Electrical behavior of lithium intercalated layered In-Se compounds

InSe and In₂Se₃ was lithium intercalated by mean of a spontaneous intercalation reaction. The electrical conductivity was studied and was found to be altered by 3-orders of magnitude with respect to non-intercalated samples. An interesting time dependent anisotropy appeared during intercalation, associed to the initial non-uniform Li distribution and the movement of Li concentration kinks.     

Gathering asynchronous oblivious mobile robots in a ring

We consider the problem of gathering identical, memoryless, mobile robots in one node of an anonymous unoriented ring. Robots start from different nodes of the ring. They operate in Look–Compute–Move cycles and have to end up in the same node. In one cycle, a robot takes a snapshot of the current configuration (Look), makes a decision to stay idle or to move to one of its adjacent nodes (Compute), and in the latter case makes an instantaneous move to this neighbor (Move). Cycles are performed asynchronously for each robot. For an odd number of robots we prove that gathering is feasible if and only if the initial configuration is not periodic, and we provide a gathering algorithm for any such configuration. For an even number of robots we decide the feasibility of gathering except for one type of symmetric initial configurations, and provide gathering algorithms for initial configurations proved to be gatherable.     

n–p transformation in TlBi(1−x)SbxTe2 system

TlBi_(1?x)Sb_xTe₂ quaternary crystals that crystallize in a rhombohedral structure and according to their properties are classified between semimetals and narrow energy gap semiconductors, are studied. The study of their optical and electrical behavior reveal that they are quite sensitive to the Sb content x, and it is found that the substitution of Bi- with Sb-atoms in TlBiTe₂ crystals leads initially to a decrease in the plasma frequency. However, for higher Sb contents, the plasma frequency increases. At room temperature, samples with x < 0.8 are n-type semiconductors, becoming p-type ones for x > 0.8.A model suggesting a suppression of the free electron concentration induced by the incorporation of Sb atoms into the crystal lattice of TlBiTe₂ is used to explain this transition in the conductivity type.     

Macro and Micro-Scale Features of Thermoelectric PbTe (Br,Na) Systems: Micro-FTIR Spectroscopy,Micro-Seebeck Measurements,and SEM/EDX Observations

In this work, n-type and p-type PbTe doped with Br and Na, respectively, were thoroughly examined to determine the effect of the dopant on microstructure. Macro and micro homogeneity of the samples were studied by means of micro-Fourier-transform infrared (micro-FTIR) spectroscopy, micro-Seebeck measurements, and scanning electron microscopy with energy-dispersive x-ray analysis (SEM/EDX). SEM/EDX observations showed the samples were not single-phase materials—second phases were created by inclusions that disturbed the coherence of the matrix and, subsequently, drastically affected the Seebeck coefficient. In a micro-scale study, local variations of sodium content were detected in Na-doped samples; in Br-doped samples a second, PbBr₂, phase was observed in the PbTe matrix. A direct effect of matrix dopant on Seebeck coefficient and plasmon frequency for the Br-doped and Na-doped samples was observed by use of the three complementary techniques.     

Analysis of Phase Separation in High Performance PbTe–PbS Thermoelectric Materials

Phase immiscibility in PbTe–based thermoelectric materials is an effective means of top‐down synthesis of nanostructured composites exhibiting low lattice thermal conductivities. PbTe_1‐x S_x thermoelectric materials can be synthesized as metastable solid solution alloys through rapid quenching. Subsequent post‐annealing induces phase separation at the nanometer scale, producing nanostructures that increase phonon scattering and reduce lattice thermal conductivity. However, there has yet to be any study investigating in detail the local chemical structure of both the solid solution and nanostructured variants of this material system. Herein, quenched and annealed (i.e., solid solution and phase‐separated) samples of PbTe–PbS are analyzed by in situ high‐resolution synchrotron powder X‐ray diffraction, solid‐state ¹²⁵Te nuclear magnetic resonance (NMR), and infrared (IR) spectroscopy analysis. For high concentrations of PbS in PbTe, e.g., x >16%, NMR and IR analyses reveal that rapidly quenched samples exhibit incipient phase separation that is not detected by state‐of‐the‐art synchrotron X‐ray diffraction, providing an example of a PbTe thermoelectric “alloy” that is in fact phase inhomogeneous. Thermally‐induced PbS phase separation in PbTe–PbS occurs close to 200 °C for all compositions studied, and the solubility of the PbS phase in PbTe at elevated temperatures >500 °C is reported. The findings of this study suggest that there may be a large number of thermoelectric alloy systems that are phase inhomogeneous or nanostructured despite adherence to Vegard's Law of alloys, highlighting the importance of careful chemical characterization to differentiate between thermoelectric alloys and composites.     

Atmospheric deposition and marine sedimentation fluxes of polycyclic aromatic hydrocarbons in the Eastern Mediterranean Basin

Atmospheric input was studied and found to be the major source of PAHs in the eastern Mediterranean open marine ecosystem. Dry and wet atmospheric deposition, air-sea exchange, and sediment trap fluxes of polycyclic aromatic hydrocarbons (PAHs) in the eastern Mediterranean basin were estimated from November 2000 to July 2002. Seven dry and four wet deposition samples were analyzed in total and PAH concentrations were determined. Airsea exchange fluxes based on air-water concentration gradientwere drawn from five air and water samples collected concurrently from a coastal area in the eastern Mediterranean. Total annual average deposition fluxes of dry, wet, and air-sea exchange sigma35PAHs were 58.0, 165.7, and -706.4 microg m(-2) y(-1), respectively. Only 1.1 and 0.7% of the total atmospheric deposition flux of PAHs was measured in the sediment traps at 280 and 1440 m depth, respectively.     

Gas/particle partitioning and size distribution of primary and secondary carbonaceous aerosols in public buildings

The gas and particulate phase of semi-volatile organic compounds (six samples) and the composition of organic aerosol as a function of particle size (six samples) were studied in two public buildings in Greece. The objectives of this study were: i) to chemically characterize the organic content of indoor gas and particulate phases; ii) to classify indoor organic aerosol constituents as a function of particle size; and iii) to reconcile the sources of organic compounds indoors. Non-polar, semi-polar, polar, and acidic compounds were identified in both gas and particulate phases by using gas chromatography/mass spectrometry (GC/MS). Branched iso- and anteiso-alkanes were used to trace environmental tobacco smoke (ETS) concurrently with other compounds. Polycyclic aromatic hydrocarbons (PAHs) in the gas phase gave a pattern more characteristic to ETS than the corresponding pattern in the particulate phase. The chemical composition observed for n-alkanols and n-alkanoic acids in both gas and particulate phases indicated ETS as one of their main sources indoors. PAHs and n-alkanols were evenly associated between fine and coarse particles and their corresponding total mean mass median aerodynamic diameter (MMAD) was 1.27 and 1.38 microns respectively, indicating a mixed origin. Conversely, the MMAD of n-alkanes, unresolved complex mixture (UCM), iso- and anteiso-alkanes and free fatty acids varied from 0.30 to 0.62 micron denoting a stronger association with indoor sources.     

Efficient Exploration of Faulty Trees

We consider the problem of the exploration of trees, some of whose edges are faulty. A robot, situated in a starting node and unaware of the location of faults, has to explore the connected fault-free component of this node by visiting all its nodes. The cost of the exploration is the number of edge traversals. For a given tree and given starting node, the overhead of an exploration algorithm is the worst-case ratio (taken over all fault configurations) of its cost to the cost of an optimal algorithm which knows where faults are situated. An algorithm, for a given tree and given starting node, is called perfectly competitive if its overhead is the smallest among all exploration algorithms not knowing the location of faults. We design a perfectly competitive exploration algorithm for any line, and an exploration algorithm for any tree, whose overhead is at most 9/8 larger than that of a perfectly competitive algorithm. Both our algorithms are fairly natural and the total time of local computations used during exploration is linear in the size of the explored tree. Our main contribution is the analysis of the performance of these algorithms, showing that natural exploration strategies perform well in faulty trees.     

Similarity searching in the CORDIS text database

Similarity searching in text databases with multiple field types is still an open problem. We focus our attention on the ‘Community Research and Development Information Service’ (CORDIS) database of the European Union and we evaluate the effectiveness of many text retrieval methods in terms of precision, recall and ranking quality. Our experiments indicate that different field types should be handled by different retrieval methods. Copyright © 2000 John Wiley & Sons, Ltd.     

Emergency Connectivity in Ad-hoc Networks with Selfish Nodes

Inspired by the CONFIDANT protocol (Buchegger and Boudec in Proceedings of the 3rd ACM International Symposium on Mobile Ad Hoc Networking & Computing, pp. 226–236, 2002), we define and study a basic reputation-based protocol in multihop wireless networks with selfish nodes. Its reputation mechanism is implemented through the ability of any node to define a threshold of tolerance for any of its neighbors, and to cut the connection to any of these neighbors that refuse to forward an amount of flow above that threshold. The main question we would like to address is whether one can set the initial conditions so that the system reaches an equilibrium state where a non-zero amount of every commodity is routed. This is important in emergency situations, where all nodes need to be able to communicate even with a small bandwidth. Following a standard approach, we model this protocol as a game, and we give necessary and sufficient conditions for the existence of non-trivial Nash equilibria. Then we enhance these conditions with extra conditions that give a set of necessary and sufficient conditions for the existence of connected Nash equilibria. We note that it is not always necessary for all the flow originating at a node to reach its destination at equilibrium. For example, a node may be using unsuccessful flow in order to effect changes in a distant part of the network that will prove quite beneficial to it. We show that we can decide in polynomial time whether there exists a (connected) equilibrium without unsuccessful flows. In that case we calculate (in polynomial time) initial values that impose such an equilibrium on the network. On the negative side, we prove that it is NP-hard to decide whether a connected equilibrium exists in general (i.e., with some nodes using unsuccessful flows at equilibrium).