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Item Open Access Outage Probability Analysis of Multi-Relay Delay-Limited Hybrid-ARQ Channels(2010 IEEE 72nd Vehicular Technology Conference - Fall, 2010) Maham, Behrouz; Hjorungnes, Are; Debbah, MerouaneWe consider a wireless relay network with with hybrid-automatic retransmission request (HARQ) and Rayleigh fading channels. In this paper, we analyze the outage probability of the multi-relay delay-limited HARQ system with opportunistic relaying scheme in decode-and-forward mode. A simple and distributed relay selection strategy is proposed for multi-relay HARQ channels. Then, we analyze the performance of the system. We first derive the cumulative density function (CDF) and probability density function (PDF) of the selected relay channels. Then, the CDF and PDF are used to determine the outage probability in the l-th round of HARQ. The packet delay constraint is represented by L, the maximum number of HARQ rounds. Furthermore, closed-form upper-bounds on outage probability are derived, which are used to investigate the diversity order of the system. Based on the derived upper-bound expressions, it is shown that the proposed schemes achieve the full spatial diversity order of N + 1, where N is the number of potential relays. Our analytical results are confirmed by simulation results.Item Open Access VELOS: A VR Platform for Ship-Evacuation Analysis(Computer-Aided Design. Elsevier, 2010) Ginnis, A.I.; Kostas, Konstantinos; Politis, C.G.; Kaklis, P.D.“Virtual Environment for Life On Ships” (VELOS) is a multi-user Virtual Reality (VR) system that aims to support designers to assess (early in the design Process) passenger and crew activities on a ship for both normal and hectic Conditions of operations and to improve ship design accordingly. This paper focuses On presenting the novel features of VELOS related to both its VR and Evacuation-specific functionalities. These features include: i) capability of multiple Users’ immersion and active participation in the evacuation process, ii) Real-time interactivity and capability for making on-the-fly alterations of environment Events and crowd-behavior parameters, iii) capability of agents and Avatars to move continuously on decks, iv) integrated framework for both the Simplified and the advanced method of analysis according to the IMO/MSC 1033 Circular, v) enrichment of the ship geometrical model with a topological model Suitable for evacuation analysis, vi) efficient interfaces for the dynamic specification and handling of the required heterogeneous input data, and vii) post Processing of the calculated agent trajectories for extracting useful information For the evacuation process. VELOS evacuation functionality is illustrated using Three evacuation test cases for a ro-ro passenger ship.Item Open Access Orthogonal Code Design for MIMO Amplify-and-Forward Cooperative Networks(2010 IEEE Information Theory Workshop on Information Theory (ITW 2010, Cairo), 2010) Maham, Behrouz; Hjørungnes, AreThis paper is on the design of practical distributed space-time codes for wireless relay networks with multiple antennas terminals. The amplify-and-forward scheme is used in a way that each relay transmits a scaled version of the linear combination of the received symbols. We propose distributed orthogonal space-time codes which are distributed among the source node's antennas and relays. Using linear orthogonal decoding in the destination makes it feasible to employ large number of potential relays to improve the diversity order. Assuming multiple amplitude modulation, we derive a formula for the symbol error probability of the investigated scheme over Rayleigh fading channels. Our analytical results have been confirmed by simulation results, using full-rate, full-diversity distributed codes.Item Open Access Evaluation of Interphase Drag Models for the Determination of Gas Hold-Up of an Air-Water System in a Spouted Bed using CFD(2011-04-14) Riera Ortiz, Jaime. A.; Zeppieri, Susana; Rojas-Solorzano, L.; Derjani-Bayeh, SylvanaAbstract: The hydrodynamics of a dispersed air-water system within a spouted column with a concentric draft tube and a conical base is simulated using CFD based on a two–fluid Euler–Euler (E-E) modeling framework and k-ε two-equation turbulence closures. The interaction between the dispersed gas phase and the continuous liquid phase is characterized by bubble–liquid interphase forces (drag, turbulent dispersion and lift forces). The Ishii-Zuber drag model [1] and Grace adjusted drag model [2], the latter represented by: GraceDpg Grace dense D C C , , are compared for their capability to match experimental gas hold- up. Numerical results of Reynolds-averaged Navier-Stokes equations with k-ε two-equation turbulence closures models when compared with Pironti experimental data [3] indicated that both drag models, predicted the air hold-up within experimental error. Furthermore, Ishii-Zuber liquid-gas drag model consistently provided better agreement of experimental results; it correctly determines the hold-up within 0.14%. Numerical agreement with adjusted Grace liquid-gas drag model, is exponent dependent 4 p 0.5, turning down that the best computed hold-up is within 0.44%. for p 0.5.Item Open Access A BEM-Isogeometric method with application to the wavemaking resistance problem of ships at constant speed(ASME 2011 30th International Conference on Ocean, Offshore and Arctic Engineering, 2011-06-11) Konstantinos, Belibassakis; Theodoros, Gerostathis; Konstantinos, Kostas; Constantinos, Politis; Panagiotis, Kaklis; Alexandros, Ginnis; Christian, FeurerIn the present work IsoGeometric Analysis (IGA), initially proposed by Hughes et al (2005), is applied to the solution of the boundary integral equation associated with the Neumann-Kelvin (NK) problem and the calculation of the wave resistance of ships, following the formulation by Brard (1972) and Baar & Price (1988). As opposed to low-order panel methods, where the body is represented by a large number of quadrilateral panels and the velocity potential is assumed to be piecewise constant (or approximated by low degree polynomials) on each panel, the isogeometric concept is based on exploiting the NURBS basis, which is used for representing exactly the body geometry and adopts the very same basis functions for approximating the singularity distribution (or in general the dependent physical quantities). In order to examine the accuracy of the present method, in a previous paper Belibassakis et al (2009), numerical results obtained in the case of submerged bodies are compared against analytical and benchmark solutions and low-order panel method predictions, illustrating the superior efficiency of the isogeometric approach. In the present paper we extent previous analysis to the case of wave-making resistance problem of surface piercing bodies. The present approach, although focusing on the linear NK problem which is more appropriate for thin ship hulls, it carries the IGA novelty of integrating CAD systems for ship-hull design with computational hydrodynamics solvers.Item Open Access Use of VELOS platform for modelling and accessing crew assistance and passenger grouping in ship-evacuation analysis(CRC Press, 2011-09-13) Konstantinos, Kostas; Alexandros, Ginnis; Constantinos, Politis; Panagiotis, KaklisVELOS, which stands for “Virtual Environment for Life On Ships”, is a multi-user VR system that aims to support designers, early in the design process, to assess passenger and crew activities on ship and improve ship design accordingly. VELOS functionalities provide design aids required for both normal and hectic operational conditions. This has been accomplished by integrating a broad range of software components in VELOS platform which includes tools targeting geometric and VR modelling, crowd microscopic modelling based on steering behaviours technology, as well as communication interfaces with external computational software packages. In the present work, we focus on the evacuation-specific functionality of VELOS by enhancing it with passenger-grouping and crew-assistance behaviour. This is mainly achieved by combining and extending steering behaviours, already used within VELOS, for crowd modelling, as, e.g., Leader-Follow and Cohere behaviour. This enhancement allows simulating the evacuation process more realistically and comparing results acquired for the scenarios prescribed by the IMO, with and without the consideration of grouping and crew-assistance behaviour.Item Open Access LiMnPO4 olivine as a cathode for lithium batteries(The Open Materials Science Journal, http://www.researchgate.net/publication/260969132, 2011-12-02) Bakenov, Zhumabay; Taniguchi, IzumiThe olivine structured mixed lithium-transition metal phosphates LiMPO4 (M = Fe, Mn, Co) have attracted tremendous attention of many research teams worldwide as a promising cathode materials for lithium batteries. Among them, lithium manganese phosphate LiMnPO4 is the most promising considering its high theoretical capacity and operating voltage, low cost and environmental safety. Various techniques were applied to prepare this perspective cathode for lithium batteries. The solution based synthetic routes such as spray pyrolysis, precipitation, sol-gel, hydrothermal and polyol synthesis allow preparing nanostructured powders of LiMnPO4 with enhanced electrochemical properties, which is mostly attributed to the higher chemical homogeneity and narrow particle size distribution of the material. Up-to-date, the LiMnPO4/C composites prepared by the spray pyrolysis route have the best electrochemical performance among the reported in the literature.Item Open Access Assessment of a Shallow Water Model using a Linear Turbulence Model for Obstruction-Induced Discontinuous Flows(2012) Pu, Jaan Hui; Bakenov, Zhumabay; Adair, DesmondAssessment of the performance of a shallow water model with closure using a linear k-ε turbulence model is made for various obstruction-induced discontinuous flows. The monotone upwind scheme of conservative laws (MUSCL) - Hancock scheme is used, together with the Harten Lax van Leer (HLL) approximate Riemann solver in the discretization of the finite volume shallow water model. These kinds of models contribute to the improvement of optimized design of various processes in chemical engineering and technology. Two obstructed flow applications are presented, namely, single obstruction and multiple obstruction induced discontinuous flows; and the ability of the shallow water model with the k-ε based turbulence model to predict these applications are assessed. The simulation results of the shallow water model are compared with those found by direct numerical simulation (DNS) and experimental measurements in the literatureItem Open Access A BEM-ISOGEOMETRIC method for the ship wave-resistance problem(Ocean Engineering, 2012) Belibassakis, K.A.; Gerostathis, Th.P.; Kostas, Konstantinos; Politis, C.G.; Kaklis, P.D.; Ginnis, A.I.; Feurer, C.In the present work IsoGeometric Analysis is applied to the solution of the Boundary Integral Equation associated with the Neumann-Kelvin problem and the calculation of the wave resistance of ships. As opposed to low-order panel methods, where the body is represented by a large number of quadrilateral panels and the velocity potential is assumed to be piecewise constant (or approximated by low degree polynomials) on each panel, the isogeometric concept is based on exploiting the same NURBS basis, used for representing exactly the body geometry, for approximating the singularity distribution (and, in general, the dependent physical quantities). In order to examine the accuracy of the present method, numerical results obtained in the case of submerged and surface piercing bodies are * Corresponding author. Tel: (+30) 2107721138, Fax: (+30) 2107721397, e-mail: kbel@fluid.mech.ntua.gr 2 compared against analytical solutions, experimental data and predictions provided by the low-order panel or other similar methods appeared in the pertinent literature, illustrating the superior efficiency of the isogeometric approach. The present approach by applying Isogeometric Analysis and Boundary Element Method to the linear NK problem has the novelty of combining modern CAD systems for ship-hull design with computational hydrodynamics tools.Item Open Access Advanced Numerical Solver for Dam-Break Flow Application(Eurasian chemico-technological journal., http://www.researchgate.net/publication/283813681, 2012-01) Hui Pu, Jaan; Bakenov, Zhumabay; Adair, DesmondIn this paper, a HLL (Harten Lax van Leer) approximate Riemann solver with MUSCL scheme (Monotonic Upwind Schemes for Conservative Laws) is implemented in the presented FV (Finite Volume) model. The presented model is used to simulate different dam-break flow events to verify its capability. Four test cases are presented in this paper. In the first test case, a 1-Dimensional (1D) dambreak flow is simulated over a rectangular channel with different slope limiters of the FV model (namely Godunov, Superbee, Minmod, van Leer, and van Albada). The second test case consists of a simulation of shallow water discontinuous dam-break flow over a dry-downstream bed channel. The third test simulates the shallow water dam-break flow with the existence of bed slope and bed shear stress. Finally, in the last test, the HLL-MUSCL model used in this paper and some other solver models used in literature are compared against the referred exact solution in dam-break flow application. The presented HLL-MUSCL scheme is found to give the best agreement to the exact solution.Item Metadata only Approximate Explicit MPC on Simplicial Partitions with Guaranteed Stability for Constrained Linear Systems(IFAC Proceedings Volumes, 2012-01-01) Rubagotti, Matteo; Barcelli, Davide; Bemporad, Alberto; Matteo, RubagottiAbstract This paper proposes an approximate explicit model predictive control design approach for regulating linear time-invariant systems subject to both state and control constraints. The proposed control law is implemented as a piecewise-affine function defined on a regular simplicial partition, and has two main positive features. First, the regularity of the simplicial partition allows a very efficient implementation of the control law on digital circuits, with computation performed in tens of nanoseconds. Second, the asymptotic stability of the closed-loop system is enforced a priori by design.Item Metadata only One-step synthesis of branched sulfur/polypyrrole nanocomposite cathode for lithium rechargeable batteries(Journal of Power Sources, 2012-06-15) Zhang, Yongguang; Bakenov, Zhumabay; Zhao, Yan; Konarov, Aishuak; Doan, The Nam Long; Malik, Muhammad; Paron, Todd; Chen, P.; Yongguang, ZhangAbstract A nanostructured sulfur/polypyrrole binary composite was prepared by a simple one-step ballmilling without heat-treatment. High resolution transmission and scanning electronic microscopy showed the formation of a highly developed branched structure consisting of polypyrrole with uniform sulfur coating on its surface. Exclusion of heat-treatment in the composite preparation avoided the sulfur loss; the composite contained 65wt% of sulfur. AC impedance spectroscopy data exhibited remarkable reduction in charge transfer resistance of the composite compared with pristine sulfur. This may be due to the high conductivity and large surface area of polypyrrole. This charge transfer enhancement led to the electrochemical performance improvement of the composite cathode, delivering first discharge capacity of 1320mAhg−1.Item Open Access Numerical simulation of droplet formation in a microchannel device(2013) Rojas-Solórzano, L.; Rodríguez Granado, Katherine V.; Anna, Shelley L.; Verma, SalmanThe formation of droplets is a phenomenon with particular importance in the development of industrial emulsions. The quality of these compounds is associated with droplet size and stability over time. Anna et al. (2003) developed a methodology named ¨flow focusing¨ to improve droplet formation processes for engineering applications. In this work, Computational Fluid Dynamics (CFD) based techniques are used to assess the capacity of a pseudo-2D numerical model to reproduce water droplets formation within silicon oil, as obtained in Anna et al.’s experiments. Average time of droplet onset obtained via numerical analysis was 1.5 times larger than observed experimentally, whereas droplets convection velocity and diameter predictions differed by 40-45% and 60%, respectively. Nevertheless, calculated velocity profiles downstream the discharge slot reproduced the expected free-jet shear layer according to outer/inner flow ratio.Item Open Access Cognitive Radio Ad Hoc Networks for Smart Grid Communications: A Disaster Management Approach(2013 IEEE/CIC International Conference on Communications in China (ICCC), 2013) Khayami, Hossein; Ghassemi, Mohsen; Ardekani, Kamyar; Maham, Behrouz; Saad, WalidThe explosive growth in users' demand in both areas of wireless communications and power generation has led to design of new key technologies that will be dominant in the near future; cognitive radio networks in communications and smart grid in power field. This paper proposes a novel scenario to marry these technologies together by using a cognitive radio ad hoc network (CRAHN) as the foundation of smart grid communications. It discusses formation and throughput of such a citywide network, the information transferred by the network, and how this structure can be relied upon in disasters, compared to the state-of-the-art.Item Open Access Ternary sulfur/polyacrylonitrile/Mg0.6Ni0.4O composite cathodes for high performance lithium/sulfur batteries(Journal of materials chemistry., http://www.researchgate.net/publication/235654118, 2013-01) Zhang, Yongguang; Zhao, Yan; Yermukhambetova, Assiya; Bakenov, Zhumabay; Chen, P.Nanostructured magnesium nickel oxide (Mg0.6Ni0.4O) was synthesized by a self-propagating high temperature synthesis method followed by heat treatment. The particles of the resulting oxide were used as additives to prepare the sulfur/polyacrylonitrile/Mg0.6Ni0.4O (S/PAN/Mg0.6Ni0.4O) composite via wet ballmilling. The SEM observation revealed that the composite morphology was drastically changed by the addition of Mg0.6Ni0.4O, from smooth bulky particles of S/PAN to rough nanostructured agglomerates with two times the increase in the specific surface area, favouring the reactivity of the composite, and a homogeneous component distribution. Cyclic voltammetry, discharge–charge tests and ac impedance spectroscopy have shown improved conductivity and electrochemical properties of the composite by the addition of Mg0.6Ni0.4O, leading to high sulfur utilization and interfacial stabilization in a Li/S cell upon discharge–charge cycling. The cell demonstrated enhanced reversibility, resulting in a discharge capacity of about 1223 mA h g 1 at the second cycle and retained about 100% of this value over 100 cycles. Furthermore, the S/PAN/Mg0.6Ni0.4O composite cathode exhibited a good rate capability with discharge capacities of 887, 710 and 445 mA h g 1 at 0.5, 0.7 and 1 C, respectively.Item Metadata only Cryogels: Morphological, structural and adsorption characterisation(Advances in Colloid and Interface Science, 2013-01-01) Gun'ko, Vladimir M.; Savina, Irina N.; Mikhalovsky, Sergey V.; Vladimir M., Gun'koAbstract Experimental results on polymer, protein, and composite cryogels and data treatment methods used for morphological, textural, structural, adsorption and diffusion characterisation of the materials are analysed and compared. Treatment of microscopic images with specific software gives quantitative structural information on both native cryogels and freeze-dried materials that is useful to analyse the drying effects on their structure. A combination of cryoporometry, relaxometry, thermoporometry, small angle X-ray scattering (SAXS), equilibrium and kinetic adsorption of low and high-molecular weight compounds, diffusion breakthrough of macromolecules within macroporous cryogel membranes, studying interactions of cells with cryogels provides a consistent and comprehensive picture of textural, structural and adsorption properties of a variety of cryogels. This analysis allows us to establish certain regularities in the cryogel properties related to narrow (diameter 0.4100μm) with boundary sizes within modified life science pore classification. Particular attention is paid to water bound in cryogels in native superhydrated or freeze-dried states. At least, five states of water — free unbound, weakly bound (changes in the Gibbs free energy−ΔG<0.5–0.8kJ/mol) and strongly bound (−ΔG>0.8kJ/mol), and weakly associated (chemical shift of the proton resonance δH=1–2ppm) and strongly associated (δH=3–6ppm) waters can be distinguished in hydrated cryogels using 1H NMR, DSC, TSDC, TG and other methods. Different software for image treatment or developed to analyse the data obtained with the adsorption, diffusion, SAXS, cryoporometry and thermoporometry methods and based on regularisation algorithms is analysed and used for the quantitative morphological, structural and adsorption characterisation of individual and composite cryogels, including polymers filled with solid nano- or microparticles.Item Metadata only Effect of nanosized Mg0.6Ni0.4O prepared by self-propagating high temperature synthesis on sulfur cathode performance in Li/S batteries(Powder Technology, 2013-02-01) Zhang, Yongguang; Bakenov, Zhumabay; Zhao, Yan; Konarov, Aishuak; Doan, The Nam Long; Sun, Kyung Eun Kate; Yermukhambetova, Assiya; Chen, P.; Yongguang, ZhangAbstract Nanostructured magnesium nickel oxide Mg0.6Ni0.4O was successfully synthesized by self-propagating high temperature synthesis (SHS) followed by heat treatment. The effect of the precursor composition and calcination temperature on the Mg0.6Ni0.4O powder properties was investigated. These particles were used as an additive to prepare S/Mg0.6Ni0.4O composite via ball-milling with sulfur. The composite preparation conditions were optimized to achieve the higher specific surface area without compromising the sample crystallinity. The SEM observation revealed that the sulfur morphology was drastically changed by the Mg0.6Ni0.4O addition, from smooth to rough agglomerated particles. This change has enhanced the electrochemical performance of the composite cathode. Cyclic voltammetry and charge–discharge tests demonstrated enhanced reversibility and high sulfur utilization in a Li/S cell with S/Mg0.6Ni0.4O cathode, delivering about 850mAhg−1 of reversible capacity at the initial cycle. The effect of the Mg0.6Ni0.4O heat treatment temperature on the S/Mg0.6Ni0.4O cycling performance was also investigated. The cathode with Mg0.6Ni0.4O calcined at 700°C exhibited enhanced capacity retention which could be due to its high specific surface area and nanosized structure.Item Metadata only Electrochemical performance of lithium gel polymer battery with nanostructured sulfur/carbon composite cathode(Solid State Ionics, 2013-03-07) Zhao, Yan; Zhang, Yongguang; Bakenov, Zhumabay; Chen, P.; Yan, ZhaoAbstract A gel polymer electrolyte was formed by trapping lithium bistrifluoromethane-sulfonamide in tetraethylene glycol dimethyl ether electrolyte in a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)/poly(methylmethacrylate) (PMMA) polymer matrix. The electrochemical properties of the resulting gel were investigated. This electrolyte was used in a lithium polymer cell with a nanostructured sulfur/ketjen black binary composite cathode prepared by wet ball-milling and heat-treatment. The gel polymer battery exhibited a high specific capacity of 753.8mAhg−1 at the initial cycle, stable reversible cycling and a capacity retention about 80% over 40cycles along with a high coulombic efficiency, while the liquid electrolyte cell, in comparison, had low capacity retention and coulombic efficiency. The performance enhancement was attributed to the suppression of shuttle effect by the gel polymer electrolyte leading to higher sulfur utilization in the cell.Item Metadata only Annihilation of the triplet excitons in the nanoporous glass matrices(Journal of Luminescence, 2013-04-01) Afanasyev, D.A.; Ibrayev, N.Kh.; Saletsky, A.M.; Starokurov, Y.V.; Gun'ko, V.M.; Mikhalovsky, S.V.; D.A., AfanasyevAbstract The spectra and kinetics of fluorescence decay of 1,2-benzanthracene (1,2-BA) molecular clusters adsorbed in nanoporous borosilicate glasses were investigated. It has been shown that the type of the decay kinetics of delayed fluorescence is determined by the annihilation of triplet excitons in crystalline and percolation clusters. The influence of an external magnetic field on the annihilation rate constant of triplet excitons in the adsorbed 1,2-BA molecules has been studied. The response of the molecular clusters to the magnetic field strongly depends on temperature, pore size and time scale of the observation. Clusters with the crystal structure dominate in the decay kinetics of triplet–triplet annihilation (TTA) and delayed fluorescence in the initial microsecond period of time after excitation. Amorphous clusters determine the form of decay kinetics of delayed fluorescence in the millisecond range. The increase in the pore size and concentration of the adsorbate lead to the dominance of crystalline components. The results presented here can be used to develop techniques for probing the structure of the adsorbed layer in nanoporous systems examining the effect of an external magnetic field on the annihilation delayed fluorescence (ADF) kinetics.Item Open Access Polyurethane–poly(2-hydroxyethyl methacrylate) semi- IPN–nanooxide composites(RSC Advances, 2013-05-30) Mikhalovsky, S. V.; Bershtein, Vladimir A.; Gun’ko, Vladimir M.; Karabanova, Lyudmila V.; Sukhanova, Tatiana E.; Yakushev, Pavel N.; Egorova, Larisa; Turova, Anna A.; Zarko, Vladimir I.; Pakhlov, Eugene M.; Vylegzhaninad, Milana E.Two sets of hybrid polyurethane–poly(2-hydroxyethyl methacrylate) semi-interpenetrating polymer network–nanooxide composites with 0.25 or 3 wt% nanosilica or nanoalumina functionalised with OH, NH2 or CHLCH2 groups were prepared. A combination of atomic force microscopy, infrared spectroscopy, thermally stimulated depolarisation current measurement, differential scanning calorimetry and creep rate spectroscopy analysis of the nanostructure and properties of the composites was performed. The pronounced dynamic heterogeneity and the strong impact of oxide additives, basically suppression of the dynamics and temperature-dependent increasing modulus of elasticity, were observed. The effects correlated with either interfacial interactions (for silica) or the nanostructure (for alumina). A low oxide content strongly affected the matrix due to the formation of an unusual cross-linked, via double covalent hybridisation of three components, structure of the nanocomposites.