A formula for frequency responses of distributed systems with one spatial variable

We develop a method for the exact determination of frequency responses for a class of infinite dimensional systems. In particular, we consider distributed systems in which a spatial independent variable belongs to a finite interval, and in which the inputs and outputs are spatially distributed over the same interval. We show that an explicit formula for the Hilbert–Schmidt norm of the operator-valued frequency response can be obtained whenever the underlying operators are represented by a forced two point boundary value state-space realizations (TPBVSR). This formula involves finite dimensional computations with matrices whose dimension is at most four times larger than the order of the underlying differential operator. Two examples are provided to illustrate the procedure.     

Synthesis and rheological study of some maleic acid polyamides

The contributions of the cis and trans configurations of the main chain double bonds to the transition temperatures and rheological properties were determined for four well-defined polymaleamides, which were prepared by the room temperature ring-opening, step-growth polymerization reactions of N,N′-bisisomaleimide monomers with bifunctional primary diamines. The polymaleamides were glassy solids, which could be thermally isomerized into related polyfumaramides. The glass transition temperatures of the polyfumaramides, as determined by mechanical spectrometry, are systematically and markedly higher than those of the polymaleamides from which they were derived.     

In vitro control of multiplication of some food-associated bacteria by thyme, rosemary and sage isolates

Antibacterial activity of thyme, rosemary and sage isolates obtained by supercritical fluid extraction and hydrodistillation was investigated on Geobacillus stearotermophillus, Bacillus cereus, Bacillus subtilis var. niger, Enterococcus faecium, Salmonella enteritidis and Escherichia coli strains. Bacillus species were the most susceptible to all tested isolates. The thyme isolates showed the strongest antibacterial activity against tested bacteria with MIC values of 40-640 μg/ml, followed by rosemary (MIC = 320-1280 μg/ml) and sage (MIC = 160-2560 μg/ml) isolates. Therefore, the antibacterial activity of the most abundant components found in the thyme isolates, thymol, p-cymene and their mixture was investigated as well. The thyme isolates, especially supercritical extract, showed stronger antibacterial activity against Bacillus strains compared to the single components and their mixture, which indicated synergetic effect of the other components. Results of this study indicated thyme as a valuable source of natural antibacterial agents and supercritical fluid extraction as an efficient isolation method.     

Composition and radical‐scavenging activity of Thymus glabrescens Willd. (Lamiaceae) essential oil

BACKGROUND: Knowledge about the chemical and therapeutic properties of Thymus glabrescens Willd. (Lamiaceae) is scarce and inconsistent. Therefore the main objectives of this study were to determine the yield and chemical composition of essential oils from wild‐growing T. glabrescens populations, to assess their radical scavenging activity and to correlate the results with published data in order to deduce which components are responsible for the activity. RESULTS: The plant material yielded between 4.0 and 8.0 mL kg^?1 of essential oil. All samples contained considerable but variable concentrations of thymol (22.3–55.1%), depending on the source. Radical‐scavenging activities of the oils were estimated by 1,1‐diphenyl‐2‐picrylhydrazyl free radical (DPPH) assay against butylated hydroxytoluene (BHT) and thymol as positive controls. The observed activities (IC₅₀ values ranged from 94 to 230 µg mL^?1) were strongly influenced by thymol concentration, as verified by rapid screening for DPPH radical‐scavenging activity on thin layer chromatography (TLC) plates and regression analysis. CONCLUSION: These results represent the first report on the free radical‐scavenging activity of T. glabrescens essential oil and one of the first comprehensive reports on its composition. Thymus glabrescens could be used in the food industry for seasoning purposes or for preserving processed foods from oxidative degradation. Copyright © 2008 Society of Chemical Industry     

Efficient registration of NURBS geometry

The paper presents an implementation of free-form surface registration in relation to inspection of engineering components, defined as NURBS. Registration is principally performed through the Iterative Closest Point (ICP) method. The time-critical step in ICP was found to be the determination of the closest points on NURBS to a given point in space. Significant speed improvements were achieved through the adoption of a dual surface representation, involving approximation of NURBS entities by a polyhedral mesh. A criterion for sufficient polyhedral approximation was derived and implemented, producing encouraging results. Original solutions are suggested in order to further improve the computational speed. Extensive testing has been carried out, showing that the proposed registration method handles a full six degrees of freedom and achieves global convergence. Performance of the implemented algorithms is discussed with reference to registration of a turbine blade airfoil.     

On the peaking phenomenon in the control of vehicular platoons

We investigate the peaking phenomenon in the control of large-scale vehicular platoons. These systems are of considerable practical importance as they represent an example of systems on lattices in which different subsystems are dynamically coupled only through feedback controls. We demonstrate that imposing a uniform rate of convergence for all vehicles towards their desired trajectories may generate large transient peaks in both velocity and control. We further derive explicit constraints on feedback gains–for any given set of initial conditions–to achieve desired position transients without magnitude and rate peaking. These constraints are used to generate the trajectories around which the states of the platoon system are driven towards their desired values without the excessive use of control effort. All results are illustrated using computer simulations of platoons containing a large number of vehicles.     

Determination and exchange of supply information for co-operation in complex production networks

Today's manufacturing industry is characterised by strong interdependencies between companies operating in globally distributed production networks. The operation of such value-added chains has been enabled by recent developments in information and communication technologies (ICT) and computer networking. To gain competitive advantages and efficiency improvements such as reduced inventory and higher delivery reliability, companies are introducing information exchange systems that communicate demand to suppliers and production progress information to customers in the network. This article proposes a system that supports co-operation in complex production networks by enabling companies to determine and exchange supply information with their customers. The requirements for such a system are analysed and it is embedded in a framework of supply chain management business processes. The system facilitates the determination and exchange of meaningful, reliable and up-to-date order status information from the supplier to the customer. Based on comparing the progress of an internal production order with a pre-defined milestone model for each product, the status of the customer order is determined and—in case of lateness—communicated to the customer together with an early warning. To demonstrate the developed supply information concepts and processes, the business process is implemented as a pilot system and evaluated by the user companies participating in the 5th Framework IST project Co-OPERATE.     

Supercritical carbon dioxide extraction of sesquiterpenes from valerian root

Supercritical carbon dioxide extraction of sesquiterpenes from valerian root was investigated. Extractions from cultivar Arterner züctung and two wild grown valerian subspecies were performed. The influence of extraction conditions on extraction yield and chemical composition of obtained extracts was investigated at temperatures from 40 °C to 50 °C and pressures from 10 MPa to 20 MPa. Chemical composition of obtained extracts was analyzed by GC/FID and GC/MS methods. The influence of particle size on extraction process was investigated at 40 °C and 10 MPa. The major constituents of supercritical extracts were valerianol, valerenal, bornyl acetate and kessanyl acetate. Optimal extraction conditions for the cyclopentanoid sesquiterepenes isolation, referred to the content of cyclopentanoid sesquiterpenes in extract, were found to be 50 °C and 15 MPa. Extract obtained from the cultivar was characterized by the higher content of cyclopentanoid sesquiterpenes, as well as valerenal comparing to extracts from wild grown species. At 40 °C and 20 MPa 19.6% of cyclopentanoid sequiterpenes isolated with methanol can be extracted. At 40 °C and 10 MPa, 17.4% of cyclopentanoid sequiterpenes isolated with methanol can be extracted. However, the extract obtained with methanol was characterized by the high content (42.51%) of unwanted isovaleric as well as by the lower content of cyclopentanoid sequiterpenes than the extracts obtained with supercritical carbon dioxide. The process of supercritical extraction was influenced by particle size. In order to simulate the process, mathematical model on the secretory structure scale was derived. Results of the model showed good agreement with the experimental data.