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141.
S. Nielsen E. Spagnuolo M. Violay S. Smith G. Di Toro A. Bistacchi 《Journal of Seismology》2016,20(4):1187-1205
Recent estimates of fracture energy G ′ in earthquakes show a power-law dependence with slip u which can be summarized as G ′ ∝ u a where a is a positive real slightly larger than one. For cracks with sliding friction, fracture energy can be equated to G f : the post-failure integral of the dynamic weakening curve. If the dominant dissipative process in earthquakes is friction, G ′ and G f should be comparable and show a similar scaling with slip. We test this hypothesis by analyzing experiments performed on various cohesive and non-cohesive rock types, under wet and dry conditions, with imposed deformation typical of seismic slip (normal stress of tens of MPa, target slip velocity > 1 m/s and fast accelerations ≈ 6.5 m/s2). The resulting fracture energy G f is similar to the seismological estimates, with G f and G ′ being comparable over most of the slip range. However, G f appears to saturate after several meters of slip, while in most of the reported earthquake sequences, G ′ appears to increase further and surpasses G f at large magnitudes. We analyze several possible causes of such discrepancy, in particular, additional off-fault damage in large natural earthquakes. 相似文献
142.
Real-time PCR and NASBA for rapid and sensitive detection of Vibrio cholerae in ballast water 总被引:2,自引:0,他引:2
Fykse EM Nilsen T Nielsen AD Tryland I Delacroix S Blatny JM 《Marine pollution bulletin》2012,64(2):200-206
Transport of ballast water is one major factor in the transmission of aquatic organisms, including pathogenic bacteria. The IMO-guidelines of the Convention for the Control and Management of Ships' Ballast Water and Sediments, states that ships are to discharge <1 CFU per 100 ml ballast water of toxigenic Vibrio cholerae, emphasizing the need to establish test methods. To our knowledge, there are no methods sensitive and rapid enough available for cholera surveillance of ballast water. In this study real-time PCR and NASBA methods have been evaluated to specifically detect 1 CFU/100ml of V. cholerae in ballast water. Ballast water samples spiked with V. cholerae cells were filtered and enriched in alkaline peptone water before PCR or NASBA detection. The entire method, including sample preparation and analysis was performed within 7 h, and has the potential to be used for analysis of ballast water for inspection and enforcement control. 相似文献
143.
Michael H. Stevens Christoph R. Englert Mark Hervig Svetlana V. Petelina Werner Singer Kim Nielsen 《Journal of Atmospheric and Solar》2009,71(3-4):401-407
We present the first measurement of polar mesospheric cloud (PMC) occurrence frequency over the diurnal cycle from a satellite. The observations are made during the 2007 northern hemisphere PMC season by the Spatial Heterodyne IMager for MEsospheric Radicals (SHIMMER), which views the limb near 309 nm typically between 34 and 98 km. The PMC diurnal variation is derived between 50 and 58°N, where local times at the tangent point precess by ~30 min/day allowing for observations between 0330 and 2130 local time during the PMC season. We find that the occurrence frequencies exhibit a strong semidiurnal behavior with peaks near 0600 and 1800 local time and a minimum between 0900 and 1600 during which they are on average an order of magnitude less. The semidiurnal dependence is strongly correlated with concurrent ground-based measurements of meridional winds and temperatures measured at the same latitude. Our results for PMC frequency over the diurnal cycle can be used to help reconcile observations from other satellites that only permit cloud measurements at discrete local times. 相似文献
144.
High-altitude data assimilation system experiments for the northern summer mesosphere season of 2007 总被引:1,自引:0,他引:1
Stephen D. Eckermann Karl W. Hoppel Lawrence Coy John P. McCormack David E. Siskind Kim Nielsen Andrew Kochenash Michael H. Stevens Christoph R. Englert Werner Singer Mark Hervig 《Journal of Atmospheric and Solar》2009,71(3-4):531-551
A global numerical weather prediction system is extended to the mesosphere and lower thermosphere (MLT) and used to assimilate high-altitude satellite measurements of temperature, water vapor and ozone from MLS and SABER during May–July 2007. Assimilated temperature and humidity from 100 to 0.001 hPa show minimal biases compared to satellite data and existing analysis fields. Saturation ratios derived diagnostically from these assimilated temperature and water vapor fields at PMC altitudes and latitudes compare well with seasonal variations in PMC frequency measured from the aeronomy of ice in the mesosphere (AIM) satellite. Synoptic maps of these diagnostic saturation ratios correlate geographically with three independent transient mesospheric cloud events observed at midlatitudes by SHIMMER on STPSat-1 and by ground observers during June 2007. Assimilated temperatures and winds reveal broadly realistic amplitudes of the quasi 5-day wave and migrating tides as a function of latitude and height. For example, analyzed winds capture the dominant semidiurnal MLT wind patterns at 55°N in June 2007 measured independently by a meteor radar. The 5-day wave and migrating diurnal tide also modulate water vapor mixing ratios in the polar summer MLT. Possible origins of this variability are discussed. 相似文献
145.
S.B. Nielsen K. Gallagher D.L. Egholm O.R. Clausen M. Summerfield 《Journal of Geodynamics》2009,48(2):101-106
In this reply, we address the issues raise by the comment of Lidmar-Bergström and Bonow [Lidmar-Bergström, K., Bonow, J., 2009. Hypotheses and observations on the origin of the landscape of southern Norway – a reply regarding the isostasy–climate–erosion hypothesis by Nielsen et al., 2008. Journal of Geodynamics, in press]. We reject them and maintain all our suggestions regarding western Scandinavia unaltered. 相似文献
146.
Morphological records of storm floods exemplified by the impact of the 1872 Baltic storm on a sandy spit system in south‐eastern Denmark
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Lars B. Clemmensen Mette Bendixen Mikkel U. Hede Aart Kroon Lars Nielsen Andrew S. Murray 《地球表面变化过程与地形》2014,39(4):499-508
Beach‐ridge systems are important geo‐archives providing evidence for past wave climate including catastrophic storm flood events. This study investigates the morphological impacts of the 1872 Baltic storm flood on a beach‐ridge system (sandy spit) in south‐eastern Denmark and evaluates the frequency of extreme storm flood events in the area over a longer time perspective. This paper combines field studies of morphology and sedimentary deposits, studies of historical maps, digital terrain model, ground‐penetrating radar profiles, and luminescence dating. Sea water reached 2.8 m above mean sea level (amsl) during peak inundation and, based on studies of the morphological impacts of the 1872 storm flood, the event can be divided into four phases. Phase 1: increasing mean water levels and wave activity at the beach brought sediments from the beach (intertidal bars and normal berm) higher up in the profile and led to the formation of a storm‐berm. Phase 2: water levels further increased and sediment in the upper part of the profile continued to build up the storm‐berm. Phase 3: water levels now reached the top of the dune ridge and were well above the storm‐berm level. Sea water was breaching the dune ridge at several sites and wash‐over fans were generated until a level where the mean water level had dropped too much. Phase 4: the non‐vegetated wash‐over fans functioned as pathways for aeolian sand transport and relatively high dunes were formed in particular along the margins of the fan where aeolian sand was trapped by existing vegetation. The studied beach‐ridge system records about 4500 years of accumulation; the storm flood sediments described are unique suggesting that the 1872 Baltic storm flood event was an extreme event. Thus studies of beach‐ridge systems form a new source for understanding storm surge risk. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
147.
Public participation geographic information systems (PPGIS) are an increasingly important tool for collecting spatial information about the social attributes of place. The availability of Internet‐based options for implementing PPGIS presents new opportunities for increased efficiency and new modes of access. Here we used a mixed‐mode approach to evaluate paper versus Internet mapping methods for the same PPGIS survey in Wyoming. We compared participant characteristics, mapping participation, and the spatial distribution of mapped attributes between participants who responded to the paper versus Internet option. The response rate for those who completed the paper version of the survey was nearly 2.5 times the response rate of the Internet version. Paper participants also mapped significantly more places than did Internet participants (43 vs. 18). Internet participants tended to be younger, more likely to have a college degree, and had lived in the region for less time than paper participants. For all but one attribute there was no difference in the spatial distribution of places mapped between Internet and paper methods. Using a paper‐based PPGIS survey resulted in a higher response rate, reduced participant bias, and greater mapping participation. However, survey mode did not influence the spatial distribution of the PPGIS data. 相似文献
148.
Sea‐level rise has been related to global warming. The modern system on the northern coast of Anholt, Denmark, may well be analogous to other beach ridge systems formed in microtidal regimes and our results should have impact on estimation of past sea‐level variation. Ground‐penetrating radar data collected across the modern (<30 years old) berm, beach ridge and swale deposits resolve downlapping reflections interpreted to mark sea level at the time of deposition. Existing time series of sea‐level data constrain actual sea‐level variation. Nineteen readings of sea‐level markers made along our profile fluctuate within ?0.42 and 0.57 m above present mean sea level, consistent with 95% of the sea‐level data. These fluctuations reflect tidal effects and meteorological conditions. Main data uncertainties are well‐known and the sea‐level markers may be identified with a high degree of confidence. 相似文献
149.
Hanne Dalsgaard Nielsen 《Marine pollution bulletin》2010,60(5):710-717
The relationship between light acclimation and Cu2+ tolerance was studied in two populations of Fucus serratus known to be naturally non-tolerant and tolerant to Cu2+. Acclimation to high irradiances increased the photosynthetic tolerance to Cu2+. The xanthophyll cycle was apparently not involved in protecting the photosynthetic apparatus against Cu2+ toxicity, as results showed that Cu2+ did not induce dynamic photoinhibition. The higher photosynthetic Cu2+ resistance of high light algae did not result in increased growth. The excess energy acquired by high light-adapted algae appeared to be utilized in Cu2+ defense mechanisms in the Cu2+ non-tolerant population. The polyphenol content of the algae was reciprocal to the CuT content, suggesting that polyphenol may be the primary Cu2+ defense of non-tolerant low light algae, acting through secretion and extracellular chelating of Cu2+, while the compounds do not seem to be involved in the primary Cu2+ tolerance mechanism in Cu2+ tolerant algae. 相似文献
150.
John Davis Jakeman Ole M. Nielsen Kristy Van Putten Richard Mleczko David Burbidge Nick Horspool 《Ocean Dynamics》2010,60(5):1115-1138
This paper presents a framework and data for spatially distributed assessment of tsunami inundation models. Our associated
validation test is based upon the 2004 Indian Ocean tsunami, which affords a uniquely large amount of observational data for
events of this kind. Specifically, we use eyewitness accounts to assess onshore flow depths and speeds as well as a detailed
inundation survey of Patong City, Thailand to compare modelled and observed inundation. Model predictions matched well the
detailed inundation survey as well as altimetry data from the JASON satellite, eyewitness accounts of wave front arrival times
and onshore flow speeds. Important buildings and other structures were incorporated into the underlying elevation model and
are shown to have a large influence on inundation extent. 相似文献