Comparison of different methods to calibrate torsional spring constant and photodetector for atomic force microscopy friction measurements in air and liquid

A number of atomic force microscopy cantilevers have been exhaustively calibrated by a number of techniques to obtain both normal and frictional force constants to evaluate the relative accuracy of the different methods. These were of either direct or indirect character-the latter relies on cantilever resonant frequencies. The so-called Sader [Rev. Sci. Instrum. 70, 3967 (1999)] and Cleveland [Rev. Sci. Instrum. 64, 403 (1993)] techniques are compared for the normal force constant calibration and while agreement was good, a systematic difference was observed. For the torsional force constants, all the techniques displayed a certain scatter but the agreement was highly encouraging. By far the simplest technique is that of Sader, and it is suggested in view of this validation that this method should be generally adopted. The issue of the photodetector calibration is also addressed since this is necessary to obtain the cantilever twist from which the torsional force is calculated. Here a technique of obtaining the torsional photodetector sensitivity by combining the direct and indirect methods is proposed. Direct calibration measurements were conducted in liquid as well as air, and a conversion factor was obtained showing that quantitative friction measurements in liquid are equally feasible provided the correct calibration is performed.     

Design of Embedded Filters for Inner‐Loop Power Control in Wireless CDMA Communication Systems

We study inner‐loop power control for mobile wireless communication systems using code division multiple access transmission. We focus on the uplink, i.e., on communication from the mobile‐ to the base‐station, and show how to minimise the variance of the signal‐to‐interference ratio (SIR) tracking error through incorporation of recursive filters. These filters complement existing power controllers and are designed by using a linear model which takes into account quantisation of the power control signal, dynamics of channel gains, interference from other users, target SIR, and SIR estimation errors. Simulation results indicate that significant performance gains can be obtained, even in situations where the models used for design are only an approximation. Copyright © 2011 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society     

Variations in fuel characteristics of corn (Zea mays) stovers: General spatial patterns and relationships to soil properties

The geographic variations in corn stover fuel and soil characteristics from 22 sites in the Kerchin region (43.8–45.0°N, 122.7–125.1°E), north-east China, were examined in both 2006 and 2007. The correlations between fuel characteristics and soil parameters were analysed using principal component analysis (PCA) and partial least squares regression (PLS). The main emphasis was on the feasibility of using corn stovers as feedstock in direct combustion for heat and power generation. The examined corn stovers from Kerchin generally have similar characteristics to energy grasses grown in Europe and may be used as biofuels. However, large variations, up to several orders of magnitude, in the fuel characteristics existed among the samples. With PCA, the studied soils showed a clear distinction between soluble and less soluble elements, with a trend for higher insoluble element (such as Si) concentrations in south-western soils and a higher pH in the more northern soils. The component for fuel characteristics showed a distinct trend with latitude that can be explained by the above-mentioned soil component pattern. PLS regression models suggested some important relationships that may be used to predict corn stover fuel characteristics using soil and environment properties; for example, latitude, soil pH and Si are the most important predictors for Ca content in corn stovers, but not for K that is best predicted by soil K. Although limited by numbers of samples and sites, this study indicated that this approach can be used to predict biofuel quality.     

Exploring the phenomenon of company-specific production systems: one-best-way or own-best-way?

This explorative study investigates the phenomenon of the company-specific production system (XPS). It has been a strong and recent trend across many manufacturing industries to develop and deploy such a corporate improvement programme. Five propositions regarding the uniqueness of XPSs are derived from universalistic versus contingent perspectives on improvement programmes. The main XPS principles of 30 renowned multinationals are analysed for similarities and differences. In conclusion, XPSs largely represent variants of the same in content. They represent an own-best-way approach to the one-best-way paradigm. Even though a tight relationship to the Toyota Production System (TPS) and lean production is established, the findings raise a red flag that XPSs might suffer under a too rigid, path-dependent development process from what has become an overly technical understanding of the TPS. This study also questions whether modern manufacturers have sufficiently integrated other essential elements of modern operations such as the use of ERP, automation and real-time response technologies in their XPSs. These findings have direct implications for practitioners and provide interesting opportunities for further research.     

Allocation of Link Flow Detectors for Origin‐Destination Matrix Estimation—A Comparative Study

Abstract: Origin‐destination (OD) matrices are essential for various analyses in the field of traffic planning, and they are often estimated from link flow observations. We compare methods for allocating link flow detectors to a traffic network with respect to the quality of the estimated OD‐matrix. First, an overview of allocation methods proposed in the literature is presented. Second, we construct a controlled experimental environment where any allocation method can be evaluated, and compared to others, in terms of the quality of the estimated OD‐matrix. Third, this environment is used to evaluate and compare three fundamental allocation methods. Studies are made on the Sioux Falls network and on a network modeling the city of Linköping. Our conclusion is, that the most commonly studied approach for detector allocation, maximizing the coverage of OD‐pairs, seems to be unfavorable for the quality of the estimated OD‐matrix.     

Effects of gadolinium oxide nanoparticles on the oxidative burst from human neutrophil granulocytes

We have previously shown that gadolinium oxide (Gd(2)O(3)) nanoparticles are promising candidates to be used as contrast agents in magnetic resonance (MR) imaging applications. In this study, these nanoparticles were investigated in a cellular system, as possible probes for visualization and targeting intended for bioimaging applications. We evaluated the impact of the presence of Gd(2)O(3) nanoparticles on the production of reactive oxygen species (ROS) from human neutrophils, by means of luminol-dependent chemiluminescence. Three sets of Gd(2)O(3) nanoparticles were studied, i.e. as synthesized, dialyzed and both PEG-functionalized and dialyzed Gd(2)O(3) nanoparticles. In addition, neutrophil morphology was evaluated by fluorescent staining of the actin cytoskeleton and fluorescence microscopy. We show that surface modification of these nanoparticles with polyethylene glycol (PEG) is essential in order to increase their biocompatibility. We observed that the as synthesized nanoparticles markedly decreased the ROS production from neutrophils challenged with prey (opsonized yeast particles) compared to controls without nanoparticles. After functionalization and dialysis, more moderate inhibitory effects were observed at a corresponding concentration of gadolinium. At lower gadolinium concentration the response was similar to that of the control cells. We suggest that the diethylene glycol (DEG) present in the as synthesized nanoparticle preparation is responsible for the inhibitory effects on the neutrophil oxidative burst. Indeed, in the present study we also show that even a low concentration of DEG, 0.3%, severely inhibits neutrophil function. In summary, the low cellular response upon PEG-functionalized Gd(2)O(3) nanoparticle exposure indicates that these nanoparticles are promising candidates for MR-imaging purposes.     

Controlling the charge of a specific surface atom by the addition of a non-site-specific single impurity in a Si nanocrystal

We show, by use of self-consistent calculations, that the charge on a radical surface site (RSS) on a hydrogen-terminated silicon nanocrystal can be controlled by the addition of a non-site-specific dopant atom. An RSS is a surface defect where the H-termination is missing. This new effect has important implications for future hybrid semiconductor/molecular nanoelectronics. We also calculate the energy and wave function of the RSS state and its nanoscale interactions with the dopant atom.     

A longitudinal and cross-sectional study of Swedish biomedical PhD processes 1991–2009 with emphasis on international and gender aspects

This longitudinal survey of Swedish biomedical PhDs from 1991 to 2009 found a 2.5-fold increase in biomedical PhD graduates, especially women, and mainly non-MDs, while the number of MDs remained fairly constant. The proportion obtaining a biomedical PhD in Sweden in 2006 was two and a half times that in USA compared to population and three and a half times by GDP, but similar to that of the Netherlands. Female non-MD but not female MD candidates were more likely than men to be examined by female examiners. Fewer of the non-MD than MD women continued to publish in English after their PhD. The median number of authors per paper in a thesis had increased by 1 (from 4 to 5) compared with 15–20 years ago. Swedish biomedical research was already well internationalized in 1991, when 38% of the external examiners came from abroad. This rose to 53% in 2003 but in 2009 had returned to 42%. USA and UK were the most common countries but Australia accounted for 2%. When assessed by connection with foreign research teams, Swedish researchers were also internationally well connected. Studies in other countries are needed to assess how generally applicable these findings are. Our findings suggest that the policy and management of Swedish scientific research systems needs revision to harmonize with the national economic capacity.