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排序方式: 共有115条查询结果,搜索用时 15 毫秒
1.
The curing behavior of two kinds of commercial powdered resol phenolic resins was studied by differential scanning calorimetry. Liquid‐state 13C‐NMR spectroscopy was used to aid in understanding the curing behavior by detecting the structure of powdered resins. The reaction mechanism was interpreted with the dependency of activation energy on the degree of conversion. The results indicate that there are differences in the curing mechanism between core and face phenolic resins. The curing process of core resin was faster than that of face resin at the same reaction temperature. The water added in the curing system played an important role of plasticizer or diluent according to different curing stages and water content. In the initial curing stage, water mainly diluted the system and retarded the curing reactions. However, at the higher degrees of conversion, water played the role of plasticizer to decrease the effect of diffusion on the curing reactions to make the curing reactions more complete. The excess water added in the curing system played the role of diluent at almost all stages during the curing process. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1371–1378, 2003 相似文献
2.
In this paper, we present a new irradiance caching scheme using Monte Carlo ray tracing for efficiently rendering participating media. The irradiance cache algorithm is extended to participating media. Our method allows to adjust the density of cached records depending on illumination changes. Direct and indirect contributions can be stored in the records but also multiple scattering. An adaptive shape of the influence zone of records, depending on geometrical features and irradiance variations, is introduced. To avoid a high density of cached records in low interest areas, a new method controls the density of the cache when adding new records. This record density control depends on the interpolation quality and on the photometric characteristics of the medium. Reducing the number of records accelerates both the computation pass and the rendering pass by decreasing the number of queries to the cache data structure (Kd-tree). Finally, instead of using an expensive ray marching to find records that cover the ray, we gather all the contributive records along the ray. With our method, pre-computing and rendering passes are significantly speeded-up. 相似文献
3.
Using vanishing points for camera calibration and coarse 3D reconstruction from a single image 总被引:5,自引:0,他引:5
In this paper, we show how to calibrate a camera and to recover the geometry and the photometry (textures) of objects from
a single image. The aim of this work is to make it possible walkthrough and augment reality in a 3D model reconstructed from
a single image. The calibration step does not need any calibration target and makes only four assumptions: (1) the single
image contains at least two vanishing points, (2) the length (in 3D space) of one line segment (for determining the translation
vector) in the image is known, (3) the principle point is the center of the image, and (4) the aspect ratio is fixed by the
user. Each vanishing point is determined from a set of parallel lines. These vanishing points help determine a 3D world coordinate
system R
o. After having computed the focal length, the rotation matrix and the translation vector are evaluated in turn for describing
the rigid motion between R
o and the camera coordinate system R
c. Next, the reconstruction step consists in placing, rotating, scaling, and translating a rectangular 3D box that must fit
at best with the potential objects within the scene as seen through the single image. With each face of a rectangular box,
a texture that may contain holes due to invisible parts of certain objects is assigned. We show how the textures are extracted
and how these holes are located and filled. Our method has been applied to various real images (pictures scanned from books,
photographs) and synthetic images. 相似文献
4.
Using Fuzzy Cost‐Based FMEA,GRA and Profitability Theory for Minimizing Failures at a Healthcare Diagnosis Service
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Samira Abbasgholizadeh Rahimi Afshin Jamshidi Daoud Ait‐Kadi Angel Ruiz 《Quality and Reliability Engineering International》2015,31(4):601-615
This paper proposes an integrated approach to identify, evaluate and improve the potential failures in a service setting. This integrated approach combines Fuzzy cost‐based service‐specific FMEA (FCS‐FMEA), Grey Relational Analysis (GRA) and profitability theory for better prioritization of the service failures by considering cost as an important issue and using the profitability theory in a way that the corrective actions costs are taken into account. Considering profitability with FCS‐FMEA and GRA reduces the losses caused by failure occurrence. Besides, a maximization linear mathematical problem is used to select the best mix of failures to be repaired. We apply our approach to an academic example concerning the potential failures diagnosis of the Internal Medicine service of a hospital located in Seoul, Korea. We applied our approach and solved the associated maximization problem by a commercial solver, producing an optimal solution which indicates the most convenient mix of failures to be repaired by considering available budget. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
5.
Kinetics and Thermodynamics of Oil Extraction from Olive Cake 总被引:2,自引:0,他引:2
The kinetics of oil extraction from olive cake by using ethanol 96% was studied for different solvent-to-solids ratios and
temperatures. The thermodynamic aspect of the extraction process was also examined. In the kinetic study, the results produced
by the model of So and Macdonald (a model involving two main mechanisms of oil extraction: a washing process and a diffusion
process with two stages) were found to be in good agreement with the experimental data. The yield of oil in the extract increased
with increasing contact time, solvent-to-solids ratio and extraction temperature. The calculated values of the mass transfer
coefficients of various stages of the extraction were found to increase linearly with solvent-to-solids ratio and temperature.
In all cases, the predominant mechanism in the extraction was the washing of the oil occurring on the particle surface. The
values of the activation energy were 8.56 kJ mol−1 for the washing stage, 9.88 kJ mol−1 for the first stage of diffusion and 17.55 kJ mol−1 for the second stage of diffusion by changing temperature from 20 to 50 °C. Further, the results obtained from thermodynamic
study of extraction process gave positive values of enthalpy and entropy changes and negative values of change in free energy.
Under the equilibrium conditions, the temperature coefficient was found to be 1.02. 相似文献
6.
The authors present a real-time grass rendering technique that works for large, arbitrary terrains with dynamic lighting, shadows, and a good parallax effect. A novel combination of geometry and lit volume slices provides accurate, per-pixel lighting. A fast grass-density management scheme allows the rendering of arbitrarily shaped patches of grass. 相似文献
7.
Artificial Neural Networks (ANN) have been successfully used in predicting the fatigue behavior of fiber-reinforced composite
materials. In most cases, the predictions were obtained for the same material used in training subjected to different loading
conditions. The method would be of greater value if one could predict the failure of materials other than those used for training
the network. In a recent paper, ANN trained using the experimental fatigue data obtained for composites subjected to a constant
stress ratio ( R = s min/s max ) \left( {{\hbox{R}} = {\sigma_{{ \min }}}/{\sigma_{{ \max }}}} \right) was successfully used to predict the cyclic behavior of a composite made of a different material. In this work, this method
is extended to include the stress ratio effect. The results show that ANN can provide accurate fatigue life prediction for
different materials under different values of the stress ratio. These results can allow for the development of a materials
smart database that can be used for various engineering applications. 相似文献
8.
Enzymatic synthesis of two phenyl xylopyranosyl glucopyranosides, through transfer reaction by Trichoderma longibrachiatum endoxylanase, was achieved in the presence of n-hexane used as solvent, phenyl glucoside (10 mM) as acceptor and xylan (2 g/l) as donor. Kinetic study showed that only one compound, identified by 1H and 13C NMR and heteronuclear 2D (1H–13C) chemical shift correlation as phenyl primeveroside (phenyl 6-O-β-xylopyranosyl-1-β-d-glucopyranoside), was synthesized when the reaction time was beyond 1 h. Benzyl and hexyl primeverosides were obtained under the same conditions. When several phenyl glucoside concentrations, from 5 to 50 mM, were used with 2 g/l of xylan, a phenyl primeveroside isomer, identified as phenyl 4-O-β-xylopyranosyl-β-d-glucopyranoside, accumulated in the medium whereas the production of phenyl primeveroside decreased. Only phenyl primeveroside was produced when several xylan concentrations from 2 to 10 g/l were used with 10 mM of phenyl glucoside and its concentration in the reaction mixture increased with the increase of xylan concentration. 相似文献
9.
Noting that the group may be viewed as a 6-parameter gauge group that leaves the Lagrangian of elasticity theory invariant, the Yang-Mills universal gauge theory construction is used to erect a complete continuum theory of material bodies with dislocation and disclination fields. Breaking of the homogeneity of the action of is shown to give rise to disclinations and rotational dislocations while homogeneity breaking of gives rise to translational dislocations. A rigorous justification for replacing displacement gradients by the components of the distortion tensor and Newtonian kinematic velocity by distortional velocity is obtained. Exact determinations are made of the elastic excess forces, the forces on dislocations and the forces on disclinations, and these forces are shown to be totally equilibrating in all instances. Implications of the theory are given and an analysis is made of the field equations and associated dispersion relations that obtain in a disclination free material in the linear elasticity approximation. 相似文献
10.
F. Kadi Allah L. Cattin M. Morsli A. Khelil N. Langlois J. C. Bernède 《Journal of Materials Science: Materials in Electronics》2010,21(2):179-184
Zinc oxide films have been prepared via spray pyrolysis using a perfume atomizer. ZnCl2 has been used as precursor. The influence of the precursor solution and dopant concentration has been investigated. Homogeneous films are obtained with a precursor concentration ranging between 0.3 and 0.4 M and a SnCl2 dopant concentration of 1–2%. The films exhibit broad band gaps and small conductivity. The microstructural properties of these films have been compared with that of films deposited using a classical nozzle. Films deposited by perfume atomizer are rougher, with smaller grain size, compared to films deposited with a classical nozzle. 相似文献