ChemInform Abstract: Unusual Inorganic Biradicals: A Theoretical Analysis.

Quantum chemical calculations at the CASSCF level of theory on the O₃‐homologous molecules CX₂^2‐, NX₂^‐, X₃, OX₂, and FX₂⁺ (X: O, S, Se, Te, Po) indicate that the triatomic inorganic biradicals in the FX₂⁺ series have unusually high biradical character.     

Reductions of peak-to-average power ratio and optical beat interference in cost-effective OFDMA-PONs

The peak-to-average power ratio (PAPR) and optical beat interference (OBI) effects are examined thoroughly in orthogonal frequency-division multiplexing access (OFDMA)-passive optical networks (PONs) at a signal bit rate up to $\sim 20\,\mathrm{{Gb}}/{\hbox {s}}$ per channel using cost-effective intensity-modulation and direct-detection (IM/DD). Single-channel OOFDM and upstream multichannel OFDM-PONs are investigated for up to six users. A number of techniques for mitigating the PAPR and OBI effects are presented and evaluated including adaptive-loading algorithms such as bit/power-loading, clipping for PAPR reduction, and thermal detuning (TD) for the OBI suppression. It is shown that the bit-loading algorithm is a very efficient PAPR reduction technique by reducing it at about 1.2 dB over 100 Km of transmission. It is also revealed that the optimum method for suppressing the OBI is the TD + bit-loading. For a targeted BER of $1 \times 10 ^{-3}$ , the minimum allowed channel spacing is 11 GHz when employing six users.     

Uniform nanoparticles by flame-assisted spray pyrolysis (FASP) of low cost precursors

A new flame-assisted spray pyrolysis (FASP) reactor design is presented, which allows the use of inexpensive precursors and solvents (e.g., ethanol) for synthesis of nanoparticles (10–20 nm) with uniform characteristics. In this reactor design, a gas-assisted atomizer generates the precursor solution spray that is mixed and combusted with externally fed inexpensive fuel gases (acetylene or methane) at a defined height above the atomizing nozzle. The gaseous fuel feed can be varied to control the combustion enthalpy content of the flame and onset of particle formation. This way, the enthalpy density of the flame is decoupled from the precursor solution composition. Low enthalpy content precursor solutions are prone to synthesis of non-uniform particles (e.g., bimodal particle size distribution) by standard flame spray pyrolysis (FSP) processes. For example, metal nitrates in ethanol typically produce nanosized particles by gas-to-particle conversion along with larger particles by droplet-to-particle conversion. The present FASP design facilitates the use of such low enthalpy precursor solutions for synthesis of homogeneous nanopowders by increasing the combustion enthalpy density of the flame with low-cost, gaseous fuels. The effect of flame enthalpy density on product properties in the FASP configuration is explored by the example of Bi₂O₃ nanoparticles produced from bismuth nitrate in ethanol. Product powders were characterized by nitrogen adsorption, X-ray diffraction, X-ray disk centrifuge, and transmission electron microscopy. Homogeneous Bi₂O₃ nanopowders were produced both by increasing the gaseous fuel content and, most notably, by cutting the air entrainment prior to ignition of the spray.     

Modular polymer biosensors by solvent immersion imprint lithography

We recently demonstrated Solvent Immersion Imprint Lithography (SIIL), a rapid benchtop microsystem prototyping technique, including polymer functionalization, imprinting and bonding. Here, we focus on the realization of planar polymer sensors using SIIL through simple solvent immersion without imprinting. We describe SIIL's impregnation characteristics, including an inherent mechanism that not only achieves practical doping concentrations, but their unexpected 2‐fold enhancement compared to the immersion solution. Subsequently, we developed and characterized optical sensors for detecting molecular O₂. To this end, a substantially high dynamic range is reported, including its control through the immersion duration, a manifestation of SIIL's modularity. Overall, SIIL exhibits the potential of improving the operating characteristics of polymer sensors, while significantly accelerating their prototyping, as it requires a few seconds of processing and no need for substrates or dedicated instrumentation. These are critical for O₂ sensing as probed by way of example here, as well as any polymer permeable reactant. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 98–103     

High-pressure liquid dispersion and fragmentation of flame-made silica agglomerates

The influence of primary particle diameter and the degree of agglomeration of flame-made silica agglomerate suspensions in aqueous solutions is studied by high-pressure dispersion (up to 1500 bar) through a nozzle with a 125 microm inner diameter. These particles were produced (4-15 g/h) by oxidation of hexamethyldisiloxane (HMDSO) in a coflow diffusion flame reactor. Their average primary particle size (10-50 nm) and degree of agglomeration were controlled by varying the oxygen and precursor flow rates. The particles were characterized by nitrogen adsorption, electron microscopy, and small-angle X-ray scattering. Hydrodynamic stresses break up soft agglomerates and yield hard agglomerate sizes in the range of 100-180 nm, as characterized by dynamic light scattering. Soft agglomerates exhibited decreasing light scattering diameters with increasing dispersion pressure, while hard agglomerates were insensitive.     

Radiocolorings in periodic planar graphs: PSPACE-completeness and efficient approximations for the optimal range of frequencies

The Frequency Assignment Problem (FAP) in radio networks is the problem of assigning frequencies to transmitters exploiting frequency reuse while keeping signal interference to acceptable levels. The FAP is usually modelled by variations of the graph coloring problem. A Radiocoloring (RC) of a graph G(V,E) is an assignment function such that |Λ(u)−Λ(v)|2, when u,v are neighbors in G, and |Λ(u)−Λ(v)|1 when the distance of u,v in G is two. The discrete number of frequencies used is called order and the range of frequencies used, span. The optimization versions of the Radiocoloring Problem (RCP) are to minimize the span (min span RCP) or the order (min order RCP).In this paper, we deal with an interesting, yet not examined until now, variation of the radiocoloring problem: that of satisfying frequency assignment requests which exhibit some periodic behavior. In this case, the interference graph (modelling interference between transmitters) is some (infinite) periodic graph. Infinite periodic graphs usually model finite networks that accept periodic (in time, e.g. daily) requests for frequency assignment. Alternatively, they can model very large networks produced by the repetition of a small graph.A periodic graph G is defined by an infinite two-way sequence of repetitions of the same finite graph G_i(V_i,E_i). The edge set of G is derived by connecting the vertices of each iteration G_i to some of the vertices of the next iteration G_i+1, the same for all G_i. We focus on planar periodic graphs, because in many cases real networks are planar and also because of their independent mathematical interest.We give two basic results:

• We prove that the min span RCP is PSPACE-complete for periodic planar graphs.

• We provide an O(n(Δ(G_i)+σ)) time algorithm (where|V_i|=n, Δ(G_i) is the maximum degree of the graph G_i and σ is the number of edges connecting each G_i to G_i+1), which obtains a radiocoloring of a periodic planar graph G that approximates the minimum span within a ratio which tends to as Δ(G_i)+σ tends to infinity.

We remark that, any approximation algorithm for the min span RCP of a finite planar graph G, that achieves a span of at most αΔ(G)+constant, for any α and where Δ(G) is the maximum degree of G, can be used as a subroutine in our algorithm to produce an approximation for min span RCP of asymptotic ratio α for periodic planar graphs.

Energy balanced data propagation in wireless sensor networks

We study the problem of energy-balanced data propagation in wireless sensor networks. The energy balance property guarantees that the average per sensor energy dissipation is the same for all sensors in the network, during the entire execution of the data propagation protocol. This property is important since it prolongs the network’:s lifetime by avoiding early energy depletion of sensors. We propose a new algorithm that in each step decides whether to propagate data one-hop towards the final destination (the sink), or to send data directly to the sink. This randomized choice balances the (cheap) one-hop transimssions with the direct transimissions to the sink, which are more expensive but “bypass” the sensors lying close to the sink. Note that, in most protocols, these close to the sink sensors tend to be overused and die out early. By a detailed analysis we precisely estimate the probabilities for each propagation choice in order to guarantee energy balance. The needed estimation can easily be performed by current sensors using simple to obtain information. Under some assumptions, we also derive a closed form for these probabilities. The fact (shown by our analysis) that direct (expensive) transmissions to the sink are needed only rarely, shows that our protocol, besides energy-balanced, is also energy efficient. This work has been partially supported by the IST/FET/GC Programme of the European Union under contract numbers IST-2001-33135 (CRESCCO) and 6FP 001907 (DELIS). A perliminary version of the work appeared in WMAN 2004 [11]. Charilaos Efthymiou graduated form the Computer Engineering and Informatics Department (CEID) of the University of Patras, Greece. He received his MSc from the same department with advisor in S. Nikoletseas. He currently continuous his Ph.D studies in CEID with advisor L. Kirousis. His research interest include Probabilistic Techniques and Random Graphs, Randomized Algorithms in Computationally Hard Problems, Stochastic Processes and its Applications to Computer Science. Dr. Sotiris Nikoletseas is currently a Senior Researcher and Managing Director of Research Unit 1 (“Foundations of Computer Science, Relevant Technologies and Applications”) at the Computer Technology Institute (CTI), Patras, Greece and also a Lecturer at the Computer Engineering and Informatics Department of Patras University, Greece. His research interests include Probabilistic Techniques and Random Graphs, Average Case Analysis of Graph Algorithms and Randomized Algorithms, Fundamental Issues in Parallel and Distributed Computing, Approximate Solutions to Computationally Hard Problems. He has published scientific articles in major international conferences and journals and has co-authored (with Paul Spirakis) a book on Probabilistic Techniques. He has been invited speaker in important international scientific events and Universities. He has been a referee for the Theoretical Computer Science (TCS) Journal and important international conferences (ESA, ICALP). He has participated in many EU funded R&D projects (ESPRIT/ALCOM-IT, ESPRIT/GEPPCOM). He currently participates in 6 Fifth Framework projects: ALCOM-FT, ASPIS, UNIVERSAL, EICSTES (IST), ARACNE, AMORE (IMPROVING). Jose Rolim is Full Professor at the Department of Computer Science of the University of Geneva where he leads the Theoretical Computer Science and Sensor Lab (TCSensor Lab). He received his Ph.D. degree in Computer Science at the University of California, Los Angeles working together with Prof. S. Greibach. He has published several articles on the areas of distributed systems, randomization and computational complexity and leads two major projects on the area of Power Aware Computing and Games and Complexity, financed by the Swiss National Science Foundation. Prof. Rolim participates in the editorial board of several journals and conferences and he is the Steering Committee Chair and General Chair of the IEEE Distributed Computing Conference in Sensor Systems.     

Solid-phase fluoroimmunoassay for the determination of mesotrione--a novel triketone herbicide--in water with direct measurement of the fluorescence onto the solid support

A straightforward, low-cost fluoroimmunoassay (FIA) for the determination of the new triketone herbicide mesotrione has been developed and optimized. The protein-mesotrione conjugate, immobilized on white opaque microtitration wells competes with the mesotrione in the sample or standard for the limited binding sites of a liquid phase anti-mesotrione antibody. The assay is based on the measurement of fluorescence intensity directly onto the solid support, using a fluorescein labeled second antibody and a fluorescence plate reader. To stabilize and enhance the fluorescence signal a glycerine-based treatment of the microtitration wells was included in the protocol. The detection limit of the assay is 40 ng 1(-1) (4 pg per well), the working range extends up to 9 microg l(-1), whereas the within and between run CVs are 0.7-4.2% and 2.1-5.5%, respectively. To evaluate the assay specificity, the cross-reactivities of two mesotrione metabolites: 4-methylsulfonyl-2-nitrobenzoic acid and 2-amino-4-methylsulfonyl-benzoic acid and several other compounds similar in structure to mesotrione such as: fomesafen, prosulfocarb, fluazinam, sulcotrione, 1,2-cyclohexanedione, 1,3-cyclohexanedione, 2-acetyl-1,3-cyclohexanedione were assessed. Most of the substances tested presented very low ( < 0.05%) cross-reactivity values with the exception of sulcotrione that cross-reacted 23% in the mesotrione assay. The assay was used for the determination of mesotrione in bottled natural waters fortified with the analyte and in a commercial herbicide formulation, namely CALLISTO.     

Discrete X-wave formation in nonlinear waveguide arrays

We present experimental evidence for the spontaneous formation of discrete X waves in AlGaAs waveguide arrays. This new family of optical waves has been excited, for the first time, by using the interplay between discrete diffraction and normal temporal dispersion, in the presence of Kerr nonlinearity. Our experimental results are in good agreement with theoretical predictions.