Empirical Charts Research Articles

Detection and Evaluation of Geopressured Subsurface Formations Based on Dielectric ( Electromagnetic Wave Propagation) Measurements

Abstract Dielectric logs can be used to locate and quantitatively evaluate geopressured environments by (a)establishing empirical calibration charts for a given formation or geologic region and/ or (b) using the equivalent depth method.

Empirical Correlation of Soil Liquefaction Based on SPT N-Value and Fines Content

A critical review of field performance of sandy soil deposits during past earthquakes is conducted with special emphasis being placed on Standard Penetration Test N-values and fines content. The field relationship between adjusted dynamic shear stress ratio and normalized SPT N-values together with laboratory tests on undisturbed sands indicate that (1) sands containing more than 10 percent fines has much greater resistance to liquefaction than clean sands having the same SPT N-values, (2) extensive damage would not occur for clean sands with SPT N1-values (N-values normalized for effective overburden stress of 1 kgf/cm2) greater than 25, silty sands containing more than 10 percent fines with SPT N1-values greater than 20, or sandy silts with more than 20 percent clay, and (3) sands containing gravel particles seem to have less resistance to liquefaction than clean sands without gravel having the same SPT N-values. On the basis of the above findings, an improved empirical chart separating liquefiable and non-liquefiable conditions is presented in terms of dynamic shear stress ratio, SPT N-values, fines content, and shear strain amplitude.

Prediction of downward flux of atmospheric radiation from clear skies

At present, there are two approaches to the prediction of downward flux of atmospheric radiation at the earth's surface. One can use either empirical correlations or radiation charts. The empirical correlations, being very elementary, do not always agree with observations made under different conditions. The radiation charts on the other hand require detailed knowledge of temperature and water vapour profiles. In the present paper, a semi-empirical approach is advocated. The emissivity of water vapour measured in the laboratory is used to predict the atmospheric downward radiation. Since the laboratory data are based on a homogeneous atmosphere, suitable pressure scaling is employed to take into account the non-homogeneity in the earth's atmosphere. The atmospheric downward radiation is obtained as a function of local temperature, water vapour scale height, and temperature lapse rate. It is shown that the resulting predictions agree somewhat better with observations than do the predictions based on empirical correlations.

Tides of the Caribbean Sea

Analysis of tidal characteristics from 45 gauge locations indicates that the Caribbean Sea hs a microtidal range, for the most part between 10 and 20 cm. The tide is primarily either mixed semidiurnal or mixed diurnal but a substantial section from Puerto Rico to Venezuela experiences diurnal tides. Empirical charts of six component tides (M2, S2, N2, K1, O1, and P1) show local detail of phase and amplitude. Each of the semidiurnal compnent tides is characterized by anticlockwise rotating amphidromes centered in the eastern Caribbean. There is evidence of strong radiational forcing of the S2 tide in the southwestern Caribbean. The diurnal component tides are largely uniform in both phase and amplitude for most of the western and central Caribbean. However, the diurnal phases increase rapidly toward the northwest and the Yucatan Channel.

Finite strip evaluation of effective flange width of bridge girders: Discussion

The authors are commended for doing a useful study on the effective widths of flanges in beam and slab and box-girder bridges. The fact that the effective flange widths increase with the level of load in the zone of nonlinear behaviour is confirmed by several research workers. Dowling et al. (1977), after testing models of steel box girders, concluded that shear lag has little weakening effect on the flange strength. Maisel et al. (1973) , made similar remarks about concrete box girders. Consideration of the shear-lag effects can be important for working loads but at ultimate loads the usefulness of such consideration tends to diminish. In Fig. 1 the authors have shown BE to be measured from the edges of the beam flange for beam-slab bridges, from the centre line of webs for multispine box-girder bridges and from the face of webs for multicell box-girder bridges. Considering that the actual flange width of AASHTO and steel wide-flange girders was not directly considered in the idealization, why do these differences in determining 2B and BE exist? It might be appropriate to measure BE and 2B from the centre line of the webs in all cases. Such a simplification would make the use of Fig. 7 a and b even simpler. For serviceability limit states the Ontario highway bridge design code requires one-lane loaded conditions to be considered for all bridges. The empirical effective-width charts appear to have been developed for all design lane loaded conditions. Will the charts be still applicable if only one of the design lanes is loaded ? The authors clearly state that the purpose of the exercise was to determine effective widths of com-

Tidal loading: crustal structure of Nova Scotia and the M2 tide in the northwest Atlantic from tilt and gravity observations

Summary. Earth-tide tilt and gravity observations from five locations in Nova Scotia, Canada are used to study both the structure of the Earth beneath Nova Scotia and the structure of the M2 ocean tide around Nova Scotia. The observed Earth tides are functions of the spatial distribution of the ocean tides and the elastic properties of the Earth. It is therefore possible, in principle, to invert tidal loading observations for both the distribution of the ocean tides, and the elastic properties of the Earth. In practice our observations from Nova Scotia are imperfectly suited to this task. They contain both observational errors and are poorly distributed. However, it is possible to separate the loading due to tides in waters adjacent to Nova Scotia from that due to the remaining ocean, thereby removing errors that result from uncertainties in the global tide distribution. This is done by considering the spatial derivative of the tilt, since the tilt due to distant loads is virtually the same at all stations within a small geographic area. Differencing pairs of stations nearly eliminates the load tilt caused by distant oceans. Using differenced tilt data the problem is reduced to the estimation of the elastic properties of the Earth beneath Nova Scotia because the tidal load in adjacent waters is reasonably well known. The crustal model inferred from a comparison of observed and theoretical difference tilts is in agreement with the results of seismic refraction experiments conducted along the Atlantic coast of Nova Scotia. Both tilt and seismic data suggest that the crust is 35 km thick, consists of two major layers and is underlain by normal mantle. Having determined an approximate crustal structure, the tilt and gravity observations (as opposed to difference observations) are used to demonstrate that the M2 tidal distribution in the northwest Atlantic is intermediate between the co-tidal charts of Tiron et al. and Zahel and is in fact closely described by Dietrich's empirical chart. A finite element model of loading on the continental margin is used to demonstrate that the lateral changes in crustal structure across the continental margin in no way influence the conclusions. The results also indicate that variations in crustal structure will modify the gravity load tide by at most 10 per cent. Consequently, the inverse problem of inferring the global tide distribution from gravity observations may be considered to be linear to a first approximation.

Force-Frequency Coefficient of Singly Rotated Vibrating Quartz Crystals

Frequency perturbations in vibrating quartz crystals, caused by externally applied forces, have been investigated for some time. The parameters affecting the force-frequency sensitivity were recently established and evaluated, making possible the derivation of a normalized coefficient K <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</inf> . An empirical chart, showing the coefficient K <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</inf> for all singly rotated crystals, (yxl)θ, is presented for all directions of force in the azimuth angle ψ. The maximum force-frequency coefficient is found to be |K <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</inf> | ≅ 30 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−15</sup> (msN <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> ) for angles θ = +17°, +26.5° and +64°. A crystal cut (yxl) − 18.5° shows a constant coefficient K <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</inf> = +5.3 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−15</sup> (msN <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> ) for all angles of ψ. Coefficients K <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</inf> (ψ) for BT-, Y- and AT-cut crystals are also shown on separate graphs. The force-frequency behavior of every crystal cut in the singly rotated Y-cut group can be determined from the chart. The chart is a useful tool for the design of frequency standards and precise force-sensing elements. More significantly, the chart provides normalized experimental data to form a basis for a theoretical treatment of the force-frequency effect.

Simplified procedures for estimating band and total emissivities of polyatomic molecules

We present a qualitative description of the essential physical ideas which we have used in obtaining a successful molecular description of Hottel's empirical emissivity charts for CO2, H2O, and for CO2−H2O mixtures.

Ionization charts of the upper atmosphere

In this paper Prof. Chapman's theory of the ionization of the upper atmosphere by solar radiation has been applied to construct a set of charts giving contour lines of equal ionic density over the surface of the earth. A simple approximate method of solving the fundamental differential equation of the theory by a rapid arithmetical process is described. Charts are drawn for winter, equinox and summer conditions for the values 0.5 and 1 of the parameter σ0 and the value 150 of the parameter R. A brief comparison of these charts with existing empirical charts is given with a short discussion of its practical and theoretical significance.