3D Convolution Conjugate Gradient Inversion of Potential Fields in Acoculco Geothermal Prospect, Mexico

Potential field data have long been used in geophysical exploration for archeological, mineral, and reservoir targets. For all these targets, the increased search of highly detailed three-dimensional subsurface volumes has also promoted the recollection of high-density contrast data sets. While there are several approaches to handle these large-scale inverse problems, most of them rely on either the extensive use of high-performance computing architectures or data-model compression strategies that may sacrifice some level of model resolution. We posit that the superposition and convolutional properties of the potential fields can be easily used to compress the information needed for data inversion and also to reduce significantly redundant mathematical computations. For this, we developed a convolution-based conjugate gradient 3D inversion algorithm for the most common types of potential field data. We demonstrate the performance of the algorithm using a resolution test and a synthetic experiment. We then apply our algorithm to gravity and magnetic data for a geothermal prospect in the Acoculco caldera in Mexico. The resulting three-dimensional model meaningfully determined the distribution of the existent volcanic infill in the caldera as well as the interrelation of various intrusions in the basement of the area. We propose that these intrusive bodies play an important role either as a low-permeability host of the heated fluid or as the heat source for the potential development of an enhanced geothermal system.

Dynamics of machines with ideal inertial motion

The term "inertioid" and its first design in 1936 was invented by engineer V. N. Tolchin. Despite the demonstration of unsupported motion using a physical model, the mystery of the inertioid has existed for almost a century. There are several theories explaining the motion of the inertioid (or mechanisms with inertial motion). These theories include the theory of friction, which proves that the movement of the device occurs due to the difference between the coefficients of friction and the coefficients of rolling resistance in contact between the bottom of the machine and the road. In some works, to explain the physical nature of this phenomenon, it is often legitimate to use A. Einstein's theory of relativity from a scientific point of view. In our opinion, the approach to the study of the process of motion of the inertioid should be based on the theory of the gravitational field. In the theory of relativity, A. Einstein notes that rapidly moving frames of reference create their own gravitational fields. Rotating weights create their own potential fields, since they are affected by centripetal accelerations. When the field of rotating loads is imposed on the gravitational field of the earth, accelerations appear that cause the movement of an inertioid (machines with an inertial mover). In fact, we constantly encounter this kind of overlap of potential fields in our daily life. For example, the effect of latitude on the value of the free fall acceleration of a body above the earth's surface is explained by the imposition of the earth's gravitational field of the potential field of its rotation around its axis. In the paper an inertioid with an idealized engine, which creates a constant driving (traction) force directed towards the movement has been investigated. As a result of the study, the equations of the translational motion of a machine with an ideal inertial engine were obtained, an expression for calculating its maximum speed was determined, and the maximum required engine power for the movement of a machine with an ideal inertial engine was determined.

Control of mobile robot formations using A-star algorithm and artificial potential fields

Formations or groups of robots become essential in cases where a single robot is insufficient to satisfy a given task. With an increasingly automated world, studies on various topics related to robotics have been carried out in both the industrial and academic arenas. In this paper, the control of the formation of differential mobile robots based on the leader-follower approach is presented. The leader's movement is based on the least cost path obtained by the A-star algorithm, thus ensuring a safe and shortest possible route for the leader. Follower robots track the leader's position in real time. Based on this information and the desired distance and angle values, the leader robot is followed. To ensure that the followers do not collide with each other and with the obstacles in the environment, a controller based on Artificial Potential Fields is designed. Stability analysis using Lyapunov theory is performed on the linearized model of the system. To verify the implemented technique, a simulator was designed using the MATLAB programming language. Seven experiments are conducted under different conditions to show the performance of the approach. The distance and orientation errors are less than 0.1 meters and 0.1 radians, respectively. Overall, mobile robots are able to reach the goal position, maintaining the desired formation, in finite time.

GEODYNAMICS

The aim of the research presented in this article is to analyze the properties and geological informative value of the anisotropic transformations of gravitational and magnetic fields, which use averaging procedures, including analysis of Andreev-Klushin's method. Anisotropic transformations of potential fields are designed to detect and track elongated anomalies or their chains, caused by deep linear dislocations in the geological section. The study of the anisotropic transformations properties is based on the analysis of their depth characteristics, as well as theoretical and practical experiments. The study applies the analysis method of fault tectonics reflection features in anisotropic anomalies of gravimagnetic fields, in particular, on the example of the South-East of the Ukrainian Carpathians. It is based on the search of morphological signs of manifestation of deep faults and other long structural-tectonic dislocations in gravitational and magnetic anisotropic anomalies. The method also suggests tracing these elements, relying on the comparison of morphology, intensity, size and direction of anisotropic anomalies with published regional tectonic and geological maps. Results. The paper presents definitions and algorithms of such anisotropic transformations as Andreev-Klushin's methods of anticlinal and terrace types, anisotropic averaging and anisotropic difference averaging. The research allowed us to perform study of the geological informative value of anisotropic transformations of potential fields on theoretical and practical examples. It is shown that in the morphology of anisotropic gravitational and magnetic anomalous fields in the south-east of the Ukrainian Carpathians long local anomalies are traced. They are caused by fault tectonics, in particular deep longitudinal and transverse faults, as well as linear complications into sedimentary cover. The analysis of anisotropic anomalous fields reveals a number of characteristic features of large tectonic zones reflecting regional behavior of the foundation surface and deep faults; on its basis fault tectonics schemes of the South-Eastern region of the Ukrainian Carpathians can be constructed. The study traced a significant extension of the foundation of the Eastern European platform from the Maidan's ledge and the Pokutsko-Bukovynian Carpathians under the Folded Carpathians. The definition of a number of anisotropic transformations is given and their properties are considered. The work substantiated geological informative value of the anisotropic transformations morphology of potential fields in the study of the Ukrainian Carpathians and adjacent depressions fault tectonics. The use of anisotropic transformations of potential fields will increase the reliability and detail of tracing deep faults, as well as other linear dislocations both in the foundation and in the sedimentary cover. The study of fault tectonics is an important factor in the successful solution of problems in the search and exploration of areas which are promising for oil and gas deposits.

Formation control method based on artificial potential fields for aircraft flight simulation

As simulation becomes more present in the military context for variate purposes, the need for accurate behaviors is of paramount importance. In the air domain, a noteworthy behavior relates to how a group of aircraft moves in a coordinated way. This can be defined as formation flying, which, combined with a move-to-goal behavior, is the focus of this work. The objective of the formation control problem considered is to ensure that simulated aircraft fly autonomously, seeking a formation, while moving toward a goal waypoint. For that, we propose the use of artificial potential fields, which reduce the complexities that implementing a complete cognition model could pose. These fields define forces that control the movement of the entities into formation and to the prescribed waypoint. Our formation control approach is parameterizable, allowing modifications that translate how the aircraft prioritize its sub-behaviors. Instead of defining this prioritization on an empirical basis, we elaborate metrics to evaluate the chosen parameters. From these metrics, we use an optimization methodology to find the best parameter values for a set of scenarios. Thus, our main contribution is bringing together artificial potential fields and simulation optimization to achieve more robust results for simulated military aircraft to fly in formation. We use a large set of scenarios for the optimization process, which evaluates its objective function through the simulations. The results show that the use of the proposed approach may generate gains of up to 27% if compared to arbitrarily selected parameters, with respect to one of the metrics adopted. In addition, we were able to observe that, for the scenarios considered, the presence of a formation leader was an obstacle to achieving the best results, demonstrating that our approach may lead to conclusions with direct operational impacts.

The Bumpy Road to Relevance: Croatia, Hungary and Lithuania in Perspective

This chapter examines how has the relevance of political science developed in Croatia, Hungary and Lithuania, that is how is the profession engaged with important audiences, namely the student body, society at large and pragmatic politics. Similar to the Western context the normative and pragmatic understanding of relevance appear in these emerging political science communities while identity formation and the achievement and preservation of legitimacy also define how political science can become relevant. The concept of relevance is built on three dimensions related to three potential fields of engagement: knowledge provision, social presence and practical impact. This chapter highlights that the profession continues to be beset by problems relating to the issue of relevance but differences between the countries are pronounced. Moreover, the three main aspects of relevance have not been achieved to the same level within the same country although we can duly expect a degree of adjustment as the three aspects are interconnected and will influence one another. This chapter argues that the development of relevance is a two-way process: government and university policies act as the external context, while the profession’s interests, commitment and ambitions constitute the internal force marking the way forward.

Benchmark forward gravity schemes: the gravity field of a realistic lithosphere model WINTERC-G

Several alternative gravity forward modelling methodologies and associated numerical codes with their own advantages and limitations are available for the Solid Earth community. With the upcoming state-of-the-art lithosphere density models and accurate global gravity field data sets it is vital to understand the opportunities and limitations of the various approaches. In this paper, we discuss the four widely used techniques: global spherical harmonics (GSH), tesseroid integration (TESS), triangle integration (TRI), and hexahedral integration (HEX). A constant density shell benchmark shows that all four codes can produce similar precise gravitational potential fields. Two additional shell tests were conducted with more complicated density structures: lateral varying density structures and a Moho density interface between crust and mantle. The differences between the four codes were all below 1.5 percent of the modeled gravity signal suitable for reproducing satellite-acquired gravity data. TESS and GSH produced the most similar potential fields (< 0.3 percent). To examine the usability of the forward modelling codes for realistic geological structures, we use the global lithosphere model WINTERC-G, that was constrained, among other data, by satellite gravity field data computed using a spectral forward modeling approach. This spectral code was benchmarked against the GSH and it was confirmed that both approaches produce similar gravity solution with negligible differences between them. In the comparison of the different WINTERC-G-based gravity solutions, again GSH and TESS performed best. Only short-wavelength noise is present between the spectral and tesseroid forward modelling approaches, likely related to the different way in which the spherical harmonic analysis of the varying boundaries of the mass layer is performed. The Spherical harmonic basis functions produces small differences compared to the tesseroid elements especially at sharp interfaces, which introduces mostly short-wavelength differences. Nevertheless, both approaches (GSH and TESS) result in accurate solutions of the potential field with reasonable computational resources. Differences below 0.5 percent are obtained, resulting in residuals of 0.076 mGal standard deviation at 250 km height. The biggest issue for TRI is the characteristic pattern in the residuals that is related to the grid layout. Increasing the resolution and filtering allows for the removal of most of this erroneous pattern, but at the expense of higher computational loads with respect to the other codes. The other spatial forward modelling scheme HEX has more difficulty in reproducing similar gravity field solutions compared to GSH and TESS. These particular approaches need to go to higher resolutions, resulting in enormous computation efforts. The hexahedron-based code performs less than optimal in the forward modelling of the gravity signature, especially of a lateral varying density interface. Care must be taken with any forward modelling software as the approximation of the geometry of the WINTERC-G model may deteriorate the gravity field solution.

Time Delay in Electron Collision with a Spherical Target as a Function of the Scattering Angle

We have studied the angular time delay in slow-electron elastic scattering by spherical targets as well as the average time delay of electrons in this process. It is demonstrated how the angular time delay is connected to the Eisenbud–Wigner–Smith (EWS) time delay. The specific features of both angular and energy dependencies of these time delays are discussed in detail. The potentialities of the derived general formulas are illustrated by the numerical calculations of the time delays of slow electrons in the potential fields of both absolutely hard-sphere and delta-shell potential well of the same radius. The conducted studies shed more light on the specific features of these time delays.

Boundary rigidity for Randers metrics

If a non-reversible Finsler norm is the sum of a reversible Finsler norm and a closed 1-form, then one can uniquely recover the 1-form up to potential fields from the boundary distance data. We also show a boundary rigidity result for Randers metrics where the reversible Finsler norm is induced by a Riemannian metric which is boundary rigid. Our theorems generalize Riemannian boundary rigidity results to some non-reversible Finsler manifolds. We provide an application to seismology where the seismic wave propagates in a moving medium.