Drop of Activity of the Oxygen Electrode on the Base of Ag Catalyst (Polytetrafluorethylene)

The article describes the determination of the effect of »impurities«, o,riginating from dissolution of the cell components, upon the activity of the oxygen electrode Ag-catalyst .in 7 N KOH. It was confirmed that the silver surface plays a more serious part in electrochemical processes than it had been assumed previously. It refers, above all, to the formation and solubility of silver oxides and further to eventual adsorption of ions [Ag(OH) 2]- on the active surface of the oxygen electrode silver catalyst, especially with positive potentials in unloaded conditions. For the determination of the total effect of events upon the activity of the oxygen electrode, methods comparing the changes of current density, in dependence on time, were applied. Current density was measured with electrode potential of -300 mV vs. Hg/HgO. The experiments proved that the activity of the oxygen electrode on the base of Ag catalyst ~ PTFE in unloaded conditions and without oxygen pressure in 7 N KOH at the approximate temperature of 63° C, drops expressively with time. More we observed the influence of the collector material construction, effect of Zn, Ni, Cd and Fe, effect of amalgamation of the oxygen electrode and effect of CO i- upon its activity. It was proved, on the basis of experimental results, that the oxygen electrode on the basis of Ag/PTFE is practically inapplicable. »Selfpoisoning « occurs here probably due to the effect of ions [Ag(OH) 2]-. On the other hand, the formation of [Ag(OH)2]- can be utilized in the production technology of electron conductive skeleton of the electrode by the application of a mixture of silver and electronegative metal, e. g. Zn

Elasticity, Stability and Ideal Strength of β\beta -SiC in plane-wave-based ab initio calculations

On the basis of the pseudopotential plane-wave(PP-PW) method and the local-density-functional theory(LDFT), this paper studies energetics, stress-strain relation, stability and ideal strength of $\beta$-SiC under various loading modes, where uniform uniaxial extension and tension, biaxial proportional extension are considered along directions [001] and [111]. The lattice constant, elastic constants and moduli of equilibrium state are calculated, and the results agree well with the experimental data. As the four Si-C bonds along directions [111], [$\bar{1}$11], [11$\bar{1}$] and [1$\bar{1}$1] are not the same under the loading along [111], internal relaxation and the corresponding internal displacements must be considered. We find that, at the beginning of loading, the effect of internal displacement through shuffle and glide plane diminishes the difference among the four Si-C bonds length, but will increase the difference at the subsequent loading, which will result in a crack nucleated on \{111\} shuffle plane and a subsequently cleavage fracture. Thus the corresponding theoretical strength is 50.8 GPa, which agrees well with the recent experiment value, 53.4 GPa. However, with the loading along [001], internal relaxation is not important for tetragonal symmetry. Elastic constants during the uniaxial tension along [001] are calculated. Based on the stability analysis with stiffness coefficients, we find that the spinodal and Born instabilities are triggered almost at the same strain, which agrees with the previous molecular dynamics simulation. During biaxial proportional extension, stress and strength vary proportionally with the biaxial loading ratio at the same longitudinal strain.Comment: 9 pages, 10 figure

Climate and habitat configuration limit range expansion and patterns of dispersal in a non-native lizard

Invasive species are one of the main causes of biodiversity loss worldwide. As introduced, populations increase in abundance and geographical range, so does the potential for negative impacts on native communities. As such, there is a need to better understand the processes driving range expansion as species become established in recipient landscapes. Through an investigation into capacity for population growth and range expansion of introduced populations of a non‐native lizard (Podarcis muralis), we aimed to demonstrate how multi‐scale factors influence spatial spread, population growth, and invasion potential in introduced species. We collated location records of P. muralis presence in England, UK through data collected from field surveys and a citizen science campaign. We used these data as input for presence‐background models to predict areas of climate suitability at a national‐scale (5 km resolution), and fine‐scale habitat suitability at the local scale (2 m resolution). We then integrated local models into an individual‐based modeling platform to simulate population dynamics and forecast range expansion for 10 populations in heterogeneous landscapes. National‐scale models indicated climate suitability has restricted the species to the southern parts of the UK, primarily by a latitudinal cline in overwintering conditions. Patterns of population growth and range expansion were related to differences in local landscape configuration and heterogeneity. Growth curves suggest populations could be in the early stages of exponential growth. However, annual rates of range expansion are predicted to be low (5–16 m). We conclude that extensive nationwide range expansion through secondary introduction is likely to be restricted by currently unsuitable climate beyond southern regions of the UK. However, exponential growth of local populations in habitats providing transport pathways is likely to increase opportunities for regional expansion. The broad habitat niche of P. muralis, coupled with configuration of habitat patches in the landscape, allows populations to increase locally with minimal dispersal