Homogenization of a reaction�Cdiffusion system modeling sulfate corrosion of concrete in locally periodic perforated domains

A reaction?Cdiffusion system modeling concrete corrosion in sewer pipes is discussed. The system is coupled, semi-linear, and partially dissipative. It is defined on a locally periodic perforated domain with nonlinear Robin-type boundary conditions at water?Cair and solid?Cwater interfaces. Asymptotic homogenization techniques are applied to obtain upscaled reaction?Cdiffusion models together with explicit formulae for the effective transport and reaction coefficients. It is shown that the averaged system contains additional terms appearing due to the deviation of the assumed geometry from a purely periodic distribution of perforations for two relevant parameter regimes: (a) all diffusion coefficients are of order of ${\mathcal{O}(1)}$ and (b) all diffusion coefficients are of order of ${\mathcal{O}(\varepsilon^2)}$ except the one for H₂S(g) which is of order of ${\mathcal{O}(1)}$ . In case (a) a set of macroscopic equations is obtained, while in case (b) a two-scale reaction?Cdiffusion system is derived that captures the interplay between microstructural reaction effects and the macroscopic transport.     

A moving cluster architecture and an intelligent resource reuse protocol for vehicular networks

Real-time data transmission, especially video delivery over high-speed networks have very stringent constraints in terms of network connectivity and offered data rate. However, in high-speed vehicular networks, direct communication between vehicles and road side units (RSU) often breaks down, resulting in loss of information. On the other hand, a peer-to-peer based multihop network topology is not sufficient for efficient data communication due to large packet loss and delay. In this paper, a novel ‘moving cluster multiple forward’ (MCMF) architecture is proposed and investigated for efficient real-time data communication in high speed vehicular networks. MCMF involves novel aspects in relation to the formation of clusters and managing the communication between groups of vehicles and introduction of a hierarchical multiple forwarding mechanism which enables communication between any vehicle and RSU via other vehicles. Additionally, a novel protocol called ‘alternate cluster resource reuse’ (ACRR) is proposed and its detailed communication mechanism is presented. Simulation tests show how the use of MCMF and the ACRR protocol results in superior bit-rate performance—around three times that obtained in peer-to-peer multihop communications and twice that of MCMF with no ACRR protocol. Further, the average delay in MCMF-based transmissions from vehicle to RSU is around 50 % that of a peer-to-peer multihop communication mechanism. MCMF/ACRR has the potential to support multimedia traffic according to the IEEE 802.11p standard, even with a sparse investment in the infrastructure.     

Moving carbonation fronts in concrete: A moving-sharp-interface approach

We present a new modeling strategy for predicting the penetration of carbonation reaction fronts in concrete. The approach relies on the assumption that carbonation reaction concentrates macroscopically on an a priori unknown narrow strip (called reaction front) moving into concrete gradually changing its mechanical and chemical properties. We propose a moving-interface model to forecast the maximum penetration depth of gaseous CO₂ in the porous concrete matrix. The main questions driving this research are: How fast does the carbonation front move? and How long does it take until the front reaches the reinforcement?. As model output, we determine simultaneously the position of the carbonation front and the profiles of the active concentrations. The model equations are solved using a specially tailored finite element scheme and are validated relying on experimental data from the Ph.D. thesis by D. Bunte Zum Karbonatisierungsbedingten Verlust der Dauerhaftigkeit von Außenbauteilen aus Stahlbeton, Ph.D. thesis, TU Braunschweig (1994). Our approach should be viewed as an alternative to the standard carbonation models.     

Video streaming distribution over mobile Internet: a survey

In recent times, mobile Internet has witnessed the explosive growth of video applications, embracing user-generated content, Internet Protocol television (IPTV), live streaming, video-on-demand, video conferencing, and FaceTime-like video communications. The exponential rise of video traffic and dynamic user behaviors have proved to be a major challenge to video resource sharing and delivery in the mobile environment. In this article, we present a survey of state-of-the-art video distribution solutions over the Internet. We first discuss the challenges of mobile peer-to-peer (MP2P)-based solutions and categorize them into two groups. We discuss the design idea, characteristics, and drawbacks of solutions in each group.We also give a reviewfor solutions of video transmission in wireless heterogeneous networks. Furthermore, we summarize the information-centric networking (ICN)-based video solutions in terms of in-network caching and name-based routing. Finally, we outline the open issues for mobile video systems that require further studies.     

Region of Interest-Based Adaptive Multimedia Streaming Scheme

Adaptive multimedia streaming aims at adjusting the transmitted content based on the available bandwidth such as losses that often severely affect the end-user perceived quality are minimized and consequently the transmission quality increases. Current solutions affect equally the whole viewing area of the multimedia frames, despite research showing that there are regions on which the viewers are more interested in than on others. This paper presents a novel region of interest-based adaptive scheme (ROIAS) for multimedia streaming that when performing transmission-related quality adjustments, selectively affects the quality of those regions of the image the viewers are the least interested in. As the quality of the regions the viewers are the most interested in will not change (or will involve little change), the proposed scheme provides higher overall end-user perceived quality than any of the existing adaptive solutions.     

Investigation of Iridium Nanoparticles Supported on Sub-stoichiometric Titanium Oxides as Anodic Electrocatalysts in PEM Electrolysis. Part I.: Synthesis and Characterization

Topics in Catalysis - A novel route for obtaining iridium-based electrocatalysts supported on sub-stoichiometric titanium oxides for catalytic applications is presented. Chloride-free titanium...     

Effective removal of methylene blue from aqueous solution using a new magnetic iron oxide nanosorbent prepared by combustion synthesis

A magnetic iron oxide nanopowder (MnP) prepared by a new combustion technique was characterized and tested as adsorbent for methylene blue (MB) removal from aqueous solution. The effects of pH, adsorbent dose, initial dye concentration, contact time, and temperature on the amount of MB adsorbed were studied. The adsorption kinetics were described by a pseudo-second-order model, and the equilibrium experimental data were well fitted to the Langmuir isotherm, yielding a maximum adsorption capacity of 25.54 mg g^?1. The adsorption mechanism is governed by electrostatic forces and is highly dependent on the pH. The MnP adsorbent demonstrated excellent stability, showing good removal efficiency even after eight cycles of reuse, suggesting its potential large-scale application for the removal and recovery of MB from wastewater.