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Dong Zhijie Sasha Meng Lingyu Christenson Lauren Fulton Lawrence 《Natural Hazards》2021,106(3):2077-2109
Natural Hazards - Prediction in ungauged basins (PUB) is as crucial as it is challenging. Thus far, there have been abundant regionalization studies on PUB, whereas "regionalization" is... 相似文献
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Anatolii V. Fisenko Sasha B. Verchovsky Andrei A. Shiryaev Luba F. Semjonova 《Meteoritics & planetary science》2017,52(1):60-71
A nanodiamond‐rich fraction (NDF) separated from the Orgueil meteorite was subjected to a high‐intensity ultrasonic treatment in a weakly acidic aqueous solution. After sedimentation by centrifugation, two fractions of grains (suspension, designated as OD7C and sediment, designated as OD7D) with different properties have been obtained. The following effects of the sonication were revealed from comparison of the contents and isotope compositions of C, N, and Xe released during stepped pyrolysis and combustion of the fractions OD7C and OD7D, the initial NDF and two grain‐size fractions (OD10 and OD15) produced without sonication (a) surface layer of the sonicated diamond grains is modified to different extent in comparison with nontreated ones, (b) in some grains concentrations of the bulk N and Xe a reduced significantly, and (c) nondiamond nitrogen containing phases (e.g., Si3N4) have been destroyed. It is suggested that combined effects of the sonication and centrifugation observed for the fractions OD7C and OD7D are due to differences in surface chemistry of the nanodiamond grains, which statistically influences behavior of nanoparticles during the sonication resulting in their preferential modification in the different reaction zones of the cavitating fluid. 相似文献
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John a. Herring Daniel a. Jaffe Harald J. Beine Sasha Madronich Donald R. Blake 《Journal of Atmospheric Chemistry》1997,27(2):155-178
A seven-year record of surface ozone measurements from Denali NationalPark, Alaska shows a persistent spring maximum. These data, combined withmeasurements of NOx, hydrocarbons, O3, and PANfrom a continental site in Alaska during the spring of 1995 are used as thebasis for a sensitivity study to explore tropospheric photochemistry in thisregion. Because of the relatively high concentrations of NOx(mean of 116, median of 91 pptv), the net tendency was for photochemicalozone production. The range of net O3 production for averageconditions measured at this site during spring is between 0.96–3.9ppbv/day depending on the assumptions used; in any case, this productionmust contribute to the observed springtime maximum in O3.Model calculations showed that of the anthropogenic ozone precursors, onlyNOx had a strong effect on the rate of ozone production; themeasured concentrations of anthropogenic hydrocarbons did not significantlyaffect the ozone budget. Naturally produced biogenic hydrocarbons, such asisoprene, may also have a significant effect on ozone production, even atconcentrations of a few 10's of pptv. An observed temperature-isoprenerelationship from a boreal site in Canada indicates that isoprene may bepresent during the Alaskan spring. Measurements of isoprene taken duringthe spring of 1996 suggest that reactive biogenic hydrocarbon emissionsbegin before the emergence of leaves on deciduous trees and that theconcentrations were sufficient to accelerate ozone production. 相似文献
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Bernard Aumont Sasha Madronich Isabelle Bey Geoffrey S. Tyndall 《Journal of Atmospheric Chemistry》2000,35(1):59-75
Measurements show that 20–60% of the carbon mass present in fine atmospheric particulate matter consists of water soluble organic compounds (WSOC). However, only 5–20% of this WSOC has been identified, mainly as dicarboxylic acids. Because of their high solubility in water, multifunctional secondary compounds derived from the gas-phase oxidation of volatile organic compounds (VOC) are suspected to be key contributors to the WSOC. To test this assumption, an estimate of aqueous uptake of secondary VOC was included in a highly detailed gas-phase mechanism which treats explicitly the formation of the secondary VOC from a set of representative primary species. Simulations were conducted for 2 scenarios, representing typical rural and urban areas. It was observed that the uptake of secondary VOC can lead to WSOC mass concentrations in the range of a few C m–3, in fairly good agreement with typical WSOC mass concentrations measured. Speciation of WSOC was found to be mainly as tri- or higher multifunctional hydroxy-carbonyl species and hydroxy-hydroperoxide-carbonyl species, in urban and rural environments, respectively. However, it was also found that taking into account only the absorption of secondary VOC does not bring the carboxylic acids mass concentration in agreement with measurements. An attempt was made to explain this discrepancy by introducing chemistry occurring within deliquescent aerosols. 相似文献
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Antonietta Quigg Jason B. Sylvan Anne B. Gustafson Thomas R. Fisher Rod L. Oliver Sasha Tozzi James W. Ammerman 《Aquatic Geochemistry》2011,17(4-5):519-544
To investigate controls on phytoplankton production along the Louisiana coastal shelf, we mapped salinity, nutrient concentrations (dissolved inorganic nitrogen (DIN) and phosphorus (Pi), silicate (Si)), nutrient ratios (DIN/Pi), alkaline phosphatase activity, chlorophyll and 14C primary productivity on fine spatial scales during cruises in March, May, and July 2004. Additionally, resource limitation assays were undertaken in a range of salinity and nutrient regimes reflecting gradients typical of this region. Of these, seven showed Pi limitation, five revealed nitrogen (N) limitation, three exhibited light (L) limitation, and one bioassay had no growth. We found the phytoplankton community to shift from being predominately N limited in the early spring (March) to P limited in late spring and summer (May and July). Light limitation of phytoplankton production was recorded in several bioassays in July in water samples collected after peak annual flows from both the Mississippi and Atchafalaya Rivers. We also found that organic phosphorus, as glucose-6-phosphate, alleviated P limitation while phosphono-acetic acid had no effect. Whereas DIN/Pi and DIN/Si ratios in the initial water samples were good predictors of the outcome of phytoplankton production in response to inorganic nutrients, alkaline phosphatase activity was the best predictor when examining organic forms of phosphorus. We measured the rates of integrated primary production (0.33?C7.01 g C m?2 d?1), finding the highest rates within the Mississippi River delta and across Atchafalaya Bay at intermediate salinities. The lowest rates were measured along the outer shelf at the highest salinities and lowest nutrient concentrations (<0.1 ??M DIN and Pi). The results of this study indicate that Pi limitation of phytoplankton delays the assimilation of riverine DIN in the summer as the plume spreads across the shelf, pushing primary production over a larger region. Findings from water samples, taken adjacent the Atchafalaya River discharge, highlighted the importance of this riverine system to the overall production along the Louisiana coast. 相似文献
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Jason B. Sylvan Antonietta Quigg Sasha Tozzi James W. Ammerman 《Estuaries and Coasts》2011,34(6):1220-1233
Seasonal phosphorus limitation occurs on the Louisiana continental shelf as a result of high nitrogen loads in the spring
and early summer. Prior studies have assessed such nutrient limitation by laborious and time-consuming nutrient analyses,
enzyme assays, and nutrient addition bioassays. We undertook surface (0.5–1 m) mapping of fast repetition rate fluorescence
(FRRF) parameters to assess nutrient limitation in real time on the Louisiana continental shelf and Mississippi River plume
from 29 June to 08 July, 2002 in an effort to further understand phytoplankton productivity in this region, as well as to
better inform effective nutrient management strategies. Surface nutrient concentrations (NO3−, NO2−, NH4+, PO43−), chlorophyll a biomass, alkaline phosphatase (AP) activity, and four FRRF parameters: the maximum quantum yield of photochemistry (F
v
/F
m
), the functional absorption cross section for PSII, the time constant for Q
A
reoxidation, and the connectivity factor, were measured during continuous underway mapping. Results from traditional methods
to assess phytoplankton nutrient stress indicated widespread phosphorus limitation from the Mississippi River plume to the
Atchafalaya River, manifested as high inorganic N/P ratios and elevated AP activities associated with phytoplankton biomass.
The FRRF data indicated complex patterns of phytoplankton physiology that were likely driven by the rapidly changing conditions
in local surface waters and heterogeneous phytoplankton community structure. Correlations of nutrient data and enzyme assays
with FRRF parameters were significant but low, potentially due to differences in the manner and time scale with which nutrient
limitation affects the different techniques used, indicating that further work is needed to interpret FRRF parameters in large,
heterogeneous environments such as estuaries and continental shelves. 相似文献
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Sasha Tsenkova 《GeoJournal》2014,79(4):433-447
The paper provides an overview of trends and processes of change affecting new social housing provision in Prague and Warsaw. The local responses are reviewed within the context of changes to the national housing system defining the performance of municipal and non-profit housing sectors. The research analyses the mix of policy instruments implemented in three major policy domains—regulatory, fiscal and financial—to promote the production of new social housing in the two cities. The system of new social housing provision is examined as a dynamic process of interaction between public and private institutions defining housing policy outcomes. The outcomes are evaluated through a series of indicators related to housing output, stability of investment, differentiation of rents, affordability and choice. The overview demonstrates how significant shifts in regulatory and fiscal policy, coupled with decentralization of responsibilities for social housing, limit the opportunities for more efficient performance in the sector and its growth. This is particularly evident in Warsaw, where the sector operates as a social safety net. New social housing in both cities has better quality and remains affordable, but access is constrained and waiting times have increased. The research highlights the problem of declining output, dwindling financial resources, and lack of cost recovery due to universal rent control. This is eroding the sustainability of social housing, potentially leading to lower investment and subsequent privatisation. In Warsaw, housing allowances are a municipal responsibility making the liberalization of rents difficult, while Prague has moved in the direction of rent deregulation with a more robust system of means-tested housing support provided by the central government. Such policy choices map a different trajectory for the future of social housing. 相似文献
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