Structural Parameters of Star Clusters: Signal to Noise Effects

We study the impact of photometric signal to noise on the accuracy of derived structural parameters of unresolved star clusters using MCMC model fitting techniques. Star cluster images were simulated as a smooth surface brightness distribution following a King profile convolved with a point spread function. The simulation grid was constructed by varying the levels of sky background and adjusting the cluster's flux to a specified signal to noise. Poisson noise was introduced to a set of cluster images with the same input parameters at each node of the grid. Model fitting was performed using emcee algorithm. The presented posterior distributions of the parameters illustrate their uncertainty and degeneracies as a function of signal to noise. By defining the photometric aperture containing 80% of the cluster's flux, we find that in all realistic sky background level conditions a signal to noise ratio of $\sim$50 is necessary to constrain the cluster's half-light radius to an accuracy better than $\sim$20%. The presented technique can be applied to synthetic images simulating various observations of extragalactic star clusters.Comment: 9 pages, 5 figure

DART-RAY: a 3D ray-tracing radiative transfer code for calculating the propagation of light in dusty galaxies

We present DART-Ray, a new ray-tracing 3D dust radiative transfer (RT) code designed specifically to calculate radiation field energy density (RFED) distributions within dusty galaxy models with arbitrary geometries. In this paper, we introduce the basic algorithm implemented in . DART-Ray which is based on a pre-calculation of a lower limit for the RFED distribution. This pre-calculation allows us to estimate the extent of regions around the radiation sources within which these sources contribute significantly to the RFED. In this way, ray-tracing calculations can be restricted to take place only within these regions, thus substantially reducing the computational time compared to a complete ray-tracing RT calculation. Anisotropic scattering is included in the code and handled in a similar fashion. Furthermore, the code utilizes a Cartesian adaptive spatial grid and an iterative method has been implemented to optimize the angular densities of the rays originated from each emitting cell. In order to verify the accuracy of the RT calculations performed by DART-Ray, we present results of comparisons with solutions obtained using the dusty 1D RT code for a dust shell illuminated by a central point source and existing 2D RT calculations of disc galaxies with diffusely distributed stellar emission and dust opacity. Finally, we show the application of the code on a spiral galaxy model with logarithmic spiral arms in order to measure the effect of the spiral pattern on the attenuation and RFED. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society

The immunomodulatory function of vitamin D and its role in autoimmune thyroid diseases

Introducere. S-a demonstrat că vitamina D acționează ca un hormon imunomodulator și, în consecință, deficiența de vitamina D a fost descoperită ca un factor de risc pentru bolile tiroidiene autoimune. Prin urmare, este necesar să se dezvăluie rolul și mecanismul de acțiune a vitaminei D în dezvoltarea bolilor tiroidiene autoimune. Scopul lucrării. Rezumarea datelor recente cu privire la posibila asociere dintre vitamina D si tiroidita Hashimoto. Material și metode. Reviul al literaturii în baza de date PubMed publicată din februarie 2021 până în mai 2023 folosind combinații ale următoarelor Cuvinte-cheie: vitamina D, insuficiență de vitamina D, boală tiroidiană autoimună, tiroidita Hashimoto. Rezultate. Studiile actuale au arătat că dezechilibrul celulelor Th1/Th2 și creșterea activității celulelor Th1 reprezintă principalii factori patogeni a tiroiditei Hashimoto. Vitamina D poate juca un rol imunosupresiv prin inhibarea mai multor componente ale răspunsului imun in tiroidita Hashimoto, cum ar fi: legarea vitaminei D de receptorul său pentru a preveni activarea celulelor T dependente de celulele dendritice, reducând astfel producția de citokine pro-inflamatorii (IL-2, IL-5, IL-17 și TNF-α). Un studiu de caz a constatat că fiecare creștere a nivelurilor serice de 25(OH)D cu 5 nmol/L a redus riscul tiroiditei Hashimoto de 1,62 ori Concluzii. Ca un hormon de reglementare imunitar, vitamina D a devenit un accent de cercetare. Mai multe studii au observat o relație între hipovitaminoza D și bolile tiroidiene, unde deficitul de vitamina D crește riscul de bolilor tiroidiene autoimune. Datele din literatură au raportat că tratamentul cu vitamina D poate îmbunătăți starea pacienților cu boala Hashimoto.Background. Vitamin D has been shown to act as an immunomodulatory hormone, and consequently vitamin D deficiency has been discovered as a risk factor for autoimmune thyroid diseases. Therefore, it is necessary to reveal the role and mechanism of action of vitamin D in development of autoimmune thyroid diseases. Objective of the study. Summary of recent data on the possible association between vitamin D and thyroid diseases. Materials and methods. Literature review in the PubMed database published from February 2021 to May 2023 using combinations of the following Keywords: vitamin D or vitamin D deficiency, autoimmune thyroid disease and Hashimoto’s thyroiditis. Results. Current studies have shown that Th1/Th2 cell imbalance and Th1 cell activity enhancement are the main pathogenic factors of Hashimoto’s Thyroiditis. Vitamin D may play an immunosuppressive role by inhibiting multiple parts of the HT immune response, such as: vitamin D binding to its receptor to prevent activation of dendritic cell-dependent T cells, thereby reducing the production of pro-inflammatory cytokines (IL-2, IL-5, IL-17, and TNF-α), and decreasing the cytokine-mediated immune response. A case-control study found that each increase in serum 25(OH) Vit.D levels by 5 nmol/L reduced the risk of HT by 1.62 times. Conclusions. As a hormone of immune regulation, vitamin D has become a research focus. Several studies observed a relationship between hypovitaminosis D and thyroid diseases, where vitamin D deficiency increases the risk of AITD. Literature data reported that vitamin D treatment can improve the condition of patients with Hashimoto’s thyroiditis

Experiments on the Artificial Disturbance Evolution in 2D and 3D Spanwise Modulated Boundary Layers at Mach 2 and 2.5

AbstractExperimental data on the nonlinear wave train development in 3D supersonic boundary layer over swept wing and experimental investigation of wave train development in spanwise modulated boundary layer on flat plate and swept wing at Mach number 2 and 2.5 are presented. Artificial disturbances in the boundary layer were excited by periodical glow discharge mainly at 10 and 20kHz. It was found, that some disturbance excitation downstream cannot be explained by linear stability theory. It was obtained that receptivity of supersonic boundary layer to the surface excited controlled pulsations and the wave train development essentially depends on the Mach number

Compact Star Clusters in the M31 Disk

We have carried out a survey of compact star clusters (apparent size <3 arcsec) in the southwest part of the M31 galaxy, based on the high-resolution Suprime-Cam images (17.5 arcmin x 28.5 arcmin), covering ~15% of the deprojected galaxy disk area. The UBVRI photometry of 285 cluster candidates (V < 20.5 mag) was performed using frames of the Local Group Galaxies Survey. The final sample, containing 238 high probability star cluster candidates (typical half-light radius r_h ~ 1.5 pc), was selected by specifying a lower limit of r_h > 0.15 arcsec (>0.6 pc). We derived cluster parameters based on the photometric data and multiband images by employing simple stellar population models. The clusters have a wide range of ages from ~5 Myr (young objects associated with 24 um and/or Ha emission) to ~10 Gyr (globular cluster candidates), and possess mass in a range of 3.0 < log(m/M_sol) < 4.3 peaking at m ~ 4000 M_sol. Typical age of these intermediate-mass clusters is in the range of 30 Myr < t < 3 Gyr, with a prominent peak at ~70 Myr. These findings suggest a rich intermediate-mass star cluster population in M31, which appears to be scarce in the Milky Way galaxy.Comment: 16 pages, 8 figures, 1 table, accepted for publication in Ap