Labyrinth seals with application to turbomachinery

It is well known that there exist losses of fluid through axial and radial gaps in turbomachines, leading to less efficiency. Every 1 % decrease in leakage flow through a high‐pressure gas turbine seals would result in a 0.4 % decrease in the specific fuel consumption [1]. Last decades, a number of solutions have been applied to overcome losses of fluid through axial and radial gaps. A feasible solution is the application of labyrinth seals to act as an obstacle on the way of flow leakages. This research is targeted to attain a seal configuration that has good dynamic sealing properties, higher compliance with the shaft, simple geometry for manufacturing and maintenance. The labyrinth seal must produce significant losses of kinetic energy in order to stop leaks passing through the sealed places. It is known that the turbine shaft exhibits modal and stress loads. Also, seals must be designed to resist loads and operate at maximum efficiency. The fulfilled numerical analysis shows that the proposed geometry causes intensive reduction of leakage flow rates and thus contributes to increase in the efficiency performance of stages under consideration.     

Gold Nanoparticle‐Based Sensors Activated by External Radio Frequency Fields

A novel molecular beacon (a nanomachine) is constructed that can be actuated by a radio frequency (RF) field. The nanomachine consists of the following elements arranged in molecular beacon configuration: a gold nanoparticle that acts both as quencher for fluorescence and a localized heat source; one reporter fluorochrome, and; a piece of DNA as a hinge and recognition sequence. When the nanomachines are irradiated with a 3 GHz RF field the fluorescence signal increases due to melting of the stem of the molecular beacon. A control experiment, performed using molecular beacons synthesized by substituting the gold nanoparticle by an organic quencher, shows no increase in fluorescence signal when exposed to the RF field. It may therefore be concluded that the increased fluorescence for the gold nanoparticle‐conjugated nanomachines is not due to bulk heating of the solution, but is caused by the presence of the gold nanoparticles and their interaction with the RF field; however, existing models for heating of gold nanoparticles in a RF field are unable to explain the experimental results. Due to the biocompatibility of the construct and RF treatment, the nanomachines may possibly be used inside living cells. In a separate experiment a substantial increase in the dielectric losses can be detected in a RF waveguide setup coupled to a microfluidic channel when gold nanoparticles are added to a low RF loss liquid. This work sheds some light on RF heating of gold nanoparticles, which is a subject of significant controversy in the literature.     

Design of new gold catalysts supported on mechanochemically activated ceria-alumina, promoted by molybdena for complete benzene oxidation

Gold catalysts, supported on mechanochemically activated ceria-alumina, nonpromoted and promoted by molybdena, were studied in the reaction of complete benzene oxidation. Higher activity of Au-Mo catalysts was established in the low temperature region, while high temperatures samples, containing only gold exhibit higher benzene conversion and the cross-point of the curves depends on alumina content. The addition of alumina by mechanochemical treatment leads to a surface modification of ceria, e.g. oxygen vacancies are formed prevailing on the ceria surface. The molybdena loading leads to the oxygen vacancies occupation. The calculated hydrogen consumption and the enhanced reduction of ceria surface layers in general correlate with the activities of the catalysts. The XPS data supported the role of Ce³⁺ and partially charged gold particles in the formation of the complex AuV₀Ce³⁺ as the active site for the redox processes. The modification of ceria in the presence of gold and the formation of oxygen vacancies in close contact with Ce³⁺ ensure the enhanced electron transfer.     

Disinhibitory psychopathology and delay discounting in alcohol dependence: Personality and cognitive correlates.

Increased discounting of delayed rewards may reflect a decision bias that contributes to excessive use of alcohol and more generally, to an impulsive, disinhibitory predisposition that is characterized by a preference for immediate over long-term rewards. The current study examined the association between delay discounting of rewards and the covariation among several types of disinhibitory problems that are often comorbid with alcohol dependence (AD). Lifetime problems with alcohol, marijuana, other drugs, childhood conduct disorder, and adult antisocial behavior were assessed in a sample of 426 young adults, 257 of whom had a lifetime diagnosis of AD. Higher delay discounting rates were associated with the covariation among all domains of disinhibitory problems and were not uniquely associated with any one domain. Higher delay discounting rates also were associated with lower intelligence, lower working memory capacity, and higher trait impulsivity. The results suggest that increased delay discounting of rewards may reflect aspects of a general vulnerability to externalizing, disinhibitory disorders. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Grundwassergefährdungspotenzial von Additiven in Wärmeträgerflüssigkeiten aus Erdwärmesonden

The number of installed vertical borehole heat exchangers is continuing to grow continuously which increases the risk of a local groundwater contamination with heat exchanger fluids due to a system leakage. This study evaluates the groundwater pollution potential of organic additives applied in heat exchanger fluids. In the first step of the project a data survey was carried out to collect detailed information about the identity, frequency of use and concentrations of the applied additives. In total, 35 different additives were disclosed by producers and/or distributors of heat exchanger fluids. The additives were classified as corrosion inhibitors, alkalis, dyes, solvents, scentsflavours, defoamers, and surfactants. The groundwater pollution potential of the additives was assessed based on their frequency of usage in the declared fluids and on their environmental fate (mobility, persistence and aquatic toxicity). Based on our analysis, the corrosion inhibitors benzotriazole, tolyltriazole, 2-ethylhexanoate, benzoate and sebacate exhibit a potentially exhibit a significant risk for groundwater contamination.     

First Experiments Aiming for Precise Lamb Shift Measurements on Hydrogen-Like Heavy Ions with Low Temperature Calorimeters

The precise determination of the Lamb shift in hydrogen-like heavy ions provides a sensitive test of quantum electrodynamics in very strong Coulomb fields, not accessible otherwise. To increase the accuracy of the Lamb shift measurement on stored heavy ions at the ESR storage ring at GSI, a calorimetric low temperature detector for hard X-rays was developed. A prototype array consisting of 8 pixels with silicon thermistors and Sn or Pb absorbers was applied in first experiments with stored ²³⁸U⁹¹⁺ and ²⁰⁷Pb⁸¹⁺ ions interacting with an internal gas-jet target. In both experiments the Lyman-α lines were, for the first time by using calorimetric low temperature detectors, clearly identified in clean, almost background-free spectra. A total detection efficiency of 1×10⁻⁷ for the Lyman-α lines was reached and an energy resolution of 115 eV was obtained under the present experimental conditions, which corresponds to a considerable improvement of about half an order of magnitude if compared to conventional Ge semiconductor detectors. Finally preliminary results of the data analysis and future perspectives are discussed.      

TiO2/WO3 hybrid structures produced through a sacrificial polymer layer technique for pollutant photo- and photoelectrooxidation under ultraviolet and visible light illumination

TiO₂/WO₃ hybrid structures were produced on graphite substrates following a three step procedure: (i) electrochemical deposition of WO₃ under potentiostatic conditions, (ii) electrochemical deposition of TiO₂–polyaniline (PANI) composite layers by potentiostatic polymerization of aniline in the presence of TiO₂ nanoparticles, (iii) high temperature (450 °C) treatment for decomposition of the PANI structure. Experiments on the photoelectrochemical response of the composite layers were carried out by cyclic voltammetry and chronoamperommetry in the dark and under illumination by using low power lamps emitting in the visible and UV spectrum ranges. The oxidation of three pollutants—oxalate ions, methanol and malachite green was used to evaluate the photoelectrocatalytic activity of the TiO₂/WO₃ structures. The photocurrents registered for the photooxidation of oxalate were higher than photocurrents measured at hybrid TiO₂/WO₃ electrodes obtained in conventional two-step electrodeposition of WO₃ and subsequently TiO₂ from corresponding salt solutions. The efficiency of the malachite green photodegradation in our experiments was also about two orders of magnitude higher than that obtained in TiO₂/WO₃ structures synthesized in a conventional way. These results are (very probably) due to the proposed synthetic approach involving PANI polymer layer as an immobilizing matrix and the opportunity to disperse homogeneously TiO₂ nanoparticles on the WO₃ surface provided.     

Verification of the VVER-440 pressure vessel neutron fluence calculation by activity measurement

To qualify the calculation methodology, measurements of neutron flux responses of a VVER-440/230 reactor pressure vessel have been carried out.The activity of shavings sampled out from the inner pressure vessel wall of Unit 1 of Kozloduy NPP after the 14th cycle has been measured. Calculation of the expected activity at the shaving positions has been carried out, taking into account the local power distribution. Comparison of calculated and measured activity values has indicated that the computed value for the fast neutron fluence is underestimated by up to 20%.     

ASYNT — An adjoint synthesis method for neutron irradiation estimation on the vessels of VVER/PWR reactors

The new ASYNT method is developed and proposed for neutron fluence calculations. This method uses the solution of adjoint neutron transport equation for flux/responses evaluation. The evaluation of flux/responses is reduced to the space and energy integration of the product of 3D adjoint solution and the neutron source distribution, determined by realized loading patterns and operational regimes. The adjoint solution does not depend on the neutron source distribution and is obtained only once for every surveillance site, response and type of reactor. The application of this method results in separability of azimuthal and axial dependence in the 3D adjoint solution. That is why the 3D adjoint solution could be synthesised from the 2D and 1D adjoint solutions. The circular cylinder reactor core presentation of the solution axial dependence is the only approximation used in the ASYNT method.