Identifying core documents with a multiple evidence relevance filter

A method to identify core documents within a given subject domain has been developed by the author. The method builds on the concept of polyrepresentation by using different search rationales in several databases and isolating the overlaps between them. This paper delineates the ideas behind the method and describes the study done to measure its effectiveness. This revised version was published online in June 2006 with corrections to the Cover Date.     

The effect of backbone fluorination on the carrier mobility in alkoxy and alkyl substituted conducting polymers of the poly(phenylenevinylene) type

Summary We report the synthesis of some new backbone fluorinated polymers of the poly(phenylenevinylene) type. The new polymers were characterised by NMR, SEC and X-ray powder diffraction. The charge carrier mobilities were determined using pulse radiolysis time resolved microwave conductivity (PR-TRMC) and the carrier mobilities were compared to the similar non-fluorinated analogues. The changes in charge carrier mobilities as a function of molecular substitution pattern is discussed in terms of other materials properties such as electronic structure and absorption properties. The major result is that it was found possible for this type of material to alter the electronic energy levels by molecular substitution without imparting significant changes in the magnitude of the charge carrier mobilities and the optical properties.     

The influence of urea on lipogenesis in renal papillae of rats

The osmolality has been determined for the papillary interstitial fluids obtained from the isolated papillae of rats in different states of water balance. Hypertonic buffers for in vitro experiments were prepared by addition of urea to regular Krebs-Ringer phosphate buffers (340 mosmol/kg H₂O) since urea is the most changeable solute of the renal papillary tissue in response to external influences. The effect of such hypertonic buffers on papillary lipogenesis was very pronounced. The fatty acid synthesis from acetate decreased by a factor of 7–9 in response to increased osmolality from 340 to 1370 mosmol/kg H₂O. In the physiological range of osmolalities (500–1800 mosmol/kg H₂O), the de novo synthesis of papillary glycerolipids from glucose decreased by a factor of ca. 5. A possible specific inhibitory effect of hypertonic buffers on the pentose phosphate cycle was studied with a negative result. It is concluded that the addition of urea causes a decrease of total energy metabolism in the tissue.     

High‐ versus Low‐Quality Graphene: A Mechanistic Investigation of Electrografted Diazonium‐Based Films for Growth of Polymer Brushes

Electrografting using aryldiazonium salts provides a fast and efficient technique to functionalize commercially available 3?5 layered graphene (vapour‐deposited) on nickel. In this study, Raman spectroscopy is used to quantify the grafting efficiency of cyclic voltammetry which is one of the most versatile, yet simple, electrochemical techniques available. To a large extent the number of defects/substituents introduced to the basal plane of high‐quality graphene by this procedure can be controlled through the sweeping conditions employed. After extended electrografting the defect density reaches a saturation level (～10¹³ cm^?2) which is independent of the quality of the graphene expressed through its initial content of defects. However, it is reached within fewer voltammetric cycles for low‐quality graphene. Based on these results it is suggested that the grafting occurs (a) directly at defect sites for, in particular, low‐quality graphene, (b) directly at the basal plane for, in particular, high‐quality graphene, and/or (c) at already grafted molecules to give a mushroom‐like film growth for all films. Moreover, it is shown that a tertiary alkyl bromide can be introduced at a given surface density to serve as radical initiator for surface‐initiated atom transfer radical polymerization (SI‐ATRP). Brushes of poly(methyl methacrylate) are grown from these substrates, and the relationship between polymer thickness and sweeping conditions is studied.     

Specificities of red cell membrane sites transporting three long chain fatty acids

We studied the specificities of human red cell membrane bindings of three long chain fatty acids, palmitic- arachidonic- and oleic acid, using resealed membranes, ghosts. Previously estimated binding capacities, affinities and inside/outside distributions suggest separated binding sites. This possibility is explored by estimating the binding properties of one fatty acid in the presence of one or two of the others. Binding capacities, nmol g-1 ghosts, of palmitic and arachidonic acid estimated simultaneously vs. separately are 27.4 +/- 2.7 vs. 29.0 +/- 2.1 (P < 0.6) and 6.5 +/- 0.6 vs. 5.5 +/- 0.5 (P < 0.2) respectively. The corresponding estimates for oleic- and palmitic acid are 36.5 +/- 2.0 vs. 34.0 +/- 2.2 (P < 0.4) and 28.4 +/- 1.8 versus 29.1 +/- 2.1 (P < 0.8). The binding sites are therefore independent. For each of the three fatty acids in the absence or in the presence of one or two of the others, the inside/outside distributions of the binding sites and the membrane transfer rate constants are elucidated by exchange efflux kinetics at 0 degrees C from ghosts with and without enclosed albumin. Packed ghosts loaded with radioactive acids are injected rapidly into a large volume of vigorously stirred buffer with albumin. With a resolution time of about 1-sec serial filtered ghost-free aliquots are collected and counted. The analyses show that palmitic- and oleic acid sites of transport are entirely independent but do not exclude that palmitic- and/or oleic acid binding may diminish the arachidonic acid affinity a little. The diversity combined with specificity suggests that the transport sites for long chain fatty acids are protein-determined microdomains of phospholipids.     

Elasticity,hardness, and fracture toughness of sodium aluminoborosilicate glasses

Due to an increasing demand for oxide glasses with a better mechanical performance, there is a need to improve our understanding of the composition-structure-mechanical property relations in these brittle materials. At present, some properties such as Young's modulus can to a large extent be predicted based on the chemical composition, while others—in particular fracture-related properties—are typically optimized based on a trial-and-error approach. In this work, we study the mechanical properties of a series of 20 glasses in the quartenary Na₂O–Al₂O₃–B₂O₃–SiO₂ system with fixed soda content, thus accessing different structural domains. Ultrasonic echography is used to determine the elastic moduli and Poisson's ratio, while Vickers indentation is used to determine hardness. Furthermore, the single-edge precracked beam method is used to estimate the fracture toughness (K_Ic) for some compositions of interest. The compositional evolutions of Vickers hardness and Young's modulus are in good agreement with those predicted from models based on bond constraint density and strength. Although there is a larger deviation, the overall compositional trend in K_Ic can also be predicted by a model based on the strength of the bonds assumed to be involved in the fracture process.     

A self‐calibrating led‐based solar test platform

A compact platform for testing solar cells is presented. The light source comprises a multi‐wavelength high‐power LED (light emitting diode) array allowing the homogenous illumination of small laboratory solar cell devices (substrate size 50 × 25 mm) within the 390–940 nm wavelength range. The spectrum can be synthesized by independent tuning of the 18 different wavelengths to mimic AM1.5G as well as various indoor lamp spectra. The intensity can be controlled with a 2¹⁴‐bit accuracy and intensities up to 3 suns are possible with an approximate AM1.5G spectral distribution. For several wavelengths intensities up to 10 suns is possible, and for a few wavelengths up to 30 suns can be reached. The setup is equipped with reference diodes and an optical fibre coupling enabling calibration, monitoring and control of the light impinging on the sample. Through a computer controlled interface, it is possible to perform all the commonly employed measurements on the solar cell at very high speed without moving the sample. In particular, the LED‐based illumination system provides an alternative to light‐biased incident photon‐to‐current efficiency measurement to be performed which we demonstrate. Both top and bottom contact is possible and the atmosphere can be controlled around the sample during measurements. The setup was developed for the field of polymer and organic solar cells with particular emphasis on enabling different laboratories to perform measurements in the same manner and obtain a common basis for comparing data. The use of the platform is demonstrated using a standard P3HT:PCBM polymer solar cell but is generally applicable to any solar cell technology with a spectral response in the 390–950 nm region. Copyright © 2010 John Wiley & Sons, Ltd.     

Considerations on Probe Design for Affinity-Guided Protein Conjugation

The plethora of methods developed for the creation of protein conjugates often differs significantly with regard to the heterogeneity of the resulting products, in the degree of genetic manipulation of the protein required, and in the technical skills required to perform the conjugation procedure. Affinity-guided protein conjugation is a protein labeling methodology based on noncovalent binding interactions between a labeling probe and the protein of interest. These interactions increase the local concentration of a reactive group in the probe on the protein surface thus facilitating the conjugation in proximity of the complexation site. The ability to produce high-quality conjugates from nongenetically modified proteins both in vitro, but also in cells, demonstrates the power of affinity-guided protein conjugation. Here, we present the progress of affinity-guided protein conjugation in relation to selective protein labeling in living systems and the formation of high-quality protein conjugates. Furthermore, the probe design will be discussed in relation to the utility of the probe for labeling in vitro or in living systems.     

Performance Comparison of Controllers with Fault-Dependent Control Allocation for UAVs

This paper combines fault-dependent control allocation with three different control schemes to obtain fault tolerance in the longitudinal control of unmanned aerial vehicles. The paper shows that fault-dependent control allocation is able to accommodate actuator faults that would otherwise be critical and it makes a performance assessment for the different control algorithms: an \(\mathcal {L}_{1}\) adaptive backstepping controller; a robust sliding mode controller; and a standard PID controller. The actuator faults considered are the partial to total loss of the elevator, which is a critical component for the safe operation of unmanned aerial vehicles. During nominal operation, only the main actuator, namely the elevator, is active for pitch control. In the event of a partial or total loss of the elevator, fault-dependent control allocation is used to redistribute control to available healthy actuators. Using simulations of a Cessna 182 aircraft model, controller performance and robustness are evaluated by metrics that assess control accuracy and energy use. System uncertainties are investigated over an envelope of pertinent variation, showing that sliding mode and \(\mathcal {L}_{1}\) adaptive backstepping provide robustness, where PID control falls short. Additionally, a key finding is that the fault-dependent control allocation is instrumental when handling actuator faults.