Navegando por Assunto "Anomalias"

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Acesso aberto (Open Access)
Anomalias da água: uma abordagem para educação básica
(Universidade Federal do Pará, 2024-08-08) SANTOS, Jaqueliane Souza dos; CRISPINO, Luis Carlos Bassalo
This work is part of a line of research aimed at exploring the anomalous behavior of water in Physics and Science Teaching. Anomaly consists of an irregularity or abnormality that can be seen, for example, in the behavior of a particular material. Water, in particular, exhibits various so-called anomalous behaviors, which make it a fluid that is quite different from the rest and has great potential for teaching physics and science. The anomalies of water are associated with some of its physical properties, such as surface tension, specific heat and thermal expansion, which are the subject of this research. The research was carried out in collaboration with the Demonstration Laboratory (LABDEMON) of the Federal University of Pará (UFPA). Our proposal includes the production and publication of videos on the YouTube channel "Demonstration Laboratory - UFPA" and the production of a teaching sequence on the subject of water anomalies, with the aim of contributing to the teaching activities of Physics and Science teachers in Basic Education. Thus, experiments associated with the theme were developed in the classroom, using the Sequences of Teaching by Investigation (SEI) as a theoretical-methodological framework and, together with the videos produced, the effective application of the proposal represented one of the students' first contacts with experimental demonstration activities. The didactic material produced allows teachers and students to reproduce the experiments and also to analyze and discuss the results in different educational contexts, both in basic education and at technical and higher education levels.
Acesso aberto (Open Access)
Anomalias eletromagnéticas de corpos tubulares inclinados em contato com o manto de intemperismo usando diferentes arranjos de bobinas-modelamento analógico
(Universidade Federal do Pará, 1997-03-16) SILVA, Roberto Cesar Alves; VERMA, Om Prakash; http://lattes.cnpq.br/2723609019309173
Electromagnetic methods are mainly applied in the prospection of massive sulphide deposits. These deposits are frequently long in extension and thin, therefore the interpretation can be carried out considering a half-plane model in a resistive ambient. However, in Amazon region or in semi-arid and tropical regions where a partialy conductive to conductive overburden is encountered, interpretations using a resistive ambient model give erroneous results. The objective of this work is to study the influence of the conducting overburden on electromagnetic anomalies of inclined sheet-like bodies in ohmic contact with the overburden, using coil configurations - horizontal coplanar (HCP), vertical coplanar (VCP), vertical coaxial (VCA) and minium couple system (PERP). These studies are realized with the aid of analog modelling where the ore-body is simulated by a graphite sheet and the conducting overburden by ammonium choride solution. Generally, the diferente coil systems studied here show the similar characteristics of the overburden effects, reserving some peculiar effects of each coil system. The effects of a conductive overburden in ohmic contact with the orebody could be briefly described as follows: (i) There is an anti-clockwise phase rotation initially with the increase in the overburden induction number, but with further increase the phase rotates clockwise; (ii) The form of the quadrature anomaly profile is altered due to the appearence of an extra peak on the down-dip side of the ore-body, and (iii) The peak to peak quadrature anomaly on the up-dip side increases uniformly with increase in the overburden induction number. Highest anomalies are obtained with the horizontal coplanar system and lowest with vertical coplanar. No extra-peak in the quadrature profile is observed with the vertical coaxial system in this study. Also, the overbuden effects are more prominent in the horizontal coplanar system compared to vertical coil systems, and in the anomalies of the less inclined half-planes and at lesser depths.
Acesso aberto (Open Access)
Avaliação de métodos eletromagnéticos aplicando campos polarizados e focalizados
(Universidade Federal do Pará, 2006-01-17) BARBOSA, Antônio Vinícius Corrêa; VERMA, Om Prakash; http://lattes.cnpq.br/2723609019309173
In the near surface investigations employing advanced electromagnetic induction methods, the low induction number – LIN targets produce very low anomalies which are difficult to interpret. To overcome this difficulty, in this thesis I have studied the applicability of the Polarized Focused Electromagnetic – POLFOCEM fields as a primary inductive source. The horizontal end vertical E.M. field polarizations are obtained by the vectorial combinations of the fields due to the coil pairs in the central region between them; and the focalization occurs in this region at a depth 0.25 of the spacing between the transmitting coils – L. Therefore, maximum coupling can be obtained by selecting the field polarizations depending upon the geometry of the target and focusing the magnetic flux on it by varying L; consequently producing higher anomalies. This study has been realized by computing anomalies employing the Finite Element Technique for 2.5D problem. In all these numerical experiments a comparative qualitative and quantitative study has been done between the POLFOCEM anomalies and the conventional system anomalies where only one transmitter is used (dipole-dipole system). The POLFOCEM system anomalies, wherein both transmitters T1 and T2 are energized simultaneously, correspond to the sum of the anomalies produced by the T1-R and R- T2 dipoles independently; obeying in this way the linearity the electromagnetic fields. These numerical experiments have been carried out for a bidimensional prismatic model in a resistive half-space at three different inclinations and using radio frequencies. The asymmetrical anomalies obtained in a conventional coil system become symmetrical in POLFOCEM system, and have their amplitudes reduced in relation to that of the conventional system. On the other hand conventional anomalies, symmetrical or asymmetrical, become anti-symmetrical in POLFOCEM, and have their amplitude increased. As a consequence, the Argand diagrams of LIN targets for conventional coil system suffer respectively anticlockwise or clockwise rotation for POLFOCEM system. The experiments, to verify the quality in identifying the two nearby targets, shows that the conventional system is superior in relation to the POLFOCEM system.
Acesso aberto (Open Access)
Efeitos do manto de intemperismo sobre anomalias eletromagnéticas provocadas por corpos tabulares inclinados: um estudo através de modelamento reduzido
(Universidade Federal do Pará, 1981-09-18) SILVA, Lúcia Maria da Costa e; VERMA, Om Prakash; http://lattes.cnpq.br/2723609019309173
Electromagnetic methods have been extensively applied in the prospecting of sulphide bodies and other conducting materials. The interpretation of e. m. data is based on the results obtained either with reduced scale or analytical modelling. In most models, the host rocks, the overburden as well as the halo of disseminated sulphides are considered highly resistive although in nature they are often weakly conductive. Presence of a well-developed conducting overburden in tropical and sub-tropical regions and a saline rich crustal layer in semi-arid regions have been found to modify significantly the e. m. anomalies in practice. Therefore, the parameters of the target, determined on the basis of simple models where the presence of the conducting environment is neglected, are found to be in considerable error. The effects of the overburden on the e. m. anomalies of a dipping tabular ore body were studied with reduced scale models for varying response parameters of both the overburden and the orebody, and also for different depths and dips of the target. The overburden and the orebody were represented by metallic sheets of varying thickness in the scale model developed in accordance with the law of electromagnetic similitude. The results of these investigations show that the overburden affects the anomaly by causing: a) phase rotation; b) amplitude reduction; c) base level displacement; d) reversion of the quadrature; and e) appearance of an extra peak in the quadrature in the case of low dipping models. The last two effects complicate the quantification of the anomalies but, on the other hand, provide a qualitative indication of the response parameters of both the ore body and the overburden. The results were assembled in the form of Argand diagrams and, finally, an interpretation scheme is suggested for the e. m. field data on the basis of these diagrams.
Acesso aberto (Open Access)
Estudo de anomalias eletromagnéticas de um condutor tabular vertical sob camadas parcialmente condutiva em multifrequência e multiseparação através de modelamento analógico
(Universidade Federal do Pará, 1986-05-09) QUEIROZ, Joaquim Carlos Barbosa; VERMA, Om Prakash; http://lattes.cnpq.br/2723609019309173
Partially conducting environment surrouding an one body highly affect its electromagnetic response. Conducting host rock, overburden and disseminated sulphide halo, for example, affect the electromagnetic response in different ways depending upon their electrical properties, areal and geometrical relation with the target, and in particular to the EM system used for prospecting. In the thesis, EM anomalies due to vertical tabular conducting bodies under am overburden, obtained through reduced scale models, are analised for different ground EM systems - horizontal coplanar, vertical coplanar and vertical coaxial - in 8 frequencies between 250 Hz to 35 kHz and the coil separation 0,15; 0,20 and 0,25m. Overburden was simulated by horizontally placed thin stainless steel sheet and the main conducting target by thin aluminium shets placed vertically below the former. The dimensions of these sheets were determined according to the modelling conditions for a plane and half-plane. Various geological situations were represented in modelling using the combinations of the three metallic sheets of varying thicknesses and conductivities to simulate the ore body and another three sheets to simulated the overburden. Set of diagrams are plotted using peak-to-peak in phase and quadrature anomalies for analyzing the results. However, another set of diagrams show that the maximum in phase anomaly occurs when the quadrature countpart is zero at relatively low frequencies when the ore-body together with the overburden is studied. On the other hand, the maximum amplitude in quadrature is obtained at relatively high frequencies when the in phase component attains the minimum, almost zero. With this type of analysis, it was to known the band of frequencies, for each of prospecting systems studied, in wich the EM response of the ore body is least affected by the overburden. Highest response was obtained with the horizontal coplanar system and the least with the vertical coplanar coils. An increase in the separation between the transmitter-receiver resulted in dislocating the peaks to lower frequencies. Widest band of frequencies, in wich the EM response of the body is least affected by the overburden, is obtained in case of vertical coaxial system and narrowest for the horizontal coplanar coils. These results helps us in planning the EM prospecting systems by knowing the position and the band with of frequencies to be used along with otimum transmitter-receiver separation such that the EM response remains free from undesired signals, for example those caused by to overburden.
Acesso aberto (Open Access)
Estudos dos efeitos do manto de intemperismo sobre anomalias de VLF geradas por corpos inclinados: modelagem numérica através de programa eGs
(Universidade Federal do Pará, 2005-09-02) VOGADO, Gilberto Emanoel Reis; VERMA, Om Prakash; http://lattes.cnpq.br/2723609019309173
In this dissertation I have studied the effect of partially conducting overburden on the VLF anomalies of an underlying inclined conducting half-plane. In tropical climate, overburden is normally well developed due to climatic conditions. This study is realized through numerical modeling using finite elements and algorithms computing the results employing the eGs developed by Luiz Rijo of the Department of Geophysics of the Federal University of Pará, Brazil. In these numerical experiments two geoelectrical situations between the overburden and the underlying half-plane are considered: one when they are in galvanic contact called as “galvanic overburden” and the other when they are not in contact called as “inductive overburden”. The depth, dip and conductance of the half-plane is varied alongwith the conductance of the overburden in this study. The results are presented in the form of Tilt-Angle and Ellipticity profiles. The Ellipticity profiles are highly affected by the presence of both types of the conducting overburden. The minor positive and negative peaks in the central part of the profile disappear as the overburden conductance increases. Initially there is an enhancement in the ellipticity anomaly at the lower conductance of the overburden but then it decreases as the overburden conductance increases. However, the tilt-angle anomalies decrease monotonously. Also, in both the ellipticity and the tilt-angle profiles, the distance between the peaks become shorter due the overburden. Consequently, the target depth is interpreted as shallower than the real. The index of asymmetry, used to determine the dip of the half-plane, is also affected by the overburden. Therefore, the dip determination is hampered in the presence of the overburden. An anticlock wise rotation in Argand diagram due to increase in the overburden conductance, result in interpretation a target of less conductance than the real value. Therefore, the presence of the conducting overburden should be taken into the consideration during interpretation of the VLF anomalies.
Acesso aberto (Open Access)
Uma nova abordagem para interpretação de anomalias gravimétricas regionais e residuais aplicada ao estudo da organização crustal: exemplo da Região Norte do Piauí e Noroeste do Ceará
(Universidade Federal do Pará, 1989-12-18) BELTRÃO, Jacira Felipe; HASUI, Yociteru; http://lattes.cnpq.br/3392176511494801; SILVA, João Batista Corrêa da; http://lattes.cnpq.br/1870725463184491
Despite its great importance to the study of global geologic structures, interpreting gravity anomalies is not a trivial task because the observed gravity field is the resultant of every gravity effect produced by every elementary density contrast. Therefore, in order to isolate the effects produced by shallow sources from those produced by deep sources, I present a new method for regional-residual separation and methods for interpreting each isolated component. The regional-residual separation is perfomed by approximating the regional field by a polynomial fitted to the observed field by a robust method. This method is iterative and its starting value is the least-squares fitting. Also, the influence of observations containing substantial contributions of the residual field in the regional field fitting is minimized. The computed regional field is transformed into a map of vertical distances relative to a given datum. This transformation consists of two stages. The first one is the downward continuation of the regional field which is assumed to be produced by a smooth interface separating two homogeneous media: the crust and the mantle. The density contrast between the media is presumably known. The second stage consists in transforming the downward continued field into a map of vertical distances relative to a given datum by means of simple operations. This method presents two difficulties. The first one is related to the instability inherent to the downward continuation operation. The use of a stabilizer is therefore mandatory, leading to an inevitable loss of resolution of the features being mapped. The second difficulty, inherent to the gravity method, is the impossibility of determining the interface absolute depths. However, the knowledge of the absolute depth at one single point of the interface by independent means allows the computation of all absolute depths. The computed residual component is transformed into an apparent density map. This transformation consists in calculating the intensity of several prismatic sources by linear inversion, assuming that the real sources are confined to a horizontal slab and have density contrasts varying only along the horizontal directions. The performance of the regional-residual separation method was assessed in tests using synthetic data, always producing better results as compared either with polynomial fitting by least-squares or with the spectral analysis method. The method for interpreting the regional component was applied to synthetic data producing interfaces very close to the true ones. The limit of resolution of the features being mapped depend not only on the degree of the fitting polynomial, but also on the limitation imposed by the gravity method itself. In interpreting the residual component, a priori information is needed about the depth and thickness of the slab confining the true sources. However, results of tests using synthetic data showed that reasonable estimates for the h6rizontal limits of the sources can be obtained, even when the depth and thickness of the slab are not known. The ambiguity involving depth to the top, thickness and the apparent density can be visualized by means of curves of apparent density as a function of the presumed depth to the top of the slab, each curve corresponding to a particular assumed value for the slab thickness. An analysis of the configuration of the curves allows a semi-quantitative interpretation of the real sources depths. The sequence of all three methods described above was applied to gravity data from northern Piauí and northwestern Ceará state. As a result, a crustal organization model was obtained consisting of crustal thickenings and thinnings related to a compressive event which caused the raise of dense, lower crust rocks to shallower depths. This model is consistent with surface geological information. Also, the .gravity interpretation suggests the continuity of the Northwestern Ceará Shear Belt for more than 200 km under the Parnaíba Basin sedimentary cover. Although the sequence of methods presented here has been developed for the study of large scale crustal structures, it could also be applied to the interpretation of smaller structures, as, for example, the basement relief of a sedimentary basin where the sediments have been intruded by mafic rocks.