Single-bonded cubic form of nitrogen

Nitrogen usually consists of molecules where two atoms are strongly triple-bonded. Here, we report on an allotropic form of nitrogen where all atoms are connected with single covalent bonds, similar to carbon atoms in diamond. The compound was synthesized directly from molecular nitrogen at temperatures above 2,000 K and pressures above 110 GPa using a laser-heated diamond cell. From X-ray and Raman scattering we have identified this as the long-sought-after polymeric nitrogen with the theoretically predicted cubic gauche structure (cg-N). This cubic phase has not been observed previously in any element. The phase is a stiff substance with bulk modulus >or=300 GPa, characteristic of strong covalent solids. The polymeric nitrogen is metastable, and contrasts with previously reported amorphous non-molecular nitrogen, which is most likely a mixture of small clusters of non-molecular phases. The cg-N represents a new class of single-bonded nitrogen materials with unique properties such as energy capacity: more than five times that of the most powerfully energetic materials.     

A comparative evaluation of length estimators of digital curves

This paper compares previously published length estimators in image analysis having digitized curves as input. The evaluation uses multigrid convergence (theoretical results and measured speed of convergence) and further measures as criteria. This paper also suggests a new gradient-based method for length estimation, and combines a previously proposed length estimator for straight segments with a polygonalization method.     

Development of a class-specific ELISA for sulfonylurea herbicides (sulfuron screen)

The development of a direct competitive ELISA for the detection of a broad range of sulfonylurea herbicides (SUs) is described. Polyclonal antibodies were generated in rabbits using three different immunizing haptens. Antiserum with the broadest specificity was obtained with a mesosulfuronbenzylamine derivative which was coupled via a succinic acid spacer to keyhole limpet hemocyanine. A heterologous enzyme tracer which did not contain the succinic acid bridge was prepared using activated horseradish peroxidase. The direct competitive ELISA was optimized and applied for spiked tap and surface water samples. From 30 SUs, 8 compounds showed a molar cross-reactivity (CR) higher than 100% (this value was set for the hapten) and 11 compounds CRs between 10% and 100%. The ELISA can detect 16 SUs at a concentration of 0.1 microg/L or lower. Different surface and tap water samples were spiked with chlorimuron ethyl, metsulfuron methyl, or primisulfuron methyl at concentrations of 100, 200, or 500 ng/L and subsequently analyzed by both ELISA and HPLC-UV. Correlation analysis revealed good agreement between both methods (r2 = 0.983/0.948/0.982; n = 21 for each analyte). Using ELISA, no sample pretreatment other than filtration was necessary.     

Microanalysis by laser-induced plasma spectroscopy in the vacuum ultraviolet

A new setup for microanalysis by laser-induced plasma spectroscopy in the VUV range is presented and described in detail. The system features an integrated ablation and detection module with a newly designed VUV echelle system. The echelle permits a full spectral coverage between 150 and 300 nm with a resolving power lambda/Deltalambda between 11,000 and 15,000. At present, the ablation module permits a microanalysis with a crater size of 25 microm and a nominal depth resolution with an ablation rate of 150 nm/pulse. The VUV performance was demonstrated for bulk analysis of steel; detection limits for sulfur, carbon, and phosphorus were in the lower milligram per kilogram range. The VUV scanning and mapping performance for heterogeneous matrixes was illustrated for mineral bottom ash samples from a waste incineration process.     

Studies on the structure and behaviour of reactively sputtered iron oxide layers on steel surfaces

In a simple diode system for asymmetric radio frequency sputtering, steel specimens were covered with iron oxide and the corrosion behaviour was studied by electrochemical methods. The specimens, which were covered with a compact layer of Fe₂O₃, had film resistances of 10⁸–10¹⁵ Ω cm, due to the conditions of production and the purity of the target material. Potentiometric measurements on steel electrodes covered with quasi-crystalline α-Fe₂O₃ showed a distinct passivation of the basic material in neutral and slightly acid media. An outlook is given concerning future fundamental studies on this problem.     

Partikelgrößenanalysen < 10 μm Meßmethoden und Schwierigkeiten

Particle size analysis of particles < 10 μm – methods and difficulties . A review of possible methods for the determination of particle size distributions in the range < 10 μm is presented. Important factors regarding the specimen dispersion are dealt with, particularly those which must be taken into consideration in the “fines” region, and the limits and difficulties of individual analytical equipment are illustrated with the aid of examples. Finally, analytical results obtained by various methods of measurement are compared and the criteria of assessment such as operational possibility and costing are discussed.     

Oxygen determination in oxygen-supersaturated drinking waters by NMR relaxometry

In recent years, a rising number of different table waters supersaturated with oxygen have hit the market with claims of both positive health effects and an increase in athletic performance. In addition to research on the correctness of these claims and their possible physiological reasons, the appearance of oxygen supersaturation as a marketing promise also creates a need for appropriate analytical techniques allowing a rapid and reliable determination of oxygen contents in such waters. Here, we present NMR relaxometry as a possible analytical tool for such studies. NMR relaxation in oxygen supersaturated water is not only of interest in the context of monitoring the oxygen content in such drinking water products, but also might offer some interesting possibilities in medical and environmental science MRI applications. As a contact-less measuring method, NMR relaxometry avoids disturbance of the measurement due to outgassing. The method was applied in the concentration range from 10 mg l(-1) to over 100 mg l(-1) dissolved oxygen. In addition to freshly sampled drinking waters, also oxygen losses during storage of the water in open drinking vials was studied.     

Microarrays for the screening of allergen-specific IgE in human serum

The described in vitro test system for allergy diagnosis is based on microscope glass slides activated with (3-glycidyloxypropyl)trimethoxysilane. Allergen solutions are immobilized as small droplets (approximately 10 nL) on the activated glass slides with a piezoelectric arrayer. In contrast to other tests for specific IgE, such as Pharmacia CAP FEIA, AlaSTAT, or FAST, only a 25-microL serum sample is needed for the screening of allergen-specific IgE against a multitude of allergens and the test can be performed in less than 1 h. Compared with multiallergen dipstick screening tests (e.g., IgEquick, CMG Immunodot) based on multiallergen-coated nitrocellulose strips, the measurement of the microarray-based system can be performed automatically. The chemiluminescence intensities are detected with a sensitive CCD camera. Allergen extracts and recombinant/purified allergens (24 preparations) have been used on the same modified surface for the screening of allergen-specific IgE. With these disposable microarray slides, it is possible to distinguish between patients with and without elevated levels of allergen-specific IgE. Repeated measurements of serum samples demonstrated a sufficient reproducibility. Detection limits (microg/L) of 0.35 (r Betvl), 0.16 (PLA2), and 1.9 (Der p1) were achieved.     

Cost accounting for shared IT infrastructures

IT infrastructure, such as servers and networking equipment, accounts for a large proportion of the IT costs in modern organizations. Typically, this IT infrastructure is shared among multiple applications and customers. Cost allocation of shared IT infrastructure is difficult and regularly based on biased cost allocation keys, which often causes free-rider problems. Measuring usage is technically difficult and incurs high costs. In this paper we propose a method to derive adequate estimators for the resource consumption of a customer-oriented service. These so-called resource profiles can then provide a basis for cost allocation keys. The estimators are derived from a series of load tests, as they are typically done before an application is launched in larger organizations. Such profiles need to be unbiased and precise even in cases of varying workloads and in rather heterogeneous environments. We describe the results of a set of experiments in an infrastructure provided by the BMW Group, and illustrate how the estimation can be integrated into existing IT service management processes. In our experiments we use Queuing Networks to validate the estimated resource profiles under different workloads.