A low-cost 2D fluorescence detection system for μm sized beads on-chip

In this paper we describe a compact fluorescence detection system for on-chip analysis of beads, comprising a low-cost optical HD-DVD pickup. The complete system consists of a fluorescence detection unit, a control unit and a microfluidic chip containing microchannels and optical markers. With these markers the laser beam of the optical pickup can be automatically focused at the centre of the microchannel. With the complete system a two-dimensional fluorescent profile across the channel width can be obtained such that there is no need for hydrodynamic or electrokinetic focusing of the particles in a specific part of the channel. Fluorescent μm sized beads suspended in medium have been detected with the system. Since on both sides of the main beam two additional laser beams at a known distance are generated, also the velocity of individual beads has been determined.     

Communication and Cooperation in Public Network Situations

This paper focuses on sharing the costs and revenues of maintaining a public network communication structure. Revenues are assumed to be bilateral and communication links are publicly available but costly. It is assumed that agents are located at the vertices of an undirected graph in which the edges represent all possible communication links. We take the approach from cooperative game theory and focus on the corresponding network game in coalitional form which relates any coalition of agents to its highest possible net benefit, i.e., the net benefit corresponding to an optimal operative network. Although finding an optimal network in general is a difficult problem, it is shown that corresponding network games are (totally) balanced. In the proof of this result a specific relaxation, duality and techniques of linear production games with committee control play a role. Sufficient conditions for convexity of network games are derived. Possible extensions of the model and its results are discussed. The research of Jeroen Suijs has been made possible by a fellowship of the Royal Netherlands Academy of Arts and Sciences.     

Fast atom bombardment mass spectrometry of hydroxybenzoic acids

Summary Ten hydroxybenzoic acids were analysed by positive and negative-ion fast atom bombardment mass spectrometry. FAB-MS of all acids investigated gave intense (M+H)⁺ or (M-H)^– ion peaks. Isomers could be distinguished by the metastabile ion or collisional activation spectra of selected ions, except for m- and p-hydroxybenzoic acid. These compounds could be distinguished, however, by the charge stripping spectra of the (M-H)^– ions.

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FAB-Massenspektrometrie von Hydroxybenzoesäuren

Zusanunenfassung Zehn Hydroxybenzoesäuren wurden mit Hilfe der FAB-Massenspektrometrie (positive und negative Ionen) analysiert. Alle untersuchten Säuren ergaben intensive (M+H)⁺-oder (M–H)^–-Ionenpeaks. Isomere konnten mit Hilfe der Spektren metastabiler Ionen oder von Kollisions-Aktivierungsspektren ausgewahlter Ionen unterschieden werden, außer m- und p-Hydroxybenzoesäure, die durch Charge-stripping-Spektren der (M-H)^–-Ionen unterschieden wurden.

     

The giant muon Knight shift in antimony: Evidence for a Kondo impurity

A detailed study has been undertaken of the muon Knight shift in high purity antimony single crystals. No periodic variations with magnetic field (de Haas–van Alphen oscillations) are observed. The temperature dependence below 175 K is close to that expected for a Kondo‐like impurity with an anisotropic muon–electron hyperfine interaction. At higher temperatures the paramagnetic state becomes unstable and a transition occurs to a second state. The longitudinal relaxation rate rises from an apparently non‐zero value at T=0 to a maximum at 50 K, followed by a slow decline. This leads to a Korringa product which is strongly temperature dependent. This revised version was published online in August 2006 with corrections to the Cover Date.     

Heterogeneous cost sharing, the directional serial rule

The directional serial rule is introduced as a natural serial extension, generalizing the Moulin–Shenker cost sharing rule to heterogeneous cost sharing models. It is the unique regular rule compatible with the radial serial principle. In particular, this shows the incompatibility of the serial principle with differentiability of a cost sharing rule as a function of the individual demands.I would like to thank the editor and the referee for their comments which have been most useful.     

Micro-heterogeneity study of trace elements in BCR CRM 680 by means of synchrotron micro-XRF

BCR CRM 680 is a newly released reference material (RM) with a polyolefinic matrix, doped with various metallic compounds in trace concentrations, to be used for calibration of multi-element trace analytical methods. The micro-heterogeneity of this new CRM was investigated to evaluate the suitability as a RM for trace-level micro analytical techniques. Synchrotron micro-XRF, a trace-level micro analytical method, allows to quantitatively measure the degree of heterogeneity of inorganic trace constituents in solid materials with a homogeneous matrix. The procedure for calculating the minimal sampling mass for homogeneous measurements was employed for BCR CRM 680. By repeating the entire procedure on several samples of the same material, the repeatability of the micro-heterogeneity characterization based on micro-XRF was investigated. Afterwards, the micro-heterogeneity results from the BCR CRM 680 material were used to evaluate the suitability of the micro-heterogeneity procedure by means of a Monte Carlo simulation model. Also the existence of nuggets in the polymer material is looked into.     

Multiple solid-phase microextraction of drugs from human urine

Summary The applicability of multiple solid-phase microextraction to the analysis of biological samples has been shown by extraction of a variety of compounds from human urine. Multiple solid-phase microextraction, in which extraction and desorption are repeated and analytes are collected at the head of the separation system before starting the analysis, has been combined with gas chromatography. Amphetamine, lidocaine, procaine, and mepivacaine were extracted from buffered urine by direct immersion of a 100-μm polydimethylsiloxane-coated fiber, to demonstrate that multiple SPME can be used for analytes with different extraction behavior. Multiple solid-phase microextraction was optimized for high extraction yield or short extraction time. For example, the total sample-handling time (extraction plus desorption) for the extraction of mepivacaine from urine can be reduced from approximately 60 min (one extraction) to 33 min (three extractions) without reducing extraction yield. In addition, the extraction yield for mepivacaine can be increased from 14.6% (one extraction) to 27.0% (five extractions) within the same total sample handling time of approximately 60 min. A good match between theoretical and experimental values was obtained. Chromatograms are shown to illustrate the usefulness of the procedure.     

On the Convergence and Stability of a Pressure–Velocity Iteration of Chorin Type with Natural Boundary Conditions

Because of the implementation of numerical solution algorithms for the nonstationary Navier–Stokes equations of an incompressible fluid on massively parallel computers iterative methods are of special interest.

A red–black pressure–velocity iteration that allows an efficient parallelization based on a domain decomposition [3 G. Bärwolff and H. Schwandt ( 1996 ). A parallel domain decomposition algorithm in 3D turbulence modeling . In : Proceedings of the Int. Conf. on Parallel and Distributed Processing Techniques and Applications (PDPTA’96), August 8–11, 1996, Sunnyvale/CA . USA (Ed. H. Arabnia ), CSREA Press , pp. 44 – 45 . [Google Scholar]] will be analyzed in this paper.

We prove the equivalence of the pressure–velocity iteration (PUI) by Chorin/Hirt/Cook [1 A.J. Chorin ( 1968 ). Numerical Solution of the Navier–Stokes equations . Comp. Math. 22 : 745 – 762 .[Crossref] , [Google Scholar], 2 C.W. Hirt and J.L. Cook ( 1972 ). Calculating three-dimensional flows around structures and over rough terrain . J. Comp. Phy. 10 : 324 – 340 .[Crossref], [Web of Science ®] , [Google Scholar]] with a SOR iteration to solve a Poisson equation for the pressure. We show this on a 2D rectangle with some special outflow boundary conditions and Dirichlet data for the velocity elsewhere. This equivalence allows us to prove the convergence of that iteration scheme. We also discuss the stability of the occurring discrete Laplacian in discrete Sobolev spaces.     

Robust flows over time: models and complexity results

Mathematical Programming - The problem of finding a zero of the sum of two maximally monotone operators is of central importance in optimization. One successful method to find such a zero is the...