Accelerated plate motion and rates of volcanicity as controls on Archean climates

Although vulcanicity is seen as a possible mechanism of climatic change, under present rates of eruptions it is difficult to envisage volcanic activity acting independently of other factors in causing significant and lasting global climate changes. This note considers the global plate-tectonic regime which may have prevailed during the Archean, and which, as a consequence, should have resulted in rates of volcanic eruptions significantly higher than at present. From this would follow atmospheric CO₂ levels significantly higher than those which prevail today. In this note we attempt to establish a link between the Archean global plate-tectonic regime and the high atmospheric CO₂ levels which are thought to have existed at that time.     

Effect of magnetic fields on leveling

Normally, the establishment of national leveling networks was for the purpose of supporting national mapping programs of engineering projects. They are also used as a base on which to establish national gravity networks. During recent years, much study and investigation have been done concerning the characteristics and capabilities of these networks to provide data for determining height velocity changes due to crustal movements.

In the early 1960's the use of automatic (compensator) leveling instruments became common for establishing precise geodetic leveling networks. In 1981, at FIG, Montreux, Professor W.E. Rumpt and Mr. H. Meurisch reported the influence of DC-AC magnetic fields on the line of sight of compensator instruments. As a result, several manufacturers modified their automatic leveling instruments to minimize the AC-DC magnetic effect. Wild Heerbrugg, whose unmodified NA-2 level was least affected by magnetic fields, further reduced the effect by shielding it's compensator.

At the very least, the impact of this discovery will cause national geodetic agencies to modify their existing automatic leveling equipment and possibly embark on a releveling or reanalysis of their existing network. When studying micro/macro earth crustal movements, the geodesist must take this new factor into account in analysing data.     

Parameterization of subsurface heating for soil and concrete using net radiation data

The variability of surface sensible heat flux depends strongly on the heating rate of the material beneath the surface. This variability is expected to be large in urban areas where the surfaces are layered with a variety of man-made materials. Parameterization of the ground heat storage as a function of surface materials is presented based on analyses of data obtained during the U.S. Environmental Protection Agency's Regional Air Pollution Study conducted in St. Louis, Missouri. Ground heat flux data are derived from observations of surface and subsurface temperatures for a soil layer and for concrete slabs resting on soil. The data show that the presence of the concrete slabs increases the ground storage term relative to that for soil alone. The ground storage and sensible heat flux terms for a blackened concrete slab are larger than for an unpainted concrete slab. For the concrete surfaces, the ratio of ground storage to net radiation is >1 at night and <1 during the day. This ratio is discontinuous at sunrise and sunset transition periods. For soil, the ratio shows similar temporal behavior except that on average, there is a smoother transition at sunrise. Simple mathematical expressions giving the ratio of ground heat storage to net radiation as a function of time are presented.Now with Enviroplan, Incorporated, West Orange, NJ 07052, U.S.A.On assignment from the National Oceanic and Atmospheric Administration, U.S. Department of Commerce.     

Spatial and temporal variations of spatial population accessibility to public hospitals: a case study of rural–urban comparison

Quantification and assessment of nationwide population access to health-care services is a critical undertaking for improving population health and optimizing the performance of national health systems. Rural–urban unbalance of population access to health-care services is widely involved in most of the nations. This unbalance is also potentially affected by varied weather and road conditions. This study investigates the rural and urban performances of public health system by quantifying the spatiotemporal variations of accessibility and assessing the impacts of potential factors. Australian health-care system is used as a case study for the rural–urban comparison of population accessibility. A nationwide travel time-based modified kernel density two-step floating catchment area (MKD2SFCA) model is utilized to compute accessibility of travel time within 30, 60, 120, and 240 min to all public hospitals, hospitals that provide emergency care, and hospitals that provide surgery service, respectively. Results show that accessibility is varied both temporally and spatially, and the rural–urban unbalance is distinct for different types of hospitals. In Australia, from the perspective of spatial distributions of health-care resources, spatial accessibility to all public hospitals in remote and very remote areas is not lower (and may even higher) than that in major cities, but the accessibility to hospitals that provide emergency and surgery services is much higher in major cities than other areas. From the angle of temporal variation of accessibility to public hospitals, reduction of traffic speed is 1.00–3.57% due to precipitation and heavy rain, but it leads to 18–23% and 31–50% of reduction of accessibility in hot-spot and cold-spot regions, respectively, and the impact is severe in New South Wales, Queensland, and Northern Territory during wet seasons. Spatiotemporal analysis for the variations of accessibility can provide quantitative and accurate evidence for geographically local and dynamic strategies of allocation decision-making of medical resources and optimizing health-care systems both locally and nationally.     

Geological and hydrogeological environment in Tianjin with potential geohazards and groundwater control during excavation

This paper discusses the geological and hydrogeological features of Quaternary deposits in Tianjin as well as the geohazards related to groundwater hydrology in this region. The soft soil deposits, comprising silt, sand, silty clay and clay, are composed of four aquifer groups. In the first aquifer group, one phreatic aquifer and two confined aquifers have relationships with underground construction in the urban area. These three aquifers are separated by two aquitards and collectively form a multi-aquifer system. During geotechnical construction, potential geohazards present are related to the groundwater, which include water-in-rushing, quicksand and piping hazards. To prevent the aforementioned geohazards, dewatering is conducted; however, groundwater pumping may result in large settlements of the surrounding ground. To reduce pumping-induced settlement, the dewatering–waterproofing system has been adopted. According to the characteristics of the subsoil, excavation depth and the surrounding environment, the dewatering system can be divided into five patterns. In the first four patterns, when pumping is conducted in the excavation pit, the groundwater head in the adjacent aquifers outside the pit decreases due to the leakage effect of the aquitards located between the aquifers. In the fifth pattern, waterproof curtain has cut off the aquifers completely and dewatering in the pit cannot result in settlement around excavation pit. To avoid geohazards related to groundwater hydrology, countermeasures recommended include construction of an effective waterproof curtain, selection of a reasonable excavation dewatering pattern and withdrawal of required groundwater.