Scaling of the turbulence transition threshold in a pipe

We report the results of an experimental investigation of the transition to turbulence in a pipe over approximately an order of magnitude range in $Re$. A novel scaling law is uncovered using a systematic experimental procedure which permits contact to be made with modern theoretical thinking. The principal result we uncover is a scaling law which indicates that the amplitude of perturbation required to cause transition scales as $O(Re^{-1})$.Comment: 4 pages, RevTex (submitted to Phys. Rev. Lett.

Round-robin tournaments with minimum number of breaks and two teams per club

We study round-robin tournaments for 2n teams. Here n is either interpreted as the number of clubs, each having two teams, or the number of strength groups with two teams each. For even n we give a construction of a single round-robin tournament for 2n teams with 2n - 2 breaks, where the teams of the same club have complementary home-away patterns and play against each other in the first round. If the pairs of teams are strength groups, then a cyclic permutation of the constructed schedule results in a group-balanced tournament

Design and evaluation of dynamic policy-based flow redirection for multihomed mobile netwotks

This paper presents the design, implementation and evaluation of a solution for dynamic redirection of traffic flows for multihomed mobile networks. The solution was developed for a mobile user that disposes of a Personal Area Network (PAN) with a Personal Mobile Router (PMR), in order to achieve Always Best Connected(ABC) service by distributing flows belonging to different applications among the most appropriate access networks. Designed in a modular way for a NEMO based mobility and multihoming support, the proposed flow redirection solution can be easily coupled with and controlled by dynamic traffic policies that come from advanced network intelligence, according to the currently available network resources and user and application requirements. A prototype implementation was validated and assessed on a testbed as proof-of-concept

A hollow fiber membrane probe for the measurement of the hydrogen concentration in a liquid

A new method is introduced to measure the hydrogen concentration in liquids by applying a polyethersulfone hollow fiber membrane as a probe. Hydrogen rapidly diffuses through the fiber wall after which it is carried to a thermal conductivity detector by an inert gas flow. Stationary measurements in a pure hydrogen atmosphere as well as in a silicone oil are conducted. Polyethersulfone was shown to be more suitable as fiber material for a selective hydrogen probe than polysulfone. From nonstationary measurements it could be concluded that the response time of the polyethersulfone probe is fast enough to monitor the hydrogen concentration during instationary processes which involve hydrogen, like gas-liquid or liquid-solid mass transfer and homogeneous/heterogeneous reactions

Forbidden induced subgraphs and the price of connectivity for feedback vertex set.

Let fvs(G) and cfvs(G) denote the cardinalities of a minimum feedback vertex set and a minimum connected feedback vertex set of a graph G, respectively. For a graph class G, the price of connectivity for feedback vertex set (poc-fvs) for G is defined as the maximum ratio cfvs(G)/fvs(G) over all connected graphs G in G. It is known that the poc-fvs for general graphs is unbounded. We study the poc-fvs for graph classes defined by a finite family H of forbidden induced subgraphs. We characterize exactly those finite families H for which the poc-fvs for H-free graphs is bounded by a constant. Prior to our work, such a result was only known for the case where |H|=1

Hadwiger number of graphs with small chordality

The Hadwiger number of a graph G is the largest integer h such that G has the complete graph K_h as a minor. We show that the problem of determining the Hadwiger number of a graph is NP-hard on co-bipartite graphs, but can be solved in polynomial time on cographs and on bipartite permutation graphs. We also consider a natural generalization of this problem that asks for the largest integer h such that G has a minor with h vertices and diameter at most $s$. We show that this problem can be solved in polynomial time on AT-free graphs when s>=2, but is NP-hard on chordal graphs for every fixed s>=2

Exploiting structure to cope with NP-hard graph problems: Polynomial and exponential time exact algorithms

An ideal algorithm for solving a particular problem always finds an optimal solution, finds such a solution for every possible instance, and finds it in polynomial time. When dealing with NP-hard problems, algorithms can only be expected to possess at most two out of these three desirable properties. All algorithms presented in this thesis are exact algorithms, which means that they always find an optimal solution. Demanding the solution to be optimal means that other concessions have to be made when designing an exact algorithm for an NP-hard problem: we either have to impose restrictions on the instances of the problem in order to achieve a polynomial time complexity, or we have to abandon the requirement that the worst-case running time has to be polynomial. In some cases, when the problem under consideration remains NP-hard on restricted input, we are even forced to do both. Most of the problems studied in this thesis deal with partitioning the vertex set of a given graph. In the other problems the task is to find certain types of paths and cycles in graphs. The problems all have in common that they are NP-hard on general graphs. We present several polynomial time algorithms for solving restrictions of these problems to specific graph classes, in particular graphs without long induced paths, chordal graphs and claw-free graphs. For problems that remain NP-hard even on restricted input we present exact exponential time algorithms. In the design of each of our algorithms, structural graph properties have been heavily exploited. Apart from using existing structural results, we prove new structural properties of certain types of graphs in order to obtain our algorithmic results

Detection of autism in childhood

The objective of this thesis by Maarten van ‘t Hof was to identify factors to enhance the detection of autism spectrum disorder (ASD) in childhood.This thesis indicate that the global age at ASD diagnosis is currently still relatively high as results found a global mean age at ASD diagnosis of 60 months. More standardized research on the age at ASD diagnosis is needed to compare results and identify weak points in local or national healthcare systems and improve the early detection of ASD. Research on the detection of ASD by Dutch preventive care physicians show that they have low levels of specific ASD knowledge (e.g. early signs, diagnostic criteria and comorbidity). A live online educational program had a positive effect on level of ASD knowledge and self-confidence in detection ASD among preventive care physicians, highlighting the importance of such educational programs.Van ‘t Hof also evaluated the relationship between ASD traits and eating behavior using the Generation R cohort. Results indicate an association between ASD and eating behavior throughout childhood that can potentially be useful in the (early) detection of ASD. CV – Maarten van ‘t HofMaarten van ’t Hof (1984) worked for Sarr Expert Centre for Autism (Lucertis, now Youz Child and adolescent psychiatry) during during writing this thesis. He currently works as an account manager (mental healthcare) for Parnassia Group. All articles included in this thesis are published (https://pubmed.ncbi.nlm.nih.gov/?term=van+%27t+Hof+M+AND+Ester+W&sort=date)