Supermassive black hole formation and role of galaxy mergers in their evolution.

Mehanizam formiranja supermasivnih crnih rupa posmatranih u ranom Univerzumu nije u potpunosti razjasnjen...Formation mechanism of supermassive black holes (SMBHs) observed in the early Universe is still not fully understood..

Spatial field reconstruction with INLA: Application to simulated galaxies

Aims. Monte Carlo Radiative Transfer (MCRT) simulations are a powerful tool for understanding the role of dust in astrophysical systems and its influence on observations. However, due to the strong coupling of the radiation field and medium across the whole computational domain, the problem is non-local and non-linear and such simulations are computationally expensive in case of realistic 3D inhomogeneous dust distributions. We explore a novel technique for post-processing MCRT output to reduce the total computational run time by enhancing the output of computationally less expensive simulations of lower-quality. Methods. We combine principal component analysis (PCA) and non-negative matrix factorization (NMF) as dimensionality reduction techniques together with Gaussian Markov random fields and the Integrated nested Laplace approximation (INLA), an approximate method for Bayesian inference, to detect and reconstruct the non-random spatial structure in the images of lower signal-to-noise or with missing data. Results. We test our methodology using synthetic observations of a galaxy from the SKIRT Auriga project - a suite of high resolution magneto-hydrodynamic Milky Way-sized galaxies simulated in cosmological environment by 'zoom-in' technique. With this approach, we are able to reproduce high photon number reference images $\sim5$ times faster with median residuals below $\sim20\%$.Comment: To be published in Numerical methods and codes of Astronomy and Astrophysic

EmulART: Emulating Radiative Transfer - A pilot study on autoencoder based dimensionality reduction for radiative transfer models

Dust is a major component of the interstellar medium. Through scattering, absorption and thermal re-emission, it can profoundly alter astrophysical observations. Models for dust composition and distribution are necessary to better understand and curb their impact on observations. A new approach for serial and computationally inexpensive production of such models is here presented. Traditionally these models are studied with the help of radiative transfer modelling, a critical tool to understand the impact of dust attenuation and reddening on the observed properties of galaxies and active galactic nuclei. Such simulations present, however, an approximately linear computational cost increase with the desired information resolution. Our new efficient model generator proposes a denoising variational autoencoder (or alternatively PCA), for spectral compression, combined with an approximate Bayesian method for spatial inference, to emulate high information radiative transfer models from low information models. For a simple spherical dust shell model with anisotropic illumination, our proposed approach successfully emulates the reference simulation starting from less than 1% of the information. Our emulations of the model at different viewing angles present median residuals below 15% across the spectral dimension, and below 48% across spatial and spectral dimensions. EmulART infers estimates for ~85% of information missing from the input, all within a total running time of around 20 minutes, estimated to be 6x faster than the present target high information resolution simulations, and up to 50x faster when applied to more complicated simulations.Comment: 85 pages, 33 figures, 9 table

Influence analysis of test speed on technical filament yarns behaviour in tensile test

V prispevku sta predstavljena dva različna načina nateznega preizkušanja linijskih tekstilij: natezno preizkušanje pri standardnih pogojih preizkušanja s standardnim dinamometrom in natezno preizkušanje pri ve- likih hitrostih. Raziskovali smo obnašanje treh tipov tehničnih filamentnih prej: dveh poliamidnih (PA 6.6 in PA 4.6) in polietilenteraftalatnega (PET) multifilamenta visokih trdnosti. Na podlagi rezultatov raziskave sklepamo, da deformacijska hitrost ($dot{epsilon}$) pri vseh treh preizkuševalnih prejah vpliva na natezne lastnosti materiala. To pomeni, da se mehanskih lastnosti in nateznega obnašanja prej pri velikih hitrostih obremenitve ne da pojasnjevati zgolj s podatki, dobljenimi pri standardnih pogojih preizkušanja, temveč je treba uvesti ustrezno metodo z višjimi hitrostmi preizkušanja.Two different ways of tensile testing of liner textiles, namely the tensile testing under standard conditions with a standard dynamometer and high-speed tensile testing are presented in the article. Within this research, we studied the behaviour of three types of high-tenacity multifilament technical filament yarns, i.e. two polyamide yarns (PA 6.6 and PA 4.6) and polyethylene terephthalate (PET). Based on the results of the research, we can conclude that the strain rate ($dot{epsilon}$) in all three tested yarns affected the material tensile properties. This means that the mechanical properties and tensile behaviour of technical yarns cannot be explained only with the data obtained under standard test conditions. For better understanding of the behaviour of technical yarns, it is necessary to introduce an appropriate method with high-speed testin

Polysaccharide based nanofibers with pH-sensitive function

Svrha istraživanja je bila izraditi nanovlaknasti senzor na bazi polisaharida za otkrivanje promjene pH-vrijednosti u području rane. Za izradu nanovlakana od celuloznog acetata (CA) kao otapalo je korištena octena kiselina, a vlakna su izrađena u uređaju za beziglično elektroispredanje. Duga CA vlakna jednolikih svojstava, promjera od 250 do 300 nm dobivena su elektroispredanjem smjese 15 mas. % CA i 85 mas. % octene kiseline uz dodatak halokromnog bojila (Bromocrezol Green). Dodatak Bromocrezol Green bojila u masu za ispredanje nije utjecao na oblikovanje vlakana. Analizom boje CIE sustavom karakterizirani su izrađeni nanovlaknasti senzori kako bi se ocijenila promjena boje uslijed promjene pH-vrijednosti. Pri pH 4 i manje od 4 imaju žutu boju i tako simuliraju okolinu rane koja je povoljna za zacjeljivanje rane, a plavu boju kada se izlože pH 9 i većoj od 9 i tako simuliraju okolinu koja ometa zacjeljivanje rane (kronične, inficirane rane).The aim of the present study was to prepare a polysaccharide based nanofibrous sensor for detection of pH change in the wound environment. In order to prepare cellulose acetate (CA) nanofibers, acetic acid was used as a solvent, and fabrication of fibers was performed on the needle-less electrospinning apparatus. Long uniform CA nanofibers, with diameters ranging from 250 to 300 nm, were electrospun from 15 wt% CA and 85% acetic acid, with addition of halochromic dye (Bromocrezol Green). The addition of Bromocrezol Green in the spinning formulation did not affect the fiber formation. Prepared nanofibrous sensors were characterized using CIE color space analysis in order to evaluate the color due to pH change. Nanofibrous sensors exhibit yellow color when exposed to pH4 and lower, simulating the wound environment beneficial to the wound healing, and blue color when exposed to pH 9 and higher, simulating the environment that hampers wound healing (chronic, infected wounds)

Application of Spectrophotometric Methods in Assessing the Influence of Alkaline Treatment on the Degree of Crosslinking of Cotton Cellulose with BTCA

Polycarboxylic acids appear to be the most promising nonformaldehyde crosslinking agents to replace the traditional, mostly formaldehyde-based, compounds. The most effective among these acids is 1,2,3,4-butanetetracarboxylic acid (BTCA). In this study, a comparison was made of the crosslinking effect on mercerized and on unmercerized as well as with different BTCA mass fractions crosslinked cotton fibres using FT-IR spectroscopy, the methylene blue method and water retention determination. The main purpose of the research was to evaluate how the structural changes of mercerized cotton (transformation of cellulose I into cellulose II) influence the crosslinking of cellulose fibres

Black holes, gravitational waves and fundamental physics: a roadmap

The grand challenges of contemporary fundamental physics—dark matter, dark energy, vacuum energy, inflation and early universe cosmology, singularities and the hierarchy problem—all involve gravity as a key component. And of all gravitational phenomena, black holes stand out in their elegant simplicity, while harbouring some of the most remarkable predictions of General Relativity: event horizons, singularities and ergoregions. The hitherto invisible landscape of the gravitational Universe is being unveiled before our eyes: the historical direct detection of gravitational waves by the LIGO-Virgo collaboration marks the dawn of a new era of scientific exploration. Gravitational-wave astronomy will allow us to test models of black hole formation, growth and evolution, as well as models of gravitational-wave generation and propagation. It will provide evidence for event horizons and ergoregions, test the theory of General Relativity itself, and may reveal the existence of new fundamental fields. The synthesis of these results has the potential to radically reshape our understanding of the cosmos and of the laws of Nature. The purpose of this work is to present a concise, yet comprehensive overview of the state of the art in the relevant fields of research, summarize important open problems, and lay out a roadmap for future progress. This write-up is an initiative taken within the framework of the European Action on 'Black holes, Gravitational waves and Fundamental Physics'