Large scale experiments with a 5 MW sodium/air heat exchanger for decay heat removal

Sodium experiments in the large scale test facility ILONA were performed to demonstrate proper operation of a passive decay heat removal system for LMFBRs based on pure natural convection flow. Temperature and flow distributions on the sodium and the air side of a 5 MW sodium/air heat exchanger in a natural draught stack were measured during steady state and transient operation in good agreement with calculations using a two dimensional computer code ATTICA/DIANA.     

Double series and double parallel unit cells for transmission line metamaterials

Two new types of unit cells for transmission line metamaterials are introduced and studied, namely the double series and double parallel unit cells. Similar to the well known composite right/left handed unit cell they consist of a series and a parallel tank each composed of two reactances. Characteristic dispersion properties of the homogeneous and discrete unit cell are derived and discussed.     

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Ohne Zusammenfassung     

Robust transient stabilisation problem for a synchronous generator in a power network

The robust transient stabilisation problem (with stability proof) of a synchronous generator in an uncertain power network with transfer conductances is rigorously formulated and solved. The generator angular speed and electrical power are required to be kept close, when mechanical and electrical perturbations occur, to the synchronous speed and mechanical input power, respectively, while the generator terminal voltage is to be regulated, when perturbations are removed, to its pre-fault reference constant value. A robust adaptive nonlinear feedback control algorithm is designed on the basis of a third-order model of the synchronous machine: only two system parameters (synchronous machine damping and inertia constants) along with upper and lower bounds on the remaining uncertain ones are supposed to be known. The conditions to be satisfied by the remote network dynamics for guaranteeing ?₂ and ?_∞ robustness and asymptotic relative speed and voltage regulation to zero are weaker than those required by the single machine-infinite bus approximation: dynamic interactions between the local deviations of the generator states from the corresponding equilibrium values and the remote generators states are allowed.     

Kinetics of the oxidation of methyl tert-butyl ether (MTBE) by potassium permanganate

The occurrence of the fuel oxygenate methyl tert-butyl ether (MTBE) in the environment has received considerable scientific attention. The pollutant is frequently found in the groundwater due to leaking of underground storage tanks or pipelines. Concentrations of more than several mg/L MTBE were detected in groundwater at several places in the US and Germany in the last few years. In situ chemical oxidation is a promising treatment method for MTBE-contaminated plumes. This research investigated the reaction kinetics for the oxidation of MTBE by permanganate. Batch tests demonstrated that the oxidation of MTBE by permanganate is second order overall and first order individually with respect to permanganate and MTBE. The second-order rate constant was 1.426 x 10(-6) L/mg/h. The influence of pH on the reaction rate was demonstrated to have no significant effect. However, the rate of MTBE oxidation by potassium permanganate is 2-3 orders of magnitude lower than of other advanced oxidation processes. The slower rates of MTBE oxidation by permanganate limit the applicability of this process for rapid MTBE cleanup strategies. However, permanganate oxidation of MTBE has potential for passive oxidation risk management strategies.     

Site-specific cleavage--a model system for the identification of lipid-modified glutamate residues in proteins

Numerous proteins are modified post-translationally after their biosynthesis at the ribosomes of the cell. One such modification, only poorly characterized to date, is the formation of lipid esters of glutamate side chains in the skin proteins of land-living mammals; here a subset of very long chain fatty acids, ceramides and/or glucosylceramides, are bound through their omega-hydroxy groups to structural proteins of the so-called "cornified envelope" in the outermost layer of the skin, the stratum corneum. We report an approach for the identification of proteins containing ester-modified glutamic acid residues and the determination of their positions within the peptide sequence, designed for mass spectrometric investigation of human skin proteins.     

Spectral variable selection for partial least squares calibration applied to authentication and quantification of extra virgin olive oils using Fourier transform Raman spectroscopy

The limits of quantitative multivariate assays for the analysis of extra virgin olive oil samples from various Greek sites adulterated by sunflower oil have been evaluated based on their Fourier transform (FT) Raman spectra. Different strategies for wavelength selection were tested for calculating optimal partial least squares (PLS) models. Compared to the full spectrum methods previously applied, the optimum standard error of prediction (SEP) for the sunflower oil concentrations in spiked olive oil samples could be significantly reduced. One efficient approach (PMMS, pair-wise minima and maxima selection) used a special variable selection strategy based on a pair-wise consideration of significant respective minima and maxima of PLS regression vectors, calculated for broad spectral intervals and a low number of PLS factors. PMMS provided robust calibration models with a small number of variables. On the other hand, the Tabu search strategy recently published (search process guided by restrictions leading to Tabu list) achieved lower SEP values but at the cost of extensive computing time when searching for a global minimum and less robust calibration models. Robustness was tested by using packages of ten and twenty randomly selected samples within cross-validation for calculating independent prediction values. The best SEP values for a one year's harvest with a total number of 66 Cretian samples were obtained by such spectral variable optimized PLS calibration models using leave-20-out cross-validation (values between 0.5 and 0.7% by weight). For the more complex population of olive oil samples from all over Greece (total number of 92 samples), results were between 0.7 and 0.9% by weight with a cross-validation sample package size of 20. Notably, the calibration method with Tabu variable selection has been shown to be a valid chemometric approach by which a single model can be applied with a low SEP of 1.4% for olive oil samples across three different harvest years.     

Ammonia detection and monitoring with photofragmentation fluorescence

Excimer laser fragmentation-fluorescence spectroscopy is an effective detection strategy for NH(3) in combustion exhausts at atmospheric pressure and high temperatures. Two-photon photofragmentation of NH(3) with 193-nm light yields emission from the NH(A-X) band at 336 nm. There are no major interferences in this spectral region, and the sensitivity is at the parts per billion (ppb) level. Quenching of the NH(A) state radical by the major combustion products is measured and does not limit the applicability of the detection method. Detection limits in practical situations are of the order of 100 ppb for a 100-shot (1-s) average. This technique could prove useful in monitoring ammonia emissions from catalytic and noncatalytic NO(x) reduction processes involving ammonia injection.     

Treatment of wx corn starch dispersions in a microwave reactor and their hydrodynamic properties determined using asymmetrical flow field‐flow fractionation

Hydrodynamic properties of aqueous wx corn starch (native, un‐pregelatinised) dispersions treated in a dedicated single‐mode microwave reactor at temperatures ranging from 180 to 210°C were determined using asymmetrical flow field‐flow fractionation coupled with an RI detector. The dedicated microwave reactor enabled the fine control and monitoring of heating parameters (especially temperature) during the treatment. The translational diffusion co‐efficient and hydrodynamic radii (R_h) values determined for wx corn starch treated at 180 and 200°C indicate that the majority of the material (∼98%) consisted of highly mobile, small and compact molecules/particles, with R_h values ranging from 10 to 90 nm, while the remaining ∼2% of the material consisted of considerably larger molecules/particles R_h values ranging from ∼100 to ∼200 nm). Degradation of wx corn starch was observed at 210°C.