Seismic investigations in South West African river beds

Summary In sand-filled river channels in arid parts of South West Africa it is of importance to find methods of locating the rock surface under the sand, for purposes of water supply. This paper describes preliminary investigations in three such river beds, to test the applicability to this problem of the seismic refraction method, using the hammer-electronic seismic instrument previously developed by one of the writers for shallow refraction work. Both the method in general, and the instrument in particular, proved satisfactory. Examples are given of travel-time diagrams, interpretation is discussed, and channel profiles deduced from the work are shown. Depths ranged from a few feet to a few tens of feet. At two of the three sites, variations in velocity in the sand made standard calculations of dip and depth from two-way shooting inapplicable. In such situations depth could still be estimated reasonably reliably near the origin of the traverse. There was evidence of a superficial layer in which the velocity was less than that of sound in air.     

Spatial and social transformations in a secondary city: the role of mobility in Sekondi-Takoradi,Ghana

Abstract

Existing research on urban Ghana mainly focuses on processes occurring within the country’s major cities, thereby reproducing a trend within the social sciences to overlook the role of intermediate and secondary cities. This paper aims to address this shortcoming by exploring spatial and social transformations in Sekondi–Takoradi, one of Ghana’s secondary cities and the metropolitan area serving the region’s emerging rubber industries as well as the country’s oil and gas economy. Using qualitative interviews conducted with residents in five of the city’s neighbourhoods, and a modified version of Kaufmann’s typology of mobility, we examine migration into Sekondi–Takoradi, residential mobility within the city and the daily mobility of the city’s residents. The paper highlights how these diverse forms of mobility interact with processes taking place both within and outside Sekondi–Takoradi, most notably influencing and being influenced by livelihood strategies. It is argued that the city and its hinterlands can best be envisaged as a mobile networked whole, rather than consisting of disconnected and compartmentalized locales. The paper thus contributes to broader debates on how mobility shapes urbanization by providing new empirical data on events unfolding in Africa’s secondary cities, and extends existing research by providing a counter-narrative to literature that examines the city and its surrounding rural areas separately.     

VIRGO: Experiment for helioseismology and solar irradiance monitoring

The scientific objective of the VIRGO experiment (Variability of solar IRradiance and Gravity Oscillations) is to determine the characteristics of pressure and internal gravity oscillations by observing irradiance and radiance variations, to measure the solar total and spectral irradiance and to quantify their variability over periods of days to the duration of the mission. With these data helioseismological methods can be used to probe the solar interior. Certain characteristics of convection and its interaction with magnetic fields, related to, for example, activity, will be studied from the results of the irradiance monitoring and from the comparison of amplitudes and phases of the oscillations as manifest in brightness from VIRGO, in velocity from GOLF, and in both velocity and continuum intensity from SOI/MDI. The VIRGO experiment contains two different active-cavity radiometers for monitoring the solar constant, two three-channel sunphotometers (SPM) for the measurement of the spectral irradiance at 402, 500 and 862 nm, and a low-resolution imager (LOI) with 12 pixels, for the measurement of the radiance distribution over the solar disk at 500 um. In this paper the scientific objectives of VIRGO are presented, the instruments and the data acquisition and control system are described in detail, and their measured performance is given.died 13 October 1994     

Phaeopigment distribution during the 1990 spring bloom in the northeastern Atlantic

The temporal and depth distributions of phaeopigments were determined during a spring bloom in the northeastern Atlantic in 1990 using reverse phase high performance liquid chromatography. Phaeopigment concentrations were very low (<8% by mole relative to chlorophyll a) and two forms of phaeophorbide and two forms of phaeophytin were separated and quantified. Phaeophorbides were the dominant phaeopigments, accounting for 80% of the total phaeopigment molar concentration, and phaeopigments closely tracked the variations in chlorophyll a by increasing during the development phase of the bloom and decliningin the post bloom stage. Production of phaeopigments was found to occur predominantly at night, and these rates exceeded the rates of phaeopigment destruction during the day. Lower phaeopigment-chlorophyll a ratios were determined for the surface waters, suggesting that photodegradation was possibly the primary mechanism of phaeopigment disappearance in the euphotic zone. A comparison of phaeopigment data and phyto- and zooplankton structure indicates that greater phaeopigment production and grazing pressure occurred in the development phase when diatoms dominated, while grazing and phaeopigment production declined in the post bloom stage dominated by prymnesiophytes.     

Geochemical gradients in soil O-horizon samples from southern Norway: Natural or anthropogenic?

Forty soil O- and C-horizon samples were collected along a south-to-north transect extending inland for approximately 200 km from the southern tip of Norway. The elements As, Au, Bi, Cd, Cu, Ga, Ge, Hf, Hg, In, Mg, Mn, Mo, Na, Ni, Pb, Sb, Se, V, W, Zn and Zr all show a distinct decrease in concentration in soil O-horizons with increasing distance from the coast. The elements showing the strongest coastal enrichment, some by more than an order of magnitude compared to inland samples, are Au, Bi, As, Pb, Sb and Sn. Furthermore, the elements Cd (median O-/median C-horizon = 31), C, Sb, Ag, K, S, Ge (10), Hg, Pb, As, Bi, Sr (5), Se, Au, Ba, Na, Zn, P, Cu and Sn (2) are all strongly enriched in the O-horizon when compared to the underlying C-horizon. Lead isotope ratios, however, do not show any gradient with distance from the coast (declining Pb concentration). Along a 50 km topographically steep east–west transect in the centre of the survey area, far from the coast but crossing several vegetation zones, similar element enrichment patterns and concentration gradients can be observed in the O-horizon. Lead isotope ratios in the O-horizon correlate along both transects with pH and the C/N-ratio, both proxies for the quality of the organic material. Natural conditions in southern Norway, related to climate and vegetation, rather than long range atmospheric transport of air pollutants (LRT), cause the observed features.     

A review of: “A perspective of physics,vol. 3”

Abstract

Edited by Sir Harrie Massey. Gordon and Breach, New York, London, Paris, 1979. 354 pp. ($35.50 (ISBN 0 677 15970 6))     

北美地区大湖水位的变化研究

在数十年来大湖水位变化历史记录背景下，考察了近年来大湖处于低水位的问题，并且比较了下游湖区水位最近的回升与上游湖区持续的低水位状况．探讨了气候变化对大湖水位的潜在影响。     

Comments on thaw-freeze algorithms for multilayered soil, using the Stefan equation

The Stefan equation provides a useful and widely used method for predicting the depth of thawing and freezing in a soil where little site-specific information is available. The original Stefan equation was derived for only a homogeneous medium, and some algorithms have been developed for its use in a multilayered system. However, although the Stefan equation was derived more than 100 years ago, there is not a unified understanding for its use in a multilayered system. This paper examines the use of the Stefan equation in multilayered soil, based on comparing three algorithms(JL-algorithm, NM-algorithm, and XG-algorithm). We conclude that the JL and NM algorithms are incorrect, as they arose from flawed mathematical derivations. Both of these algorithms failed to recognize that the thawing depth in a multilayered soil is a piecewise function and not a continuous function of time. This work asserts that the XG-algorithm is a correct and rigorous method to determine the freezing–thawing fronts in multilayered soil.