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1

A Modelling Approach for Workflow Constrained by Inputs and Outputs

Zheng C., Huang S., Liu X., Yao Y.

Przegląd Elektrotechniczny

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2013

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R. 89, nr 3b

156--160

EN

Workflow systems have been studied for years, but there is not so much research in workflow testing. The key point for workflow testing is to model a workflow. In this paper, a formalized definition of workflow constrained by inputs and outputs is presented first. Based on the definition and the traditional Petri Net, a kind of I/O_WF_NET model is proposed. In that model, the activities of the workflow are modelled as transitions and the inputs and outputs of an activity are modelled as places. The modelling approach for workflow constrained by inputs and outputs is also presented. And a case study is given to show how to apply this approach and the validity of the proposed modelling method.

PL

W artykule przedstawiono model przepływu pracy (workflow), oparty na schemacie Petri Net. Wstępnie zdefiniowano sam model wraz z ograniczeniami wejść i wyjść. Na tej podstawie prowadzono dalsze prace. Opisano sposób modelowania przepływu informacji oraz elementów wejścia i wyjścia. Przeprowadzono także badanie warunkach rzeczywistych w celu weryfikacji proponowanego modelu.

2

Advanced microstructure diagnostics and interface analysis of modern materials by high-resolution analytical transmission electron microscopy

Neumann W., Kirmse H., Hausler I., Mogilatenko A., Zheng C., Hetaba W.

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2010

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Vol. 58, nr 2

237-253

EN

Transmission electron microscopy (TEM) is a powerful diagnostic tool for the determination of structure/property relationships of materials. A comprehensive analysis of materials requires a combined use of a variety of complementary electron microscopical techniques of imaging, diffraction and spectroscopy at an atomic level of magnitude. The possibilities and limitations of quantitative TEM analysis will be demonstrated for interface studies of the following materials and materials systems: Nickel-based superalloy CMSX-10, (Zn,Cd)O/ZnO/Al2O3, (Al,Ga)N/AlN/Al2O3, GaN/LiAlO2 and FeCo-based nanocrystalline alloys.

3

A comparison of models for ductile fracture prediction in forging processes

Zheng C., Cesar de Sa J. M. A., Pires F.

Computer Methods in Materials Science

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2007

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Vol. 7, No. 4

389-396

EN

The possibility of predicting ductile fracture plays an important role in the design of components by forging processes. Experimental observations showed that the nucleation, growth and coalescence of voids are the mechanisms that control the initiation and propagation of fracture and that these mechanisms are influenced in different ways by factors like the hydrostatic stress, the equivalent stress or by the maximal principal stress. Many ductile fracture indicators, based on some or all of those factors, are available and used in many practical situations in the design of those components. In this work a comparative work of many of those criteria was undertaken. Different criteria were chosen amongst the more popular ones and from different groups, in which they may be classified, namely those based on micromechanics and those based on the geometry of voids or their growth mechanisms. The criteria based on the Continuous Damage Mechanics, in which a coupling between plastic deformation and material degradation is taken into account and that include different damage evolution descriptions for traction or compressive stress states give a more correct and clear localization for the fracture initiation site.

PL

Możliwość przewidywania plastycznego pękania odgrywa ważną rolę w projektowaniu wyrobów kutych. Badania doświadczalne pokazują, że zarodkowanie, wzrost i łączenie się pustek są mechanizmami kontrolującymi powstawanie i rozprzestrzenianie się pęknięć. Na te mechanizmy oddziałują w różnym stopniu, takie parametry jak ciśnienie hydrostatyczne , intensywność naprężenia i maksymalne naprężenie główne. Znanych i używanych w praktyce jest wiele kryteriów pękania plastycznego opartych na tych parametrach. W niniejszej pracy te kryteria są porównywane. Spośród najbardziej popularnych wybrano kryteria pękania przynależne do różnych grup, klasyfikowane według podstaw danego kryterium, a więc kryteria oparte na mikrostrukturze materiału, kształcie pustek lub me chanizmie ich wzrostu. Kryteria oparte na mechanizmie kontinuum pękania, w których bierze się pod uwagę sprzężenie między odkształceniem plastycznym i degradacją materiału poprzez analizę różnych możliwości rozwoju zniszczenia dla rozciągającego i ściskającego stanu naprężenia, dają bardziej poprawną lokalizację obszarów, w których następuje inicjacja pęknięcia.

4

A comparison of meshless and finite element approaches to ductile damage in forming processes

Cesar de Sa J., Zheng C.

Computer Methods in Materials Science

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2007

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Vol. 7, No. 2

262-268

EN

In metal forming processes the damage associated with large deformations is a phenomenon that should be minimized or simply avoided as it usually leads to flawed parts. The initiation of plasticity and damage is caused by movement and accumulation of dislocations in metals but their nature and evolution is different. Ductile damage evolution in metals is usually associated with the initiation and growth of micro cracks and cavities, resulting in a progressive material softening. Damage growing influences indirectly the plastic behaviour by locally reducing the elementary area of resistance and therefore plasticity and damage should be coupled at the constitutive level. In the theory of Continuum Damage Mechanics the damage is represented by internal variables (of scalar, vectorial or tensor type) which give a measure of the deteriorated state at each representative volume of the material. This variable may then be used to define the effective stress state. Another important aspect is related with the fact that in ductile damage localization is similar to that associated with plastic strain. These physical phenomena are characterised by the accumulation of damage and large deformations within narrow bands. In experiments these localization zones display a finite width which may be related to the micro structure of the material. Classical theories of plasticity and damage mechanics, based on internal variable approaches, are local theories and do not include size effects associated to a characteristic dimension of the material. Their implementation in a finite element setting shows a pathologic effect of spatial mesh dependence because the constitutive models are unable to capture the limitation of the localization upon mesh refinement. In fact, the original hypothesis of homogeneous continuous models does not take into account large changes in the internal variables, like plastic strain and damage, in the localization zone. The aforementioned effect can be adequately explained by micro mechanical theories but their numerical implementation is still rather expensive. Non-local models have been proposed to bridge the gap between classical continuum theories and the micromechanical ones. In these models the evolution of some internal variables describing strain and damage in a specific point is also determined by the history of the surrounding material by including in the formulation averages or gradients of part or all of them. Some of theses models have proved to be effective when implemented in a finite element framework. Some claims have been made that the new class of computational methods, i.e. meshless methods, could be more effective when dealing with localization problems. Typically these new methods use a set of points and local support functions to represent the problem domain with no need of an additional mesh. This local support functions could then be broadened for the evaluation of the evolution of the internal variables, giving a non-local character to the solution. Therefore, in this work, an incursion was made into the application of these methods to this particular type of problems in order to investigate how meshless methods deal with ductile damage phenomena, if the unacceptable discretization dependence is also present and to assess how effectively the non-local and gradient models work in these settings. The chosen meshless method was the Reproducing Kernel Particle Method (RKPM). The material model was extended in order to include ductile damage effects by coupling the elastoplastic constitutive law with the damage evolution equations. Non-local and related gradient (explicit and implicit) models were also implemented using the RKPM. A set of numerical examples showed that the meshless solution scheme on ductile damage, exhibits the same type of dependence of solutions upon refinement of the geometrical discretization. Both implicit and explicit gradient and non-local models can alleviate this pathological behaviour. Nevertheless the explicit gradient model still presents a local behaviour by concentrating the damage on a narrower zone.

PL

Możliwość wykorzystania metody bez siatkowej Reproducing Kernel Particle Method (RKPM) do symulacji plastycznego pękania w procesach przeróbki plastycznej jest tematem niniejszej pracy. Zalety metody RKPM są porównane z konwencjonalnymi modelami MES, szczególnie pod względem problemów z dyskretyzacją badanego obszaru. Zastosowany model pękania bazuje na podejściu Lemaitre z uwzględnieniem rozgraniczenia pękania dla lokalnych obszarów rozciąganych i spęczanych. Zaimplementowane lokalne i globalne modele w formie jawnej i niejawnej są porównane i omówione w niniejszej pracy.

5

Fuzzy c-means clustering algorithm with a novel penalty term for image segmentation

Yang Y., Zheng C., Lin P.

Opto-Electronics Review

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2005

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Vol. 13, No. 4

309-315

EN

Fuzzy clustering techniques, especially fuzzy c-means (FCM) clustering algorithm, have been widely used in automated image segmentation. However, as the conventional FCM algorithm does not incorporate any information about spatial context, it is sensitive to noise. To overcome this drawback of FCM algorithm, a novel penalized fuzzy c-means (PFCM) algorithm for image segmentation is presented in this paper. The algorithm is formulated by incorporating the spatial neighbourhood information into the original FCM algorithm with a penalty term. The penalty term acts as a regularizer in this algorithm, which is inspired by the neighbourhood expectation maximization (NEM) algorithm and is modified in order to satisfy the criterion of the FCM algorithm. Experimental results on synthetic, simulated and real images indicate that the proposed algorithm is effective and more robust to noise and other artifacts than the standard FCM algorithm.

6

X-ray carpal-bone image boundary feature analysis using region statistical feature based level set method for skeletal age assessment application

Lin P., Zheng C., Zhang F., Yang Y.

Optica Applicata

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2005

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Vol. 35, nr 2

283-294

EN

Skeletal age assessment is one of the important applications of hand radiography in the area of pediatric radiology. Feature analysis of the carpal-bones can reveal the important information for skeletal age assessment. The present work in this paper faces the problem of the detection of carpal-bone features from X-ray image. A novel and effective segmentation technique is presented in this work with carpal-bone image for skeletal age estimation. Carpal-bone segmentation is a critical operation of the automatic skeletal age assessment system. This method consists of two procedures. First, the original carpal-bone image is preprocessed via anisotropic diffusion filter. Then, the carpal-bone image is segmented by region based level set method. The basic idea of the region based level set method is to add a force that takes into account the information within the regions in order to add robustness and more efficiently separate homogeneous regions. Experiments are carried out on X-ray images of carpal-bone. The experimental results show that incorporating region statistical information into the level set method, an accurate and robust segmentation can be achieved.

7

Fuzzy clustering with spatial constraints for image thresholding

Yang Y., Zheng C., Lin P.

Optica Applicata

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2005

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Vol. 35, nr 4

943-954

EN

Image thresholding plays an important role in image segmentation. This paper presents a novel fuzzy clustering based image thresholding technique, which incorporates the spatial neighborhood information into the standard fuzzy c-means (FCM) clustering algorithm. The prior spatial constraint, which is defined as weight in this paper, is inspired by the k-nearest neighbor (k-NN) algorithm and is modified from two aspects in order to improve the performance of image thresholding. The algorithm is initialized by a fast FCM algorithm, in which the iteration is carried out with the statistical gray level histogram of image instead of the conventional whole data of image; therefore its convergence is fast. Extensive experiment results and both qualitative and quantitative comparative studies with several existing methods on the thresholding of some synthetic and real images illustrate the effectiveness and robustness of the proposed algorithm.