A central problem in this field is to understand the mechanism by which these materials resolve these conflicting tendencies.In this letter we identify the electronic mechanisms responsible for the anomalous behaviour of late actinides. We revisit the concept of valence using theoretical approach that treats magnetism, Kondo screening, atomic multiplet effects, spin orbit coupling and crystal field splitting on the same footing.Plutonium is found to be in a rare mixed valent state, namely its ground state is a
The electrocatalytic activity of bulk Au and Au nanoparticles (AuNPs) toward the oxygen reduction reaction (ORR), before and after the electrochemical pretreatment, was investigated in a 0.05 M phosphate buffer solution (pH = 7.4). Both the Au and AuNPs were pretreated by repetitive potential cycling between −0.2 and +1.0 V (vs SCE). Rotating disk electrode (RDE) voltammetric studies showed that a more favorable ORR occurred at the AuNPs than at the Au. Interestingly, increased number of electrons (n) transferred in the ORR (∼4) and more positive ORR onset potential were observed at both the Au and AuNPs after the pretreatment. In particular, for the bulk Au, a simple electrochemical pretreatment produced remarkably improved ORR activity, i.e., a considerable positive shift in the ORR onset potential by ∼300 mV as well as a significant increase in the n number (from <2 to ∼4). The greatest catalytic activity was observed at the pretreated AuNPs. The enhanced catalytic activity by the electrochemical pretreatment was attributed to the formation of thick Au oxide layers, which was also demonstrated with a thermally pretreated Au microwire electrode. The pretreated Au and AuNPs also showed higher activity toward the oxidation of hydrogen peroxide than the corresponding untreated ones.
This paper reports the simple synthesis and characterization of carbon-supported Pd layer-coated Au nanoparticles (AuPd/C). A series of AuPd/C with various Pd/Au weight percentage ratios were prepared by the spontaneous deposition of a Pd shell on a Au nanoparticle core using different Pd precursor concentrations (0.5, 5, 10, 20 mM PdCl2). Au nanospheres encapsulated by the porous Pd shells are confirmed by transmission electron microscopy (TEM), UV–vis absorption spectroscopy, and scanning TEM. The catalytic activity of the AuPd/C for the oxygen reduction reaction (ORR) was investigated by rotating disk electrode voltammetry in 0.5 M H2SO4. In particular, a AuPd/C with a Pd/Au ratio of 0.61 shows superior ORR activity along with satisfactory stability and methanol tolerance under acidic conditions.
Focusing on both small separations and Baryonic Acoustic Oscillation scales, the cosmic evolution of the clustering properties of peak, void, wall and filament-type critical points is measured using two-point correlation functions in ΛCDM dark matter simulations as a function of their relative rarity. A qualitative comparison to the corresponding theory for Gaussian random fields allows us to understand the following observed features: i) the appearance of an exclusion zone at small separation, whose size depends both on rarity and signature (i.e the number of negative eigenvalues) of the critical points involved; ii) the amplification of the Baryonic Acoustic Oscillation bump with rarity and its reversal for cross correlations involving negatively biased critical points; iii) the orientation-dependent small-separation divergence of the cross-correlations of peaks and filaments (resp. voids and walls) which reflects the relative loci of such points in the filament’s (resp. wall’s) eigenframe. The (cross-) correlations involving the most non-linear critical points (peaks, voids) display significant variation with redshift, while those involving less non-linear critical points seem mostly insensitive to redshift evolution, which should prove advantageous to model. The ratios of distances to the maxima of the peak-to-wall and peak-to-void over that of the peak-to-filament cross-correlation are $\sim \sqrt{2}$ and $\sim \sqrt{3}$, respectively which could be interpreted as the cosmic crystal being on average close to a cubic lattice. The insensitivity to redshift evolution suggests that the absolute and relative clustering of critical points could become a topologically robust alternative to standard clustering techniques when analysing upcoming surveys such as Euclid or LSST.
Glass nanopore-based all-solid-state ion-selective electrodes (ISEs) have been developed to probe the distribution of ionic species at micro- or submicrometer-length scales, e.g., mapping of ion flux through micrometer-sized pores. The all-solid-state ISE was fabricated by sealing a conically etched platinum wire (d = 25-microm; radius of etched tip <10 nm) into a soda lime glass capillary. A Pt disk was exposed by gentle polishing the glass and the disk etched to form a conical pore of submicrometer dimension (radius < approximately 500 nm; depth < approximately 30 microm). Ag was electroplated on the Pt electrode in the pore and gently chloridated to obtain a AgCl/Ag layer within the pore. The AgCl/Ag layer-coated ISE was used as a highly selective Cl- probe in scanning electrochemical microscope experiments to map the ion flux through a micropore. The same ISE was also used as the base transducer of the neutral carrier-doped solvent polymeric membrane. The optimized polymer membranes used for the glass nanopore-based all-solid-state ISE require a higher ratio of plasticizer/polymer (9/1) compared to those for conventional ISE (2/1). An ISE based on deposition of an IrO2 layer at the base of a glass nanopore electrode exhibited a highly sensitive response (79.7 +/- 2.3 mV/pH) to variations in pH and could be used for approximately 3 weeks.
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