4,478 research outputs found
Global solutions of nonlinear transport equations for chemosensitive movement (vol 36, pg 1177, 2005)
No full textThe purpose of this erratum is to correct Assumption 4.2 in [H. J. Hwang, K. Kang, and A. Stevens, SIAM J. Math. Anal., 36 (2005), pp. 1177-1199]. We also modify some errors caused by the incorrectly stated assumption.X110sciescopu
FIR filter synthesis algorithms for minimizing the delay and the number of adders
No full textAs the complexity of digital filters is dominated by the number of multiplications, many works have focused on minimizing the complexity of multiplier blocks that compute the constant coefficient multiplications required in filters. Although the complexity of multiplier blocks is significantly reduced by using efficient techniques such as decomposing multiplications into simple operations and sharing common subexpressions, previous works have not considered the delay of multiplier blocks which is a critical factor in the design of complex filters. In this paper, we present new algorithms to minimize the complexity of multiplier blocks under the given delay constraints. By analyzing multiplier blocks in view of delay, three delay reduction methods are proposed and combined into previous algorithms. Since the proposed algorithms can generate multiplier blocks that meet the specified delay, a trade-off between delay and hardware complexity is enabled by changing the delay constraints. Experimental results show that the proposed algorithms can reduce the delay of multiplier blocks at the cost of a little increase of complexity
Unstructured mesh Navier-Stokes calculations of the flow field of a helicopter rotor in hover
No full textThree-dimensional viscous flow field around a lifting helicopter rotor in hover is calculated by using an unstructured mesh methodology. The flow solver utilizes a cell-centered finite-volume scheme that is based on Roe's flux-difference splitting and an implicit Jacobi/Gauss-Seidel time integration. The effect of turbulence is estimated by the Spalart-Allmaras one-equation model coupled with a wall function boundary condition. A soIution-adaptive mesh refinement technique is used for efficient capturing of the tip vortex. Calculations are performed at two operating conditions with varying tip Mach number and collective pitch setting. Formation of the tip vortex is well captured through a series of adaptive mesh refinement procedure starting from a coarse initial mesh. Good agreements are obtained between the numerical result and the experiment for both the blade loading and the tip vortex behavior. It is demonstrated that the rotor performance and the flow field are significantly affected by viscosity. The process of tip vortex formation around the blade tip is also qualitatively investigated
Digital filter synthesis based on an algorithm to generate all minimal signed digit representations
No full textIn this paper, the authors propose an algorithm to find all the minimal signed digit (MSD) representations of a constant and present an algorithm to synthesize digital filters based on the MSD representation. The hardware complexity of a digital signal processing system is dependent on the number system used for the implementation. Although the canonical signed digit (CSD) representation is widely employed, as it is unique and guarantees the minimal number of nonzero digits for a constant, the MSD representation provides multiple representations that have the same number of nonzero digits as the CSD representation. The proposed filter synthesis algorithm utilizes this redundancy of the MSD representation to make common subexpressions, as many as possible, leading to smaller filters. By applying the proposed algorithm to the hardware synthesis of finite impulse response filters, the authors obtained multiplier blocks that are 7% smaller than those generated from the CSD representation
SAT-based unbounded symbolic model checking
No full textThis paper describes a Boolean satisfiability checking (SAT)-based unbounded symbolic model-checking algorithm. The conjunctive normal form is used to represent sets of states and transition relation. A logical operation on state sets is implemented as an operation on conjunctive normal form formulas. A satisfy-all procedure is proposed to compute the existential quantification required in obtaining the preimage and fix point. The proposed satisfy-all procedure is implemented by modifying a SAT procedure to generate all the satisfying assignments of the input formula, which is based on new efficient techniques such as line justification to make an assignment covering more search space, excluding clause management, and two-level logic minimization to compress the set of found assignments. In addition, a cache table is introduced into the satisfy-all procedure. It is a difficult problem for a satisfy-all procedure to detect the case that a previous result can be reused. This paper shows that the case can be detected by comparing sets of undetermined variables and clauses. Experimental results show that the proposed algorithm can check more circuits than binary decision diagram-based and previous SAT-based model-checking algorithms.This work was supported in part by the Korea
Science and Engineering Foundation through the MICROS Center, in part by the
Ministry of Science and Technology and the Ministry of Commerce, Industry
and Energy through the System IC 2010 project, and in part by the Ministry of
Information and Communication through the IT-SoC project. This paper was
recommended by Associate Editor J. H. Kukula
Effect of wake adaptation on rotor hover simulations using unstructured meshes
No full textA three-dimensional inviscid flow solver is developed for simulating the flowfield of hovering helicopter rotor using unstructured meshes. The flow solver utilizes a cell-centered finite volume scheme that is based on the Roe's flux-difference splitting with an implicit Jacobi/Gauss-Seidel time integration. Calculations are performed at two operating conditions of subsonic and transonic tip Mach numbers. A solution-adaptive mesh refinement technique is adopted to improve the resolution of flow features on the blade surface. It is demonstrated that the trajectory of the tip vortex can be captured through a series of adaptive mesh refinements starting from a very coarse initial grid. It was found that not only the strength of the tip vortex, but also its trajectory, is strongly dependent on the mesh resolution in the wake. Good agreement is obtained between the numerical result and the experiment for both the blade loading and the tip vortex behavior
A NONITERATIVE SCHEME FOR ORTHOGONAL GRID GENERATION WITH CONTROL FUNCTION AND SPECIFIED BOUNDARY CORRESPONDENCE ON 3 SIDES
No full textA new numerical scheme is proposed for generating an orthogonal grid in a simply-connected 2D domain. The scheme is based on the idea of decomposition of a global orthogonal transform into consecutive mappings of a conformal mapping and an auxiliary orthogonal mapping, which was suggested by Kang and Leal (J. Comput. Phys. 102, 78 (1992)). The method is non-iterative and flexible in the adjustment of grid spacing. The grid spacing can be controlled mainly by specification of the boundary correspondence up to three sides of the boundary. The method is also equipped with a control function that provides further degrees of freedom in the grid spacing adjustment. From a mathematical viewpoint, the proposed scheme can also be regarded as a numerical implementation of the constructive proof for the existence of a solution of the orthogonal mapping problem in an arbitrary simply-connected domain under the condition thal the boundary correspondence is specified on three sides. (C) 1994 Academic Press, Inc.X1110sciescopu
Interactions among the toxic dinoflagellate Amphidinium carterae, the heterotrophic dinoflagellate Oxyrrhis marina, and the calanoid copepods Acartia spp.
No full textTo investigate the interactions among a toxic dinoflagellate Amphidinium carterae, the heterotrophic dinoflagellate Oxyrrhis marina, and the calanoid copepods. Acartia spp, (A. omorii and A. hongi), we measured toxicity of A, carterae, the growth and ingestion rates of O. marina on A. carterae, the ingestion rate of Acartia spp. on A. carterae, the ingestion rate of Acartia spp, on O. marina fed a non-toxic strain of Prorocentrum minimum, and the ingestion rate of Acartia spp. on O. marina, the latter originally satiated with A. carterae and then starved, as a function of elapsed starvation time. The toxicity of A. carterae was 1 MU/1.3 x 10(8) cells when measured using the mouse bioassay, O. marina grew well on A. carterae. When the data were fitted to the Michaelis-Menten equation, maximum specific growth rate (mu (max)) and threshold prey concentration of O. marina on A. carterae were 1.17 d(-1) and 1.3 ng C ml(-1) (13 cells ml-1), respectively. Maximum ingestion and clearance rates of O. marina were 2.8 ng C grazer(-1) d(-1) (28 cells grazer(-1) d(-1)) and 2.4 mul grazer(-1) h(-1), respectively. Grazing by Acartia spp. on A. carterae was undetectable. The ingestion rate of Acartia spp. on O. marina was very low (maximum = 749 Oxyrrhis predator(-1) d(-1)) at Day 0 (O. marina starved for 0 to 1 d after satiation with A, carterae), but increased with increasing elapsed starvation time. The maximum ingestion rate was 4710 Oxyrrhis predator(-1) d(-1) at Day 11 (O. marina starved for 11 to 12 d). The average ingestion rates of Acartia spp, on O. marina fed P. minimum were not significantly higher than on O. marina fed A. carterae at Day 11 at similar mean prey concentrations, but much higher than those fed A. carterae at Day 0. This evidence suggests that O. marina can reduce its mortality rate due to the predation by Acartia spp, if it is satiated with A. carterae, and the grazing of A. carterae by O. marina can sometimes transfer the carbon of A. carterae to Acartia spp., which cannot feed on A. carterae.Y
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