Path following using transverse feedback linearization: Application to a maglev positioning system

This article presents an approach to path following control design based on transverse feedback linearization. A “transversal” controller is designed to drive the output of the plant to the path. A “tangential” controller meets the application-specific requirements on the path, such as speed regulation and internal stability. This methodology is applied to a five-degree-of-freedom (5-DOF) magnetically levitated positioning system. Experimental results are provided that demonstrate the effectiveness of our control design.     

Continuous Chain Ladder: Reformulating and generalizing a classical insurance problem

The single most important number in the accounts of a non-life insurance company is likely to be the estimate of the outlying liabilities. Since non-life insurance is a major part of our financial industry (amounting to up to 5% of BNP in western countries), it is perhaps surprising that mathematical statisticians and experts of operational research (the natural experts of the underlying problem) have left the intellectual work on estimating this number to actuaries. This paper establishes this important problem in a vocabulary accessible to experts of operations research and mathematical statistics and it can be seen as an open invitation to these two important groups of scholars to join this research. The paper introduces a number of new methodologies and approaches to estimating outstanding liabilities in non-life insurance. In particular it reformulates the classical actuarial technique as a histogram type of approach and improves this classical technique by replacing this histogram by a kernel smoother.     

Evaluation of AVHRR PAL and GIMMS 10‐day composite NDVI time series products using SPOT‐4 vegetation data for the African continent

Global 8 km resolution AVHRR (advanced very high resolution radiometer) NDVI (normalized difference vegetation index) 10‐day composite data sets have been used for numerous local to global scale vegetation time series studies during recent years. AVHRR Pathfinder (PAL) NDVI was available from 1981 until 2001, and the new AVHRR GIMMS NDVI was available from 1981 to the present time. A number of aspects potentially introduce noise in the NDVI data set due to the AVHRR sensor design and data processing. NDVI from SPOT‐4 VGT data is considered an improvement over AVHRR, and for this reason it is important to examine how and if the differences in sensor design and processing influence continental scale NDVI composite products. In this study, the quality of these AVHRR NDVI time series are evaluated by the continental scale 1 km resolution SPOT‐4 vegetation (VGT) 10‐day composite (S10) NDVI data. Three years of AVHRR PAL (1998–2000) and seven years of GIMMS (1998–2004) have been compared to 8 km resampled SPOT‐4 VGT (1998–2004) data. The dynamic range of SPOT‐4 VGT NDVI tends to be higher than the AVHRR PAL NDVI, whereas there is an exact match between AVHRR GIMMS NDVI and SPOT‐4 VGT NDVI. Ortho‐regression analysis on annually integrated values of AVHRR PAL/GIMMS and SPOT‐4 VGT on a continental scale reveals high correlations amongst the AVHRR and the SPOT data set, with lowest RMSE (root mean square error) on the GIMMS/SPOT‐4 VGT compared to the PAL/SPOT‐4 VGT.

Analyses on decade data likewise show that a linear relation exists between Spot‐4 VGT NDVI and the two AVHRR composite products; GIMMS explaining most of the Spot‐4 VGT NDVI variance compared to PAL. These results show that the AVHRR GIMMS NDVI is more consistent with Spot‐4 VGT NDVI compared to AVHRR PAL versus Spot‐4 VGT NDVI (in terms of RMSE and dynamic range) and can therefore be considered the more accurate long time AVHRR data record. Analyses performed on monthly maximum composites and decade composite data, however, reveal intra‐annual variations in the correlation between SPOT‐4 VGT and the two AVHRR data sets, which are attributed to different cloud masking algorithms. The SPOT‐4 VGT cloud‐screening algorithm is insufficient, thereby suppressing the rainy season NDVI.     

An empirical model for estimating fracture toughness using the DCDC geometry

The double cleavage drilled compression (DCDC) geometry is useful for creating large cracks in a material in a controlled manner. Several models for estimating fracture toughness from DCDC measurements have been proposed, but each is suitable for a subset of geometries and material properties. In this work, a series of finite element fracture simulations are performed over a range of sample widths, hole sizes, heights, Young’s moduli, Poisson’s ratios, critical stress intensity factors, and boundary conditions. Analyzing the simulation results, fracture toughness is found to be a simple function of sample width, hole size, and an extrapolated stress at zero crack length obtained from a linear fit of the data. Experimental results in the literature are found to agree with this simple relationship.     

High-performance ambipolar diketopyrrolopyrrole-thieno[3,2-b]thiophene copolymer field-effect transistors with balanced hole and electron mobilities

Ambipolar OFETs with balanced hole and electron field-effect mobilities both exceeding 1 cm(2) V(-1) s(-1) are achieved based on a single-solution-processed conjugated polymer, DPPT-TT, upon careful optimization of the device architecture, charge injection, and polymer processing. Such high-performance OFETs are promising for applications in ambipolar devices and integrated circuits, as well as model systems for fundamental studies.     

Preparation of ester terminated poly(alkyl vinyl ether) oligomers and block copolymers using a combination of living cationic and group transfer polymerization

Summary This paper reports the synthesis and characterization of new, functionalized poly(alkyl vinyl ether) oligomers, and block copolymers containing poly(alkyl vinyl ether) and poly(methyl methacrylate). Using the HI/ZnI₂ initiating system in nonpolar solvents (hexane, toluene) at -15 °C, both monofunctional and difunctional poly(alkyl vinyl ether) oligomers of predicted molecular weights precisely terminated with ester end groups have been prepared. Novel diblock copolymers comprised of poly(methyl methacrylate) and poly(alkyl vinyl ether) have also been synthesized using a combination of living cationic and living group transfer polymerization (GTP) techniques.     

Introduction: Perspectives on Cold War Science in Small European States

With this introduction we aim to illuminate Western Europe's place on the map of Cold War science and, specifically, to draw attention to the differences in and the diversity of Western European Cold War science in comparison to the United States. By discussing narratives of Cold War science in small states and asking how they fit into the European condition, we suggest that the fact of being a small state affects the conditions for and the scope of Cold War science. As a whole, this special issue also emphasizes the importance of the spatial dimension; that is, the significant dependence of Cold War science on geographical relations and geopolitical interests.     

Fourier transform Raman difference spectroscopy for detection of lignin oxidation products in thermomechanical pulp

Spruce thermomechanical pulp (TMP) was oxidized by the 2,2'azinobis-3-ethylbenzthiazoline-6-sulfonate cation radical (ABTS*+) in the presence and absence of oxygen. The pulp modification was monitored by Fourier transform (FT) Raman difference spectroscopy and other nondestructive spectroscopic methods. The ABTS*+ oxidative system resulted in modifications very similar to the laccase-ABTS-oxygen system, except for the FT-Raman results, which showed a difference in mechanisms attributed to a difference in produced Raman bands. Oxygen resulted in no oxygen-derived products, but only enhanced the production of a specific Raman band of several oxidation-produced bands. Detailed information on lignin reactions can be obtained from FT-Raman signals.     

Technological Trajectories in the Making: Two Case Studies from the Contemporary History of Wind Power

This paper traces the origins of two technological trajectories in the contemporary history of wind power technology: the American Smith‐Putnam Wind Turbine and the Danish Gedser Wind Turbine. Describing the two wind turbine projects in terms of their technical design characteristics, the professional background of the individuals involved, the organizational features of the technological knowledge production, and the historical context, the paper builds on the notion of technological trajectories in the making as a means of identifying emerging selection mechanisms for possible engineering problem solutions, scientific methods, material artifacts, and financial assessment techniques. Conceived during the Great Depression and World War II, respectively, both projects promoted the idea that wind power could make a cost‐effective contribution to the existing electric utility system. The two projects resulted in distinctive wind turbine innovations that paved the way for two technological trajectories in the contemporary history of wind power. Studying the emergence of technological trajectories, it is argued, requires the historian of technology to attend to well‐known features of technological design and its cultural context that in retrospect appear to be significant, but also to tackle the creation of novelty and the inevitability of technological uncertainties about which the logic of trajectories has little to say.     

A self-calibrating robot based upon a virtual machine model of parallel kinematics

A delta-type parallel kinematics system for Additive Manufacturing has been created, which through a probing system can recognise its geometrical deviations from nominal and compensate for these in the driving inverse kinematic model of the machine. Novelty is that this model is derived from a virtual machine of the kinematics system, built on principles from geometrical metrology. Relevant mathematically non-trivial deviations to the ideal machine are identified and decomposed into elemental deviations. From these deviations, a routine is added to a physical machine tool, which allows it to recognise its own geometry by probing the vertical offset from tool point to the machine table, at positions in the horizontal plane. After automatic calibration the positioning error of the machine tool was reduced from an initial error after its assembly of ±170?µm to a calibrated error of ±3?µm. Excelling by speed, the calibration was executed in less than 3?min.