Small D-Spacing WC/SiC Multilayers for Future Hard X-Ray Telescope Designs     

Carsten P. Jensen  Kristin K. Madsen  Finn E. Christensen 《Experimental Astronomy》2005,20(1-3):93-103

Multilayer coatings for reflecting hard X-rays up to 80 keV, like W/Si and Pt/C, have been studied for several years. To go to higher energies, in the range of 100 keV to 250 keV, one needs coatings with smaller d-spacings than can currently be made with these material combinations, and a lower interfacial roughness. With the new material combinations of WC/SiC the interface roughness can be reduced down to between 0.23 nm and 0.25 nm enabling bi-layer thicknesses down to 1.0 nm to reflect efficiently. The production of thinner period coatings thus enables the possibility for focusing optic designs with reasonable focal lengths and throughput up to 250 keV.  相似文献   

Spatiotemporal evolution of the completeness magnitude of the Icelandic earthquake catalogue from 1991 to 2013     

Francesco Panzera  Arnaud Mignan  Kristin S. Vogfjörð 《Journal of Seismology》2017,21(4):615-630

In 1991, a digital seismic monitoring network was installed in Iceland with a digital seismic system and automatic operation. After 20 years of operation, we explore for the first time its nationwide performance by analysing the spatiotemporal variations of the completeness magnitude. We use the Bayesian magnitude of completeness (BMC) method that combines local completeness magnitude observations with prior information based on the density of seismic stations. Additionally, we test the impact of earthquake location uncertainties on the BMC results, by filtering the catalogue using a multivariate analysis that identifies outliers in the hypocentre error distribution. We find that the entire North-to-South active rift zone shows a relatively low magnitude of completeness M_c in the range 0.5–1.0, highlighting the ability of the Icelandic network to detect small earthquakes. This work also demonstrates the influence of earthquake location uncertainties on the spatiotemporal magnitude of completeness analysis.  相似文献   

Shallow Circulations: Relevance and Strategies for Satellite Observation     

Gilles Bellon  Oliver Reitebuch  Ann Kristin Naumann 《Surveys in Geophysics》2017,38(6):1509-1528

Shallow circulations are central to many tropical cloud systems. We investigate the potential of existing and upcoming data to document these circulations. Different methods to observe or constrain atmospheric circulations rely on satellite-borne instruments. Direct observations of the wind are currently possible at the ocean surface or using tracer patterns. Satellite-borne wind lidar will soon be available, with a much better coverage and accuracy. Meanwhile, circulations can be constrained using satellite observations of atmospheric diabatic heating. We evaluate the commonalities and discrepancies of these estimates together with reanalysis in systems that include shallow circulations. It appears that existing datasets are in qualitative agreement, but that they still differ too much to provide robust evaluation criteria for general circulation models. This state of affairs highlights the potential of satellite-borne wind lidar and of further work on current satellite retrievals.  相似文献   

Patterns in the abundance of hyperbenthic zooplankton and colonization of marine benthic invertebrates on the seafloor of Saanich Inlet,a seasonally hypoxic fjord     

Kristin M. Dinning  Anna Metaxas 《Marine Ecology》2013,34(1):2-13

This study describes changes in abundance of hyperbenthic zooplankton (including meroplankton) and benthic colonists at the seasonally hypoxic seabed of Saanich Inlet, British Columbia, Canada. We used the Victoria Experimental Network Under the Sea (VENUS) cabled observatory to measure water properties and to sample hyperbenthos with a sediment trap at 97 m from September 2008 to September 2009. Some faunal groups exhibited seasonal reproduction, and abundance peaked during their reproductive periods. These included larvae of the barnacle Balanus crenatus, and the crabs Petrolisthes eriomerus, Oregonia gracilis, and Lophopanopeus bellus bellus. Other groups were most abundant in spring and summer when food and oxygen levels were highest and temperature was lowest. These included cumaceans, the siphonophore Diphyes sp., the bryozoan Triticella pedicellata, and tintinnids. We also collected benthic colonists, predominantly bryozoans and polychaetes, on colonization plates deployed in spring/summer 2008, fall 2008/winter 2009, and spring/summer 2009. The total abundance of colonists and of bryozoans did not vary seasonally or with substrate complexity, whereas polychaetes were more numerous in spring/summer deployments and on a highly complex substrate. Taxon richness of colonists was higher in spring/summer 2008 than in fall 2008/winter 2009, whereas an anoxic episode in spring/summer 2009 reduced richness to similar values with that of fall 2008/winter 2009 levels. Substrate complexity had no effect on richness. Juvenile squat lobsters, digitally imaged in fall 2008/winter 2009, were most numerous when oxygen levels were lowest and potentially excluding larger predators. Our study illustrates how season, food availability, temperature, and oxygen can interact to shape community structure in a seasonally hypoxic habitat.  相似文献   

Divergent Perspectives on Water Security: Bridging the Policy Debate     

Patricia A. Gober  Graham E. Strickert  Douglas A. Clark  Kwok P. Chun  Diana Payton  Kristin Bruce 《The Professional geographer》2013,65(1):62-71

Environmental policy discussion is replete with references to water security, food security, ecosystem health, community resilience, sustainable development, and sustainable urbanism. These terms are, by their very nature, ambiguous and difficult to define; they allow room, however, for a variety of actors to conceptualize water, food, ecological, economic, and urban problems in ways that allow them to move forward on contentious issues. This article focuses on the idea of water security and asks how it is conceptualized and used for regional policy debate in western Canada. We asked fifty-eight water stakeholders from the Saskatchewan River Basin to define water security, identify major barriers to security, and prioritize water problems. Responses showed there are myriad ways to think about water security, ranging from narrow conceptualizations, such as reliability, quality, and quantity, to broader sustainability perspectives about the nature of resource development and its social and economic consequences. The human dimensions of water security (governance, land use, and competing demands) were assigned higher priority than its biophysical aspects (flooding, droughts, and climate change). Framing water security to emphasize the human capacity to manage uncertain and rapid biophysical and societal change offers the opportunity to unite actors who otherwise would be separated by core environmental values, definitions of water security, provincial context (Alberta vs. Saskatchewan), and occupation.  相似文献   

Using Ground‐Penetrating Radar to Examine Spatial Organization at the Late Classic Maya Site of El Baúl,Cotzumalhuapa, Guatemala     

Kristin N. Safi  Oswaldo Chinchilla Mazariegos  Carl P. Lipo  Hector Neff 《Geoarchaeology》2012,27(5):410-425

The Cotzumalhuapa Nuclear Zone (CNZ) is a Late Classic site consisting of three large architectural compounds linked by a series of stone‐paved causeways and bridges. The majority of the site, however, lies beneath layers of recent tephra, leaving the structure of this settlement largely unknown. This study uses ground‐penetrating radar (GPR) to map the subsurface near El Baúl, one of the main compounds, in order to examine the spatial relationship among urban architectural features. Excavation within areas of the GPR survey provides fine‐grain detail of one major architectural feature in the region, the Gavarrete Causeway. The complimentary nature of these data sets characterizes the architectural organization of the settlement at two scales. Spatial patterning between large‐scale architectural features supports the hypothesis that the CNZ represents an integrated urban center with evidence of planned community organization characteristic of other Late Classic period centers across Mesoamerica.  相似文献   

Spatial Variation in the Optical Properties of Dissolved Organic Matter (DOM) in Lakes on the Canadian Precambrian Shield and Links to Watershed Characteristics   总被引：1，自引：0，他引：1  

Kristin K. Mueller  Claude Fortin  Peter G. C. Campbell 《Aquatic Geochemistry》2012,18(1):21-44

In the present study, we explored the use of various optical parameters to detect differences in the composition of the dissolved organic matter (DOM) in a set of lakes that are all located on the Canadian Precambrian Shield, but within which Cu and Ni speciation predictions were previously shown to diverge from measured values in some lakes but not in others. Water samples were collected with in situ diffusion samplers in 2007 (N = 18 lakes) and 2008 (N = 8 lakes). Significant differences in DOM quality were identified between the sampling regions (Rouyn-Noranda, Québec and Sudbury, Ontario) and among lakes, based on dissolved organic carbon concentrations ([DOC]), specific UV absorbance (SUVA₂₅₄), fluorescence indices (FI), and excitation–emission matrix (EEM) fluorescence measurements. Parallel factor analysis (PARAFAC) of the EEM spectra revealed four components, two of which (C3, oxidized quinone fluorophore of allochthonous origin, and C4, tryptophan-like protein fluorescence of autochthonous origin) showed the greatest inter-regional variation. The inter-lake differences in DOM quality were consistent with the regional watershed characteristics as determined from satellite imagery (e.g., watershed-to-lake surface area ratios and relative percentages of surface water, rock outcrops vegetative cover and urban development). Source apportionment plots, built upon PARAFAC components ratios calculated for our lakes, were used to discriminate among DOM sources and to compare them to sources identified in the literature. These results have implications for other areas of research, such as quantifying lake-to-lake variations in the influence of organic matter on the speciation of trace elements in natural aquatic environments.  相似文献   

In situ atomic force microscopy measurements of biotite basal plane reactivity in the presence of oxalic acid     

Simon J. Haward  Mark M. Smits  Kristín Vala Ragnarsdóttir  Jonathan R. Leake  Terence J. McMaster 《Geochimica et cosmochimica acta》2011,75(22):6870-6881

We have used a direct imaging technique, in situ atomic force microscopy (AFM), to observe the dissolution of the basal biotite surface by oxalic acid over a range of temperatures close to ambient conditions, using a specially designed AFM liquid cell and non-invasive intermittent contact mode of operation. From the 3-dimensional nanometre-resolution data sets, we observe a process characterised by the slow formation of shallow etch pits in the (0 0 1) surface and fast growth of etch pits from the resulting steps, which represent proxies for the {h k 0} surface. Measurements of dissolution rates as a function of temperature allow a determination of an apparent activation energy (E_a,app) for the process, via mass-loss calculations from image analysis. We obtain a value of E_a,app = 49 ± 2 kJ mol⁻¹, which is consistent with separate calculations based on planar area etch pit growth, and measurements of etch pit perimeters, indicating that this value of E_a,app is representative of {h k 0} surface dissolution. The measurement of etch pit perimeters also enables an estimation of apparent activation energy as a function of step density indicating substantially higher apparent activation energy, up to E_a,app = 140 kJ mol⁻¹, on extrapolation towards a pristine surface with no defects. We suggest that this higher value of E_a,app represents the slow formation of etch pits into the (0 0 1) surface.  相似文献   

Multi-proxy paleolimnological assessment of biogeochemical versus food web controls on the trophic states of two shallow,mesotrophic lakes     

Bjorn A. Lake  Courtney R. Wigdahl  Kristin E. Strock  Jasmine E. Saros  Aria Amirbahman 《Journal of Paleolimnology》2011,46(1):45-57

The frequency of nuisance algal blooms has been increasing during the last two decades in the shallow, headwater East Pond (Smithfield, Maine, USA). Meanwhile, the hydrologically linked North Pond has not experienced an increase in algal blooms, despite similar morphometry and higher external nutrient loads. Possible explanations for this difference include stronger trophic cascade effects from planktivorous white perch (Morone americana) in East Pond as well as differences in phosphorus (P) release from the sediments of these two lakes. We conducted a paleolimnological investigation of these two lakes to assess whether sedimentary evidence supported trophic cascade effects based on cladoceran ephippia size, diatom fossils, and fossil pigments or biogeochemical controls based on potential sedimentary P release as the primary driver of these increased algal blooms in East Pond. At the time of white perch introduction (~1930–1950), ephippia size increases in East Pond, although no changes are observed in either diatom abundance or trends in the algal pigments. Instead, algal pigments increase in recent decades (~1980 to present) along with an increase in diatom taxa with higher TP optima These results suggest that predation by white perch is not resulting in top-down effects on algal abundance in East Pond, as predicted by the trophic cascade hypothesis. While the P content of sediments from both lakes is relatively equal, the releasable P in the top 10 cm of sediment in East Pond constitutes a greater percentage of the P extracted. Also, North Pond sediments exhibit a greater capacity to permanently bury P via the mechanisms of sorption to Al(OH)_3(s) and a slower mineralization of organic P compounds. The results of this investigation suggest that the ultimate driver of the recent algal blooms in East Pond is internal P release from the sediments instead of trophic cascade effects.  相似文献   

Mass fluxes of xenobiotics below cities: challenges in urban hydrogeology     

Mario Schirmer  Frido Reinstorf  Sebastian Leschik  Andreas Musolff  Ronald Krieg  Gerhard Strauch  John W. Molson  Marion Martienssen  Kristin Schirmer 《Environmental Earth Sciences》2011,64(3):607-617

Urban areas are the focus of major ecological, social and economical activity. They are thus also prime locations of increasing conflict with regard to water use and water protection. As a direct and/or indirect consequence of urban land use and human activity, urban water systems are frequently polluted with organic contaminants including waste water-born xenobiotics such as pharmaceuticals, personal care products (collectively known as PPCPs) and endocrine-active substances. This study reviews new integrated methodologies including flux calculations as well as chemical investigations for determining the impact of human activities on urban water systems and on processes within the urban watershed. The use of indicator substances, representing different contaminant sources and pathways, integral pumping tests and mass balance approaches are suitable alternatives within these environments. The issues are explored using contaminant mass balance examples from Halle/Saale and Leipzig, Germany.  相似文献