Density Inversion Research Articles

Shock detachment and drag in hypersonic flow over wedges and circular cylinders

Abstract

Rayleigh-Bénard convection of a gas-vapor mixture with abnormal dependence of thermal expansion coefficient on temperature

In order to reveal basic characteristics of Rayleigh-Bénard convection (RBC) of a gas mixture, which has abnormal dependence of thermal expansion coefficient on temperature, we presented a direct numerical simulation on RBC of a gas mixture of oxygen and cyclohexane near its maximum density. The influences of the density inversion parameter and the Rayleigh (Ra) number on the critical conditions of the flow onset and destabilization were analyzed. The flow evolution with Ra was exhibited. The results show the critical value of Rayleigh number of the flow onset is approximately proportional to the fourth power of the thickness of the upper stable sublayer. Regardless of density inversion parameter, the flow pattern at the flow appearance always has a multicellular structure. With increasing Ra, the multicellular flow structure would be transformed into various steady flow patterns, including parallel flow and pendant pattern. When the density inversion parameter is small, the unsteady flow cells exhibit a back and forth motion along the border. However, at a large density inversion parameter, the cells swing around the centers of the flow rolls. We also found that the local Nusselt (Nu) number on the bottom depends on the flow pattern. The average Nu increases gradually with increasing Ra under a small density inversion parameter. However, an abrupt rise of the average Nu appeared under a large density inversion parameter.

Pedagogically fast model to evaluate and optimize passively Q-switched Nd-doped solid-state lasers.

The coupled rate equations with the spatial overlap effect for four-level passively Q-switched lasers are fully considered. A transcendental equation is derived for the residual fraction of the inversion density after the finish of the Q-switched pulse. Comprehensive calculations for the transcendental equation were executed to attain an analytical function for precisely fitting the residual fraction of the inversion density. With the fitting function, a pedagogical model with the correction for high output coupling is developed to straightforwardly analyze the output pulse energy and peak power. Detailed experiments are carried out to validate the model.

Off-shell diagrammatics for quantum gravity

This article reports on how diagrammatic identities of Yang–Mills theory translate to diagrammatics for pure gravity. For this, we consider the Einstein–Hilbert action and follow the approach of Capper, Leibbrandt, and Medrano and expand the inverse metric density around the Minkowski metric. By analogy to Yang–Mills theory, cancellation identities are constructed for the graviton as well as the ghost vertices up to the valency of six.

Density inversion of selected microgravity anomalies using L2-smoothing and minimum support focusing stabilizers

Interpretation and inversion of microgravity anomalies belong to important tasks of near-surface geophysics, mostly in cavities detection in engineering, environmental and archaeological applications. One of the mostly used concepts of inversion in applied gravimetry is based on the approximation of the model space by means of 2D or 3D elementary sources with the aim to estimate their densities by means of the solution of a corresponding linear equation system. There were published several approaches trying to obtain correct and realistic results, which describe real parameters of the sources. In the proposed contribution we analyse the properties of two additional functionals, which describe additional properties of the searched solution – namely so-called L2-smoothing and minimum support focusing stabilizers. For the inversion itself, we have used the regularized conjugate gradient method. We have studied properties of these two stabilizers in the case of one synthetic model and one real-world dataset (microgravity data from St. Nicholas church in Trnava). Results have shown that proposed algorithm with the minimum support stabilizer can generate satisfactory model results, from which we can describe real geometry, dimensions and physical properties of interpreted cavities.

Exploring the Variation Trend of Urban Expansion, Land Surface Temperature, and Ecological Quality and Their Interrelationships in Guangzhou, China, from 1987 to 2019

This study explored the model of urban impervious surface (IS) density, land surface temperature (LST), and comprehensive ecological evaluation index (CEEI) from urban centers to suburbs. The interrelationships between these parameters in Guangzhou from 1987 to 2019 were analyzed using time-series Landsat-5 TM (Thematic Mapper), Landsat-8 OLI (Operational Land Imager), and TIRS (Thermal Infrared Sensor) images. The urban IS densities were calculated in concentric rings using time-series IS fractions, which were used to construct an inverse S-shaped urban IS density function to depict changes in urban form and the spatio-temporal dynamics of urban expansion from the urban center to the suburbs. The results indicated that Guangzhou experienced expansive urban growth, with the patterns of urban spatial structure changing from a single-center to a multi-center structure over the past 32 years. Next, the normalized LST and CEEI in each concentric ring were calculated, and their variation trends from the urban center to the suburbs were modeled using linear and nonlinear functions, respectively. The results showed that the normalized LST had a gradual decreasing trend from the urban center to the suburbs, while the CEEI showed a significant increasing trend. During the 32-year rapid urban development, the normalized LST difference between the urban center and suburbs increased gradually with time, and the CEEI significantly decreased. This indicated that rapid urbanization significantly expanded the impervious surface areas in Guangzhou, leading to an increase in the LST difference between urban centers and suburbs and a deterioration in ecological quality. Finally, the potential interrelationships among urban IS density, normalized LST, and CEEI were also explored using different models. This study revealed that rapid urbanization has produced geographical convergence between several ISs, which may increase the risk of the urban heat island effect and degradation of ecological quality.

Electronic quantum coherence encoded in temporal structures of N2+ lasing

We experimently and theoretically investigate temporal structures of ${{\mathrm{N}}_{2}}^{+}$ lasing at the wavelengths of 391 and 428 nm. Our results show that the resonant interaction of a femtosecond laser with ${{\mathrm{N}}_{2}}^{+}$ ions with a picosecond dipole relaxation time will induce a long-lasting polarization, which exists in cases of both absorption and amplification of the external seed. The induced polarization will be amplified in population-inverted ${{\mathrm{N}}_{2}}^{+}$ ions, giving rise to the retarded radiation (i.e., ${{\mathrm{N}}_{2}}^{+}$ lasing). The temporal profile of the retarded radiation is closely related to the dipole relaxation time, population inversion density, and propagation length. The combined experimental and theoretical study reveals the physical origin of the retarded seed amplification in ${{\mathrm{N}}_{2}}^{+}$ ions.

Emergent Hierarchy Through Conductance-based Degree Constraints

The presence of hierarchy in many real-world networks is not yet fully understood. We observe that complex interaction networks are often coarse-grain models of vast modular networks, where tightly connected subgraphs are agglomerated into nodes for simplicity of representation and computational feasibility. The emergence of hierarchy in such growing complex networks may stem from one particular property of these ignored subgraphs: their graph conductance. Being a quantification of the main bottleneck of flow through the coarse-grain node, this scalar quantity implies a structural limitation and supports the consideration of heterogeneous degree constraints. The internal conductance values of the subgraphs are mapped onto integer degree restrictions, which we call internal bottlenecks, by using inverse cumulative density functions. This leads to a hidden variable model based on the rich-get-richer scheme. It is shown that imposing such restrictions generally leads to an increased measure of hierarchy and alters the tail of the degree distribution in a predictable way. Thus, a mechanism is provided whereby inherent limitations on network flow leads to hierarchical self-organization.

Hall Coefficient of Semimetals.

A recently developed formula for the Hall coefficient [A. Auerbach, Phys. Rev. Lett. 121, 066601 (2018)PRLTAO0031-900710.1103/PhysRevLett.121.066601] is applied to nodal line and Weyl semimetals (including graphene) and to spin-orbit split semiconductor bands in two and three dimensions. The calculation reduces to a ratio of two equilibrium susceptibilities, where corrections are negligible at weak disorder. Deviations from Drude's inverse carrier density are associated with band degeneracies, Fermi surface topology, and interband currents. Experiments which can measure these deviations are proposed.

Spatiotemporal patterns of cutaneous leishmaniasis in the district upper and lower Dir, Khyber Pakhtunkhwa, Pakistan: A GIS-based spatial approaches

While Cutaneous leishmaniasis (CL) is not a life-threatening disease, it leads to devastating effects on local community. CL is widely scattered manifesting a noticeable epidemiological pattern around the globe. The present study was planned to address the role of Geographic Information System (GIS) using CL clinico-epidemiological data to determine the high-risk areas of CL. Recorded data (2014-2018) of 3630 positive individuals was collected from Basic Health Units of the Upper and Lower Dir Districts, Khyber Pakhtunkhwa, Pakistan. Descriptive and statistical analysis was used for clinico-epidemiological characterization. For spatial analysis, ArcGIS V.10.3 was used and the CL average incidence was tagged on the proportional, choropleth, and digital elevation model maps. For focal transmission and high-risk zones, Inverse Density Weight (IDW) spatial interpolation, focal statistics, hot spot, cluster and outlier, and Bayesian geostatistical analysis were used. The trend of CL cases was elevated from 2014 to 2016 except for 2017 and 2018. Individuals of both genders younger than 20 years old were highly susceptible. Single lesions were more prominent (56%) and frequently affected facial parts (51%). The size and pretreatment duration of the CL lesion was significantly associated. Spatially, a choropleth map displayed the maximum CL incidences in Tehsil Balambat, Khal, and Termergara (31%-13%) located within a range of 948-1947m elevation in the central regions with proximal CL transmissions. Hot spot and cluster and outlier analysis affirmed that Tehsil Khal was the high-risk CL foci. The Bayesian geostatistical analysis revealed high temperature, less altitude, and annual precipitation as important risk factors. An increasing trend in CL transmission has become evident, affecting both genders and <20 years old children. GIS resolute the concealed CL hubs in the least elevated central regions which warrant the control strategies to restrict future epidemics.

3D Inversion modelling of gravity data integrated with aeromagnetic and GLDAS data for water storage tracing in Golden Triangular area, Central Eastern Desert, Egypt

The study area of Golden Triangular (South Wadi Qena “S.W. Qena”) area is located in the central Eastern Desert of Egypt, which is a promising area and it is between three towns (Safaga, Qena and El-Qosier). The Golden Triangle is one of the largest industrial society was built between Qena town and the Red Sea shoreline. So, this study focused on water storage tracing by GLDAS data with structure evaluation using gravity and aeromagnetic data. Moreover, detecting the basement surface and Precambrian Nubian sandstone depths by density inversion to determine which area is suitable for agricultural reclamation and has a good storage of water that will use for developing this area. Geophysical Data as Bouguer gravity and Aeromagnetic maps are used to achieve the aim of this study by clarifying the structure's evaluation of this area. The 3D density inversion modelling was built along the area. That explains the depth map of the relief basement surface, which increased in the west direction to − 3500 m and outcropped in the Red Sea shoreline. The depth of Precambrian Nubian sandstone, which parallel to the relief basement surface and increases in the west direction reached − 1700 m. The change in water storage during the last 20 years supported the charging information of aquifers and their locations. Therefore, the correlation between topography, structure map, basement surface and Precambrian Nubian sandstone depths maps suggests that the best location of aquifers in our study area in the NW and SE parts where the Precambrian Nubian sandstone depth is reached to − 1700 m.

On the Potential Optical Signature of Convective Turbulence over the West Florida Shelf

Atmospheric cold front propagation across the northern Gulf of Mexico is characterized by elevated surface wind velocities and a ~10–15 °C drop in surface air temperatures. These meteorological conditions result in significant heat energy losses from the surface ocean to the overlying atmosphere. These seasonally recurring cold-air outbreak events may penetrate the southern portion of the West Florida continental shelf and initiate turbulent and convective overturn of the water column. Examination of true color images derived from ocean-viewing, satellite-based radiometer data reveals coincident and substantial surface water discolorations that are optically similar to smaller-scale “whiting events,” despite the regional-scale extent of the observed phenomenon (&gt;25,000 km2). Coupled air–sea numerical simulations suggest the surface water discoloration occurs and is sustained where the entire water column is dynamically unstable. The simulation results indicate significant density (σt) inversions between the surface and bottom waters. Thus, the combined numerical model and remote sensing analysis suggest that convective turbulence may be contributing to the sustained ventilation of bottom waters containing a high concentration of suspended particulates. High-temporal resolution true color images rendered from the GOES-R Advanced Baseline Imager (ABI) data appear to support the surface water discoloration’s turbulent-driven nature.

Discrete singular convolution–polynomial chaos expansion method for free vibration analysis of non-uniform uncertain beams

This article enhances the discrete singular convolution method for free vibration analysis of non-uniform thin beams with variability in their geometrical and material properties such as thickness, specific volume (inverse of density) and Young’s modulus. The discrete singular convolution method solves the differential equation of motion of a structure with a high accuracy using a small number of discretisation points. The method uses polynomial chaos expansion to express these variabilities simulating uncertainty in a closed form. Non-uniformity is locally provided by changing the cross section and Young’s modulus of the beam along its length. In this context, firstly natural frequencies of deterministic uniform and non-uniform beams are predicted via the discrete singular convolution. These results are compared with finite element calculations and analytical solutions (if available) for the purpose of verification. Next, the uncertainty of the beam because of geometrical and material variabilities is modelled in a global manner by polynomial chaos expansion to predict probability distribution functions of the natural frequencies. Monte Carlo simulations are then performed for validation purpose. Results show that the proposed algorithm of the discrete singular convolution with polynomial chaos expansion is very accurate and also efficient, regarding computation cost, in handling non-uniform beams having material and geometrical variabilities. Therefore, it promises that it can be reliably applied to more complex structures having uncertain parameters.

Simultaneous inversion for S-wave velocity and density from the SV-SV wave

Knowledge of the S-wave velocity ([Formula: see text]) and density ([Formula: see text]) is essential for oil and gas reservoir detection and characterization. However, reliable recovery of both parameters, especially density, from the reflected PP-wave data is a difficult issue because this inverse problem is highly ill-conditioned. The reflected SV-SV wave is easier to process than the PS-wave, and it can provide better estimates of [Formula: see text] and [Formula: see text] than the PP-wave because it is more sensitive to these parameters than the PP-wave. I have developed a simultaneous inversion for [Formula: see text] and [Formula: see text] based on a modified approximation of the SV-SV wave reflection coefficient. The modified equation includes only two parameters (natural logarithms of [Formula: see text] and [Formula: see text]) to be inverted, and it has high accuracy even at large incident angles and for strong impedance contrasts. I find that simultaneous inversion based on the modified approximation is well-posed when using data of small-to-moderate incident angle (20o–30o) and that the misfit function can be easily regularized. The new simultaneous inversion method is applied to an SV-SV wave prestack data set acquired from a 2D nine-component survey. The field data example demonstrates that the new method can recover stable and high-resolution density and S-wave velocity information, which can be used to investigate rock mineral composition, porosity, and fluid content.

Application of an Improved Ultrasound Full-Waveform Inversion in Bone Quantitative Measurement

Inspired by the large number of applications for symmetric nonlinear equations, an improved full waveform inversion algorithm is proposed in this paper in order to quantitatively measure the bone density and realize the early diagnosis of osteoporosis. The isotropic elastic wave equation is used to simulate ultrasonic propagation between bone and soft tissue, and the Gauss–Newton algorithm based on symmetric nonlinear equations is applied to solve the optimal solution in the inversion. In addition, the authors use several strategies including the frequency-grid multiscale method, the envelope inversion and the new joint velocity–density inversion to improve the result of conventional full-waveform inversion method. The effects of various inversion settings are also tested to find a balanced way of keeping good accuracy and high computational efficiency. Numerical inversion experiments showed that the improved full waveform inversion (FWI) method proposed in this paper shows superior inversion results as it can detect small velocity–density changes in bones, and the relative error of the numerical model is within 10%. This method can also avoid interference from small amounts of noise and satisfy the high precision requirements for quantitative ultrasound measurements of bone.

Excitation energy and angular momentum dependence of the nuclear level density parameter around A≈110

Neutron kinetic energy spectra in coincidence with low-energy $\ensuremath{\gamma}$-ray multiplicities have been measured around $A\ensuremath{\approx}110$ in the $^{16}\mathrm{O}+^{93}\mathrm{Nb}$ and $^{20}\mathrm{Ne}+^{93}\mathrm{Nb}$ reactions in a compound nuclear excitation energy range of $\ensuremath{\approx}90--140$ MeV. The excitation energy (temperature) dependence and the angular momentum (spin) dependence of the inverse level density parameter $k$ have been investigated by comparing the experimental data with statistical Hauser-Feshbach calculations. In contrast to the available systematic in this mass region, the inverse level density parameter showed an appreciable increase as a function of the excitation energy. The extracted $k$ values at different angular momentum regions, corresponding to different $\ensuremath{\gamma}$ multiplicities, also showed an overall increase with the average nuclear spins. The experimental results have been compared with a microscopic statistical-model calculation and found to be in reasonable agreement with the data. The results provide useful information to understand the variation of nuclear level density at high temperature and spins.

A new software for gravity gradiometry data forwarding and inversion

A new software has been developed specially for gravity gradiometry data forwarding and joint inversion. It is developed with hybrid programming technique and some powerful function libraries, including language of Python and C, Matplotlib, PyQt and so on. The software could help the users with graphical user interface, implement the data import/export and some management, the simple visualization in 2/3 dimension, modeling for gravity exploration data, and 3D density inversion. One of the advantages of this software is combining the popular development techniques to make the research of the forwarding and inversion easily, another one is simple secondary development, which allows the users to add their algorithms to the platform. The software is mainly used for the teaching and scientific research purposes, suitable for the geophysical scientists, engineers and graduate student.

Research on the detection effect of microgravity method in urban mined-out area

The mined-out area is a potential geological hazard for urban safety. In particular, there are many mined-out areas in the Longgui nitrate mine in Guangzhou, which poses a serious threat to the safety of large-scale buildings in the city. Therefore, it is necessary to find out its specific spatial distribution location and center depth information. The micro-gravity detection method uses the residual density inversion and the re-focus weighted inversion method to identify the spatial distribution of urban underground goaf by observing the weak change of gravity field in the area The microgravity detection method combined with the effective processing and inversion interpretation method can realize the delineation of the specific distribution range and spatial distribution form of the cave in the goaf.

Structural signatures of the Amazonian Craton in eastern Colombia from gravity and magnetometry data interpretation

Geophysical interpretation of potential field data plays an important role in the integration of geological data. Estimation of density and magnetic susceptibility variations within the upper crust helps evaluating the continuity of geological structures in the field. In the present study we use gravity and magnetic data in NW Amazonian Craton in Colombia. Total horizontal gradient of the reduction to magnetic pole were used to delineate magnetic lineaments and domains showing four zones, each with its own features. Multiscale edge detection (worming) of the data help delineate upper crustal structures that we interpret as tectonic boundaries that correlate with the four zones identified. 3D density and magnetic susceptibility inversion showed high density and/or high magnetic susceptibility sources correlated with these crustal structures. Zone (1) is located south of the Guaviare River, with predominant NW-SE and NE-SW magnetic lineaments; zone (2), located from south of the Guaviare River to the north, present nearly E-W magnetic lineaments and a deep E-W edge interpreted as a possible shear zone parallel to Guaviare, Orinoco and Ventuari rivers; zone (3) from south of the Vichada River to the north, with NE-SW and NW-SE lineaments; N-S zone (4) cuts the zones (2) and (3), characterized by high density/magnetic susceptibility source bounded by N-S deep edges. A more complete tectonic evolution interpretation requires further work, but we speculate that the zone (4) could indicate an aborted rift/collision suture and that the zone (2) is indicative of a younger deformation event. Shear direction at (2) is not clear: geological maps show NEE-SWW right-lateral faulting, but geophysical anomalies suggest left-lateral displacement, highlighted by left dislocation of the Orinoco River. We also speculate that a N-S edge located at the SE of the area can be related with the Atabapo Belt and the limit of Ventuari-Tapajós and Rionegro geochronological provinces.

Modified prediction partitioning algorithm for Gaussian inverse Wishart probability hypothesis density filter using measurement labeling method

The Gaussian inverse Wishart probability hypothesis density filter is a promising approach for tracking multiple extended targets. However, if targets are closely spaced and performing maneuvers, the performance of a Gaussian inverse Wishart probability hypothesis density filter will decline. The reason for this is that the measurement partitioning approaches fail to provide accurate partitions, which influences the component updating process directly. This paper presents a modified prediction partitioning algorithm for the Gaussian inverse Wishart probability hypothesis density filter in order to solve the partitioning problem of closely spaced targets. The inaccuracy of the target prediction information occurred by target maneuvers leads to the above problem, thus a modified prediction partitioning algorithm will label the components and corresponding measurements to improve the prediction accuracy. Simulation results show that the use of modified prediction partitioning can improve the performance of a Gaussian inverse Wishart probability hypothesis density filter by providing more accurate partition results when targets are closely spaced and performing maneuvers.