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Turner, Jordan A., Daniel A. Dale, Janice C. Lee, Médéric Boquien, Rupali Chandar, Sinan Deger, Kirsten L. Larson et al. "PHANGS–HST: star cluster spectral energy distribution fitting with cigale". Monthly Notices of the Royal Astronomical Society 502, n. 1 (11 gennaio 2021): 1366–85. http://dx.doi.org/10.1093/mnras/stab055.
Testo completoAbstract (sommario):
ABSTRACT The sensitivity and angular resolution of photometric surveys executed by the Hubble Space Telescope (HST) enable studies of individual star clusters in galaxies out to a few tens of megaparsecs. The fitting of spectral energy distributions (SEDs) of star clusters is essential for measuring their physical properties and studying their evolution. We report on the use of the publicly available Code Investigating GALaxy Emission (cigale) SED fitting package to derive ages, stellar masses, and reddenings for star clusters identified in the Physics at High Angular resolution in Nearby GalaxieS–HST (PHANGS–HST) survey. Using samples of star clusters in the galaxy NGC 3351, we present results of benchmark analyses performed to validate the code and a comparison to SED fitting results from the Legacy Extragalactic Ultraviolet Survey. We consider procedures for the PHANGS–HST SED fitting pipeline, e.g. the choice of single stellar population models, the treatment of nebular emission and dust, and the use of fluxes versus magnitudes for the SED fitting. We report on the properties of clusters in NGC 3351 and find, on average, the clusters residing in the inner star-forming ring of NGC 3351 are young (<10 Myr) and massive (105 M⊙) while clusters in the stellar bulge are significantly older. Cluster mass function fits yield β values around −2, consistent with prior results with a tendency to be shallower at the youngest ages. Finally, we explore a Bayesian analysis with additional physically motivated priors for the distribution of ages and masses and analyse the resulting cluster distributions.
2
Danilovich, T., A. M. S. Richards, L. Decin, M. Van de Sande e C. A. Gottlieb. "An ALMA view of SO and SO2 around oxygen-rich AGB stars". Monthly Notices of the Royal Astronomical Society 494, n. 1 (13 marzo 2020): 1323–47. http://dx.doi.org/10.1093/mnras/staa693.
Testo completoAbstract (sommario):
ABSTRACT We present and analyse SO and SO2, recently observed with high angular resolution and sensitivity in a spectral line survey with ALMA, for two oxygen-rich AGB stars: the low mass-loss rate R Dor and high mass-loss rate IK Tau. We analyse 8 lines of SO detected towards both stars, 78 lines of SO2 detected towards R Dor, and 52 lines of SO2 detected towards IK Tau. We detect several lines of 34SO, 33SO, and 34SO2 towards both stars, and tentatively S18O towards R Dor, and hence derive isotopic ratios for these species. The spatially resolved observations show us that the two sulphur oxides are co-located towards R Dor and trace out the same wind structures in the circumstellar envelope. Much of the emission is well reproduced with a Gaussian abundance distribution spatially centred on the star. Emission from the higher energy levels of SO and SO2 towards R Dor provides evidence in support of a rotating inner region of gas identified in earlier work. The new observations allow us to refine the abundance distribution of SO in IK Tau derived from prior observations with single antennas, and confirm that the distribution is shell like with the peak in the fractional abundance not centred on the star. The confirmation of different types of SO abundance distributions will help fine-tune chemical models and allows for an additional method to discriminate between low and high mass-loss rates for oxygen-rich AGB stars.
3
Amarante, João A. S., e Helio J. Rocha-Pinto. "Planetary populations according to the orbital angular momentum". Proceedings of the International Astronomical Union 5, S265 (agosto 2009): 420–21. http://dx.doi.org/10.1017/s1743921310001122.
Testo completoAbstract (sommario):
AbstractWe investigate the angular momentum distribution of known exoplanetary systems, as a function of the planetary mass, orbital semimajor axis and metallicity of the host star. We find exoplanets seems to be classified according to at least two ‘populations’, with respect to their angular momentum properties. This classification is independent on the composition of the planet and seems to be valid for both jovian and neptunian planets, and probably can be extrapolated to the terrestrial planets of the Solar System. We analyse these ‘populations’ considering the phenomenon of planetary migration.
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Ferrero, Alejandro, e Joaquín Campos. "Angular and Spectral Bandwidth Considerations in BRDF Measurements of Interference- and Diffraction-Based Coatings". Coatings 10, n. 11 (21 novembre 2020): 1128. http://dx.doi.org/10.3390/coatings10111128.
Testo completoAbstract (sommario):
The Bidirectional Reflectance Distribution Function (BRDF) of iridescent (or goniochromatic) surfaces may vary notably with both spectral and angular variables, and, therefore, finite spectral bandwidth and collection solid angles inherent to any measuring instrument introduce a deviation from the correct value. Experimental data of highly goniochromatic samples are used to analyse their impact on measurement uncertainty. The results indicate that it is advisable to standardize spectral and angular bandwidths because the systematic error is not negligible for typical measuring systems. The 95th percentile of the error distribution of the measurement of the BRDF due to these finite bandwidths, and also the 95th percentile of the calculated resulting color differences, are used as criteria to establish recommended values of spectral and angular bandwidths. The impact of the bandwidth is more critical in the measurement of the BRDF of diffraction-based than of interference-based coatings.
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Rasouli, Soleiman, A. N. Behkami, R. Razavi, Amir Abbas Sabouri Dodaran e M. R. Bayati. "Investigation on Neutron-Induced Fission Fragment Angular Distribution of 232Th and 238U". Zeitschrift für Naturforschung A 73, n. 11 (25 ottobre 2018): 1075–81. http://dx.doi.org/10.1515/zna-2018-0267.
Testo completoAbstract (sommario):
AbstractFission fragment angular distribution (FFAD) data would help obtain new insights into both the fission process and the mechanism of the projectile’s interaction with the nucleus. Recently, a structure has been reported in neutron-induced FFAD of even-even actinide nuclei near threshold. Statistical modelling is used in this article to analyse FFAD from neutron-induced fission of 238U and 232Th. The statistical variance K02 is obtained by fitting the measured fragment anisotropies with a theoretical model. Accurate analysis is performed to deduce the variance K02 of the K-distribution of the levels in the transition nucleus at neutron energies from threshold to 50 MeV. We show the method by which quantitative values of K02 can be obtained. The results not only present high-resolution data in these even-even nuclei but also show that for the 238U(n,f) reaction, the strength for the K-transition states comes mainly from the higher angular momenta, in agreement with the Nilsson model orbitals. We also study the periodic structure of anisotropy related to the set of (n,f) reactions in comparison with the related cross section performed with the TALYS code. The comparison of the variance with the cross section clearly illustrates the strong correlation between the value of the variance and the opening of a fission chance. We show that whenever the probability of reaction in a new channel and cross section increases, K02 decreases versus the incident neutron energy, so the minimum of K02 can show the maximum probability of the (n,f)xn reaction.
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Katona, M., K. Trampert, C. Schwanengel, U. Krüger e C. Neumann. "Geometric system analysis of ILMD-based LID measurement systems using Monte-Carlo simulation". Journal of Physics: Conference Series 2149, n. 1 (1 gennaio 2022): 012015. http://dx.doi.org/10.1088/1742-6596/2149/1/012015.
Testo completoAbstract (sommario):
Abstract Imaging Luminance Measuring Device (ILMD) based luminous intensity distribution measurement systems are an established method for measuring the luminous intensity distribution (LID) of light sources in the far field. The advantage of this system is the high-resolution acquisition of a large angular range with one image. For the uncertainty budget, the mathematical description of the system can be divided into photometric and geometric contributions. In the following, we will present a Monte-Carlo approach to analyse the geometric contributions which are the uncertainty of measurement direction and measurement distance. Therefore, we set up a geometric system description based on kinematic transformations that describes the connection between detector and light source position. To consider all relevant input quantities we simulate the adjustment and measurement process. Finally, an analysis of the geometric input parameters is shown.
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Pedrosa, Susana, Patricia Tissera e Cecilia Scannapieco. "Baryons and Dark Matter halo distributions in ΛCDM Cosmology". Proceedings of the International Astronomical Union 5, S262 (agosto 2009): 404–5. http://dx.doi.org/10.1017/s1743921310003431.
Testo completoAbstract (sommario):
AbstractWe analyse the dark matter (DM) distribution in a ≈1012M⊙ halo extracted from a simulation consistent with the concordance cosmology, where the physics regulating the transformation of gas into stars was allowed to change producing galaxies with different morphologies. Although the DM profiles get more concentrated as baryons are collected at the centre of the haloes compared to a pure dynamical run, the total baryonic mass alone is not enough to fully predict the reaction of the DM profile. Our findings suggest that the response of the DM halo is driven by the history of assembly of baryons into a galaxy. The accretion of satellites could be associated with an expansion of the dark matter profiles, triggered by angular momentum transfer from the incoming satellites. However, we also found that these mechanism have different efficiencies which are set by the history of formation of the structure.
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Wan, Zhen, William H. Oliver, Geraint F. Lewis, Justin I. Read e Michelle L. M. Collins. "On the origin of the asymmetric dwarf galaxy distribution around andromeda". Monthly Notices of the Royal Astronomical Society 492, n. 1 (12 dicembre 2019): 456–67. http://dx.doi.org/10.1093/mnras/stz3477.
Testo completoAbstract (sommario):
ABSTRACT The dwarf galaxy distribution surrounding M31 is significantly anisotropic in nature. Of the 30 dwarf galaxies in this distribution, 15 form a disc-like structure and 23 are contained within the hemisphere facing the Milky Way. Using a realistic local potential, we analyse the conditions required to produce and maintain these asymmetries. We find that some dwarf galaxies are required to have highly eccentric orbits in order to preserve the presence of the hemispherical asymmetry with an appropriately large radial dispersion. Under the assumption that the dwarf galaxies originate from a single association or accretion event, we find that the initial size and specific energy of that association must both be relatively large in order to produce the observed hemispherical asymmetry. However if the association was large in physical size, the very high-energy required would enable several dwarf galaxies to escape from the M31 and be captured by the Milky Way. Furthermore, we find that associations that result in this structure have total specific energies concentrated around $E = V_{\rm esc}^{2} - V_{\rm init}^{2} \sim 200^2$ – $300^2\ \rm {km^2\ s^{-2}}$, implying that the initial velocity and initial position needed to produce the structure are strongly correlated. The overlap of initial conditions required to produce the radial dispersion, angular dispersion, and the planar structure is small and suggests that either they did not originate from a single accretion event, or that these asymmetric structures are short-lived.
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Du, Hangci, Shude Mao, E. Athanassoula, Juntai Shen e Pawel Pietrukowicz. "Kinematics of RR Lyrae stars in the Galactic bulge with OGLE-IV and Gaia DR2". Monthly Notices of the Royal Astronomical Society 498, n. 4 (31 agosto 2020): 5629–42. http://dx.doi.org/10.1093/mnras/staa2601.
Testo completoAbstract (sommario):
ABSTRACT We analyse the kinematics and spatial distribution of 15 599 fundamental-mode RR Lyrae (RRL) stars in the Milky Way bulge by combining OGLE-IV photometric data and Gaia DR2 proper motions. We show that the longitudinal proper motions and the line-of-sight velocities can give similar results for the rotation in the Galactic central regions. The angular velocity of bulge RRLs is found to be around 35 km s−1 kpc−1, significantly smaller than that for the majority of bulge stars (50–60 km s−1 kpc−1); bulge RRLs have larger velocity dispersion (120–140 km s−1) than younger stars. The dependence of the kinematics of the bulge RRLs on their metallicities is shown by their rotation curves and spatial distributions. Metal-poor RRLs ([Fe/H]<−1) show a smaller bar angle than metal-rich ones. We also find clues suggesting that RRLs in the bulge are not dominated by halo stars. These results might explain some previous conflicting results over bulge RRLs and help understand the chemodynamical evolution of the Galactic bulge.
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van Gils, Dennis P. M., Sander G. Huisman, Siegfried Grossmann, Chao Sun e Detlef Lohse. "Optimal Taylor–Couette turbulence". Journal of Fluid Mechanics 706 (3 luglio 2012): 118–49. http://dx.doi.org/10.1017/jfm.2012.236.
Testo completoAbstract (sommario):
AbstractStrongly turbulent Taylor–Couette flow with independently rotating inner and outer cylinders with a radius ratio of $\eta = 0. 716$ is experimentally studied. From global torque measurements, we analyse the dimensionless angular velocity flux ${\mathit{Nu}}_{\omega } (\mathit{Ta}, a)$ as a function of the Taylor number $\mathit{Ta}$ and the angular velocity ratio $a= \ensuremath{-} {\omega }_{o} / {\omega }_{i} $ in the large-Taylor-number regime $1{0}^{11} \lesssim \mathit{Ta}\lesssim 1{0}^{13} $ and well off the inviscid stability borders (Rayleigh lines) $a= \ensuremath{-} {\eta }^{2} $ for co-rotation and $a= \infty $ for counter-rotation. We analyse the data with the common power-law ansatz for the dimensionless angular velocity transport flux ${\mathit{Nu}}_{\omega } (\mathit{Ta}, a)= f(a)\hspace{0.167em} {\mathit{Ta}}^{\gamma } $, with an amplitude $f(a)$ and an exponent $\gamma $. The data are consistent with one effective exponent $\gamma = 0. 39\pm 0. 03$ for all $a$, but we discuss a possible $a$ dependence in the co- and weakly counter-rotating regimes. The amplitude of the angular velocity flux $f(a)\equiv {\mathit{Nu}}_{\omega } (\mathit{Ta}, a)/ {\mathit{Ta}}^{0. 39} $ is measured to be maximal at slight counter-rotation, namely at an angular velocity ratio of ${a}_{\mathit{opt}} = 0. 33\pm 0. 04$, i.e. along the line ${\omega }_{o} = \ensuremath{-} 0. 33{\omega }_{i} $. This value is theoretically interpreted as the result of a competition between the destabilizing inner cylinder rotation and the stabilizing but shear-enhancing outer cylinder counter-rotation. With the help of laser Doppler anemometry, we provide angular velocity profiles and in particular identify the radial position ${r}_{n} $ of the neutral line, defined by $ \mathop{ \langle \omega ({r}_{n} )\rangle } \nolimits _{t} = 0$ for fixed height $z$. For these large $\mathit{Ta}$ values, the ratio $a\approx 0. 40$, which is close to ${a}_{\mathit{opt}} = 0. 33$, is distinguished by a zero angular velocity gradient $\partial \omega / \partial r= 0$ in the bulk. While for moderate counter-rotation $\ensuremath{-} 0. 40{\omega }_{i} \lesssim {\omega }_{o} \lt 0$, the neutral line still remains close to the outer cylinder and the probability distribution function of the bulk angular velocity is observed to be monomodal. For stronger counter-rotation the neutral line is pushed inwards towards the inner cylinder; in this regime the probability distribution function of the bulk angular velocity becomes bimodal, reflecting intermittent bursts of turbulent structures beyond the neutral line into the outer flow domain, which otherwise is stabilized by the counter-rotating outer cylinder. Finally, a hypothesis is offered allowing a unifying view and consistent interpretation for all these various results.
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Collier, Angela, Isaac Shlosman e Clayton Heller. "Dark matter bars in spinning haloes". Monthly Notices of the Royal Astronomical Society 488, n. 4 (5 agosto 2019): 5788–801. http://dx.doi.org/10.1093/mnras/stz2144.
Testo completoAbstract (sommario):
ABSTRACT We study non-linear response of spinning dark matter (DM) haloes to dynamic and secular evolution of stellar bars in the embedded galactic discs, using high-resolution numerical simulations. For a sequence of haloes with the cosmological spin parameter λ = 0–0.09, and a representative angular momentum distribution, we analyse evolution of induced DM bars amplitude and quantify parameters of the response as well as trapping of DM orbits and angular momentum transfer by the main and secondary resonances. We find that (1) maximal amplitude of DM bars depends strongly on λ, while that of the stellar bars is indifferent to λ; (2) efficiency of resonance trapping of DM orbits by the bar increases with λ, and so is the mass and the volume of DM bars; (3) contribution of resonance transfer of angular momentum to the DM halo increases with λ, and for larger spin, the DM halo ‘talks’ to itself, by moving the angular momentum to larger radii – this process is maintained by resonances; and (4) prograde and retrograde DM orbits play different roles in angular momentum transfer. The ‘active’ part of the halo extends well beyond the bar region, up to few times the bar length in equatorial plane and away from this plane. (5) We model evolution of discless DM haloes and haloes with frozen discs, and found them to be perfectly stable to any Fourier modes. Finally, further studies adopting a range of mass and specific angular momentum distributions of the DM halo will generalize the dependence of DM response on the halo spin and important implications for direct detection of DM and that of the associated stellar tracers, such as streamers.
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Dodd, Emma, Amina Helmi e Helmer H. Koppelman. "Substructures, resonances, and debris streams". Astronomy & Astrophysics 659 (marzo 2022): A61. http://dx.doi.org/10.1051/0004-6361/202141354.
Testo completoAbstract (sommario):
Context. The local stellar halo of the Milky Way contains the debris from several past accretion events. Aims. Here we study in detail the structure and properties of nearby debris associated with the Helmi streams, which was originally identified as an overdensity in integrals of motion space. Methods. We use 6D phase-space information from Gaia EDR3 combined with spectroscopic surveys, and we analyse the orbits and frequencies of the stars in the streams using various Galactic potentials. We also explore how the Helmi streams constrain the flattening, q, of the Galactic dark matter halo. Results. We find that the streams are split into substructures in integrals of motion space, most notably into two clumps in angular momentum space. The clumps have consistent metallicity distributions and stellar populations, supporting a common progeny. In all the realistic Galactic potentials explored, the Helmi streams’ stars depict a diffuse distribution close to Ωz/ΩR ∼ 0.7. At the same time, the reason for the substructure in angular momentum space appears to be a Ωz : Ωϕ resonance close to 1:1. This resonance is exactly 1:1 in the case where the (density) flattening of the dark halo is q = 1.2. For this halo shape, the substructure in angular momenta is also long-lasting. Conclusions. Our findings suggest that the structure of the Galactic potential leaves a clear imprint on the properties of phase-mixed debris streams.
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Colombo, D., A. Duarte-Cabral, A. R. Pettitt, J. S. Urquhart, F. Wyrowski, T. Csengeri, K. R. Neralwar et al. "The SEDIGISM survey: The influence of spiral arms on the molecular gas distribution of the inner Milky Way". Astronomy & Astrophysics 658 (31 gennaio 2022): A54. http://dx.doi.org/10.1051/0004-6361/202141287.
Testo completoAbstract (sommario):
The morphology of the Milky Way is still a matter of debate. In order to shed light on uncertainties surrounding the structure of the Galaxy, in this paper, we study the imprint of spiral arms on the distribution and properties of its molecular gas. To do so, we take full advantage of the SEDIGISM (Structure, Excitation, and Dynamics of the Inner Galactic Interstellar Medium) survey that observed a large area of the inner Galaxy in the 13CO (2–1) line at an angular resolution of 28′′. We analyse the influences of the spiral arms by considering the features of the molecular gas emission as a whole across the longitude–velocity map built from the full survey. Additionally, we examine the properties of the molecular clouds in the spiral arms compared to the properties of their counterparts in the inter-arm regions. Through flux and luminosity probability distribution functions, we find that the molecular gas emission associated with the spiral arms does not differ significantly from the emission between the arms. On average, spiral arms show masses per unit length of ~105–106 M⊙ kpc−1. This is similar to values inferred from data sets in which emission distributions were segmented into molecular clouds. By examining the cloud distribution across the Galactic plane, we infer that the molecular mass in the spiral arms is a factor of 1.5 higher than that of the inter-arm medium, similar to what is found for other spiral galaxies in the local Universe. We observe that only the distributions of cloud mass surface densities and aspect ratio in the spiral arms show significant differences compared to those of the inter-arm medium; other observed differences appear instead to be driven by a distance bias. By comparing our results with simulations and observations of nearby galaxies, we conclude that the measured quantities would classify the Milky Way as a flocculent spiral galaxy, rather than as a grand-design one.
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Walo-Martín, D., J. Falcón-Barroso, C. Dalla Vecchia, I. Pérez e A. Negri. "Kinematic analysis of eagle simulations: evolution of λRe and its connection with mergers and gas accretion". Monthly Notices of the Royal Astronomical Society 494, n. 4 (12 maggio 2020): 5652–65. http://dx.doi.org/10.1093/mnras/staa1066.
Testo completoAbstract (sommario):
ABSTRACT We have developed a new tool to analyse galaxies in the eagle simulations as close as possible to observations. We investigated the evolution of their kinematic properties by means of the angular momentum proxy parameter, λRe, for galaxies with M⋆ ≥ 5 × 109 M⊙ in the RefL0100N1504 simulation up to redshift two (z = 2). Galaxies in the simulation show a wide variety of kinematic features, similiar to those found in integral-field spectroscopic studies. At z = 0 the distribution of galaxies in the λRe–ε plane is also in good agreement with results from observations. Scaling relations at z = 0 indicate that there is a critical mass, Mcrit /M⊙ = 1010.3, that divides two different regimes when we include the λRe parameter. The simulation shows that the distribution of galaxies in the λRe–ε plane evolves with time until z = 2 when galaxies are equally distributed in both λRe and ε. We studied the evolution of λRe with time and found that there is no connection between the angular momentum at z = 2 and z = 0. All systems reach their maximum λRe at z = 1 and then steadily lose angular momentum regardless of their merger history, except for the high star-forming systems that sustain that maximum value over time. The evolution of λRe in galaxies that have not experienced any merger in the last 10 Gyr can be explained by their level of gas accretion.
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Irodotou, Dimitrios, e Peter A. Thomas. "Using angular momentum maps to detect kinematically distinct galactic components". Monthly Notices of the Royal Astronomical Society 501, n. 2 (10 dicembre 2020): 2182–97. http://dx.doi.org/10.1093/mnras/staa3804.
Testo completoAbstract (sommario):
ABSTRACT In this work, we introduce a physically motivated method of performing disc/spheroid decomposition of simulated galaxies, which we apply to the eagle sample. We make use of the healpix package to create Mollweide projections of the angular momentum map of each galaxy’s stellar particles. A number of features arise on the angular momentum space which allows us to decompose galaxies and classify them into different morphological types. We assign stellar particles with angular separation of less/greater than 30° from the densest grid cell on the angular momentum sphere to the disc/spheroid components, respectively. We analyse the spatial distribution for a subsample of galaxies and show that the surface density profiles of the disc and spheroid closely follow an exponential and a Sérsic profile, respectively. In addition discs rotate faster, have smaller velocity dispersions, are younger and are more metal rich than spheroids. Thus, our morphological classification reproduces the observed properties of such systems. Finally, we demonstrate that our method is able to identify a significant population of galaxies with counter-rotating discs and provide a more realistic classification of such systems compared to previous methods.
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Cui, Baoli, Yongjun Cheng, Pengyang Jia, Zhihui Liu, Bi Wang, Jun Ye, Yangsen Li, Weiyu Chen e Zixi Wang. "Temperature Field Analysis and Temperature Control of Vacuum Ultra High Speed Angular Contact Ball Bearings". Journal of Physics: Conference Series 2784, n. 1 (1 giugno 2024): 012009. http://dx.doi.org/10.1088/1742-6596/2784/1/012009.
Testo completoAbstract (sommario):
Abstract In order to investigate the temperature field distribution of bearings under vacuum and ultra-high-speed conditions and put forward a good temperature control method, this paper adopts the local method to analyse and calculate the temperature of various parts of the bearing, and establishes a simulation model of the bearing by using the finite element analysis method of ANSYS, and carries out a test on the experimental platform of the vacuum and ultra-high-speed motors, which proves that the temperature of the rollers is the highest, followed by the inner-ring raceway and the outer-ring raceway, and provides effective theoretical methods for the analysis of the temperature field of the angular contact ball bearing under the conditions of high vacuum and high speed; the temperature of the bearing as a whole is controlled by the structure of the installed water jacket.
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Chakraborty, Arnab, Prasun Dutta, Abhirup Datta e Nirupam Roy. "The study of the angular and spatial distribution of radio-selected AGNs and star-forming galaxies in the ELAIS N1 field". Monthly Notices of the Royal Astronomical Society 494, n. 3 (9 aprile 2020): 3392–404. http://dx.doi.org/10.1093/mnras/staa945.
Testo completoAbstract (sommario):
ABSTRACT The cosmic evolution of bias of different source populations with underlying dark matter density field in post-reionization era can shed light on large-scale structures. Studying the angular and spatial distribution of different compact sources using deep radio catalogue at low frequency is essential to understand the matter distribution of the present Universe. Here, we investigate the relationship of luminous matter with their host dark matter haloes by measuring the angular and spatial clustering of sources (two-point statistics), using deep radio observation of ELAIS N1 (EN1) field with upgraded Giant Metrewave Radio Telescope (uGMRT) at 300–500 MHz. We also analyse the 612 MHz GMRT archival data of the same field to understand the cosmic evolution of clustering of different source populations. We classify the sources as star-forming galaxies (SFGs) and active galactic nuclei (AGNs) based on their radio luminosity. We find that the spatial clustering length and bias to the dark matter density field of SFGs are smaller than AGNs at both frequencies. This proves that AGNs are mainly hosted by massive haloes and hence strongly clustered. However, a small decrease in the bias for both kind of sources at higher frequency indicates that we are most likely tracing the faint objects residing in less-massive haloes at higher frequencies. Our results are in excellent agreement with previous findings at radio and multifrequency surveys. However, comparison with SKADS simulation suggests that the halo mass for different populations used in the simulation is systematically lower. This work quantifies the spatial distribution of extragalactic compact objects in EN1 field and bridges the gap between shallow and deep surveys.
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Alamo-Martínez, Karla A., Ana L. Chies-Santos, Michael A. Beasley, Rodrigo Flores-Freitas, Cristina Furlanetto, Marina Trevisan, Allan Schnorr-Müller, Ryan Leaman e Charles J. Bonatto. "Globular cluster systems of relic galaxies". Monthly Notices of the Royal Astronomical Society 503, n. 2 (25 febbraio 2021): 2406–22. http://dx.doi.org/10.1093/mnras/stab538.
Testo completoAbstract (sommario):
ABSTRACT We analyse the globular cluster (GC) systems of a sample of 15 massive, compact early-type galaxies (ETGs), 13 of which have already been identified as good relic galaxy candidates on the basis of their compact morphologies, old stellar populations and stellar kinematics. These relic galaxy candidates are likely the nearby counterparts of high-redshift red nugget galaxies. Using F814W (≈I) and F160W (≈H) data from the WFC3 camara onboard the Hubble Space Telescope, we determine the total number, luminosity function, specific frequency, colour, and spatial distribution of the GC systems (GCSs). We find lower specific frequencies (SN < 2.5 with a median of SN = 1) than ETGs of comparable mass. This is consistent with a scenario of rapid, early dissipative formation, with relatively low levels of accretion of low-mass, high-SN satellites. The GC half-number radii are compact, but follow the relations found in normal ETGs. We identify an anticorrelation between the specific angular momentum (λR) of the host galaxy and the (I − H) colour distribution width of their GCSs. Assuming that λR provides a measure of the degree of dissipation in massive ETGs, we suggest that the (I − H) colour distribution width can be used as a proxy for the degree of complexity of the accretion histories in these systems.
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Gallego-Cano, E., R. Schödel, H. Dong, F. Nogueras-Lara, A. T. Gallego-Calvente, P. Amaro-Seoane e H. Baumgardt. "The distribution of stars around the Milky Way’s central black hole". Astronomy & Astrophysics 609 (22 dicembre 2017): A26. http://dx.doi.org/10.1051/0004-6361/201730451.
Testo completoAbstract (sommario):
Context. The existence of dynamically relaxed stellar density cusps in dense clusters around massive black holes is a long-standing prediction of stellar dynamics, but it has so far escaped unambiguous observational confirmation. Aims. In this paper we aim to revisit the problem of inferring the innermost structure of the Milky Way’s nuclear star cluster via star counts, to clarify whether it displays a core or a cusp around the central black hole. Methods. We used judiciously selected adaptive optics assisted high angular resolution images obtained with the NACO instrument at the ESO VLT. Through image stacking and improved point spread function fitting we pushed the completeness limit about one magnitude deeper than in previous, comparable work. Crowding and extinction corrections were derived and applied to the surface density estimates. Known young, and therefore dynamically not relaxed stars, are excluded from the analysis. Contrary to previous work, we analyse the stellar density in well-defined magnitude ranges in order to be able to constrain stellar masses and ages. Results. We focus on giant stars, with observed magnitudes K = 12.5−16, and on stars with observed magnitudes K ≈ 18, which may have similar mean ages and masses than the former. The giants display a core-like surface density profile within a projected radius R ≤ 0.3 pc of the central black hole, in agreement with previous studies, but their 3D density distribution is not inconsistent with a shallow cusp if we take into account the extent of the entire cluster, beyond the radius of influence of the central black hole. The surface density of the fainter stars can be described well by a single power-law at R < 2 pc. The cusp-like profile of the faint stars persists even if we take into account the possible contamination of stars in this brightness range by young pre-main sequence stars. The data are inconsistent with a core-profile for the faint stars. Finally, we show that a 3D Nuker law provides a good description of the cluster structure. Conclusions. We conclude that the observed density of the faintest stars detectable with reasonable completeness at the Galactic centre, is consistent with the existence of a stellar cusp around the Milky Way’s central black hole, Sagittarius A*. This cusp is well developed inside the influence radius of Sagittarius A* and can be described by a single three-dimensional power-law with an exponent γ = 1.43 ± 0.02 ± 0.1sys. This corroborates existing conclusions from Nbody simulations performed in a companion paper. An important caveat is that the faint stars analysed here may be contaminated significantly by dynamically unrelaxed stars that formed about 100 Myr ago. The apparent lack of giants at projected distances of R ≲ 0.3 pc (R ≲ 8′′) of the massive black hole may indicate that some mechanism may have altered their distribution or intrinsic luminosity. We roughly estimate the number of possibly missing giants to about 100.
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Chauvineau, J. P., e F. Bridou. "Analyse angulaire de la fluorescence du fer dans une multicouche périodique Fe/C". Le Journal de Physique IV 06, n. C7 (novembre 1996): C7–53—C7–64. http://dx.doi.org/10.1051/jp4:1996707.
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Beugre, Jean-Bertin, Moussa Diomande, Assi Raoul Assi, Mariam Kadi Koueita e Frédéric Vaysse. "Analyse photogrammétrique angulaire et évaluation esthétique faciale de jeunes ivoiriens en normocclusion dentaire". International Orthodontics 15, n. 1 (marzo 2017): 25–39. http://dx.doi.org/10.1016/j.ortho.2016.12.016.
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Ema, Sonia Akter, Md Rasel Hossen, Krzysztof Bolejko e Geraint F. Lewis. "The density distributions of cosmic structures: impact of the local environment on weak-lensing convergence". Monthly Notices of the Royal Astronomical Society 509, n. 2 (29 ottobre 2021): 3004–14. http://dx.doi.org/10.1093/mnras/stab3134.
Testo completoAbstract (sommario):
ABSTRACT Whilst the underlying assumption of the Friedman-Lemaître-Robertson-Walker (FLRW) cosmological model is that matter is homogeneously distributed throughout the universe, gravitational influences over the life of the universe have resulted in mass clustered on a range of scales. Hence we expect that, in our inhomogeneous Universe, the view of an observer will be influenced by the location and local environment. Here, we analyse the one-point probability distribution functions and angular power spectra of weak-lensing (WL) convergence and magnification numerically to investigate the influence of our local environment on WL statistics in relativistic N-body simulations. To achieve this, we numerically solve the null geodesic equations which describe the propagation of light bundles backwards in time from today, and develop a ray-tracing algorithm, and from these calculate various WL properties. Our findings demonstrate how cosmological observations of large-scale structure through WL can be impacted by the locality of the observer. We also calculate the constraints on the cosmological parameters as a function of redshift from the theoretical and numerical study of the angular power spectrum of WL convergence. This study concludes the minimal redshift for the constraint on the parameter Ωm (H0) is $z$ ∼ 0.2 ($z$ ∼ 0.6) beyond which the local environment’s effect is negligible and the data from WL surveys are more meaningful above that redshift. The outcomes of this study will have direct consequences for future surveys, where per cent-level-precision is necessary.
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Du, Xu, Bin Wang e Junqiang Zheng. "Geometric Error Analysis of a 2UPR-RPU Over-Constrained Parallel Manipulator". Machines 10, n. 11 (29 ottobre 2022): 990. http://dx.doi.org/10.3390/machines10110990.
Testo completoAbstract (sommario):
For a 2UPR-RPU over-constrained parallel manipulator, some geometric errors result in internal forces and deformations, which limit the improvement of the pose accuracy of the moving platform and shorten the service life of the manipulator. Analysis of these geometric errors is important for restricting them. In this study, an evaluation model is established to analyse the influence of geometric errors on the limbs’ comprehensive deformations for this manipulator. Firstly, the nominal inverse and actual forward kinematics are analysed according to the vector theory and the local product of the exponential formula. Secondly, the evaluation model of the limbs’ comprehensive deformations is established based on kinematics. Thirdly, 41 geometric errors causing internal forces and deformations are identified and the results are verified through simulations based on the evaluation model. Next, two global sensitivity indices are proposed and a sensitivity analysis is conducted using the Monte Carlo method throughout the reachable workspace of the manipulator. The results of the sensitivity analysis indicate that 10 geometric errors have no effects on the average angular comprehensive deformation and that the identified geometric errors have greater effects on the average linear comprehensive deformation. Therefore, the distribution of the global sensitivity index of the average linear comprehensive deformation is more meaningful for accuracy synthesis. Finally, simulations are performed to verify the results of sensitivity analysis.
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Zhong, Zhimeng, Jianyao Zhao e Chao Li. "Outdoor-to-Indoor Channel Measurement and Coverage Analysis for 5G Typical Spectrums". International Journal of Antennas and Propagation 2019 (16 settembre 2019): 1–10. http://dx.doi.org/10.1155/2019/3981678.
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The fifth-generation (5G) mobile communications system will adopt the millimeter wave (mmWave) band for outdoor-to-indoor (O2I) coverage to achieve ultrahigh data rate. However, it is a challenging task because of the large path loss and almost total blocking by building walls. In this work, we performed extensive measurements on the O2I propagation at 3.5, 4.9, and 28 GHz simultaneously by using a multiband channel sounder. We captured the path loss distribution and angular power arrival profiles. We also measured the penetration loss at 28 GHz through different kinds of glass windows. The widely adopted ordinary glass windows introduce the penetration loss of 3 to 12 dB that is acceptable and makes mmWave O2I coverage feasible. But the low-emissivity (low-E) windows that will be more popular in the future introduce 10 dB higher loss. The measurement results in this work can help analyse and anticipate the O2I coverage by mmWave, which is important for the design and deployment of the 5G network.
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Karatepe, Şule, İsmail Boztosun e Mahmut Doğru. "Analysis of Elastic Scattering Angular Distributions of 11Be + 64Zn System: Compression with Different Models". Indian Journal of Science and Technology 12, n. 44 (30 novembre 2019): 01–04. http://dx.doi.org/10.17485/ijst/2019/v12i44/145523.
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Salmi, Tuomo, Valery F. Suleimanov e Juri Poutanen. "Effects of Compton scattering on the neutron star radius constraints in rotation-powered millisecond pulsars". Astronomy & Astrophysics 627 (27 giugno 2019): A39. http://dx.doi.org/10.1051/0004-6361/201935442.
Testo completoAbstract (sommario):
The aim of this work is to study the possible effects and biases on the radius constraints for rotation-powered millisecond pulsars when using Thomson approximation to describe electron scattering in the atmosphere models, instead of using exact formulation for Compton scattering. We compare the differences between the two models in the energy spectrum and angular distribution of the emitted radiation. We also analyse a self-generated, synthetic, phase-resolved energy spectrum, based on Compton atmosphere and the most X-ray luminous, rotation-powered millisecond pulsars observed by the Neutron star Interior Composition ExploreR (NICER). We derive constraints for the neutron star parameters using both the Compton and Thomson models. The results show that the method works by reproducing the correct parameters with the Compton model. However, biases are found in both the size and the temperature of the emitting hotspot, when using the Thomson model. The constraints on the radius are still not significantly changed, and therefore the Thomson model seems to be adequate if we are interested only in the radius measurements using NICER.
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Tracheva, Natalya V., e Sergey A. Ukhinov. "Two-dimensional projection Monte Carlo estimators for the study of angular characteristics of polarized radiation". Russian Journal of Numerical Analysis and Mathematical Modelling 33, n. 3 (26 giugno 2018): 187–97. http://dx.doi.org/10.1515/rnam-2018-0016.
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Abstract The paper presents a Monte Carlo algorithm for the study of bidirectional angular characteristics of a scattered polarized radiation based on projection expansion of the density of the corresponding angular distribution over hemispherical harmonics. The results of numerical estimation of two-dimensional angular distributions of the intensity and the polarization degree of the radiation passed through and reflected from optically thick layers of scattering and absorbing substance are presented.
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Koppelman, Helmer H., Roy O. Y. Bos e Amina Helmi. "The messy merger of a large satellite and a Milky Way-like galaxy". Astronomy & Astrophysics 642 (ottobre 2020): L18. http://dx.doi.org/10.1051/0004-6361/202038652.
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Aims. About 10 billion years ago the Milky Way merged with a massive satellite, Gaia-Enceladus. To gain insight into the properties of its debris we analyse in detail a suite of simulations that includes an experiment that produces a good match to the kinematics of nearby halo stars inferred from Gaia data. Methods. We compare the kinematic distributions of stellar particles in the simulations and study the distribution of debris in orbital angular momentum, eccentricity, and energy, and its relation to the mass loss history of the simulated satellite. Results. We confirm that Gaia-Enceladus probably fell in on a retrograde, 30° inclination orbit. We find that while 75% of the debris in our preferred simulation has high eccentricity (> 0.8), roughly 9% has eccentricity lower than 0.6. Star particles lost early have large retrograde motions, and a subset of these have low eccentricity. Such stars would be expected to have lower metallicities as they stem from the outskirts of the satellite, and hence naively they could be confused with debris associated with a separate system. These considerations seem to apply to some of the stars from the postulated Sequoia galaxy. Conclusions. When a massive disc galaxy undergoes a merger event, it leaves behind debris with a complex phase-space structure, a wide range of orbital properties, and a range of chemical abundances. Observationally, this results in substructures with very different properties, which can be misinterpreted as implying independent progeny. Detailed chemical abundances of large samples of stars and tailored hydrodynamical simulations are critical to resolving such conundrums.
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Uegaki, E., e Y. Abe. "Resonances in 28Si + 28Si. II: --Analyses for the Angular Distributions and Angular Correlations--". Progress of Theoretical Physics 127, n. 5 (1 maggio 2012): 877–905. http://dx.doi.org/10.1143/ptp.127.877.
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Klein, Matthias, Holger Israel, Aarti Nagarajan, Frank Bertoldi, Florian Pacaud, Adrian T. Lee, Martin Sommer e Kaustuv Basu. "Weak lensing measurements of the APEX-SZ galaxy cluster sample". Monthly Notices of the Royal Astronomical Society 488, n. 2 (3 giugno 2019): 1704–27. http://dx.doi.org/10.1093/mnras/stz1491.
Testo completoAbstract (sommario):
ABSTRACT We present a weak lensing analysis for galaxy clusters from the APEX-SZ survey. For 39 massive galaxy clusters that were observed via the Sunyaev–Zel’dovich effect (SZE) with the APEX telescope, we analyse deep optical imaging data from WFI(@2.2mMPG/ESO) and Suprime-Cam(@SUBARU) in three bands. The masses obtained in this study, including an X-ray selected sub-sample of 27 clusters, are optimized for and used in studies constraining the mass to observable scaling relations at fixed cosmology. A novel focus of our weak lensing analysis is the multicolour background selection to suppress effects of cosmic variance on the redshift distribution of source galaxies. We investigate the effects of cluster member contamination through galaxy density, shear profile, and recovered concentrations. We quantify the impact of variance in source redshift distribution on the mass estimate by studying nine sub-fields of the COSMOS survey for different cluster redshift and magnitude limits. We measure a standard deviation of ∼6 per cent on the mean angular diameter distance ratio for a cluster at z = 0.45 and shallow imaging data of R ≈ 23 mag. It falls to ∼1 per cent for deep, R = 26 mag, observations. This corresponds to 8.4 per cent and 1.4 per cent scatter in M200. Our background selection reduces this scatter by 20−40 per cent, depending on cluster redshift and imaging depth. We derived cluster masses with and without using a mass concentration relation and find consistent results, and concentrations consistent with the used mass–concentration relation.
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Diomandé, Aboubacar Sidiki. "L’enfant soldat confronté au processus de désarmement, démobilisation et réinsertion (ddr)". Études internationales 44, n. 4 (23 aprile 2014): 567–95. http://dx.doi.org/10.7202/1024652ar.
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Résumé Cet article analyse le phénomène des enfants soldats à l’aune du processus de désarmement, démobilisation et réinsertion (ddr). Ce processus qui vise à réintégrer socialement les soldats tient-il compte spécifiquement de ces derniers ? Le constat demeure que, si l’enfant soldat est pris en considération par les programmes ddr, cette prise en compte reste lacunaire, faute d’intégration de certains facteurs constituant la pierre angulaire de son succès. C’est pourquoi cet article se propose de rendre plus efficaces les programmes ddr pour une meilleure réinsertion sociale de l’enfant soldat. À défaut d’une application de ces mesures, ces programmes resteront incomplets et inefficaces pour les nombreux enfants soldats recrutés par les forces gouvernementales ou par des groupes armés.
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Banet, Alon, Rennan Barkana, Anastasia Fialkov e Or Guttman. "Quantiles as robust probes of non-Gaussianity in 21-cm images". Monthly Notices of the Royal Astronomical Society 503, n. 1 (4 febbraio 2021): 1221–32. http://dx.doi.org/10.1093/mnras/stab318.
Testo completoAbstract (sommario):
ABSTRACT The epoch in which the first stars and galaxies formed is among the most exciting unexplored eras of the Universe. A major research effort is focused on probing this era with the 21-cm spectral line of hydrogen. While most research works focus on statistics like the 21-cm power spectrum or the sky-averaged global signal, there are other ways to analyse tomographic 21-cm maps, which may lead to novel insights. We suggest statistics based on quantiles as a method to probe non-Gaussianities of the 21-cm signal. We show that they can be used in particular to probe the variance, skewness, and kurtosis of the temperature distribution, but are more flexible and robust than these standard statistics. We test these statistics on a range of possible astrophysical models, including different galactic halo masses, star formation efficiencies, and spectra of the X-ray heating sources, plus an exotic model with an excess early radio background. Simulating data with angular resolution and thermal noise as expected for the Square Kilometre Array (SKA), we conclude that these statistics can be measured out to redshifts above 20 and offer a promising statistical method for probing early cosmic history.
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Wang, Jingxiu. "Analyses of Vector Magnetograms". International Astronomical Union Colloquium 141 (1993): 425–34. http://dx.doi.org/10.1017/s0252921100029559.
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Abstract(1) Current techniques may now permit an acceptable resolution of the 180 degree ambiguity in determining the direction of transverse fields. (2) The non-potentiality of active regions can be described by parameters of angular shear, source field, line-of-sight current, force-free factor and force-free current. A 2-dimensional description of angular shear is necessary, and an alternative, FFT method of calculating the line-of-sight current seems recommendable. (3) For a sampling region, the degree of non-potentiality quantified by all the parameters shows great enhancement right before a 1M flare, and reduces somehow during the flare. (4) A highly intermittent distribution of force-free factor with fully mixed signs is obtained, consistent with a theoretical approach.
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Khan, Md Ishaque, e Rajib Saha. "Isotropy statistics of CMB hot and cold spots". Journal of Cosmology and Astroparticle Physics 2022, n. 06 (1 giugno 2022): 006. http://dx.doi.org/10.1088/1475-7516/2022/06/006.
Testo completoAbstract (sommario):
Abstract Statistical Isotropy of the Cosmic Microwave Background (CMB) radiation has been studied and debated extensively in recent years. Under this assumption, the hot spots and cold spots of the CMB are expected to be uniformly distributed over a 2-sphere. We use the orientation matrix, first proposed by Watson (1965) and Scheidegger (1965) and associated shape and strength parameters (Woodcock, 1977) to analyse whether the hot and cold spots of the observed CMB temperature anisotropy field are uniformly placed. We demonstrate the usefulness of our estimators by using simulated toy models containing non-uniform data. We apply our method on several foreground minimized CMB maps observed by WMAP and Planck over large angular scales. The shape and strength parameters constrain geometric features of possible deviations from uniformity (isotropy) and the power of the anomalous signal. We find that distributions of hot or cold spots in cleaned maps show no unusual signature of clustering or girdling. Instead, we notice a strikingly uniform distribution of hot spots over the full sky. The signal remains robust with respect to the four cleaned maps used and presence or absence of the non-Gaussian cold spot (NGCS). On the partial sky with WMAP KQ75 and Planck U73 masks we find anomalously low strength of non-uniformity for cold spots which is found to be robust with respect to various cleaning methods, masks applied, instruments, frequencies, and the presence or absence of the NGCS. Interestingly we find that the signal of anomalously weak non-uniformity could be due to contributions from the quadrupole and octupole and may be related with the low CMB temperature variance anomaly.
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Amard, L., A. Palacios, C. Charbonnel, F. Gallet, C. Georgy, N. Lagarde e L. Siess. "First grids of low-mass stellar models and isochrones with self-consistent treatment of rotation". Astronomy & Astrophysics 631 (22 ottobre 2019): A77. http://dx.doi.org/10.1051/0004-6361/201935160.
Testo completoAbstract (sommario):
Aims.We present an extended grid of state-of-the art stellar models for low-mass stars including updated physics (nuclear reaction rates, surface boundary condition, mass-loss rate, angular momentum transport, rotation-induced mixing, and torque prescriptions). We evaluate the impact of wind braking, realistic atmospheric treatment, rotation, and rotation-induced mixing on the structural and rotational evolution from the pre-main sequence (PMS) to the turn-off.Methods.Using the STAREVOL code, we provide an updated PMS grid. We computed stellar models for seven different metallicities, from [Fe/H] = −1 dex to [Fe/H] = +0.3 dex with a solar composition corresponding toZ = 0.0134. The initial stellar mass ranges from 0.2 to 1.5M⊙with extra grid refinement around one solar mass. We also provide rotating models for three different initial rotation rates (slow, median, and fast) with prescriptions for the wind braking and disc-coupling timescale calibrated on observed properties of young open clusters. The rotational mixing includes the most recent description of the turbulence anisotropy in stably stratified regions.Results.The overall behaviour of our models at solar metallicity, and their constitutive physics, are validated through a detailed comparison with a variety of distributed evolutionary tracks. The main differences arise from the choice of surface boundary conditions and initial solar composition. The models including rotation with our prescription for angular momentum extraction and self-consistent formalism for angular momentum transport are able to reproduce the rotation period distribution observed in young open clusters over a wide range of mass values. These models are publicly available and can be used to analyse data coming from present and forthcoming asteroseismic and spectroscopic surveys such asGaia, TESS, and PLATO.
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Powell, Devon, Simona Vegetti, John P. McKean, Cristiana Spingola, Francesca Rizzo e Hannah R. Stacey. "A novel approach to visibility-space modelling of interferometric gravitational lens observations at high angular resolution". Monthly Notices of the Royal Astronomical Society 501, n. 1 (11 settembre 2020): 515–30. http://dx.doi.org/10.1093/mnras/staa2740.
Testo completoAbstract (sommario):
ABSTRACT We present a new gravitational lens modelling technique designed to model high-resolution interferometric observations with large numbers of visibilities without the need to pre-average the data in time or frequency. We demonstrate the accuracy of the method using validation tests on mock observations. Using small data sets with ∼103 visibilities, we first compare our approach with the more traditional direct Fourier transform (DFT) implementation and direct linear solver. Our tests indicate that our source inversion is indistinguishable from that of the DFT. Our method also infers lens parameters to within 1 to 2 per cent of both the ground truth and DFT, given sufficiently high signal-to-noise ratio (SNR). When the SNR is as low as 5, both approaches lead to errors of several tens of per cent in the lens parameters and a severely disrupted source structure, indicating that this is related to the SNR and choice of priors rather than the modelling technique itself. We then analyse a large data set with ∼108 visibilities and a SNR matching real global Very Long Baseline Interferometry observations of the gravitational lens system MG J0751+2716. The size of the data is such that it cannot be modelled with traditional implementations. Using our novel technique, we find that we can infer the lens parameters and the source brightness distribution, respectively, with an RMS error of 0.25 and 0.97 per cent relative to the ground truth.
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Malla, Janak Ratna, Walter Saurer e B. Aryal. "Spatial orientations of angular momentum vectors of galaxies in Supercluster S [173+014+0082]". BIBECHANA 18, n. 1 (1 gennaio 2021): 26–32. http://dx.doi.org/10.3126/bibechana.v18i1.29165.
Testo completoAbstract (sommario):
The spin vector orientation of 1302 SDSS (Sloan Digital Sky Survey) galaxies in Supercluster S[173+014+0082] having redshift 0.076 to 0.091 has been analysed. The positions, position angles and inclination angles of galaxies are used to convert two-dimensional observed parameters into three-dimensional angular momentum vectors of the galaxy using the `position angle-inclination' method. The expected isotropic distribution curves are determined performing numerical simulation by generating 107 virtual galaxies. The observed distribution is compared with the expected isotropic distribution curves using three statistical tools namely Chi-square test, auto-correlation test and Fourier test. Redshift map is studied and found that the distributions fit with the Gaussian. No preferred alignment of angular momentum vectors is noticed, supporting Hierarchy model of galaxy formation.
BIBECHANA 18 (2021) 26-32
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KIM, YONG JOO, e MOON HOE CHA. "SECOND-ORDER EIKONAL MODEL ANALYSIS OF16O+16OELASTIC SCATTERING". International Journal of Modern Physics E 10, n. 04n05 (agosto 2001): 373–86. http://dx.doi.org/10.1142/s0218301301000563.
Testo completoAbstract (sommario):
We analyze the elastic scattering angular distributions of the16O +16O system at Elab=480 MeV and 704 MeV within the framework of the second-order eikonal model based on Coulomb trajectories of colliding nuclei. The diffractive oscillatory structure observed in the elastic angular distribution could be explained due to the interference between the near- and far-side scattering amplitudes. The presence of a nuclear rainbow in this system is evidenced through a classical deflection function. The effective optical potential is developed from the second-order non-eikonal phase shifts.
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Mollerach, S., E. Roulet e O. Taborda. "Large-scale anisotropies of extragalactic cosmic rays below the ankle". Journal of Cosmology and Astroparticle Physics 2022, n. 12 (1 dicembre 2022): 021. http://dx.doi.org/10.1088/1475-7516/2022/12/021.
Testo completoAbstract (sommario):
Abstract We study the anisotropies on large angular scales which can be present in the flux of cosmic rays reaching the Earth from a population of extragalactic sources, focusing on the energy range between the second knee and the ankle. In this energy range the particles are significantly affected by the Galactic magnetic field, which then plays a relevant role in shaping the expected anisotropies. The Galactic magnetic field deflects the cosmic-ray trajectories and thus modifies the anisotropies present outside the halo of the Galaxy, in particular the dipolar one associated with the translational motion of the observer (Compton-Getting effect). Also, due to the Galactic rotation, in the reference frame of an observer at Earth there is an electric component of the Galactic field that produces a small change in the particles' momentum. This acceleration depends on the cosmic-ray arrival direction and it hence induces anisotropies in the flux observed in a given energy range. We analyse the expected amplitude and phase of the resulting dipolar component of the flux and discuss the possibility to explain via these effects the change in the phase of the right-ascension distribution which is observed at energies around 1 EeV.
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Godin, Laurence. "Entre plaisir et contrôle". Ethnologies 33, n. 2 (4 aprile 2013): 69–97. http://dx.doi.org/10.7202/1015026ar.
Testo completoAbstract (sommario):
Cet article traite du lien qui existe entre les habitudes alimentaires et les discours normatifs sur l’alimentation. La notion d’équilibre est le point central autour duquel s’organise l’opposition entre plaisir et contrôle. Les conclusions tirées de cet article proviennent d’une série d’entretiens menés auprès d’individus qui font de l’entraînement physique sur une base régulière. Pour eux, l’équilibre s’obtient par les pratiques alimentaires, mais surtout par la mise en oeuvre du dosage entre plaisir et contrôle. Selon l’auteur, le lien social est la pierre angulaire de cet équilibre et son analyse l’amène à postuler qu’une propension forte au contrôle semble déranger le fonctionnement relationnel, exposant ainsi le mangeur à l’isolement et à la stigmatisation. C’est dans cet horizon que se dessine la frontière entre le normal et le pathologique.
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Tsuji, Kyoko, Naoto Haruyama, Shunsuke Nomura, Naohisa Murata, Keigo Yoshizaki, Takeshi Mitsuyasu, Hiroyuki Nakano, Seiji Nakamura, Yoshihide Mori e Ichiro Takahashi. "Characteristics of craniofacial morphology and factors affecting them in patients with isolated cleft palate". PeerJ 9 (20 aprile 2021): e11297. http://dx.doi.org/10.7717/peerj.11297.
Testo completoAbstract (sommario):
Background Myriad maxillo-mandibular occlusal relationships are observed in patients with isolated cleft palate (ICP), unlike in patients with other cleft types, such as cleft lip and palate. Objectives This study aimed to categorise the characteristics of craniofacial morphology in patients with ICP, and investigate the clinical factors affecting these categorised morphological characteristics. Methods Thirty-six girls with ICP (age (mean ± SD): 5.36 ± 0.36 years) underwent cephalometric measurement. Their craniofacial morphology was categorised using cluster analysis. Profilograms were created and superimposed onto the standard Japanese profilograms to visualise the morphological characteristics of each group (cluster). The mean values and variations in the linear and angular measurements of each group were compared with the Japanese standards and statistically analysed using Dunnett’s test after the analysis of variance. Fisher’s exact test was used to analyse the differences between the cleft types (cleft in the hard and/or soft palate) and skills of the operating surgeons in the groups. Results Cluster analysis of craniofacial morphologies in patients with ICP resulted in the formation of three categories: the first cluster exhibited a relatively harmonious anteroposterior relationship between the maxilla and the mandible (22.2%); the second cluster exhibited crossbite owing to a significantly smaller maxilla (33.3%); and the third cluster exhibited a smaller mandible with posterior rotation showing skeletal class II malocclusion (44.4%). Differences in cleft types and surgeons were not associated with the distribution of patients in each cluster. Conclusions Patients with ICP exhibited characteristic morphological patterns, such as bimaxillary retrusion or severe mandibular retrusion, besides the anterior crossbite frequently found in patients with cleft lip and palate . Understanding the typical morphological characteristics could enable better diagnostic categorisation of patients with ICP, which may eventually improve orthodontic treatment planning.
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Tiongco, Maria A., Enrico Vesperini e Anna Lisa Varri. "Kinematical evolution of multiple stellar populations in star clusters". Monthly Notices of the Royal Astronomical Society 487, n. 4 (25 giugno 2019): 5535–48. http://dx.doi.org/10.1093/mnras/stz1595.
Testo completoAbstract (sommario):
ABSTRACT We present the results of a suite of N-body simulations aimed at understanding the fundamental aspects of the long-term evolution of the internal kinematics of multiple stellar populations in globular clusters. Our models enable us to study the cooperative effects of internal, relaxation-driven processes and external, tidally induced perturbations on the structural and kinematic properties of multiple-population globular clusters. To analyse the dynamical behaviour of the multiple stellar populations in a variety of spin-orbit coupling conditions, we have considered three reference cases in which the tidally perturbed star cluster rotates along an axis oriented in different directions with respect to the orbital angular momentum vector. We focus specifically on the characterization of the evolution of the degree of differential rotation and anisotropy in the velocity space, and we quantify the process of spatial and kinematic mixing of the two populations. In light of recent and forthcoming explorations of the internal kinematics of this class of stellar systems by means of line-of sight and astrometric measurements, we also investigate the implications of projection effects and spatial distribution of the stars adopted as tracers. The kinematic and structural richness emerging from our models further emphasizes the need and the importance of observational studies aimed at building a complete kinematical picture of the multiple population phenomenon.
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Chikuse, Yasuko. "The matrix angular central Gaussian distribution". Journal of Multivariate Analysis 33, n. 2 (maggio 1990): 265–74. http://dx.doi.org/10.1016/0047-259x(90)90050-r.
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Zhang, Yuxiang, Jianhua Zhang, Jian Zhang, Guangyi Liu, Yuan Zhang e Yuan Yao. "A Theoretical Analysis of Favorable Propagation on Massive MIMO Channels with Generalized Angle Distributions". Electronics 11, n. 14 (9 luglio 2022): 2150. http://dx.doi.org/10.3390/electronics11142150.
Testo completoAbstract (sommario):
Massive MIMO obtains the multiuser performance gain based on the favorable propagation (FP) assumption, defined as the mutual orthogonality of different users’ channel vectors. Until now, most of the theoretical analyses of FP are based on uniform angular distributions and only consider the horizontal dimension. However, the real propagation channel contains full dimensions, and the spatial angle varies with the environment. Thus, it remains unknown whether the FP condition holds in real deployment scenarios and how it impacts the massive MIMO system performance. In this paper, we analyze the FP condition theoretically based on a cluster-based three-dimensional (3D) MIMO channel with generalized angle distributions. Firstly, the FP condition’s unified mathematical expectation and variance expressions with full-dimensional angular integral are given. Since the closed-form expressions are hard to derive, we decompose generalized angle distributions, i.e., wrapped Gaussian (WG), Von Mises (VM), and truncated Laplacian (TL) into the functions of Bessel and Cosine basis by introducing Jacobi-Anger expansions and Fourier series. Thus the closed-form expressions of the FP condition are derived. Based on the above, we theoretically analyze the asymptotically FP condition under generalized angle distributions and then compare the impact of angular spreads on the FP performance. Furtherly, the FP condition is also investigated by numerical simulations and practical measurements. It is observed that environments with larger angle spreads and larger antenna spacing are more likely to realize FP. This paper provides valuable insights for the theoretical analysis of the practical application of massive MIMO systems.
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Mikhailov, Gennady A., Natalya V. Tracheva e Sergey A. Ukhinov. "A new kernel-projective statistical estimator in the Monte Carlo method". Russian Journal of Numerical Analysis and Mathematical Modelling 35, n. 6 (16 dicembre 2020): 341–53. http://dx.doi.org/10.1515/rnam-2020-0028.
Testo completoAbstract (sommario):
AbstractIn the present paper, we propose a new combined kernel-projective statistical estimator of the two-dimensional distribution density, where the first ‘main’ variable is processed with the kernel estimator, and the second one is processed with the projective estimator for the conditional distribution density. In this case, statistically estimated coefficients of some orthogonal expansion of the conditional distribution density are used for each ‘kernel’ interval defined by a micro-sample. The root-mean-square optimization of such an estimator is performed under the assumptions concerning the convergence rate of the used orthogonal expansion. The numerical study of the constructed estimator is implemented for angular distributions of the radiation flux forward-scattered and backscattered by a layer of matter. A comparative analysis of the results is performed for molecular and aerosol scattering.
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Biscoveanu, Sylvia, Colm Talbot e Salvatore Vitale. "The effect of spin mismodelling on gravitational-wave measurements of the binary neutron star mass distribution". Monthly Notices of the Royal Astronomical Society 511, n. 3 (9 febbraio 2022): 4350–59. http://dx.doi.org/10.1093/mnras/stac347.
Testo completoAbstract (sommario):
Abstract The binary neutron star (BNS) mass distribution measured with gravitational-wave observations has the potential to reveal information about the dense matter equation of state, supernova physics, the expansion rate of the Universe, and tests of general relativity. As most current gravitational-wave analyses measuring the BNS mass distribution do not simultaneously fit the spin distribution, the implied population-level spin distribution is the same as the spin prior applied when analysing individual sources. In this work, we demonstrate that introducing a mismatch between the implied and true BNS spin distributions can lead to biases in the inferred mass distribution. This is due to the strong correlations between the measurements of the mass ratio and spin components aligned with the orbital angular momentum for individual sources. We find that applying a low-spin prior that excludes the true spin magnitudes of some sources in the population leads to significantly overestimating the maximum neutron star mass and underestimating the minimum neutron star mass at the population level with as few as six BNS detections. The safest choice of spin prior that does not lead to biases in the inferred mass distribution is one that allows for high spin magnitudes and tilts misaligned with the orbital angular momentum.
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Jiang, Jonathan H., Remo Burn, Xuan Ji, Kristen A. Fahy e Patrick Eggenberger. "Angular Momentum Distributions for Observed and Modeled Exoplanetary Systems". Astrophysical Journal 924, n. 2 (1 gennaio 2022): 118. http://dx.doi.org/10.3847/1538-4357/ac3242.
Testo completoAbstract (sommario):
Abstract The distribution of angular momentum of planets and their host stars provides important information on the formation and evolution of the planetary system. However, mysteries still remain, partly due to bias and uncertainty of the current observational data sets and partly due to the fact that theoretical models for the formation and evolution of planetary systems are still underdeveloped. In this study, we calculate the spin angular momentum of host stars and the orbital angular momentum of their planets using data from the NASA Exoplanet Archive along with detailed analysis of observation dependent biases and uncertainty ranges. We also analyze the angular momentum of the planetary system as a function of star age to understand their variation in different evolutionary stages. In addition, we use a population of planets from theoretical model simulations to reexamine the observed patterns and compare the simulated population with the observed samples to assess variations and differences. We found the majority of exoplanets discovered thus far do not have the angular momentum distribution similar to that of planets in our solar system, though this could be due to the observation bias. When filtered by the observational biases, the model simulated angular momentum distributions are comparable to the observed pattern in general. However, the differences between the observation and model simulation in the parameter (angular momentum) space provide more rigorous constraints and insights on the issues that needed future improvement.
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Mughrabi, H., H. W. Höppel, M. Kautz e R. Z. Valiev. "Annealing treatments to enhance thermal and mechanical stability of ultrafine-grained metals produced by severe plastic deformation". International Journal of Materials Research 94, n. 10 (1 ottobre 2003): 1079–83. http://dx.doi.org/10.1515/ijmr-2003-0197.
Testo completoAbstract (sommario):
Abstract Ultrafine-grained (UFG) metals produced by techniques of severe plastic deformation, such as equal channel angular pressing (ECAP), exhibit extraordinary strength properties. However, in the as-ECAP-processed state, the heavily deformed microstructure of such UFG metals is rather unstable and is prone to undergo grain coarsening (recrystallization) at moderate temperatures. This microstructural instability is enhanced in the presence of modest mechanical stressing as, for example, in cyclic deformation. Thus, all measures to enhance the thermal stability are also considered as beneficial for the improvement of the mechanical stability. One main objective of the present work is to analyse the thermal and mechanical stability of ECAP-processed metals during specific annealing and cyclic deformation tests. As a by-product, some conclusions relating to the separate effects of dislocation density, grain size (in the UFG regime) and internal stresses on the (micro)yielding behaviour will be drawn. Another goal is to explore the potential of different annealing treatments with respect to the stabilization of the microstructure and the optimization of the mechanical properties of ECAP-processed UFG metals in terms of an optimal combination of strength and ductility. In order to demonstrate the potential and the limitations of this approach, experimental work performed on UFG copper, aluminium and α-brass produced by ECAP will be reported and discussed. The results presented indicate strongly that a heat treatment leading to a bimodal grain size distribution provides the best compromise between strength and ductility.
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Marangotto, Daniele. "Angular and CP-Violation Analyses of B-→D⁎+l-ν-l Decays at Hadron Collider Experiments". Advances in High Energy Physics 2019 (28 agosto 2019): 1–16. http://dx.doi.org/10.1155/2019/5274609.
Testo completoAbstract (sommario):
The B-→D⁎+l-ν-l branching fractions ratio between muon and tau lepton decay modes R(D⁎) has shown intriguing discrepancies between the Standard Model prediction and measurements performed at BaBar, Belle, and LHCb experiments, a possible sign of beyond the Standard Model physics. Theoretical studies show how observables related to the B-→D⁎+l-ν-l differential decay distribution can be used to further constrain New Physics contributions, but their experimental measurements are lacking to date. This article proposes the measurement of B-→D⁎+l-ν-l angular and CP-violating observables at hadron collider experiments, by exploiting approximate reconstruction algorithms using information from detectable final-state particles only. The resolution on the phase space variables is studied using B-→D⁎+l-ν-l decays simulated in a forward detector geometry like LHCb. A method to correct the observable values for the reconstruction inaccuracies based on detector simulation is successfully tested on simulated data and the decrease in precision with respect to a perfect reconstruction is evaluated. The D⁎+ longitudinal polarization fraction and the AT(2)CP-violating observable can be measured losing a factor of 2 and 5 in precision, respectively. The extraction of angular distributions from the template fit selecting B-→D⁎+l-ν-l decays and associated systematic uncertainties are also discussed.
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Kobbert, Jonas, Anil Erkan, John D. Bullough e Tran Quoc Khanh. "A Novel Way of Optimizing Headlight Distributions Based on Real-Life Traffic and Eye Tracking Data Part 3: Driver Gaze Behaviour on Real Roads and Optimized Light Distribution". Applied Sciences 13, n. 17 (1 settembre 2023): 9898. http://dx.doi.org/10.3390/app13179898.
Testo completoAbstract (sommario):
In order to find optimized headlight distributions based on real traffic data, a three-step approach has been chosen. The complete investigations are too extensive to fit into a single paper; this paper is the last of a three part series. Over the three papers, a novel way to optimize automotive headlight distributions based on real-life traffic and eye tracking data is presented. Across all three papers, a total of 119 test subjects participated in the studies with over 15,000 km of driving, including recordings of gaze behaviour, light data, detection distances, and other objects in traffic. In this third paper, driver gaze behaviour is recorded while driving a 128 km round course, covering urban roads, country roads, and motorways. This gaze behaviour is then analysed and compared to prior work covering driver gaze behaviour. Comparing the gaze distributions with roadway object distributions from part two of this series, Analysis of Real-World Traffic Data in Germany and combining them with the idealized baseline headlight distribution from part one, different optimized headlight distributions can be generated. These headlight distributions can be optimized for different driving requirements based on the data that is used and weighting the different road types differently. The resulting headlight distribution is then compared to a standard light distribution in terms of the required luminous flux, angular distribution, and overall shape. Nonetheless, it is the overall approach that has been taken that we see as the primary novel outcome of this investigation, even more than the actual distribution resulting from this effort.