A ‘Boscastle-type’ quasi-stationary convective system over the UK Southwest Peninsula

An investigation is presented of a quasi-stationary convective system (QSCS) which occurred over the UK Southwest Peninsula on 21 July 2010. This system was remarkably similar in its location and structure to one which caused devastating flash flooding in the coastal village of Boscastle, Cornwall on 16 August 2004. However, in the 2010 case rainfall accumulations were around four times smaller and no flooding was recorded. The more extreme nature of the Boscastle case is shown to be related to three factors: (1) higher rain rates, associated with a warmer and moister tropospheric column and deeper convective clouds; (2) a more stationary system, due to slower evolution of the large-scale flow; and (3) distribution of the heaviest precipitation over fewer river catchments. Overall, however, the synoptic setting of the two events was broadly similar, suggesting that such conditions favour the development of QSCSs over the Southwest Peninsula. A numerical simulation of the July 2010 event was performed using a 1.5-km grid length configuration of the Met Office Unified Model. This reveals that convection was repeatedly initiated through lifting of low-level air parcels along a quasi-stationary coastal convergence line. Sensitivity tests are used to show that this convergence line was a sea breeze front which temporarily stalled along the coastline due to the retarding influence of an offshore-directed background wind component. Several deficiencies are noted in the 1.5-km model’s representation of the storm system, including delayed convective initiation; however, significant improvements are observed when the grid length is reduced to 500 m. These result in part from an improved representation of the convergence line, which enhances the associated low-level ascent allowing air parcels to more readily reach their level of free convection. The implications of this finding for forecasting convective precipitation are discussed.

Relationship of dayside auroral precipitations to the open-closed separatrix and the pattern of convective flow

The implications are discussed of acceleration of magnetospheric ions by reflection off two magnetopause Alfvén waves, launched by the reconnection site into the inflow regions on both sides of the boundary. The effects of these waves on the ion populations, predicted using the model described by Lockwood et al. [1996], offer a physical interpretation of all the various widely used classifications of precipitation into the dayside ionosphere, namely, central plasma sheet, dayside boundary plasma sheet (BPS), void, low-latitude boundary layer (LLBL), cusp, mantle, and polar cap. The location of the open-closed boundary and the form of the convection flow pattern are discussed in relation to the regions in which these various precipitations are typically found. Specifically, the model predicts that both the LLBL and the dayside BPS precipitations are on newly opened field lines and places the convection reversal within the LLBL, as is often observed. It is shown that this offers solutions to a number of paradoxes and problems that arise if the LLBL and BPS precipitations are thought of as being on closed field lines. This model is also used to make quantitive predictions of the longitudinal extent and latitudinal width of the cusp, as a function of solar wind density.

Label-free enrichment of avian Leucocytozoon using flow cytometric sorting

The group of haemosporidian parasites is of general interest to basic and applied science, since several species infect mammals, leading to malaria and associated disease symptoms. Although the great majority of haemosporidian parasites appear in bird hosts, as in the case of Leucocytozoon buteonis, there is little genomic information about genetic aspects of their co-evolution with hosts. Consequently, there is a high need for parasite-enrichment strategies enabling further analyses of the genomes, namely without exposure to DNA-intercalating dyes. Here, we used flow cytometry without an additional labelling step to enrich L. buteonis from infected buzzard blood. A specific, defined area of two-dimensional scattergramms was sorted and the fraction was further analysed. The successful enrichment of L. buteonis in the sorted fraction was demonstrated by Giemsa-staining and qPCR revealing a clear increase of parasite-specific genes, while host-specific genes were significantly decreased. This is the first report describing a labelling-free enrichment approach of L. buteonis from infected buzzard blood. The enrichment of parasites presented here is free of nucleic acid-intercalating dyes which may interfere with fluorescence-based methods or subsequent sequencing approaches.

Improving a global model from the boundary layer: total turbulent energy and the neutral limit Prandtl number

Model intercomparisons have identified important deficits in the representation of the stable boundary layer by turbulence parametrizations used in current weather and climate models. However, detrimental impacts of more realistic schemes on the large-scale flow have hindered progress in this area. Here we implement a total turbulent energy scheme into the climate model ECHAM6. The total turbulent energy scheme considers the effects of Earth’s rotation and static stability on the turbulence length scale. In contrast to the previously used turbulence scheme, the TTE scheme also implicitly represents entrainment flux in a dry convective boundary layer. Reducing the previously exaggerated surface drag in stable boundary layers indeed causes an increase in southern hemispheric zonal winds and large-scale pressure gradients beyond observed values. These biases can be largely removed by increasing the parametrized orographic drag. Reducing the neutral limit turbulent Prandtl number warms and moistens low-latitude boundary layers and acts to reduce longstanding radiation biases in the stratocumulus regions, the Southern Ocean and the equatorial cold tongue that are common to many climate models.

Impact of Laptev Sea flaw polynyas on the atmospheric boundary layer and ice production using idealized mesoscale simulations

The interaction between polynyas and the atmospheric boundary layer is examined in the Laptev Sea using the regional, non-hydrostatic Consortium for Small-scale Modelling (COSMO) atmosphere model. A thermodynamic sea-ice model is used to consider the response of sea-ice surface temperature to idealized atmospheric forcing. The idealized regimes represent atmospheric conditions that are typical for the Laptev Sea region. Cold wintertime conditions are investigated with sea-ice–ocean temperature differences of up to 40 K. The Laptev Sea flaw polynyas strongly modify the atmospheric boundary layer. Convectively mixed layers reach heights of up to 1200 m above the polynyas with temperature anomalies of more than 5 K. Horizontal transport of heat expands to areas more than 500 km downstream of the polynyas. Strong wind regimes lead to a more shallow mixed layer with strong near-surface modifications, while weaker wind regimes show a deeper, well-mixed convective boundary layer. Shallow mesoscale circulations occur in the vicinity of ice-free and thin-ice covered polynyas. They are forced by large turbulent and radiative heat fluxes from the surface of up to 789 W m−2, strong low-level thermally induced convergence and cold air flow from the orographic structure of the Taimyr Peninsula in the western Laptev Sea region. Based on the surface energy balance we derive potential sea-ice production rates between 8 and 25 cm d−1. These production rates are mainly determined by whether the polynyas are ice-free or covered by thin ice and by the wind strength.

Evaluation of a bounded high order upwind scheme for 3D incompressible free surface flow computations

fit the context of normalized variable formulation (NVF) of Leonard and total variation diminishing (TVD) constraints of Harten. this paper presents an extension of it previous work by the authors for solving unsteady incompressible flow problems. The main contributions of the paper are threefold. First, it presents the results of the development and implementation of a bounded high order upwind adaptative QUICKEST scheme in the 3D robust code (Freeflow), for the numerical solution of the full incompressible Navier-Stokes equations. Second, it reports numerical simulation results for 1D hock tube problem, 2D impinging jet and 2D/3D broken clam flows. Furthermore, these results are compared with existing analytical and experimental data. And third, it presents the application of the numerical method for solving 3D free surface flow problems. (C) 2007 IMACS. Published by Elsevier B.V. All rights reserved,

Under flow impedimetric measurements using magnetic particles for label-free detection affinity target

The necessity to adapt sensors based on electrochemical techniques for high throughput analysis control increases the interest to develop new analytical systems able to perform measurements under buffer now. In this report we explored the possibility of employing a new system to make impedimetric measurements to detect the interaction between proteins and small molecules. The well-known biotin-streptavidin interaction was adopted to evaluate the proposed assembly. This system allows us to perform experiments under flow. Magnetic beads functionalized with streptavidin were used and first characterized using AFM and FTIR. Non-faradic impedance spectroscopy allowed the detection of the biotin-streptavidin interaction. Using our new system and under a flow of PBS buffer, 5 10-5 M of biotin was detected with a stable signal. (c) 2007 Elsevier B.V. All rights reserved.

Evaluation of a bounded high order upwind scheme for 3D incompressible free surface flow computations

fit the context of normalized variable formulation (NVF) of Leonard and total variation diminishing (TVD) constraints of Harten. this paper presents an extension of it previous work by the authors for solving unsteady incompressible flow problems. The main contributions of the paper are threefold. First, it presents the results of the development and implementation of a bounded high order upwind adaptative QUICKEST scheme in the 3D robust code (Freeflow), for the numerical solution of the full incompressible Navier-Stokes equations. Second, it reports numerical simulation results for 1D hock tube problem, 2D impinging jet and 2D/3D broken clam flows. Furthermore, these results are compared with existing analytical and experimental data. and third, it presents the application of the numerical method for solving 3D free surface flow problems. (C) 2007 IMACS. Published by Elsevier B.V. All rights reserved,

Flow injection analysis of free glycerol in biodiesel using a copper electrode as an amperometric detector

The main goal of this work was to develop a simple analytical method for quantification of glycerol based on the electrocatalytic oxidation of glycerol on the copper surface adapted in a flow injection system. Under optimal experimental conditions, the peak current response increases linearly with glycerol concentration over the range 60-3200 mg kg(-1) (equivalent to 3-160 mg L(-1) in solution). The repeatability of the electrode response in the flow injection analysis (FIA) configuration was evaluated as 5% (n = 10), and the detection limit of the method was estimated to be 5 mg kg(-1) in biodiesel (equivalent to 250 mu g L(-1) in solution) (S/N = 3). The sample throughput under optimised conditions was estimated to be 90 h(-1). Different types of biodiesel samples (B100), as in the types of vegetable oils or animal fats used to produce the fuels, were analysed (seven samples). The only sample pre-treatment used was an extraction of glycerol from the biodiesel sample containing a ratio of 5 mL of water to 250 mg of biodiesel. The proposed method improves the analytical parameters obtained by other electroanalytical methods for quantification of glycerol in biodiesel samples, and its accuracy was evaluated using a spike-and-recovery assay, where all the biodiesel samples used obtained admissible values according to the Association of Official Analytical Chemists. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.

Metabolic and thermodynamic responses to dehydration-induced reductions in muscle blood flow in exercising humans

[EN] 1. The present study examined whether reductions in muscle blood flow with exercise-induced dehydration would reduce substrate delivery and metabolite and heat removal to and from active skeletal muscles during prolonged exercise in the heat. A second aim was to examine the effects of dehydration on fuel utilisation across the exercising leg and identify factors related to fatigue. 2. Seven cyclists performed two cycle ergometer exercise trials in the heat (35 C; 61 +/- 2 % of maximal oxygen consumption rate, VO2,max), separated by 1 week. During the first trial (dehydration, DE), they cycled until volitional exhaustion (135 +/- 4 min, mean +/- s.e.m.), while developing progressive DE and hyperthermia (3.9 +/- 0.3 % body weight loss and 39.7 +/- 0.2 C oesophageal temperature, Toes). On the second trial (control), they cycled for the same period of time maintaining euhydration by ingesting fluids and stabilising Toes at 38.2 +/- 0.1 degrees C. 3. After 20 min of exercise in both trials, leg blood flow (LBF) and leg exchange of lactate, glucose, free fatty acids (FFA) and glycerol were similar. During the 20 to 135 +/- 4 min period of exercise, LBF declined significantly in DE but tended to increase in control. Therefore, after 120 and 135 +/- 4 min of DE, LBF was 0.6 +/- 0.2 and 1.0 +/- 0.3 l min-1 lower (P < 0.05), respectively, compared with control. 4. The lower LBF after 2 h in DE did not alter glucose or FFA delivery compared with control. However, DE resulted in lower (P < 0.05) net FFA uptake and higher (P < 0.05) muscle glycogen utilisation (45 %), muscle lactate accumulation (4.6-fold) and net lactate release (52 %), without altering net glycerol release or net glucose uptake. 5. In both trials, the mean convective heat transfer from the exercising legs to the body core ranged from 6.3 +/- 1.7 to 7.2 +/- 1.3 kJ min-1, thereby accounting for 35-40 % of the estimated rate of heat production ( approximately 18 kJ min-1). 6. At exhaustion in DE, blood lactate values were low whereas blood glucose and muscle glycogen levels were still high. Exhaustion coincided with high body temperature ( approximately 40 C). 7. In conclusion, the present results demonstrate that reductions in exercising muscle blood flow with dehydration do not impair either the delivery of glucose and FFA or the removal of lactate during moderately intense prolonged exercise in the heat. However, dehydration during exercise in the heat elevates carbohydrate oxidation and lactate production. A major finding is that more than one-half of the metabolic heat liberated in the contracting leg muscles is dissipated directly to the surrounding environment. The present results indicate that hyperthermia, rather than altered metabolism, is the main factor underlying the early fatigue with dehydration during prolonged exercise in the heat.

Statistical analysis of a viscoelastic turbulent channel flow

Statiscal analysis related to a viscoelastic turbulent channel flow characterized as dilute polymer solution.

Testing of subgrid scale (SGS) models for large-eddy simulation (LES) of turbulent channel flow

Sub-grid scale (SGS) models are required in order to model the influence of the unresolved small scales on the resolved scales in large-eddy simulations (LES), the flow at the smallest scales of turbulence. In the following work two SGS models are presented and deeply analyzed in terms of accuracy through several LESs with different spatial resolutions, i.e. grid spacings. The first part of this thesis focuses on the basic theory of turbulence, the governing equations of fluid dynamics and their adaptation to LES. Furthermore, two important SGS models are presented: one is the Dynamic eddy-viscosity model (DEVM), developed by \cite{germano1991dynamic}, while the other is the Explicit Algebraic SGS model (EASSM), by \cite{marstorp2009explicit}. In addition, some details about the implementation of the EASSM in a Pseudo-Spectral Navier-Stokes code \cite{chevalier2007simson} are presented. The performance of the two aforementioned models will be investigated in the following chapters, by means of LES of a channel flow, with friction Reynolds numbers $Re_\tau=590$ up to $Re_\tau=5200$, with relatively coarse resolutions. Data from each simulation will be compared to baseline DNS data. Results have shown that, in contrast to the DEVM, the EASSM has promising potentials for flow predictions at high friction Reynolds numbers: the higher the friction Reynolds number is the better the EASSM will behave and the worse the performances of the DEVM will be. The better performance of the EASSM is contributed to the ability to capture flow anisotropy at the small scales through a correct formulation for the SGS stresses. Moreover, a considerable reduction in the required computational resources can be achieved using the EASSM compared to DEVM. Therefore, the EASSM combines accuracy and computational efficiency, implying that it has a clear potential for industrial CFD usage.