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We calculate the exact formation probability of primordial black holes generated during the collapse at horizon re-entry of large fluctuations produced during inflation, such as those ascribed to a period of ultra-slow-roll. We show that it interpolates between a Gaussian at small values of the average density contrast and a Cauchy probability distribution at large values. The corresponding abundance of primordial black holes may be larger than the Gaussian one by several orders of magnitude. The mass function is also shifted towards larger masses., 4 pages, 3 figures, minor additions, references added, matches published version

The choked accretion model consists of a purely hydrodynamical mechanism in which, by setting an equatorial to polar density contrast, a spherically symmetric accretion flow transitions to an inflow-outflow configuration. This scenario has been studied in the case of a (non-rotating) Schwarzschild black hole as central accretor, as well as in the non-relativistic limit. In this article, we generalize these previous works by studying the accretion of a perfect fluid onto a (rotating) Kerr black hole. We first describe the mechanism by using a steady-state, irrotational analytic solution of an ultrarelativistic perfect fluid, obeying a stiff equation of state. We then use hydrodynamical numerical simulations in order to explore a more general equation of state. Analyzing the effects of the black hole's rotation on the flow, we find in particular that the choked accretion inflow-outflow morphology prevails for all possible values of the black hole's spin parameter, showing the robustness of the model., 25 pages, 15 figures. Accepted for publication in PRD. Comments welcome

SUMMARY We provide a high-resolution image of the Ivrea Geophysical Body (IGB) in the Western Alps with new gravity data and 3-D density modelling, integrated with surface geological observations and laboratory analyses of rock properties. The IGB is a sliver of Adriatic lower lithosphere that is located at shallow depths along the inner arc of the Western Alps, and associated with dense rocks that are exposed in the Ivrea-Verbano Zone (IVZ). The IGB is known for its high seismic velocity anomaly at shallow crustal depths and a pronounced positive gravity anomaly. Here, we investigate the IGB at a finer spatial scale, merging geophysical and geological observations. We compile existing gravity data and we add 207 new relative gravity measurements, approaching an optimal spatial coverage of 1 data point per 4–9 km2 across the IVZ. A compilation of tectonic maps and rock laboratory analyses together with a mineral properties database is used to produce a novel surface rock-density map of the IVZ. The density map is incorporated into the gravity anomaly computation routine, from which we defined the Niggli gravity anomaly. This accounts for Bouguer Plate and terrain correction, both considering the in situ surface rock densities, deviating from the 2670 kg m–3 value commonly used in such computations. We then develop a 3-D single-interface crustal density model, which represents the density distribution of the IGB, including the above Niggli-correction. We retrieve an optimal fit to the observations by using a 400 kg m–3 density contrast across the model interface, which reaches as shallow as 1 km depth below sea level. The model sensitivity tests suggest that the ∼300–500 kg m–3 density contrast range is still plausible, and consequently locates the shallowest parts of the interface at 0 km and at 2 km depth below sea level, for the lowest and the highest density contrast, respectively. The former model requires a sharp density discontinuity, the latter may feature a vertical transition of densities on the order of few kilometres. Compared with previous studies, the model geometry reaches shallower depths and suggests that the width of the anomaly is larger, ∼20 km in west–east direction and steeply E–SE dipping. Regarding the possible rock types composing the IGB, both regional geology and standard background crustal structure considerations are taken into account. These exclude both felsic rocks and high-pressure metamorphic rocks as suitable candidates, and point towards ultramafic or mantle peridotite type rocks composing the bulk of the IGB.

Dehydration melting in subduction zones often produces cold plumes, initiated by Rayleigh-Taylor instabilities in the buoyant partially molten zones lying above the dipping subducting slabs. We use scaled laboratory experiments to demonstrate how the slab dip (α) can control the evolution of such plumes. For α > 0°, Rayleigh-Taylor instabilities evolve as two orthogonal waves, one trench perpendicular with wavelength λL and the other one trench parallel with wavelength λT (λT > λL). We show that two competing processes, (1) λL-controlled updip advection of partially molten materials and (2) λT/λL interference, determine the modes of plume growth. The λT/λL interference gives rise to an areal distribution of plumes (Mode 1), whereas advection leads to a linear distribution of plumes (Mode 2) at the upper fringe of the partially molten layer. The λT wave instabilities do not grow when α exceeds a threshold value (α* = 30°). For α > α*, λL-driven advection takes the control to produce exclusively Mode 2 plumes. We performed a series of 2-D and 3-D computational fluid dynamics simulations to test the criticality of slab dip in switching the Mode 1 to Mode 2 transition at α*. We discuss the effects of viscosity ratio (R) and the density contrast (Δρ) between the source layers and ambient mantle, source layer thickness (Ts), and slab velocity (Us) on the development of cold plumes. Finally, we discuss the areal versus linear distributions of volcanoes from natural subduction zones as possible examples of Mode 1 versus Mode 2 plume products.

We develop, after Dellar (P. J. Dellar, Phys. Rev. E. 65, 036309 (2002), J. Comput. Phys. 190, pp351 (2003)), a multiple-relaxation time (MRT), chromodynamic, multi-component lattice Boltzmann equation (MCLBE) scheme for simulation of isothermal, immiscible fluid flow with a density contrast. It is based on Lishchuk's method (J. U. Brackbill, D. B. Kothe and C. Zemach, J. Comp. Phys. 100, 335-354 (1992), S. V. Lishchuk, C. M. Care and I. Halliday, Phys. Rev. E. 67(3), 036701(2), (2003)) and the segregation of d'Ortona et al. (U. D'Ortona, D. Salin, M. Cieplak, R. B. Rybka and J. R. Banavar Phys. Rev. E. 51, 3718, (1995)). We focus on fundamental model verifiability but do relate some of our data to that from previous approaches, due to Ba et al. (Y. Ba, H. Liu, Q. Li, Q. Kang and J. Sun, Phys. Rev. E 94, 023310 (2016)) and earlier Liu et al. (H. Liu, A. J. Valocchi and Q. Kang, Phys. Rev. E 85, 046309 (2012)), who pioneered large density difference chromodynamic MCLBE and showed the practical benefits of a MRT collision model. Specifically, we test the extent to which chromodynamic MCLBE MRT schemes comply with the kinematic condition of mutual impenetrability and the continuous traction condition by developing analytical benchmarking flows. We conclude that our data, taken with those of Ba et al., verify the utility of MRT chromodynamic MCLBE., submitted to PRE

The structured winds of single massive stars can be classified into two broad groups: stochastic structure and organized structure. While the former is typically identified with clumping, the latter is typically associated with rotational modulations, particularly the paradigm of Co-rotating Interaction Regions (CIRs). While CIRs have been explored extensively in the UV band, and moderately in the X-ray and optical, here we evaluate radio variability from CIR structures assuming free-free opacity in a dense wind. Our goal is to conduct a broad parameter study to assess the observational feasibility, and to this end, we adopt a phenomenological model for a CIR that threads an otherwise spherical wind. We find that under reasonable assumptions, it is possible to obtain radio variability at the 10% level. The detailed structure of the folded light curve depends not only on the curvature of the CIR, the density contrast of the CIR relative to the wind, and viewing inclination, but also on wavelength. Comparing light curves at different wavelengths, we find that the amplitude can change, that there can be phase shifts in the waveform, and the the entire waveform itself can change. These characterstics could be exploited to detect the presence of CIRs in dense, hot winds., to appear inn MNRAS

Simulations of tracer experiments conducted with a three‐dimensional primitive‐equation hydrodynamic and transport model are used to understand the processes controlling the rate of mixing between two rivers (Ebro and Segre), with distinct physical and chemical properties, at their confluence, upstream of a meandering reservoir (Ribarroja reservoir). Mixing rates downstream of the confluence are subject to hourly scale oscillations, driven partly by changes in inflow densities and also as a result of turbulent eddies that develop within the shear layer between the confluent rivers and near a dead zone located downstream of the confluence. Even though density contrasts are low—at most O(10−1) kg m−3difference among sources—and almost negligible from a dynamic point of view—compared with inertial forces—they are important for mixing. Mixing rates between the confluent streams under weakly buoyant conditions can be of up to 40% larger than those occurring under neutrally buoyant conditions. The buoyancy effects on mixing rates are interpreted as the result of changes in the contact area available for mixing (distortion of the mixing layer). For strong density contrasts, though, when the contact area between the streams becomes nearly horizontal, larger density differences between streams will lead to weaker mixing rates, as a result of the stabilizing effect of vertical density gradients.

SUMMARY The emergence of high resolution satellite measurements of the gravitational field (GOCE mission) offers promising perspectives for the study of the Earth’s interior. These new data call for the development of innovant analysis and interpretation methods. Here we combine a forward prism computation with a Bayesian resolution approach to invert for these gravity gradient data configuration. We apply and test our new method on satellite data configuration, that is 225 km height with a global and homogeneous geographic distribution. We first quantify the resolution of our method according to both data and parametrization characteristics. It appears that for reasonable density contrast values (0.1 g cm−3) crustal structures have to be wider than ∼28 km to be detectable in the GOCE signal. Deeper bodies are distinguishable for greater size (35 km size at 50 km depth, ∼80 km at 300 km depth). We invert the six tensor components, among which five are independent. By carefully testing each of them and their different combinations, we enlighten a trade off between the recovery of data and the sensitivity to inversion parameters. We particularly discussed this characteristic in terms of geometry of the synthetic model tested (structures orientation, 3-D geometry, etc.). In terms of RMS value, each component is always better explained if inverted solely, but the result is strongly affected by the inversion parametrization (smoothing, variances, etc.). On the contrary, the simultaneous inversion of several components displays a significant improvement for the global tensor recovery, more dependent on data than on density variance or on smoothness control. Comparing gravity and gradient inversions, we highlight the superiority of the GG data to better reproduce the structures especially in terms of vertical location. We successfully test our method on a realistic case of a complex subduction case for both gradient and gravity data. While the imaging of small crustal structures requires terrestrial gravity data set, the longest wavelength of the slab is well recovered with both data sets. The precision and homogeneous coverage of GOCE data however, counterbalance the heterogeneous and often quite non-existence coverage of terrestrial gravity data. This is particularly true in large areas which requires a coherent assemblage of heterogeneous data sets, or in high relief, vegetally covered and offshore zones.

We explore the possibility of using a gigaparsec-scale local void to reconcile the Hubble tension. Such a gigaparsec-scale void can be produced by multi-stream inflation where different parts of the observable universe follow different inflationary trajectories. The impact of such a void for cosmological observations is studied, especially those involving supernovae, Baryon Acoustic Oscillations (BAO) and the kinetic Sunyaev-Zel'dovich (kSZ) effect. As a benchmark model, a 1.7Gpc scale with boundary width 0.7Gpc and density contrast -0.14 may ease the Hubble tension., 11 pages, 8 figures

High-energy scattering spectroscopy is a widely-established technique for probing the characteristic properties of complex physical systems. Motivated by the recent observation of long-sought supersolid states in dipolar quantum Bose gases, I investigate the general relationships existing between the density contrast, the superfluid fraction, and the response to a high-energy scattering probe of density-modulated states within a classical-field approach. I focus on the two extreme regimes of "shallow" and "deep" supersolids, which are of particular interest in describing the phase transitions of the supersolid to a uniform superfluid and an incoherent crystal state, respectively. Using relevant Ans\"atze for the fields of dipolar supersolid states in these regimes, I specify and illustrate the scaling laws relating the three observables. This work was first prompted to develop an intuitive understanding of a concomitant study based on experiments and mean-field numerical simulations. Beyond this specific application, this works provides a simple and general framework to describe density-modulated states, and in particular the intriguing case of supersolids. It describes key properties characterizing the supersolid order and highlights new possibilities for probing such properties based on high-energy scattering response.

The ultrasonic attenuation mechanism is dissimilar under different density contrast and particle sizes. For liquid-solid dispersions with large particle size and low density contrast, the multi-frequency ultrasonic measurements of phase fraction is established. By analyzing the ultrasonic attenuation response under different particle sizes, the phase fraction measurement for the liquid-solid dispersions of large particle size and low density contrast is realized with the attenuation mechanism. The numerical results of different ultrasonic attenuation mechanisms are compared, and the influence of attenuation mechanisms on the experimental results is discussed. Taking the millimeter-sized acrylic spheres as test samples, the experiments were carried out on single size and multiple sizes of dispersed phase under different phase fraction. The experimental results show that the measurement method based on the ultrasonic attenuation of 1-5MHz multi-frequency has a good discrimination for the particle size, and the measurement error of phase fraction is less than 4%, which can effectively achieve the measurement of phase fraction in the liquid-solid dispersions.

The cosmological scalar perturbations of standard matter are investigated in the context of extended teleparallel $f(T)$ gravity theories using the $1+3$ covariant formalism. After a review of the background, gravitational field equations of $f(T)$ gravity and the introduction of the covariant perturbation variables, the usual scalar and harmonic decomposition have been performed, and the analysis of the growth of the density contrasts in the quasi-static approximation for two non-interacting fluids scenarios, namely torsion-dust and torsion-radiation mixtures is presented for the generic $f(T)$ gravity theory. Special applications to two classes of $f(T)$ gravity toy models, namely $f(T) = \mu T_0 (T/T_0)^n$ and $f(T) = T + \mu T_0 (-T/T_0)^n$, have then been made within the observationally viable regions of their respective parameter spaces, and the growth of the matter density contrast for both torsion-dust and torsion-radiation epochs of the Universe has been examined. The exact solutions of the dust perturbations, with growing amplitudes in cosmic time, are obtained for some limiting cases of n. Similarly, the long- and short-wavelength modes in the torsion-radiation case are treated, with the amplitudes either oscillating or monotonically growing with time. Overall, it is noted that $f(T)$ models contain a richer set of observationally viable structure growth scenarios that can be tested against up- and-coming observational data and can accommodate currently known features of the large-scale structure power spectrum in the general relativistic and $\Lambda$CDM limits., Comment: Published version

In attempting to quantify statistically the density structure of the interstellar medium, astronomers have considered a variety of fractal models. Here, we argue that, to properly characterize a fractal model, one needs to define precisely the algorithm used to generate the density field, and to specify – at least – three parameters: one parameter constrains the spatial structure of the field, one parameter constrains the density contrast between structures on different scales, and one parameter constrains the dynamic range of spatial scales over which self-similarity is expected (either due to physical considerations, or due to the limitations of the observational or numerical technique generating the input data). A realistic fractal field must also be noisy and non-periodic. We illustrate this with the exponentiated fractional Brownian motion (xfBm) algorithm, which is popular because it delivers an approximately lognormal density field, and for which the three parameters are, respectively, the power spectrum exponent, β, the exponentiating factor, ${\cal S}$, and the dynamic range, ${\cal R}$. We then explore and compare two approaches that might be used to estimate these parameters: machine learning and the established Δ-Variance procedure. We show that for 2 ≤ β ≤ 4 and $0\le {\cal S}\le 3$, a suitably trained Convolutional Neural Network is able to estimate objectively both β (with root-mean-square error $\epsilon _{_\beta }\sim 0.12$) and ${\cal S}$ (with $\epsilon _{_{\cal S}}\sim 0.29$). Δ-variance is also able to estimate β, albeit with a somewhat larger error ($\epsilon _{_\beta }\sim 0.17$) and with some human intervention, but is not able to estimate ${\cal S}$.

An adaptive mesh form of the gravity-geologic method, known as improved Gravity-Geologic Method (iGGM), was implemented on free-air gravity anomalies and shipborne depths to obtain an improved 1′ × 1′ bathymetry model of the Gulf of Guinea (15°W–5°E, 4°S–4°N). An optimal density contrast of 8000 kg/m3 was used for the whole area. The iGGM model compared well with NGDC, ETOPO1, and SIO models; with difference standard deviations and correlation coefficients being 180.20 m, 0.9248, 184.34 m, 0.9551, and 179.84 m, 0.8886, respectively. These prove generally that iGGM is efficient for estimating bathymetry with limited shipborne depths. The influence of shipborne depths quantity and optimal density contrast on bathymetry inversion are analysed, respectively, for the whole region and three subregions (15°W–8°W, 4°S–2°N; 7°W–2°E, 2°S–2°N; and 1°E–5°E, 4°S–0°N). Results showed that, compared with the mountainous areas, higher inversion accuracy (standard deviation of test differences less than 50 m) is achievable in the low-lying region using fewer shipborne depths. With 75% of shipborne depths used for the entire model, the standard deviation of differences between iGGM and shipborne depths at test points was 184.74 m. This indicates that to further improve the region’s bathymetry, more ship sounding is required in the mountainous areas. Numerical results showed different optimal densities should be selected for different areas, especially for the mountainous areas. Using a common density contrast in the whole region may limit the accuracy of the bathymetry inversion.

We present a new inverse approach to invert satellite gravity gradients for the Moho depth under consideration of a laterally varying density contrast between crust and mantle. The inverse problem is linearized and solved with the classical Gauss-Newton algorithm in a spherical geometry. To ensure stable solutions, the Jacobian is smoothed with second-order Tikhonov regularization. During the inversion, the Moho depth is discretized into tesseroids by reference Moho depth and density contrast, from which the gravitational effect can be calculated. As a computational benefit, the Jacobian is calculated only once and afterwards weighted with the laterally varying density contrast. We look for a Moho depth model that simultaneously explains the gravity gradient field and a least misfit to existing seismic Moho depth determinations. We perform the inversion both on regional and global scale.The laterally varying density contrast is based on different tectonic units, which are defined by independent global geological and geophysical data, such as regionalization of dispersion curves. This is beneficial in remote areas, where seismic investigations are very sparse and the crustal structure is to a large extent unknown. Applying the inversion to the Amazonian Craton and its surroundings shows a lower density contrast at the Moho depth for the continental interior compared to oceanic domains. This is in accordance with the tectono-thermal architecture of the lithosphere. The inverted values of the density vary between 300-450 kg/m3. The inverted Moho depth shows a clear separation between the Sao Francisco Craton and shallower Amazonian Craton.Gravity inversion with a laterally varying density contrast requires a uniform reference Moho depth. On a global scale, we utilize our inversion to estimate a reference Moho depth that is in accordance with crustal buoyancy. The inverted density contrasts show a similar trend like the regional study area. The inverted Moho depth shows expected tectonic features. Our method of computing the Jacobian once and weighting with lateral variable density contrasts is a valuable optimization of standard gravity inversion.

This article explores in depth a watershed concept to partition the universe, introduced in \cite{2019MNRAS.489L...1D} and applied to the {\it Cosmicflows-3} observational dataset. We present a series of tests conducted with cosmological dark matter simulations. In particular we are interested in quantifying the evolution with redshift of large scale structures when defined as segmented basins of attraction. This new dynamical definition in the field of measuring standard rulers demonstrates robustness since all basins show a density contrast $\delta$ above one (mean universe density) independently of the simulation spatial resolution or the redshift. Another major finding is that density profiles of the basins show universality in slope. Consequently, there is a unique definition of what is a gravitational watershed at large scale, that can be further used as a probe for cosmology studies., Comment: 8 pages, 11 figures, submitted to MNRAS

Flow focusing is a key operation in microfluidics, involving applications that range from flow cytometry to nanoprecipitation on chips. Attaining a rational control of the width of the focused stream has been a concern since the development of the technique. The available analytical models effectively predict the focusing width as a function of the imposed flow rates, but they are limited to density-matched fluids. The present work addresses the flow focusing of liquids with unmatched densities. Experiments were performed in microfluidic chips with slit microchannels. It is vividly shown how the flow focusing pattern depends on the orientation of the chip in relation to the gravitational field. When the flow is transverse to gravity, the flow focusing is seriously disturbed. When the flow is aligned with gravity, the flow focusing pattern holds, but the focused stream widens/narrows if the sample is less dense/denser than the sheath fluid. A mathematical model was derived, which quantitatively predicts the width of the focused stream for fluids with unmatched densities in slit microchannels. The model rationally captures the variations of the focusing width in terms of the critical parameters of the system: the flow rate ratio, the viscosity ratio, the density ratio, and the total flow rate. Therefore, the proposed model results a practical tool for the design and optimization of different applications based on flow focusing. Fil: Giorello, Antonella. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Minetti, Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina Fil: Nicastro, Alcides. Lipomize S.r.l.; Argentina Fil: Berli, Claudio Luis Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina

International audience; Context. Characterization of the internal structure of the superclusters of galaxies (walls, filaments, and knots where the clusters are located) is crucial for understanding the formation of the large-scale structure and for outlining the environment where galaxies evolved in the last few gigayears.Aims. We aim to detect the compact regions of high relative density (clusters and rich groups of galaxies), to map the elongated structures of low relative density (filaments, bridges, and tendrils of galaxies), and to characterize the galaxies that populate the filaments and study the environmental effects they are subject to.Methods. We used optical galaxies with spectroscopic redshifts from the SDSS-DR13 inside rectangular boxes encompassing the volumes of a sample of 46 superclusters of galaxies up to z = 0.15. A virial approximation was applied to correct the positions of the galaxies in the redshift space for the “finger of God” projection effect. Our methodology implements different classical pattern recognition and machine-learning techniques (Voronoi tessellation, hierarchical clustering, graph-network theory, and minimum spanning trees, among others), pipelined in the Galaxy System-Finding algorithm and the Galaxy Filament-Finding algorithm.Results. In total, we detected 2705 galaxy systems (clusters and groups, of which 159 are new) and 144 galaxy filaments in the 46 superclusters of galaxies. The filaments we detected have a density contrast of above 3, with a mean value of around 10, a radius of about 2.5 h70−1 Mpc, and lengths of between 9 and 130 h70−1 Mpc. Correlations between the galaxy properties (mass, morphology, and activity) and the environment in which they reside (systems, filaments, and the dispersed component) suggest that galaxies closer to the skeleton of the filaments are more massive by up to 25% compared to those in the dispersed component; 70% of the galaxies in the filament region present early-type morphologies and the fractions of active galaxies (both AGNs and star-forming galaxies) seem to decrease as galaxies approach the filament.Conclusions. Our results support the idea that galaxies in filaments are subject to environmental effects leading them to be more massive (probably due to larger rates of both merging and gas accretion), less active both in star formation and nuclear activity, and prone to the density–morphology relation. These results suggest that preprocessing in large-scale filaments could have significant effects on galaxy evolution.Key words: galaxies: groups: general / galaxies: clusters: general / large-scale structure of Universe / methods: data analysis / galaxies: evolution⋆ Full Table 4 is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/637/A31

We validate the chromo-dynamic multi-component lattice Boltzmann equation (MCLBE) simulation for immiscible fluids with a density contrast against analytical results for complex flow geometries, with particular emphasis on the fundamentals of the method, i.e. compliance with inter-facial boundary conditions of continuum hydrodynamics. To achieve the necessary regimes for the chosen validations, we develop, from a three-dimensional, axially-symmetric flow formulation, a novel, two-dimensional, pseudo Cartesian, MCLBE scheme. This requires the inclusion in lattice Boltzmann methodology of a continuously distributed source and a velocity-dependent force density (here, the metric force terms of the cylindrical Navier–Stokes equations). Specifically, we apply our model to the problem of flow past a spherical liquid drop in Re = 0, Ca regime and, also, flow past a lightly deformed drop. The resulting simulation data, once corrected for the simulation’s inter-facial micro-current (using a method we also advance herein, based on freezing the phase field) show good agreement with theory over a small range of density contrasts. In particular, our data extend verified compliance with the kinematic condition from flat (Burgin et al 2019 Phys. Rev. E 100 043310) to the case of curved fluid–fluid interfaces. More generally, our results indicate a route to eliminate the influence of the inter-facial micro-current.

We conduct a thorough investigation into the possibility that residing in an overdense region of the Universe may induce bias in measurements of the large-scale structure. We compute the conditional correlation function and angular power spectrum of density and lensing fluctuations while holding the local spherically averaged density fixed and show that for Gaussian fields this has no effect on the angular power at $l>0$. We identify a range of scales where a perturbative approach allows analytic progress to be made, and we compute leading-order conditional power spectra using an Edgeworth expansion and second-order perturbation theory. We find no evidence for any significant bias to cosmological power spectra from our local density contrast. We show that when smoothed over a large region around the observer, conditioning on the local density typically affects density power spectra by less than a percent at cosmological distances, below cosmic variance. We find that while typical corrections to the lensing angular power spectrum can be at the 10% level on the largest angular scales and for source redshifts $z_s \lesssim 0.1$, for the typical redshifts targeted by upcoming wide imaging surveys the corrections are sub-percent and negligible, in contrast to previous claims in the literature. Using an estimate of the local spherically averaged density from a composite galaxy redshift catalogue we find that the corrections from conditioning on our own local density are below cosmic variance and subdominant to other non-linear effects. We discuss the potential implications of our results for cosmology and point out that a measurement of the local density contrast may be used as a consistency test of cosmological models., 20 pages, 10 figures. Added new Figure 9 showing (mild) dependence on smoothing scale. Minor changes to match version published in Physical Review D

In this paper the development of a physically consistent phase-field theory of solidification shrinkage is presented. The coarse-grained hydrodynamic equations are derived directly from the N-body Hamiltonian equations in the framework of statistical physics, while the constitutive relations are developed in the framework of the standard Phase-field Theory, by following the variational formalism and the principles of non-equilibrium thermodynamics. To enhance the numerical practicality of the model, quasi-incompressible hydrodynamic equations are derived, where sound waves are absent (but density change is still possible), and therefore the time scale of solidification is accessible in numerical simulations. The model development is followed by a comprehensive mathematical analysis of the equilibrium and propagating 1-dimensional solid-liquid interfaces for different density-phase couplings. It is shown, that the fluid flow decelerates/accelerates the solidification front in case of shrinkage/expansion of the solid compared to the case when no density contrast is present between the phases. Furthermore, such a free energy construction is proposed, in which the equilibrium planar phase-field interface is independent from the density-phase coupling, and the equilibrium interface represents an exact propagating planar interface solution of the quasi-incompressible hydrodynamic equations. Our results are in excellent agreement with previous theoretical predictions., 18 pages, 5 figures, submitted to the Journal of Physics: Condensed Matter

In this work we study the growth of cold dark matter density perturbations in the nonlinear regime on a conformally coupled quintessence model in which the background is designed to mimic a $\Lambda$CDM cosmology. The spherical collapse of overdense regions is analyzed. We highlight the role of the coupling on the overall dynamics, trace the evolution of the density contrast throughout the cosmic history and compute perturbative parameters such as the critical density contrast. We find that the coupling has the influence of delaying the collapse due to the slower growth of matter perturbations. We follow to compute the cluster number counts using the Press-Schechter and Sheth-Tormen mass functions. In both cases, the transfer of energy between the dark energy field and dark matter suppresses the number of objects at low redshifts and enhances the number at high redshifts. Finally, we compute the expected cluster number counts for the future eROSITA mission and the current South Pole Telescope survey., Comment: 11 pages, 9 figures. V2: Matches published version

International audience; The continuous spontaneous localization model solves the measurement problem of standard quantum mechanics by coupling the mass density of a quantum system to a white-noise field. Since the mass density is not uniquely defined in general relativity, this model is ambiguous when applied to cosmology. We however show that most natural choices of the density contrast already make current measurements of the cosmic microwave background incompatible with other laboratory experiments.

Muography or muon radiography is a non-invasive emerging image technology relying on high energy atmospheric muons, which complements other standard geophysical tools to understand the Earth’s subsurface.\ud \ud This work discusses a geophysical inversion methodology for volcanic muography, based on the Simulated Annealing algorithm, using a semi-empirical model of the muon flux to reach the volcano topography and a framework for the energy loss of muons in rock.\ud \ud The Metropolis-Simulated-Annealing algorithm starts from an “observed” muon flux and obtains the best associated inner density distribution function inside a syntetic model of the Cerro Machín Volcano (Tolima-Colombia). The estimated initial density model was obtained with GEOMODELER, adapted to the volcano topography. We improved this model by including rock densities from samples taken from the crater, the dome and the areas associated with fumaroles.\ud \ud In this paper we determined the minimum muon energy (a function of the arrival direction) needed to cross the volcanic building, the emerging integrated flux of muons, and the density profile inside a model of Cerro Machin. The present inversion correctly reconstructed the density differences inside the Machín, within a 1% error concerning our initial simulation model, giving a remarkable density contrast between the volcanic duct, the encasing rock and the fumaroles area.

We investigate the turbulence driving mode of ionizing radiation from massive stars on the surrounding interstellar medium (ISM). We run hydrodynamical simulations of a turbulent cloud impinged by a plane-parallel ionization front. We find that the ionizing radiation forms pillars of neutral gas reminiscent of those seen in observations. We quantify the driving mode of the turbulence in the neutral gas by calculating the driving parameter $b$, which is characterised by the relation $\sigma_s^2 = \ln({1+b^2\mathcal{M}^2})$ between the variance of the logarithmic density contrast $\sigma_s^2$ (where $s = \ln({\rho/\rho_0})$ with the gas density $\rho$ and its average $\rho_0$), and the turbulent Mach number $\mathcal{M}$. Previous works have shown that $b\sim1/3$ indicates solenoidal (divergence-free) driving and $b\sim1$ indicates compressive (curl-free) driving, with $b\sim1$ producing up to ten times higher star formation rates than $b\sim1/3$. The time variation of $b$ in our study allows us to infer that ionizing radiation is inherently a compressive turbulence driving source, with a time-averaged $b\sim 0.76 \pm 0.08$. We also investigate the value of $b$ of the pillars, where star formation is expected to occur, and find that the pillars are characterised by a natural mixture of both solenoidal and compressive turbulent modes ($b\sim0.4$) when they form, and later evolve into a more compressive turbulent state with $b\sim0.5$--$0.6$. A virial parameter analysis of the pillar regions supports this conclusion. This indicates that ionizing radiation from massive stars may be able to trigger star formation by producing predominately compressive turbulent gas in the pillars., Comment: 10 pages, 6 figures. Accepted for publication in MNRAS

International audience; Magmatic reservoirs located in the upper crust have been shown to result from the repeated intrusions of new magmas, and spend much of the time as a crystal-rich mush. The geometry of the intrusion of new magmas may greatly affect the thermal and compositional evolution of the reservoir. Despite advances in our understanding of the physical processes that may occur in a magmatic reservoir, the resulting architecture of the composite system remains poorly constrained. Here we performed numerical simulations coupling a computational fluid dynamics and a discrete element method in order to illuminate the geometry and emplacement dynamics of a new intrusion into mush and the relevant physical parameters controlling it. Our results show that the geometry of the intrusion is to first order controlled by the density contrast that exists between the melt phases of the intrusion and resident mush rather than the bulk density contrast as is usually assumed. When the intruded melt is denser than the host melt, the intrusion pounds at the base of the mush and emplaced as a horizontal layer. The occurrence of Rayleigh-Taylor instability leading to the rapid ascent of the intruded material through the mush was observed when the intruded melt was lighter than the host one and was also unrelated to the bulk density contrast. In the absence of density contrasts between the two melt phases, the intrusion may fluidize the host crystal network and slowly ascend through the mush. The effect of the viscosity contrast between the intruded and host materials was found to have a lesser importance on the architecture of intrusions in a mush. Analyzing the eruptive sequence of well documented eruptions involving an intrusion as the trigger shows a good agreement with our modeling results, highlighting the importance of specifically considering granular dynamics when evaluating magmas and mush physical processes.

We present a detailed study of the collapse of a spherical matter overdensity and the non-linear growth of large scale structures in the Galileon ghost condensate (GGC) model. This model is an extension of the cubic covariant Galileon (G3) which includes a field derivative of type $(\nabla_\mu\phi\nabla^\mu\phi)^2$ in the Lagrangian. We find that the cubic term activates the modifications in the main physical quantities whose time evolution is then strongly affected by the additional term. Indeed, the GGC model shows largely mitigated effects in the linearised critical density contrast, non-linear effective gravitational coupling and the virial overdensity with respect to G3 but still preserves peculiar features with respect to the standard $\Lambda$CDM cosmological model, e.g. both the linear critical density contrast and the virial overdensity are larger than those in $\Lambda$CDM. The results of the spherical collapse model are then used to predict the evolution of the halo mass function, non-linear matter and lensing power spectra. While at low masses the GGC model presents about 10% fewer objects with respect to $\Lambda$CDM, at higher masses for $z>0$ it predicts 10% ($z=0.5$)-20% ($z=1$) more objects per comoving volume. Using a phenomenological approach to include the screening effect in the matter power spectrum, we show that the difference induced by the modifications of gravity are strongly dependent on the screening scale and that differences can be up to 20% with respect to $\Lambda$CDM. These differences translate to the lensing power spectrum where qualitatively the largest differences with respect to the standard cosmological model are for $\ell, Comment: 15 pages, 11 figures, 2 tables. Figures 8, 9 and 10 updated; new figure 11 added. Extended discussion in Sections 6 and 7. Matches the PDU journal version

The results of the study of the large-scale distribution of galaxies up to z ~0.8 in the field HS 47.5-22 on the basis of photometric data of the 1-meter Schmidt telescope of the BAO NAS Armenia are presented. The full sample contains 28,398 galaxies. Candidates for large-scale structures were determined using two independent methods for reconstructing density contrast maps in 57 narrow slices of the three-dimensional distribution of galaxies: adaptive aperture algorithm with smoothing and 2D Voronoi tessellation. We have identified more than 250 statistically significant overdense structures. The obtained results demonstrate a wide range of overdense structures over the full range of redshifts up to z ~0.8., Comment: Accepted for publication in Astrophysical Bulletin, 16 pages, 14 figures, 2 tabels

International audience; Predicting the instabilities that occur during the chemical reaction between a percolating fluid and a soluble rock leading to the development of macroscopic channels called wormholes is a key for understanding many geological processes. Their shape and their spatial distribution depend on two dimensionless numbers, namely Damköhler (Da) and Péclet (Pe) numbers. Although the dissolution phenomenon has been extensively studied both in the context of acid stimulation of oil wells in carbonate rocks and carbon capture and storage, few works have focused on the influence of the physical properties of fluids on wormhole patterns. Consequently, through interpretation of images acquired during the injection of pure water into a 2D reconstituted salt massif and considering different configurations of injection, we illustrate the buoyancy effects on wormhole formation. Contrarily to observation in fractures, experimental results suggest that dissolution regimes can still be described by the classical dimensionless numbers Da and Pe. As for the regime diagram, it remains practically unchanged for strong Péclet and weak Damköhler and undergoes a slow down of the propagation of the dissolution front when the number of Richardson's increases. Analysis of morphological descriptors such as area, interface and tortuosity shows that density contrast has an influence on intermediate to high‐Richardson dissolution regimes that may be explained by the existence of buoyancy effects.

We study the reconstruction of overdensity maps of galaxies as function of redshift in the range $0 < \mathrm z < 0.8$ using data from 1-m Schmidt Telescope of Byurakan Astrophysical Observatory (Armenia) in 16 medium band $\sim 250$ A and four broad band (u,g,r,i) filters. The data used in this work homogeneously cover $2.39$ sq. deg with accurate photometric redshiftss, down to $\mathrm R < 23$ mag (AB). We reconstructed the density contrast maps for the whole galaxy sample of the HS 47.5-22 ROSAT field in narrow slices for full range of redshifts. We select groups and clusters of galaxies with adaptive kernel based on density peaks which are larger than two times the mean density. The reconstructed overdensity field of galaxies consists of cluster-like structures outlining void-like regions for full redshift range $0 \leq \mathrm z \leq 0.8$. We detect known galaxy clusters in this field with software specially developed for this project. This gives us a possibility to study how star formation properties and galaxy morphology depend on the environments of the galaxies in this field., 13 pages, 7 figures, 1 Table

This study investigates the feasibility of using potential field (magnetic and gravity) data for geophysical exploration of sodium sulfate (salt-cake) resources; more specifically glauberite (sodium sulfate) and Eugsterite (sodium calcium sulfate) are two prevalent minerals of the Garmab mine in Semnan province, Iran. The geophysical data were collected on several profiles perpendicular to geological structures of the area and the residual magnetic and gravity maps were generated. Based on the magnetic susceptibility and density measurements of ore and waste samples, the areas identified by low magnetic and high gravity anomalies were associated with high potential zones for glauberite mineralization . Three-dimensional inversion of potential field data was applied to the residual data, leading to a petrophysical model of the magnetic susceptibility and density contrast of sought salt rocks . We found that the ore bodies could be successfully characterized by low-susceptibility and high-density. In this paper, the susceptibility and density models from inversion are consistent with the geological and drilling data. Results of the integrated application of magnetic and gravity data can be used to delineate sodium sulfate prospects as well.

In terrestrial studies, Bouguer gravity data is routinely computed by adopting various numerical schemes, starting from the most basic concept of approximating the actual topography by an infinite Bouguer plate, through adding a planar terrain correction to account for a local/regional terrain geometry, to more advanced schemes that involve the computation of the topographic gravity correction by taking into consideration a gravitational contribution of the whole topography while adopting a spherical (or ellipsoidal) approximation. Moreover, the topographic density information has significantly improved the gravity forward modeling and interpretations, especially in polar regions (by accounting for a density contrast of polar glaciers) and in regions characterized by a complex geological structure. Whereas in geodetic studies (such as a gravimetric geoid modeling) only the gravitational contribution of topographic masses above the geoid is computed and subsequently removed from observed (free-air) gravity data, geophysical studies focusing on interpreting the Earth’s inner structure usually require the application of additional stripping gravity corrections that account for known anomalous density structures in order to reveal an unknown (and sought) density structure or density interface. In planetary studies, numerical schemes applied to compile Bouguer gravity maps might differ from terrestrial studies due to two reasons. While in terrestrial studies the topography is defined by physical heights above the geoid surface (i.e., the geoid-referenced topography), in planetary studies the topography is commonly described by geometric heights above the geometric reference surface (i.e., the geometric-referenced topography). Moreover, large parts of a planetary surface have negative heights. This obviously has implications on the computation of the topographic gravity correction and consequently Bouguer gravity data because in this case the application of this correction not only removes the gravitational contribution of a topographic mass surplus, but also compensates for a topographic mass deficit. In this study, we examine numerically possible options of computing the topographic gravity correction and consequently the Bouguer gravity data in planetary applications. In agreement with a theoretical definition of the Bouguer gravity correction, the Bouguer gravity maps compiled based on adopting the geoid-referenced topography are the most relevant. In this case, the application of the topographic gravity correction removes only the gravitational contribution of the topography. Alternative options based on using geometric heights, on the other hand, subtract an additional gravitational signal, spatially closely correlated with the geoidal undulations, that is often attributed to deep mantle density heterogeneities, mantle plumes or other phenomena that are not directly related to a topographic density distribution.

In this study, we measure the response of matter and halo projected power spectra $P^{\rm 2D}_{\rm XY}(k)$ (X, Y are matter and/or halos), to a large-scale density contrast, $\delta_{\rm b}$, using separate universe simulations. We show that the fractional response functions, i.e., $\mathrm{d}\ln P^{\rm 2D}_{\rm XY}(k)/\mathrm{d}\delta_{\rm b}$, are identical to their respective three-dimensional power spectra within simulation measurement errors. Then, using various $N$-body simulation combinations (small-box simulations with periodic boundary conditions and sub-volumes of large-box simulations) to construct {mock observations of projected fields}, we study how super-survey modes, in both parallel and perpendicular directions to the projection direction, affect the covariance matrix of $P^{\rm 2D}_{\rm XY}(k)$, known as super-sample covariance (SSC). Our results indicate that the SSC term provides dominant contributions to the covariances of matter-matter and matter-halo spectra at small scales but does not provide significant contributions in the halo-halo spectrum. We observe that the large-scale density contrast in each redshift shell causes most of the SSC effect, and we did not observe a SSC signature arising from large-scale tidal field within the levels of measurement accuracy. We also develop a response approach to calibrate the SSC term for cosmic shear correlation function and galaxy--galaxy weak lensing, and validate the method by comparison with the light-cone ray-tracing simulations. Our method provides a reasonably accurate, albeit computationally inexpensive, way to calibrate the covariance matrix for clustering observables available from wide-area galaxy surveys., Comment: 26 pages, 11 figures, accepted for publication in MNRAS

We present an experimental and theoretical analysis of non-Boussinesq inertial (large Reynolds number flow) gravity currents (GCs) flowing in rectangular cross-sections. Attention is focused on the effects of the open upper boundary, which become pronounced when the density contrast between the current and the ambient is significant (non-Boussinesq case). The study is conducted deriving first a two-layer shallow-water (SW) model for the release of a constant fluid volume into an ambient of given height with a free-surface boundary condition, with an arbitrary density ratio r between the ambient and the intruding fluid. The jump conditions at the front are provided by the novel extension of Benjamin (1968) analysis , subject to energy-dissipation and sub-critical speed requests, as detailed in Ungarish (2017). The resulting SW lock-release problem is solved via a finite difference approach. Lock-release experiments are then conducted in this configuration with r = 0.837 − 0.950 , full-depth and part-depth locks, and two different lock lengths. Experimental results obtained for the front position and speed of the intruding current, its thickness, and the free-surface depression of the ambient fluid (a signature of these experiments marking the position of the intruding front) agree, to various degrees, with their theoretical counterparts, with a better agreement for the front position and depression than for the other quantities, but demonstrating in all cases the consistency of the trend. Some of the experiments were repeated with a top-lid boundary condition, to discern its effect on the current propagation. These effects turn out to be relatively minor except for the obvious absence of interface-height depression. The range of density ratio r examined is further extended by conducting a numerical simulations with r = 0.7 using a numerical commercial Computational Fluid Dynamics code (CFD) based on Reynolds Averaged Navier-Stokes equations (RANS). A comparison among SW theory, experiments, and the numerical simulations is conducted in terms of the trough behind the current nose, leading to an overestimation of theoretical results with respect to experiments. The length of the through adequately scales with the lock-length.

The determination of the oceanic Moho (or crust-mantle) density contrast derived from seismic acquisitions suffers from severe lack of data in large parts of the oceans, where have not yet been sufficiently covered by such data. In order to overcome this limitation, gravitational field models obtained by means of satellite altimetry missions can be proficiently exploited, as they provide global uniform information with a sufficient accuracy and resolution for such a task. In this article, we estimate a new Moho density contrast model named MDC2018, using the marine gravity field from satellite altimetry in combination with a seismic-based crustal model and Earth’s topographic/bathymetric data. The solution is based on the theory leading to Vening Meinesz-Moritz’s isostatic model. The study results in a high-accuracy Moho density contrast model with a resolution of 1° × 1° in oceanic areas. The numerical investigations show that the estimated density contrast ranges from 14.2 to 599.7 kg/m3 with a global average of 293 kg/m3. In order to evaluate the accuracy of the MDC2018 model, the result was compared with some published global models, revealing that our altimetric model is able to image rather reliable information in most of the oceanic areas. However, the differences between this model and the published results are most notable along the coastal and polar zones, which are most likely due to that the quality and coverage of the satellite altimetry data are worsened in these regions.

This research proposes a novel three-dimensional gravity inversion based on sparse recovery in compress sensing. Zero norm is selected as the objective function, which is then iteratively solved by the approximate zero norm solution. The inversion approach mainly employs forward modeling; a depth weight function is introduced into the objective function of the zero norms. Sparse inversion results are obtained by the corresponding optimal mathematical method. To achieve the practical geophysical and geological significance of the results, penalty function is applied to constrain the density values. Results obtained by proposed provide clear boundary depth and density contrast distribution information. The method’s accuracy, validity, and reliability are verified by comparing its results with those of synthetic models. To further explain its reliability, a practical gravity data is obtained for a region in Texas, USA is applied. Inversion results for this region are compared with those of previous studies, including a research of logging data in the same area. The depth of salt dome obtained by the inversion method is 4.2 km, which is in good agreement with the 4.4 km value from the logging data. From this, the practicality of the inversion method is also validated.

A microgravity investigation on bedrock topography was conducted at Maluri Park in Kuala Lumpur, Malaysia. The study characterized the subsurface structure to delineate soil structure for the geotechnical application. Cross-section modelling of the residual anomaly generated the Maluri Bouguer Anomaly model for test site. The 2D microgravity models produced the contour map, displaying the characterization due to density contrast in rock types while mapping the subsurface geological structure at different depths. Moreover, a synthetic model was initiated with the assumption of lateral distance on the left and right sides taken at 50 m and a depth of 60 m. The results of modeling confirmed that the soil and rock type composition on models test site, i.e: topsoil (1.1 g/cm3), soil (1.8 g/cm3), clay (1.63 g/cm3), gravel (2.0 g/cm3), sand (1.7 g/cm3), shale (2.40 g/cm3), sandstone (2.76 g/cm3) and limestone (2.9 g/cm3). The 2D gravity synthetic model show a good match with the observed microgravity data.

We consider an all-sky sample of 1029 Local Volume (LV) galaxies situated within a distance of 11 Mpc. Their majority have precise distances, estimates of hydrogen mass fraction and star-formation rate derived from far-ultraviolet or Halpha fluxes. To describe an environment, we attribute two dimensionless values: the density contrast created by the most significant neighbour and the local density contrast produced by all neighbours within a separation of 1 Mpc. The hydrogen mass fraction exhibits a weak effect of HI deficiency being the most pronounced for dwarf irregular galaxies. The specific star-formation rate (sSFR) is more sensitive to the environment than the hydrogen mass fraction. Almost all (99 per cent) LV galaxies have their sSFR below -9.4 dex (1/yr). We notice that irregular dwarfs as well as late-type bulgeless galaxies are capable to reproduce their stellar mass with the observed sSFR over the cosmic time. Thus, the transformation of gas into stars in dIrs and spiral disks is rather sluggish unlike that in E, S0, dSph galaxies, whose star-formation history has been stormy and short. Scatter of SFR(Halpha)-to-SFR(FUV) ratio increases from Sc, Sd, Sm galaxies towards BCD, Im, Ir types that favours the idea of bursty star formations in low-mass galaxies. However, this bursty activity is caused rather by internal processes than by an external tidal action. A fraction of quenched E, S0, dSph galaxies increases from ~5 per cent in the field up to ~50 per cent in the densest regions., Comment: 22 pages, 12 figures; accepted for publication in MNRAS

Observations by the New Horizons spacecraft have determined that Pluto has a larger bulk density than Charon by 153 ± 44 kg m − 3 (2σ uncertainty). We use a thermal model of Pluto and Charon to determine if this density contrast could be due to porosity variations alone, with Pluto and Charon having the same bulk composition. We find that Charon can preserve a larger porous ice layer than Pluto due to its lower gravity and lower heat flux but that the density contrast can only be explained if the initial ice porosity is ≳ 30%, extends to ≳100 km depth and Pluto retains a subsurface ocean today. We also find that other processes such as a modern ocean on Pluto, self-compression, water-rock interactions, and volatile (e.g., CO) loss cannot, even in combination, explain this difference in density. Although an initially high porosity cannot be completely ruled out, we conclude that it is more probable that Pluto and Charon have different bulk compositions. This difference could arise either from forming Charon via a giant impact, or via preferential loss of H2O on Pluto due to heating during rapid accretion.

We present general closed-form solutions for the vertical gravitational anomaly caused by a polyhedral prism with mass density contrast varying with depth. Our equations are the first ones to imple ...

Using Non-equilibrium Molecular Dynamics (NEMD) simulations, we study the statistical properties of an atomic fluid undergoing planar Couette flow, in which particles interact via a Lennard-Jones potential. We draw a connection between local density contrast and temporal fluctuations in the shear stress, which arise naturally through the equivalence between the dissipation function and entropy production according to the fluctuation theorem. We focus on the shear stress and the spatio-temporal density fluctuations and study the autocorrelations and spectral densities of the shear stress. The bispectral density of the shear stress is used to measure the degree of departure from a Gaussian model and the degree of nonlinearity induced in the system owing to the applied strain rate. More evidence is provided by the probability density function of the shear stress. We use the Information Theory to account for the departure from Gaussian statistics and to develop a more general probability distribution function that captures this broad range of effects. By accounting for negative shear stress increments, we show how this distribution preserves the violations of the Second Law of Thermodynamics observed in planar Couette flow of atomic fluids, and also how it captures the non-Gaussian nature of the system by allowing for non-zero higher moments. We also demonstrate how the temperature affects the band-width of the shear-stress and how the density affects its Power Spectral Density, thus determining the conditions under which the shear-stress acts is a narrow-band or wide-band random process. We show that changes in the statistical characteristics of the parameters of interest occur at a critical strain rate at which an ordering transition occurs in the fluid causing shear thinning and affecting its stability. A critical strain rate of this kind is also predicted by the Loose–Hess stability criterion.

Knowledge of isostasy provides insights into how excess (or deficit) of mass on and within the lithosphere is maintained over different time scales, and also helps decipher the vertical dynamics. In continental regions, isostasy is primarily manifested as a crustal root, the extent of which is defined by the lithospheric strength and the density contrast at the Moho. In this study, we briefly review the methodology for extracting the density contrast across the Moho using the amplitudes of the P-to-s converted and free-surface reverberating phases in a receiver function (RF). We test the efficacy of this technique by applying it on synthetic and real data from 10 broadband seismic stations sited on diverse tectonic provinces in the Indian shield. We determine the density contrast after parameterizing the shear-wave velocity structure beneath the stations using the nearest neighbourhood algorithm. We find considerable variation in the density contrast across the Moho beneath the stations (0.4–0.65 gm/cc). This is explained in terms of isostatic compensation, incorporating the existing estimates of lithospheric strength (Te). Crustal roots computed using the estimated Te and the deduced density contrast substantiate the crustal thickness values inferred through RF analysis, and vice versa. This illustrates isostasy as a combination of variation in density contrast and Te. The density contrasts and crustal thicknesses inferred from RF analysis explain well the isostatic compensation mechanism in different regions. However, unusually large density contrasts (∼0.6 gm/cc) corresponding to elevated regions are intriguing and warrant further investigations. Our observation of varied density contrasts at the Moho in a Precambrian continental setting is interesting and raises a question about the existence of such situations in other parts of the world.

Gravity data analysis and interpretation are based, among others, on their spatial variation represented by horizontal and vertical gradients. The gradient or derivative of a gravity field can be calculated either in the spatial domain or the wave-number domain. Historically, the second vertical derivative (SVD) of gravity data can be used to delineate the boundaries of anomalous sources. This paper addresses inappropriate use of the SVD of gravity data, with reference to current practices in Indonesia. The SVD's relative magnitude along a profile is widely used to define whether a density contrast and its dipping orientation correspond to a normal or reverse fault, which may be geologically incorrect. Furthermore, the SVD is calculated by approximation using the horizontal derivative, which may be erroneous especially with poorly distributed data and anomalous 3D sources. We exemplify our analysis with synthetic data and propose a more appropriate spectral-based analysis using field data.

We investigate the clustering effect of dark energy (DE) in the formation of galaxy clusters using the spherical collapse model. Assuming a fully clustered DE component, the spherical overdense region is treated as an isolated system which conserves the energy separately for both matter and DE inside the spherical region. Then, by introducing a parameter r to characterize the degree of DE clustering, which is defined by the nonlinear density contrast ratio of matter to DE at turnaround in the recollapsing process, i.e. r ≡ δ de , ta NL ∕ δ m , ta NL , we are able to uniquely determine the spherical collapsing process and hence obtain the virialized overdensity Δ vir through a proper virialization scheme. Estimation of the virialized overdensities from current observation on galaxy clusters suggests that 0 . 5 r 0 . 8 at 1 σ level for the clustered DE with w − 0 . 9 . Also, we compare our method to the linear perturbation theory that deals with the growth of DE perturbation at early times. While both results are consistent with each other, our method is practically simple and it shows that the collapse process is rather independent of initial DE perturbation and its evolution at early times.

This work presents an integrated application of potential field data to discover potash-bearing evaporite sources in Aji-Chai salt deposit, located in east Azerbaijan province, northwest of Iran. Low density and diamagnetic effect of salt minerals, i.e. potash, give rise to promising potential field anomalies that assist to localize sought blind targets. The halokinetic-type potash-bearing salts in the prospect zone have flowed upward and intruded into surrounded sedimentary sequences dominated frequently by marl, gypsum and alluvium terraces. Processed gravity and magnetic data delineated a main potash source with negative gravity and magnetic amplitude responses. To better visualize these evaporite deposits, 3D model of density contrast and magnetic susceptibility was constructed through constrained inversion of potential field data. A mixed-norm regularization technique was taken into account to generate sharp and compact geophysical models. Since tectonic pressure causes vertical movement of the potash in the studied region, a simple vertical cylindrical shape is an appropriate geometry to simulate these geological targets. Therefore, structural index (i.e. decay rate of potential field amplitude with distance) of such assumed source was embedded in the inversion program as a geometrical constraint to image these geologically plausible sources. In addition, the top depth of the main and the adjacent sources were estimated 39 m and 22 m, respectively, via the combination of the analytic signal and the Euler deconvolution techniques. Drilling result also indicated that the main source of potash starts at a depth of 38 m. The 3D models of the density contrast and the magnetic susceptibility (assuming a superficial sedimentary cover as a hard constraint in the inversion algorithm) demonstrated that potash source has an extension in depth less than 150 m.

Gravity anomalies in parts of the Niger Delta region, Nigeria, were investigated through the interpretation of aerogarvity data with the objectives to determine the thickness of the sedimentary basin, establish the basement topography, density contrasts and the geological models which will give information about variation of geological structures. Four sheets of digital airborne gravity data were used for the study. Source parameter imaging (SPI), Standard Euler deconvolution and forward and inverse modeling techniques were employed in quantitative interpretation. The Bouguer anomaly of the study area varied from -20.0 to 37.7 mGal, while the residual Bouguer anomaly varied from -19.6 to 25.7 mGal. The SPI gave depth values ranging from -539.7 to -4276.0 m for shallow and deep lying gravity anomalous bodies. The windowed Euler-3D for Bouguer gravity result revealed the depth range of 1355.5 to -1518.1 m for structural index of one; 2384.5 to -3283.2 m for structural index of two and 2426.0 to -5011 m for structural index of three. The forward and inverse modeling gave the density values for the modeled profiles 1, 2, 3, 4 and 5 as 1.820, 2.410, 0.720, 2.310 and 2.100 gcm-3, respectively, with their respective depths of 3872, 4228, 4880, 3560 and 2527 m. The results from this study have shown that the depth to basement and density contrast have influence on the petroleum/hydrocarbon accumulation. Key words: Aerogravity, basement, density contrast, sedimentary.