Cosmological Principle Research Articles

Strong 21-cm fluctuations and anisotropy due to the line-of-sight effect of radio galaxies at cosmic dawn

ABSTRACT The reported detection of the global 21-cm signal by the EDGES collaboration is significantly stronger than standard astrophysical predictions. One possible explanation is an early radio excess above the cosmic microwave background. Such a radio background could have been produced by high-redshift galaxies, if they were especially efficient in producing low-frequency synchrotron radiation. We have previously studied the effects of such an inhomogeneous radio background on the 21-cm signal; however, we made a simplifying assumption of isotropy of the background seen by each hydrogen cloud. Here, we perform a complete calculation that accounts for the fact that the 21-cm absorption occurs along the line of sight, and is therefore sensitive to radio sources lying behind each absorbing cloud. We find that the complete calculation strongly enhances the 21-cm power spectrum during cosmic dawn, by up to two orders of magnitude; on the other hand, the effect on the global 21-cm signal is only at the 5 per cent level. In addition to making the high-redshift 21-cm fluctuations potentially more easily observable, the line-of-sight radio effect induces a new anisotropy in the 21-cm power spectrum. While these effects are particularly large for the case of an extremely enhanced radio efficiency, they make it more feasible to detect even a moderately enhanced radio efficiency in early galaxies. This is especially relevant since the EDGES signal has been contested by the SARAS experiment.

Optimal Pose Estimation and Covariance Analysis with Simultaneous Localization and Mapping Applications

This work provides a theoretical analysis for optimally solving the pose estimation problem using total-least-squares for vector observations from landmark features, which is central to applications involving simultaneous localization and mapping. First, the optimization process is formulated with observation vectors extracted from point-cloud features. Then, error-covariance expressions are derived. The attitude and position estimates obtained via the derived optimization process are proven to reach the bounds defined by the Cramér–Rao lower bound under the small-angle approximation of attitude errors. A fully populated observation noise-covariance matrix is assumed as the weight in the cost function to cover the most general case of the sensor uncertainty. This includes more generic correlations in the errors than previous cases involving an isotropic noise assumption. The proposed solution is verified using Monte Carlo simulations, a Gazebo simulation in a robotics operating system, and an experiment with an actual light detection and ranging sensor to validate the error-covariance analysis.

A data-driven method for modelling dissipation rates in stratified turbulence

We present a deep probabilistic convolutional neural network (PCNN) model for predicting local values of small-scale mixing properties in stratified turbulent flows, namely the dissipation rates of turbulent kinetic energy and density variance, $\varepsilon$ and $\chi$ . Inputs to the PCNN are vertical columns of velocity and density gradients, motivated by data typically available from microstructure profilers in the ocean. The architecture is designed to enable the model to capture several characteristic features of stratified turbulence, in particular the dependence of small-scale isotropy on the buoyancy Reynolds number $Re_b:=\varepsilon /(\nu N^2)$ , where $\nu$ is the kinematic viscosity and $N$ is the background buoyancy frequency, the correlation between suitably locally averaged density gradients and turbulence intensity and the importance of capturing the tails of the probability distribution functions of values of dissipation. Empirically modified versions of commonly used isotropic models for $\varepsilon$ and $\chi$ that depend only on vertical derivatives of density and velocity are proposed based on the asymptotic regimes $Re_b\ll 1$ and $Re_b\gg 1$ , and serve as an instructive benchmark for comparison with the data-driven approach. When trained and tested on a simulation of stratified decaying turbulence which accesses a range of turbulent regimes (associated with differing values of $Re_b$ ), the PCNN outperforms assumptions of isotropy significantly as $Re_b$ decreases, and additionally demonstrates improvements over the fitted empirical models. A differential sensitivity analysis of the PCNN facilitates a comparison with the theoretical models and provides a physical interpretation of the features enabling it to make improved predictions.

Third‐order elasticity of transversely isotropic field shales

AbstractThe formations above a producing reservoir can exhibit large mechanical changes, creating a risk of significant subsidence and loss of rock integrity. These changes can be monitored by time‐lapse seismic acquisition, which measures the corresponding velocity changes via time‐shifts. Third‐order elastic theory can be used to connect subsurface strains and stress changes to these seismic attribute changes. Existing models assume isotropic strain dependence of the dynamic stiffness in shales. It is important to re‐evaluate this isotropic assumption considering the inherent anisotropy of shales and their abundance in the overburden. Thus, we instead propose a third‐order elastic model with a transversely isotropic strain dependence of the dynamic stiffness. When calibrated, this new model satisfactorily predicted P‐wave velocity changes determined in undrained laboratory experiments conducted on overburden field shales, covering a wide range of propagation directions and stress variations. The shales exhibit anisotropic dynamic strain sensitivity, resulting in a significantly higher strain sensitivity predicted for Thomsen's anisotropy parameters epsilon and delta subjected to a uniaxial strain parallel to the horizontal bedding plane compared to the vertical direction. Geomechanical modelling, considering a depleting disk‐shaped reservoir surrounded by shales, was employed to predict the dynamic stiffness changes of the overburden using the laboratory‐calibrated third‐order elastic model. The overburden time‐shifts increased with offset angle, peaking at about 45°, suggesting a strong influence of shear strains on the time‐shifts. In contrast, a corresponding model with an isotropic third‐order elastic tensor, calibrated to the same data, exhibited a significantly lower sensitivity to the shear strains. These results underscore the importance of considering the anisotropic strain dependence of the dynamic stiffness when studying shales. Interpreting offset‐dependent trends in pre‐stack time‐lapse seismic data, along with geomechanical modelling and an appropriate strain‐dependent rock physics model, can assist in quantifying subsurface strains and stress changes.

Theoretical Analysis on Thermo-Mechanical Bending Behavior of Timber–Concrete Composite Beams

In this study, an analytical approach is introduced for predicting the bending behavior of a timber–concrete composite (TCC) beam subjected to a mechanical load and a non-uniform temperature field, in which the orthotropy of timber as well as interfacial slip are taken into consideration. The analytical model addresses the non-uniform temperature field using Fourier series expansion based on the heat transport theory. The stresses and displacements of the TCC beam under the thermo-mechanical condition are governed by the thermo-elasticity theory, and the corresponding solution is derived analytically by solving a group of non-homogeneous partial differential equations. The proposed solution is in good agreement with the finite element solution and exhibits higher accuracy compared to the Euler–Bernoulli beam solution that relies on the assumption of transverse shear deformation and isotropy. An extensive investigation is carried out to analyze how the bending behavior of TCC beams is influenced by variations in interfacial shear stiffness and temperature field.

PERANCANGAN PLAZA LAMONGAN DENGAN TEMA ARSITEKTUR NEO VERNAKULAR

Plaza is a certain area consisting of one or several shops that are erected vertically orhorizontally in a city, which are sold or leased to business actors or managed independently toconduct goods trading activities. The use of neo vernacular architectural themes aims to preservelocal elements formed empirically by a tradition which then more or less undergoes renewaltowards a more modern or advanced work without putting aside local traditional values. Buildingsthat are more varied, flexible, innovative, dynamic and diverse, both in material and technologyare able to achieve visual targets, rooms and outdoor spaces that achieve harmony in the Plazadesign. And also this concept in principle pays attention to normative, cosmological principles,the role and local culture in people's lives and the harmony between buildings, nature and theenvironment. The whole building has 3 zoning, namely the private zone, the semi-public zone, andthe public zone.

The cosmic dipole in the Quaia sample of quasars: a Bayesian analysis

ABSTRACT We present a Bayesian analysis of the Quaia sample of 1.3 million quasars as a test of the cosmological principle. This principle postulates that the Universe is homogeneous and isotropic on sufficiently large scales, forming the basis of prevailing cosmological models. However, recent analyses of quasar samples have found a matter dipole inconsistent with the inferred kinematic dipole of the cosmic microwave background (CMB), representing a tension with the expectations of the cosmological principle. Here, we explore various hypotheses for the distribution of quasars in Quaia, finding that the sample is influenced by selection effects with significant contamination near the Galactic Plane. After excising these regions, we find significant evidence that the Quaia quasar dipole is consistent with the CMB dipole, both in terms of the expected amplitude and direction. This result is in conflict with recent analyses, lending support to the cosmological principle and the interpretation that the observed dipole is due to our local departure from the Hubble flow.

Spatially homogeneous universes with late-time anisotropy

The cosmological principle asserts that on sufficiently large scales the Universe is homogeneous and isotropic on spatial slices. To deviate from this principle requires a departure from the FLRW ansatz. In this paper we analyze the cosmological evolution of two spatially homogeneous but anisotropic universes, namely the spatially closed Kantowski–Sachs Universe and the open axisymmetric Bianchi type III Universe. These models are characterized by two scale factors and we study their evolution in universes with radiation, matter and a cosmological constant. In all cases, the two scale factors evolve differently and this anisotropy leads to a lensing effect in the propagation of light. We derive explicit formulae for computing redshifts, angular diameter distances and luminosity distances and discuss the predictions of these models in relation to observations for type Ia supernovae and the CMB. We comment on the possibility of explaining the observed luminosity distance plot for type Ia supernovae within the context of cosmologies featuring late-time anisotropy and a vanishing cosmological constant.

Weld-line strength prediction for glass fiber reinforced polyamide-6 material through integrative simulation and its experimental validation

Injection molding is one of the preliminary production methods for plastic components. Typically, injection molding Moldflow simulations predicts potential issues like air void, weld-line, warpage etc. This work focuses on weld-line defect, which occurs when two or more flow fronts are meets each other during filling of the cavity. Most of the commercial algorithms are based on isotropic and homogeneous material assumptions however plastic materials are anisotropic and heterogeneous in nature. Therefore, accuracy with isotropic solvers may vary with actual reality. To consider material anisotropy and heterogeneous nature of the material, an integrative simulation is advantageous technology which gives more realistic results. A unique approach of integrative simulations has been used in this work to predict the strength of the weld-line as there is no direct standard procedure or software available to get weld-line strength. Moldflow simulation is performed on specially designed plaque wherein the weld-line is reproduced considering 30% glass-filled polyamide-6 material. The new material model is developed by mapping the structural model of tensile specimens on the Moldflow simulated plaque with integrative mapping approach. The mapped model considers fiber orientation and weld-line characteristics of the material which is then solved in the Abaqus structural solver. Experimental validation is performed by manufacturing of weld-line plaques, specimen preparation, and experimental testing. The results correlation is done for an isotropic and anisotropic material model with experimental results. The correlation study shows, a significant difference in results for isotropic simulation and integrative anisotropic simulations. The failure pattern and load-displacement behavior of integrative simulation is close match with experimental results with minimum 93% accuracy.

Geometric Methods for Cosmological Data on the Sphere.

This review is devoted to recent developments in the statistical analysis of spherical data, strongly motivated by applications in cosmology. We start from a brief discussion of cosmological questions and motivations, arguing that most cosmological observables are spherical random fields. Then, we introduce some mathematical background on spherical random fields, including spectral representations and the construction of needlet and wavelet frames. We then focus on some specific issues, including tools and algorithms for map reconstruction (i.e., separating the different physical components that contribute to the observed field), geometric tools for testing the assumptions of Gaussianity and isotropy, and multiple testing methods to detect contamination in the field due to point sources. Although these tools are introduced in the cosmological context, they can be applied to other situations dealing with spherical data. Finally, we discuss more recent and challenging issues, such as the analysis of polarization data, which can be viewed as realizations of random fields taking values in spin fiber bundles. Expected final online publication date for the Annual Review of Statistics and Its Application, Volume 11 is March 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Taiyi: The Axis of Philosophy of the Laozi

Taiyi 太一, the void and dark central region of the celestial sphere, carries symbolic implications that resonate with the essence of ultimate reality in the philosophical framework of the Laozi 老子. It assumes a metaphorical representation of the ultimate reality and its movement pattern, serving as the axis from which the fundamental concepts and principal branches of this philosophy unfurl. The concept of Taiyi exerts a profound and far-reaching impact on the philosophical discourse of the Laozi. It assumes the mantle of a signifier for the ultimate reality within the philosophical framework of the Laozi, while its dynamic motion patterns imbue the cosmological principles of this philosophy. On a pragmatic level, Taiyi unveils profound and nuanced insights into human nature and the epistemology expounded by the Laozi.

Energy transfer and third-order law in forced anisotropic magneto-hydrodynamic turbulence with hyper-viscosity

The third-order law links energy transfer rates in the inertial range of magneto- hydrodynamic (MHD) turbulence with third-order structure functions. Anisotropy, a typical property in the solar wind, challenges the applicability of the third-order law with the isotropic assumption. To shed light on the energy transfer process in the presence of anisotropy, we conducted direct numerical simulations of forced MHD turbulence with normal and hyper-viscosity under various strengths of the external magnetic field ( $B_0$ ), and calculated three forms of third-order structure function with or without averaging of the azimuthal or polar angles with respect to $B_0$ direction. Correspondingly, three estimated energy transfer rates were obtained. The result shows that the peak of normalized third-order structure function occurs at larger scales closer to the $B_0$ direction, and the maximum of longitudinal transfer rates shifts away from the $B_0$ direction at larger $B_0$ . Compared with normal viscous cases, hyper-viscous cases can attain better separated inertial range, thus facilitating the estimation of the energy cascade rates. We find that the widespread use of the isotropic form of the third-order law in estimating the energy transfer rates is questionable in some cases, especially when the anisotropy arising from the mean magnetic field is inevitable. In contrast, the direction-averaged third-order structure function properly accounts for the effect of anisotropy and predicts the energy transfer rates and inertial range accurately, even at very high $B_0$ . With limited statistics, the third-order structure function shows a stronger dependence on averaging of azimuthal angles than the time, especially for high $B_0$ cases. These findings provide insights into the anisotropic effect on the estimation of energy transfer rates.

The relic radiation blunder and the cosmometric contradiction in Big Bang cosmology

The cosmic microwave background radiation is routinely cited as evidence for a hot Big Bang. Its near isotropy harmonizes with the cosmological principle. However, in prototypical Big Bang models, all matter originates from a primeval fireball that also emits the light that is redshifted into these microwaves. Since light escapes from its source faster than matter can move, it would need to return for it to still be visible to material observers, but the universe is considered ‘flat’ and non-reflective. This prevents us from observing the redshifted glow of a primeval fireball. This is concealed by considering the light to expand with the ‘Hubble flow’ while disregarding that it would escape at _c_. This “relic radiation blunder” reflects the assumption that model universes in General Relativity are filled with a spatially homogeneous fluid. For radiation, this becomes inappropriate when it is no longer scattered. What we actually observe remains unexplained. Moreover, current standard cosmology allows an expanding view into a large pre-existing universe, while for some aspects it assumes the universe to have been smaller before. This creates geometric, i.e., “cosmometric” contradictions such as between the observed source of the cosmic microwaves and the much smaller and closer assumed emitting source of the same. The criticism expressed here goes against the ‘hard core’ of an established research program. Experts in the field normally view these cores as untouchable. This attitude blocks foundational advances in science.

Thickness detection of anisotropic variable cross-section bone based on ultrasonic guided waves

We measured cortical bone thickness of long bones by ultrasonic guided waves for diagnosis of osteoporosis. Current studies were limited to the detection of isotropic cortical bone with uniform thickness, which did not reflect the actual situation. This paper considered the anisotropic cortical bone and proposed an inversion method for measuring the thickness of variable cross-section cortical bone. Firstly, the propagation characteristics of guided waves in cortical bone could be verified by experimentally measuring the guided wave velocity. Then, the inversion method used the A0 mode wavenumber distribution to characterize the thickness of bone plates. Through error analysis, when the signal frequency remains constant, the thinner the cortical bone thickness to be measured, the more accurate the measurement results are. For the thickness inversion of the quantitative experiments in vitro bovine tibia, the error was within 1.1 mm for the oblique bone plate and within 0.9 mm for the concave bone plate. The thickness inversion error of the transverse isotropic assumption decreased by 7.8% compared to the isotropic assumption, which is more realistic for the cortical bone. The method can effectively invert the local thickness of cortical bone, thus providing a reliable basis for evaluating bone health status.

A tilt instability in the cosmological principle

We show that the Friedmann–Lemaître–Robertson–Walker (FLRW) framework has an instability towards the growth of fluid flow anisotropies, even if the Universe is accelerating. This flow (tilt) instability in the matter sector is invisible to Cosmic No-Hair Theorem-like arguments, which typically only flag shear anisotropies in the metric. We illustrate our claims in the setting of “dipole cosmology”, the maximally Copernican generalization of FLRW that can accommodate a flow. Simple models are sufficient to show that the cosmic flow need not track the shear, even in the presence of a positive cosmological constant. We also emphasize that the growth of the tilt hair is fairly generic if the effective equation of state w rightarrow -1 at late times (as it does in standard cosmology), irrespective of the precise model of dark energy. The generality of our theoretical result puts various recent observational claims about late time anisotropies and cosmic dipoles in a new light.

Imaging upper mantle anisotropy with traveltime and splitting intensity observations from teleseismic shear waves: insights from tomographic reconstructions of subduction simulations

SUMMARYTeleseismic traveltime tomography remains one of the most popular methods for obtaining images of Earth’s upper mantle. However, despite extensive evidence for an elastically anisotropic mantle, the isotropic assumption remains commonplace in such imaging studies. This can result in significant model artefacts which in turn may yield misguided inferences regarding mantle dynamics. The nature of anisotropy-induced apparent velocity anomalies has been well-documented in P-wave imaging and various strategies have been proposed to constrain both isotropic and anisotropic heterogeneity from these data. In contrast, few studies have explored the consequences for shear wave tomography and no practical framework for the anisotropic inversion of S-wave delays exists. Here, we propose a new method for constraining arbitrarily oriented hexagonal anisotropy using both traveltime and splitting intensity observations from direct S phases. Our approach accounts for polarization and finite-frequency effects and allows for isotropic starting models. The imaging method is validated through the tomographic analysis of a realistic synthetic dataset produced from waveform simulations through a geodynamic model of subduction. Results illustrate that neglecting anisotropy produces distortions in slab geometry and the appearance of sub- and supraslab low-velocity zones. Anisotropic inversions remove these artefacts while also constraining geodynamically relevant fabric properties including dip.

Potential signature of a quadrupolar hubble expansion in Pantheon+supernovae

ABSTRACT The assumption of isotropy – that the Universe looks the same in all directions on large scales – is fundamental to the standard cosmological model. It is therefore critical to empirically test in which regimes this assumption holds. Anisotropies in the cosmic expansion are expected due to non-linear structures in the late Universe. However, the extent to which these anisotropies might impact our low-redshift observations remains to be fully tested. We use general relativistic simulations to determine that the expected anisotropies in the Hubble and deceleration parameters are quadrupolar and dipolar, respectively. We constrain these multipoles simultaneously in the new Pantheon+supernova compilation. In the rest frame of the cosmic microwave background (CMB), including peculiar velocity (PV) corrections, we find an ∼2σ deviation from isotropy. We constrain the eigenvalues of the quadrupole in the Hubble parameter to be λ1 = 0.021 ± 0.011 and λ2 = 0.00 ± 0.012 and place a 1σ upper limit on its amplitude of 2.88 per cent. We find no significant dipole in the deceleration parameter, with amplitude $q_{\rm dip} = 4.5^{+1.9}_{-5.4}$. However, in the rest frame of the CMB without PV corrections, we find a >2σ positive amplitude with $q_{ \rm dip} = 9.6^{+4.0}_{-6.9}$. Incorporating these anisotropies, the monopole of the Hubble parameter shifts by only 0.30 km s−1 Mpc−1 with respect to the isotropic constraints.

On the perimeter estimation of pixelated excursion sets of two‐dimensional anisotropic random fields

AbstractWe are interested in creating statistical methods to provide informative summaries of random fields through the geometry of their excursion sets. To this end, we introduce an estimator for the length of the perimeter of excursion sets of random fields on observed over regular square tilings. The proposed estimator acts on the empirically accessible binary digital images of the excursion regions and computes the length of a piecewise linear approximation of the excursion boundary. The estimator is shown to be consistent as the pixel size decreases, without the need of any normalization constant, and with neither assumption of Gaussianity nor isotropy imposed on the underlying random field. In this general framework, even when the domain grows to cover , the estimation error is shown to be of smaller order than the side length of the domain. For affine, strongly mixing random fields, this translates to a multivariate Central Limit Theorem for our estimator when multiple levels are considered simultaneously. Finally, we conduct several numerical studies to investigate statistical properties of the proposed estimator in the finite‐sample data setting.

Space-time correlations of passive scalar in Kraichnan model

We consider the two-point, two-time (space-time) correlation of passive scalar R(r,τ) in the Kraichnan model under the assumption of homogeneity and isotropy. Using the fine-gird PDF method, we find that R(r,τ) satisfies a diffusion equation with constant diffusion coefficient determined by velocity variance and molecular diffusion. Its solution can be expressed in terms of the two-point, one time correlation of passive scalar, i.e., R(r,0). Moreover, the decorrelation of R^(k,τ), which is the Fourier transform of R(r,τ), is determined by R^(k,0) and a diffusion kernal.

Detector induced anisotropies on the angular distribution of gravitational wave sources and opportunities of constraining horizon scale anisotropies

ABSTRACT The cosmological principle has been verified using electromagnetic observations. However its verification with high accuracy is challenging due to various foregrounds and selection effects, and possible violation of the cosmological principle has been reported in the literature. In contrast, gravitational wave (GW) observations are free of these foregrounds and related selection biases. This may enable future GW experiments to test the cosmological principle robustly with full sky distribution of millions of standard bright/dark sirens. However, the sensitivities of GW detectors are highly anisotropic, resulting in significant instrument induced anisotropies in the observed GW catalogue. We investigate these instrumental effects for 3rd generation detector networks in term of multipoles aℓm of the observed GW source distribution, using Monte Carlo simulations. (1) We find that the instrument induced anisotropy primarily exists at the m = 0 modes on large scales (ℓ ≲ 10), with amplitude 〈|aℓ0|2〉 ∼ 10−3 for two detectors (ET-CE) and ∼10−4 for three detectors (ET-2CE). This anisotropy is correlated with the sky distribution of signal-to-noise ratio and localization accuracy. Such anisotropy sets a lower limit on the detectable cosmological aℓ0. (2) However, we find that the instrument induced anisotropy is efficiently cancelled by rotation of the Earth in m ≠ 0 components of aℓm. Therefore aℓm (m ≠ 0) are clean windows to detect cosmological anisotropies. (3) We investigate the capability of 3rd generation GW experiments to measure the cosmic dipole. Through Monte Carlo simulations, we find that cosmic dipole with an amplitude of ∼10−2 reported in the literature can be detected/ruled out by ET-CE and ET-2CE robustly, through the measurement of a11.