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排序方式: 共有2092条查询结果,搜索用时 281 毫秒
21.
A new image segmentation system is presented to automatically segment and label brain magnetic resonance (MR) images to show normal and abnormal brain tissues using self-organizing maps (SOM) and knowledge-based expert systems. Elements of a feature vector are formed by image intensities, first-order features, texture features extracted from gray-level co-occurrence matrix and multiscale features. This feature vector is used as an input to the SOM. SOM is used to over segment images and a knowledge-based expert system is used to join and label the segments. Spatial distributions of segments extracted from the SOM are also considered as well as gray level properties. Segments are labeled as background, skull, white matter, gray matter, cerebrospinal fluid (CSF) and suspicious regions. 相似文献
22.
Summary The polymerization of methyl methacrylate (MMA), ethyl acrylate (EA), styrene (St) and 2-vinyl pyridine (VP) is initiated upon irradiation at >350 nm of dichloromethane solutions containing N-ethoxy-2-methylpyridinium hexafluorophosphate (EMP+PF6
-) and anthracene or thioxanthone. Initiation mechanisms involving the formation of ethoxyl radicals during the decomposition of EMP+ ions via electron transfer are proposed. 相似文献
23.
The chemical shift difference between signals of C() and C() of unsaturated ketones, , which we used before to measure acid strengths, has now been used to evaluate the hydrogen bond donor ability of solvents which are not acidic enough to hydronate the indicator. For such solvents there is no general correlation between H-bond donor ability and acid strength: hexa-fluoroisopropanol is a much weaker acid than acetic acid, but it is a stronger H-bond donor. The method can be applied to evaluate the H-bonding properties of solid surfaces, and it was thus found that silica gel has a much stronger H-bond donor ability than methanol or acetic acid. 相似文献
24.
25.
Atilla Savaş 《中国工程学刊》2016,39(2):211-220
This paper describes the application of the CFD code, Comsol Multiphysics, to modeling the 3-D metal flow in friction stir welding of AA 2024-T3 aluminum alloy in order to investigate the influence of tool shape over the metal flow. Heat transfer and non-Newtonian flow equations were solved simultaneously. The results from the benchmark experiments found in the literature were used for validation purposes. Scrolled shoulders and threaded pins were given as kinematic boundary conditions. This made the computational problem an easy one. A welding engineer can predict the metal flow around the tool with different scrolls and threads under any welding conditions without making expensive experiments. Investigation of the velocity field before actual welding can save a lot of engineering hours. 相似文献
26.
This article studied the effects of low-velocity impact on the failure stresses and stiffness using a pendulum test. The specimens were of variable depth (20, 30, and 40 mm), a width of 50 mm, length of 650 mm, and span-length of 480 mm. The smallest specimen depth was similar to specimen sizes tested in the literature used to create the duration of load curve, while the largest specimen depth are considered structural size specimens. The impact was predicted using a numerical approach with Euler–Bernoulli beam, as well as Timoshenko beam theory, with a plastic contact law. The models were validated for impact from a low release-angle (where the beam remained elastic), but could use improvement for the force prediction at a high incidence velocity. The measured force signals were used as forcing functions to obtain the dynamic failure stresses for all of the evaluated specimens, and the Timoshenko–Goens–Hearmon Method to derive the dynamic E. The resulting strain rates ranged from 9.11?×?10?5 s?1 for the quasi-static specimens up to 25 s?1 for the greatest incidence velocity. The results from this study suggest different duration of load factors than the Madison Curve, influencing the design of structures subjected to dynamic loading. 相似文献
27.
The axisymmetric crack problem in a non-homogeneous interfacial region between homogeneous half-spaces 总被引:3,自引:0,他引:3
In this paper, the axisymmetric crack problem in a non-homogeneous interfacial region between two homogeneous half-spaces is considered. It is assumed that the shear modulus varies continuously between that of the two half-spaces; and the shear modulus for the interface region is approximated by = 0 emz. By using Hankel transform technique the problem is reduced to a pair of singular integral equations. The solutions of the problem are obtained for different material combinations and loading conditions; and modes I and II stress intensity factors, and the direction of a probable crack growth are calculated. 相似文献
28.
Efficient monitoring of parametric context-free patterns 总被引:1,自引:0,他引:1
Patrick O’Neil Meredith Dongyun Jin Feng Chen Grigore Roşu 《Automated Software Engineering》2010,17(2):149-180
Recent developments in runtime verification and monitoring show that parametric regular and temporal logic specifications
can be efficiently monitored against large programs. However, these logics reduce to ordinary finite automata, limiting their
expressivity. For example, neither can specify structured properties that refer to the call stack of the program. While context-free
grammars (CFGs) are expressive and well-understood, existing techniques for monitoring CFGs generate large runtime overhead
in real-life applications. This paper demonstrates that monitoring parametric CFGs is practical (with overhead on the order of 12% or lower in most cases). We present a monitor synthesis algorithm for CFGs based on an
LR(1) parsing algorithm, modified to account for good prefix matching. In addition, a logic-independent mechanism is introduced
to support matching against the suffixes of execution traces. 相似文献
29.
Cost estimation and effort allocation are the key challenges for successful project planning and management in software development.
Therefore, both industry and the research community have been working on various models and techniques to accurately predict
the cost of projects. Recently, researchers have started debating whether the prediction performance depends on the structure
of data rather than the models used. In this article, we focus on a new aspect of data homogeneity, “cross- versus within-application
domain”, and investigate what kind of training data should be used for software cost estimation in the embedded systems domain.
In addition, we try to find out the effect of training dataset size on the prediction performance. Based on our empirical
results, we conclude that it is better to use cross-domain data for embedded software cost estimation and the optimum training
data size depends on the method used. 相似文献
30.
C. Başyigit Iskender Akkurt S. Kilincarslan A. Beycioglu 《Neural computing & applications》2010,19(4):507-513
The compressive strength of heavyweight concrete which is produced using baryte aggregates has been predicted by artificial
neural network (ANN) and fuzzy logic (FL) models. For these models 45 experimental results were used and trained. Cement rate,
water rate, periods (7–28–90 days) and baryte (BaSO4) rate (%) were used as inputs and compressive strength (MPa) was used as output while developing both ANN and FL models.
In the models, training and testing results have shown that ANN and FL systems have strong potential for predicting compressive
strength of concretes containing baryte (BaSO4). 相似文献