Nonlinear c-axis transport in Bi_2Sr_2CaCu_2O_(8+d) from two-barrier tunneling

Motivated by the peculiar features observed through intrinsic tunneling spectroscopy of Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ mesas in the normal state, we have extended the normal state two-barrier model for the c-axis transport [M. Giura et al., Phys. Rev. B {\bf 68}, 134505 (2003)] to the analysis of $dI/dV$ curves. We have found that the purely normal-state model reproduces all the following experimental features: (a) the parabolic $V$-dependence of $dI/dV$ in the high-$T$ region (above the conventional pseudogap temperature), (b) the emergence and the nearly voltage-independent position of the "humps" from this parabolic behavior lowering the temperature, and (c) the crossing of the absolute $dI/dV$ curves at a characteristic voltage $V^\times$. Our findings indicate that conventional tunneling can be at the origin of most of the uncommon features of the c axis transport in Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$. We have compared our calculations to experimental data taken in severely underdoped and slightly underdoped Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ small mesas. We have found good agreement between the data and the calculations, without any shift of the calculated dI/dV on the vertical scale. In particular, in the normal state (above $T^\ast$) simple tunneling reproduces the experimental dI/dV quantitatively. Below $T^\ast$ quantitative discrepancies are limited to a simple rescaling of the voltage in the theoretical curves by a factor $\sim$2. The need for such modifications remains an open question, that might be connected to a change of the charge of a fraction of the carriers across the pseudogap opening.Comment: 7 pages, 5 figure

Performance of processing tomatoes under different supply levels of crop evapotranspiration.

This study was installed to evaluate productive performance of two processing tomato hybrids submitted to five water depths under drip irrigation system. Five levels of crop evapotranspiration (ETc) replacement (60%, 100%, 140%, 180% and 220%) and two tomato hybrids (BRS Sena and H 9992) were tested

Anaerobic biodegradation of cassava wastewater under different temperatures and inoculums.

The production of starch generates, as a by-product, the cassava wastewater (manipueira), which can be treated by anaerobic digestion to provide biogas and minimize its polluting potential. The most commonly utilized biomass in the anaerobic digestion is the anaerobic sludge. The literature presents, as an alternative to sludge, bovine manure and ruminal fluids, being scarce the studies with the cassava wastewater. This research evaluated the influence of temperature on the microbial ability of cattle and goat rumen in anaerobically biodegrading the manipueira in substitution to the anaerobic sludge. The cattle and goat rumen specific methanogenic activities (SMA) were compared with that of the anaerobic sludge. Subsequently, by using the inoculum which had the best SMA results, cassava wastewater biodegradability tests were performed, investigating the kinetics of the organic matter removal and methane production at 32 ° C and 39 ° C. The bovine rumen presented better results in the SMA (0,315 g COD-CH4 g VSS.d-1) and methane production (1,026 mL). The temperature of 32 °C did not influence the activity of bovine ruminal inoculum as the kinetics of the biodegradation of the manipueira did not differ for the evaluated temperatures (0.1799 d-1 at 32°C and 0.1781 d-1 at 39°C). Bovine rumen achieved glucose reduction of 76% and 80% and methane yield of 77% and 79% for the tests at 32°C and 39°C, respectively. It is inferred that this type of inoculum might be used in reactors of anaerobic digestion processes for the treatment of the cassava wastewater at the ambient temperature of the semiarid region

Tunnel and thermal c-axis transport in BSCCO in the normal and pseudogap state

We consider the problem of c-axis transport in double-layered cuprates, in particular with reference to Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$ compounds. We exploit the effect of the two barriers on the thermal and tunnel transport. The resulting model is able to describe accurately the normal state c-axis resistivity in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+\delta}$, from the underdoped side up to the strongly overdoped. We extend the model, without introducing additional parameters, in order to allow for the decrease of the barrier when an external voltage bias is applied. The extended model is found to describe properly the c-axis resistivity for small voltage bias above the pseudogap temperature $T^{*}$, the c-axis resistivity for large voltage bias even below $T_c$, and the differential $dI/dV$ curves taken in mesa structures.Comment: 12 pages, 6 figures. Submitted to Superconductor Science and Technolog

Insights into the fracture mechanisms and strength of amorphous and nanocomposite carbon

Tight-binding molecular dynamics simulations shed light into the fracture mechanisms and the ideal strength of tetrahedral amorphous carbon and of nanocomposite carbon containing diamond crystallites, two of the hardest materials. It is found that fracture in the nanocomposites, under tensile or shear load, occurs inter-grain and so their ideal strength is similar to the pure amorphous phase. The onset of fracture takes place at weakly bonded sp^3 sites in the amorphous matrix. On the other hand, the nanodiamond inclusions significantly enhance the elastic moduli, which approach those of diamond.Comment: 6 pages, 4 figure

Comprimento e diâmetro de frutos de tomate para processametno industrial sob lâminas de irrigação.

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