75392 research outputs found
Sort by
Design of the structural joints of bars with axially symmetric cross-sections
No full textabstractEN: In this paper a technique for designing structural joints of bars with axially symmetric cross-sections is presented. This technique consists of the use of solutions of planar statically admissible discontinuous stress fields. Numerous practically important solutions are obtained which make it possible to estimate the joint shape and to find the load-carrying capacity of the bars (limit forces and moments). It is also demonstrated that shapes of some joints manufactured in practice do not allow for the full exploitation of the strength of the material used.score: 35collation: 75-8
Miniaturized tools and devices for bioanalytical applications: an overview
No full textabstractEN: This article presents an overview of various miniaturized devices and technologies developed by our group. Innovative, fast and cheap procedures for the fabrication of laboratory microsystems based on commercially available materials are reported and compared with well-established microfabrication techniques. The modules fabricated and tested in our laboratory can be used independently or they can be set up in different configurations to form functional measurement systems. We also report further applications of the presented modules e.g. disposable poly(dimethylsiloxane) (PDMS) microcuvettes, fibre optic detectors, potentiometric sensors platforms, microreactors and capillary electrophoresis (CE) microchips as well as integrated microsystems e.g. double detection microanalytical systems, devices for studying enzymatic reactions and a microsystem for cell culture and lysis.score: 0collation: 647-66
Experimental study and modeling of polymer granular structures submitted to internal underpressure
No full textabstractEN: The paper deals with a system that consists of a granular material encapsulated in a tight, flexible envelope and submitted to an internal underpressure using a vacuum pump. It is found that the underpressure value has a considerable impact on the behavior and properties of the medium. Experimental studies and modeling of this phenomenon are provided in this work. Results of uniaxial tensile tests carried out on special cylindrical samples and characteristic hardening curves are presented for structures filled up with plastic grains. The nonlinear behavior of these materials is modeled using the viscoplastic constitutive Chaboche law, that requires the determination of several material parameters. The parameters identification problem is formulated as an optimization problem and solved by using an evolutionary algorithm. The numerically simulated graphs follow the experimental curves well. A modified version of Chaboche model, capable of capturing the polymer granular structure response to external loading and including underpressure parameter, is proposed. The presented methodology can be easily adapted to other constitutive models and experiments of special granular structures submitted to internal underpressure.score: 40collation: 75-8
An active electromagnetic stabilization of the Leipholz column
No full textabstractEN: We study the application of electromagnetic actuators for the active stabilization of the Leipholz column. The cases of the compressive and tensional load of the column placed in air and in water are considered. The partial differential equation of the column is discretized by Galerkin's procedure, and the stability of the obtained control system is evaluated by the eigenvalues of its linearization. Four different methods of active stabilization are investigated. They incorporate control systems based on feedback proportional to the transverse displacement of the column, its velocity and the current in the electromagnets. Conditions in which these strategies are effective in securing safe operation of the column are discussed in detail.score: 9collation: 161-17
Influence of chitosan characteristics on polymer properties: II. Platinum sorption properties
No full textabstractEN: The sorption of platinum on glutaraldehyde cross-linked chitosan was investigated at pH 2, using several chitosan samples prepared from different origins and characterized by different mol fractions of N-acetylation (FA). The influence of material conditioning was also tested: chitosan was dissolved and then re-precipitated and/or dried (using either oven-drying or freeze-drying). The influence of the different characteristics and treatments on both sorption isotherms and uptake kinetics was checked. Part I has studied the effect of preparation and source on sample crystallinity. Shrimp chitosan has a greater sorption affinity for platinum than fungal chitosan and squid chitosan respectively. Sorption kinetics were found comparable for fungal chitosan and shrimp chitosan, while diffusion was more restricted in squid chitosan due to the higher crystallinity. Decreasing the FA increased sorption capacity for shrimp chitosan but decreased sorption levels for squid material. While FA did not influence sorption kinetics for shrimp material it strongly decreased kinetics for squid chitosan. The type of drying procedure hardly affected sorption kinetics and isotherms but when a re-precipitation step was included in the preparation procedure, the material had to be freeze-dried to maintain high sorption properties. The freeze-drying did not control sorption performance, except in the case of re-precipitated material.© 2003 Society of Chemical Industryscore: 30collation: 206-21
Three-dimensional fluidic microsystem fabricated in Low Temperature Cofired Ceramic Technology
No full textscore: 0collation: 145-15
Optimisation of a direct plating method for the detection and enumeration of Alicyclobacillus acidoterrestris spores
No full textabstractEN: A direct plating method for the detection and enumeration of Alicyclobacillus acidoterrestris spores has been optimised. The results of the application of four types of growth media (BAT agar, YSG agar, K agar and SK agar) regarding the recovery and enumeration of A. acidoterrestris spores were compared. The influence of the type of applied growth medium, heat shock conditions, incubation temperature, incubation time, plating technique and the presence of apple juice in the sample on the accuracy of the detection and enumeration of A. acidoterrestris spores was investigated. Among the investigated media, YSG agar was the most sensitive medium, and its application resulted in the highest recovery of A. acidoterrestris spores, while K agar and BAT agar were the least suitable media. The effect of the heat shock time on the recovery of spores was negligible. When there was a low concentration of spores in a sample, the membrane filtration method was superior to the spread plating method. The obtained results show that heat shock carried out at 80 °C for 10 min and plating samples in combination with membrane filtration on YSG agar, followed by incubation at 46 °C for 3 days provided the optimal conditions for the detection and enumeration of A. acidoterrestris spores. Application of the presented method allows highly efficient, fast and sensitive identification and enumeration of A. acidoterrestris spores in food products. This methodology will be useful for the fruit juice industry for identifying products contaminated with A. acidoterrestris spores, and its practical application may prevent economic losses for manufacturers.score: 25collation: 1-
Heating system design support
No full textabstractEN: Computer support for certain engineering tasks such as analysis, calculation, drafting, configuration and simulation tends to be integrated into one system where all modules are coherent. Because of that a software layer should also be capable to provide communication between modules and to keep data and knowledge visible and available for every module playing a particular role in the system. This paper presents results of the development of such sample integrated environment. Though our system supports heating installation design, methods and techniques can be applicable in other domains.score: 3collation: 60-6
Photovaractor for remote optical control of microwave circuits
No full textabstractEN: A photovaractor for the remote optical control of microwave circuits was studied. The photovaractor was fabricated as a p-i-n photodiode placed in a pigtailed fiber optical module. The study of the impedance in the frequency range up to 3 GHz in darkness and under illumination has shown that the photovaractor capacitance strongly depends on the incident optical power. The capacitance variation of the photovaractor diode under illumination is discussed.score: 30collation: 201-20
Application of nanofibers to improve the filtration efficiency of the most penetrating aerosol particles in fibrous filters
No full textabstractEN: Conventional, mechanical fibrous filters made of microfibers exhibit a local minimum of fractional collection efficiency in the aerosol particle size-range between 100 and 500 nm, which is called the most penetrating particle size (MPPS). Simple theoretical calculations predict that this efficiency may be significantly increased using nanofibrous media. The main objective of this paper is an experimental verification of these expectations and simultaneously checking whether this anticipated gain in the filtration efficiency is not overpaid with an excessive pressure drop. For this purpose we developed a modified melt-blown technology, which allowed us to produce filters composed of micrometer as well as nanometer sized fibers. One conventional microfibrous filter and five nanofibrous filters were examined. The complete structural characteristics, pressure drop and efficiency of removal of aerosol particles with diameters 10–500 nm were determined for all media. The results of the experiments confirmed that using nanofibrous filters a significant growth of filtration efficiency for the MPPS range can be achieved and the pressure drop rises moderately. Simultaneously, we noticed a shift of the MPPS towards smaller particles. Consequently, the quality factor for bilayer systems composed of a microfibrous support and a nanofibrous facial layer was considerably higher than this one for a conventional microfibrous filter alone. Additionally, it was found that utilization of many-layer nanofibrous filters combined with a single microfibrous backing layer is even more profitable from the quality factor standpoint. Comparing experimental results with theoretical calculations based on the single-fiber theory we concluded that for microfibrous filters a fairly good agreement can be obtained if the resistance-equivalent fiber diameter is used in calculations instead of the mean count diameter determined from the SEM images analysis; in the latter case, filtration efficiency computed theoretically is slightly overestimated. This is even more evident for nanofibrous media, suggesting that in such case a structural filter inhomogeneity has a strong influence on the filter efficiency and its resistance and one should strive for minimization of this effect manufacturing nanofibrous filters as homogeneous as possible. We can finally conclude that fibrous filters containing nanofibers, which are produced using the melt-blown technique, are very promising and economic tools to enhance filtration of the most penetrating aerosol particles.score: 35collation: 6804-681