The Holy Grail of science policy: Exploring and combining bibliometric tools in search of scientific excellence

Evaluation studies of scientific performance conducted during the past years more and more focus on the identification of research of the 'highest quality', 'top' research, or 'scientific excellence'. This shift in focus has lead to the development of new bibliometric methodologies and indicators. Technically, it meant a shift from bibliometric impact scores based on average values such as the average impact of all papers published by some unit to be evaluated towards indicators reflecting the topof the citation distribution, such as the number of 'highly cited' or 'top' articles. In this study we present a comparative analysis of a number of standard and new indicators of research performance or 'scientific excellence', using techniques applied in studies conducted by CWTS in recent years. It will be shown that each type of indicator reflects a particular dimension of the general concept of research performance. Consequently, the application of one single indicator only may provide an incomplete picture of a unit's performance. It is argued that one needs to combine the various types of indicators in order to offer policy makers and evaluators valid and useful assessment tools. This revised version was published online in August 2006 with corrections to the Cover Date.     

A W-band monolithic downconverter

The design, fabrication, and evaluation of a fully integrated W-band monolithic downconverter based on InGaAs pseudomorphic HEMT technology are presented. The monolithic downconverter consists of a two-stage low-noise amplifier and a single-balanced mixer. The single-balanced mixer has been designed using the HEMT gate Schottky diodes inherent to the process. Measured results of the complete downconverter show conversion gain of 5.5 dB and a double-sideband noise figure of 6.7 dB at 94 GHz. Also presented is the downconverter performance characterized over the -35°C to +65°C temperature range. The downconverter design was a first pass success and has a high circuit yield     

Edge exchanges in the degree-constrained minimum spanning tree problem

We describe a branch and bound algorithm to solve the degree-constrained minimum spanning tree problem. We propose an edge exchange analysis frequently used in the algorithm and three types of heuristic methods. Computational results are reported for problems with up to 200 vertices. These results are much better than known results from the literature.     

Localized measurement of optical attenuation coefficients of atherosclerotic plaque constituents by quantitative optical coherence tomography

Optical coherence tomography (OCT) is a novel, high-resolution diagnostic tool that is capable of imaging the arterial wall and plaques. The differentiation between different types of atherosclerotic plaque is based on qualitative differences in gray levels and structural appearance. We hypothesize that a quantitative data analysis of the OCT signal allows measurement of light attenuation by the local tissue components, which can facilitate quantitative spatial discrimination between plaque constituents. High-resolution OCT images (at 800 nm) of human atherosclerotic arterial segments obtained at autopsy were histologically validated. Using a new, simple analysis algorithm, which incorporates the confocal properties of the OCT system, the light attenuation coefficients for these constituents were determined: for diffuse intimal thickening (5.5 +/- 1.2 mm(-1)) and lipid-rich regions (3.2 +/- 1.1 mm(-1)), the attenuation differed significantly from media (9.9 +/- 1.8 mm(-1)), calcifications (11.1 +/- 4.9 mm(-1) ) and thrombi (11.2 +/- 2.3 mm(-1)) (p < 0.01). These proof of principle studies show that simple quantitative analysis of the OCT signals allows spatial determination of the intrinsic optical attenuation coefficient of atherosclerotic tissue components within regions of interest. Combining morphological imaging by OCT with the observed differences in optical attenuation coefficients of the various regions may enhance discrimination between various plaque types.     

Fungal Infection Reduces Herbivore-Induced Plant Volatiles of Maize but does not Affect Naïve Parasitoids

Plants attacked by insects release volatile compounds that attract the herbivores' natural enemies. This so-called indirect defense is plastic and may be affected by an array of biotic and abiotic factors. We investigated the effect of fungal infection as a biotic stress agent on the emission of herbivore-induced volatiles and the possible consequences for the attraction of two parasitoid species. Maize seedlings that were simultaneously attacked by the fungus Setosphaeria turcica and larvae of Spodoptera littoralis emitted a blend of volatiles that was qualitatively similar to the blend emitted by maize that was damaged by only the herbivore, but there was a clear quantitative difference. When simultaneously challenged by fungus and herbivore, the maize plants emitted in total 47% less of the volatiles. Emissions of green leaf volatiles were unaffected. In a six-arm olfactometer, the parasitoids Cotesia marginiventris and Microplitis rufiventris responded equally well to odors of herbivore-damaged and fungus- and herbivore-damaged maize plants. Healthy and fungus-infected plants were not attractive. An additional experiment showed that the performance of S. littoralis caterpillars was not affected by the presence of the pathogen, nor was there an effect on larvae of M. rufiventris developing inside the caterpillars. Our results confirm previous indications that naïve wasps may respond primarily to the green leaf volatiles.     

A novel nonlinear observer‐based LQ control system design for wind energy conversion systems with single measurement

The issue of tracking the optimal power for wind energy conversion systems (WECSs) via regulating the rotor speed of the generator is taken into account in this study. Additionally, a novel polynomial observer is proposed for estimating not only aerodynamic torque in WECSs but also d‐axis and electromagnetic torque. Therefore, in this new approach, only the rotor speed of the generator is required to be measured instead of measuring all state variables. With the new observer form, the aerodynamic torque does not need to satisfy any constraints, which are mandatory in the previous methods. It should be noted that this methodology has not been investigated for the WECSs in any previous papers. To design a complete control system, a linear optimal control method cooperated with the polynomial observer is employed to track the optimal trajectory of a generator. Moreover, in this paper, the permanent magnet synchronous generator is used. In addition, on the basis of the Lyapunov theory and sum‐of‐square (SOS) technique, the conditions for observer synthesis are derived in the main theorems. Finally, the simulation results are provided to prove the effectiveness and merit of the proposed method.