This paper summarizes current practices for the estimation of flow resistance caused by floodplain vegetation in emergent flow conditions. The current state-of-the-art for the parameterization of ...vegetative form drag and associated flow resistance was explored with a view on practical applicability. Specifically, the dissimilar resistance behaviour of simply shaped rigid elements and foliated natural vegetation was emphasized by compiling and reanalysing data published by the authors' research teams as well as others. It was shown that describing the key hydraulic properties of plants, geometry, and flexibility, with species-specific parameters is superior to the rigid cylinder analogy commonly used in hydraulic engineering practice. The discussion on the limitations of many existing approaches for the determination of vegetative flow resistance is intended to advance the use of modern practices such as the parameterization of vegetation density with the leaf area index, a parameter that can be derived using remote sensing techniques.
Both the foliage and stem essentially influence the flow resistance of woody plants, but their different biomechanical properties complicate the parameterization of foliated vegetation for modeling. ...This paper investigates whether modeling of flow resistance caused by natural woody vegetation can be improved using explicit description of both the foliage and stem. For this purpose, we directly measured the drag forces of Alnus glutinosa, Betula pendula, Salix viminalis, and Salix x rubens twigs in a laboratory flume at four foliation levels, parameterized with the leaf‐area‐to‐stem‐area ratio AL/AS. The species differed in the foliage drag but had approximately equal stem drag. For the foliated twigs, increasing AL/AS was found to increase the reconfiguration and the share of the foliage drag to the total drag. The experiments provided new insight into the factors governing the flow resistance of natural woody vegetation and allowed us to develop a model for estimating the vegetative friction factor using the linear superposition of the foliage and stem drag. The model is novel in that the foliage and stem are separately described with physically based parameters: drag coefficients, reconfiguration parameters, and leaf area and frontal‐projected stem area per ground area. The model could satisfactorily predict the flow resistance of twig to sapling‐sized specimens of the investigated species at velocities of 0.05–1 m/s. As a further benefit, the model allows exploring the variability in drag and reconfiguration associated with differing abundance of the foliage in relation to the stem.
Key Points
Leaf‐area‐to‐stem‐area ratio‐controlled flow resistance of foliated vegetation
Separate parameterization of foliage and stem improved description of drag
New flow resistance model based on the superposition principle was proposed
•New insights into the flow resistance of foliated vegetation were obtained.•We measured drag and alternative reference areas for natural poplars in a flume.•Partly and just submerged plants had ...similar drag and frontal area per reference area.•Drag and reconfiguration were controlled by the foliage–stem reference area ratio.•The alternative reference areas satisfactorily predicted the drag and flow resistance.
Reliable estimation of vegetative flow resistance calls for physically sound and readily measurable plant properties. Laboratory flume investigations were conducted to examine four reference area properties in relation to the drag, reconfiguration, and flow resistance of foliated Black Poplar twigs. The experiments were novel in that three characteristic reference areas (leaf area AL, frontal projected area under flow AP, and still-air frontal projected area A0) as well as the foliage–stem reference area ratio (AL/AS) were evaluated. The drag forces were simultaneously measured for up to eight specimens in a plant stand at both partly and just submerged conditions. Due to the high AL/AS of the twigs, leaves contributed 74–98% of the total drag at mean velocities of 0.1–0.9m/s. Both the partly and just submerged poplars had similar AP and drag per characteristic reference area. Thus, the derived parameter values could be used to estimate the friction factors of the poplar stands at low to just submerged conditions, with each of the three characteristic reference areas providing satisfactory estimates. The flow resistance estimation with AL may be further improved by using AL/AS as a secondary area parameter to take into account the share of the stem to the total drag. Comparison to literature data on other deciduous species suggested that the foliage–stem reference area ratio was an essential property for explaining the between-species variation in AP and flow resistance per AL.
Flume studies were carried out to investigate flow structure above flexible vegetation. A new data set of mean velocity profiles and turbulence characteristics is reported from experiments with ...wheat. The flow above the wheat reasonably followed the log law. Maximum values of the turbulence intensity
u
rms and Reynolds stress
−
u
′
w
′
¯
were found approximately at the level of the maximum observed deflected plant height. A recent approach for describing vertical velocity profiles above aquatic vegetation Stephan, U., 2002. Zum Fließwiderstandsverhalten flexibler Vegetation. Wiener Mitteilungen 180. Doctoral Thesis. Institute of Hydraulics, Hydrology and Water Resources Management, Faculty of Civil Engineering, Technical University of Vienna. was evaluated with these new data, which represent a different vegetal roughness type. The approach proved to be successful beyond the original scope. However, a new definition for the shear velocity based on the deflected plant height is suggested. The benefit of this modification is that complex turbulence measurements can be avoided, which enhances the practical applicability of the approach.
This paper investigates the structural properties of four common riparian tree species and their reconfiguration under hydrodynamic loading in a towing tank in foliated and defoliated conditions. 3D ...tree models were generated by digitizing twenty 0.8–3.3m tall specimens at branch level. Branch diameters and lengths were measured in order to calculate the one-sided stem area and stem volume over the plant height. The novelty of the investigations originated from the characterization of the reconfiguration which was achieved by combining the contracted width, the deflected height, and the underwater projected area in order to determine the porosity at different velocities. The results showed that the basal diameter could be used to predict the entire total one-sided stem area, although this method was not capable of reproducing the observed non-linear vertical distributions. The flow-induced width contraction contributed significantly to the reduction of the rectangular cross-sectional area occupied by the plant. The porosity of the foliated trees increased at the lower velocities, and then decreased at the higher velocities. Overall, detailed spatial–structural analyses of woody vegetation provided valuable information about plant behaviour under load, and thus are helpful for improving the determination of the physically based parameters of complex vegetative elements which is highly relevant for environmental modelling in order to fill the gap of knowledge concerning the hydrodynamic and aerodynamic flow around trees.
Detailed modeling of floodplain flows and associated processes requires data on mixed, heterogeneous vegetation at river reach scale, though the collection of vegetation data is typically limited in ...resolution or lack spatial information. This study investigates physically-based characterization of mixed floodplain vegetation by means of terrestrial laser scanning (TLS). The work aimed at developing an approach for deriving the characteristic reference areas of herbaceous and foliated woody vegetation, and estimating the vertical distribution of woody vegetation. Detailed experimental data on vegetation properties were gathered both in a floodplain site for herbaceous vegetation, and under laboratory conditions for 2-3 m tall trees. The total plant area (Atot) of woody vegetation correlated linearly with the TLS-based voxel count, whereas the Atot of herbaceous vegetation showed a linear correlation with TLS-based vegetation mean height. For woody vegetation, 1 cm voxel size was found suitable for estimating both the Atot and its vertical distribution. A new concept was proposed for deriving Atot for larger areas from the point cloud attributes of small sub-areas. The results indicated that the relationships between the TLS attributes and Atot of the sub-areas can be derived either by mm resolution TLS or by manual vegetation sampling.
Abstract Background Although there is a relationship between the extent of striatal dopaminergic defect and the severity of motor symptoms in Parkinson's disease (PD), studies investigating ...associations between dopamine and mortality in PD have been scarce. If a relationship were established, dopamine restoring neuroprotective treatments could be used to decrease mortality. The objective of this study was to determine whether the initial degree of hypodopaminergic defect, as measured by 6-18 Ffluoro-L-DOPA positron emission tomography (FDOPA-PET), can predict patient survival. Methods The study population included a cohort of 88 recently diagnosed and untreated patients with PD who were clinically examined and scanned with FDOPA-PET between the years 1998 and 2000. The date of exit for the survival analysis was in April 2013 with a follow-up interval of 13–15 years. The survival model included FDOPA uptake, age, sex and symptom severity as explaining factors. Death certificates of the patients were obtained, and causes of death were analyzed. Results Mortality rate was 56.8%. Although higher age ( p < 0.001) and greater motor symptom severity ( p < 0.05) were associated with increased mortality, there was no association between survival and FDOPA uptake in any striatal subregion ( p > 0.48). Conclusion Unlike age and early motor symptom severity, dopamine synthesis capacity, as measured with PET, does not predict survival in PD.
Cross-flooding ducts are used to equalize asymmetric flooding and, thus, to decrease the heel angle of a ship in an emergency. The present design guidelines for cross-flooding arrangements involve ...uncertainties associated with the effect of variable structural factors. In this study, scale model experiments were carried out to determine discharge coefficients of a typical cross-duct, with a focus on the effect of structural components such as the girders, stiffeners, and web frame. Flow conditions and configuration of the components were varied in the experiments. The structural stiffeners in the cross-duct were found to notably increase the discharge coefficient whereas the effects of the web frame and the inclination of the duct at an angle of 7° were negligible. The experimentally obtained discharge coefficient values for the cross-duct were considerably lower than the corresponding values computed according to the generally used guidelines of the IMO Resolution MSC.245(83). This indicates that the geometrical properties of the girders in the cross-ducts need to be properly addressed to avoid overestimating the discharge coefficients. Overall, the experimental results formed an indispensable dataset for the validation and further development of CFD approaches.
In the postnatal rodent hippocampus status epilepticus (SE) leads to age- and region-specific excitotoxic neuronal damage, the precise mechanisms of which are still incompletely known. Recent studies ...suggest that the activation of inflammatory responses together with glial cell reactivity highly contribute to excitotoxic neuronal damage. However, pharmacological tools to attenuate their activation in the postnatal brain are still poorly elucidated. In this study, we investigated the role of inflammatory mediators in kainic acid (KA)-induced neuronal damage in organotypic hippocampal slice cultures (OHCs). A specific cyclooxygenase-2 (COX-2) inhibitor N-2-(cyclohexyloxy)-4-nitrophenyl-methanesulfonamide (NS-398) was used to study whether or not it could ameliorate neuronal death. Our results show that KA treatment (24 h) resulted in a dose-dependent degeneration of CA3a/b pyramidal neurons. Furthermore, COX-2 immunoreactivity was pronouncedly enhanced particularly in CA3c pyramidal neurons, microglial and astrocyte morphology changed from a resting to active appearance, the expression of the microglial specific protein, Iba1, increased, and prostaglandin E
2 (PGE
2) production increased. These indicated the activation of inflammatory processes. However, the expression of neither proinflammatory cytokines, i.e. tumour necrosis factor-alpha (TNF-α) and interleukin-1 beta (IL-1β), nor the anti-inflammatory cytokine IL-10 mRNA was significantly altered by KA treatment as studied by real-time PCR. Despite activation of an array of inflammatory processes, neuronal damage could not be rescued either with the combined pre- and co-treatment with a specific COX-2 inhibitor, NS-398. Our results suggest that KA induces activation of a repertoire of inflammatory processes in immature OHCs, and that the timing of anti-inflammatory treatment to achieve neuroprotection is a challenge due to developmental properties and the complexity of inflammatory processes activated by noxious stimuli.
This article is part of a Special Issue entitled ‘Trends in Neuropharmacology: In Memory of Erminio Costa’.
Summary
Purpose: Epileptic seizures lead to age‐dependent neuronal damage in the developing brain, particularly in the hippocampus, but the mechanisms involved have remained poorly elucidated. In ...this study, we investigated the contribution of apoptosis and inflammatory processes to neuronal damage after status epilepticus (SE) in postnatal rats.
Methods: SE was induced by an intraperitoneal injection of kainic acid (KA) in 21‐ and 9‐day‐old (P21 and P9) rats. The expression of Bax, Bcl‐2 and caspase‐3, markers for apoptosis, and cyclooxygenase‐2 (COX‐2), an indicator for activation of inflammatory processes, were studied from 6 h up to 1 week after SE by Western blotting and immunocytochemistry. Neuronal damage was verified by Fluoro‐Jade B staining.
Results: In P21 rats, SE resulted in neuronal damage in the CA1 neurons of the hippocampus. COX‐2 expression was extensively, but transiently, increased and its immunoreactivity pronouncedly enhanced in several hippocampal subregions, amygdala, and piriform cortex by 24 h after SE. The expression of Bax and caspase‐3 remained unchanged, whereas the antiapoptotic factor Bcl‐2 transiently decreased by 24 h. Single caspase‐3 positive neurons appeared in the CA1 region of both control and KA‐treated rats. In P9 rats, no neuronal death was detected, and COX‐2 expression and immunoreactivity remained at the control level.
Discussion: Our results suggest that SE provokes age‐specific effects on COX‐2 expression. This together with the activation of putative inflammatory processes may contribute to neuronal cell death in the hippocampus of postnatal rats, whereas caspase‐dependent apoptosis seems not to be involved in the death process.
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