A Class of Algorithms for Collision Resolution with Multiplicity Estimation

The wireless connectivity in pervasive computing has ephemeral character and can be used for creating ad hoc networks, sensor networks, connection with RFID (Radio Frequency Identification) tags etc. The communication tasks in such wireless networks often involve an inquiry over a shared channel, which can be invoked for: discovery of neighboring devices in ad hoc networks, counting the number of RFID tags that have a certain property, estimating the mean value contained in a group of sensors etc. Such an inquiry solicits replies from possibly large number of terminals n. This necessitates the usage of algorithms for resolving batch collisions (conflicts) with unknown conflict multiplicity n. In this paper we present a novel approach to the problem of collision resolution for batch conflicts. We show how the conventional tree algorithms for collision resolution can be used to obtain progressively accurate estimation of the multiplicity. We use the estimation to propose a more efficient binary tree algorithm, termed Estimating Binary Tree (EBT) algorithm. The EBT algorithm is suited for implementation when the conflicting nodes are passive, such as e.g. RFID tags. We extend the approach to design the Interval Estimation Conflict Resolution (IECR) algorithm. For n→∞ we prove that the efficiency achieved by IECR for batch arrivals is identical with the efficiency that Gallager’s FCFS algorithm achieves for Poisson packet arrivals. For finite n, the simulation results show that IECR is, to the best of our knowledge, the most efficient batch resolution algorithm reported to date.     

Study of structural and electrochemical characteristics of Co-based hypo-hyper d-electrocatalysts for hydrogen evolution

Structural and electrochemical characteristics of hypo-hyper d-electrocatalytic materials aimed for preparation of electrodes for hydrogen evolution were studied. The basic catalytic material was prepared of 10% amorphous Co (grain size <2 nm), 18% amorphous TiO₂ and Vulcan XC-72, by sol-gel procedure. A number of modifications were applied aimed at improving the materials performances: (i) TiO₂ was transformed into anatase by heating at 480 °C for 1 h, (ii) multiwalled carbon nanotubes (MWCNT) were used as a catalyst support instead of Vulcan XC-72 and (iii) Mo was added to Co phase in a quantity of 25 at.% (Mo:Co = 1:3).Both, material's intrinsic catalytic activity and surface area were affected by these modifications. As a result, the electrocatalytic activity for hydrogen evolution was improved, e.g. transformation of TiO₂ into anatase form lowers the HER overpotential (η) for 15 mV at 60 mA cm⁻². Introduction of MWCNTs lowered η for 30 mV, while addition of Mo to metallic phase for 40 mV.The complete modification of all three catalyst's components (10% MoCo₃ + 18% anatase + MWCNTs) was the most effective with 60 mV decrease of overpotential.Characterization was made by XRD, SEM, IR and XPS methods. Surface area was measured by means of cyclic voltammetry.     

Biosorption of nickel ions from aqueous solutions by natural and modified peanut husks: equilibrium and kinetics

The toxicity and non‐biodegradation of heavy metals, as well as their tendency to accumulate in the soils, water resources and the living organisms, makes them the significant environmental pollutants. Therefore, the reduction and elimination of heavy metal ions from aqueous systems is very important from the ecological, nutritional and environmental reasons. The aim of this study is to investigate whether the natural peanut husks, an agricultural waste, and their chemically modified form are capable to remove Ni(II) ions from aqueous solutions using batch method and to compare their efficiency. The effects of the mass of the natural peanut husks and the initial pH of the solution were studied to find the optimal conditions for maximal removal of Ni(II) ions. MATLAB/Curve Fitting Toolbox was implemented to determine the adequate adsorption isotherm as well as to optimise the equilibrium state of the investigated systems.     

New Paradigms in Wireless Communication Systems

This paper discusses what a new paradigm can be in wireless communication systems of the twenty-first century. First, it suggests two directions for the new paradigm; one is “micro- and nano-device communication system” which is the projected scenario considering that the entities in source and destination have been shrinking throughout the history of wireless communication systems. The second direction is “networked robot system”, which emerges as a natural extension of mobile ad hoc networking where the networking is closely related to motion control of robots. Secondly, it shows two interesting research topics, “the new communication protocol design” and “signal processing”, respectively, that arise in the wake of the fusion between the two directions in the novel communication paradigm. Finally, it considers a new science of wireless communications in the twenty-first century. Shinsuke Hara received the B.Eng., M.Eng. and Ph.D. degrees in communications engineering from Osaka University, Osaka, Japan, in 1985, 1987 and 1990, respectively. From April 1990 to March 1997, he was an assistant professor in the Department of Communication Engineering, School of Engineering, Osaka University, and from October 1997 to September 2005, he was an associate professor in the Department of Electronic, Information and Energy Engineering, Graduate School of Engineering, Osaka University. Since October 2005, he has been a professor in the Department of Physical Electronics and Informatics, Graduate School of Engineering, Osaka City University. In addition, from April 1995 to March 1996, he was a visiting scientist at Telecommunications and Traffic Control Systems Group, Delft University of Technology, Delft, The Netherlands. His research interests include wireless communications systems and digital signal processing. Hiroyuki Yomo received B.S. degree in communication engineering from Department of Communication Engineering, Osaka University, Osaka, Japan, in 1997, and M.S. and Ph.D. degrees in communication engineering from Department of Electronic, Information, and Energy Engineering, Graduate School of Engineering, Osaka University, Osaka Japan, in 1999 and 2002, respectively. From April 2002 to March 2004, he was a Post-doctoral Fellow in Department of Communication Technology, Aalborg University, Denmark. From April 2004 to September 2004, he was at Internet System Laboratory, NEC Corporation, Japan. Since October 2004, he has been an Assistant Research Professor in Center for TeleInfrastructure (CTIF), Aalborg University, Denmark. His main research interests are access technologies, radio resource management, and link-layer techniques in the area of short-range communication, cellular network, cognitive radio, and sensor network. Petar Popovski received the Dipl.-Ing. in electrical engineering and M.Sc. in communication engineering from the Faculty of Electrical Engineering, Sts. Cyril and Methodius University, Skopje, Republic of Macedonia, in 1997 and 2000, respectively. He received a Ph.D. degree from Aalborg University, Denmark, in 2004. From 1998 to 2001 he was a teaching and research assistant at the Institute of Telecommunications, Faculty of Electrical Engineering in Skopje. He is currently Assistant Professor at the Department of Communication Technology at the Aalborg University. His research interests are related to the PHY-MAC aspects of wireless protocols, wireless sensor networks, random access protocols, and network coding. Kazunori Hayashi received the B.E., M.E. and Ph.D. degrees in communication engineering from Osaka University, Osaka, Japan, in 1997, 1999 and 2002, respectively. He spent 3 months in 2000 at Aalborg University, Denmark, as a Visiting Scholar. Since 2002, he has been with the Department of Systems Science, Graduate School of Informatics, Kyoto University. He is currently an Assistant Professor there. His research interests include digital signal processing for communications systems.     

The Complexity of Modellability in Finite and Computable Signatures of a Constraint Logic for Head-Driven Phrase Structure Grammar

The SRL (speciate re-entrant logic) of King (1989) is a sound, complete and decidable logic designed specifically to support formalisms for the HPSG (head-driven phrase structure grammar) of Pollard and Sag (1994). The SRL notion of modellability in a signature is particularly important for HPSG, and the present paper modifies an elegant method due to Blackburn and Spaan (1993) in order to prove that

Co-Magneli phases electrocatalysts for hydrogen/oxygen evolution

The subject of this work is the use of non-stoichiometric titanium oxides – Magneli phases as support material of Co-based electrocatalysts aimed for hydrogen/oxygen evolution reaction. Commercial micro-scaled Ebonex (Altraverda, UK) was mechanically treated for 4, 8, 12, 16 and 20 h and further Co metallic phase was grafted by sol-gel method. Morphology of Co/Ebonex electrocatalysts was observed by means of TEM and SEM microscopy, while electrochemical behavior by means of cyclic voltammetry and steady-state galvanostatic method.     

Geothermal energy in agriculture in Yugoslavia

SFR Yugoslavia has natural hot water springs practically all over its territory, indicating the presence of geothermal reservoirs underground. There is no final estimate of how much energy can be expected from this new resource, except for figures based on the results of studies and investigations.The first use of geothermal energy in Yugoslavia in numerous spas dates back to the 19th century. Some remarkable examples of central heating are known, but the most widespread use is in agriculture (in greenhouse heating, farm heating and drying of agricultural products).     

Interference Cancellation and Avoidance for Secondary Users Co-existing with TDD-based Primary Systems

This paper proposes a new interference cancellation/avoidance scheme for secondary spectrum usage, which takes advantage of the features of Time Division Duplex (TDD) based primary systems. We focus on the co-existence between the heterogeneous systems, where the primary and the secondary are using the same spectrum simultaneously. The secondary systems have to accurately find the possible interference from/to the primary systems for discreet and efficient secondary transmission. In order to judge the arrival of interference from/to the primary system, the secondary access point (AP) compares the difference in power between the up and downlink signals in TDD-based primary systems. This scheme enables the secondary AP to know the level of interference from the primary systems that arrives at the AP without employing complex signal detection. The proposed scheme also determines the level of interference induced to the primary system by measuring the difference in power. To cancel and avoid interference in the proposed scheme, we introduce an adaptive array at only the AP that creates a null toward the interference with a higher power level between the up and downlink signals. Moreover, new algorithms by using scheduling information of the multiple primary nodes are introduced in the proposed method, in order to enhance the transmission quality of a secondary mobile station (MS) while maintaining a simple control scheme for the MS. Finally, we verify the effectiveness of the proposed method based on computer simulations.

Preparation and characterization of Co-Ru/TiO2/MWCNTs electrocatalysts in PEM hydrogen electrolyzer

The subject of this study is preparation and characterization of hypo-hyper d-electrocatalysts with reduced amount of precious metals aimed for water electrolysis. The studied electrocatalysts contain 10% mixed metallic phase (Co:Ru = 1:1 wt., Co:Ru = 4:1 wt. and Co:Ru:Pt = 4:0.5:0.5 wt.), 18% TiO₂ as a crystalline anatase deposited on multiwalled carbon nanotubes (MWCNTs). Previously, MWCNTs were activated in 28% nitric acid. As a reference electrocatalyst for hydrogen evolution reaction, corresponding electrocatalysts with pure Pt metallic phase and mixed CoPt (Co:Pt = 1:1 wt.) metallic phase were prepared. Also, as a reference electrocatalyst for oxygen evolution reaction, electrocatalyst with pure Ru metallic phase was prepared.The prepared electrocatalysts were structurally characterized by means of XPS, XRD, TEM, SEM and FTIR analysis.Electrochemical characterization was performed by means of cyclic voltammetry and potentiodynamic method in the PEM hydrogen electrolyzer. The range of the catalytic activity for hydrogen evolution of studied electrocatalysts was the following: CoRuPt (4:0.5:0.5) > CoPt (1:1) > Pt > CoRu (1:1) > CoRu (4:1). The order of the catalytic activity for oxygen evolution was the following: CoRu (1:1) > Ru > CoRu (4:1) > Pt > CoRuPt (4:0.5:0.5) > CoPt (1:1).     

Maximum Likelihood Approach for RFID Tag Set Cardinality Estimation with Detection Errors

Estimation schemes of Radio Frequency IDentification (RFID) tag set cardinality are studied in this paper using Maximum Likelihood (ML) approach. We consider the estimation problem under the model of multiple independent reader sessions with detection errors due to unreliable radio communication links and/or collisions. In every reader session, both the detection error probability and the total number of tags are estimated. In particular, after the $R$ -th reader session, the number of tags detected in $j$ ( $j=1,2,...,R$ ) reader sessions out of $R$ sessions is updated, which we call observed evidence. Then, in order to maximize the likelihood function of the number of tags and the detection error probability given the observed evidences, we propose three different estimation methods depending on how to treat the discrete nature of the tag set cardinality. The performance of the proposed methods is evaluated under different system parameters and compared with that of the conventional method via computer simulations assuming flat Rayleigh fading environments and framed-slotted ALOHA based protocol.