Design of active and stable oxygen reduction reaction catalysts by embedding Co<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> nanoparticles into nitrogen-doped carbon

The oxygen reduction reaction (ORR) is essential in research pertaining to life science and energy. In applications, platinum-based catalysts give ideal reactivity, but, in practice, are often subject to high costs and poor stability. Some cost-efficient transition metal oxides have exhibited excellent ORR reactivity, but the stability and durability of such alternative catalyst materials pose serious challenges. Here, we present a facile method to fabricate uniform Co _x O _y nanoparticles and embed them into N-doped carbon, which results in a composite of extraordinary stability and durability, while maintaining its high reactivity. The half-wave potential shows a negative shift of only 21 mV after 10,000 cycles, only one third of that observed for Pt/C (63 mV). Furthermore, after 100,000 s testing at a constant potential, the current decreases by only 17%, significantly less than for Pt/C (35%). The exceptional stability and durability results from the system architecture, which comprises a thin carbon shell that prevents agglomeration of the Co _x O _y nanoparticles and their detaching from the substrate.

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Communication-efficient and crash-quiescent Omega with unknown membership

The failure detector class Omega (Ω) provides an eventual leader election functionality, i.e., eventually all correct processes permanently trust the same correct process. An algorithm is communication-efficient if the number of links that carry messages forever is bounded by n, being n the number of processes in the system. It has been defined that an algorithm is crash-quiescent if it eventually stops sending messages to crashed processes. In this regard, it has been recently shown the impossibility of implementing Ω crash quiescently without a majority of correct processes. We say that the membership is unknown if each process pi only knows its own identity and the number of processes in the system (that is, i and n), but pi does not know the identity of the rest of processes of the system. There is a type of link (denoted by ADD link) in which a bounded (but unknown) number of consecutive messages can be delayed or lost.In this work we present the first implementation (to our knowledge) of Ω in partially synchronous systems with ADD links and with unknown membership. Furthermore, it is the first implementation of Ω that combines two very interesting properties: communication-efficiency and crash-quiescence when the majority of processes are correct. Finally, we also obtain with the same algorithm a failure detector () such that every correct process eventually and permanently outputs the set of all correct processes.     

Online Text Prediction with Recurrent Neural Networks

Arithmetic coding is one of the most outstanding techniques for lossless data compression. It attains its good performance with the help of a probability model which indicates at each step the probability of occurrence of each possible input symbol given the current context. The better this model, the greater the compression ratio achieved. This work analyses the use of discrete-time recurrent neural networks and their capability for predicting the next symbol in a sequence in order to implement that model. The focus of this study is on online prediction, a task much harder than the classical offline grammatical inference with neural networks. The results obtained show that recurrent neural networks have no problem when the sequences come from the output of a finite-state machine, easily giving high compression ratios. When compressing real texts, however, the dynamics of the sequences seem to be too complex to be learned online correctly by the net.     

Laser‐induced surface structures on gold‐coated polymers: Influence of morphology on surface‐enhanced Raman scattering enhancement

The fabrication of highly sensitive and reproducible substrates for Surface‐Enhanced Raman Scattering (SERS) remains a challenging scientific and technological issue. In this work, laser‐induced periodic surface structures are generated on poly(trimethylen terephthalate) films upon laser irradiation with the linearly polarized beams of a Nd:YAG laser (4th harmonic, 266 nm), an ArF excimer laser (193 nm), and a Titanium:sapphire laser (795 nm), resulting in periods close to the laser wavelength when irradiating at normal incidence, and larger periods for different angles of incidence. Additional irradiation with a circularly polarized beam at 266 nm produces superficial circular structures. The nanostructured polymers are coated with a nanoparticle assembled gold layer by pulsed laser deposition at 213 nm. The capabilities of these substrates for SERS are evaluated using benzenethiol as a test molecule and different degrees of Raman signal enhancement are observed depending on the nanostructure type. The highest enhancement factor is obtained by for nanostructured substrates with the highest values of period, depth, and roughness. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42770.     

Polymers beyond standard optical fibres – fabrication of microstructured polymer optical fibres

This paper reports the overall fabrication process of microstructured polymer optical fibres (mPOFs). mPOF fabrication involves a two‐step process: on the one hand, the design and creation of a preform containing a large‐scale version of the desired fibre and, on the other, the precise heating and drawing of the preform to the final fibre. The preforms are produced either by an improved drilling technique or by capillary stacking. For a correct and accurate drawing of the fibre, a controlled and precise heating unit has to be designed, an issue that will be explained in detail in this work. The quality and optical performance of the final mPOF depends strongly on key factors such as the preform annealing, the accuracy of the technique selected for the creation of the preform structure, the heating stage, as well as on the drawing parameters. All of them are analysed in detail and some drawn mPOFs of interest are reported as well. © 2018 Society of Chemical Industry     

Implementing the Omega failure detector in the crash-recovery failure model

Unreliable failure detectors are mechanisms providing information about process failures, that allow to solve several problems in asynchronous systems, e.g., Consensus. A particular failure detector, Omega, provides an eventual leader election functionality. This paper addresses the implementation of Omega in the crash-recovery failure model. We first propose an algorithm assuming that processes are reachable from the correct process that crashes and recovers a minimum number of times. Then, we propose two algorithms which assume only that processes are reachable from some correct process. Besides this, one of the algorithms requires the membership to be known a priori, while the other two do not.     

Semi-discretization for stability analysis of in-feed cylindrical grinding with continuous workpiece speed variation

This paper presents the advances of semi-discretization approach for the dynamic stability analysis of in-feed cylindrical grinding process. The corresponding mathematical model is an autonomous delay-differential equation and the application of continuous workpiece speed variation (CWSV) in the process leads to a time-varying delay. Discretization techniques are a good way of dealing with differential equations for which the solution cannot be given in closed forms. Therefore, the semi-discretization method is proposed to analyze the equation. Stability maps are devised to study the influence of the CWSV application. Contrary to milling and turning processes, stability in grinding is very much influenced by the residual flexibility due to the deformation of the grinding wheel-workpiece system, so this term has been included in the approach. The validation has been carried out experimentally and good correlation between test and simulation results has been achieved.     

Siliceous spicules and skeleton frameworks in sponges: origin, diversity, ultrastructural patterns, and biological functions

Silica deposition is a fundamental process in sponges. Most sponges in the Classes Demospongiae and Hexactinellida secrete siliceous elements, which can subsequently fuse, interlock with each other, or form three-dimensional structures connected by spongin. The resulting skeletal frameworks allow sponges to grow upwards and facilitate water exchange with minimal metabolic cost. Several studies on sponge skeletogenesis have been published. We are beginning to understand the mechanisms of spicule secretion and the role of spicules and skeletal frameworks in the biology, ecology, and evolution of sponges. Molecular techniques and ecological experiments have demonstrated the genetic control of the process and the contribution of environmental factors to the expression of a sponge spicule, respectively. However, other classic topics such as the role of membranes in silicon transport or whether spicules are formed in situ or secreted anywhere in the sponge mesohyl and then transported to the skeletal framework require further investigation. We review the process of silica deposition in sponges at the molecular and cellular levels, as well as the biological and ecological functions of spicules and skeletons. The genetic control of spicule shapes makes them useful in the reconstruction of sponge phylogeny, although recent experiments have demonstrated the influence of environmental factors in modulating spicule size, shape, and the presence or absence of one or more spicule types. The implications of such variations in sponge taxonomy may be important. Besides supporting sponge cells, spicules can help larvae stay buoyant while in the plankton or reach the bottom at settlement, enhance reproduction success, or catch prey. Conversely, the role of spicules and skeletons in deterring predation has not been demonstrated. Knowledge of several aspects is still based on a single or a few species and extrapolations should be made only with caution. With the advent of new molecular techniques, new lines of research are presently open and active in this field.