Articles de revues : « Gravity network »

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Prodous, Oleg A., et Dmitriy I. Shlychkov. « Forecasting continued operation of gravity drainage networks with deposits in pipe water troughs ». Journal «Izvestiya vuzov. Investitsiyi. Stroyitelstvo. Nedvizhimost» 11, n^o 4 (2021) : 646–53. http://dx.doi.org/10.21285/2227-2917-2021-4-646-653.

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In this work, the formula for forecasting the continued operation of gravity drainage networks with deposits in pipe water troughs is deduced and refined. In the authors' opinion, such a forecast should be based on the hydraulic principle for assessing the efficiency of a network operation, as the most accurate. To this end, the concept associated with the efficiency of gravity drainage networks was introduced, and a criterion for its assessment was proposed. In the study, the characteristics of hydraulic potential for concrete pipes with a diameter of 400 mm were calculated as an example. An empirical formula was proposed for determining the efficiency factor of the gravity drainage network, and its deviation range was shown. It was concluded that the expert prognosis of continued operation of gravity drainage networks should be based on the efficiency factor of the network, calculated using the obtained formula. It is recommended that a method for calculating an efficiency factor describing gravity drainage networks and special tables for the hydraulic calculation of pipes having a sediment layer of different thicknesses be elaborated. The data presented in the article allow servicing of gravity drainage network to be improved by forecasting its continued operation using the efficiency factor К_ef.

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Goodacre, A. K., J. O. Liard, P. N. Courtier, R. V. Cooper, P. J. Winter et R. K. McConnell. « Absolute gravity measurements on the canadian gravity standardization network ». Bulletin Géodésique 65, n^o 3 (septembre 1991) : 170–78. http://dx.doi.org/10.1007/bf00806346.

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Ho, Angelina M. Y., Hawa Ze Jaafar, Ionel Valeriu Grozescu et Muhammad Zaharul Asyraf Bin Zaharin. « Solar Powered Gravity-Feed Drip Irrigation System Using Wireless Sensor Network ». International Journal of Environmental Science and Development 6, n^o 12 (2015) : 970–73. http://dx.doi.org/10.7763/ijesd.2015.v6.731.

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Lagios, E. « A gravity network in central Greece for secular gravity studies ». Pure and Applied Geophysics PAGEOPH 123, n^o 1 (1985) : 81–90. http://dx.doi.org/10.1007/bf00877050.

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Colafranceschi, Eugenia, et Gerardo Adesso. « Holographic entanglement in spin network states : A focused review ». AVS Quantum Science 4, n^o 2 (juin 2022) : 025901. http://dx.doi.org/10.1116/5.0087122.

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In the long-standing quest to reconcile gravity with quantum mechanics, profound connections have been unveiled between concepts traditionally pertaining to a quantum information theory, such as entanglement, and constitutive features of gravity, like holography. Developing and promoting these connections from the conceptual to the operational level unlock access to a powerful set of tools which can be pivotal toward the formulation of a consistent theory of quantum gravity. Here, we review recent progress on the role and applications of quantum informational methods, in particular tensor networks, for quantum gravity models. We focus on spin network states dual to finite regions of space, represented as entanglement graphs in the group field theory approach to quantum gravity, and illustrate how techniques from random tensor networks can be exploited to investigate their holographic properties. In particular, spin network states can be interpreted as maps from bulk to boundary, whose holographic behavior increases with the inhomogeneity of their geometric data (up to becoming proper quantum channels). The entanglement entropy of boundary states, which are obtained by feeding such maps with suitable bulk states, is then proved to follow a bulk area law with corrections due to the entanglement of the bulk state. We further review how exceeding a certain threshold of bulk entanglement leads to the emergence of a black hole-like region, revealing intriguing perspectives for quantum cosmology.

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Ozaki, Yushi, Kazuki Kawano et Hiroshi Gotoda. « Gravitational effect on the nonlinear dynamics of a buoyant turbulent flame ». Chaos : An Interdisciplinary Journal of Nonlinear Science 32, n^o 8 (août 2022) : 083147. http://dx.doi.org/10.1063/5.0086140.

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This study numerically examines the gravitational effect on the nonlinear dynamics of a buoyant turbulent flame utilizing analytical methods based on complex networks and dynamical systems. A dense (sparse) network structure is formed in the near (far) field in low gravity, as shown by the degree and cluster coefficient in the spatial network. The global dynamics of the vertical flow velocity fluctuations in the intermittent luminous zone is synchronous with that of the temperature fluctuations in low gravity. The synchronized state disappears as the gravity level is increased, leading to a desynchronized state. These behaviors are clearly identified by the symbolic recurrence plots.

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Zahorec, Pavol, Juraj Papčo, Peter Vajda, Filippo Greco, Massimo Cantarero et Daniele Carbone. « Refined prediction of vertical gradient of gravity at Etna volcano gravity network (Italy) ». Contributions to Geophysics and Geodesy 48, n^o 4 (1 décembre 2018) : 299–317. http://dx.doi.org/10.2478/congeo-2018-0014.

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Abstract Predicted values of the vertical gradient of gravity (VGG) on benchmarks of Etna’s monitoring system, based on calculation of the topographic contribution to the theoretical free-air gradient, are compared with VGG values observed in situ. The verification campaign indicated that improvements are required when predicting the VGGs at such networks. Our work identified the following factors to be resolved: (a) accuracy of the benchmark position; (b) gravitational effect of buildings and roadside walls adjacent to benchmarks; (c) accuracy of the digital elevation model (DEM) in the proximity of benchmarks. Benchmark positions were refined using precise geodetic methods. The gravitational effects of the benchmark-adjacent walls and buildings were modeled and accounted for in the prediction. New high-resolution DEMs were produced in the innermost zone at some benchmarks based on drone-flown photogrammetry to improve the VGG prediction at those benchmarks. The three described refinements in the VGG prediction improved the match between predicted and in situ observed VGGs at the network considerably. The standard deviation of differences between the measured and predicted VGG values decreased from 36 to 13 μGal/m.

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WARD, MICHAEL D., JOHN S. AHLQUIST et ARTURAS ROZENAS. « Gravity's Rainbow : A dynamic latent space model for the world trade network ». Network Science 1, n^o 1 (avril 2013) : 95–118. http://dx.doi.org/10.1017/nws.2013.1.

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AbstractThe gravity model, long the empirical workhorse for modeling international trade, ignores network dependencies in bilateral trade data, instead assuming that dyadic trade is independent, conditional on a hierarchy of covariates over country, time, and dyad. We argue that there are theoretical as well as empirical reasons to expect network dependencies in international trade. Consequently, standard gravity models are empirically inadequate. We combine a gravity model specification with “latent space” networks to develop a dynamic mixture model for real-valued directed graphs. The model simultaneously incorporates network dependencies in both trade incidence and trade volumes. We estimate this model using bilateral trade data from 1990 to 2008. The model substantially outperforms standard accounts in terms of both in- and out-of-sample predictive heuristics. We illustrate the model's usefulness by tracking trading propensities between the USA and China.

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Wojahn, Oliver W. « Airline network structure and the gravity model ». Transportation Research Part E : Logistics and Transportation Review 37, n^o 4 (août 2001) : 267–79. http://dx.doi.org/10.1016/s1366-5545(00)00026-0.

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Maniadakis, Dimitris, et Dimitris Varoutas. « Network congestion analysis of gravity generated models ». Physica A : Statistical Mechanics and its Applications 405 (juillet 2014) : 114–27. http://dx.doi.org/10.1016/j.physa.2014.03.023.

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Osazuwa, I. B., et D. E. Ajakaiye. « Gravity control network at airports in nigeria ». Journal of Geodynamics 7, n^o 3-4 (juillet 1987) : 307–17. http://dx.doi.org/10.1016/0264-3707(87)90016-0.

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Eckhardt, Donald H. « Isomorphic geodetic and electrical networks : An application to the analysis of airborne gravity gradiometer survey data ». GEOPHYSICS 51, n^o 11 (novembre 1986) : 2145–55. http://dx.doi.org/10.1190/1.1442066.

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Early in 1987, the Bell Aerospace/Textron Gravity Gradiometer Survey System (GGSS) will be tested by the Air Force Geophysics Laboratory in an airborne survey of a 300 × 300 km region of Oklahoma and Texas. The survey pattern will be a grid with a 5 km separation between adjacent tracks, both north‐south and east‐west. One way to process the GGSS survey data is to analyze an electrical network that is isomorphic to the survey network. The integrated gradients between the nodes where the survey lines cross correspond to the applied voltages between the nodes of the electrical network; the gradient variances correspond to the internodal resistances; the elements of the adjusted gravity vector correspond to the nodal voltages; and the solution variances correspond to the resistances to ground. An error analysis is performed by calculating the resistance to ground of the electrical network; a technique for making the calculations in large networks is explored in detail. For sample survey scenarios with one ground‐truth control point near each corner of the survey square and with realistic values for the survey parameters, the standard deviation in the gravity disturbance is less than 1 mGal and the deflection of the vertical standard deviation is less than 0.25 arc-s at all nodes. With no ground truth, but with a gravimeter on the aircraft that can independently determine gravity to 10 mGal at all nodes, the adjusted standard deviation in gravity disturbance is less than 1 mGal.

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Hu, Zunguo, et Jujing Zhou. « Convergence of City Relational Network, Production Sector Structure, and Regional Development ». Discrete Dynamics in Nature and Society 2021 (5 août 2021) : 1–13. http://dx.doi.org/10.1155/2021/8913858.

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There is a strong correlation between government intervention and urban production structure in China. Particularly, the outputs of the cities partly come from the economic rent of city relational network (CRN), which is a unique regional policy and administrative hierarchy. In order to analyze the gravity flows of CRN under the nonmarket mechanism, we attempt to build a new gravity model that adopts the production sector. The new gravity produces relational data with direction, which makes it possible to use social network analysis (SNA) and overcome the endogeneity of the linear model. The empirical results show that (1) modified new gravity model can effectively capture the distribution of CRN gravity flows and the convergence of regional development in China, (2) the CRN, which especially stems from the government financial intervention, increases the share of nontradable sectors in cities, and (3) adjustment of the production sector leads to the difference of CRN gravity flows, so asymmetric flows distribution leads to the heterogeneity of regional economic performance. Cities with higher share of nontradables have relatively slower productivity growth in long-term.

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Chen, Y., Q. Guo, M. Liu et J. G. Liu. « Improved gravity model for identifying the influential nodes ». Europhysics Letters 136, n^o 6 (1 décembre 2021) : 68004. http://dx.doi.org/10.1209/0295-5075/ac49d1.

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Abstract Identifying the influential nodes in a network is essential for network dynamic analysis. In this letter, inspired by the gravity model, we present an improved gravity model (EDGM) to identify the influential nodes in the network through the effective distance. Firstly, we calculate the degree of nodes. Then we construct the effective distance combined with the interaction frequency between nodes, so as to establish the effective distance gravity model. Comparing with the susceptible-infected model, the results show that Kendall's τ correlation coefficient of the EDGM could be enhanced by 2.36% for the gravity model. Compared with other methods, Kendall's τ correlation coefficient of the EDGM could be enhanced by 11.55%, 17.29%, 7.17% and 10.00% for the degree centrality, betweenness centrality, eigenvector centrality, and PageRank, respectively. The results show that the improved gravity model could effectively identify the influential nodes in the network.

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Dumor, Koffi, Li Yao, Jean-Paul Ainam, Edem Koffi Amouzou et Williams Ayivi. « Quantitative Dynamics Effects of Belt and Road Economies Trade Using Structural Gravity and Neural Networks ». SAGE Open 11, n^o 3 (juillet 2021) : 215824402110326. http://dx.doi.org/10.1177/21582440211032662.

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Recent research suggests that China’s Belt and Road Initiative (BRI) would improve the bilateral trade between China and its partners. This article uses detailed bilateral export data from 1990 to 2017 to investigate the impact of China’s BRI on its trade partners using neural network analysis techniques and structural gravity model estimations. Our main findings suggest that the BRI countries would raise exports by a modest 5.053%. This indicates that export and network upgrades should be considered from economic and policy perspectives. The results also show that neural networks is more robust compared with structural gravity framework.

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Zhao, Shuheng, Denghong Liu, Qiangqiang Yuan et Jie Li. « A Global Gravity Reconstruction Method for Mercury Employing Deep Convolutional Neural Network ». Remote Sensing 12, n^o 14 (17 juillet 2020) : 2293. http://dx.doi.org/10.3390/rs12142293.

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Mercury, the enigmatic innermost planet in the solar system, is one of the most important targets of space exploration. High-quality gravity field data are significant to refine the physical characterization of Mercury in planetary exploration missions. However, Mercury’s gravity model is limited by relatively low spatial resolution and stripe noises, preventing fine-scale analysis and applications. By analyzing Mercury’s gravity data and topography data in the 2D spatial field, we find they have fairly high spatial structure similarity. Based on this, in this paper, a novel convolution neural network (CNN) approach is proposed to improve the quality of Mercury’s gravity field data. CNN can extract the spatial structure features of gravity data and construct a nonlinear mapping between low- and high-degree data directly. From a low-degree gravity input, the corresponding initial high-degree result can be obtained. Meanwhile, the structure characteristics of the high-resolution digital elevation model (DEM) are extracted and fused to the initial data, to get the final stripe-free result with improved resolution. Given the paucity of Mercury’s data, high-quality lunar datasets are employed as pretraining data after verifying the spatial similarity between gravity and terrain data of the Moon. The HgM007 gravity field obtained by the MErcury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) mission at Mercury is selected for experiments to test the ability of the proposed algorithm to remove the stripes caused by quality differences of the highly eccentric orbit data. Experimental results show that our network can directly obtain stripe-free and higher-degree data via inputting low-degree data and implicitly assuming a lunar-like relation between crustal density and porosity. Albeit the CNN-based method cannot be sensitive to subsurface features not present in the initial dataset, it still provides a new perspective for the gravity field refinement.

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Wu, Qiong, Shi Liu, Bin Wang, Linshan Zhong, Lijiang Zhao, Shengpeng Zhang et Hongqing Li. « Data Processing of Gravity Base Network in Plateau Area : The Case of Qinghai Province, China ». Remote Sensing 14, n^o 5 (25 février 2022) : 1142. http://dx.doi.org/10.3390/rs14051142.

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The latest gravity survey of the gravity base network in Qinghai Province, China, was conducted with six Scintrex CG gravimeters and this gravity survey was tied to existed gravity reference stations. In this gravity network with long segments and very rugged topography, the calibration of scale factors is a time-consuming progress and its accuracy may be affected by many uncertainties, and the change in drift rates of the relative gravimeters are complex over time in this long-term survey. The reasonable calculation of scale factors and drift rates plays an important role in improving the gravity estimation accuracy. In this paper, based on the least squares, robust least squares, and Bayesian methods, various parameter calculation methods were employed to process this gravity network. The performance and practicality of each method were analyzed in terms of internal and external accuracy. The results indicated that the scale factors calibrated in the baseline field had poor applicability due to insufficient gravity difference, in this case, the scale factors estimated by the adjustment models were more accurate, which weakened the correlation between gravity differences and mutual differences. The drift rates estimated by the Bayesian method were relatively smooth over time, while drift rates estimated using symmetric observations were more practical for the gravimeter with highly variable drift. The weight constraints of observations can be optimized by the robust least squares method, the gravity values obtained by it were more consistent with absolute gravity values than those obtained by the least squares method, and the robust least squares method was recommended to process gravity data in plateau areas.

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Liu, Jin-Hu, Zi-Ke Zhang, Lingjiao Chen, Chuang Liu, Chengcheng Yang et Xueqi Wang. « Gravity Effects on Information Filtering and Network Evolving ». PLoS ONE 9, n^o 3 (12 mars 2014) : e91070. http://dx.doi.org/10.1371/journal.pone.0091070.

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Gambini, Rodolfo, Jorge Griego et Jorge Pullin. « Chern-Simons states in spin-network quantum gravity ». Physics Letters B 413, n^o 3-4 (novembre 1997) : 260–66. http://dx.doi.org/10.1016/s0370-2693(97)01048-4.

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Ducruet, César, Hidekazu Itoh et Justin Berli. « Urban gravity in the global container shipping network ». Journal of Transport Geography 85 (mai 2020) : 102729. http://dx.doi.org/10.1016/j.jtrangeo.2020.102729.

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Al-Garni, Mansour A. « Inversion of residual gravity anomalies using neural network ». Arabian Journal of Geosciences 6, n^o 5 (22 novembre 2011) : 1509–16. http://dx.doi.org/10.1007/s12517-011-0452-y.

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Dueñas, Marco, et Giorgio Fagiolo. « Modeling the International-Trade Network : a gravity approach ». Journal of Economic Interaction and Coordination 8, n^o 1 (24 janvier 2013) : 155–78. http://dx.doi.org/10.1007/s11403-013-0108-y.

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Pachuau, Joseph L., Arnab Roy, Gopal Krishna et Anish Kumar Saha. « Estimation of Traffic Matrix from Links Load using Genetic Algorithm ». Scalable Computing : Practice and Experience 22, n^o 1 (9 février 2021) : 29–38. http://dx.doi.org/10.12694/scpe.v22i1.1834.

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Traffic Matrix (TM) is a representation of all traffic flows in a network. It is helpful for traffic engineering and network management. It contains the traffic measurement for all parts of a network and thus for larger network it is difficult to measure precisely. Link load are easily obtainable but they fail to provide a complete TM representation. Also link load and TM relationship forms an under-determined system with infinite set of solutions. One of the well known traffic models Gravity model provides a rough estimation of the TM. We have proposed a Genetic algorithm (GA) based optimization method to further the solutions of the Gravity model. The Gravity model is applied as an initial solution and then GA model is applied taking the link load-TM relationship as a objective function. Results shows improvement over Gravity model.

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Wang, Linhai, Shi Chen, Jiancang Zhuang et Weimin Xu. « Simultaneous calibration of instrument scale factor and drift rate in network adjustment for continental-scale gravity survey campaign ». Geophysical Journal International 228, n^o 3 (14 octobre 2021) : 1541–55. http://dx.doi.org/10.1093/gji/ggab419.

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SUMMARY The scale factor of each relative gravimeter must be calibrated both before and after the fieldwork of a terrestrial gravity survey, to reduce uncertainties and ensure high precision. Conventionally, such calibration is a time-consuming process performed following well-established baselines. We propose a new Bayesian method to estimate the scale factor in a hybrid gravity network that includes several absolute gravity observation stations. In this approach, the scale factor is estimated as a hyperparameter using the Akaike Bayesian information criterion and using known absolute gravity stations in the network or/and calibrated instruments as constraints. Testing the sensitivity of the gravity values and the residuals of the gravity difference between two successive stations to the change of the scale factor demonstrates the robustness of this method. We also test the sensitivity of the estimated scale factor in the presence of Gaussian noise and the non-linear instrumental drift rate. Moreover, if the maximum absolute gravity interval is greater than 60 per cent of the range of gravity values in the network, or if the known scale factors of calibrated gravimeters are well calibrated, this approach can provide reasonable estimates of the daily drift rate and the unknown scale factors, where the latter has an error of <3 × 10−5. We apply this approach to real gravity campaign data from Yunnan in China and use a cross-validation method to compare estimated gravity values and corresponding gravity values obtained from absolute gravity observations at the same stations, to validate how the proposed method improves estimation accuracy of the gravity value at each station.

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Han, Lie, et Ning Zhang. « Hub-and-Spoke Airline Network Design Method and Application Based on Gravity Model ». Applied Mechanics and Materials 178-181 (mai 2012) : 1941–46. http://dx.doi.org/10.4028/www.scientific.net/amm.178-181.1941.

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Considering that lengthened transit airline route will reduce the quantity of customers in hub-and-spoke airline networks, the saved cost and reduced quantity of customers must be traded off when hub-and-spoke networks are designed. We apply gravity model to indicate the influence of quantity of customers due to different selection of hub airports. This paper presents a new network design method and mathematic optimization model whose object is to maximize total social net welfare. The hub-and-spoke network of Chinese fifteen cities is constructed using this method to demonstrate the effectiveness and practicability of this model.

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CHAPLINE, GEORGE. « SUPERSTRINGS AND QUANTUM GRAVITY ». Modern Physics Letters A 05, n^o 26 (20 octobre 1990) : 2165–72. http://dx.doi.org/10.1142/s0217732390002468.

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It is suggested that the quantum geometry of asymptotically locally Euclidean spaces underlies the dynamics of superstrings moving on Calabi-Yau manifolds. In particular, it is pointed out that solving the Wheeler-DeWitt equation is akin to using a neural network to color maps on a Riemann surface. In the infrared limit such map colorings are formally equivalent to Calabi-Yau vacua for superstrings.

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Majkráková, Miroslava, Juraj Papčo, Pavol Zahorec, Branislav Droščák, Ján Mikuška et Ivan Marušiak. « An analysis of methods for gravity determination and their utilization for the calculation of geopotential numbers in the Slovak national levelling network ». Contributions to Geophysics and Geodesy 46, n^o 3 (1 septembre 2016) : 179–202. http://dx.doi.org/10.1515/congeo-2016-0012.

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Abstract The vertical reference system in the Slovak Republic is realized by the National Levelling Network (NLN). The normal heights according to Molodensky have been introduced as reference heights in the NLN in 1957. Since then, the gravity correction, which is necessary to determine the reference heights in the NLN, has been obtained by an interpolation either from the simple or complete Bouguer anomalies. We refer to this method as the “original”. Currently, the method based on geopotential numbers is the preferred way to unify the European levelling networks. The core of this article is an analysis of different ways to the gravity determination and their application for the calculation of geopotential numbers at the points of the NLN. The first method is based on the calculation of gravity at levelling points from the interpolated values of the complete Bouguer anomaly using the CBA2G_SK software. The second method is based on the global geopotential model EGM2008 improved by the Residual Terrain Model (RTM) approach. The calculated gravity is used to determine the normal heights according to Molodensky along parts of the levelling lines around the EVRF2007 datum point EH-V. Pitelová (UELN-1905325) and the levelling line of the 2nd order NLN to Kráľova hoľa Mountain (the highest point measured by levelling). The results from our analysis illustrate that the method based on the interpolated value of gravity is a better method for gravity determination when we do not know the measured gravity. It was shown that this method is suitable for the determination of geopotential numbers and reference heights in the Slovak national levelling network at the points in which the gravity is not observed directly. We also demonstrated the necessity of using the precise RTM for the refinement of the results derived solely from the EGM2008.

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Lv, Yuejiao, et Yajuan Chen. « Research on the Evolution Characteristics and Synergistic Relationship between HSR Network and Economic Network in Hubei Province ». Sustainability 14, n^o 15 (25 juillet 2022) : 9076. http://dx.doi.org/10.3390/su14159076.

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We construct high-speed railway (HSR) networks for 15 cities in Hubei Province based on the HSR daily operating frequency panel data from 2009 to 2019 and construct economic networks for these cities through a gravity model. Then, we use social network analysis to explore the topological structure and evolutionary characteristics of the HSR and economic networks and use quadratic assignment procedure (QAP) analysis and coupling coordination to analyze the synergistic relationship between the HSR network and economic network. The results show that both the connectivity of the HSR network in Hubei Province and its interactive structure have improved significantly. The development of the HSR network has promoted the interaction of economic networks, but the economic connection among these cities is still weak. Overall, the two networks show a high correlation, but the development trend of both is not clear in the later stage. In general, the province’s level of coupling and coordination has increased, but local disequilibrium still exists.

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Berrino, Giovanna, et Giuseppe Ricciardi. « Repeated absolute gravity measurements on a dense network at Campi Flegrei – a reliable tool for volcano monitoring ». Advances in Geosciences 52 (25 août 2020) : 41–54. http://dx.doi.org/10.5194/adgeo-52-41-2020.

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Abstract. Since 1981, relative gravity measurements have routinely carried out at the Campi Flegrei caldera, a densely populated area. The gravity network also includes two absolute stations periodically measured with a laboratory absolute gravimeter, which does not permit field measurements. At the end of 2014, the Osservatorio Vesuviano, Section of Napoli of the Istituto Nazionale di Geofisica e Vulcanologia (INGV-OV), acquired a portable absolute gravimeter that allows field operations on outdoor sites. Therefore, in 2015 a dense absolute gravity network was established in Campi Flegrei. This will permit an advanced approach for volcano monitoring. The net consists of 36 stations, 34 of which located inside the caldera and placed upon or very close to gravity stations belonging to the relative network. Five surveys were carried out on June 2015, on February and November 2017, on October 2018 and on October 2019. The comparison with height changes suggests that significant Δg are partly due to the uplift occurred over the same time intervals and mostly to shallow processes associated to the dynamic of the local hydrothermal system. The comparison with the gradients observed during the last large uplift (1982–1984) and the following subsidence (1985–2003) confirms this observation. These results suggest that the present activity may be due to a transient or pulsating phenomenon as the alternating recharge/discharge of fluids in the surface hydrothermal system. Gravity changes detected by absolute measurements are in good agreement with those obtained by relative ones, and confirms the feasibility of this methodology for volcano monitoring. Finally, they also encourage replacing the relative networks with absolute ones, with all the consequent advantages.

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Sun, Qipeng, Sijie Wang, Kaiqi Zhang, Fei Ma, Xiaozhuang Guo et Tingzhen Li. « Spatial Pattern of Urban System Based on Gravity Model and Whole Network Analysis in Eight Urban Agglomerations of China ». Mathematical Problems in Engineering 2019 (20 août 2019) : 1–17. http://dx.doi.org/10.1155/2019/6509726.

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An urban agglomeration (shorted as UA) is a highly developed spatial form of integrated city and an important driving force for regional economic development. The network of UA mainly reflects the spatial connections and organizational structure of all cities, which is of great significance for understanding the development status of UAs and revealing their development laws. However, there are few horizontal studies comparing the network structure of China’s UAs. This study constructs the economic network of China’s eight UAs with the gravity model and explores the overall network structure and city centrality using indicators in network analysis. Then, two groups of UAs with similar network structures are compared. Finally, the association between the gravity model and empirical data is discussed. The results show that the spatial pattern of cities in UAs can be expressed by the gravity model approximately. Besides, UAs with different development levels present different spatial network structures, but the network structures cannot reflect the development levels of UAs directly. We also find that the cities with high betweenness centrality have greater development potential to be the next growth pole.

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Krynski, Jan, Tomasz Olszak, Marcin Barlik et Przemyslaw Dykowski. « New gravity control in Poland – needs, the concept and the design ». Geodesy and Cartography 62, n^o 1 (1 juin 2013) : 3–21. http://dx.doi.org/10.2478/geocart-2013-0001.

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Abstract The existing Polish gravity control (POGK) established in the last few years of 20th century according to the international standards is spanned on 12 absolute gravity stations surveyed with four different types of absolute gravimeters. Relative measurements performed by various groups on nearly 350 points of POGK with the use of LaCoste&Romberg (LCR) gravimeters were linked to those 12 stations. The construction of the network, in particular the limited number of non homogeneously distributed absolute gravity stations with gravity determined with different instruments in different epochs is responsible for systematic errors in g on POGK stations. The estimate of those errors with the use of gravity measurements performed in 2007-2008 is given and their possible sources are discussed. The development of absolute gravity measurement technologies, in particular instruments for precise field absolute gravity measurements, provides an opportunity to establish new type of gravity control consisting of stations surveyed with absolute gravimeters. New gravity control planned to be established in 2012-2014 will consist of 28 fundamental points (surveyed with the FG5 - gravimeter), and 169 base points (surveyed with the A10 gravimeter). It will fulfill recent requirements of geodesy and geodynamics and it will provide good link to the existing POGK. A number of stations of the new gravity control with precisely determined position and height will form the national combined geodetic network. Methodology and measurement schemes for both absolute gravimeters as well as the technology for vertical gravity gradient determinations in the new gravity control were developed and tested. The way to assure proper gravity reference level with relation to ICAG and ECAG campaigns as well as local absolute gravimeter comparisons are described highlighting the role of metrology in the project. Integral part of the project are proposals of re-computation of old gravity data and their transformation to a new system (as 2nd order network) as well as a definition of gravity system as “zero-tide” system. Seasonal variability of gravity has been discussed indicating that the effects of environmental changes when establishing modern gravity control with absolute gravity survey cannot be totally neglected.

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Mouzong Pemi, Marcelin, Joseph Kamguia, Severin Nguiya et Eliezer Manguelle-Dicoum. « Depth and Lineament Maps Derived from North Cameroon Gravity Data Computed by Artificial Neural Network ». International Journal of Geophysics 2018 (5 juillet 2018) : 1–13. http://dx.doi.org/10.1155/2018/1298087.

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Accurate interpretation of geological structures inverted from gravity data is highly dependent on the coverage of the recorded gravity data. In this work, Artificial Neural Networks (ANNs) are implemented using Levenberg-Marquardt algorithm (LMA) to construct a background density model for predicting gravity data across Northern Cameroon and its surroundings. This approach yields statistical predictions of gravity values (low values of errors) with 97.48%, 0.10, and 0.89, respectively, for correlation, Mean Bias Error, and Root Mean Square Error for two inputs (latitude, longitude) and 97.08%, 0.13, and 1.14 for three inputs (latitude, longitude, and elevation) for a set of anomalies as output. The model validation is obtained by comparing the results to other classical approaches and to the computed Bouguer, lineaments, and Euler maps obtained from measured gravity data. The depth of most of the deep faults and their orientation are in agreement with those obtained from other studies. The results achieved in this study establish the possibility of enhancing the quality of the analysis, interpretation, and modeling of gravity data collected on sparse grid of recording stations.

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SWAIN, JOHN. « ENTROPY AND AREA IN LOOP QUANTUM GRAVITY ». International Journal of Modern Physics D 14, n^o 12 (décembre 2005) : 2301–5. http://dx.doi.org/10.1142/s0218271805007954.

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Black hole thermodynamics suggests that the maximum entropy that can be contained in a region of space is proportional to the area enclosing it rather than its volume. We argue that this follows naturally from loop quantum gravity and a result of Kolmogorov and Bardzin' on the the realizability of networks in three dimensions. This represents an alternative to other approaches in which some sort of correlation between field configurations helps limit the degrees of freedom within a region. It also provides an approach to thinking about black hole entropy in terms of states inside rather than on its surface. Intuitively, a spin network complicated enough to imbue a region with volume only lets that volume grow as quickly as the area bounding it.

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Tsuji, Toshio, Masataka Nishida, Toshiaki Takahashi et Koji Ito. « Gravity Compensation for Manipulator Control by Neural Networks with Partially Preorganized Structure ». Journal of Robotics and Mechatronics 2, n^o 4 (20 août 1990) : 282–87. http://dx.doi.org/10.20965/jrm.1990.p0282.

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The gravity torque of a manipulator can be compensated if the equation of motion can be correctly introduced, but in general industrial manipulators, there are many cases when the parameter values such as the position of center of mass are not clear, and these values largely change by the exchange of hand portions and the grasping of substances. Furthermore, in addition to unclear parameters, there are factors which occur by structural gravity compensation (spring and counter-balance) and which in many cases are difficult to express with the equation of motion. In this paper, compensation of the gravity torque of the manipulator is studied by, the use of neural networks. For this purpose, a model which makes the structure known to be contained in mapping as a unit with preorganized characteristics prepared in parallel with hidden unit of error back propagation-type neural network is proposed, by which the characteristics of the link system which is the object for learning can be imbedded into the network as preorganized knowledge beforehand. Finally, the results of experiments done with the use of industrial manipulators are given, and it is made clear that the compensation of gravity torque of manipulator and adaptive learning for end-point load are possible by the use of this model.

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Korvin, G., D. M. Boyd et R. O'Dowd. « Fractal characterization of the South Australian gravity station network ». Geophysical Journal International 100, n^o 3 (mars 1990) : 535–39. http://dx.doi.org/10.1111/j.1365-246x.1990.tb00705.x.

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Moffat-Griffin, Tracy, Mike J. Taylor, Takuji Nakamura, Andrew J. Kavanagh, J. Scott Hosking et Andrew Orr. « 3rd ANtarctic Gravity Wave Instrument Network (ANGWIN) science workshop ». Advances in Atmospheric Sciences 34, n^o 1 (14 décembre 2016) : 1–3. http://dx.doi.org/10.1007/s00376-016-6197-5.

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Repanić, Marija. « New adjustment of the Croatian first order gravity network ». Geodetski vestnik 61, n^o 04 (2017) : 630–48. http://dx.doi.org/10.15292/geodetski-vestnik.2017.04.630-648.

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Fagiolo, Giorgio. « The international-trade network : gravity equations and topological properties ». Journal of Economic Interaction and Coordination 5, n^o 1 (13 mars 2010) : 1–25. http://dx.doi.org/10.1007/s11403-010-0061-y.

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Fuxiang, Liu, et Yu Zitong. « The regional economic spatial pattern of Northeast China and its economic integration trend based on network perspective ». E3S Web of Conferences 251 (2021) : 01109. http://dx.doi.org/10.1051/e3sconf/202125101109.

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Based on the modified gravity model and social network analysis method, the paper constructed the economic linkage intensity matrix of 34 prefecture-level cities of Northeast China and analyzed the density and structure of urban linkage networks. The results show that at present, the urban linkage network in the Northeast region is getting closer, and the radiation role of core cities is gradually increasing. However, the degree of regional integration in Northeast China is not high, and some remote cities are still semi-isolated from the network.

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Greco, Filippo, Federica Riguzzi et Giovanna Berrino. « Insights into Seismogenetic Areas in Central Italy from Combined Absolute Gravity and GNSS Measurements ». Remote Sensing 13, n^o 22 (18 novembre 2021) : 4649. http://dx.doi.org/10.3390/rs13224649.

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In this study we present and discuss gravity and ground deformation variations, at different time scales, observed in a wide mesh absolute gravity and GNSS network set up in central Italy. The network was installed in the area affected by the 2009 (L’Aquila; Mw 6.1) and 2016 (Amatrice-Norcia; Mw 6.0 and 6.5) seismic activity, in order to verify if gravity and ground deformation variations could be related to seismic effects. The new network includes 5 stations distributed between the Lazio, Umbria, and Abruzzo regions. From 2018 to 2020 three campaigns were carried out using the transportable Micro-g LaCoste FG5#238 and the portable Micro-g LaCoste A10#39 absolute gravimeters and completed with two simultaneous GNSS measurements. Topographic instruments, measurement and analysis techniques enabling accurate measurements in the positioning of the stations and to control their variations over time were applied. The high reliability and accuracy of the absolute gravity data gathered, after being corrected for known effects, showed a negative short-term (2018–2020) pattern throughout the area, up to −30 µGal. Since some stations of the new network coincided with benchmarks already measured in the past, an analysis of long-term gravity changes was carried out and a fair degree of stability was observed in two stations, while positive large variations, of approximately 70 and 157 µGal, were recorded in the other two stations in the time intervals 1954–2020 and 2005–2010, respectively. On the other hand, variations highlighted by GNSS height measurements were all below 3 cm. Here, the first long-lasting gravity measurements carried out with absolute gravimeters in a seismic area in Italy are presented, providing meaningful geophysical information. The obtained results, in terms of availability of a combined absolute gravity and GNSS network, definition of data acquisition and analysis procedures, as well as creation of a high quality data archive, lay the foundations for a multidisciplinary approach towards improving the knowledge of this seismogenetic area of Italy.

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NÕMMIK, Allan, et Sven KUKEMELK. « DEVELOPING GRAVITY MODEL FOR AIRLINE REGIONAL ROUTE MODELLING ». Aviation 20, n^o 1 (11 avril 2016) : 32–37. http://dx.doi.org/10.3846/16487788.2016.1168007.

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The gravity model is a method that is used by transportation researchers, airline network planners and analysts to explain how traffic is distributed between city pairs in correlation to the distance or travelling time between them, which as a result indicates the behaviour of travellers or the performance of the transport connection. How ever, the applicability of the model depends on the reliability of the results, which poses a major issue for researches. The major difficulty is to obtain comparable qualitative insights into the key parameters that are selected. This paper presents a possibility study for the use of the gravity model for regional route planning from the scientific point of view and suggests possibilities of gravity model calibration for airline network analysis including alternative methods for estimating the gravity potential of destinations and measurement of the influence of distance on the potential. The focus of the research is the ability to explain and forecast the development of regional air transportation routes in the commercial aviation network when there is a lack of recorded booking demand data.

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Kim, Jinsoo, Youngcheol Lee, Sungyeoul Cha, Chuluong Choi et Seongkyu Lee. « Development of a Network RTK Positioning and Gravity-Surveying Application with Gravity Correction Using a Smartphone ». Sensors 13, n^o 7 (12 juillet 2013) : 8879–94. http://dx.doi.org/10.3390/s130708879.

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Zhu, Chengcheng, Jinyun Guo, Jiajia Yuan, Xin Jin, Jinyao Gao et Chengming Li. « Refining Altimeter-Derived Gravity Anomaly Model from Shipborne Gravity by Multi-Layer Perceptron Neural Network : A Case in the South China Sea ». Remote Sensing 13, n^o 4 (8 février 2021) : 607. http://dx.doi.org/10.3390/rs13040607.

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Shipborne gravity can be used to refine altimeter-derived gravity whose accuracy is low in shallow waters and areas with complex submarine topography. As altimeter-derived gravity only within a small radius around the shipborne data can be corrected by traditional methods, a new method based on multi-layer perceptron (MLP) neural network is proposed to refine the altimeter-derived gravity. Input variables of MLP include the positional information at observation points and geophysical information (from our own South China Sea gravity anomaly model (SCSGA) V1.0 and bathymetry model ETOPO1) at grid points around observation points. Output variables of MLP are the refined residual gravity anomalies at observation points. Training shipborne data are classified into four cases to train four MLP models, which are used to predict the refined gravity anomaly model SCSGA V1.1. Then all of the training shipborne data are used for training an MLP model to predict the refined gravity anomaly model SCSGA V1.2. Assessed by testing shipborne data, the accuracy of SCSGA V1.2 is 0.14 mGal higher than that of SCSGA V1.0, and similar to that of SCSGA V1.1. Compared with the original gravity anomaly model (SCSGA V1.0), the accuracy of the refined gravity anomaly model (SCSGA V1.2) by MLP is improved by 4.4% in areas where the training data are concentrated, and also improved by 2.2% in other areas. Therefore, the method of MLP can be used to refine the altimeter-derived gravity model by shipborne gravity, overcoming the problem of limited correction radius for traditional methods.

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Wu, Zongning, Hongbo Cai, Ruining Zhao, Ying Fan, Zengru Di et Jiang Zhang. « A Topological Analysis of Trade Distance : Evidence from the Gravity Model and Complex Flow Networks ». Sustainability 12, n^o 9 (25 avril 2020) : 3511. http://dx.doi.org/10.3390/su12093511.

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As a classical trade model, the gravity model plays an important role in the trade policy-making process. However, the effect of physical distance fails to capture the effects of globalization and even ignores the multilateral resistance of trade. Here, we propose a general model describing the effective distance of trade according to multilateral trade paths information and the structure of the trade flow network. Quantifying effective trade distance aims to identify the hidden resistance information from trade networks data, and then describe trade barriers. The results show that flow distance, hybrid by multi-path constraint, and international trade network contribute to the forecasting of trade flows. Meanwhile, we also analyze the role of flow distance in international trade from two perspectives of network science and econometric model. At the econometric model level, flow distance can collapse to the predicting results of geographic distance in the proper time lagging variable, which can also reflect that flow distance contains geographical factors. At the international trade network level, community structure detection by flow distances and flow space embedding instructed that the formation of international trade networks is the tradeoff of international specialization in the trade value chain and geographical aggregation. The methodology and results can be generalized to the study of all kinds of product trade systems.

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Dardani, Ian, et Gerard F. Jones. « Algorithms for optimization of branching gravity-driven water networks ». Drinking Water Engineering and Science 11, n^o 1 (15 mai 2018) : 67–85. http://dx.doi.org/10.5194/dwes-11-67-2018.

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Abstract. The design of a water network involves the selection of pipe diameters that satisfy pressure and flow requirements while considering cost. A variety of design approaches can be used to optimize for hydraulic performance or reduce costs. To help designers select an appropriate approach in the context of gravity-driven water networks (GDWNs), this work assesses three cost-minimization algorithms on six moderate-scale GDWN test cases. Two algorithms, a backtracking algorithm and a genetic algorithm, use a set of discrete pipe diameters, while a new calculus-based algorithm produces a continuous-diameter solution which is mapped onto a discrete-diameter set. The backtracking algorithm finds the global optimum for all but the largest of cases tested, for which its long runtime makes it an infeasible option. The calculus-based algorithm's discrete-diameter solution produced slightly higher-cost results but was more scalable to larger network cases. Furthermore, the new calculus-based algorithm's continuous-diameter and mapped solutions provided lower and upper bounds, respectively, on the discrete-diameter global optimum cost, where the mapped solutions were typically within one diameter size of the global optimum. The genetic algorithm produced solutions even closer to the global optimum with consistently short run times, although slightly higher solution costs were seen for the larger network cases tested. The results of this study highlight the advantages and weaknesses of each GDWN design method including closeness to the global optimum, the ability to prune the solution space of infeasible and suboptimal candidates without missing the global optimum, and algorithm run time. We also extend an existing closed-form model of Jones (2011) to include minor losses and a more comprehensive two-part cost model, which realistically applies to pipe sizes that span a broad range typical of GDWNs of interest in this work, and for smooth and commercial steel roughness values.

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Prodous, Oleg A., Dmitriy I. Shlychkov, Petr P. Jakubchik et Sergey V. Parkhomenko. « Influence of the thickness of the layer of internal deposits in pipelines of water supply and discharge systems on their remaining service life ». Vestnik MGSU, n^o 6 (juin 2022) : 738–46. http://dx.doi.org/10.22227/1997-0935.2022.6.738-746.

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Introduction. The practical operation of water supply networks, made of steel and gray cast iron, has proven that deposits accumulate on the inner surface of pipes under certain conditions. Deposition depends on the quality of transported water and the water flow regime, same as in gravity sewerage networks. A sediment layer accumulates in the flume of pipes if the actual flow rate is smaller than the minimum standard one. A layer of deposits in metal water pipes changes the value of the actual inner diameter of pipes and rises the pressure loss due to resistance along the pipeline length, which contributes to an increase in the energy consumption by the pumping equipment and affects the pressure value at the end point of a network. A layer of sediment in the flume of a gravity drainage network also rises losses along its length, slows down the flow rate and may block the water flow in the network. The purpose of the study is to find dependence between the remaining service life of water supply and sewerage networks, having internal deposits, and the thickness of the layer of deposits on pipe walls. Materials and methods. The authors use the dependences, that they have already derived for the hydraulic analysis of metal water supply networks and gravity sewerage networks, having internal deposits. Results. The authors have identified dependence between the remaining service life of water supply pipelines and sewerage systems and the thickness of deposits on the inner walls of pipes. Examples, confirming such a relationship, are provided. They are substantiated by graphs showing dependence between the remaining service life and the thickness of the layer of deposits in pipelines. A hydraulic criterion is proposed for projecting the term of operation of water supply and sewerage networks with internal deposits. Conclusions. The authors have proven the need to use special tables to analyze the characteristics of pipes within the framework of a hydraulic analysis of water supply and sewerage networks, having internal deposits.

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Fischer, M. M. « Computational Neural Networks : A New Paradigm for Spatial Analysis ». Environment and Planning A : Economy and Space 30, n^o 10 (octobre 1998) : 1873–91. http://dx.doi.org/10.1068/a301873.

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In this paper a systematic introduction to computational neural network models is given in order to help spatial analysts learn about this exciting new field. The power of computational neural networks viz-à-viz conventional modelling is illustrated for an application field with noisy data of limited record length: spatial interaction modelling of telecommunication data in Austria. The computational appeal of neural networks for solving some fundamental spatial analysis problems is summarized and a definition of computational neural network models in mathematical terms is given. Three definitional components of a computational neural network—properties of the processing elements, network topology and learning—are discussed and a taxonomy of computational neural networks is presented, breaking neural networks down according to the topology and type of interconnections and the learning paradigm adopted. The attractiveness of computational neural network models compared with the conventional modelling approach of the gravity type for spatial interaction modelling is illustrated before some conclusions and an outlook are given.

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Cao, Chun-Jun. « From Quantum Codes to Gravity : A Journey of Gravitizing Quantum Mechanics ». Universe 8, n^o 1 (21 décembre 2021) : 1. http://dx.doi.org/10.3390/universe8010001.

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In this note, I review a recent approach to quantum gravity that “gravitizes” quantum mechanics by emerging geometry and gravity from complex quantum states. Drawing further insights from tensor network toy models in AdS/CFT, I propose that approximate quantum error correction codes, when re-adapted into the aforementioned framework, also have promise in emerging gravity in near-flat geometries.

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Shymanskyi, Oleksandr, Jue Wang et Yue Pu. « Global tourist flows under the Belt and Road Initiative : A complex network analysis ». PLOS ONE 17, n^o 8 (16 août 2022) : e0272964. http://dx.doi.org/10.1371/journal.pone.0272964.

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This study applies complex network analysis to examine global tourist flows network in the context of Belt and Road Initiative (BRI). Using tourist flows data between 221 countries/regions over 1995–2018, we investigate the nature and development patterns of structural properties of global network as well as factors influencing its formation. The descriptive analysis indicates that global tourist network was a sparse network with small world network characteristics. According to centrality characteristics, China showed the most influence in the BRI group, while Germany and the United States possessed key roles among non-BRI countries/regions. Exploratory analysis demonstrated significant influence of gravity variables in global, BRI and non-BRI tourist networks. This research advances existing tourism theory and provides practical implications for policymakers.

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Stober, Gunter, Alexander Kozlovsky, Alan Liu, Zishun Qiao, Masaki Tsutsumi, Chris Hall, Satonori Nozawa et al. « Atmospheric tomography using the Nordic Meteor Radar Cluster and Chilean Observation Network De Meteor Radars : network details and 3D-Var retrieval ». Atmospheric Measurement Techniques 14, n^o 10 (8 octobre 2021) : 6509–32. http://dx.doi.org/10.5194/amt-14-6509-2021.

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Abstract. Ground-based remote sensing of atmospheric parameters is often limited to single station observations by vertical profiles at a certain geographic location. This is a limiting factor for investigating gravity wave dynamics as the spatial information is often missing, e.g., horizontal wavelength, propagation direction or intrinsic frequency. In this study, we present a new retrieval algorithm for multistatic meteor radar networks to obtain tomographic 3-D wind fields within a pre-defined domain area. The algorithm is part of the Agile Software for Gravity wAve Regional Dynamics (ASGARD) and called 3D-Var, and based on the optimal estimation technique and Bayesian statistics. The performance of the 3D-Var retrieval is demonstrated using two meteor radar networks: the Nordic Meteor Radar Cluster and the Chilean Observation Network De Meteor Radars (CONDOR). The optimal estimation implementation provide statistically sound solutions and diagnostics from the averaging kernels and measurement response. We present initial scientific results such as body forces of breaking gravity waves leading to two counter-rotating vortices and horizontal wavelength spectra indicating a transition between the rotational k−3 and divergent k-5/3 mode at scales of 80–120 km. In addition, we performed a keogram analysis over extended periods to reflect the latitudinal and temporal impact of a minor sudden stratospheric warming in December 2019. Finally, we demonstrate the applicability of the 3D-Var algorithm to perform large-scale retrievals to derive meteorological wind maps covering a latitude region from Svalbard, north of the European Arctic mainland, to central Norway.

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