Vertical Prism Research Articles

3-D paleotemperature modeling of the geothermal regime of sedimentary basins: Example of the Lunskaya depression, Sakhalin Island

The task of 3-D modeling of the thermal field of a sedimentary basin during sedimentation is considered. The aim of the modeling is to determine the temperature at any point of the basin at a given moment of geological time. The mathematical model is based on a system of equations of thermal conductivity for a heterogeneous layered medium with dynamic boundaries. The conditions of the continuous temperature and thermal flow are given at the boundaries of the adjacent layers. The temperature values, which are determined by the values of the secular course of the earth temperature, are given at the upper boundary coinciding with the sedimentation surface. The thermal flow value is considered to be given at the lower boundary. The medium is approximated using a vertical triangle prism, which is accepted in algorithms of interpretation of the gravitation field and characterized by random upper and lower basements and given values of the thermal physical parameters. The equations of thermal conductivity are solved on the basis of potential theory. The precision of this algorithm is demonstrated by calculation of a test example. The thermal evolution of the sedimentary complexes and dynamics of the major zone of oil formation are reconstructed and possible errors of paleotemperature interpretations caused by ignored 3-D modeling medium are determined on the example of the sedimentary basin of the Lunskaya depression of Sakhalin.

The 3D inversion of airborne gamma-ray spectrometric data

We present a new method for the inversion of airborne gamma-ray spectrometric line data to a regular grid of radioelement concentration estimates on the ground. The method incorporates the height of the aircraft, the 3D terrain within the field of view of the spectrometer, the directional sensitivity of rectangular detectors, and a source model comprising vertical rectangular prisms with the same horizontal dimensions as the required grid cell size. The top of each prism is a plane surface derived from a best-fit plane to the digital elevation model of the earth’s surface within each grid cell area.The method is a significant improvement on current methods, and gives superior interpolation between flight lines. It also eliminates terrain effects that would normally remain in the data after the conventional processing of these data assuming a flat-earth model.

A 1-Diopter Vertical Prism Induces a Decrease of Head Rotation: A Pilot Investigation.

Clinical studies in non-specific chronic arthralgia and back pain seem to indicate an association between vertical heterophoria (VH – latent vertical retinal misalignment) and asymmetrical head rotation. Such clinical observations suggest a link between VH and head rotation, but this was never tested. The purpose of this study was to simulate a VH in healthy subjects and examine its influence on the amplitude of active head rotation during 3D motion capture in upright stance. Subjects were asked to rotate their head three times from the straight ahead position and then to the right, back to straight ahead, to the left, and back to the straight ahead again. Three randomized conditions were run: normal viewing, with a 1-diopter prism base down on the dominant eye, or the non-dominant eye. The most important finding is that the experimental VH whichever the eye with the prism induces a significant decrease in the mean angle of head rotation compared to the normal viewing condition. This decrease was significant for rotation to the left. We suggest that the prism-induced VH modifies the reference posture and thereby affects head rotation; further studies are needed to confirm this effect and to extend to other types of dynamic activities.

Apparent magnetization mapping in the presence of strong remanent magnetization: The space-domain inversion approach

Apparent magnetization mapping is a technique to estimate magnetization distribution in the subsurface magnetic layer from the observed magnetic data, of benefit in identifying lithologic units and delineating magnetic geologic boundaries. The conventional approaches for apparent magnetization mapping usually neglect effects of remanence, resulting in large geologic deviation and the occurrence of negative magnetization when the magnetic layer contains strong remanent magnetization. We have developed a space-domain inversion approach for apparent magnetization mapping based on the amplitude of magnetic anomaly (AMA), the analytic signal (AS), and the normalized source strength (NSS) to reduce effects of remanent magnetization. The AMA, AS, and NSS are three common quantities insensitive or weakly sensitive to the remanence transformed from the magnetic total field anomaly or components. The magnetic layer underground is first divided into a regular grid of vertical rectangular prisms, each having a cross-sectional area of one grid square and a uniform magnetization. Then, an iterative algorithm is adopted to invert each quantity of the AMA, AS, and NSS to obtain an optimum value of magnetization of each prism in the magnetic layer. The inversion approach permits the top and bottom surfaces of the magnetic layer to be constant or variable in depth, and requires no prior information of magnetization directions. Our tests on the synthetic and real data from the metallic ores area in the southern margin of North China have proved the feasibility and robustness of the presented inversion approach. All of the AMA, AS, and NSS inversions produced nonnegative magnetization distribution in the magnetic layer. Also, the AS and NSS inversions produced a better resolution of magnetization distribution than that of the AMA.

Gravitational attraction of a vertical pyramid model of flat top-and-bottom with depth-wise parabolic density variation

In 3D gravity modelling, right rectangular vertical prism model with linear and nonlinear density and polyhedral bodies with linear density variation exist in geophysical literature. Here, we propose a vertical pyramid model with depth-wise parabolic density contrast variation. Initially, we validate our analytic expression against the gravity effect of a right rectangular parallelepiped of constant density contrast. We provide two synthetic examples and a case study for illustrating the effectiveness of our pyramid model in gravity modelling. The included case study of Los Angeles basin, California demonstrates the comparative advantages of our pyramid model over a conventional right rectangular vertical prism model. Our pyramid model could be quite effective as a building block for evaluating the gravity effect of an arbitrarily-shaped 3D or 2.5-D source(s).

Gravitational Attraction of a Vertical Pyramid Model of Flat Top and Bottom with Depth-Wise Linear Density Variation

In 3D gravity modelling, a right rectangular parallelepiped with either constant density or variable density functions in spatial and spectral domains enjoys wide popularity. However, better unit models are needed to meet the large variety of geological scenarios. Here, we present an analytical expression for the gravity effect of a vertical pyramid model with depthwise linear density variation. Initially, we validate our analytic expression against the gravity effect of a right rectangular parallelepiped and provide two synthetic examples and a case study for illustrating the effectiveness of our pyramid model in gravity modelling. The included case study of Los Angeles basin, California, USA, demonstrates the comparative advantages of our pyramid model over the conventional right rectangular vertical prism model. Thus, our pyramid model could be quiet effective as a building block for evaluating the gravity effect of an arbitrarily-shaped 3D or 2.5D source(s).

Using genetic algorithm to determine 2-D gravity modeling of sedimentary basins with density contrast varying parabolically with depth

A program of genetic algorithm has been developed to estimate the depth of a 2-D sedimentary basin whose density contrast varies with depth according to a parabolic law. The model was built consisting of 2-D vertical juxtaposed prisms. Depths of the prisms, computed by genetic algorithm based on random values and optimal depths were finally found after many generations of evolution. The genetic algorithm using the fitness function was combined by root mean square error of data and "norm" model and the latter was multiplied by a Tikhonov regularization parameter to stabilize the solutions. Firstly, the method was tested on a model and its result were coincident with the model. Secondly, it was applied to interprete a profile of gravity anomaly in Mekong Delta. The results showed that the calculate and observed gravity anomalies were well fitted.

Determination of Sedimentary Basin Basement Depth: A Space Domain Based Gravity Inversion using Exponential Density Function

An automatic inversion using ridge regression algorithm is developed in the space domain to analyze the gravity anomalies of sedimentary basins, among which the density contrast decreases with depth following a prescribed exponential function. A stack of vertical prisms having equal widths, whose depths become the unknown parameters to be estimated, describes the geometry of a sedimentary basin above the basement complex. Because no closed form analytical equation can be derivable in the space domain using the exponential density-depth function, a combination of analytical and numerical approaches is used to realize forward gravity modeling. The depth estimates of sediment-basement interface are initiated and subsequently improved iteratively by minimizing the objective function between the observed and modeled gravity anomalies within the specified convergence criteria. Two gravity anomaly profiles, one synthetic and a real, are interpreted using the proposed technique to demonstrate its applicability.

수직사위 교정 전·후 시기능 변화에 대한 연구

수직사위 교정 전·후 시기능 변화에 대한 연구

Are toric soft contact lenses prism free in the optic zone?

Purpose: Rotational stability for toric soft contact lenses (TSCLs) is achieved using a range of designs. Designs utilising prism or peripheral ballast may result in residual prism in the optic zone. TSCLs with varying stabilisation methods were calculated for vertical prism in the central 6 mm.

Panopea abbreviata(Bivalvia: Hiatellidae) in the Southwestern Atlantic Ocean, Taxonomic Revision and Anatomy

The taxonomy and anatomy of the southwestern Atlantic geoduck, Panopea abbreviata Valenciennes, 1839, are revised. Materials from several institutions, as well as new living specimens collected from the coast of Argentina were studied. Type materials of all related nominal species are illustrated. The shell morphology, shell ultrastructure, hinge, ligament and mantle cavity organs are described. The symbiotic relationship with the nemertean Malacobdella arrokeana, attached to host mantle tissues, is mentioned. Panopea abbreviata is abundant in the gulfs of northern Patagonia. It occurs in the subtidal zone from 8 to 25 meters deep, deeply buried in the sediment. It has a large thick shell, shortener at the posterior end, with exposed siphons covered by a dark brownish periostracum; a hinge plate characterized by a single cardinal tooth in each valve; and shell ultrastructure with three layers: an outer layer of nearly vertical and composite prisms, a middle, true homogeneous layer, and an inner layer of alternating sublayers of fine complex crossed lamellar and irregular simple prisms. The fused mantle is only interrupted in the pedal gape. Ctenidia and labial palps association belongs to the Category III and ctenidia type C(1). Panopea antarctica is its only synonym. The fossil taxa Panopea truncata, P. inferior, P. hauthali, P. coquimbensis and P. guayacanensis are excluded from the synonymy.

Comparative assessment of linear and bilinear prism-based strategies for terrain correction computations

We address the evaluation of the potential and of the gravitational attraction of mass distributions, assigned by means of a Digital Terrain Model (DTM), for terrain correction computations. In particular, we improve a recent analytical formulation based on the approximation of topographic masses by vertical prisms with linear top surfaces and compare the computational features of the enhanced formulation with alternative ones based on polyhedral modeling on bilinear approximation of the surface relief or on numerical approaches. The numerical tests carried out on the DTM of an area near Cassino (Italy) proved that the proposed enhanced analytical formulation, besides providing exact values of the potential and of the gravitational attraction, turns out to be faster than alternative approaches.

The Effects of Rotating the Self Out of the Body in the Full Virtual Body Ownership Illusion

It has been shown that it is possible to induce a strong illusion that a virtual body (VB) is one's own body. However, the relative influence of a first-person-perspective (1PP) view of the VB and spatial coincidence of the real body and VB remains unclear. We demonstrate a method that permits separation of these two factors. It provides a 1PP view of a VB, supporting visuomotor synchrony between real body and VB movements, but where the entire scene including the body is rotated 15 degrees upwards through the axis connecting the eyes, so that the VB and real body are coincident only through this axis. In a within-subjects study that compared this 15 degrees rotation with a 0 degrees rotation condition, participants reported only slightly diminished levels of perceived ownership of the VB in the rotated condition and did not detect the rotation of the scene. These results indicate that strong spatial coincidence of the virtual and real bodies is not necessary for a full-body ownership illusion. The rotation method used, similar to the effects of vertical prisms, did not produce significant negative side-effects, thus providing a useful methodology for further investigations of body ownership.

Accuracy of Double Maddox Rod with Induced Hypertropia in Normal Subjects

Background and PurposeThe double Maddox rod is a commonly used instrument to test for cyclotorsion in the clinical setting. This paper assesses the ability of patients without torsional complaint to accurately demonstrate torsional status with varying degrees of induced hypertropia as tested by double Maddox rod.MethodsThirty-seven orthophoric subjects underwent double Maddox rod testing with vertical prism of 3Δ, 10Δ, 16Δ, 20Δ, and 30Δ. Subjective torsion was recorded for each prism diopter.ResultsMean subjective torsion was recorded as 0.95°, 1.6°, 1.9°, 2.1°, and 2.2° for 3Δ, 10Δ, 16Δ, 20Δ, and 30Δ, respectively. Torsion increased in a logarithmic manner as modeled by R™ software version 2.15.2.ConclusionsThe double Maddox rod test as commonly used in clinical practice is both subjective and prone to administrator and subject error. Subjects have more difficulty properly aligning the double Maddox rod as distance between images is increased. It is also possible that recruitment of the oblique muscles during attempted vertical fusion leads to subjective torsion during double Maddox rod testing in otherwise normal participants.

Are the fluctuations in dynamic anterior surface aberrations of the human eye chaotic?

The purpose of the study is to measure chaos in dynamic anterior surface aberrations and examine how it varies between the eyes of an individual. Noninvasive tear breakup time and dynamic corneal surface aberrations were measured for two open-eye intervals of 15 s. The maximal Lyapunov exponent (MLE) was calculated to test the nature of the fluctuations of the dynamic anterior surface aberrations. The average MLE for total higher-order aberration (HOA) was found to be small (+0.0102±0.0072) μm/s. No significant difference in MLE was found between the eyes for HOA (t-test; p=0.131). Data analysis was carried out for individual Zernike coefficients, including vertical prism as it gives a direct measure of the thickness of the tear film over time. The results show that the amount of chaos was small for each Zernike coefficient and not significantly correlated between the eyes.

Gravity Anomaly Modeling of Sedimentary Basins by Means of Multiple Structures and Exponential Density Contrast-depth Variations: A Space Domain Approach

Abstract An automatic modeling scheme is developed in the space domain to interpret the gravity anomalies of sedimentary basins, among which the density contrast decreases exponentially with depth. Forward modeling is realized in the space domain using a combination of both analytical and numerical approaches. A collage of vertical prisms having equal widths, whose depths are to be estimated, describes the geometry of a sedimentary basin. Initial depths of a sedimentary basin are predicted using the Bouguer slab formula and subsequently updated, iteratively, based on the differences between the observed and theoretical gravity anomalies until the modeled gravity anomalies mimic the observed ones. The validity and applicability of the method is demonstrated with a synthetic and two real field gravity anomalies, one each over the Chintalpudi sub-basin in India and the other over the San Jacinto graben, California. In case of synthetic example, the assumed structure resembles a typical intracratonic rift basin formed by normal block faulting and filled with thick section of sediments. The proposed modeling technique yielded information that is consistent with the assumed parameters in the case of synthetic structure and with the available/drilling depths in case of field examples.

Induced Vertical Disparity Effects on Local and Global Stereopsis

Purpose: Although significant amounts of vertical misalignment could have a noticeable effect on visual performance, there is no conclusive evidence about the effect of very small amount of vertical disparity on stereopsis and binocular vision. Hence, the aim of this study was to investigate the effects of induced vertical disparity on local and global stereopsis at near.Materials and Methods: Ninety participants wearing best-corrected refraction had local and global stereopsis tested with 0.5 and 1.0 prism diopter (Δ) vertical prism in front of their dominant and non-dominant eye in turn. This was compared to local and global stereopsis in the same subjects without vertical prism. Data were analyzed in SPSS.17 software using the independent samples T and the repeated measures ANOVA tests.Results: Induced vertical disparity decreases local and global stereopsis. This reduction is greater when vertical disparity is induced in front of the non-dominant eye and affects global more than local stereopsis. Repeated measures ANOVA showed differences in the mean stereopsis between the different measured states for local and global values. Local stereopsis thresholds were reduced by 10 s of arc or less on average with 1.0Δ of induced vertical prism in front of either eye. However, global stereopsis thresholds were reduced by over 100 s of arc by the same 1.0Δ of induced vertical prism.Conclusion: Induced vertical disparity affects global stereopsis thresholds by an order of magnitude (or a factor of 10) more than local stereopsis. Hence, using a test that measures global stereopsis such as the TNO is more sensitive to vertical misalignment than a test such as the Stereofly that measures local stereopsis.

Is Adaptation to Perceived Interocular Differences in Height Explained by Vertical Fusional Eye Movements?

To find out whether adaptation to a vertical prism involves more than fusional vertical eye movements. Adaptation to a vertical base-up 3 prism diopter prism was measured in a custom-programmed Maddox test in nine visually normal emmetropic subjects (mean age 27.0 ± 2.8 years). Vertical eye movements were binocularly measured in six of the subjects with a custom-programmed binocular video eye tracker. In the Maddox test, some subjects adjusted the perceived height as expected from the power of the prism while others appeared to ignore the prism. After 15 minutes of adaptation, the interocular difference in perceived height was reduced by on average 51% (from 0.86°-0.44°). The larger the initially perceived difference in height in a subject, the larger the amplitude of adaptation was. Eye tracking showed that the prism generated divergent vertical eye movements of 1.2° on average, which was less than expected from its power. Differences in eye elevation were maintained as long as the prism was in place. Small angles of lateral head tilt generated large interocular differences in eye elevation, much larger than the effects introduced by the prism. Vertical differences in retinal image height were compensated by vertical fusional eye movements but some subjects responded poorly to a vertical prism in both experiments; fusional eye movements were generally too small to realign both foveae with the fixation target; and the prism adaptation in the Maddox test was fully explained by the changes in vertical eye position, suggesting that no further adaptational mechanism may be involved.

The application of rapid potential field methods for the targeting of IOCG mineralisation based on physical property data, Great Bear magmatic zone, Canada

Abstract New techniques for the integration of gravity and aeromagnetic data through rock physical property relationships are tested for the rapid location of potential iron oxide–copper–gold (IOCG) exploration targets across the Great Bear magmatic zone (GBMZ). These techniques are based on the recognition of coincident or near-offset magnetic and gravity anomalies associated with IOCG deposits, resulting from their intense and combined iron-oxide and alkali alteration. In the GBMZ, the NICO (Au–Co–Bi–Cu) deposit is an atypical magnetite-group IOCG hosted within an intensely hydrothermally-altered metasedimentary sequence. Prospectivity maps for the NICO area are derived from the integration of high-resolution aeromagnetic and surface gravity data with physical property measurements of magnetic susceptibility and density. Method 1 combines the pseudo-gravity (derived from the aeromagnetic data) and Bouguer gravity data to determine the locations of superimposed high anomalies. Method 2 estimates the apparent susceptibility and density subsurface distribution based on vertical prism models of the magnetic and gravity data. The apparent susceptibility data are transformed to apparent density using physical property relationships. The two apparent density datasets are then combined to determine the location of coincident magnetic and gravity derived anomalies. The results of these methods are supported by, and compared with, similar prospectivity maps generated through weights of evidence techniques. At NICO, the prospectivity maps accurately locate the deposit and nearby occurrences. Despite the lower resolution of the regional gravity data, application of the techniques across the GBMZ is successful at locating mineralised IOCG systems including the magnetite-group systems at Grouard, Fab, DeVries and Cole Lake, the magnetite to hematite-group systems of the Port Radium-Echo Bay district, and has highlighted possible targets for future exploration.

MODTOHAFSD — A GUI based JAVA code for gravity analysis of strike limited sedimentary basins by means of growing bodies with exponential density contrast–depth variation: A space domain approach

Based on the principles of modeling and inversion, two interpretation methods are developed in the space domain along with a GUI based JAVA code, MODTOHAFSD, to analyze the gravity anomalies of strike limited sedimentary basins using a prescribed exponential density contrast-depth function. A stack of vertical prisms all having equal widths, but each one possesses its own limited strike length and thickness, describes the structure of a sedimentary basin above the basement complex. The thicknesses of prisms represent the depths to the basement and are the unknown parameters to be estimated from the observed gravity anomalies. Forward modeling is realized in the space domain using a combination of analytical and numerical approaches. The algorithm estimates the initial depths of a sedimentary basin and improves them, iteratively, based on the differences between the observed and modeled gravity anomalies within the specified convergence criteria. The present code, works on Model-View-Controller (MVC) pattern, reads the Bouguer gravity anomalies, constructs/modifies regional gravity background in an interactive approach, estimates residual gravity anomalies and performs automatic modeling or inversion based on user specification for basement topography. Besides generating output in both ASCII and graphical forms, the code displays (i) the changes in the depth structure, (ii) nature of fit between the observed and modeled gravity anomalies, (iii) changes in misfit, and (iv) variation of density contrast with iteration in animated forms. The code is used to analyze both synthetic and real field gravity anomalies. The proposed technique yielded information that is consistent with the assumed parameters in case of synthetic structure and with available drilling depths in case of field example. The advantage of the code is that it can be used to analyze the gravity anomalies of sedimentary basins even when the profile along which the interpretation is intended fails to bisect the strike length.