Gravity Measurements Research Articles

Method for determining the drift of the CG-6 Autograv gravimeter to provide high-precision gravity measurements

Вопрос обеспечения высокоточными данными о силе тяжести Земли в рамках реализации проекта «Разработка модели геоида Республики Казахстан, как основа единой государственной системы координат и высот» является первостепенной задачей для достижения поставленной цели. Построение модели геоида и гравиметрического полигона невозможно без применения современных технологий. Сегодня измерить силу тяжести с высокой точностью возможно лишь с применением гравиметров. Современные гравиметры просты в использовании, надежны и эффективны при проведении гравиметрических измерений. В статье проведены тестовые измерения относительных значений силы тяжести на территории кампуса Satbayev University цифровым гравиметром CG-6 Autograv. Определена скорость дрейфа гравиметра, дана оценка точности проводимых измерений «Координаттар мен биіктіктердің біртұтас мемлекеттік жүйесінің негізі ретінде Қазақстан Республикасының геоидтық моделін жасау» жобасын іске асыру шеңберінде Жердің ауырлық күші туралы жоғары дәлдіктегі деректермен қамтамасыз ету мәселесі алға қойылған мақсатқа қол жеткізу үшін бірінші кезектегі міндет болып табылады. Геоид пен гравиметриялық полигон моделін құру заманауи технологияларды қолданбай мүмкін емес. Бүгінгі таңда ауырлық күшін гравиметрлерді қолдану арқылы ғана жоғары дәлдікпен өлшеуге болады. Қазіргі гравиметрлерді пайдалану оңай, сенімді және гравиметриялық өлшеулер жүргізуде тиімді. Мақалада CG-6 Autograv сандық гравиметрімен Satbayev University кампусындағы ауырлық күшінің салыстырмалы мәндерін сынақтан өткізді. Гравиметрдің дрейф жылдамдығы анықталды, өлшеулердің дәлдігі бағаланды The issue of providing high-precision data on the Earth’s gravity within the framework of the project «Development of a geoid model of the Republic of Kazakhstan as the basis of a unified state coordinate system and heights» is a primary task to achieve this goal. Building a model of a geoid and a gravimetric polygon is impossible without the use of modern technologies. Today, it is possible to measure gravity with high accuracy only with the use of gravimeters. Modern gravimeters are easy to use, reliable and effective in carrying out gravimetric measurements. In the article, test measurements of relative gravity values on the campus of Satbayev University with a digital gravimeter CG-6 Autograv were carried out. The gravimeter drift velocity was determined, and the accuracy of the measurements was estimated

Precise Geoid Determination in the Eastern Swiss Alps Using Geodetic Astronomy and GNSS/Leveling Methods

Astrogeodetic deflections of the vertical (DoVs) are close indicators of the slope of the geoid. Thus, DoVs observed along horizontal profiles may be integrated to create geoid undulation profiles. In this study, we collected DoV data in the Eastern Swiss Alps using a Swiss Digital Zenith Camera, the COmpact DIgital Astrometric Camera (CODIAC), and two total station-based QDaedalus systems. In the mountainous terrain of the Eastern Swiss Alps, the geoid profile was established at 15 benchmarks over a two-week period in June 2021. The elevation along the profile ranges from 1185 to 1800 m, with benchmark spacing ranging from 0.55 km to 2.10 km. The DoV, gravity, GNSS, and levelling measurements were conducted on these 15 benchmarks. The collected gravity data were primarily used for corrections of the DoV-based geoid profiles, accounting for variations in station height and the geoid-quasigeoid separation. The GNSS/levelling and DoV data were both used to compute geoid heights. These geoid heights are compared with the Swiss Geoid Model 2004 (CHGeo2004) and two global gravity field models (EGM2008 and XGM2019e). Our study demonstrates that absolute geoid heights derived from GNSS/leveling data achieve centimeter-level accuracy, underscoring the precision of this method. Comparisons with CHGeo2004 predictions reveal a strong correlation, closely aligning with both GNSS/leveling and DoV-derived results. Additionally, the differential geoid height analysis highlights localized variations in the geoid surface, further validating the robustness of CHGeo2004 in capturing fine-scale geoid heights. These findings confirm the reliability of both absolute and differential geoid height calculations for precise geoid modeling in complex mountainous terrains.

Temporal gravimetry, campaign and permanent GNSS, and interferometric radar techniques: A comparative approach to quantifying land deformation rates in coastal Texas

Land subsidence and local sea-level rise are well-known on-going hazards that negatively impacting coastal regions, exacerbating coastal flooding, threatening infrastructure stability, accelerating erosion, and amplifying the risks of inundation and property damage. This study used four techniques to quantify land deformation rates in the Texas Coastal Bend region and to investigate the controlling factors on two different spatiotemporal scales: (1) local scale, where biweekly temporal gravity and campaign Global Navigation Satellite System (GNSS) measurements were acquired at six locations over 2 years (October 2020–September 2022); and (2) regional scale, where vertical displacement time series were extracted from the Interferometric Synthetic Aperture Radar (InSAR) and 15 permanent GNSS stations over 5 years (January 2017–November 2021). The observed inconsistency between land deformation rates derived from gravity (range: −33.32 ± 149.30 to +338.68 ± 107.93 mm/yr) and campaign GNSS (range: −17.91 ± 14.90 to +5.69 ± 9.93 mm/yr) surveys could be attributed to the short campaign period and the infrequency of data acquisition. The InSAR-derived deformation rates (range: −12.16 ± 0.12 to +11.70 ± 0.00 mm/yr) were consistent with the permanent GNSS-derived rates (range: −14.0 ± 0.6 to +9.0 ± 3.0 mm/yr); both indicated spatiotemporal variability in land deformation rates across the Texas Coastal Bend. A total of 4 coastal towns (−2.3 ± 3.3 mm/yr), 3 cities (−1.4 ± 2.6 mm/yr), 3 inland towns (−3.6 ± 4.2 mm/yr), and 7 industrial plants (−3.8 ± 5.8 mm/yr) were found to have significant land subsidence rates due to sediment compaction, growth faulting, oil/gas extraction, and groundwater extraction. Results of this study emphasize the advantages and limitations of four different techniques in quantifying land deformation rates; can enhance estimates of local sea-level rise; and offer valuable insights to support coastal communities in mitigating the impacts of land subsidence and improving their resilience.

Testing Whether Gravity Acts as a Quantum Entity When Measured

A defining signature of classical systems is “in principle measurability” without disturbance: a feature manifestly violated by quantum systems. We describe a multi-interferometer experimental setup that can, in principle, reveal the nonclassicality of a spatial superposition-sourced gravitational field if an irreducible disturbance is caused by a measurement of gravity. While one interferometer sources the field, the others are used to measure the gravitational field created by the superposition. This requires neither any specific form of nonclassical gravity, nor the generation of entanglement between any relevant degrees of freedom at any stage, thus distinguishing it from the experiments proposed so far. This test, when added to the recent entanglement-witness based proposals, enlarges the domain of quantum postulates being tested for gravity. Moreover, the proposed test yields a signature of quantum measurement induced disturbance for any finite rate of decoherence, and is device independent. Published by the American Physical Society 2024

Optimizing in-situ upgrading of heavy crude oil via catalytic aquathermolysis using a novel graphene oxide-copper zinc ferrite nanocomposite as a catalyst

Unconventional resources, such as heavy oil, are increasingly being explored and exploited due to the declining availability of conventional petroleum resources. Heavy crude oil poses challenges in production, transportation, and refining, due to its high viscosity, low API gravity, and elevated sulfur and metal content. Improving the quality of heavy oil can be achieved through the application of steam injection, which lowers the oil’s viscosity and enhances its flow. However, steam injection alone falls short of meeting the growing demand for higher-quality petroleum products. Catalytic upgrading is therefore being investigated as a viable solution to improve heavy oil quality. This study experimentally investigates the application of two novel catalysts, namely copper-substituted zinc ferrite (ZCFO) synthesized via the sol–gel combustion method and a graphene oxide-based nanocomposite (GO-ZCFO) with different ratios, for catalyzing aquathermolysis reactions in the steam injection process, with the aim of enhancing the in-situ upgrading of heavy oil. These catalysts underwent characterization using X-ray powder diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and Transmission Electron Microscopy (TEM). Their catalytic performance was assessed utilizing a high-pressure/high-temperature reactor (300 ml), with a comprehensive analysis of the changes in the physical and chemical properties of the heavy oil before and after upgrading. This analysis included measurements of sulfur content, SARA fractions, viscosity, API gravity, and Gas Chromatography (GC) of saturated hydrocarbons and evolved gases. All upgrading experiments, including both catalytic and non-catalytic aquathermolysis processes, were conducted under a reaction time of 6 h, a reaction temperature of 320 °C, and high pressure (86–112 bar). The results indicated that the introduction of the proposed catalysts as additives into the upgrading system resulted in a significant reduction in sulfur content. This, in turn, led to a decrease in resin and asphaltene content, an increase in the content of saturated hydrocarbon, particularly low-molecular-weight alkanes, and ultimately, a reduction in viscosity along with higher API gravity of the crude oil. GO-ZCFO with a weight ratio (50:50) exhibited the best catalytic performance. The heavy crude oil, upgraded with this 50:50 ratio, exhibited significant enhancements, including a 29.26% reduction in sulfur content, a 21.27% decrease in resin content, a 37.60% decrease in asphaltene content, a 46.92% increase in saturated hydrocarbon content, a 66.48% reduction in viscosity, and a 25.49% increase in API gravity. In comparison, the oil upgraded through non-catalytic aquathermolysis showed only marginal improvements, with slight reductions in sulfur content by 5.41%, resin content by 3.60%, asphaltene content by 11.36%, viscosity by 17.89%, and inconsiderable increases in saturated hydrocarbon content by 9.9% and API gravity by 3.02%. The GO-ZCFO, with its high catalytic activity, stands as a promising catalyst that contributes to improving the in-situ upgrading and thermal conversion of heavy crude oil.

Evidence of renal tubular injury in canine patients after elective desexing.

To investigate the frequency of perioperative acute kidney injury (AKI) in American Society of Anesthesiologists (SA) Grade I canine patients undergoing elective desexing using urine microscopy techniques and assess if pre- and intraoperative factors affect risk of developing AKI. Prospective observational clinical study conducted between September 2020 and October 2020. University teaching hospital. Thirty-two female and four male dogs between 5 months and 5 years of age classified as ASA I undergoing elective desexing surgery. Urinalysis was performed preoperatively and 20-24 h postoperatively to identify markers of renal tubular injury (RTI), particularly the presence of granular and renal tubular epithelial cell (RTEC) casts on sediment analysis. Dogs underwent a full physical examination and a preoperative assessment including measurement of urine specific gravity (USG), packed cell volume (PCV), total plasma protein and serum creatinine (sCr) was conducted as a part of the desexing programme. Anaesthetic records were examined for any evidence of intraoperative hypotension, defined as a mean arterial pressure (MAP) of <60 mmHg for any duration of time. MAP was measured using an indirect oscillometric technique. For analysis, animals were subdivided into affected and nonaffected groups, with affected animals those that hadpostoperative increases in granular and RTEC casts. Categorical and comparative analyses were then performed between groups to identify associations of increased casts with pre-, intra- and postoperative variables. A frequency of RTI of 5.6% was identified. This was accompanied by a significant association between increases in casts with total duration (p = 0.027) and number (p = 0.016) of hypotensive episodes. RTI is an anaesthetic consideration in ASA I veterinary patients undergoing elective desexing surgery. The identification of an association between the total duration and number of hypotensive episodes and the frequency of RTI highlights the importance of early detection of hypotension along with prompt and effective intervention in veterinary patients.

Conformally invariant random fields, Liouville quantum gravity measures, and random Paneitz operators on Riemannian manifolds of even dimension

AbstractFor large classes of even‐dimensional Riemannian manifolds , we construct and analyze conformally invariant random fields. These centered Gaussian fields , called co‐polyharmonic Gaussian fields, are characterized by their covariance kernels k which exhibit a precise logarithmic divergence: . They share a fundamental quasi‐invariance property under conformal transformations. In terms of the co‐polyharmonic Gaussian field , we define the Liouville Quantum Gravity measure, a random measure on , heuristically given as and rigorously obtained as almost sure weak limit of the right‐hand side with replaced by suitable regular approximations . In terms on the Liouville Quantum Gravity measure, we define the Liouville Brownian motion on and the random GJMS operators. Finally, we present an approach to a conformal field theory in arbitrary even dimension with an ansatz based on Branson's ‐curvature: we give a rigorous meaning to the Polyakov–Liouville measure and we derive the corresponding conformal anomaly. The set of admissible manifolds is conformally invariant. It includes all compact 2‐dimensional Riemannian manifolds, all compact non‐negatively curved Einstein manifolds of even dimension, and large classes of compact hyperbolic manifolds of even dimension. However, not every compact even‐dimensional Riemannian manifold is admissible. Our results concerning the logarithmic divergence of the kernel rely on new sharp estimates for heat kernels and higher order Green kernels on arbitrary closed manifolds.

A convolutional neural network to optimize multi-mission satellite altimeter fusion for improving the marine gravity field

Satellite altimetry is the main tool for constructing global or regional marine gravity fields. To improve the accuracy and spatial resolution, it is necessary to fuse multi-mission altimeters. How to determine the weights of multi-mission altimeters is a crucial issue, making the conventional calculation process very complex. In addition, traditional satellite inversion methods are often independent of shipborne gravity, which is used only as validation data, thus not take full advantages of high accuracy and resolution of shipborne gravity. In this study, we introduce a convolutional neural network (CNN) to merge the vertical deflections (DOVs) obtained from multi-altimeter missions to construct a marine gravity model in the South China Sea. High-accuracy shipborne gravity and a dataset comprising DOVs and geo-locations are employed as input data for neural network training. For the validation of CNN method, the gravity model is also computed by conventional Inverse Vening Meinesz (IVM) method. Independent shipborne gravity measurements and SIO V32.1, DTU17 models are used as validation data. The evaluation results show that the CNN-derived model achieves a higher level of accuracy, yielding a standard deviation (STD) of 3.21 mGal, with an improvement of 36.56% compared to IVM-derived model. More than 92% of the differences between the CNN-derived model and shipborne gravity are less than 5 mGal. In addition, spectral analysis results further show that the CNN-derived model has stronger energy at short wavelengths (less than 25 km) compared to other models. These findings reveal that CNN method is feasible for marine gravity recovery and the CNN-derived model can achieve higher accuracy. The CNN method can improve the accuracy and spectral characteristics of the constructed gravity model by taking advantage of the high accuracy and high resolution of shipborne gravity.Graphical

Geophysical investigation of the ground fissures and ground subsidence near Karla lake (eastern Thessaly basin, Greece)

Ground fissures have occurred in the last four decades across the eastern Thessaly basin (Greece) resulting in damage to the villages of the area. Several studies for the area refer to the over-pumping of ground water as the main reason for their occurrence, causing sediment compaction due to the reduction of the aquifer level. In this paper, we depict the results of a joint geophysical survey trying to determine the subsurface regime of the basin and the exact reasons contributing to the existence of the ground fissures. The focal part of the survey includes gravity measurements for deeper investigation, combined with existing and already presented geoelectrical and electromagnetic data. Several borehole data have also been used for the calibration of the geophysical interpretation. The differential GNSS data of the gravity campaign revealed the ground subsidence of the area, reaching up to 9.16 m. The alpine basement of the area is comprised mainly of metamorphic rocks, such as marbles, mica schists and gneiss-schists, covered by thick fluviοterrestrial and alluvial deposits. Several structural maps were generated in order to delineate the lateral density variations that could be related to fault zones along with the interpretive sections for geological modelling. The alpine bedrock was adumbrated in relatively great depths, with a large anticline of NW-SE direction, rising and separating the basin in two parts. In the east part, the fluvioterrestrial deposits, which are expected to play an important role in the compaction due to their water aquifer, are located only west of this anticline. At the east part, where the old lake Karla was hosted, the alluvial deposits lay directly on the alpine basement in smaller depths. This complicated regime is responsible for differential sediment compaction and the ground subsidence of the surface.

Examining the Hydration Status and Pulse/Oxygen Saturation of Underwater Hockey Players

Objectives: This study was planned to determine the hydration status and tissue oxygen saturation of underwater hockey players during exercise. Materials and Methods: Hydration status (fluid intake/loss amounts, repeatedly weight measurements) and tissue oxygen saturation measurements of 14 underwater hockey players were performed before and after the land/water training, separately. Hydration status was assessed by monitoring weight and urine specific gravity (USG) measurements, whereas tissue oxygen saturation was measured by using finger-type pulse oximeter. Results: The study was completed with14 elite players (age=19.4±6.2 years, female=4(29%), and male=10(71%)). The body fat percentage was calculated to be male:14.2±9.4%; female: 18.8±4.0%. The mean USG of athletes was determined to be 1020.1±5.6 g/cm3. During the water training, only 5 athletes consumed water (680±383.4 mL). All the athletes (except for 1 athlete [7.1%]) completed the training with loss of body fluid. Mean loss of water was 310±213.2 mL after land training and 723.1±501.9 mL after water training. Dehydration ratio was measured 0.97±0.64% after trainings. The first oxygen saturation was measured 96.1±1.6, that was decreased after water training (94.6±2.2; p=0.044, p=0.049). Pulse increased after water training in reverse proportion to oxygen saturation (p=0.004), but there was no difference between before and after land training (p=0.132). Conclusion: It was found that several Underwater hockey players began training dehydrated and loss of water continued since they didn’t consume enough water during training. Oxygen saturation significantly decreased after water training. Fluid consumption of underwater hockey players, especially during water training, should be monitored and adequate fluid consumption should be ensured.

The Moon’s Tides Hint at a Melty Lunar Layer

New lunar gravity measurements support the idea that a partially molten mantle layer is sandwiched between the rest of the Moon’s mantle and its core.

Finite element analysis for the measurement error of electrostatic accelerometer due to the electrode misalignment

Abstract The electrostatic accelerometer is the key payload of many space missions, such as satellite gravity measurements, space gravitational experiments, with a typical precision requirement from nano-g to femto-g. The measurement error model analysis is an important issue for the electrostatic accelerometer with numerous error sources. The traditional method by theoretical analysis is complicated to evaluate the complete measurement error models quantitatively especially when the machining and assembly errors of the sensor head are considered. Limited by the earth gravity and seismic noise which is much higher than the intrinsic noise, the complete error model of electrostatic accelerometers can also hardly be tested on ground. In this paper, the method by using finite element analysis of the sensor head is studied. The simulation model for an electrostatic accelerometer sensor head is built, and the multi-conductor capacitance matrix data is simulated. The accuracy of the capacitance simulation is evaluated in three ways including the convergence check of the capacitance with the mesh size, the symmetry verification, and the sensitivity comparison with the theoretical model. Finally, the accelerometer measurement model is analyzed based on the simulation data, using the case of rotating installation misalignment of the upper electrode as an example. The measurement model and error items of one horizontal axis and one rotating axis are quantitatively evaluated. The method proposed in this paper provide a new effective approach to the measurement model analysis of the electrostatic accelerometers in complex working scenarios both in orbit and on ground, which could be helpful to enhance the performance and the efficiency of application.

Evaluation and homogenization of a marine gravity database from shipborne and satellite altimetry-derived gravity data over the coastal region of Nigeria

Abstract Accurate geoid modelling in marine areas requires the integration of gravity data from multiple sources including shipborne gravity measurements, global geopotential models, and satellite altimetry-derived gravity data. This study aims to develop homogenized gravity data for the coastal region of Nigeria to improve geoid modelling accuracy. Residual linear drifts in the shipborne gravity dataset from the Bureau Gravimétrique International (BGI) were corrected using crossover adjustments for each survey leg. We eliminated gross errors for each survey leg by using the 2-sigma method. Outliers in the historical shipborne gravity data were identified and removed using the leave-one-out cross-validation technique, resulting in a refined shipborne gravity dataset. The refined shipborne data were compared with the gravity data predicted by DTU21GRA, SSv29.1, SGG-UGM-2, XGM2019e_2159, GECO, EIGEN-6C4, and EGM2008. Our findings show that DTU21GRA outperformed the other models in the same region when compared with shipborne gravity data. The refined shipborne gravity data were merged with the DTU21GRA data using Least-Squares Collocation (LSC) to create a combined gravity dataset. The results of comparison between the complete refined shipborne gravity data and DTU21GRA before and after the integration process, shows that both the mean offset and the SD values decreased from 0.43 to −0.02 mGal and 3.14 to 2.69 mGal, respectively, which reveal an improvement in the final combined data. The geoid model constructed using the combined gravity data before and after the integration process showed an improvement in the SD values, decreasing from 0.023 m to 0.016 m when evaluated against the CNES-CLS22 MDT.

Three-dimensional joint inversion of surface wave dispersion and gravity data using a petrophysical approach: an application to Los Humeros Geothermal Field

SUMMARY We present a method to jointly invert surface wave dispersion data and gravity measurements for 3-D shear wave velocity and density models. We implemented a petrophysical approach to combine the kernels of both methodologies in a single process. The synthetic experiments show that jointly inverted models recover shear wave velocity and density better than separate inversions. In particular, density models benefit from the good vertical resolution of surface wave dispersion data, while shear velocity models benefit from the good lateral resolution of gravity data. We also proposed two methods to stabilize the solution when using high-grade polynomials. We applied the methodology to the Los Humeros Geothermal area to demonstrate its applicability in a complex geological scenario. Compared with separate inversion, the joint inversion contributes to enhancing key aspects of the geothermal system by (i) delimitating better the geometry of the caldera deposits in the first 0–2.8 km deep by increasing the vertical resolution in density, (ii) delimitating better the lateral borders of low-Vs bodies at different depths interpreted as a part of a complex magmatic chamber system and (iii) estimating the local shear wave velocity–density relationship that conforms to other known relationships for sedimentary and igneous rocks but with some differences that bring us additional information.

CYSTOCENTESIS AND URINALYSIS IN ZOOMEDICINE: AN UNDERESTIMATED TOOL FOR LARGE FELID STANDARD HEALTH CHECKS.

Chronic kidney disease (CKD) is a prevalent disease among felids; yet its origin is still poorly understood, and the disease often remains asymptomatic for years, underscoring the need for early diagnosis. This study aimed to investigate the diagnostic value of urinalysis in accurately staging CKD, particularly as routine health checks in large felids often overlook its significance. In this research, ultrasound-guided cystocentesis (UGC) was performed on 50 captive nondomestic felids during routine veterinary health checks under general anesthesia. Urinalysis included microscopic examination of the sediment, measurement of urine specific gravity (USG) and protein to creatinine ratio (UPC). Additional serum kidney markers, such as creatinine and symmetric dimethylarginine, were compared with USG and UPC to assess their diagnostic value as urinary biomarkers. The results demonstrated proteinuria (UPC > 0.4) or borderline proteinuria (UPC 0.2-0.4) in 49% of the animals. Among these cases, 62% were of renal origin, and 38% were postrenal causes. USG was significantly higher in felids with borderline proteinuria compared to those with proteinuria. A moderate, but significant negative correlation between serum parameters and USG was observed, emphasizing the importance of assessing both diagnostic parameters during kidney evaluations. Additionally, felids with CKD have an increased risk of urinary tract infections, necessitating microscopic urinalysis and bacterial culture analysis. Abnormalities, including hematuria, pyuria, crystalluria, and bacteriuria, were found in approximately 38% of cases through microscopical examination of urine. No complications associated with UGC were observed and abnormal findings were detected in 60% of the cases. Based on these results, the authors recommend the inclusion of UGC and urinalysis as standard diagnostic tools in general health checks for nondomestic felids. This approach provides valuable insights into the early detection and staging of CKD, supporting early intervention and supportive medical care to prolong renal health in these animals.

Qualitative analysis of rivers sand sources (Silica sand, Ravi river sand, Indus river sand, and Jhelum river sand) for metal casting: a comparative study

Abstract Recent geological investigations revealed extensive use of Silica sand in Pakistan resulting in depletion of tectonic resources. Hence, it is important to explore cost-effective and alternative sources of sand for its applications. Also, Pakistan has a river network that provides river sand as a potential substitute for Silica sand. However, it is essential to systematically study and assess the potential applicability of river sand as an alternative to Silica sand. In this context, this study examined sand samples collected from various rivers in Pakistan to investigate their suitability for metal-casting molds. For that purpose, random samples were selected from major rivers in Pakistan for characterization by utilizing chemical composition analysis, microscopy, XRD, TGA-DSC (thermogravimetric analysis), clay content analysis, grain size distribution analysis, pH measurement, green and dry compression strength testing, shear strength testing, permeability analysis, shatter index analysis, compactibility testing, and Specific gravity measurement. The chemical composition analysis revealed that all types of sands contained over 90% SiO2 content. The mechanical tests demonstrated that river sand exhibited acceptable mechanical properties, with a moisture content ranging from 4.5-5%. The pH value of all the sands exceeded 7, making them suitable for casting purposes. These investigations suggest that river sand can be effectively utilized in casting applications by implementing pre-processing techniques and incorporating additives.

Modeling of the effect of transportation system accessibility on residential real estate prices: The case of Washington metropolitan area, USA

Deep learning accurate predictions of house prices are essential for prospective homeowners, investors, appraisers, and insurers. However, some studies lack accuracy as they overlook critical factors like accessibility and economic attributes that influence house prices. This paper aims to predict house prices by considering structural, locational, accessibility, and economic attributes, while also exploring the effect of accessibility on housing prices. The dataset contains 2,019,663 real estate transaction records from 1975 to 2018 in the Washington metropolitan area, obtained from the Zillow website. In this study, the accessibility index is calculated using Distance, Cumulative Opportunities, and Gravity measures, with the gravity measure surpassing others due to its consideration of both land use and transportation aspects. Economic attributes are then utilized to predict the average monthly house price using deep learning algorithms such as LSTM, GRU, and Simple RNN, with the Simple RNN demonstrating superior performance. Following the amalgamation of structural and locational attributes with the accessibility index and average house prices, various machine learning algorithms—including Linear Regression, Lasso, Ridge, Random Forest, GBM, LightGBM, XGBoost, Decision Tree, AdaBoost, Artificial Neural Network, and Stacked Generalization—are employed for prediction. Subsequent evaluation reveals that Stacked Generalization (ANN + LightGBM) provides the best performance, with an R-squared value of 0.96 and RMSE of $23,290. Moreover, this paper identifies accessibility index thresholds (80,003 for large buildings and 160,103 for small buildings) and demonstrates that a higher accessibility index leads to lower housing prices, attributed to noise pollution, decreased privacy, and increased supply responses.

Ground-based simulation of laser link acquisition for inter-satellite laser interferometry

Laser link acquisition and pointing technique is one of the essential techniques for the inter-satellite laser interferometry for space-based gravitational waves detection and next-generation Earth gravity measurement missions. The first step of building up inter-satellite laser link is using an acquisition camera to capture the inter-satellite laser beam signals within a pre-scanning uncertain cone. Subsequently, high-precision angle measurement technology, namely differential wavefront sensing, is used to achieve a high pointing precision required. Due to the distance constraint of a ground-based simulation experiment, it is difficult to verify directly the feasibility of an inter-satellite laser link acquisition and pointing control scheme. By means of controlling the optical properties of the received laser beam, the long-distance beam propagation is simulated with two optical benches of an inter-satellite interferometer, and the process of a laser link acquisition experiment has been demonstrated. The experimental results show that the inter-satellite laser beams could establish the dual-way locking successfully. The fluctuation of the laser beam pointing direction (in-loop) can be suppressed to about 5 µrad in atmospheric environment. The results verify the feasibility of the laser link acquisition scheme. The experimental setup can be extended to conduct experiments with various parameters, providing technical support for further testing of the inter-satellite laser link acquisition and pointing control methods.

Seismic noise effect suppression for the performance testing of high-precision space electrostatic accelerometers using a torsion pendulum with differential configuration

Abstract To test the performance of high-precision electrostatic accelerometers for next generation satellite gravity measurement missions, a torsion pendulum integrated with two electrostatic accelerometers is proposed. In this differential configuration scheme, the seismic noise effect can be further suppressed due to common-mode rejection. Theoretical analysis shows that the seismic noise effect rejection ratio is determined by the inconsistency factors of two accelerometers, and after the compensation for inconsistency, the seismic noise effect can be suppressed by at least 85 dB below 0.1 Hz. Preliminary experimental results are agreed with the theoretical analysis, and its detection sensitivity comes to 2 × 10 − 11 m s−2 Hz − 1 / 2 at 10 mHz, which is limited by the intrinsic noises of accelerometers used here.

Autonomous ground vehicle gravity anomaly measurement and dynamic error compensation

Abstract To address the issue that dynamic gravity anomaly measurement is overly dependent on GNSS and can’t be measured autonomously at this stage, this paper proposes an autonomous ground vehicle dynamic gravity anomaly measurement method based on a strapdown inertial navigation system (SINS), odometer (OD), barometer and platform gravimeter. The SINS/OD /barometer integrated navigation solution delivers high-precision navigation parameters, completes the calculation of correction terms, and performs the autonomous dynamic gravity anomaly measurement combined with the primary measurement results of the platform gravimeter. Numerical calculations provide the requirements for the application of the proposed method, and the cut-off frequency for extracting gravity anomalies is 0.02 Hz, as determined by power spectral density analysis. In order to further improve the measurement accuracy and account for dynamic errors caused by vehicle maneuvering, a long-short-term memory (LSTM) model of recurrent neural network (RNN) is introduced. A series of experiments under multiple circumstances with repeated lines were conducted in Tianjin, China, and the static measurements along the line were taken using CG-5 to provide true values of gravity anomalies. The results demonstrate that the autonomous measurement scheme can achieve accuracy comparable to GNSS-assisted, and that dynamic error compensation algorithm based on LSTM improves the dynamic gravity measurements accuracy significantly without sacrificing the spatial resolution of gravity anomalies.