Competition between surface energy and elastic anisotropies in the growth of coherent solid-state dendrites

A new phase-field model of microstructural evolution is presented that includes the effects of elastic strain energy. The model’s thin interface behavior is investigated by mapping it onto a recent model developed by Echebarria et al. [Echebarria B, Folch R, Karma A, Plapp M. Phys Rev E 2004;70:061604]. Exploiting this thin interface analysis, the growth of solid-state dendrites are simulated with diffuse interfaces and the phase-field and mechanical equilibrium equations are solved in real space on an adaptive mesh. A morphological competition between surface energy anisotropy and elastic anisotropy is examined. Two dimensional simulations are reported that show that solid-state dendritic structures undergo a transition from a surface-dominated [Meiron DI. Phys Rev A 1986;33:2704] growth direction to an elastically driven [Steinbach I, Apel M. Phys D – Nonlinear Phenomena 2006;217:153] growth direction due to changes in the elastic anisotropy, the surface anisotropy and the supersaturation. Using the curvature and strain corrections to the equilibrium interfacial composition and linear stability theory for isotropic precipitates as calculated by Mullins and Sekerka, the dominant growth morphology is predicted.     

Observability-based consistent EKF estimators for multi-robot cooperative localization

In this paper, we investigate the consistency of extended Kalman filter (EKF)-based cooperative localization (CL) from the perspective of observability. We analytically show that the error-state system model employed in the standard EKF-based CL always has an observable subspace of higher dimension than that of the actual nonlinear CL system. This results in unjustified reduction of the EKF covariance estimates in directions of the state space where no information is available, and thus leads to inconsistency. To address this problem, we adopt an observability-based methodology for designing consistent estimators in which the linearization points are selected to ensure a linearized system model with observable subspace of correct dimension. In particular, we propose two novel observability-constrained (OC)-EKF estimators that are instances of this paradigm. In the first, termed OC-EKF 1.0, the filter Jacobians are calculated using the prior state estimates as the linearization points. In the second, termed OC-EKF 2.0, the linearization points are selected so as to minimize their expected errors (i.e., the difference between the linearization point and the true state) under the observability constraints. The proposed OC-EKFs have been tested in simulation and experimentally, and have been shown to significantly outperform the standard EKF in terms of both accuracy and consistency.     

Quantifying adsorption of heparin on a PVC substrate using ATR‐FTIR

The surface modification of poly(vinyl chloride) (PVC) tubing by heparin was performed to increase its blood compatibility. A solution of benzalkonium heparinate was used in the treatment of two types of plasticized PVC. The modification of the PVC surface was monitored after various treatment conditions, and quantitative results were obtained by using ATR‐FTIR spectroscopy. The treatment times and the PVC type have a strong influence on the observed amount of heparin. A partial removal (20–30 %) of heparin was observed after rinsing the PVC surface with a 0.9 wt% NaCl aqueous solution. The more flexible PVC tubing, having a lower T_g, had a higher concentration of heparin. Final heparin concentrations on the PVC surfaces were found to be in the range 1–17 µg cm^?2. Copyright © 2004 Society of Chemical Industry     

A context-aware middleware for real-time semantic enrichment of distributed multimedia metadata

This paper investigates the problem of the real-time integration and processing of multimedia metadata collected by a distributed sensor network. The discussed practical problem is the efficiency of the technologies used in creating a Knowledge Base in real-time. Specifically, an approach is proposed for the real-time, rule-based semantic enrichment of lower level context features with higher-level semantics. The distinguishing characteristic is the provision of an intelligent middleware-based architecture on which low level components such as sensors, feature extraction algorithms, data sources, and high level components such as application-specific ontologies can be plugged. Throughout the paper, Priamos, a middleware architecture based on Semantic Web technologies is presented, together with a stress-test of the system’s operation under two test case scenarios: A smart security surveillance application and a smart meeting room application. Performance measurements are conducted and corresponding results are exposed.     

Sojourn time distributions and time scale separation results for multiclass state-dependent processor sharing systems with a finite service pool and exponential service requirements

The paper addresses multiclass processor sharing systems with general state-dependent service rates, exponential service requirements and a finite service pool. By considering the amount of service received by a permanent customer and associating this service with the evolution of a Markov Reward process, the sojourn time distribution is formulated in terms of a matrix exponential expression. When the service rates are balanced, this expression can be diagonalized. Tail asymptotics are also discussed. The matrix exponential expression is subsequently exploited towards the study of time scale separation regimes. Unlike the standard practice of assuming a distinct time scale per class, the paper groups more realistically all customer classes in two time scales. Provably tight approximations, of a known, small degree of error, are developed for the sojourn time distribution of a given class (with either fast or slow dynamics), in terms of reduced models containing only the customer classes operating in the same time scale. The approximation for the fast classes gives rise to further characterization of the tail behavior. Additionally, the paper studies another, more specialized variant of the time scale separation regime, in which the service rates take a special form that leads to even simpler approximations. Finally, it is shown that the essence of the main results applies also to the more general setting of service requirement distributions with Markovian phase-type form.     

Enforcing Effective Rates for Packet-Level QoS Control in IP Networks: Theory and Validation Based on Real Traffic Data

This paper presents experimental results aiming at underpinning a traffic engineering framework for traffic control and resource management in IP-based networks, which has significant theoretical qualities. Initially, the paper reviews the major components of a packet level traffic control framework: (a) a general traffic shaping algorithm for effective rate enforcement (b) mechanisms for aggregating, splitting and policing streams shaped with this algorithm, and (c) a calculus for quantitative end-to-end QoS. Following the illustration of the theoretical concepts the paper focuses on aspects pertaining to the applicability of the framework. Specifically, we study the impact of the shaping delay and we provide insight into the issue of enforcing effective rates to traffic streams. These studies take into account results from simulating the shaping algorithm, which are based on analyzing, processing and simulating real traffic traces collected from an HTTP server. Moreover, traffic modeling conclusions related to the proposed shaping algorithm, are derived and presented.     

Influence of turbulence on transient premixed flame propagation inside closed vessels

The explosion behaviour of CH₄/air mixtures inside a closed 0.065 m³ spherical and a 1 m³ cylindrical vessel was investigated to determine the effect of turbulence on the structure and propagation rate of transient turbulent flames for different initial turbulence levels generated by 4 ventilators installed inside the equipment. Laser-Doppler and hot wire anemometry were used to measure the turbulent motion. It was found that fairly uniform turbulence could be achieved in the central zones of the vessels and that the RMS-values of flow velocity were proportional to the ventilator speed. The evaluation of burning velocity from the pressure/time records showed that, starting from an initial burning velocity which depends on the initial turbulence level, the flame accelerates as a result of pressure, temperature and turbulence effects. Maximum burning velocity coincides with the inflexion point of the pressure/time curve, and is followed by a rapid deceleration of the flame front. A linear relationship between burning velocity and measured RMS-velocity is recognized in the observed range of RMS-values.