Estimating Clock Uncertainty for Efficient Duty-Cycling in Sensor Networks

Radio duty cycling has received significant attention in sensor networking literature, particularly in the form of protocols for medium access control and topology management. While many protocols have claimed to achieve significant duty-cycling benefits in theory and simulation, these benefits have often not translated into practice. The dominant factor that prevents the optimal usage of the radio in real deployment settings is time uncertainty between sensor nodes which results in overhead in the form of long packet preambles, guard bands, and excessive control packets for synchronization. This paper proposes an uncertainty-driven approach to duty-cycling, where a model of long-term clock drift is used to minimize the duty-cycling overhead. First, we use long-term empirical measurements to evaluate and analyze in-depth the interplay between three key parameters that influence long-term synchronization: synchronization rate, history of past synchronization beacons, and the estimation scheme. Second, we use this measurement-based study to design a rate-adaptive, energy-efficient long-term time synchronization algorithm that can adapt to changing clock drift and environmental conditions, while achieving application-specific precision with very high probability. Finally, we integrate our uncertainty-driven time synchronization scheme with the BMAC medium access control protocol, and demonstrate one to two orders of magnitude reduction in transmission energy consumption with negligible impact on packet loss rate.     

Mixed Dimensional Coupling in Finite Element Stress Analysis

Many analysis models utilize finite elements of reduced dimension. However, to capture stress concentrations at local details, it would be desirable to combine the reduced dimensional element types with higher dimensional elements in a single finite element model. It is therefore important in such cases to integrate into the analyses some scheme for coupling the element types that conforms to the governing equations of the problem. In this paper, a novel method that can correctly couple beams to solids, beams to shells and shells to solids for elastic problems is presented. The approach adopted is to equate the work done on either side of the interface between dimensions, and this leads to multi-point constraint equations, thus providing a relationship among nodal degrees of freedom between the differing element types. Example results show that the proposed technique does not introduce any spurious stresses at the dimensional interfaces. ID="A1" Correspondence and offprint requests to: C. G. Armstrong, School of Mechanical and Manufacturing Engineering, The Queen's University of Belfast, Ashby Building, Stranmillis Road, Belfast BT9 5AH, Northern Ireland. E-mail: c.armstrong@qub.ac.uk     

Thermodynamic properties of the BaO-MnO flux system

Although a great number of works on BaO-bearing fluxes for refining Fe-Cr and Fe-Mn alloys have been carried out, there still remain several unresolved problems on using them in the refining process. The principal aim of the present study is to understand the thermodynamic properties of the BaO-MnO system, which has been shown to be very effective for dephosphorization of Fe-Mn alloys. The activity of manganese oxide in the BaO-MnO flux was measured at 1573 and 1673 K by equilibrating the flux, a Ag-Mn alloy, and a gas mixture of CO and CO₂ as functions of the flux composition and temperature. The influence of BaF₂, which is an effective additive for lowering the melting temperature of the flux, on the thermodynamics of the BaO-MnO system, including the solubility of MnO in the BaO-BaF₂ system, was also investigated.     

Functional properties of cholesterol-removed whipping cream treated by beta-cyclodextrin

The present study was carried out to examine the changes in functional properties of cholesterol-removed whipping cream by beta-cyclodextrin (beta-CD) treatment. The cholesterol removal rate reached over 90% in cream before whipping in all conditions (different stirring time and speed) applied. The apparent viscosity of beta-CD treated cream after whipping increased with increased stirring time and speed. Comparatively, the overrun percentage reached to 150%, and foam instability was measured as 2.5 ml deformed cream with lower stirring time (10 min) and speed (400 rpm). The thiobarbituric acid value of cholesterol-removed whipping cream increased from 0.08 to 0.14 stored at 4 degrees C during 4 wk; however, no difference was found compared with that of control. Above results indicated that beta-CD treatment process for cholesterol removal did not show a profound adverse effect on functional properties of cream after whipping.     

Characterization of poly(L-lactide)-block-poly(ethylene oxide)-block-poly(L-lactide) triblock copolymer by liquid chromatography at the critical condition and by MALDI-TOF mass spectrometry

Poly(L-lactide)-block-poly(ethylene oxide)-block-poly(L-lactide) triblock copolymers (PLLA-b-PEO-b-PLLA) were fractionated in terms of the number of LLA units by liquid chromatography at the critical condition (LCCC) of PEO block. The fractionated samples were identified using MALDI-TOF mass spectrometry. The dependence of the LCCC retention of the diblock and triblock copolymers on the degree of polymerization of PLLA block(s) follows Martin's rule very well. Unlike the case of PEO-b-PLLA diblock copolymer reported earlier (Lee, H.; et al. Macromolecules 1999, 32, 4143), however, a splitting of the elution peaks containing the same number of LLA units was found. The peak splitting was ascribed to the different length distributions of PLLA blocks at the two ends of the PEO block. From the relative intensities of the peaks, the split peaks were assigned to different isomeric structures of the PLLA blocks. From these results we conclude that the interaction of the triblock copolymers with the stationary phase is affected by the distribution of the interacting blocks at the two ends of the center PEO block, in addition to the total number of LLA units in the triblock copolymer.     

Effect of MDA-endcapped CTBN on the cure kinetics of epoxy system by autocatalytic cure rate expression

The cure rate of diglycidyl ether of bisphenol A (DGEBA)/4,4-methylene dianiline (MDA) system with or without MDA-endcapped carboxyl-terminated butadiene acrylonitrile (CTBN) rubber was studied by autocatalytic cure rate expression. All the cumulative conversion curves for DGEBA/MDA system with or without MDA-endcapped CTBN (20 phr) showed s-shape and this meant that the two systems followed the typical autocatalytic reaction. The cure rate of the system with MDA-endcapped CTBN (20 phr) was faster than that of the system without MDA-endcapped CTBN (20 phr). The activation energies of k ₁ and k ₂ for DGEBA/MDA system were 54.01 kJ/mol and 44.06 kJ/mol, respectively and those of k ₁ and k ₂ for the system with MDA-endcapped CTBN (20 phr) were 47.71 kJ/mol and 40.95 kJ/mol.     

Level Set Based Simulations of Two-Phase Oil–Water Flows in Pipes

We simulate the axisymmetric pipeline transportation of oil and water numerically under the assumption that the densities of the two fluids are different and that the viscosity of the oil core is very large. We develop the appropriate equations for core-annular flows using the level set methodology. Our method consists of a finite difference scheme for solving the model equations, and a level set approach for capturing the interface between two liquids (oil and water). A variable density projection method combined with a TVD Runge–Kutta scheme is used to advance the computed solution in time. The simulations succeed in predicting the spatially periodic waves called bamboo waves, which have been observed in the experiments of [Bai et al. (1992) J. Fluid Mech. 240, 97–142.] on up-flow in vertical core flow. In contrast to the stable case, our simulations succeed in cases where the oil breaks up in the water, and then merging occurs. Comparisons are made with other numerical methods and with both theoretical and experimental results.     

A vehicle routing problem solved by using a hybrid genetic algorithm

The main purpose of this study is to find out the best solution of the vehicle routing problem simultaneously considering heterogeneous vehicles, double trips, and multiple depots by using a hybrid genetic algorithm. This study suggested a mathematical programming model with a new numerical formula which presents the amount of delivery and sub-tour elimination. This model gives an optimal solution by using OPL-STUDIO(ILOG CPLEX). This study also suggests a hybrid genetic algorithm (HGA) which considers the improvement of generation for an initial solution, three different heuristic processes, and a float mutation rate for escaping from the local solution in order to find the best solution. The suggested HGA is also compared with the results of a general genetic algorithm and existing problems suggested by Eilon and Fisher. We found better solutions rather than the existing genetic algorithms.     

Nonsmooth feedback stabilizer for strict-feedback nonlinear systems that may not be linearizable at the origin

We present a continuous feedback stabilizer for nonlinear systems in the strict-feedback form, whose chained integrator part has the power of positive odd rational numbers. Since the power is not restricted to be larger than or equal to one, the linearization of the system at the origin may fail. Nevertheless, we show that the closed loop system is globally asymptotically stable (GAS) with the proposed continuous (but, possibly not differentiable) feedback. We formulate a condition that enables our design by characterizing the powers of the given system. The condition also shows that our result is an extension of Qian and Lin [Non-lipschitz continuous stabilizers for nonlinear systems with uncontrollable unstable linearization, Systems Control Lett. 42 (2001) 185–200] where the power of odd positive integers has been considered. New result on the global finite time stabilization problem is also presented.