A new view of UHECRs with the Pierre Auger Observatory
Denise Boncioli, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2025, published scientific conference contribution

Abstract: In its Phase I, the Pierre Auger Observatory has led to several observations, driving the field of ultra- high-energy cosmic ray (UHECR) research over the last 20 years. Major achievements obtained so far include the unprecedented precise energy spectrum and its features, the observables linked to the UHECR mass composition and the distribution of arrival directions of the most energetic events. These results, together with the non-observation of high-energy neutrinos and photons, strongly disfavor the pre-Auger pure-proton paradigm. In this talk, we will provide an overview on the main results of the Observatory, and describe possible astrophysical scenarios for their interpretation. The prospects of improving the current understanding about UHECR characteristics during the Phase II of the Observatory will be also shown.
Keywords: ultra-high-energy cosmic rays, Pierre Auger Observatory, UHE neutrinos, UHE photons, Auger Phase I, AugerPrime upgrade, Auger Phase II, UHECR mass composition, UHECR energy spectrum, UHECR anisotropy studies, UHECR astrophysical scenarios, UHECR data interpretation
Published in RUNG: 24.03.2025; Views: 460; Downloads: 4
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2.
Magnetocaloric effect in amorphous and partially crystallized Fe[sub](40)Ni[sub](38)Mo[sub]4B[sub](18) alloys
Thanveer Thajudheen, R. V. Ramanujan, Senoy Thomas, 2016, original scientific article

Abstract: A study of magnetocaloric effect in amorphous and partially crystallized Fe40Ni38Mo4B18 alloys is reported. Amorphous Fe40Ni38Mo4B18, near its magnetic ordering temperature (600K) showed a magnetic entropy change ΔSM of 1.1 J/KgK and a relative cooling power of 36J/Kg in a field change of 10 kOe. Amorphous samples were partially crystallized by annealing at 700 K at different time intervals. Partially crystallized samples showed two distinct magnetic ordering temperature, one corresponding to the precipitated FeNi nanocrystals and the other one corresponding to the boron rich amorphous matrix. Magnetic ordering temperature of the residual amorphous matrix got shifted to the lower temperatures on increasing the annealing duration. Partially crystallised samples showed a magnetic entropy change of about 0.27J/kgK near the magnetic ordering temperature of the amorphous matrix (540K) in a field change of 10 kOe. The decrease in ΔSM on partial crystallisation is attributed to the biphasic magnetic nature of the s
Keywords: magnetism, phase transitions, entropy, equations of state, alloys, amorphous materials, annealing
Published in RUNG: 07.11.2024; Views: 870; Downloads: 5
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3.
Sequence disorder-induced first order phase transition in confined polyelectrolytes
V. Stepanyan, Artem Badasyan, V. Morozov, Yevgeni S. Mamasakhlisov, Rudolf Podgornik, 2024, original scientific article

Abstract: We consider a statistical mechanical model of a generic flexible polyelectrolyte, comprised of identically charged monomers with long-range electrostatic interactions and short-range interactions quantified by a disorder field along the polymer contour sequence, which is randomly quenched. The free energy and the monomer density profile of the system for no electrolyte screening are calculated in the case of a system composed of two infinite planar bounding surfaces with an intervening oppositely charged polyelectrolyte chain. We show that the effect of the contour sequence disorder, mediated by short-range interactions, leads to an enhanced localization of the polyelectrolyte chain and a first order phase transition at a critical value of the inter-surface spacing. This phase transition results in an abrupt change of the pressure from negative to positive values, effectively eliminating polyelectrolyte mediated bridging attraction.
Keywords: polyelectrolyte, Anderson localization, Poisson-Boltzmann equation, phase transitions, electrostatics, polyelectrolytes, Edwards equation, nonlinear schrodinger equation, nucleic acids
Published in RUNG: 04.10.2024; Views: 1103; Downloads: 2
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4.
Crystallizing covalent organic frameworks from metal organic framework through chemical induced-phase engineering
Abdul Khayum Mohammed, Safa Gaber, Jesus Raya, Tina Škorjanc, Nada Elmerhi, Sasi Stephen, Pilar Pena-Sánchez, Felipe Gándara, Steven Hinder, Mark A. Baker, Kyriaki Polychronopoulou, Dinesh Shetty, 2023, original scientific article

Abstract: The ordered porous frameworks like MOFs and COFs are generally constructed using the monomers through distinctive metal-coordinated and covalent linkages. Meanwhile, the inter-structural transition between each class of these porous materials is an under-explored research area. However, such altered frameworks are expected to have exciting features compared to their pristine versions. Herein, we have demonstrated a chemical-induction phase-engineering strategy to transform a two dimensional conjugated Cu-based SA-MOF (Cu-Tp) into 2D-COFs (Cu-TpCOFs). The structural phase transition offered in-situ pore size engineering from 1.1 nm to 1.5–2.0 nm. Moreover, the Cu-TpCOFs showed uniform and low percentage-doped (~ 1–1.5%) metal distribution and improved crystallinity, porosity, and stability compared to the parent Cu-Tp MOF. The construction of a framework from another framework with new linkages opens interesting opportunities for phase-engineering.
Keywords: metal organic framework, covalent organic framework, phase engineering, chemical transformation, porous materials
Published in RUNG: 10.11.2023; Views: 4076; Downloads: 7
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ULTRAFAST ELECTRON DYNAMICS IN CORRELATED SYSTEMS PROBED BY TIME-RESOLVED PHOTOEMISSION SPECTROSCOPY
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: 3336; Downloads: 44
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Photopyroelectric spectroscopy and calorimetry
D Dadarlat, C Tripon, Iain R. White, Dorota Korte, 2022, review article

Abstract: In this tutorial, we present an overview of the development of the photopyroelectric (PPE) technique, from its beginnings in 1984, through to the present day. The tutorial is organized in five sections, exploring both theoretical and experimental aspects of PPE detection, as well as some important spectroscopic and calorimetric applications. In the “Introduction” section we present the fundamental basics of photothermal phenomena and the state-of-the-art of the photopyroelectric technique. In the “Theoretical aspects” section we describe some specific cases of experimental interest, with examples in both back and front detection configurations. Several mathematical expressions for the PPE signal in specific detection modes (combined back-front configurations and PPE-IRT methods) are also deduced. The “Instrumentation and experiment” section contains two sub-sections. The first describes several examples of set-ups used for both room temperature and temperature-controlled experiments. The second sub-section is dedicated to the configuration of detection cells and to the various sensor/sample assemblies that are currently used in spectroscopic and calorimetric experiments for both liquid and solid samples. The “Applications” section is in fact a collection of experimental results dedicated to the thermal characterization of a wide range of solid and liquid samples. At the end of this section we present some examples that have been selected to convey that the PPE technique is not only useful in the investigation of optical and thermal properties of a variety of condensed matter samples, but also to study physical and chemical processes such as molecular associations, food adulteration or phase transitions. In “Concluding remarks” we summarize the advantages of this technique in spectroscopic and calorimetric applications.
Keywords: photopyroelectric spectroscopy, photopyroelectric calorimetry, phase transitions, condensed matter samples, thermal parameters
Published in RUNG: 16.11.2022; Views: 2644; Downloads: 25
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10.
Higgs boson decay into two photons at ATLAS : diploma seminar
Bojana Stefanoska, 2022, research project (high school)

Keywords: Higgs boson, ATLAS detector, photon decay channel, photons, ferromagnetic phase transition
Published in RUNG: 25.08.2022; Views: 2542; Downloads: 0
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