Experimental validation of a boundary element solver for exterior acoustic radiation problems

The relation between harmonic structural vibrations and the corresponding acoustic radiation is given by the Helmholtz integral equation (HIE). To solve this integral equation a new solver (BEMSYS) based on the boundary element method (BEM) has been implemented. This numerical tool can be used for both sound radiation and nearfield acoustic source localization purposes. After validation of the solver with analytic solutions of simple test problems, a well-defined experimental setup has been designed. The setup consists of a thick walled aluminum box covered with a flexible plate. Inside the box a speaker generates a sound field which is transmitted through the flexible plate into the surrounding medium. This paper describes this experimental setup and briefly explains the properties of the boundary element solver. A comparison is made between the computed and measured sound pressures and particle velocities surrounding the acoustic source. In order to obtain a boundary condition for the BEM computation, the structural vibrations of the flexible plate are measured with a laser Doppler vibrometer. The acoustic pressures are measured with a condenser microphone. The particle velocities are measured with a novel Microflown sensor, which directly measures particle velocity. From the comparison between numerical and measured results, it becomes evident that a good agreement is obtained and thus that the BEMSYS solver is successfully validated

On the use of Higher Order and Irregularly Shaped Boundary Elements in Nearfield Acoustical Holography

Nearfield acoustical holography (NAH) is used to find the regions of acoustic activity on the surface of a sound radiating object. One of the most general NAH approaches is the inverse frequency response function (IFRF) technique, since it imposes no limitations on the geometry of the radiating boundary. In the IFRF method acoustic measurements on a grid in the nearfield of the object are used to determine the corresponding normal velocity distribution on the surface of the object. The measured sound field is related to the surface vibrations via a transfer matrix, which is calculated using a boundary element method. The required inversion of the transfer matrix is not that simple, because the system is ill-conditioned. Hence, a physically meaningful solution can only be obtained by applying regularization techniques. In the literature, the boundary surface of the source is usually meshed with constant or linear elements of equal shape and size. Most likely, this is done to avoid the effect that the regularized inversion process favors nodes that are associated with a high mean square surface normal velocity. This effect is due to the fact that such nodes have a more effective contribution to the sound field. In this paper it is demonstrated that the problem in which the inverse solution is affected by the topology of the mesh gets even worse when quadratic elements are applied. A new technique will be described that circumvents this problem completely by the introduction of an appropriate smoothing operator. As a result all boundary nodes are treated in an equal way, irrespective of their associated area or type of shape function. With the presented approach, irregular meshes and/or higher order boundary elements can be successfully used in NAH applications

PVC pipes in gas distribution: still going strong!

In the Netherlands (impact-modified) PVC is the preferred material for low-pressure (30 and 100 mbar) gas distribution systems. More than 50% of the total length (about 122,000 km) of this system is rigid PVC or impact-modified PVC. The installation of rigid PVC (uPVC) pipelines started about 50 years ago. Presently, about 22,500 km of rigid PVC is still in operation. In this paper the good experiences with rigid PVC gas distribution systems in the Netherlands will be illustrated by results of regular leak surveys and test results on pipe samples taken from the gas grid. It will be shown that the leakage rate of uPVC pipe systems is very low and about equal to that of PE and steel pipe systems. Impact tests show no significant decrease in ductility with respect to time of use. Furthermore, the ductility of the PVC pipeline materials which have been in use for many years is shown to be mainly dependent on the (initial) quality (degree of gelation). The good performance of PVC gas pipeline systems is also proven by modelling studies. It will be shown that the long-term failure behaviour of uPVC is determined by the ability to yield. Failure will occur if a certain critical value of the plastic strain is surpassed. Using this model the long-term behaviour under internal pressure of rigid PVC pipes can be predicted quantitatively

On protecting farmers' new varieties: new approaches to rights on collective innovations in plant genetic resources

"Current farmers' breeding goes beyond the gradual selection in landraces, and includes development and maintenance of major new farmers' varieties that are rather uniform, in particular in South-East Asia. Modern varieties developed in the formal sector have simply replaced landraces as the source of diversity, but have not abolished farmers' breeding practices. Interpretations of the new international agreements on plant genetic resources should protect the development of modern farmers' varieties. However, ensuring recognition of collective innovation, allowing access to relevant germplasm sources for farmers' breeding activities, keeping materials freely available, and arranging for effective benefit sharing, all form major challenges. This paper proposes a new protective measure: namely “origin recognition rights." Author's AbstractLandraces, Farmers' varieties, Collective rights, Declaration of origin, Origin recognition, Germplasm resources,

An operational management model for a coal mining production unit

The coal mining industry faces increased pressure for higher quality coal at lower cost and increased volumes. To satisfy these requirements the industry needs technically skilled first line supervisors with operational management skills. Most first line supervisors possess the necessary technical, but not the required operational management skills. Various operational management philosophies, describing world-class operational management practices exist; however, it is not possible to implement these philosophies as-is in a mining environment due to the various differences between manufacturing and mining. The solution is to provide an operational management model, adapted from these philosophies, to first line supervisors in the coal mining industry.Die steenkoolmynbedryf ervaar groeiende druk van die mark vir hoër gehalte steenkool, laer koste en verhoogde volumes. Om hierdie behoefte te bevredig benodig die myn tegniesgeskoolde eerstelyntoesighouers met bedryfsbestuursvaardighede. Ongelukkig beskik die meeste toesighouers wel oor die nodige tegniese kennis, maar nie die nodige bedryfsbestuursvaardighede nie. Daar bestaan verskeie bedryfsbestuursfilosofieë wat wêreldklas bedryfsbestuurspraktyke omskryf. Dit is egter nie moontlik om die filisofieë net so in die mynbedryf te implimenteer nie a.g.v. die verskille tussen vervaardiging en mynbou. Die oplossing is om ‘n bedryfsbestuurmodel wat op hierdie filosofieë geskoei is, aan eerstelyntoesighouers in die steenkoolbedryf te verskaf.http://sajie.journals.ac.z

Reliable identification at the species level of Brucella isolates with MALDI-TOF-MS

<p>Abstract</p> <p>Background</p> <p>The genus <it>Brucella </it>contains highly infectious species that are classified as biological threat agents. The timely detection and identification of the microorganism involved is essential for an effective response not only to biological warfare attacks but also to natural outbreaks. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) is a rapid method for the analysis of biological samples. The advantages of this method, compared to conventional techniques, are rapidity, cost-effectiveness, accuracy and suitability for the high-throughput identification of bacteria. Discrepancies between taxonomy and genetic relatedness on the species and biovar level complicate the development of detection and identification assays.</p> <p>Results</p> <p>In this study, the accurate identification of <it>Brucella </it>species using MALDI-TOF-MS was achieved by constructing a <it>Brucella </it>reference library based on multilocus variable-number tandem repeat analysis (MLVA) data. By comparing MS-spectra from <it>Brucella </it>species against a custom-made MALDI-TOF-MS reference library, MALDI-TOF-MS could be used as a rapid identification method for <it>Brucella </it>species. In this way, 99.3% of the 152 isolates tested were identified at the species level, and <it>B. suis </it>biovar 1 and 2 were identified at the level of their biovar. This result demonstrates that for <it>Brucella</it>, even minimal genomic differences between these serovars translate to specific proteomic differences.</p> <p>Conclusions</p> <p>MALDI-TOF-MS can be developed into a fast and reliable identification method for genetically highly related species when potential taxonomic and genetic inconsistencies are taken into consideration during the generation of the reference library.</p