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Gravity forward modeling as a basic tool has been widely used for topography correction and 3D density inversion. The source region is usually discretized into tesseroids (i.e., spherical prisms) to consider the influence of the curvature of planets in global or large-scale problems. Traditional gravity forward modeling methods in spherical coordinates, including the Taylor expansion and Gaussian–Legendre quadrature, are all based on spatial domains, which mostly have low computational efficiency. This study proposes a high-efficiency forward modeling method of gravitational fields in the spherical harmonic domain, in which the gravity anomalies and gradient tensors can be expressed as spherical harmonic synthesis forms of spherical harmonic coefficients of 3D density distribution. A homogeneous spherical shell model is used to test its effectiveness compared with traditional spatial domain methods. It demonstrates that the computational efficiency of the proposed spherical harmonic domain method is improved by four orders of magnitude with a similar level of computational accuracy compared with the optimized 3D GLQ method. The test also shows that the computational time of the proposed method is not affected by the observation height. Finally, the proposed forward method is applied to the topography correction of the Moon. The results show that the gravity response of the topography obtained with our method is close to that of the optimized 3D GLQ method and is also consistent with previous results. [ABSTRACT FROM AUTHOR]

Novel Si3N4/PAN/SiZrOCN ceramic aerogel composites, which have excellent wave transmission functions, were prepared through electrospinning, freeze-drying, and high-temperature pyrolysis. Polyvinyl alcohol was used as the aerogel carbon skeleton, polystyrene served as the pore-forming substance, Si3N4/PAN fiber was used as the reinforcement material. The pore size distribution and dielectric properties of the composites were systematically studied at different pyrolysis temperatures. An increase in pyrolysis temperatures led to a decrease in the specific surface area and dielectric constant. Fourier infrared spectroscopy, X-ray photoelectron spectroscopy, and X-ray diffraction were employed to investigate the polymerization mechanism and ceramic process of the precursor. The Brunauer–Emmett–Teller test revealed that the maximum specific surface area of Si3N4/PAN/SiZrOCN ceramic aerogel composites was 109.261 m2/g, and the average pore size was 4.56 nm when sintered at 600 °C. The dielectric properties test results showed a dielectric constant ranging between 3.1 and 3.7 and a dielectric loss tangent value between 2.6 × 10–3 and 1.6 × 10–2 for the sample. Si3N4/PAN/SiZrOCN ceramic aerogel composites exhibited excellent dielectric properties at room temperature and demonstrated exceptional dielectric stability across different frequency bands (1.8–18.0 GHz), making them a potential high-temperature wave-transmittance material. [ABSTRACT FROM AUTHOR]

Pipeline inspection is important to ensure the safe operation of pipelines. Obtaining the location of an underground pipeline is a prerequisite for most inspection technologies. Existing pipeline location methods can find a pipeline's location, but they require multiple measurements and cannot be used by automatic inspection robots. In this paper, a tunnel magnetoresistance (TMR)-sensor-array-based pipeline location method is proposed to solve this problem. Firstly, a detection probe is designed using a TMR sensor array. It is calibrated by the improved ellipsoid fitting method to measure the magnetic field around the pipeline accurately. Secondly, a relative pipeline-position-locating method is proposed by detecting the phases of the magnetic induction signals at different frequencies. Thirdly, a three-dimensional pipeline location method is proposed. The horizontal and vertical distances and the angle between the pipeline and the probe are calculated by measuring the magnetic induction amplitude. Finally, a simulation model and a test platform are established, and the experimental results illustrate that, by adopting the TMR array, the three-dimensional pipeline location method can locate a pipeline in real time in three dimensions with good accuracy. [ABSTRACT FROM AUTHOR]