Repozitorij Univerze v Novi Gorici

Iskanje po repozitoriju
A+ | A- | Pomoč | SLO | ENG

Iskalni niz: išči po
išči po
išči po
išči po
* po starem in bolonjskem študiju

Opcije:
  Ponastavi


1 - 10 / 41
Na začetekNa prejšnjo stran12345Na naslednjo stranNa konec
1.
Degradation of microplastics in the environment : dissertation
Vaibhav Budhiraja, 2024, doktorska disertacija

Opis: Plastics are based on organic polymers that are sensitive to the environment in which they find themselves and will gradually decay through a variety of chemical reactions. This process is of great importance for the transformation and persistence of microplastics (MPs) that pollute the environment. The rate of degradation depends on two major factors: Firstly, the intrinsic properties of the polymers, such as chemical structure, molecular weight, crystallinity and the presence of additives, fillers or reinforcement and secondly, the environment to which they are exposed. The degradation rate of plastic will vary in different environmental matrices like soil, freshwater, seawater, wastewater, land etc., as well as in diverse environmental conditions like UV radiation, temperature, humidity, the effect of pollutants etc. Plastic mainly undergoes two fundamental reactions: oxidation and hydrolysis and the chemical structure of the polymer and its additives plays a key role in the degradation mechanism of plastic. Polyolefins having a carbon-only main chain are resistant to hydrolysis but susceptible to oxidation, whereas polyesters and polyamides containing heteroatoms are sensitive to hydrolysis and much more resistant to oxidation. In the context of the present work, five different studies were done involving both naturally degraded plastic and accelerated weathering of plastics in the form of small particles, MPs. In the first study, natural degraded polyethylene (PE) and polypropylene (PP) samples with a life span of more than forty years were collected from the environment and their physiochemical properties were analysed. The results show that red coloured PE samples were more degraded as compared to blue coloured samples, indicating that pigment plays a key role in the degradation. The PP sample shows extreme surface degradation, leading to fragmentation and the generation of MPs. In the second study, the effect of hydrodynamic cavitation on MPs in waste water treatment plant sludge was evaluated. PE, PP, polyethylene terephthalate and polyamide were extracted from the sludge. It was found that hydrodynamic cavitation does not disintegrate the MPs, although it removes some toxic metals and shows cell disruption mechanisms. Other studies were done with accelerated weathered MPs, which include PE, PP and tire wear particles (TWP), that were treated in accordance with an ISO 4892 standard weathering procedure that mimics natural weathered conditions. In the third study, we used weathered PE films to evaluate the synergistic adsorption behaviour of two pollutants, namely triclosan (TCS) and methylparaben (MeP). It was found that weathered MPs adsorb more pollutants and the adsorption behaviour of TCS is enhanced in the presence of MeP. In the fourth study, the magnetic extraction of pristine and weathered PE and TWP particles was performed. The results confirmed that the magnetic VI extraction of weathered MPs is difficult as compared to pristine MPs as their surface becomes more hydrophilic with weathering. In the fifth study, the effect of weathering on the density of PE and PP was evaluated. We found that weathering enhances the density of polyolefins, which is one of the main reasons for the observed sinking of polyolefin MPs in water.
Ključne besede: accelerated weathering, aging, density, magnetic separation, pigment, plastic degradation, pollutants, polyethylene, polyolefin, polypropylene, sinking, tire wear particles, dissertations
Objavljeno v RUNG: 04.06.2024; Ogledov: 474; Prenosov: 0
.pdf Celotno besedilo (7,35 MB)

2.
Possible interpretations of the joint observations of UHECR arrival directions using data recorded at the Telescope Array and the Pierre Auger Observatory
Mikhail Kuznetsov, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2023, objavljeni znanstveni prispevek na konferenci

Opis: Various hints for anisotropies in the distribution of arrival directions of ultra-high-energy cosmic rays (UHECRs) have been reported. Still, our poor knowledge about extragalactic and Galactic magnetic fields and about the UHECR mass composition makes it non-trivial to interpret such results in terms of possible models of UHECR sources. In this work, we apply the same analyses that have been performed on the Pierre Auger Observatory and the Telescope Array UHECR data to a variety of Monte Carlo simulations generated according to many different combinations of hypotheses about the sources, composition and magnetic deflections of UHECRs. We find that only some of these models can yield results similar to those obtained with the real data.
Ključne besede: Pierre Auger Observatory, ultra-high energy cosmic rays, anisotropy, galactic magnetic fields, telescope array, arrival directions
Objavljeno v RUNG: 23.01.2024; Ogledov: 739; Prenosov: 6
.pdf Celotno besedilo (1,30 MB)
Gradivo ima več datotek! Več...

3.
Update on the searches for anisotropies in UHECR arrival directions with the Pierre Auger Observatory and the Telescope Array
Lorenzo Caccianiga, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2023, objavljeni znanstveni prispevek na konferenci

Opis: The origin of ultra-high-energy cosmic rays (UHECRs), particles from outer space with energies �≥1 EeV, is still unknown, though the near-isotropy of their arrival direction distribution excludes a dominant Galactic contribution, and interactions with background photons prevent them from travelling cosmologically large distances. This suggests that their sources must be searched for in nearby galaxy groups and clusters. Deflections by intergalactic and Galactic magnetic fields are expected to hinder such searches but not preclude them altogether. So far, the only anisotropy detected with statistical significance ≥ 5� is a modulation in right ascension in the data from the Pierre Auger Observatory at �≥8 EeV interpretable as a 7% dipole moment. Various hints for higher-energy, smaller-scale anisotropies have been reported. UHECR arrival direction data from both the Pierre Auger Observatory and the Telescope Array experiment have been searched for anisotropies by a working group with members from both collaborations; combining the two datasets requires a cross-calibration procedure due to the different systematic uncertainties on energy measurements but allows us to perform analyses that are less model-dependent than what can be done with partial sky coverage. We report a significant dipole pointing away from the Galactic Center and a ∼4.6� anisotropy found when comparing the directions of UHECRs with a catalog of starburst galaxies.
Ključne besede: Pierre Auger Observatory, ultra-high energy cosmic rays, anisotropy, galactic magnetic fields, telescope array, arrival directions
Objavljeno v RUNG: 23.01.2024; Ogledov: 718; Prenosov: 5
.pdf Celotno besedilo (4,36 MB)
Gradivo ima več datotek! Več...

4.
Combined fit to the spectrum and composition data measured by the Pierre Auger Observatory including magnetic horizon effects
Juan Manuel González, Andrej Filipčič, Jon Paul Lundquist, Shima Ujjani Shivashankara, Samo Stanič, Serguei Vorobiov, Danilo Zavrtanik, Marko Zavrtanik, 2023, objavljeni znanstveni prispevek na konferenci

Opis: The measurements by the Pierre Auger Observatory of the energy spectrum and mass composition of cosmic rays can be interpreted assuming the presence of two extragalactic source populations, one dominating the flux at energies above a few EeV and the other below. To fit the data ignoring magnetic field effects, the high-energy population needs to accelerate a mixture of nuclei with very hard spectra, at odds with the approximate �−2 shape expected from diffusive shock acceleration. The presence of turbulent extragalactic magnetic fields in the region between the closest sources and the Earth can significantly modify the observed CR spectrum with respect to that emitted by the sources, reducing the flux of low-rigidity particles that reach the Earth. We here take into account this magnetic horizon effect in the combined fit of the spectrum and shower depth distributions, exploring the possibility that a spectrum for the high-energy population sources with a shape closer to �^(−2) be able to explain the observations. We find that a large inter-source separation �s and a large magnetic field RMS amplitude within the Local Supercluster region, such that �rms ≃ 100 nG (40 Mpc/�s) √︁25 kpc/�coh, are needed to interpret the data within this scenario, where �coh is the magnetic field coherence length.
Ključne besede: ultra-high energy cosmic rays, Pierre Auger Observatory, mass composition, extragalactic magnetic fiels
Objavljeno v RUNG: 22.01.2024; Ogledov: 700; Prenosov: 6
.pdf Celotno besedilo (623,35 KB)
Gradivo ima več datotek! Več...

5.
A study of analysis method for the identification of UHECR source type
F. Yoshida, Jon Paul Lundquist, 2022, objavljeni znanstveni prispevek na konferenci

Opis: The autocorrelation analysis using the arrival direction of Ultra High Energy Cosmic Rays (UHECRs) has been previously reported by the Telescope Array (TA) experiment. It is expected that the autocorrelation function reflects the source distribution. We simulate the expected arrival direction distribution of the cosmic rays using the catalogs of candidate sources. We take into account random deflection in the magnetic fields, with the magnitude of deflection determined by the charge and energy of the cosmic rays, coherence length and magnitude of the extragalactic magnetic field (EGMF), and by distance to source. In addition, in order to compare with the results of TA experiment, we consider the TA exposure. We compare the autocorrelation of the arrival directions corresponding to different source catalogs with the isotropic distribution. We calculate the autocorrelation function for each type of source candidates using this procedure. We will discuss the ability of this method to identify the source type of UHECRs.
Ključne besede: Telescope Array, indirect detection, surface detection, ground array, ultra-high energy, cosmic rays, energy spectrum, composition, anisotropy, autocorrelation, source models, magnetic fields
Objavljeno v RUNG: 04.10.2023; Ogledov: 1128; Prenosov: 9
.pdf Celotno besedilo (2,71 MB)
Gradivo ima več datotek! Več...

6.
UHECR mass composition from anisotropy of their arrival directions with the Telescope Array SD
M. Kuznetsov, Jon Paul Lundquist, 2022, objavljeni znanstveni prispevek na konferenci

Opis: We propose a new method for the estimation of ultra-high energy cosmic ray (UHECR) mass composition from a distribution of their arrival directions. The method employs a test statistic (TS) based on a characteristic deflection of UHECR events with respect to the distribution of luminous matter in the local Universe modeled with a flux-weighed 2MRS catalog. Making realistic simulations of the mock UHECR sets, we show that this TS is robust to the presence of galactic and non-extreme extra-galactic magnetic fields and sensitive to the mass composition of events in a set. We apply the method to Telescope Array surface detector data for 11 years and derive new independent constraints on fraction of protons and iron in p-Fe mix at E>10 EeV. At 10100 EeV --- pure iron or even more massive composition. This result is in tension with Auger composition model inferred from spectrum-Xmax fit at 2.7σ (2.0σ) for PT'11 (JF'12) regular GMF model.
Ključne besede: Telescope Array, indirect detection, surface detection, ground array, ultra-high energy, cosmic rays, composition, anisotropy, magnetic fields, 2MRS
Objavljeno v RUNG: 04.10.2023; Ogledov: 1035; Prenosov: 5
.pdf Celotno besedilo (3,02 MB)
Gradivo ima več datotek! Več...

7.
Effects of Galactic magnetic field on the UHECR anisotropy studies
R. Higuchi, Jon Paul Lundquist, 2022, objavljeni znanstveni prispevek na konferenci

Opis: Telescope Array (TA) and Auger experiments reported anisotropies in the arrival direction of ultrahigh-energy cosmic rays (UHECRs). In particular, Auger Collaboration reported a correlation between UHECR events and the flux model of assumed sources and suggested a contribution of starburst galaxies (SBGs) to the anisotropy of UHECRs. However, in their study, the effect of coherent deflections by the galactic magnetic field (GMF) is not taken into account. In this study, we investigated the effect of the GMF on the arrival directions of UHECRs using the cosmic ray propagation code CRPropa3. We used a backtracking technique which consists of propagating antiparticles to map the flux outside the galaxy to at the earth. We estimate the systematic effects caused by GMF in the reported likelihood analysis. We conduct likelihood analysis for mock UHECR datasets based on the flux pattern through the GMF model. We found systematic decrease of (f_ani, �) due to GMF. As prospects for the TAx4 experiment and joint analysis of Auger and TA collaborations, we develop the likelihood analysis method with the convolution of the rigidity spectrum.
Ključne besede: Telescope Array, TAx4, ultra-high energy, cosmic rays, anisotropy, galactic magnetic field, starburst galaxies
Objavljeno v RUNG: 29.09.2023; Ogledov: 892; Prenosov: 5
.pdf Celotno besedilo (1,97 MB)
Gradivo ima več datotek! Več...

8.
Saturation magnetisation as an indicator of the disintegration of barium hexaferrite nanoplatelets during the surface functionalisation
Darja Lisjak, Iztok Arčon, Matic Poberžnik, Gabriela Herrero‑Saboya, Ali Tufani, Andraž Mavrič, Matjaž Valant, Patricija Hribar Boštjančič, Alenka Mertelj, Darko Makovec, Layla Martin‑Samos, 2023, izvirni znanstveni članek

Opis: Barium hexaferrite nanoplatelets (BHF NPLs) are permanent nanomagnets with the magnetic easy axis aligned perpendicular to their basal plane. By combining this specific property with optimised surface chemistry, novel functional materials were developed, e.g., ferromagnetic ferrofluids and porous nanomagnets. We compared the interaction of chemically different phosphonic acids, hydrophobic and hydrophilic with 1–4 phosphonic groups, with BHF NPLs. A decrease in the saturation magnetisation after functionalising the BHF NPLs was correlated with the mass fraction of the nonmagnetic coating, whereas the saturation magnetisation of the NPLs coated with a tetraphosphonic acid at 80 °C was significantly lower than expected. We showed that such a substantial decrease in the saturation magnetisation originates from the disintegration of BHF NPLs, which was observed with atomic-resolution scanning transmission electron microscopy and confirmed by a computational study based on state-of-the-art first-principles calculations. Fe K-edge XANES (X-ray absorption near-edge structure) and EXAFS (Extended X-ray absorption fine structure) combined with Fourier-transformed infrared (FTIR) spectroscopy confirmed the formation of an Fe–phosphonate complex on the partly decomposed NPLs. Comparing our results with other functionalised magnetic nanoparticles confirmed that saturation magnetisation can be exploited to identify the disintegration of magnetic nanoparticles when insoluble disintegration products are formed.
Ključne besede: barium hexaferrite, Fe XANES, EXAFS, magnetic nanoparticles
Objavljeno v RUNG: 06.07.2023; Ogledov: 1592; Prenosov: 4
.pdf Celotno besedilo (3,60 MB)
Gradivo ima več datotek! Več...

9.
10.
Magnetic materials : GIAN Course 2022. Course name: Functional Materials
Blaž Belec, predavanje na tuji univerzi

Ključne besede: magnetic materials, nanomaterials, permanent magnets
Objavljeno v RUNG: 28.02.2022; Ogledov: 1721; Prenosov: 0
Gradivo ima več datotek! Več...

Iskanje izvedeno v 0.05 sek.
Na vrh