Consolidation with threshold gradients

Evidence for threshold gradients is reviewed. The consolidation problem, with threshold gradient, is properly formulated and solved numerically. An approximate analytical solution is also developed. The influence of a threshold gradient on the time rate of settlement is examined, and it is shown that by modifying the definition of the degree of consolidation a good approximation to the threshold gradient problem can be obtained directly from the Terzaghi solution. It is also shown that threshold gradients will have no influence on odometer testing and their effect is, therefore, to reduce the primary compression below that predicted from standard tests.     

Some tests of the Vaníček Method of spectral analysis

One of the chief claims of the Vaníček Method of spectrum analysis is its, ability to remove ‘systematic noise’ from a time series with minimal distortion of the spectrum of the remaining series. In this paper, comparisons are made between the Vaníček Method and the more usual method consisting of preliminary removal of the systematic noise followed by fourier analysis. Formulas relating the two methods are developed and a series of comparative plots of simple spectra are presented. Results indicate that the Vaníček Method does not displace a spectral peak falling close to the systematic noise, that it distorts the amplitude of the peak less than the conventional method of analysis, and that it tends to intensify the side lobes.     

Occultation of ε Geminorum by Mars: IV. Oblateness of the martian upper atmosphere

The oblateness of the Martian upper atmosphere was determined from analysis of photoelectric observations of the 8 April 1976 occultation of ε Geminorum by Mars at seven stations. The oblatness is 0.0096 ± 0.0023, consistent with a mean equator-to-pole temperature difference in excess of ～ 50°K, vertically averaged from the surface to the occulation altitude of ～70 km. The astrometric solution provides precise determination of the occultation path relative to the Martian shadow, and absolute vertical alignment of upper atmospheric temperature profiles obtained by inversion of occultation light curves. The observations can be compared directly with models of atmospheric tides computed for the conditions at the suboccultation regions on Mars.     

Observed composition of the ionosphere of Venus: Implications for the ionization peak and the maintenance of the nightside ionosphere

Across the nightside of Venus, daily measurements from the PV Orbiter Ion Mass Spectrometer often indicate an ionosphere of relatively abundant concentration, with a composition characteristic of the dayside ionosphere. Such conditions are interspersed by other days on which the ionosphere appears to largely “disappear” down to about 200 km, with ion concentrations at lower heights also much reduced. These characteristics, coupled with observations of strong day to night flows of O⁺ in the upper ionosphere, support arguments that ion transport from the dayside is important for the maintenance of the nightside ionosphere. Also, U.S. and Soviet observations of nightside energetic electron fluxes have prompted consideration of impact ionization as an additional nightside ion source. The details of the ion and neutral composition at low altitudes on the nightside provide an important input for further analysis of the maintenance process. In the range 140–160 km, strong concentrations of O₂⁺ and NO⁺ indicate that the ionization peak is at times composed of at least two prominent ion species. Nightside concentrations of O₂⁺ and NO⁺ as large as 10⁵ and 10⁴/cm³, respectively, appear to require sources in addition to that provided by transport. The most probable sources are considered briefly, and no satisfactory explanation is yet found for the observed NO⁺ concentrations. Further analysis beyond the scope of this paper is required to resolve this issue.     

A finite element model for the analysis of tailored pulse stimulation of boreholes

A constitutive model is described for the prediction of dynamic crack formation in geological media. The model includes a simple tensile failure criterion for crack formation and a soil plasticity model for both deviatoric and volumetric plasticity. Numerical results are presented which show that the model reproduces the observed dependence of fracture formation on loding rate for dynamic pressure loading of boreholes. The use of the model as a numerical tool for design is demonstrated through two example parameter studies.