Search Results (7)

We resume our analysis of Newtonian Fractional-Dimension Gravity (NFDG), an alternative gravitational model that does not require the dark matter (DM) paradigm. We add three more galaxies (NGC 6946, NGC 3198, NGC 2841) to the catalog of those studied with NFDG methods. Once again, NFDG can successfully reproduce the observed rotation curves by using a variable fractional dimension $D\left(R\right)$, as with the nine other galaxies previously studied with these methods. In addition, we introduce a mass-dimension field equation for our model, which is capable of deriving the fractional mass dimension $D_m\left(R\right)$ from a single equation, as opposed to the previous $D\left(R\right)$, which was obtained simply by matching the experimental rotational velocity data for each galaxy. While the NFDG predictions computed with this new $D_m\left(R\right)$ dimension are not as accurate as those based on the original $D\left(R\right)$, they nevertheless confirm the validity of our fractional-dimension approach. Three previously studied galaxies (NGC 7814, NGC 6503, NGC 3741) were analyzed again with these new methods, and their structure was confirmed to be free from any dark matter components. Full article

This study investigates the effect of pyrite content on the flocculation and sedimentation of clay-based tailings composed of kaolin, quartz, and pyrite in seawater at pH 8. A high-molecular-weight anionic hydrolyzed polyacrylamide (SNF 704) was used in batch settling tests, supported by floc characterization with FBRM, zeta potential measurements, and molecular dynamics (MD) simulations. Results showed that increasing pyrite content reduced the maximum floc size and increased the fraction of unflocculated fines, particularly at 10 g/t dosage. Although the fractal dimension remained nearly constant (1.92–1.97 at 10 g/t and 2.05–2.08 at 30 g/t), floc density increased linearly with pyrite proportion due to its higher specific gravity. Zeta potential analysis confirmed strong polymer–pyrite interactions, with charge inversion from +5.3 to −4.5 mV, while MD simulations indicated that adsorption occurs mainly through aliphatic chain segments, in contrast to hydrogen bonding observed for quartz and kaolinite. These findings demonstrate that pyrite affects flocculation dynamics both by its density and by specific polymer–surface interactions, directly influencing floc size, density, and sedimentation performance in seawater thickening systems. Full article

Jet fuel in aircraft fuel tanks moves due to acceleration resulting from maneuvers. The movement mentioned here directly impacts the Center of Gravity (CG). The aircraft’s flight mechanics are significantly affected by the deviation of its CG on the aircraft body, and excessive deviation is undesirable. Preventing CG deviation is achieved by designing various baffles within the fuel tank. In this study, design details of the baffles were investigated with the help of an artificial neural network (ANN) model, 1D simulations, and computational fluid dynamics (CFD) calculations. The 1D simulations, which model the fuel movement, were used to understand the general behavior of the fluid in the tank. CFD calculations simulating turbulent fluid flow in three dimensions were used to confirm the results of the 1D simulations and provide more detailed information. A simulation set is created utilizing five parameters: barrier usage, volume fraction, cutout diameter, number of cutouts, and cutout location. Compared to the barrierless design, the barrier usage as a parameter changes either on baffle number 1, 3, and 6, or on baffle number 2, 4, and 7. The fuel volume fraction parameter accounts for 30%, 45%, and 60% of the interior volume. The diameters of the cutout holes vary between 30 mm and 156 mm and are used as categorized among the baffles. Cutout holes are applied on baffles in single, twin, and triplet forms and their locations are subjected to a divergence of either −20 mm or +20 mm from the z-axis. Based on these parameters, the maximum deviation and the retreat time of CG constitute the output parameters. The importance of the input parameters on the outputs was obtained with the help of an ANN algorithm created from the results of all possible combinations of a sufficient number of 1D simulations. To obtain more detailed results and confirm the importance of input parameters on outputs, selected cases were simulated with CFD. As a result of all analyses, it was revealed that barrier usage is the most dominant input parameter on CG deviation followed by volume fraction, cutout hole diameter, cutout divergence, and finally, the number of cutout holes. This study identifies the dominant input parameters to control fuel sloshing, specifically CG deviation and retreat time in the fuel tank, and proposes baffle designs to promote robust flight stability. Full article

Our main goal here is to conduct a comparative analysis between the well-known MOND theory and a more recent model called the $\kappa$-model. An additional connection, between the $\kappa$-model and two other novel MOND-type theories, Newtonian Fractional-Dimension Gravity (NFDG) and Refracted Gravity (RG), is likewise presented. All these models are built to overtake the DM paradigm, or at least to strongly reduce the dark matter content. Whereas they rely on different formalisms, however, all four seem to suggest that the universal parameter, $a_0$, appearing in MOND theory could intrinsically be correlated to either the sole baryonic mean mass density (RG and $\kappa$-model) and/or to the dimension of the object under consideration (NFDG and $\kappa$-model). We then confer to parameter $a_0$ a more flexible status of multiscale parameter, as required to explain the dynamics together in galaxies and in galaxy clusters. Eventually, the conformal gravity theory (CFT) also seems to have some remote link with the $\kappa$-model, even though the first one is an extension of general relativity, and the second one is Newtonian in essence. The $\kappa$-model has been tested on a small sample of spiral galaxies and in galaxy clusters. Now, we test this model on a large sample of galaxies issued from the SPARC database. Full article

We apply Newtonian fractional-dimension gravity (NFDG), an alternative gravitational model, to some notable cases of galaxies with little or no dark matter. In the case of the ultra-diffuse galaxy AGC 114905, we show that NFDG methods can effectively reproduce the observed rotation curve using a variable fractional dimension $D\left(R\right)$, as was performed for other galaxies in previous studies. For AGC 114905, we obtain a variable dimension in the range $D\approx$ 2.2–3.2, but our fixed D = 3 curve can still fit all the experimental data within their error bars. This confirms other studies indicating that the dynamics of this galaxy can be described almost entirely by the baryonic mass distribution alone. In the case of NGC 1052-DF2, we use an argument based on the NFDG extension of the virial theorem applied to the velocity dispersion of globular clusters showing that, in general, discrepancies between observed and predicted velocity dispersions can be attributed to an overall fractal dimension $D<3$ of the astrophysical structure considered, and not to the presence of dark matter. For NGC 1052-DF2, we estimate $D\approx 2.9$, thus confirming that this galaxy almost follows standard Newtonian behavior. We also consider the case of the Bullet Cluster merger (1E0657-56), assumed to be one of the strongest proofs of dark matter existence. A simplified but effective NFDG model of the collision shows that the observed infall velocity of this merger can be explained by a fractional dimension of the system in the range $D\simeq$ 2.4–2.5, again, without using any dark matter. Full article

This paper presents a relativistic version of Newtonian Fractional-Dimension Gravity (NFDG), an alternative gravitational model recently introduced and based on the theory of fractional-dimension spaces. This extended version—Relativistic Fractional-Dimension Gravity (RFDG)—is based on other existing theories in the literature and might be useful for astrophysical and cosmological applications. In particular, in this work, we review the mathematical theory for spaces with non-integer dimensions and its connections with the non-relativistic NFDG. The Euler–Lagrange equations for scalar fields can also be extended to spaces with fractional dimensions, by adding an appropriate weight factor, and then can be used to generalize the Laplacian operator for rectangular, spherical, and cylindrical coordinates. In addition, the same weight factor can be added to the standard Hilbert action in order to obtain the field equations, following methods used for scalar-tensor models of gravity, multi-scale spacetimes, and fractional gravity theories. We then apply the field equations to standard cosmology and to the Friedmann-Lemaître-Robertson-Walker metric. Using a suitable weight $v_t\left(t\right)$, depending on the synchronous time t and on a single time-dimension parameter ${\alpha }_t$, we extend the Friedmann equations to the RFDG case. This allows for the computation of the scale factor $a\left(t\right)$ for different values of the fractional time-dimension ${\alpha }_t$ and the comparison with standard cosmology results. Future additional work on the subject, including studies of the cosmological late-time acceleration, type Ia supernovae data, and related dark energy theory will be needed to establish this model as a relativistic alternative theory of gravity. Full article

Theories of quantum gravity suggest that Lorentz invariance, the fundamental symmetry of the Theory of Relativity, may be broken at the Planck energy scale. While any deviation from conventional Physics must be minuscule in particular at attainable energies, this hypothesis motivates ever more sensitive tests of Lorentz symmetry. In the photon sector, astrophysical observations, in particular polarization measurements, are a very powerful tool because tiny deviations from Lorentz invariance will accumulate as photons propagate over cosmological distances. The Standard-Model Extension (SME) provides a theoretical framework in the form of an effective field theory that describes low-energy effects due to a more fundamental quantum gravity theory by adding additional terms to the Standard Model Lagrangian. These terms can be ordered by the mass dimension d of the corresponding operator and lead to a wavelength, polarization, and direction dependent phase velocity of light. Lorentz invariance violation leads to an energy-dependent change of the Stokes vector as photons propagate, which manifests itself as a rotation of the polarization angle in measurements of linear polarization. In this paper, we analyze optical polarization measurements from 63 Active Galactic Nuclei (AGN) and Gamma-ray Bursts (GRBs) to search for Lorentz violating signals. We use both spectropolarimetric measurements, which directly constrain the change of linear polarization angle, as well as broadband spectrally integrated measurements. In the latter, Lorentz invariance violation manifests itself by reducing the observed net polarization fraction. Any observation of non-vanishing linear polarization thus leads to constraints on the magnitude of Lorentz violating effects. We derive the first set limits on each of the 10 individual birefringent coefficients of the minimal SME with $d=4$ , with 95% confidence limits on the order of 10⁻³⁴ on the dimensionless coefficients. Full article