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121.
John T. Wilson Cherri Adair Hal White Robert L. Howard 《Ground Water Monitoring & Remediation》2016,36(4):50-61
The risk that benzene and toluene from spills of gasoline will impact drinking water wells is largely controlled by the natural anaerobic biodegradation of benzene and toluene. Benzene and toluene, as well as ethanol and other biofuels, are degraded under anaerobic conditions to the same pool of degradation products. Biodegradation of biofuels may produce concentrations of degradation products that make the thermodynamics for degradation of benzene and toluene infeasible under methanogenic conditions and produce larger plumes of benzene and toluene. This study evaluated the concentrations of fuel alcohols that are necessary to inhibit the anaerobic degradation of benzene and toluene under methanogenic conditions. At two ethanol spill sites, concentrations of ethanol greater ≥42 mg/L inhibited the anaerobic degradation of toluene. The pH and concentrations of acetate, dissolved inorganic carbon, and molecular hydrogen were used to calculate the Gibbs free energy for the biodegradation of toluene. In general, the anaerobic biodegradation of toluene was not thermodynamically feasible in water with ≥42 mg/L ethanol. In a microcosm study, when the concentrations of ethanol were ≥14 mg/L or the concentrations of n‐butanol were ≥16 mg/L, the biodegradation of the alcohols consistently produced concentrations of hydrogen, dissolved inorganic carbon, and acetate that would preclude natural anaerobic biodegradation of benzene and toluene by syntrophic organisms. In contrast, iso‐butanol and n‐propanol only occasionally produced conditions that would preclude the biodegradation of benzene and toluene. 相似文献
122.
Howard Veregin 《International journal of geographical information science》2013,27(6):595-619
Abstract This study examines the propagation of thematic error through GIS overlay operations. Existing error propagation models for these operations are shown to yield results that are inconsistent with actual levels of propagation error. An alternate model is described that yields more consistent results. This model is based on the frequency of errors of omission and commission in input data. Model output can be used to compute a variety of error indices for data derived from different overlay operations. 相似文献
123.
The hyporheic zone is an ecologically important ecotone that describes the extent to which nutrient-rich surface waters penetrate the shallow subsurface adjacent to a flowing surface water body. Although steady-state models satisfactorily explain the incursion of surface water into the subsurface as a function of head gradients developed across streambed riffles, they fail to account for the depth that surface water is observed to penetrate the subsurface or for the extent to which the hyporheic zone develops adjacent to the stream channel. To investigate these issues, transient flow modeling has been conducted at the riffle scale and supported by data for an instrumented site in northern Ontario where stream-stage fluctuations are strictly regulated. Model results show that daily stream-stage fluctuations between 0.6 and 4 m produce oscillating solute flow paths that typically reduce residence times of water and solutes in the hyporheic zone from 60 days or more under steady-state conditions to less than 1 day. Furthermore, similar stream-stage fluctuations increase the depth that solutes pervade the subsurface and banks lateral to the stream from around 1 m under steady-state conditions to as much as 2 and 10 m, respectively. The results demonstrate that the transient flow conditions triggered in the subsurface by variable stream stage can exert a strong influence on hyporheic zone development and have important implications for the hyporheos. The results are especially important for hyporheic communities that may survive gradual changes to their living conditions by migrating to more hospitable aquatic habitats, but are unable to respond to rapid changes provoked by more extreme hydrological events. 相似文献
124.
125.
InSAR detection of residual settlement of an ocean reclamation engineering project: a case study of Hong Kong International Airport 总被引:2,自引:1,他引:1
Qing Zhao Hui Lin Wei Gao Howard A. Zebker Albert Chen Kin Yeung 《Journal of Oceanography》2011,67(4):415-426
Man-made land or islands that are reclaimed from the sea are suitable for building airports, harbors, and industry parks for
material transportation because of their broad air and land spaces. However, the reclaimed foundation settlement process is
of public concern, including the continuous impact of ocean processes on its stability. The majority of the buildings and
facilities of Hong Kong International Airport (HKIA) are built on a reclaimed foundation. The reclaimed foundation has been
in residual settlement since completion of the filling project in 1994. In this study, we use persistent scatterer interferometry
(PSI) and ENVISAT (European Satellite) advanced synthetic aperture radar (ASAR) data to detect the residual settlement rates
from 19 April 2006 to 9 January 2008. We use ground truth data to develop empirical correction models for correcting systematic
biases in the ASAR PSI-detected settlement rates. The corrected data follow the Lorentz distribution well, implying that the
residual settlement process is dominated by two modes or categories of settlement rates. The first category represents a relatively
stable state and the second category represents a continuous settlement state. A ground settlement rate map of HKIA shows
that an area of the Passenger Terminal Building and an area of the Southern Runway are two relatively stable areas. There
are two major continuous settlement areas. One covers the airport Midfield. Another is along the coastline, implying that
attention should be paid to impacts of ocean processes on the stability of airport foundations. 相似文献
126.
Re-inscribing the urban abject: Ngai Tahu and the Gothic Revival 总被引:1,自引:1,他引:0
Howard McNaughton 《New Zealand geographer》2009,65(1):48-58
Abstract: The 1960s, in Fredric Jameson's analysis, saw a radical re-formulation of global imperialism, with pockets of the 'third world' being incorporated into the first (Jameson 1991, p. 128). On a local level, this implied for colonized peoples a re-negotiation of social space in the face of urbanization. One culture's civilizing mission becomes another's grid of control, resulting in ghettoization, the marginalization of 'abject zones' where the visibility of the clean and proper city is suspended. This paper examines the case of Christchurch, where the garden as an index to civility becomes a paradoxical veneer in the face of biculturalism and decolonization. 相似文献
127.
Fresh-water lenses are the major sources of water supply in many atoll islands in the Pacific and Indian Oceans, particularly
in dry seasons. Several two- and three-dimensional models are currently available for the simulation of atoll-island aquifers;
however, 2D models cannot include 3D spatial variability of material properties, they must simplify the boundary conditions,
and they cannot correctly simulate pumping wells. In an attempt to overcome these difficulties, a 3D model, SALTFLOW, was
adopted for the simulation of Home Island in the Indian Ocean. This exercise required a discretisation on the order of a few
metres and time steps of a few hours requiring significantly high CPU times. High CPU demand proved to be a difficult challenge
but cannot be considered a serious practical limitation with today's advanced computers. The exhaustive data demands of the
model (e.g., 3D distributions of hydraulic conductivity, porosity, dispersivities, and spatial and temporal variations of
recharge and extraction rates) proved to be more problematical. Although the Home Island data set is unusually comprehensive
by any standards, nonetheless the quality and quantity of the available data proved inadequate to meet the calibration needs
of a highly karstic aquifer system. The Home Island modeling demonstrates the practical limitations of 3D models. It raises
the concern that our ability to develop computer codes capable of simulating complex systems now exceeds our ability to supply
the input data necessary for reliable calibration. Finally, the paper demonstrates the importance of the transient calibration
in reliable simulation of various management options and emphasises that transient calibration should be considered as an
integral part of any similar 2D or 3D modeling.
Electronic Publication 相似文献
128.
Robert F. Howard 《Journal of Astrophysics and Astronomy》2000,21(3-4):119-125
The tilt angles of sunspot groups are defined, using the Mount Wilson data set. It is shown that groups with tilt angles greater
than or less than the average value (≈ 5 deg) show different latitude dependences. This effect is also seen in
synoptic magnetic field data defining plages. The fraction of the total sunspot group area that is found in the leading spots
is discussed as a parameter that can be useful in studying the dynamics of sunspot groups. This parameter is larger for low
tilt angles, and small for extreme tilt angles in either direction. The daily variations of sunspot group tilt angles are
discussed. The result that sunspot tilt angles tend to rotate toward the average value is reviewed. It is suggested that at
some depth, perhaps 50 Mm, there is a flow relative to the surface that results from a rotation rate faster than the surface
rate by about 60 m/sec and a meridional drift that is slower than the surface rate by about 5 m/sec. This results in a slanted
relative flow at that depth that is in the direction of the average tilt angle and may be responsible for the tendency for
sunspot groups (and plages) to rotate their magnetic axes in the direction of the average tilt angle. 相似文献
129.
M. Karovska B. Wood J. Chen J. Cook R. Howard 《Journal of Astrophysics and Astronomy》2000,21(3-4):403-406
We applied advanced image enhancement techniques to explore in detail the characteristics of the small-scale structures and/or
the low contrast structures in several Coronal Mass Ejections (CMEs) observed by SOHO. We highlight here the results from
our studies of the morphology and dynamical evolution of CME structures in the solar corona using two instruments on board
SOHO: LASCO and EIT. 相似文献
130.