bluuebunny/crossref_metadata_2025 huggingface dataset:
Clinical and immunoregulatory effects of roxithromycin therapy for chronic respiratory tract infection
Authors: Nakamura H , Fujishima S , Inoue T , Ohkubo Y , Soejima K , Waki Y , Mori M , Urano T , Sakamaki F , Tasaka S , Ishizaka A , Kanazawa M , Yamaguchi K
Published: October 2002

The clinical and immunoregulatory effects of long-term macrolide antibiotic therapy for patients with chronic lower respiratory tract infections (CLRTI) were investigated. Clinical parameters and neutrophil chemotactic mediators in the epithelial lining fluid (ELF) of CLRTI patients (n = 10) were examined before and after 3 months oral administration of roxithromycin (RXM). The in vitro effects of RXM were also examined on the release of these mediators from alveolar macrophages (AM) and neutrophils. Arterial oxygen tension (p<0.05), vital capacity (VC) (p<0.001), %VC (p<0.05) and forced expiratory volume in one second (p<0.01) were improved after RXM treatment, but airway bacteria were not eradicated. Among the mediators, the levels of interleukin (IL)-8, neutrophil elastase (NE) and leukotriene B4 (LTB4) were higher in ELF than in plasma of CLRTI patients and they decreased after RXM treatment (n = 7, p<0.05 for each). RXM concentrations were significantly increased in the bronchoalveolar lavage cells of the treated patients. In in vitro experiments, RXM showed inhibitory effects on IL-8 release from AM and neutrophils. In conclusion, interleukin-8, neutrophil elastase and leukotriene B4 contribute to the neutrophilic inflammation in the airways of chronic lower respiratory tract infection patients and the clinical effects of roxithromycin may, in part, be attributable to the suppression of excess release of the chemotactic mediators from inflammatory cells.
Modulation of the acute respiratory effects of winter air pollution by serum and dietary antioxidants: a panel study
Authors: Grievink L , van der Zee SC , Hoek G , Boezen HM , van't Veer P , Brunekreef B
Published: October 2002

This study investigated whether a high dietary intake or serum concentration of antioxidant (pro-) vitamins could attenuate the acute respiratory effects of air pollution in panels of adults (n = 227) aged 50-70 yrs with chronic respiratory symptoms in two winters starting in 1993/1994. Subjects performed daily peak expiratory flow (PEF) measurements in the morning and evening and reported the occurrence of respiratory symptoms in two regions (urban and nonurban) each winter. Logistic regression analysis was used with the prevalences of large PEF decrements as dependent variables and air pollution levels as independent variables. Analyses were performed separately for subjects below and above the median levels of serum beta-carotene and the intake of dietary vitamin C and beta-carotene. Subjects with low levels of serum beta-carotene more often had large PEF decrements when particles <10 microm in diameter or black smoke levels which were higher compared to subjects with high levels of serum beta-carotene. The same results tended to be observed for dietary vitamin C or beta-carotene, but there were less significant air pollution effects in the low dietary antioxidant group. The results suggest that serum beta-carotene and to a lesser extent dietary vitamin C and beta-carotene may attenuate peak expiratory flow decrements due to air pollution in subjects with chronic respiratory symptoms.
Increased expression of apoptosis signalling receptors by alveolar macrophages in sarcoidosis
Authors: Dai H , Guzman J , Costabel U
Published: October 2002

The Fas receptor (FasR) and the tumour necrosis factor (TNF) receptor 55/60 kDa (TNFR1) are recognized as apoptosis signalling receptors. They are known to be expressed by lymphocytes in association with immune regulation and immunological disorders. This study aimed to investigate the expression of FasR and TNFR1 by alveolar macrophages (AM) in patients with sarcoidosis. Bronchoalveolar lavage (BAL) was performed in 12 patients with active sarcoidosis and 11 control subjects. BAL cells were characterized by monoclonal antibodies using a peroxidase-antiperoxidase method. Both FasR and TNFR1 were expressed on a higher percentage of AM in sarcoidosis with respect to control subjects (mean +/-sem 40.8+/-3.1% versus 14.9+/-1.7%, p<0.001 and 61.9+/-3.3% versus 23.1+/-4.1%, p<0.001, respectively). There was a close relationship between the expression of FasR and TNFR1 on AM (r = 0.86, p<0.001). The percentages of FasR+ AM and TNFR1+ AM were in direct proportion to the percentage of BAL lymphocytes (r = 0.75 and 0.84), the CD4/CD8 ratio (r = 0.78 and 0.78), and the percentage of the CD14+ AM subset (r = 0.77 and 0.87), p<0.001 for all correlations. This study indicates that alveolar macrophages expressing apoptotic receptors are increased in patients with active sarcoidosis. Further studies are required to determine whether these alveolar macrophages from patients with sarcoidosis undergo apoptosis more readily than those from control subjects.
Physiotherapy and bronchial mucus transport
Authors: van der Schans CP , Postma DS , Koeter GH , Rubin BK
Published: October 2002

Cough and expectoration of mucus are the best-known symptoms in patients with pulmonary disease. The most applied intervention for these symptoms is the use of chest physiotherapy to increase bronchial mucus transport and reduce retention of mucus in the airways. Chest physiotherapy interventions can be evaluated using different outcome variables, such as bronchial mucus transport measurement, measurement of the amount of expectorated mucus, pulmonary function, medication use, frequency of exacerbation and quality of life. Measurement of the transport rate of mucus in the airways using a radioactive tracer appears to be an appropriate outcome variable for short-term studies. Evaluation of chest physiotherapy only with pulmonary function tests appears to be inadequate in short-term studies. The popularity of using pulmonary function tests is probably based more on the availability of the instruments than on a theoretical basis related to the question of chest physiotherapy improving mucus transport. Quality of life and progression of the disease are not often used as outcome variables, but it may be worthwhile to use these in the future.
VISUAL PRESENTATION OF ELASTIC WAVE PATTERNS UNDER VARIOUS STRUCTURAL CONDITIONS
Authors: Rieber Frank
Published: October 2002

The usual form of reflection seismograph operates satisfactorily over simple structural conditions, but frequently fails to obtain part or all of the desired information when structures are steeply folded, faulted or otherwise complicated. The reasons for this are plainly evident if the paths of the waves in the earth can be visualized. This has been done by the use of a technic originally developed for acoustical measurements. A miniature explosion radiates waves into various models of structure, where reflection and diffraction take place in the same manner as in the earth. The various moving waves are actually photographed in flight. A series of plates is presented, showing wave patterns in various types of structures, ranging from simple to complex. A new type of equipment and technic are briefly described, with which exploration may be carried into the more complex structural regions successfully.
ESTIMATING ORE MASSES IN GRAVITY PROSPECTING
Authors: Hammer Sigmund
Published: October 2002

The interpretation of the results of gravitational prospecting surveys is considered, from a theoretical point of view, in terms of the magnitude of the causative mass as distinct from the conventional interpretation in terms of the mass distribution (size, shape and depth). A general proof is given, based on Gauss’ Theorem in potential theory, that the former problem is unique and the uniqueness is illustrated by an analytical example which also serves to demonstrate the well‐known lack of uniqueness of the latter problem. Practical formulae are presented for estimating the total mass directly from the gravity data and the precision of the mass estimate is considered. The method is applied to a practical gravimeter survey over a known chromite ore body and the estimated mass is found to be in excellent agreement with estimates from core drilling.
THE AIRBORNE MAGNETOMETER
Authors: Muffly Gary
Published: October 2002

This paper discusses the problem of magnetic exploration for oil from an aircraft. A new type of saturation magnetometer is described. Various orientation and stabilization schemes and their application to submarine detection and geophysical prospecting are discussed. It is shown that total‐field measurement is far superior to vertical‐component measurement. The newest Gulf apparatus using an automatically‐stabilized continuously‐recording total‐field magnetometer is described.
UNIVERSAL SLIDE RULE FOR LINEAR VELOCITY VS. DEPTH CALCULATIONS
Authors: Mansfield Robert H.
Published: October 2002

Described in detail in the main body of the paper is a circular slide rule designed to use for many calculations where the seismic velocity varies linearly with distance from a datum plane (usually horizontal), i.e., where [Formula: see text]. Here [Formula: see text] is the velocity at datum and a is the rate of change of velocity with respect to depth z. Table I lists, in the first column, data that must be given and, in the second column, what may be found from it by using the present slide rule. Except for that of line 10, all calculations are limited only by the accuracy of reading the scales, which is sufficient for most practical purposes. The calculation of line 10 is approximate only, but needs correcting over only about 5 percent of its usually used range; this correction is very simply made.
BARON ROLAND EÖTVÖS
Authors: Vajk Raoul
Published: October 2002

Baron Roland Eötvös, inventor of the torsion balance, was born one hundred years ago, on July 27, 1848, in Budapest, Hungary. His father, Joseph Eötvös, was a prominent author and politician, who provided young Eötvös (the only son among his four children) with the best possible education. He graduated from high school in Budapest and became a student of law at the University of Budapest, as this was the suitable study for a young aristocrat in those days. However, Roland Eötvös had a strong inclination toward natural sciences and attended also lectures on astronomy, worked in the chemical laboratory of the university, and learned mathematics privately. Finally he turned entirely to physics and mathematics.
THE GRAVITY METER AS A GEODETIC INSTRUMENT
Authors: Woollard George Prior
Published: October 2002

A special Worden temperature compensated gravity meter having a range of 5,500 mgals, and a reading sensitivity of 0.1 mgal was used to tie together various primary gravity base stations around the world and to establish new stations. Air transport was used and in a 3 month period over 80,000 miles were flown. Thirty‐three pendulum stations were reoccupied involving a change in gravity of 3,800 mgals, and 125 gravity stations were established. The investigation demonstrated that this instrument could be used satisfactorily for long range geodetic work and the results appear to be the equal of good pendulum observations. Drift was corrected for on the basis of the drift rate established immediately before and after flights. Closures after correcting for drift averaged less than 0.4 mgals, and the closure for the world girdling loop was 0.33 mgals. The probable error based upon the gravity values at the reoccupied pendulum station was ±0.5 mgals. Reoccupation of the absolute gravity stations at the U. S. Bureau of Standards in Washington, D. C. and the National Physical Laboratory in Teddington, England, indicated an approximate 5 mgal error in these pendulum determinations. Indirect ties to the absolute gravity base in Potsdam, Germany, through the primary national gravity bases tied to it, indicated a 15 to 19 mgal error in the Potsdam absolute value. Most of the primary national gravity bases tied directly to Potsdam were found to agree among themselves to within 1 mgal, and the U. S. Bureau of Standards Absolute Base in Washington, D. C. to have a perfect connection within the limits of accuracy of the present measurements. This investigation was made under the auspices of the Office of Naval Research.
THE SECOND DERIVATIVE METHOD OF GRAVITY INTERPRETATION
Authors: Elkins Thomas A.
Published: October 2002

The second derivative method of interpreting gravity data, although its use is justifiable only on data of high accuracy, offers a simple routine method of locating some types of geologic anomalies of importance in oil and mineral reconnaissance. The theoretical formula by which it is possible to compute the second (vertical) derivative of any harmonic function from its values in a horizontal plane is derived for both the two‐dimensional and the three‐dimensional cases. The graphical method of computing the second derivative is discussed, especially as to the sources of error. A numerical coefficient equivalent of the graphical method is also presented. Formulas and graphs for the second derivative of the gravity effect of such geometrically simple shapes as the sphere, the infinite horizontal cylinder, the semi‐infinite horizontal plane, and the vertical fault, are presented with discussions of their value in the interpretation of practical data. Finally, the gravity and second derivative maps of portions of some important oil provinces are presented and compared to show the higher resolving power of the second derivative.
TRANSIENT ELECTROMAGNETIC PROPAGATION IN A CONDUCTING MEDIUM
Authors: Wait James R.
Published: October 2002

The transient electric fields will be calculated for several types of step function current sources embedded in a conducting medium. These will be developed by the aid of the Laplace Transformation. The types of source elements considered are the electric dipole, the magnetic dipole and the linear grounded current element of finite and infinite length.
NEUTRON LOGGING OF DRILL HOLES: THE NEUTRON‐NEUTRON METHOD
Authors: Tittle C. W. , Faul Henry , Goodman Clark
Published: October 2002

Experiments were performed to determine the distribution of thermal neutrons and of indium resonance neutrons in continuous hydrogenous media and in pipes passing through hydrogenous media. Included in the study were water, brine, mixtures of sand and water, and mixtures of sand and brine. Experiments in a continuous typical barite drilling mud showed that the neutron distributions were essentially the same as in water. Also, from the point of view of these experiments, oil and fresh water are nearly identical. These experiments show that well fluid (and, by inference, cement) imposes serious limitations on the sensitivity and accuracy of the neutron‐neutron logging method. The indium resonance neutron response (or, in general, the intensity of epithermal neutrons) is a more reliable indicator of hydrogen content of the formation than is the thermal neutron response. The neutron‐neutron method of chlorine determination was found to be not sensitive enough to be useful with brines of the concentrations ordinarily found in reservoirs.
REGIONALS, RESIDUALS, AND STRUCTURES
Authors: Nettleton L. L.
Published: October 2002

A critical review of the various methods for determining regional effects indicates that neither the graphical systems nor the various numerical and mathematical systems provide a philosophically sound basis for separating a potential field into regional and residual components. The former depend on the judgment of the operator and the latter on assumptions or empirical steps in the mathematical derivation of the numerical factors or coefficients used in the calculations. Each system has its advantages and disadvantages and a proper appreciation of these is necessary for the successful application of either or both systems to a given problem. The various published mathematical systems are compared by reducing their numerical factors to a common basis and listing them in tabular form. This comparison shows the gross variation in numerical coefficients and weighting factors derived by different mathematical approaches. Comparisons of the graphical system and certain of the grid systems, made by carrying them out over a gravity map of the same area, show the effect of these variations on second derivative maps. Other examples of applications are listed from maps in the geophysical literature. It is concluded that the lack of an objective criterion for the isolation of anomalies is due to the inherent ambiguity in the sources of potential fields, but that in spite of the empirical nature of any regional method, the proper application of a system appropriate to the particular problem encountered can give very useful results.
DETERMINATION OF DIPS AND DEPTHS OF GEOLOGICAL LAYERS BY THE SEISMIC REFRACTION METHOD
Authors: Mota Lindonor
Published: October 2002

Equations are developed for computing depths and dips of 1, 2, 3, ⋯, n inclined interfaces from seismic refraction data without the aid of graphical techniques.
GRAVITATIONAL SURVEYING WITH THE GRAVITY‐METER
Authors: Mott‐Smith L. M.
Published: October 2002

The paper discusses briefly the history of gravity meters and the importance of gravity surveys for the prospector. The relative advantages claimed for the gravity meter over the torsion balance and pendulum, from the points of view of adaptability to field work, corrections and accuracy, are brought out. The paper also discusses the methods of observation, particularly in regard to “drift.”
GRAVIMETER DESIGN AND OPERATION
Authors: Bryan A. B.
Published: October 2002

An elementary general discussion of gravimeters and a brief comparison of gravimeter with torsion balance are given. Details as to construction, accuracy, speed of operation and methods of making field observations are given for one type of instrument which is being widely used in geophysical exploration work.
PROSPECTING FOR GROUND WATER BY INDUCED ELECTRICAL POLARIZATION
Authors: Vacquier Victor , Holmes Charles R. , Kintzinger Paul R. , Lavergne Michel
Published: October 2002

When direct current introduced into the ground at two points is interrupted, a small voltage, which may take several minutes to decay, appears between another pair of electrodes. This effect, called by C. Schlumberger “provoked polarization,” is found useful in prospecting for ground water. Laboratory experiments indicate that induced polarization (I.P.) depends on cation exchange in the clay minerals contaminating the aquifers. It is suggested that the effect is due to electrodialysis of the clay within the aquifer, which acts as a distributed electronegative membrane. The magnitude of the I.P. depends on the kind of clay and the kind of positive ions in the water. It is inversely proportional to the conductivity of the water and independent of the kind of negative ion dissolved therein. The rapidity with which the I.P. decays appears to depend only on the grain size of the aquifer. Field trials and experiments on laboratory models give promise of useful application of the method to depths of about 350 feet.
FREQUENCY ANALYSIS FOR GRAVITY AND MAGNETIC INTERPRETATION
Authors: Dean William C.
Published: October 2002

The operations of second derivative, analytic continuation, smoothing, the removing of residuals or regionals, and others in gravity and magnetic interpretation are analogous mathematically to the filtering action of electric circuits. The main difference between the two is that electrical filters act on functions of one variable (time), whereas the geophysical filters must act on functions of the two space variables (x and y). This paper develops linear filter theory for gravity and magnetic interpretation. As an application of the theory, downward continuation is discussed in some detail. The frequency response of upward continuation is an exponential function decreasing with increasing frequency. The inverse process of downward continuation has a frequency response which is the reciprocal of the upward continuation response. This paper discusses a method of matching frequency responses by coefficient sets and shows by examples some of the inherent difficulties in downward continuation. A final example calculated analytically shows how good a downward continuation can be expected from a finite coefficient set.
MEASUREMENT OF THE THICKNESS OF THE EARTH’S CRUST IN THE ALBERTAN PLAINS OF WESTERN CANADA
Authors: Richards T. C. , Walker D. J.
Published: October 2002

Following seismic observations in the Albertan Plains from the Ripple Rock explosion, a refraction line some 81 miles long and parallel to the frontal thrust of the Rocky Mountains and about 60 miles to the east thereof was observed by two‐way shooting. Fifteen seismic parties, spaced at roughly uniform intervals along the line and using the method of close geophone correlation, were employed, the object being to map as many refractors or reflectors as possible as far as the Mohorovicic discontinuity. The results indicate that this discontinuity occurs at a minimum depth of 43 km where the velocity is about 8.2 km/sec, while an intermediate layer with a minimum depth of 29 km and velocity 7.2 km/sec has been registered. Other intermediate refractors were observed. These results are compared with those obtaining in other parts of the American continent and elsewhere. The operational, instrumental, and theoretical aspects of the work are discussed.
AFMAG—AIRBORNE AND GROUND
Authors: Ward S. H.
Published: October 2002

The existence of natural magnetic fields in the audio and subaudio frequency range has been known for some time. The primary source of energy for these fields is usually considered to be distant and local thunderstorms. Because of this origin, the fields are quasi‐random with both amplitudes and directions changing drastically over short periods of time. Hence, use of these fields in geophysical prospecting has been extremely limited. A new development, AFMAG, however, essentially eliminates the time variance in recording these fields without any sacrifice of the intelligence of their space variance. Since the space variance can be correlated with geologic features, AFMAG provides a new method of exploration with particular application to prospecting for conductive mineral deposits. Instrumentation of the AFMAG method currently is available for both ground and airborne operation; the tilt of the plane of polarization of the natural magnetic fields is recorded simultaneously at two frequencies. Examples drawn from airborne and ground surveys show that the method has a much greater depth of exploration than its conventional cousin, the induction electromagnetic method. Numerous other advantages, such as the possibility of choosing discrete operating frequencies over a broad band from 1 cps to 1,000 cps, are discussed. The chief disadvantage of the method lies in a sometimes restricted daily measuring period during which the fields are of an amplitude too low to permit measurement with current instrumentation; this is not a serious problem and is being minimized as the technology improves.
INDUCED POLARIZATION, A STUDY OF ITS CAUSES
Authors: Marshall Donald J. , Madden Theodore R.
Published: October 2002

The causes of induced electrical polarization include not only the polarization of metal‐solution interfaces, but also effects associated with the coupling of different flows. Electro‐osmotic, thermal electric, and ion diffusion effects are among such examples. A study of the physical properties of geologic materials indicates that only electrode interface and diffusion flow phenomena are important sources of induced polarization effects. It was attempted to find characteristic differences between these two phenomena. Theoretical and experimental considerations show that the kinetic processes involved are quite similar in the two cases. This leads to difficulties in identifying the polarizing agent from electrical measurements, although the effects of well mineralized zones are easily recognized.
STUDIES OF ELASTIC WAVE ATTENUATION IN POROUS MEDIA
Authors: Wyllie M. R. J. , Gardner G. H. F. , Gregory A. R.
Published: October 2002

Elastic wave attenuation in porous media is due in part to the relative motion of the liquid and the solid. Biot’s theory expresses this component in terms of permeability, fluid viscosity, frequency, and the elastic constants of the material. Experiments were performed to measure attenuation in the frequency range f <20,000 cps by a resonant bar method; attempts to measure attenuation at very high frequencies gave more equivocal results. Alundum bars were used to test the validity of the theory, for with these the loss not due to fluid motion is relatively small. Experiments were also made with natural specimens of rock. These showed that when not subjected to compacting pressure both the velocities and decrements of specimens were affected chemically and physically by the presence of liquid pore saturants. It is concluded that Biot’s theory seems generally applicable to the determination of the fluid‐solid or “sloshing” losses in resonated porous media. There is still some doubt about the applicability of the theory in the case of measurements made by pulse techniques. The use of attenuation measurements as a logging technique, possibly to estimate permeability, is also discussed.
TERRAIN CORRECTION TABLES FOR GRAVITY
Authors: Bible John L.
Published: October 2002

The terrain correction table presented by Sigmund Hammer (1939) is herein expanded to accommodate the areas of rugged topography encountered by modern surveys. It has also been simplified somewhat to facilitate use and to improve the accuracy by reducing the limitation of certain estimates.
COMMON REFLECTION POINT HORIZONTAL DATA STACKING TECHNIQUES
Authors: Mayne W. Harry
Published: October 2002

Techniques are described whereby multiple coverage of the subsurface is obtained. Detector spreads and shotpoints are arranged so that the channels representing common depth points are recorded with appreciably different horizontal distances between the shotpoints and detector stations. The channels which have a common reflection point are combined, or stacked, after appropriate corrections for angularity and travel time to datum have been applied. Reflections which follow the assumed travel paths are greatly enhanced, and other events are reduced. Methods for attenuating multiple reflections with respect to primaries are discussed in considerable detail. Typical field comparisons between conventional and stacked traverses are shown to illustrate the degree of improvement which can be obtained in the signal‐to‐noise ratio. General considerations applicable to field usage, and the geographic range of field experience are summarized.
NUMERICAL CALCULATION OF THE FORMULA OF REDUCTION TO THE MAGNETIC POLE
Authors: Baranov V. , Naudy H.
Published: October 2002

Some important aspects of the principle of the reduction to the pole are examined first. Secondly, a numerical calculation method is presented, followed by two examples, one theoretical, the other practical.
SEISMIC SIGNAL ENHANCEMENT WITH THREE‐COMPONENT DETECTORS
Authors: Shimshoni Michael , Smith Stewart W.
Published: October 2002

The time‐averaged cross‐product of vertical and radial components of ground motion is multiplied by the original signal producing a function of ground motion in which rectilinearly polarized motion is enhanced. This provides some separation of seismic signals from noise when both occupy the same frequency and velocity bands. The vertical and radial motion is decomposed into its Fourier components, and the parameters of an equivalent ellipse are computed at each instant of time. The eccentricity, major axis, and angle of inclination of the ellipse provide criteria for identifying P and SV waves of different velocities.
OIL FIELDS AND AEROMAGNETIC ANOMALIES
Authors: Steenland Nelson C.
Published: October 2002

Six examples of relationships between aeromagnetic anomalies and producing areas are presented by maps of subsurface structure, observed aeromagnetics, second vertical derivatives of the aeromagnetic fields, and maps of the magnetic basement computed from the aeromagnetic data whenever all these are available. In addition, a copy of an original aeromagnetic traverse is included. The examples embrace Puckett in the Delaware Basin of West Texas, Grieve in the Wind River Basin of Wyoming, Tioga and Onstad in the Williston Basin of North Dakota, Swanson River in the Cook Inlet Basin of Alaska, and Zelten in the Sirte Basin of Libya. These include both “before and after” examples with basement maps prepared in some cases before discoveries, and in other cases afterwards. The paper purports to demonstrate that correlative magnetic anomalies exist in either event. Moreover, these anomalies would be disclosed by any competent technique, so techniques of interpretation are not a part of the argument. It is well known that the larger observed aeromagnetic anomalies result from intrabasement contrasts of magnetization. Anomalies resulting from structure alone ordinarily are smaller by a factor of the magnitude of ten. Of the six cases, Puckett, Tioga, and Onstad represent structures with associated intrabasement effects, whereas anomalies at Grieve, Swanson River, and Zelten are considered to be purely structural effects. There are difficulties involved in using either type of anomaly quantitatively for determination of depth to basement and the relief of possible basement structure. But these examples are part of a much larger amount of evidence which seems to justify improving the definition of the observed aeromagnetic field so that the small residual structural effects can be better defined in order to find more of them and to interpret them more accurately. New instrumentation with higher sensitivities is now available for this second venture in aeromagnetic prospecting.
A CONFIRMATION BY GRAVITY MEASUREMENTS OF AN UNDERGROUND DENSITY PROFILE BASED ON CORE DENSITIES
Authors: McCulloh Thane H.
Published: October 2002

Accurate laboratory measurements of dry bulk densities of 79 samples of Paleozoic sedimentary rocks from a 2,851‐ft deep core hole near Barberton, Ohio, are the basis of a vertical profile of “natural” density which differs on the average [Formula: see text] or less from a profile of in‐situ density calculated from gravity variations observed using a LaCoste and Romberg gravimeter in an adjacent 2,247‐ft‐deep vertical mine shaft. Both profiles agree well with the most meaningful Barberton core sample densities reported by Hammer (1950, Fig. 3), but are significantly lower than in‐situ interval densities calculated by Hammer from gravity variations observed in the shaft using a Gulf gravimeter. The [Formula: see text] average discrepancy between the old and new in‐situ density profiles is probably attributable to a 12‐percent error in calibration of the Gulf gravimeter. The close agreement between the new profiles of “natural” and in‐situ density suggests that changes in bulk volume of compact sedimentary rocks that occur during or following the coring process are probably ordinarily so small that properly constructed core sample density profiles are reproducible and reliable even when small numbers of samples of aged cores are used. If they are to be used for determination of in‐situ density, underground gravity measurements must be accurate as well as precise.
CONTINUOUS SPECTRUM OF THE TOTAL‐MAGNETIC‐FIELD ANOMALY DUE TO A RECTANGULAR PRISMATIC BODY
Authors: Bhattacharyya B. K.
Published: October 2002

The Fourier transform of the total‐magnetic‐field anomaly due to a rectangular prismatic body with arbitrary magnetization yields the two‐dimensional spectrum of the anomaly. In the expression for the spectrum the individual effects of the horizontal and vertical dimensions of the body appear as separate factors. Another factor in the expression takes into account the combined influence of the orientation of the magnetization vector and the dip and declination of the earth’s magnetic field. The expression for the two‐dimensional spectrum is used to obtain analytical formulas of the spectra for magnetic‐field values along profiles parallel to the two horizontal axes of the body. This theoretical study provides a quantitative picture of the shift of the spectrum to the low‐frequency end with increase in either depth or horizontal dimension, or in both, of the magnetized body. It has thus been possible to realize the feasibility of a method for separating the effects of near‐surface high‐amplitude components from those of deep crustal sources in total‐field aeromagnetic maps. Separation of these effects is, however, not unique because of spectral overlap between anomalies due to “shallow” and “deep” sources. A detailed discussion has been made about the characteristics of amplitude and phase spectra of anomalies due to prismatic bodies of differing dimensions. The spectra of anomalies seem to be useful in rapid estimation of the dimensions of a body under suitable conditions. The effect of demagnetization on the fields due to prismatic bodies has been ignored in this paper.
LACOSTE AND ROMBERG STABILIZED PLATFORM SHIPBOARD GRAVITY METER
Authors: Lacoste Lucien , Clarkson Neal , Hamilton George
Published: October 2002

The LaCoste and Romberg gravity meter designed for operation in gimbals was redesigned for satisfactory stabilized platform operation and a suitable stabilized platform was made. A major modification of the gravity meter was redesign of the suspension to more nearly restrict motion to a single degree of freedom. Errors due to cross coupling between horizontal and vertical accelerations and an unsuspected type of cross coupling due to gravity meter imperfections are important but correctable. The stabilized platform gravity meter has been tested at sea. Compared to the gimbal type of gravity meter, it is simpler to operate; it will operate in rough weather; and it is considerably more accurate.
DEEP CRUSTAL SEISMIC REFLECTIONS AT NEAR‐VERTICAL INCIDENCE
Authors: Clowes R. M. , Kanasewich E. R. , Cumming G. L.
Published: October 2002

Seismic reflections from discontinuities deep within the crust (reflection times of 8 to 16 sec) have been recorded along four different lines over a widespread area in southern Alberta, resulting in a total of 90 km of near‐vertical‐incidence profiling. Systems of geophone and hole patterns were designed to form an effective filter against long period surface waves. The data were recorded on FM analog magnetic tape and the results were digitized in order to apply digital processing techniques. Power‐spectra calculations indicate that the energy of the reflected wavelets is concentrated in the range 5 to 15 Hz. Synthetic seismograms were made for comparison with field recordings and they suggest that velocity transition zones within the deep crust are less than one kilometer in vertical extent. Along one profile an expanding spread was utilized and a strong reflection at 11.6 sec was continuously correlated over nearly 25 km. A least‐squares analysis of the [Formula: see text], [Formula: see text] plot gives an average vertical velocity of 6.2 km/sec to a depth of 34 km. Other weaker reflections have been recorded from layers at or near the base of the crust, and some events are evident at shallower depths as well. Continuous profiling along a line 40 km long has resulted in a seismic cross section which shows structural relief of 8 km over a distance of 25 km. These results indicate that the reflection technique with its high resolving power may be used to map complicated structures which even a detailed refraction survey may fail to delineate. It is probable that many continental areas have similar crustal complexities, but these have been undetected due to the inherently lower resolution of the refraction method.
AFMAG—INTERPRETATION
Authors: Ward S. H. , O’Brien D. P. , Parry J. R. , McKnight B. K.
Published: October 2002

In electromagnetic prospecting it is customary to use scale model experiments as the basis for interpretation of field data. The model data is compiled into a catalog of families of anomaly profiles where each family illustrates the effect of varying a single parameter such as depth, depth extent, dip, thickness, conductivity, etc. An interpretation diagram of quadrature secondary field versus in‐phase secondary field is used in some systems to obtain the conductivity‐thickness product of a thin semi‐infinite sheet conductor. In fact, the semi‐infinite sheet conductor is the basic model used in dipolar‐source electromagnetic systems. In a uniform field method like Afmag, the semi‐infinite sheet model is unsatisfactory because the induction through the sheet, and hence the secondary fields, increase without bound as the area of the sheet increases. We have found it satisfactory, on the other hand, to employ the thin‐disk model for which the response may be written approximately as [Formula: see text]where [Formula: see text] is the inducing field, X and Y are the in‐phase and quadrature components of the reflection coefficient, and where GF is a vector quantity describing the geometry of the fields scattered from a thin disk whose radius is A. The quantities X and Y are functions of the induction number [Formula: see text] where σ and μ are the conductivity and permeability of the disk, ω is the angular frequency of the inducing field, and t is the thickness of the disk. From the response function one may compute an expression for tilt angle. We have computed tilt angle profiles and grouped them into families according to dip and to depth divided by radius. Interpretation diagrams have been constructed for each dip of a circular disk and from these one may estimate, for field data, the dip, depth of burial, radius, and conductivity‐thickness product.
STATISTICAL MODELS FOR INTERPRETING AEROMAGNETIC DATA
Authors: Spector A. , Grant F. S.
Published: October 2002

A mathematical basis for the application of power spectrum analysis to aeromagnetic map interpretation is developed. An ensemble of blocks of varying depth, width, thickness, and magnetization is considered as a statistical model. With the use of the fundamental postulate of statistical mechanics, a formula which can be used to analyze the power spectrum of an aeromagnetic map is developed. The influences of horizontal size, depth, thickness, and depth extent of the blocks on the shape of the power spectrum are assessed. Examples which include power spectra of maps from Canada and Central America demonstrate the application of the approach. In the cases studied a double ensemble of blocks appears to best explain the observed power spectrum characteristics.
APPLICATION OF HOMOMORPHIC DECONVOLUTION TO SEISMOLOGY
Authors: Ulrych T. J.
Published: October 2002

Homomorphic systems (Oppenheim, 1965a and 1965b) are a class of nonlinear systems which satisfy a generalized principle of superposition. Such systems are particularly useful in separating signals which have been combined through convolution. This paper deals with the application of homomorphic deconvolution to the recovery of the seismic wavelet from a time series formed by the convolution of this wavelet with an impulse train. The unique point about this approach is that it does not require the usual assumptions of a minimum‐phase wavelet and a random distribution of impulses.
DEPTH OF INVESTIGATION IN DIRECT CURRENT METHODS
Authors: Roy A. , Apparao A.
Published: October 2002

The depth of investigation in any direct current resistivity method of surface geophysical prospecting is defined, following Evjen (1938), as that depth at which a thin horizontal (parallel to ground surface) layer of ground contributes the maximum amount to the total measured signal at the ground surface. Using the equivalence between static and stationary fields, we have found the following values for the absolute depths of investigation in homogeneous ground.
THE USE OF LINEAR FILTERING IN GRAVITY PROBLEMS
Authors: Ku C. C. , Telford W. M. , Lim S. H.
Published: October 2002

The technique of Fourier analysis is reviewed and the equivalence and relative advantages of convolution filtering in the space domain and multiplication filtering in the frequency domain are demonstrated with actual field examples. We discuss the design of ideal filters in terms of the relationships between the main lobe and the side lobes. Cut‐and‐try methods appear to favor the hanning window or the hamming window, since these windows minimize the Gibbs phenomenon associated with the downward continuation or high‐pass filtering operation. New sets of coefficients for convolution filtering, based upon Fourier transform theory and the sampling theory, are derived.
THE MAGNETOTELLURIC METHOD IN THE EXPLORATION OF SEDIMENTARY BASINS
Authors: Vozoff Keeva
Published: October 2002

The paper describes the theory of the magnetotelluric (MT) method, and some of the experimental, analytical, and interpretive techniques developed for its use in petroleum exploration in the past five years. Particular emphasis is placed on interpretation, since it is the area least amenable to routine treatment. Whereas present interpretation techniques are adequate, interpretation is the area of both the greatest progress and the greatest need for improvement. Field results are presented from traverses in South Texas bordering on the Gulf of Mexico, and the Anadarko Basin of southwestern Oklahoma. Wide station spacings were used, such as might typify basin evaluations. The South Texas results are compared directly with smoothed induction logs. No useable logs could be found for Oklahoma. Comparisons with known and inferred geology show that the surveys mapped resistivity successfully in the known parts of these basins as well as in portions inaccessible seismically. The capabilities and economics of the MT method justify its consideration for evaluating large unexplored blocks and “no record” areas.
THE ANALYTIC SIGNAL OF TWO‐DIMENSIONAL MAGNETIC BODIES WITH POLYGONAL CROSS‐SECTION: ITS PROPERTIES AND USE FOR AUTOMATED ANOMALY INTERPRETATION
Authors: Nabighian Misac N.
Published: October 2002

This paper presents a procedure to resolve magnetic anomalies due to two‐dimensional structures. The method assumes that all causative bodies have uniform magnetization and a cross‐section which can be represented by a polygon of either finite or infinite depth extent. The horizontal derivative of the field profile transforms the magnetization effect of these bodies of polygonal cross‐section into the equivalent of thin magnetized sheets situated along the perimeter of the causative bodies. A simple transformation in the frequency domain yields an analytic function whose real part is the horizontal derivative of the field profile and whose imaginary part is the vertical derivative of the field profile. The latter can also be recognized as the Hilbert transform of the former. The procedure yields a fast and accurate way of computing the vertical derivative from a, given profile. For the case of a single sheet, the amplitude of the analytic function can be represented by a symmetrical function maximizing exactly over the top of the sheet. For the case of bodies with polygonal cross‐section, such symmetrical amplitude functions can be recognized over each corner of each polygon. Reduction to the pole, if desired, can be accomplished by a simple integration of the analytic function, without any cumbersome transformations. Narrow dikes and thin flat sheets, of thickness less than depth, where the equivalent magnetic sheets are close together, are treated in the same fashion using the field intensity as input data, rather than the horizontal derivative. The method can be adapted straightforwardly for computer treatment.It is also shown that the analytic signal can be interpreted to represent a complex “field intensity,” derivable by differentiation from a complex “potential.” This function has simple poles at each polygon corner. Finally, the Fourier spectrum due to finite or infinite thin sheets and steps is given in the Appendix.
DRILL‐CORE SCANNING FOR RADIOELEMENTS BY GAMMA‐RAY SPECTROMETRY
Authors: Løvborg Leif , Wollenberg Harold , Rose‐Hansen John , Nielsen Bjarne Leth
Published: October 2002

A system has been developed for the continuous and stepwise scanning of rock drill cores for gamma‐ray spectrometric determinations of uranium, thorium, and potassium. The apparatus accomodates 3‐ to 4‐cm‐diameter core as it passes two opposing 2‐inch diameter by 3‐inch‐ thick NaI(Tl) detectors, either continuously, at speeds ranging from one to several meters per hour, or in steps of 5 cm or more. Resulting gamma‐ray spectra, as recorded with a multi channel analyzer, are computer processed, furnishing scale diagrams of individual radioelement contents and Th/U ratios in the core. Whole‐rock assays of one‐meter‐long core sections by continuous scanning are accurate and precise to within 10 percent or better. In the step‐scanning mode, the system can resolve peak concentrations of U and Th with an accuracy of about 15 percent. Continuous one‐meter scans of 3500 m of core from the Ilímaussaq intrusion, South Greenland, provided an evaluation of uranium resources in the course of seven months. Examination of the continuous‐scan diagrams indicated areas of geochemical interest, such as sharp and transitional contacts and mineralized zones. These were investigated more closely by step scanning, disclosing detailed variations of U and Th. Contents of U and Th determined by scanning of drill core were consistent with the gross gamma‐ray counting rates measured in the boreholes.
DIVERGENCE EFFECTS IN A LAYERED EARTH
Authors: Newman P.
Published: October 2002

Of the various factors which influence reflection amplitudes in a seismic recording, divergence effects are possibly of least direct interest to the interpreter. Nevertheless, proper compensation for these effects is mandatory if reflection amplitudes are to be of diagnostic value. For an earth model consisting of horizontal, isotropic layers, and assuming a point source, we apply ray theory to determine an expression for amplitude correction factors in terms of initial incidence, source‐receiver offset, and reflector depth. The special case of zero offset yields an expression in terms of two‐way traveltime, velocity in the initial layer, and the time‐weighted rms velocity which characterizes reflections. For this model it follows that information which is needed for divergence compensation in the region of normal incidence is available from the customary analysis of normal moveout (NMO). It is hardly surprising that NMO and divergence effects are intimately related when one considers the expanding wavefront situation which is responsible for both phenomena. However, it is evident that an amplitude correction which is appropriate for the primary reflection sequence cannot in general be appropriate for the multiples. At short offset distances the disparity in displayed amplitude varies as the square of the ratio of primary to multiple rms velocities, and favors the multiples. These observations are relevant to a number of concepts which are founded upon plane‐wave theory, notably multiple attenuation processes and record synthesis inclusive of multiples.
MACHINE CONTOURING USING MINIMUM CURVATURE
Authors: Briggs Ian C.
Published: October 2002

Machine contouring must not introduce information which is not present in the data. The one‐dimensional spline fit has well defined smoothness properties. These are duplicated for two‐dimensional interpolation in this paper, by solving the corresponding differential equation. Finite difference equations are deduced from a principle of minimum total curvature, and an iterative method of solution is outlined. Observations do not have to lie on a regular grid. Gravity and aeromagnetic surveys provide examples which compare favorably with the work of draftsmen.