排序方式: 共有26条查询结果,搜索用时 15 毫秒
1.
The permeation behaviour of different types of adhesives (urea-formaldehyde resin, dispersion glue (PVA) and Polyurethane) was investigated by light microscopy, scanning electron microscopy and neutron radiography. Clear differences in the permeation behaviour of the adhesives could be determined. Urea resin showed under the chosen conditions the strongest permeation of wood. The glue allocation was quantified and the permeation visualised by means of neutron radiography. By this a differentiation between wood and the glue joint was possible. The penetration depth of the glue was conspicuously different between spring wood and late wood areas. 相似文献
2.
3.
Vontobel P.O. Kavcic A. Arnold D.M. Loeliger H.-A. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2008,54(5):1887-1918
The classical Blahut-Arimoto algorithm (BAA) is a well-known algorithm that optimizes a discrete memoryless source (DMS) at the input of a discrete memoryless channel (DMC) in order to maximize the mutual information between channel input and output. This paper considers the problem of optimizing finite-state machine sources (FSMSs) at the input of finite-state machine channels (FSMCs) in order to maximize the mutual information rate between channel input and output. Our main result is an algorithm that efficiently solves this problem numerically; thus, we call the proposed procedure the generalized BAA. It includes as special cases not only the classical BAA but also an algorithm that solves the problem of finding the capacity-achieving input distribution for finite-state channels with no noise. While we present theorems that characterize the local behavior of the generalized BAA, there are still open questions concerning its global behavior; these open questions are addressed by some conjectures at the end of the paper. Apart from these algorithmic issues, our results lead to insights regarding the local conditions that the information-rate-maximizing FSMSs fulfill; these observations naturally generalize the well-known Kuhn-Tucker conditions that are fulfilled by capacity-achieving DMSs at the input of DMCs. 相似文献
4.
Neutron radiography, a powerful method to determine time-dependent moisture distributions in concrete 总被引:1,自引:0,他引:1
Peng Zhang Folker H. Wittmann Tie-jun Zhao Eberhard H. Lehmann Peter Vontobel 《Nuclear Engineering and Design》2011,241(12):4758-4766
Service life of reinforced concrete structures is often limited by penetration of water and compounds dissolved in water into concrete. Concrete can be damaged in this way and corrosion of steel reinforcement can be initiated. There is an urgent need to study water penetration into concrete in order to better understand deterioration mechanisms and to find appropriate ways to improve durability. Neutron radiography provides us with an advanced non-destructive technique with high spatial resolution and extraordinary sensitivity. In this contribution, neutron radiography was successfully applied to study the process of water absorption of two types of concrete with different water–cement ratios, namely 0.4 and 0.6. The influence cracks and of water repellent treatment on water absorption has been studied on mortar specimens. It is possible to visualize migration of water into concrete and other cement-based composites and to quantify the time-dependent moisture distributions as function of time with high spatial resolution by means of neutron radiography. Water penetration depth obtained from neutron radiography is in good agreement with corresponding values obtained from capillary suction tests. Surface impregnation of concrete with silane prevents capillary uptake of water. Even fine cracks are immediately filled with water as soon as the surface gets in contact. Results provide us with a solid basis for a better understanding of deteriorating processes in concrete and other cement-based materials. 相似文献
5.
Mikael Solymar Eberhard Lehmann Peter Vontobel Anders Nordlund 《Bulletin of Engineering Geology and the Environment》2003,62(1):85-88
Neutron tomography experiments were undertaken on a quartz arenite sample in order to determine saturation variations in
the sample after the initially water-saturated sample was subjected to air flushing. The experiments were carried out in order
to study the applicability of the neutron tomography facility at the Paul Scherrer Institute, Switzerland, for imaging fluid
distribution in porous rocks. The variation in water saturation was related to the pore geometry of the sample as investigated
by petrographic image analysis of thin sections. A variation in fluid saturation was successfully imaged. The spatial saturation
distribution noted from the neutron tomography corresponds well with variations in pore geometry, indicating that the water
was preferentially flushed from the coarse-grained laminae.
Résumé. Des mesures tomographiques neutroniques ont été réalisées sur un échantillon de grès quartzeux dans le but d'y déterminer
des variations de degré de saturation après que l'échantillon initialement saturé en eau ait été soumis à un drainage forcé.
Les expériences ont été conduites afin d'étudier la capacité d'un dispositif de tomographie neutronique de l'Institut Paul
Scheerer (Suisse) à donner une image de la répartition des fluides dans les roches poreuses. Des variations de degré de saturation
ont été identifiées avec succès, variations en relation avec la géométrie des pores de l'échantillon comme cela a pu être
identifié par des techniques d'analyse d'image de lames minces. La répartition spatiale du degré de saturation observée à
partir de la tomographie neutronique correspond bien à des variations dans la géométrie des pores, indiquant que l'eau avait
été préférentiellement chassée des lamines constituées de gros grains.
Electronic Publication 相似文献
6.
Quantitative determination of bound water diffusion in multilayer boards by means of neutron imaging
Walter Sonderegger Stefan Hering David Mannes Peter Vontobel Eberhard Lehmann Peter Niemz 《Holz als Roh- und Werkstoff》2010,68(3):341-350
Diffusion processes into multilayered samples of Norway spruce (Picea abies [L.] Karst.) exposed to a differentiating climate (dry side/wet side) were determined and quantified by means of neutron imaging (NI). The experiments were carried out at the neutron imaging facility NEUTRA at the Paul Scherrer Institute (PSI) in Villigen (Switzerland). With NI the influence of different adhesives (polyvinyl acetate (PVAc), urea formaldehyde resin (UF), epoxy resin (EP), one-component polyurethane (1C PUR)) on the diffusion process could be determined by varying the layer number and the thickness of adhesive joints of the samples. Thereby, neutron transmission images were used to measure time dependent water profiles in the diffusion direction. Using Fick’s second law, diffusion coefficients for radial and tangential water transport in spruce wood and in the adhesive joints were calculated depending on moisture content (MC). It was found that the diffusion coefficients of the adhesives (1C PUR, EP at high MC) were up to three orders of magnitude lower than those of spruce wood. PVAc and UF had a smaller barrier effect compared to wood, which in contrast to 1C PUR and EP, clearly depends on the MC. 相似文献
7.
D. Goers M. Holzapfel W. Scheifele E. Lehmann P. Vontobel P. Novk 《Journal of power sources》2004,130(1-2):221-226
In situ neutron radiography (NR) was used to study the gas evolution on graphite electrodes in lithium-ion cells containing different PVDF-based gel-type electrolytes. The amount of gas bubbles and channels was calculated by image analysis. Gas production was extremely high in the case of the electrolyte containing ethylene carbonate (EC) and propylene carbonate (PC) (2:3, w/w), 1 M LiClO4. About 60% of the electrode surface consisted of the gas phase which resulted in an inhomogeneous local current distribution. In contrast, the electrolyte containing EC and γ-butyrolactone (GBL) (1:1, w/w), 1 M LiBF4 only showed a small increase of the gas volume between the electrodes of about 3%. In situ NR also revealed the displacement of the electrolyte due to gas evolution and volume changes of the electrodes. 相似文献
8.
Urological diagnosis is considerably improved by the application of sonography. The best results are undoubtedly obtained if the investigations are carried out by an appropriately trained urologist familiar with clinical differential diagnosis. Various sonographic techniques which have proved helpful in this field are discussed, and a novel method for assessing the residual urinary volume is described. 相似文献
9.
Marjan Sedighi-Gilani Peter Vontobel Eberhard Lehmann Jan Carmeliet Dominique Derome 《Materials and Structures》2014,47(6):1083-1096
Non-destructive neutron radiography is used to study the different processes of liquid transport in Scots pine sapwood and heartwood. The spatial and temporal changes in moisture content and saturation degree, measured at high resolution, are provided for water uptake in longitudinal, radial and tangential directions. Liquid uptake in sapwood, compared to in heartwood, is found to be faster and more homogeneous. Latewood cells are the preferential pathways for longitudinal and tangential uptake in both sapwood and heartwood resulting in strongly non-uniform water fronts. In radial uptake, water accumulates first in the border between growth layers. While the moisture content profiles vary strongly between earlywood and latewood layers, the corresponding swelling strain profiles change smoothly due to the mechanical interaction between the different layers. Long term experiments in laboratory show three phases of uptake: a first fast phase, a second slower phase and a third phase reaching capillary saturation. The main difference between sapwood and heartwood uptake takes place in the first phase when liquid is mainly transported in the lumen, until moisture reaches the top of the sample. After that, both wood types behave similarly, uptake is followed by a slower adsorption in the wood cell walls and liquid redistribution in perpendicular to the uptake direction until the sample is almost totally saturated. These findings are of interest for future studies on durability and treatability of pine sapwood and hardwood. 相似文献
10.