Influence of saltmarsh vegetation canopies on hydrodynamics in the intertidal zone

Recent estimates of global sea level rise indicate mean values around 3.1 mm yr"1. As a result, many coastlines face an increasing risk of coastal erosion, and the threat of flooding is becoming a major concern. Unfortunately, coastal defences can be very costly with recent estimates as high as £5000 per metre length of seawall in the UK. There is a need to consider more economically feasible options, and by accounting for the ability of saltmarshes to absorb wave energy, reduce flow velocities and stabilise sediments, the costs of coastal defence structures may be significantly reduced. But first, an improved understanding of the implications of saltmarsh vegetation on hydrodynamics is fundamental to their inclusion in the design of coastal protection schemes. This includes the influence of saltmarsh vegetation on velocity and turbulence structures and the drag forces that arise due to the obstruction to the flow created by the vegetation. Two contrasting areas of coastal saltmarsh were selected for the location of a field survey to identify typical field conditions, such as bed gradients, submergence levels, vegetation types and densities. The two sites differ in that the first was non- grazed, while the second was heavily grazed to assess the impact of sheep farming on vegetation characteristics. The vegetation species, stem densities and submergence levels observed during the field survey were used as a guideline for designing a series of laboratory experiments to investigate the impact of saltmarsh vegetation on hydrodynamics. Uniform cylinder models are widely used to simulate vegetation canopies in hydrodynamic studies, yet the cylinder model can lead to an oversimplification of vegetation morphology. A comparison was made by conducting experiments under uniform flow conditions where uniform cylinder arrays and vegetation canopies were installed onto a flume bed at stem densities of 800, 1160 and 1850 stems m*2. There were differences in velocity and turbulence structures through the two types of canopy. For the same stem density, the proportion of the total flow passing through the canopy region was approximately 10% greater for the uniform cylinder arrays. The foliage found in the upper part of vegetation canopies resulted in a considerably higher level of obstruction and contributed towards reducing velocities and Reynolds stresses within the canopy. Reynolds stress penetration depths were up to 15 times greater for the uniform cylinder arrays compared to the vegetation canopies. Computational fluid dynamics models can be a useful tool for predicting the impact of saltmarsh vegetation on hydrodynamics for coastal management. Applying such models to vegetated flows requires knowledge of the drag coefficient to determine the drag term in the Navier-Stokes equations. However, in the absence of measured data, such models are often applied with the assumption that the drag coefficient is constant in value, and commonly used values include '1.0' and '1.2'. Such assumptions may be easily linked to the uniform cylinder model. However, drag coefficients calculated for Common Cordgrass ranged between 0.4 and 1.7. Values were dependent on numerous parameters, including the Reynolds number, the submergence level, the stem density and the maturity of the vegetation. Instead of the traditional drag-force approach for determining canopy hydrodynamics, a method for predicting velocity and turbulence structures based on the projected area of the vegetation was proposed. For the emergent canopy, the mean velocity was estimated by relating to a reference canopy of known projected area and mean velocity. For the submerged canopy, the surface flow layer velocity was determined effectively using the Manning's roughness approach and the depth- averaged canopy velocity was a function of the surface layer velocity and the canopy density. Velocity profile shapes for both canopies were obtained by linking the mean canopy velocity to the projected area profile. Reynolds stresses for the emergent canopy and lower part of the submerged canopy were negligible and a function of depth-averaged canopy velocity. For the upper part of a submerged canopy, Reynolds stresses were a function of the depth-averaged surface layer and canopy velocities. The proportion of the submerged canopy region experiencing higher Reynolds stresses is also a function of the vegetation density.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Influence of saltmarsh vegetation canopies on hydrodynamics in the intertidal zone

Recent estimates of global sea level rise indicate mean values around 3.1 mm yr"1. As a result, many coastlines face an increasing risk of coastal erosion, and the threat of flooding is becoming a major concern. Unfortunately, coastal defences can be very costly with recent estimates as high as £5000 per metre length of seawall in the UK. There is a need to consider more economically feasible options, and by accounting for the ability of saltmarshes to absorb wave energy, reduce flow velocities and stabilise sediments, the costs of coastal defence structures may be significantly reduced. But first, an improved understanding of the implications of saltmarsh vegetation on hydrodynamics is fundamental to their inclusion in the design of coastal protection schemes. This includes the influence of saltmarsh vegetation on velocity and turbulence structures and the drag forces that arise due to the obstruction to the flow created by the vegetation. Two contrasting areas of coastal saltmarsh were selected for the location of a field survey to identify typical field conditions, such as bed gradients, submergence levels, vegetation types and densities. The two sites differ in that the first was non- grazed, while the second was heavily grazed to assess the impact of sheep farming on vegetation characteristics. The vegetation species, stem densities and submergence levels observed during the field survey were used as a guideline for designing a series of laboratory experiments to investigate the impact of saltmarsh vegetation on hydrodynamics. Uniform cylinder models are widely used to simulate vegetation canopies in hydrodynamic studies, yet the cylinder model can lead to an oversimplification of vegetation morphology. A comparison was made by conducting experiments under uniform flow conditions where uniform cylinder arrays and vegetation canopies were installed onto a flume bed at stem densities of 800, 1160 and 1850 stems m*2. There were differences in velocity and turbulence structures through the two types of canopy. For the same stem density, the proportion of the total flow passing through the canopy region was approximately 10% greater for the uniform cylinder arrays. The foliage found in the upper part of vegetation canopies resulted in a considerably higher level of obstruction and contributed towards reducing velocities and Reynolds stresses within the canopy. Reynolds stress penetration depths were up to 15 times greater for the uniform cylinder arrays compared to the vegetation canopies. Computational fluid dynamics models can be a useful tool for predicting the impact of saltmarsh vegetation on hydrodynamics for coastal management. Applying such models to vegetated flows requires knowledge of the drag coefficient to determine the drag term in the Navier-Stokes equations. However, in the absence of measured data, such models are often applied with the assumption that the drag coefficient is constant in value, and commonly used values include '1.0' and '1.2'. Such assumptions may be easily linked to the uniform cylinder model. However, drag coefficients calculated for Common Cordgrass ranged between 0.4 and 1.7. Values were dependent on numerous parameters, including the Reynolds number, the submergence level, the stem density and the maturity of the vegetation. Instead of the traditional drag-force approach for determining canopy hydrodynamics, a method for predicting velocity and turbulence structures based on the projected area of the vegetation was proposed. For the emergent canopy, the mean velocity was estimated by relating to a reference canopy of known projected area and mean velocity. For the submerged canopy, the surface flow layer velocity was determined effectively using the Manning's roughness approach and the depth- averaged canopy velocity was a function of the surface layer velocity and the canopy density. Velocity profile shapes for both canopies were obtained by linking the mean canopy velocity to the projected area profile. Reynolds stresses for the emergent canopy and lower part of the submerged canopy were negligible and a function of depth-averaged canopy velocity. For the upper part of a submerged canopy, Reynolds stresses were a function of the depth-averaged surface layer and canopy velocities. The proportion of the submerged canopy region experiencing higher Reynolds stresses is also a function of the vegetation density

Risk Prediction for Clonal Cytopenia: Multicenter Real-World Evidence.

Clonal cytopenia of undetermined significance (CCUS) represents a distinct disease entity characterized by myeloid-related somatic mutations with a variant allele fraction of ≥2% in individuals with unexplained cytopenia(s) but without a myeloid neoplasm (MN). Notably, CCUS carries a risk of progressing to MN, particularly in cases featuring high-risk mutations. Understanding CCUS requires dedicated studies to elucidate its risk factors and natural history. Our analysis of 357 CCUS patients investigated the interplay between clonality, cytopenia, and prognosis. Multivariate analysis identified 3 key adverse prognostic factors: the presence of splicing mutation(s) (score = 2 points), platelet count <100×109/L (score = 2.5), and ≥2 mutations (score = 3). Variable scores were based on the coefficients from the Cox proportional hazards model. This led to the development of the Clonal Cytopenia Risk Score (CCRS), which stratified patients into low- (score <2.5 points), intermediate- (score 2.5-<5), and high-risk (score ≥5) groups. The CCRS effectively predicted 2-year cumulative incidence of MN for low- (6.4%), intermediate- (14.1%), and high- (37.2%) risk groups, respectively, by Gray's test (P <.0001). We further validated the CCRS by applying it to an independent CCUS cohort of 104 patients, demonstrating a c-index of 0.64 (P =.005) in stratifying the cumulative incidence of MN. Our study underscores the importance of integrating clinical and molecular data to assess the risk of CCUS progression, making the CCRS a valuable tool that is practical and easily calculable. These findings are clinically relevant, shaping the management strategies for CCUS and informing future clinical trial designs

oropharyngeal infection in a neutropenic patient: unusual presentation

Introduction: Saprochete capitata is unusual etiologic agent in immunocompromised patients, particularly in those with hematologic malignancy and severe neutropenia. Most often, infections of the oral cavity are manifested clinically as oral candidiasis. Invasive forms are rarely described. Observation: a 63-year-old man consulted for pseudomembranous lesions associated with ulcero perforating lesion of the tongue and palatal region ulcerations. All evolving in a context of profound physical deterioration and severe neutropenia. Mycological examination showed Saprochaete capitata. The evolution was favorable with oral voriconazole. Comment: Saprochaete capitata invasive fungal infections have become an important cause of morbidity and mortality, particularly in hematology-oncology patients. Invasive or non-invasive, oropharyngeal involvement with this pathogen should not be underestimated in the neutropenic patient. They are the main starting point for fongemia of this pathogen, which is often fatal. Conclusion: Saprochete capitata is now recognized emerging etiologic agent in patients with hematological malignancy and severe neutropenia. Early detection and diagnosis of these fungal infections could lead to reduced morbidity and mortality, particularly in locally invasive infection

Inter-comparison and validation of computational fluid dynamics codes in two-stage meandering channel flows

This paper presents a study in the inter-comparison and validation of three-dimensional computational fluid dynamics codes which are currently used in river engineering. Finite volume codes PHOENICS, FLUENT and SSIIM; and finite element code TELEMAC3D are considered in this study. The work has been carried out by competent hydraulic modellers who are users of the codes and not involved in their development. This paper is therefore written from the perspective of independent practitioners of the techniques. In all codes, the flow calculations are performed by solving the three-dimensional continuity and Reynolds-averaged Navier–Stokes equations with the k–ε turbulence model. The application of each code was carried out independently and this led to slightly different, but nonetheless valid, models. This is particularly seen in the different boundary conditions which have been applied and which arise in part from differences in the modelling approaches and methodology adopted by the different research groups and in part from the different assumptions and formulations implemented in the different codes. Similar finite volume meshes are used in the simulations with PHOENICS, FLUENT and SSIIM while in TELEMAC3D, a triangular finite element mesh is used. The ASME Journal of Fluids Engineering editorial policy is taken as a minimum framework for the control of numerical accuracy. In all cases, grid convergence is demonstrated and conventional criteria, such as Y+, are satisfied. A rigorous inter-comparison of the codes is performed using large-scale experimental data from the UK Flood Channel Facility for a two-stage meandering channel. This example data set shows complex hydraulic behaviour without the additional complications found in natural rivers. Standardised methods are used to compare each model with the available experimental data. Results are shown for the streamwise and transverse velocities, secondary flow, turbulent kinetic energy, bed shear stress and free surface elevation. They demonstrate that the models produce similar results overall, although there are some differences in the predicted flow field and greater differences in turbulent kinetic energy and bed shear stress. This study is seen as an essential first step in the inter-comparison of some of the computational fluid dynamics codes used in the field of river engineering