Streamer branching rationalized by conformal mapping techniques

Spontaneous branching of discharge channels is frequently observed, but not well understood. We recently proposed a new branching mechanism based on simulations of a simple continuous discharge model in high fields. We here present analytical results for such streamers in the Lozansky-Firsov limit where they can be modelled as moving equipotential ionization fronts. This model can be analyzed by conformal mapping techniques which allow the reduction of the dynamical problem to finite sets of nonlinear ordinary differential equations. The solutions illustrate that branching is generic for the intricate head dynamics of streamers in the Lozansky-Firsov-limit.Comment: 4 pages, 2 figure

Publisher's Note: Streamer branching rationalized by conformal mapping techniques (Physical Review E (2004) 69 (067402))

No abstract

How CREM can measure added value of building design : knowledge sharing in research buildings

Purpose- In present day society, focused on innovation, knowledge sharing (KS) is essential. Corporate Real Estate Management (CREM) needs to provide accommodation designed for people to meet more often and share both tacit and explicit knowledge. Most workplace descriptions do not provide quantitative information on how the design actually stimulates KS. They cannot be implemented straight into a design nor convince general management in budget discussions. This paper tests the suitability of spatial network methodologies to provide this proof. Design/methodology/approach - After developing a conceptual model from literature, the model is tested with a case-study of one large research driven organisation in the Netherlands. For each possible dyad between 138 employees (= 9453 dyads), several KS indicators and workplace aspects are studied with statistical analyses. Findings - KS is clearly related to the allocation of people to the rooms and workplaces in a research building. Bumping into each other does not appear the reason for this relation. Up to distances of 22 meters dyads share average or higher amounts of knowledge. It is ambiguous whether the spatial network analysis methodology is relevant for measuring added value of the workplace for KS. Originality/value - This paper provides empirical evidence on a ‘softer’ added value of the workplace, which is scarce. Previous studies relied mainly on qualitative descriptions of the workplace, while this paper tests a methodology to quantify the workplace in measurable aspects and correlate them statistically to organisational outcome measures. Keywords Corporate Real Estate Management, Knowledge sharing, Added value, Spatial network analysis, Building desig

Regularization of moving boundaries in a Laplacian field by a mixed Dirichlet-Neumann boundary condition: exact results

The dynamics of ionization fronts that generate a conducting body, are in simplest approximation equivalent to viscous fingering without regularization. Going beyond this approximation, we suggest that ionization fronts can be modeled by a mixed Dirichlet-Neumann boundary condition. We derive exact uniformly propagating solutions of this problem in 2D and construct a single partial differential equation governing small perturbations of these solutions. For some parameter value, this equation can be solved analytically which shows that the uniformly propagating solution is linearly convectively stable.Comment: 4 pages, 1 figur

Effective and Efficient Stand Magnifier Use in Visually Impaired Children

Contains fulltext : 167758.pdf (publisher's version ) (Open Access)PURPOSE: The main objective of this study was to analyze the effectiveness and efficiency of magnifier use in children with visual impairment who did not use a low vision aid earlier, in an ecologically valid goal-directed perceptuomotor task. METHODS: Participants were twenty-nine 4- to 8-year-old children with visual impairment and 47 age-matched children with normal vision. After seeing a first symbol (an Lea Hyvarinen [LH] symbol), children were instructed to (1) move the stand magnifier as quickly as possible toward a small target symbol (another LH symbol that could only be seen by using the magnifier), (2) compare the two symbols, and (3) move the magnifier to one of two response areas to indicate whether the two symbols were identical. Performance was measured in terms of accuracy, response time, identification time, and movement time. Viewing distance, as well as hand and eye dominance while using the magnifier was assessed. RESULTS: There were no significant differences between the two groups in accuracy, reaction time, and movement time. Contrary to the prediction, children with visual impairment required less time to identify small symbols than children with normal vision. Both within-subject and between-subject variability in viewing distance were smaller in the visually impaired group than in the normally sighted group. In the visually impaired group, a larger viewing distance was associated with shorter identification time, which in turn was associated with higher accuracy. In the normally sighted group, a faster movement with the magnifier and a faster identification were associated with increasing age. CONCLUSION: The findings indicate that children with visual impairment can use the stand magnifier adequately and efficiently. The normally sighted children show an age-related development in movement time and identification time and show more variability in viewing distance, which is not found in visually impaired children. Visually impaired children seem to choose a standard but less adaptive strategy in which they primarily used their preferred hand to manipulate the magnifier and their preferred eye to identify the symbol. TRIAL REGISTRATION: Registered at http://www.trialregister.nl; NTR2380.11 p

Intrinsic route to melt fracture in polymer extrusion: a weakly nonlinear subcritical instability of viscoelastic Poiseuille flow

As is well known, the extrusion rate of polymers from a cylindrical tube or slit (a die ) is in practice limited by the appearance of melt fracture instabilities which give rise to unwanted distortions or even fracture of the extrudate. We present the results of a weakly nonlinear analysis which gives evidence for an intrinsic generic route to melt fracture via a weakly nonlinear subcritical instability of viscoelastic Poiseuille flow. This instability and the onset of associated melt fracture phenomena appear at a well-defined ratio of the elastic stresses to viscous stresses of the polymer solution

Experimental evidence for an intrinsic route to polymer melt fracture phenomena: a nonlinear instability of viscoelastic Poiseuille flow

The production rate of polymer fibers by extrusion is usually limited by the appearance of a series of instabilities ("melt fracture") that lead to unwanted undulations of the surface. We present both qualitative and quantitative experimental evidence that-in addition to previously known polymer-specific scenarios-there is an intrinsic route towards melt fracture type phenomena: a nonlinear ("subcritical") instability of viscoelastic Poiseuille flow.Theoretical Physic

On interference effects in concurrent perception and action

Recent studies have reported repulsion effects between the perception of visual motion and the concurrent production of hand movements. Two models, based on the notions of common coding and internal forward modeling, have been proposed to account for these phenomena. They predict that the size of the effects in perception and action should be monotonically related and vary with the amount of similarity between what is produced and perceived. These predictions were tested in four experiments in which participants were asked to make hand movements in certain directions while simultaneously encoding the direction of an independent stimulus motion. As expected, perceived directions were repelled by produced directions, and produced directions were repelled by perceived directions. However, contrary to the models, the size of the effects in perception and action did not covary, nor did they depend (as predicted) on the amount of perception–action similarity. We propose that such interactions are mediated by the activation of categorical representations