New perspectives on magnetotail dynamic processes from combined cluster and double star observations

In this thesis, observations of the Earth's magnetotail from ESA's four Cluster and the two Sino-European Double Star spacecraft are presented. The observations are of intervals where data from the combination of Cluster and Double Star provide insights into the dynamics of the magnetotail that are not possible using data from one mission alone. In the �first study, observations of three magnetic flux ropes are presented, two of which were detected near-simultaneously at Cluster and Double Star TC-1, while the third was detected by Cluster, along with a TCR a few minutes later. The observations represent the �first observations of multiple flux ropes existing in the magnetotail simultaneously, providing evidence that flux rope orientation is influenced by neutral sheet tilt and provide further evidence that TCRs in the lobes are caused by the passage of flux ropes in the plasma sheet. In the second study, a detailed analysis of a plasma bubble is presented, including the �first direct observations of the return flows around the flanks of the plasma bubble that are expected from theory and simulation. Furthermore a partially stagnant depleted wake behind the plasma bubble, not predicted by theory or simulation was discovered and the cross-tail extent of the bubble was measured to be 3RE. The fi�rst observations of near-Earth bubble features are also reported. Finally, in the third study, the substorm onset process itself is investigated using a wide array of space- and ground-based instrumentation. A pseudobreakup and later substorm onset are distinguished using both geomagnetic and auroral data and the establishment of the substorm current wedge is observed in-situ using the TC-2 and GOES12 spacecraft. A link between higher latitude geomagnetic activity and the fast flows and plasma sheet expansion related to the reconnection of lobe fi�eld lines is also posited

Force modelling of the crankshaft pin grinding process.

A force model was developed for crankshaft pin grinding to predict the forces generated during grinding. The force model developed builds on the authors&rsquo; previously developed model, which predicted the out-of-roundness in crankshaft pin grinding. The model includes key grinding variables, such as the work removal parameter (WRP), system sti€ ness and Young&rsquo;s modulus to determine the end forces produced. The model also includes the important geometrical relationships that are unique to this type of grinding. The model was veriŽ ed using an experiential set-up involving sophisticated strain gauge force measurements on a commercial Landis CP grinding machine, with close correlation between the results and the model.<br /

Resonant Diffraction Radiation and Smith-Purcell Effect

An approach has been developed where the Smith-Purcell radiation (SPR), i.e. emission of electrons moving close to a periodic structure, is treated as the resonant diffraction radiation. Simple formulas have been designed for the SPR intensity for a grating having perfectly conducting strips spaced by a vacuum gap. The results have been compared with those obtained via other techniques. It has been shown that the intensity of radiation for the said gratings for a relativistic case sufficiently exceeds the SPR intensity for the grating made up by a periodically deformed continuous surface.Comment: 9 pages, LATEX, 3 Postscript figures, uses epsf.sty, submitted to Phys.Letters

Elastic moduli of model random three-dimensional closed-cell cellular solids

Most cellular solids are random materials, while practically all theoretical results are for periodic models. To be able to generate theoretical results for random models, the finite element method (FEM) was used to study the elastic properties of solids with a closed-cell cellular structure. We have computed the density ($\rho$) and microstructure dependence of the Young's modulus ($E$) and Poisson's ratio (PR) for several different isotropic random models based on Voronoi tessellations and level-cut Gaussian random fields. The effect of partially open cells is also considered. The results, which are best described by a power law $E\propto\rho^n$ ($1 < n <2$), show the influence of randomness and isotropy on the properties of closed-cell cellular materials, and are found to be in good agreement with experimental data.Comment: 13 pages, 13 figure

Approximate Bayesian computation in large-scale structure: constraining the galaxy-halo connection

FWN – Publicaties zonder aanstelling Universiteit Leide

Structural characterization suggests models for monomeric and dimeric forms of full-length ezrin

Ezrin is a member of the ERM (ezrin–radixin–moesin) family of proteins that have been conserved through metazoan evolution. These proteins have dormant and active forms, where the latter links the actin cytoskeleton to membranes. ERM proteins have three domains: an N-terminal FERM [band Four-point-one (4.1) ERM] domain comprising three subdomains (F1, F2, and F3); a helical domain; and a C-terminal actin-binding domain. In the dormant form, FERM and C-terminal domains form a stable complex. We have determined crystal structures of the active FERM domain and the dormant FERM:C-terminal domain complex of human ezrin. We observe a bistable array of phenylalanine residues in the core of subdomain F3 that is mobile in the active form and locked in the dormant form. As subdomain F3 is pivotal in binding membrane proteins and phospholipids, these transitions may facilitate activation and signaling. Full-length ezrin forms stable monomers and dimers. We used small-angle X-ray scattering to determine the solution structures of these species. As expected, the monomer shows a globular domain with a protruding helical coiled coil. The dimer shows an elongated dumbbell structure that is twice as long as the monomer. By aligning ERM sequences spanning metazoan evolution, we show that the central helical region is conserved, preserving the heptad repeat. Using this, we have built a dimer model where each monomer forms half of an elongated antiparallel coiled coil with domain-swapped FERM:C-terminal domain complexes at each end. The model suggests that ERM dimers may bind to actin in a parallel fashion

Effects of a multisensory supervised training for six weeks in balance and quality of life of the elderly

Modelo do Estudo: Estudo experimental. Objetivo: Avaliar o equilíbrio e a qualidade de vida de idosos submetidos a um treino multissensorial supervisionado. Metodologia: Os sujeitos foram 20 idosos que participaram de um programa de treinamento multissensorial, duas vezes por semana, por seis semanas. Para avaliação do equilíbrio utilizou-se: Escala de Berg(EB), Teste de Romberg Sensibilizado(TRS), Teste de Alcance Funcional(TAF) e Teste Timed Up and Go(TUG) e da qualidade de vida foram aplicados os questionários WHOQOL-BREF e WHOQOL-OLD. Foi realizada análise descritiva das variáveis seguida de comparação pelo teste T-pareado. Resultados: A idade variou entre 60 a 81 anos (67±6,0 anos). A maioria era do sexo feminino (95%), brancos (60%) e casados (60%). Todas as variáveis relacionadas ao equilíbrio avaliadas apresentaram resultados significativamente melhores, após o treino multissensorial. Em relação à avaliação da qualidade de vida, no WHOQOL-BREF houve aumento significativo em todos os domínios, com exceção do meio ambiente. Já o WHOQOL-OLD apresentou melhora significativa apenas para o domínio autonomia. Conclusão: este estudo mostrou que a prática de um treino multissensorial proporciona benefícios em curto prazo, com ganhos de equilíbrio e qualidade de vida de idosos, sendo uma importante estratégia de promoção de saúde para esta populaçãoStudy design: This is an experimental study. Objective: Evaluate the balance and the quality of life of elderly submitted to a multi-sensory training supervised. Methodology: The subjects were 20 seniors who participated in a multi-sensory training program twice a week for six weeks. Balance evaluation instruments were used: Berg Scale (BS), Sensitize Romberg Test (SRT), Functional Reach Test (FRT) and Test Timed Up and Go (TUG) and of the quality of life were performed using WHOQOL-BREF and WHOQOL-OLD questionnaires. The variables were analysed using descriptive and comparative methods (paired t-test). Results: The age ranged from 60-81 years (67 ± 6,0 years). Most were female (95%) and white (60%) and married (60%). All related variables assessed balance showed significantly better results after the multisensory training. Regarding the assessment of quality of life, WHOQOL-BREF significant increase in all areas, except the environment. But the WHOQOL-OLD improved significantly only for the domain autonomy. Conclusion: This study showed that the practice of a multisensory training provides short-term benefits, balancing gains and quality of life of elderly and it is an important health promotion strategy for this populatio

Transport in rough self-affine fractures

Transport properties of three-dimensional self-affine rough fractures are studied by means of an effective-medium analysis and numerical simulations using the Lattice-Boltzmann method. The numerical results show that the effective-medium approximation predicts the right scaling behavior of the permeability and of the velocity fluctuations, in terms of the aperture of the fracture, the roughness exponent and the characteristic length of the fracture surfaces, in the limit of small separation between surfaces. The permeability of the fractures is also investigated as a function of the normal and lateral relative displacements between surfaces, and is shown that it can be bounded by the permeability of two-dimensional fractures. The development of channel-like structures in the velocity field is also numerically investigated for different relative displacements between surfaces. Finally, the dispersion of tracer particles in the velocity field of the fractures is investigated by analytic and numerical methods. The asymptotic dominant role of the geometric dispersion, due to velocity fluctuations and their spatial correlations, is shown in the limit of very small separation between fracture surfaces.Comment: submitted to PR

High-contrast imaging constraints on gas giant planet formation - The Herbig Ae/Be star opportunity

Planet formation studies are often focused on solar-type stars, implicitly considering our Sun as reference point. This approach overlooks, however, that Herbig Ae/Be stars are in some sense much better targets to study planet formation processes empirically, with their disks generally being larger, brighter and simply easier to observe across a large wavelength range. In addition, massive gas giant planets have been found on wide orbits around early type stars, triggering the question if these objects did indeed form there and, if so, by what process. In the following I briefly review what we currently know about the occurrence rate of planets around intermediate mass stars, before discussing recent results from Herbig Ae/Be stars in the context of planet formation. The main emphasis is put on spatially resolved polarized light images of potentially planet forming disks and how these images - in combination with other data - can be used to empirically constrain (parts of) the planet formation process. Of particular interest are two objects, HD100546 and HD169142, where, in addition to intriguing morphological structures in the disks, direct observational evidence for (very) young planets has been reported. I conclude with an outlook, what further progress we can expect in the very near future with the next generation of high-contrast imagers at 8-m class telescopes and their synergies with ALMA.Comment: Accepted by Astrophysics and Space Science as invited short review in special issue about Herbig Ae/Be stars; 12 pages incl. 5 figures, 2 tables and reference

Time-integrated luminosity recorded by the BABAR detector at the PEP-II e+e- collider

This article is the Preprint version of the final published artcile which can be accessed at the link below.We describe a measurement of the time-integrated luminosity of the data collected by the BABAR experiment at the PEP-II asymmetric-energy e+e- collider at the ϒ(4S), ϒ(3S), and ϒ(2S) resonances and in a continuum region below each resonance. We measure the time-integrated luminosity by counting e+e-→e+e- and (for the ϒ(4S) only) e+e-→μ+μ- candidate events, allowing additional photons in the final state. We use data-corrected simulation to determine the cross-sections and reconstruction efficiencies for these processes, as well as the major backgrounds. Due to the large cross-sections of e+e-→e+e- and e+e-→μ+μ-, the statistical uncertainties of the measurement are substantially smaller than the systematic uncertainties. The dominant systematic uncertainties are due to observed differences between data and simulation, as well as uncertainties on the cross-sections. For data collected on the ϒ(3S) and ϒ(2S) resonances, an additional uncertainty arises due to ϒ→e+e-X background. For data collected off the ϒ resonances, we estimate an additional uncertainty due to time dependent efficiency variations, which can affect the short off-resonance runs. The relative uncertainties on the luminosities of the on-resonance (off-resonance) samples are 0.43% (0.43%) for the ϒ(4S), 0.58% (0.72%) for the ϒ(3S), and 0.68% (0.88%) for the ϒ(2S).This work is supported by the US Department of Energy and National Science Foundation, the Natural Sciences and Engineering Research Council (Canada), the Commissariat à l’Energie Atomique and Institut National de Physique Nucléaire et de Physiquedes Particules (France), the Bundesministerium für Bildung und Forschung and Deutsche Forschungsgemeinschaft (Germany), the Istituto Nazionale di Fisica Nucleare (Italy), the Foundation for Fundamental Research on Matter (The Netherlands), the Research Council of Norway, the Ministry of Education and Science of the Russian Federation, Ministerio de Ciencia e Innovación (Spain), and the Science and Technology Facilities Council (United Kingdom). Individuals have received support from the Marie-Curie IEF program (European Union) and the A.P. Sloan Foundation (USA)