1,721,269 research outputs found
OPNETS - AN OBJECT-ORIENTED HIGH-LEVEL PETRI NET MODEL FOR REAL-TIME SYSTEM MODELING
No full textThis article describes an approach, called OPNets, for modeling real-time systems based on the object-oriented formalization of high-level Petri nets. To increase the maintainability and reusability of objects in Petri net modeling, the approach focuses on the decoupling of interobject communication knowledges and the separation of synchronization constraints from the internal structure of objects. To validate the overall system, which is composed of the hierarchically organized objects and interconnection relations, we used a two-step validation procedure that reduces the complexity and computational efforts required. As an illustration, a manufacturing cell with machining centers and robots is modeled using OPNets. The modeling experiences with OPNets demonstrate that the decoupling and separation of knowledges and constraints clearly enhances maintenance and reusability in real-time system modeling
Development of a grid-based mesh generation technique and its application to remeshing during the finite element simulation of a metal forming process
No full textAn easy and robust grid-based approach is proposed to construct the fully hexahedral mesh in three-dimensional case and its application for the mesh regeneration or remeshing during the finite element simulation of a metal forming process is presented to show the validity and effectiveness of the scheme. The proposed scheme enables the construction of the provisional mesh by superimposing the regular cubical grid over the object to be meshed and removing the. exterior grid points and cells. Because the constructed provisional mesh has the discrete rugged boundary that is quite different from the boundary geometry of the object to be meshed, the nodes on the boundary of the provisional mesh are Projected onto the object boundary. The main disadvantage of the mesh constructed by grid-based approaches is its severely distorted elements on the boundary owing to the projection of the rugged boundary onto the object boundary. In order to improve the quality of boundary elements, some layers of elements an the boundary surface are constructed and the nodes are repositioned by mesh smoothing. Consequently, the quality of boundary elements is effectively improved
Characteristics of an inductively coupled plasma source using a parallel resonance antenna
No full textWe report experimental results from a new inductively coupled plasma (ICP) source for next generation plasma processing. The new source, which we have called a parallel resonance antenna, is designed to reduce problems caused by a large antenna inductance and to improve the plasma density uniformity for large area processing. The key techniques of this new source are reduction of the inductance of the antenna system in parallel connection and induction of LC-resonance with external capacitance variation. The parallel connection of the coils reduces the antenna inductance and the low inductance decreases the antenna voltage. In addition, it allows the antenna size to be easily scaled up to a 300 mm process. An external variable capacitor is connected in series to an outer coil to obtain good plasma uniformity. Because the current distribution in each coil is adjusted by varying the external capacitance, the radial profile of the plasma density can be controlled. The LC-resonance effect is elucidated by observing the reduction in the antenna voltage and variation in the current in the outer coil. We can control the radial plasma density with 3% uniformity by only varying the external capacitance with various discharge powers and pressures. The plasma parameters measured by the rf-compensated Langmuir probe show properties similar to those of general ICPs. These results are consistent with previous modelling work
Poly(3-hydroxybutyrate) production from whey using recombinant Escherichia coli
No full textRecombinant Escherichia coli strains harboring the genes from Alcaligenes eutrophus for polyhydroxyalkanoate biosynthesis were constructed and compared for their ability to synthesize poly(3-hydroxybutyrate) in a defined medium with whey as the sole carbon source. The highest PHB concentration and PHB content obtained were 5.2 g/L and 81% of dry cell weight, respectively.We thank Mary Berlyn for kindly providing the GCSC
strains. This work was supported by KAIST and
KOSEF. Anton Middelberg thanks KOSEF and the
Australian Academy of Science for support under the
joint exchange program
Stimulatory effects of amino aciAppl. Environ.ds and oleic acid on poly(3-hydroxybutyric acid) synthesis by recombinant Escherichia coli
No full textAddition of cysteine, isoleucine, methionine, or proline promoted poly(3-hydroxybutyric acid) [PHB] synthesis by recombinant Escherichia coli more than two-fold. Oleic acid also enhanced PHB synthesis more than three-fold. A PHB concentration of 70 g/l could be obtained by fed-batch culture of recombinant E. coli in a defined medium supplemented with small amounts of isoleucine, methionine, and proline. The stimulatory effects of amino acids and oleic acid on PHB synthesis seems to be due to the availability of more acetyl-CoA and/or NADPH
A fast tree-structured motion estimation for variable blocks
No full textA fast motion estimation algorithm is proposed, which performs a tree-structured motion vector search for variable blocks in the integer-pixel unit. The proposed method is based on the inequality of sum norms to find the best estimate of the motion vectors for variable blocks. The proposed motion estimation algorithm is applied to the Joint Video Team (JVT) encoder that performs variable-block motion estimation (ME) with quarter-pixel unit. In terms of computational complexity, the proposed motion estimation algorithm searches motion vectors about 10.7 times as fast as the spiral full search with early termination and 6.6 times as fast as the fast full search using the hierarchical sum of absolute difference (SAD), while the PSNR (peak signal-to-noise ratio) of the reconstructed image is slightly degraded
Global lock escalation in database management systems
No full textSince database management systems (DBMSs) have limited lock resources, transactions requesting locks beyond the limit must be aborted, degrading the performance abruptly. Lock escalation can be effectively used in such circumstances to alleviate the problem. Many lock escalation methods have been proposed and implemented in commercial DBMSs. However, they have certain problems due to the local nature of their decisions on when to execute lock escalation. In this paper, we propose a new lock escalation method, global lock escalation. that makes such decision globally based on the total number of locks. Through extensive simulation, we show that the global lock escalation method outperforms the existing ones significantly. Especially, we show that the number of concurrent transactions allowable increases by 2-16 times. We believe our method can be easily implemented in the commercial DBMSs enhancing the performance significantly under excessive lock requests. (C) 2002 Elsevier Science B.V. All rights reserved
Ethylene Polymerization by multimetallic Ziegler-Natta Catalysts: molecular weight distribution and polymerization rate
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