DESP: a distributed economics-based subcontracting protocol for computation distribution in power-aware mobile ad hoc networks

In this paper, we present a new economics-based power-aware protocol, called the distributed economic subcontracting protocol (DESP) that dynamically distributes task computation among mobile devices in an ad hoc wireless network. Mobile computation devices may be energy buyers, contractors, or subcontractors. Tasks are transferred between devices via distributed bargaining and transactions. When additional energy is required, buyers and contractors negotiate energy prices within their local markets. Contractors and subcontractors spend communication and computation energy to relay or execute buyers' tasks. Buyers pay the negotiated price for this energy. Decision-making algorithms are proposed for buyers, contractors, and subcontractors, each of which has a different optimization goal. We have built a wireless network simulator, called ESIM, to assist in the design and analysis of these algorithms. When the average communication energy required transferring a task is less than the average energy required to execute a task, our experimental results indicate that markets based on our protocol and decision-making algorithms fairly and effectively allocate energy resources among different tasks in both cooperative and competitive scenarios.     

Elastic solutions of a cylindrical rod containing periodically distributed inclusions with axisymmetric eigenstrains

Summary. In this paper, we give the elastic solution for a special type of microstructure – a circular cylindrical rod containing periodically distributed inclusions along its axial direction. Each inclusion has the same uniform axisymmetric transformation strain (eigenstrain). Analytical elastic solutions are obtained for the displacements, stresses and elastic strain energy of the rod. The effects of microstructure and its evolution (growth of inclusions) on the elastic stress and strain fields as well as the strain energy of the rod are quantitatively demonstrated. As a result of such microstructure evolution nominal stress-strain relation with strain softening is derived for a rod under uniaxial tension.     

Stable high-order delta-sigma digital-to-analog converters

Stability analysis of high-order delta-sigma loops is a challenge. In this brief, a sufficient design criterion is presented for high-order multibit error-feedback digital-to-analog converters (DACs) which are especially suitable for high-speed operation. This analytical criterion might be too conservative, but it allows for the design of stable, robust, and high-resolution delta-sigma DACs. Both analytical and numerical analysis are performed for verification. Also, experimental results of a discrete-component multiplier-free prototype demonstrate 10-b operation at a very low oversampling ratio of 4.     

From "macro" to "micro" manipulation: models and experiments

This paper addresses various problems related to manipulation in the micro domain, a field which is increasingly important for research and application. Grasping and manipulating parts with size ranging between a few micrometers and about 1 millimeter (defined in this paper as "micro parts") are required for an increasing number of applications: the assembly of micro systems and micro machines; and the operation in tiny and unpredictable environments, such as for inspection and interventions in pipes and for micro surgery. The aim of this work is to find out similarities and differences between traditional manipulation and micro manipulation, by investigating which requirements are still valid and which must be redefined when the object size scales down. The similarities between the two application domains "macro" and "micro" are pointed out along with the differences, and both are taken into account for the evaluation of different grasping typologies. Dedicated models for the adhesion forces arising at the micro level are presented, preliminarily tested, and discussed.     

Efficient and accurate approach for powder compaction problems

 In this paper, a new approach for powder cold compaction simulations is presented. A density-dependent plastic model within the framework of finite strain multiplicative hyperelastoplasticity is used to describe the highly nonlinear material behaviour; the Coulomb dry friction model is used to capture friction effects at die-powder contact; and an Arbitrary Lagrangian–Eulerian (ALE) formulation is used to avoid the (usual) excessive distortion of Lagrangian meshes caused by large mass fluxes. Several representative examples, involving structured and unstructured meshes are simulated. The results obtained agree with the experimental data and other numerical results reported in the literature. It is shown that, contrary to other Lagrangian and adaptive h-remeshing approaches recently reported for this type of problems, the present approach verifies the mass conservation principle with very low relative errors (less than 1% in all ALE examples and exactly in the pure Lagrangian examples). Moreover, thanks to the use of an ALE formulation and in contrast with other simulations, the presented density distributions do not present spurious oscillations. Received: 20 March 2002 / Accepted: 15 October 2002 The partial financial support of the Ministerio de Ciencia y Tecnología (grant number DPI 2001-2204) is gratefully acknowledged.     

Efficient design of oversampled NPR GDFT filterbanks

We propose a flexible, efficient design technique for the prototype filter of an oversampled near perfect reconstruction (NPR) generalized discrete Fourier transform (GDFT) filterbank. Such filterbanks have several desirable properties for subband processing systems that are sensitive to aliasing, such as subband adaptive filters. The design criteria for the prototype filter are explicit bounds (derived herein) on the aliased components in the subbands and the output, the distortion induced by the filterbank, and the imaged subband errors in the output. It is shown that the design of an optimal prototype filter can be transformed into a convex optimization problem, which can be efficiently solved. The proposed design technique provides an efficient and effective tool for exploring many of the inherent tradeoffs in the design of the prototype filter, including the tradeoff between aliasing in the subbands and the distortion induced by the filterbank. We calculate several examples of these tradeoffs and demonstrate that the proposed method can generate filters with significantly better performance than filters obtained using current design methods.     

Catalytic dehydrogenation of ethylbenzene with carbon dioxide: promotional effect of antimony in supported vanadium–antimony oxide catalyst

Alumina-supported vanadium oxide, VO_x/Al₂O₃, and binary vanadium–antimony oxides, VSbO_x/Al₂O₃, have been tested in the ethylbenzene dehydrogenation with carbon dioxide and characterized by S_BET, X-ray diffraction, X-ray photoelectron spectroscopy, hydrogen temperature-programmed reduction and CO₂ pulse methods. VSbO_x/Al₂O₃ exhibited enhanced catalytic activity and especially on-stream stability compared to VO_x/Al₂O₃ catalyst. Incorporation of antimony into VO_x/Al₂O₃ increased dispersion of active VO_x species, enhanced redox properties of the systems and formed a new mixed vanadium–antimony oxide phase in the most catalytically efficient V_0.43Sb_0.57O_x/Al₂O₃ system.     

An alternative blind feedforward symbol timing estimator using two samples per symbol

Recently, S.J. Lee proposed a blind feedforward symbol timing estimator that exhibits low computational complexity and requires only two samples per symbol (see IEEE Commun. Lett., vol.6, p.205-7, 2002). We analyze Lee's estimator rigorously by exploiting efficiently the cyclostationary statistics present in the received oversampled signal; its asymptotic (large sample) bias and mean-square error (MSE) are derived in closed-form expression. A new blind feedforward timing estimator that requires only two samples per symbol and presents the same computational complexity as Lee's estimator is proposed. It is shown that the proposed new estimator is asymptotically unbiased and exhibits smaller MSE than Lee's estimator. Computer simulations are presented to illustrate the performance of the proposed new estimator with respect to Lee's estimator and existing conventional estimators.     

Formation of C49-TiSi2 in flash memories: a nucleation controlled phenomenon?

The formation of Ti silicides has been examined in flash memories with 0.25 μm linewidth by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. It has been observed that, after the first rapid thermal process and the selective metal etch, there is no silicide on the source and on a majority of drain contacts while C49-TiSi₂ is found on the gate. A pre-amorphisation implant increases drastically the formation of C49-TiSi₂ in the drain zone while modifications of annealing conditions have little impact. These results indicate that the formation of C49-TiSi₂ is most likely controlled by nucleation and that this nucleation is sensitive to both the width and the length of the reaction zone. The formation of a Ti rich silicide may play an important role in this nucleation by decreasing the driving force for the formation of C49-TiSi₂. Curiously enough, the formation of C49-TiSi₂ appears thus as a major concern for the salicide process in flash memories.