Journal articles on the topic 'Earth resistance (Geophysics) Mathematical models'
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Mishra, Jagriti, and Takuya Inoue. "Alluvial cover on bedrock channels: applicability of existing models." Earth Surface Dynamics 8, no. 3 (August 13, 2020): 695–716. http://dx.doi.org/10.5194/esurf-8-695-2020.
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Abstract. Several studies have demonstrated the importance of alluvial cover; furthermore, several mathematical models have also been introduced to predict the alluvial cover on bedrock channels. Here, we provide an extensive review of research exploring the relationship between alluvial cover, sediment supply and bed topography of bedrock channels, describing various mathematical models used to analyse the deposition of alluvium. To test one-dimensional theoretical models, we performed a series of laboratory-scale experiments with varying bed roughness under simple conditions without bar formation. Our experiments show that alluvial cover is not merely governed by increasing sediment supply and that bed roughness is an important controlling factor of alluvial cover. A comparison between the experimental results and the five theoretical models shows that (1) two simple models that calculate alluvial cover as a linear or exponential function of the ratio of the sediment supplied to the capacity of the channel produce good results for rough bedrock beds but not for smoother bedrock beds; (2) two roughness models which include changes in roughness with alluviation and a model including the probability of sediment accumulation can accurately predict alluvial cover in both rough and smooth beds; and (3), however, except for a model using the observed hydraulic roughness, it is necessary to adjust model parameters even in a straight channel without bars.
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Lugoe, Furaha N. "Rigorous mathematical models for the densification and integration of geodetic networks." Bulletin Géodésique 64, no. 3 (September 1990): 219–29. http://dx.doi.org/10.1007/bf02519177.
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Tague, John A., and Kerry D. Schutz. "Seismic transient deconvolution with model‐based signal processing." GEOPHYSICS 62, no. 4 (July 1997): 1321–30. http://dx.doi.org/10.1190/1.1444234.
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Short duration seismic disturbances, obscured by earth noise and distorted by the seismometers used to measure them, can be reconstructed using model‐based signal processing. “Model based” means that mathematical models of the seismic transient, earth noise, and seismometer dynamics are infused into the signal processor that estimates the disturbance. The processor imposes no predetermined structure on the transient and the earth noise need not be white. Model‐based processors produce good quality estimates for a broad class of transient waveforms.
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Langel, R. A. "International Geomagnetic Reference Field, 1991 Revision: International Association of Geomagnetism and Aeronomy (IAGA) Division V, Working Group 8: Analysis of the main field and secular variation." GEOPHYSICS 57, no. 7 (July 1992): 956. http://dx.doi.org/10.1190/1.1443310.
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The International Geomagnetic Reference Field (IGRF) is a series of mathematical models of the main geomagnetic field and its secular variation. Each model consists of a set of spherical harmonic (or Gauss) coefficients, g and h in a series expansion of the geomagnetic potential [Formula: see text], where a is the mean radius of the Earth (6371.2 km); r the radial distance from the center of the Earth; ϕ the east longitude measured from Greenwich; θ the geocentric colatitude; and [Formula: see text] the associated Legendre function of degree n and order m, normalized according to the convention of Schmidt [see, e.g., Langel (1987)]. In principle, N should be ∞ but the Working Group is of the opinion that in practice the available data for most epochs do not justify N greater than 10. This value is chosen to maintain consistency between models at different epochs. The coefficients are in units of nanotesla (nT).
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Niwas, Sri, and M. Israil. "Computation of apparent resistivities using an exponential approximation of kernel functions." GEOPHYSICS 51, no. 8 (August 1986): 1594–602. http://dx.doi.org/10.1190/1.1442210.
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We present a fresh approach to the mathematical computation of apparent resistivities in electrical prospecting. The method is based on an exponential approximation of the kernel function which reduces the integral equation for the potential over a layered earth to a simple algebraic equation. The coefficients in the approximation are obtained using a least‐squares inversion technique. A single, unified matrix equation allows computation of apparent resistivity values for arbitrary four‐electrode arrays over a layered earth. The unified G function automatically reduces to that of a symmetrical four‐electrode array and dipole array function with the proper interelectrode separation. Computations for some two‐, three‐, and four‐layer earth models (Schlumberger configuration), along with a few Wenner and radial dipole apparent resistivity values, demonstrate the versatility of this unified equation.
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Aksenov, A. L., and O. I. Kozlov. "Satellite and aerial imagery geo-referencing using ground features." Geodesy and Cartography 975, no. 9 (October 20, 2021): 21–29. http://dx.doi.org/10.22389/0016-7126-2021-975-9-21-29.
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The method of geo-referencing satellite- and aerial imagery using reference points, linear and non-linear features, and segments of geodetic tracks as elements of a plan-altitude basis is discussed in this article. The method can be used for any mathematical model of satellite- and aerial imagery. The parametric description of the features, that can be used for the geo-referencing and various mathematical models of the above-mentioned imagery are presented. The mathematical formulation of the matter of satellite and aerial imagery geo-referencing using terrain objects and reference points is presented. A list of linear and non-linear features that can be included in a high-raised basis along with reference points is made. A generalized algorithm for geo-referencing satellite and aerial imagery using reference points and terrain features is given. The algorithm includes making a nonlinear system of equations for reference points and items, linearizing the system and solving by the sequential approximation technique according to the least squares method. An example of clarifying the satellite RPC-model and aerial imagery using reference points, linear and non-linear features is given. The advantages of the proposed method of using features created according to the measurements on satellite and aerial imagery compared with method, when the model of the feature is created according to the measurements on the ground are described.
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Mondragón, Román, Joaquín Alonso-Montesinos, David Riveros-Rosas, Mauro Valdés, Héctor Estévez, Adriana E. González-Cabrera, and Wolfgang Stremme. "Attenuation Factor Estimation of Direct Normal Irradiance Combining Sky Camera Images and Mathematical Models in an Inter-Tropical Area." Remote Sensing 12, no. 7 (April 9, 2020): 1212. http://dx.doi.org/10.3390/rs12071212.
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Nowadays, it is of great interest to know and forecast the solar energy resource that will be constantly available in order to optimize its use. The generation of electrical energy using CSP (concentrated solar power) plants is mostly affected by atmospheric changes. Therefore, forecasting solar irradiance is essential for planning a plant’s operation. Solar irradiance/atmospheric (clouds) interaction studies using satellite and sky images can help to prepare plant operators for solar surface irradiance fluctuations. In this work, we present three methodologies that allow us to estimate direct normal irradiance (DNI). The study was carried out at the Solar Irradiance Observatory (SIO) at the Geophysics Institute (UNAM) in Mexico City using corresponding images obtained with a sky camera and starting from a clear sky model. The multiple linear regression and polynomial regression models as well as the neural networks model designed in the present study, were structured to work under all sky conditions (cloudy, partly cloudy and cloudless), obtaining estimation results with 82% certainty for all sky types.
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Melis, M. T., F. Mundula, F. DessÌ, R. Cioni, and A. Funedda. "Tracing the boundaries of Cenozoic volcanic edifices from Sardinia (Italy): a geomorphometric contribution." Earth Surface Dynamics 2, no. 2 (September 25, 2014): 481–92. http://dx.doi.org/10.5194/esurf-2-481-2014.
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Abstract. Unequivocal delimitation of landforms is an important issue for different purposes, from science-driven morphometric analysis to legal issues related to land conservation. This study is aimed at giving a new contribution to the morphometric approach for the delineation of the boundaries of volcanic edifices, applied to 13 monogenetic volcanoes (scoria cones) related to the Pliocene–Pleistocene volcanic cycle in Sardinia (Italy). External boundary delimitation of the edifices is discussed based on an integrated methodology using automatic elaboration of digital elevation models together with geomorphological and geological observations. Different elaborations of surface slope and profile curvature have been proposed and discussed; among them, two algorithms based on simple mathematical functions combining slope and profile curvature well fit the requirements of this study. One of theses algorithms is a modification of a function introduced by Grosse et al. (2011), which better performs for recognizing and tracing the boundary between the volcanic scoria cone and its basement. Although the geological constraints still drive the final decision, the proposed method improves the existing tools for a semi-automatic tracing of the boundaries.
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Epov, M. I., V. N. Glinskikh, M. N. Nikitenko, A. A. Lapkovskaya, A. R. Leonenko, A. M. Petrov, K. V. Sukhorukova, and D. I. Gornostalev. "MODERN ALGORITHMS AND SOFTWARE FOR INTERPRETATION OF RESISTIVITY LOGGING DATA." Geodynamics & Tectonophysics 12, no. 3S (October 19, 2021): 669–82. http://dx.doi.org/10.5800/gt-2021-12-3s-0546.
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The electrodynamics of geological media investigates the interrelations of resistivity logging signals and properties of fluid-containing rocks and creates innovative well logging technologies. Its development is inextricably linked with modern techniques for mathematical modeling and quantitative interpretation of high-precision data. In order to increase the information content of galvanic and electromagnetic logging, we have developed algorithms and software for numerical simulation and inversion of field data. In our study of the Cretaceous and Jurassic deposits of West Siberia, a quantitative interpretation of high-frequency electromagnetic and lateral logging signals was carried out. To create geoelectric models, we interpreted the field resistivity logging data by an unconventional quantitative technique based on their joint numerical inversion and estimations of the vertical resistivity of permeable deposits. Another line of our research was aimed at a scientific substantiation of a new technology for mapping and spatial tracking of lateral heterogeneities and oil-promising zones in the Bazhenov Formation. The aim was achieved by using the TEM sounding data on a spatially distributed system of directional and horizontal wells.
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Xing, Guangchi, and Tieyuan Zhu. "A viscoelastic model for seismic attenuation using fractal mechanical networks." Geophysical Journal International 224, no. 3 (November 17, 2020): 1658–69. http://dx.doi.org/10.1093/gji/ggaa549.
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SUMMARY Seismic attenuation (quantified by the quality factor Q) has a significant impact on the seismic waveforms, especially in the fluid-saturated rocks. This dissipative process can be phenomenologically represented by viscoelastic models. Previous seismological studies show that the Q value of Earth media exhibits a nearly frequency-independent behaviour (often referred to as constant-Q in literature) in the seismic frequency range. Such attenuation can be described by the mathematical Kjartansson constant-Q model, which lacks of a physical representation in the viscoelastic sense. Inspired by the fractal nature of the pore fluid distribution in patchy-saturated rocks, here we propose two fractal mechanical network (FMN) models, that is, a fractal tree model and a quasi-fractal ladder model, to phenomenologically represent the frequency-independent Q behaviour. As with the classic viscoelastic models, the FMN models are composed of mechanical elements (spring and dashpots) arranged in different hierarchical patterns. A particular parametrization of each model can produce the same complex modulus as in the Kjartansson model, which leads to the constant-Q. Applying the theory to several typical rock samples, we find that the seismic attenuation signature of these rocks can be accurately represented by either one of the FMN models. Besides, we demonstrate that the ladder model in particular exhibits the realistic multiscale fractal structure of the saturated rocks. Therefore, the FMN models as a proxy could provide a new way to estimate the microscopic rock structure property from macroscopic seismic attenuation observation.
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Edmaier, K., P. Burlando, and P. Perona. "Mechanisms of vegetation uprooting by flow in alluvial non-cohesive sediment." Hydrology and Earth System Sciences Discussions 8, no. 1 (January 28, 2011): 1365–98. http://dx.doi.org/10.5194/hessd-8-1365-2011.
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Abstract. The establishment of riparian pioneer vegetation is of crucial importance within river restoration projects. After germination or vegetative reproduction on river bars juvenile plants are often exposed to mortality by uprooting caused by floods. At later stages of root development vegetation uprooting by flow is seen to occur as a consequence of a marked erosion gradually exposing the root system and accordingly reducing the mechanical anchoring. How time scales of flow-induced uprooting do depend on vegetation stages growing in alluvial non-cohesive sediment is currently an open question that we conceptually address in this work. After reviewing vegetation root issues in relation to morphodynamic processes, we then propose two modelling mechanisms (Type I and Type II), respectively concerning the uprooting time scales of early germinated and of mature vegetation. Type I is a purely flow-induced drag mechanism, which causes alone a nearly instantaneous uprooting when exceeding root resistance. Type II arises as a combination of substantial sediment erosion exposing the root system and resulting in a decreased anchoring resistance, eventually degenerating into a Type I mechanism. We support our conceptual models with some preliminary experimental data and discuss the importance of better understanding such mechanisms in order to formulate sounding mathematical models that are suitable to plan and to manage river restoration projects.
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Golovkov, Aleksandr A., and Aleksey V. Fomin. "Parametrical synthesis of radio devices with the set quantity of identical cascades for variants of inclusion of jet two-port networks between a source of a signal and a nonlinear part." Physics of Wave Processes and Radio Systems 24, no. 3 (November 18, 2021): 46–55. http://dx.doi.org/10.18469/1810-3189.2021.24.3.46-55.
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The algorithm of parametrical synthesis of various radio devices with any quantity of cascades of type the jet two-port network a nonlinear part by criterion of maintenance of the set frequency characteristics is developed. Nonlinear parts are presented in the form of a nonlinear element and parallel either consecutive on a current or pressure of a feedback. According to this criterion systems of the algebraic equations are generated and solved. Models of optimum two-port networks in the form of mathematical expressions for definition of interrelations between elements of their classical matrix of transfer and for search of dependences of resistance of two-poles from frequency are as a result received. It is shown, that frequency characteristics of investigated radio devices from identical cascades are identical or similar to frequency characteristics of radio devices from one cascade, but with resistance of a source of a signal and the loading, changed definitely. Such schemes are named by equivalent. The comparative analysis of the theoretical results received by mathematical modelling in system MathCad, and the experimental results received by circuit simulation in systems OrCad and MicroCap, shows their satisfactory coincidence.
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Golovkov, Aleksandr A., Vladimir A. Golovkov, and Aleksey V. Fomin. "Parametrical synthesis of radio devices with the set quantity of unequal cascades for variants of inclusion of jet two-port networks between a nonlinear part and loading." Physics of Wave Processes and Radio Systems 24, no. 3 (November 18, 2021): 63–70. http://dx.doi.org/10.18469/1810-3189.2021.24.3.63-70.
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The algorithm of parametrical synthesis of various radio devices with any quantity of cascades of type a nonlinear part the jet two-port network by criterion of maintenance of the set frequency characteristics is developed. Nonlinear parts are presented in the form of a nonlinear element and parallel either consecutive on a current or pressure of a feedback. According to this criterion systems of the algebraic equations are generated and solved. Models of optimum two-port networks of one of cascades in the form of mathematical expressions for definition of interrelations between elements of their classical matrix of transfer and for search of dependences of resistance of two-poles from frequency are as a result received. It is spent mathematical and circuit simulation of the two-cascade amplifier. It is shown, that the increase in quantity of cascades with the optimised parametres leads to substantial growth of a working strip of frequencies. The comparative analysis of the theoretical results received by mathematical modelling in system MathCad, and the experimental results received by circuit simulation in systems OrCad and MicroCap, shows their satisfactory coincidence.
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Ray, Anandaroop. "Bayesian inversion using nested trans-dimensional Gaussian processes." Geophysical Journal International 226, no. 1 (March 26, 2021): 302–26. http://dx.doi.org/10.1093/gji/ggab114.
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SUMMARY To understand earth processes, geoscientists infer subsurface earth properties such as electromagnetic resistivity or seismic velocity from surface observations of electromagnetic or seismic data. These properties are used to populate an earth model vector, and the spatial variation of properties across this vector sheds light on the underlying earth structure or physical phenomenon of interest, from groundwater aquifers to plate tectonics. However, to infer these properties the spatial characteristics of these properties need to be known in advance. Typically, assumptions are made about the length scales of earth properties, which are encoded a priori in a Bayesian probabilistic setting. In an optimization setting, appeals are made to promote model simplicity together with constraints which keep models close to a preferred model. All of these approaches are valid, though they can lead to unintended features in the resulting inferred geophysical models owing to inappropriate prior assumptions, constraints or even the nature of the solution basis functions. In this work it will be shown that in order to make accurate inferences about earth properties, inferences can first be made about the underlying length scales of these properties in a very general solution basis. From a mathematical point of view, these spatial characteristics of earth properties can be conveniently thought of as ‘properties’ of the earth properties. Thus, the same machinery used to infer earth properties can be used to infer their length scales. This can be thought of as an ‘infer to infer’ paradigm analogous to the ‘learning to learn’ paradigm which is now commonplace in the machine learning literature. However, it must be noted that (geophysical) inference is not the same as (machine) learning, though there are many common elements which allow for cross-pollination of useful ideas from one field to the other, as is shown here. A non-stationary trans-dimensional Gaussian Process (TDGP) is used to parametrize earth properties, and a multichannel stationary TDGP is used to parametrize the length scales associated with the earth property in question. Using non-stationary kernels, that is kernels with spatially variable length scales, models with sharp discontinuities can be represented within this framework. As GPs are multidimensional interpolators, the same theory and computer code can be used to solve geophysical problems in 1-D, 2-D and 3-D. This is demonstrated through a combination of 1-D and 2-D non-linear regression examples and a controlled source electromagnetic field example. The key difference between this and previous work using TDGP is generalized nested inference and the marginalization of prior length scales for better posterior subsurface property characterization.
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Armitage, John J., Alexander C. Whittaker, Mustapha Zakari, and Benjamin Campforts. "Numerical modelling of landscape and sediment flux response to precipitation rate change." Earth Surface Dynamics 6, no. 1 (February 15, 2018): 77–99. http://dx.doi.org/10.5194/esurf-6-77-2018.
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Abstract. Laboratory-scale experiments of erosion have demonstrated that landscapes have a natural (or intrinsic) response time to a change in precipitation rate. In the last few decades there has been growth in the development of numerical models that attempt to capture landscape evolution over long timescales. However, there is still an uncertainty regarding the validity of the basic assumptions of mass transport that are made in deriving these models. In this contribution we therefore return to a principal assumption of sediment transport within the mass balance for surface processes; we explore the sensitivity of the classic end-member landscape evolution models and the sediment fluxes they produce to a change in precipitation rates. One end-member model takes the mathematical form of a kinetic wave equation and is known as the stream power model, in which sediment is assumed to be transported immediately out of the model domain. The second end-member model is the transport model and it takes the form of a diffusion equation, assuming that the sediment flux is a function of the water flux and slope. We find that both of these end-member models have a response time that has a proportionality to the precipitation rate that follows a negative power law. However, for the stream power model the exponent on the water flux term must be less than one, and for the transport model the exponent must be greater than one, in order to match the observed concavity of natural systems. This difference in exponent means that the transport model generally responds more rapidly to an increase in precipitation rates, on the order of 105 years for post-perturbation sediment fluxes to return to within 50 % of their initial values, for theoretical landscapes with a scale of 100×100 km. Additionally from the same starting conditions, the amplitude of the sediment flux perturbation in the transport model is greater, with much larger sensitivity to catchment size. An important finding is that both models respond more quickly to a wetting event than a drying event, and we argue that this asymmetry in response time has significant implications for depositional stratigraphies. Finally, we evaluate the extent to which these constraints on response times and sediment fluxes from simple models help us understand the geological record of landscape response to rapid environmental changes in the past, such as the Paleocene–Eocene thermal maximum (PETM). In the Spanish Pyrenees, for instance, a relatively rapid (10 to 50 kyr) duration of the deposition of gravel is observed for a climatic shift that is thought to be towards increased precipitation rates. We suggest that the rapid response observed is more easily explained through a diffusive transport model because (1) the model has a faster response time, which is consistent with the documented stratigraphic data, (2) there is a high-amplitude spike in sediment flux, and (3) the assumption of instantaneous transport is difficult to justify for the transport of large grain sizes as an alluvial bedload. Consequently, while these end-member models do not reproduce all the complexity of processes seen in real landscapes, we argue that variations in long-term erosional dynamics within source catchments can fundamentally control when, how, and where sedimentary archives can record past environmental change.
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Clarke, Garry K. C. "Lumped-element model for subglacial transport of solute and suspended sediment." Annals of Glaciology 22 (1996): 152–59. http://dx.doi.org/10.3189/1996aog22-1-152-159.
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Present understanding of the subglacial water system and its role in transporting solute and sediment is largely based on subglacial observations of water pressure, turbidity and electrical conductivity and on portal measurements. Such data reveal a wealth of intriguing phenomena, but convincing interpretations can be elusive. Although a proper mathematical description of the subglacial water system would unquestionably lead to a coupled system of non-linear partial differential equations, it is not fruitful to introduce this level of complexity until the important physical processes have been identified and quantified. Lumped-element models offer an efficient approach to examining the complex but dimly perceived physics of the subglacial water system. Water volume, hydraulic head, discharge and flow resistance have the respective electrical analogues of charge, voltage, current and ohmic resistance. Thus, subglacial hydraulic circuits can be approximated by electrical circuits. Mathematically, this circuit description commonly leads to a coupled system of algebraic and differential equations which can be solved numerically. It is straightforward to enrich this representation by adding sources and sinks of solute and sediment. To demonstrate the method, model results are compared to records of subglacial pressure, electrical conductivity and turbidity measured beneath Trapridge Glacier, Yukon Territory, Canada.
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Shchekin, Alexander I., Vyacheslav V. Verzhbitsky, Tatiana A. Gunkina, and Alexander V. Handzel. "Factor analysis of gas wells’ operating parameters." Georesursy 24, no. 2 (September 30, 2022): 139–48. http://dx.doi.org/10.18599/grs.2022.3.12.
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The paper discusses methodological approaches to the use of deterministic factor analysis for identifying the sources of changes in gas wells’ parameters under steady-state gas inflow obeying linear and non-linear filtration laws. Factor analysis methods make it possible to quantify the degree of influence of individual factors on the deviation of the indicator under study. In accordance with the methodology of factor analysis, mathematical models of the factor system were substantiated for linear and non-linear gas filtration, a set of factors of influence was determined, and ready-made solutions for factor analysis of gas wells’ operating parameters were obtained. In the paper, the method of weighted finite differences was substantiated and investigated with the aim of factor analyzing gas wells’ mode of operation and obtaining formulas to calculate the increment in gas production caused by changes in factors. Approbation of working formulas for assessing the degree of influence of factors on either positive or negative deviations in the gas flow rate was carried out with respect to the parameters of the wells of underground gas storages in the cycles of withdrawal and injection. The obtained formulas for factor analysis of gas wells make it possible to quantify the influence of such factors as reservoir and bottomhole pressures, filtration resistance coefficients, on the deviation of gas flow rate. Further ranking of wells by factors constitutes the basis for managing gas withdrawal (injection) processes and for well interventions planning.
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Pyroh, Y. "Models of psychophysiological indicators qualified judokas." Єдиноборства, no. 4(26) (November 1, 2022): 63–74. http://dx.doi.org/10.15391/ed.2022-4.07.
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Purpose: on the basis of the developed models of psychophysiological indicators, to establish evaluation criteria of sensorimotor reactions and specific perceptions for qualified judokas. Material and methods. The following methods were used: analysis of scientific and methodological information and the Internet, generalization of best practical experience; psychophysiological research methods; methods of mathematical statistics. 18 qualified judokas (10 athletes from KMSU and 8 athletes from MSU), aged 21,00±1,29 years, took part in the research. Assessment of psychophysiological indicators was carried out using a complex of tests developed for tablet personal computers. For the convenience of the research, all tests were divided into three groups: assessment of simple sensorimotor reactions; assessment of complex sensorimotor reactions; assessment of specific perceptions. Results: the analysis of scientific and methodical literature, the Internet and the generalization of best practical experience made it possible to establish that training and competitive activities in martial arts contribute to the formation of a whole complex of specific reactions and perceptions in athletes. It is based on the threshold of perception of stimuli, which are composed of different sensory systems. The main role is played by the levels of muscle-motor, visual, vestibular and auditory sensations. The higher the level of sportsmanship of the athlete, the higher the level of importance of psychophysiological functions to achieve a competitive result. In the course of the study, the results of psychophysiological indicators were obtained in the following tests: «Simple motor skills and resistance to distracting factors», «Simple visual-motor reaction», «Simple auditory-motor reaction», «Reaction of choosing from static objects», «Reaction of discrimination», «Reaction to a moving object», «Reaction of selection from dynamic objects», «Evaluation of the sense of tempo», «Evaluation of accuracy and speed when reproducing a given line», «Evaluation of perception of a change in size object»). Conclusions. Based on the obtained results, models of psychophysiological indicators were developed, which made it possible to establish evaluation criteria of sensorimotor reactions and specific perceptions for qualified judokas. It was established that the specifics of the competitive activity of martial artists leaves its mark on the level of development of the leading psychophysiological qualities that ensure high sports achievements in the chosen type of martial arts. Keywords: modeling, psychophysiological indicators, judo, qualified athletes.
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Deng, Wubing, and Igor B. Morozov. "Mechanical interpretation and generalization of the Cole-Cole model in viscoelasticity." GEOPHYSICS 83, no. 6 (November 1, 2018): MR345—MR352. http://dx.doi.org/10.1190/geo2017-0821.1.
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The mechanical basis of the popular Cole-Cole rheological model in viscoelasticity is investigated by using Lagrangian mechanics with nonlinear energy dissipation. The Cole-Cole model is usually viewed as a convenient way to fit the observed frequency-dependent attenuation and velocity-dispersion spectra, but its time-domain and numerical formulations are complex and contradict standard physical principles. For example, time-domain modeling of Cole-Cole media requires special mathematical tools such as fractional derivatives, convolutional integrals, and/or memory variables. Nevertheless, we find that Cole-Cole spectra naturally arise from conventional mechanics with nonlinear internal friction (non-Newtonian viscosity). The Lagrangian mechanical formulation is applied to a finite body (a rock sample in a laboratory experiment) and a wave-propagating medium, in both cases providing rigorous differential equations of motion and revealing the time- and frequency-independent material properties. The model also leads to a generalized Cole-Cole (GCC) model with multiple internal variables (relaxation mechanisms), similar to the generalized standard linear solid (GSLS). As a practical application, the GSLS and GCC models are compared on interpretations of recent P-wave attenuation and dispersion measurements on bitumen-sand samples in the laboratory. The GSLS and GCC models can be used to predict the observed strain/stress ratios with adequate accuracy. However, each of these models offers certain advantages, which are the linearity (for GSLS) and potentially smaller number of dynamic variables and broader peaks in attenuation spectra (for GCC). Therefore, additional experiments focusing on linearity of internal friction are required to establish which of these models may be preferable for rock. The Lagrangian approach provides a simple and physically meaningful way for comparing all types of observations, formulating numerical modeling schemes, and predicting the propagation of waves and behavior of other deformations of earth media.
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Ghosh, Santi Kumar, and Animesh Mandal. "Feasibility of approximate broadband estimation of acoustic impedance profile from first principles and band-limited reflection data." GEOPHYSICS 81, no. 3 (May 2016): R57—R74. http://dx.doi.org/10.1190/geo2015-0056.1.
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Because seismic reflection data are band limited, acoustic impedance profiles derived from them are nonunique. The conventional inversion methods counter the nonuniqueness either by stabilizing the answer with respect to an initial model or by imposing mathematical constraints such as sparsity of the reflection coefficients. By making a nominal assumption of an earth model locally consisting of a stack of homogeneous and horizontal layers, we have formulated a set of linear equations in which the reflection coefficients are the unknowns and the recursively integrated seismic trace constitute the data. Drawing only on first principles, the Zoeppritz equation in this case, the approach makes a frontal assault on the problem of reconstructing reflection coefficients from band-limited data. The local layer-cake assumption and the strategy of seeking a singular value decomposition solution of the linear equations counter the nonuniqueness, provided that the objective is to reconstruct a smooth version of the impedance profile that includes only its crude structures. Tests on synthetic data generated from elementary models and from measured logs of acoustic impedance demonstrated the efficacy of the method, even when a significant amount of noise was added to the data. The emergence of consistent estimates of impedance, approximating the original impedance, from synthetic data generated for several frequency bands has inspired our confidence in the method. The other attractive outputs of the method are as follows: (1) an accurate estimate of the impedance mean, (2) an accurate reconstruction of the direct-current (DC) frequency of the reflectivity, and (3) an acceptable reconstruction of the broad outline of the original impedance profile. These outputs can serve as constraints for either more refined inversions or geologic interpretations. Beginning from the restriction of band-limited data, we have devised a method that neither requires a starting input model nor imposes mathematical constraints on the earth reflectivity and still yielded significant and relevant geologic information.
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Mudd, Simon M., Fiona J. Clubb, Boris Gailleton, and Martin D. Hurst. "How concave are river channels?" Earth Surface Dynamics 6, no. 2 (June 22, 2018): 505–23. http://dx.doi.org/10.5194/esurf-6-505-2018.
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Abstract. For over a century, geomorphologists have attempted to unravel information about landscape evolution, and processes that drive it, using river profiles. Many studies have combined new topographic datasets with theoretical models of channel incision to infer erosion rates, identify rock types with different resistance to erosion, and detect potential regions of tectonic activity. The most common metric used to analyse river profile geometry is channel steepness, or ks. However, the calculation of channel steepness requires the normalisation of channel gradient by drainage area. This normalisation requires a power law exponent that is referred to as the channel concavity index. Despite the concavity index being crucial in determining channel steepness, it is challenging to constrain. In this contribution, we compare both slope–area methods for calculating the concavity index and methods based on integrating drainage area along the length of the channel, using so-called “chi” (χ) analysis. We present a new χ-based method which directly compares χ values of tributary nodes to those on the main stem; this method allows us to constrain the concavity index in transient landscapes without assuming a linear relationship between χ and elevation. Patterns of the concavity index have been linked to the ratio of the area and slope exponents of the stream power incision model (m∕n); we therefore construct simple numerical models obeying detachment-limited stream power and test the different methods against simulations with imposed m and n. We find that χ-based methods are better than slope–area methods at reproducing imposed m∕n ratios when our numerical landscapes are subject to either transient uplift or spatially varying uplift and fluvial erodibility. We also test our methods on several real landscapes, including sites with both lithological and structural heterogeneity, to provide examples of the methods' performance and limitations. These methods are made available in a new software package so that other workers can explore how the concavity index varies across diverse landscapes, with the aim to improve our understanding of the physics behind bedrock channel incision.
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Narivskii, А., Т. Pulina, and S. Subbotin. "Mathematical modeling of selective dissolution of AISI 304 steel in circulating chloride-containing waters during operation of heat exchangers." Innovative Materials and Technologies in Metallurgy and Mechanical Engineering, no. 2 (December 7, 2021): 42–49. http://dx.doi.org/10.15588/1607-6885-2021-3-7.
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Purpose. Investigation of the effect of chloride-containing medium, chemical composition and structural heterogeneity of AiSi304 steel on selective dissolution of metals ΔCr, ΔNi and ΔFe from stable pits.
Research methods. X-ray structural analysis, optical microscopy, energy dispersive microanalysis, analysis of the developed linear regression mathematical models of the second order for corrosion losses of metals from pits.
Results. Based on the analysis of the developed linear regression mathematical models of the second order for corrosion losses of metals from pits, it was found that ΔFe from pits on the surface of AISI 304 steel in model circulating water with pH = 4...8 and chloride concentration of 300 and 600 mg / l decrease with an increase in it. the amount of oxides (1.98...3.95 microns), the average diameter of the austenite grain and increase when the average distance between the oxides and the volume of b- ferite in steel increases. It is proved that ΔNi from pits decreases with an increase in the amount of oxides in steel (1.98...3.95 μm), the volume of b- ferite and a decrease in the average diameter of austenite grain.
It was determined that ΔCr of steel from pits mainly depends on the concentration of chlorides in the model circulating water, the amount of oxides (1.98 ... 3.95 μm), the average diameter of the austetin grain and the volume of b-ferite. It is hypothesized that this is due to the intensity of adsorption of chlorine ions on imperfections in the structure of AISI304 steel near these oxides at the intersection with the grain boundaries of austenite, where pits nucleate and grow.
Scientific novelty. It was established for the first time that the coefficient of selective dissolution of Cr from pits on the surface of AISI 304 (ZCr ) steel in the circulating waters of the river decreases with an increase in the volume of b-ferite in the steel, the average diameter of austenite grain and a decrease in the amount of oxides. This can facilitate the transition of metastable pits to stable ones. Moreover, this process is autocatalytic; therefore, it does not depend on the parameters of the model circulating water.
Statement of tasks. Based on the established features of selective dissolution of ΔCr, ΔNi and ΔFe from pits on the surface of AISI304 steel, to study the effect of its plastic defermation on pitting resistance in chloride-containing model circulating waters.
Practical value. The developed mathematical models are used to assess the pitting resistance of AISI304 steel in model circulating waters, depending on its parameters and the environment where heat exchangers made of this steel operate.
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Osipov, A. G., V. V. Dmitriev, and V. F. Kovyazin. "Methods of assessing and mapping the natural and agricultural potential of landscapes." Geodesy and Cartography 975, no. 9 (October 20, 2021): 11–20. http://dx.doi.org/10.22389/0016-7126-2021-975-9-11-20.
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In order to increase the efficiency of land use- and territorial planning, cartographic materials of various thematic contents are required. In the article, the authors propose a methodology of assessing and mapping the favorability of the natural and agricultural potential of landscapes for agricultural use to increase its efficiency using GIS technologies. It is proposed to obtain information on landscapes by means of geoecological assessment, including a multivariate mathematical-cartographic, and spatial analysis of landscape conditions for sustainable environment-friendly agricultural production. Geoecological conditions make an integral indicator of the natural and agricultural landscape. To assess the land for agricultural production, maps are used, according to which the quality of the land plot is determined through the convolution of normalized indicators of the territory’s favorability, while the map is created in the GIS environment of spatially-linked information on the degree of the agro-resource suitability and geoecological conditions for agricultural production. Indicators of agro-resource and geoecological state of landscapes were established. The first ones include the agroclimatic potential and soil bonitet, and the second – the ecological and geochemical resistance of soils to acidification, erosion, ecosystem diversity of the territory, the density of the hydrographic network, the depth of groundwater, and the erosion potential of the relief. The developed technique is tested on Volkhov landscape of Leningrad oblast. The aim of the research is to develop a methodology for assessing and mapping the natural and agricultural potential of landscapes in the GIS environment and to test it on the territory of the region.
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Heimann, F. U. M., D. Rickenmann, M. Böckli, A. Badoux, J. M. Turowski, and J. W. Kirchner. "Calculation of bedload transport in Swiss mountain rivers using the model sedFlow: proof of concept." Earth Surface Dynamics 3, no. 1 (January 12, 2015): 35–54. http://dx.doi.org/10.5194/esurf-3-35-2015.
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Abstract. Fully validated numerical models specifically designed for simulating bedload transport dynamics in mountain streams are rare. In this study, the recently developed modelling tool sedFlow has been applied to simulate bedload transport in the Swiss mountain rivers Kleine Emme and Brenno. It is shown that sedFlow can be used to successfully reproduce observations from historic bedload transport events with plausible parameter set-ups, meaning that calibration parameters are only varied within ranges of uncertainty that have been pre-determined either by previous research or by field observations in the simulated study reaches. In the Brenno river, the spatial distribution of total transport volumes has been reproduced with a Nash–Sutcliffe goodness of fit of 0.733; this relatively low value is partially due to anthropogenic extraction of sediment that was not considered. In the Kleine Emme river, the spatial distribution of total transport volumes has been reproduced with a goodness of fit of 0.949. The simulation results shed light on the difficulties that arise with traditional flow-resistance estimation methods when macro-roughness is present. In addition, our results demonstrate that greatly simplified hydraulic routing schemes, such as kinematic wave or uniform discharge approaches, are probably sufficient for a good representation of bedload transport processes in reach-scale simulations of steep mountain streams. The influence of different parameters on simulation results is semi-quantitatively evaluated in a simple sensitivity study. This proof-of-concept study demonstrates the usefulness of sedFlow for a range of practical applications in alpine mountain streams.
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Phillips, C. B., and D. J. Jerolmack. "Dynamics and mechanics of bed-load tracer particles." Earth Surface Dynamics 2, no. 2 (December 19, 2014): 513–30. http://dx.doi.org/10.5194/esurf-2-513-2014.
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Abstract. Understanding the mechanics of bed load at the flood scale is necessary to link hydrology to landscape evolution. Here we report on observations of the transport of coarse sediment tracer particles in a cobble-bedded alluvial river and a step-pool bedrock tributary, at the individual flood and multi-annual timescales. Tracer particle data for each survey are composed of measured displacement lengths for individual particles, and the number of tagged particles mobilized. For single floods we find that measured tracer particle displacement lengths are exponentially distributed; the number of mobile particles increases linearly with peak flood Shields stress, indicating partial bed load transport for all observed floods; and modal displacement distances scale linearly with excess shear velocity. These findings provide quantitative field support for a recently proposed modeling framework based on momentum conservation at the grain scale. Tracer displacement is weakly negatively correlated with particle size at the individual flood scale; however cumulative travel distance begins to show a stronger inverse relation to grain size when measured over many transport events. The observed spatial sorting of tracers approaches that of the river bed, and is consistent with size-selective deposition models and laboratory experiments. Tracer displacement data for the bedrock and alluvial channels collapse onto a single curve – despite more than an order of magnitude difference in channel slope – when variations of critical Shields stress and flow resistance between the two are accounted for. Results show how bed load dynamics may be predicted from a record of river stage, providing a direct link between climate and sediment transport.
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Cohen, Denis, and Massimiliano Schwarz. "Tree-root control of shallow landslides." Earth Surface Dynamics 5, no. 3 (August 17, 2017): 451–77. http://dx.doi.org/10.5194/esurf-5-451-2017.
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Abstract. Tree roots have long been recognized to increase slope stability by reinforcing the strength of soils. Slope stability models usually include the effects of roots by adding an apparent cohesion to the soil to simulate root strength. No model includes the combined effects of root distribution heterogeneity, stress-strain behavior of root reinforcement, or root strength in compression. Recent field observations, however, indicate that shallow landslide triggering mechanisms are characterized by differential deformation that indicates localized activation of zones in tension, compression, and shear in the soil. Here we describe a new model for slope stability that specifically considers these effects. The model is a strain-step discrete element model that reproduces the self-organized redistribution of forces on a slope during rainfall-triggered shallow landslides. We use a conceptual sigmoidal-shaped hillslope with a clearing in its center to explore the effects of tree size, spacing, weak zones, maximum root-size diameter, and different root strength configurations. Simulation results indicate that tree roots can stabilize slopes that would otherwise fail without them and, in general, higher root density with higher root reinforcement results in a more stable slope. The variation in root stiffness with diameter can, in some cases, invert this relationship. Root tension provides more resistance to failure than root compression but roots with both tension and compression offer the best resistance to failure. Lateral (slope-parallel) tension can be important in cases when the magnitude of this force is comparable to the slope-perpendicular tensile force. In this case, lateral forces can bring to failure tree-covered areas with high root reinforcement. Slope failure occurs when downslope soil compression reaches the soil maximum strength. When this occurs depends on the amount of root tension upslope in both the slope-perpendicular and slope-parallel directions. Roots in tension can prevent failure by reducing soil compressive forces downslope. When root reinforcement is limited, a crack parallel to the slope forms near the top of the hillslope. Simulations with roots that fail across this crack always resulted in a landslide. Slopes that did not form a crack could either fail or remain stable, depending on root reinforcement. Tree spacing is important for the location of weak zones but tree location on the slope (with respect to where a crack opens) is as important. Finally, for the specific cases tested here, intermediate-sized roots (5 to 20 mm in diameter) appear to contribute most to root reinforcement. Our results show more complex behaviors than can be obtained with the traditional slope-uniform, apparent-cohesion approach. A full understanding of the mechanisms of shallow landslide triggering requires a complete re-evaluation of this traditional approach that cannot predict where and how forces are mobilized and distributed in roots and soils, and how these control shallow landslides shape, size, location, and timing.
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Hergarten, S., and J. Robl. "Modelling rapid mass movements using the shallow water equations in Cartesian coordinates." Natural Hazards and Earth System Sciences 15, no. 3 (March 30, 2015): 671–85. http://dx.doi.org/10.5194/nhess-15-671-2015.
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Abstract. We propose a new method to model rapid mass movements on complex topography using the shallow water equations in Cartesian coordinates. These equations are the widely used standard approximation for the flow of water in rivers and shallow lakes, but the main prerequisite for their application – an almost horizontal fluid table – is in general not satisfied for avalanches and debris flows in steep terrain. Therefore, we have developed appropriate correction terms for large topographic gradients. In this study we present the mathematical formulation of these correction terms and their implementation in the open-source flow solver GERRIS. This novel approach is evaluated by simulating avalanches on synthetic and finally natural topographies and the widely used Voellmy flow resistance law. Testing the results against analytical solutions and the proprietary avalanche model RAMMS, we found a very good agreement. As the GERRIS flow solver is freely available and open source, it can be easily extended by additional fluid models or source areas, making this model suitable for simulating several types of rapid mass movements. It therefore provides a valuable tool for assisting regional-scale natural hazard studies.
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Morgun, A., I. Met, and I. Shevchenko. "METHOD OF CALCULATING THE FOUNDATIONS IN COMPACTED PIT USING BOUNDARY ELEMENT METHOD." Modern technology, materials and design in construction 30, no. 1 (2021): 71–74. http://dx.doi.org/10.31649/2311-1429-2021-1-71-74.
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The main mission of civil engineer is to ensure he reliability of the structure with maximum efficiency of time, materials and energy. In construction, everything must be provided in the design workshop - both strength and economic feasibility. Balancing on the "edge of the abyss" requires a precise mathematical apparatus. The modern mathematical apparatus of soil mechanics is based on the solutions of the theory of elasticity and the theory of limit equilibrium. In this case, the calculation of the bases is carried out from the conditions of purely elastic connection and the ultimate loads are determined without connection with deformations. Most of the elastic-plastic deformation - from the end of the elastic stage to the loss of stability is not covered by the calculation models. At the same time, the reserves of the elastic-plastic zone allow to increase the load on the foundation, provided that the subsidence of the elastic stage does not yet reach the maximum allowable value for this structure. The boundary element method (BEM) allows to solve problems of this kind. The main disadvantage of foundations on a natural basis is the complexity of its manufacture and high material consumption. These shortcomings can be eliminated by building foundations in cavities of a predetermined shape, which are formed in the soil. These include foundations in compacted ditches, which are arranged in wells with expansion at the bottom. The soil retains its full-fledged composition, so that the work includes a side surface that receives part of the vertical load and provides significant resistance to horizontal forces. The paper presents a method of integration of a mathematical model of behavior under load of foundations in a compacted pit with a numerical BEM. A theoretical study presents the effect of the addition of sand-gravel mixture on the bottom of the compacted pit on the bearing capacity of pyramidal piles.
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Lambert, Valère, and Nadia Lapusta. "Rupture-dependent breakdown energy in fault models with thermo-hydro-mechanical processes." Solid Earth 11, no. 6 (November 26, 2020): 2283–302. http://dx.doi.org/10.5194/se-11-2283-2020.
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Abstract. Substantial insight into earthquake source processes has resulted from considering frictional ruptures analogous to cohesive-zone shear cracks from fracture mechanics. This analogy holds for slip-weakening representations of fault friction that encapsulate the resistance to rupture propagation in the form of breakdown energy, analogous to fracture energy, prescribed in advance as if it were a material property of the fault interface. Here, we use numerical models of earthquake sequences with enhanced weakening due to thermal pressurization of pore fluids to show how accounting for thermo-hydro-mechanical processes during dynamic shear ruptures makes breakdown energy rupture-dependent. We find that local breakdown energy is neither a constant material property nor uniquely defined by the amount of slip attained during rupture, but depends on how that slip is achieved through the history of slip rate and dynamic stress changes during the rupture process. As a consequence, the frictional breakdown energy of the same location along the fault can vary significantly in different earthquake ruptures that pass through. These results suggest the need to reexamine the assumption of predetermined frictional breakdown energy common in dynamic rupture modeling and to better understand the factors that control rupture dynamics in the presence of thermo-hydro-mechanical processes.
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Prémaillon, Mélody, Vincent Regard, Thomas J. B. Dewez, and Yves Auda. "GlobR2C2 (Global Recession Rates of Coastal Cliffs): a global relational database to investigate coastal rocky cliff erosion rate variations." Earth Surface Dynamics 6, no. 3 (August 9, 2018): 651–68. http://dx.doi.org/10.5194/esurf-6-651-2018.
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Abstract. Rocky coast erosion (i.e., cliff retreat) is caused by a complex interaction of various forcings that can be marine, subaerial or due to rock mass properties. From Sunamura's seminal work in 1992, it is known that cliff retreat rates are highly variable over at least four orders of magnitude, from 1 to 10 mm yr−1. While numerous local studies exist and explain erosion processes at specific sites, there is a lack of knowledge at the global scale. In order to quantify and rank the various parameters influencing erosion rates, we compiled existing local studies into a global database called GlobR2C2 (which stands for Global Recession Rates of Coastal Cliffs). This database reports erosion rates from publications, cliff setting and measurement specifications; it is compiled from peer-reviewed articles and national databases. In order to be homogeneous, marine and climatic forcings were recorded from global models and reanalyses. Currently, GlobR2C2 contains 58 publications that represent 1530 studied cliffs and more than 1680 estimated erosion rate. A statistical analysis was conducted on this database to explore the links between erosion rates and forcings at a global scale. Rock resistance, inferred using the criterion of Hoek and Brown (1997), is the strongest signal explaining variation in erosion rate. Median erosion rates are 2.9 cm yr−1 for hard rocks, 10 cm yr−1 for medium rocks and 23 cm yr−1 for weak rocks. Concerning climate, only the number of frost days (number of day per year below 0 ∘C) for weak rocks shows a significant, positive, trend with erosion rate. The other climatic and marine forcings do not show any clear or significant relationship with cliff retreat rate. In this first version, GlobR2C2, with its current encompassing vision, has broad implications. Critical knowledge gaps have come to light and prompt a new coastal rocky shore research agenda. Further study of these questions is paramount if we one day hope to answer questions such as what the coastal rocky shore response to sea-level rise or increased storminess may be.
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Gholami, Ali. "A fast automatic multichannel blind seismic inversion for high-resolution impedance recovery." GEOPHYSICS 81, no. 5 (September 2016): V357—V364. http://dx.doi.org/10.1190/geo2015-0654.1.
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The inversion of seismic reflection data for acoustic impedance (AI) is a common and accepted method for the interpretation of poststack seismic data. The original mathematical problem is nonlinear due to the nonlinearity of relation between the AI and the earth reflectivity series and also the insufficiency of information about the source wavelet. Furthermore, the problem is ill posed due to the lack of low and high frequencies in the data. We have developed a multichannel blind inversion and solved it for obtaining the AI model and the wavelet directly from seismic reflection data. We found a solution to the overall problem by alternating between two subproblems, corresponding to the AI and wavelet recovery. Having an estimation of the wavelet, the algorithm directly inverts multichannel data for a high-resolution AI model, having blocky structures in the sense of total variation (TV) regularization, while satisfying a priori low-frequency information. The advantages of the split Bregman technique and the discrete cosine transform are used to build a fast and efficient algorithm for solving the nonlinear impedance inversion with TV regularization. Having an estimate of the AI model, the wavelet is updated by restricting it to have a sparse representation in a wavelet transformation domain while predicting the observed data. Numerical tests using simulated 2D data obtained from the benchmark Marmousi model and also 2D field data confirm that the proposed algorithm stably generates accurate estimates of complex AI models and complicated wavelets, simultaneously.
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Andronova, Natalia G., and Michael E. Schlesinger. "The application of cause-and-effect analysis to mathematical models of geophysical phenomena: 1. Formulation and sensitivity analysis." Journal of Geophysical Research 96, no. D1 (1991): 941. http://dx.doi.org/10.1029/90jd02278.
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Mansouri, Edris, Faranak Feizi, Alireza Jafari Rad, and Mehran Arian. "Remote-sensing data processing with the multivariate regression analysis method for iron mineral resource potential mapping: a case study in the Sarvian area, central Iran." Solid Earth 9, no. 2 (March 28, 2018): 373–84. http://dx.doi.org/10.5194/se-9-373-2018.
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Abstract. This paper uses multivariate regression to create a mathematical model for iron skarn exploration in the Sarvian area, central Iran, using multivariate regression for mineral prospectivity mapping (MPM). The main target of this paper is to apply multivariate regression analysis (as an MPM method) to map iron outcrops in the northeastern part of the study area in order to discover new iron deposits in other parts of the study area. Two types of multivariate regression models using two linear equations were employed to discover new mineral deposits. This method is one of the reliable methods for processing satellite images. ASTER satellite images (14 bands) were used as unique independent variables (UIVs), and iron outcrops were mapped as dependent variables for MPM. According to the results of the probability value (p value), coefficient of determination value (R2) and adjusted determination coefficient (Radj2), the second regression model (which consistent of multiple UIVs) fitted better than other models. The accuracy of the model was confirmed by iron outcrops map and geological observation. Based on field observation, iron mineralization occurs at the contact of limestone and intrusive rocks (skarn type).
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KACHURIN, Nikolai, Galina STAS, and Alexander KACHURIN. "DYNAMICS OF GAS EMISSION FROM EXPOSED SURFACE OF GAS-BEARING COAL SEAMS HAVING MEDIUM THICKNESS." Sustainable Development of Mountain Territories 13, no. 3 (September 30, 2021): 441–48. http://dx.doi.org/10.21177/1998-4502-2021-13-3-441-448.
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The goal of the research was to clarify the regularities of the dynamics of gas release from the surface of the outcrop of the developed coal seam. The main research methods were theoretical methods of mathematical physics and non-equilibrium thermodynamics. Gas-bearing coal seams are usually mined underground. When driving development workings, outcropping surfaces of gas-bearing coal seams appear and gases in the seams under excessive pressure are released into the atmosphere of the mine workings. Gas-bearing coal seams are usually mined underground. When driving preparatory workings, surfaces of outcropping of gas-bearing coal seams arise and gases that are in the seams under excessive pressure are released into the atmosphere of the mine workings. The most important gas-dynamic characteristic of this process is the rate of gas release, which represents the volume of gases released from a unit area of exposure of a coal seam per unit of time. A generalized law of resistance for gas filtration in a rock mass is recommended, and a fairly rigorous thermodynamic substantiation is given. It is shown that the densities of gas mass flows in accordance with the postulate of their linear relationship with the driving forces are determined by the Onsager relation. The results obtained and their discussion is presented. Mathematical models are proposed for engineering calculations of the dynamics of methane release from the outcropping surface of medium-thick coal seams. The error of the adopted approximations does not exceed 3%. The intensity of methane release is directly related to the planogram of work in the working face. Analysis of this dependence indicates that during the extraction cycle, methane release increases due to an increase in the area of the gas-release surface. The main conclusions are as follows: mathematical modeling of the processes of gas movement in a porous sorbing medium using approximate mathematical models representing linearized equations of mathematical physics; the regularities of the dynamics of the rate of gas release from the surface of the outcrop of a gas-bearing coal seam is the theoretical basis for the mathematical description of the process of gas release; the use of a linearized hyperbolic filtration equation most accurately describes the processes of methane release from the outcropping surface of mined coal seams.
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An, Chenge, Andrew J. Moodie, Hongbo Ma, Xudong Fu, Yuanfeng Zhang, Kensuke Naito, and Gary Parker. "Morphodynamic model of the lower Yellow River: flux or entrainment form for sediment mass conservation?" Earth Surface Dynamics 6, no. 4 (November 6, 2018): 989–1010. http://dx.doi.org/10.5194/esurf-6-989-2018.
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Abstract. Sediment mass conservation is a key factor that constrains river morphodynamic processes. In most models of river morphodynamics, sediment mass conservation is described by the Exner equation, which may take various forms depending on the problem in question. One of the most widely used forms of the Exner equation is the flux-based formulation, in which the conservation of bed material is related to the stream-wise gradient of the sediment transport rate. An alternative form of the Exner equation, however, is the entrainment-based formulation, in which the conservation of bed material is related to the difference between the entrainment rate of bed sediment into suspension and the deposition rate of suspended sediment onto the bed. Here we represent the flux form in terms of the local capacity sediment transport rate and the entrainment form in terms of the local capacity entrainment rate. In the flux form, sediment transport is a function of local hydraulic conditions. However, the entrainment form does not require this constraint: only the rate of entrainment into suspension is in local equilibrium with hydraulic conditions, and the sediment transport rate itself may lag in space and time behind the changing flow conditions. In modeling the fine-grained lower Yellow River, it is usual to treat sediment conservation in terms of an entrainment (nonequilibrium) form rather than a flux (equilibrium) form, in consideration of the condition that fine-grained sediment may be entrained at one place but deposited only at some distant location downstream. However, the differences in prediction between the two formulations have not been comprehensively studied to date. Here we study this problem by comparing the results predicted by both the flux form and the entrainment form of the Exner equation under conditions simplified from the lower Yellow River (i.e., a significant reduction of sediment supply after the closure of the Xiaolangdi Dam). We use a one-dimensional morphodynamic model and sediment transport equations specifically adapted for the lower Yellow River. We find that in a treatment of a 200 km reach using a single characteristic bed sediment size, there is little difference between the two forms since the corresponding adaptation length is relatively small. However, a consideration of sediment mixtures shows that the two forms give very different patterns of grain sorting: clear kinematic waves occur in the flux form but are diffused out in the entrainment form. Both numerical simulation and mathematical analysis show that the morphodynamic processes predicted by the entrainment form are sensitive to sediment fall velocity. We suggest that the entrainment form of the Exner equation might be required when the sorting process of fine-grained sediment is studied, especially when considering relatively short timescales.
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Fraters, Menno, Cedric Thieulot, Arie van den Berg, and Wim Spakman. "The Geodynamic World Builder: a solution for complex initial conditions in numerical modeling." Solid Earth 10, no. 5 (October 29, 2019): 1785–807. http://dx.doi.org/10.5194/se-10-1785-2019.
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Abstract. The Geodynamic World Builder is an open-source code library intended to set up initial conditions for computational geodynamic models in both Cartesian and spherical geometries. The inputs for the JavaScript Object Notation (JSON)-style parameter file are not mathematical but rather a structured nested list describing tectonic features, e.g., a continental, an oceanic or a subducting plate. Each of these tectonic features can be assigned a specific temperature profile (e.g., plate model) or composition label (e.g., uniform). For each point in space, the Geodynamic World Builder can return the composition and/or temperature. It is written in C++ but can be used in almost any language through its C and Fortran wrappers. Various examples of 2-D and 3-D subduction settings are presented. The Geodynamic World Builder comes with an extensive online user manual.
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Vallée, Marc A., William A. Morris, Stéphane Perrouty, Robert G. Lee, Ken Wasyliuk, Julia J. King, Kevin Ansdell, et al. "Geophysical inversion contributions to mineral exploration: lessons from the Footprints project." Canadian Journal of Earth Sciences 56, no. 5 (May 2019): 525–43. http://dx.doi.org/10.1139/cjes-2019-0009.
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Magnetic and gravity inversions are used to create 2D or 3D models of the magnetic susceptibility and density, respectively, using potential field data. Unconstrained inversions generate an output based on mathematical constraints imposed by the inversion algorithm. Constrained inversions integrate lithological, structural, and petrophysical information in the inversion process to produce more geologically meaningful results. This study analyses the validity of this assertion in the context of the NSERC-CMIC Mineral Exploration Footprints project. Unconstrained and constrained geophysical inversions were computed for three mining sites: a gold site (Canadian Malartic, Québec), a copper site (Highland Valley, British Columbia), and a uranium site (Millennium – McArthur River, Saskatchewan). After initially computing unconstrained inversions, constrained inversions were developed using physical property measurements, which directly link geophysics to geology, and lithological boundaries extracted from an interpreted geological model. While each derived geological model is consistent with the geophysical data, each site exhibited some magnetic complexity that confounded the inversion. The gold site includes regions with a strong magnetic signature that masks the more weakly magnetic zone, thereby hiding the magnetic signature associated with the ore body. Initial unconstrained inversions for the copper site yielded solutions with invalid depth extent. A consistency between the constrained model and the geological model is reached with iterative changes to the depth extent of the model. At the uranium site, the observed magnetic signal is weak, but the inversion provided some insights that could be interpreted in terms of an already known complexly folded geological model.
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Flecha, I., R. Carbonell, and R. W. Hobbs. "Study on the limitations of travel-time inversion applied to sub-basalt imaging." Solid Earth 4, no. 2 (December 23, 2013): 543–54. http://dx.doi.org/10.5194/se-4-543-2013.
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Abstract. The difficulties of seismic imaging beneath high velocity structures are widely recognised. In this setting, theoretical analysis of synthetic wide-angle seismic reflection data indicates that velocity models are not well constrained. A two-dimensional velocity model was built to simulate a simplified structural geometry given by a basaltic wedge placed within a sedimentary sequence. This model reproduces the geological setting in areas of special interest for the oil industry as the Faroe-Shetland Basin. A wide-angle synthetic dataset was calculated on this model using an elastic finite difference scheme. This dataset provided travel times for tomographic inversions. Results show that the original model can not be completely resolved without considering additional information. The resolution of nonlinear inversions lacks a functional mathematical relationship, therefore, statistical approaches are required. Stochastic tests based on Metropolis techniques support the need of additional information to properly resolve sub-basalt structures.
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Huang, Zehui, John Shimeld, Mark Williamson, and John Katsube. "Permeability prediction with artificial neural network modeling in the Venture gas field, offshore eastern Canada." GEOPHYSICS 61, no. 2 (March 1996): 422–36. http://dx.doi.org/10.1190/1.1443970.
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Estimating permeability from well log information in uncored borehole intervals is an important yet difficult task encountered in many earth science disciplines. Most commonly, permeability is estimated from various well log curves using either empirical relationships or some form of multiple linear regression (MLR). More sophisticated, multiple nonlinear regression (MNLR) techniques are not as common because of difficulties associated with choosing an appropriate mathematical model and with analyzing the sensitivity of the chosen model to the various input variables. However, the recent development of a class of nonlinear optimization techniques known as artificial neural networks (ANNs) does much to overcome these difficulties. We use a back‐propagation ANN (BP-ANN) to model the interrelationships between spatial position, six different well logs, and permeability. Data from four wells in the Venture gas field (offshore eastern Canada) are organized into training and supervising data sets for BP-ANN modeling. Data from a fifth well in the same field are retained as an independent data set for testing. When applied to this test data, the trained BP-ANN produces permeability values that compare well with measured values in the cored intervals. Permeability profiles calculated with the trained BP-ANN exhibit numerous low permeability horizons that are correlatable between the wells at Venture. These horizons likely represent important, intra‐reservoir barriers to fluid migration that are significant for future reservoir production plans at Venture. For discussion, we also derive predictive equations using conventional statistical methods (i.e., MLR, and MNLR) with the same data set used for BP-ANN modeling. These examples highlight the efficacy of BP-ANNs as a means of obtaining multivariate, nonlinear models for difficult problems such as permeability estimation.
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Lampe, Bernhard, and Klaus Holliger. "Resistively loaded antennas for ground-penetrating radar: A modeling approach." GEOPHYSICS 70, no. 3 (May 2005): K23—K32. http://dx.doi.org/10.1190/1.1926574.
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The design of surface ground-penetrating radar (GPR) antennas is inherently difficult, primarily because the presence of the air-soil interface greatly complicates both analytic and laboratory-based approaches aimed at characterizing the antennas. Versatile numerical simulation techniques capable of describing the key physical principles governing GPR antenna radiation offer new solutions to this problem. We use a finite-difference time-domain (FDTD) solution of Maxwell's equations in three dimensions to explore the radiation characteristics of various bow-tie antennas (including quasi-linear antennas) operating in different environments. The antenna panels are either modeled as having an infinite conductivity [i.e., a perfect electrical conductor (PEC)], a constant finite conductivity, or a Wu-King finite-conductivity profile. Finite conductivities are accommodated through a subcell extension of the classical FDTD approach, with the model space surrounded by highly efficient generalized perfectly matched layer (GPML) absorbing boundary conditions. Our results show that input impedances, radiated waveforms, and radiation patterns of bow-tie antennas with Wu-King conductivity profiles are largely invariant when placed in free space or above diverse half-space earth models. By comparison, antennas with PEC or constant finite-conductivity panels have variable characteristics that depend somewhat on their operating environment. Quasi-linear antenna designs tend to be less sensitive in this respect, and hence may be suitable for a somewhat larger variety of soil conditions than planar bow-tie antennas characterized by large flare angles. Antennas with constant finite-conductivity panels are considerably more robust (i.e., less sensitive to their environment) than their PEC analogs because the loss resistance is increased, and the range over which a significant amount of current flow occurs is decreased when the antenna panels are resistively loaded. For the extreme case of Wu-King conductivity profiles, the current in the antenna panels approaches that of a quasi-infinitesimal electric dipole. This is shown by the surface-charge distributions on the various antennas and by the corresponding energy radiation patterns. Unfortunately, the favorable characteristics of the latter antennas are counterbalanced by markedly lower radiation efficiency. For the antenna designs considered in this study, we found that the peak energy radiated into earth models from bow-tie antennas with Wu-King conductivity profiles is about one order of magnitude lower than for antennas with PEC terminals.
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Costa, Lorena Vila Bela, and Willames de Albuquerque Soares. "Avaliações de Funções de Pedotransferência para Solos Brasileiros." Revista Brasileira de Geografia Física 14, no. 4 (2021): 2028–41. http://dx.doi.org/10.26848/rbgf.v14.4.p2028-2041.
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Pedotransfer Functions (FPT) are mathematical models that estimate difficult-to-measure soil properties through more accessible variables, generating optimization of time and financial resources. In this study, six Pedotransfer Functions, based on the equation of Van Genuchten, analyzed for the prediction of volumetric moisture of Brazilian soils, with data from the global database Soil Data Task. Applied for pressures of 0, 0.01, 0.03, 0.10, 0.20, 0.50, 2.50 and 15.0 bar, the resulting values of the equations were compared with the measured volumetric moistures through five statistical parameters: confidence index, mean square error, deviation ratio, modeling efficiency and residual mass coefficient. Of the functions studied it was possible to verify that the FPT proposed by Barros, with 4 parameters, was the one that presented the best results, while that of Rawls and Brakensied obtained the lowest performance. It has been observed that the efficiency of a FPT is related to two factors: a) similarity between the pedological data of the soil studied and those used in the development of the FPT, and b) the amount of variables analyzed.
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Schierjott, Jana, Antoine Rozel, and Paul Tackley. "On the self-regulating effect of grain size evolution in mantle convection models: application to thermochemical piles." Solid Earth 11, no. 3 (June 4, 2020): 959–82. http://dx.doi.org/10.5194/se-11-959-2020.
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Abstract. Seismic studies show two antipodal regions of lower shear velocity at the core–mantle boundary (CMB) called large low-shear-velocity provinces (LLSVPs). They are thought to be thermally and chemically distinct and therefore might have a different density and viscosity than the ambient mantle. Employing a composite rheology, using both diffusion and dislocation creep, we investigate the influence of grain size evolution on the dynamics of thermochemical piles in evolutionary geodynamic models. We consider a primordial layer and a time-dependent basalt production at the surface to dynamically form the present-day chemical heterogeneities, similar to earlier studies, e.g. by Nakagawa and Tackley (2014). Our results show that, relative to the ambient mantle, grain size is higher inside the piles, but, due to the high temperature at the CMB, the viscosity is not remarkably different from ambient mantle viscosity. We further find that although the average viscosity of the detected piles is buffered by both grain size and temperature, the viscosity is influenced predominantly by grain size. In the ambient mantle, however, depending on the convection regime, viscosity can also be predominantly controlled by temperature. All pile properties, except for temperature, show a self-regulating behaviour: although grain size and viscosity decrease when downwellings or overturns occur, these properties quickly recover and return to values prior to the downwelling. We compute the necessary recovery time and find that it takes approximately 400 Myr for the properties to recover after a resurfacing event. Extrapolating to Earth values, we estimate a much smaller recovery time. We observe that dynamic recrystallisation counteracts grain growth inside the piles when downwellings form. Venus-type resurfacing episodes reduce the grain size in piles and ambient mantle to a few millimetres. More continuous mobile-lid-type downwellings limit the grain size to a centimetre. Consequently, we find that grain-size-dependent viscosity does not increase the resistance of thermochemical piles to downgoing slabs. Mostly, piles deform in grain-size-sensitive diffusion creep, but they are not stiff enough to counteract the force of downwellings. Hence, we conclude that the location of subduction zones could be responsible for the location and stability of the thermochemical piles of the Earth because of dynamic recrystallisation.
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Orlando, Francisco Cristiano, Edilson De Souza Bias, and Abimael Cereda Junior. "SRTM: Para uma melhor Utilização - Conhecendo um pouco mais da qualidade planialtimétrica, da influência da resolução espacial e dos modelos de superfície equipotenciais de referência." Revista Brasileira de Geografia Física 15, no. 2 (April 21, 2022): 1153. http://dx.doi.org/10.26848/rbgf.v15.2.p1153-1168.
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Mundialmente, o uso de modelos de terreno a partir de um tratamento matemático sobre dados disponibilizados gratuitamente é uma constante, como são os casos dos dados Shuttle Radar Topography Mission (SRTM), Advanced Land Observing Satellite Phased Array type L-band Synthetic Aperture Radar (ALOS PALSAR), Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), Alos World 3D (AW3D), Global Digital Elevation Model (GDEM), entre outros, sem conhecer a verdadeira qualidade altimétrica e planimétrica dos dados. A maior parte dos usuários desprezam a avaliação planimétrica e focam apenas no refinamento da componente altimétrica, desconsiderando que o erro da componente planimétrica interfere diretamente na qualidade altimétrica do modelo. Desta forma, o objetivo deste estudo é fazer uma avaliação planimétrica do SRTM, além da avaliação altimétrica do mesmo para todo o território brasileiro. Diversos estudos avaliaram o SRTM, utilizando pontos de referência sem uma cobertura de todo o território brasileiro, aplicando simplesmente metodologias de expansão dos resultados obtidos para outras áreas, enquanto no presente estudo utilizou-se pontos de referência distribuídos por todo o território brasileiro, obtidos por satélite, Ice Cloud and Land Elevation Satellite (ICESat). Este estudo tem como finalidade, além da avaliação da qualidade do SRTM, avaliar a influência da discrepância entre as superfícies de referência dos dados (MapGeo2015 para os pontos de controle X EGM96 para o SRTM). Tem-se a ideia que a qualidade do modelo está ligado diretamente ao tamanho do pixel, sendo que os resultados deste estudo mostram que a melhora da qualidade do MDE não é proporcional à melhora da resolução espacial do dado, mostra também, que a superfície EGM96 é satisfatória para escalas de 1/50.000 ou menores.Palavras-chave: Modelos Matemáticos, ICESat, Qualidade de dados geoespaciais. SRTM: For a better user – knowing a little more about planialtimetric quality, the influence of spatial resolution and reference equipotential surface models A B S T R A C TWorldwide, the use of terrain models based on a mathematical treatment of freely available data is a constant, as in the case of Shuttle Radar Topography Mission (SRTM) data, Advanced Land Observing Satellite Phased Array type L-band Synthetic Aperture Radar (ALOS PALSAR), Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), Alos World 3D (AW3D), Global Digital Elevation Model (GDEM), among others, without knowing the true altimetric and planimetric quality of the data. Most users despise the planimetric evaluation and focus only on the refinement of the altimetric component, ignoring that the error of the planimetric component directly interferes with the altimetric quality of the model. Thus, the objective of this study is to carry out a planimetric evaluation of the SRTM, in addition to its altimetric evaluation for the entire Brazilian territory. Several studies have evaluated the SRTM, using reference points without coverage of the entire Brazilian territory, simply applying methodologies to expand the results obtained to other areas, while in the present study reference points distributed throughout the Brazilian territory were used, obtained by satellite, Ice Cloud and Land Elevation Satellite (ICESat). This study aims, in addition to evaluating the quality of the SRTM, to assess the influence of the discrepancy between the reference surfaces of the data (MapGeo2015 for control points X EGM96 for the SRTM). There is the idea that the quality of the model is directly linked to the pixel size, and the results of this study show that the improvement in the quality of the MDE is not proportional to the improvement in the spatial resolution of the data, it also shows that the EGM96 surface it is satisfactory for scales of 1/50,000 or less.Key-words: Mathematical Models, ICESat, Geospacial data quality.
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Rustamov, Kamoliddin, Samandar Komilov, Mavlon Kudaybergenov, Shamshir Shermatov, and Shahzod Xudoyqulov. "Experimental study of hydraulic equipment operation process." E3S Web of Conferences 264 (2021): 02026. http://dx.doi.org/10.1051/e3sconf/202126402026.
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Relevance. When the hydraulic fluid is operated for several cycles, the impact on hydraulic performance and longevity is greatly increased. So, there are several ways to fix this problem. To increase the efficiency of the hydraulic system, it is necessary to study the working processes, the hydraulic systems of the quick-change equipment of the machine with a lawn of the kshp are made as a whole, and the equipment of the machine is attached to the suspension device. The complexity of these processes lies in the fact that they allow experimental research and verification of results using mathematical models. Aim. The purpose of the experimental study in this dissertation is to study the effect of forces acting on the hydraulic system when excavating the hydraulic system of a multipurpose machine and substantiate the parameters by assessing power use efficiency. Methods. Checking the suitability of the working fluid during earthworks, as well as the mathematical model. In this case, we studied the hydraulic system of a single-bucket excavator, the device of quick-change equipment for a universal machine. Results. The theoretical work performed has been verified and the confirmation of the operation of a multipurpose machine designed with earth and dozer equipment. The installation of equipment based on TTZ-80 made it possible to carry out experimental research with the most energy-intensive workflow, determining energy efficiency indicators for excavation and leveling. Conclusion. Comprehensive tests made it possible to conclude that the characteristics of the developed design and the characteristics of the engine of the base machine - the TTZ-80.10 - KM-1 tractor, overcome the resistance encountered during technological operations of a multipurpose machine.
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Dibrova, Anatolii, Larysa Dibrova, Maksym Dibrova, and Alla Chmil. "Forecasting the Consequences of the Cost of Mineral Fertilisers on the Development of the Corn Market in Ukraine Using AGMEMOD Models." Ekonomika APK 29, no. 3 (May 19, 2022): 23–41. http://dx.doi.org/10.32317/2221-1055.202203023.
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In the past decade, from 2012 to 2021, Ukraine has doubled its maize production. The increase in gross corn yields is associated with the use of modern cultivation technologies by farmers, which increase the resistance of plants to adverse environmental factors and adjust the mineral nutrition of plants with regard to weather conditions. One of the most important components of such technologies is the use of mineral fertilisers, the optimal amount of application of which depends not only on the level of grain yield, but also on the efficiency of production and grain quality. However, the rapid increase in world natural gas prices during 2021 has created new challenges and threats for the further development of the grain market in Ukraine. After all, world prices for mineral fertilisers have increased by 110% since 2021, according to the World Bank. Under these conditions, a radical increase in the cost of mineral fertilisers threatens to ensure the competitiveness of Ukrainian corn in the domestic and foreign markets, which would eventually lead to higher food prices and deterioration in the level of food security in the country. This may negatively affect the gross yields and export potential of the grain industry. The purpose of the study is to assess the current state of supply and demand in the corn market in Ukraine and predict the consequences of the impact of changes in the cost of mineral fertilisers on the main parameters of its development according to probable scenarios, using the AGMEMOD econometric partial equilibrium model for the period up to 2025, which creates prerequisites for improving the efficiency of making and implementing management decisions and contributes to achieving the goals of national agrarian policy. The following methods were applied: monographic, abstract and logical, comparative analysis and expert assessments, tabular, statistical and economic, factor analysis, economic and mathematical modelling. The result of the study is an assessment of the current state and identification of the main factors influencing supply and demand in the corn market. Using multiple linear regression, the influence of the main factors on the yield of corn for grain in agricultural enterprises of Ukraine for 2001-2020 is determined. The dynamics of the balance of supply and demand in the corn grain market in Ukraine is analysed. The consequences of changes in the cost of mineral fertilisers on the main parameters of the corn market development in Ukraine are predicted according to probable scenarios using the AGMEMOD econometric partial equilibrium model for the period up to 2025. Based on the calculations made, it is proved that the high yield of corn and the favourable current price environment for grain will ensure a sufficient level of profitability of this grain crop. Methods for improving the mechanism of reducing the cost or compensation of expenses for the purchase of mineral fertilisers for commodity producers are proposed. Methodological and practical aspects of forecasting the consequences of changes in the cost of mineral fertilisers on the main parameters of corn market development in Ukraine using the AGMEMOD econometric partial equilibrium model for the period up to 2025 have been further developed. The proposed methodological approaches and findings can be used by state and industry management bodies in the development of priority areas for improving the effectiveness of the grain industry in Ukraine.
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Zhang, H., G. D. Egbert, A. D. Chave, Q. Huang, A. Kelbert, and S. Y. Erofeeva. "Constraints on the resistivity of the oceanic lithosphere and asthenosphere from seafloor ocean tidal electromagnetic measurements." Geophysical Journal International 219, no. 1 (July 11, 2019): 464–78. http://dx.doi.org/10.1093/gji/ggz315.
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SUMMARY The electromagnetic (EM) field generated by ocean tidal flow is readily detectable in both satellite magnetic field data, and in ocean-bottom measurements of electric and magnetic fields. The availability of accurate charts of tidal currents, constrained by assimilation of modern satellite altimetry data, opens the possibility of using tidal EM fields as a source to image mantle electrical resistivity beneath the ocean basins, as highlighted by the recent success in defining the globally averaged lithosphere–asthenosphere boundary (LAB) with satellite data. In fact, seafloor EM data would be expected to provide better constraints on the structure of resistive oceanic lithosphere, since the toroidal magnetic mode, which can constrain resistive features, is a significant component of the tidal EM field within the ocean, but is absent above the surface (in particular in satellite data). Here we consider this issue in more detail, using a combination of simplified theoretical analysis and 1-D and 3-D numerical modelling to provide a thorough discussion of the sensitivity of satellite and seafloor data to subsurface electrical structure. As part of this effort, and as a step toward 3-D inversion of seafloor tidal data, we have developed a new flexible 3-D spherical-coordinate finite difference scheme for both global and regional scale modelling, with higher resolution models nested in larger scale solutions. We use the new 3-D model, together with Monte Carlo simulations of errors in tidal current estimates, to provide a quantitative assessment of errors in the computed tidal EM signal caused by uncertainty in the tidal source. Over the open ocean this component of error is below 0.01 nT in Bz at satellite height and 0.05 nT in Bx on the seafloor, well below typical signal levels. However, as coastlines are approached error levels can increase substantially. Both analytical and 3-D modelling demonstrate that the seafloor magnetic field is most sensitive to the lithospheric resistance (the product of resistivity and thickness), and is more weakly influenced (primarily in the phase) by resistivity of the underlying asthenosphere. Satellite data, which contain only the poloidal magnetic mode, are more sensitive to the conductive asthenosphere, but have little sensitivity to lithospheric resistance. For both seafloor and satellite data’s changes due to plausible variations in Earth parameters are well above error levels associated with source uncertainty, at least in the ocean interior. Although the 3-D modelling results are qualitatively consistent with theoretical analysis, the presence of coastlines and bathymetric variations generates a complex response, confirming that quantitative interpretation of ocean tidal EM fields will require a 3-D treatment. As an illustration of the nested 3-D scheme, seafloor data at five magnetic and seven electric stations in the northeastern Pacific (41○N, 165○W) are fit with trial-and-error forward modelling of a local domain. The simulation results indicate that the lithospheric resistance is roughly 7 × 108 Ωm2. The phase of the seafloor data in this region are inconsistent with a sharp transition between the resistive lithosphere and conductive asthenosphere.
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Candioti, Lorenzo G., Thibault Duretz, Evangelos Moulas, and Stefan M. Schmalholz. "Buoyancy versus shear forces in building orogenic wedges." Solid Earth 12, no. 8 (August 10, 2021): 1749–75. http://dx.doi.org/10.5194/se-12-1749-2021.
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Abstract. The dynamics of growing collisional orogens are mainly controlled by buoyancy and shear forces. However, the relative importance of these forces, their temporal evolution and their impact on the tectonic style of orogenic wedges remain elusive. Here, we quantify buoyancy and shear forces during collisional orogeny and investigate their impact on orogenic wedge formation and exhumation of crustal rocks. We leverage two-dimensional petrological–thermomechanical numerical simulations of a long-term (ca. 170 Myr) lithosphere deformation cycle involving subsequent hyperextension, cooling, convergence, subduction and collision. Hyperextension generates a basin with exhumed continental mantle bounded by asymmetric passive margins. Before convergence, we replace the top few kilometres of the exhumed mantle with serpentinite to investigate its role during subduction and collision. We study the impact of three parameters: (1) shear resistance, or strength, of serpentinites, controlling the strength of the evolving subduction interface; (2) strength of the continental upper crust; and (3) density structure of the subducted material. Densities are determined by linearized equations of state or by petrological-phase equilibria calculations. The three parameters control the evolution of the ratio of upward-directed buoyancy force to horizontal driving force, FB/FD=ArF, which controls the mode of orogenic wedge formation: ArF≈0.5 causes thrust-sheet-dominated wedges, ArF≈0.75 causes minor wedge formation due to relamination of subducted crust below the upper plate, and ArF≈1 causes buoyancy-flow- or diapir-dominated wedges involving exhumation of crustal material from great depth (>80 km). Furthermore, employing phase equilibria density models reduces the average topography of wedges by several kilometres. We suggest that during the formation of the Pyrenees ArF⪅0.5 due to the absence of high-grade metamorphic rocks, whereas for the Alps ArF≈1 during exhumation of high-grade rocks and ArF⪅0.5 during the post-collisional stage. In the models, FD increases during wedge growth and subduction and eventually reaches magnitudes (≈18 TN m−1) which are required to initiate subduction. Such an increase in the horizontal force, required to continue driving subduction, might have “choked” the subduction of the European plate below the Adriatic one between 35 and 25 Ma and could have caused the reorganization of plate motion and subduction initiation of the Adriatic plate.
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Rajashekhar Rao, B. K. "Kinetics of potassium release in sweet potato cropped soils: a case study in the highlands of Papua New Guinea." Solid Earth 6, no. 1 (February 17, 2015): 217–25. http://dx.doi.org/10.5194/se-6-217-2015.
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Abstract. The present study attempts to employ potassium (K) release parameters to identify soil-quality degradation due to changed land use patterns in sweet potato (Ipomoea batatas (L.) Lam) farms of the highlands of Papua New Guinea. Rapid population increase in the region increased pressure on the land to intensify subsistence production mainly by reducing fallow periods. Such continuous cropping practice coupled with lack of K fertilization practices could lead to a rapid loss of soil fertility and soil-resource degradation. The study aims to evaluate the effects of crop intensification on the K-release pattern and identify soil groups vulnerable to K depletion. Soils with widely differing exchangeable and non-exchangeable K contents were sequentially extracted for periods between 1 and 569 h in 0.01 M CaCl2, and K-release data were fitted to four mathematical models: first order, power, parabolic diffusion and Elovich equations. Results showed two distinct parts in the K-release curves, and 58–80% of total K was released to solution phase within 76 h (first five extractions) with 20–42% K released in the later parts (after 76 h). Soils from older farms that were subjected to intensive and prolonged land use showed significantly (P < 0.05) lower cumulative K-release potential than the farms recently brought to cultivation (new farms). Among the four equations, first-order and power equations best described the K-release pattern; the constant b, an index of K-release rates, ranged from 0.005 to 0.008 mg kg−1 h−1 in the first-order model and was between 0.14 and 0.83 mg kg−1 h−1 in the power model for the soils. In the non-volcanic soils, model constant b values were significantly (P < 0.05) higher than the volcanic soils, thus indicating the vulnerability of volcanic soils to K deficiency. The volcanic soils cropped for several crop cycles need immediate management interventions either through improved fallow management or through mineral fertilizers plus animal manures to sustain productivity.
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Ol’shanetskii, V., O. Glotka, V. Greshta, and V. Khvostak. "IMPROVING THE PROPERTIES OF NICKEL-BASED SUPERALLOYS OF DIRECTED CRYSTALLIZATION BY OPTIMIZING THE CHEMICAL COMPOSITION." Innovative Materials and Technologies in Metallurgy and Mechanical Engineering, no. 2 (January 5, 2023): 8–12. http://dx.doi.org/10.15588/1607-6885-2022-2-1.
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Purpose. It consists in establishing the influence of the chemical composition on the type, chemical composition and morphology of the primary carbides of the nickel-based superalloy, which allows to increase the operational properties of the parts through the structure of the carbide component.
Research methods. Process modeling was carried out using the CALPHAD method. The initial data were the chemical compositions of model alloys with different concentrations of carbide-forming elements. The result of the calculation was the chemical composition of the carbides released in the corresponding systems. The experimental values were processed by statistical methods to obtain correlation dependencies of the “parameter-property” type and establish mathematical equations of regression models that optimally describe these dependencies.
Results. The regularities of the effect of metal chemical composition on the morphology of carbides of MC type have been established. It is shown that depending on chemical elements introduced in the system, the basis of carbides can change, which causes a change in their shape and an increase in the crack resistance of the material. It is shown that the obtained dependences are closely correlated with metallographic studies of alloys of this class.
Scientific novelty. The dependences of the influence of the chemical composition variation of the multicomponent system Ni-Cr-Co-Al-W-Re-Ta-Mo-Nb-C on the chemical composition and morphology of carbides have been established. This makes it possible to change the basis of the carbides, their composition and morphology, thereby improving the mechanical properties of the material, especially fatigue and heat-resistant characteristics.
Practical value. An effective solution for establishing the structural-phase state of nickel-based superalloys by optimizing their chemical composition is proposed, which made it possible to improve the operational properties of the material. The established dependencies can be used in the optimization of the composition of industrial cast nickel-based superalloys and in the development of new compositions.
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Plunder, Alexis, Cédric Thieulot, and Douwe J. J. van Hinsbergen. "The effect of obliquity on temperature in subduction zones: insights from 3-D numerical modeling." Solid Earth 9, no. 3 (June 14, 2018): 759–76. http://dx.doi.org/10.5194/se-9-759-2018.
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Abstract. The geotherm in subduction zones is thought to vary as a function of the subduction rate and the age of the subducting lithosphere. Along a single subduction zone the rate of subduction may strongly vary due to changes in the angle between the trench and the plate convergence vector, i.e., the subduction obliquity, due to trench curvature. We currently observe such curvature in, e.g., the Marianas, Chile and Aleutian trenches. Recently, strong along-strike variations in subduction obliquity were proposed to have caused a major temperature contrast between Cretaceous geological records of western and central Turkey. We test here whether first-order temperature variation in a subduction zone may be caused by variation in the trench geometry using simple thermo-kinematic finite-element 3-D numerical models. We prescribe the trench geometry by means of a simple mathematical function and compute the mantle flow in the mantle wedge by solving the equation of mass and momentum conservation. We then solve the energy conservation equation until steady state is reached. We analyze the results (i) in terms of mantle wedge flow with emphasis on the trench-parallel component and (ii) in terms of temperature along the plate interface by means of maps and the depth–temperature path at the interface. In our experiments, the effect of the trench curvature on the geotherm is substantial. A small obliquity yields a small but not negligible trench-parallel mantle flow, leading to differences of 30 °C along-strike of the model. Advected heat causes such temperature variations (linked to the magnitude of the trench-parallel component of velocity). With increasing obliquity, the trench-parallel component of the velocity consequently increases and the temperature variation reaches 200 °C along-strike. Finally, we discuss the implication of our simulations for the ubiquitous oblique systems that are observed on Earth and the limitations of our modeling approach. Lateral variations in plate sinking rate associated with curvature will further enhance this temperature contrast. We conclude that the synchronous metamorphic temperature contrast between central and western Turkey may well have resulted from reconstructed major variations in subduction obliquity.