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Supervised learning is one of the significant research contents in spiking neural networks (SNNs). Aiming at enhancing the performance and efficiency of supervised learning algorithms for multilayer SNNs, this paper proposes a spike optimization mechanism to select optimal presynaptic spikes for computing the change amount of synaptic weights during the learning process. The proposed spike optimization mechanism comprehensively considers the correlation between the desired and actual output spikes of the network. The synaptic weight adjustment is determined by the presynaptic spikes within an optimized time interval, which makes the network output spikes similar to the desired output spikes as much as possible. The spike optimization mechanism is applied to two representative supervised learning algorithms of multilayer SNNs (Multi-STIP and Multi-ReSuMe) to improve their learning performance. The spike train learning results show that the improved algorithms can achieve higher learning accuracy and require fewer learning epochs than the original algorithms. In addition, the spike optimization mechanism can shorten the running time of the algorithms. It indicates that the learning algorithms based on spike optimization are very efficient for learning spatio-temporal spike patterns. [ABSTRACT FROM AUTHOR]

Uncovering the dynamics of active sites in the working conditions is crucial to realizing increased activity, enhanced stability and reduced cost of oxygen evolution reaction (OER) electrocatalysts in proton exchange membrane electrolytes. Herein, we identify at the atomic level potential-driven dynamic-coupling oxygen on atomically dispersed hetero-nitrogen-configured Ir sites (AD-HN-Ir) in the OER working conditions to successfully provide the atomically dispersed Ir electrocatalyst with ultrahigh electrochemical acidic OER activity. Using in-situ synchrotron radiation infrared and X-ray absorption spectroscopies, we directly observe that one oxygen atom is formed at the Ir active site with an O-hetero-Ir-N4 structure as a more electrophilic active centre in the experiment, which effectively promotes the generation of key *OOH intermediates under working potentials; this process is favourable for the dissociation of H2O over Ir active sites and resistance to over-oxidation and dissolution of the active sites. The optimal AD-HN-Ir electrocatalyst delivers a large mass activity of 2860 A gmetal−1 and a large turnover frequency of 5110 h−1 at a low overpotential of 216 mV (10 mA cm−2), 480–510 times larger than those of the commercial IrO2. More importantly, the AD-HN-Ir electrocatalyst shows no evident deactivation after continuous 100 h OER operation in an acidic medium. Uncovering the dynamics of active sites in the working conditions is important yet challenging. Here the authors identify dynamic-coupling oxygen on atomically dispersed iridium sites during oxygen evolution reaction using in situ techniques. [ABSTRACT FROM AUTHOR]

Background and aims: Metal species in rhizosphere soil profoundly influence their mobility and phytoavailability. Clarifying the speciation transformation of heavy metals helps understand their translocation and accumulation in plants. Methods: Single extraction, selective sequential extraction (SSE) and X-ray absorption near-edge structure (XANES) spectroscopy were employed to investigate the speciation transformation of lead (Pb) and its influence on metal accumulation in tea plants after the addition of tea polyphenols (TPs). Results: Pb content was decreased in young leaves and stems, whereas increased in roots, after TPs were amended to soil. Both SSE and XANES analysis suggested bioavailable Pb was transformed to organically bound Pb after the addition of TPs. The increased percentage of organically bound Pb might be fixed in the cell wall of plant root through a ternary complex formed between the Pb-organic matter complex and cell wall components. Therefore, Pb translocation from roots to young tissues was decreased. Conclusions: Pb phytoavailability change was driven by its speciation transformation after the addition of TPs. Combined SSE and XANES spectroscopy represent powerful tools to study metal speciation transformation in plant and soil systems. [ABSTRACT FROM AUTHOR]

The catalyst obtained through the co-precipitation of Mn(Ac) and (NH)CO (denoted as Mn-Ac-NH) displays the highest performance for soot oxidation. Compared with other MnOx catalysts, the catalyst Mn-Ac-NH exhibits much better reducibility and more uniform sponge-like nanostructure. The characterization results indicate that the oxygen species on the surface of Mn-Ac-NH are more active for soot combustion. The NO species can also be captured and oxidized by these oxygen species, generating more reactive NO which can enhance soot oxidation. Graphical Abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

In this paper, we have investigated the formation of the third-phase in tertiary amine (N235)-PtCl-HCl system and the microscopic phase structural evolution of platinum-loaded organic phases before and after the occurrence of the third-phase. The third-phase is characterized by various spectroscopic techniques, and the small angle X-ray scattering (SAXS) experiments demonstrate the appearance of nano-aggregates, i.e., water-in-oil reversed micelles, in the third phase. The experimental results indicate that (1) formation of the third phase is related to the aggregation behaviors of nano-reversed micelles in which a super-concentrated hydrochloric acid formed with the H+ to H2O molar ratio being much higher than that of the conventional 37 wt% saturated hydrochloric acid. (2) The occurrence of the super-concentrated HCl results in a great amount of H+ and Cl− ions enriched and confined within the nano-water pools of W/O reversed micelles in third phase. Therefore, the coordination behaviors of platinum complex ions in that super-concentrated hydrochloric acid are very different from their corresponding behaviors in bulk aqueous solutions. It is possible that H+ ions participate in the formation of such complexes as H m PtCl in the super-concentrated hydrochloric acid. (3) The relative contents of various H m PtCl complexes are different corresponding to the H+ ion concentrations in confined nano-water pools. The association ability of the acidified tertiary amine N235 molecules (R3NH+) with various H m PtCl complexes plays an important role in affecting the platinum extraction behaviors. [ABSTRACT FROM AUTHOR]

Synchrotron radiation extended X-ray absorption fine structure (SR EXAFS) was employed to study the transformation of coordination environment and the redox speciation of arsenic in a newly discovered arsenic hyperaccumulator, Cretan brake ( Pteris cretica L. var nervosa Thunb). It showed that the arsenic in the plant mainly coordinated with oxygen, except that some arsenic coordinated with S as As-GSH in root. The complexation of arsenic with GSH might not be the predominant detoxification mechanism in Cretan brake. Although some arsenic in root presented as As(V) in Na2HAsO4 treatments, most of arsenic in plant presented as As(III)-O in both treatments, indicating that As(V) tended to be reduced to As(III) after it was taken up into the root, and arsenic was kept as As(III) when it was transported to the above-ground tissues. The reduction of As(V) primarily proceeded in the root. [ABSTRACT FROM AUTHOR]

The NOx storage catalyst Pt/BaAl2O4-Al2O3 was prepared by a coprecipitation--impregnation method. For fresh sample, the barium mainly exists as the BaAl2O4 phase except for some BaCO3 phase. The BaAl2O4 phase is the primary NOx storage phase of the sample. EXAFS and TPD were used for investigating the mechanism of NOx storage. It is found that two kinds of Pt sites are likely to operate. Site 1 is responsible for NO chemisorption and site 2 for oxidizing NO to nitrates and nitrites. When NO adsorbs on the sample below 200 °C, it mainly chemisorbs in the form of molecular states. Such adsorption results in an increase of the coordination magnitude of Pt-O, and a decrease of that of Pt-Pt and Pt-Cl. The coordination distance of Pt-Pt, Pt-Cl and Pt-O also increases. When the adsorption occurs above 200 °C, NO can be easily oxidized by O2, and stored as nitrites or nitrates at the basic BaAl2O4. Site 2 is regenerated quickly. A high adsorption temperature is favorable for nitrate formation. [ABSTRACT FROM AUTHOR]

Based on the structure of characterization of Au/FeO catalysts, the mechanism of gold activation in supported gold catalysts was proposed as follow: The possible catalytic active state is the partially oxidized gold (Au) with unoccupied outer d orbitals, similar to the outer d orbital structure of Pt. Thus "inert" gold can become very active for CO oxidation. [ABSTRACT FROM AUTHOR]

The role of magnetoelastic coupling effects in nanocrystalline ferromagnets is investigated by means of high-field magnetization and Doppler-broadening spectrum measurements. For the nanocrystalline Fe73 5Cu1Nb3Si13.5B9 alloy, the results show that the pinning effects resulting from the quasidislocation dipole intensely influence the movement of domain wall; by coupling with the magnetostriction the defects-induced stress fields determine the magnetic properties at the early stage of crystallization. In view of the effective anisotropy and magnetoelastic coupling energy the optimal annealing conditions of alloys are discussed. [ABSTRACT FROM AUTHOR]

Studies the structures and properties of liquid materials quantitatively. X-ray absorption fine structure (XAFS) as a tool used to probe the local structure of disordered systems such as liquid materials; Factors attributed to the lack of application of the XAFS technique in liquid systems.