106 research outputs found
Analytical solutions to slender-ribbon theory
The low-Reynolds number hydrodynamics of slender ribbons is accurately
captured by slender-ribbon theory, an asymptotic solution to the Stokes
equation which assumes that the three length scales characterising the ribbons
are well separated. We show in this paper that the force distribution across
the width of an isolated ribbon located in a infinite fluid can be determined
analytically, irrespective of the ribbon's shape. This, in turn, reduces the
surface integrals in the slender-ribbon theory equations to a line integral
analogous to the one arising in slender-body theory to determine the dynamics
of filaments. This result is then used to derive analytical solutions to the
motion of a rigid plate ellipsoid and a ribbon torus and to propose a ribbon
resistive-force theory, thereby extending the resistive-force theory for
slender filaments
The boundary integral formulation of Stokes flows includes slender-body theory
The incompressible Stokes equations can classically be recast in a boundary
integral (BI) representation, which provides a general method to solve
low-Reynolds number problems analytically and computationally. Alternatively,
one can solve the Stokes equations by using an appropriate distribution of flow
singularities of the right strength within the boundary, a method particularly
useful to describe the dynamics of long slender objects for which the numerical
implementation of the BI representation becomes cumbersome. While the BI
approach is a mathematical consequence of the Stokes equations, the singularity
method involves making judicious guesses that can only be justified a
posteriori. In this paper we use matched asymptotic expansions to derive an
algebraically accurate slender-body theory directly from the BI representation
able to handle arbitrary surface velocities and surface tractions. This
expansion procedure leads to sets of uncoupled linear equations and to a single
one-dimensional integral equation identical to that derived by Keller and
Rubinow (1976) and Johnson (1979) using the singularity method. Hence we show
that it is a mathematical consequence of the BI approach that the leading-order
flow around a slender body can be represented using a distribution of
singularities along its centreline. Furthermore when derived from either the
single-layer or double-layer modified BI representation, general slender
solutions are only possible in certain types of flow, in accordance with the
limitations of these representations
Clinicopathologic and genetic aspects of primary cutaneous large B-cell lymphomas
Primary cutaneous large B-cell lymphomas can be divided into primary cutaneous follicle center lymphoma and primary cutaneous large B-cell lymphoma, leg type. Accurately making the distinction between these two lymphomas at the time of diagnosis is essential for the patient, as there are differences in prognosis (5 year overall survival >95% versus <50%) and first choice treatment (radiotherapy versus polychemotherapy). The thesis aimed to better characterize both subtypes genetically and clinicopathologically in search for markers differentiating between the subtypes. Furthermore, genetic studies were performed on primary cutaneous large B-cell lymphoma, leg type, in search for leads for targeted therapy in this aggressive type of primary cutaneous large B-cell lymphoma. Finally, a series of methotrexate-associated B-cell lymphoproliferative disorders presenting in the skin (mimicking primary cutaneous large B-cell lymphomas) were studied, in search of clinicopathologic features characteristic for this disorder.UBL - phd migration 201
Vibrations of a Columnar Vortex in a Trapped Bose-Einstein Condensate
We derive a governing equation for a Kelvin wave supported on a vortex line
in a Bose-Einstein condensate, in a rotating cylindrically symmetric parabolic
trap. From this solution the Kelvin wave dispersion relation is determined. In
the limit of an oblate trap and in the absence of longitudinal trapping our
results are consistent with previous work. We show that the derived Kelvin wave
dispersion in the general case is in quantitative agreement with numerical
calculations of the Bogoliubov spectrum and offer a significant improvement
upon previous analytical work.Comment: 5 pages with 1 figur
The WARPS Survey. VIII. Evolution of the Galaxy Cluster X-ray Luminosity Function
We present measurements of the galaxy cluster X-ray Luminosity Function (XLF)
from the Wide Angle ROSAT Pointed Survey (WARPS) and quantify its evolution.
WARPS is a serendipitous survey of the central region of ROSAT pointed
observations and was carried out in two phases (WARPS-I and WARPS-II). The
results here are based on a final sample of 124 clusters, complete above a flux
limit of 6.5 10E-15 erg/s/cm2, with members out to redshift z ~ 1.05, and a sky
coverage of 70.9 deg2. We find significant evidence for negative evolution of
the XLF, which complements the majority of X-ray cluster surveys. To quantify
the suggested evolution, we perform a maximum likelihood analysis and conclude
that the evolution is driven by a decreasing number density of high luminosity
clusters with redshift, while the bulk of the cluster population remains nearly
unchanged out to redshift z ~ 1.1, as expected in a low density Universe. The
results are found to be insensitive to a variety of sources of systematic
uncertainty that affect the measurement of the XLF and determination of the
survey selection function. We perform a Bayesian analysis of the XLF to fully
account for uncertainties in the local XLF on the measured evolution, and find
that the detected evolution remains significant at the 95% level. We observe a
significant excess of clusters in the WARPS at 0.1 < z < 0.3 and LX ~ 2 10E42
erg/s compared with the reference low-redshift XLF, or our Bayesian fit to the
WARPS data. We find that the excess cannot be explained by sample variance, or
Eddington bias, and is unlikely to be due to problems with the survey selection
function.Comment: 13 pages, 12 figures, accepted for publication in MNRA
Perturbative behaviour of a vortex in a trapped Bose-Einstein condensate
We derive a set of equations that describe the shape and behaviour of a
single perturbed vortex line in a Bose-Einstein condensate. Through the use of
a matched asymptotic expansion and a unique coordinate transform a relation for
a vortex's velocity, anywhere along the line, is found in terms of the
trapping, rotation, and distortion of the line at that location. This relation
is then used to find a set of differential equations that give the line's
specific shape and motion. This work corrects a previous similar derivation by
Anatoly A. Svidzinsky and Alexander L. Fetter [Phys. Rev. A \textbf{62}, 063617
(2000)], and enables a comparison with recent numerical results.Comment: 12 pages with 3 figure
Hydrodynamic interactions between nearby slender filaments
Cellular biology abound with filaments interacting through fluids, from intracellular microtubules, to rotating flagella and beating cilia. While previous work has demonstrated the complexity of capturing nonlocal hydrodynamic interactions between moving filaments, the problem remains difficult theoretically. We show here that when filaments are closer to each other than their relevant length scale, the integration of hydrodynamic interactions can be approximately carried out analytically. This leads to a set of simplified local equations, illustrated on a simple model of two interacting filaments, which can be used to tackle theoretically a range of problems in biology and physics.This work was funded in part by the European Union through a CIG grant and a ERC Consolidator grant to EL and by the Cambridge Trust
The non-Gaussian tops and tails of diffusing boomerangs
Experiments involving the two-dimensional passive diffusion of colloidal boomerangs tracked off their centre of mobility have shown striking non-Gaussian tails in their probability distribution function [Chakrabarty et al., Soft Matter, 2016, 12, 4318]. This in turn can lead to anomalous diffusion characteristics, including mean drift. In this paper, we develop a general theoretical explanation for these measurements. The idea relies on calculating the two-dimensional probability densities at the centre of mobility of the particle, where all distributions are Gaussian, and then transforming them to a different reference point. Our model clearly captures the experimental results, without any fitting parameters, and demonstrates that the one-dimensional probability distributions may also exhibit strongly non-Gaussian tops. These results indicate that the choice of tracking point can cause a considerable departure from Gaussian statistics, potentially causing some common modelling techniques to fail.This research was funded in part by an ERC grant to EL and a Mobility Plus Fellowship from the Polish Ministry of Science and Higher Education to ML
Serious gaming to stimulate participatory urban tourism planning.
This paper examines how a serious game approach could support a participatory planning process by bringing stakeholders together to discuss interventions that assist the development of sustainable urban tourism. A serious policy game was designed and played in six European cities by a total of 73 participants, reflecting a diverse array of tourism stakeholders. By observing in-game experiences, a pre- and post -game survey and short interviews six months after playing the game, the process and impact of the game was investigated. While it proved difficult to evaluate the value of a serious game approach, results demonstrate that enacting real-life policymaking in a serious game setting can enable stakeholders to come together, and become more aware of the issues and complexities involved with urban tourism planning. This suggests a serious game can be used to stimulate the uptake of academic insights in a playful manner. However, it should be remembered that a game is a tool and does not, in itself, lead to inclusive participatory policymaking and more sustainable urban tourism planning. Consequently, care needs to be taken to ensure inclusiveness and prevent marginalization or disempowerment both within game-design and the political formation of a wider participatory planning approach.</p
Verstand op Veilig: de waarde van publieke kennisinstellingen voor de veiligheid van Nederland
Kennisinstellingen met een taak op het gebied van publieke veiligheid hebben de afgelopen jaren allerlei afgeleide activiteiten ontwikkeld. Dit leidt de aandacht af van hun kerntaken. Expertise waar weinig vraag naar is, dreigt te verdwijnen. De aandacht voor lange termijn-vraagstukken neemt af. Dat concludeert het Rathenau Instituut in het rapport “Verstand op Veilig”, over het KNMI, RIKILT, NFI en het NVI
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