An ocean surface current radar (OSCR) in the very high frequency (VHF) mode was deployed in South Florida Ocean Measurement Center (SFOMC) during the summer of 1999. During this period, a 29-d continuous time series of vector surface currents was acquired starting on 9 July 1999 and ending 7 August 1999. Over a 20-min sample interval, the VHF radar mapped coastal ocean currents over a 7.5 km × 8 km domain with a horizontal resolution of 250 m at 700 grid points. A total of 2078 snapshots of the two-dimensional current vectors were acquired during this time series and of these samples, only 69 samples (3.3%) were missing from the time series. During this period, complex surface circulation patterns were observed that included coherent, submesoscale vortices with diameters of 2 to 3 km inshore of the Florida Current. Comparisons to subsurface measurements from moored and ship-board acoustic Doppler current profiles revealed regression slopes of close to unity with biases ranging from 4 to 8 cm s-1 between surface and subsurface measurements at 3 to 4 m beneath the surface. Correlation coefficients were 0.8 or above with phases of - 10 to - 20° suggestive of an anticyclonic veering of current with depth relative to the surface current. The radar-derived surface current field provided spatial context for an observational network using mooring-, ship- and autonomous underwater vehicle-sensor packages that were deployed at the SFOMC 相似文献
Macroscopic frictional behavior of granular materials is of great importance for studying several complex problems associated with fault slip and landslides. The main objective of this study is to model the macroscale frictional behavior of granular soils under monotonic and cyclic loadings based upon micromechanical determination of dissipated energy at particle contacts. This study is built on the general observation that the externally computed energy dissipation should be equal to the total internal energy dissipation derived from inter-particle sliding and rolling, energy losses from inter-particle collisions, and damping. For this purpose, the discrete element method is used to model a granular soil and determine the stored, dissipated, and damping energies associated with shear loading for applied monotonic and cyclic velocities. These energies are then related to the friction by an application of the Taylor-critical state power balance relationship. Also, the contributions of the different modes of energy dissipation (normal, shear, and rolling) to the total frictional resistance were studied. By changing the inter-particle friction, the simulations showed that the macroscopic friction was nearly constant, the slip friction increased almost linearly with increasing inter-particle friction, and the difference between the two was attributed to the non-energy dissipating dilatancy component. By providing a clear relationship between energy dissipated by micro-scale mechanisms versus the traditional engineering definition based on macro-scale (continuum) parameters, this study provides a means to develop a better understanding for the frictional behavior of granular media.
Natural Hazards - Effective tsunami risk reduction requires an understanding of how at-risk populations are specifically vulnerable to tsunami threats. Vulnerability assessments primarily have been... 相似文献
A new occurrence of Mn-rich rocks was discovered within the high-pressure/low-temperature metamorphic rocks on the Palos peninsula of Syros (Greece). Near the summit of Mount Príonas, a meta-conglomerate consists of calcite (~63 wt%), pink manganian phengite, blue–purple manganian aegirine–jadeite, microcline, albite and quartz. In addition, it contains abundant braunite-rich aggregates (up to ~1.5 cm in diameter) that include hollandite [(Ba0.98–1.02K<0.01Na<0.02Ca<0.03) (Mn1.02–1.523+Fe0.38–0.883+Ti0.29–0.92Mn5.11–5.764+)O16], barite and manganian hematite. Due to metamorphic recrystallization and deformation, the contacts between clasts and matrix are blurred and most clasts have lost their identity. In back-scattered electron images, many aegirine–jadeite grains appear patchy and show variable jadeite contents (Jd10–67). These pyroxenes occur in contact with either quartz or albite. Manganian phengite (3.41–3.49 Si per 11 oxygen anions) is of the 3T type and contains 1.4–2.2 wt% of Mn2O3. At the known P–T conditions of high-pressure metamorphism on Syros (~1.4 GPa/ 470 °C), the mineral sub-assemblage braunite + quartz + calcite (former aragonite) suggests high oxygen fugacities relative to the HM buffer (+7 ≤ ?fO2 ≤ + 17) and relatively high CO2 fugacities. The exact origin of the conglomerate is not known, but it is assumed that the Fe–Mn-rich and the calcite-rich particles originated from different sources. Braunite has rather low contents of Cu (~0.19 wt%) and the concentrations of Co, Ni and Zn are less than 0.09 wt%. Hollandite shows even lower concentrations of these elements. Furthermore, the bulk-rock compositions of two samples are characterized by low contents of Cu, Co and Ni, suggesting a hydrothermal origin of the manganese ore. Most likely, these Fe–Mn–Si oxyhydroxide deposits consisted of ferrihydrite, todorokite, birnessite, amorphous silica (opal-A) and nontronite. Al/(Al + Fe + Mn) ratios of 0.355 and 0.600 suggest the presence of an aluminosilicate detrital component. 相似文献
A background indoor air study has been completed which includes the collection of indoor air samples from office buildings and schools. The anonymous study was designed with input from the U.S. Environmental Protection Agency and the Massachusetts Department of Environmental Protection. The sampling was implemented in 2013, 2014, and 2015 and included the collection of 25 school building samples and 61 office building samples. The study generated 14,668 new indoor air background data points, with samples collected from buildings located in 26 cities in 18 states, including Arizona, California, Connecticut, Indiana, Kansas, Maine, Massachusetts, Minnesota, Montana, New Hampshire, New Jersey, New York, Nevada, North Carolina, Ohio, Texas, Utah, and Washington. Indoor air background concentrations of target compound volatile organic compounds (VOCs) ranged from less than the laboratory method reporting limit of 0.044 μg/m3 to concentrations up to 1190 μg/m3, with hydrocarbon ranges from less than the reporting method limit of 10 μg/m3 to concentrations up to 3000 μg/m3. Some VOCs were identified ubiquitously in indoor air background, and some were identified at concentrations which exceeded risk-based regulatory screening levels. These study results provide useful and updated information on indoor air background and air quality in offices and schools and can be used in future regulatory guidance update considerations, for further examination of relationships between these data and residential study data, in human health risk assessments and risk communication, and in planning future studies. 相似文献
Within the shallow littoral zones of lakes, periphyton is an essential component, representing an important source of primary
production and a food resource for herbivores. Periphytic communities are abundantly inhabited by meiofaunal organisms, which
are mostly dominated by nematodes. During the last 3 decades, consumer–resource interactions between herbivore consumers and
periphytic components (mainly algae) have been intensively studied. Although whole grazer community and single species effects
on periphyton are known from field and laboratory experiments, the importance of single, dominant grazer taxa in direct comparison
to whole community impacts is unknown. To investigate the continuity of grazing effects of a single, dominant macrograzer
(Theodoxus fluviatilis, Gastropoda, Prosobranchia) on epilithic meiofauna and algae with respect to the whole grazer community, a temporally structured
field experiment was carried out in Lake Erken (Sweden). Grazer impacts on periphytic algae and meiofauna were tested by controlling
macrograzer access to littoral periphyton communities for 8 weeks in an exclosure/enclosure experimental design. Overall,
the results showed macrograzer presence to have temporally constant, strongly negative effects on algal biomass as well as
meiofaunal abundance and community composition. Moreover, T. fluviatilis alone accounted for up to 80% of the grazing effects, indicative of their ability to regulate periphytic communities in lakes.
The present study yields new insights into the effects of a single grazer species and stressed temporal patterns of consumer–resource
interactions in freshwater lakes. 相似文献
AbstractEcological flow needs (EFN) frameworks incorporate a range of ecologically-relevant hydrological variables based on prior knowledge of river regime characteristics. However, when applied in cold regions, these approaches have largely ignored the influence of winter ice cover and the spring freshet on hydrological regimes: key components of river systems in cold regions with important direct effects on water quality, aquatic habitat and ecology. Here, we combine a review of the published literature on cold-regions hydrology and hydro-ecology with available hydrometric information for sites across Canada, a major cold-region country, to explore phenomena unique to these systems. We identify several ecologically-relevant hydrological measures (i.e. annual ice on/off dates, ice-cover duration, spring freshet initiation, peak water level during river ice break-up), pairing these with established metrics for incorporation into an enhanced suite of indicators specifically designed for cold regions. This paper presents the Cold-regions Hydrological Indicators of Change (CHIC), which can provide the basis for the assessment of EFN and climate change assessments in cold-region river ecosystems.
Editor Z.W. Kundzewicz; Guest editor M. AcremanCitation Peters, D.L., Monk, W.A., and Baird, D.J., 2014. Cold-regions Hydrological Indicators of Change (CHIC) for ecological flow needs assessment. Hydrological Sciences Journal, 59 (3–4), 502–516. 相似文献
We present an approach to assess and compare risk from climate change among multiple species through a risk matrix, in which managers can quickly prioritize for species that need to have strategies developed, evaluated further, or watched. We base the matrix upon earlier work towards the National Climate Assessment for potential damage to infrastructures from climate change. Risk is defined here as the product of the likelihood of an event occurring and the consequences or impact of that event. In the context of species habitats, the likelihood component is related to the potential changes in suitable habitat modeled at various times during this century. Consequences are related to the adaptability of the species to cope with the changes, especially the increasing intensity and/or frequency of disturbance events that are projected. We derived consequence scores from nine biological and 12 disturbance characteristics that were pulled from literature for each species. All data were generated from an atlas of climate change for 134 trees of the eastern United States (www.nrs.fs.fed.us/atlas). We show examples which depict a wide range of risk for tree species of northern Wisconsin, including species that may gain substantial habitat as well as lose substantial habitat, both of which will require the development of strategies to help the ecosystems adapt to such changes. 相似文献
One requirement for isotope ratio measurement results with small measurement uncertainties is that the element of interest is effectively separated from the sample matrix. Efficient chemical separation of W from matrix components, especially Ti, can be challenging, particularly for large test portion masses (> 1 g). We present a new W separation procedure that takes advantage of the distinct complexation behaviour of Ti and W with citrate ligand in a moderately low pH, oxidising solution. This preparation procedure can reduce the Ti/W ratio of large (4–10 g) basaltic (i.e., high‐matrix) test portions by a factor of 105, relative to their original compositions, in a two‐step separation procedure. The procedure additionally provides a separate, well‐purified Mo fraction. We show that optimal separation requires precise selection of reagent concentrations and sample load. The procedure was employed to determine the μ182W composition of BHVO‐2 as ?6.7 ± 4.2 (2 standard deviation, 2s). The principles derived from this method may prove useful for chemical separation of other elements used for geochemical and cosmochemical applications given an appropriate selection of organic acid. Future successful applications of this method may reveal that the use of organic acids as procedural reagents is a currently under‐utilised tool for efficient chemical separation protocols. 相似文献