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561.
Olivia J. Wilson 《GeoJournal》1998,46(3):247-255
This paper analyses the ‘Dorferneuerung’ or village renewal scheme - a key policy for rural development in the new ‘Länder’ of Germany which has been transferred from the old Länder. The contribution that Dorferneuerung can make to rural development is considered, with particular reference to the experience of participating villages in Sachsen-Anhalt. It concludes that Dorferneuerung has contributed much to improving the built environment but little to new job creation. It is indicative of the advantages and disadvantages of reunification for rural development in the new Länder. 相似文献
562.
The 1995 Water Consumer Protection Act of Tucson, Arizona, USA (hereafter known as the Act) was passed following complaints
from Tucson Water customers receiving treated Central Arizona Project (CAP) water. Consequences of the Act demonstrate the
uncertainties and difficulties that arise when the public is asked to vote on a highly technical issue. The recharge requirements
of the Act neglect hydrogeological uncertainties because of confusion between "infiltration" and "recharge." Thus, the Act
implies that infiltration in stream channels along the Central Wellfield will promote recharge in the Central Wellfield. In
fact, permeability differences between channel alluvium and underlying basin-fill deposits may lead to subjacent outflow.
Additionally, even if recharge of Colorado River water occurs in the Central Wellfield, groundwater will become gradually
salinized. The Act's restrictions on the use of CAP water affect the four regulatory mechanisms in Arizona's 1980 Groundwater
Code as they relate to the Tucson Active Management Area: (a) supply augmentation; (b) requirements for groundwater withdrawals
and permitting; (c) Management Plan requirements, particularly mandatory conservation and water-quality issues; and (d) the
requirement that all new subdivisions use renewable water supplies in lieu of groundwater. Political fallout includes disruption
of normal governmental activities because of the demands in implementing the Act.
Received, December 1996 · Revised, October 1997 · Accepted, October 1997 相似文献
563.
F. Krennrich C.W. Akerlof J.H. Buckley J. Bussóns-Gordo D.A. Carter-Lewis M.F. Cawley M.A. Catanese V. Connaughton D.J. Fegan J.P. Finley J.A. Gaidos K.H. Harris A.M. Hillas R.C. Lamb M.J. Lang G. Mohanty J. Quinn A.J. Rodgers H.J. Rose A.C. Rovero M.S. Schubnell G.H. Sembroski T.C. Weekes C. Wilson 《Astroparticle Physics》1998,8(4):213-221
Observations of photons at E ≥ 550 GeV from the Crab Nebula are presented and used to assess the potential of multi-telescope systems for γ-ray astronomy.
The Whipple observatory 10 m and 8 m imaging atmospheric erenkov telescopes have been used to provide a stereoscopic view of air showers to make a more complete measurement of air shower parameters. Here we present a measurement of the spread in the arrival direction of primary γ-rays originating from a point source. The data show that the shower arrival direction can be reconstructed with an accuracy of σ = 0.°14. 相似文献
564.
Water requirements for germination and early seedling establishment in four African savanna woody plant species 总被引:1,自引:0,他引:1
The aim of this study was to determine the water requirements for germination and early seedling establishment of four African savanna tree species, namelyAcacia karroo, A. nilotica, A. tortilisandMundulea sericea. The acacias are characteristic of nutrient-rich, andM. sericeaof nutrient-poor savannas. Imbibition times of scarified seeds ofA. karroo(4 h),M. sericea(6 h) andA. tortilis(8 h) were rapid relative toA. nilotica(28 h) and were inversely correlated with seed size. Imbibed water is lost in about 2 h after drying at 25°C for all species exceptA. nilotica(only 70% moisture loss). Seeds ofA. karrooandM. sericeakept at 40°C dried to below their original moisture contents within 2 h. Seeds ofA. niloticaandA. tortilisdried at 40°C lost viability relative to (undried) control seeds, while there was no significant loss of viability forA. karrooandM. sericea. For fully imbibed seeds to germinate in sandy savanna soils, all four species required at least the equivalent of 3 mm rainfall every 2 days under mild greenhouse conditions. However, most ungerminated seeds were still viable despite drying-out from a fully imbibed state. Maintenance of soil at 50% field capacity (FC), or watering to FC every 9th day is the maintenance requirements for 2-week-old seedlings ofA. niloticaandM. sericeato continue growth for a further 5 weeks under greenhouse conditions, althoughA. niloticamostly survived 25% FC with one seedling surviving 12·5% FC. Root penetration was rapid in sandy soils, withA. niloticaandM. sericeaattaining a depth of 40 cm within 15 days. Frequent, but not necessarily high, rainfall appears to be essential for germination and seedling survival over the first 7 weeks. 相似文献
565.
566.
L. Wilson 《Planetary and Space Science》1973,21(1):113-118
The angular light scattering properties of an Apollo 11 lunar regolith ‘fines’ sample have been determined experimentally for both flat and undulating sample surface preparations. The light scattering curves, whose shapes are known to be a function of the porosity and slope distribution of the measured surface, have been compared with corresponding Earth-based lunar measurements. The comparison method involves the numerical fitting of theoretical photometric functions to both the astronomical and laboratory data.It is deduced that regolith material can, under favourable circumstances, maintain a very underdense structure (porosity of the surface layer greater than 90 per cent) in air, so that vacuum cold-welding is not essential in the formation of such a structure. Photometric scanning is shown to provide a rapid method of determining the effective porosity of regolith sample surfaces in the laboratory. 相似文献
567.
Nearby examples of the antimatter chunks postulated by Sofia and Van Horn to explain the cosmic gamma ray bursts may produce detectable gamma ray events when struck by solar system meteoroids. These events would have a much shorter time scale and higher energy spectrum than the bursts already observed. In order to have a reasonably high event rate, the local meteoroid population must extend to a distance from the Sun of the order of 0.1 pc, but the required distance could become much lower if the instrumental threshold is improved. We also examine the expected gamma ray flux for interaction of the antimatter bodies with the solar wind, and find it far below present instrumental capabilities. 相似文献
568.
Preliminary results are presented of observations of the solar Na D lines obtained with high space and time resolution (2.4″ × 2.4″), (6 s). The following conclusions may be drawn.
- The line profiles vary strongly with space and time implying that time averaging over a long period and large area will not produce the ‘true’ profile.
- The centre-limb increase in apparent Doppler width in the D lines is intrinsic. It is not due to space or time averaging.
- The amplitude of the 300-s oscillation may range up to 1.5 km/s in the region of formation of the D lines. Large line asymmetries are associated with this motion. Observations which do not resolve this motion can not be considered adequate.
- The variation of the D line profile caused by the 300-s oscillation may be described as follows: (a) The core is raised and lowered without change of shape, (b) The wings broaden as the central intensity rises and narrow as it falls. These variations are qualitatively explained by the scanning of the line formation region through the solar atmosphere.
- Doppler width values derived from pairs of D line profiles are strongly correlated with the motion of the element observed. Hotter elements move upward, cooler downward.
- Indications of running waves have been found in the time variation of the core line bisectors.
569.
570.
Numerical implementation of a backward probabilistic model of ground water contamination 总被引:4,自引:0,他引:4
Backward location and travel time probabilities can be used to characterize known and unknown sources or prior positions of ground water contamination. Backward location probability describes the position of the observed contamination at some time in the past; backward travel time probability describes the amount of time prior to observation that the contamination was released from its source or was at a particular upgradient location. The governing equation for backward probabilities is the adjoint of the governing equation for contaminant transport, but with new load terms. Numerical codes that have been written to solve the forward equations of contaminant transport, e.g., the advection-dispersion equation, can also be used to solve the adjoint equation for location and travel time probabilities; however, the interpretation of the results is different and some new approximations must be made for the load terms. We present the governing equations for backward location and travel time probabilities, and provide appropriate numerical approximations for these load terms using the cell-centered finite difference method, one of the most popular numerical methods in ground water hydrology. We discuss some additional numerical considerations for the backward model including boundary conditions, reversal of the flow field, and interpretation of the results. We illustrate the implementation of the backward probability model using hypothetical examples in one- and two-dimensional domains. We also present a three-dimensional application of a pump-and-treat remediation capture zone delineation at the Massachusetts Military Reservation. The illustrations are performed using MODFLOW-96 for flow simulations and MT3DMS for transport simulations. 相似文献