Artículos de revistas sobre el tema "Hydrodynamical limits"
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Lopes Garcia, Nancy. "Hydrodynamical limits for epidemic models". Communications in Statistics. Stochastic Models 14, n.º 3 (enero de 1998): 497–508. http://dx.doi.org/10.1080/15326349808807485.
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Katsoulakis, Markos A. y Anders Szepessy. "Stochastic hydrodynamical limits of particle systems". Communications in Mathematical Sciences 4, n.º 3 (2006): 513–49. http://dx.doi.org/10.4310/cms.2006.v4.n3.a3.
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Miyoshi, Hironari y Masayoshi Tsutsumi. "Convergence of Hydrodynamical Limits for Generalized Carleman Models". Funkcialaj Ekvacioj 59, n.º 3 (2016): 351–82. http://dx.doi.org/10.1619/fesi.59.351.
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Sowers, Richard B. "Hydrodynamical Limits and Geometric Measure Theory: Mean Curvature Limits from a Threshold Voter Model". Journal of Functional Analysis 169, n.º 2 (diciembre de 1999): 421–55. http://dx.doi.org/10.1006/jfan.1999.3477.
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Gabetta, E., L. Pareschi y M. Ronconi. "Central schemes for hydrodynamical limits of discrete-velocity kinetic models". Transport Theory and Statistical Physics 29, n.º 3-5 (abril de 2000): 465–77. http://dx.doi.org/10.1080/00411450008205885.
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Montarnal, Philippe. "Study of hydrodynamical limits in a multicollision scale Boltzmann equation for semiconductors". Journal of Mathematical Physics 39, n.º 5 (mayo de 1998): 2781–99. http://dx.doi.org/10.1063/1.532420.
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Jacobus, Cooper, Peter Harrington y Zarija Lukić. "Reconstructing Lyα Fields from Low-resolution Hydrodynamical Simulations with Deep Learning". Astrophysical Journal 958, n.º 1 (1 de noviembre de 2023): 21. http://dx.doi.org/10.3847/1538-4357/acfcb5.
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Abstract Hydrodynamical cosmological simulations are a powerful tool for accurately predicting the properties of the intergalactic medium (IGM) and for producing mock skies that can be compared against observational data. However, the need to resolve density fluctuation in the IGM puts a stringent requirement on the resolution of such simulations, which in turn limits the volumes that can be modeled, even on the most powerful supercomputers. In this work, we present a novel modeling method that combines physics-driven simulations with data-driven generative neural networks to produce outputs that are qualitatively and statistically close to the outputs of hydrodynamical simulations employing eight times higher resolution. We show that the Lyα flux field, as well as the underlying hydrodynamic fields, have greatly improved statistical fidelity over a low-resolution simulation. Importantly, the design of our neural network allows for sampling multiple realizations from a given input, enabling us to quantify the model uncertainty. Using test data, we demonstrate that this model uncertainty correlates well with the true error of the Lyα flux prediction. Ultimately, our approach allows for training on small simulation volumes and applying it to much larger ones, opening the door to producing accurate Lyα mock skies in volumes of Hubble size, as will be probed with DESI and future spectroscopic sky surveys.
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CHEVALIER, C., F. DEBBASCH y J. P. RIVET. "STOCHASTIC MODELS OF THERMODIFFUSION". Modern Physics Letters B 23, n.º 09 (10 de abril de 2009): 1147–55. http://dx.doi.org/10.1142/s0217984909019260.
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New stochastic models of thermodiffusion are constructed and their hydrodynamical limits are studied through a first-order Chapman–Enskog expansion. These models differ from earlier ones by taking into account all first-order contributions proportional to the temperature gradient and, thus, allow for both positive and negative Soret coefficients, in accordance with observations.
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Baraffe, I., M. Viallet y R. Walder. "Towards a New Generation of Multi-Dimensional Stellar Models: Can Our Models Meet the Challenges?" Proceedings of the International Astronomical Union 7, S285 (septiembre de 2011): 138. http://dx.doi.org/10.1017/s1743921312000464.
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SummaryThe talk described the first steps of development of a new multi-dimensional time-implicit code devoted to the study of hydrodynamical processes in stellar interiors. The main motivation stemmed from the fact that our physical understanding of stellar interiors and evolution still largely relies on one-dimensional calculations. The description of complex physical processes like time-dependent turbulent convection, rotation or MHD processes mostly relies on simplified, phenomenological approaches, with a predictive power hampered by the use of several free parameters. These approaches have now reached their limits in the understanding of stellar structure and evolution. The development of multi-dimensional hydrodynamical simulations becomes crucial to progress in the field of stellar physics and to meet the enormous observational efforts aimed at producing data of unprecedented quality (COROT, Kepler GAIA). The code we are developing solves the hydrodynamical equations in spherical geometry and is based on the finite volume method. The talk presented a global simulation of turbulent convective motions in a cold giant envelope, covering 80% in radius of the stellar structure. Our first developments show that the use of an implicit scheme applied to a stellar evolution context is perfectly thinkable.
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Sanchis, E., G. Picogna, B. Ercolano, L. Testi y G. Rosotti. "Detectability of embedded protoplanets from hydrodynamical simulations". Monthly Notices of the Royal Astronomical Society 492, n.º 3 (11 de enero de 2020): 3440–58. http://dx.doi.org/10.1093/mnras/staa074.
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ABSTRACT We predict magnitudes for young planets embedded in transition discs, still affected by extinction due to material in the disc. We focus on Jupiter-sized planets at a late stage of their formation, when the planet has carved a deep gap in the gas and dust distributions and the disc starts to being transparent to the planet flux in the infrared (IR). Column densities are estimated by means of three-dimensional hydrodynamical models, performed for several planet masses. Expected magnitudes are obtained by using typical extinction properties of the disc material and evolutionary models of giant planets. For the simulated cases located at 5.2 au in a disc with a local unperturbed surface density of 127 $\mathrm{g} \, \mathrm{cm}^{-2}$, a 1MJ planet is highly extinct in the J, H, and Kbands, with predicted absolute magnitudes ≥ 50 mag. In the L and Mbands, extinction decreases, with planet magnitudes between 25 and 35 mag. In the Nband, due to the silicate feature on the dust opacities, the expected magnitude increases to ∼40 mag. For a 2MJ planet, the magnitudes in the J, H, and Kbands are above 22 mag, while for the L, M, and Nbands, the planet magnitudes are between 15 and 20 mag. For the 5MJ planet, extinction does not play a role in any IR band, due to its ability to open deep gaps. Contrast curves are derived for the transition discs in CQ Tau, PDS 70, HL Tau, TW Hya, and HD 163296. Planet mass upper limits are estimated for the known gaps in the last two systems.
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Chistyakov, Alexander, Alena Filina y Vladimir Litvinov. "NUMERICAL MODELING OF HYDRODYNAMIC PROCESSES IN THE TAGANROG BAY OF THE AZOV SEA". Computational Mathematics and Information Technologies 1, n.º 2 (2020): 101–13. http://dx.doi.org/10.23947/2587-8999-2020-1-2-101-113.
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This paper covers the creation and numerical realization of proposed mathematical model of hydrodynamical processes in shallow water based on contemporary information technology and new computational methods that allow improve the prediction accuracy of the environmental situation using the example of the Taganrog Bay in the Azov Sea basin. The proposed mathematical hydrodynamics model takes into account surges, dynamically reconstructed geometry, elevation of the level and coastline, wind currents and friction against the bottom, Coriolis force, turbulent exchange, evaporation, river flow, deviation of the pressure field value from the hydrostatic approximation, the salinity and temperature impact. The discretization of the mathematical model of hydrodynamics was performed using the splitting schemes for physical processes. The constructed discrete analogs possess the properties of conservatism, stability, and convergence. Numerical algorithms are also proposed for solving the arising SLAEs that improve the accuracy of predictive modeling. The practical significance of this research is software implementation of the developed model and the determination of limits and prospects of its application. The experimental software development was based on a graphics accelerator for mathematical simulation the possible scenarios of shallow water ecosystems in consideration the environmental factors influence. The decomposition methods taking into account the CUDA architecture specifications were used at parallel implementation for computationally labors diffusion-convection problems.
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Abdellaoui, S., J. Krtička y P. Kurfürst. "Intrinsic polarization of Wolf-Rayet stars due to the rotational modulation of the stellar wind". Astronomy & Astrophysics 658 (28 de enero de 2022): A46. http://dx.doi.org/10.1051/0004-6361/202141732.
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Context. Fast rotating Wolf-Rayet stars are expected to be progenitors of long duration gamma-ray bursts. However, the observational test of this model is problematic. Spectral lines of Wolf-Rayet stars originate in expanding stellar wind, therefore a reliable spectroscopical determination of their rotational velocities is difficult. Intrinsic polarization of Wolf-Rayet stars due to the rotational modulation of the stellar wind may provide an indirect way to determine the rotational velocities of these stars. However, detailed wind models are required for this purpose. Aims. We determine the intrinsic polarization of Wolf-Rayet stars from hydrodynamical wind models as a function of rotational velocity. Methods. We used 2.5D hydrodynamical simulations to calculate the structure of rotating winds of Wolf-Rayet stars. The simulations account for the deformation of the stellar surface due to rotation, gravity darkening, and nonradial forces. From the derived models, we calculated the intrinsic stellar polarization. The mass loss rate was scaled to take realistic wind densities of Wolf-Rayet stars into account. Results. The hydrodynamical wind models predict a prolate wind structure, which leads to a relatively low level of polarization. Even relatively large rotational velocities are allowed by observational constrains. The obtained wind structure is similar to that obtained previously for rotating optically thin winds. Conclusions. Derived upper limits of rotational velocities of studied Wolf-Rayet stars are not in conflict with the model of long duration gamma-ray bursts.
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Fraija, N., A. Galvan-Gamez, B. Betancourt Kamenetskaia, M. G. Dainotti, S. Dichiara, P. Veres, R. L. Becerra y A. C. Caligula do E. S. Pedreira. "Modeling Gamma-Ray Burst Afterglow Observations with an Off-axis Jet Emission". Astrophysical Journal 940, n.º 2 (1 de diciembre de 2022): 189. http://dx.doi.org/10.3847/1538-4357/ac68e1.
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Abstract Gamma-ray bursts (GRBs) are fascinating extragalactic objects. They represent a fantastic opportunity to investigate unique properties not exhibited in other sources. Multiwavelength afterglow observations from some short- and long-duration GRBs reveal an atypical long-lasting emission that evolves differently from the canonical afterglow light curves favoring the off-axis emission. We present an analytical synchrotron afterglow scenario and the hydrodynamical evolution of an off-axis top-hat jet decelerated in a stratified surrounding environment. The analytical synchrotron afterglow model is shown during the coasting, deceleration (off- and on-axis emission), and post–jet break decay phases, and the hydrodynamical evolution is computed by numerical simulations showing the time evolution of the Doppler factor, the half-opening angle, the bulk Lorentz factor, and the deceleration radius. We show that numerical simulations are in good agreement with those derived with our analytical approach. We apply the current synchrotron model and successfully describe the delayed nonthermal emission observed in a sample of long and short GRBs with evidence of off-axis emission. Furthermore, we provide constraints on the possible afterglow emission by requiring the multiwavelength upper limits derived for the closest Swift-detected GRBs and promising gravitational-wave events.
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Cavus, Huseyin. "On the Effects of Viscosity on the Shock Waves for a Hydrodynamical Case—Part I: Basic Mechanism". Advances in Astronomy 2013 (2013): 1–6. http://dx.doi.org/10.1155/2013/582965.
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The interaction of shock waves with viscosity is one of the central problems in the supersonic regime of compressible fluid flow. In this work, numerical solutions of unmagnetised fluid equations, with the viscous stress tensor, are investigated for a one-dimensional shock wave. In the algorithm developed the viscous stress terms are expressed in terms of the relevant Reynolds number. The algorithm concentrated on the compression rate, the entropy change, pressures, and Mach number ratios across the shock wave. The behaviour of solutions is obtained for the Reynolds and Mach numbers defining the medium and shock wave in the supersonic limits.
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Gómez, Jonathan S., G. Yepes, A. Jiménez Muñoz y W. Cui. "Galaxy catalogs from the Sage Semi-Analytic Model calibrated on The Three Hundred hydrodynamical simulations: A method to push the limits toward lower mass galaxies in dark matter only clusters simulations". EPJ Web of Conferences 293 (2024): 00023. http://dx.doi.org/10.1051/epjconf/202429300023.
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The new generation of upcoming deep photometric and spectroscopic surveys will allow us to measure the astrophysical properties of faint galaxies in massive clusters. This would demand to produce simulations of galaxy clusters with better mass resolution than the ones available today if we want to make comparisons between the upcoming observations and predictions of cosmological models. But producing full-physics hydrodynamical simulations of the most massive clusters is not an easy task. This would involve billions of computational elements to reliably resolve low mass galaxies similar to those measured in observations. On the other hand, dark matter only simulations of cluster size halos can be done with much larger mass resolution but at the cost of having to apply a model that populate galaxies within each of the subhalos in these simulations. In this paper we present the results of a new set of dark matter only simulations with different mass resolutions within the The Three Hundred project. We have generated catalogs of galaxies with stellar and luminosity properties by applying the Sage Semi-Analytical Model of galaxy formation. To obtain the catalogs consistent with the results from hydrodynamical simulations, the internal physical parameters of Sage were calibrated with the Particle Swarm Optimization method using a subset of full-physics runs with the same mass resolution than the dark matter only ones.
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Thompson, M. C. "Rapidly Rotating Core-Collapse Models". Publications of the Astronomical Society of Australia 6, n.º 2 (1985): 214–16. http://dx.doi.org/10.1017/s1323358000018130.
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AbstractVery few (if any at all) three dimensional models of the final evolutionary stages of a star’s life have appeared in the literature. Such models may be important if the stellar core maintains sufficient rotational energy during it’s lifetime so that when collapse finally occurs, the increase of rotational energy to gravitational energy, may lead to a non-axisymmetric instability.A sequence of core collapse models with decreasing rotation rate is considered. These models were calculated using a three dimensional, post-Newtonian, hydrodynamical, numerical code. The results show that for high precollapse rotational energies the core can become unstable resulting in the formation of what resemble ‘spiral arms’. Unfortunately, because of limits on computer time, the calculations had to be discontinued shortly after this development occurred.
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Szewczyk, Paweł, Dorota Gondek-Rosińska, Kamil Kolasa y Parita Mehta. "Are hypermassive neutron stars stable against a prompt collapse?" Proceedings of the International Astronomical Union 16, S363 (junio de 2020): 350–51. http://dx.doi.org/10.1017/s1743921322000977.
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AbstractDifferential rotation in neutron stars allows for significantly larger masses than rigid rotation. Some of those hypermassive objects are, however, unstable and collapse to a black hole immediately after formation. Yet, the exact threshold of dynamical stability is still unknown.In our work we explore the limits on masses of neutron stars with various degrees of differential rotation which could be stable against a prompt collapse to a black hole by using turning-point (j-constant) criterion. We considered both spheroidal and quasi-toroidal differentially rotating neutron stars described by the polytropic equation of state. We find that massive configurations could be temporarily stabilized by differential rotation. Such objects are important sources of gravitational waves. Our results are a starting point for more detailed studies of stability using hydrodynamical codes.
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Sharipov, V. M., G. O. Kotiev, Yu S. Shchetinin, M. V. Vyaznikov, S. V. Gaev y M. G. Rozenoer. "On the selection of parameters of double-flow hydromechanical transmission for industrial and forestry tractors". Traktory i sel hozmashiny 83, n.º 3 (15 de marzo de 2016): 8–14. http://dx.doi.org/10.17816/0321-4443-66117.
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Double-flow hydromechanical transmissions are widely used in industrial and forestry tractors. The main advantage of such transmission is the higher value of the maximum efficiency coefficient in comparison with the single-flow one. The article presents a method of selection of parameters of such transmissions for industrial and forestry tractors. In this case, it considers the hydromechanical transmission with a differential unit at the input and at the output. Three-link differential devices with mixed type of gear engagement are used as the differential unit. All of the twelve possible schemes of double-flow hydrodynamical transmissions are considered. It is shown that double-flow hydrodynamical transmission has an operation mode when the torque converter turbine is rotating counter to the rotation of pump wheel. This factor is taken into account during the selection of parameters of double-flow hydrodynamical transmission. The article describes the method of construction of external characteristic of the transmission and matching of its load characteristic with the full-load curve of diesel engine. The matching is performed by three ways: the selection of required value of active diameter of torque converter; the selection of reduction ratio of matching gear; the selection of characteristic of planetary gear set. It is found that for the most common scheme of double-flow hydromechanical transmission when the characteristic of planetary gear set is reduced, its maximum efficiency coefficient is increased, the active diameter of torque converter is reduced and the relative rotation frequency of satellite gears of three-link differential device is increased. In this case, the rotation frequency of satellite gears limits the minimum value of characteristic of planetary gear set. Increasing of characteristic of planetary gear set leads to the reducing of transparency of the hydromechanical transmission and to increasing of its transformation ratio. It is shown that the double-flow hydromechanical transmission allows to utilize more fully the converting properties of engine in comparison with the single-flow one; it allows to change the torque value if external engine load is changing, that is very important for industrial and forestry tractors.
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Chavanis, Pierre-Henri. "Jeans Instability of Dissipative Self-Gravitating Bose–Einstein Condensates with Repulsive or Attractive Self-Interaction: Application to Dark Matter". Universe 6, n.º 12 (27 de noviembre de 2020): 226. http://dx.doi.org/10.3390/universe6120226.
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We study the Jeans instability of an infinite homogeneous dissipative self-gravitating Bose–Einstein condensate described by generalized Gross–Pitaevskii–Poisson equations [Chavanis, P.H. Eur. Phys. J. Plus2017, 132, 248]. This problem has applications in relation to the formation of dark matter halos in cosmology. We consider the case of a static and an expanding universe. We take into account an arbitrary form of repulsive or attractive self-interaction between the bosons (an attractive self-interaction being particularly relevant for the axion). We consider both gravitational and hydrodynamical (tachyonic) instabilities and determine the maximum growth rate of the instability and the corresponding wave number. We study how they depend on the scattering length of the bosons (or more generally on the squared speed of sound) and on the friction coefficient. Previously obtained results (notably in the dissipationless case) are recovered in particular limits of our study.
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Rodríguez-Ramírez, J. C., E. M. de Gouveia Dal Pino y R. Alves Batista. "Numerical models of VHE emission by magnetic reconnection in X-ray binaries: GRMHD simulations and Monte Carlo cosmic-ray emission". Proceedings of the International Astronomical Union 14, S346 (agosto de 2018): 388–93. http://dx.doi.org/10.1017/s1743921319001261.
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AbstractGalactic microquasars have been detected at very-high-energies (VHE) (> 100 GeV) and the particle acceleration mechanisms that produce this emission are not yet well-understood. Here we investigate a hadronic emission scenario where cosmic-rays (CRs) are accelerated in magnetic reconnection events by the turbulent, advected-dominated accretion flow (ADAF) believed to be present in the hard state of black hole binaries. We present Monte Carlo simulations of CR emission plus γ-γ and inverse Compton cascades, injecting CRs with a total energy consistent with the magnetic energy of the plasma. The background gas density, magnetic, and photon fields where CRs propagate and interact are modelled with general relativistic (GR), magneto-hydrodynamical simulations together with GR radiative transfer calculations. Our approach is applied to the microquasar Cygnus X-1, where we show a model configuration consistent with the VHE upper limits provided by MAGIC collaboration.
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Boliasova, O. O. y V. N. Krivoruchko. "Longitudinal Spin Dynamics in the Heisenberg Antiferromagnet: Two-Magnon Excitations". Ukrainian Journal of Physics 65, n.º 10 (9 de octubre de 2020): 865. http://dx.doi.org/10.15407/ujpe65.10.865.
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Understanding the ultrafast spin dynamics in magnetically ordered materials is important for the comprehenssion of fundamental limits in spin-based magnetic electronics – magnonics. We have studied a microscopic model of magnetization dynamics in a two-sublattice antiferromagnet with the emphasis on longitudinal spin excitations. The diagrammatic technique for spin operators has been used to overcome limitations typical of phenomenological approaches. The graphical representations of spin wave propagators allow us to summing up the infinite series of distinctive diagrams. Its sum is transformed into an analytic expression for the longitudinal spin susceptibility xzz (q, w) applicable in all regions of the frequency w and wave vector q spaces beyond the hydrodynamical and critical regimes. It is found that the longitudinal magnetization dynamics consists of two types of excitations, which have different dependences on the temperature and wave vector q. The obtained result could be important for understanding the physics of nonequilibrium magnetic dynamics under the effect of ultrafast laser pulses in antiferromagnetic materials.
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Hsueh, J.-W., W. Enzi, S. Vegetti, M. W. Auger, C. D. Fassnacht, G. Despali, L. V. E. Koopmans y J. P. McKean. "SHARP – VII. New constraints on the dark matter free-streaming properties and substructure abundance from gravitationally lensed quasars". Monthly Notices of the Royal Astronomical Society 492, n.º 2 (15 de noviembre de 2019): 3047–59. http://dx.doi.org/10.1093/mnras/stz3177.
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ABSTRACT We present an analysis of seven strongly gravitationally lensed quasars and the corresponding constraints on the properties of dark matter. Our results are derived by modelling the lensed image positions and flux-ratios using a combination of smooth macro-models and a population of low-mass haloes within the mass range of 106–109 M⊙. Our lens models explicitly include higher order complexity in the form of stellar discs and luminous satellites, as well as low-mass haloes located along the observed lines of sight for the first time. Assuming a cold dark matter (CDM) cosmology, we infer an average total mass fraction in substructure of $f_{\rm sub} = 0.012^{+0.007}_{-0.004}$ (68 per cent confidence limits), which is in agreement with the predictions from CDM hydrodynamical simulations to within 1σ. This result is closer to the predictions than those from previous studies that did not include line-of-sight haloes. Under the assumption of a thermal relic dark matter model, we derive a lower limit on the particle relic mass of mth > 5.58 keV (95 per cent confidence limits), which is consistent with a value of mth > 5.3 keV from the recent analysis of the Ly α forest. We also identify two main sources of possible systematic errors and conclude that deeper investigations in the complex structure of lens galaxies as well as the size of the background sources should be a priority for this field.
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Callingham, Thomas M., Marius Cautun, Alis J. Deason, Carlos S. Frenk, Wenting Wang, Facundo A. Gómez, Robert J. J. Grand, Federico Marinacci y Ruediger Pakmor. "The mass of the Milky Way from satellite dynamics". Monthly Notices of the Royal Astronomical Society 484, n.º 4 (5 de febrero de 2019): 5453–67. http://dx.doi.org/10.1093/mnras/stz365.
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Abstract We present and apply a method to infer the mass of the Milky Way (MW) by comparing the dynamics of MW satellites to those of model satellites in the eagle cosmological hydrodynamics simulations. A distribution function (DF) for galactic satellites is constructed from eagle using specific angular momentum and specific energy, which are scaled so as to be independent of host halo mass. In this two-dimensional space, the orbital properties of satellite galaxies vary according to the host halo mass. The halo mass can be inferred by calculating the likelihood that the observed satellite population is drawn from this DF. Our method is robustly calibrated on mock eagle systems. We validate it by applying it to the completely independent suite of 30 auriga high-resolution simulations of MW-like galaxies: the method accurately recovers their true mass and associated uncertainties. We then apply it to 10 classical satellites of the MW with six-dimensional phase-space measurements, including updated proper motions from the Gaia satellite. The mass of the MW is estimated to be $M_{200}^{\rm {MW}}=1.17_{-0.15}^{+0.21}\times 10^{12}\, \mathrm{M}_{\odot }$ (68 per cent confidence limits). We combine our total mass estimate with recent mass estimates in the inner regions of the Galaxy to infer an inner dark matter (DM) mass fraction $M^\rm {DM}(\lt 20~\rm {kpc})/M^\rm {DM}_{200}=0.12$, which is typical of ${\sim }10^{12}\, \mathrm{M}_{\odot }$ lambda cold dark matter haloes in hydrodynamical galaxy formation simulations. Assuming a Navarro, Frenk and White (NFW) profile, this is equivalent to a halo concentration of $c_{200}^{\rm {MW}}=10.9^{+2.6}_{-2.0}$.
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Moon, Jun-Sung y Jounghun Lee. "Reoriented Memory of Galaxy Spins for the Early Universe". Astrophysical Journal 952, n.º 2 (20 de julio de 2023): 101. http://dx.doi.org/10.3847/1538-4357/acd9ac.
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Abstract Galaxy spins are believed to retain the initially acquired tendency of being aligned with the intermediate principal axis of the linear tidal field, which disseminates the prospect of using them as a probe of early universe physics. This roseate prospect, however, is contingent upon the key assumption that the observable stellar spins of present galaxies measured at inner radii have the same alignment tendency toward the initial tidal field as their dark matter counterparts measured at virial limits. We test this assumption directly against a high-resolution hydrodynamical simulation by tracing the galaxy component particles back to the protogalactic stage. It is discovered that the galaxy stellar spins at z = 0 have strong but reoriented memory for the early universe, exhibiting a significant signal of cross-correlation with the major principal axis of the initial tidal field at z = 127. An analytic single-parameter model for this reorientation of the present galaxy stellar spins relative to the initial tidal field is devised and shown to be in good accord with the numerical results.
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Calderón, D., J. Cuadra, M. Schartmann, A. Burkert, J. Prieto y C. M. P. Russell. "Three-dimensional simulations of clump formation in stellar wind collisions". Monthly Notices of the Royal Astronomical Society 493, n.º 1 (14 de enero de 2020): 447–67. http://dx.doi.org/10.1093/mnras/staa090.
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ABSTRACT The inner parsec of our Galaxy contains tens of Wolf–Rayet stars whose powerful outflows are constantly interacting while filling the region with hot, diffuse plasma. Theoretical models have shown that, in some cases, the collision of stellar winds can generate cold, dense material in the form of clumps. However, their formation process and properties are not well understood yet. In this work, we present, for the first time, a statistical study of the clump formation process in unstable wind collisions. We study systems with dense outflows (${\sim }10^{-5}\rm \ M_{\odot }\ yr^{-1}$), wind speeds of 500–$1500\rm \ km\ s^{-1}$, and stellar separations of ∼20–$200\rm \ au$. We develop three-dimensional high-resolution hydrodynamical simulations of stellar wind collisions with the adaptive-mesh refinement grid-based code ramses. We aim at characterizing the initial properties of clumps that form through hydrodynamic instabilities, mostly via the non-linear thin-shell instability (NTSI). Our results confirm that more massive clumps are formed in systems whose winds are close to the transition between the radiative and adiabatic regimes. Increasing either the wind speed or the degree of asymmetry increases the dispersion of the clump mass and ejection speed distributions. Nevertheless, the most massive clumps are very light (∼10−3–$10^{-2}\rm \ M_{\oplus }$), about three orders of magnitude less massive than theoretical upper limits. Applying these results to the Galactic Centre, we find that clumps formed through the NTSI should not be heavy enough either to affect the thermodynamic state of the region or to survive for long enough to fall on to the central supermassive black hole.
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Naiman, J. P., M. Soares-Furtado y E. Ramirez-Ruiz. "Modelling gas evacuation mechanisms in present-day globular clusters: stellar winds from evolved stars and pulsar heating". Monthly Notices of the Royal Astronomical Society 491, n.º 4 (9 de diciembre de 2019): 4602–14. http://dx.doi.org/10.1093/mnras/stz3353.
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ABSTRACT We employ hydrodynamical simulations to investigate the underlying mechanism responsible for the low levels of gas and dust in globular clusters. Our models examine the competing effects of energy and mass supply from the various components of the evolved stellar population for globular clusters 47 Tucanae, M15, NGC 6440, and NGC 6752. Ignoring all other gas evacuation processes, we find that the energy output from the stars that have recently turned off the main sequence are capable of effectively clearing the evolved stellar ejecta and producing intracluster gas densities consistent with current observational constraints. This result distinguishes a viable gas and dust evacuation mechanism that is ubiquitous among globular clusters. In addition, we extend our analysis to probe the efficiency of pulsar wind feedback in globular clusters. We find that if the energy supplied by the pulsar winds is effectively thermalized within the intracluster medium, the material would become unbound. The detection of intracluster ionized gas in 47 Tucanae allows us to place particularly strict limits on pulsar wind thermalization efficiency, which must be extremely low in the cluster’s core in order to be in accordance with the observed density constraints.
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Smith-Orlik, Adam, Nima Ronaghi, Nassim Bozorgnia, Marius Cautun, Azadeh Fattahi, Gurtina Besla, Carlos S. Frenk et al. "The impact of the Large Magellanic Cloud on dark matter direct detection signals". Journal of Cosmology and Astroparticle Physics 2023, n.º 10 (1 de octubre de 2023): 070. http://dx.doi.org/10.1088/1475-7516/2023/10/070.
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Abstract We study the effect of the Large Magellanic Cloud (LMC) on the dark matter (DM) distribution in the Solar neighborhood, utilizing the Auriga magneto-hydrodynamical simulations of Milky Way (MW) analogues that have an LMC-like system. We extract the local DM velocity distribution at different times during the orbit of the LMC around the MW in the simulations. As found in previous idealized simulations of the MW-LMC system, we find that the DM particles in the Solar neighborhood originating from the LMC analogue dominate the high speed tail of the local DM speed distribution. Furthermore, the native DM particles of the MW in the Solar region are boosted to higher speeds as a result of a response to the LMC's motion. We simulate the signals expected in near future xenon, germanium, and silicon direct detection experiments, considering DM interactions with target nuclei or electrons. We find that the presence of the LMC causes a considerable shift in the expected direct detection exclusion limits towards smaller cross sections and DM masses, with the effect being more prominent for low mass DM. Hence, our study shows, for the first time, that the LMC's influence on the local DM distribution is significant even in fully cosmological MW analogues.
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Fung, Jeffrey y Tomohiro Ono. "Cooling-induced Vortex Decay in Keplerian Disks". Astrophysical Journal 922, n.º 1 (1 de noviembre de 2021): 13. http://dx.doi.org/10.3847/1538-4357/ac1d4e.
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Abstract Vortices are readily produced by hydrodynamical instabilities, such as the Rossby wave instability, in protoplanetary disks. However, large-scale asymmetries indicative of dust-trapping vortices are uncommon in submillimeter continuum observations. One possible explanation is that vortices have short lifetimes. In this paper, we explore how radiative cooling can lead to vortex decay. Elliptical vortices in Keplerian disks go through adiabatic heating and cooling cycles. Radiative cooling modifies these cycles and generates baroclinicity that changes the potential vorticity of the vortex. We show that the net effect is typically a spin down, or decay, of the vortex for a subadiabatic radial stratification. We perform a series of two-dimensional shearing box simulations, varying the gas cooling (or relaxation) time, t cool, and initial vortex strength. We measure the vortex decay half-life, t half, and find that it can be roughly predicted by the timescale ratio t cool/t turn, where t turn is the vortex turnaround time. Decay is slow in both the isothermal (t cool ≪ t turn) and adiabatic (t cool ≫ t turn) limits; it is fastest when t cool ∼ 0.1 t turn, where t half is as short as ∼300 orbits. At tens of astronomical units where disk rings are typically found, t turn is likely much longer than t cool, potentially placing vortices in the fast decay regime.
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Rubio-Díez, M. M., J. O. Sundqvist, F. Najarro, A. Traficante, J. Puls, L. Calzoletti y D. Figer. "Upper mass-loss limits and clumping in the intermediate and outer wind regions of OB stars". Astronomy & Astrophysics 658 (febrero de 2022): A61. http://dx.doi.org/10.1051/0004-6361/202040116.
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Context. Mass loss is a key parameter throughout the evolution of massive stars, and it determines the feedback with the surrounding interstellar medium. The presence of inhomogeinities in stellar winds (clumping) leads to severe discrepancies not only among different mass-loss rate diagnostics, but also between empirical estimates and theoretical predictions. Aims. We aim to probe the radial clumping stratification of OB stars in the intermediate and outer wind regions (r ≳ 2 R*; radial distance to the photosphere) to derive upper limits for mass-loss rates and to compare that to current mass-loss implementation. Our sample includes 13 B supergiants, which is the largest sample of such objects in which clumping has been analysed so far. Methods. Together with archival optical to radio observations, we obtained new far-infrared continuum observations for a sample of 25 OB stars. Our new data uniquely constrain the clumping properties of the intermediate wind region. By using density-squared diagnostics, we further derived the minimum radial stratification of the clumping factor through the stellar wind, fclmin (r), and the corresponding maximum mass-loss rate, Ṁmax, normalising clumping factors to the outermost wind region (fclfar = 1). Results. We find that the clumping degree for r ≳ 2 R* decreases or stays constant with an increasing radius, regardless of the luminosity class or spectral type for 22 out of 25 sources in our sample. However, a dependence of the clumping degree on the luminosity class and spectral type at the intermediate region relative to the outer ones has been observed: O supergiants (OSGs) present, on average, a factor 2 larger clumping factors than B supergiants (BSGs). Interestingly, the clumping structure of roughly one-third of the OB supergiants in our sample is such that the maximum clumping occurs close to the wind base (r ≲ 2 R*), and then it decreases monotonically. This is in contrast to the more frequent case where the lowermost clumping increases towards a maximum and needs to be addressed by theoretical models. In addition, we find that the estimated Ṁmax for BSGs is at least one order of magnitude (before finally decreasing) lower than the values usually adopted by stellar evolution models, whereas the upper observational limits and predictions of OSGs agree within errors. This implies large reductions of mass-loss rates applied in evolution models for BSGs, independently of the actual clumping properties of these winds. However, hydrodynamical models of clumping suggest absolute clumping factors in the outermost radio-emitting wind of the order of fclfar ≈ 4–9, assuming these values would imply a reduction in mass-loss rates included in stellar evolution models by a factor 2–3 for OSGs (above Teff ~ 26 500 K) and by factors 6–200 for BSGs below the so-called first bi-stability jump (below Teff ~ 22 000 K). While such reductions agree well with new theoretical mass-loss calculations for OSGs, our empirical findings call for a thorough re-investigation of BSG mass-loss rates and their associated effects on stellar evolution.
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Witstok, Joris, Ewald Puchwein, Girish Kulkarni, Renske Smit y Martin G. Haehnelt. "Prospects for observing the low-density cosmic web in Lyman-α emission". Astronomy & Astrophysics 650 (junio de 2021): A98. http://dx.doi.org/10.1051/0004-6361/202040187.
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Mapping the intergalactic medium (IGM) in Lyman-α emission would yield unprecedented tomographic information on the large-scale distribution of baryons and potentially provide new constraints on the UV background and various feedback processes relevant to galaxy formation. In this work, we use a cosmological hydrodynamical simulation to examine the Lyman-α emission of the IGM resulting from collisional excitations and recombinations in the presence of a UV background. We focus on gas in large-scale-structure filaments in which Lyman-α radiative transfer effects are expected to be moderate. At low density the emission is primarily due to fluorescent re-emission of the ionising UV background as a result of recombinations, while collisional excitations dominate at higher densities. We discuss prospects of current and future observational facilities to detect this emission and find that the emission of filaments of the cosmic web are typically dominated by the halos and galaxies embedded in these filaments, rather than by the lower-density filament gas outside halos. Detecting filament gas directly would require a very long exposure with a MUSE-like instrument on the ELT. Our most robust predictions that act as lower limits indicate this would be slightly less challenging at lower redshifts (z ≲ 4). We also find that there is a large amount of variance between fields in our mock observations. High-redshift protoclusters appear to be the most promising environment to observe the filamentary IGM in Lyman-α emission.
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Li, Yeping. "The combined semi-classical and relaxation limit in a quantum hydrodynamic semiconductor model". Proceedings of the Royal Society of Edinburgh: Section A Mathematics 140, n.º 1 (febrero de 2010): 119–34. http://dx.doi.org/10.1017/s030821050800036x.
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We discuss the combined semi-classical and relaxation limit of a one-dimensional isentropic quantum hydrodynamical model for semiconductors. The quantum hydrodynamic equations consist of the isentropic Euler equations for the particle density and current density, including the quantum potential and a momentum relaxation term. The momentum equation is highly nonlinear and contains a dispersive term with third-order derivatives. The equations are self-consistently coupled to the Poisson equation for the electrostatic potential. With the help of the Maxwell-type iteration, we prove that, as the relaxation time and Planck constant tend to zero, periodic initial-value problems of a scaled one-dimensional isentropic quantum hydrodynamic model have unique smooth solutions existing in the time interval where the classical drift-diffusion model has smooth solutions. Meanwhile, we justify a formal derivation of the classical drift-diffusion model from the quantum hydrodynamic model.
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Heitsch, F., A. Marchal, M.-A. Miville-Deschênes, J. M. Shull y A. J. Fox. "Mass, morphing, metallicities: the evolution of infalling high velocity clouds". Monthly Notices of the Royal Astronomical Society 509, n.º 3 (13 de noviembre de 2021): 4515–31. http://dx.doi.org/10.1093/mnras/stab3266.
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ABSTRACT We revisit the reliability of metallicity estimates of high velocity clouds with the help of hydrodynamical simulations. We quantify the effect of accretion and viewing angle on metallicity estimates derived from absorption lines. Model parameters are chosen to provide strong lower limits on cloud contamination by ambient gas. Consistent with previous results, a cloud traveling through a stratified halo is contaminated by ambient material to the point that <10 per cent of its mass in neutral hydrogen consists of original cloud material. Contamination progresses nearly linearly with time, and it increases from head to tail. Therefore, metallicity estimates will depend on the evolutionary state of the cloud, and on position. While metallicities change with time by more than a factor of 10, well beyond observational uncertainties, most lines-of-sight range only within those uncertainties at any given time over all positions. Metallicity estimates vary with the cloud’s inclination angle within observational uncertainties. The cloud survives the infall through the halo because ambient gas continuously condenses and cools in the cloud’s wake and thus appears in the neutral phase. Therefore, the cloud observed at any fixed time is not a well-defined structure across time, since material gets constantly replaced. The thermal phases of the cloud are largely determined by the ambient pressure. Internal cloud dynamics evolve from drag gradients caused by shear instabilities, to complex patterns due to ram-pressure shielding, leading to a peloton effect, in which initially lagging gas can catch up to and even overtake the head of the cloud.
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Verma, Kuldeep, Robert J. J. Grand, Víctor Silva Aguirre y Amalie Stokholm. "An observational testbed for cosmological zoom-in simulations: constraining stellar migration in the solar cylinder using asteroseismology". Monthly Notices of the Royal Astronomical Society 506, n.º 1 (22 de junio de 2021): 759–74. http://dx.doi.org/10.1093/mnras/stab1766.
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ABSTRACT Large-scale stellar surveys coupled with recent developments in magneto-hydrodynamical simulations of the formation of Milky Way-mass galaxies provide an unparalleled opportunity to unveil the physical processes driving the evolution of the Galaxy. We developed a framework to compare a variety of parameters with their corresponding predictions from simulations in an unbiased manner, taking into account the selection function of a stellar survey. We applied this framework to a sample of over 7000 stars with asteroseismic, spectroscopic, and astrometric data available, together with six simulations from the Auriga project. We found that some simulations are able to produce abundance dichotomies in the [Fe/H]−[α/Fe] plane which look qualitatively similar to observations. The peak of their velocity distributions match the observed data reasonably well; however, they predict hotter kinematics in terms of the tails of the distributions and the vertical velocity dispersion. Assuming our simulation sample is representative of Milky Way-like galaxies, we put upper limits of 2.21 and 3.70 kpc on radial migration for young (<4 Gyr) and old (∈[4, 8] Gyr) stellar populations in the solar cylinder. Comparison between the observed and simulated metallicity dispersion as a function of age further constrains migration to about 1.97 and 2.91 kpc for the young and old populations. These results demonstrate the power of our technique to compare numerical simulations with high-dimensional data sets, and paves the way for using the wider field TESS asteroseismic data together with the future generations of simulations to constrain the sub-grid models for turbulence, star formation, and feedback processes.
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Klitsch, Anne, Céline Péroux, Martin A. Zwaan, Ian Smail, Dylan Nelson, Gergö Popping, Chian-Chou Chen et al. "ALMACAL – VI. Molecular gas mass density across cosmic time via a blind search for intervening molecular absorbers". Monthly Notices of the Royal Astronomical Society 490, n.º 1 (21 de septiembre de 2019): 1220–30. http://dx.doi.org/10.1093/mnras/stz2660.
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ABSTRACT We are just starting to understand the physical processes driving the dramatic change in cosmic star formation rate between z ∼ 2 and the present day. A quantity directly linked to star formation is the molecular gas density, which should be measured through independent methods to explore variations due to cosmic variance and systematic uncertainties. We use intervening CO absorption lines in the spectra of mm-bright background sources to provide a census of the molecular gas mass density of the Universe. The data used in this work are taken from ALMACAL, a wide and deep survey utilizing the ALMA calibrator archive. While we report multiple Galactic absorption lines and one intrinsic absorber, no extragalactic intervening molecular absorbers are detected. However, due to the large redshift path surveyed (Δz = 182), we provide constraints on the molecular column density distribution function beyond z ∼ 0. In addition, we probe column densities of N(H2) > 1016 atoms cm−2, 5 orders of magnitude lower than in previous studies. We use the cosmological hydrodynamical simulation IllustrisTNG to show that our upper limits of $\rho ({\rm H}_2)\lesssim 10^{8.3}\, \text{M}_{\odot }\, \text{Mpc}^{-3}$ at 0 < z ≤ 1.7 already provide new constraints on current theoretical predictions of the cold molecular phase of the gas. These results are in agreement with recent CO emission-line surveys and are complementary to those studies. The combined constraints indicate that the present decrease of the cosmic star formation rate history is consistent with an increasing depletion of molecular gas in galaxies compared to z ∼ 2.
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Feliachi, Ouassim, Marc Besse, Cesare Nardini y Julien Barré. "Fluctuating kinetic theory and fluctuating hydrodynamics of aligning active particles: the dilute limit". Journal of Statistical Mechanics: Theory and Experiment 2022, n.º 11 (1 de noviembre de 2022): 113207. http://dx.doi.org/10.1088/1742-5468/ac9fc6.
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Abstract Kinetic and hydrodynamic theories are widely employed for describing the collective behavior of active matter systems. At the fluctuating level, these have been obtained from explicit coarse-graining procedures in the limit where each particle interacts weakly with many others, so that the total forces and torques exerted on each of them is of order unity at all times. Such limit is however not relevant for dilute systems that mostly interact via alignment; there, collisions are rare and make the self-propulsion direction to change abruptly. We derive a fluctuating kinetic theory, and the corresponding fluctuating hydrodynamics, for aligning self-propelled particles in the limit of dilute systems. We discover that fluctuations at kinetic level are not Gaussian and depend on the interactions among particles, but that only their Gaussian part survives in the hydrodynamic limit. At variance with fluctuating hydrodynamics for weakly interacting particles, we find that the noise variance at hydrodynamic level depends on the interaction rules among particles and is proportional to the square of the density, reflecting the binary nature of the aligning process. The results of this paper, which are derived for polar self-propelled particles with polar alignment, could be straightforwardly extended to polar particles with nematic alignment or to fully nematic systems.
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De Masi, Anna y Stefano Olla. "Quasi-Static Hydrodynamic Limits". Journal of Statistical Physics 161, n.º 5 (5 de octubre de 2015): 1037–58. http://dx.doi.org/10.1007/s10955-015-1383-x.
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LESHANSKY, ALEXANDER M., JEFFREY F. MORRIS y JOHN F. BRADY. "Collective diffusion in sheared colloidal suspensions". Journal of Fluid Mechanics 597 (1 de febrero de 2008): 305–41. http://dx.doi.org/10.1017/s0022112007009834.
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Collective diffusivity in a suspension of rigid particles in steady linear viscous flows is evaluated by investigating the dynamics of the time correlation of long-wavelength density fluctuations. In the absence of hydrodynamic interactions between suspended particles in a dilute suspension of identical hard spheres, closed-form asymptotic expressions for the collective diffusivity are derived in the limits of low and high Péclet numbers, where the Péclet number ${\it Pe}\,{=}\,\gamdot a^2/D_0$ with $\gamdot$ being the shear rate and D0 = kBT/6πη a is the Stokes–Einstein diffusion coefficient of an isolated sphere of radius a in a fluid of viscosity η. The effect of hydrodynamic interactions is studied in the analytically tractable case of weakly sheared (Pe ≪ 1) suspensions.For strongly sheared suspensions, i.e. at high Pe, in the absence of hydrodynamics the collective diffusivity Dc = 6 Ds∞, where Ds∞ is the long-time self-diffusivity and both scale as $\phi \gamdot a^2$, where φ is the particle volume fraction. For weakly sheared suspensions it is shown that the leading dependence of collective diffusivity on the imposed flow is proportional to D0 φPeÊ, where Ê is the rate-of-strain tensor scaled by $\gamdot$, regardless of whether particles interact hydrodynamically. When hydrodynamic interactions are considered, however, correlations of hydrodynamic velocity fluctuations yield a weakly singular logarithmic dependence of the cross-gradient-diffusivity on k at leading order as ak → 0 with k being the wavenumber of the density fluctuation. The diagonal components of the collective diffusivity tensor, both with and without hydrodynamic interactions, are of O(φPe2), quadratic in the imposed flow, and finite at k = 0.At moderate particle volume fractions, 0.10 ≤ φ ≤ 0.35, Brownian Dynamics (BD) numerical simulations in which there are no hydrodynamic interactions are performed and the transverse collective diffusivity in simple shear flow is determined via time evolution of the dynamic structure factor. The BD simulation results compare well with the derived asymptotic estimates. A comparison of the high-Pe BD simulation results with available experimental data on collective diffusivity in non-Brownian sheared suspensions shows a good qualitative agreement, though hydrodynamic interactions prove to be important at moderate concentrations.
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Sunol, Alp M. y Roseanna N. Zia. "Confined Brownian suspensions: Equilibrium diffusion, thermodynamics, and rheology". Journal of Rheology 67, n.º 2 (marzo de 2023): 433–60. http://dx.doi.org/10.1122/8.0000520.
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We examine the impact of confinement on the structure, dynamics, and rheology of spherically confined macromolecular suspensions, with a focus on the role played by entropic forces, by comparing the limits of strong hydrodynamics and no hydrodynamics. We present novel measurements of the osmotic pressure, intrinsic viscosity, and long-time self-diffusivity in spherical confinement and find confinement induces strong structural correlations and restrictions on configurational entropy that drive up osmotic pressure and viscosity and drive down self-diffusion. Even in the absence of hydrodynamics, confinement produces distinct short-time and long-time self-diffusion regimes. This finding revises the previous understanding that short-time self-diffusion is a purely hydrodynamic quantity. The entropic short-time self-diffusion is proportional to an entropic mobility, a direct analog to the hydrodynamic mobility. A caging plateau following the short-time regime is stronger and more durable without hydrodynamics, and entropic drift—a gradient in volume fraction—drives particles out of their cages. The distinct long-time regime emerges when an entropic mobility gradient arising from heterogeneous distribution of particle volume drives particles out of local cages. We conclude that entropic mobility gradients produce a distinct long-time dynamical regime in confinement and that hydrodynamic interactions weaken this effect. From a statistical physics perspective, confinement restricts configurational entropy, driving up confined osmotic pressure, viscosity, and (inverse) long-time dynamics as confinement tightens. We support this claim by rescaling the volume fraction as the distance from confinement-dependent maximum packing, which collapses the data for each rheological measure onto a single curve.
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Jacobson-Galán, W. V., L. Dessart, D. O. Jones, R. Margutti, D. L. Coppejans, G. Dimitriadis, R. J. Foley et al. "Final Moments. I. Precursor Emission, Envelope Inflation, and Enhanced Mass Loss Preceding the Luminous Type II Supernova 2020tlf". Astrophysical Journal 924, n.º 1 (1 de enero de 2022): 15. http://dx.doi.org/10.3847/1538-4357/ac3f3a.
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Abstract We present panchromatic observations and modeling of supernova (SN) 2020tlf, the first normal Type II-P/L SN with confirmed precursor emission, as detected by the Young Supernova Experiment transient survey. Pre-SN activity was detected in riz-bands at −130 days and persisted at relatively constant flux until first light. Soon after discovery, “flash” spectroscopy of SN 2020tlf revealed narrow, symmetric emission lines that resulted from the photoionization of circumstellar material (CSM) shed in progenitor mass-loss episodes before explosion. Surprisingly, this novel display of pre-SN emission and associated mass loss occurred in a red supergiant (RSG) progenitor with zero-age main-sequence mass of only 10–12 M ⊙, as inferred from nebular spectra. Modeling of the light curve and multi-epoch spectra with the non-LTE radiative-transfer code CMFGEN and radiation-hydrodynamical code HERACLES suggests a dense CSM limited to r ≈ 1015 cm, and mass-loss rate of 10−2 M ⊙ yr−1. The luminous light-curve plateau and persistent blue excess indicates an extended progenitor, compatible with an RSG model with R ⋆ = 1100 R ⊙. Limits on the shock-powered X-ray and radio luminosity are consistent with model conclusions and suggest a CSM density of ρ < 2 × 10−16 g cm−3 for distances from the progenitor star of r ≈ 5 × 1015 cm, as well as a mass-loss rate of M ̇ < 1.3 × 10 − 5 M ☉ yr − 1 at larger distances. A promising power source for the observed precursor emission is the ejection of stellar material following energy disposition into the stellar envelope as a result of gravity waves emitted during either neon/oxygen burning or a nuclear flash from silicon combustion.
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Pallero, Diego, Facundo A. Gómez, Nelson D. Padilla, S. Torres-Flores, R. Demarco, P. Cerulo y D. Olave-Rojas. "Tracing the quenching history of cluster galaxies in the EAGLE simulation". Monthly Notices of the Royal Astronomical Society 488, n.º 1 (27 de junio de 2019): 847–58. http://dx.doi.org/10.1093/mnras/stz1745.
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ABSTRACT We use the Evolution and Assembly of GaLaxies and their Environments (EAGLE) hydrodynamical simulation to trace the quenching history of galaxies in its 10 most massive clusters. We use two criteria to identify moments when galaxies suffer significant changes in their star formation activity: (i) the instantaneous star formation rate (SFR) strongest drop, $\Gamma _{\rm SFR}^{\rm SD}$, and (ii) a ‘quenching’ criterion based on a minimum threshold for the specific SFR of ≲10$^{-11}\,\rm yr^{-1}$. We find that a large fraction of galaxies (${\gtrsim} 60\,{\rm per\,cent}$) suffer their $\Gamma _{\rm SFR}^{\rm SD}$ outside the cluster’s R200. This ‘pre-processed’ population is dominated by galaxies that are either low mass and centrals or inhabit low-mass hosts (1010.5 ≲ Mhost ≲ 1011.0 M⊙). The host mass distribution is bimodal, and galaxies that suffered their $\Gamma _{\rm SFR}^{\rm SD}$ in massive hosts ($10^{13.5} \lesssim M_{\rm host} \lesssim 10^{14.0}\, \mathrm{M}_{\odot }$) are mainly processed within the clusters. Pre-processing mainly limits the total stellar mass with which galaxies arrive in the clusters. Regarding quenching, galaxies preferentially reach this state in high-mass haloes ($10^{13.5} \lesssim M_{\rm host} \lesssim 10^{14.5}\, \mathrm{M}_{\odot }$). The small fraction of galaxies that reach the cluster already quenched have also been pre-processed, linking both criteria as different stages in the quenching process of those galaxies. For the z = 0 satellite populations, we find a sharp rise in the fraction of quenched satellites at the time of first infall, highlighting the role played by the dense cluster environment. Interestingly, the fraction of pre-quenched galaxies rise with final cluster mass. This is a direct consequence of the hierarchical cosmological model used in these simulations.
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Denny, M. W. "Limits to optimization: fluid dynamics, adhesive strength and the evolution of shape in limpet shells". Journal of Experimental Biology 203, n.º 17 (1 de septiembre de 2000): 2603–22. http://dx.doi.org/10.1242/jeb.203.17.2603.
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Limpets are commonly found on wave-swept rocky shores, where they may be subjected to water velocities in excess of 20 m s(−1). These extreme flows can impose large forces (lift and drag), challenging the animal's ability to adhere to the substratum. It is commonly thought that the conical shape of limpet shells has evolved in part to reduce these hydrodynamic forces while providing a large aperture for adhesion. This study documents how lift and drag actually vary with the shape of limpet-like models and uses these data to explore the potential of hydrodynamic forces to serve as a selective factor in the evolution of limpet shell morphology. At a low ratio of shell height to shell radius, lift is the dominant force, while at high ratios of height to radius drag is dominant. The risk of dislodgment is minimized when the ratio of height to radius is 1.06 and the apex is in the center of the shell. Real limpets are seldom optimally shaped, however, with a typical height-to-radius ratio of 0.68 and an apex well anterior of the shell's center. The disparity between the actual and the hydrodynamically optimal shape of shells may be due to the high tenacity of limpets' adhesive system. Most limpets adhere to the substratum so strongly that they are unlikely to be dislodged by lift or drag regardless of the shape of their shell. The evolution of a tenacious adhesion system (perhaps in response to predation) has thus preempted selection for a hydrodynamically optimal shell, allowing the shell to respond to alternative selective factors.
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Samper, Yaiza, María Liste, Marc Mestres, Manuel Espino, Agustín Sánchez-Arcilla, Joaquim Sospedra, Daniel González-Marco, María Isabel Ruiz y Enrique Álvarez Fanjul. "Water Exchanges in Mediterranean Microtidal Harbours". Water 14, n.º 13 (23 de junio de 2022): 2012. http://dx.doi.org/10.3390/w14132012.
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Mediterranean ports feature complex layouts and exert important environmental pressures in squeezed coastal zones. They experience mild meteo-oceanographic conditions during part of the year, leading to water velocities that are close to the resolution limits of observation equipment. The paper addresses the challenge of characterising summer port hydrodynamics by designing intensive field campaigns, focused on hydrodynamic variables, such as harbour entrance fluxes. The approach was developed for three Spanish microtidal harbours with different domain sizes and one or two entrances. These elements play a key role in harbour exchanges through the entrance and the subsequent water renovation. The paper will present and discuss the meteocean data and inferred variables, such as renovation times, which is a key indicator of water quality. From this basis, the paper will discuss the changing estuarine circulation patterns and the role of upwelling and downwelling on observed water temperature peaks. The conclusions will address the role of harbour hydrodynamics in integrated coastal water quality and port engineering, particularly for ports’ environmental impacts on adjacent beaches. To assess the full hydrodynamic domain, forecasting models are helpful. The continuous observations presented in this work would also help in the implementation and validation of these models.
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Roncarelli, M., M. Baldi y F. Villaescusa-Navarro. "The kinematic Sunyaev–Zel’dovich effect of the large-scale structure (II): the effect of modified gravity". Monthly Notices of the Royal Astronomical Society 481, n.º 2 (29 de agosto de 2018): 2497–506. http://dx.doi.org/10.1093/mnras/sty2225.
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ABSTRACT The key to understand the nature of dark energy lies in our ability to probe the distant Universe. In this framework, the recent detection of the kinematic Sunyaev–Zel’dovich (kSZ) effect signature in the cosmic microwave background obtained with the South Pole Telescope (SPT) is extremely useful since this observable is sensitive to the high-redshift diffuse plasma. We analyse a set of cosmological hydrodynamical simulation with four different realizations of a Hu & Sawicki f(R) gravity model, parametrized by the values of $\overline{f}_{\rm R,0}$= (0, −10−6, −10−5, −10−4), to compute the properties of the kSZ effect due to the ionized Universe and how they depend on $\overline{f}_{\rm R,0}$ and on the redshift of reionization, zre. In the standard General Relativity limit ($\overline{f}_{\rm R,0}$= 0) we obtain an amplitude of the kSZ power spectrum of $\mathcal {D}^{\rm kSZ}_{3000}$$= 4.1\,$$\mu$K2 (zre= 8.8), close to the +1σ limit of the $\mathcal {D}^{\rm kSZ}_{3000}$$= (2.9\pm 1.3)\,$$\mu$K2 measurement by SPT. This corresponds to an upper limit on the kSZ contribute from patchy reionization of $\mathcal {D}^{\rm kSZ,patchy}_{3000}$$\lt 0.9\,$$\mu$K2 (95 per cent confidence level). Modified gravity boosts the kSZ signal by about 3, 12, and 50 per cent for $\overline{f}_{\rm R,0}$=(− 10−6, −10−5, −10−4), respectively, with almost no dependence on the angular scale. This means that with modified gravity the limits on patchy reionization shrink significantly: for $\overline{f}_{\rm R,0}$=−10−5 we obtain $\mathcal {D}^{\rm kSZ,patchy}_{3000}$$\lt 0.4\,$$\mu$K2. Finally, we provide an analytical formula for the scaling of the kSZ power spectrum with zre and $\overline{f}_{\rm R,0}$ at different multipoles: at ℓ = 3000 we obtain $\mathcal {D}^{\rm kSZ}_{3000}$ ∝ zre$^{0.24}\left(1+\sqrt{\left|\overline{f}_{\rm R,0}\right|}\right)^{41}$.
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Machado, R. E. G., P. B. Tissera, G. B. Lima Neto y L. Sodré. "Properties of the circumgalactic medium in simulations compared to observations". Astronomy & Astrophysics 609 (enero de 2018): A66. http://dx.doi.org/10.1051/0004-6361/201628886.
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Context. Galaxies are surrounded by extended gaseous halos that store significant fractions of chemical elements. These are syntethized by the stellar populations and later ejected into the circumgalactic medium (CGM) by different mechanism, of which supernova feedback is considered one of the most relevant. Aims. We aim to explore the properties of this metal reservoir surrounding star-forming galaxies in a cosmological context aiming to investigate the chemical loop between galaxies and their CGM, and the ability of the subgrid models to reproduce observational results. Methods. Using cosmological hydrodynamical simulations, we have analysed the gas-phase chemical contents of galaxies with stellar masses in the range 109−1011 M⊙. We estimated the fractions of metals stored in the different CGM phases, and the predicted O vi and Si iii column densities within the virial radius. Results. We find roughly 107 M⊙ of oxygen in the CGM of simulated galaxies having M⋆ ~ 1010 M⊙, in fair agreement with the lower limits imposed by observations. The Moxy is found to correlate with M⋆, at odds with current observational trends but in agreement with other numerical results. The estimated profiles of O vi column density reveal a substantial shortage of that ion, whereas Si iii, which probes the cool phase, is overpredicted. Nevertheless, the radial dependences of both ions follow the respective observed profiles. The analysis of the relative contributions of both ions from the hot, warm and cool phases suggests that the warm gas (105 K < T < 106 K) should be more abundant in order to bridge the mismatch with the observations, or alternatively, that more metals should be stored in this gas-phase. These discrepancies provide important information to improve the subgrid physics models. Our findings show clearly the importance of tracking more than one chemical element and the difficulty of simultaneously satisfying the observables that trace the circumgalactic gas at different physical conditions. Additionally, we find that the X-ray coronae around the simulated galaxies have luminosities and temperatures in decent agreement with the available observational estimates.
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Garba, Usman, David Rouzineau y Michel Meyer. "EXPERIMENTAL STUDY OF THE PRESSURE DROP AND FLOODING IN A ROTATING PACKED BED REACTOR". Malaysian Journal of Catalysis 7, n.º 2 (28 de diciembre de 2023): 42–48. http://dx.doi.org/10.11113/mjcat.v7n2.174.
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In conventional packed beds, mass transfer and flooding limitations lower the productivity of many processes. The almost zero sensitivity to variations in gravitational force has made centrifugal processes to have great potential for enhancing heterogeneous catalytic reactions. We studied a rotating packed bed (RPB) reactor as a gas/liquid contactor for multi-phase catalytic reactions. The scarcity of fundamental data on the hydrodynamics and mass transfer of the reactor limits the design, scale-up, and retrofitting of RPB reactors. Hence, we focused on the hydrodynamic behavior of the device. Previous studies on RPB reactor flooding and operating limits dwelled on visual observations and pressure drop variations only. However, physical visualizations are subjective because RPB reactor pressure drop variations are too inconsistent to be used to determine the upper operating limit during their operations. A robust quantitative method of obtaining RPB reactor flooding limits based on the flow rate of the ejected liquid, supported by visual observation and pressure drop measurement, was presented. The aim was to identify, with greater certainty, RPB reactor hydrodynamic characteristics and provide a more standard method of identifying it. The average increase in single-phase pressure drop per unit increase in rotation speed in the range investigated was 0.75Pa/rpm, and the average increase in pressure drop per unit increase in gas flow rate was 4.11Pa/Nm3h-1 within the operating range investigated.
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Caprino, S., R. Esposito, R. Marra y M. Pulvirenti. "Hydrodynamic limits of the vlasov equation". Communications in Partial Differential Equations 18, n.º 5-6 (enero de 1993): 805–20. http://dx.doi.org/10.1080/03605309308820951.
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Девисилов, Vladimir Devisilov, Шарай y E. Sharay. "Current Stability Limits in Hydrodynamic Filter". Safety in Technosphere 2, n.º 4 (25 de agosto de 2013): 23–29. http://dx.doi.org/10.12737/717.
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The phenomenon related to a loss of laminar stability of fluid flow in hydrodynamic filter’s working zone with formation of toroidal vortexes is considered. Estimated results related to numerical modeling of liquid’s stationary current in a gap between two coaxial cylinders are presented under various boundary conditions. It is shown that existence of liquid suction from rotating internal cylinder surface leads to stabilization and increase of flow’s stability margin in hydrodynamic filters. The flow stability limits depending on Taylor´s number, rotating cylinder’s angular velocity and liquid suction speed through the cylinder’s surface are defined.
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Costantini, C. y R. Marra. "Hydrodynamic limits for the Boltzmann process". Journal of Statistical Physics 67, n.º 1-2 (abril de 1992): 229–49. http://dx.doi.org/10.1007/bf01049032.
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Gavassino, Lorenzo, Marco Antonelli y Brynmor Haskell. "Multifluid Modelling of Relativistic Radiation Hydrodynamics". Symmetry 12, n.º 9 (18 de septiembre de 2020): 1543. http://dx.doi.org/10.3390/sym12091543.
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The formulation of a universal theory for bulk viscosity and heat conduction represents a theoretical challenge for our understanding of relativistic fluid dynamics. Recently, it was shown that the multifluid variational approach championed by Carter and collaborators has the potential to be a general and natural framework to derive (hyperbolic) hydrodynamic equations for relativistic dissipative systems. Furthermore, it also allows keeping direct contact with non-equilibrium thermodynamics, providing a clear microscopic interpretation of the elements of the theory. To provide an example of its universal applicability, in this paper we derive the fundamental equations of the radiation hydrodynamics directly in the context of Carter’s multifluid theory. This operation unveils a novel set of thermodynamic constraints that must be respected by any microscopic model. Then, we prove that the radiation hydrodynamics becomes a multifluid model for bulk viscosity or heat conduction in some appropriate physical limits.
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Pavlov, Evgen, Makoto Taiji, Arturs Scukins, Anton Markesteijn, Sergey Karabasov y Dmitry Nerukh. "Visualising and controlling the flow in biomolecular systems at and between multiple scales: from atoms to hydrodynamics at different locations in time and space". Faraday Discuss. 169 (2014): 285–302. http://dx.doi.org/10.1039/c3fd00159h.
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A novel framework for modelling biomolecular systems at multiple scales in space and time simultaneously is described. The atomistic molecular dynamics representation is smoothly connected with a statistical continuum hydrodynamics description. The system behaves correctly at the limits of pure molecular dynamics (hydrodynamics) and at the intermediate regimes when the atoms move partly as atomistic particles, and at the same time follow the hydrodynamic flows. The corresponding contributions are controlled by a parameter, which is defined as an arbitrary function of space and time, thus, allowing an effective separation of the atomistic ‘core’ and continuum ‘environment’. To fill the scale gap between the atomistic and the continuum representations our special purpose computer for molecular dynamics, MDGRAPE-4, as well as GPU-based computing were used for developing the framework. These hardware developments also include interactive molecular dynamics simulations that allow intervention of the modelling through force-feedback devices.