Abstract
Sediment transport in estuaries and the formation of estuarine turbidity maxima (ETM) highly depend on the ability of suspended particulate matter (SPM) to flocculate into larger aggregates. ...While most literature focuses on the small-scale impact of biological flocculants on the formation of larger aggregates, the influence of the flocculation process on large-scale estuarine SPM profiles is still largely unknown. In this paper, we study the impact of flocculation of SPM on the formation of ETM. For this, a semianalytical width-integrated model called iFlow is utilized and extended by a flocculation model. Starting from a complex one-class flocculation model, we show that flocculation may be described as a linear relation between settling velocity and suspended sediment concentration to capture its leading-order effect on the ETM formation. The model is applied to a winter case in the Scheldt estuary (Belgium, Netherlands) and calibrated to a unique, long-term, two-dimensional set of turbidity (cf. SPM) observations. First, model results with and without the effect of flocculation are compared, showing that the spatial and temporal variations of the settling velocity due to flocculation are essential to reproduce the observed magnitude of the suspended sediment concentrations and its dependence on river discharge. Second, flocculation results in tidally averaged land-inward sediment transport. Third, we conduct a sensitivity analysis of the freshwater discharge and floc breakup parameter, which shows that flocculation can cause additional estuarine turbidity maxima and can prevent flushing of the ETM for high freshwater inflow.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The aim of this study is to compare spironolactone versus clonidine as the fourth drug in patients with resistant hypertension in a multicenter, randomized trial. Medical therapy adherence was ...checked by pill counting. Patients with resistant hypertension (no office and ambulatory blood pressure BP monitoring control, despite treatment with 3 drugs, including a diuretic, for 12 weeks) were randomized to an additional 12-week treatment with spironolactone (12.5–50 mg QD) or clonidine (0.1–0.3 mg BID). The primary end point was BP control during office (<140/90 mm Hg) and 24-h ambulatory (<130/80 mm Hg) BP monitoring. Secondary end points included BP control from each method and absolute BP reduction. From 1597 patients recruited, 11.7% (187 patients) fulfilled the resistant hypertension criteria. Compared with the spironolactone group (n=95), the clonidine group (n=92) presented similar rates of achieving the primary end point (20.5% versus 20.8%, respectively; relative risk, 1.01 0.55–1.88; P=1.00). Secondary end point analysis showed similar office BP (33.3% versus 29.3%) and ambulatory BP monitoring (44% versus 46.2%) control for spironolactone and clonidine, respectively. However, spironolactone promoted greater decrease in 24-h systolic and diastolic BP and diastolic daytime ambulatory BP than clonidine. Per-protocol analysis (limited to patients with ≥80% adherence to spironolactone/clonidine treatment) showed similar results regarding the primary end point. In conclusion, clonidine was not superior to spironolactone in true resistant hypertensive patients, but the overall BP control was low (≈21%). Considering easier posology and greater decrease in secondary end points, spironolactone is preferable for the fourth-drug therapy.
CLINICAL TRIAL REGISTRATION—URLhttp://www.clinicaltrials.gov. Unique identifierNCT01643434.
This paper focuses on the stabilization problem of Takagi-Sugeno fuzzy systems via a sampled-data controller using a fuzzy dependent functional. By employing a property of convex combination, a new ...approach to deal with the time derivatives of the fuzzy membership functions (FMFs) in the stabilization conditions is proposed, and less conservative conditions are derived in the form of linear matrix inequalities (LMIs). Moreover, the proposed approach introduces a switching function which opens up possibilities to use a switched controller and take advantage of its benefits well known in the literature. Therefore, two sampled-data control strategies are proposed, where the first one is a fuzzy controller and the second is a robust switched controller, that does not require the expressions of the FMFs to implement the control law, which guarantees the robustness of the controlled system in cases where the FMFs depend on uncertain parameters. Finally, the effectiveness of the proposed strategies is verified by two examples.
Many estuaries exhibit seasonality in the estuary‐scale distribution of suspended particulate matter (SPM). This SPM distribution depends on various factors, including freshwater discharge, salinity ...intrusion, erodibility, and the ability of cohesive SPM to flocculate into larger aggregates. Various authors indicate that biotic factors, such as the presence of algae and their excretion of sticky transparent exopolymer particles (TEP), affect the flocculation and erosion processes. Consequently, seasonality in these biotic factors may play a role in the observed seasonality in SPM. Whereas the impact of abiotic factors on seasonality in SPM is well studied, the relative contribution of biotically induced seasonality is largely unknown. In this study, we employ two approaches to assess the aggregated importance of biotically induced seasonality in flocculation and erosion on seasonality in SPM in the Scheldt estuary. In the first approach, we focus on seasonality of in situ observations in the Scheldt estuary of turbidity, floc size, Chlorophyll‐a, and TEP, showing that the abiotic parameters show seasonality, while seasonality in TEP is ambiguous. The second approach concerns a reverse engineering method to calibrate biotically affected parameters of a coupled sediment transport‐flocculation model to turbidity observations, allowing us to compare the modeled SPM concentrations to the observations. Driven by seasonality in freshwater discharge, the model captures the observed seasonality in SPM without requiring biotically induced seasonality in flocculation and erosion, which is supported by the absence of seasonality in TEP.
Plain Language Summary
Estuaries often show regions in which the water is more turbid due to a local elevation of suspended sediment. This local elevation regularly displays seasonality, which is partially driven by seasonality in the erosion properties of the sediment bed and the ability of suspended sediment to flocculate into larger flocs. Two crucial factors impacting the erosion and flocculation processes are the presence of algae and the corresponding excreted sticky substances, which are reported to stabilize the sediment bed but can also glue the suspended sediment particles together. In the present study, we study the aggregated importance of such biotic factors to seasonality in suspended sediment concentrations, applied to the Scheldt estuary. We first focus on seasonality of field observations of suspended sediment concentration, floc size, algal abundance, and the sticky substances excreted by the algae, all showing seasonality except the sticky substances. Next, we use a model that simulates the erosion, flocculation, and accumulation of suspended sediment to quantify a potential seasonality in the impact of biotic factors on flocculation and erosion. Surprisingly, we do not require seasonality in the impact of biotic factors on flocculation and erosion to explain the observed seasonality in sediment dynamics, which is supported by the absence of seasonality in the sticky substances excreted by the algae.
Key Points
New observations over various seasons in the Scheldt estuary show strong seasonality in floc size and Chlorophyll‐a (Chl‐a) but not in transparent exopolymer particles
We develop a robust method to detect the importance of seasonal variation in biota on sediment dynamics using an idealized numerical model
In the Scheldt estuary, seasonal variations in biota are not necessary to explain seasonal variations in sediment dynamics
A prospective analysis evaluating neurologic outcome after early versus late surgery for cervical spinal cord trauma.
The study was conducted to determine whether neurologic and functional outcome is ...improved in traumatic cervical spinal cord-injured patients (C3-T1, American Spinal Injury Association grades A-D) who had early surgery (<72 hours after spinal cord injury) compared with those patients who had late surgery (>5 days after spinal cord injury).
There is considerable controversy as to the appropriate timing of surgical decompression and stabilization for cervical spinal cord trauma. There have been numerous retrospective studies, but no prospective studies, to determine whether neurologic outcome is best after early versus late surgical treatment for cervical spinal cord injury.
Patients meeting appropriate inclusion criteria were randomized to an early (<72 hours after spinal cord injury) or late (>5 days after spinal cord injury) surgical treatment protocol. The neurologic and functional outcomes were recorded from the acute hospital admission to the most recent follow-up.
Comparison of the two groups showed no significant difference in length of acute postoperative intensive care stay, length of inpatient rehabilitation, or improvement in American Spinal Injury Association grade or motor score between early (mean, 1.8 days) versus late (mean, 16.8 days) surgery.
The results of this study reveal no significant neurologic benefit when cervical spinal cord decompression after trauma is performed less than 72 hours after injury (mean, 1.8 days) as opposed to waiting longer than 5 days (mean, 16.8 days).
Aims: Studies of community structure and co-occurrence patterns rely on the premise that community data reflect where species successfully grow and which species they grow with. However, plant ...censuses generally do not distinguish between species with reproductive individuals and those only represented by non-reproductive individuals. We tested whether inclusion of non-reproductive species, which may not reflect success in that location, significantly impacts evaluations of community structure and co-occurrence. Location: Queen's University Biological Station, Ontario, Canada, old-field plant communities. Methods: We quantified the impact of non-reproductive species in two plant communities by comparing community structure and co-occurrence patterns when non-reproductive species were included or excluded. Results: Including non-reproductive species significantly increased plot-level species richness in both communities (54% and 13% increases), altered species evenness in both communities, significantly impacted beta-diversity among plots in one site, and disproportionately impacted assessments of diversity in species-rich plots. Excluding non-reproductive species resulted in reduced negative co-occurrence patterns in both communities, with a substantially larger impact in one community. In that community, the impact of non-reproductive species was even more pronounced when abundance data were used in analysis, and when pair-wise co-occurrence patterns were assessed. Additionally, including non-reproductive species drastically decreased the number of species pairs with perfect negative co-occurrence across sites, indicating that these species can add 'noise' to co-occurrence patterns. We examined possible explanations for the presence of non-reproductive species. In one community, non-reproductive species were 22 times less abundant (per plot) than reproductive species within plots, although they were not rare overall. Differences in the number of nonreproductive species per plot across our focal communities were not clearly driven by differences in clonality, stress from extreme weather or low N. While these patterns are consistent with the interpretation that non-reproductive species are present due to mass effects, this possibility requires further research. Conclusions: Including non-reproductive plant species in censuses can significantly impact assessments of community structure and species co-occurrence. The divergent impact of their inclusion on our two communities highlights the possibility that excluding non-reproductive species from surveys may remove noise from community data and clarify theories of plant species co-existence.
Scanning tunneling microscopy can be utilized to individually probe single‐molecule magnets that have been deposited on gold substrates (see schematic). Dilute solutions (in THF/H2O/NH4OH) of a ...dodecamanganese(III,IV) cluster surrounded by acetyl‐protected thiol groups, Mn12O12(L)16(H2O)4, have been used to prepare Au(111) adsorbates that are a first step towards ultra‐high‐density information storage using single‐molecule magnets.
•The impact of temporal variability in different parameters shows opposing trends.•These trends highly depend on the season and system characteristics.•Temporal fluctuations in light-climate ...significantly limit phytoplankton growth.•Temporal variations in light-climate delay the onset of an algal bloom by two weeks.
Phytoplankton primary production (PP) in turbid estuaries is often limited by light-availability. Two important factors altering light-climate are solar irradiance at the water surface and exponential light-extinction coefficient within the water column. Additionally, the depth of the water body changes the light-climate and corresponding PP by altering the ratio of the euphotic and mixing depth in a well-mixed estuary. These three parameters are highly variable yet are often assumed to be constant by both experimental scientists and modelers because of a lack of data or to reduce complexity. Because assuming constant parameters introduces an error, we utilize an idealized model of depth-integrated primary production to analyze the (individual) impact of temporal variability in these three parameters. We only consider the main tidal and solar constituents in temporal variability of the forcings and apply a second-order moment approximation to analyze the bias introduced to time-averaged PP estimates by neglecting temporal fluctuations. We demonstrate that the sign and magnitude of this bias are system-specific and depend on two non-dimensional parameters that characterize the system. The first is equivalent to the ratio of mixing and photic depth. The second accounts for typical incident irradiance and the photosynthetic parameters of the phytoplankton population present. To demonstrate the applicability of our approach, we apply the model to two cases in the Scheldt estuary (Belgium) in the brackish and freshwater part. In the first application, we study the impact of fluctuations on phytoplankton in dynamic equilibrium, where biomass is assumed to be constant. We show that variability in solar irradiance has the largest impact on time-averaged PP in dynamic equilibrium, resulting in a 30 percent decrease compared to time-invariant forcing. By comparing with a numerical integrator, we show that a second-order moment approximation correctly predicts the order of magnitude of the impact of temporal variability of the individual parameters. In the second application, we study the impact of fluctuations on unbounded exponential phytoplankton growth. Also here, fluctuations in solar irradiance have the largest impact and lead to a significant decrease in exponential growth. In this case study, we show that temporal fluctuations delay the onset of the biomass by two weeks and decrease the biomass by a factor 14 after two weeks compared to time invariant forcing. Additionally, we show that the temporal fluctuations induce low-frequency variability in phytoplankton biomass with similar periodicity as the spring-neap cycle, making it difficult to observe these phenomena in real-world time series.
Estuaries often show regions in which Chlorophyll-a (Chl-a) accumulates. The location and magnitude corresponding to such accumulation result from a complex interplay between processes such as river ...flushing, salinity, nutrients, grazing on phytoplankton, and the light climate in the water column. An example is the multi-annual evolution of the estuary-scale Chl-a distribution in the Scheldt estuary (Belgium/Netherlands) in spring. From 2004–2007, we observed a limited spring bloom in the brackish region (km 60–90 from the mouth, salinity ∼ 1–10 ppt). This bloom intensified in 2008–2014 and disappeared after 2015. This multi-annual evolution of Chl-a has been hypothesized to be linked to simultaneous multi-annual trends in the suspended particulate matter (SPM) distribution in summer and winter between 1995–2015 and the improvement of the water quality (e.g., reduction of ammonium), which affects grazing on phytoplankton by zooplankton. However, this hypothesis has not been systematically investigated. In this contribution, we apply a modeling approach in which observations are the core. We first analyze multi-annual in situ observations covering the full estuary. These observations include the SPM concentration, zooplankton abundance, and other variables affecting the Chl-a concentration. They show a multi-annual estuary-scale evolution not only in the SPM distribution but also in zooplankton abundance, freshwater discharge, and phytoplankon photosynthetic characteristics. Next, we apply a model approach that consists of an extensive sensitivity study and four model scenarios that are supported by these observations to constrain the processes and corresponding parameter variability that may have caused the observed change in Chl-a. Our results suggest that a change in SPM alone cannot explain the Chl-a observations. Instead, a multi-annual change in mortality rate, which we can attribute to both grazing by zooplankton and phytoplankton community (i.e., mortality dependence on salinity), may explain the multi-annual estuary-scale evolution of Chl-a in spring. Different model parameter choices may thus lead to similar model results (equifinality). Our results highlight that insight into the zooplankton dynamics and phytoplankton community characteristics is essential to understand the phytoplankton (cf. Chl-a) dynamics in the Scheldt estuary and that additional data regarding mortality and grazing rates is required to further constrain the model parameters.
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•Data shows a multi-annual disappearance of phytoplankton accumulation in the Scheldt.•A multi-annual change in sediment cannot explain the change in Chlorophyll-a (Chl-a).•Multi-annual changes in mortality rate by a factor ∼ 3 may explain the trend in Chl-a.•The change in mortality rate can be linked to multiple processes.•To further constrain the mortality rate, additional data on grazing rates is required.
A simple, sensitive, and reproducible sensing technique is described for the unambiguous detection of unlabeled single-stranded DNA by surface-enhanced Raman spectroscopy (SERS). By self-assembling ...probe-tethered Ag nanoparticles to a moderately smooth Ag film using the complementary target species, electromagnetic “hot spots” are created which strongly enhance the Raman signal of the species present in the hot spot. These species can include a Raman label (a molecule with a very large Raman cross-section) that dominates the spectrum and generates highly reproducible signals. The self-assembly process does not take place in the absence of the target species. Consequently, a strong SERS signal is observed only in the presence of the target. The SERS signal was also absent in the presence of noncomplementary species. AFM analysis indicates that strong SERS signal intensity arises from only a few surface-bound nanoparticles which generate an enhancement factor ∼105−106 greater than the metal film alone. Notably, this nanoparticle−film DNA detection method does not require any chemical deposition of silver to read out the SERS spectrum from the surface-bound labels.
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