Optimization of the test method for determining the bonding quality of core plywood (blockboard)

Over the last few decades, thanks mainly to their specific technological features and their stability of dimension and shape, wood-based panels have seen flourishing industrial and commercial development. Of these, blockboard consists of a central layer (core) made up of solid wood strips which is stiffened and bound together by glued, hot-pressed rotary cut veneers overlaid with grain (main wood fibre direction) perpendicular one to another. The panel made in this way is considered a distinct type of plywood. Although blockboard is widely used in furniture-making and carpentry in general, and plays an important role in the production of some EU countries, its physicalmechanical properties are largely unknown and the combination of wood components having very different thickness (strips and veneers) makes it difficult to precisely determine the bonding quality. The aim of this work is to contribute to setting up a testing method to objectively assess the above property as well as to achieve more efficient production process control. To this end the main testing methodologies, and in particular those on solid wood panels (prEN 13354), glulam (EN 392) and plywood (EN 314) were evaluated. The tension shear test seemed to be the most significant for assessing the actual resistance of the pair of glue lines bonding the wooden elements that make up the blockboard. In order to obtain symmetrical test pieces, the determination of the bonding quality also made it necessary to further glue two portions of the panel realizing a compound (5 layers) specimen whose core layer consisted of two overlaid veneers with parallel grain. Because of the encouraging results obtained, the method proposed has been included in the recent revision of the standard EN 314, the contents of which is also going to be adopted by ISO.

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Résumé Au cours des dernières décennies, grace surtout à leurs intéressantes caractéristiques technologiques et leur stabilité en matière de dimensions et de formes, les panneaux à base de bois ont enregistré un croissant développment industriel et commercial. L'un d'entre eux, le panneau latté, est constitué d'une couche centrale (ame) d'éléments en bois massif qui est rendue solidaire par la superposition, par collage et pressage à chaud, d'un placage avec direction des fibres perpendiculaires. Pour la composition susmentionnée, le panneau qui en dérive est considéré comme étant un type particulier de contre-plaqué. Bien que le panneau latté utilisé largement dans le secteur de l'ameublement et de la menuiserie en général, et qu'il occupe une place capitale dans le cadre de la production de plusieurs pays de l'UE, ses propriétés mécaniques sont peu connues, alors que la présence actuelle de composants en bois d'épaisseur très différente (liteaux et placages) rend difficile une détermination correcte de la qualité du collage. à ce propos, les principales méthodologies d'essai sur cet aspect ont été soigneusement évaluées, en particulier celles qui concernent les panneaux de bois massif (prEN 13354), le bois lamellé collé (EN 392) et le contre-plaqué (EN 314). L'essai de cisaillement par traction s'est révélé être le plus significatif pour évaluer la résistance effective des deux lignes de colle qui relient les éléments en bois composant le panneau. Toutefois, pour obtenir des éprouvettes symétriques, la détermination recherchée nécessite le collage de deux portions de panneau ce qui permet de réaliser une éprouvette composée (à cinq couches) dans laquelle la couche centrale est constituée par deux placages superposés avec direction des fibres parallèles. En considération des résultats obtenus, la méthodologie proposée a été introduite dans la révision de la norme EN 314, dont le contenu sera aussi adopté par l'ISO.

     

Thermally and plastically induced residual strains in textured Zircaloy-2 plate

The residual intergranular strains in textured Zircaloy-2 plate samples induced by cooling from 823 K to ambient temperatures, by cold-rolling by 1.5% and 25% and by deforming in tension by 1.5% were measured by neutron diffraction. The strong rolling texture, which gives rise to two ideal orientations, permitted the interpretation of much of the data in terms of strain tensors for the two orientations. The experimental results were compared with calculations based on the elasto-plastic self-consistent model with no adjustable parameters. Close agreement was obtained for samples in the as-cooled state and deformation in tension by 1.5% but the agreement is less satisfactory for cold-rolling.     

Solutions for Cooperative Games

A new concept of the characteristic function is defined. It matches cooperative games far better than the classical characteristic function and is useful in reducing the number of decisions that can be used as the unique solution of a game.     

Effects of Sc2O3 and MgO passivation layerson the output power of AlGaN/GaN HEMTs

The low temperature (100°C) deposition of Sc₂O₃ or MgO layers is found to significantly increase the output power of AlGaN/GaN HEMTs. At 4 GHz, there was a better than 3 dB increase in output power of 0.5×100 μm² HEMTs for both types of oxide passivation layers. Both Sc₂ O₃ and MgO produced larger output power increases at 4 GHz than conventional plasma-enhanced chemical vapor deposited (PECVD) SiN_x passivation which typically showed ⩽2 dB increase on the same types of devices. The HEMT gain also in general remained linear over a wider input power range with the Sc₂O₃ or MgO passivation. These films appear promising for reducing the effects of surface states on the DC and RF performance of AlGaN/GaN HEMTs     

Electromagnetic interference mitigation by using a spread-spectrumapproach

We investigate a new technique, referred to as spread-spectrum clock generation (SSCG), for reducing the level of radiated emission from devices with digital clock signals. To calculate the radiated emissions from such devices, we model the radiating geometry and compute the radiated field at a multitude of frequencies by using NEC-4, which is an electromagnetic field solver based on the method of moments (MoM). We consider a variety of modulating profiles for the spread spectrum clock and demonstrate that by using a frequency deviation of only 1%, we can achieve from 10 to 30 dB reduction in the radiated emission levels     

High-finesse large band Fabry-Perot fibre filter with superimposedchirped Bragg gratings

Filters with 100 GHz free spectral range (FSR) and finesse up to 16 are demonstrated over the 1525 to 1583 nm band. The photoinduced birefringence results in a polarisation-dependent spectral response. Finesse and FSR uniformity are addressed     

Adaptive Spread-Spectrum Systems Using Least-Squares Lattice Algorithms

Practical communication systems must cope with many uncertainties in addition to determining the transmitted data, e.g., the direction, timing, and distortion of the desired signal, and the spectral and spatial distribution of the interference, all of which may change with time. This paper describes exact least-squares (LS) recursive lattice algorithms which resolve these uncertainties in a direct-sequence spread-spectrum digital communication system. The adaptive LS algorithm is recursive beth in order and time, and converges rapidly to the uncertain parameters. Time-discrete algorithms may be mechanized by a receiver containing integrate-and-dump circuits operating at the chip rate of the pseudonoise (PN) sequence, one in each in-phase and each quadrature channel of each sensor array element's output. Different configurations of optimal time-discrete receivers are presented and transformed into adaptive receivers by taking advantage of the spectral properties of the different kinds of LS filters. Simulation results are presented and some guide lines are given for the architecture of an adaptive direct-sequence spread-spectrum system.     

Hardware monitoring of a multiprocessor system

The Testbed for Distributed Processing, or Ted, consists of Intel Corp.'s iSBC 8086 single board computers (SBCs) organized into groups or clusters. Each cluster consists of several SBCs that communicate via a shared memory. Intercluster communication occurs through an Ethernet interface. A hardware monitor designed and implemented to handle the monitoring activities within a cluster in the Ted system is described. By using specified patterns and don't-care masks, the system can detect accesses to selected data, addresses, or blocks of addresses. This function helps monitor events such as the access or usage of a memory location or a group of mailbox addresses. It also determines the amount of time consumed by the performance of specific operations     

Separation of serotonin from catechols by capillary zone electrophoresis with electrochemical detection

Capillary zone electrophoresis with electrochemical detection is demonstrated with columns having only 9-microns inner diameter. Amperometric detection limits of 0.7 amol are reported for serotonin. The difficult problem of resolving serotonin and dopamine--two neurotransmitters of interest having similar electrophoretic mobilities--is addressed by chemical means to improve selectivity. These include buffer modification with 2-propanol and a system employing borate complexation of the catechol in combination with sodium dodecyl sulfate micelles.