Discovery of Infection Associated Metabolic Markers in Human African Trypanosomiasis

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Quantification of fungal growth: models, experiment, and observations

This thesis is concerned with the growth of microscopic mycelial fungi (Section I), and that of macroscopic fungi, which form specialised hyphal structures such as rhizomorphs (Section II). A growth model is developed in Section I in relation to soil organic matter decomposition, dealing with detailed dynamics of carbon and nitrogen. Substrate with a certain carbon:nitrogen ratio is supplied at a constant rate, broken down and then taken up by fungal mycelium. The nutrients are first stored internally in metabolic pools and then incorporated into structural fungal biomass. Analysis of the overall-steady states of the variables (implicitly from a cubic equation) showed that the conditions for existence had a clear biological interpretation. The 'energy' (in terms of carbon) invested in breakdown of substrate should be less than the 'energy' resulting from breakdown of substrate, leading to a positive carbon balance. For growth the 'energy' necessary for production of structural fungal biomass and for maintenance should be less than this positive carbon balance in the situation where all substrate is colonised. Under the assumption that nutrient dynamics are much faster than the dynamics of fungal biomass and substrate, a quasi-steady analysis was performed. From the resulting simplified model an explicit fungal invasion criterion was derived, which was not possible in the analysis of the original fungal growth model. The fungal invasion criterion takes two forms: one for systems where carbon is limiting, another for systems where nitrogen is limiting. For cases where only carbon is limiting, nitrogen dynamics were excluded from the model, and this further simplification resulted in a model that was fitted to data on growth of the soil-borne plant pathogen Rhizoctonia solani . Fungal growth and colonisation of discrete nutrient sites in Petri plates were assessed microscopically for two carbon concentrations of the substrate. Colonisation was faster at the higher carbon concentration. The model predicted a lower asymptote for non-colonised substrate and this value was estimated from the data by non-linear regression for each carbon concentration. A key composite parameter, the positive carbon balance per carbon unit of colonised substrate, was lower for the higher carbon concentration. The carbon decomposition rate was estimated by least squares minimisation, after correction for a lag phase expected after robust handling of the inoculated fungus. The delay in subsequent fungal growth after inoculation was extended when there was less carbon available for physical recovery and physiological adaptation to the new environment. The simplified mean-field model with parameters estimated as described above produced a good fit to the data.In Section II quantitative studies on the epidemiology of Armillaria root rot are reviewed. This fungus is a serious disease in many forests and horticultural tree crops world-wide, and consequently there is much interest in options for avoiding or restricting the spread of disease through growth of the specialised rhizomorphs in soil. Two rhizomorph networks of A. lutea growing through a natural soil were observed over areas of 25 m 2in Pinus nigra and Picea abies tree plantations. Both rhizomorph systems had numerous branches and anastomoses resulting in cyclic paths, i.e. regions of the system that start and end at the same point. Each rhizomorph network exhibited both exploitative and explorative characteristics within its overall network structure. One of the observed rhizomorph networks of A. lutea was restricted to the cyclic paths only, and the resulting graph was drawn in the plane. The plane graph consisted of 169 rhizomorphs, termed edges, and 107 rhizomorph nodes, termed vertices. The connectivity of the rhizomorph network was explored by focusing on each bridge, i.e. an edge whose removal disconnects the graph into two components. In only two instances was a nutrient source connected to the cycles, and disruption of these two connecting edges would remove the whole network from the sources. A shortest path from a given vertex to a nutrient source was defined in terms of number of edges, and also in terms of length (m). The length of the edges enclosing the faces, i.e. two-dimensional regions defined by the edges in the plane drawing, showed that the fungus exhibited both exploitative and explorative growth, and we speculate about the underlying reasons for these foraging strategies. The introduction of graph-theoretic concepts to fungal growth might lead to an improved ecological understanding of fungal networks in general, provided that relevant biological interpretations can be made

Extension of charge-state-distribution calculations for ion-solid collisions towards low velocities and many-electron ions

Knowledge of the detailed evolution of the whole charge-state distribution of projectile ions colliding with targets is required in several fields of research such as material science and atomic and nuclear physics but also in accelerator physics, and in particular in regard to the several foreseen large-scale facilities. However, there is a lack of data for collisions in the nonperturbative energy domain and that involve many-electron projectiles. Starting from the etacha model we developed [Rozet, Nucl. Instrum. Methods Phys. Res., Sect. B 107, 67 (1996)10.1016/0168-583X(95)00800-4], we present an extension of its validity domain towards lower velocities and larger distortions. Moreover, the system of rate equations is able to take into account ions with up to 60 orbital states of electrons. The computed data from the different new versions of the etacha code are compared to some test collision systems. The improvements made are clearly illustrated by 28.9MeVu-1Pb56+ ions, and laser-generated carbon ion beams of 0.045 to 0.5MeVu-1, passing through carbon or aluminum targets, respectively. Hence, those new developments can efficiently sustain the experimental programs that are currently in progress on the "next-generation" accelerators or laser facilities.Fil: Lamour, E.. Centre National de la Recherche Scientifique; Francia. Universite de Paris; FranciaFil: Fainstein, Pablo Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Galassi, Mariel Elisa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Prigent, C.. Centre National de la Recherche Scientifique; Francia. Universite de Paris; FranciaFil: Ramirez, C. A.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Rivarola, Roberto Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Rozet, J. P.. Centre National de la Recherche Scientifique; Francia. Universite de Paris; FranciaFil: Trassinelli, M.. Centre National de la Recherche Scientifique; Francia. Universite de Paris; FranciaFil: Vernhet, D.. Centre National de la Recherche Scientifique; Francia. Universite de Paris; Franci

How can video feedback be used in physical education to support novice learning in gymnastics? Effects on motor learning, self-assessment and motivation

Background: Much of the existing research concerning the use of video feedback (VFB) to enhance motor learning has been undertaken under strictly controlled experimental conditions. Few studies have sought to explore the impact of VFB on the skill learning experience of the students in a structured, school-based physical education (PE) setting. Most of those studies have only used qualitative approaches to implicate the potential value of VFB to enhance skill acquisition, students ’ engagement or self- assessment ability. Using a quantitative approach, the aim of this study was to investigate effects of using VFB on motor skill acquisition, self- assessment ability and motivation in a school-based learning environment (structured PE programme) with novice children learning a gymnastic skill. Method: Two French classes of beginners took part in a typical five-week learning programme in gymnastics. During each of the five, weekly lessons participants carried out the same warm-up routine and exercises. The experimental group (10 girls – 8 boys, 12.4 ± 0.5 years) received VFB intermittently when learning a front handstand to flat back landing. VFB was given after every five attempts, combined with self-assessment and verbal instructions from the teacher. The control group (12 girls – 13 boys, 12.6 ± 0.4 years) received exactly the same training but was not given VFB. In order to assess progress in motor skills, the arm-trunk angle (hand- shoulder-hip) was measured in the sagittal plane just as the hips formed a vertical line with the shoulders. Motivation was assessed using the Situational Motivation Scale questionnaire (Guay, F., R. J. Vallerand, and C. Blanchard. 2000. “ On the Assessment of Situational Intrinsic and Extrinsic Motivation: The Situational Motivation Scale (SIMS). ” Motivation and Emotion 24 (3): 175 – 213), and self-assessment ability was measured by self-perception task scores. Results: Statistical analysis of arm-trunk angle values showed significant differences only for the VFB group between the fifth lesson and all other lessons. Between lessons 4 and 5, the arm-trunk angle value increased significantly from 146.6 ± 16.9 degrees to 161.2 ± 14.2 degrees ( p < .001; ES = 0.94). Self-assessment scores improved significantly for the VFB group between lesson 1 and lesson 2 ( p < 0.01, ES = 1.79) and between lesson 4 to lesson 5 ( p < .01, ES = 0.94). Amotivation decreased significantly for the VFB group between lesson 1 and lesson 5 (3.06 ± 1.42 vs. 2.12 ± 0.62, p < .001, ES = − 0.89). Discussion/conclusion: Our quantitative data, identifying key movement changes as a function of experience in a structured PE programme, were congruent with outcomes of previous qualitative research supporting the role of VFB. This study highlights the potential relevance of using VFB in fostering motor learning, motivation and self-assessment during a PE programme with young children. Future pedagogical research is needed to examine the ways students could use VFB technology for greater self- regulation, with the potential to deliver appropriate movement feedback, based on different levels of experience in students

Modulating the phase transition temperature of giant magnetocaloric thin films by ion irradiation

Magnetic refrigeration based on the magnetocaloric effect at room temperature is one of the most attractive alternative to the current gas compression/expansion method routinely employed. Nevertheless, in giant magnetocaloric materials, optimal refrigeration is restricted to the narrow temperature window of the phase transition (Tc). In this work, we present the possibility of varying this transition temperature into a same giant magnetocaloric material by ion irradiation. We demonstrate that the transition temperature of iron rhodium thin films can be tuned by the bombardment of ions of Ne 5+ with varying fluences up to 10 14 ions cm --2 , leading to optimal refrigeration over a large 270--380 K temperature window. The Tc modification is found to be due to the ion-induced disorder and to the density of new point-like defects. The variation of the phase transition temperature with the number of incident ions opens new perspectives in the conception of devices using giant magnetocaloric materials

Measurement of the electric dipole moments for transitions to rubidium Rydberg states via Autler-Townes splitting

We present the direct measurements of electric-dipole moments for $5P_{3/2}\to nD_{5/2}$ transitions with $20<n<48$ for Rubidium atoms. The measurements were performed in an ultracold sample via observation of the Autler-Townes splitting in a three-level ladder scheme, commonly used for 2-photon excitation of Rydberg states. To the best of our knowledge, this is the first systematic measurement of the electric dipole moments for transitions from low excited states of rubidium to Rydberg states. Due to its simplicity and versatility, this method can be easily extended to other transitions and other atomic species with little constraints. Good agreement of the experimental results with theory proves the reliability of the measurement method.Comment: 12 pages, 6 figures; figure 6 replaced with correct versio

Rabi oscillations between ground and Rydberg states and van der Waals blockade in a mesoscopic frozen Rydberg gas

We present a detailed analysis of our recent observation of synchronous Rabi oscillations between the electronic ground state and Rydberg states in a mesoscopic ensemble containing roughly 100 ultracold atoms [M. Reetz-Lamour \textit{et al.}, submitted, arXiv:0711.4321]. The mesoscopic cloud is selected out of a sample of laser-cooled Rb atoms by optical pumping. The atoms are coupled to a Rydberg state with principal quantum number around 30 by a two-photon scheme employing flat-top laser beams. The influence of residual spatial intensity fluctuations as well as sources of decoherence such as redistribution to other states, radiative lifetime, and laser bandwidth are analysed. The results open up new possibilities for the investigation of coherent many-body phenomena in dipolar Rydberg gases. As an example we demonstrate the van der Waals blockade, a variant of the dipole blockade, for a mesoscopic atom sample

Biologically active Phytophthora mating hormone prepared by catalytic asymmetric total synthesis

A Phytophthora mating hormone with an array of 1,5-stereogenic centers has been synthesized by using our recently developed methodology of catalytic enantioselective conjugate addition of Grignard reagents. We applied this methodology in a diastereo- and enantioselective iterative route and obtained two of the 16 possible stereoisomers of Phytophthora hormone α1. These synthetic stereoisomers induced the formation of sexual spores (oospores) in A2 mating type strains of three heterothallic Phytophthora species, P. infestans, P. capsici, and P. nicotianae but not in A1 mating type strains. The response was concentration-dependent, and the oospores were viable. These results demonstrate that the biological activity of the synthetic hormone resembles that of the natural hormone α1. Mating hormones are essential components in the sexual life cycle of a variety of organisms. For plant pathogens like Phytophthora, sexual reproduction is important as a source of genetic variation. Moreover, the thick-walled oospores are the most durable propagules that can survive harsh environmental conditions. Sexual reproduction can thus greatly affect disease epidemics. The availability of synthetic compounds mimicking the activity of Phytophthora mating hormone will be instrumental for further unravelling sexual reproduction in this important group of plant pathogens.