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931.
932.
Abstract The structure and collapse of linear three-dimensional magnetic neutral points is studied by varying the four parameters (p, q,j|,j⊥ ) that define, in general, the linear field of a neutral point. The effect of these parameters on both the skeleton structure (i.e. the fan and spine) and the actual field line structure of the null is considered. It is found that one current component (j⊥ ) causes the skeleton structure of the null to fold up from its potential state, whereas the other current component (j |;) causes the field lines to bend. The two other parameters (p,q) determine the potential structure of the null and cause the null to transform from a three-dimensional null to a two-dimensional null and from a positive (type B) null to a negative (type A) null. To investigate the collapse of three-dimensional nulls, solutions to the linear, low-β ideal magnetohydrodynamic equations are found. It is found that three-dimensional null points can collapse if the field line foot-points are free and energy can propagate into the system. 相似文献
933.
Ten selected compounds were tested on Thermocyclops oblongatus to determine their ability to be used for treatment of drinking water sources. None were shown to be interesting for individual application in household water tanks. Tested compounds, such as potassium permanganate or chlorine-releasing products, were ineffective or affected dramatically the taste or colour of the water. For collective application in water sources, temephos appeared to be the most valuable pesticide because it was effective against cyclops and harmless for environment. Other pesticides should be proposed as substitutes in case of cyclops resistance to temephos. 相似文献
934.
James Flocks Michael D. Miner David C. Twichell Dawn L. Lavoie Jack Kindinger 《Geo-Marine Letters》2009,29(6):359-378
The barrier-island systems of the Mississippi River Delta plain are currently undergoing some of the highest rates of shoreline
retreat in North America (~20 m/year). Effective management of this coastal area requires an understanding of the processes
involved in shoreline erosion and measures that can be enacted to reduce loss. The dominant stratigraphy of the delta plain
is fluvial mud (silts and clays), delivered in suspension via a series of shallow-water delta lobes that prograded across
the shelf throughout the Holocene. Abandonment of a delta lobe through avulsion leads to rapid land subsidence through compaction
within the muddy framework. As the deltaic headland subsides below sea level, the marine environment transgresses the bays
and wetlands, reworking the available sands into transgressive barrier shorelines. This natural process is further complicated
by numerous factors: (1) global sea-level rise; (2) reduced sediment load within the Mississippi River; (3) diversion of the
sediment load away from the barrier shorelines to the deep shelf; (4) storm-induced erosion; and (5) human alteration of the
littoral process through the construction of hardened shorelines, canals, and other activities. This suite of factors has
led to the deterioration of the barrier-island systems that protect interior wetlands and human infrastructure from normal
wave activity and periodic storm impact. Interior wetland loss results in an increased tidal prism and inlet cross-sectional
areas, and expanding ebb-tidal deltas, which removes sand from the littoral processes through diversion and sequestration.
Shoreface erosion of the deltaic headlands does not provide sufficient sand to balance the loss, resulting in thinning and
dislocation of the islands. Abatement measures include replenishing lost sediment with similar material, excavated from discrete
sandy deposits within the muddy delta plain. These sand bodies were deposited by the same cyclical processes that formed the
barrier islands, and understanding these processes is necessary to characterize their location, extent, and resource potential.
In this paper we demonstrate the dominant fluvial and marine-transgressive depositional processes that occur on the inner
shelf, and identify the preservation and resource potential of fluvio-deltaic deposits for coastal management in Louisiana. 相似文献
935.
Hydro-mechanical evaluation of stabilized mine tailings 总被引:3,自引:0,他引:3
936.
This paper addresses temporal variability in bottom hypoxia in broad shallow areas of Mobile Bay, Alabama. Time-series data
collected in the summer of 2004 from one station (mean depth of 4 m) exhibit bottom dissolved oxygen (DO) variations associated
with various time scales of hours to days. Despite a large velocity shear, stratification was strong enough to suppress vertical
mixing most of the time. Bottom DO was closely related to the vertical salinity gradient (ΔS). Hypoxia seldom occurred when
ΔS (over 2.5 m) was <2 psu and occurred almost all the time when ΔS was >8 psu in the absence of extreme events like hurricanes.
Oxygen balance between vertical mixing and total oxygen demand was considered for bottom water from which oxygen demand and
diffusive oxygen flux were estimated. The estimated decay rates at 20°C ranging between 0.175–0.322 d−1 and the corresponding oxygen consumption as large as 7.4 g O2 m−2 d−1 fall at the upper limit of previously reported ranges. The diffusive oxygen flux and the corresponding vertical diffusivity
estimated for well mixed conditions range between 8.6–9.5 g O2 m−2 d−1 and 2.6–2.9 m2 d−1, respectively. Mobile Bay hypoxia is likely to be associated with a large oxygen demand, supported by both water column and
sediment oxygen demands, so that oxygen supply from surface water during destratification events would be quickly exhausted
to return to hypoxic conditions within a few hours to days after destratification events are terminated. 相似文献
937.
938.
939.
Social housing in Australia is at a significant juncture. High levels of housing stress, increasing levels of socio-spatial polarisation and reduced government funding are posing complex policy challenges. Social mix policies are one response to these challenges, arising from the problematisation of social housing estates as socially excluded. This problematisation is examined through case studies of two Sydney social housing renewal projects: Telopea and Riverwood North. Drawing on interviews with government, private-sector and not-for-profit housing practitioners, the paper identifies two distinct discourses of social exclusion within this problematisation—culture of poverty discourse and equity discourse—that shape the implementation of social mix. These discourses reveal that implementing social mix is more complex than simply managing the cohabitation of residents in different tenures. Rather, the practice of social mix is embedded within discourses about the nature and causes of social exclusion. These discourses, in their turn, inform the multiple and sometimes conflicting aspirations pursued through social mix policies. 相似文献
940.
Design and Long-Term Monitoring of Tokyo International Airport Extension Project Constructed on Super-Soft Ground 总被引:1,自引:0,他引:1
K. Morohoshi K. Yoshinaga M. Miyata I. Sasaki H. Saitoh M. Tokoro N. Fukuda T. Fujii K. Yamada M. Ishikawa 《Geotechnical and Geological Engineering》2010,28(3):223-232
To meet the increasing demand for air transportation, Ministry of Land, Infrastructure and Transport had carried out the offshore
extension project at Tokyo International Airport (Haneda Airport). The airport should be constructed to be perfectly level,
but the ground conditions with very thick layers of super soft dredged soils and need for reclamation made the task very difficult.
Because of large amount of consolidation settlement, ground improvement by combined vertical drain method was applied to decrease
residual and differential settlement after opening of new airport. This paper is aimed to introduce the design concept and
method of ground improvement for this project. In addition the result of ground improvement is keeping satisfactory performance
for operating airport confirmed by long-term monitoring for airport facilities. 相似文献