Adaptive Low-Rank Approximation of Collocation Matrices

This article deals with the solution of integral equations using collocation methods with almost linear complexity. Methods such as fast multipole, panel clustering and ℋ-matrix methods gain their efficiency from approximating the kernel function. The proposed algorithm which uses the ℋ-matrix format, in contrast, is purely algebraic and relies on a small part of the collocation matrix for its blockwise approximation by low-rank matrices. Furthermore, a new algorithm for matrix partitioning that significantly reduces the number of blocks generated is presented. Received August 15, 2002; revised September 20, 2002 Published online: March 6, 2003     

Using the acoustic sound pressure level for quality prediction of surfaces created by abrasive waterjet

The paper deals with an innovative way of cutting materials by abrasive waterjet with a view to increase its quality. In the research work, we were concerned with the search for a relationship between surface roughness and noise in the abrasive waterjet cutting process. Innovation lies in the use of negative characteristic of the technology—noise, which is a carrier of information about the quality of cutting process. In this way, the noise can be positively used in the on-line control of the technological process. The final result is a project for control of the process of abrasive waterjet cutting of materials by means of feedback according to the on-line measurement of acoustic pressure level L _aeq (dB). Instantaneous information about the state of cut according to the instantaneous value of L _aeq amplitude allows the automatic regulation of traverse speed of cutting head v _p (mm.min^?1), which is, together with the pressure p (MPa), one of the most important technological factors of control of production technology from the point of view of economic indicators and qualitative indicators of a semiproduct. The proposed model has been experimentally verified and was simulated in Matlab.     

On finite-time and fixed-time consensus algorithms for dynamic networks switching among disconnected digraphs

ABSTRACT

This paper aims to analyse the stability of a class of consensus algorithms with finite-time or fixed-time convergence for dynamic networks composed of agents with first-order dynamics. In particular, in the analysed class a single evaluation of a nonlinear function of the consensus error is performed per each node. The classical assumption of switching among connected graphs is dropped here, allowing to represent failures and intermittency in the communications between agents. Thus, conditions to guarantee finite and fixed-time convergence, even while switching among disconnected graphs, are provided. Moreover, the algorithms of the considered class are computationally simpler than previously proposed finite-time consensus algorithms for dynamic networks, which is an essential feature in scenarios with computationally limited nodes and energy efficiency requirements such as in sensor networks. Simulations illustrate the performance of the proposed consensus algorithms. In the presented scenarios, results show that the settling time of the considered algorithms grows slower than other consensus algorithms for dynamic networks as the number of nodes increases.     

A multi-objective method of hinge-free compliant mechanism optimization

A new multi-objective formulation for topology synthesis of hinge-free compliant mechanisms is presented based on the SIMP method. A weighted sum formed objective function is developed by taking into consideration the input and output mean compliances. The weighting factors are set based on the information that is obtained from the previous iteration and automatically updated with each optimization iteration step. Shape sensitivity analysis is addressed. Some numerical examples are presented to illustrate the validity of the proposed method.     

Characterization of Failure Behavior in Distorted WC-Co Tip of Coal Mining Picks

Journal of Failure Analysis and Prevention - The present paper deals with the characterization of failure behavior in the cemented carbide (WC 94–Co 6%) tips of two cutters, i.e., conical...     

The Reaction of Ozone with Bisulfide (HS−) in Aqueous Solution – Mechanistic Aspects

The ozone demand to oxidize HS^?/H₂S [pK_a(H₂S) = 6.9, k(HS^? + O₃) = 3 × 10⁹ M^?1 s^?1, k(H₂S + O₃) = 3 × 10⁴ M^?1 s^?1] to SO₄ ^2? is only 2.4 mol ozone per mol SO₄ ^2? formed, much lower than stoichiometric 4.0 mol/mol if a series of O-transfer reactions would occur. As primary step, the formation of an ozone adduct to HS^?, HSOOO^–, is suggested that decomposes into HSO^– and singlet oxygen (16%) or rearranges into peroxysulfinate ion, HS(O)OO^– (84%). Potential reactions of the above intermediates are discussed. Some of these can account for the low ozone demand.