scholarly journals A full treatment of peculiar velocities on the reionization light cone

2019 ◽  
Vol 490 (1) ◽  
pp. 1255-1269 ◽  
Author(s):  
Emma Chapman ◽  
Mario G Santos
Keyword(s):  
Temperature Distribution ◽  
Brightness Temperature ◽  
Light Cone ◽  
Cosmological Parameters ◽  
Line Of Sight ◽  
Physical Parameters ◽  
Hydrogen Atoms ◽  
Peculiar Velocities ◽  
Full Treatment ◽  
Full Calculation

ABSTRACT Accurate simulations of the 21-cm signal from the Epoch of Reionization require the generation of maps at specific frequencies given the values of astrophysical and cosmological parameters. The peculiar velocities of the hydrogen atoms producing the 21-cm radiation result in a shift in the observed frequency of the 21-cm radiation and changes the amplitude of the signal itself. This is not an effect we can remove but instead needs to be accurately modelled to ensure we infer the correct physical parameters from an observation. We describe the full calculation of the distortion of the 21-cm signal, and propose a new code that integrates the 21-cm intensity along the line of sight for each individual light cone pixel to fully capture the intensity contributions from multiple redshifts. This algorithm naturally deals with the typical divergences found in standard approaches, allowing for large optical depths and 21-cm absorption events at high redshifts. We find the new method results in up to a 60 per cent decrease in power on the largest scales on the sky, and an increase of over 80 per cent on the smallest scales on the sky. We find that the new implementation of the light cone results in a longer tail of bright temperatures in the brightness temperature distribution, as a result of the successful circumventing of a previous cap that had to be implemented to avoid a divergence in the brightness temperature. We conclude that this full treatment of the evolution of the light cone pixel can be an important effect.

Large‐Scale Power Spectrum and Cosmological Parameters from SFI Peculiar Velocities

1999 ◽  
Vol 523 (1) ◽  
pp. 1-15 ◽  
Author(s):  
Wolfram Freudling ◽  
Idit Zehavi ◽  
Luiz N. da Costa ◽  
Avishai Dekel ◽  
Amiram Eldar ◽  
...  
Keyword(s):  
Power Spectrum ◽  
Large Scale ◽  
Cosmological Parameters ◽  
Peculiar Velocities

scholarly journals The X-ray/UV ratio in active galactic nuclei: dispersion and variability

2018 ◽  
Vol 619 ◽  
pp. A95 ◽  
Author(s):  
E. Chiaraluce ◽  
F. Vagnetti ◽  
F. Tombesi ◽  
M. Paolillo
Keyword(s):  
Black Hole ◽  
Cosmological Parameters ◽  
Multivariate Regression Analysis ◽  
Physical Parameters ◽  
Distance Modulus ◽  
X Rays ◽  
Viewing Angle ◽  
Black Hole Mass ◽  
Intrinsic Variability ◽  
X Ray

Context. The well established negative correlation between the αOX spectral slope and the optical/ultraviolet (UV) luminosity, a by-product of the relation between X-rays and optical/UV luminosity, is affected by relatively large dispersion. The main contributors to this dispersion can be variability in the X-ray/UV ratio and/or changes in fundamental physical parameters. Aims. We want to quantify the contribution from variability within single sources (intra-source dispersion) and that from variations of other quantities different from source to source (inter-source dispersion). Methods. We use archival data from the XMM-Newton Serendipitous Source Catalog (XMMSSC) and from the XMM-OM Serendipitous Ultraviolet Source Survey (XMMOM-SUSS3). We select a sub-sample in order to decrease the dispersion of the relation due to the presence of radio-loud and broad absorption line objects, and that due to absorptions in both X-ray and optical/UV bands. We use the structure function (SF) to estimate the contribution from variability to the dispersion. We analyse the dependence of the residuals of the relation on various physical parameters in order to characterise the inter-source dispersion. Results. We find a total dispersion of σ ∼ 0.12 and find that intrinsic variability contributes 56% of the variance of the αOX − LUV relation. If we select only sources with a larger number of observational epochs (≥3) the dispersion of the relation decreases by approximately 15%. We find weak but significant dependencies of the residuals of the relation on black-hole mass and on Eddington ratio, which are also confirmed by a multivariate regression analysis of αOX as a function of UV luminosity and black-hole mass and/or Eddington ratio. We find a weak positive correlation of both the αOX index and the residuals of the αOX − LUV relation with inclination indicators, such as the full width at half maximum (Hβ) and the equivalent width (EW)[OIII], suggesting a weak increase of X-ray/UV ratio with the viewing angle. This suggests the development of new viewing angle indicators possibly applicable at higher redshifts. Moreover, our results suggest the possibility of selecting a sample of objects, based on their viewing angle and/or black-hole mass and Eddington ratio, for which the αOX − LUV relation is as tight as possible, in light of the use of the optical/UV – X-ray luminosity relation to build a distance modulus (DM)-z plane and estimate cosmological parameters.

The VSOP 5 GHz Active Galactic Nucleus Survey. IV. The Angular Size/Brightness Temperature Distribution

2004 ◽  
Vol 616 (1) ◽  
pp. 110-122 ◽  
Author(s):  
S. Horiuchi ◽  
E. B. Fomalont ◽  
W. K. Scott, A. R. Taylor ◽  
J. E. J. Lovell ◽  
G. A. Moellenbrock ◽  
...  
Keyword(s):  
Temperature Distribution ◽  
Brightness Temperature ◽  
Active Galactic Nucleus ◽  
Angular Size ◽  
5 Ghz

scholarly journals Marangoni Convection of Dust Particles in the Boundary Layer of Maxwell Nanofluids with Varying Surface Tension and Viscosity

Coatings ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 1072
Author(s):  
Khaled S. AlQdah ◽  
Naseer M. Khan ◽  
Habib Ben Bacha ◽  
Jae-Dong Chung ◽  
Nehad Ali Shah
Keyword(s):  
Surface Tension ◽  
Nusselt Number ◽  
Temperature Distribution ◽  
Dust Particles ◽  
Physical Parameters ◽  
Temperature Dependent Viscosity ◽  
Liquid Phases ◽  
Variable Surface ◽  
Basic Equations ◽  
Dependent Viscosity

The flow of nanofluids is very important in industrial refrigeration systems. The operation of nuclear reactors and the cooling of the entire installation to improve safety and economics are entirely dependent on the application of nanofluids in water. Therefore, a model of Maxwell’s dusty nanofluid with temperature-dependent viscosity, surface suction and variable surface tension under the action of solar radiation is established. The basic equations of momentum and temperature of the dust and liquid phases are solved numerically using the MATLAB bvp4c scheme. In the current evaluation, taking into account variable surface tension and varying viscosity, the effect of dust particles is studied by immersing dust particles in a nanofluid. Qualitative and quantitative discussions are provided to focus on the effect of physical parameters on mass and heat transfer. The propagation results show that this mixing effect can significantly increase the thermal conductivity of nanofluids. With small changes in the surface tension parameters, a stronger drop in the temperature distribution is observed. The suction can significantly reduce the temperature distribution of the liquid and dust phases. The stretchability of the sheet is more conducive to temperature rise. The tables are used to explain how physical parameters affect the Nusselt number and mass transfer. The increased interaction of the liquid with nanoparticles or dust particles is intended to improve the Nusselt number. This model contains features that have not been previously studied, which stimulates demand for this model among all walks of life now and in the future.

scholarly journals Long-term observations of pulsars in the globular clusters 47 Tucanae and M15

2017 ◽  
Vol 13 (S337) ◽  
pp. 251-254
Author(s):  
A. Ridolfi ◽  
P. C. C. Freire ◽  
M. Kramer ◽  
C. G. Bassa ◽  
F. Camilo ◽  
...  
Keyword(s):  
Gravitational Potential ◽  
Globular Clusters ◽  
Higher Order ◽  
The Other ◽  
Line Of Sight ◽  
Physical Parameters ◽  
Spin Period ◽  
Emission Beam ◽  
System Geometry

AbstractMulti-decade observing campaigns of the globular clusters 47 Tucanae and M15 have led to an outstanding number of discoveries. Here, we report on the latest results of the long-term observations of the pulsars in these two clusters. For most of the pulsars in 47 Tucanae we have measured, among other things, their higher-order spin period derivatives, which have in turn provided stringent constraints on the physical parameters of the cluster, such as its distance and gravitational potential. For M15, we have studied the relativistic spin precession effect in PSR B2127+11C. We have used full-Stokes observations to model the precession effect, and to constrain the system geometry. We find that the visible beam of the pulsar is swiftly moving away from our line of sight and may very soon become undetectable. On the other hand, we expect to see the opposite emission beam sometime between 2041 and 2053.

scholarly journals Void Dynamics

2014 ◽  
Vol 11 (S308) ◽  
pp. 530-537
Author(s):  
Nelson D. Padilla ◽  
Dante Paz ◽  
Marcelo Lares ◽  
Laura Ceccarelli ◽  
Diego Garcí a Lambas ◽  
...  
Keyword(s):  
Dark Matter ◽  
Correlation Functions ◽  
Cross Correlation ◽  
Cosmological Parameters ◽  
Matter Field ◽  
Sloan Digital Sky Survey ◽  
Density Profiles ◽  
Peculiar Velocities ◽  
Sky Survey ◽  
Space Data

AbstractCosmic voids are becoming key players in testing the physics of our Universe. Here we concentrate on the abundances and the dynamics of voids as these are among the best candidates to provide information on cosmological parameters. Cai, Padilla & Li (2014) use the abundance of voids to tell apart Hu & Sawicki f(R) models from General Relativity. An interesting result is that even though, as expected, voids in the dark matter field are emptier in f(R) gravity due to the fifth force expelling away from the void centres, this result is reversed when haloes are used to find voids. The abundance of voids in this case becomes even lower in f(R) compared to GR for large voids. Still, the differences are significant and this provides a way to tell apart these models. The velocity field differences between f(R) and GR, on the other hand, are the same for halo voids and for dark matter voids. Paz et al. (2013), concentrate on the velocity profiles around voids. First they show the necessity of four parameters to describe the density profiles around voids given two distinct void populations, voids-in-voids and voids-in-clouds. This profile is used to predict peculiar velocities around voids, and the combination of the latter with void density profiles allows the construction of model void-galaxy cross-correlation functions with redshift space distortions. When these models are tuned to fit the measured correlation functions for voids and galaxies in the Sloan Digital Sky Survey, small voids are found to be of the void-in-cloud type, whereas larger ones are consistent with being void-in-void. This is a novel result that is obtained directly from redshift space data around voids. These profiles can be used to remove systematics on void-galaxy Alcock-Pacinsky tests coming from redshift-space distortions.

Effect of Variable Thermal Conductivity Calibration Functions on Fin Temperature Distribution

2019 ◽  
Vol 393 ◽  
pp. 47-58 ◽  
Author(s):  
Partner Luyanda Ndlovu ◽  
Raseelo Joel Moitsheki
Keyword(s):  
Thermal Conductivity ◽  
Temperature Distribution ◽  
Variational Iteration Method ◽  
Variable Thermal Conductivity ◽  
Solution Technique ◽  
Physical Parameters ◽  
Calibration Function ◽  
Shooting Technique ◽  
Extended Surfaces ◽  
Fourth Order Method

In this article, we introduce a new thermal conductivity calibration function in modeling heat transfer through extended surfaces. The variable thermal conductivity functions are studied on a stand alone basis and further compared to one another. The calculations are carried out using the Variational Iteration Method (VIM) which is an analytical solution technique. The series solutions are bench-marked against the numerical results obtained by applying the Runge-Kutta fourth order method coupled with shooting technique. The effects of some physical parameters such as the thermogeometric fin parameter and thermal conductivity gradient, on temperature distribution are illustrated and explained.

scholarly journals The Temperature Structure of NGC 7027

1989 ◽  
Vol 131 ◽  
pp. 176-176
Author(s):  
C. T. Daub ◽  
J. P. Basart
Keyword(s):  
Temperature Distribution ◽  
Electron Temperature ◽  
Angular Resolution ◽  
Hot Spot ◽  
Emission Measure ◽  
The Other ◽  
Radio Continuum ◽  
Line Of Sight ◽  
Temperature Structure ◽  
Ngc 7027

Radio maps of the free-free radio continuum flux (angular resolution ≅ 1.3 arcseconds) from NGC 7027 were made with the VLA operating at 20-cm, 6-cm, and 2-cm wavelengths which are near and straddle unit optical depth. Mean line-of-sight electron temperature and emission measure distributions were calculated by pairing the 2-cm and 6-cm maps, and the electron temperature distribution on the near side of the nebula was then obtained from the 20-cm map. The results suggest that the energy balance is complex in this planetary. For example, mean line-of-sight temperatures are higher than average in the direction of one of the bright lobes but not in the direction of the other. Especially noteworthy is an apparent “hot spot” on the near side of the nebula which has no apparent relation to either of the bright lobes, but it is approximately coincident with the brightest portion of the optical image.

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