651 research outputs found
A macroscopic model for sessile droplet evaporation on a flat surface
The evaporation of sessile droplets on a flat surface involves a complex
interplay between phase change, diffusion, advection and surface forces. In an
attempt to significantly reduce the complexity of the problem and to make it
manageable, we propose a simple model hinged on a surface free energy-based
relaxation dynamics of the droplet shape, a diffusive evaporation model and a
contact line pinning mechanism governed by a yield stress. Our model reproduces
the known dynamics of droplet shape relaxation and of droplet evaporation, both
in the absence and in the presence of contact line pinning. We show that shape
relaxation during evaporation significantly affects the lifetime of a drop. We
find that the dependence of the evaporation time on the initial contact angle
is a function of the competition between the shape relaxation and evaporation,
and is strongly affected by any contact line pinning.Comment: 13 pages, 8 figure
Compound redistribution due to droplet evaporation on a thin polymeric film: theory
A thin polymeric film in contact with a fluid body may leach
low-molecular-weight compounds into the fluid. If this fluid is a small
droplet, the compound concentration within the liquid increases due to ongoing
leaching in combination with the evaporation of the droplet. This may
eventually lead to an inversion of the transport process and a redistribution
of the compounds within the thin film. In order to gain an understanding of the
compound redistribution, we apply a macroscopic model for the evaporation of a
droplet and combine that with a diffusion model for the compound transport. In
the model, material deposition and the resulting contact line pinning are
associated with the precipitation of a fraction of the dissolved material. We
find three power law regimes for the size of the deposit area as a function of
the initial droplet size, dictated by the competition between evaporation,
diffusion and the initial compound concentrations in the droplet and the thin
film. The strength of the contact line pinning determines the deposition
profile of the precipitate, characterised by a pronounced edge and a linearly
decaying profile towards the centre of the stain. Our predictions for the
concentration profile within the solid substrate resemble patterns found
experimentally.Comment: 12 pages, 10 figure
Time-of-flight estimation based on covariance models
We address the problem of estimating the time-of-flight (ToF) of a waveform that is disturbed heavily by additional reflections from nearby objects. These additional reflections cause interference patterns that are difficult to predict. The introduction of a model for the reflection in terms of a non-stationary auto-covariance function leads to a new estimator for the ToF of an acoustic tone burst. This estimator is a generalization of the well known matched filter. In many practical circumstances, for instance beacon-based position estimation in indoor situations, lack of knowledge of the additional reflections can lead to large estimation errors. Experiments show that the application of the new estimator can reduce these errors by a factor of about four. The cost of this improvement is an increase in computational complexity by a factor of about seven
Competitiveness at Leiden University
Proceeding of: Strategies for International Excellence of European Research Universities. Sharing best practices. April 16, 2010. Getafe, Madri
On estimating the size of overcoverage with the latent class model. A critique of the paper "Population Size Estimation Using Multiple Incomplete Lists with Overcoverage" by di Cecco, di Zio, Filipponi and Rocchetti (2018, JOS 34 557-572)
We read with interest the article by di Cecco et al. (2018), but have
reservations about the usefulness of the latent class model specifically for
estimating overcoverage. In particular, we question the interpretation of the
parameters of the fitted latent class model.Comment: 5 page
On the use of positive test strategies when diagnosing mental disorders
Background: Despite the adverse impact diagnostic errors can have, clinical interviewing and decision-making in psychiatric practice have received relatively little empirical attention. When diagnosing patients, clinicians tend to fall back on a specific (heuristic) rule of thumb, the positive test strategy, a confirmatory approach that increases the risk of confirmation bias. Method and results: A group of 83 clinical psychologists and psychiatrists was asked to give their diagnostic hypotheses about two vignettes. We found them to self-generate significantly (i.e., p < .01; d = 1.57) more confirming than disconfirming questions to test their initial diagnostic impressions, with supervisors considering significantly more differential diagnoses than the less experienced post-grads/residents. When offered a list of 100 potentially relevant diagnostic queries, the supervisors selected fewer confirming and proportionally more disconfirming themes. Conclusions: Our results demonstrate that irrespective of clinical experience mental-health clinicians indeed tend to use a confirmatory thinking style that contrasts with the stricter principle of falsification. More field-based research on this topic is needed, as well as studies probing whether a systematized diagnostic approach is feasible in psychiatric practice and increases diagnostic accuracy and patient satisfaction
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