Percolation of straight slots on a square grid.

This work is devoted to the emergence of a connected network of slots (cracks) on a square grid. Accordingly, extensive Monte Carlo simulations and finite-size scaling analysis have been conducted to study the site percolation of straight slots with length l measured in the number of elementary cells of the grid with the edge size L. A special focus was made on the dependence of the percolation threshold p_{C}(l,L) on the slot length l varying in the range 1≤l≤L-2 for the square grids with edge size in the range 50≤L≤1000. In this way, we found that p_{C}(l,L) strongly decreases with increase of l, whereas the variations of p_{C}(l=const,L) with the variation of ratio l/L are very small. Consequently, we acquire the functional dependencies of the critical filling factor and percolation strength on the slot length. Furthermore, we established that the slot percolation model interpolates between the site percolation on square lattice (l=1) and the continuous percolation of widthless sticks (l→∞) aligned in two orthogonal directions. In this regard, we note that the critical number of widthless sticks per unit area is larger than in the case of randomly oriented sticks. Our estimates for the critical exponents indicate that the slot percolation belongs to the same universality class as standard Bernoulli percolation.

Unraveling the effects on lithium-ion cathode performance by cation doping M-Li2CuO2 solid solution samples (M = Mn, Fe and Ni).

Cation doping is one of the most dynamic strategies to enhance the electrochemical properties of cathode materials for lithium-ion batteries. Nevertheless, the maximum partial substitution capacity depends on the solubility of each metal ion, and so the formation of impurities is a very common consequence. Thus, the correlation between electrochemical performance and the doping effect is frequently unknown. In this study, the effect of the partial substitution of copper by manganese, iron or nickel in Li2CuO2 is evaluated, as well as the effect on the electrochemical performance of the modified Li2CuO2 samples as lithium ion battery cathode materials. XRD characterization confirmed single phase formation for all samples, and the incorporation of the transition metal in the Li2CuO2 structure was evaluated by XRD profile fitting, EPR and 7Li-NMR. The results showed modifications in intra- and inter-chain interactions, associated with the variations in the Cu-O-Cu bond angle and changes in magnetic order, due to the presence of the doping transition metal. Among all samples, only manganese partial substitution reveals a drastic improvement in the electrochemical stability during the charge/discharge processes even at potentials higher than 3.9 V. It was corroborated that the higher stability is attributed to (i) the increase in the superexchange interactions between the copper sites and manganese, directly modifying lithium diffusivity and electronic conductivity, both inferred from dynamic thermogravimetric analysis for CO2 sorption and conductivity tests, respectively and (ii) the lower propensity to enable O2 evolution during several charge cycles. These results are totally attributed to manganese cation partial substitution, which has a huge impact on the utilization of copper-based materials in real applications.

Lectin activity from the cattle tick (Boophilus microplus) saliva.

The capability of Boophilus microplus saliva (BmS) and lectins to induce immunosuppression in mice and to agglutinate erythrocytes from distinct animal species were compared. CD-1 mice were distributed into groups (two for each substance) of 4-5 animals/group and treated intraperitoneally (i.p.) with 50 mg and 150 mg of BmS; concanavalin A (Con A); potato's lectin (PL), striped bean lectin (SBL) or 0.1 ml of phosphate buffered saline (PBS). All mice were immunized i.p. with 2 x 108 sheep erythrocytes (SE) 48 hours after treatment. Five days after immunization sera was obtained from mice to determine anti-SE antibody titer by direct hemagglutination. The mean antibody titers (Log2) obtained was 5.5 and 4.2 for BmS, 4.4 and 0 for Con A, 5.2 and 4.8 for PL, 4.6 and 0 for SBL and 7.4 for PBS. BmS and lectins were tested to agglutinate mouse (M), rat (Rt), rabbit (Rb), sheep (S) and human A (HA), human B (HB) and human O (HO) erythrocytes. BmS agglutinated Rb, S, HA, HB and HO erythrocytes at titer (Log2) of 1, 1, 6, 1 and 2 respectively. Con A and PL agglutinated erythrocytes from all species tested, while SBL agglutinated M, S and HA erythrocytes. A 50% inhibition of agglutination of HA erythrocytes by BmS was observed when D(+) Galactosamine and D(+) Glucosamine, at 0.2 M, were used. The results obtained indicate that BmS contains a weak nonspecific lectin which is inhibited by aminated sugars, and that induces immunosuppression in mice as other lectins.